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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 TEAS Working Group Italo Busi (Ed.) 2 Internet Draft Huawei 3 Intended status: Standard Track Sergio Belotti (Ed.) 4 Expires: May 2019 Nokia 5 Victor Lopez 6 Oscar Gonzalez de Dios 7 Telefonica 8 Anurag Sharma 9 Google 10 Yan Shi 11 China Unicom 12 Ricard Vilalta 13 CTTC 14 Karthik Sethuraman 15 NEC 17 November 4, 2018 19 Yang model for requesting Path Computation 20 draft-ietf-teas-yang-path-computation-04.txt 22 Status of this Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF), its areas, and its working groups. Note that 29 other groups may also distribute working documents as Internet- 30 Drafts. 32 Internet-Drafts are draft documents valid for a maximum of six 33 months and may be updated, replaced, or obsoleted by other documents 34 at any time. It is inappropriate to use Internet-Drafts as 35 reference material or to cite them other than as "work in progress." 37 The list of current Internet-Drafts can be accessed at 38 http://www.ietf.org/ietf/1id-abstracts.txt 40 The list of Internet-Draft Shadow Directories can be accessed at 41 http://www.ietf.org/shadow.html 42 This Internet-Draft will expire on May 4, 2019. 44 Copyright Notice 46 Copyright (c) 2018 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (http://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with 54 respect to this document. Code Components extracted from this 55 document must include Simplified BSD License text as described in 56 Section 4.e of the Trust Legal Provisions and are provided without 57 warranty as described in the Simplified BSD License. 59 Abstract 61 There are scenarios, typically in a hierarchical SDN context, where 62 the topology information provided by a TE network provider may not 63 be sufficient for its client to perform end-to-end path computation. 64 In these cases the client would need to request the provider to 65 calculate some (partial) feasible paths. 67 This document defines a YANG data model for a stateless RPC to 68 request path computation. This model complements the stateful 69 solution defined in [TE-TUNNEL]. 71 Moreover this document describes some use cases where a path 72 computation request, via YANG-based protocols (e.g., NETCONF or 73 RESTCONF), can be needed. 75 Table of Contents 77 1. Introduction...................................................3 78 1.1. Terminology...............................................4 79 2. Use Cases......................................................5 80 2.1. Packet/Optical Integration................................5 81 2.2. Multi-domain TE Networks.................................10 82 2.3. Data center interconnections.............................12 83 3. Motivations...................................................14 84 3.1. Motivation for a YANG Model..............................14 85 3.1.1. Benefits of common data models......................14 86 3.1.2. Benefits of a single interface......................15 87 3.1.3. Extensibility.......................................15 88 3.2. Interactions with TE Topology............................16 89 3.2.1. TE Topology Aggregation.............................17 90 3.2.2. TE Topology Abstraction.............................20 91 3.2.3. Complementary use of TE topology and path computation21 92 3.3. Stateless and Stateful Path Computation..................24 93 4. Path Computation and Optimization for multiple paths..........25 94 5. YANG Model for requesting Path Computation....................26 95 5.1. Synchronization of multiple path computation requests....27 96 5.2. Returned metric values...................................29 97 6. YANG model for stateless TE path computation..................30 98 6.1. YANG Tree................................................30 99 6.2. YANG Module..............................................39 100 7. Security Considerations.......................................49 101 8. IANA Considerations...........................................50 102 9. References....................................................50 103 9.1. Normative References.....................................50 104 9.1. Informative References...................................51 105 10. Acknowledgments..............................................52 106 Appendix A. Examples of dimensioning the "detailed connectivity 107 matrix" 53 109 1. Introduction 111 There are scenarios, typically in a hierarchical SDN context, where 112 the topology information provided by a TE network provider may not 113 be sufficient for its client to perform end-to-end path computation. 114 In these cases the client would need to request the provider to 115 calculate some (partial) feasible paths, complementing his topology 116 knowledge, to make his end-to-end path computation feasible. 118 This type of scenarios can be applied to different interfaces in 119 different reference architectures: 121 o ABNO control interface [RFC7491], in which an Application Service 122 Coordinator can request ABNO controller to take in charge path 123 calculation (see Figure 1 in [RFC7491]). 125 o ACTN [RFC8453], where a controller hierarchy is defined, the need 126 for path computation arises on both interfaces CMI (interface 127 between Customer Network Controller (CNC) and Multi Domain 128 Service Coordinator (MDSC)) and/or MPI (interface between MSDC- 129 PNC). [RFC8454] describes an information model for the Path 130 Computation request. 132 Multiple protocol solutions can be used for communication between 133 different controller hierarchical levels. This document assumes that 134 the controllers are communicating using YANG-based protocols (e.g., 135 NETCONF or RESTCONF). 137 Path Computation Elements, Controllers and Orchestrators perform 138 their operations based on Traffic Engineering Databases (TED). Such 139 TEDs can be described, in a technology agnostic way, with the YANG 140 Data Model for TE Topologies [TE-TOPO]. Furthermore, the technology 141 specific details of the TED are modeled in the augmented TE topology 142 models (e.g. [OTN-TOPO] for OTN ODU technologies). 144 The availability of such topology models allows providing the TED 145 using YANG-based protocols (e.g., NETCONF or RESTCONF). Furthermore, 146 it enables a PCE/Controller performing the necessary abstractions or 147 modifications and offering this customized topology to another 148 PCE/Controller or high level orchestrator. 150 Note: This document assumes that the client of the YANG data model 151 defined in this document may not implement a "PCE" functionality, as 152 defined in [RFC4655]. 154 The tunnels that can be provided over the networks described with 155 the topology models can be also set-up, deleted and modified via 156 YANG-based protocols (e.g., NETCONF or RESTCONF) using the TE-Tunnel 157 Yang model [TE-TUNNEL]. 159 This document proposes a YANG model for a path computation request 160 defined as a stateless RPC, which complements the stateful solution 161 defined in [TE-TUNNEL]. 163 Moreover, this document describes some use cases where a path 164 computation request, via YANG-based protocols (e.g., NETCONF or 165 RESTCONF), can be needed. 167 1.1. Terminology 169 TED: The traffic engineering database is a collection of all TE 170 information about all TE nodes and TE links in a given network. 172 PCE: A Path Computation Element (PCE) is an entity that is capable 173 of computing a network path or route based on a network graph, and 174 of applying computational constraints during the computation. The 175 PCE entity is an application that can be located within a network 176 node or component, on an out-of-network server, etc. For example, a 177 PCE would be able to compute the path of a TE LSP by operating on 178 the TED and considering bandwidth and other constraints applicable 179 to the TE LSP service request. [RFC4655] 181 2. Use Cases 183 This section presents different use cases, where a client needs to 184 request underlying SDN controllers for path computation. 186 The presented uses cases have been grouped, depending on the 187 different underlying topologies: a) Packet-Optical integration; b) 188 Multi-domain Traffic Engineered (TE) Networks; and c) Data center 189 interconnections. 191 2.1. Packet/Optical Integration 193 In this use case, an Optical network is used to provide connectivity 194 to some nodes of a Packet network (see Figure 1). 196 +----------------+ 197 | | 198 | Packet/Optical | 199 | Coordinator | 200 | | 201 +---+------+-----+ 202 | | 203 +------------+ | 204 | +-----------+ 205 +------V-----+ | 206 | | +------V-----+ 207 | Packet | | | 208 | Network | | Optical | 209 | Controller | | Network | 210 | | | Controller | 211 +------+-----+ +-------+----+ 212 | | 213 .........V......................... | 214 : Packet Network : | 215 +----+ +----+ | 216 | R1 |= = = = = = = = = = = = = = = =| R2 | | 217 +-+--+ +--+-+ | 218 | : : | | 219 | :................................ : | | 220 | | | 221 | +-----+ | | 222 | ...........| Opt |........... | | 223 | : | C | : | | 224 | : /+--+--+\ : | | 225 | : / | \ : | | 226 | : / | \ : | | 227 | +-----+ / +--+--+ \ +-----+ | | 228 | | Opt |/ | Opt | \| Opt | | | 229 +---| A | | D | | B |---+ | 230 +-----+\ +--+--+ /+-----+ | 231 : \ | / : | 232 : \ | / : | 233 : \ +--+--+ / Optical<---------+ 234 : \| Opt |/ Network: 235 :..........| E |..........: 236 +-----+ 238 Figure 1 - Packet/Optical Integration Use Case 240 Figure 1 as well as Figure 2 below only show a partial view of the 241 packet network connectivity, before additional packet connectivity 242 is provided by the Optical network. 244 It is assumed that the Optical network controller provides to the 245 packet/optical coordinator an abstracted view of the Optical 246 network. A possible abstraction could be to represent the whole 247 optical network as one "virtual node" with "virtual ports" connected 248 to the access links, as shown in Figure 2. 250 It is also assumed that Packet network controller can provide the 251 packet/optical coordinator the information it needs to setup 252 connectivity between packet nodes through the Optical network (e.g., 253 the access links). 255 The path computation request helps the coordinator to know the real 256 connections that can be provided by the optical network. 258 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,. 259 , Packet/Optical Coordinator view , 260 , +----+ , . 261 , | | , 262 , | R2 | , . 263 , +----+ +------------ + /+----+ , 264 , | | | |/-----/ / / , . 265 , | R1 |--O VP1 VP4 O / / , 266 , | |\ | | /----/ / , . 267 , +----+ \| |/ / , 268 , / O VP2 VP5 O / , . 269 , / | | +----+ , 270 , / | | | | , . 271 , / O VP3 VP6 O--| R4 | , 272 , +----+ /-----/|_____________| +----+ , . 273 , | |/ +------------ + , 274 , | R3 | , . 275 , +----+ ,,,,,,,,,,,,,,,,, 276 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, ,. 277 . Packet Network Controller view +----+ , 278 only packet nodes and packet links | | , . 279 . with access links to the optical network | R2 | , 280 , +----+ /+----+ , . 281 . , | | /-----/ / / , 282 , | R1 |--- / / , . 283 . , +----+\ /----/ / , 284 , / \ / / , . 285 . , / / , 286 , / +----+ , . 287 . , / | | , 288 , / ---| R4 | , . 289 . , +----+ /-----/ +----+ , 290 , | |/ , . 291 . , | R3 | , 292 , +----+ ,,,,,,,,,,,,,,,,,. 293 .,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, , 294 Optical Network Controller view , . 295 . only optical nodes, +--+ , 296 optical links and /|OF| , . 297 . access links from the +--++--+ / , 298 packet network |OA| \ /-----/ / , . 299 . , ---+--+--\ +--+/ / , 300 , \ | \ \-|OE|-------/ , . 301 . , \ | \ /-+--+ , 302 , \+--+ X | , . 304 . , |OB|-/ \ | , 305 , +--+-\ \+--+ , . 306 . , / \ \--|OD|--- , 307 , /-----/ +--+ +--+ , . 308 . , / |OC|/ , 309 , +--+ , . 310 ., ,,,,,,,,,,,,,,,,,, 311 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, , 312 . Actual Physical View +----+ , 313 , +--+ | | , 314 . , /|OF| | R2 | , 315 , +----+ +--++--+ /+----+ , 316 . , | | |OA| \ /-----/ / / , 317 , | R1 |---+--+--\ +--+/ / / , 318 . , +----+\ | \ \-|OE|-------/ / , 319 , / \ | \ /-+--+ / , 320 . , / \+--+ X | / , 321 , / |OB|-/ \ | +----+ , 322 . , / +--+-\ \+--+ | | , 323 , / / \ \--|OD|---| R4 | , 324 . , +----+ /-----/ +--+ +--+ +----+ , 325 , | |/ |OC|/ , 326 . , | R3 | +--+ , 327 , +----+ , 328 .,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 330 Figure 2 - Packet and Optical Topology Abstractions 332 In this use case, the coordinator needs to setup an optimal 333 underlying path for an IP link between R1 and R2. 335 As depicted in Figure 2, the coordinator has only an "abstracted 336 view" of the physical network, and it does not know the feasibility 337 or the cost of the possible optical paths (e.g., VP1-VP4 and VP2- 338 VP5), which depend from the current status of the physical resources 339 within the optical network and on vendor-specific optical 340 attributes. 342 The coordinator can request the underlying Optical domain controller 343 to compute a set of potential optimal paths, taking into account 344 optical constraints. Then, based on its own constraints, policy and 345 knowledge (e.g. cost of the access links), it can choose which one 346 of these potential paths to use to setup the optimal end-to-end path 347 crossing optical network. 349 ............................ 350 : : 351 O VP1 VP4 O 352 cost=10 /:\ /:\ cost=10 353 / : \----------------------/ : \ 354 +----+ / : cost=50 : \ +----+ 355 | |/ : : \| | 356 | R1 | : : | R2 | 357 | |\ : : /| | 358 +----+ \ : /--------------------\ : / +----+ 359 \ : / cost=55 \ : / 360 cost=5 \:/ \:/ cost=5 361 O VP2 VP5 O 362 : : 363 :..........................: 365 Figure 3 - Packet/Optical Path Computation Example 367 For example, in Figure 3, the Coordinator can request the Optical 368 network controller to compute the paths between VP1-VP4 and VP2-VP5 369 and then decide to setup the optimal end-to-end path using the VP2- 370 VP5 Optical path even this is not the optimal path from the Optical 371 domain perspective. 373 Considering the dynamicity of the connectivity constraints of an 374 Optical domain, it is possible that a path computed by the Optical 375 network controller when requested by the Coordinator is no longer 376 valid/available when the Coordinator requests it to be setup up. 377 This is further discussed in section 3.3. 379 2.2. Multi-domain TE Networks 381 In this use case there are two TE domains which are interconnected 382 together by multiple inter-domains links. 384 A possible example could be a multi-domain optical network. 386 +--------------+ 387 | Multi-domain | 388 | Controller | 389 +---+------+---+ 390 | | 391 +------------+ | 392 | +-----------+ 393 +------V-----+ | 394 | | | 395 | TE Domain | +------V-----+ 396 | Controller | | | 397 | 1 | | TE Domain | 398 +------+-----+ | Controller | 399 | | 2 | 400 | +------+-----+ 401 .........V.......... | 402 : : | 403 +-----+ : | 404 | | : .........V.......... 405 | X | : : : 406 | | +-----+ +-----+ : 407 +-----+ | | | | : 408 : | C |------| E | : 409 +-----+ +-----+ /| | | |\ +-----+ +-----+ 410 | | | |/ +-----+ +-----+ \| | | | 411 | A |----| B | : : | G |----| H | 412 | | | |\ : : /| | | | 413 +-----+ +-----+ \+-----+ +-----+/ +-----+ +-----+ 414 : | | | | : 415 : | D |------| F | : 416 : | | | | +-----+ 417 : +-----+ +-----+ | | 418 : : : | Y | 419 : : : | | 420 : Domain 1 : : Domain 2 +-----+ 421 :..................: :.................: 423 Figure 4 - Multi-domain multi-link interconnection 425 In order to setup an end-to-end multi-domain TE path (e.g., between 426 nodes A and H), the multi-domain controller needs to know the 427 feasibility or the cost of the possible TE paths within the two TE 428 domains, which depend from the current status of the physical 429 resources within each TE network. This is more challenging in case 430 of optical networks because the optimal paths depend also on vendor- 431 specific optical attributes (which may be different in the two 432 domains if they are provided by different vendors). 434 In order to setup a multi-domain TE path (e.g., between nodes A and 435 H), the multi-domain controller can request the TE domain 436 controllers to compute a set of intra-domain optimal paths and take 437 decisions based on the information received. For example: 439 o The multi-domain controller asks TE domain controllers to provide 440 set of paths between A-C, A-D, E-H and F-H 442 o TE domain controllers return a set of feasible paths with the 443 associated costs: the path A-C is not part of this set(in optical 444 networks, it is typical to have some paths not being feasible due 445 to optical constraints that are known only by the optical domain 446 controller) 448 o The multi-domain controller will select the path A-D-F-H since it 449 is the only feasible multi-domain path and then request the TE 450 domain controllers to setup the A-D and F-H intra-domain paths 452 o If there are multiple feasible paths, the multi-domain controller 453 can select the optimal path knowing the cost of the intra-domain 454 paths (provided by the TE domain controllers) and the cost of the 455 inter-domain links (known by the multi-domain controller) 457 This approach may have some scalability issues when the number of TE 458 domains is quite big (e.g. 20). 460 In this case, it would be worthwhile using the abstract TE topology 461 information provided by the TE domain controllers to limit the 462 number of potential optimal end-to-end paths and then request path 463 computation to fewer TE domain controllers in order to decide what 464 the optimal path within this limited set is. 466 For more details, see section 3.2.3. 468 2.3. Data center interconnections 470 In these use case, there is a TE domain which is used to provide 471 connectivity between data centers which are connected with the TE 472 domain using access links. 474 +--------------+ 475 | Cloud Network| 476 | Orchestrator | 477 +--------------+ 478 | | | | 479 +-------------+ | | +------------------------+ 480 | | +------------------+ | 481 | +--------V---+ | | 482 | | | | | 483 | | TE Network | | | 484 +------V-----+ | Controller | +------V-----+ | 485 | DC | +------------+ | DC | | 486 | Controller | | | Controller | | 487 +------------+ | +-----+ +------------+ | 488 | ....V...| |........ | | 489 | : | P | : | | 490 .....V..... : /+-----+\ : .....V..... | 491 : : +-----+ / | \ +-----+ : : | 492 : DC1 || : | |/ | \| | : DC2 || : | 493 : ||||----| PE1 | | | PE2 |---- |||| : | 494 : _|||||| : | |\ | /| | : _|||||| : | 495 : : +-----+ \ +-----+ / +-----+ : : | 496 :.........: : \| |/ : :.........: | 497 :.......| PE3 |.......: | 498 | | | 499 +-----+ +---------V--+ 500 .....|..... | DC | 501 : : | Controller | 502 : DC3 || : +------------+ 503 : |||| : | 504 : _|||||| <------------------+ 505 : : 506 :.........: 508 Figure 5 - Data Center Interconnection Use Case 510 In this use case, there is need to transfer data from Data Center 1 511 (DC1) to either DC2 or DC3 (e.g. workload migration). 513 The optimal decision depends both on the cost of the TE path (DC1- 514 DC2 or DC1-DC3) and of the data center resources within DC2 or DC3. 516 The cloud network orchestrator needs to make a decision for optimal 517 connection based on TE Network constraints and data centers 518 resources. It may not be able to make this decision because it has 519 only an abstract view of the TE network (as in use case in 2.1). 521 The cloud network orchestrator can request to the TE network 522 controller to compute the cost of the possible TE paths (e.g., DC1- 523 DC2 and DC1-DC3) and to the DC controller to provide the information 524 it needs about the required data center resources within DC2 and DC3 525 and then it can take the decision about the optimal solution based 526 on this information and its policy. 528 3. Motivations 530 This section provides the motivation for the YANG model defined in 531 this document. 533 Section 3.1 describes the motivation for a YANG model to request 534 path computation. 536 Section 3.2 describes the motivation for a YANG model which 537 complements the TE Topology YANG model defined in [TE-TOPO]. 539 Section 3.3 describes the motivation for a stateless YANG RPC which 540 complements the TE Tunnel YANG model defined in [TE-TUNNEL]. 542 3.1. Motivation for a YANG Model 544 3.1.1. Benefits of common data models 546 The YANG data model for requesting path computation is closely 547 aligned with the YANG data models that provide (abstract) TE 548 topology information, i.e., [TE-TOPO] as well as that are used to 549 configure and manage TE Tunnels, i.e., [TE-TUNNEL]. 551 There are many benefits in aligning the data model used for path 552 computation requests with the YANG data models used for TE topology 553 information and for TE Tunnels configuration and management: 555 o There is no need for an error-prone mapping or correlation of 556 information. 558 o It is possible to use the same endpoint identifiers in path 559 computation requests and in the topology modeling. 561 o The attributes used for path computation constraints are the same 562 as those used when setting up a TE Tunnel. 564 3.1.2. Benefits of a single interface 566 The system integration effort is typically lower if a single, 567 consistent interface is used by controllers, i.e., one data modeling 568 language (i.e., YANG) and a common protocol (e.g., NETCONF or 569 RESTCONF). 571 Practical benefits of using a single, consistent interface include: 573 1. Simple authentication and authorization: The interface between 574 different components has to be secured. If different protocols 575 have different security mechanisms, ensuring a common access 576 control model may result in overhead. For instance, there may be 577 a need to deal with different security mechanisms, e.g., 578 different credentials or keys. This can result in increased 579 integration effort. 581 2. Consistency: Keeping data consistent over multiple different 582 interfaces or protocols is not trivial. For instance, the 583 sequence of actions can matter in certain use cases, or 584 transaction semantics could be desired. While ensuring 585 consistency within one protocol can already be challenging, it is 586 typically cumbersome to achieve that across different protocols. 588 3. Testing: System integration requires comprehensive testing, 589 including corner cases. The more different technologies are 590 involved, the more difficult it is to run comprehensive test 591 cases and ensure proper integration. 593 4. Middle-box friendliness: Provider and consumer of path 594 computation requests may be located in different networks, and 595 middle-boxes such as firewalls, NATs, or load balancers may be 596 deployed. In such environments it is simpler to deploy a single 597 protocol. Also, it may be easier to debug connectivity problems. 599 5. Tooling reuse: Implementers may want to implement path 600 computation requests with tools and libraries that already exist 601 in controllers and/or orchestrators, e.g., leveraging the rapidly 602 growing eco-system for YANG tooling. 604 3.1.3. Extensibility 606 Path computation is only a subset of the typical functionality of a 607 controller. In many use cases, issuing path computation requests 608 comes along with the need to access other functionality on the same 609 system. In addition to obtaining TE topology, for instance also 610 configuration of services (setup/modification/deletion) may be 611 required, as well as: 613 1. Receiving notifications for topology changes as well as 614 integration with fault management 616 2. Performance management such as retrieving monitoring and 617 telemetry data 619 3. Service assurance, e.g., by triggering OAM functionality 621 4. Other fulfilment and provisioning actions beyond tunnels and 622 services, such as changing QoS configurations 624 YANG is a very extensible and flexible data modeling language that 625 can be used for all these use cases. 627 3.2. Interactions with TE Topology 629 The use cases described in section 2 have been described assuming 630 that the topology view exported by each underlying SDN controller to 631 the orchestrator is aggregated using the "virtual node model", 632 defined in [RFC7926]. 634 TE Topology information, e.g., as provided by [TE-TOPO], could in 635 theory be used by an underlying SDN controllers to provide TE 636 information to its client thus allowing a PCE available within its 637 client to perform multi-domain path computation by its own, without 638 requesting path computations to the underlying SDN controllers. 640 In case the client does not implement a PCE function, as discussed 641 in section 1, it could not perform path computation based on TE 642 Topology information and would instead need to request path 643 computation to the underlying controllers to get the information it 644 needs to compute the optimal end-to-end path. 646 This section analyzes the need for a client to request underlying 647 SDN controllers for path computation even in case it implements a 648 PCE functionality, as well as how the TE Topology information and 649 the path computation can be complementary. 651 In nutshell, there is a scalability trade-off between providing all 652 the TE information needed by PCE, when implemented by the client, to 653 take optimal path computation decisions by its own versus sending 654 too many requests to underlying SDN Domain Controllers to compute a 655 set of feasible optimal intra-domain TE paths. 657 3.2.1. TE Topology Aggregation 659 Using the TE Topology model, as defined in [TE-TOPO], the underlying 660 SDN controller can export the whole TE domain as a single abstract 661 TE node with a "detailed connectivity matrix". 663 The concept of a "detailed connectivity matrix" is defined in [TE- 664 TOPO] to provide specific TE attributes (e.g., delay, SRLGs and 665 summary TE metrics) as an extension of the "basic connectivity 666 matrix", which is based on the "connectivity matrix" defined in 667 [RFC7446]. 669 The information provided by the "detailed connectivity matrix" would 670 be equivalent to the information that should be provided by "virtual 671 link model" as defined in [RFC7926]. 673 For example, in the Packet/Optical integration use case, described 674 in section 2.1, the Optical network controller can make the 675 information shown in Figure 3 available to the Coordinator as part 676 of the TE Topology information and the Coordinator could use this 677 information to calculate by its own the optimal path between R1 and 678 R2, without requesting any additional information to the Optical 679 network Controller. 681 However, when designing the amount of information to provide within 682 the "detailed connectivity matrix", there is a tradeoff to be 683 considered between accuracy (i.e., providing "all" the information 684 that might be needed by the PCE available to Orchestrator) and 685 scalability. 687 Figure 6 below shows another example, similar to Figure 3, where 688 there are two possible Optical paths between VP1 and VP4 with 689 different properties (e.g., available bandwidth and cost). 691 ............................ 692 : /--------------------\ : 693 : / cost=65 \ : 694 :/ available-bw=10G \: 695 O VP1 VP4 O 696 cost=10 /:\ /:\ cost=10 697 / : \----------------------/ : \ 698 +----+ / : cost=50 : \ +----+ 699 | |/ : available-bw=2G : \| | 700 | R1 | : : | R2 | 701 | |\ : : /| | 702 +----+ \ : /--------------------\ : / +----+ 703 \ : / cost=55 \ : / 704 cost=5 \:/ available-bw=3G \:/ cost=5 705 O VP2 VP5 O 706 : : 707 :..........................: 709 Figure 6 - Packet/Optical Path Computation Example with multiple 710 choices 712 Reporting all the information, as in Figure 6, using the "detailed 713 connectivity matrix", is quite challenging from a scalability 714 perspective. The amount of this information is not just based on 715 number of end points (which would scale as N-square), but also on 716 many other parameters, including client rate, user 717 constraints/policies for the service, e.g. max latency < N ms, max 718 cost, etc., exclusion policies to route around busy links, min OSNR 719 margin, max preFEC BER etc. All these constraints could be different 720 based on connectivity requirements. 722 Examples of how the "detailed connectivity matrix" can be 723 dimensioned are described in Appendix A. 725 It is also worth noting that the "connectivity matrix" has been 726 originally defined in WSON, [RFC7446], to report the connectivity 727 constrains of a physical node within the WDM network: the 728 information it contains is pretty "static" and therefore, once taken 729 and stored in the TE data base, it can be always being considered 730 valid and up-to-date in path computation request. 732 Using the "basic connectivity matrix" with an abstract node to 733 abstract the information regarding the connectivity constraints of 734 an Optical domain, would make this information more "dynamic" since 735 the connectivity constraints of an Optical domain can change over 736 time because some optical paths that are feasible at a given time 737 may become unfeasible at a later time when e.g., another optical 738 path is established. The information in the "detailed connectivity 739 matrix" is even more dynamic since the establishment of another 740 optical path may change some of the parameters (e.g., delay or 741 available bandwidth) in the "detailed connectivity matrix" while not 742 changing the feasibility of the path. 744 The "connectivity matrix" is sometimes confused with optical reach 745 table that contain multiple (e.g. k-shortest) regen-free reachable 746 paths for every A-Z node combination in the network. Optical reach 747 tables can be calculated offline, utilizing vendor optical design 748 and planning tools, and periodically uploaded to the Controller: 749 these optical path reach tables are fairly static. However, to get 750 the connectivity matrix, between any two sites, either a regen free 751 path can be used, if one is available, or multiple regen free paths 752 are concatenated to get from src to dest, which can be a very large 753 combination. Additionally, when the optical path within optical 754 domain needs to be computed, it can result in different paths based 755 on input objective, constraints, and network conditions. In summary, 756 even though "optical reachability table" is fairly static, which 757 regen free paths to build the connectivity matrix between any source 758 and destination is very dynamic, and is done using very 759 sophisticated routing algorithms. 761 There is therefore the need to keep the information in the "detailed 762 connectivity matrix" updated which means that there another tradeoff 763 between the accuracy (i.e., providing "all" the information that 764 might be needed by the client's PCE) and having up-to-date 765 information. The more the information is provided and the longer it 766 takes to keep it up-to-date which increases the likelihood that the 767 client's PCE computes paths using not updated information. 769 It seems therefore quite challenging to have a "detailed 770 connectivity matrix" that provides accurate, scalable and updated 771 information to allow the client's PCE to take optimal decisions by 772 its own. 774 Instead, if the information in the "detailed connectivity matrix" is 775 not complete/accurate, we can have the following drawbacks 776 considering for example the case in Figure 6: 778 o If only the VP1-VP4 path with available bandwidth of 2 Gb/s and 779 cost 50 is reported, the client's PCE will fail to compute a 5 780 Gb/s path between routers R1 and R2, although this would be 781 feasible; 783 o If only the VP1-VP4 path with available bandwidth of 10 Gb/s and 784 cost 60 is reported, the client's PCE will compute, as optimal, 785 the 1 Gb/s path between R1 and R2 going through the VP2-VP5 path 786 within the Optical domain while the optimal path would actually 787 be the one going thought the VP1-VP4 sub-path (with cost 50) 788 within the Optical domain. 790 Using the approach proposed in this document, the client, when it 791 needs to setup an end-to-end path, it can request the Optical domain 792 controller to compute a set of optimal paths (e.g., for VP1-VP4 and 793 VP2-VP5) and take decisions based on the information received: 795 o When setting up a 5 Gb/s path between routers R1 and R2, the 796 Optical domain controller may report only the VP1-VP4 path as the 797 only feasible path: the Orchestrator can successfully setup the 798 end-to-end path passing though this Optical path; 800 o When setting up a 1 Gb/s path between routers R1 and R2, the 801 Optical domain controller (knowing that the path requires only 1 802 Gb/s) can report both the VP1-VP4 path, with cost 50, and the 803 VP2-VP5 path, with cost 65. The Orchestrator can then compute the 804 optimal path which is passing thought the VP1-VP4 sub-path (with 805 cost 50) within the Optical domain. 807 3.2.2. TE Topology Abstraction 809 Using the TE Topology model, as defined in [TE-TOPO], the underlying 810 SDN controller can export an abstract TE Topology, composed by a set 811 of TE nodes and TE links, representing the abstract view of the 812 topology controlled by each domain controller. 814 Considering the example in Figure 4, the TE domain controller 1 can 815 export a TE Topology encompassing the TE nodes A, B, C and D and the 816 TE Link interconnecting them. In a similar way, TE domain controller 817 2 can export a TE Topology encompassing the TE nodes E, F, G and H 818 and the TE Link interconnecting them. 820 In this example, for simplicity reasons, each abstract TE node maps 821 with each physical node, but this is not necessary. 823 In order to setup a multi-domain TE path (e.g., between nodes A and 824 H), the multi-domain controller can compute by its own an optimal 825 end-to-end path based on the abstract TE topology information 826 provided by the domain controllers. For example: 828 o Multi-domain controller's PCE, based on its own information, can 829 compute the optimal multi-domain path being A-B-C-E-G-H, and then 830 request the TE domain controllers to setup the A-B-C and E-G-H 831 intra-domain paths 833 o But, during path setup, the domain controller may find out that 834 A-B-C intra-domain path is not feasible (as discussed in section 835 2.2, in optical networks it is typical to have some paths not 836 being feasible due to optical constraints that are known only by 837 the optical domain controller), while only the path A-B-D is 838 feasible 840 o So what the multi-domain controller computed is not good and need 841 to re-start the path computation from scratch 843 As discussed in section 3.2.1, providing more extensive abstract 844 information from the TE domain controllers to the multi-domain 845 controller may lead to scalability problems. 847 In a sense this is similar to the problem of routing and wavelength 848 assignment within an Optical domain. It is possible to do first 849 routing (step 1) and then wavelength assignment (step 2), but the 850 chances of ending up with a good path is low. Alternatively, it is 851 possible to do combined routing and wavelength assignment, which is 852 known to be a more optimal and effective way for Optical path setup. 853 Similarly, it is possible to first compute an abstract end-to-end 854 path within the multi-domain Orchestrator (step 1) and then compute 855 an intra-domain path within each Optical domain (step 2), but there 856 are more chances not to find a path or to get a suboptimal path that 857 performing per-domain path computation and then stitch them. 859 3.2.3. Complementary use of TE topology and path computation 861 As discussed in section 2.2, there are some scalability issues with 862 path computation requests in a multi-domain TE network with many TE 863 domains, in terms of the number of requests to send to the TE domain 864 controllers. It would therefore be worthwhile using the TE topology 865 information provided by the domain controllers to limit the number 866 of requests. 868 An example can be described considering the multi-domain abstract 869 topology shown in Figure 7. In this example, an end-to-end TE path 870 between domains A and F needs to be setup. The transit domain should 871 be selected between domains B, C, D and E. 873 .........B......... 874 : _ _ _ _ _ _ _ _ : 875 :/ \: 876 +---O NOT FEASIBLE O---+ 877 cost=5| : : | 878 ......A...... | :.................: | ......F...... 879 : : | | : : 880 : O-----+ .........C......... +-----O : 881 : : : /-------------\ : : : 882 : : :/ \: : : 883 : cost<=20 O---------O cost <= 30 O---------O cost<=20 : 884 : /: cost=5 : : cost=5 :\ : 885 : /------/ : :.................: : \------\ : 886 : / : : \ : 887 :/ cost<=25 : .........D......... : cost<=25 \: 888 O-----------O-------+ : /-------------\ : +-------O-----------O 889 :\ : cost=5| :/ \: |cost=5 : /: 890 : \ : +-O cost <= 30 O-+ : / : 891 : \------\ : : : : /------/ : 892 : cost>=30 \: :.................: :/ cost>=30 : 893 : O-----+ +-----O : 894 :...........: | .........E......... | :...........: 895 | : /-------------\ : | 896 cost=5| :/ \: |cost=5 897 +---O cost >= 30 O---+ 898 : : 899 :.................: 901 Figure 7 - Multi-domain with many domains (Topology information) 903 The actual cost of each intra-domain path is not known a priori from 904 the abstract topology information. The Multi-domain controller only 905 knows, from the TE topology provided by the underlying domain 906 controllers, the feasibility of some intra-domain paths and some 907 upper-bound and/or lower-bound cost information. With this 908 information, together with the cost of inter-domain links, the 909 Multi-domain controller can understand by its own that: 911 o Domain B cannot be selected as the path connecting domains A and 912 E is not feasible; 914 o Domain E cannot be selected as a transit domain since it is know 915 from the abstract topology information provided by domain 916 controllers that the cost of the multi-domain path A-E-F (which 917 is 100, in the best case) will be always be higher than the cost 918 of the multi-domain paths A-D-F (which is 90, in the worst case) 919 and A-E-F (which is 80, in the worst case) 921 Therefore, the Multi-domain controller can understand by its own 922 that the optimal multi-domain path could be either A-D-F or A-E-F 923 but it cannot known which one of the two possible option actually 924 provides the optimal end-to-end path. 926 The Multi-domain controller can therefore request path computation 927 only to the TE domain controllers A, D, E and F (and not to all the 928 possible TE domain controllers). 930 .........B......... 931 : : 932 +---O O---+ 933 ......A...... | :.................: | ......F...... 934 : : | | : : 935 : O-----+ .........C......... +-----O : 936 : : : /-------------\ : : : 937 : : :/ \: : : 938 : cost=15 O---------O cost = 25 O---------O cost=10 : 939 : /: cost=5 : : cost=5 :\ : 940 : /------/ : :.................: : \------\ : 941 : / : : \ : 942 :/ cost=10 : .........D......... : cost=15 \: 943 O-----------O-------+ : /-------------\ : +-------O-----------O 944 : : cost=5| :/ \: |cost=5 : : 945 : : +-O cost = 15 O-+ : : 946 : : : : : : 947 : : :.................: : : 948 : O-----+ +-----O : 949 :...........: | .........E......... | :...........: 950 | : : | 951 +---O O---+ 952 :.................: 954 Figure 8 - Multi-domain with many domains (Path Computation 955 information) 957 Based on these requests, the Multi-domain controller can know the 958 actual cost of each intra-domain paths which belongs to potential 959 optimal end-to-end paths, as shown in Figure 8, and then compute the 960 optimal end-to-end path (e.g., A-D-F, having total cost of 50, 961 instead of A-C-F having a total cost of 70). 963 3.3. Stateless and Stateful Path Computation 965 The TE Tunnel YANG model, defined in [TE-TUNNEL], can support the 966 need to request path computation. 968 It is possible to request path computation by configuring a 969 "compute-only" TE tunnel and retrieving the computed path(s) in the 970 LSP(s) Record-Route Object (RRO) list as described in section 3.3.1 971 of [TE-TUNNEL]. 973 This is a stateful solution since the state of each created 974 "compute-only" TE tunnel needs to be maintained and updated, when 975 underlying network conditions change. 977 It is very useful to provide options for both stateless and stateful 978 path computation mechanisms. It is suggested to use stateless 979 mechanisms as much as possible and to rely on stateful path 980 computation when really needed. 982 Stateless RPC allows requesting path computation using a simple 983 atomic operation and it is the natural option/choice, especially 984 with stateless PCE. 986 Since the operation is stateless, there is no guarantee that the 987 returned path would still be available when path setup is requested: 988 this does not cause major issues in case the time between path 989 computation and path setup is short (especially if compared with the 990 time that would be needed to update the information of a very 991 detailed connectivity matrix). 993 In most of the cases, there is even no need to guarantee that the 994 path that has been setup is the exactly same as the path that has 995 been returned by path computation, especially if has the same or 996 even better metrics. Depending on the abstraction level applied by 997 the server, the client may also not know the actual computed path. 999 The most important requirement is that the required global 1000 objectives (e.g., multi-domain path metrics and constraints) are 1001 met. For this reason a path verification phase is necessary to 1002 verify that the actual path that has been setup meets the global 1003 objectives (for example in a multi-domain network, the resulting 1004 end-to-end path meets the required end-to-end metrics and 1005 constraints). 1007 In most of the cases, even if the setup path is not exactly the same 1008 as the path returned by path computation, its metrics and 1009 constraints are "good enough" (the path verification passes 1010 successfully). In the few corner cases where the path verification 1011 fails, it is possible repeat the whole process (path computation, 1012 path setup and path verification). 1014 In case the stateless solution is not sufficient, a stateful 1015 solution, based on "compute-only" TE tunnel, could be used to get 1016 notifications in case the computed path has been changed. 1018 It is worth noting that also the stateful solution, although 1019 increasing the likelihood that the computed path is available at 1020 path setup, does not guaranteed that because notifications may not 1021 be reliable or delivered on time. Path verification is needed also 1022 when stateful path computation is used. 1024 The stateful path computation has also the following drawbacks: 1026 o Several messages required for any path computation 1028 o Requires persistent storage in the provider controller 1030 o Need for garbage collection for stranded paths 1032 o Process burden to detect changes on the computed paths in order 1033 to provide notifications update 1035 4. Path Computation and Optimization for multiple paths 1037 There are use cases, where it is advantageous to request path 1038 computation for a set of paths, through a network or through a 1039 network domain, using a single request [RFC5440]. 1041 In this case, sending a single request for multiple path 1042 computations, instead of sending multiple requests for each path 1043 computation, would reduce the protocol overhead and it would consume 1044 less resources (e.g., threads in the client and server). 1046 In the context of a typical multi-domain TE network, there could 1047 multiple choices for the ingress/egress points of a domain and the 1048 Multi-domain controller needs to request path computation between 1049 all the ingress/egress pairs to select the best pair. For example, 1050 in the example of section 2.2, the Multi-domain controller needs to 1051 request the TE network controller 1 to compute the A-C and the A-D 1052 paths and to the TE network controller 2 to compute the E-H and the 1053 F-H paths. 1055 It is also possible that the Multi-domain controller receives a 1056 request to setup a group of multiple end to end connections. The 1057 multi-domain controller needs to request each TE domain controller 1058 to compute multiple paths, one (or more) for each end to end 1059 connection. 1061 There are also scenarios where it can be needed to request path 1062 computation for a set of paths in a synchronized fashion. 1064 One example could be computing multiple diverse paths. Computing a 1065 set of diverse paths in a not-synchronized fashion, leads to the 1066 possibility of not being able to satisfy the diversity requirement. 1067 In this case, it is preferable to compute a sub-optimal primary path 1068 for which a diversely routed secondary path exists. 1070 There are also scenarios where it is needed to request optimizing a 1071 set of paths using objective functions that apply to the whole set 1072 of paths, see [RFC5541], e.g. to minimize the sum of the costs of 1073 all the computed paths in the set. 1075 5. YANG Model for requesting Path Computation 1077 This document define a YANG stateless RPC to request path 1078 computation as an "augmentation" of tunnel-rpc, defined in [TE- 1079 TUNNEL]. This model provides the RPC input attributes that are 1080 needed to request path computation and the RPC output attributes 1081 that are needed to report the computed paths. 1083 augment /te:tunnels-rpc/te:input/te:tunnel-info: 1084 +---- path-request* [request-id] 1085 ........... 1087 augment /te:tunnels-rpc/te:output/te:result: 1088 +--ro response* [response-id] 1089 +--ro response-id uint32 1090 +--ro (response-type)? 1091 +--:(no-path-case) 1092 | +--ro no-path! 1093 +--:(path-case) 1094 +--ro computed-path 1095 ........... 1097 This model extensively re-uses the grouping defined in [TE-TUNNEL] 1098 to ensure maximal syntax and semantics commonality. 1100 5.1. Synchronization of multiple path computation requests 1102 The YANG model permits to synchronize a set of multiple path 1103 requests (identified by specific request-id) all related to a "svec" 1104 container emulating the syntax of "SVEC" PCEP object [RFC5440]. 1106 +---- synchronization* [synchronization-id] 1107 +---- synchronization-id uint32 1108 +---- svec 1109 | +---- relaxable? boolean 1110 | +---- disjointness? te-types:te-path-disjointness 1111 | +---- request-id-number* uint32 1112 +---- svec-constraints 1113 | +---- path-metric-bound* [metric-type] 1114 | +---- metric-type identityref 1115 | +---- upper-bound? uint64 1116 +---- path-srlgs-values 1117 | +---- usage? identityref 1118 | +---- values* srlg 1119 +---- path-srlgs-names 1120 | +---- path-srlgs-name* [usage] 1121 | +---- usage identityref 1122 | +---- srlg-name* [name] 1123 | +---- name string 1124 +---- exclude-objects 1125 ........... 1126 +---- optimizations 1127 +---- (algorithm)? 1128 +--:(metric) 1129 | +---- optimization-metric* [metric-type] 1130 | +---- metric-type identityref 1131 | +---- weight? uint8 1132 +--:(objective-function) 1133 +---- objective-function 1134 +---- objective-function-type? identityref 1136 The model, in addition to the metric types, defined in [TE-TUNNEL], 1137 which can be applied to each individual path request, defines 1138 additional specific metrics types that apply to a set of 1139 synchronized requests, as referenced in [RFC5541]. 1141 identity svec-metric-type { 1142 description 1143 "Base identity for svec metric type"; 1144 } 1146 identity svec-metric-cumul-te { 1147 base svec-metric-type; 1148 description 1149 "TE cumulative path metric"; 1150 } 1152 identity svec-metric-cumul-igp { 1153 base svec-metric-type; 1154 description 1155 "IGP cumulative path metric"; 1156 } 1158 identity svec-metric-cumul-hop { 1159 base svec-metric-type; 1160 description 1161 "Hop cumulative path metric"; 1162 } 1164 identity svec-metric-aggregate-bandwidth-consumption { 1165 base svec-metric-type; 1166 description 1167 "Cumulative bandwith consumption of the set of 1168 synchronized paths"; 1169 } 1171 identity svec-metric-load-of-the-most-loaded-link { 1172 base svec-metric-type; 1173 description 1174 "Load of the most loaded link"; 1175 } 1177 5.2. Returned metric values 1179 This YANG model provides a way to return the values of the metrics 1180 computed by the path computation in the output of RPC, together with 1181 other important information (e.g. srlg, affinities, explicit route), 1182 emulating the syntax of the "C" flag of the "METRIC" PCEP object 1183 [RFC5440]: 1185 augment /te:tunnels-rpc/te:output/te:result: 1186 +--ro response* [response-id] 1187 +--ro response-id uint32 1188 +--ro (response-type)? 1189 +--:(no-path-case) 1190 | +--ro no-path! 1191 +--:(path-case) 1192 +--ro computed-path 1193 +--ro path-id? yang-types:uuid 1194 +--ro path-properties 1195 +--ro path-metric* [metric-type] 1196 | +--ro metric-type identityref 1197 | +--ro accumulative-value? uint64 1198 +--ro path-affinities-values 1199 | +--ro path-affinities-value* [usage] 1200 | +--ro usage identityref 1201 | +--ro value? admin-groups 1202 +--ro path-affinity-names 1203 | +--ro path-affinity-name* [usage] 1204 | +--ro usage identityref 1205 | +--ro affinity-name* [name] 1206 | +--ro name string 1207 +--ro path-srlgs-values 1208 | +--ro usage? identityref 1209 | +--ro values* srlg 1210 +--ro path-srlgs-names 1211 | +--ro path-srlgs-name* [usage] 1212 | +--ro usage identityref 1213 | +--ro srlg-name* [name] 1214 | +--ro name string 1215 +--ro path-route-objects 1216 ........... 1218 It also allows to request in the input of RPC which information 1219 (metrics, srlg and/or affinities) should be returned: 1221 module: ietf-te-path-computation 1222 augment /te:tunnels-rpc/te:input/te:tunnel-info: 1223 +---- path-request* [request-id] 1224 | +---- request-id uint32 1225 ........... 1226 | +---- requested-metrics* [metric-type] 1227 | | +---- metric-type identityref 1228 | +---- return-srlgs? boolean 1229 | +---- return-affinities? boolean 1230 ........... 1232 This feature is essential for using a stateless path computation in 1233 a multi-domain TE network as described in section 2.2. In this case, 1234 the metrics returned by a path computation requested to a given TE 1235 network controller must be used by the client to compute the best 1236 end-to-end path. If they are missing the client cannot compare 1237 different paths calculated by the TE network controllers and choose 1238 the best one for the optimal e2e path. 1240 6. YANG model for stateless TE path computation 1242 6.1. YANG Tree 1244 Figure 9 below shows the tree diagram of the YANG model defined in 1245 module ietf-te-path-computation.yang. 1247 module: ietf-te-path-computation 1248 augment /te:tunnels-rpc/te:input/te:tunnel-info: 1249 +---- path-request* [request-id] 1250 | +---- request-id uint32 1251 | +---- te-topology-identifier 1252 | | +---- provider-id? te-types:te-global-id 1253 | | +---- client-id? te-types:te-global-id 1254 | | +---- topology-id? te-types:te-topology-id 1255 | +---- source? inet:ip-address 1256 | +---- destination? inet:ip-address 1257 | +---- src-tp-id? binary 1258 | +---- dst-tp-id? binary 1259 | +---- bidirectional? boolean 1260 | +---- encoding? identityref 1261 | +---- switching-type? identityref 1262 | +---- explicit-route-objects 1263 | | +---- route-object-exclude-always* [index] 1264 | | | +---- index uint32 1265 | | | +---- (type)? 1266 | | | +--:(num-unnum-hop) 1267 | | | | +---- num-unnum-hop 1268 | | | | +---- node-id? te-types:te-node-id 1269 | | | | +---- link-tp-id? te-types:te-tp-id 1270 | | | | +---- hop-type? te-hop-type 1271 | | | | +---- direction? te-link-direction 1272 | | | +--:(as-number) 1273 | | | | +---- as-number-hop 1274 | | | | +---- as-number? binary 1275 | | | | +---- hop-type? te-hop-type 1276 | | | +--:(label) 1277 | | | +---- label-hop 1278 | | | +---- te-label 1279 | | | +---- (technology)? 1280 | | | | +--:(generic) 1281 | | | | +---- generic? 1282 | | | | rt-types:generalized-label 1283 | | | +---- direction? te-label-direction 1284 | | +---- route-object-include-exclude* [index] 1285 | | +---- explicit-route-usage? identityref 1286 | | +---- index uint32 1287 | | +---- (type)? 1288 | | +--:(num-unnum-hop) 1289 | | | +---- num-unnum-hop 1290 | | | +---- node-id? te-types:te-node-id 1291 | | | +---- link-tp-id? te-types:te-tp-id 1292 | | | +---- hop-type? te-hop-type 1293 | | | +---- direction? te-link-direction 1294 | | +--:(as-number) 1295 | | | +---- as-number-hop 1296 | | | +---- as-number? binary 1297 | | | +---- hop-type? te-hop-type 1298 | | +--:(label) 1299 | | | +---- label-hop 1300 | | | +---- te-label 1301 | | | +---- (technology)? 1302 | | | | +--:(generic) 1303 | | | | +---- generic? 1304 | | | | rt-types:generalized-label 1305 | | | +---- direction? te-label-direction 1306 | | +--:(srlg) 1307 | | +---- srlg 1308 | | +---- srlg? uint32 1309 | +---- path-constraints 1310 | | +---- te-bandwidth 1311 | | | +---- (technology)? 1312 | | | +--:(generic) 1313 | | | +---- generic? te-bandwidth 1314 | | +---- setup-priority? uint8 1315 | | +---- hold-priority? uint8 1316 | | +---- signaling-type? identityref 1317 | | +---- path-metric-bounds 1318 | | | +---- path-metric-bound* [metric-type] 1319 | | | +---- metric-type identityref 1320 | | | +---- upper-bound? uint64 1321 | | +---- path-affinities-values 1322 | | | +---- path-affinities-value* [usage] 1323 | | | +---- usage identityref 1324 | | | +---- value? admin-groups 1325 | | +---- path-affinity-names 1326 | | | +---- path-affinity-name* [usage] 1327 | | | +---- usage identityref 1328 | | | +---- affinity-name* [name] 1329 | | | +---- name string 1330 | | +---- path-srlgs-values 1331 | | | +---- usage? identityref 1332 | | | +---- values* srlg 1333 | | +---- path-srlgs-names 1334 | | | +---- path-srlgs-name* [usage] 1335 | | | +---- usage identityref 1336 | | | +---- srlg-name* [name] 1337 | | | +---- name string 1338 | | +---- disjointness? te-types:te-path- 1339 disjointness 1340 | +---- optimizations 1341 | | +---- (algorithm)? 1342 | | +--:(metric) {path-optimization-metric}? 1343 | | | +---- optimization-metric* [metric-type] 1344 | | | | +---- metric-type 1345 identityref 1346 | | | | +---- weight? uint8 1347 | | | | +---- explicit-route-exclude-objects 1348 | | | | | +---- route-object-exclude-object* [index] 1349 | | | | | +---- index uint32 1350 | | | | | +---- (type)? 1351 | | | | | +--:(num-unnum-hop) 1352 | | | | | | +---- num-unnum-hop 1353 | | | | | | +---- node-id? te-types:te- 1354 node-id 1355 | | | | | | +---- link-tp-id? te-types:te- 1356 tp-id 1357 | | | | | | +---- hop-type? te-hop-type 1358 | | | | | | +---- direction? te-link- 1359 direction 1360 | | | | | +--:(as-number) 1361 | | | | | | +---- as-number-hop 1362 | | | | | | +---- as-number? binary 1363 | | | | | | +---- hop-type? te-hop-type 1364 | | | | | +--:(label) 1365 | | | | | | +---- label-hop 1366 | | | | | | +---- te-label 1367 | | | | | | +---- (technology)? 1368 | | | | | | | +--:(generic) 1369 | | | | | | | +---- generic? 1370 | | | | | | | rt- 1371 types:generalized-label 1372 | | | | | | +---- direction? 1373 | | | | | | te-label-direction 1374 | | | | | +--:(srlg) 1375 | | | | | +---- srlg 1376 | | | | | +---- srlg? uint32 1377 | | | | +---- explicit-route-include-objects 1378 | | | | +---- route-object-include-object* [index] 1379 | | | | +---- index uint32 1380 | | | | +---- (type)? 1381 | | | | +--:(num-unnum-hop) 1382 | | | | | +---- num-unnum-hop 1383 | | | | | +---- node-id? te-types:te- 1384 node-id 1385 | | | | | +---- link-tp-id? te-types:te- 1386 tp-id 1387 | | | | | +---- hop-type? te-hop-type 1388 | | | | | +---- direction? te-link- 1389 direction 1390 | | | | +--:(as-number) 1391 | | | | | +---- as-number-hop 1392 | | | | | +---- as-number? binary 1393 | | | | | +---- hop-type? te-hop-type 1394 | | | | +--:(label) 1395 | | | | +---- label-hop 1396 | | | | +---- te-label 1397 | | | | +---- (technology)? 1398 | | | | | +--:(generic) 1399 | | | | | +---- generic? 1400 | | | | | rt- 1401 types:generalized-label 1402 | | | | +---- direction? 1403 | | | | te-label-direction 1404 | | | +---- tiebreakers 1405 | | | +---- tiebreaker* [tiebreaker-type] 1406 | | | +---- tiebreaker-type identityref 1407 | | +--:(objective-function) 1408 | | {path-optimization-objective-function}? 1409 | | +---- objective-function 1410 | | +---- objective-function-type? identityref 1411 | +---- requested-metrics* [metric-type] 1412 | | +---- metric-type identityref 1413 | +---- return-srlgs? boolean 1414 | +---- return-affinities? boolean 1415 | +---- path-in-segment! 1416 | | +---- label-restrictions 1417 | | +---- label-restriction* [index] 1418 | | +---- restriction? enumeration 1419 | | +---- index uint32 1420 | | +---- label-start 1421 | | | +---- te-label 1422 | | | +---- (technology)? 1423 | | | | +--:(generic) 1424 | | | | +---- generic? rt-types:generalized- 1425 label 1426 | | | +---- direction? te-label-direction 1427 | | +---- label-end 1428 | | | +---- te-label 1429 | | | +---- (technology)? 1430 | | | | +--:(generic) 1431 | | | | +---- generic? rt-types:generalized- 1432 label 1433 | | | +---- direction? te-label-direction 1434 | | +---- label-step 1435 | | | +---- (technology)? 1436 | | | +--:(generic) 1437 | | | +---- generic? int32 1438 | | +---- range-bitmap? binary 1439 | +---- path-out-segment! 1440 | +---- label-restrictions 1441 | +---- label-restriction* [index] 1442 | +---- restriction? enumeration 1443 | +---- index uint32 1444 | +---- label-start 1445 | | +---- te-label 1446 | | +---- (technology)? 1447 | | | +--:(generic) 1448 | | | +---- generic? rt-types:generalized- 1449 label 1450 | | +---- direction? te-label-direction 1451 | +---- label-end 1452 | | +---- te-label 1453 | | +---- (technology)? 1454 | | | +--:(generic) 1455 | | | +---- generic? rt-types:generalized- 1456 label 1457 | | +---- direction? te-label-direction 1458 | +---- label-step 1459 | | +---- (technology)? 1460 | | +--:(generic) 1461 | | +---- generic? int32 1462 | +---- range-bitmap? binary 1463 +---- synchronization* [synchronization-id] 1464 +---- synchronization-id uint32 1465 +---- svec 1466 | +---- relaxable? boolean 1467 | +---- disjointness? te-types:te-path-disjointness 1468 | +---- request-id-number* uint32 1469 +---- svec-constraints 1470 | +---- path-metric-bound* [metric-type] 1471 | +---- metric-type identityref 1472 | +---- upper-bound? uint64 1473 +---- path-srlgs-values 1474 | +---- usage? identityref 1475 | +---- values* srlg 1476 +---- path-srlgs-names 1477 | +---- path-srlgs-name* [usage] 1478 | +---- usage identityref 1479 | +---- srlg-name* [name] 1480 | +---- name string 1481 +---- exclude-objects 1482 | +---- excludes* [index] 1483 | +---- index uint32 1484 | +---- (type)? 1485 | +--:(num-unnum-hop) 1486 | | +---- num-unnum-hop 1487 | | +---- node-id? te-types:te-node-id 1488 | | +---- link-tp-id? te-types:te-tp-id 1489 | | +---- hop-type? te-hop-type 1490 | | +---- direction? te-link-direction 1491 | +--:(as-number) 1492 | | +---- as-number-hop 1493 | | +---- as-number? binary 1494 | | +---- hop-type? te-hop-type 1495 | +--:(label) 1496 | +---- label-hop 1497 | +---- te-label 1498 | +---- (technology)? 1499 | | +--:(generic) 1500 | | +---- generic? 1501 | | rt-types:generalized-label 1502 | +---- direction? te-label-direction 1503 +---- optimizations 1504 +---- (algorithm)? 1505 +--:(metric) 1506 | +---- optimization-metric* [metric-type] 1507 | +---- metric-type identityref 1508 | +---- weight? uint8 1509 +--:(objective-function) 1510 +---- objective-function 1511 +---- objective-function-type? identityref 1512 augment /te:tunnels-rpc/te:output/te:result: 1513 +--ro response* [response-id] 1514 +--ro response-id uint32 1515 +--ro (response-type)? 1516 +--:(no-path-case) 1517 | +--ro no-path! 1518 +--:(path-case) 1519 +--ro computed-path 1520 +--ro path-id? yang-types:uuid 1521 +--ro path-properties 1522 +--ro path-metric* [metric-type] 1523 | +--ro metric-type identityref 1524 | +--ro accumulative-value? uint64 1525 +--ro path-affinities-values 1526 | +--ro path-affinities-value* [usage] 1527 | +--ro usage identityref 1528 | +--ro value? admin-groups 1529 +--ro path-affinity-names 1530 | +--ro path-affinity-name* [usage] 1531 | +--ro usage identityref 1532 | +--ro affinity-name* [name] 1533 | +--ro name string 1534 +--ro path-srlgs-values 1535 | +--ro usage? identityref 1536 | +--ro values* srlg 1537 +--ro path-srlgs-names 1538 | +--ro path-srlgs-name* [usage] 1539 | +--ro usage identityref 1540 | +--ro srlg-name* [name] 1541 | +--ro name string 1542 +--ro path-route-objects 1543 +--ro path-route-object* [index] 1544 +--ro index uint32 1545 +--ro (type)? 1546 +--:(num-unnum-hop) 1547 | +--ro num-unnum-hop 1548 | +--ro node-id? te-types:te- 1549 node-id 1550 | +--ro link-tp-id? te-types:te- 1551 tp-id 1552 | +--ro hop-type? te-hop-type 1553 | +--ro direction? te-link- 1554 direction 1555 +--:(as-number) 1556 | +--ro as-number-hop 1557 | +--ro as-number? binary 1558 | +--ro hop-type? te-hop-type 1559 +--:(label) 1560 +--ro label-hop 1561 +--ro te-label 1562 +--ro (technology)? 1563 | +--:(generic) 1564 | +--ro generic? 1565 | rt- 1566 types:generalized-label 1567 +--ro direction? 1568 te-label-direction 1570 Figure 9 - TE path computation YANG tree 1572 6.2. YANG Module 1574 file "ietf-te-path-computation@2018-10-23.yang" 1575 module ietf-te-path-computation { 1576 yang-version 1.1; 1577 namespace "urn:ietf:params:xml:ns:yang:ietf-te-path-computation"; 1578 // replace with IANA namespace when assigned 1580 prefix "tepc"; 1582 import ietf-inet-types { 1583 prefix "inet"; 1584 } 1586 import ietf-yang-types { 1587 prefix "yang-types"; 1588 } 1590 import ietf-te { 1591 prefix "te"; 1592 } 1594 import ietf-te-types { 1595 prefix "te-types"; 1596 } 1598 organization 1599 "Traffic Engineering Architecture and Signaling (TEAS) 1600 Working Group"; 1602 contact 1603 "WG Web: 1604 WG List: 1605 WG Chair: Lou Berger 1606 1608 WG Chair: Vishnu Pavan Beeram 1609 1611 "; 1613 description "YANG model for stateless TE path computation"; 1615 revision "2018-10-23" { 1616 description 1617 "Initial revision"; 1618 reference 1619 "draft-ietf-teas-yang-path-computation"; 1620 } 1622 /* 1623 * Features 1624 */ 1626 feature stateless-path-computation { 1627 description 1628 "This feature indicates that the system supports 1629 stateless path computation."; 1630 } 1632 /* 1633 * Groupings 1634 */ 1636 grouping path-info { 1637 leaf path-id { 1638 type yang-types:uuid; 1639 config false; 1640 description "path-id ref."; 1641 } 1642 uses te-types:generic-path-properties; 1643 description "Path computation output information"; 1644 } 1646 grouping requested-info { 1647 description 1648 "This grouping defines the information (e.g., metrics) 1649 which must be returned in the response"; 1650 list requested-metrics { 1651 key 'metric-type'; 1652 description 1653 "The list of the requested metrics 1654 The metrics listed here must be returned in the response. 1655 Returning other metrics in the response is optional."; 1656 leaf metric-type { 1657 type identityref { 1658 base te-types:path-metric-type; 1659 } 1660 description 1661 "The metric that must be returned in the response"; 1662 } 1663 } 1664 leaf return-srlgs { 1665 type boolean; 1666 default false; 1667 description 1668 "If true, path srlgs must be returned in the response. 1669 If false, returning path srlgs in the response optional."; 1670 } 1671 leaf return-affinities { 1672 type boolean; 1673 default false; 1674 description 1675 "If true, path affinities must be returned in the response. 1676 If false, returning path affinities in the response is 1677 optional."; 1678 } 1679 } 1680 identity svec-metric-type { 1681 description 1682 "Base identity for svec metric type"; 1683 } 1685 identity svec-metric-cumul-te { 1686 base svec-metric-type; 1687 description 1688 "TE cumulative path metric"; 1689 } 1691 identity svec-metric-cumul-igp { 1692 base svec-metric-type; 1693 description 1694 "IGP cumulative path metric"; 1695 } 1697 identity svec-metric-cumul-hop { 1698 base svec-metric-type; 1699 description 1700 "Hop cumulative path metric"; 1701 } 1703 identity svec-metric-aggregate-bandwidth-consumption { 1704 base svec-metric-type; 1705 description 1706 "Cumulative bandwith consumption of the set of 1707 synchronized paths"; 1708 } 1710 identity svec-metric-load-of-the-most-loaded-link { 1711 base svec-metric-type; 1712 description 1713 "Load of the most loaded link"; 1714 } 1716 grouping svec-metrics-bounds_config { 1717 description 1718 "TE path metric bounds grouping for computing a set of 1719 synchronized requests"; 1720 leaf metric-type { 1721 type identityref { 1722 base svec-metric-type; 1723 } 1724 description "TE path metric type usable for computing a set of 1725 synchronized requests"; 1726 } 1727 leaf upper-bound { 1728 type uint64; 1729 description "Upper bound on end-to-end svec path metric"; 1730 } 1731 } 1733 grouping svec-metrics-optimization_config { 1734 description 1735 "TE path metric bounds grouping for computing a set of 1736 synchronized requests"; 1738 leaf metric-type { 1739 type identityref { 1740 base svec-metric-type; 1741 } 1742 description "TE path metric type usable for computing a set of 1743 synchronized requests"; 1744 } 1745 leaf weight { 1746 type uint8; 1747 description "Metric normalization weight"; 1748 } 1749 } 1751 grouping svec-exclude { 1752 description "List of resources to be excluded by all the paths 1753 in the SVEC"; 1754 container exclude-objects { 1755 description "resources to be excluded"; 1756 list excludes { 1757 key index; 1758 description 1759 "List of explicit route objects to always exclude 1760 from synchronized path computation"; 1761 leaf index { 1762 type uint32; 1763 description "XRO subobject index"; 1764 } 1765 uses te-types:explicit-route-hop; 1766 } 1767 } 1768 } 1770 grouping synchronization-constraints { 1771 description "Global constraints applicable to synchronized 1772 path computation"; 1773 container svec-constraints { 1774 description "global svec constraints"; 1775 list path-metric-bound { 1776 key metric-type; 1777 description "list of bound metrics"; 1778 uses svec-metrics-bounds_config; 1779 } 1780 } 1781 uses te-types:generic-path-srlgs; 1782 uses svec-exclude; 1783 } 1785 grouping synchronization-optimization { 1786 description "Synchronized request optimization"; 1787 container optimizations { 1788 description 1789 "The objective function container that includes attributes 1790 to impose when computing a synchronized set of paths"; 1792 choice algorithm { 1793 description "Optimizations algorithm."; 1794 case metric { 1795 list optimization-metric { 1796 key "metric-type"; 1797 description "svec path metric type"; 1798 uses svec-metrics-optimization_config; 1799 } 1800 } 1801 case objective-function { 1802 container objective-function { 1803 description 1804 "The objective function container that includes 1805 attributes to impose when computing a TE path"; 1806 uses te-types:path-objective-function_config; 1807 } 1808 } 1809 } 1810 } 1811 } 1813 grouping synchronization-info { 1814 description "Information for sync"; 1815 list synchronization { 1816 key "synchronization-id"; 1817 description "sync list"; 1818 leaf synchronization-id { 1819 type uint32; 1820 description "index"; 1821 } 1822 container svec { 1823 description 1824 "Synchronization VECtor"; 1825 leaf relaxable { 1826 type boolean; 1827 default true; 1828 description 1829 "If this leaf is true, path computation process is 1830 free to ignore svec content. 1831 Otherwise, it must take into account this svec."; 1832 } 1833 uses te-types:generic-path-disjointness; 1834 leaf-list request-id-number { 1835 type uint32; 1836 description 1837 "This list reports the set of path computation 1838 requests that must be synchronized."; 1839 } 1840 } 1841 uses synchronization-constraints; 1842 uses synchronization-optimization; 1843 } 1844 } 1846 grouping no-path-info { 1847 description "no-path-info"; 1848 container no-path { 1849 presence "Response without path information, due to failure 1850 performing the path computation"; 1851 description "if path computation cannot identify a path, 1852 rpc returns no path."; 1853 } 1854 } 1856 /* 1857 * These groupings should be removed when defined in te-types 1858 */ 1860 grouping encoding-and-switching-type { 1861 description 1862 "Common grouping to define the LSP encoding and 1863 switching types"; 1865 leaf encoding { 1866 type identityref { 1867 base te-types:lsp-encoding-types; 1868 } 1869 description "LSP encoding type"; 1870 reference "RFC3945"; 1871 } 1872 leaf switching-type { 1873 type identityref { 1874 base te-types:switching-capabilities; 1876 } 1877 description "LSP switching type"; 1878 reference "RFC3945"; 1879 } 1880 } 1882 grouping end-points { 1883 description 1884 "Common grouping to define the TE tunnel end-points"; 1886 leaf source { 1887 type inet:ip-address; 1888 description "TE tunnel source address."; 1889 } 1890 leaf destination { 1891 type inet:ip-address; 1892 description "P2P tunnel destination address"; 1893 } 1894 leaf src-tp-id { 1895 type binary; 1896 description 1897 "TE tunnel source termination point identifier."; 1898 } 1899 leaf dst-tp-id { 1900 type binary; 1901 description 1902 "TE tunnel destination termination point identifier."; 1903 } 1904 leaf bidirectional { 1905 type boolean; 1906 default 'false'; 1907 description "TE tunnel bidirectional"; 1908 } 1909 } 1911 /** 1912 * AUGMENTS TO TE RPC 1913 */ 1915 augment "/te:tunnels-rpc/te:input/te:tunnel-info" { 1916 description "statelessComputeP2PPath input"; 1917 list path-request { 1918 key "request-id"; 1919 description "request-list"; 1920 leaf request-id { 1921 type uint32; 1922 mandatory true; 1923 description 1924 "Each path computation request is uniquely identified 1925 by the request-id-number."; 1926 } 1927 uses te-types:te-topology-identifier; 1928 uses end-points; 1929 uses encoding-and-switching-type; 1930 uses te-types:path-route-objects; 1931 uses te-types:generic-path-constraints; 1932 uses te-types:generic-path-optimization; 1933 uses requested-info; 1934 uses te:path-access-segment-info; 1935 } 1936 uses synchronization-info; 1937 } 1939 augment "/te:tunnels-rpc/te:output/te:result" { 1940 description "statelessComputeP2PPath output"; 1941 list response { 1942 key response-id; 1943 config false; 1944 description "response"; 1945 leaf response-id { 1946 type uint32; 1947 description 1948 "The list key that has to reuse request-id-number."; 1949 } 1950 choice response-type { 1951 config false; 1952 description "response-type"; 1953 case no-path-case { 1954 uses no-path-info; 1955 } 1956 case path-case { 1957 container computed-path { 1958 uses path-info; 1959 description "Path computation service."; 1960 } 1961 } 1962 } 1963 } 1964 } 1965 } 1966 1968 Figure 10 - TE path computation YANG module 1970 7. Security Considerations 1972 This document describes use cases of requesting Path Computation 1973 using YANG models, which could be used at the ABNO Control Interface 1974 [RFC7491] and/or between controllers in ACTN [RFC8453]. As such, it 1975 does not introduce any new security considerations compared to the 1976 ones related to YANG specification, ABNO specification and ACTN 1977 Framework defined in [RFC7950], [RFC7491] and [RFC8453]. 1979 The YANG module defined in this draft is designed to be accessed via 1980 the NETCONF protocol [RFC6241] or RESTCONF protocol [RFC8040]. The 1981 lowest NETCONF layer is the secure transport layer, and the 1982 mandatory-to-implement secure transport is Secure Shell (SSH) 1983 [RFC6242]. The lowest RESTCONF layer is HTTPS, and the mandatory-to- 1984 implement secure transport is TLS [RFC8446]. 1986 This document also defines common data types using the YANG data 1987 modeling language. The definitions themselves have no security 1988 impact on the Internet, but the usage of these definitions in 1989 concrete YANG modules might have. The security considerations 1990 spelled out in the YANG specification [RFC7950] apply for this 1991 document as well. 1993 The NETCONF access control model [RFC8341] provides the means to 1994 restrict access for particular NETCONF or RESTCONF users to a 1995 preconfigured subset of all available NETCONF or RESTCONF protocol 1996 operations and content. 1998 Note - The security analysis of each leaf is for further study. 2000 8. IANA Considerations 2002 This document registers the following URIs in the IETF XML registry 2003 [RFC3688]. Following the format in [RFC3688], the following 2004 registration is requested to be made. 2006 URI: urn:ietf:params:xml:ns:yang:ietf-te-path-computation 2007 XML: N/A, the requested URI is an XML namespace. 2009 This document registers a YANG module in the YANG Module Names 2010 registry [RFC7950]. 2012 name: ietf-te-path-computation 2013 namespace: urn:ietf:params:xml:ns:yang:ietf-te-path-computation 2014 prefix: tepc 2016 9. References 2018 9.1. Normative References 2020 [RFC3688] Mealling, M., "The IETF XML Registry", RFC 3688, January 2021 2004. 2023 [RFC5440] Vasseur, JP., Le Roux, JL. et al., "Path Computation 2024 Element (PCE) Communication Protocol (PCEP)", RFC 5440, 2025 March 2009. 2027 [RFC5541] Le Roux, JL. et al., " Encoding of Objective Functions in 2028 the Path Computation Element Communication Protocol 2029 (PCEP)", RFC 5541, June 2009. 2031 [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., 2032 and A. Bierman, Ed., "Network Configuration Protocol 2033 (NETCONF)", RFC 6241, June 2011. 2035 [RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure 2036 Shell (SSH)", RFC 6242, June 2011. 2038 [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF 2039 Protocol", RFC 8040, January 2017. 2041 [RFC8341] Bierman, A., and M. Bjorklund, "Network Configuration 2042 Access Control Model", RFC 8341, March 2018. 2044 [RFC7491] Farrel, A., King, D., "A PCE-Based Architecture for 2045 Application-Based Network Operations", RFC 7491, March 2046 2015. 2048 [RFC7926] Farrel, A. et al., "Problem Statement and Architecture for 2049 Information Exchange Between Interconnected Traffic 2050 Engineered Networks", RFC 7926, July 2016. 2052 [RFC7950] Bjorklund, M., "The YANG 1.1 Data Modeling Language", RFC 2053 7950, August 2016. 2055 [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF 2056 Protocol", RFC 8040, January 2017. 2058 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 2059 Version 1.3", RFC 8446, August 2018. 2061 [RFC8453] Ceccarelli, D., Lee, Y. et al., "Framework for Abstraction 2062 and Control of TE Networks (ACTN)", RFC8453, August 2018. 2064 [RFC8454] Lee, Y. et al., "Information Model for Abstraction and 2065 Control of TE Networks (ACTN)", RFC8454, September 2018. 2067 [TE-TOPO] Liu, X. et al., "YANG Data Model for TE Topologies", 2068 draft-ietf-teas-yang-te-topo, work in progress. 2070 [TE-TUNNEL] Saad, T. et al., "A YANG Data Model for Traffic 2071 Engineering Tunnels and Interfaces", draft-ietf-teas-yang- 2072 te, work in progress. 2074 9.1. Informative References 2076 [RFC4655] Farrel, A. et al., "A Path Computation Element (PCE)-Based 2077 Architecture", RFC 4655, August 2006. 2079 [RFC7139] Zhang, F. et al., "GMPLS Signaling Extensions for Control 2080 of Evolving G.709 Optical Transport Networks", RFC 7139, 2081 March 2014. 2083 [RFC7446] Lee, Y. et al., "Routing and Wavelength Assignment 2084 Information Model for Wavelength Switched Optical 2085 Networks", RFC 7446, February 2015. 2087 [RFC8233] Dhody, D. et al., "Extensions to the Path Computation 2088 Element Communication Protocol (PCEP) to Compute Service- 2089 Aware Label Switched Paths (LSPs)", RFC 8233, September 2090 2017 2092 [OTN-TOPO] Zheng, H. et al., "A YANG Data Model for Optical 2093 Transport Network Topology", draft-ietf-ccamp-otn-topo- 2094 yang, work in progress. 2096 [ITU-T G.709-2016] ITU-T Recommendation G.709 (06/16), "Interface 2097 for the optical transport network", June 2016. 2099 10. Acknowledgments 2101 The authors would like to thank Igor Bryskin and Xian Zhang for 2102 participating in the initial discussions that have triggered this 2103 work and providing valuable insights. 2105 The authors would like to thank the authors of the TE Tunnel YANG 2106 model [TE-TUNNEL], in particular Igor Bryskin, Vishnu Pavan Beeram, 2107 Tarek Saad and Xufeng Liu, for their inputs to the discussions and 2108 support in having consistency between the Path Computation and TE 2109 Tunnel YANG models. 2111 The authors would like to thank Adrian Farrel, Dhruv Dhody, Igor 2112 Bryskin, Julien Meuric and Lou Berger for their valuable input to 2113 the discussions that has clarified that the path being setup is not 2114 necessarily the same as the path that have been previously computed 2115 and, in particular to Dhruv Dhody, for his suggestion to describe 2116 the need for a path verification phase to check that the actual path 2117 being setup meets the required end-to-end metrics and constraints. 2119 This document was prepared using 2-Word-v2.0.template.dot. 2121 Appendix A. Examples of dimensioning the "detailed connectivity matrix" 2123 In the following table, a list of the possible constraints, 2124 associated with their potential cardinality, is reported. 2126 The maximum number of potential connections to be computed and 2127 reported is, in first approximation, the multiplication of all of 2128 them. 2130 Constraint Cardinality 2131 ---------- ------------------------------------------------------- 2133 End points N(N-1)/2 if connections are bidirectional (OTN and WDM), 2134 N(N-1) for unidirectional connections. 2136 Bandwidth In WDM networks, bandwidth values are expressed in GHz. 2138 On fixed-grid WDM networks, the central frequencies are 2139 on a 50GHz grid and the channel width of the transmitters 2140 are typically 50GHz such that each central frequency can 2141 be used, i.e., adjacent channels can be placed next to 2142 each other in terms of central frequencies. 2144 On flex-grid WDM networks, the central frequencies are on 2145 a 6.25GHz grid and the channel width of the transmitters 2146 can be multiples of 12.5GHz. 2148 For fixed-grid WDM networks typically there is only one 2149 possible bandwidth value (i.e., 50GHz) while for flex- 2150 grid WDM networks typically there are 4 possible 2151 bandwidth values (e.g., 37.5GHz, 50GHz, 62.5GHz, 75GHz). 2153 In OTN (ODU) networks, bandwidth values are expressed as 2154 pairs of ODU type and, in case of ODUflex, ODU rate in 2155 bytes/sec as described in section 5 of [RFC7139]. 2157 For "fixed" ODUk types, 6 possible bandwidth values are 2158 possible (i.e., ODU0, ODU1, ODU2, ODU2e, ODU3, ODU4). 2160 For ODUflex(GFP), up to 80 different bandwidth values can 2161 be specified, as defined in Table 7-8 of [ITU-T G.709- 2162 2016]. 2164 For other ODUflex types, like ODUflex(CBR), the number of 2165 possible bandwidth values depends on the rates of the 2166 clients that could be mapped over these ODUflex types, as 2167 shown in Table 7.2 of [ITU-T G.709-2016], which in theory 2168 could be a countinuum of values. However, since different 2169 ODUflex bandwidths that use the same number of TSs on 2170 each link along the path are equivalent for path 2171 computation purposes, up to 120 different bandwidth 2172 ranges can be specified. 2174 Ideas to reduce the number of ODUflex bandwidth values in 2175 the detailed connectivity matrix, to less than 100, are 2176 for further study. 2178 Bandwidth specification for ODUCn is currently for 2179 further study but it is expected that other bandwidth 2180 values can be specified as integer multiples of 100Gb/s. 2182 In IP we have bandwidth values in bytes/sec. In 2183 principle, this is a countinuum of values, but in 2184 practice we can identify a set of bandwidth ranges, where 2185 any bandwidth value inside the same range produces the 2186 same path. 2187 The number of such ranges is the cardinality, which 2188 depends on the topology, available bandwidth and status 2189 of the network. Simulations (Note: reference paper 2190 submitted for publication) show that values for medium 2191 size topologies (around 50-150 nodes) are in the range 4- 2192 7 (5 on average) for each end points couple. 2194 Metrics IGP, TE and hop number are the basic objective metrics 2195 defined so far. There are also the 2 objective functions 2196 defined in [RFC5541]: Minimum Load Path (MLP) and Maximum 2197 Residual Bandwidth Path (MBP). Assuming that one only 2198 metric or objective function can be optimized at once, 2199 the total cardinality here is 5. 2201 With [RFC8233], a number of additional metrics are 2202 defined, including Path Delay metric, Path Delay 2203 Variation metric and Path Loss metric, both for point-to- 2204 point and point-to-multipoint paths. This increases the 2205 cardinality to 8. 2207 Bounds Each metric can be associated with a bound in order to 2208 find a path having a total value of that metric lower 2209 than the given bound. This has a potentially very high 2210 cardinality (as any value for the bound is allowed). In 2211 practice there is a maximum value of the bound (the one 2212 with the maximum value of the associated metric) which 2213 results always in the same path, and a range approach 2214 like for bandwidth in IP should produce also in this case 2215 the cardinality. Assuming to have a cardinality similar 2216 to the one of the bandwidth (let say 5 on average) we 2217 should have 6 (IGP, TE, hop, path delay, path delay 2218 variation and path loss; we don't consider here the two 2219 objective functions of [RFC5541] as they are conceived 2220 only for optimization)*5 = 30 cardinality. 2222 Technology 2223 constraints For further study 2225 Priority We have 8 values for setup priority, which is used in 2226 path computation to route a path using free resources 2227 and, where no free resources are available, resources 2228 used by LSPs having a lower holding priority. 2230 Local prot It's possible to ask for a local protected service, where 2231 all the links used by the path are protected with fast 2232 reroute (this is only for IP networks, but line 2233 protection schemas are available on the other 2234 technologies as well). This adds an alternative path 2235 computation, so the cardinality of this constraint is 2. 2237 Administrative 2238 Colors Administrative colors (aka affinities) are typically 2239 assigned to links but when topology abstraction is used 2240 affinity information can also appear in the detailed 2241 connectivity matrix. 2243 There are 32 bits available for the affinities. Links can 2244 be tagged with any combination of these bits, and path 2245 computation can be constrained to include or exclude any 2246 or all of them. The relevant cardinality is 3 (include- 2247 any, exclude-any, include-all) times 2^32 possible 2248 values. However, the number of possible values used in 2249 real networks is quite small. 2251 Included Resources 2253 A path computation request can be associated to an 2254 ordered set of network resources (links, nodes) to be 2255 included along the computed path. This constraint would 2256 have a huge cardinality as in principle any combination 2257 of network resources is possible. However, as far as the 2258 Orchestrator doesn't know details about the internal 2259 topology of the domain, it shouldn't include this type of 2260 constraint at all (see more details below). 2262 Excluded Resources 2264 A path computation request can be associated to a set of 2265 network resources (links, nodes, SRLGs) to be excluded 2266 from the computed path. Like for included resources, 2267 this constraint has a potentially very high cardinality, 2268 but, once again, it can't be actually used by the 2269 Orchestrator, if it's not aware of the domain topology 2270 (see more details below). 2271 As discussed above, the Orchestrator can specify include or exclude 2272 resources depending on the abstract topology information that the 2273 domain controller exposes: 2275 o In case the domain controller exposes the entire domain as a 2276 single abstract TE node with his own external terminations and 2277 detailed connectivity matrix (whose size we are estimating), no 2278 other topological details are available, therefore the size of 2279 the detailed connectivity matrix only depends on the combination 2280 of the constraints that the Orchestrator can use in a path 2281 computation request to the domain controller. These constraints 2282 cannot refer to any details of the internal topology of the 2283 domain, as those details are not known to the Orchestrator and so 2284 they do not impact size of the detailed connectivity matrix 2285 exported. 2287 o Instead in case the domain controller exposes a topology 2288 including more than one abstract TE nodes and TE links, and their 2289 attributes (e.g. SRLGs, affinities for the links), the 2290 Orchestrator knows these details and therefore could compute a 2291 path across the domain referring to them in the constraints. The 2292 detailed connectivity matrixes, whose size need to be estimated 2293 here, are the ones relevant to the abstract TE nodes exported to 2294 the Orchestrator. These detailed connectivity matrixes and 2295 therefore theirs sizes, while cannot depend on the other abstract 2296 TE nodes and TE links, which are external to the given abstract 2297 node, could depend to SRLGs (and other attributes, like 2298 affinities) which could be present also in the portion of the 2299 topology represented by the abstract nodes, and therefore 2300 contribute to the size of the related detailed connectivity 2301 matrix. 2303 We also don't consider here the possibility to ask for more than one 2304 path in diversity or for point-to-multi-point paths, which are for 2305 further study. 2307 Considering for example an IP domain without considering SRLG and 2308 affinities, we have an estimated number of paths depending on these 2309 estimated cardinalities: 2311 Endpoints = N*(N-1), Bandwidth = 5, Metrics = 6, Bounds = 20, 2312 Priority = 8, Local prot = 2 2314 The number of paths to be pre-computed by each IP domain is 2315 therefore 24960 * N(N-1) where N is the number of domain access 2316 points. 2318 This means that with just 4 access points we have nearly 300000 2319 paths to compute, advertise and maintain (if a change happens in the 2320 domain, due to a fault, or just the deployment of new traffic, a 2321 substantial number of paths need to be recomputed and the relevant 2322 changes advertised to the upper controller). 2324 This seems quite challenging. In fact, if we assume a mean length of 2325 1K for the json describing a path (a quite conservative estimate), 2326 reporting 300000 paths means transferring and then parsing more than 2327 300 Mbytes for each domain. If we assume that 20% (to be checked) of 2328 this paths change when a new deployment of traffic occurs, we have 2329 60 Mbytes of transfer for each domain traversed by a new end-to-end 2330 path. If a network has, let say, 20 domains (we want to estimate the 2331 load for a non-trivial domain setup) in the beginning a total 2332 initial transfer of 6Gigs is needed, and eventually, assuming 4-5 2333 domains are involved in mean during a path deployment we could have 2334 240-300 Mbytes of changes advertised to the higher order controller. 2336 Further bare-bone solutions can be investigated, removing some more 2337 options, if this is considered not acceptable; in conclusion, it 2338 seems that an approach based only on the information provided by the 2339 detailed connectivity matrix is hardly feasible, and could be 2340 applicable only to small networks with a limited meshing degree 2341 between domains and renouncing to a number of path computation 2342 features. 2344 Contributors 2346 Dieter Beller 2347 Nokia 2348 Email: dieter.beller@nokia.com 2350 Gianmarco Bruno 2351 Ericsson 2352 Email: gianmarco.bruno@ericsson.com 2354 Francesco Lazzeri 2355 Ericsson 2356 Email: francesco.lazzeri@ericsson.com 2358 Young Lee 2359 Huawei 2360 Email: leeyoung@huawei.com 2362 Carlo Perocchio 2363 Ericsson 2364 Email: carlo.perocchio@ericsson.com 2366 Authors' Addresses 2368 Italo Busi (Editor) 2369 Huawei 2370 Email: italo.busi@huawei.com 2372 Sergio Belotti (Editor) 2373 Nokia 2374 Email: sergio.belotti@nokia.com 2376 Victor Lopez 2377 Telefonica 2378 Email: victor.lopezalvarez@telefonica.com 2379 Oscar Gonzalez de Dios 2380 Telefonica 2381 Email: oscar.gonzalezdedios@telefonica.com 2383 Anurag Sharma 2384 Google 2385 Email: ansha@google.com 2387 Yan Shi 2388 China Unicom 2389 Email: shiyan49@chinaunicom.cn 2391 Ricard Vilalta 2392 CTTC 2393 Email: ricard.vilalta@cttc.es 2395 Karthik Sethuraman 2396 NEC 2397 Email: karthik.sethuraman@necam.com 2399 Michael Scharf 2400 Nokia 2401 Email: michael.scharf@gmail.com 2403 Daniele Ceccarelli 2404 Ericsson 2405 Email: daniele.ceccarelli@ericsson.com