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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group Eiji Oki 2 Internet Draft NTT 3 Category: Informational Jean-Louis Le Roux 4 Expires: August 2006 France Telecom 5 Adrian Farrel 6 Old Dog Consulting 7 February 2006 9 PCE Applicability for Inter-Layer MPLS and GMPLS Traffic 10 Engineering 12 draft-oki-pce-inter-layer-app-00.txt 14 Status of this Memo 16 By submitting this Internet-Draft, each author represents that any 17 applicable patent or other IPR claims of which he or she is aware 18 have been or will be disclosed, and any of which he or she becomes 19 aware will be disclosed, in accordance with Section 6 of BCP 79. 21 Internet-Drafts are working documents of the Internet Engineering 22 Task Force (IETF), its areas, and its working groups. Note that 23 other groups may also distribute working documents as Internet- 24 Drafts. 26 Internet-Drafts are draft documents valid for a maximum of six 27 months and may be updated, replaced, or obsoleted by other 28 documents at any time. It is inappropriate to use Internet- Drafts 29 as reference material or to cite them other than as "work in 30 progress." 32 The list of current Internet-Drafts can be accessed at 33 http://www.ietf.org/ietf/1id-abstracts.txt. 35 The list of Internet-Draft Shadow Directories can be accessed at 36 http://www.ietf.org/shadow.html. 38 Abstract 40 A network may comprise of multiple layers. It is important to 41 globally optimize network resources utilization, taking into 42 account all layers, rather than optimizing resource utilization at 43 each layer independently. This allows better network efficiency to 44 be achieved through a process that we call inter-layer traffic 45 engineering. The Path Computation Element (PCE) can be a powerful 46 tool to achieve inter-layer traffic engineering. 48 This document describes the applicability of the PCE-based path 49 computation architecture to inter-layer MPLS and GMPLS traffic 50 engineering. It provides suggestions for the deployment of PCE in 51 support of multi-layer networks. This document also describes 52 network models where PCE performs inter-layer traffic engineering, 53 and the relationship between PCE and a functional component called 54 the Virtual Network Topology Manager (VNTM). 56 Conventions used in this document 58 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 59 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in 60 this document are to be interpreted as described in RFC 2119 61 [RFC2119]. 63 Table of Contents 65 1. Terminology.....................................................2 66 2. Introduction....................................................2 67 3. Inter-Layer Path Computation....................................3 68 4. Inter-layer Path Computation Models.............................5 69 4.1. Single PCE Inter-Layer Path Computation......................5 70 4.2. Multiple PCE Inter-Layer Path Computation....................6 71 4.3. General observation..........................................6 72 5. Inter-Layer Path Control........................................7 73 5.1. VNT Management...............................................7 74 5.2. Inter-Layer Path Control Models..............................7 75 5.2.1. Cooperation model between PCE and VNTM.....................7 76 5.2.2. Higher-Layer Signaling Trigger Model.......................9 77 5.2.3. Examples of multi-layer ERO...............................11 78 6. Choosing between inter-layer path control models...............11 79 7. Security Considerations........................................13 80 8. Acknowledgment.................................................13 81 9. References.....................................................13 82 9.1. Normative Reference.........................................13 83 9.2. Informative Reference.......................................14 84 10. Authors�EAddresses...........................................14 85 11. Intellectual Property Statement..............................15 87 1. Terminology 89 This document uses terminology from the PCE-based path computation 90 Architecture [PCE-ARCH] and also common terminology from Multi 91 Protocol Label Switching (MPLS) [RFC3031], Generalized MPLS (GMPLS) 92 [RFC3945] and Multi-Layer Networks [MLN-REQ]. 94 2. Introduction 96 A network may comprise of multiple layers. These layers may 97 represent separations of technologies (e.g., packet switch capable 98 (PSC), time division multiplex (TDM) lambda switch capable (LSC)) 99 [RFC3945], separation of data plane switching granularity levels 100 (e.g. PSC-1, PSC-2, VC4, VC12) [MLN-REQ], or a distinction between 101 client and server networking roles. In this multi-layer network, 102 LSPs in a lower layer are used to carry higher-layer LSPs across 104 Oki et al Expires August 2006 2 105 the lower-layer network. The network topology formed by lower-layer 106 LSPs and advertised to the higher layer is called a Virtual Network 107 Topology (VNT) [MLN-REQ]. 109 It is important to optimize network resource utilization globally, 110 i.e. taking into account all layers, rather than optimizing 111 resource utilization at each layer independently. This allows 112 better network efficiency to be achieved and is what we call inter- 113 layer traffic engineering. This includes mechanisms allowing the 114 computation of end-to-end paths across layers (known as inter-layer 115 path computation), and mechanisms for control and management of the 116 VNT by setting up and releasing LSPs in the lower layers [MLN-REQ]. 118 Inter-layer traffic engineering is included in the scope of the 119 PCE-based path computation architecture [PCE-ARCH], and PCE can 120 provide a suitable mechanism for resolving inter-layer path 121 computation issues. 123 PCE Communication Protocol requirements for inter-layer traffic 124 engineering are set forth in [PCE-INTER-LAYER-REQ]. 126 This document describes the applicability of the PCE-based path 127 computation Architecture to inter-layer traffic engineering. It 128 provides suggestions for the deployment of PCE in support of multi- 129 layer networks. This document also describes network models where 130 PCE performs inter-layer traffic engineering, and the relationship 131 between PCE and a functional component in charge of the control and 132 management of the VNT, and called the Virtual Network Topology 133 Manager (VNTM). 135 3. Inter-Layer Path Computation 137 This section describes key topics of inter-layer path computation 138 in MPLS and GMPLS networks. 140 [RFC4206] defines a way to signal a higher-layer LSP, whose 141 explicit route includes hops traversed by LSPs in lower layers. The 142 computation of end-to-end paths across layers is called Inter-Layer 143 Path Computation. 145 An LSR in the higher-layer may not have information on the lower- 146 layer topology, particularly in an overlay or augmented model, and 147 hence may not be able to compute an end-to-end path across layers. 149 PCE-based inter-layer path computation, consists of relying on one 150 or more PCEs to compute an end-to-end path across layers. This 151 could rely on a single PCE path computation where the PCE has 152 topology information about multiple layers and can directly compute 153 an end-to-end path across layers considering the topology of all of 154 the layers. Alternatively, the inter-layer path computation could 155 be performed as a multiple PCE computation where each member of a 156 set of PCEs have information about the topology of one or more 157 layers, but not all layers, and collaborate to compute an end-to- 158 end path. 160 Oki et al Expires August 2006 3 161 Consider a two-layer network where the higher-layer network is a 162 packet-based IP/MPLS network or GMPLS network and the lower-layer 163 network is a GMPLS optical network. An ingress LSR in the higher- 164 layer network tries to set up an LSP to an egress LSR also in the 165 higher-layer network across the lower-layer network, and needs a 166 path in the higher-layer network. However, suppose that there is no 167 TE link between border LSRs, which are located on the boundary 168 between the higher-layer and lower-layer networks, and that the 169 ingress LSR does not have topology visibility in the lower layer. 170 If a single-layer path computation is applied for the higher-layer, 171 the path computation fails. On the other hand, inter-layer path 172 computation is able to provide a route in the higher-layer and a 173 suggestion that a lower-layer LSP be setup between border LSRs, 174 considering both layers�ETE topologies. 176 Lower-layer LSPs form a Virtual Network Topology (VNT), which can 177 be used for routing higher-layer LSPs or to carry IP traffic. 178 Inter-layer path computation for end-to-end LSPs in the higher- 179 layer network that span the lower-layer network may utilize the VNT, 180 and PCE is a candidate for computing the paths of such higher-layer 181 LSPs within the higher-layer network. The PCE-based path 182 computation model can: 184 - Perform a single computation on behalf of the ingress LSR using 185 information gathered from more than one layer. This mode is 186 referred to as Single PCE Computation in [PCE-ARCH]. 188 - Compute a path on behalf of the ingress LSR through cooperation 189 between PCEs responsible for each layer. This mode is referred to 190 as Multiple PCE Computation with inter-PCE communication in [PCE- 191 ARCH]. 193 - Perform separate path computations on behalf of the TE-LSP head- 194 end and each transit LSR that is the entry point to a new layer. 195 This mode is referred to as Multiple PCE Computation (without 196 inter-PCE communication) in [PCE-ARCH]. This option utilizes per- 197 layer path computation performed independently by successive PCEs. 199 The PCE computes and returns a path to the PCC that the PCC can use 200 to build an MPLS or GMPLS LSP once converted to an Explicit Route 201 Object (ERO) for use in RSVP-TE signaling. There are two options. 203 - Option 1: Mono-layer path. 204 The PCE computes a "mono layer" path, i.e. a path that includes 205 only TE-links from the same layer. There are two cases for this 206 option. In the first case the PCE computes a path that includes 207 already established lower-layer LSPs: that is the resulting ERO 208 includes sub-object(s) corresponding to lower-layer hierarchical 209 LSPs expressed as the TE link identifiers, which can be numbered 210 or unnumbered ones, of the hierarchical LSPs when advertised as TE 211 links in the higher-layer network. The TE link may be a regular TE 212 link that is actually established, or a virtual TE link that is not 213 established yet (see [MLN-REQ]). If it is a regular TE link, this 215 Oki et al Expires August 2006 4 216 does not trigger new lower-layer LSP setup, but the utilization of 217 existing lower-layer LSPs. If it is a virtual TE link, this 218 triggers a new lower-layer LSP setup (provided that there are 219 available resources in the lower layer). A transit LSR 220 corresponding to the entry point of the virtual TE link is expected 221 to trigger the new lower-layer LSP setup. Note that the path of a 222 virtual TE link is not necessarily known in advance, and this may 223 require path computation either on the entry point or on a PCE. The 224 second case is that the PCE computes a path that includes loose 225 hop(s). The higher layer would select which lower layers to use and 226 would select the entry and exit points from those layers, but would 227 not select the path across the layers. A transit LSR corresponding 228 to the entry point is expected to expand the loose hop (either 229 itself or relying on the services of a PCE). Path expansion process 230 on border LSR may result either in the selection of an existing 231 lower-layer LSP, or in the computation and setup of a new lower- 232 layer LSP. 234 - Option 2: Multi-layer path. The PCE computes a "multi-layer" path, 235 i.e. a path that includes TE links from distinct layers [RFC4206]. 236 Such a path can include the complete path of one or more lower- 237 layer LSPs that already exist or are not yet established. In the 238 latter case, the signaling of the higher-layer LSP will trigger the 239 establishment of the lower-layer LSPs. 241 4. Inter-layer Path Computation Models 243 As stated in Section 3, two PCE modes defined in the PCE 244 architecture can be used to perform inter-layer path computation. 245 They are discussed below. 247 4.1. Single PCE Inter-Layer Path Computation 249 In this model Inter-layer path computation is performed by a single 250 PCE that has topology visibility in all layers. Such a PCE is 251 called a multi-layer PCE. 253 In Figure 1, the network is comprised of two layers. LSR H1, H2, H3 254 and H4 belong to the higher layer, and LSRs L1 and L2 belong to the 255 lower layer. The PCE is a multi-layer PCE that has visibility into 256 both layers. It can perform end-to-end path computation across 257 layers (single PCE path computation). For instance, it can compute 258 an optimal path H2-L1-L2-H3-H4, for a higher layer LSP from H1 to 259 H4. This path includes the path of a lower layer LSP from H2 to H3, 260 already established or not. 262 ----- 263 | PCE | 264 ----- 265 ----- ----- ----- ----- 266 | LSR |--| LSR |................| LSR |--| LSR | 267 | H1 | | H2 | | H3 | | H4 | 268 ----- -----\ /----- ----- 270 Oki et al Expires August 2006 5 271 \----- -----/ 272 | LSR |--| LSR | 273 | L1 | | L2 | 274 ----- ----- 276 Figure 1 : Multi-Layer PCE �EA single PCE with multi-layer 277 visibility 279 4.2. Multiple PCE Inter-Layer Path Computation 281 In this model there is at least one PCE per layer, and each PCE has 282 topology visibility restricted to its own layer. These PCEs are 283 called mono-layer PCEs. Mono-layer PCEs collaborate to compute an 284 end-to-end optimal path across layers. 286 In Figure 2, there is one PCE in each layer. The PCEs from each 287 layer collaborate to compute an end-to-end path across layers. PCE 288 Hi is responsible for computations in the higher layer and may 289 �consult�Ewith PCE Lo to compute paths across the lower layer. PCE 290 Lo is responsible for path computation in the lower layer. A simple 291 example of cooperation between the PCEs could be: PCE Hi requests a 292 path H2-H3 from PCE Lo. Of course more complex cooperation may be 293 required if an end-to-end optimal path is desired. 295 ----- 296 | PCE | 297 | Hi | 298 --+-- 299 | 300 ----- ----- | ----- ----- 301 | LSR |--| LSR |............|...........| LSR |--| LSR | 302 | H1 | | H2 | | | H3 | | H4 | 303 ----- -----\ --+-- /----- ----- 304 \ | PCE | / 305 \ | Lo | / 306 \ ----- / 307 \ / 308 \----- -----/ 309 | LSR |--| LSR | 310 | L1 | | L2 | 311 ----- ----- 313 Figure 2 : Cooperating Mono-Layer PCEs �EMultiple PCEs with single- 314 layer visibility 316 4.3. General observation 318 - Depending on implementation details, inter-layer path computation 319 time in the Single PCE inter-layer path computation model may be 320 less than that of the Multiple PCE model with cooperating mono- 321 layer PCEs, because there is no requirement to exchange messages 322 between cooperating PCEs. 324 Oki et al Expires August 2006 6 325 - When TE topology for all layered networks is visible within one 326 routing domain, the single PCE inter-layer path computation model 327 may be adopted because a PCE is able to collect all layers�ETE 328 topologies by participating in only one routing domain. 330 - As the single PCE inter-layer path computation model uses more TE 331 topology information than is used by PCEs in the Multiple PCE path 332 computation model, it requires more computation power and memory. 334 5. Inter-Layer Path Control 336 5.1. VNT Management 338 As a result of inter-layer path computation, a PCE may determine 339 that there is insufficient bandwidth available in the higher-layer 340 network to support this or future higher-layer LSPs. The problem 341 might be resolved if new LSPs are provisioned across the lower- 342 layer network. Further, the modification, re-organization and new 343 provisioning of lower-layer LSPs may enable better utilization of 344 lower-layer network resources given the demands of the higher-layer 345 network. In other words, the VNT needs to be controlled or managed 346 in cooperation with inter-layer path computation. 348 A VNT Manager (VNTM) is defined as a network element that manages 349 and controls the VNT. PCE and "VNT Management" are distinct 350 functions that may or may not be co-located. To describe each 351 function clearly, VNTM is considered as a functional element in 352 this draft. 354 5.2. Inter-Layer Path Control Models 356 5.2.1. Cooperation model between PCE and VNTM 358 ----- ------ 359 | PCE |--->| VNTM | 360 ----- ------ 361 ^ : 362 : : 363 : : 364 v V 365 ----- ----- ----- ----- 366 | LSR |----| LSR |................| LSR |----| LSR | 367 | H1 | | H2 | | H3 | | H4 | 368 ----- -----\ /----- ----- 369 \----- -----/ 370 | LSR |--| LSR | 371 | L1 | | L2 | 372 ----- ----- 374 Figure 3: Cooperation model between PCE and VNTM 376 A multi-layer network consists of higher-layer and lower-layer 377 networks. LSRs H1, H2, H3, and H4 belong to the higher-layer 378 network, LSRs H2, L1, L2, and H3 belong to the lower-layer network, 380 Oki et al Expires August 2006 7 381 as shown in Figure 3. Consider that H1 requests PCE to compute an 382 inter-layer path between H1 and H4. There is no TE link in the 383 higher-layer between H2 and H3 before the path computation request. 385 The roles of PCE and VNTM are as follows. PCE performs inter-layer 386 path computation and is unable to supply a path because there is 387 not TE link between H2 and H3. The computation fails, but PCE 388 suggests to VNTM that a lower-layer LSP (H2-H3) should be 389 established to support future LSP requests. VNTM uses local policy 390 and possibly management/configuration input to determine how to 391 process the suggestion from PCE, and may request an ingress LSR 392 (e.g. H2) to establish a lower-layer LSP. VNTM or the ingress LSR 393 (H2) may use a PCE with visibility into the lower layer to compute 394 the path of this new LSP. 396 If the PCE cannot compute a path for the higher-layer LSP without 397 the establishment of a further lower-layer LSP, the PCE may notify 398 VNTM and wait for the lower-layer LSP to be set up and advertised 399 as a TE link. It can then compute the complete end-to-end path for 400 the higher-layer LSP and return the result to the PCC. In this case, 401 the PCC may be kept waiting some time, and it is important that the 402 PCC understands this. It is also important that the PCE and VNTM 403 have an agreement that the lower-layer LSP will be set up in a 404 timely manner, the PCE operates a timeout, or the PCE will be 405 notified by VNTM that no new LSP will become available. An example 406 of such a cooperative procedure between PCE and VNTM is as follows. 408 Step 1: H1 (PCC) requests PCE to compute a path between H1 and H4. 409 In the request, it indicates that inter-layer path computation is 410 allowed. 412 Step 2: As a result of the inter-layer path computation, PCE judges 413 that a new lower-layer LSP needs to be established. 415 Step 3: PCE suggests to VNTM that a new lower-layer LSP should be 416 established if necessary and if acceptable within VNTM�s policy 417 constraints. The inter-layer path route computed by PCE may include 418 one or more virtual TE links. If PCE knows the inclusion of the 419 virtual TE link(s) in the inter-layer route, PCE may suggest VNTM 420 that the corresponding new lower-layer LSP(s) should be established. 421 Otherwise, new lower-layer LSP(s) may be setup according to the 422 higher-layer signaling trigger model. 424 Step 4: VNTM requests an ingress LSR (e.g. H2) to establish a 425 lower-layer LSP. The request message may include a pre-computed 426 lower-layer LSP route obtained from the PCE responsible for the 427 lower-layer network. 429 Step 5: The ingress LSR starts signaling to establish a lower-layer 430 LSP. 432 Step 6: If the lower-layer LSP setup is completed, the ingress LSR 433 notifies VNTM that the LSP is complete and supplies the tunnel 434 information. 436 Oki et al Expires August 2006 8 437 Step 7: VNTM replies to PCE to inform it that the lower-layer LSP 438 is now established, and includes the lower-layer tunnel information. 439 Alternatively, PCE may get to know about the existence of the 440 lower-layer LSP when a new TE link in the higher-layer 441 corresponding to the lower-layer LSP is advertised to PCE through 442 the IGP. 444 Step 8: PCE replies to H1 (PCC) with a computed higher-layer LSP 445 route. The computed path is categorized as a mono-layer path that 446 includes the already-established lower layer-LSP. The higher-layer 447 route is specified as H2-H3-H4, where all hops are strict. 449 Step 9: H1 initiates signaling with the computed path H2-H3-H4 to 450 establish the higher-layer LSP. 452 5.2.2. Higher-Layer Signaling Trigger Model 454 ----- 455 | PCE | 456 ----- 457 ^ 458 : 459 : 460 v 461 ----- ----- ----- ----- 462 | LSR |----| LSR |................| LSR |--| LSR | 463 | H1 | | H2 | | H3 | | H4 | 464 ----- -----\ /----- ----- 465 \----- -----/ 466 | LSR |--| LSR | 467 | L1 | | L2 | 468 ----- ----- 470 Figure 4: Higher-layer signaling trigger model 472 Figure 4 shows the higher-layer signaling trigger model. As in the 473 case described in section 5.2.1, consider that H1 requests PCE to 474 compute an inter-layer path between H1 and H4. There is no TE link 475 in the higher-layer between H2 and H3 before the path computation 476 request. 478 If PCE judges that a lower-layer LSP needs to be established based 479 on the inter-layer path computation result, a lower-layer LSP is 480 established during the higher-layer signaling procedure. After PCE 481 completes inter-layer path computation, PCE sends a reply message 482 including explicit route to the ingress LSR (PCC). There are two 483 ways to express the higher-layer LSP route, which are a multi-layer 484 path and a mono-layer path that includes loose hop(s). 486 In the higher-layer signaling trigger model with a multi-layer path, 487 a high-layer LSP route includes a route for a lower-layer LSP that 488 is not yet established. An LSR that is located at the boundary 489 between the higher-layer and lower-layer networks, called a border 491 Oki et al Expires August 2006 9 492 LSR, receives a higher-layer signaling message and then starts to 493 setup the lower-layer LSP. 495 An example procedure of the signaling trigger model with a multi- 496 layer path is as follows. 498 Step 1: H1 (PCC) requests PCE to compute a path between H1 and H4. 499 The request indicates that inter-layer path computation is allowed. 501 Step 2: As a result of the inter-layer path computation, PCE judges 502 that a new lower-layer LSP needs to be established. 504 Step 3: PCE replies to H1 (PCC) with a computed multi-layer route 505 including higher-layer and lower-layer LSP routes. The route may be 506 specified as H2-L1-L2-H3-H4, where all hops are strict. 508 Step 4: H1 initiates higher-layer signaling using the computed 509 explicit router of H2-L1-L2-H3-H4. 511 Step 5: The border LSR (H2) that receives the higher-layer 512 signaling message starts lower-layer signaling to establish a 513 lower-layer LSP along the specified lower-layer route of L1-L2-H3. 514 That is, the border LSR recognizes the hops within the explicit 515 route that apply to the lower-layer network, verifies with local 516 policy that a new LSP is acceptable, and establishes the required 517 lower-layer LSP. Note that it is possible that a suitable lower- 518 layer LSP has been established (or become available) between the 519 time that the computation was performed and the moment when the 520 higher-layer signaling message reached the border LSR. In this case, 521 the border LSR may select such a lower-layer LSP without the need 522 to signal a new LSP provided that the lower-layer LSP satisfies the 523 explicit route in the higher-layer signaling request. 525 Step 6: After the lower-layer LSP is established, the higher-layer 526 signaling continues along the specified higher-layer route of H2- 527 H3-H4. 529 On the other hand, in the signaling trigger model with mono-layer 530 path, a higher-layer LSP route includes a loose or strict hop to 531 traverse the lower-layer network between the two border LSRs. In 532 the strict hop case, a virtual TE link may be advertised, but a 533 lower-layer LSP is not setup. A border LSR that receives a higher- 534 layer signaling message needs to determine a path for a new lower- 535 layer LSP. It applies local policy to verify that a new LSP is 536 acceptable and then either consults a PCE with responsibility for 537 the lower-layer network or computes the path by itself, and 538 initiates signaling to establish a lower-layer LSP. Again, it is 539 possible that a suitable lower-layer LSP has been established (or 540 become available) between the time that the higher-layer 541 computation was performed and the moment when the higher-layer 542 signaling message reached the border LSR. In this case, the border 543 LSR may select such a lower-layer LSP without the need to signal a 544 new LSP provided that the lower-layer LSP satisfies the explicit 545 route in the higher-layer signaling request. Since the higher-layer 547 Oki et al Expires August 2006 10 548 signaling request used a loose hop without specifying any specifics 549 of the path within the lower-layer network, the border LSR has 550 greater freedom to choose a lower-layer LSP than in the previous 551 example. 553 The difference between procedures of the signaling trigger model 554 with a multi-layer path and a mono-layer path is Step 5. Step 5 of 555 the signaling trigger model with a mono layer path is as follows: 557 Step 5�E The border LSR (H2) that receives the higher-layer 558 signaling message applies local policy to verify that a new LSP is 559 acceptable and then initiates establishment of a lower-layer LSP. 560 It either consults a PCE with responsibility for the lower-layer 561 network or computes the route by itself to expand the loose hop 562 route in the higher-layer path. 564 5.2.3. Examples of multi-layer ERO 566 PCE 567 ^ 568 : 569 : 570 V 571 H1--H2 H3--H4 572 \ / 573 L1==L2==L3--L4--L5 574 | 575 | 576 L6--L7 577 \ 578 H5--H6 580 Figure 5 Example of multi-layer network 582 This section describes how lower-layer LSP setup is performed in 583 the higher-layer signaling trigger model using an ERO that can 584 include subobjects in both the higher and lower layers. It gives 585 rise to several options for the ERO when it reaches the last LSR in 586 the higher layer network (H2). 587 1. The next subobject is a loose hop to H3 (mono layer ERO). 588 2. The next subobject is a strict hop to L1 followed by a loose hop 589 to H3. 590 3. The next subobjects are a series of hops (strict or loose) in 591 the lower-layer network followed by H3. For example, {L1(strict), 592 L3(loose), L5(loose), H3(strict)} 594 In the first, the lower layer can utilize any LSP tunnel that will 595 deliver the end-to-end LSP to H3. In the third case, the lower 596 layer must select an LSP tunnel that traverses L3 and L5. However, 597 this does not mean that the lower layer can or should use an LSP 598 from L1 to L3 and another from L3 to L5. 600 6. Choosing between inter-layer path control models 602 Oki et al Expires August 2006 11 603 This section compares the cooperation model between PCE and VNTM, 604 and the higher-layer signaling trigger model, in terms of VNTM 605 functions, border LSR functions, and higher-layer signaling time. 607 VNTM functions: 609 In the cooperation model, VNTM functions are required. In this 610 model, additional overhead communications between PCE and VNTM and 611 between VNTM and a border LSR are required. 613 In the higher-layer signaling trigger model, no VNTM functions are 614 required, and no such communications are required. 616 If VNTM functions are not supported in a multi-layer network, the 617 higher-layer signaling trigger model has to be chosen. 619 The inclusion of VNTM functionality allows better coordination of 620 cross-network LSP tunnels and application of network-wide policy 621 that is not available in the trigger model. 623 Border LSR functions: 625 In the higher-layer signaling trigger model, a border LSR must have 626 some additional functions. It needs to trigger lower-layer 627 signaling when a higher-layer path message suggests that lower- 628 layer LSP setup is necessary. The triggering signaling is also 629 required in the cooperation case when the VNTM support virtual TE 630 links. Note that, if only the cooperation model is applied, it is 631 required that a PCE knows whether a link is a regular TE link or 632 virtual TE link. 634 If the ERO in the higher-layer Path message uses a mono-layer path 635 or specifies loose hop, a border LSR receiving the Path message 636 MUST obtain a lower-layer route either by consulting PCE or by 637 using its own computation engine. If the ERO in the higher-layer 638 Path message uses multi-layer path, the border LSR MUST judge 639 whether lower-layer signaling is needed. 641 In the cooperation model, no additional function for triggered 642 signaling in border LSRs is required except when virtual TE links 643 are used. Therefore, if these additional functions are not 644 supported in border LSRs, the cooperation model, where a border LSR 645 is controlled by VNTM to set up a lower-layer LSP, has to be chosen. 647 Complete inter-layer LSP setup time: 649 Complete inter-layer LSP setup time includes inter-layer path 650 computation, signaling, and communication time between PCC and PCE, 651 PCE and VNTM, and VNTM and LSR. In the cooperation model, the 652 additional communication steps are required compared with the 653 higher-layer signaling trigger model. On the other hand, the 654 cooperation model provides better control at the cost of a longer 655 service setup time. 657 Oki et al Expires August 2006 12 658 Note that, in terms of higher-layer signaling time, in the higher- 659 layer signaling trigger model, the required time from when higher- 660 layer signaling starts to when it is completed, is more than that 661 of the cooperation model except when any virtual TE link is 662 included. This is because the former model requires lower-layer 663 signaling to take place during the higher-layer signaling. A 664 higher-layer ingress LSR has to wait for more time until the 665 higher-layer signaling is completed. A higher-layer ingress LSR is 666 required to be tolerant of longer path setup times. 668 An appropriate model is chosen, taking into all of the above 669 considerations. 671 7. Security Considerations 673 Inter-layer traffic engineering with PCE may raise new security 674 issues in both inter-layer path control models. 676 In the cooperation model between PCE and VNTM, when PCE judges a 677 new lower-layer LSP, communications between PCE and VNTM and 678 between VNTM and a border LSR are needed. In this case, there are 679 some security concerns that need to be addressed for these 680 communications. These communications should have some security 681 mechanisms to ensure authenticity, privacy and integrity. 683 In the higher-layer signaling trigger model, there are several 684 security concerns. First, PCE may inform PCC, which is located in 685 the higher-layer network, of multi-layer path information that 686 includes an ERO in the lower-layer network, while the PCC may not 687 have TE topology visibility into the lower-layer network. This 688 raises a security concern, where lower-layer hop information is 689 known to transit LSRs supporting a higher-layer LSP. Some security 690 mechanisms to ensure authenticity, privacy and integrity may be 691 used. 693 Security issues may also exist when a single PCE is granted full 694 visibility of TE information that applies to multiple layers. 696 8. Acknowledgment 698 We would like to thank Kohei Shiomoto, Ichiro Inoue, Julien Meuric 699 and Jean-Francois Peltier for their useful comments. 701 9. References 703 9.1. Normative Reference 705 [RFC2119] Bradner, S., "Key words for use in RFCs to indicate 706 requirements levels", RFC 2119, March 1997. 708 [RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching 709 Architecture", RFC 3945, October 2004. 711 Oki et al Expires August 2006 13 713 [RFC4206] Kompella, K., and Rekhter, Y., "Label Switched Paths 714 (LSP) Hierarchy with Generalized Multi-Protocol Label Switching 715 (GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005. 717 [RFC4208] G. Swallow et al., "Generalized Multiprotocol Label 718 Switching (GMPLS) User-Network Interface (UNI): Resource 719 ReserVation Protocol-Traffic Engineering (RSVP-TE) Support for the 720 Overlay Model", RFC 4208, October 2005. 722 9.2. Informative Reference 724 [PCE-ARCH] A. Farrel, JP. Vasseur and J. Ash, "Path Computation 725 Element (PCE) Architecture", draft-ietf-pce-architecture (work in 726 progress). 728 [PCE-COM-REQ] J. Ash, J.L Le Roux et al., "PCE Communication 729 Protocol Generic Requirements", draft-ietf-pce-comm-protocol-gen- 730 reqs (work in progress). 732 [PCE-DISC-REQ] JL Le Roux et al., "Requirements for Path 733 Computation Element (PCE) Discovery", draft-ietf-pce-discovery-reqs 734 (work in progress). 736 [MLN-REQ] K. Shiomoto et al., "Requirements for GMPLS-based multi- 737 region networks (MRN) ", draft-ietf-ccamp-gmpls-mln-reqs (work in 738 progress). 740 [PCE-INTER-LAYER-REQ] E. Oki et al., "PCC-PCE Communication 741 Requirements for Inter-Layer Traffic Engineering�E draft-ietf-pce- 742 inter-layer-req (work in progress). 744 [PCEP] JP. Vasseur et al, "Path Computation Element (PCE) 745 communication Protocol (PCEP) - Version 1 -�E draft-ietf-pce-pcep 746 (work in progress). 748 10. Authors' Addresses 750 Eiji Oki 751 NTT 752 3-9-11 Midori-cho, 753 Musashino-shi, Tokyo 180-8585, Japan 754 Email: oki.eiji@lab.ntt.co.jp 756 Jean-Louis Le Roux 757 France Telecom R&D, 758 Av Pierre Marzin, 759 22300 Lannion, France 760 Email: jeanlouis.leroux@francetelecom.com 762 Adrian Farrel 763 Old Dog Consulting 764 Email: adrian@olddog.co.uk 766 Oki et al Expires August 2006 14 768 11. 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