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'2' Summary: 2 errors (**), 0 flaws (~~), 3 warnings (==), 12 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Working Group: ForCES J. Halpern 3 Internet-Draft Self 4 Intended status: Standards Track J. Hadi Salim 5 Expires: February 25, 2009 Znyx Networks 6 August 24, 2008 8 ForCES Forwarding Element Model 9 draft-ietf-forces-model-14.txt 11 Status of this Memo 13 By submitting this Internet-Draft, each author represents that any 14 applicable patent or other IPR claims of which he or she is aware 15 have been or will be disclosed, and any of which he or she becomes 16 aware will be disclosed, in accordance with Section 6 of BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 This Internet-Draft will expire on February 25, 2009. 36 Comments are solicited and should be addressed to the working group's 37 mailing list at forces@peach.ease.lsoft.com and/or the author(s). 39 Abstract 41 This document defines the forwarding element (FE) model used in the 42 Forwarding and Control Element Separation (ForCES) protocol [2]. The 43 model represents the capabilities, state and configuration of 44 forwarding elements within the context of the ForCES protocol, so 45 that control elements (CEs) can control the FEs accordingly. More 46 specifically, the model describes the logical functions that are 47 present in an FE, what capabilities these functions support, and how 48 these functions are or can be interconnected. This FE model is 49 intended to satisfy the model requirements specified in the ForCES 50 requirements document, RFC3654 [4]. 52 Table of Contents 54 1. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 5 55 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 7 56 2.1. Requirements on the FE model . . . . . . . . . . . . . . 7 57 2.2. The FE Model in Relation to FE Implementations . . . . . 8 58 2.3. The FE Model in Relation to the ForCES Protocol . . . . . 8 59 2.4. Modeling Language for the FE Model . . . . . . . . . . . 9 60 2.5. Document Structure . . . . . . . . . . . . . . . . . . . 9 61 3. ForCES Model Concepts . . . . . . . . . . . . . . . . . . . . 10 62 3.1. ForCES Capability Model and State Model . . . . . . . . . 11 63 3.1.1. FE Capability Model and State Model . . . . . . . . . 12 64 3.1.2. Relating LFB and FE Capability and State Model . . . 13 65 3.2. Logical Functional Block (LFB) Modeling . . . . . . . . . 14 66 3.2.1. LFB Outputs . . . . . . . . . . . . . . . . . . . . . 17 67 3.2.2. LFB Inputs . . . . . . . . . . . . . . . . . . . . . 20 68 3.2.3. Packet Type . . . . . . . . . . . . . . . . . . . . . 23 69 3.2.4. Metadata . . . . . . . . . . . . . . . . . . . . . . 24 70 3.2.5. LFB Events . . . . . . . . . . . . . . . . . . . . . 26 71 3.2.6. Component Properties . . . . . . . . . . . . . . . . 28 72 3.2.7. LFB Versioning . . . . . . . . . . . . . . . . . . . 28 73 3.2.8. LFB Inheritance . . . . . . . . . . . . . . . . . . . 29 74 3.3. ForCES Model Addressing . . . . . . . . . . . . . . . . . 30 75 3.3.1. Addressing LFB Components: Paths and Keys . . . . . . 31 76 3.4. FE Datapath Modeling . . . . . . . . . . . . . . . . . . 32 77 3.4.1. Alternative Approaches for Modeling FE Datapaths . . 32 78 3.4.2. Configuring the LFB Topology . . . . . . . . . . . . 36 79 4. Model and Schema for LFB Classes . . . . . . . . . . . . . . 40 80 4.1. Namespace . . . . . . . . . . . . . . . . . . . . . . . . 41 81 4.2. Element . . . . . . . . . . . . . . . . . . 41 82 4.3. Element . . . . . . . . . . . . . . . . . . . . . 43 83 4.4. Element for Frame Type Declarations . . . . . 44 84 4.5. Element for Data Type Definitions . . . . 44 85 4.5.1. Element for Renaming Existing Data Types . 47 86 4.5.2. Element for Deriving New Atomic Types . . . 48 87 4.5.3. Element to Define Arrays . . . . . . . . . . 49 88 4.5.4. Element to Define Structures . . . . . . . . 53 89 4.5.5. Element to Define Union Types . . . . . . . . 54 90 4.5.6. Element . . . . . . . . . . . . . . . . . . . 55 91 4.5.7. Augmentations . . . . . . . . . . . . . . . . . . . . 55 92 4.6. Element for Metadata Definitions . . . . . 56 93 4.7. Element for LFB Class Definitions . . . . 57 94 4.7.1. Element to Express LFB Inheritance . . 60 95 4.7.2. Element to Define LFB Inputs . . . . . . 60 96 4.7.3. Element to Define LFB Outputs . . . . . 62 97 4.7.4. Element to Define LFB Operational 98 Components . . . . . . . . . . . . . . . . . . . . . 65 99 4.7.5. Element to Define LFB Capability 100 Components . . . . . . . . . . . . . . . . . . . . . 68 101 4.7.6. Element for LFB Notification Generation . . 69 102 4.7.7. Element for LFB Operational 103 Specification . . . . . . . . . . . . . . . . . . . . 76 104 4.8. Properties . . . . . . . . . . . . . . . . . . . . . . . 76 105 4.8.1. Basic Properties . . . . . . . . . . . . . . . . . . 77 106 4.8.2. Array Properties . . . . . . . . . . . . . . . . . . 79 107 4.8.3. String Properties . . . . . . . . . . . . . . . . . . 79 108 4.8.4. Octetstring Properties . . . . . . . . . . . . . . . 80 109 4.8.5. Event Properties . . . . . . . . . . . . . . . . . . 81 110 4.8.6. Alias Properties . . . . . . . . . . . . . . . . . . 84 111 4.9. XML Schema for LFB Class Library Documents . . . . . . . 85 112 5. FE Components and Capabilities . . . . . . . . . . . . . . . 96 113 5.1. XML for FEObject Class definition . . . . . . . . . . . . 97 114 5.2. FE Capabilities . . . . . . . . . . . . . . . . . . . . . 103 115 5.2.1. ModifiableLFBTopology . . . . . . . . . . . . . . . . 104 116 5.2.2. SupportedLFBs and SupportedLFBType . . . . . . . . . 104 117 5.3. FE Components . . . . . . . . . . . . . . . . . . . . . . 107 118 5.3.1. FEState . . . . . . . . . . . . . . . . . . . . . . . 107 119 5.3.2. LFBSelectors and LFBSelectorType . . . . . . . . . . 107 120 5.3.3. LFBTopology and LFBLinkType . . . . . . . . . . . . . 108 121 5.3.4. FENeighbors and FEConfiguredNeighborType . . . . . . 108 122 6. Satisfying the Requirements on FE Model . . . . . . . . . . . 109 123 7. Using the FE model in the ForCES Protocol . . . . . . . . . . 110 124 7.1. FE Topology Query . . . . . . . . . . . . . . . . . . . . 112 125 7.2. FE Capability Declarations . . . . . . . . . . . . . . . 113 126 7.3. LFB Topology and Topology Configurability Query . . . . . 114 127 7.4. LFB Capability Declarations . . . . . . . . . . . . . . . 114 128 7.5. State Query of LFB Components . . . . . . . . . . . . . . 115 129 7.6. LFB Component Manipulation . . . . . . . . . . . . . . . 116 130 7.7. LFB Topology Re-configuration . . . . . . . . . . . . . . 116 131 8. Example LFB Definition . . . . . . . . . . . . . . . . . . . 116 132 8.1. Data Handling . . . . . . . . . . . . . . . . . . . . . . 123 133 8.1.1. Setting up a DLCI . . . . . . . . . . . . . . . . . . 124 134 8.1.2. Error Handling . . . . . . . . . . . . . . . . . . . 125 135 8.2. LFB Components . . . . . . . . . . . . . . . . . . . . . 125 136 8.3. Capabilities . . . . . . . . . . . . . . . . . . . . . . 126 137 8.4. Events . . . . . . . . . . . . . . . . . . . . . . . . . 126 138 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 127 139 9.1. URN Namespace Registration . . . . . . . . . . . . . . . 127 140 9.2. LFB Class Names and LFB Class Identifiers . . . . . . . . 128 141 10. Authors Emeritus . . . . . . . . . . . . . . . . . . . . . . 129 142 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 129 143 12. Security Considerations . . . . . . . . . . . . . . . . . . . 130 144 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 130 145 13.1. Normative References . . . . . . . . . . . . . . . . . . 130 146 13.2. Informative References . . . . . . . . . . . . . . . . . 130 147 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 131 148 Intellectual Property and Copyright Statements . . . . . . . . . 132 150 1. Definitions 152 The use of compliance terminology (MUST, SHOULD, MAY) is used in 153 accordance with RFC2119 [1]. Such terminology is used in describing 154 the required behavior of ForCES forwarding elements or control 155 elements in supporting or manipulating information described in this 156 model. 158 Terminology associated with the ForCES requirements is defined in 159 RFC3654 [4] and is not copied here. The following list of 160 terminology relevant to the FE model is defined in this section. 162 FE Model -- The FE model is designed to model the logical processing 163 functions of an FE. The FE model proposed in this document includes 164 three components: the modeling of individual logical functional 165 blocks (LFB model), the logical interconnection between LFBs (LFB 166 topology) and the FE level attributes, including FE capabilities. 167 The FE model provides the basis to define the information elements 168 exchanged between the CE and the FE in the ForCES Protocol [2]. 170 Datapath -- A conceptual path taken by packets within the forwarding 171 plane inside an FE. Note that more than one datapath can exist 172 within an FE. 174 LFB (Logical Functional Block) Class (or type) -- A template that 175 representing a fine-grained, logically separable aspect of FE 176 processing. Most LFBs relate to packet processing in the data path. 177 LFB classes are the basic building blocks of the FE model. 179 LFB Instance -- As a packet flows through an FE along a datapath, it 180 flows through one or multiple LFB instances, where each LFB is an 181 instance of a specific LFB class. Multiple instances of the same LFB 182 class can be present in an FE's datapath. Note that we often refer 183 to LFBs without distinguishing between an LFB class and LFB instance 184 when we believe the implied reference is obvious for the given 185 context. 187 LFB Model -- The LFB model describes the content and structures in an 188 LFB, plus the associated data definition. XML is used to provide a 189 formal definition of the necessary structures for the modeling. Four 190 types of information are defined in the LFB model. The core part of 191 the LFB model is the LFB class definitions; the other three types of 192 information define constructs associated with and used by the class 193 definition. These are reusable data types, supported frame formats, 194 and metadata. 196 Element -- Element is generally used in this document in accordance 197 with the XML usage of the term. It refers to an XML tagged part of 198 an XML document. For a precise definition, please see the full set 199 of XML specifications from the W3C. This term is included in this 200 list for completeness because ForCES formal model uses XML. 202 Attribute -- Attribute is used in the ForCES formal modelling in 203 accordance with standard XML usage of the term. i.e to provide 204 attribute information include in an XML tag. 206 LFB Metadata -- Metadata is used to communicate per-packet state from 207 one LFB to another, but is not sent across the network. The FE model 208 defines how such metadata is identified, produced and consumed by the 209 LFBs, but not how the per-packet state is implemented within actual 210 hardware. Metadata is sent between the FE and the CE on redirect 211 packets. 213 ForCES Component -- a ForCES Component is a well defined, uniquely 214 identifiable and addressable ForCES model building block. A 215 component has a 32-bit ID, name, type and an optional synopsis 216 description. These are often referred to simply as components. 218 LFB Component -- A ForCES component that defines the Operational 219 parameters of the LFBs that must be visible to the CEs. 221 Structure Component -- A ForCES component that is part of a complex 222 data structure to be used in LFB data definitions. The individual 223 parts which make up a structured set of data are referred to as 224 Structure Components. These can themselves be of any valid data 225 type, including tables and structures. 227 Property -- ForCES components have properties associated with them, 228 such as readability. Other examples include lengths for variable 229 sized components. These properties are acessed by the CE for reading 230 (or, where appropriate, writing.) Details on the ForCES properties 231 are found in section 4.8. 233 LFB Topology -- A representation of the logical interconnection and 234 the placement of LFB instances along the datapath within one FE. 235 Sometimes this representation is called intra-FE topology, to be 236 distinguished from inter-FE topology. LFB topology is outside of the 237 LFB model, but is part of the FE model. 239 FE Topology -- A representation of how multiple FEs within a single 240 NE are interconnected. Sometimes this is called inter-FE topology, 241 to be distinguished from intra-FE topology (i.e., LFB topology). An 242 individual FE might not have the global knowledge of the full FE 243 topology, but the local view of its connectivity with other FEs is 244 considered to be part of the FE model. The FE topology is discovered 245 by the ForCES base protocol or by some other means. 247 Inter-FE Topology -- See FE Topology. 249 Intra-FE Topology -- See LFB Topology. 251 LFB class library -- A set of LFB classes that has been identified as 252 the most common functions found in most FEs and hence should be 253 defined first by the ForCES Working Group. 255 2. Introduction 257 RFC3746 [5] specifies a framework by which control elements (CEs) can 258 configure and manage one or more separate forwarding elements (FEs) 259 within a networking element (NE) using the ForCES protocol. The 260 ForCES architecture allows Forwarding Elements of varying 261 functionality to participate in a ForCES network element. The 262 implication of this varying functionality is that CEs can make only 263 minimal assumptions about the functionality provided by FEs in an NE. 264 Before CEs can configure and control the forwarding behavior of FEs, 265 CEs need to query and discover the capabilities and states of their 266 FEs. RFC3654 [4] mandates that the capabilities, states and 267 configuration information be expressed in the form of an FE model. 269 RFC3444 [8] observed that information models (IMs) and data models 270 (DMs) are different because they serve different purposes. "The main 271 purpose of an IM is to model managed objects at a conceptual level, 272 independent of any specific implementations or protocols used". 273 "DMs, conversely, are defined at a lower level of abstraction and 274 include many details. They are intended for implementors and include 275 protocol-specific constructs." Sometimes it is difficult to draw a 276 clear line between the two. The FE model described in this document 277 is primarily an information model, but also includes some aspects of 278 a data model, such as explicit definitions of the LFB class schema 279 and FE schema. It is expected that this FE model will be used as the 280 basis to define the payload for information exchange between the CE 281 and FE in the ForCES protocol. 283 2.1. Requirements on the FE model 285 RFC3654 [4]defines requirements that must be satisfied by a ForCES FE 286 model. To summarize, an FE model must define: 288 o Logically separable and distinct packet forwarding operations in 289 an FE datapath (logical functional blocks or LFBs); 291 o The possible topological relationships (and hence the sequence of 292 packet forwarding operations) between the various LFBs; 294 o The possible operational capabilities (e.g., capacity limits, 295 constraints, optional features, granularity of configuration) of 296 each type of LFB; 298 o The possible configurable parameters (e.g., components) of each 299 type of LFB; 301 o Metadata that may be exchanged between LFBs. 303 2.2. The FE Model in Relation to FE Implementations 305 The FE model proposed here is based on an abstraction using distinct 306 logical functional blocks (LFBs), which are interconnected in a 307 directed graph, and receive, process, modify, and transmit packets 308 along with metadata. The FE model is designed, and any defined LFB 309 classes should be designed, such that different implementations of 310 the forwarding datapath can be logically mapped onto the model with 311 the functionality and sequence of operations correctly captured. 312 However, the model is not intended to directly address how a 313 particular implementation maps to an LFB topology. It is left to the 314 forwarding plane vendors to define how the FE functionality is 315 represented using the FE model. Our goal is to design the FE model 316 such that it is flexible enough to accommodate most common 317 implementations. 319 The LFB topology model for a particular datapath implementation must 320 correctly capture the sequence of operations on the packet. Metadata 321 generation by certain LFBs MUST always precede any use of that 322 metadata by subsequent LFBs in the topology graph; this is required 323 for logically consistent operation. Further, modification of packet 324 fields that are subsequently used as inputs for further processing 325 MUST occur in the order specified in the model for that particular 326 implementation to ensure correctness. 328 2.3. The FE Model in Relation to the ForCES Protocol 330 The ForCES base Protocol [2] is used by the CEs and FEs to maintain 331 the communication channel between the CEs and FEs. The ForCES 332 protocol may be used to query and discover the inter-FE topology. 333 The details of a particular datapath implementation inside an FE, 334 including the LFB topology, along with the operational capabilities 335 and attributes of each individual LFB, are conveyed to the CE within 336 information elements in the ForCES protocol. The model of an LFB 337 class should define all of the information that needs to be exchanged 338 between an FE and a CE for the proper configuration and management of 339 that LFB. 341 Specifying the various payloads of the ForCES messages in a 342 systematic fashion is difficult without a formal definition of the 343 objects being configured and managed (the FE and the LFBs within). 344 The FE Model document defines a set of classes and components for 345 describing and manipulating the state of the LFBs within an FE. 346 These class definitions themselves will generally not appear in the 347 ForCES protocol. Rather, ForCES protocol operations will reference 348 classes defined in this model, including relevant components and the 349 defined operations. 351 Section 7 provides more detailed discussion on how the FE model 352 should be used by the ForCES protocol. 354 2.4. Modeling Language for the FE Model 356 Even though not absolutely required, it is beneficial to use a formal 357 data modeling language to represent the conceptual FE model described 358 in this document. Use of a formal language can help to enforce 359 consistency and logical compatibility among LFBs. A full 360 specification will be written using such a data modeling language. 361 The formal definition of the LFB classes may facilitate the eventual 362 automation of some of the code generation process and the functional 363 validation of arbitrary LFB topologies. These class definitions form 364 the LFB Library. Documents which describe LFB Classes are therefore 365 referred to as LFB Library documents. 367 Human readability was the most important factor considered when 368 selecting the specification language, whereas encoding, decoding and 369 transmission performance was not a selection factor. The encoding 370 method for over the wire transport is not dependent on the 371 specification language chosen and is outside the scope of this 372 document and up to the ForCES protocol to define. 374 XML is chosen as the specification language in this document, because 375 XML has the advantage of being both human and machine readable with 376 widely available tools support. This document uses XML Schema to 377 define the structure of the LFB Library documents, as defined in [9] 378 and [10] and [11]. While these LFB Class definitions are not sent in 379 the ForCES protocol, these definitions comply with the 380 recommendations in RFC3470 [9] on the use of XML in IETF protocols. 382 2.5. Document Structure 384 Section 3 provides a conceptual overview of the FE model, laying the 385 foundation for the more detailed discussion and specifications in the 386 sections that follow. Section 4 and Section 5 constitute the core of 387 the FE model, detailing the two major aspects of the FE model: a 388 general LFB model and a definition of the FE Object LFB, with its 389 components, including FE capabilities and LFB topology information. 391 Section 6 directly addresses the model requirements imposed by the 392 ForCES requirements defined in RFC3654 [4] while Section 7 explains 393 how the FE model should be used in the ForCES protocol. 395 3. ForCES Model Concepts 397 Some of the important ForCES concepts used throughout this document 398 are introduced in this section. These include the capability and 399 state abstraction, the FE and LFB model construction, and the unique 400 addressing of the different model structures. Details of these 401 aspects are described in Section 4 and Section 5. The intent of this 402 section is to discuss these concepts at the high level and lay the 403 foundation for the detailed description in the following sections. 405 The ForCES FE model includes both a capability and a state 406 abstraction. 408 o The FE/LFB capability model describes the capabilities and 409 capacities of an FE/LFB by specifying the variation in functions 410 supported and any limitations. Capacity describes the limits of 411 specific components (example would be a table size limit). 413 o The state model describes the current state of the FE/LFB, that 414 is, the instantaneous values or operational behavior of the FE/ 415 LFB. 417 Section 3.1 explains the difference between a capability model and a 418 state model, and describes how the two can be combined in the FE 419 model. 421 The ForCES model construction laid out in this document allows an FE 422 to provide information about its structure for operation. This can 423 be thought of as FE level information and information about the 424 individual instances of LFBs provided by the FE. 426 o The ForCES model includes the constructions for defining the class 427 of logical function blocks (LFBS) that an FE may support. These 428 classes are defined in this and other documents. The definition 429 of such a class provides the information content for monitoring 430 and controlling instances of the LFB class for ForCES purposes. 431 Each LFB model class formally defines the operational LFB 432 components, LFB capabilities, and LFB events. Essentially, 433 Section 3.2 introduces the concept of LFBs as the basic functional 434 building blocks in the ForCES model. 436 o The FE model also provides the construction necessary to monitor 437 and control the FE as a whole for ForCES purposes. For 438 consistency of operation and simplicity, this information is 439 represented as an LFB, the FE Object LFB class and a singular LFB 440 instance of that class, defined using the LFB model. The FE 441 Object class defines the components to provide information at the 442 FE level, particularly the capabilities of the FE at a coarse 443 level, i.e. not all possible capabilities nor all details about 444 the capabilities of the FE. Part of the FE level information is 445 the LFB topology, which expresses the logical inter-connection 446 between the LFB instances along the datapath(s) within the FE. 447 Section 3.3 discusses the LFB topology. The FE Object also 448 includes information about what LFB classes the FE can support. 450 The ForCES model allows for unique identification of the different 451 constructs it defines. This includes identification of the LFB 452 classes, and of LFB instances within those classes, as well as 453 identification of components within those instances. 455 The ForCES Protocol [2] encapsulates target address(es) to eventually 456 get to a fine-grained entity being referenced by the CE. The 457 addressing hierarchy is broken into the following: 459 o An FE is uniquely identified by a 32 bit FEID. 461 o Each Class of LFB is uniquely identified by a 32 bit LFB ClassID. 462 The LFB ClassIDs are global within the Network Element and may be 463 issued by IANA. 465 o Within an FE, there can be multiple instances of each LFB class. 466 Each LFB Class instance is identified by a 32 bit identifier which 467 is unique within a particular LFB class on that FE. 469 o All the components within an LFB instance are further defined 470 using 32 bit identifiers. 472 Refer to Section 3.3 for more details on addressing. 474 3.1. ForCES Capability Model and State Model 476 Capability and state modelling applies to both the FE and LFB 477 abstraction. 479 Figure 1 shows the concepts of FE state, capabilities and 480 configuration in the context of CE-FE communication via the ForCES 481 protocol. 483 +-------+ +-------+ 484 | | FE capabilities: what it can/cannot do. | | 485 | |<-----------------------------------------| | 486 | | | | 487 | CE | FE state: what it is now. | FE | 488 | |<-----------------------------------------| | 489 | | | | 490 | | FE configuration: what it should be. | | 491 | |----------------------------------------->| | 492 +-------+ +-------+ 494 Figure 1: Illustration of FE capabilities, state and configuration 495 exchange in the context of CE-FE communication via ForCES. 497 3.1.1. FE Capability Model and State Model 499 Conceptually, the FE capability model tells the CE which states are 500 allowed on an FE, with capacity information indicating certain 501 quantitative limits or constraints. Thus, the CE has general 502 knowledge about configurations that are applicable to a particular 503 FE. 505 3.1.1.1. FE Capability Model 507 The FE capability model may be used to describe an FE at a coarse 508 level. For example, an FE may be defined as follows: 510 o the FE can handle IPv4 and IPv6 forwarding; 512 o the FE can perform classification based on the following fields: 513 source IP address, destination IP address, source port number, 514 destination port number, etc; 516 o the FE can perform metering; 518 o the FE can handle up to N queues (capacity); 520 o the FE can add and remove encapsulating headers of types including 521 IPsec, GRE, L2TP. 523 While one could try to build an object model to fully represent the 524 FE capabilities, other efforts found this approach to be a 525 significant undertaking. The main difficulty arises in describing 526 detailed limits, such as the maximum number of classifiers, queues, 527 buffer pools, and meters that the FE can provide. We believe that a 528 good balance between simplicity and flexibility can be achieved for 529 the FE model by combining coarse level capability reporting with an 530 error reporting mechanism. That is, if the CE attempts to instruct 531 the FE to set up some specific behavior it cannot support, the FE 532 will return an error indicating the problem. Examples of similar 533 approaches include DiffServ PIB RFC3317 [6] and Framework PIB RFC3318 534 [7]. 536 3.1.1.2. FE State Model 538 The FE state model presents the snapshot view of the FE to the CE. 539 For example, using an FE state model, an FE may be described to its 540 corresponding CE as the following: 542 o on a given port, the packets are classified using a given 543 classification filter; 545 o the given classifier results in packets being metered in a certain 546 way and then marked in a certain way; 548 o the packets coming from specific markers are delivered into a 549 shared queue for handling, while other packets are delivered to a 550 different queue; 552 o a specific scheduler with specific behavior and parameters will 553 service these collected queues. 555 3.1.1.3. LFB Capability and State Model 557 Both LFB Capability and State information is defined formally using 558 LFB modelling XML schema. 560 Capability information at the LFB level is an integral part of the 561 LFB model and provides for powerful semantics. For example, when 562 certain features of an LFB class are optional, the CE MUST be able to 563 determine whether those optional features are supported by a given 564 LFB instance. The schema for the definition of LFB classes provides 565 a means for identifying such components. 567 State information is defined formally using LFB components 568 constructs. 570 3.1.2. Relating LFB and FE Capability and State Model 572 Capability information at the FE level describes the LFB classes that 573 the FE can instantiate, the number of instances of each that can be 574 created, the topological (linkage) limitations between these LFB 575 instances, etc. Section 5 defines the FE level components including 576 capability information. Since all information is represented as 577 LFBs, this is provided by a single instance of the FE Object LFB 578 Class. By using a single instance with a known LFB Class and a known 579 instance identification, the ForCES protocol can allow a CE to access 580 this information whenever it needs to, including while the CE is 581 establishing the control of the FE. 583 Once the FE capability is described to the CE, the FE state 584 information can be represented by two levels. The first level is the 585 logically separable and distinct packet processing functions, called 586 LFBs. The second level of information describes how these individual 587 LFBs are ordered and placed along the datapath to deliver a complete 588 forwarding plane service. The interconnection and ordering of the 589 LFBs is called LFB Topology. Section 3.2 discusses high level 590 concepts around LFBs, whereas Section 3.3 discusses LFB topology 591 issues. This topology information is represented as components of 592 the FE Object LFB instance, to allow the CE to fetch and manipulate 593 this. 595 3.2. Logical Functional Block (LFB) Modeling 597 Each LFB performs a well-defined action or computation on the packets 598 passing through it. Upon completion of its prescribed function, 599 either the packets are modified in certain ways (e.g., decapsulator, 600 marker), or some results are generated and stored, often in the form 601 of metadata (e.g., classifier). Each LFB typically performs a single 602 action. Classifiers, shapers and meters are all examples of such 603 LFBs. Modeling LFBs at such a fine granularity allows us to use a 604 small number of LFBs to express the higher-order FE functions (such 605 as an IPv4 forwarder) precisely, which in turn can describe more 606 complex networking functions and vendor implementations of software 607 and hardware. These fine grained LFBs will be defined in detail in 608 one or more documents to be published separately, using the material 609 in this model. 611 It is also the case that LFBs may exist in order to provide a set of 612 components for control of FE operation by the CE (i.e. a locus of 613 control), without tying that control to specific packets or specific 614 parts of the data path. An example of such an LFB is the FE Object 615 which provides the CE with information about the FE as a whole, and 616 allows the FE to control some aspects of the FE, such as the datapath 617 itself. Such LFBs will not have the packet oriented properties 618 described in this section. 620 In general, multiple LFBs are contained in one FE, as shown in 621 Figure 2, and all the LFBs share the same ForCES protocol termination 622 point that implements the ForCES protocol logic and maintains the 623 communication channel to and from the CE. 625 +-----------+ 626 | CE | 627 +-----------+ 628 ^ 629 | Fp reference point 630 | 631 +--------------------------|-----------------------------------+ 632 | FE | | 633 | v | 634 | +----------------------------------------------------------+ | 635 | | ForCES protocol | | 636 | | termination point | | 637 | +----------------------------------------------------------+ | 638 | ^ ^ | 639 | : : Internal control | 640 | : : | 641 | +---:----------+ +---:----------| | 642 | | :LFB1 | | : LFB2 | | 643 | =====>| v |============>| v |======>...| 644 | Inputs| +----------+ |Outputs | +----------+ | | 645 | (P,M) | |Components| |(P',M') | |Components| |(P",M") | 646 | | +----------+ | | +----------+ | | 647 | +--------------+ +--------------+ | 648 | | 649 +--------------------------------------------------------------+ 651 Figure 2: Generic LFB Diagram 653 An LFB, as shown in Figure 2, may have inputs, outputs and components 654 that can be queried and manipulated by the CE via an Fp reference 655 point (defined in RFC3746 [5]) and the ForCES protocol termination 656 point. The horizontal axis is in the forwarding plane for connecting 657 the inputs and outputs of LFBs within the same FE. The vertical axis 658 between the CE and the FE denotes the Fp reference point where 659 bidirectional communication between the CE and FE occurs: the CE to 660 FE communication is for configuration, control, and packet injection, 661 while FE to CE communication is used for packet redirection to the 662 control plane, reporting of monitoring and accounting information, 663 reporting of errors, etc. Note that the interaction between the CE 664 and the LFB is only abstract and indirect. The result of such an 665 interaction is for the CE to manipulate the components of the LFB 666 instances. 668 An LFB can have one or more inputs. Each input takes a pair of a 669 packet and its associated metadata. Depending upon the LFB input 670 port definition, the packet or the metadata may be allowed to be 671 empty (or equivalently to not be provided.) When input arrives at an 672 LFB, either the packet or its associated metadata must be non-empty 673 or there is effectively no input. (LFB operation generally may be 674 triggered by input arrival, by timers, or by other system state. It 675 is only in the case where the goal is to have input drive operation 676 that the input must be non-empty.) 678 The LFB processes the input, and produces one or more outputs, each 679 of which is a pair of a packet and its associated metadata. Again, 680 depending upon the LFB output port definition, either the packet or 681 the metadata may be allowed to be empty (or equivalently to be 682 absent.) Metadata attached to packets on output may be metadata that 683 was received, or may be information about the packet processing that 684 may be used by later LFBs in the FEs packet processing. 686 A namespace is used to associate a unique name and ID with each LFB 687 class. The namespace MUST be extensible so that a new LFB class can 688 be added later to accommodate future innovation in the forwarding 689 plane. 691 LFB operation is specified in the model to allow the CE to understand 692 the behavior of the forwarding datapath. For instance, the CE must 693 understand at what point in the datapath the IPv4 header TTL is 694 decremented. That is, the CE needs to know if a control packet could 695 be delivered to it either before or after this point in the datapath. 696 In addition, the CE MUST understand where and what type of header 697 modifications (e.g., tunnel header append or strip) are performed by 698 the FEs. Further, the CE MUST verify that the various LFBs along a 699 datapath within an FE are compatible to link together. 701 Selecting the right granularity for describing the functions of the 702 LFBs is an important aspect of this model. There is value to vendors 703 if the operation of LFB classes can be expressed in sufficient detail 704 so that physical devices implementing different LFB functions can be 705 integrated easily into an FE design. However, the model, and the 706 associated library of LFBs, must not be so detailed and so specific 707 as to significantly constrain implementations. Therefore, a semi- 708 formal specification is needed; that is, a text description of the 709 LFB operation (human readable), but sufficiently specific and 710 unambiguous to allow conformance testing and efficient design, so 711 that interoperability between different CEs and FEs can be achieved. 713 The LFB class model specifies information such as: 715 o number of inputs and outputs (and whether they are configurable) 717 o metadata read/consumed from inputs; 719 o metadata produced at the outputs; 720 o packet type(s) accepted at the inputs and emitted at the outputs; 722 o packet content modifications (including encapsulation or 723 decapsulation); 725 o packet routing criteria (when multiple outputs on an LFB are 726 present); 728 o packet timing modifications; 730 o packet flow ordering modifications; 732 o LFB capability information components; 734 o events that can be detected by the LFB, with notification to the 735 CE; 737 o LFB operational components; 739 o etc. 741 Section 4 of this document provides a detailed discussion of the LFB 742 model with a formal specification of LFB class schema. The rest of 743 Section 3.2 only intends to provide a conceptual overview of some 744 important issues in LFB modeling, without covering all the specific 745 details. 747 3.2.1. LFB Outputs 749 An LFB output is a conceptual port on an LFB that can send 750 information to another LFB. The information sent on that port is a 751 pair of a packet and associated metadata, one of which may be empty. 752 (If both were empty, there would be no output.) 754 A single LFB output can be connected to only one LFB input. This is 755 required to make the packet flow through the LFB topology 756 unambiguously. 758 Some LFBs will have a single output, as depicted in Figure 3.a. 760 +---------------+ +-----------------+ 761 | | | | 762 | | | OUT +--> 763 ... OUT +--> ... | 764 | | | EXCEPTIONOUT +--> 765 | | | | 766 +---------------+ +-----------------+ 768 a. One output b. Two distinct outputs 770 +---------------+ +-----------------+ 771 | | | EXCEPTIONOUT +--> 772 | OUT:1 +--> | | 773 ... OUT:2 +--> ... OUT:1 +--> 774 | ... +... | OUT:2 +--> 775 | OUT:n +--> | ... +... 776 +---------------+ | OUT:n +--> 777 +-----------------+ 779 c. One output group d. One output and one output group 781 Figure 3: Examples of LFBs with various output combinations. 783 To accommodate a non-trivial LFB topology, multiple LFB outputs are 784 needed so that an LFB class can fork the datapath. Two mechanisms 785 are provided for forking: multiple singleton outputs and output 786 groups, which can be combined in the same LFB class. 788 Multiple separate singleton outputs are defined in an LFB class to 789 model a pre-determined number of semantically different outputs. 790 That is, the LFB class definition MUST include the number of outputs, 791 implying the number of outputs is known when the LFB class is 792 defined. Additional singleton outputs cannot be created at LFB 793 instantiation time, nor can they be created on the fly after the LFB 794 is instantiated. 796 For example, an IPv4 LPM (Longest-Prefix-Matching) LFB may have one 797 output (OUT) to send those packets for which the LPM look-up was 798 successful, passing a META_ROUTEID as metadata; and have another 799 output (EXCEPTIONOUT) for sending exception packets when the LPM 800 look-up failed. This example is depicted in Figure 3.b. Packets 801 emitted by these two outputs not only require different downstream 802 treatment, but they are a result of two different conditions in the 803 LFB and each output carries different metadata. This concept assumes 804 the number of distinct outputs is known when the LFB class is 805 defined. For each singleton output, the LFB class definition defines 806 the types of frames and metadata the output emits. 808 An output group, on the other hand, is used to model the case where a 809 flow of similar packets with an identical set of permitted metadata 810 needs to be split into multiple paths. In this case, the number of 811 such paths is not known when the LFB class is defined because it is 812 not an inherent property of the LFB class. An output group consists 813 of a number of outputs, called the output instances of the group, 814 where all output instances share the same frame and metadata emission 815 definitions (see Figure 3.c). Each output instance can connect to a 816 different downstream LFB, just as if they were separate singleton 817 outputs, but the number of output instances can differ between LFB 818 instances of the same LFB class. The class definition may include a 819 lower and/or an upper limit on the number of outputs. In addition, 820 for configurable FEs, the FE capability information may define 821 further limits on the number of instances in specific output groups 822 for certain LFBs. The actual number of output instances in a group 823 is an component of the LFB instance, which is read-only for static 824 topologies, and read-write for dynamic topologies. The output 825 instances in a group are numbered sequentially, from 0 to N-1, and 826 are addressable from within the LFB. To use Output Port groups, the 827 LFB has to have a built-in mechanism to select one specific output 828 instance for each packet. This mechanism is described in the textual 829 definition of the class and is typically configurable via some 830 attributes of the LFB. 832 For example, consider a redirector LFB, whose sole purpose is to 833 direct packets to one of N downstream paths based on one of the 834 metadata associated with each arriving packet. Such an LFB is fairly 835 versatile and can be used in many different places in a topology. 836 For example, a redirector can be used to divide the data path into an 837 IPv4 and an IPv6 path based on a FRAMETYPE metadata (N=2), or to fork 838 into color specific paths after metering using the COLOR metadata 839 (red, yellow, green; N=3), etc. 841 Using an output group in the above LFB class provides the desired 842 flexibility to adapt each instance of this class to the required 843 operation. The metadata to be used as a selector for the output 844 instance is a property of the LFB. For each packet, the value of the 845 specified metadata may be used as a direct index to the output 846 instance. Alternatively, the LFB may have a configurable selector 847 table that maps a metadatum value to output instance. 849 Note that other LFBs may also use the output group concept to build 850 in similar adaptive forking capability. For example, a classifier 851 LFB with one input and N outputs can be defined easily by using the 852 output group concept. Alternatively, a classifier LFB with one 853 singleton output in combination with an explicit N-output re- 854 director LFB models the same processing behavior. The decision of 855 whether to use the output group model for a certain LFB class is left 856 to the LFB class designers. 858 The model allows the output group to be combined with other singleton 859 output(s) in the same class, as demonstrated in Figure 3.d. The LFB 860 here has two types of outputs, OUT, for normal packet output, and 861 EXCEPTIONOUT for packets that triggered some exception. The normal 862 OUT has multiple instances, thus, it is an output group. 864 In summary, the LFB class may define one output, multiple singleton 865 outputs, one or more output groups, or a combination thereof. 866 Multiple singleton outputs should be used when the LFB must provide 867 for forking the datapath and at least one of the following conditions 868 hold: 870 o the number of downstream directions is inherent from the 871 definition of the class and hence fixed; 873 o the frame type and set of permitted metadata emitted on any of the 874 outputs are different from what is emitted on the other outputs 875 (i.e., they cannot share their frame-type and permitted metadata 876 definitions). 878 An output group is appropriate when the LFB must provide for forking 879 the datapath and at least one of the following conditions hold: 881 o the number of downstream directions is not known when the LFB 882 class is defined; 884 o the frame type and set of metadata emitted on these outputs are 885 sufficiently similar or, ideally, identical, such they can share 886 the same output definition. 888 3.2.2. LFB Inputs 890 An LFB input is a conceptual port on an LFB on which the LFB can 891 receive information from other LFBs. The information is typically a 892 pair of a packet and its associated metadata. Either the packet, or 893 the metadata, may for some LFBs and some situations be empty. They 894 can not both be empty, as then there is no input. 896 For LFB instances that receive packets from more than one other LFB 897 instance (fan-in) there are three ways to model fan-in, all supported 898 by the LFB model and can all be combined in the same LFB: 900 o Implicit multiplexing via a single input 901 o Explicit multiplexing via multiple singleton inputs 903 o Explicit multiplexing via a group of inputs (input group) 905 The simplest form of multiplexing uses a singleton input (Figure 4 906 .a). Most LFBs will have only one singleton input. Multiplexing 907 into a single input is possible because the model allows more than 908 one LFB output to connect to the same LFB input. This property 909 applies to any LFB input without any special provisions in the LFB 910 class. Multiplexing into a single input is applicable when the 911 packets from the upstream LFBs are similar in frame-type and 912 accompanying metadata, and require similar processing. Note that 913 this model does not address how potential contention is handled when 914 multiple packets arrive simultaneously. If contention handling needs 915 to be explicitly modeled, one of the other two modeling solutions 916 must be used. 918 The second method to model fan-in uses individually defined singleton 919 inputs (Figure 4.b). This model is meant for situations where the 920 LFB needs to handle distinct types of packet streams, requiring 921 input-specific handling inside the LFB, and where the number of such 922 distinct cases is known when the LFB class is defined. For example, 923 a Layer 2 Decapsulation/Encapsulation LFB may have two inputs, one 924 for receiving Layer 2 frames for decapsulation, and one for receiving 925 Layer 3 frames for encapsulation. This LFB type expects different 926 frames (L2 vs. L3) at its inputs, each with different sets of 927 metadata, and would thus apply different processing on frames 928 arriving at these inputs. This model is capable of explicitly 929 addressing packet contention by defining how the LFB class handles 930 the contending packets. 932 +--------------+ +------------------------+ 933 | LFB X +---+ | | 934 +--------------+ | | | 935 | | | 936 +--------------+ v | | 937 | LFB Y +---+-->|input Meter LFB | 938 +--------------+ ^ | | 939 | | | 940 +--------------+ | | | 941 | LFB Z |---+ | | 942 +--------------+ +------------------------+ 944 (a) An LFB connects with multiple upstream LFBs via a single input. 946 +--------------+ +------------------------+ 947 | LFB X +---+ | | 948 +--------------+ +-->|layer2 | 949 +--------------+ | | 950 | LFB Y +------>|layer3 LFB | 951 +--------------+ +------------------------+ 953 (b) An LFB connects with multiple upstream LFBs via two separate 954 singleton inputs. 956 +--------------+ +------------------------+ 957 | Queue LFB #1 +---+ | | 958 +--------------+ | | | 959 | | | 960 +--------------+ +-->|in:0 \ | 961 | Queue LFB #2 +------>|in:1 | input group | 962 +--------------+ |... | | 963 +-->|in:N-1 / | 964 ... | | | 965 +--------------+ | | | 966 | Queue LFB #N |---+ | Scheduler LFB | 967 +--------------+ +------------------------+ 969 (c) A Scheduler LFB uses an input group to differentiate which queue 970 LFB packets are coming from. 972 Figure 4: Examples of LFBs with various input combinations. 974 The third method to model fan-in uses the concept of an input group. 975 The concept is similar to the output group introduced in the previous 976 section and is depicted in Figure 4.c. An input group consists of a 977 number of input instances, all sharing the properties (same frame and 978 metadata expectations). The input instances are numbered from 0 to 979 N-1. From the outside, these inputs appear as normal inputs, i.e., 980 any compatible upstream LFB can connect its output to one of these 981 inputs. When a packet is presented to the LFB at a particular input 982 instance, the index of the input where the packet arrived is known to 983 the LFB and this information may be used in the internal processing. 984 For example, the input index can be used as a table selector, or as 985 an explicit precedence selector to resolve contention. As with 986 output groups, the number of input instances in an input group is not 987 defined in the LFB class. However, the class definition may include 988 restrictions on the range of possible values. In addition, if an FE 989 supports configurable topologies, it may impose further limitations 990 on the number of instances for a particular port group(s) of a 991 particular LFB class. Within these limitations, different instances 992 of the same class may have a different number of input instances. 993 The number of actual input instances in the group is a component 994 defined in the LFB class, which is read-only for static topologies, 995 and is read-write for configurable topologies. 997 As an example for the input group, consider the Scheduler LFB 998 depicted in Figure 4.c. Such an LFB receives packets from a number 999 of Queue LFBs via a number of input instances, and uses the input 1000 index information to control contention resolution and scheduling. 1002 In summary, the LFB class may define one input, multiple singleton 1003 inputs, one or more input groups, or a combination thereof. Any 1004 input allows for implicit multiplexing of similar packet streams via 1005 connecting multiple outputs to the same input. Explicit multiple 1006 singleton inputs are useful when either the contention handling must 1007 be handled explicitly, or when the LFB class must receive and process 1008 a known number of distinct types of packet streams. An input group 1009 is suitable when contention handling must be modeled explicitly, but 1010 the number of inputs is not inherent from the class (and hence is not 1011 known when the class is defined), or when it is critical for LFB 1012 operation to know exactly on which input the packet was received. 1014 3.2.3. Packet Type 1016 When LFB classes are defined, the input and output packet formats 1017 (e.g., IPv4, IPv6, Ethernet, etc.) MUST be specified. These are the 1018 types of packets that a given LFB input is capable of receiving and 1019 processing, or that a given LFB output is capable of producing. This 1020 model requires that distinct packet types be uniquely labeled with a 1021 symbolic name and/or ID. 1023 Note that each LFB has a set of packet types that it operates on, but 1024 does not care whether the underlying implementation is passing a 1025 greater portion of the packets. For example, an IPv4 LFB might only 1026 operate on IPv4 packets, but the underlying implementation may or may 1027 not be stripping the L2 header before handing it over. Whether such 1028 processing is happening or not is opaque to the CE. 1030 3.2.4. Metadata 1032 Metadata is state that is passed from one LFB to another alongside a 1033 packet. The metadata passed with the packet assists subsequent LFBs 1034 to process that packet. 1036 The ForCES model defines metadata as precise atomic definitions in 1037 the form of label, value pairs. 1039 The ForCES model provides to the authors of LFB classes a way to 1040 formally define how to achieve metadata creation, modification, 1041 reading, as well as consumption(deletion). 1043 Inter-FE metadata, i.e, metadata crossing FEs, while likely 1044 semantically similar to this metadata, is out of scope for this 1045 document. 1047 Section 4 has informal details on metadata. 1049 3.2.4.1. Metadata lifecycle within the ForCES model 1051 Each metadata is modeled as a pair, where the label 1052 identifies the type of information, (e.g., "color"), and its value 1053 holds the actual information (e.g., "red"). The label here is shown 1054 as a textual label, but for protocol processing it is associated with 1055 a unique numeric value (identifier). 1057 To ensure inter-operability between LFBs, the LFB class specification 1058 must define what metadata the LFB class "reads" or "consumes" on its 1059 input(s) and what metadata it "produces" on its output(s). For 1060 maximum extensibility, this definition should neither specify which 1061 LFBs the metadata is expected to come from for a consumer LFB, nor 1062 which LFBs are expected to consume metadata for a given producer LFB. 1064 3.2.4.2. Metadata Production and Consumption 1066 For a given metadata on a given packet path, there MUST be at least 1067 one producer LFB that creates that metadata and SHOULD be at least 1068 one consumer LFB that needs that metadata. 1070 In the ForCES model, the producer and consumer LFBs of a metadatum 1071 are not required to be adjacent. In addition, there may be multiple 1072 producers and consumers for the same metadata. When a packet path 1073 involves multiple producers of the same metadata, then subsequent 1074 producers overwrite that metadata value. 1076 The metadata that is produced by an LFB is specified by the LFB class 1077 definition on a per-output-port-group basis. A producer may always 1078 generate the metadata on the port group, or may generate it only 1079 under certain conditions. We call the former an "unconditional" 1080 metadata, whereas the latter is a "conditional" metadata. For 1081 example, deep packet inspection LFB might produce several pieces of 1082 metadata about the packet. The first metadatum might be the carried 1083 IP protocol (TCP, UDP, SCTP, ...), and two additional metadata items 1084 might be the source and destination and destination port number. 1085 These additional metadata items are conditional on the value of the 1086 first metadatum (IP carried protocol) as they are only produced for 1087 protocols which use port number. In the case of conditional 1088 metadata, it should be possible to determine from the definition of 1089 the LFB when a "conditional" metadata is produced. The consumer 1090 behavior of an LFB, that is, the metadata that the LFB needs for its 1091 operation, is defined in the LFB class definition on a per-input- 1092 port-group basis. An input port group may "require" a given 1093 metadata, or may treat it as "optional" information. In the latter 1094 case, the LFB class definition MUST explicitly define what happens if 1095 an optional metadata is not provided. One approach is to specify a 1096 default value for each optional metadata, and assume that the default 1097 value is used if the metadata is not provided with the packet. 1099 When specifying the metadata tags, some harmonization effort must be 1100 made so that the producer LFB class uses the same tag as its intended 1101 consumer(s), or vice versa. 1103 3.2.4.3. LFB Operations on Metadata 1105 When the packet is processed by an LFB (i.e., between the time it is 1106 received and forwarded by the LFB), the LFB may perform read, write, 1107 and/or consume operations on any active metadata associated with the 1108 packet. If the LFB is considered to be a black box, one of the 1109 following operations is performed on each active metadata. 1111 * IGNORE: ignores and forwards the metadata 1113 * READ: reads and forwards the metadata 1114 * READ/RE-WRITE: reads, over-writes and forwards the metadata 1116 * WRITE: writes and forwards the metadata (can also be used to 1117 create new metadata) 1119 * READ-AND-CONSUME: reads and consumes the metadata 1121 * CONSUME consumes metadata without reading 1123 The last two operations terminate the life-cycle of the metadata, 1124 meaning that the metadata is not forwarded with the packet when the 1125 packet is sent to the next LFB. 1127 In the ForCES model, a new metadata is generated by an LFB when the 1128 LFB applies a WRITE operation to a metadatum type that was not 1129 present when the packet was received by the LFB. Such implicit 1130 creation may be unintentional by the LFB, that is, the LFB may apply 1131 the WRITE operation without knowing or caring if the given metadata 1132 existed or not. If it existed, the metadata gets over-written; if it 1133 did not exist, the metadata is created. 1135 For LFBs that insert packets into the model, WRITE is the only 1136 meaningful metadata operation. 1138 For LFBs that remove the packet from the model, they may either READ- 1139 AND-CONSUME (read) or CONSUME (ignore) each active metadata 1140 associated with the packet. 1142 3.2.5. LFB Events 1144 During operation, various conditions may occur that can be detected 1145 by LFBs. Examples range from link failure or restart to timer 1146 expiration in special purpose LFBs. The CE may wish to be notified 1147 of the occurrence of such events. The description of how such 1148 messages are sent, and their format, is part of the Forwarding and 1149 Control Element Separation (ForCES) protocol [2] document. 1150 Indicating how such conditions are understood is part of the job of 1151 this model. 1153 Events are declared in the LFB class definition. The LFB event 1154 declaration constitutes: 1156 o a unique 32 bit identifier. 1158 o An LFB component which is used to trigger the event. This entity 1159 is known as the event target. 1161 o A condition that will happen to the event target that will result 1162 in a generation of an event to the CE. Example of a condition 1163 include something getting created, deleted, config change, etc. 1165 o What should be reported to the CE by the FE if the declared 1166 condition is met. 1168 The declaration of an event within an LFB class essentially defines 1169 what part of the LFB component(s) need to be monitored for events, 1170 what condition on the LFB monitored LFB component an FE should detect 1171 to trigger such an event, and what to report to the CE when the event 1172 is triggered. 1174 While events may be declared by the LFB class definition, runtime 1175 activity is controlled using built-in event properties using LFB 1176 component Properties (discussed in Section 3.2.6). A CE subscribes 1177 to the events on an LFB class instance by setting an event property 1178 for subscription. Each event has a subscription property which is by 1179 default off. A CE wishing to receive a specific event needs to turn 1180 on the subscription property at runtime. 1182 Event properties also provide semantics for runtime event filtering. 1183 A CE may set an event property to further suppress subscribed to 1184 events. The LFB model defines such filters to include threshold 1185 values, hysteris, time intervals, number of events, etc. 1187 The reports with events are designed to allow for the common, closely 1188 related information that the CE can be strongly expected to need to 1189 react to the event. It is not intended to carry information the CE 1190 already has, nor large volumes of information, nor information 1191 related in complex fashions. 1193 From a conceptual point of view, at runtime, event processing is 1194 split into: 1196 1. detection of something happening to the (declared during LFB 1197 class definition) event target. Processing the next step happens 1198 if the CE subscribed (at runtime) to the event. 1200 2. checking of the (declared during LFB class definition) condition 1201 on the LFB event target. If the condition is met, proceed with 1202 the next step. 1204 3. checking (runtime set) event filters if they exist to see if the 1205 event should be reported or suppressed. If the event is to be 1206 reported proceed to the next step. 1208 4. Submitting of the declared report to the CE. 1210 Section 4.7.6 discusses events in more details. 1212 3.2.6. Component Properties 1214 LFBs and structures are made up of Components, containing the 1215 information that the CE needs to see and/or change about the 1216 functioning of the LFB. These Components, as described in detail in 1217 Section 4.7, may be basic values, complex structures (containing 1218 multiple Components themselves, each of which can be values, 1219 structures, or tables), or tables (which contain values, structures 1220 or tables). Components may be defined such that their appearence in 1221 LFB instances is optional. Components may be readable or writeable 1222 at the discretion of the FE implementation. The CE needs to know 1223 these properties. Additionally, certain kinds of Components (arrays 1224 / tables, aliases, and events) have additional property information 1225 that the CE may need to read or write. This model defines the 1226 structure of the property information for all defined data types. 1228 Section 4.8 describes properties in more details. 1230 3.2.7. LFB Versioning 1232 LFB class versioning is a method to enable incremental evolution of 1233 LFB classes. In general, an FE is not allowed to contain an LFB 1234 instance for more than one version of a particular class. 1235 Inheritance (discussed next in Section 3.2.8) has special rules. If 1236 an FE datapath model containing an LFB instance of a particular class 1237 C also simultaneously contains an LFB instance of a class C' 1238 inherited from class C; C could have a different version than C'. 1240 LFB class versioning is supported by requiring a version string in 1241 the class definition. CEs may support multiple versions of a 1242 particular LFB class to provide backward compatibility, but FEs MUST 1243 NOT support more than one version of a particular class. 1245 Versioning is not restricted to making backwards compatible changes. 1246 It is specifically expected to be used to make changes that cannot be 1247 represented by inheritance. Often this will be to correct errors, 1248 and hence may not be backwards compatible. It may also be used to 1249 remove components which are not considered useful (particularly if 1250 they were previously mandatory, and hence were an implementation 1251 impediment.) 1253 3.2.8. LFB Inheritance 1255 LFB class inheritance is supported in the FE model as a method to 1256 define new LFB classes. This also allows FE vendors to add vendor- 1257 specific extensions to standardized LFBs. An LFB class specification 1258 MUST specify the base class and version number it inherits from (the 1259 default is the base LFB class). Multiple inheritance is not allowed, 1260 however, to avoid unnecessary complexity. 1262 Inheritance should be used only when there is significant reuse of 1263 the base LFB class definition. A separate LFB class should be 1264 defined if little or no reuse is possible between the derived and the 1265 base LFB class. 1267 An interesting issue related to class inheritance is backward 1268 compatibility between a descendant and an ancestor class. Consider 1269 the following hypothetical scenario where a standardized LFB class 1270 "L1" exists. Vendor A builds an FE that implements LFB "L1" and 1271 vendor B builds a CE that can recognize and operate on LFB "L1". 1272 Suppose that a new LFB class, "L2", is defined based on the existing 1273 "L1" class by extending its capabilities incrementally. Let us 1274 examine the FE backward compatibility issue by considering what would 1275 happen if vendor B upgrades its FE from "L1" to "L2" and vendor C's 1276 CE is not changed. The old L1-based CE can interoperate with the new 1277 L2-based FE if the derived LFB class "L2" is indeed backward 1278 compatible with the base class "L1". 1280 The reverse scenario is a much less problematic case, i.e., when CE 1281 vendor B upgrades to the new LFB class "L2", but the FE is not 1282 upgraded. Note that as long as the CE is capable of working with 1283 older LFB classes, this problem does not affect the model; hence we 1284 will use the term "backward compatibility" to refer to the first 1285 scenario concerning FE backward compatibility. 1287 Backward compatibility can be designed into the inheritance model by 1288 constraining LFB inheritance to require the derived class be a 1289 functional superset of the base class (i.e. the derived class can 1290 only add functions to the base class, but not remove functions). 1291 Additionally, the following mechanisms are required to support FE 1292 backward compatibility: 1294 1. When detecting an LFB instance of an LFB type that is unknown to 1295 the CE, the CE MUST be able to query the base class of such an 1296 LFB from the FE. 1298 2. The LFB instance on the FE SHOULD support a backward 1299 compatibility mode (meaning the LFB instance reverts itself back 1300 to the base class instance), and the CE SHOULD be able to 1301 configure the LFB to run in such a mode. 1303 3.3. ForCES Model Addressing 1305 Figure 5 demonstrates the abstraction of the different ForCES model 1306 entities. The ForCES protocol provides the mechanism to uniquely 1307 identify any of the LFB Class instance components. 1309 FE Address = FE01 1310 +--------------------------------------------------------------+ 1311 | | 1312 | +--------------+ +--------------+ | 1313 | | LFB ClassID 1| |LFB ClassID 91| | 1314 | | InstanceID 3 |============>|InstanceID 3 |======>... | 1315 | | +----------+ | | +----------+ | | 1316 | | |Components| | | |Components| | | 1317 | | +----------+ | | +----------+ | | 1318 | +--------------+ +--------------+ | 1319 | | 1320 +--------------------------------------------------------------+ 1322 Figure 5: FE Entity Hierarchy 1324 At the top of the addressing hierachy is the FE identifier. In the 1325 example above, the 32-bit FE identifier is illustrated with the 1326 mnemonic FE01. The next 32-bit entity selector is the LFB ClassID. 1327 In the illustration above, two LFB classes with identifiers 1 and 91 1328 are demonstrated. The example above further illustrates one instance 1329 of each of the two classes. The scope of the 32-bit LFB class 1330 instance identifier is valid only within the LFB class. To emphasize 1331 that point, each of class 1 and 91 has an instance of 3. 1333 Using the described addressing scheme, a message could be sent to 1334 address FE01, LFB ClassID 1, LFB InstanceID 3, utilizing the ForCES 1335 protocol. However, to be effective, such a message would have to 1336 target entities within an LFB. These entities could be carrying 1337 state, capability, etc. These are further illustrated in Figure 6 1338 below. 1340 LFB Class ID 1,InstanceID 3 Components 1341 +-------------------------------------+ 1342 | | 1343 | LFB ComponentID 1 | 1344 | +----------------------+ | 1345 | | | | 1346 | +----------------------+ | 1347 | | 1348 | LFB ComponentID 31 | 1349 | +----------------------+ | 1350 | | | | 1351 | +----------------------+ | 1352 | | 1353 | LFB ComponentID 51 | 1354 | +----------------------+ | 1355 | | LFB ComponentID 89 | | 1356 | | +-----------------+ | | 1357 | | | | | | 1358 | | +-----------------+ | | 1359 | +----------------------+ | 1360 | | 1361 | | 1362 +-------------------------------------+ 1364 Figure 6: LFB Hierarchy 1366 Figure 6 zooms into the components carried by LFB Class ID 1, LFB 1367 InstanceID 3 from Figure 5. 1369 The example shows three components with 32-bit component identifiers 1370 1, 31, and 51. LFB ComponentID 51 is a complex structure 1371 encapsulating within it an entity with LFB ComponentID 89. LFB 1372 ComponentID 89 could be a complex structure itself but is restricted 1373 in the example for the sake of clarity. 1375 3.3.1. Addressing LFB Components: Paths and Keys 1377 As mentioned above, LFB components could be complex structures, such 1378 as a table, or even more complex structures such as a table whose 1379 cells are further tables, etc. The ForCES model XML schema 1380 (Section 4) allows for uniquely identifying anything with such 1381 complexity, utilizing the concept of dot-annotated static paths and 1382 content addressing of paths as derived from keys. As an example, if 1383 the LFB Component 51 were a structure, then the path to LFB 1384 ComponentID 89 above will be 51.89. 1386 LFB ComponentID 51 might represent a table (an array). In that case, 1387 to select the LFB Component with ID 89 from within the 7th entry of 1388 the table, one would use the path 51.7.89. In addition to supporting 1389 explicit table element selection by including an index in the dotted 1390 path, the model supports identifying table elements by their 1391 contents. This is referred to as using keys, or key indexing. So, 1392 as a further example, if ComponentID 51 was a table which was key 1393 index-able, then a key describing content could also be passed by the 1394 CE, along with path 51 to select the table, and followed by the path 1395 89 to select the table structure element, which upon computation by 1396 the FE would resolve to the LFB ComponentID 89 within the specified 1397 table entry. 1399 3.4. FE Datapath Modeling 1401 Packets coming into the FE from ingress ports generally flow through 1402 one or more LFBs before leaving out of the egress ports. How an FE 1403 treats a packet depends on many factors, such as type of the packet 1404 (e.g., IPv4, IPv6, or MPLS), header values, time of arrival, etc. 1405 The result of LFB processing may have an impact on how the packet is 1406 to be treated in downstream LFBs. This differentiation of packet 1407 treatment downstream can be conceptualized as having alternative 1408 datapaths in the FE. For example, the result of a 6- tuple 1409 classification performed by a classifier LFB could control which rate 1410 meter is applied to the packet by a rate meter LFB in a later stage 1411 in the datapath. 1413 LFB topology is a directed graph representation of the logical 1414 datapaths within an FE; with the nodes representing the LFB instances 1415 and the directed link depicting the packet flow direction from one 1416 LFB to the next. Section 3.4.1 discusses how the FE datapaths can be 1417 modeled as LFB topology; while Section 3.4.2 focuses on issues 1418 related to LFB topology reconfiguration. 1420 3.4.1. Alternative Approaches for Modeling FE Datapaths 1422 There are two basic ways to express the differentiation in packet 1423 treatment within an FE, one represents the datapath directly and 1424 graphically (topological approach) and the other utilizes metadata 1425 (the encoded state approach). 1427 o Topological Approach 1429 Using this approach, differential packet treatment is expressed by 1430 splitting the LFB topology into alternative paths. In other words, 1431 if the result of an LFB operation controls how the packet is further 1432 processed, then such an LFB will have separate output ports, one for 1433 each alternative treatment, connected to separate sub-graphs, each 1434 expressing the respective treatment downstream. 1436 o Encoded State Approach 1438 An alternate way of expressing differential treatment is by using 1439 metadata. The result of the operation of an LFB can be encoded in a 1440 metadatum, which is passed along with the packet to downstream LFBs. 1441 A downstream LFB, in turn, can use the metadata and its value (e.g., 1442 as an index into some table) to determine how to treat the packet. 1444 Theoretically, either approach could substitute for the other, so one 1445 could consider using a single pure approach to describe all datapaths 1446 in an FE. However, neither model by itself results in the best 1447 representation for all practically relevant cases. For a given FE 1448 with certain logical datapaths, applying the two different modeling 1449 approaches will result in very different looking LFB topology graphs. 1450 A model using only the topological approach may require a very large 1451 graph with many links or paths, and nodes (i.e., LFB instances) to 1452 express all alternative datapaths. On the other hand, a model using 1453 only the encoded state model would be restricted to a string of LFBs, 1454 which is not an intuitive way to describe different datapaths (such 1455 as MPLS and IPv4). Therefore, a mix of these two approaches will 1456 likely be used for a practical model. In fact, as we illustrate 1457 below, the two approaches can be mixed even within the same LFB. 1459 Using a simple example of a classifier with N classification outputs 1460 followed by other LFBs, Figure 7.a shows what the LFB topology looks 1461 like when using the pure topological approach. Each output from the 1462 classifier goes to one of the N LFBs where no metadata is needed. 1463 The topological approach is simple, straightforward and graphically 1464 intuitive. However, if N is large and the N nodes following the 1465 classifier (LFB#1, LFB#2, ..., LFB#N) all belong to the same LFB type 1466 (e.g., meter), but each has its own independent components, the 1467 encoded state approach gives a much simpler topology representation, 1468 as shown in Figure 7.b. The encoded state approach requires that a 1469 table of N rows of meter components is provided in the Meter node 1470 itself, with each row representing the attributes for one meter 1471 instance. A metadatum M is also needed to pass along with the packet 1472 P from the classifier to the meter, so that the meter can use M as a 1473 look-up key (index) to find the corresponding row of the attributes 1474 that should be used for any particular packet P. 1476 What if those N nodes (LFB#1, LFB#2, ..., LFB#N) are not of the same 1477 type? For example, if LFB#1 is a queue while the rest are all 1478 meters, what is the best way to represent such datapaths? While it 1479 is still possible to use either the pure topological approach or the 1480 pure encoded state approach, the natural combination of the two 1481 appears to be the best option. Figure 7.c depicts two different 1482 functional datapaths using the topological approach while leaving the 1483 N-1 meter instances distinguished by metadata only, as shown in 1484 Figure 7.c. 1486 +----------+ 1487 P | LFB#1 | 1488 +--------->|(Compon-1)| 1489 +-------------+ | +----------+ 1490 | 1|------+ P +----------+ 1491 | 2|---------------->| LFB#2 | 1492 | classifier 3| |(Compon-2)| 1493 | ...|... +----------+ 1494 | N|------+ ... 1495 +-------------+ | P +----------+ 1496 +--------->| LFB#N | 1497 |(Compon-N)| 1498 +----------+ 1500 (a) Using pure topological approach 1502 +-------------+ +-------------+ 1503 | 1| | Meter | 1504 | 2| (P, M) | (Compon-1) | 1505 | 3|---------------->| (Compon-2) | 1506 | ...| | ... | 1507 | N| | (Compon-N) | 1508 +-------------+ +-------------+ 1510 (b) Using pure encoded state approach to represent the LFB 1511 topology in 5(a), if LFB#1, LFB#2, ..., and LFB#N are of the 1512 same type (e.g., meter). 1514 +-------------+ 1515 +-------------+ (P, M) | queue | 1516 | 1|------------->| (Compon-1) | 1517 | 2| +-------------+ 1518 | 3| (P, M) +-------------+ 1519 | ...|------------->| Meter | 1520 | N| | (Compon-2) | 1521 +-------------+ | ... | 1522 | (Compon-N) | 1523 +-------------+ 1525 (c) Using a combination of the two, if LFB#1, LFB#2, ..., and 1526 LFB#N are of different types (e.g., queue and meter). 1528 Figure 7: An example of how to model FE datapaths 1530 From this example, we demonstrate that each approach has a distinct 1531 advantage depending on the situation. Using the encoded state 1532 approach, fewer connections are typically needed between a fan-out 1533 node and its next LFB instances of the same type because each packet 1534 carries metadata the following nodes can interpret and hence invoke a 1535 different packet treatment. For those cases, a pure topological 1536 approach forces one to build elaborate graphs with many more 1537 connections and often results in an unwieldy graph. On the other 1538 hand, a topological approach is the most intuitive for representing 1539 functionally different datapaths. 1541 For complex topologies, a combination of the two is the most 1542 flexible. A general design guideline is provided to indicate which 1543 approach is best used for a particular situation. The topological 1544 approach should primarily be used when the packet datapath forks to 1545 distinct LFB classes (not just distinct parameterizations of the same 1546 LFB class), and when the fan-outs do not require changes, such as 1547 adding/removing LFB outputs, or require only very infrequent changes. 1548 Configuration information that needs to change frequently should be 1549 expressed by using the internal attributes of one or more LFBs (and 1550 hence using the encoded state approach). 1552 +---------------------------------------------+ 1553 | | 1554 +----------+ V +----------+ +------+ | 1555 | | | | |if IP-in-IP| | | 1556 ---->| ingress |->+----->|classifier|---------->|Decap.|---->---+ 1557 | ports | | |---+ | | 1558 +----------+ +----------+ |others +------+ 1559 | 1560 V 1561 (a) The LFB topology with a logical loop 1563 +-------+ +-----------+ +------+ +-----------+ 1564 | | | |if IP-in-IP | | | | 1565 --->|ingress|-->|classifier1|----------->|Decap.|-->+classifier2|-> 1566 | ports | | |----+ | | | | 1567 +-------+ +-----------+ |others +------+ +-----------+ 1568 | 1569 V 1570 (b)The LFB topology without the loop utilizing two independent 1571 classifier instances. 1573 Figure 8: An LFB topology example. 1575 It is important to point out that the LFB topology described here is 1576 the logical topology, not the physical topology of how the FE 1577 hardware is actually laid out. Nevertheless, the actual 1578 implementation may still influence how the functionality is mapped to 1579 the LFB topology. Figure 8 shows one simple FE example. In this 1580 example, an IP-in-IP packet from an IPSec application like VPN may go 1581 to the classifier first and have the classification done based on the 1582 outer IP header; upon being classified as an IP-in-IP packet, the 1583 packet is then sent to a decapsulator to strip off the outer IP 1584 header, followed by a classifier again to perform classification on 1585 the inner IP header. If the same classifier hardware or software is 1586 used for both outer and inner IP header classification with the same 1587 set of filtering rules, a logical loop is naturally present in the 1588 LFB topology, as shown in Figure 8.a. However, if the classification 1589 is implemented by two different pieces of hardware or software with 1590 different filters (i.e., one set of filters for the outer IP header 1591 and another set for the inner IP header), then it is more natural to 1592 model them as two different instances of classifier LFB, as shown in 1593 Figure 8.b. 1595 3.4.2. Configuring the LFB Topology 1597 While there is little doubt that an individual LFB must be 1598 configurable, the configurability question is more complicated for 1599 LFB topology. Since the LFB topology is really the graphic 1600 representation of the datapaths within an FE, configuring the LFB 1601 topology means dynamically changing the datapaths, including changing 1602 the LFBs along the datapaths on an FE (e.g., creating/instantiating, 1603 updating or deleting LFBs) and setting up or deleting 1604 interconnections between outputs of upstream LFBs to inputs of 1605 downstream LFBs. 1607 Why would the datapaths on an FE ever change dynamically? The 1608 datapaths on an FE are set up by the CE to provide certain data plane 1609 services (e.g., DiffServ, VPN, etc.) to the Network Element's (NE) 1610 customers. The purpose of reconfiguring the datapaths is to enable 1611 the CE to customize the services the NE is delivering at run time. 1612 The CE needs to change the datapaths when the service requirements 1613 change, such as adding a new customer or when an existing customer 1614 changes their service. However, note that not all datapath changes 1615 result in changes in the LFB topology graph. Changes in the graph 1616 are dependent on the approach used to map the datapaths into LFB 1617 topology. As discussed in Section 3.4.1, the topological approach 1618 and encoded state approach can result in very different looking LFB 1619 topologies for the same datapaths. In general, an LFB topology based 1620 on a pure topological approach is likely to experience more frequent 1621 topology reconfiguration than one based on an encoded state approach. 1622 However, even an LFB topology based entirely on an encoded state 1623 approach may have to change the topology at times, for example, to 1624 bypass some LFBs or insert new LFBs. Since a mix of these two 1625 approaches is used to model the datapaths, LFB topology 1626 reconfiguration is considered an important aspect of the FE model. 1628 We want to point out that allowing a configurable LFB topology in the 1629 FE model does not mandate that all FEs are required to have this 1630 capability. Even if an FE supports configurable LFB topology, the FE 1631 may impose limitations on what can actually be configured. 1632 Performance-optimized hardware implementations may have zero or very 1633 limited configurability, while FE implementations running on network 1634 processors may provide more flexibility and configurability. It is 1635 entirely up to the FE designers to decide whether or not the FE 1636 actually implements reconfiguration and if so, how much. Whether a 1637 simple runtime switch is used to enable or disable (i.e., bypass) 1638 certain LFBs, or more flexible software reconfiguration is used, is 1639 an implementation detail internal to the FE and outside of the scope 1640 of FE model. In either case, the CE(s) MUST be able to learn the 1641 FE's configuration capabilities. Therefore, the FE model MUST 1642 provide a mechanism for describing the LFB topology configuration 1643 capabilities of an FE. These capabilities may include (see Section 5 1644 for full details): 1646 o Which LFB classes the FE can instantiate 1648 o The maximum number of instances of the same LFB class that can be 1649 created 1651 o Any topological limitations, for example: 1653 * The maximum number of instances of the same class or any class 1654 that can be created on any given branch of the graph 1656 * Ordering restrictions on LFBs (e.g., any instance of LFB class 1657 A must be always downstream of any instance of LFB class B). 1659 The CE needs some programming help in order to cope with the range of 1660 complexity. In other words, even when the CE is allowed to configure 1661 LFB topology for the FE, the CE is not expected to be able to 1662 interpret an arbitrary LFB topology and determine which specific 1663 service or application (e.g. VPN, DiffServ, etc.) is supported by 1664 the FE. However, once the CE understands the coarse capability of an 1665 FE, the CE MUST configure the LFB topology to implement the network 1666 service the NE is supposed to provide. Thus, the mapping the CE has 1667 to understand is from the high level NE service to a specific LFB 1668 topology, not the other way around. The CE is not expected to have 1669 the ultimate intelligence to translate any high level service policy 1670 into the configuration data for the FEs. However, it is conceivable 1671 that within a given network service domain, a certain amount of 1672 intelligence can be programmed into the CE to give the CE a general 1673 understanding of the LFBs involved to allow the translation from a 1674 high level service policy to the low level FE configuration to be 1675 done automatically. Note that this is considered an implementation 1676 issue internal to the control plane and outside the scope of the FE 1677 model. Therefore, it is not discussed any further in this draft. 1679 +----------+ +-----------+ 1680 ---->| Ingress |---->|classifier |--------------+ 1681 | | |chip | | 1682 +----------+ +-----------+ | 1683 v 1684 +-------------------------------------------+ 1685 +--------+ | Network Processor | 1686 <----| Egress | | +------+ +------+ +-------+ | 1687 +--------+ | |Meter | |Marker| |Dropper| | 1688 ^ | +------+ +------+ +-------+ | 1689 | | | 1690 +----------+-------+ | 1691 | | | 1692 | +---------+ +---------+ +------+ +---------+ | 1693 | |Forwarder|<------|Scheduler|<--|Queue | |Counter | | 1694 | +---------+ +---------+ +------+ +---------+ | 1695 +--------------------------------------------------------------+ 1697 Figure 9: The Capability of an FE as reported to the CE 1699 Figure 9 shows an example where a QoS-enabled router has several line 1700 cards that have a few ingress ports and egress ports, a specialized 1701 classification chip, and a network processor containing codes for FE 1702 blocks like meter, marker, dropper, counter, queue, scheduler, and 1703 Ipv4 forwarder. Some of the LFB topology is already fixed and has to 1704 remain static due to the physical layout of the line cards. For 1705 example, all of the ingress ports might be hardwired into the 1706 classification chip so all packets flow from the ingress port into 1707 the classification engine. On the other hand, the LFBs on the 1708 network processor and their execution order are programmable. 1709 However, certain capacity limits and linkage constraints could exist 1710 between these LFBs. Examples of the capacity limits might be: 1712 o 8 meters 1714 o 16 queues in one FE 1716 o the scheduler can handle at most up to 16 queues 1717 o The linkage constraints might dictate that: 1719 * the classification engine may be followed by: 1721 + a meter 1723 + marker 1725 + dropper 1727 + counter 1729 + queue or IPv4 forwarder, but not a scheduler 1731 * queues can only be followed by a scheduler 1733 * a scheduler must be followed by the IPv4 forwarder 1735 * the last LFB in the datapath before going into the egress ports 1736 must be the IPv4 forwarder 1738 +-----+ +-------+ +---+ 1739 | A|--->|Queue1 |--------------------->| | 1740 ------>| | +-------+ | | +---+ 1741 | | | | | | 1742 | | +-------+ +-------+ | | | | 1743 | B|--->|Meter1 |----->|Queue2 |------>| |->| | 1744 | | | | +-------+ | | | | 1745 | | | |--+ | | | | 1746 +-----+ +-------+ | +-------+ | | +---+ 1747 classifier +-->|Dropper| | | IPv4 1748 +-------+ +---+ Fwd. 1749 Scheduler 1751 Figure 10: An LFB topology as configured by the CE and accepted by 1752 the FE 1754 Once the FE reports these capabilities and capacity limits to the CE, 1755 it is now up to the CE to translate the QoS policy into a desirable 1756 configuration for the FE. Figure 9 depicts the FE capability while 1757 Figure 10 and Figure 11 depict two different topologies that the CE 1758 may request the FE to configure. Note that Figure 11 is not fully 1759 drawn, as inter-LFB links are included to suggest potential 1760 complexity, without drawing in the endpoints of all such links. 1762 Queue1 1763 +---+ +--+ 1764 | A|------------------->| |--+ 1765 +->| | | | | 1766 | | B|--+ +--+ +--+ +--+ | 1767 | +---+ | | | | | | 1768 | Meter1 +->| |-->| | | 1769 | | | | | | 1770 | +--+ +--+ | Ipv4 1771 | Counter1 Dropper1 Queue2| +--+ Fwd. 1772 +---+ | +--+ +--->|A | +-+ 1773 | A|---+ | |------>|B | | | 1774 ------>| B|------------------------------>| | +-->|C |->| |-> 1775 | C|---+ +--+ | +>|D | | | 1776 | D|-+ | | | +--+ +-+ 1777 +---+ | | +---+ Queue3 | |Scheduler 1778 Classifier1 | | | A|------------> +--+ | | 1779 | +->| | | |-+ | 1780 | | B|--+ +--+ +-------->| | | 1781 | +---+ | | | | +--+ | 1782 | Meter2 +->| |-+ | 1783 | | | | 1784 | +--+ Queue4 | 1785 | Marker1 +--+ | 1786 +---------------------------->| |---+ 1787 | | 1788 +--+ 1790 Figure 11: Another LFB topology as configured by the CE and accepted 1791 by the FE 1793 Note that both the ingress and egress are omitted in Figure 10 and 1794 Figure 11 to simplify the representation. The topology in Figure 11 1795 is considerably more complex than Figure 10 but both are feasible 1796 within the FE capabilities, and so the FE should accept either 1797 configuration request from the CE. 1799 4. Model and Schema for LFB Classes 1801 The main goal of the FE model is to provide an abstract, generic, 1802 modular, implementation-independent representation of the FEs. This 1803 is facilitated using the concept of LFBs, which are instantiated from 1804 LFB classes. LFB classes and associated definitions will be provided 1805 in a collection of XML documents. The collection of these XML 1806 documents is called a LFB class library, and each document is called 1807 an LFB class library document (or library document, for short). Each 1808 of the library documents MUST conform to the schema presented in this 1809 section. The root element of the library document is the 1810 element. 1812 It is not expected that library documents will be exchanged between 1813 FEs and CEs "over-the-wire". But the model will serve as an 1814 important reference for the design and development of the CEs 1815 (software) and FEs (mostly the software part). It will also serve as 1816 a design input when specifying the ForCES protocol elements for CE-FE 1817 communication. 1819 The following sections describe the portions of an LFBLibrary XML 1820 Document. The descriptions primarily provide the necessary semantic 1821 information to understand the meaning and uses of the XML elements. 1822 The XML Schema below provides the final definition on what elements 1823 are permitted, and their base syntax. Unfortunately, due to the 1824 limitations of english and XML, there are constraints described in 1825 the semantic sections which are not fully captured in the XML Schema, 1826 so both sets of information need to be used to build a compliant 1827 library document. 1829 4.1. Namespace 1831 A namespace is needed to uniquely identify the LFB type in the LFB 1832 class library. The reference to the namespace definition is 1833 contained in Section 9, IANA Considerations. 1835 4.2. Element 1837 The element serves as a root element of all library 1838 documents. A library document contains a sequence of top level 1839 elements. The following is a list of all the elements which can 1840 occur directly in the element. If they occur, they must 1841 occur in the order listed. 1843 o providing a text description of the purpose of the 1844 library document. 1846 o for loading information from other library documents. 1848 o for the frame declarations; 1850 o for defining common data types; 1852 o for defining metadata, and 1854 o for defining LFB classes. 1856 Each element is optional. One library document may contain only 1857 metadata definitions, another may contain only LFB class definitions, 1858 yet another may contain all of the above. 1860 A library document can import other library documents if it needs to 1861 refer to definitions contained in the included document. This 1862 concept is similar to the "#include" directive in C. Importing is 1863 expressed by the use of elements, which must precede all the 1864 above elements in the document. For unique referencing, each 1865 LFBLibrary instance document has a unique label defined in the 1866 "provide" attribute of the LFBLibrary element. Note that what this 1867 performs is a ForCES inclusion, not an XML inclusion. The semantic 1868 content of the library referenced by the element is included, 1869 not the xml content. Also, in terms of the conceptual processing 1870 elements, the total set of documents loaded are considered to 1871 form a single document for processing. A given document is included 1872 in this set only once, even if it is referenced by elements 1873 several times, even from several different files. As the processing 1874 of LFBLibrary information is not order dependent, the order for 1875 processing loaded elements is up to the implementor, as long as the 1876 total effect is as if all of the information from all the files were 1877 available for referencing when needed. Note that such computer 1878 processing of ForCES model library documents may be helpful for 1879 various implementations, but is not required to define the libraries, 1880 or for the actual operation of the protocol itself. 1882 The following is a skeleton of a library document: 1884 1885 1888 1890 1892 1893 1894 ... 1896 1897 1898 ... 1899 1901 1902 1903 ... 1904 1906 1907 1908 ... 1909 1911 1915 1917 1918 1920 4.3. Element 1922 This element is used to refer to another LFB library document. 1923 Similar to the "#include" directive in C, this makes the objects 1924 (metadata types, data types, etc.) defined in the referred library 1925 document available for referencing in the current document. 1927 The load element MUST contain the label of the library document to be 1928 included and may contain a URL to specify where the library can be 1929 retrieved. The load element can be repeated unlimited times. Three 1930 examples for the elements: 1932 1933 1934 1937 4.4. Element for Frame Type Declarations 1939 Frame names are used in the LFB definition to define the types of 1940 frames the LFB expects at its input port(s) and emits at its output 1941 port(s). The optional element in the library document 1942 contains one or more elements, each declaring one frame 1943 type. 1945 Each frame definition MUST contain a unique name (NMTOKEN) and a 1946 brief synopsis. In addition, an optional detailed description may be 1947 provided. 1949 Uniqueness of frame types MUST be ensured among frame types defined 1950 in the same library document and in all directly or indirectly 1951 included library documents. 1953 The following example defines two frame types: 1955 1956 1957 ipv4 1958 IPv4 packet 1959 1960 This frame type refers to an IPv4 packet. 1961 1962 1963 1964 ipv6 1965 IPv6 packet 1966 1967 This frame type refers to an IPv6 packet. 1968 1969 1970 ... 1971 1973 4.5. Element for Data Type Definitions 1975 The (optional) element can be used to define commonly 1976 used data types. It contains one or more elements, 1977 each defining a data type with a unique name. Such data types can be 1978 used in several places in the library documents, including: 1980 o Defining other data types 1982 o Defining components of LFB classes 1984 This is similar to the concept of having a common header file for 1985 shared data types. 1987 Each element MUST contain a unique name (NMTOKEN), a 1988 brief synopsis, and a type definition element. The name MUST be 1989 unique among all data types defined in the same library document and 1990 in any directly or indirectly included library documents. The 1991 element may also include an optional longer 1992 description, For example: 1994 1995 1996 ieeemacaddr 1997 48-bit IEEE MAC address 1998 ... type definition ... 1999 2000 2001 ipv4addr 2002 IPv4 address 2003 ... type definition ... 2004 2005 ... 2006 2008 There are two kinds of data types: atomic and compound. Atomic data 2009 types are appropriate for single-value variables (e.g. integer, 2010 string, byte array). 2012 The following built-in atomic data types are provided, but additional 2013 atomic data types can be defined with the and 2014 elements: 2016 Meaning 2017 ---- ------- 2018 char 8-bit signed integer 2019 uchar 8-bit unsigned integer 2020 int16 16-bit signed integer 2021 uint16 16-bit unsigned integer 2022 int32 32-bit signed integer 2023 uint32 32-bit unsigned integer 2024 int64 64-bit signed integer 2025 uint64 64-bit unsigned integer 2026 boolean A true / false value where 2027 0 = false, 1 = true 2028 string[N] A UTF-8 string represented in at most 2029 N Octets. 2030 string A UTF-8 string without a configured 2031 storage length limit. 2032 byte[N] A byte array of N bytes 2033 octetstring[N] A buffer of N octets, which may 2034 contain fewer than N octets. Hence 2035 the encoded value will always have 2036 a length. 2037 float16 16-bit floating point number 2038 float32 32-bit IEEE floating point number 2039 float64 64-bit IEEE floating point number 2041 These built-in data types can be readily used to define metadata or 2042 LFB attributes, but can also be used as building blocks when defining 2043 new data types. The boolean data type is defined here because it is 2044 so common, even though it can be built by sub-ranging the uchar data 2045 type. 2047 Compound data types can build on atomic data types and other compound 2048 data types. Compound data types can be defined in one of four ways. 2049 They may be defined as an array of components of some compound or 2050 atomic data type. They may be a structure of named components of 2051 compound or atomic data types (ala C structures). They may be a 2052 union of named components of compound or atomic data types (ala C 2053 unions). They may also be defined as augmentations (explained in 2054 Section 4.5.7) of existing compound data types. 2056 Given that the FORCES protocol will be getting and setting component 2057 values, all atomic data types used here must be able to be conveyed 2058 in the FORCES protocol. Further, the FORCES protocol will need a 2059 mechanism to convey compound data types. However, the details of 2060 such representations are for the ForCES Protocol [2] document to 2061 define, not the model document. Strings and octetstrings must be 2062 conveyed by the protocol with their length, as they are not 2063 delimited, the value does not itself include the length, and these 2064 items are variable length. 2066 With regard to strings, this model defines a small set of 2067 restrictions and definitions on how they are structured. String and 2068 octetstring length limits can be specified in the LFB Class 2069 definitions. The component properties for string and octetstring 2070 components also contain actual lengths and length limits. This 2071 duplication of limits is to allow for implementations with smaller 2072 limits than the maximum limits specified in the LFB Class definition. 2073 In all cases, these lengths are specified in octets, not in 2074 characters. In terms of protocol operation, as long as the specified 2075 length is within the FE's supported capabilities, the FE stores the 2076 contents of a string exactly as provided by the CE, and returns those 2077 contents when requested. No canonicalization, transformations, or 2078 equivalences are performed by the FE. components of type string (or 2079 string[n]) may be used to hold identifiers for correlation with 2080 components in other LFBs. In such cases, an exact octet for octet 2081 match is used. No equivalences are used by the FE or CE in 2082 performing that matching. The ForCES Protocol [2] does not perform 2083 or require validation of the content of UTF-8 strings. However, 2084 UTF-8 strings SHOULD be encoded in the shortest form to avoid 2085 potential security issues described in [12]. Any entity displaying 2086 such strings is expected to perform its own validation (for example 2087 for correct multi-byte characters, and for ensuring that the string 2088 does not end in the middle of a multi-byte sequence.) Specific LFB 2089 class definitions may restrict the valid contents of a string as 2090 suited to the particular usage (for example, a component that holds a 2091 DNS name would be restricted to hold only octets valid in such a 2092 name.) FEs should validate the contents of SET requests for such 2093 restricted components at the time the set is performed, just as range 2094 checks for range limited components are performed. The ForCES 2095 protocol behavior defines the normative processing for requests using 2096 that protocol. 2098 For the definition of the actual type in the element, 2099 the following elements are available: , , , 2100 , and . 2102 The predefined type alias is somewhere between the atomic and 2103 compound data types. It behaves like a structure, one component of 2104 which has special behavior. Given that the special behavior is tied 2105 to the other parts of the structure, the compound result is treated 2106 as a predefined construct. 2108 4.5.1. Element for Renaming Existing Data Types 2110 The element refers to an existing data type by its name. 2111 The referred data type MUST be defined either in the same library 2112 document, or in one of the included library documents. If the 2113 referred data type is an atomic data type, the newly defined type 2114 will also be regarded as atomic. If the referred data type is a 2115 compound type, the new type will also be compound. Some usage 2116 examples follow: 2118 2119 short 2120 Alias to int16 2121 int16 2122 2123 2124 ieeemacaddr 2125 48-bit IEEE MAC address 2126 byte[6] 2127 2129 4.5.2. Element for Deriving New Atomic Types 2131 The element allows the definition of a new atomic type from 2132 an existing atomic type, applying range restrictions and/or providing 2133 special enumerated values. Note that the element can only 2134 use atomic types as base types, and its result MUST be another atomic 2135 type. 2137 For example, the following snippet defines a new "dscp" data type: 2139 2140 dscp 2141 Diffserv code point. 2142 2143 uchar 2144 2145 2146 2147 2148 2149 DSCP-BE 2150 Best Effort 2151 2152 ... 2153 2154 2155 2157 4.5.3. Element to Define Arrays 2159 The element can be used to create a new compound data type as 2160 an array of a compound or an atomic data type. Depending upon 2161 context, this document, and others, refer to such arrays as tables or 2162 arrays interchangeably, without semantic or syntactic implication. 2163 The type of the array entry can be specified either by referring to 2164 an existing type (using the element) or defining an unnamed 2165 type inside the element using any of the , , 2166 , or elements. 2168 The array can be "fixed-size" or "variable-size", which is specified 2169 by the "type" attribute of the element. The default is 2170 "variable-size". For variable size arrays, an optional "maxlength" 2171 attribute specifies the maximum allowed length. This attribute 2172 should be used to encode semantic limitations, not implementation 2173 limitations. The latter should be handled by capability components 2174 of LFB classes, and should never be included in a data type array 2175 which is regarded as of unlimited-size. 2177 For fixed-size arrays, a "length" attribute MUST be provided that 2178 specifies the constant size of the array. 2180 The result of this construct MUST always be a compound type, even if 2181 the array has a fixed size of 1. 2183 Arrays MUST only be subscripted by integers, and will be presumed to 2184 start with index 0. 2186 In addition to their subscripts, arrays may be declared to have 2187 content keys. Such a declaration has several effects: 2189 o Any declared key can be used in the ForCES protocol to select a 2190 component for operations (for details, see the ForCES Protocol 2191 [2]). 2193 o In any instance of the array, each declared key must be unique 2194 within that instance. No two components of an array may have the 2195 same values on all the fields which make up a key. 2197 Each key is declared with a keyID for use in the ForCES Protocol [2], 2198 where the unique key is formed by combining one or more specified key 2199 fields. To support the case where an array of an atomic type with 2200 unique values can be referenced by those values, the key field 2201 identifier may be "*" (i.e., the array entry is the key). If the 2202 value type of the array is a structure or an array, then the key is 2203 one or more components of the value type, each identified by name. 2204 Since the field may be a component of the contained structure, a 2205 component of a component of a structure, or further nested, the field 2206 name is actually a concatenated sequence of component identifiers, 2207 separated by decimal points ("."). The syntax for key field 2208 identification is given following the array examples. 2210 The following example shows the definition of a fixed size array with 2211 a pre-defined data type as the array content type: 2213 2214 dscp-mapping-table 2215 2216 A table of 64 DSCP values, used to re-map code space. 2217 2218 2219 dscp 2220 2221 2223 The following example defines a variable size array with an upper 2224 limit on its size: 2226 2227 mac-alias-table 2228 A table with up to 8 IEEE MAC addresses 2229 2230 ieeemacaddr 2231 2232 2234 The following example shows the definition of an array with a local 2235 (unnamed) content type definition: 2237 2238 classification-table 2239 2240 A table of classification rules and result opcodes. 2241 2242 2243 2244 2245 rule 2246 The rule to match 2247 classrule 2248 2249 2250 opcode 2251 The result code 2252 opcode 2253 2254 2255 2256 2258 In the above example, each entry of the array is a of two 2259 components ("rule" and "opcode"). 2261 The following example shows a table of IP Prefix information that can 2262 be accessed by a multi-field content key on the IP Address, prefix 2263 length, and information source. This means that in any instance of 2264 this table, no two entries can have the same IP address, prefix 2265 length, and information source. 2267 2268 ipPrefixInfo_table 2269 2270 A table of information about known prefixes 2271 2272 2273 2274 2275 address-prefix 2276 the prefix being described 2277 ipv4Prefix 2278 2279 2280 source 2281 2282 the protocol or process providing this information 2283 2284 uint16 2285 2286 2287 prefInfo 2288 the information we care about 2289 hypothetical-info-type 2290 2291 2292 2293 address-prefix.ipv4addr 2294 address-prefix.prefixlen 2295 source 2296 2297 2298 2300 Note that the keyField elements could also have been simply address- 2301 prefix and source, since all of the fields of address-prefix are 2302 being used. 2304 4.5.3.1. Key Field References 2306 In order to use key declarations, one must refer to components that 2307 are potentially nested inside other components in the array. If 2308 there are nested arrays, one might even use an array element as a key 2309 (but great care would be needed to ensure uniqueness.) 2311 The key is the combination of the values of each field declared in a 2312 keyField element. 2314 Therefore, the value of a keyField element MUST be a concatenated 2315 Sequence of field identifiers, separated by a "." (period) character. 2316 Whitespace is permitted and ignored. 2318 A valid string for a single field identifier within a keyField 2319 depends upon the current context. Initially, in an array key 2320 declaration, the context is the type of the array. Progressively, 2321 the context is whatever type is selected by the field identifiers 2322 processed so far in the current key field declaration. 2324 When the current context is an array, (e.g., when declaring a key for 2325 an array whose content is an array) then the only valid value for the 2326 field identifier is an explicit number. 2328 When the current context is a structure, the valid values for the 2329 field identifiers are the names of the components of the structure. 2330 In the special case of declaring a key for an array containing an 2331 atomic type, where that content is unique and is to be used as a key, 2332 the value "*" can be used as the single key field identifier. 2334 4.5.4. Element to Define Structures 2336 A structure is comprised of a collection of data components. Each 2337 data components has a data type (either an atomic type or an existing 2338 compound type) and is assigned a name unique within the scope of the 2339 compound data type being defined. These serve the same function as 2340 "struct" in C, etc. These components are defined using 2341 elements. A element may contain an optional derivation 2342 indication, a element. The structure definition MUST 2343 contain a sequence of one or more elements. 2345 The actual type of the component can be defined by referring to an 2346 existing type (using the element), or can be a locally 2347 defined (unnamed) type created by any of the , , 2348 , or elements. 2350 The element must include a componentID attribute. This 2351 provides the numeric ID for this component, for use by the protocol. 2352 The MUST contain a component name and a synopsis. It may 2353 contain a =description> element giving a textual description of the 2354 component. The definition may also include a element, 2355 which indicates that the component being defined is optional. The 2356 definition MUST contain elements to define the data type of the 2357 component, as described above. 2359 For a dataTypeDef of a struct, the structure definition may be 2360 inherited from, and augment, a previously defined structured type. 2361 This is indicated by including the optional derivedFrom attribute in 2362 the struct declaration before the definition of the augmenting or 2363 replacing components. 2365 The result of this construct MUST be a compound type, even when the 2366 contains only one field. 2368 An example: 2370 2371 ipv4prefix 2372 2373 IPv4 prefix defined by an address and a prefix length 2374 2375 2376 2377 address 2378 Address part 2379 ipv4addr 2380 2381 2382 prefixlen 2383 Prefix length part 2384 2385 uchar 2386 2387 2388 2389 2390 2391 2392 2394 4.5.5. Element to Define Union Types 2396 Similar to the union declaration in C, this construct allows the 2397 definition of overlay types. Its format is identical to the 2398 element. 2400 The result of this construct MUST be a compound type, even when the 2401 union contains only one element. 2403 4.5.6. Element 2405 It is sometimes necessary to have a component in an LFB or structure 2406 refer to information (a component) in other LFBs. This can, for 2407 example, allow an ARP LFB to share the IP->MAC Address table with the 2408 local transmission LFB, without duplicating information. Similarly, 2409 it could allow a traffic measurement LFB to share information with a 2410 traffic enforcement LFB. The declaration creates the 2411 constructs for this. This construct tells the CE and FE that any 2412 manipulation of the defined data is actually manipulation of data 2413 defined to exist in some specified part of some other LFB instance. 2414 The content of an element MUST be a named type. Whatever 2415 component the alias references (which is determined by the alias 2416 component properties, as described below) that component must be of 2417 the same type as that declared for the alias. Thus, when the CE or 2418 FE dereferences the alias component, the type of the information 2419 returned is known. The type can be a base type or a derived type. 2420 The actual value referenced by an alias is known as its target. When 2421 a GET or SET operation references the alias element, the value of the 2422 target is returned or replaced. Write access to an alias element is 2423 permitted if write access to both the alias and the target are 2424 permitted. 2426 The target of a component declared by an element is 2427 determined by it the components properties. Like all components, the 2428 properties MUST include the support / read / write permission for the 2429 alias. In addition, there are several fields (components) in the 2430 alias properties which define the target of the alias. These 2431 components are the ID of the LFB class of the target, the ID of the 2432 LFB instance of the target, and a sequence of integers representing 2433 the path within the target LFB instance to the target component. The 2434 type of the target element must match the declared type of the alias. 2435 Details of the alias property structure are described in Section 4.8 2436 of this document on properties. 2438 Note that the read / write property of the alias refers to the value. 2439 The CE can only determine if it can write the target selection 2440 properties of the alias by attempting such a write operation. 2441 (Property components do not themselves have properties.) 2443 4.5.7. Augmentations 2445 Compound types can also be defined as augmentations of existing 2446 compound types. If the existing compound type is a structure, 2447 augmentation may add new elements to the type. The type of an 2448 existing component can be replaced in the definition of an augmenting 2449 structure, but only with an augmentation derived from the current 2450 type of the existing component. An existing component cannot be 2451 deleted. If the existing compound type is an array, augmentation 2452 means augmentation of the array element type. 2454 One consequence of this is that augmentations are backwards 2455 compatible with the compound type from which they are derived. As 2456 such, augmentations are useful in defining components for LFB 2457 subclasses with backward compatibility. In addition to adding new 2458 components to a class, the data type of an existing components may be 2459 replaced by an augmentation of that component, and still meet the 2460 compatibility rules for subclasses. 2462 For example, consider a simple base LFB class A that has only one 2463 component (comp1) of type X. One way to derive class A1 from A can be 2464 by simply adding a second component (of any type). Another way to 2465 derive a class A2 from A can be by replacing the original component 2466 (comp1) in A of type X with one of type Y, where Y is an augmentation 2467 of X. Both classes A1 and A2 are backward compatible with class A. 2469 The syntax for augmentations is to include a element in 2470 a structure definition, indicating what structure type is being 2471 augmented. Component names and component IDs for new components 2472 within the augmentation must not be the same as those in the 2473 structure type being augmented. For those components where the data 2474 type of an existing component is being replaced with a suitable 2475 augmenting data type, the existing Component name and component ID 2476 must be used in the augmentation. 2478 4.6. Element for Metadata Definitions 2480 The (optional) element in the library document 2481 contains one or more elements. Each 2482 element defines a metadatum. 2484 Each element MUST contain a unique name (NMTOKEN). 2485 Uniqueness is defined to be over all metadata defined in this library 2486 document and in all directly or indirectly included library 2487 documents. The element MUST also contain a brief 2488 synopsis, the tag value to be used for this metadata, and value type 2489 definition information. Only atomic data types can be used as value 2490 types for metadata. The element may contain a detailed 2491 description element. 2493 Two forms of type definitions are allowed. The first form uses the 2494 element to refer to an existing atomic data type defined in 2495 the element of the same library document or in one of 2496 the included library documents. The usage of the element 2497 is identical to how it is used in the elements, except 2498 here it can only refer to atomic types. The latter restriction is 2499 not enforced by the XML schema. 2501 The second form is an explicit type definition using the 2502 element. This element is used here in the same way as in the 2503 elements. 2505 The following example shows both usages: 2507 2508 2509 NEXTHOPID 2510 Refers to a Next Hop entry in NH LFB 2511 17 2512 int32 2513 2514 2515 CLASSID 2516 2517 Result of classification (0 means no match). 2518 2519 21 2520 2521 int32 2522 2523 2524 NOMATCH 2525 2526 Classification didn't result in match. 2527 2528 2529 2530 2531 2532 2534 4.7. Element for LFB Class Definitions 2536 The (optional) element can be used to define one or 2537 more LFB classes using elements. Each 2538 element MUST define an LFB class and include the following elements: 2540 o provides the symbolic name of the LFB class. Example: 2541 "ipv4lpm" 2543 o provides a short synopsis of the LFB class. Example: 2544 "IPv4 Longest Prefix Match Lookup LFB" 2546 o is the version indicator 2548 o is the inheritance indicator 2550 o lists the input ports and their specifications 2552 o lists the output ports and their specifications 2554 o defines the operational components of the LFB 2556 o defines the capability components of the LFB 2558 o contains the operational specification of the LFB 2560 o The LFBClassID attribute of the LFBClassDef element defines the ID 2561 for this class. These must be globally unique. 2563 o defines the events that can be generated by instances of 2564 this LFB. 2566 LFB Class Names must be unique, in order to enable other documents to 2567 reference the classes by name, and to enable human readers to 2568 understand references to class names. While a complex naming 2569 structure could be created, simplicity is preferred. As given in the 2570 IANA considerations section of this document, the IANA will maintain 2571 a registry of LFB Class names and Class identifiers, along with a 2572 reference to the document defining the class. 2574 Below is a skeleton of an example LFB class definition. Note that in 2575 order to keep from complicating the XML Schema, the order of elements 2576 in the class definition is fixed. Elements, if they appear, must 2577 appear in the order shown. 2579 2580 2581 ipv4lpm 2582 IPv4 Longest Prefix Match Lookup LFB 2583 1.0 2584 baseclass 2586 2587 ... 2588 2590 2591 ... 2592 2594 2595 ... 2596 2598 2599 ... 2600 2602 2603 ... 2604 2606 2607 This LFB represents the IPv4 longest prefix match lookup 2608 operation. 2609 The modeled behavior is as follows: 2610 Blah-blah-blah. 2611 2613 2614 ... 2615 2617 The individual components and capabilities will have componentIDs for 2618 use by the ForCES protocol. These parallel the componentIDs used in 2619 structs, and are used the same way. Component and capability 2620 componentIDs must be unique within the LFB class definition. 2622 Note that the , , and elements are 2623 required, all other elements are optional in . However, 2624 when they are present, they must occur in the above order. 2626 4.7.1. Element to Express LFB Inheritance 2628 The optional element can be used to indicate that this 2629 class is a derivative of some other class. The content of this 2630 element MUST be the unique name () of another LFB class. The 2631 referred LFB class MUST be defined in the same library document or in 2632 one of the included library documents. In the absence of a 2633 the class is conceptually derived from the common, 2634 empty, base class. 2636 It is assumed that a derived class is backwards compatible with its 2637 base class. 2639 4.7.2. Element to Define LFB Inputs 2641 The optional element is used to define input ports. An 2642 LFB class may have zero, one, or more inputs. If the LFB class has 2643 no input ports, the element MUST be omitted. The 2644 element can contain one or more elements, 2645 one for each port or port-group. We assume that most LFBs will have 2646 exactly one input. Multiple inputs with the same input type are 2647 modeled as one input group. Input groups are defined the same way as 2648 input ports by the element, differentiated only by an 2649 optional "group" attribute. 2651 Multiple inputs with different input types should be avoided if 2652 possible (see discussion in Section 4.7.3). Some special LFBs will 2653 have no inputs at all. For example, a packet generator LFB does not 2654 need an input. 2656 Single input ports and input port groups are both defined by the 2657 element; they are differentiated by only an optional 2658 "group" attribute. 2660 The element MUST contain the following elements: 2662 o provides the symbolic name of the input. Example: "in". 2663 Note that this symbolic name must be unique only within the scope 2664 of the LFB class. 2666 o contains a brief description of the input. Example: 2667 "Normal packet input". 2669 o lists all allowed frame formats. Example: {"ipv4" 2670 and "ipv6"}. Note that this list should refer to names specified 2671 in the element of the same library document or in any 2672 included library documents. The element can also 2673 provide a list of required metadata. Example: {"classid", 2674 "vifid"}. This list should refer to names of metadata defined in 2675 the element in the same library document or in any 2676 included library documents. For each metadata, it must be 2677 specified whether the metadata is required or optional. For each 2678 optional metadata, a default value must be specified, which is 2679 used by the LFB if the metadata is not provided with a packet. 2681 In addition, the optional "group" attribute of the 2682 element can specify if the port can behave as a port group, i.e., it 2683 is allowed to be instantiated. This is indicated by a "true" value 2684 (the default value is "false"). 2686 An example element, defining two input ports, the second 2687 one being an input port group: 2689 2690 2691 in 2692 Normal input 2693 2694 2695 ipv4 2696 ipv6 2697 2698 2699 classid 2700 vifid 2701 vrfid 2702 2703 2704 2705 2706 ... another input port ... 2707 2708 2710 For each , the frame type expectations are defined by the 2711 element using one or more elements (see example 2712 above). When multiple frame types are listed, it means that "one of 2713 these" frame types is expected. A packet of any other frame type is 2714 regarded as incompatible with this input port of the LFB class. The 2715 above example list two frames as expected frame types: "ipv4" and 2716 "ipv6". 2718 Metadata expectations are specified by the 2719 element. In its simplest form, this element can contain a list of 2720 elements, each referring to a metadatum. When multiple 2721 instances of metadata are listed by elements, it means that 2722 "all of these" metadata must be received with each packet (except 2723 metadata that are marked as "optional" by the "dependency" attribute 2724 of the corresponding element). For a metadatum that is 2725 specified "optional", a default value MUST be provided using the 2726 "defaultValue" attribute. The above example lists three metadata as 2727 expected metadata, two of which are mandatory ("classid" and 2728 "vifid"), and one being optional ("vrfid"). 2730 The schema also allows for more complex definitions of metadata 2731 expectations. For example, using the element, a list of 2732 metadata can be specified to express that at least one of the 2733 specified metadata must be present with any packet. For example: 2735 2736 2737 prefixmask 2738 prefixlen 2739 2740 2742 The above example specifies that either the "prefixmask" or the 2743 "prefixlen" metadata must be provided with any packet. 2745 The two forms can also be combined, as it is shown in the following 2746 example: 2748 2749 classid 2750 vifid 2751 vrfid 2752 2753 prefixmask 2754 prefixlen 2755 2756 2758 Although the schema is constructed to allow even more complex 2759 definitions of metadata expectations, we do not discuss those here. 2761 4.7.3. Element to Define LFB Outputs 2763 The optional element is used to define output ports. 2764 An LFB class may have zero, one, or more outputs. If the LFB class 2765 has no output ports, the element MUST be omitted. The 2766 element can contain one or more elements, 2767 one for each port or port-group. If there are multiple outputs with 2768 the same output type, we model them as an output port group. Some 2769 special LFBs may have no outputs at all (e.g., Dropper). 2771 Single output ports and output port groups are both defined by the 2772 element; they are differentiated by only an optional 2773 "group" attribute. 2775 The element MUST contain the following elements: 2777 o provides the symbolic name of the output. Example: "out". 2778 Note that the symbolic name must be unique only within the scope 2779 of the LFB class. 2781 o contains a brief description of the output port. 2782 Example: "Normal packet output". 2784 o lists the allowed frame formats. Example: {"ipv4", 2785 "ipv6"}. Note that this list should refer to symbols specified in 2786 the element in the same library document or in any 2787 included library documents. The element may also 2788 contain the list of emitted (generated) metadata. Example: 2789 {"classid", "color"}. This list should refer to names of metadata 2790 specified in the element in the same library 2791 document or in any included library documents. For each generated 2792 metadata, it should be specified whether the metadata is always 2793 generated or generated only in certain conditions. This 2794 information is important when assessing compatibility between 2795 LFBs. 2797 In addition, the optional "group" attribute of the 2798 element can specify if the port can behave as a port group, i.e., it 2799 is allowed to be instantiated. This is indicated by a "true" value 2800 (the default value is "false"). 2802 The following example specifies two output ports, the second being an 2803 output port group: 2805 2806 2807 out 2808 Normal output 2809 2810 2811 ipv4 2812 ipv4bis 2813 2814 2815 nhid 2816 nhtabid 2817 2818 2819 2820 2821 exc 2822 Exception output port group 2823 2824 2825 ipv4 2826 ipv4bis 2827 2828 2829 errorid 2830 2831 2832 2833 2835 The types of frames and metadata the port produces are defined inside 2836 the element in each . Within the 2837 element, the list of frame types the port produces is listed in the 2838 element. When more than one frame is listed, it 2839 means that "one of" these frames will be produced. 2841 The list of metadata that is produced with each packet is listed in 2842 the optional element of the . In its 2843 simplest form, this element can contain a list of elements, 2844 each referring to a metadatum type. The meaning of such a list is 2845 that "all of" these metadata are provided with each packet, except 2846 those that are listed with the optional "availability" attribute set 2847 to "conditional". Similar to the element of the 2848 , the element supports more complex 2849 forms, which we do not discuss here further. 2851 4.7.4. Element to Define LFB Operational Components 2853 Operational parameters of the LFBs that must be visible to the CEs 2854 are conceptualized in the model as the LFB components. These 2855 include, for example, flags, single parameter arguments, complex 2856 arguments, and tables. Note that the components here refer to only 2857 those operational parameters of the LFBs that must be visible to the 2858 CEs. Other variables that are internal to LFB implementation are not 2859 regarded as LFB components and hence are not covered. 2861 Some examples for LFB components are: 2863 o Configurable flags and switches selecting between operational 2864 modes of the LFB 2866 o Number of inputs or outputs in a port group 2868 o Various configurable lookup tables, including interface tables, 2869 prefix tables, classification tables, DSCP mapping tables, MAC 2870 address tables, etc. 2872 o Packet and byte counters 2874 o Various event counters 2876 o Number of current inputs or outputs for each input or output group 2878 There may be various access permission restrictions on what the CE 2879 can do with an LFB component. The following categories may be 2880 supported: 2882 o No-access components. This is useful when multiple access modes 2883 may be defined for a given component to allow some flexibility for 2884 different implementations. 2886 o Read-only components. 2888 o Read-write components. 2890 o Write-only components. This could be any configurable data for 2891 which read capability is not provided to the CEs. (e.g., the 2892 security key information) 2894 o Read-reset components. The CE can read and reset this resource, 2895 but cannot set it to an arbitrary value. Example: Counters. 2897 o Firing-only components. A write attempt to this resource will 2898 trigger some specific actions in the LFB, but the actual value 2899 written is ignored. 2901 The LFB class may define only one possible access mode for a given 2902 component. 2904 The components of the LFB class are listed in the 2905 element. Each component is defined by an element. An 2906 element may contain any of the following elements, some 2907 of which are mandatory: 2909 o MUST occur, and defines the name of the component. This 2910 name must be unique among the components of the LFB class. 2911 Example: "version". 2913 o is also mandatory, and provides a brief description of 2914 the purpose of the component. 2916 o is an optional element, and if present indicates that 2917 this component is optional. 2919 o The data type of the component can be defined either via a 2920 reference to a predefined data type or providing a local 2921 definition of the type. The former is provided by using the 2922 element, which must refer to the unique name of an 2923 existing data type defined in the element in the 2924 same library document or in any of the included library documents. 2925 When the data type is defined locally (unnamed type), one of the 2926 following elements can be used: , , , and 2927 . Their usage is identical to how they are used inside 2928 elements (see Section 4.5). Some form of data type 2929 definition MUST be included in the component definition. 2931 o The element is optional, and if present is used to 2932 specify a default value for a component. If a default value is 2933 specified, the FE must ensure that the component has that value 2934 when the LFB is initialized or reset. If a default value is not 2935 specified for a component, the CE may make no assumptions as to 2936 what the value of the component will be upon initalization. The 2937 CE must either read the value, or set the value, if it needs to 2938 know what it is. 2940 o The element may also appear. If included, it 2941 provides a longer description of the meaning or usage of the 2942 particular component being defined. 2944 The element also MUST have an componentID attribute, 2945 which is a numeric value used by the ForCES protocol. 2947 In addition to the above elements, the element includes 2948 an optional "access" attribute, which can take any of the following 2949 values: "read-only", "read-write", "write-only", "read-reset", and 2950 "trigger-only". The default access mode is "read-write". 2952 Whether optional components are supported, and whether components 2953 defined as read-write can actually be written can be determined for a 2954 given LFB instance by the CE by reading the property information of 2955 that component. An access control setting of "trigger-only" means 2956 that this component is included only for use in event detection. 2958 The following example defines two components for an LFB: 2960 2961 2962 foo 2963 number of things 2964 uint32 2965 2966 2967 bar 2968 number of this other thing 2969 2970 uint32 2971 2972 2973 2974 2975 10 2976 2977 2979 The first component ("foo") is a read-only 32-bit unsigned integer, 2980 defined by referring to the built-in "uint32" atomic type. The 2981 second component ("bar") is also an integer, but uses the 2982 element to provide additional range restrictions. This component has 2983 access mode of read-write allowing it to be both read and written. A 2984 default value of 10 is provided for bar. although the access for bar 2985 is read-write, some implementations may offer only more restrictive 2986 access, and this would be reported in the component properties. 2988 Note that not all components are likely to exist at all times in a 2989 particular implementation. While the capabilities will frequently 2990 indicate this non-existence, CEs may attempt to reference non- 2991 existent or non-permitted components anyway. The FORCES protocol 2992 mechanisms should include appropriate error indicators for this case. 2994 The mechanism defined above for non-supported component can also 2995 apply to attempts to reference non-existent array elements or to set 2996 read-only components. 2998 4.7.5. Element to Define LFB Capability Components 3000 The LFB class specification provides some flexibility for the FE 3001 implementation regarding how the LFB class is implemented. For 3002 example, the instance may have some limitations that are not inherent 3003 from the class definition, but rather the result of some 3004 implementation limitations. Some of these limitations are captured 3005 by the property information of the LFB components. The model allows 3006 for the notion of additional capability information. 3008 Such capability related information is expressed by the capability 3009 components of the LFB class. The capability components are always 3010 read-only attributes, and they are listed in a separate 3011 element in the . The 3012 element contains one or more elements, each defining one 3013 capability component. The format of the element is 3014 almost the same as the element, it differs in two 3015 aspects: it lacks the access mode attribute (because it is always 3016 read-only), and it lacks the element (because default 3017 value is not applicable to read-only attributes). 3019 Some examples of capability components follow: 3021 o The version of the LFB class that this LFB instance complies with; 3023 o Supported optional features of the LFB class; 3025 o Maximum number of configurable outputs for an output group; 3027 o Metadata pass-through limitations of the LFB; 3029 o Additional range restriction on operational components; 3031 The following example lists two capability attributes: 3033 3034 3035 version 3036 3037 LFB class version this instance is compliant with. 3038 3039 version 3040 3041 3042 limitBar 3043 3044 Maximum value of the "bar" attribute. 3045 3046 uint16 3047 3048 3050 4.7.6. Element for LFB Notification Generation 3052 The element contains the information about the occurrences 3053 for which instances of this LFB class can generate notifications to 3054 the CE. High level view on the declaration and operation of LFB 3055 events is described in Section 3.2.5. 3057 The element contains 0 or more elements, each of 3058 which declares a single event. The element has an eventID 3059 attribute giving the unique (per LFB class) ID of the event. The 3060 element will include: 3062 o element indicating which LFB field (component) is 3063 tested to generate the event; 3065 o element indicating what condition on the field will 3066 generate the event from a list of defined conditions; 3068 o element indicating what values are to be reported 3069 in the notification of the event. 3071 The example below demonstrates the different constructs. 3073 The element has a baseID attribute value, which is normally 3074 . The value of the baseID is the starting 3075 componentID for the path which identifies events. It must not be the 3076 same as the componentID of any top level components (including 3077 capabilities) of the LFB class. In derived LFBs (i.e. ones with a 3078 element) where the parent LFB class has an events 3079 declaration, the baseID must not be present in the derived LFB 3080 element. Instead, the baseID value from the parent LFB 3081 class is used. In the example shown the baseID is 7. 3083 3084 3085 Foochanged 3086 3087 An example event for a scalar 3088 3089 3090 foo 3091 3092 3093 3094 3095 3096 foo 3097 3098 3099 3101 3102 Goof1changed 3103 3104 An example event for a complex structure 3105 3106 3107 3108 goo 3109 f1 3110 3111 3112 3113 3114 3115 goo 3116 f1 3117 3118 3119 3121 3122 NewbarEntry 3123 3124 Event for a new entry created on table bar 3125 3126 3127 bar 3128 _barIndex_ 3129 3130 3131 3132 3133 bar 3134 _barIndex_ 3135 3136 3137 foo 3138 3139 3140 3142 3143 Gah11changed 3144 3145 Event for table gah, entry index 11 changing 3146 3147 3148 gah 3149 11 3150 3151 3152 3153 3154 gah 3155 11 3156 3157 3158 3160 3161 Gah10field1 3162 3163 Event for table gah, entry index 10, column field1 changing 3164 3165 3166 gah 3167 10 3168 field1 3169 3170 3171 3172 3173 gah 3174 10 3175 3177 3178 3179 3181 4.7.6.1. Element 3183 The element contains information identifying a field in 3184 the LFB that is to be monitored for events. 3186 The element contains one or more each of 3187 which may be followed by one or more elements. Each 3188 of these two elements represent the textual equivalent of a path 3189 select component of the LFB. 3191 The element contains the name of a component in the LFB 3192 or a component nested in an array or structure within the LFB. The 3193 name used in MUST identify a valid component within the 3194 containing LFB context. The first element in a MUST be 3195 an element. In the example shown, four LFB components 3196 foo, goo, bar and gah are used as s. 3198 In the simple case, an identifies an atomic component. 3199 This is the case illustrated in the event named Foochanged. 3200 is also used to address complex components such as 3201 arrays or structures. 3203 The first defined event, Foochanged, demonstrates how a scalar LFB 3204 component, foo, could be monitored to trigger an event. 3206 The second event, Goof1changed, demonstrates how a member of the 3207 complex structure goo could be monitored to trigger an event. 3209 The events named NewbarEntry, Gah11changed and Gah10field1 3210 represent monitoring of arrays bar and gah in differing details. 3212 If an identifies a complex component then a further 3213 may be used to refine the path to the target element. 3214 Defined event Goof1changed demonstrates how a second is 3215 used to point to member f1 of the structure goo. 3217 If an identifies an array then the following rules 3218 apply: 3220 o elements MUST be present as the next XML element 3221 after an which identifies an array component. 3222 MUST NOT occur other than after an array 3223 reference, as it is only meaningful in that context. 3225 o An may contain: 3227 * A numeric value to indicate that the event applies to a 3228 specific entry (by index) of the array. As an example, event 3229 Gah11changed shows how table gah's index 11 is being targeted 3230 for monitoring. 3232 * It is expected that the more common usage is to have the event 3233 being defined across all elements of the array (i.e a wildcard 3234 for all indices). In that case, the value of the 3235 MUST be a name rather than a numeric value. 3236 That same name can then be used as the value of 3237 in elements as described below. 3238 An example of a wild card table index is shown in event 3239 NewBarentry where the value is named 3240 _barIndex_ 3242 o An may follow an to further refine 3243 the path to the target element (Note: this is in the same spirit 3244 as the case where is used to further refine 3245 in the earlier example of a complex structure example 3246 of Goof1changed). The example event Gah10field1 illustrates how 3247 the column field1 of table gah is monitored for changes. 3249 It should be emphasized that the name in an element 3250 in defined event NewbarEntry is not a component name. It is a 3251 variable name for use in the elements (described in 3252 Section 4.7.6.3) of the given LFB definition. This name MUST be 3253 distinct from any component name that can validly occur in the 3254 clause. 3256 4.7.6.2. Element 3258 The event condition element represents a condition that triggers a 3259 notification. The list of conditions is: 3261 o the target must be an array, ending with a 3262 subscript indication. The event is generated when an entry in the 3263 array is created. This occurs even if the entry is created by CE 3264 direction. The event example NewbarEntry demonstrates the 3265 condition. 3267 o the target must be an array, ending with a 3268 subscript indication. The event is generated when an entry in the 3269 array is destroyed. This occurs even if the entry is destroyed by 3270 CE direction. 3272 o the event is generated whenever the target 3273 component changes in any way. For binary components such as up/ 3274 down, this reflects a change in state. It can also be used with 3275 numeric attributes, in which case any change in value results in a 3276 detected trigger. Event examples Foochanged, Gah11changed, and 3277 Gah10field1 illustrate the condition. 3279 o the event is generated whenever the target 3280 component becomes greater than the threshold. The threshold is an 3281 event property. 3283 o the event is generated whenever the target 3284 component becomes less than the threshold. The threshold is an 3285 event property. 3287 4.7.6.3. Element 3289 The element of an declare the information to 3290 be delivered by the FE along with the notification of the occurrence 3291 of the event. 3293 The element contains one or more 3294 elements. Each element identifies a piece of data from 3295 the LFB class to be reported. The notification carries that data as 3296 if the collection of elements had been defined in a 3297 structure. The syntax is exactly the same as used in the 3298 element, using and 3299 elements and so the same rules apply. Each element 3300 thus MUST identify a component in the LFB class. may 3301 contain integers. If they contain names, they MUST be names from 3302 elements of the in the event. The 3303 selection for the report will use the value for the subscript that 3304 identifies that specific element triggering the event. This can be 3305 used to reference the component causing the event, or to reference 3306 related information in parallel tables. 3308 In the example shown, in the case of the event Foochanged, the report 3309 will carry the value of foo; in the case of the defined event 3310 NewbarEntry acting on LFB component bar, which is an array, there are 3311 two items that are reported as indicated by the two 3312 declarations: 3314 o The first details what new entry was added in the 3315 table bar. Recall that _barIndex_ is declared as the event's 3316 and that by virtue of using a name 3317 instead of a numeric value, the is implied to be a 3318 wildcard and will carry whatever index of the new entry. 3320 o The second includes the value of LFB component foo 3321 at the time the new entry was created in bar. Reporting foo in 3322 this case is provided to demonstrate the flexibility of event 3323 reporting. 3325 This event reporting structure is designed to allow the LFB designer 3326 to specify information that is likely not known a priori by the CE 3327 and is likely needed by the CE to process the event. While the 3328 structure allows for pointing at large blocks of information (full 3329 arrays or complex structures) this is not recommended. Also, the 3330 variable reference/subscripting in reporting only captures a small 3331 portion of the kinds of related information. Chaining through index 3332 fields stored in a table, for example, is not supported. In general, 3333 the mechanism is an optimization for cases that have 3334 been found to be common, saving the CE from having to query for 3335 information it needs to understand the event. It does not represent 3336 all possible information needs. 3338 If any components referenced by the eventReport are optional, then 3339 the report MUST use a protocol format that supports optional elements 3340 and allows for the non-existence of such elements. Any components 3341 which do not exist are not reported. 3343 4.7.6.4. Runtime control of events 3345 High level view on the declaration and operation of LFB events is 3346 described in Section 3.2.5. 3348 The provides additional components used in the path to 3349 reference the event. The path constitutes the baseID for events, 3350 followed by the ID for the specific event, followed by a value for 3351 each element if it exists in the . 3353 The event path will uniquely identify a specific occurrence of the 3354 event in the event notification to the CE. In the example provided 3355 above, at the end of Section 4.7.6, a notification with path of 7.7 3356 uniquely identifies the event to be that caused by the change of foo; 3357 an event with path 7.9.100 uniquely identifies the event to be that 3358 caused by a creation of table bar entry with index/subscript 100. 3360 As described in the Section 4.8.5, event elements have properties 3361 associated with them. These properties include the subscription 3362 information indicating whether the CE wishes the FE to generate event 3363 reports for the event at all, thresholds for events related to level 3364 crossing, and filtering conditions that may reduce the set of event 3365 notifications generated by the FE. Details of the filtering 3366 conditions that can be applied are given in that section. The 3367 filtering conditions allow the FE to suppress floods of events that 3368 could result from oscillation around a condition value. For FEs that 3369 do not wish to support filtering, the filter properties can either be 3370 read only or not supported. 3372 In addition to identifying the event sources, the CE also uses the 3373 event path to activate runtime control of the event via the event 3374 properties (defined in Section 4.8.5) utilizing SET-PROP as defined 3375 in ForCES Protocol [2] operation. 3377 To activate event generation on the FE, a SET-PROP message 3378 referencing the event and registration property of the event is 3379 issued to the FE by the CE with any prefix of the path of the event. 3380 So, for an event defined on the example table bar, a SET-PROP with a 3381 path of 7.9 will subscribe the CE to all occurrences of that event on 3382 any entry of the table. This is particularly useful for the 3383 and conditions on tables. Events 3384 using those conditions will generally be defined with a field/ 3385 subscript sequence that identifies an array and ends with an 3386 element. Thus, the event notification will indicate 3387 which array entry has been created or destroyed. A typical 3388 subscriber will subscribe for the array, as opposed to a specific 3389 entry in an array, so it will use a shorter path. 3391 In the example provided, subscribing to 7.8 implies receiving all 3392 declared events from table bar. Subscribing to 7.8.100 implies 3393 receiving an event when subscript/index 100 table entry is created. 3395 Threshold and filtering conditions can only be applied to individual 3396 events. For events defined on elements of an array, this 3397 specification does not allow for defining a threshold or filtering 3398 condition on an event for all elements of an array. 3400 4.7.7. Element for LFB Operational Specification 3402 The element of the provides unstructured 3403 text (in XML sense) to verbally describe what the LFB does. 3405 4.8. Properties 3407 Components of LFBs have properties which are important to the CE. 3408 The most important property is the existence / readability / 3409 writeability of the element. Depending on the type of the component, 3410 other information may be of importance. 3412 The model provides the definition of the structure of property 3413 information. There is a base class of property information. For the 3414 array, alias, and event components there are subclasses of property 3415 information providing additional fields. This information is 3416 accessed by the CE (and updated where applicable) via the PL 3417 protocol. While some property information is writeable, there is no 3418 mechanism currently provided for checking the properties of a 3419 property element. Writeability can only be checked by attempting to 3420 modify the value. 3422 4.8.1. Basic Properties 3424 The basic property definition, along with the scalar dataTypeDef for 3425 accessibility is below. Note that this access permission information 3426 is generally read-only. 3428 3429 accessPermissionValues 3430 3431 The possible values of component access permission 3432 3433 3434 uchar 3435 3436 3437 None 3438 Access is prohibited 3439 3440 3441 Read-Only 3442 3443 Access to the component is read only 3444 3445 3446 3447 Write-Only 3448 3449 The component may be written, but not read 3450 3451 3452 3453 Read-Write 3454 3455 The component may be read or written 3456 3457 3458 3459 3460 3461 3462 baseElementProperties 3463 basic properties, accessibility 3464 3465 3466 accessibility 3467 3468 does the component exist, and 3469 can it be read or written 3470 3471 accessPermissionValues 3472 3473 3474 3476 4.8.2. Array Properties 3478 The properties for an array add a number of important pieces of 3479 information. These properties are also read-only. 3481 3482 arrayElementProperties 3483 Array Element Properties definition 3484 3485 baseElementProperties 3486 3487 entryCount 3488 the number of entries in the array 3489 uint32 3490 3491 3492 highestUsedSubscript 3493 the last used subscript in the array 3494 uint32 3495 3496 3497 firstUnusedSubscript 3498 3499 The subscript of the first unused array element 3500 3501 uint32 3502 3503 3504 3506 4.8.3. String Properties 3508 The properties of a string specify the actual octet length and the 3509 maximum octet length for the element. The maximum length is included 3510 because an FE implementation may limit a string to be shorter than 3511 the limit in the LFB Class definition. 3513 3514 stringElementProperties 3515 string Element Properties definition 3516 3517 baseElementProperties 3518 3519 stringLength 3520 the number of octets in the string 3521 uint32 3522 3523 3524 maxStringLength 3525 3526 the maximum number of octets in the string 3527 3528 uint32 3529 3530 3531 3533 4.8.4. Octetstring Properties 3535 The properties of an octetstring specify the actual length and the 3536 maximum length, since the FE implementation may limit an octetstring 3537 to be shorter than the LFB Class definition. 3539 3540 octetstringElementProperties 3541 octetstring Element Properties definition 3542 3543 3544 baseElementProperties 3545 3546 octetstringLength 3547 3548 the number of octets in the octetstring 3549 3550 uint32 3551 3552 3553 maxOctetstringLength 3554 3555 the maximum number of octets in the octetstring 3556 3557 uint32 3558 3559 3560 3562 4.8.5. Event Properties 3564 The properties for an event add three (usually) writeable fields. 3565 One is the subscription field. 0 means no notification is generated. 3566 Any non-zero value (typically 1 is used) means that a notification is 3567 generated. The hysteresis field is used to suppress generation of 3568 notifications for oscillations around a condition value, and is 3569 described in the text for events. The threshold field is used for 3570 the and conditions. It 3571 indicates the value to compare the event target against. Using the 3572 properties allows the CE to set the level of interest. FEs which do 3573 not supporting setting the threshold for events will make this field 3574 read-only. 3576 3577 eventElementProperties 3578 event Element Properties definition 3579 3580 baseElementProperties 3581 3582 registration 3583 3584 has the CE registered to be notified of this event 3585 3586 uint32 3587 3588 3589 threshold 3590 comparison value for level crossing events 3591 3592 3593 uint32 3594 3595 3596 eventHysteresis 3597 region to suppress event recurrence notices 3598 3599 3600 uint32 3601 3602 3603 eventCount 3604 number of occurrences to suppress 3605 3606 3607 uint32 3608 3609 3610 eventInterval 3611 time interval in ms between notifications 3612 3613 3614 uint32 3615 3616 3617 3619 4.8.5.1. Common Event Filtering 3621 The event properties have values for controlling several filter 3622 conditions. Support of these conditions is optional, but all 3623 conditions SHOULD be supported. Events which are reliably known not 3624 to be subject to rapid occurrence or other concerns may not support 3625 all filter conditions. 3627 Currently, three different filter condition variables are defined. 3628 These are eventCount, eventInterval, and eventHysteresis. Setting 3629 the condition variables to 0 (their default value) means that the 3630 condition is not checked. 3632 Conceptually, when an event is triggered, all configured conditions 3633 are checked. If no filter conditions are triggered, or if any 3634 trigger conditions are met, the event notification is generated. If 3635 there are filter conditions, and no condition is met, then no event 3636 notification is generated. Event filter conditions have reset 3637 behavior when an event notification is generated. If any condition 3638 is passed, and the notification is generated, the notification reset 3639 behavior is performed on all conditions, even those which had not 3640 passed. This provides a clean definition of the interaction of the 3641 various event conditions. 3643 An example of the interaction of conditions is an event with an 3644 eventCount property set to 5 and an eventInterval property set to 500 3645 milliseconds. Suppose that a burst of occurrences of this event is 3646 detected by the FE. The first occurrence will cause a notification 3647 to be sent to the CE. Then, if four more occurrences are detected 3648 rapidly (less than 0.5 seconds) they will not result in 3649 notifications. If two more occurrences are detected, then the second 3650 of those will result in a notification. Alternatively, if more than 3651 500 milliseconds has passed since the notification and an occurrence 3652 is detected, that will result in a notification. In either case, the 3653 count and time interval suppression is reset no matter which 3654 condition actually caused the notification. 3656 4.8.5.2. Event Hysteresis Filtering 3658 Events with numeric conditions can have hysteresis filters applied to 3659 them. The hysteresis level is defined by a property of the event. 3660 This allows the FE to notify the CE of the hysteresis applied, and if 3661 it chooses, the FE can allow the CE to modify the hysteresis. This 3662 applies to for a numeric field, and to 3663 and . The content of a 3664 element is a numeric value. When supporting hysteresis, 3665 the FE MUST track the value of the element and make sure that the 3666 condition has become untrue by at least the hysteresis from the event 3667 property. To be specific, if the hysteresis is V, then 3669 o For a condition, if the last notification was for 3670 value X, then the notification MUST NOT be generated 3671 until the value reaches X +/- V. 3673 o For a condition with threshold T, once the 3674 event has been generated at least once it MUST NOT be generated 3675 again until the field first becomes less than or equal to T - V, 3676 and then exceeds T. 3678 o For a condition with threshold T, once the event 3679 has been generate at least once it MUST NOT be generated again 3680 until the field first becomes greater than or equal to T + V, and 3681 then becomes less than T. 3683 4.8.5.3. Event Count Filtering 3685 Events may have a count filtering condition. This property, if set 3686 to a non-zero value, indicates the number of occurrences of the event 3687 that should be considered redundant and not result in a notification. 3688 Thus, if this property is set to 1, and no other conditions apply, 3689 then every other detected occurrence of the event will result in a 3690 notification. This particular meaning is chosen so that the value 1 3691 has a distinct meaning from the value 0. 3693 A conceptual implementation (not required) for this might be an 3694 internal suppression counter. Whenever an event is triggered, the 3695 counter is checked. If the counter is 0, a notification is 3696 generated. Whether a notification is generated or not, the counter 3697 is incremented. If the counter exceeds the configured value, it is 3698 reset to 0. In this conceptual implementation the reset behavior 3699 when a notification is generated can be thought of as setting the 3700 counter to 1. 3702 4.8.5.4. Event Time Filtering 3704 Events may have a time filtering condition. This property represents 3705 the minimum time interval (in the absence of some other filtering 3706 condition being passed) between generating notifications of detected 3707 events. This condition MUST only be passed if the time since the 3708 last notification of the event is longer than the configured interval 3709 in milliseconds. 3711 Conceptually, this can be thought of as a stored timestamp which is 3712 compared with the detection time, or as a timer that is running that 3713 resets a suppression flag. In either case, if a notification is 3714 generated due to passing any condition then the time interval 3715 detection MUST be restarted. 3717 4.8.6. Alias Properties 3719 The properties for an alias add three (usually) writeable fields. 3720 These combine to identify the target component the subject alias 3721 refers to. 3723 3724 aliasElementProperties 3725 alias Element Properties defintion 3726 3727 baseElementProperties 3728 3729 targetLFBClass 3730 the class ID of the alias target 3731 uint32 3732 3733 3734 targetLFBInstance 3735 the instance ID of the alias target 3736 uint32 3737 3738 3739 targetComponentPath 3740 3741 the path to the component target 3742 each 4 octets is read as one path element, 3743 using the path construction in the PL protocol, 3744 [2]. 3745 3746 octetstring[128] 3747 3748 3749 3751 4.9. XML Schema for LFB Class Library Documents 3753 3754 3760 3761 3762 Schema for Defining LFB Classes and associated types (frames, 3763 data types for LFB attributes, and metadata). 3764 3765 3766 3767 3768 3769 3770 3771 3772 3773 3775 3777 3779 3781 3783 3784 3785 3786 3787 3788 3789 3790 3791 3792 3793 3794 3795 3796 3797 3798 3799 3800 3801 3802 3803 3804 3805 3806 3807 3808 3809 3810 3811 3812 3813 3814 3815 3816 3818 3819 3820 3821 3822 3823 3824 3825 3826 3827 3828 3829 3830 3831 3832 3833 3834 3835 3836 3842 3843 3844 3845 3846 3847 3848 3849 3850 3851 3852 3853 3854 3855 3856 3857 3858 3859 3860 3861 3862 3863 3865 3867 3868 3869 3870 3871 3872 3873 3875 3877 3878 3879 3880 3881 3882 3883 3884 3885 3886 3887 3888 3889 3890 3891 3892 3893 3894 3895 3896 3897 3899 3900 3901 3903 3904 3906 3907 3908 3909 3910 3911 3912 3913 3914 3916 3917 3918 3919 3920 3921 3922 3923 3924 3926 3927 3928 3929 3931 3932 3933 3934 3935 3936 3937 3938 3939 3940 3942 3943 3945 3946 3947 3948 3949 3950 3951 3952 3953 3954 3955 3956 3957 3958 3959 3960 3961 3962 3963 3964 3965 3966 3967 3968 3969 3970 3971 3972 3973 3974 3975 3976 3977 3978 3980 3982 3984 3986 3988 3990 3991 3992 3994 3995 3998 3999 4000 4001 4002 4003 4004 4005 4006 4007 4008 4009 4010 4011 4012 4013 4014 4015 4016 4017 4018 4019 4020 4021 4022 4023 4024 4026 4027 4028 4029 4030 4031 4032 4033 4034 4035 4037 4038 4039 4040 4041 4042 4043 4044 4046 4047 4048 4049 4050 4051 4052 4053 4054 4056 4057 4059 4060 4061 4062 4063 4064 4065 4066 4067 4068 4069 4070 4071 4072 4073 4074 4075 4076 4077 4078 4079 4080 4082 4083 4084 4085 4086 4087 4088 4089 4091 4092 4093 4094 4095 4096 4098 4099 4100 4101 4102 4103 4104 4105 4106 4107 4109 4110 4111 4112 4113 4114 4115 4117 4119 4120 4121 4122 4123 4124 4125 4127 4128 4130 4131 4132 4133 4134 4135 4136 4137 4138 4139 4140 4141 4142 4143 4144 4145 4146 4147 4148 4149 4150 4151 4152 4153 4156 4157 4158 4159 4160 4161 4162 4163 4164 4165 4166 4167 4168 4169 4170 4171 4172 4173 4174 4175 4176 4178 4179 4181 4182 4183 4184 4185 4187 4188 4189 4190 4191 4192 4193 4194 4195 4196 4197 4198 4199 4200 4201 4202 4203 4204 4205 4206 4207 4208 4209 4210 4211 4213 4214 4215 4216 4217 4218 4219 4220 4221 4222 4223 4224 4225 4226 4228 4229 4230 4232 4233 4234 4235 4237 4238 4239 4240 4242 4244 4246 4248 4250 4251 4252 4253 4254 4255 4256 4258 4260 4262 4263 4264 4266 4267 4268 4269 4270 4271 4272 4273 4274 4276 5. FE Components and Capabilities 4278 A ForCES forwarding element handles traffic on behalf of a ForCES 4279 control element. While the standards will describe the protocol and 4280 mechanisms for this control, different implementations and different 4281 instances will have different capabilities. The CE MUST be able to 4282 determine what each instance it is responsible for is actually 4283 capable of doing. As stated previously, this is an approximation. 4284 The CE is expected to be prepared to cope with errors in requests and 4285 variations in detail not captured by the capabilities information 4286 about an FE. 4288 In addition to its capabilities, an FE will have information that can 4289 be used in understanding and controlling the forwarding operations. 4290 Some of this information will be read only, while others parts may 4291 also be writeable. 4293 In order to make the FE information easily accessible, the 4294 information is represented in an LFB. This LFB has a class, 4295 FEObject. The LFBClassID for this class is 1. Only one instance of 4296 this class will ever be present in an FE, and the instance ID of that 4297 instance in the protocol is 1. Thus, by referencing the components 4298 of class:1, instance:1 a CE can get the general information about the 4299 FE. The FEObject LFB Class is described in this section. 4301 There will also be an FEProtocol LFB Class. LFBClassID 2 is reserved 4302 for that class. There will be only one instance of that class as 4303 well. Details of that class are defined in the ForCES Protocol [2] 4304 document. 4306 5.1. XML for FEObject Class definition 4308 4309 4312 4313 4314 LFBAdjacencyLimitType 4315 Describing the Adjacent LFB 4316 4317 4318 NeighborLFB 4319 ID for that LFB Class 4320 uint32 4321 4322 4323 ViaPorts 4324 4325 the ports on which we can connect 4326 4327 4328 string 4329 4330 4331 4332 4333 4334 PortGroupLimitType 4335 4336 Limits on the number of ports in a given group 4337 4338 4339 4340 PortGroupName 4341 Group Name 4342 string 4343 4344 4345 MinPortCount 4346 Minimum Port Count 4347 4348 uint32 4349 4350 4351 MaxPortCount 4352 Max Port Count 4353 4354 uint32 4355 4356 4357 4358 4359 SupportedLFBType 4360 table entry for supported LFB 4361 4362 4363 LFBName 4364 4365 The name of a supported LFB Class 4366 4367 string 4368 4369 4370 LFBClassID 4371 the id of a supported LFB Class 4372 uint32 4373 4374 4375 LFBVersion 4376 4377 The version of the LFB Class used 4378 by this FE. 4379 4380 string 4381 4382 4383 LFBOccurrenceLimit 4384 4385 the upper limit of instances of LFBs of this class 4386 4387 4388 uint32 4389 4390 4392 4393 PortGroupLimits 4394 Table of Port Group Limits 4395 4396 4397 PortGroupLimitType 4398 4399 4400 4401 4402 CanOccurAfters 4403 4404 List of LFB Classes that this LFB class can follow 4405 4406 4407 4408 LFBAdjacencyLimitType 4409 4410 4411 4413 4414 CanOccurBefores 4415 4416 List of LFB Classes that can follow this LFB class 4417 4418 4419 4420 LFBAdjacencyLimitType 4421 4422 4423 4424 UseableParentLFBClasses 4425 4426 List of LFB Classes from which this class has 4427 inherited, and which the FE is willing to allow 4428 for references to instances of this class. 4429 4430 4431 4432 uint32 4433 4434 4435 4436 4437 4438 FEStateValues 4439 The possible values of status 4440 4441 uchar 4442 4443 4444 AdminDisable 4445 4446 FE is administratively disabled 4447 4448 4449 4450 OperDisable 4451 FE is operatively disabled 4452 4453 4454 OperEnable 4455 FE is operating 4456 4457 4458 4459 4460 4461 FEConfiguredNeighborType 4462 Details of the FE's Neighbor 4463 4464 4465 NeighborID 4466 Neighbors FEID 4467 uint32 4468 4469 4470 InterfaceToNeighbor 4471 4472 FE's interface that connects to this neighbor 4473 4474 4475 string 4476 4477 4478 NeighborInterface 4479 4480 The name of the interface on the neighbor to 4481 which this FE is adjacent. This is required 4482 In case two FEs are adjacent on more than 4483 one interface. 4484 4485 4486 string 4487 4488 4489 4490 4491 LFBSelectorType 4492 4493 Unique identification of an LFB class-instance 4494 4495 4496 4497 LFBClassID 4498 LFB Class Identifier 4499 uint32 4500 4501 4502 LFBInstanceID 4503 LFB Instance ID 4504 uint32 4505 4506 4507 4508 4509 LFBLinkType 4510 4511 Link between two LFB instances of topology 4512 4513 4514 4515 FromLFBID 4516 LFB src 4517 LFBSelectorType 4518 4519 4520 FromPortGroup 4521 src port group 4522 string 4523 4524 4525 FromPortIndex 4526 src port index 4527 uint32 4528 4529 4530 ToLFBID 4531 dst LFBID 4532 LFBSelectorType 4533 4534 4535 ToPortGroup 4536 dst port group 4537 string 4539 4540 4541 ToPortIndex 4542 dst port index 4543 uint32 4544 4545 4546 4547 4548 4549 4550 FEObject 4551 Core LFB: FE Object 4552 1.0 4553 4554 4555 LFBTopology 4556 the table of known Topologies 4557 4558 LFBLinkType 4559 4560 4561 4562 LFBSelectors 4563 4564 table of known active LFB classes and 4565 instances 4566 4567 4568 LFBSelectorType 4569 4570 4571 4572 FEName 4573 name of this FE 4574 string[40] 4575 4576 4577 FEID 4578 ID of this FE 4579 uint32 4580 4581 4582 FEVendor 4583 vendor of this FE 4584 string[40] 4585 4586 4587 FEModel 4588 model of this FE 4589 string[40] 4590 4591 4592 FEState 4593 State of this FE 4594 FEStateValues 4595 4596 4597 FENeighbors 4598 table of known neighbors 4599 4600 4601 FEConfiguredNeighborType 4602 4603 4604 4605 4606 4607 ModifiableLFBTopology 4608 4609 Whether Modifiable LFB is supported 4610 4611 4612 boolean 4613 4614 4615 SupportedLFBs 4616 List of all supported LFBs 4617 4618 4619 SupportedLFBType 4620 4621 4622 4623 4624 4625 4627 5.2. FE Capabilities 4629 The FE Capability information is contained in the capabilities 4630 element of the class definition. As described elsewhere, capability 4631 information is always considered to be read-only. 4633 The currently defined capabilities are ModifiableLFBTopology and 4634 SupportedLFBs. Information as to which components of the FEObject 4635 LFB are supported is accessed by the properties information for those 4636 components. 4638 5.2.1. ModifiableLFBTopology 4640 This component has a boolean value that indicates whether the LFB 4641 topology of the FE may be changed by the CE. If the component is 4642 absent, the default value is assumed to be true, and the CE presumes 4643 the LFB topology may be changed. If the value is present and set to 4644 false, the LFB topology of the FE is fixed. If the topology is 4645 fixed, the SupportedLFBs element may be omitted, and the list of 4646 supported LFBs is inferred by the CE from the LFB topology 4647 information. If the list of supported LFBs is provided when 4648 ModifiableLFBTopology is false, the CanOccurBefore and CanOccurAfter 4649 information should be omitted. 4651 5.2.2. SupportedLFBs and SupportedLFBType 4653 One capability that the FE should include is the list of supported 4654 LFB classes. The SupportedLFBs component, is an array that contains 4655 the information about each supported LFB Class. The array structure 4656 type is defined as the SupportedLFBType dataTypeDef. 4658 Each entry in the SupportedLFBs array describes an LFB class that the 4659 FE supports. In addition to indicating that the FE supports the 4660 class, FEs with modifiable LFB topology SHOULD include information 4661 about how LFBs of the specified class may be connected to other LFBs. 4662 This information SHOULD describe which LFB classes the specified LFB 4663 class may succeed or precede in the LFB topology. The FE SHOULD 4664 include information as to which port groups may be connected to the 4665 given adjacent LFB class. If port group information is omitted, it 4666 is assumed that all port groups may be used. This capability 4667 information on the acceptable ordering and connection of LFBs MAY be 4668 omitted if the implementor concludes that the actual constraints are 4669 such that the information would be misleading for the CE. 4671 5.2.2.1. LFBName 4673 This component has as its value the name of the LFB Class being 4674 described. 4676 5.2.2.2. LFBClassID 4678 The numeric ID of the LFB Class being described. While conceptually 4679 redundant with the LFB Name, both are included for clarity and to 4680 allow consistency checking. 4682 5.2.2.3. LFBVersion 4684 The version string specifying the LFB Class version supported by this 4685 FE. As described above in versioning, an FE can support only a 4686 single version of a given LFB Class. 4688 5.2.2.4. LFBOccurrenceLimit 4690 This component, if present, indicates the largest number of instances 4691 of this LFB class the FE can support. For FEs that do not have the 4692 capability to create or destroy LFB instances, this can either be 4693 omitted or be the same as the number of LFB instances of this class 4694 contained in the LFB list attribute. 4696 5.2.2.5. PortGroupLimits and PortGroupLimitType 4698 The PortGroupLimits component is an array of information about the 4699 port groups supported by the LFB class. The structure of the port 4700 group limit information is defined by the PortGroupLimitType 4701 dataTypeDef. 4703 Each PortGroupLimits array entry contains information describing a 4704 single port group of the LFB class. Each array entry contains the 4705 name of the port group in the PortGroupName component, the fewest 4706 number of ports that can exist in the group in the MinPortCount 4707 component, and the largest number of ports that can exist in the 4708 group in the MaxPortCount component. 4710 5.2.2.6. CanOccurAfters and LFBAdjacencyLimitType 4712 The CanOccurAfters component is an array that contains the list of 4713 LFBs the described class can occur after. The array entries are 4714 defined in the LFBAdjacencyLimitType dataTypeDef. 4716 The array entries describe a permissible positioning of the described 4717 LFB class, referred to here as the SupportedLFB. Specifically, each 4718 array entry names an LFB that can topologically precede that LFB 4719 class. That is, the SupportedLFB can have an input port connected to 4720 an output port of an LFB that appears in the CanOccurAfters array. 4721 The LFB class that the SupportedLFB can follow is identified by the 4722 NeighborLFB component (of the LFBAdjacencyLimitType dataTypeDef) of 4723 the CanOccurAfters array entry. If this neighbor can only be 4724 connected to a specific set of input port groups, then the viaPort 4725 component is included. This component is an array, with one entry 4726 for each input port group of the SupportedLFB that can be connected 4727 to an output port of the NeighborLFB. 4729 [e.g., Within a SupportedLFBs entry, each array entry of the 4730 CanOccurAfters array must have a unique NeighborLFB, and within each 4731 such array entry each viaPort must represent a distinct and valid 4732 input port group of the SupportedLFB. The LFB Class definition 4733 schema does not include these uniqueness constraints.] 4735 5.2.2.7. CanOccurBefores and LFBAdjacencyLimitType 4737 The CanOccurBefores array holds the information about which LFB 4738 classes can follow the described class. Structurally this element 4739 parallels CanOccurAfters, and uses the same type definition for the 4740 array entries. 4742 The array entries list those LFB classes that the SupportedLFB may 4743 precede in the topology. In this component, the entries in the 4744 viaPort component of the array value represent the output port groups 4745 of the SupportedLFB that may be connected to the NeighborLFB. As 4746 with CanOccurAfters, viaPort may have multiple entries if multiple 4747 output ports may legitimately connect to the given NeighborLFB class. 4749 [And a similar set of uniqueness constraints apply to the 4750 CanOccurBefore clauses, even though an LFB may occur both in 4751 CanOccurAfter and CanOccurBefore.] 4753 5.2.2.8. UseableParentLFBClasses 4755 The UseableParentLFBClasses array, if present, i sued to hold a list 4756 of parent LFB class IDs. All the entries in the list must be IDs of 4757 classes from which the SupportedLFB Class being described has 4758 inherited (either directly, or through an intermediate parent.) (If 4759 an FE includes improper values in this list, improper manipulations 4760 by the CE are likely, and operational failures are likely.) In 4761 addition, the FE, by including a given class in the last, is 4762 indicating to the CE that a given parent class may be used to 4763 manipulate an instance of this supported LFB class. 4765 By allowing such substitution, the FE allows for the case where an 4766 instantiated LFB may be of a class not known to the CE, but could 4767 still be manipulated. While it is hoped that such situations are 4768 rare, it is desirable for this to be supported. This can occur if an 4769 FE locally defines certain LFB instances, or if an earlier CE had 4770 configured some LFB instances. It can also occur if the FE would 4771 prefer to instantiate a more recent, more specific and suitable, LFB 4772 class rather than a common parent. 4774 In order to permit this, the FE MUST be more restrained in assigning 4775 LFB Instance IDs. Normally, instance IDs are qualified by the LFB 4776 class. However, if two LFB classes share a parent, and if that 4777 parent is listed in the UseableParentLFBClasses for both specific LFB 4778 classes, then all the instances of both (or any, if multiple classes 4779 are listing the common parent) MUST use distinct instances. This 4780 permits the FE to determine which LFB Instance is intended by CE 4781 manipulation operations even when a parent class is used. 4783 5.2.2.9. LFBClassCapabilities 4785 While it would be desirable to include class capability level 4786 information, this is not included in the model. While such 4787 information belongs in the FE Object in the supported class table, 4788 the contents of that information would be class specific. The 4789 currently expected encoding structures for transferring information 4790 between the CE and FE are such that allowing completely unspecified 4791 information would be likely to induce parse errors. We could specify 4792 that the information is encoded in an octetstring, but then we would 4793 have to define the internal format of that octet string. 4795 As there also are not currently any defined LFB Class level 4796 Capabilities that the FE needs to report, this information is not 4797 present now, but may be added in a future version of the FE Object. 4798 (This is an example of a case where versioning, rather than 4799 inheritance, would be needed, since the FE Object must have class ID 4800 1 and instance ID 1 so that the protocol behavior can start by 4801 finding this object.) 4803 5.3. FE Components 4805 The element is included if the class definition contains 4806 the definition of the components of the FE Object that are not 4807 considered "capabilities". Some of these components are writeable, 4808 and some are read-only, which is determinable by examining the 4809 property information of the components. 4811 5.3.1. FEState 4813 This component carries the overall state of the FE. The possible 4814 values are the strings AdminDisable, OperDisable and OperEnable. The 4815 starting state is OperDisable, and the transition to OperEnable is 4816 controlled by the FE. The CE controls the transition from OperEnable 4817 to/from AdminDisable. For details refer to the ForCES Protocol 4818 document [2]. 4820 5.3.2. LFBSelectors and LFBSelectorType 4822 The LFBSelectors component is an array of information about the LFBs 4823 currently accessible via ForCES in the FE. The structure of the LFB 4824 information is defined by the LFBSelectorType dataTypeDef. 4826 Each entry in the array describes a single LFB instance in the FE. 4827 The array entry contains the numeric class ID of the class of the LFB 4828 instance and the numeric instance ID for this instance. 4830 5.3.3. LFBTopology and LFBLinkType 4832 The optional LFBTopology component contains information about each 4833 inter-LFB link inside the FE, where each link is described in an 4834 LFBLinkType dataTypeDef. The LFBLinkType component contains 4835 sufficient information to identify precisely the end points of a 4836 link. The FromLFBID and ToLFBID components specify the LFB instances 4837 at each end of the link, and MUST reference LFBs in the LFB instance 4838 table. The FromPortGroup and ToPortGroup MUST identify output and 4839 input port groups defined in the LFB classes of the LFB instances 4840 identified by FromLFBID and ToLFBID. The FromPortIndex and 4841 ToPortIndex components select the entries from the port groups that 4842 this link connects. All links are uniquely identified by the 4843 FromLFBID, FromPortGroup, and FromPortIndex fields. Multiple links 4844 may have the same ToLFBID, ToPortGroup, and ToPortIndex as this model 4845 supports fan in of inter- LFB links but not fan out. 4847 5.3.4. FENeighbors and FEConfiguredNeighborType 4849 The FENeighbors component is an array of information about manually 4850 configured adjacencies between this FE and other FEs. The content of 4851 the array is defined by the FEConfiguredNeighborType dataTypeDef. 4853 This array is intended to capture information that may be configured 4854 on the FE and is needed by the CE, where one array entry corresponds 4855 to each configured neighbor. Note that this array is not intended to 4856 represent the results of any discovery protocols, as those will have 4857 their own LFBs. This component is optional. 4859 While there may be many ways to configure neighbors, the FE-ID is the 4860 best way for the CE to correlate entities. And the interface 4861 identifier (name string) is the best correlator. The CE will be able 4862 to determine the IP address and media level information about the 4863 neighbor from the neighbor directly. Omitting that information from 4864 this table avoids the risk of incorrect double configuration. 4866 Information about the intended forms of exchange with a given 4867 neighbor is not captured here, only the adjacency information is 4868 included. 4870 5.3.4.1. NeighborID 4872 This is the ID in some space meaningful to the CE for the neighbor. 4874 5.3.4.2. InterfaceToNeighbor 4876 This identifies the interface through which the neighbor is reached. 4878 5.3.4.3. NeighborInterface 4880 This identifies the interface on the neighbor through which the 4881 neighbor is reached. The interface identification is needed when 4882 either only one side of the adjacency has configuration information, 4883 or the two FEs are adjacent on more than one interface. 4885 6. Satisfying the Requirements on FE Model 4887 This section describes how the proposed FE model meets the 4888 requirements outlined in Section 5 of RFC3654 [4]. The requirements 4889 can be separated into general requirements (Section 5, 5.1 - 5.4) and 4890 the specification of the minimal set of logical functions that the FE 4891 model must support (Section 5.5). 4893 The general requirement on the FE model is that it be able to express 4894 the logical packet processing capability of the FE, through both a 4895 capability and a state model. In addition, the FE model is expected 4896 to allow flexible implementations and be extensible to allow defining 4897 new logical functions. 4899 A major component of the proposed FE model is the Logical Function 4900 Block (LFB) model. Each distinct logical function in an FE is 4901 modeled as an LFB. Operational parameters of the LFB that must be 4902 visible to the CE are conceptualized as LFB components. These 4903 components express the capability of the FE and support flexible 4904 implementations by allowing an FE to specify which optional features 4905 are supported. The components also indicate whether they are 4906 configurable by the CE for an LFB class. Configurable components 4907 provide the CE some flexibility in specifying the behavior of an LFB. 4908 When multiple LFBs belonging to the same LFB class are instantiated 4909 on an FE, each of those LFBs could be configured with different 4910 component settings. By querying the settings of the components for 4911 an instantiated LFB, the CE can determine the state of that LFB. 4913 Instantiated LFBs are interconnected in a directed graph that 4914 describes the ordering of the functions within an FE. This directed 4915 graph is described by the topology model. The combination of the 4916 components of the instantiated LFBs and the topology describe the 4917 packet processing functions available on the FE (current state). 4919 Another key component of the FE model is the FE components. The FE 4920 components are used mainly to describe the capabilities of the FE, 4921 but they also convey information about the FE state. 4923 The FE model includes only the definition of the FE Object LFB 4924 itself. Meeting the full set of working group requirements requires 4925 other LFBs. The class definitions for those LFBs will be provided in 4926 other documents. 4928 7. Using the FE model in the ForCES Protocol 4930 The actual model of the forwarding plane in a given NE is something 4931 the CE must learn and control by communicating with the FEs (or by 4932 other means). Most of this communication will happen in the post- 4933 association phase using the ForCES protocol. The following types of 4934 information must be exchanged between CEs and FEs via the ForCES 4935 Protocol [2]: 4937 1. FE topology query; 4939 2. FE capability declaration; 4941 3. LFB topology (per FE) and configuration capabilities query; 4943 4. LFB capability declaration; 4945 5. State query of LFB components; 4947 6. Manipulation of LFB components; 4949 7. LFB topology reconfiguration. 4951 Items 1) through 5) are query exchanges, where the main flow of 4952 information is from the FEs to the CEs. Items 1) through 4) are 4953 typically queried by the CE(s) in the beginning of the post- 4954 association (PA) phase, though they may be repeatedly queried at any 4955 time in the PA phase. Item 5) (state query) will be used at the 4956 beginning of the PA phase, and often frequently during the PA phase 4957 (especially for the query of statistical counters). 4959 Items 6) and 7) are "command" types of exchanges, where the main flow 4960 of information is from the CEs to the FEs. Messages in Item 6) (the 4961 LFB re-configuration commands) are expected to be used frequently. 4962 Item 7) (LFB topology re-configuration) is needed only if dynamic LFB 4963 topologies are supported by the FEs and it is expected to be used 4964 infrequently. 4966 The inter-FE topology (item 1 above) can be determined by the CE in 4967 many ways. Neither this document nor the ForCES Protocol [2] 4968 document mandates a specific mechanism. The LFB Class definition 4969 does include the capability for an FE to be configured with, and 4970 provides to the CE in response to a query, the identity of its 4971 neighbors. There may also be defined specific LFB classes and 4972 protocols for neighbor discovery. Routing protocols may be used by 4973 the CE for adjacency determination. The CE may be configured with 4974 the relevant information. 4976 The relationship between the FE model and the seven post-association 4977 messages are visualized in Figure 12: 4979 +--------+ 4980 ..........-->| CE | 4981 /----\ . +--------+ 4982 \____/ FE Model . ^ | 4983 | |................ (1),2 | | 6, 7 4984 | | (off-line) . 3, 4, 5 | | 4985 \____/ . | v 4986 . +--------+ 4987 e.g. RFCs ..........-->| FE | 4988 +--------+ 4990 Figure 12: Relationship between the FE model and the ForCES protocol 4991 messages, where (1) is part of the ForCES base protocol, and the 4992 rest are defined by the FE model. 4994 The actual encoding of these messages is defined by the ForCES 4995 Protocol [2] document and is beyond the scope of the FE model. Their 4996 discussion is nevertheless important here for the following reasons: 4998 o These PA model components have considerable impact on the FE 4999 model. For example, some of the above information can be 5000 represented as components of the LFBs, in which case such 5001 components must be defined in the LFB classes. 5003 o The understanding of the type of information that must be 5004 exchanged between the FEs and CEs can help to select the 5005 appropriate protocol format and the actual encoding method (such 5006 as XML, TLVs). 5008 o Understanding the frequency of these types of messages should 5009 influence the selection of the protocol format (efficiency 5010 considerations). 5012 The remaining sub-sections of this section address each of the seven 5013 message types. 5015 7.1. FE Topology Query 5017 An FE may contain zero, one or more external ingress ports. 5018 Similarly, an FE may contain zero, one or more external egress ports. 5019 In other words, not every FE has to contain any external ingress or 5020 egress interfaces. For example, Figure 13 shows two cascading FEs. 5021 FE #1 contains one external ingress interface but no external egress 5022 interface, while FE #2 contains one external egress interface but no 5023 ingress interface. It is possible to connect these two FEs together 5024 via their internal interfaces to achieve the complete ingress-to- 5025 egress packet processing function. This provides the flexibility to 5026 spread the functions across multiple FEs and interconnect them 5027 together later for certain applications. 5029 While the inter-FE communication protocol is out of scope for ForCES, 5030 it is up to the CE to query and understand how multiple FEs are 5031 inter-connected to perform a complete ingress-egress packet 5032 processing function, such as the one described in Figure 13. The 5033 inter-FE topology information may be provided by FEs, may be hard- 5034 coded into CE, or may be provided by some other entity (e.g., a bus 5035 manager) independent of the FEs. So while the ForCES Protocol [2] 5036 supports FE topology query from FEs, it is optional for the CE to use 5037 it, assuming the CE has other means to gather such topology 5038 information. 5040 +-----------------------------------------------------+ 5041 | +---------+ +------------+ +---------+ | 5042 input| | | | | | output | 5043 ---+->| Ingress |-->|Header |-->|IPv4 |---------+--->+ 5044 | | port | |Decompressor| |Forwarder| FE | | 5045 | +---------+ +------------+ +---------+ #1 | | 5046 +-----------------------------------------------------+ V 5047 | 5048 +-----------------------<-----------------------------+ 5049 | 5050 | +----------------------------------------+ 5051 V | +------------+ +----------+ | 5052 | input | | | | output | 5053 +->--+->|Header |-->| Egress |---------+--> 5054 | |Compressor | | port | FE | 5055 | +------------+ +----------+ #2 | 5056 +----------------------------------------+ 5058 Figure 13: An example of two FEs connected together 5060 Once the inter-FE topology is discovered by the CE after this query, 5061 it is assumed that the inter-FE topology remains static. However, it 5062 is possible that an FE may go down during the NE operation, or a 5063 board may be inserted and a new FE activated, so the inter-FE 5064 topology will be affected. It is up to the ForCES protocol to 5065 provide a mechanism for the CE to detect such events and deal with 5066 the change in FE topology. FE topology is outside the scope of the 5067 FE model. 5069 7.2. FE Capability Declarations 5071 FEs will have many types of limitations. Some of the limitations 5072 must be expressed to the CEs as part of the capability model. The 5073 CEs must be able to query these capabilities on a per-FE basis. 5074 Examples: 5076 o Metadata passing capabilities of the FE. Understanding these 5077 capabilities will help the CE to evaluate the feasibility of LFB 5078 topologies, and hence to determine the availability of certain 5079 services. 5081 o Global resource query limitations (applicable to all LFBs of the 5082 FE). 5084 o LFB supported by the FE. 5086 o LFB class instantiation limit. 5088 o LFB topological limitations (linkage constraint, ordering etc.) 5090 7.3. LFB Topology and Topology Configurability Query 5092 The ForCES protocol must provide the means for the CEs to discover 5093 the current set of LFB instances in an FE and the interconnections 5094 between the LFBs within the FE. In addition, sufficient information 5095 should be available to determine whether the FE supports any CE- 5096 initiated (dynamic) changes to the LFB topology, and if so, determine 5097 the allowed topologies. Topology configurability can also be 5098 considered as part of the FE capability query as described in Section 5099 9.3. 5101 7.4. LFB Capability Declarations 5103 LFB class specifications define a generic set of capabilities. When 5104 an LFB instance is implemented (instantiated) on a vendor's FE, some 5105 additional limitations may be introduced. Note that we discuss only 5106 those limitations that are within the flexibility of the LFB class 5107 specification. That is, the LFB instance will remain compliant with 5108 the LFB class specification despite these limitations. For example, 5109 certain features of an LFB class may be optional, in which case it 5110 must be possible for the CE to determine if an optional feature is 5111 supported by a given LFB instance or not. Also, the LFB class 5112 definitions will probably contain very few quantitative limits (e.g., 5113 size of tables), since these limits are typically imposed by the 5114 implementation. Therefore, quantitative limitations should always be 5115 expressed by capability arguments. 5117 LFB instances in the model of a particular FE implementation will 5118 possess limitations on the capabilities defined in the corresponding 5119 LFB class. The LFB class specifications must define a set of 5120 capability arguments, and the CE must be able to query the actual 5121 capabilities of the LFB instance via querying the value of such 5122 arguments. The capability query will typically happen when the LFB 5123 is first detected by the CE. Capabilities need not be re-queried in 5124 case of static limitations. In some cases, however, some 5125 capabilities may change in time (e.g., as a result of adding/removing 5126 other LFBs, or configuring certain components of some other LFB when 5127 the LFBs share physical resources), in which case additional 5128 mechanisms must be implemented to inform the CE about the changes. 5130 The following two broad types of limitations will exist: 5132 o Qualitative restrictions. For example, a standardized multi- 5133 field classifier LFB class may define a large number of 5134 classification fields, but a given FE may support only a subset of 5135 those fields. 5137 o Quantitative restrictions, such as the maximum size of tables, 5138 etc. 5140 The capability parameters that can be queried on a given LFB class 5141 will be part of the LFB class specification. The capability 5142 parameters should be regarded as special components of the LFB. The 5143 actual values of these components may be, therefore, obtained using 5144 the same component query mechanisms as used for other LFB components. 5146 Capability components are read-only arguments. In cases where some 5147 implementations may allow CE modification of the value, the 5148 information must be represented as an operational component, not a 5149 capability component. 5151 Assuming that capabilities will not change frequently, the efficiency 5152 of the protocol/schema/encoding is of secondary concern. 5154 Much of this restrictive information is captured by the component 5155 property information, and so can be access uniformly for all 5156 information within the model. 5158 7.5. State Query of LFB Components 5160 This feature must be provided by all FEs. The ForCES protocol and 5161 the data schema/encoding conveyed by the protocol must together 5162 satisfy the following requirements to facilitate state query of the 5163 LFB components: 5165 o Must permit FE selection. This is primarily to refer to a single 5166 FE, but referring to a group of (or all) FEs may optionally be 5167 supported. 5169 o Must permit LFB instance selection. This is primarily to refer to 5170 a single LFB instance of an FE, but optionally addressing of a 5171 group of LFBs (or all) may be supported. 5173 o Must support addressing of individual components of an LFB. 5175 o Must provide efficient encoding and decoding of the addressing 5176 info and the configured data. 5178 o Must provide efficient data transmission of the component state 5179 over the wire (to minimize communication load on the CE-FE link). 5181 7.6. LFB Component Manipulation 5183 The FE Model provides for the definition of LFB Classes. Each class 5184 has a globally unique identifier. Information within the class is 5185 represented as components and assigned identifiers within the scope 5186 of that class. This model also specifies that instances of LFB 5187 Classes have identifiers. The combination of class identifiers, 5188 instance identifiers, and component identifiers are used by the 5189 protocol to reference the LFB information in the protocol operations. 5191 7.7. LFB Topology Re-configuration 5193 Operations that will be needed to reconfigure LFB topology: 5195 o Create a new instance of a given LFB class on a given FE. 5197 o Connect a given output of LFB x to the given input of LFB y. 5199 o Disconnect: remove a link between a given output of an LFB and a 5200 given input of another LFB. 5202 o Delete a given LFB (automatically removing all interconnects to/ 5203 from the LFB). 5205 8. Example LFB Definition 5207 This section contains an example LFB definition. While some 5208 properties of LFBs are shown by the FE Object LFB, this endeavors to 5209 show how a data plane LFB might be build. This example is a 5210 fictional case of an interface supporting a coarse WDM optical 5211 interface that carries Frame Relay traffic. The statistical 5212 information (including error statistics) is omitted. 5214 Later portions of this example include references to protocol 5215 operations. The operations described are operations the protocol 5216 needs to support. The exact format and fields are purely 5217 informational here, as the ForCES Protocol [2] document defines the 5218 precise syntax and semantics of its operations. 5220 5221 5224 5225 5226 FRFrame 5227 5228 A frame relay frame, with DLCI without 5229 stuffing) 5230 5231 5232 5233 IPFrame 5234 An IP Packet 5235 5236 5237 5238 5239 frequencyInformationType 5240 5241 Information about a single CWDM frequency 5242 5243 5244 5245 LaserFrequency 5246 encoded frequency(channel) 5247 uint32 5248 5249 5250 FrequencyState 5251 state of this frequency 5252 PortStatusValues 5253 5254 5255 LaserPower 5256 current observed power 5257 uint32 5258 5259 5260 FrameRelayCircuits 5261 5262 Information about circuits on this Frequency 5263 5264 5265 frameCircuitsType 5266 5267 5268 5269 5270 5271 frameCircuitsType 5272 5273 Information about a single Frame Relay circuit 5274 5275 5276 5277 DLCI 5278 DLCI of the circuit 5279 uint32 5280 5281 5282 CircuitStatus 5283 state of the circuit 5284 PortStatusValues 5285 5286 5287 isLMI 5288 is this the LMI circuit 5289 boolean 5290 5291 5292 associatedPort 5293 5294 which input / output port is associated 5295 with this circuit 5296 5297 uint32 5298 5299 5300 5301 5302 PortStatusValues 5303 5304 The possible values of status. Used for both 5305 administrative and operational status 5306 5307 5308 uchar 5309 5310 5311 Disabled 5312 the component is disabled 5313 5314 5315 Enabled 5316 FE is operatively enabled 5317 5318 5319 5320 5321 5322 5323 5324 DLCI 5325 The DLCI the frame arrived on 5326 12 5327 uint32 5328 5329 5330 LaserChannel 5331 The index of the laser channel 5332 34 5333 uint32 5334 5335 5336 5337 5338 5339 FrameLaserLFB 5340 Fictional LFB for Demonstrations 5341 1.0 5342 5343 5344 LMIfromFE 5345 5346 Ports for LMI traffic, for transmission 5347 5348 5349 5350 FRFrame 5351 5352 5353 DLCI 5354 LaserChannel 5355 5356 5357 5358 5359 DatafromFE 5360 5361 Ports for data to be sent on circuits 5362 5363 5364 5365 IPFrame 5366 5367 5368 DLCI 5369 LaserChannel 5370 5371 5373 5374 5375 5376 5377 LMItoFE 5378 5379 Ports for LMI traffic for processing 5380 5381 5382 5383 FRFrame 5384 5385 5386 DLCI 5387 LaserChannel 5388 5389 5390 5391 5392 DatatoFE 5393 5394 Ports for Data traffic for processing 5395 5396 5397 5398 IPFrame 5399 5400 5401 DLCI 5402 LaserChannel 5403 5404 5405 5406 5407 5408 5409 AdminPortState 5410 is this port allowed to function 5411 PortStatusValues 5412 5413 5414 FrequencyInformation 5415 5416 table of information per CWDM frequency 5417 5418 5419 frequencyInformationType 5420 5422 5423 5424 5425 5426 OperationalState 5427 5428 whether the port over all is operational 5429 5430 PortStatusValues 5431 5432 5433 MaximumFrequencies 5434 5435 how many laser frequencies are there 5436 5437 uint16 5438 5439 5440 MaxTotalCircuits 5441 5442 Total supportable Frame Relay Circuits, across 5443 all laser frequencies 5444 5445 5446 uint32 5447 5448 5449 5450 5451 FrequencyState 5452 5453 The state of a frequency has changed 5454 5455 5456 FrequencyInformation 5457 _FrequencyIndex_ 5458 FrequencyState 5459 5460 5461 5462 5463 5464 FrequencyInformation 5465 _FrequencyIndex_ 5466 FrequencyState 5467 5468 5469 5470 5471 CreatedFrequency 5472 A new frequency has appeared 5473 5474 FrequencyInformation> 5475 _FrequencyIndex_ 5476 5477 5478 5479 5480 FrequencyInformation 5481 _FrequencyIndex_ 5482 LaserFrequency 5483 5484 5485 5486 5487 DeletedFrequency 5488 5489 A frequency Table entry has been deleted 5490 5491 5492 FrequencyInformation 5493 _FrequencyIndex_ 5494 5495 5496 5497 5498 PowerProblem 5499 5500 there are problems with the laser power level 5501 5502 5503 FrequencyInformation 5504 _FrequencyIndex_ 5505 LaserPower 5506 5507 5508 5509 5510 FrequencyInformation 5511 _FrequencyIndex_ 5512 LaserPower 5513 5514 5515 FrequencyInformation 5516 _FrequencyIndex_ 5517 LaserFrequency 5519 5520 5521 5522 5523 FrameCircuitChanged 5524 5525 the state of an Fr circuit on a frequency 5526 has changed 5527 5528 5529 FrequencyInformation 5530 _FrequencyIndex_ 5531 FrameRelayCircuits 5532 FrameCircuitIndex 5533 CircuitStatus 5534 5535 5536 5537 5538 FrequencyInformation 5539 _FrequencyIndex_ 5540 FrameRelayCircuits 5541 FrameCircuitIndex 5542 CircuitStatus 5543 5544 5545 FrequencyInformation 5546 _FrequencyIndex_ 5547 FrameRelayCircuits 5548 FrameCircuitIndex 5549 DLCI 5550 5551 5552 5553 5554 5555 5556 5558 8.1. Data Handling 5560 This LFB is designed to handle data packets coming in from or going 5561 out to the external world. It is not a full port, and it lacks many 5562 useful statistics, but it serves to show many of the relevant 5563 behaviors. The following paragraphs describe a potential operational 5564 device and how it might use this LFB definition. 5566 Packets arriving without error from the physical interface come in on 5567 a Frame Relay DLCI on a laser channel. These two values are used by 5568 the LFB to look up the handling for the packet. If the handling 5569 indicates that the packet is LMI, then the output index is used to 5570 select an LFB port from the LMItoFE port group. The packet is sent 5571 as a full Frame Relay frame (without any bit or byte stuffing) on the 5572 selected port. The laser channel and DLCI are sent as meta-data, 5573 even though the DLCI is also still in the packet. 5575 Good packets that arrive and are not LMI and have a frame relay type 5576 indicator of IP are sent as IP packets on the port in the DatatoFE 5577 port group, using the same index field from the table based on the 5578 laser channel and DLCI. The channel and DLCI are attached as meta- 5579 data for other use (classifiers, for example.) 5581 The current definition does not specify what to do if the Frame Relay 5582 type information is not IP. 5584 Packets arriving on input ports arrive with the Laser Channel and 5585 Frame Relay DLCI as meta-data. As such, a single input port could 5586 have been used. With the structure that is defined (which parallels 5587 the output structure), the selection of channel and DLCI could be 5588 restricted by the arriving input port group (LMI vs. data) and port 5589 index. As an alternative LFB design, the structures could require a 5590 1-1 relationship between DLCI and LFB port, in which case no meta- 5591 data would be needed. This would however be quite complex and noisy. 5592 The intermediate level of structure here allows parallelism between 5593 input and output, without requiring excessive ports. 5595 8.1.1. Setting up a DLCI 5597 When a CE chooses to establish a DLCI on a specific laser channel, it 5598 sends a SET request directed to this LFB. The request might look 5599 like 5601 T = SET 5602 T = PATH-DATA 5603 Path: flags = none, length = 4, path = 2, channel, 4, entryIdx 5604 DataRaw: DLCI, Enabled(1), false, out-idx 5606 Which would establish the DLCI as enabled, with traffic going to a 5607 specific entry of the output port group DatatoFE. (The CE would 5608 ensure that output port is connected to the right place before 5609 issuing this request.) 5611 The response would confirm the creation of the specified entry. This 5612 table is structured to use separate internal indices and DLCIs. An 5613 alternative design could have used the DLCI as index, trading off 5614 complexities. 5616 One could also imagine that the FE has an LMI LFB. Such an LFB would 5617 be connected to the LMItoFE and LMIfromFE port groups. It would 5618 process LMI information. It might be the LFBs job to set up the 5619 frame relay circuits. The LMI LFB would have an alias entry that 5620 points to the Frame Relay circuits table it manages, so that it can 5621 manipulate those entities. 5623 8.1.2. Error Handling 5625 The LFB will receive invalid packets over the wire. Many of these 5626 will simply result in incrementing counters. The LFB designer might 5627 also specify some error rate measures. This puts more work on the 5628 FE, but allows for more meaningful alarms. 5630 There may be some error conditions that should cause parts of the 5631 packet to be sent to the CE. The error itself is not something that 5632 can cause an event in the LFB. There are two ways this can be 5633 handled. 5635 One way is to define a specific component to count the error, and a 5636 component in the LFB to hold the required portion of the packet. The 5637 component could be defined to hold the portion of the packet from the 5638 most recent error. One could then define an event that occurs 5639 whenever the error count changes, and declare that reporting the 5640 event includes the LFB field with the packet portion. For rare but 5641 extremely critical errors, this is an effective solution. It ensures 5642 reliable delivery of the notification. And it allows the CE to 5643 control if it wants the notification. 5645 Another approach is for the LFB to have a port that connects to a 5646 redirect sink. The LFB would attach the laser channel, the DLCI, and 5647 the error indication as meta-data, and ship the packet to the CE. 5649 Other aspects of error handling are discussed under events below. 5651 8.2. LFB Components 5653 This LFB is defined to have two top level components. One reflects 5654 the administrative state of the LFB. This allows the CE to disable 5655 the LFB completely. 5657 The other component is the table of information about the laser 5658 channels. It is a variable sized array. Each array entry contains 5659 an identifier for what laser frequency this entry is associated with, 5660 whether that frequency is operational, the power of the laser at that 5661 frequency, and a table of information about frame relay circuits on 5662 this frequency. There is no administrative status since a CE can 5663 disable an entry simply by removing it. (Frequency and laser power 5664 of a non-operational channel are not particularly useful. Knowledge 5665 about what frequencies can be supported would be a table in the 5666 capabilities section.) 5668 The Frame Relay circuit information contains the DLCI, the 5669 operational circuit status, whether this circuit is to be treated as 5670 carrying LMI information, and which port in the output port group of 5671 the LFB traffic is to be sent to. As mentioned above, the circuit 5672 index could, in some designs, be combined with the DLCI. 5674 8.3. Capabilities 5676 The capability information for this LFB includes whether the 5677 underlying interface is operational, how many frequencies are 5678 supported, and how many total circuits, across all channels, are 5679 permitted. The maximum number for a given laser channel can be 5680 determined from the properties of the FrameRelayCircuits table. A 5681 GET-PROP on path 2.channel.4 will give the CE the properties of that 5682 FrameRelayCircuits array which include the number of entries used, 5683 the first available entry, and the maximum number of entries 5684 permitted. 5686 8.4. Events 5688 This LFB is defined to be able to generate several events that the CE 5689 may be interested in. There are events to report changes in 5690 operational state of frequencies, and the creation and deletion of 5691 frequency entries. There is an event for changes in status of 5692 individual frame relay circuits. So an event notification of 5693 61.5.3.11 would indicate that there had been a circuit status change 5694 on subscript 11 of the circuit table in subscript 3 of the frequency 5695 table. The event report would include the new status of the circuit 5696 and the DLCI of the circuit. Arguably, the DLCI is redundant, since 5697 the CE presumably knows the DLCI based on the circuit index. It is 5698 included here to show including two pieces of information in an event 5699 report. 5701 As described above, the event declaration defines the event target, 5702 the event condition, and the event report content. The event 5703 properties indicate whether the CE is subscribed to the event, the 5704 specific threshold for the event, and any filter conditions for the 5705 event. 5707 Another event shown is a laser power problem. This event is 5708 generated whenever the laser falls below the specified threshold. 5709 Thus, a CE can register for the event of laser power loss on all 5710 circuits. It would do this by: 5712 T = SET-PROP 5713 Path-TLV: flags=0, length = 2, path = 61.4 5714 Path-TLV: flags = property-field, length = 1, path = 2 5715 Content = 1 (register) 5716 Path-TLV: flags = property-field, length = 1, path = 3 5717 Content = 15 (threshold) 5719 This would set the registration for the event on all entries in the 5720 table. It would also set the threshold for the event, causing 5721 reporting if the power falls below 15. (Presumably, the CE knows 5722 what the scale is for power, and has chosen 15 as a meaningful 5723 problem level.) 5725 If a laser oscillates in power near the 15 mark, one could get a lot 5726 of notifications. (If it flips back and forth between 14 and 15, 5727 each flip down will generate an event.) Suppose that the CE decides 5728 to suppress this oscillation somewhat on laser channel 5. It can do 5729 this by setting the variance property on that event. The request 5730 would look like: 5732 T = SET-PROP 5733 Path-TLV: flags=0, length = 3, path = 61.4.5 5734 Path-TLV: flags = property-field, length = 1, path = 4 5735 Content = 2 (hysteresis) 5737 Setting the hysteresis to 2 suppress a lot of spurious notifications. 5738 When the level first falls below 10, a notification is generated. If 5739 the power level increases to 10 or 11, and then falls back below 10, 5740 an event will not be generated. The power has to recover to at least 5741 12 and fall back below 10 to generate another event. One common 5742 cause of this form of oscillation is when the actual value is right 5743 near the border. If it is really 9.5, tiny changes might flip it 5744 back and forth between 9 and 10. A variance level of 1 will suppress 5745 this sort of condition. Many other events have oscillations that are 5746 somewhat wider, so larger variance settings can be used with those. 5748 9. IANA Considerations 5750 The ForCES model creates the need for a unique XML namespace for 5751 ForCES library definition usage, and unique class names and numeric 5752 class identifiers. 5754 9.1. URN Namespace Registration 5756 IANA is requested to register a new XML namespace, as per the 5757 guidelines in RFC3688 [3]. 5759 URI: The URI for this namespace is 5760 urn:ietf:params:xml:ns:forces:lfbmodel:1.0 5762 Registrant Contact: IESG 5764 XML: none, this is an XML namespace 5766 9.2. LFB Class Names and LFB Class Identifiers 5768 In order to have well defined ForCES LFB Classes, and well defined 5769 identifiers for those classes, a registry of LFB Class names, 5770 corresponding class identifiers, and the document which defines the 5771 LFB Class is needed. The registry policy is simply first come first 5772 served(FCFS) with regard to LFB Class names. With regard to LFB 5773 Class identifiers, identifiers less than 65536 are reserved for 5774 assignment by IETF Standards Track RFCs. Identifiers above 65536 are 5775 available for assignment on a first come, first served basis. All 5776 Registry entries must be documented in a stable, publicly available 5777 form. 5779 Since this registry provides for FCFS allocation of a portion of the 5780 class identifier space, it is necessary to define rules for naming 5781 classes that are using that space. As these can be defined by 5782 anyone, the needed rule is to keep the FCFS class names from 5783 colliding with IETF defined class names. Therefore, all FCFS class 5784 names MUST start with the string "Ext-". 5786 Table 1 tabulates the above information. 5788 IANA is requested to create a register of ForCES LFB Class Names and 5789 the corresponding ForCES LFB Class Identifiers, with the location of 5790 the definition of the ForCES LFB Class, in accordance with the rules 5791 in the following table. 5793 +----------------+------------+---------------+---------------------+ 5794 | LFB Class Name | LFB Class | Place Defined | Description | 5795 | | Identifier | | | 5796 +----------------+------------+---------------+---------------------+ 5797 | Reserved | 0 | RFCxxxx | Reserved | 5798 | | | | -------- | 5799 | FE Object | 1 | RFCxxxx | Defines ForCES | 5800 | | | | Forwarding Element | 5801 | | | | information | 5802 | FE Protocol | 2 | [2] | Defines parameters | 5803 | Object | | | for the ForCES | 5804 | | | | protocol operation | 5805 | | | | -------- | 5806 | IETF defined | 3-65535 | Standards | Reserved for IETF | 5807 | LFBs | | Track RFCs | defined RFCs | 5808 | | | | -------- | 5809 | Forces LFB | >65535 | Any Publicly | First Come, First | 5810 | Class names | | Available | Served for any use | 5811 | beginning EXT- | | Document | | 5812 +----------------+------------+---------------+---------------------+ 5814 Table 1 5816 [Note to RFC Editor, RFCxxxx above is to be changed to the RFC number 5817 assigned to this document for publication.] 5819 10. Authors Emeritus 5821 The following are the authors who were instrumental in the creation 5822 of earlier releases of this document. 5824 Ellen Delganes, Intel Corp. 5825 Lily Yang, Intel Corp. 5826 Ram Gopal, Nokia Research Center 5827 Alan DeKok, Infoblox, Inc. 5828 Zsolt Haraszti, Clovis Solutions 5830 11. Acknowledgments 5832 Many of the colleagues in our companies and participants in the 5833 ForCES mailing list have provided invaluable input into this work. 5834 Particular thanks to Evangelos Haleplidis for help getting the XML 5835 right. 5837 12. Security Considerations 5839 The FE model describes the representation and organization of data 5840 sets and components in the FEs. The ForCES framework document [2] 5841 provides a comprehensive security analysis for the overall ForCES 5842 architecture. For example, the ForCES protocol entities must be 5843 authenticated per the ForCES requirements before they can access the 5844 information elements described in this document via ForCES. Access 5845 to the information contained in the FE model is accomplished via the 5846 ForCES protocol, which will be defined in separate documents, and 5847 thus the security issues will be addressed there. 5849 13. References 5851 13.1. Normative References 5853 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 5854 Levels", BCP 14, RFC 2119, March 1997. 5856 [2] Doria, A., Haas, R., Hadi Salim, J., Khosravi, H., and W. Wang, 5857 "ForCES Protocol Specification", work in progress, draft-ietf - 5858 forces-protocol-11.txt, December 2007. 5860 [3] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, 5861 January 2004. 5863 13.2. Informative References 5865 [4] Khosravi, H. and T. Anderson, "Requirements for Separation of 5866 IP Control and Forwarding", RFC 3654, November 2003. 5868 [5] Yang, L., Dantu, R., Anderson, T., and R. Gopal, "Forwarding 5869 and Control Element Separation (ForCES) Framework", RFC 3746, 5870 April 2004. 5872 [6] Chan, K., Sahita, R., Hahn, S., and K. McCloghrie, 5873 "Differentiated Services Quality of Service Policy Information 5874 Base", RFC 3317, March 2003. 5876 [7] Sahita, R., Hahn, S., Chan, K., and K. McCloghrie, "Framework 5877 Policy Information Base", RFC 3318, March 2003. 5879 [8] Pras, A. and J. Schoenwaelder, "On the Difference between 5880 Information Models and Data Models", RFC 3444, January 2003. 5882 [9] Hollenbeck, S., Rose, M., and L. Masinter, "Guidelines for the 5883 Use of Extensible Markup Language (XML) within IETF Protocols", 5884 BCP 70, RFC 3470, January 2003. 5886 [10] Thompson, H., Beech, D., Maloney, M., and N. Mendelsohn, "XML 5887 Schema Part 1: Structures", W3C REC-xmlschema-1, 5888 http://www.w3.org/TR/ xmlschema-1/, May 2001. 5890 [11] Biron, P. and A. Malhotra, "XML Schema Part 2: Datatypes", 5891 W3C REC-xmlschema-2, http://www.w3.org/TR /xmlschema-2/, 5892 May 2001. 5894 [12] Davis, M. and M. Suignard, "UNICODE Security Considerations", 5895 http://www.unicode.org/ reports/tr36/tr36-3.html, July 2005. 5897 Authors' Addresses 5899 Joel Halpern 5900 Self 5901 P.O. Box 6049 5902 Leesburg,, VA 20178 5904 Phone: +1 703 371 3043 5905 Email: jmh@joelhalpern.com 5907 Jamal Hadi Salim 5908 Znyx Networks 5909 Ottawa, Ontario 5910 Canada 5912 Email: hadi@znyx.com 5914 Full Copyright Statement 5916 Copyright (C) The IETF Trust (2008). 5918 This document is subject to the rights, licenses and restrictions 5919 contained in BCP 78, and except as set forth therein, the authors 5920 retain all their rights. 5922 This document and the information contained herein are provided on an 5923 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 5924 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 5925 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 5926 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 5927 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 5928 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 5930 Intellectual Property 5932 The IETF takes no position regarding the validity or scope of any 5933 Intellectual Property Rights or other rights that might be claimed to 5934 pertain to the implementation or use of the technology described in 5935 this document or the extent to which any license under such rights 5936 might or might not be available; nor does it represent that it has 5937 made any independent effort to identify any such rights. Information 5938 on the procedures with respect to rights in RFC documents can be 5939 found in BCP 78 and BCP 79. 5941 Copies of IPR disclosures made to the IETF Secretariat and any 5942 assurances of licenses to be made available, or the result of an 5943 attempt made to obtain a general license or permission for the use of 5944 such proprietary rights by implementers or users of this 5945 specification can be obtained from the IETF on-line IPR repository at 5946 http://www.ietf.org/ipr. 5948 The IETF invites any interested party to bring to its attention any 5949 copyrights, patents or patent applications, or other proprietary 5950 rights that may cover technology that may be required to implement 5951 this standard. Please address the information to the IETF at 5952 ietf-ipr@ietf.org.