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Brunner (Editor) 3 Internet Draft NEC 4 Category: Informational December 2002 6 Requirements for Signaling Protocols 7 9 Status of this Memo 11 This document is an Internet-Draft and is in full conformance with 12 all provisions of Section 10 of RFC2026. 14 Internet-Drafts are working documents of the Internet Engineering 15 Task Force (IETF), its areas, and its working groups. Note that 16 other groups may also distribute working documents as Internet- 17 Drafts. 19 Internet-Drafts are draft documents valid for a maximum of six 20 months and may be updated, replaced, or obsoleted by other documents 21 at any time. It is inappropriate to use Internet-Drafts as 22 reference material or to cite them other than as "work in progress." 24 The list of current Internet-Drafts can be accessed at 25 http://www.ietf.org/ietf/1id-abstracts.txt 26 The list of Internet-Draft Shadow Directories can be accessed at 27 http://www.ietf.org/shadow.html. 29 Copyright Notice 31 Copyright (C) The Internet Society (2002). All Rights Reserved. 33 Abstract 35 This document defines requirements for signaling across different 36 network environments, where different network environments mean 37 across administrative and technology domains. Signaling is mainly 38 though for QoS such as [RSVP], however in recent year several other 39 applications of signaling have been defined such as signaling for 40 MPLS label distribution [RSVP-TE]. To achieve wide applicability of 41 the requirements, the starting point is a diverse set of 42 scenarios/use cases concerning various types of networks and 43 application interactions. This memo present the assumptions and the 44 aspects not considered within scope before listing the requirements 45 grouped according to areas such as architecture and design goals, 46 signaling flows, layering, performance, flexibility, security, and 47 mobility. 49 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 50 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in 51 this document are to be interpreted as described in RFC 2119. 53 Table of Contents 54 Status of this Memo................................................1 55 Abstract...........................................................1 56 Table of Contents..................................................1 57 1 Introduction.....................................................2 58 2 Terminology......................................................3 59 3 Problem Statement and Scope......................................5 60 4 Assumptions and Exclusions.......................................6 61 4.1 Assumptions and Non-Assumptions................................6 62 4.2 Exclusions.....................................................7 63 5 Requirements.....................................................9 64 5.1 Architecture and Design Goals..................................9 65 5.2 Signaling Flows...............................................11 66 5.3 Messaging.....................................................13 67 5.4 Control Information...........................................14 68 5.5 Performance...................................................16 69 5.6 Flexibility...................................................17 70 5.7 Security......................................................18 71 5.8 Mobility......................................................20 72 5.9 Interworking with other protocols and techniques..............20 73 5.10 Operational..................................................21 74 6 Security Considerations.........................................22 75 7 Informative References..........................................22 76 8 Acknowledgments.................................................22 77 9 Author's Addresses..............................................22 78 10 Appendix: Scenarios/Use cases..................................23 79 10.1 Terminal Mobility............................................23 80 10.2 Cellular Networks............................................25 81 10.3 UMTS access..................................................26 82 10.4 Wired part of wireless network...............................27 83 10.5 Session Mobility.............................................29 84 10.6 QoS reservations/negotiation from access to core network.....30 85 10.7 QoS reservation/negotiation over administrative boundaries...30 86 10.8 QoS signaling between PSTN gateways and backbone routers.....31 87 10.9 PSTN trunking gateway........................................32 88 10.10 Application request end-to-end QoS path from the network....34 90 1 Introduction 92 This document defines requirements for signaling across different 93 network environments. It does not list any problems of existing 94 signaling protocols such as [RSVP]. 96 In order to derive requirements for signaling it is necessary to 97 first have an idea of the scope within which they are applicable. 98 Therefore, we define a conceptual model of signaling on an abstract 99 level. Additionally, we describe the entities involved in signaling 100 and typical signaling paths. In the appendix are a list of use cases 101 and scenarios where an NSIS protocol could be applied. It is though 102 of helping derive the requirements and to t4est the requirements 103 against use cases. 105 QoS and signaling for QoS is a pretty large field with a lot of 106 interaction with other protocols, mechanisms, applications etc. 107 However, it is not the only field where signaling is used in the 108 Internet. Even if this requirement documents mainly used QoS as the 109 sample application other application must be possible and are also 110 addressed. 112 There are several areas related to networking aspects which are 113 incomplete, for example, interaction with host and site multi- 114 homing, use of anycast services, and so on. These issues should be 115 considered in any future analysis work. 117 2 Terminology 119 We try to list the most often used terms in the document. However, 120 don't be to religious about it, they are not meant to prescribe any 121 solution in the document. All of them need refined definitions in 122 follow-up documents. 124 Resource Management Function (RMF): An abstract concept, 125 representing the management of resources in a domain or a node. This 126 includes admission control and resource allocation. 128 NSIS Domain (ND): Administrative domain where an NSIS protocol 129 signals for a resource or set of resources. 131 NSIS Entity (NE): The function within a node, which implements an 132 NSIS protocol. 134 NSIS Forwarder (NF): NSIS Entity on the path between a NI and NR, 135 which may interact with local resource management function (RMF) for 136 this purpose. NSIS Forwarder also propagates NSIS signaling further 137 through the network. It is responsible for interpreting the 138 signaling carrying the user parameters, optionally inserting or 139 modifying the parameters according to domain network management 140 policy. 142 NSIS Initiator (NI): NSIS Entity that initiates NSIS signaling for a 143 network resource based on user or application requirements. This can 144 be located in the end system, but may reside elsewhere in network. 146 NSIS Responder (NR): NSIS Entity that terminates NSIS signaling and 147 can optionally interact with applications as well. 149 Flow: A traffic stream (sequence of IP packets between two end 150 systems) for which a specific packet level treatment is provided. 151 The flow can be unicast (uni- or bi-directional) or multicast. For 152 multicast, a flow can diverge into multiple flows as it propagates 153 toward the receiver. For multi-sender multicast, a flow can also 154 diverge when viewed in the reverse direction (toward the senders). 156 Higher Layers: The higher layer (transport protocol and application) 157 functions that request QoS or any other service from the network 158 layer. The trigger for the request might be generated within the end 159 system, or the trigger might be provided by some entity within the 160 network (e.g. application proxy or policy server). 162 Data Path: the route across the networks taken by a flow or 163 aggregate, i.e. which domains/subdomains it passes through and the 164 egress/ingress points for each. 166 Signaling Path: the route across the networks taken by a signaling 167 flow or aggregate, i.e. which domains/subdomains it passes through 168 and the egress/ingress points for each. 170 Path Segment: The segment of a path within a single 171 domain/subdomain. 173 Control Information: the information the governs for instance the 174 QoS treatment to be applied to a flow or aggregate, including the 175 service class, flow administration, and any associated security or 176 accounting information. 178 Provisioning: the act of actually allocating resources to a flow or 179 aggregate of flows, may include mechanisms such as LSP initiation 180 for MPLS, packet scheduler configuration within a router, and so on. 181 The mechanisms depend on the overall technology and application 182 being used within the domain, and can be from static to dynamic. 184 Subdomain: a network within an administrative domain using a uniform 185 technology, e.g., a single QoS provisioning function to provision 186 resources. 188 QoS Technology: a generic term for a set of protocols, standards and 189 mechanisms that can be used within a QoS domain/subdomain to manage 190 the QoS provided to flows or aggregates that traverse the domain. 191 Examples might include MPLS, DiffServ, and so on. A QoS technology 192 is associated with certain QoS provisioning techniques. 194 Resource: something of value in a network infrastructure to which 195 rules or policy criteria are first applied before access is granted. 196 Examples of resources include the buffers in a router and bandwidth 197 on an interface. 199 Service: something provided by an entity and consumed by another. 200 It can be constructed by allocating resources. The network can 201 provide it to users or a network node can provide it to packets. 203 Sender-initiated signaling protocol: A sender-initiated signaling 204 protocol is a protocol where the NSIS Initiator initiates the 205 signaling on behalf of the sender of the data. What this means is 206 that resource management functions are processed from the data 207 sender towards the data receiver. However, the triggering instance 208 is not specified. 210 Receiver-initiated signaling protocol: A receiver-initiated protocol 211 (e.g., [RSVP]) is a protocol, where the NSIS Responder on behalf of 212 the receiver of the user data initiates the reservation. What this 213 means is that resource management functions are processed from the 214 data receiver back towards the data sender. However, the triggering 215 instance is not specified. 217 3 Problem Statement and Scope 219 We provide in the following a preliminary architectural picture as a 220 basis for discussion. We will refer to it in the following 221 requirement sections. 223 A basic goal should be to re-use these wherever possible, and to 224 focus requirements work at an early stage on those areas where a new 225 solution is needed (e.g. an especially simple one). We also try to 226 avoid defining requirements related to internal implementation 227 aspects. 229 Note that this model is intended not to constrain the technical 230 approach taken subsequently, simply to allow concrete phrasing of 231 requirements (e.g. requirements about placement of the NSIS 232 Initiator.) 234 Roughly, the scope of NSIS is assumed to be the interaction between 235 the NSIS Initiator and NSIS Forwarder(s), and NSIS Responder 236 including a protocol to carry the information, and the 237 syntax/semantics of the information that is exchanged. Further 238 statements on assumptions/exclusions are given in the next Section. 240 The main elements are: 242 1. Something that starts the request for resources, the NSIS 243 Initiator. 245 This might be in the end system or within some other part of the 246 network. The distinguishing feature of the NSIS Initiator is that it 247 acts on triggers coming (directly or indirectly) from the higher 248 layers in the end systems. It needs to map the resources requested 249 by them, and also provides feedback information to the higher 250 layers, which might be used by transport layer rate management or 251 adaptive applications. 253 2. Something that assists in managing resources further along the 254 signaling path, the NSIS Forwarder. 256 The NSIS Forwarder does not interact with higher layers, but 257 interacts with the NSIS Initiator, NSIS Responder, and possibly one 258 or more NSIS Forwarders on the signaling path, edge-to-edge or end- 259 to-end. 261 3. Something that terminates the signaling path, the NSIS Responder. 263 The NSIS responder might be in an end-system or within other 264 equipment. The distinguishing feature of the NSIS Initiator is that 265 it responds to request at the end of a signaling path. 267 4. The path segment traverses an underlying network covering one or 268 more IP hops. The underlying network might use locally different 269 technology. For instance, QoS technology has to be provisioned 270 appropriately for the service requested. In the QoS example, an NSIS 271 Forwarder maps service-specific information to technology-related 272 QoS parameters and receiving indications about success or failure in 273 response. 275 Now concentrating more on the overall end to end (multiple domain) 276 aspects, in particular: 278 1. The NSIS Initiator need not be located at an end system, and the 279 NSIS Forwarders are not assumed to be located on the flow's data 280 path. However, they must be able to identify the ingress and egress 281 points for the flow's data path as it traverses the NSIS domain. Any 282 signaling protocol must be able to find the appropriate NSIS 283 Forwarder. 285 2. We see the network at the level of domains/subdomains rather than 286 individual routers (except in the special case that the domain 287 contains one link). Domains are assumed to be administrative 288 entities, so security requirements apply to the signaling between 289 them. 291 3. Any domain may contain Resource Management Function (e.g. 292 traffic engineering, admission control, policy and so on). These are 293 assumed to interact with the NSIS Initiator, Responder, and 294 Forwarders using standard mechanisms. 296 4. The placement of the NSIS Initiators and NSIS Forwarders is not 297 fixed. 299 4 Assumptions and Exclusions 301 4.1 Assumptions and Non-Assumptions 303 1. The NSIS signaling could run end to end, end to edge, or edge to 304 edge, or network-to-network ((between providers), depending on what 305 point in the network acts as the initiator, and how far towards the 306 other end of the network the signaling propagates. In general, we 307 could expect NSIS Forwarders to become more 'dense' towards the 308 edges of the network, but this is not a requirement. An over- 309 provisioned domain might contain no NSIS Forwarders at all (and be 310 NSIS transparent); at the other extreme, NSIS Forwarders might be 311 placed at every router. In the latter case, provisioning can be 312 carried out in a local implementation-dependent way without further 313 signaling, whereas in the case of remote NSIS Forwarders, a 314 provisioning protocol might be needed to control the routers along 315 the path. This provisioning protocol is then independent of the end- 316 to-end NSIS signaling. 318 2. We do not consider 'pure' end-to-end signaling that is not 319 interpreted anywhere within the network. Such signaling is an 320 application-layer issue and IETF protocols such as SIP etc. can be 321 used. 323 3. Where the signaling does cover several NSIS domains or 324 subdomains, we do not exclude that different signaling protocols are 325 used in each path segment. We only place requirements on the 326 universality of the control information that is being transported. 327 (The goals here would be to allow the use of signaling protocols, 328 which are matched to the characteristics of the portion of the 329 network being traversed.) Note that the outcome of NSIS work might 330 result in various protocols or various flavors of the same protocol. 331 This implies the need for the translation of information into domain 332 specific format as well. 334 4. We assume that the service definitions a NSIS Initiator can ask 335 for are known in advance of the signaling protocol running. For 336 instance in the QoS example, the service definition includes QoS 337 parameters, lifetime of QoS guarantee etc., or any other service- 338 specific parameters. 340 There are many ways service requesters get to know about it. There 341 might be standardized services, the definition can be negotiated 342 together with a contract, the service definition is published at a 343 Web page, etc. 345 5. We assume that there are means for the discovery of NSIS entities 346 in order to know the signaling peers (solutions include static 347 configuration, automatically discovered, or implicitly runs over the 348 right nodes, etc.) The discovery of the NSIS entities has security 349 implications that need to be addressed properly. These implications 350 largely depend on the chosen protocol. For some security mechanisms 351 (i.e. Kerberos, pre-shared secret) it is required to know the 352 identity of the other entity. Hence the discovery mechanism may 353 provide means to learn this identity, which is then later used to 354 retrieve the required keys and parameters. 356 6. NSIS assumes to operate with networks using standard ("normal") 357 L3 routing. Where "normal" is not specified more exactly on purpose. 359 4.2 Exclusions 361 1. Development of specific mechanisms and algorithms for application 362 and transport layer adaptation are not considered, nor are the 363 protocols that would support it. 365 2. Specific mechanisms (APIs and so on) for interaction between 366 transport/applications and the network layer are not considered, 367 except to clarify the requirements on the negotiation capabilities 368 and information semantics that would be needed of the signaling 369 protocol. 371 3. Specific mechanisms for provisioning within a domain/subdomain 372 are not considered. However, NSIS can be used for signaling within a 373 domain/subdomain performing provisioning. For instance in the QoS 374 example, it means that the setting of QoS mechanisms in a domain is 375 out of scope, but if we have a tunnel, NSIS could also be used for 376 tunnel setup with QoS guaranties. It should be possible to exploit 377 these mechanisms optimally within the end-to-end context. 378 Consideration of how to do this might generate new requirements for 379 NSIS however. For example, the information needed by a NSIS 380 Forwarder to manage a radio subnetwork needs to be provided by the 381 NSIS solution. 383 4. Specific mechanisms (APIs and so on) for interaction between the 384 network layer and underlying provisioning mechanisms are not 385 considered. 387 5. Interaction with resource management capabilities is not 388 considered. Standard protocols might be used for this. This may 389 imply requirements for the sort of information that should be 390 exchanged between the NSIS entities. 392 6. Security implications related to multicasting are outside the 393 scope of the signaling protocol. 395 7. Protection of non-signaling messages is outside the scope of the 396 protocol 398 The protection of non-signaling messages (including data traffic 399 following a reservation) is not directly considered by a signaling 400 protocol. The protection of data messages transmitted along the 401 provisioned path is outside the scope of a signaling protocol. 402 Regarding data traffic there is an interaction with accounting 403 (metering) and edge routers might require packets to be integrity 404 protected to be able to securely assign incoming data traffic to a 405 particular user. 407 Additionally there might be an interaction with IPSec protected 408 traffic experiencing service-specific treatment and the established 409 state created due to signaling. One example of such an interaction is 410 the different flow identification with and without IPSec protection. 412 Many security properties are likely to be application specific and 413 may be provided by the corresponding application layer protocol. 415 8. Service definitions and in particular QoS services and classes 416 are out of scope. Together with the service definition any 417 definition of service specific parameters are not considered in this 418 document. Only the base NSIS signaling protocol for transporting the 419 service information are addressed. 421 9. Similarly, specific methods, protocols, and ways to express 422 service information in the Application/Session level are not 423 considered (e.g., SDP, SIP, RTSP, etc.). 425 10. The specification of any extensions needed to signal information 426 via application level protocols (e.g. SDP), and the mapping on NSIS 427 information are considered outside of the scope of NSIS working 428 group, as this work is in the direct scope of other IETF working 429 groups (e.g. MMUSIC). 431 11. Handoff decision and trigger sources: An NSIS protocol is not 432 used to trigger handoffs in mobile IP, nor is it used to decide 433 whether to handoff or not. As soon as or in some situation even 434 before a handoff happened, an NSIS protocol might be used for 435 signaling for the particular service again. The basic underlying 436 assumption is that the route comes first (defining the path) and the 437 signaling comes after it (following the path). This doesn't prevent 438 a signaling application at some node interacting with something that 439 modifies the path, but the requirement is then just for NSIS to live 440 with that possibility. However, NSIS must interwork with several 441 protocols for mobility management. 443 12. Service monitoring is out of scope. It is heavily dependent on 444 the type of the application and or transport service, and in what 445 scenario it is used. 447 5 Requirements 449 This section defines more detailed requirements for a signaling 450 solution, respecting the framework, scoping assumptions, and 451 terminology considered earlier. The requirements are in subsections, 452 grouped roughly according to general technical aspects: architecture 453 and design goals, topology issues, parameters, performance, 454 security, information, and flexibility. 456 Two general (and potentially contradictory) goals for the solution 457 are that it should be applicable in a very wide range of scenarios, 458 and at the same time lightweight in implementation complexity and 459 resource requirements in nodes. One approach to this is that the 460 solution could deal with certain requirements via modular components 461 or capabilities, which are optional to implement in individual 462 nodes. 464 In order to prioritize the various requirements we define different 465 'parts of the network'. In the different parts of the network a 466 particular requirement might have a different priority. 468 The parts of the networks we differentiate are the host-to-first 469 router, the access network, and the core network. The host to first 470 router part includes all the layer 2 technologies to access to the 471 Internet. In many cases, there is an application and/or user running 472 on the host initiating signaling. The access network can be 473 characterized by low capacity links, medium speed IP processing 474 capabilities, and it might consist of a complete layer 2 network as 475 well. The core network characteristics include high-speed forwarding 476 capacities and inter-domain issues. These divisions between network 477 types are not strict and do not appear in all networks, but where 478 they do exist they may influence signaling requirements and will be 479 highlighted as necessary. 481 5.1 Architecture and Design Goals 482 This section contains requirements related to desirable overall 483 characteristics of a solution, e.g. enabling flexibility, or 484 independence of parts of the framework. 486 5.1.1 MUST be applicable for different technologies. 488 The signaling protocol MUST work with various QoS and non-QoS 489 technologies. The basic information exchanged over the signaling 490 protocol MUST be in such detail and quantity that it is useful for 491 various technologies. 493 5.1.2 SHOULD provide resource availability information on request 495 NSIS SHOULD provide a mechanism to check whether resources are 496 available without performing a reservation. In some scenarios, e.g., 497 the mobile terminal scenario, it is required to query, whether 498 resources are available, without performing a reservation on the 499 resource. 501 5.1.3 NSIS MUST be designed modularly 503 A modular design allows for more lightweight implementations, if 504 fewer features are needed. Mutually exclusive solutions are 505 supported. Examples for modularity: 507 - Work over any kind of network (narrowband versus broadband, error- 508 prone versus reliable, ...). This implies low bandwidth signaling 509 and redundant information MUST be supported if necessary. 511 - Uni- and bi-directional reservations are possible 513 - Extensible in the future with different add-ons for certain 514 environments or scenarios 516 - Protocol layering, where appropriate. This means NSIS MUST provide 517 a base protocol, which can be adapted to different environments. 519 5.1.4 NSIS MUST decouple protocol and information 521 The signaling protocol MUST be clearly separated from the control 522 information being transported. This provides for the independent 523 development of these two aspects of the solution, and allows for 524 this control information to be carried within other protocols, 525 including application layer ones, existing ones or those being 526 developed in the future. The gained flexibility in the information 527 transported allows for the applicability of the same protocol in 528 various scenarios. 530 However, note that the information carried needs to be standardized; 531 otherwise interoperability is difficult to achieve. 533 5.1.5 NSIS MUST reuse existing provisioning 534 Reuse existing functions and protocols for provisioning within a 535 domain/subdomain unchanged. (Motivation: 'Don't re-invent the 536 wheel'.) 538 5.1.6 NSIS MUST support independence of signaling and provisioning 539 paradigm 541 The signaling MUST be independent of the paradigm and mechanism of 542 provisioning. E.g., in the case of signaling for QoS, the 543 independence of the signaling protocol from the QoS provisioning 544 allows for using the NSIS protocol together with various QoS 545 technologies in various scenarios. 547 5.1.7 NSIS MUST be application independent 549 The signaling protocol MUST be independent of the application. The 550 control information SHOULD be application independent, because we 551 look into network level signaling. 553 The requirement relates to the way the signaling interacts with 554 upper layer functions (users, applications, and QoS administration), 555 and lower layer technologies. 557 Opaque application information MAY get transported in the signaling 558 message, without being handled in the network. Development and 559 deployment of new applications SHOULD be possible without impacting 560 the network infrastructure. 562 5.2 Signaling Flows 564 This section contains requirements related to the possible signaling 565 flows that should be supported, e.g. over what parts of the flow 566 path, between what entities (end-systems, routers, middle boxes, 567 management systems), in which direction. 569 5.2.1 The placement of NSIS Initiator, Forwarder, Responder MUST be 570 free 572 The protocol MUST work in various scenarios such as host-to-network- 573 to-host, edge-to-edge, (e.g., just within one providers domain), 574 user-to-network (from end system into the network, ending, e.g., at 575 the entry to the network and vice versa), and network-to-network 576 (e.g., between providers). 578 Placing the NSIS Forwarder and NSIS Initiator functions at different 579 locations allows for various scenarios to work with the same 580 protocol. 582 5.2.2 No constraint MUST be posed the signaling and NSIS Forwarders to 583 be in the data path. 585 There is a set of scenarios, where signaling is not on the data 586 path. The NSIS Forwarder being in the data path is one extreme case 587 and useful in many cases. Therefore the case of having NSIS entities 588 on the data path only MUST be supported. 590 There are going to be cases where a centralized entity will take a 591 decision about service requests. In this case, there is no need to 592 have the data follow the signaling path, or have the signaling 593 follow the data path. 595 There are going to be cases without a centralized entity managing 596 resources and the signaling will be used as a tool for resource 597 management. For various reasons (such as efficient use of expensive 598 bandwidth), one will want to have fine-grained, fast, and very 599 dynamic control of the resources in the network. 601 There are going to be cases where there will be neither signaling 602 nor a centralized entity (over-provisioning). Nothing has to be done 603 anyway. 605 One can capture the requirement with the following, different 606 wording: If one views the domain as a virtual router then NSIS 607 signaling used between those virtual routers MUST follow the same 608 path as the data. 610 Routing the signaling protocol along an independent path is desired 611 by network operators/designers. Ideally, the capability to route the 612 protocol along an independent path would give the network 613 designer/operator the option to manage bandwidth utilization through 614 the topology. 616 There are other possibilities as well. An NSIS protocol MUST accept 617 all of these possibilities with a strong focus on the on-path 618 signaling. 620 5.2.3 Concealment of topology and technology information SHOULD be 621 possible 623 The NSIS protocol SHOULD allow for hiding the internal structure of 624 a NSIS domain from end-nodes and from other networks. Hence an 625 adversary should not be able to learn the internal structure of a 626 network with the help of the signaling protocol. 628 In various scenarios, topology information should be hidden for 629 various reasons. From a business point of view, some administrations 630 don't want to reveal the topology and technology used. 632 5.2.4 Transparent signaling through networks SHOULD be possible 634 It SHOULD be possible that the signaling for some flows traverse 635 path segments transparently, i.e., without interpretation at NSIS 636 Forwarders within the network. An example would be a subdomain 637 within a core network, which only interpreted signaling for 638 aggregates established at the domain edge, with the flow-related 639 signaling passing transparently through it. 641 In other words, NSIS SHOULD work in hierarchical scenarios, where 642 big pipes/trunks are setup using NSIS signaling, but also flows 643 which run within that big pipe/trunk are setup using NSIS. 645 5.3 Messaging 647 5.3.1 Explicit release of resources MUST be possible 649 When a resource reservation is no longer necessary, e.g. because the 650 application terminates, or because a mobile host experienced a hand- 651 off, it MUST be possible to explicitly release resources. In general 652 explicit release enhances the overall network utilization. 654 5.3.2 Automatic release of resources after failure SHOULD be possible 656 When the NSIS Initiator goes down, the resources it requested in the 657 network SHOULD be released, since they will no longer be necessary. 659 After detection of a failure in the network, any NSIS 660 Forwarder/Initiator MUST be able to release a reservation it is 661 involved in. For example, this may require signaling of the "Release 662 after Failure" message upstream as well as downstream, or soft state 663 timing out of reservations. 665 The goal is to prevent stale state within the network and adds 666 robustness to the operation of NSIS. So in other words, an NSIS 667 signaling protocol or mechanisms MUST provide means for an NSIS 668 entity to discover and remove local stale state. 670 Note that this might need to work together with a notification 671 mechanism. 673 5.3.3 NSIS SHOULD allow for sending notifications upstream 675 NSIS Forwarders SHOULD notify the NSIS Initiator or any other NSIS 676 Forwarder upstream, if there is a state change inside the network. 677 There are various types of network changes for instance among them: 679 Recoverable errors: the network nodes can locally repair this type 680 error. The network nodes do not have to notify the users of the 681 error immediately. This is a condition when the danger of 682 degradation (or actual short term degradation) of the provided 683 service was overcome by the network (NSIS Forwarder) itself. 685 Unrecoverable errors: the network nodes cannot handle this type of 686 error, and have to notify the users as soon as possible. 688 Service degradation/severe congestion: In case the service cannot be 689 provided completely but partially only. 691 Repair indication: If an error occurred and it has been fixed, this 692 triggers the sending of a notification. 694 Service upgrade available: If a previously requested better service 695 becomes available. 697 The content of the notification is very service specific, but it is 698 must at least carry type information. Additionally, it may carry the 699 location of the state change. 701 The notifications may or may not be in response to a NSIS message. 702 This means an NSIS entity has to be able to handle notifications at 703 any time. 705 Note however, that there are a number of security consideration 706 needs to be solved with notification, even more important if the 707 notification is sent without prior request (asynchronously). The 708 problem basically is, that everybody could send notifications to any 709 NSIS entity and the NSIS entity most likely reacts on the 710 notification. E.g., if it gets an error notification it might 711 teardown the reservation, even if everything is ok. So the 712 notification might depend on security associations between the 713 sender of the notification and its receiver. If a hop-by-hop 714 security mechanism is chosen, this implies also that notifications 715 need to be sent on the reverse path. 717 5.3.4 Feedback about success of service request MUST be provided 719 A request for service MUST be answered at least with yes or no. 720 However, it may be useful in case of a negative answer to also get a 721 description of what amount of resources a request is possible. So an 722 opaque element MAY be included into the answer. The element heavily 723 depends on the service requested. 725 5.3.5 NSIS MUST allow for local information exchange 727 The signaling protocol MUST be able to exchange local information 728 between NSIS Forwarders located within one single administrative 729 domain. The local information exchange is performed by a number of 730 separate messages not belonging to an end-to-end signaling process. 731 Local information might, for example, be IP addresses, severe 732 congestion notification, notification of successful or erroneous 733 processing of signaling messages. 735 In some cases, the NSIS signaling protocol MAY carry identification 736 of the NSIS Forwarders located at the boundaries of a domain. 737 However, the identification of edge should not be visible to the end 738 host (NSIS Initiator) and only applies within one administrative 739 domain. 741 5.4 Control Information 743 This section contains requirements related to the control 744 information that needs to be exchanged. 746 5.4.1 Mutability information on parameters SHOULD be possible 747 It SHOULD be possible for the NSIS initiator to control the 748 mutability of the signaled information. This prevents from being 749 changed in a non-recoverable way. The NSIS initiator SHOULD be able 750 to control what is requested end to end, without the request being 751 gradually mutated as it passes through a sequence of domains. This 752 implies that in case of changes made on the parameters, the original 753 requested ones must still be available. 755 Note that we do not require anything about particular parameters 756 being changed. 758 Additionally, note that a provider or that particular services 759 requested, can still influence the provisioning but in the signaling 760 message the request should stay the same. 762 5.4.2 SHOULD possible to add and remove local domain information 764 It SHOULD be possible for the Resource Management Function to add 765 and remove local scope elements. Compared to Requirement 5.3.5 this 766 requirement does use the normal signaling process and message 767 exchange for transporting local information. E.g., at the entrance 768 to a domain domain-specific information is added, which is used in 769 this domain only, and the information is removed again when a 770 signaling message leaves the domain. The motivation is in the 771 economy of re-use the protocol for domain internal signaling of 772 various information pieces. Where additional information is needed 773 within a particular domain, it should be possible to carry this at 774 the same time as the end-to-end information. 776 5.4.3 State MUST be addressed independent of flow identification 778 Addressing or identifying state MUST be independent of the flow 779 identifier (flow end-points, topological addresses). Various 780 scenarios in the mobility area require this independence because 781 flows resulting from handoff might have changed end-points etc. but 782 still have the same service requirement. Also several proxy-based 783 signaling methods profit from such independence. 785 5.4.4 Modification of already reserved resources SHOULD be seamless 787 In many case, the reservation needs to be updated (up or downgrade). 788 This SHOULD happen seamlessly without service interruption. At least 789 the signaling protocol should allow for it, even if some data path 790 elements might not be capable of doing so. 792 5.4.5 Grouping of signaling for several micro-flows MAY be provided 794 NSIS MAY group signaling information for several micro-flow into one 795 signaling message. The goal of this is the optimization in terms of 796 setup delay, which can happen in parallel. This helps applications 797 requesting several flows at once. Also potential refreshes (in case 798 of a soft state solution) might profit from grouping. 800 However, the network MUST NOT know that a relationship between the 801 grouped flows exists. There MUST NOT be any transactional semantic 802 associated with the grouping. It is only meant for optimization 803 purposes and each reservation MUST be handled separately from each 804 other. 806 5.5 Performance 808 This section discusses performance requirements and evaluation 809 criteria and the way in which these could and should be traded off 810 against each other in various parts of the solution. 812 Scalability is a must anyway. However, depending on the scenario the 813 question to which extends the protocol must be scalable. 815 Note that many of the performance issues are heavily dependent on 816 the scenario assumed and are normally a trade-off between speed, 817 reliability, complexity, and scalability. The trade-off varies in 818 different parts of the network. For example, in radio access 819 networks low bandwidth consumption will overweight the low latency 820 requirement, while in core networks it may be reverse. 822 5.5.1 Scalability 824 NSIS MUST be scalable in the number of messages received by a 825 signaling communication partner (NSIS Initiator, NSIS Forwarder, and 826 NSIS Responder). The major concern lies in the core of the network, 827 where large numbers of messages arrive. 829 It MUST be scalable in number of hand-offs in mobile environments. 830 This mainly applies in access networks, because the core is 831 transparent to mobility in most cases. 833 It MUST be scalable in the number of interactions for setting up a 834 reservation. This applies for end-systems setting up several 835 reservations. Some servers might be expected to setup a large number 836 of reservations. 838 Scalability in the number of state per entity MUST be achieved for 839 NSIS Forwarders in the core of the network. 841 And Scalability in CPU use MUST be achieved on end terminals in case 842 of many reservations at the same time and intermediate nodes mainly 843 in the core. 845 5.5.2 NSIS SHOULD allow for low latency in setup 847 NSIS SHOULD allow for low latency setup of reservations. This is 848 only needed in scenarios, where reservations are in a short time 849 scale (e.g. handover in mobile environments), or where human 850 interaction is immediately concerned (e.g., voice communication 851 setup delay). 853 5.5.3 NSIS MUST allow for low bandwidth consumption for signaling 854 protocol 856 NSIS MUST allow for low bandwidth consumption in certain access 857 networks. Again only small sets of scenarios call for low bandwidth, 858 mainly those where wireless links are involved. 860 5.5.4 NSIS SHOULD allow to constrain load on devices 862 The NSIS architecture SHOULD give the ability to constrain the load 863 (CPU load, memory space, signaling bandwidth consumption and 864 signaling intensity) on devices where it is needed. One of the 865 reasons is that the protocol handling should have a minimal impact 866 on interior (core) nodes. 868 This can be achieved by many different methods. Examples, and this 869 are only examples, include message aggregation, by ignoring 870 signaling message, header compression, or minimizing functionality. 871 The framework may choose any method as long as the requirement is 872 met. 874 5.5.5 NSIS SHOULD target highest possible network utilization 876 There are networking environments that require high network 877 utilization for various reasons, and the signaling protocol SHOULD 878 to its best ability support high resource utilization while 879 maintaining appropriate service quality. 881 In networks where resources are very expensive (as is the case for 882 many wireless networks), efficient network utilization is of 883 critical financial importance. On the other hand there are other 884 parts of the network where high utilization is not required. 886 5.6 Flexibility 888 This section lists the various ways the protocol can flexibly be 889 employed. 891 5.6.1 Flow aggregation 893 NSIS MUST allow for flow aggregation, including the capability to 894 select and change the level of aggregation. 896 5.6.2 Flexibility in the placement of the NSIS Initiator 898 NSIS MUST be flexible in placing an NSIS Initiator. The NSIS 899 Initiator might be the sender or the receiver of content. But also 900 network-initiated reservations MUST be allowed in various scenarios 901 such as PSTN gateways, some VPNs, and mobility. 903 5.6.3 Flexibility in the initiation of re-negotiation 904 The NSIS Initiator or the NSIS Responder SHOULD be able to initiate 905 a re-negotiation or change the reservation due to various reasons, 906 such as local resource shortage (CPU, memory on end-system) or a 907 user changed application preference/profiles. 909 5.6.4 SOULD support network-initiated re-negotiation 911 NSIS SHOULD support network-initiated re-negotiation. This is used 912 in cases, where the network is not able to further guarantee 913 resources and want to e.g. downgrade a reservation. 915 5.6.5 Uni / bi-directional reservation 917 Both unidirectional as well as bi-direction reservations SHOULD be 918 possible. With bi-directional reservations we mean here reservations 919 having the same end-points. But the path in the two directions does 920 not need to be the same. 922 The goal of a bi-directional reservation is mainly an optimization 923 in terms of setup delay. There is no requirements on constrains such 924 as use the same data path etc. 926 5.7 Security 928 This section discusses security-related requirements. For a 929 discussion of security threats see [SEC-THR]. The NSIS protocol MUST 930 provide means for security, but it MUST be allowed that nodes 931 implementing NSIS signaling do not need use the security means. 933 5.7.1 Authentication of signaling requests 935 A signaling protocol MUST make provision for enabling various 936 entities to be authenticated against each other using strong 937 authentication mechanisms. The term strong authentication points to 938 the fact that weak plain-text password mechanisms must not be used 939 for authentication. 941 5.7.2 Resource Authorization 943 The signaling protocol MUST provide means to authorize resource 944 requests. This requirement demands a hook to interact with a policy 945 entity to request authorization data. This allows an authenticated 946 entity to be associated with authorization data and to verify the 947 resource request. Authorization prevents reservations by unauthorized 948 entities, reservations violating policies, and theft of service. 949 Additionally it limits denial of service attacks against parts of the 950 network or the entire network caused by unrestricted reservations. 951 Additionally it might be helpful to provide some means to inform 952 other protocols of participating nodes within the same administrative 953 domain about a previous successful authorization event. 955 5.7.3 Integrity protection 956 The signaling protocol MUST provide means to protect the message 957 payloads against modifications. Integrity protection prevents an 958 adversary from modifying parts of the signaling message and from 959 mounting denial of service or theft of service type of attacks 960 against network elements participating in the protocol execution. 962 5.7.4 Replay protection 964 To prevent replay of previous signaling messages the signaling 965 protocol MUST provide means to detect old i.e. already transmitted 966 signaling messages. A solution must cover issues of synchronization 967 problems in the case of a restart or a crash of a participating 968 network element. 970 5.7.5 Hop-by-hop security 972 Hop-by-Hop security SHOULD be supported. It is a well known and 973 proven concept in Quality-of-Service and other signaling protocols 974 that allows intermediate nodes that actively participate in the 975 protocol to modify the messages as it is required by processing rule. 976 Note that this requirement does not exclude end-to-end or network-to- 977 network security of a signaling message. End-to-end security between 978 the initiator and the responder may be used to provide protection of 979 non-mutable data fields. Network-to-network security refers to the 980 protection of messages over various hops but not in an end-to-end 981 manner i.e. protected over a particular network. 983 5.7.6 Identity confidentiality and location privacy 985 Identity confidentiality SHOULD be supported. It enables privacy and 986 avoids profiling of entities by adversary eavesdropping the signaling 987 traffic along the path. The identity used in the process of 988 authentication may also be hidden to a limited extent from a network 989 to which the initiator is attached. However the identity MUST provide 990 enough information for the nodes in the access network to collect 991 accounting data. 993 Location privacy MAY be supported. It is an issue for the initiator 994 who triggers the signaling protocol. In some scenarios the initiator 995 may not be willing to reveal location information to the responder as 996 part of the signaling procedure. 998 5.7.7 Denial-of-service attacks 1000 A signaling protocol SHOULD provide prevention of Denial-of-service 1001 attacks. To effectively prevent denial-of-service attacks it is 1002 necessary that the used security and protocol mechanisms MUST have 1003 low computation complexity to verify a resource request prior to 1004 authenticating the requesting entity. Additionally the signaling 1005 protocol and the used security mechanisms SHOULD NOT require large 1006 resource consumption (for example main memory or other additional 1007 message exchanges) before a successful authentication was done. 1009 5.7.8 Confidentiality of signaling messages 1011 Based on the signaling information exchanged between nodes 1012 participating in the signaling protocol an adversary may learn both 1013 the identities and the content of the signaling messages. To prevent 1014 this from happening, confidentiality of the signaling message in a 1015 hop-by-hop manner MAY be provided. Note that the protection can be 1016 provided on a hop-by-hop basis for most message payloads since it is 1017 required that entities which actively participating in the signaling 1018 protocol must be able to read and eventually modify the content of 1019 the signaling messages. 1021 5.7.9 Ownership of a reservation 1023 When existing reservations have to be modified then there is a need 1024 to use a reservation identifier to uniquely identify the established 1025 state. A signaling protocol MUST provide the appropriate security 1026 protection to prevent other entities to modify state without having 1027 the proper ownership. 1029 5.8 Mobility 1031 5.8.1 Allow efficient service re-establishment after handover 1033 Handover is an essential function in wireless networks. After 1034 handover, the reservation may need to be completely or partially re- 1035 established due to route changes. The re-establishment may be 1036 requested by the mobile node itself or triggered by the access point 1037 that the mobile node is attached to. In the first case, the 1038 signaling MUST allow efficient re-establishment after handover. Re- 1039 establishment after handover MUST be as quick as possible so that 1040 the mobile node does not experience service interruption or service 1041 degradation. The re-establishment SHOULD be localized, and not 1042 require end-to-end signaling. 1044 5.9 Interworking with other protocols and techniques 1046 Hooks SHOULD be provided to enable efficient interworking between 1047 various protocols and techniques including: 1049 5.9.1 MUST interwork with IP tunneling 1051 IP tunneling for various applications MUST be supported. More 1052 specifically tunneling for IPSec tunnels are of importance as 1053 discussed in Section 4.2. This mainly impacts the identification of 1054 flows. Using IPSec parts of information used for flow identification 1055 (e.g. transport protocol information and ports) may not be accessible 1056 due to encryption. 1058 5.9.2 The solution MUST NOT constrain either to IPv4 or IPv6 1060 5.9.3 MUST be independent from charging model 1061 Signaling MUST NOT be constrained by charging models or the charging 1062 infrastructure used. 1064 5.9.4 SHOULD provide hooks for AAA protocols 1066 The NSIS SHOULD be developed with respect to be able to collect 1067 usage records from one or more network elements. 1069 5.9.5 SHOULD interwork with seamless handoff protocols 1071 An NSIS protocol SHOULD interwork with seamless handoff protocols 1072 such as context transfer and candidate access router (CAR) 1073 discovery. 1075 5.9.6 MAY interwork with non-traditional routing 1077 NSIS assumes traditional routing, but networks, which do non- 1078 traditional L3 routing, should not break it. 1080 5.10 Operational 1082 5.10.1 Ability to assign transport quality to signaling messages. 1084 The NSIS architecture SHOULD allow the network operator to assign 1085 the NSIS protocol messages a certain transport quality. As signaling 1086 opens up for possible denial-of-service attacks, this requirement 1087 gives the network operator a mean, but also the obligation, to 1088 trade-off between signaling latency and the impact (from the 1089 signaling messages) on devices within his/her network. From protocol 1090 design this requirement states that the protocol messages SHOULD be 1091 detectable, at least where the control and assignment of the 1092 messages priority is done. 1094 Furthermore, the protocol design must take into account reliability 1095 concerns. Communication reliability is seen as part of the quality 1096 assigned to signaling messages. So procedures MUST be defined how an 1097 NSIS signaling system behaves if some kind of request it sent stays 1098 without answer. The basic transport protocol to be used between 1099 adjacent NSIS units MAY ensure message integrity and reliable 1100 transport. 1102 5.10.2 Graceful fail over 1104 Any unit participating in NSIS signaling MUST NOT cause further 1105 damage to other systems involved in NSIS signaling when it has to go 1106 out of service. 1108 5.10.3 Graceful handling of NSIS entity problems 1110 NSIS peers SHOULD be able to detect the malfunctioning peer. It may 1111 notify the NSIS Initiator or another NSIS entity involved in the 1112 signaling process. The NSIS peer may handle the problem itself e.g. 1113 switching to a backup NSIS entity. In the latter case note that 1114 synchronization of state between the primary and the backup entity 1115 is needed. 1117 6 Security Considerations 1119 Section 5.7 of this document provides security related requirements 1120 of a signaling protocol. 1122 7 Informative References 1124 [RSVP] Braden, R., Zhang, L., Berson, S., Herzog, A., Jamin, S., 1125 "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional 1126 Specification", RFC 2205, September 1997. 1128 [RSVP-TE] D. Awduche, L. Berger, D. Gan, T. Li, V. Srinivasan, G. 1129 Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, 1130 December 2001. 1132 8 Acknowledgments 1134 Quite a number of people have been involved in the discussion of the 1135 document, adding some ideas, requirements, etc. We list them without 1136 a guarantee on completeness: Changpeng Fan (Siemens), Krishna Paul 1137 (NEC), Maurizio Molina (NEC), Mirko Schramm (Siemens), Andreas 1138 Schrader (NEC), Hannes Hartenstein (NEC), Ralf Schmitz (NEC), 1139 Juergen Quittek (NEC), Morihisa Momona (NEC), Holger Karl (Technical 1140 University Berlin), Xiaoming Fu (Technical University Berlin), Hans- 1141 Peter Schwefel (Siemens), Mathias Rautenberg (Siemens), Christoph 1142 Niedermeier (Siemens), Andreas Kassler (University of Ulm), Ilya 1143 Freytsis. 1145 Some text and/or ideas for text, requirements, scenarios have been 1146 taken from an Internet Draft written by the following authors: David 1147 Partain (Ericsson), Anders Bergsten (Telia Research), Marc Greis 1148 (Nokia), Georgios Karagiannis (Ericsson), Jukka Manner (University 1149 of Helsinki), Ping Pan (Juniper), Vlora Rexhepi (Ericsson), Lars 1150 Westberg (Ericsson), Haihong Zheng (Nokia). Some of those have 1151 actively contributed new text to this document as well. 1153 Another Internet Draft impacting this document has been written by 1154 Sven Van den Bosch, Maarten Buchli, and Danny Goderis (all Alcatel). 1155 These people contributed also new text. 1157 Thanks also to Kwok Ho Chan (Nortel) for text changes. 1159 9 Author's Addresses 1161 Marcus Brunner (Editor) 1162 NEC Europe Ltd. 1163 Network Laboratories 1164 Kurfuersten-Anlage 34 1165 D-69115 Heidelberg 1166 Germany 1167 E-Mail: brunner@ccrle.nec.de 1168 Robert Hancock 1169 Roke Manor Research Ltd 1170 Romsey, Hants, SO51 0ZN 1171 United Kingdom 1172 E-Mail: robert.hancock@roke.co.uk 1174 Eleanor Hepworth 1175 Roke Manor Research Ltd 1176 Romsey, Hants, SO51 0ZN 1177 United Kingdom 1178 E-Mail: eleanor.hepworth@roke.co.uk 1180 Cornelia Kappler 1181 Siemens AG 1182 Berlin 13623 1183 Germany 1184 E-Mail: cornelia.kappler@icn.siemens.de 1186 Hannes Tschofenig 1187 Siemens AG 1188 Otto-Hahn-Ring 6 1189 81739 Munchen 1190 Germany 1191 Email: Hannes.Tschofenig@mchp.siemens.de 1193 10 Appendix: Scenarios/Use cases 1195 In the following we describe scenarios, which are important to 1196 cover, and which allow us to discuss various requirements. Some 1197 regard this as use cases to be covered defining the use of a 1198 signaling protocol. 1200 10.1 Terminal Mobility 1202 The scenario we are looking at is the case where a mobile terminal 1203 (MT) changes from one access point to another access point. The 1204 access points are located in separate QoS domains. We assume Mobile 1205 IP to handle mobility on the network layer in this scenario and 1206 consider the various extensions (i.e., IETF proposals) to Mobile IP, 1207 in order to provide 'fast handover' for roaming Mobile Terminals. 1208 The goal to be achieved lies in providing, keeping, and adapting the 1209 requested QoS for the ongoing IP sessions in case of handover. 1210 Furthermore, the negotiation of QoS parameters with the new domain 1211 via the old connection might be needed, in order to support the 1212 different 'fast handover' proposals within the IETF. 1214 The entities involved in this scenario include a mobile terminal, 1215 access points, an access network manager, and communication partners 1216 of the MT (the other end(s) of the communication association). 1217 From a technical point of view, terminal mobility means changing the 1218 access point of a mobile terminal (MT). However, technologies might 1219 change in various directions (access technology, QoS technology, 1220 administrative domain). If the access points are within one specific 1221 QoS technology (independent of access technology) we call this 1222 intra-QoS technology handoff. In the case of an inter-QoS technology 1223 handoff, one change from e.g. a DiffServ to an IntServ domain, 1224 however still using the same access technology. Finally, if the 1225 access points are using different access technologies we call it 1226 inter-technology hand-off. 1228 The following issues are of special importance in this scenario: 1230 1) Handoff decision 1232 - The QoS management requests handoff. The QoS management can decide 1233 to change the access point, since the traffic conditions of the new 1234 access point are better supporting the QoS requirements. The metric 1235 may be different (optimized towards a single or a group/class of 1236 users). Note that the MT or the network (see below) might trigger 1237 the handoff. 1239 - The mobility management forces handoff. This can have several 1240 reasons. The operator optimizes his network, admission is no longer 1241 granted (e.g. emptied prepaid condition). Or another example is when 1242 the MT is reaching the focus of another base station. However, this 1243 might be detected via measurements of QoS on the physical layer and 1244 is therefore out of scope of QoS signaling in IP. Note again that 1245 the MT or the network (see below) might trigger the handoff. 1247 - This scenario shows that local decisions might not be enough. The 1248 rest of the path to the other end of the communication needs to be 1249 considered as well. Hand-off decisions in a QoS domain do not only 1250 depend on the local resource availability, e.g., the wireless part, 1251 but involve the rest of the path as well. Additionally, 1252 decomposition of an end-to-end reservation might be needed, in order 1253 to change only parts of it. 1255 2) Trigger sources 1257 - Mobile terminal: If the end-system QoS management identifies 1258 another (better-suited) access point, it will request the handoff 1259 from the terminal itself. This will be especially likely in the case 1260 that two different provider networks are involved. Another important 1261 example is when the current access point bearer disappears (e.g. 1262 removing the Ethernet cable). In this case, the NSIS Initiator is 1263 basically located on the mobile terminal. 1265 - Network (access network manager): Sometimes, the handoff trigger 1266 will be issued from the network management to optimize the overall 1267 load situation. Most likely this will result in changing the base- 1268 station of a single providers network. Most likely the NSIS 1269 Initiator is located on a system within the network. 1271 3) Integration with other protocols 1272 - Interworking with other protocol must be considered in one or the 1273 other form. E.g., it might be worth combining QoS signaling between 1274 different QoS domains with mobility signaling at hand-over. 1276 4) Handover rates 1278 In mobile networks, the admission control process has to cope with 1279 far more admission requests than call setups alone would generate. 1280 For example, in the GSM (Global System for Mobile communications) 1281 case, mobility usually generates an average of one to two handovers 1282 per call. For third generation networks (such as UMTS), where it is 1283 necessary to keep radio links to several cells simultaneously 1284 (macro-diversity), the handover rate is significantly higher. 1286 5) Fast reservations 1288 Handover can also cause packet losses. This happens when the 1289 processing of an admission request causes a delayed handover to the 1290 new base station. In this situation, some packets might be 1291 discarded, and the overall speech quality might be degraded 1292 significantly. Moreover, a delay in handover may cause degradation 1293 for other users. In the worst-case scenario, a delay in handover may 1294 cause the connection to be dropped if the handover occurred due to 1295 bad air link quality. Therefore, it is critical that QoS signaling 1296 in connection with handover be carried out very quickly. 1298 6) Call blocking in case of overload 1300 Furthermore, when the network is overloaded, it is preferable to 1301 keep reservations for previously established flows while blocking 1302 new requests. Therefore, the resource reservation requests in 1303 connection with handover should be given higher priority than new 1304 requests for resource reservation. 1306 10.2 Cellular Networks 1308 In this scenario, the user is using the packet service of a 3rd 1309 generation cellular system, e.g. UMTS. The region between the End 1310 Host and the edge node connecting the cellular network to another 1311 QoS domain (e.g. the GGSN in UMTS or the PDSN in 3GPP2) is 1312 considered to be a single QoS domain. 1314 The issues in such an environment regarding QoS include: 1316 1) Cellular systems provide their own QoS technology with 1317 specialized parameters to co-ordinate the QoS provided by both the 1318 radio access and wired access network. For example, in a UMTS 1319 network, one aspect of GPRS is that it can be considered as a QoS 1320 technology; provisioning of QoS within GPRS is described mainly in 1321 terms of calling UMTS bearer classes. This QoS technology needs to 1322 be invoked with suitable parameters when higher layers trigger a 1323 request for QoS, and this therefore involves mapping the requested 1324 IP QoS onto these UMTS bearer classes. This request for resources 1325 might be triggered by IP signaling messages that pass across the 1326 cellular system, and possibly other QoS domains, to negotiate for 1327 network resources. Typically, cellular system specific messages 1328 invoke the underlying cellular system QoS technology in parallel 1329 with the IP QoS negotiation, to allocate the resources within the 1330 cellular system. 1332 2) The placement of NSIS Initiators and NSIS Forwarders (terminology 1333 in the framework given here). The NSIS Initiator could be located at 1334 the End Host (triggered by applications), the GGSN/PDSN, or at a 1335 node not directly on the data path, such as a bandwidth broker. In 1336 the second case, the GGSN/PDSN could either be acting as a proxy on 1337 behalf of an End Host with little capabilities, and/or managing 1338 aggregate resources within its QoS domain (the UMTS core network). 1339 The IP signaling messages are interpreted by the NSIS Forwarders, 1340 which may be located at the GGSN/PDSN, and in any QoS sub-domains 1341 within the cellular system. 1343 3) Initiation of IP-level QoS negotiation. IP-level QoS re- 1344 negotiation may be initiated by either the End Host, or by the 1345 network, based on current network loads, which might change 1346 depending on the location of the end host. 1348 4) The networks are designed and mainly used for speech 1349 communication (at least so far). 1351 Note that in comparison to the previous scenario emphasis is much 1352 less on the mobility aspects, because mobility is mainly handled on 1353 the lower layer. 1355 10.3 UMTS access 1357 The UMTS access scenario is shown in Figure 1. The Proxy-Call State 1358 Control Function/Policy Control Function (P-CSCF/PCF) is the 1359 outbound SIP proxy of the visited domain, i.e. the domain where the 1360 mobile user wants to set-up a call. The Gateway GPRS Support Node 1361 (GGSN) is the egress router of the UMTS domain and connects the UMTS 1362 access network to the Edge Router (ER) of the core IP network. The 1363 P-CSCF/PCF communicates with the GGSN via the COPS protocol. The 1364 User Equipment (UE) consists of a Mobile Terminal (MT) and Terminal 1365 Equipment (TE), e.g. a laptop. 1367 +--------+ 1368 +----------| P-CSCF |-------> SIP signaling 1369 / +--------+ 1370 / SIP : 1371 : +--------+ NSIS +----------------+ 1372 : | PCF |---------| NSIS Forwarder | 1373 : +--------+ +----------------+ 1374 : : 1375 : : COPS 1376 : : 1377 +----+ +--------+ +----+ 1378 | UE |----------| GGSN |------| ER | 1379 +----+ +--------+ +----+ 1381 Figure 1: UMTS access scenario 1383 In this scenario the GGSN has the role of Access Gate. According to 1384 3GPP standardization, the PCF is responsible for the policy-based 1385 control of the end-user service in the UMTS access network (i.e. 1386 from UE to GGSN). In the current UMTS release R.5, the PCF is part 1387 of the P-CSCF, but in UMTS R.6 the interface between P-CSCF and PCF 1388 may evolve to an open standardized interface. In any case the PCF 1389 has all required QoS information for per-flow admission control in 1390 the UMTS access network (which it gets from the P-CSCF and/or GGSN). 1391 Thus the PCF would be the appropriate entity to host the 1392 functionality of NSIS Initiator, initiating the "NSIS" QoS signaling 1393 towards the core IP network. The PCF/P-CSCF has to do the mapping 1394 from codec type (derived from SIP/SDP signaling) to IP traffic 1395 descriptor. SDP extensions to explicitly signal QoS information are 1396 useful to avoid the need to store codec information in the PCF and 1397 to allow for more flexibility and accurate description of the QoS 1398 traffic parameters. The PCF also controls the GGSN to open and close 1399 the gates and to configure per-flow policers, i.e. to authorize or 1400 forbid user traffic. 1402 The NSIS Forwarder is (of course) not part of the standard UMTS 1403 architecture. However, to achieve end-to-end QoS a NSIS Forwarder is 1404 needed such that the PCF can request a QoS connection to the IP 1405 network. As in the previous example, the NSIS Forwarder could manage 1406 a set of pre-provisioned resources in the IP network, i.e. bandwidth 1407 pipes, and the NSIS Forwarder performs per-flow admission control 1408 into these pipes. In this way, a connection can be made between two 1409 UMTS access networks, and hence, end-to-end QoS can be achieved. In 1410 this case the NSIS Initiator and NSIS Forwarder are clearly two 1411 separate entities. 1412 This use case clearly illustrates the need for an "NSIS" QoS 1413 signaling protocol between NSIS Initiator and NSIS Forwarder. An 1414 important application of such a protocol may be its use in the 1415 inter-connection of UMTS networks over an IP backbone. 1417 10.4 Wired part of wireless network 1419 A wireless network, seen from a QoS domain perspective, usually 1420 consists of three parts: a wireless interface part (the "radio 1421 interface"), a wired part of the wireless network (i.e., Radio 1422 Access Network) and the backbone of the wireless network, as shown 1423 in Figure 2. Note that this figure should not be seen as an 1424 architectural overview of wireless networks but rather as showing 1425 the conceptual QoS domains in a wireless network. 1427 In this scenario, a mobile host can roam and perform a handover 1428 procedure between base stations/access routers. In this scenario the 1429 NSIS QoS protocol can be applied between a base station and the 1430 gateway (GW). In this case a GW can also be considered as a local 1431 handover anchor point. Furthermore, in this scenario the NSIS QoS 1432 protocol can also be applied either between two GWs, or between two 1433 edge routers (ER). 1435 |--| 1436 |GW| 1437 |--| |--| 1438 |MH|--- . 1439 |--| / |-------| . 1440 /--|base | |--| . 1441 |station|-|ER|... 1442 |-------| |--| . |--| back- |--| |---| |----| 1443 ..|ER|.......|ER|..|BGW|.."Internet"..|host| 1444 -- |-------| |--| . |--| bone |--| |---| |----| 1445 |--| \ |base |-|ER|... . 1446 |MH| \ |station| |--| . 1447 |--|--- |-------| . MH = mobile host 1448 |--| ER = edge router 1449 <----> |GW| GW = gateway 1450 Wireless link |--| BGW = border gateway 1451 ... = interior nodes 1452 <-------------------> 1453 Wired part of wireless network 1455 <----------------------------------------> 1456 Wireless Network 1458 Figure 2. QoS architecture of wired part of wireless network 1460 Each of these parts of the wireless network impose different issues 1461 to be solved on the QoS signaling solution being used: 1463 - Wireless interface: The solution for the air interface link 1464 has to ensure flexibility and spectrum efficient transmission 1465 of IP packets. However, this link layer QoS can be solved in 1466 the same way as any other last hop problem by allowing a 1467 host to request the proper QoS profile. 1469 - Wired part of the wireless network: This is the part of 1470 the network that is closest to the base stations/access 1471 routers. It is an IP network although some parts logically 1472 perform tunneling of the end user data. In cellular networks, 1473 the wired part of the wireless network is denoted as a 1474 radio access network. 1476 This part of the wireless network has different 1477 characteristics when compared to traditional IP networks: 1479 1. The network supports a high proportion of real-time 1480 traffic. The majority of the traffic transported in the 1481 wired part of the wireless network is speech, which is 1482 very sensitive to delays and delay variation (jitter). 1484 2. The network must support mobility. Many wireless 1485 networks are able to provide a combination of soft 1486 and hard handover procedures. When handover occurs, 1487 reservations need to be established on new paths. 1488 The establishment time has to be as short as possible 1489 since long establishment times for reservations degrade 1490 the performance of the wireless network. Moreover, 1491 for maximal utilization of the radio spectrum, frequent 1492 handover operations are required. 1494 3. These links are typically rather bandwidth-limited. 1496 4. The wired transmission in such a network contains a 1497 relatively high volume of expensive leased lines. 1498 Overprovisioning might therefore be prohibitively 1499 expensive. 1501 5. The radio base stations are spread over a wide 1502 geographical area and are in general situated a large 1503 distance from the backbone. 1505 - Backbone of the wireless network: the requirements imposed 1506 by this network are similar to the requirements imposed by 1507 other types of backbone networks. 1509 Due to these very different characteristics and requirements, often 1510 contradictory, different QoS signaling solutions might be needed in 1511 each of the three network parts. 1513 10.5 Session Mobility 1515 In this scenario, a session is moved from one end-system to another. 1516 Ongoing sessions are kept and QoS parameters need to be adapted, 1517 since it is very likely that the new device provides different 1518 capabilities. Note that it is open which entity initiates the move, 1519 which implies that the NSIS Initiator might be triggered by 1520 different entities. 1522 User mobility (i.e., a user changing the device and therefore moving 1523 the sessions to the new device) is considered to be a special case 1524 within the session mobility scenario. 1526 Note that this scenario is different from terminal mobility. Not the 1527 terminal (end-system) has moved to a different access point. Both 1528 terminals are still connected to an IP network at their original 1529 points. 1531 The issues include: 1533 1) Keeping the QoS guarantees negotiated implies that the end- 1534 point(s) of communication are changed without changing the 1535 reservations. 1537 2) The trigger of the session move might be the user or any other 1538 party involved in the session. 1540 10.6 QoS reservations/negotiation from access to core network 1542 The scenario includes the signaling between access networks and core 1543 networks in order to setup and change reservations together with 1544 potential negotiation. 1546 The issues to be solved in this scenario are different from previous 1547 ones. 1549 1) The entity of reservation is most likely an aggregate. 1551 2) The time scales of reservations might be different (long living 1552 reservations of aggregates, less often re-negotiation). 1554 3) The specification of the traffic (amount of traffic), a 1555 particular QoS is guaranteed for, needs to be changed. E.g., in case 1556 additional flows are added to the aggregate, the traffic 1557 specification of the flow needs to be added if it is not already 1558 included in the aggregates specification. 1560 4) The flow specification is more complex including network 1561 addresses and sets of different address for the source as well as 1562 for the destination of the flow. 1564 10.7 QoS reservation/negotiation over administrative boundaries 1566 Signaling between two or more core networks to provide QoS is 1567 handled in this scenario. This might also include access to core 1568 signaling over administrative boundaries. Compared to the previous 1569 one it adds the case, where the two networks are not in the same 1570 administrative domain. Basically, it is the inter-domain/inter 1571 provider signaling which is handled in here. 1573 The domain boundary is the critical issue to be resolved. Which as 1574 various flavors of issues a QoS signaling protocol has to be 1575 concerned with. 1577 1) Competing administrations: Normally, only basic information 1578 should be exchanged, if the signaling is between competing 1579 administrations. Specifically information about core network 1580 internals (e.g., topology, technology, etc.) should not be 1581 exchanged. Some information exchange about the "access points" of 1582 the core networks (which is topology information as well) may need 1583 to be exchanged, because it is needed for proper signaling. 1585 2) Additionally, as in scenario 4, signaling most likely is based on 1586 aggregates, with all the issues raise there. 1588 3) Authorization: It is critical that the NSIS Initiator is 1589 authorized to perform a QoS path setup. 1591 4) Accountability: It is important to notice that signaling might be 1592 used as an entity to charge money for, therefore the interoperation 1593 with accounting needs to be available. 1595 10.8 QoS signaling between PSTN gateways and backbone routers 1597 A PSTN gateway (i.e., host) requires information from the network 1598 regarding its ability to transport voice traffic across the network. 1599 The voice quality will suffer due to packet loss, latency and 1600 jitter. Signaling is used to identify and admit a flow for which 1601 these impairments are minimized. In addition, the disposition of 1602 the signaling request is used to allow the PSTN GW to make a call 1603 routing decision before the call is actually accepted and delivered 1604 to the final destination. 1606 PSTN gateways may handle thousands of calls simultaneously and there 1607 may be hundreds of PSTN gateways in a single provider network. These 1608 numbers are likely to increase as the size of the network increases. 1609 The point being that scalability is a major issue. 1611 There are several ways that a PSTN gateway can acquire assurances 1612 that a network can carry its traffic across the network. These 1613 include: 1615 1. Over-provisioning a high availability network. 1616 2. Handling admission control through some policy server 1617 that has a global view of the network and its resources. 1618 3. Per PSTN GW pair admission control. 1619 4. Per call admission control (where a call is defined as 1620 the 5-tuple used to carry a single RTP flow). 1622 Item 1 requires no signaling at all and is therefore outside the 1623 scope of this working group. 1625 Item 2 is really a better informed version of 1, but it is also 1626 outside the scope of this working group as it relies on a particular 1627 telephony signaling protocol rather than a packet admission control 1628 protocol. 1630 Item 3 is initially attractive, as it appears to have reasonable 1631 scaling properties, however, its scaling properties only are 1632 effective in cases where there are relatively few PSTN GWs. In the 1633 more general case were a PSTN GW reduces to a single IP phone 1634 sitting behind some access network, the opportunities for 1635 aggregation are reduced and the problem reduces to item 4. 1637 Item 4 is the most general case. However, it has the most difficult 1638 scaling problems. The objective here is to place the requirements on 1639 Item 4 such that a scalable per-flow admission control protocol or 1640 protocol suite may be developed. 1642 The case where per-flow signaling extends to individual IP end- 1643 points allows the inclusion of IP phones on cable, DSL, wireless or 1644 other access networks in this scenario. 1646 Call Scenario 1648 A PSTN GW signals end-to-end for some 5-tuple defined flow a 1649 bandwidth and QoS requirement. Note that the 5-tuple might include 1650 masking/wildcarding. The access network admits this flow according 1651 to its local policy and the specific details of the access 1652 technology. 1654 At the edge router (i.e., border node), the flow is admitted, again 1655 with an optional authentication process, possibly involving an 1656 external policy server. Note that the relationship between the PSTN 1657 GW and the policy server and the routers and the policy server is 1658 outside the scope of NSIS. The edge router then admits the flow into 1659 the core of the network, possibly using some aggregation technique. 1661 At the interior nodes, the NSIS host-to-host signaling should either 1662 be ignored or invisible as the Edge router performed the admission 1663 control decision to some aggregate. 1665 At the inter-provider router (i.e., border node), again the NSIS 1666 host-to-host signaling should either be ignored or invisible, as the 1667 Edge router has performed an admission control decision about an 1668 aggregate across a carrier network. 1670 10.9 PSTN trunking gateway 1672 One of the use cases for the NSIS signaling protocol is the scenario 1673 of interconnecting PSTN gateways with an IP network that supports 1674 QoS. 1675 Four different scenarios are considered here. 1676 1. In-band QoS signaling is used. In this case the Media Gateway 1677 (MG) will be acting as the NSIS Initiator and the Edge Router 1678 (ER) will be the NSIS Forwarder. Hence, the ER should do 1679 admission control (into pre-provisioned traffic trunks) for the 1680 individual traffic flows. This scenario is not further 1681 considered here. 1682 2. Out-of-band signaling in a single domain, the NSIS forwarder is 1683 integrated in the MGC. In this case no NSIS protocol is 1684 required. 1685 3. Out-of-band signaling in a single domain, the NSIS forwarder is 1686 a separate box. In this case NSIS signaling is used between the 1687 MGC and the NSIS Forwarder. 1688 4. Out-of-band signaling between multiple domains, the NSIS 1689 Forwarder (which may be integrated in the MGC) triggers the 1690 NSIS Forwarder of the next domain. 1692 When the out-of-band QoS signaling is used the Media Gateway 1693 Controller (MGC) will be acting as the NSIS Initiator. 1695 In the second scenario the voice provider manages a set of traffic 1696 trunks that are leased from a network provider. The MGC does the 1697 admission control in this case. Since the NSIS Forwarder acts both 1698 as a NSIS Initiator and a NSIS Forwarder, no NSIS signaling is 1699 required. This scenario is shown in Figure 3. 1701 +-------------+ ISUP/SIGTRAN +-----+ +-----+ 1702 | SS7 network |---------------------| MGC |--------------| SS7 | 1703 +-------------+ +-------+-----+---------+ +-----+ 1704 : / : \ 1705 : / : \ 1706 : / +--------:----------+ \ 1707 : MEGACO / / : \ \ 1708 : / / +-----+ \ \ 1709 : / / | NMS | \ \ 1710 : / | +-----+ | \ 1711 : : | | : 1712 +--------------+ +----+ | bandwidth pipe (SLS) | +----+ 1713 | PSTN network |--| MG |--|ER|======================|ER|-| MG |-- 1714 +--------------+ +----+ \ / +----+ 1715 \ QoS network / 1716 +-------------------+ 1718 Figure 3: PSTN trunking gateway scenario 1720 In the third scenario, the voice provider does not lease traffic 1721 trunks in the network. Another entity may lease traffic trunks and 1722 may use a NSIS Forwarder to do per-flow admission control. In this 1723 case the NSIS signaling is used between the MGC and the NSIS 1724 Forwarder, which is a separate box here. Hence, the MGC acts only as 1725 a NSIS Initiator. This scenario is depicted in Figure 4. 1727 +-------------+ ISUP/SIGTRAN +-----+ +-----+ 1728 | SS7 network |---------------------| MGC |--------------| SS7 | 1729 +-------------+ +-------+-----+---------+ +-----+ 1730 : / : \ 1731 : / +-----+ \ 1732 : / | NF | \ 1733 : / +-----+ \ 1734 : / : \ 1735 : / +--------:----------+ \ 1736 : MEGACO : / : \ : 1737 : : / +-----+ \ : 1738 : : / | NMS | \ : 1739 : : | +-----+ | : 1740 : : | | : 1741 +--------------+ +----+ | bandwidth pipe (SLS) | +----+ 1742 | PSTN network |--| MG |--|ER|======================|ER|-| MG |-- 1743 +--------------+ +----+ \ / +----+ 1744 \ QoS network / 1745 +-------------------+ 1747 Figure 4: PSTN trunking gateway scenario 1749 In the fourth scenario multiple transport domains are involved. In 1750 the originating network either the MGC may have an overview on the 1751 resources of the overlay network or a separate NSIS Forwarder will 1752 have the overview. Hence, depending on this either the MGC or the 1753 NSIS Forwarder of the originating domain will contact the NSIS 1754 Forwarder of the next domain. The MGC always acts as a NSIS 1755 Initiator and may also be acting as a NSIS Forwarder in the first 1756 domain. 1758 10.10 Application request end-to-end QoS path from the network 1760 This is actually the easiest case, nevertheless might be most often 1761 used in terms of number of users. So multimedia application requests 1762 a guaranteed service from an IP network. We assume here that the 1763 application is somehow able to specify the network service. The 1764 characteristics here are that many hosts might do it, but that the 1765 requested service is low capacity (bounded by the access line). 1766 Additionally, we assume no mobility and standard devices. 1768 QOS for Virtual Private Networks 1770 In a Virtual Private Network (VPN) a variety of tunnels might be 1771 used between its edges. These tunnels could be for example, IP-Sec, 1772 GRE, and IP-IP. One of the most significant issues in VPNs is 1773 related to how a flow is identified and what quality a flow gets. A 1774 flow identification might consist among others of the transport 1775 protocol port numbers. In an IP-Sec tunnel this will be problematic 1776 since the transport protocol information is encrypted. 1778 There are two types of L3 VPNs, distinguished by where the endpoints 1779 of the tunnels exist. The endpoints of the tunnels may either be on 1780 the customer (CPE) or the provider equipment or provider edge (PE). 1782 Virtual Private networks are also likely to request bandwidth or 1783 other type of service in addition to the premium services the PSTN 1784 GW are likely to use. 1786 Tunnel end points at the Customer premises 1788 When the endpoints are the CPE, the CPE may want to signal across 1789 the public IP network for a particular amount of bandwidth and QoS 1790 for the tunnel aggregate. Such signaling may be useful when a 1791 customer wants to vary their network cost with demand, rather than 1792 paying a flat rate. Such signaling exists between the two CPE 1793 routers. Intermediate access and edge routers perform the same exact 1794 call admission control, authentication and aggregation functions 1795 performed by the corresponding routers in the PSTN GW scenario with 1796 the exception that the endpoints are the CPE tunnel endpoints rather 1797 than PSTN GWs and the 5-tuple used to describe the RTP flow is 1798 replaced with the corresponding flow spec to uniquely identify the 1799 tunnels. Tunnels may be of any variety (e.g. IP-Sec, GRE, IP-IP). 1801 In such a scenario, NSIS would actually allow partly for customer 1802 managed VPNs, which means a customer can setup VPNs by subsequent 1803 NSIS signaling to various end-point. Plus the tunnel end-points are 1804 not necessarily bound to an application. The customer administrator 1805 might be the one triggering NSIS signaling. 1807 Tunnel end points at the provider premises 1809 In the case were the tunnel end-points exist on the provider edge, 1810 requests for bandwidth may be signaled either per flow, where a flow 1811 is defined from a customers address space, or between customer 1812 sites. 1814 In the case of per flow signaling, the PE router must map the 1815 bandwidth request to the tunnel carrying traffic to the destination 1816 specified in the flow spec. Such a tunnel is a member of an 1817 aggregate to which the flow must be admitted. In this case, the 1818 operation of admission control is very similar to the case of the 1819 PSTN GW with the additional level of indirection imposed by the VPN 1820 tunnel. Therefore, authentication, accounting and policing may be 1821 required on the PE router. 1823 In the case of per site signaling, a site would need to be 1824 identified. This may be accomplished by specifying the network 1825 serviced at that site through an IP prefix. In this case, the 1826 admission control function is performed on the aggregate to the PE 1827 router connected to the site in question. 1829 Full Copyright Statement 1831 Copyright (C) The Internet Society (2002). All Rights Reserved. 1833 This document and translations of it may be copied and furnished to 1834 others, and derivative works that comment on or otherwise explain it 1835 or assist in its implementation may be prepared, copied, published 1836 and distributed, in whole or in part, without restriction of any 1837 kind, provided that the above copyright notice and this paragraph are 1838 included on all such copies and derivative works. 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