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Martinez-Julia 13 NICT 14 March 4, 2018 16 Interconnecting (or Stitching) Network Slice Subnets 17 draft-defoy-coms-subnet-interconnection-03 19 Abstract 21 This document defines the network slice (NS) subnet as a general 22 management plane concept that augments a baseline network slice model 23 with management attributes and operations enabling interconnections 24 (or stitching) between network slices. The description of NS subnet 25 interconnections is technology agnostic following the approach of the 26 COMS information model. Some interconnections may be implemented 27 using the interplay between management plane and gateways in the data 28 plane. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at https://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on September 5, 2018. 47 Copyright Notice 49 Copyright (c) 2018 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (https://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 65 1.1. Motivation and Roles of NS Subnet . . . . . . . . . . . . 3 66 1.2. Usage of NS Subnets . . . . . . . . . . . . . . . . . . . 3 67 1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 68 2. Information Model . . . . . . . . . . . . . . . . . . . . . . 5 69 2.1. Base Information Model . . . . . . . . . . . . . . . . . 5 70 2.2. Interconnection Anchors . . . . . . . . . . . . . . . . . 6 71 2.3. Interconnection Instances . . . . . . . . . . . . . . . . 8 72 2.4. Stitching Operation . . . . . . . . . . . . . . . . . . . 9 73 2.4.1. Operation Overview . . . . . . . . . . . . . . . . . 9 74 2.4.2. Stitching Scenarios . . . . . . . . . . . . . . . . . 10 75 3. Security Considerations . . . . . . . . . . . . . . . . . . . 11 76 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 77 5. Informative References . . . . . . . . . . . . . . . . . . . 11 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 80 1. Introduction 82 Network Slicing enables deployment and management of services with 83 diverse requirements on end-to-end partitioned virtual networks over 84 the same infrastructure, including networking, compute and storage 85 resources. [I-D.geng-coms-problem-statement] describes a problem 86 statement for supervised heterogeneous network slicing, enabling 87 users to deploy network slices including connectivity, computing and 88 storage components. 90 A base information model for Common Operations and Management on 91 network Slices (COMS) is currently being defined in 92 [I-D.qiang-coms-netslicing-information-model]. Nevertheless, 93 defining and managing a network slice (NS) end-to-end does not always 94 have to be done directly. It may be convenient to define and manage 95 separately subsets of an end-to-end slice. The concept of network 96 slice subnet is defined originally in [NGMN_Network_Slicing], though 97 we only need to retain its definition in the most universal form: 98 network slice subnets are similar to network slices in most ways but 99 cannot be operated in isolation as a complete network slice. They 100 can however be interconnected with other NS subnets to form a 101 complete, end-to-end network slice (i.e. interconnection and/or 102 stitching of NS subnets). To summarize: a NS subnet can be seen as a 103 network slice with unconnected links. The term "network slice 104 segment" has also occasionally been used to designate a similar 105 concept. 107 1.1. Motivation and Roles of NS Subnet 109 NS subnet is a management plane concept that facilitates 110 interconnections (also known as stitching) of network slices. It 111 augments the base COMS information model, that can be used to 112 represent an end-to-end network slice. The extensions described in 113 this document can be used to represent a slice subnet instead, and 114 can also be used to represent an interconnection inside an end-to-end 115 slice, i.e. they aim to represent interconnection points both 116 "before" and "after" the interconnection takes place. Operations 117 such as stitching subnets are also described. 119 The description of NS subnet interconnections is technology agnostic 120 following the approach of the COMS information model. Some 121 interconnections may be implemented using the interplay between 122 management plane and gateways in the data plane. 123 [I-D.homma-coms-slice-gateway] describes the requirements on such 124 data plane network elements, and will provide input for the 125 management plane mechanisms described in the present document. 127 1.2. Usage of NS Subnets 129 Using NS subnets can help: 131 o Isolate management and maintenance of different portions of a 132 network slice, over multiple infrastructure domains, or even 133 within a single domain. For example, in Figure 1, NS orchestrator 134 (NSO) 2 manages subnet A, in isolation from subnets B and C 135 managed by NSO 3. NSO 1 can still manage the end-to-end slice as 136 a whole, but it does not need to deal in detail with each subnet. 138 o Isolate mapping towards different infrastructure technologies, 139 even within the same domain. This can simplify NS orchestrator 140 implementation, since each NSO can specialize in managing a 141 smaller set of technologies. 143 o Enable advanced functions such as sharing a slice subnet between 144 several slices, or substituting one slice subnet for another, e.g. 145 for coping with load. 147 +-----------+ 148 ******| NS Orch. 1|******** 149 * +-----------+ * 150 (COMS A) * * (COMS B+C) 151 * * 152 +-----------+ +-----------+ 153 | NS Orch. 2| | NS Orch. 3|***** 154 +-----------+ +-----------+ * 155 * * * 156 (COMS A) * (COMS B) * * (COMS C) 157 * A-B Inter- * B-C Inter- * 158 * connection * connection * 159 +-----------------+ . +-----------------+ . +-----------------+ 160 | +--+ | . | +--+ | . | +--+ | 161 | | +---------------------+ +--------------------+ | | 162 | ++-+ | . | ++-+ | . | ++-+ | 163 | | | . | | | . | | | 164 | +---+ | +---+ | . | +---+ | +---+ | . | +---+ | +---+ | 165 | | +-+--+ +-----------+ +-+--+ +----------+ +-+--+ | | 166 | +---+ +---+ | . | +---+ +---+ | . | +---+ +---+ | 167 +-----------------+ . +-----------------+ . +-----------------+ 169 <.. NS subnet A ..> <.. NS subnet B ..> <.. NS subnet C ..> 171 <....................... end-to-end slice .........................> 173 Figure 1: Overview of Network Slice Subnets Interconnection 175 Figure 1 illustrates how an end-to-end network slice may be composed 176 of multiple slice subnets, each managed independently by a same or 177 different NSO. In multi-administrative domain scenarios, using NS 178 subnets can help limiting the information that needs to be shared 179 between domains. At the infrastructure layer (i.e. in the data 180 plane), the interconnection between NS subnets may involve: 182 o a gateway, that performs protocol and/or identifier/label 183 translation as needed, 185 o two gateways, especially in cases where interconnected NS subnets 186 are in different administrative domains, 188 o nothing at all, in cases where the interconnection point can be 189 abstracted away, e.g. when the NS subnets share a common 190 infrastructure. In this case nodes from both NS subnets end up 191 being directly interconnected between each other. 193 More detailed usage scenarios are described in Section 2.4.2. 195 1.3. Terminology 197 Network slicing related terminology used in this document should be 198 interpreted as described in [I-D.geng-coms-problem-statement]. 200 Network Slice Subnet (NS subnet): a network system comprised of 201 groups of connectivity, compute and storage resources, possibly 202 including network functions and network management entities, forming 203 a complete instantiated logical/physical network in support of 204 certain network and service characteristics. A network slice subnet 205 cannot be activated in isolation as an overall (end-to-end) network 206 slice, but must be interconnected with other slice subnets to form 207 one. 209 NS Stitching: a management operation consisting in creating an end- 210 to-end NS or a larger NS subnet, by interconnecting a set of NS 211 subnets together. 213 Interconnection Anchor: a management plane entity, part of a NS 214 subnet model, representing an end point for use in future stitching 215 operation. 217 Interconnection Instance (or Interconnect): a management plane 218 entity, part of a NS subnet model, representing an interconnection 219 realized by a stitching operation. It is distinct from a (data 220 plane) gateway: an interconnect may be realized with or without using 221 a gateway in the data plane. 223 2. Information Model 225 2.1. Base Information Model 227 The information model we use as base for network slicing is currently 228 being defined in [I-D.qiang-coms-netslicing-information-model]. It 229 is itself based on the network topology model ietf-network defined in 230 [I-D.ietf-i2rs-yang-network-topo], in which networks are composed of 231 nodes and links, and in which termination points (TP), defined in 232 nodes, are used to define source and destination of links. 234 A network slice data model instance, i.e. a "network" attribute of 235 the "ietf-network" model augmented using 236 [I-D.qiang-coms-netslicing-information-model]), represents a network 237 slice. When such a data model instance includes at least an 238 "interconnection anchor", as defined below, it represents a network 239 slice subnet instance. 241 At high level, the extensions defined in this document will augment 242 nodes and termination points: 244 module: ietf-network 245 +--rw networks 246 +--rw network* [network-id] 247 +--rw network-id 248 +--rw network-types 249 +--rw supporting-network* [network-ref] 250 | +--rw network-ref 251 +--rw node* [node-id] 252 | +--... (augmented with attributes for 253 | | anchor/interconnection nodes) 254 | +--rw nt:termination-point* [tp-id] 255 | | ... (augmented with attributes for 256 | | anchor/interconnection TP) 258 2.2. Interconnection Anchors 260 To represent an anchor point for future interconnections (i.e. an 261 unconnected end of a link), a simple solution is to use an 262 "interconnection anchor" termination point (or anchor TP). Within 263 the data model describing a subnet, any link not entirely contained 264 within the NS subnet must be terminated with such an anchor TP as 265 source or destination. An anchor TP belongs to a "node" attribute, 266 which we refer to as interconnection anchor node (or anchor node). 267 Anchor nodes should not include non-anchor TP or serve other non- 268 anchor related purposes (e.g. should not include any compute or 269 storage unit), in order to simplify the stitching operation. For 270 example, it will be easier to handle the case where the 271 interconnection anchors are abstracted away during a stitching 272 operation. Several anchor TPs can be grouped together in an anchor 273 node, and such grouping may be used as a hint during a stitching 274 operation (e.g. to place all interconnection points at a same 275 location). 277 As described in Figure 2, we represent a network slice subnet as a 278 network slice that also has one or more anchor nodes, which terminate 279 (at anchor TPs) links that need to be interconnected with external 280 nodes (cross-subnet links). 282 Slice Provider 283 | 284 +---------------------------------v---------------------------------+ 285 | Network Slice Orchestrator | 286 | | 287 | +---------------------------------------------------------------+ | 288 | | Data model: network slice composed of NS subnet 1 and 2 | | 289 | | | | 290 | | Network Slice Subnet 1 Network Slice Subnet 2 | | 291 | | +---------------------------+ +----------------------------+ | | 292 | | | cross-subnet link | | cross-subnet | | | 293 | | | +----------------+ | | link +------+ | | | 294 | | | | | | | +--------o node | | | | 295 | | | | |Interconnection| +---o--+ | | | 296 | | |+---o--+ +-------|-----+--+------|------+ | | | | 297 | | || node | | | | | | | | | | | 298 | | |+---o--+ | +-----|---+ | | +----|----+ | | | | | 299 | | | | | | | | | | | | | | | | | | 300 | | | | | | O - - - - - - - O | | | | | | 301 | | | | | | | | | | | | | | | | 302 | | | | | | anchor | | | | anchor | | | | | | 303 | | | | | | node | | | | node | | | | | | 304 | | | | | | | | | | | | +---+ | | | 305 | | | | | | O - - - - - - - O | | | | | | 306 | | | | | | | | | | | | | | | | | | 307 | | | | | +-----|---+ | | +----|----+ | +---o--+ | | | 308 | | | | | | | | | | | node | | | | 309 | | | | +-------|-----+--+------|------+ +---o--+ | | | 310 | | | | +------+ | | | | | | | | 311 | | | +-o node o-------+ | | +----------------+ | | | 312 | | | +------+ cross-subnet| | cross-subnet | | | 313 | | | link | | link | | | 314 | | +---------------------------+ +----------------------------+ | | 315 | +---------------------------------------------------------------+ | 316 +--------------------------------+----------------------------------+ 317 | 318 v 319 Network Infrastructure 321 Legend: o = termination point, O = anchor termination point 323 Figure 2: Network Slice Subnets Interconnection 325 Attributes of interconnection anchor nodes and termination points 326 include: 328 o Information enabling NS orchestrators to match anchor nodes and 329 TPs from both NS during a stitching operation. A label may be a 330 simple way to enable this. 332 o Information to help locate the interconnection. For example, it 333 could be a (sub-)domain name or geo-location information, that 334 indicates where the interconnection point should be located. This 335 can help for example in cases where the subnet is instantiated 336 before stitching. 338 o Information to help select the type of interconnection 339 establishment: for example, this can indicate a preference for 340 using interconnection over a gateway, or for abstracting away the 341 interconnection point in the infrastructure plane. 343 +--rw node* [node-id] 344 +-- (...) 345 +-- anchor_node_config 346 | +-- label (and/or other auto stitching help) 347 | +-- hint for location (domain, geolocation, etc.) 348 | +-- hint for type (1 gateway, 2 gateways, ...) 349 +--rw nt:termination-point* [tp-id] 350 +-- (...) 351 +-- anchor_tp_config 352 +-- label (and/or other auto stitching help) 353 +-- location (domain, geolocation, etc.) 354 +-- type (1 gateway, 2 gateways, ...) 356 2.3. Interconnection Instances 358 There are two options for representing post-stitching network slices 359 (or subnets). They are not mutually exclusive: 361 o Option 1: subnet data models are updated with information 362 describing the interconnection (e.g. anchor TPs and nodes are 363 updated with new attributes representing the existing connection, 364 if necessary). 366 o Option 2: a new data model is generated to represent the resulting 367 network slice (or subnet). In this composite data model, the 368 interconnection may or may not be represented, this can be a 369 choice made by the operator. 371 Option 1 and 2 can be used concurrently in a network. For example, a 372 parent NS orchestrator may manage stitched NS subnets through 373 underlying NS orchestrators, and at the same time expose to the NS 374 operator a composite data model representing the resulting end-to-end 375 slice. 377 To represent an existing interconnection in option 1, a simple 378 solution is to add attributes to existing anchor nodes and anchor 379 TPs. Those attributes will be described below. They aim to describe 380 state and configuration associated with an active interconnection. 382 To represent an existing interconnection in option 2, a simple 383 solution is to create new interconnection instance nodes and 384 termination point. The same attributes as in option 1 may be 385 associated with these nodes and TPs. 387 Attributes of interconnection instance nodes and termination points 388 include: 390 o State information (interconnection type, status, location...). 392 o Service assurance related information: besides measurements (on 393 throughput, loss rate, etc.), triggers depending on throughput, 394 latency, etc. can be linked with a management action or event. A 395 NS operator can use such events to take the decision to disable a 396 NS subnet, replace a NS subnet with another, etc. to maintain 397 overall service performance. 399 +--rw node* [node-id] 400 +-- (...) 401 +-- interconnection_instance_node_state 402 | +-- status 403 | +-- location (domain, geolocation, etc.) 404 | +-- type (1 gateway, 2 gateways, ...) 405 +-- interconnection_instance_node_service_assurance 406 | +-- events (including triggers and event IDs) 407 | +-- measurements 408 +--rw nt:termination-point* [tp-id] 409 +-- (...) 410 +-- interconnection_instance_tp_state 411 | +-- status 412 | +-- location (domain, geolocation, etc.) 413 | +-- type (1 gateway, 2 gateways, ...) 414 +-- interconnection_instance_node_service_assurance 415 +-- events (including triggers and event IDs) 416 +-- measurements 418 2.4. Stitching Operation 420 2.4.1. Operation Overview 422 Stitching is an operation that takes two or more NS subnets as input, 423 and produces a single composite NS subnet or end-to-end slice. It 424 may occur when the slice subnets are being instantiated, or later. 426 The first step in this operation is to identify the anchors that will 427 be used in the interconnection. This may be done by an automated 428 algorithm that matches the possible interconnection points and 429 decides which one will be used, according to the policies established 430 by the NS operator. The operation in this case will require the 431 presence of semantically-rich attributes in the candidate anchors to 432 enable automatic matching without human intervention. 434 Other attributes of slices and anchors will also influence the 435 operation and the resulting stitched (composite) object. For 436 instance, network links that are interconnected must have compatible 437 QoS attributes. Moreover, available networking protocols must also 438 match among the underlying network elements that are being stitched. 439 Otherwise, the operation will fail unless the NS operator (based on 440 policy and/or NS subnet attributes) enables it to search for, and 441 use, some "bridge" element in the underlying infrastructure. 443 2.4.2. Stitching Scenarios 445 This section briefly describes examples of usage for subnet 446 stitching. 448 Traversal through a transport network. 450 Let's consider a network slice composed of (NS) subnet-A, and 451 subnet-C (Figure 3). Subnet-A and subnet-C are deployed in 452 independent domains and are mapped into a COMS information model; 453 in order to stitch these two together a transport segment is 454 needed. N1 and N2 are anchor nodes within NS subnets A and C. 455 Segment-B could be a simple link between the two NS subnets but it 456 may also be a TE-link made available by a transport network 457 provider. Segment-B may be involved in the stitching operation in 458 one of several ways: 460 Segment-B may be set up as part of the stitching operation 461 between NS subnets A and C, as a form of "bridge" mentioned in 462 Section 2.4. Segment-B will need to comply with service 463 specific traffic constraints that are determined during the 464 stitching operation, possibly using attributes from NS subnets 465 A and C. In this case, the data plane implementation of N1 and 466 N2 in the composite slice may be, for example, 2 distinct 467 gateway functions terminating segment-B. 469 Segment-B may alternatively be represented as a distinct NS 470 subnet, e.g. in cases where segment-B is complex and/or 471 involves multiple network functions. In this case, the 472 stitching operation may therefore involve 3 NS subnets A-B-C. 474 +-----------+ +----------+ 475 | +--+ | ______ | +--+ | 476 | |N1+==========(______)============|N2| | 477 | +--+ | --transport-- | +--+ | 478 +-----------+ +----------+ 479 --subnet-A--- --segment-B------ --subnet-C-- 480 <---------------end to end slice ------------> 482 Figure 3: Example of NS subnets interconnection through transport 483 network 485 Subnets in a single domain. 487 In this scenario multiple network slice subnets are defined as 488 basic building blocks with specific service functions (or chains), 489 topologies and traffic handling characteristics. These building 490 blocks can be assembled through stitching to build end-to-end 491 customized slices, but also to dynamically extend slices to adapt 492 to traffic load. Additionally, stitching can also be used to 493 share building blocks between multiple slices, e.g. to 494 interconnect multiple slices with a shared function. In all these 495 cases, interconnection instances may be entirely abstracted away, 496 although they may also be implemented through one or multiple 497 gateways, e.g. when stitched subnets belong to different sub- 498 domains. 500 3. Security Considerations 502 Access control mechanisms for managing network slices can likely be 503 reused for network slice subnets, since their models should be 504 similar to each other. 506 Stitching 2 NS subnets together may be subject to some form of 507 authorization by a NS tenant. 509 4. IANA Considerations 511 This document has no actions for IANA. 513 5. Informative References 515 [I-D.geng-coms-problem-statement] 516 67, 4., Wang, L., Slawomir, S., Qiang, L., Matsushima, S., 517 Galis, A., and L. Contreras, "Problem Statement of 518 Supervised Heterogeneous Network Slicing", draft-geng- 519 coms-problem-statement-01 (work in progress), October 520 2017. 522 [I-D.homma-coms-slice-gateway] 523 Homma, S. and X. Foy, "Gateway Function for Network 524 Slicing", draft-homma-coms-slice-gateway-00 (work in 525 progress), January 2018. 527 [I-D.ietf-i2rs-yang-network-topo] 528 Clemm, A., Medved, J., Varga, R., Bahadur, N., 529 Ananthakrishnan, H., and X. Liu, "A Data Model for Network 530 Topologies", draft-ietf-i2rs-yang-network-topo-20 (work in 531 progress), December 2017. 533 [I-D.qiang-coms-netslicing-information-model] 534 Qiang, L., Galis, A., 67, 4., kiran.makhijani@huawei.com, 535 k., Martinez-Julia, P., Flinck, H., and X. Foy, 536 "Technology Independent Information Model for Network 537 Slicing", draft-qiang-coms-netslicing-information-model-02 538 (work in progress), January 2018. 540 [NGMN_Network_Slicing] 541 NGMN, "Description of Network Slicing Concept", 10 2016, 542 . 545 Authors' Addresses 547 Xavier de Foy 548 InterDigital Inc. 549 1000 Sherbrooke West 550 Montreal 551 Canada 553 Email: Xavier.Defoy@InterDigital.com 555 Akbar Rahman 556 InterDigital Inc. 557 1000 Sherbrooke West 558 Montreal 559 Canada 561 Email: Akbar.Rahman@InterDigital.com 562 Alex Galis 563 University College London 564 Torrington Place 565 London WC1E 7JE 566 United Kingdom 568 Email: a.galis@ucl.ac.uk 570 Kiran Makhijani 571 Huawei Technologies 572 2890 Central Expressway 573 Santa Clara CA 95050 574 USA 576 Email: kiran.makhijani@huawei.com 578 Li Qiang 579 Huawei Technologies 580 Huawei Campus, No. 156 Beiqing Rd. 581 Beijing 100095 582 China 584 Email: qiangli3@huawei.com 586 Shunsuke Homma 587 NTT, Corp. 588 3-9-11, Midori-cho 589 Musashino-shi, Tokyo 180-8585 590 Japan 592 Email: homma.shunsuke@lab.ntt.co.jp 594 Pedro Martinez-Julia 595 National Institute of Information and Communications Technology 596 Japan 598 Email: pedro@nict.go.jp