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Rahman 4 Intended status: Informational InterDigital Inc. 5 Expires: September 9, 2020 A. Galis 6 University College London 7 K. Makhijani 8 L. Qiang 9 Huawei Technologies 10 S. Homma 11 NTT 12 P. Martinez-Julia 13 NICT 14 March 8, 2020 16 Interconnecting (or Stitching) Network Slice Subnets 17 draft-defoy-coms-subnet-interconnection-04 19 Abstract 21 This document defines the network slice (NS) subnet as a general 22 management plane concept that augments a baseline YANG network slice 23 model with management attributes and operations enabling 24 interconnections (or stitching) between network slices. The 25 description of NS subnet interconnections is technology agnostic, and 26 is not tied to a particular implementation of the interconnection in 27 data plane. 29 Status of This Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at https://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on September 9, 2020. 46 Copyright Notice 48 Copyright (c) 2020 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (https://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 64 1.1. Motivation and Roles of NS Subnet . . . . . . . . . . . . 3 65 1.2. Usage of NS Subnets . . . . . . . . . . . . . . . . . . . 3 66 1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 67 2. Information Model . . . . . . . . . . . . . . . . . . . . . . 5 68 2.1. Base Information Model . . . . . . . . . . . . . . . . . 5 69 2.2. Interconnection Anchors . . . . . . . . . . . . . . . . . 6 70 2.3. Interconnection Instances . . . . . . . . . . . . . . . . 8 71 2.4. Stitching Operation . . . . . . . . . . . . . . . . . . . 9 72 2.4.1. Operation Overview . . . . . . . . . . . . . . . . . 9 73 2.4.2. Stitching Scenarios . . . . . . . . . . . . . . . . . 10 74 3. Security Considerations . . . . . . . . . . . . . . . . . . . 11 75 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 76 5. Informative References . . . . . . . . . . . . . . . . . . . 11 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 79 1. Introduction 81 Network Slicing enables deployment and management of services with 82 diverse requirements on end-to-end partitioned virtual networks over 83 the same infrastructure, including networking, compute and storage 84 resources. There were recent efforts in the IETF to define a 85 transport slice ([I-D.nsdt-teas-transport-slice-definition]) and to 86 define a north-bound interface for such a transport slice 87 ([I-D.contreras-teas-slice-nbi]). The mapping of transport slices in 88 5G mobile systems is also studied in [I-D.clt-dmm-tn-aware-mobility] 89 and [I-D.geng-teas-network-slice-mapping]. 91 Network slices may be managed through usage of YANG data models. For 92 example, [I-D.liu-teas-transport-network-slice-yang] describes how 93 existing YANG models can be augmented with network slice attributes. 95 Nevertheless, defining and managing a network slice (NS) end-to-end 96 does not always have to be done directly. It may be convenient to 97 define and manage separately subsets of an end-to-end slice. The 98 concept of network slice subnet is defined originally in 99 [NGMN_Network_Slicing], though we only need to retain its definition 100 in the most universal form: network slice subnets are similar to 101 network slices in most ways but cannot be operated in isolation as a 102 complete network slice (e.g., a NS subnet can be seen as a network 103 slice with unconnected links). NS subnets are interconnected with 104 other NS subnets to form a complete, end-to-end network slice (i.e. 105 interconnection and/or stitching of NS subnets). In the present 106 draft, we describe a data model for describing interconnections 107 between NS subnets, that enables assembling them in a hierarchical 108 fashion. 110 1.1. Motivation and Roles of NS Subnet 112 NS subnet is a management plane concept that facilitates 113 interconnections (also known as stitching) of network slices. It 114 augments the base slice information model, that can be used to 115 represent an end-to-end network slice. The extensions described in 116 this document can be used to represent a slice subnet instead, and 117 can also be used to represent an interconnection inside an end-to-end 118 slice, i.e. they aim to represent interconnection points both 119 "before" and "after" the interconnection takes place. Operations 120 such as stitching subnets are also described. 122 The description of NS subnet interconnections is technology agnostic 123 following the approach of the slice information model. Some 124 interconnections may be implemented using the interplay between 125 management plane and gateways in the data plane. 126 [I-D.homma-rtgwg-slice-gateway] describes the requirements on such 127 data plane network elements, and will provide input for the 128 management plane mechanisms described in the present document. 130 1.2. Usage of NS Subnets 132 Using NS subnets can help: 134 o Isolate management and maintenance of different portions of a 135 network slice, over multiple infrastructure domains, or even 136 within a single domain. For example, in Figure 1, NS orchestrator 137 (NSO) 2 manages subnet A, in isolation from subnets B and C 138 managed by NSO 3. NSO 1 can still manage the end-to-end slice as 139 a whole, but it does not need to deal in detail with each subnet. 141 o Isolate mapping towards different infrastructure technologies, 142 even within the same domain. This can simplify NS orchestrator 143 implementation, since each NSO can specialize in managing a 144 smaller set of technologies. 146 o Enable advanced functions such as sharing a slice subnet between 147 several slices, or substituting one slice subnet for another, e.g. 148 for coping with load. 150 +-----------+ 151 ******| NS Orch. 1|******** 152 * +-----------+ * 153 * * 154 * * 155 +-----------+ +-----------+ 156 | NS Orch. 2| | NS Orch. 3|***** 157 +-----------+ +-----------+ * 158 * * * 159 * * * 160 * A-B Inter- * B-C Inter- * 161 * connection * connection * 162 +-----------------+ . +-----------------+ . +-----------------+ 163 | +--+ | . | +--+ | . | +--+ | 164 | | +---------------------+ +--------------------+ | | 165 | ++-+ | . | ++-+ | . | ++-+ | 166 | | | . | | | . | | | 167 | +---+ | +---+ | . | +---+ | +---+ | . | +---+ | +---+ | 168 | | +-+--+ +-----------+ +-+--+ +----------+ +-+--+ | | 169 | +---+ +---+ | . | +---+ +---+ | . | +---+ +---+ | 170 +-----------------+ . +-----------------+ . +-----------------+ 172 <.. NS subnet A ..> <.. NS subnet B ..> <.. NS subnet C ..> 174 <....................... end-to-end slice .........................> 176 Figure 1: Overview of Network Slice Subnets Interconnection 178 Figure 1 illustrates how an end-to-end network slice may be composed 179 of multiple slice subnets, each managed independently by a same or 180 different NSO. In multi-administrative domain scenarios, using NS 181 subnets can help limiting the information that needs to be shared 182 between domains. At the infrastructure layer (i.e. in the data 183 plane), the interconnection between NS subnets may involve: 185 o a gateway, that performs protocol and/or identifier/label 186 translation as needed, 188 o two gateways, especially in cases where interconnected NS subnets 189 are in different administrative domains, 191 o nothing at all, in cases where the interconnection point can be 192 abstracted away, e.g. when the NS subnets share a common 193 infrastructure. In this case nodes from both NS subnets end up 194 being directly interconnected between each other. 196 More detailed usage scenarios are described in Section 2.4.2. 198 1.3. Terminology 200 Network slicing terminology, especially focusing on transport slices, 201 is defined in [I-D.nsdt-teas-transport-slice-definition]. 203 Network Slice Subnet (NS subnet): a network slice designed to be 204 interconnected with other network slices. 206 NS Stitching: a management operation consisting in creating an end- 207 to-end NS or a larger NS subnet, by interconnecting a set of NS 208 subnets together. 210 Interconnection Anchor: a management plane entity, part of a NS 211 subnet model, representing an end point for use in future stitching 212 operation. 214 Interconnection Instance (or Interconnect): a management plane 215 entity, part of a NS subnet model, representing an interconnection 216 realized by a stitching operation. It is distinct from a (data 217 plane) gateway: an interconnect may be realized with or without using 218 a gateway in the data plane. 220 2. Information Model 222 2.1. Base Information Model 224 The information model we use as base for network slicing is the 225 network topology model ietf-network defined in [RFC8345], in which 226 networks are composed of nodes and links, and in which termination 227 points (TP), defined in nodes, are used to define source and 228 destination of links. 230 A network slice data model instance, i.e. a YANG data model augmented 231 using [I-D.liu-teas-transport-network-slice-yang]), represents a 232 network slice. When such a data model instance includes at least an 233 "interconnection anchor", as defined below, it represents a network 234 slice subnet instance. 236 At high level, the extensions defined in this document will augment 237 nodes and termination points: 239 module: ietf-network 240 +--rw networks 241 +--rw network* [network-id] 242 +--rw network-id 243 +--rw network-types 244 +--rw supporting-network* [network-ref] 245 | +--rw network-ref 246 +--rw node* [node-id] 247 | +--... (augmented with attributes for 248 | | anchor/interconnection nodes) 249 | +--rw nt:termination-point* [tp-id] 250 | | ... (augmented with attributes for 251 | | anchor/interconnection TP) 253 2.2. Interconnection Anchors 255 To represent an anchor point for future interconnections (i.e. an 256 unconnected end of a link), a simple solution is to use an 257 "interconnection anchor" termination point (or anchor TP). Within 258 the data model describing a subnet, any link not entirely contained 259 within the NS subnet must be terminated with such an anchor TP as 260 source or destination. An anchor TP belongs to a "node" attribute, 261 which we refer to as interconnection anchor node (or anchor node). 262 Several anchor TPs can be grouped together in an anchor node, and 263 such grouping may be used as a hint during a stitching operation 264 (e.g. to place all interconnection points at a same location). 266 Figure 2 represents 2 interconnected network slice subnets. 268 Slice Provider 269 | 270 +---------------------------------v---------------------------------+ 271 | Network Slice Orchestrator | 272 | | 273 | +---------------------------------------------------------------+ | 274 | | Data model: network slice composed of NS subnet 1 and 2 | | 275 | | | | 276 | | Network Slice Subnet 1 Network Slice Subnet 2 | | 277 | | +---------------------------+ +----------------------------+ | | 278 | | | cross-subnet link | | cross-subnet | | | 279 | | | +----------------+ | | link +------+ | | | 280 | | | | | | | +--------o node | | | | 281 | | | | |Interconnection| +---o--+ | | | 282 | | |+---o--+ +-------|-----+--+------|------+ | | | | 283 | | || node | | | | | | | | | | | 284 | | |+---o--+ | +-----|---+ | | +----|----+ | | | | | 285 | | | | | | | | | | | | | | | | | | 286 | | | | | | O - - - - - - - O | | | | | | 287 | | | | | | | | | | | | | | | | 288 | | | | | | anchor | | | | anchor | | | | | | 289 | | | | | | node | | | | node | | | | | | 290 | | | | | | | | | | | | +---+ | | | 291 | | | | | | O - - - - - - - O | | | | | | 292 | | | | | | | | | | | | | | | | | | 293 | | | | | +-----|---+ | | +----|----+ | +---o--+ | | | 294 | | | | | | | | | | | node | | | | 295 | | | | +-------|-----+--+------|------+ +---o--+ | | | 296 | | | | +------+ | | | | | | | | 297 | | | +-o node o-------+ | | +----------------+ | | | 298 | | | +------+ cross-subnet| | cross-subnet | | | 299 | | | link | | link | | | 300 | | +---------------------------+ +----------------------------+ | | 301 | +---------------------------------------------------------------+ | 302 +--------------------------------+----------------------------------+ 303 | 304 v 305 Network Infrastructure 307 Legend: o = termination point, O = anchor termination point 309 Figure 2: Network Slice Subnets Interconnection 311 Attributes of interconnection anchor nodes and termination points 312 include: 314 o Information enabling NS orchestrators to match anchor nodes and 315 TPs from both NS during a stitching operation. A label may be a 316 simple way to enable this. 318 o Information to help locate the interconnection. For example, it 319 could be a (sub-)domain name or geo-location information, that 320 indicates where the interconnection point should be located. This 321 can help for example in cases where the subnet is instantiated 322 before stitching. 324 o Information to help select the type of interconnection 325 establishment: for example, this can indicate a preference for 326 using interconnection over a gateway, or for abstracting away the 327 interconnection point in the infrastructure plane. 329 +--rw node* [node-id] 330 +-- (...) 331 +-- anchor_node_config 332 | +-- label (and/or other auto stitching help) 333 | +-- hint for location (domain, geolocation, etc.) 334 | +-- hint for type (1 gateway, 2 gateways, ...) 335 +--rw nt:termination-point* [tp-id] 336 +-- (...) 337 +-- anchor_tp_config 338 +-- label (and/or other auto stitching help) 339 +-- location (domain, geolocation, etc.) 340 +-- type (1 gateway, 2 gateways, ...) 342 2.3. Interconnection Instances 344 There are two options for representing post-stitching network slices 345 (or subnets). They are not mutually exclusive: 347 o Option 1: subnet data models are updated with information 348 describing the interconnection (e.g. anchor TPs and nodes are 349 updated with new attributes representing the existing connection, 350 if necessary). 352 o Option 2: a new data model is generated to represent the resulting 353 network slice (or subnet). In this composite data model, the 354 interconnection may or may not be represented, this can be a 355 choice made by the operator. 357 Option 1 and 2 can be used concurrently in a network. For example, a 358 parent NS orchestrator may manage stitched NS subnets through 359 underlying NS orchestrators, and at the same time expose to the NS 360 operator a composite data model representing the resulting end-to-end 361 slice. 363 To represent an existing interconnection in option 1, a simple 364 solution is to add attributes to existing anchor nodes and anchor 365 TPs. Those attributes will be described below. They aim to describe 366 state and configuration associated with an active interconnection. 368 To represent an existing interconnection in option 2, a simple 369 solution is to create new interconnection instance nodes and 370 termination point. The same attributes as in option 1 may be 371 associated with these nodes and TPs. 373 Attributes of interconnection instance nodes and termination points 374 include: 376 o State information (interconnection type, status, location...). 378 o Service assurance related information: besides measurements (on 379 throughput, loss rate, etc.), triggers depending on throughput, 380 latency, etc. can be linked with a management action or event. A 381 NS operator can use such events to take the decision to disable a 382 NS subnet, replace a NS subnet with another, etc. to maintain 383 overall service performance. 385 +--rw node* [node-id] 386 +-- (...) 387 +-- interconnection_instance_node_state 388 | +-- status 389 | +-- location (domain, geolocation, etc.) 390 | +-- type (1 gateway, 2 gateways, ...) 391 +-- interconnection_instance_node_service_assurance 392 | +-- events (including triggers and event IDs) 393 | +-- measurements 394 +--rw nt:termination-point* [tp-id] 395 +-- (...) 396 +-- interconnection_instance_tp_state 397 | +-- status 398 | +-- location (domain, geolocation, etc.) 399 | +-- type (1 gateway, 2 gateways, ...) 400 +-- interconnection_instance_node_service_assurance 401 +-- events (including triggers and event IDs) 402 +-- measurements 404 2.4. Stitching Operation 406 2.4.1. Operation Overview 408 Stitching is an operation that takes two or more NS subnets as input, 409 and produces a single composite NS subnet or end-to-end slice. It 410 may occur when the slice subnets are being instantiated, or later. 412 The first step in this operation is to identify the anchors that will 413 be used in the interconnection. This may be done by an automated 414 algorithm that matches the possible interconnection points and 415 decides which one will be used, according to the policies established 416 by the NS operator. The operation in this case will require the 417 presence of semantically-rich attributes in the candidate anchors to 418 enable automatic matching without human intervention. 420 Other attributes of slices and anchors will also influence the 421 operation and the resulting stitched (composite) object. For 422 instance, network links that are interconnected must have compatible 423 QoS attributes. Moreover, available networking protocols must also 424 match among the underlying network elements that are being stitched. 425 Otherwise, the operation will fail unless the NS operator (based on 426 policy and/or NS subnet attributes) enables it to search for, and 427 use, some "bridge" element in the underlying infrastructure. 429 2.4.2. Stitching Scenarios 431 This section briefly describes examples of usage for subnet 432 stitching. 434 Traversal through a transport network. 436 Let's consider a network slice composed of (NS) subnet-A, and 437 subnet-C (Figure 3). Subnet-A and subnet-C are deployed in 438 independent domains and are mapped into a slice information model; 439 in order to stitch these two together a transport segment is 440 needed. N1 and N2 are anchor nodes within NS subnets A and C. 441 Segment-B could be a simple link between the two NS subnets but it 442 may also be a TE-link made available by a transport network 443 provider. Segment-B may be involved in the stitching operation in 444 one of several ways: 446 Segment-B may be set up as part of the stitching operation 447 between NS subnets A and C, as a form of "bridge" mentioned in 448 Section 2.4. Segment-B will need to comply with service 449 specific traffic constraints that are determined during the 450 stitching operation, possibly using attributes from NS subnets 451 A and C. In this case, the data plane implementation of N1 and 452 N2 in the composite slice may be, for example, 2 distinct 453 gateway functions terminating segment-B. 455 Segment-B may alternatively be represented as a distinct NS 456 subnet, e.g. in cases where segment-B is complex and/or 457 involves multiple network functions. In this case, the 458 stitching operation may therefore involve 3 NS subnets A-B-C. 460 +-----------+ +----------+ 461 | +--+ | ______ | +--+ | 462 | |N1+==========(______)============|N2| | 463 | +--+ | --transport-- | +--+ | 464 +-----------+ +----------+ 465 --subnet-A--- --segment-B------ --subnet-C-- 466 <---------------end to end slice ------------> 468 Figure 3: Example of NS subnets interconnection through transport 469 network 471 Subnets in a single domain. 473 In this scenario multiple network slice subnets are defined as 474 basic building blocks with specific service functions (or chains), 475 topologies and traffic handling characteristics. These building 476 blocks can be assembled through stitching to build end-to-end 477 customized slices, but also to dynamically extend slices to adapt 478 to traffic load. Additionally, stitching can also be used to 479 share building blocks between multiple slices, e.g. to 480 interconnect multiple slices with a shared function. In all these 481 cases, interconnection instances may be entirely abstracted away, 482 although they may also be implemented through one or multiple 483 gateways, e.g. when stitched subnets belong to different sub- 484 domains. 486 3. Security Considerations 488 Security aspects relative to network slices (e.g., for transport 489 slices, in [I-D.liu-teas-transport-network-slice-yang]) are 490 applicable to slice subnets, including transport security aspects, 491 access control and protection of write operation on newly introduced 492 nodes (e.g., termination-point). 494 4. IANA Considerations 496 This document has no actions for IANA. 498 5. Informative References 500 [I-D.clt-dmm-tn-aware-mobility] 501 Chunduri, U., Li, R., Bhaskaran, S., Kaippallimalil, J., 502 Tantsura, J., Contreras, L., and P. Muley, "Transport 503 Network aware Mobility for 5G", draft-clt-dmm-tn-aware- 504 mobility-05 (work in progress), November 2019. 506 [I-D.contreras-teas-slice-nbi] 507 Contreras, L., Homma, S., and J. Ordonez-Lucena, 508 "Considerations for defining a Transport Slice NBI", 509 draft-contreras-teas-slice-nbi-00 (work in progress), 510 November 2019. 512 [I-D.geng-teas-network-slice-mapping] 513 Geng, X., Dong, J., Niwa, T., and J. Jin, "5G End-to-end 514 Network Slice Mapping from the view of Transport Network", 515 draft-geng-teas-network-slice-mapping-00 (work in 516 progress), February 2020. 518 [I-D.homma-rtgwg-slice-gateway] 519 Homma, S., Foy, X., Galis, A., and L. Contreras, "Gateway 520 Function for Network Slicing", draft-homma-rtgwg-slice- 521 gateway-01 (work in progress), November 2019. 523 [I-D.liu-teas-transport-network-slice-yang] 524 Liu, X., Tantsura, J., Bryskin, I., Contreras, L., and Q. 525 WU, "Transport Network Slice YANG Data Model", draft-liu- 526 teas-transport-network-slice-yang-00 (work in progress), 527 November 2019. 529 [I-D.nsdt-teas-transport-slice-definition] 530 Rokui, R., Homma, S., and K. Makhijani, "IETF Definition 531 of Transport Slice", draft-nsdt-teas-transport-slice- 532 definition-00 (work in progress), November 2019. 534 [NGMN_Network_Slicing] 535 NGMN, "Description of Network Slicing Concept", 10 2016, 536 . 539 [RFC8345] Clemm, A., Medved, J., Varga, R., Bahadur, N., 540 Ananthakrishnan, H., and X. Liu, "A YANG Data Model for 541 Network Topologies", RFC 8345, DOI 10.17487/RFC8345, March 542 2018, . 544 Authors' Addresses 546 Xavier de Foy 547 InterDigital Inc. 548 1000 Sherbrooke West 549 Montreal 550 Canada 552 Email: Xavier.Defoy@InterDigital.com 553 Akbar Rahman 554 InterDigital Inc. 555 1000 Sherbrooke West 556 Montreal 557 Canada 559 Email: Akbar.Rahman@InterDigital.com 561 Alex Galis 562 University College London 563 Torrington Place 564 London WC1E 7JE 565 United Kingdom 567 Email: a.galis@ucl.ac.uk 569 Kiran Makhijani 570 Huawei Technologies 571 2890 Central Expressway 572 Santa Clara CA 95050 573 USA 575 Email: kiran.makhijani@huawei.com 577 Li Qiang 578 Huawei Technologies 579 Huawei Campus, No. 156 Beiqing Rd. 580 Beijing 100095 581 China 583 Email: qiangli3@huawei.com 585 Shunsuke Homma 586 NTT, Corp. 587 3-9-11, Midori-cho 588 Musashino-shi, Tokyo 180-8585 589 Japan 591 Email: homma.shunsuke@lab.ntt.co.jp 592 Pedro Martinez-Julia 593 National Institute of Information and Communications Technology 594 Japan 596 Email: pedro@nict.go.jp