idnits 2.17.1 draft-jaclee-behave-v4v6-mcast-ps-00.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (March 07, 2011) is 4770 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 4601 (Obsoleted by RFC 7761) == Outdated reference: A later version (-09) exists of draft-boucadair-mmusic-altc-01 == Outdated reference: A later version (-18) exists of draft-ietf-mboned-auto-multicast-10 Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 BEHAVE WG C. Jacquenet 3 Internet-Draft M. Boucadair 4 Intended status: Informational France Telecom 5 Expires: September 8, 2011 Y. Lee 6 Comcast 7 J. Qin 8 ZTE 9 T. Tsou 10 Huawei Technologies (USA) 11 March 07, 2011 13 IPv4-IPv6 Multicast: Problem Statement and Use Cases 14 draft-jaclee-behave-v4v6-mcast-ps-00 16 Abstract 18 This document discusses issues and requirements raised by IPv4-IPv6 19 multicast interconnection and co-existence scenarios. It also 20 presents the various multicast use cases which may happen during IPv6 21 transitioning. 23 Requirements Language 25 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 26 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 27 document are to be interpreted as described in RFC 2119 [RFC2119]. 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 http://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 8, 2011. 46 Copyright Notice 48 Copyright (c) 2011 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 (http://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 . . . . . . . . . . . . . . . . . . . . . . . . . 3 64 1.1. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . 3 65 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 66 2. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 4 67 3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 6 68 3.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 6 69 3.2. Context . . . . . . . . . . . . . . . . . . . . . . . . . 6 70 3.3. Dual-Stack Multicast Delivery Infrastructure . . . . . . . 8 71 3.4. Mono-Stack Multicast Delivery Infrastructure . . . . . . . 9 72 3.4.1. Translation Cases . . . . . . . . . . . . . . . . . . 11 73 3.4.2. Traversal Cases . . . . . . . . . . . . . . . . . . . 12 74 4. Issues and Required Functions . . . . . . . . . . . . . . . . 15 75 4.1. Fast Zapping . . . . . . . . . . . . . . . . . . . . . . . 15 76 4.2. Group and Source Discovery Considerations . . . . . . . . 15 77 4.3. Subscription . . . . . . . . . . . . . . . . . . . . . . . 16 78 4.4. Multicast Tree Computation . . . . . . . . . . . . . . . . 16 79 4.5. SLA Considerations . . . . . . . . . . . . . . . . . . . . 16 80 4.6. Load Balancing . . . . . . . . . . . . . . . . . . . . . . 16 81 4.7. Bandwidth Consumption . . . . . . . . . . . . . . . . . . 17 82 4.8. ASM-SSM Considerations . . . . . . . . . . . . . . . . . . 17 83 4.9. Interconnection Functions . . . . . . . . . . . . . . . . 17 84 4.9.1. Interworking Functions for Control Flows . . . . . . . 17 85 4.9.2. Interconnection Function for Traffic Flows . . . . . . 18 86 5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 18 87 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 88 7. Security Considerations . . . . . . . . . . . . . . . . . . . 19 89 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19 90 8.1. Normative References . . . . . . . . . . . . . . . . . . . 19 91 8.2. Informative References . . . . . . . . . . . . . . . . . . 20 92 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20 94 1. Introduction 96 In current operational deployments, IP multicast forwarding scheme is 97 used by many service providers to deliver Live TV broadcasting 98 services. Numerous players intervene in the delivery of this 99 service: (1) Content providers: the content can be provided by the 100 same provider as the one providing the connectivity service or by 101 distinct providers (e.g., external paid channels); (2) Network 102 provider: is responsible for carrying multicast flows from head-ends 103 to receivers. 105 During the transition of multicast to IPv6, there will be various 106 issues encountered and requirements raised correspondingly. The 107 requirement of service continuity should be an essential one which 108 may include: the access to legacy contents (IPv4 framed) from 109 receivers is still available where if the assignment of a dedicated 110 global IPv4 address to the receiver is not possible anymore or even 111 after the receivers are migrated to IPv6 and; the delivery of new 112 contents (IPv6 framed) to legacy receivers is also possible and; in 113 cases where if underlying transport network(s) is of different 114 address family than that of the source and/or receivers, the delivery 115 of multicast data is still available (e.g., in the context of DS-Lite 116 deployment, the network has been firstly upgraded to IPv6 while the 117 source and receivers are not). 119 This document does make any assumption on the techniques used for the 120 delivery of multicast services (e.g., native IP multicast with or 121 without traffic isolation features, use of P2MP RSVP-TE, P2MP mLDP 122 LSPs, mVPN, etc. ). 124 This document further elaborates on the context and discusses 125 multicast-inferred issues and requirements. 127 1.1. Goals 129 The goal is to clarify the problem space and get a general consent of 130 the objectives. In particular, the ambition is to provide answers 131 to: 133 o What are the hurdles encountered for the delivery of multicast- 134 based service offering when both IPv4 and IPv6 co-exist? 136 o What standardization effort is needed: is there any missing 137 function and protocol extensions? 139 o Check if both encapsulation and translation schemes are concerned. 141 1.2. Terminology 143 This document uses the following terms: 145 o Multicast Source: Source, in short 147 o Multicast Receiver: Receiver, in short, e.g.- STB 149 o Multicast Delivery Network: Network in short, covers the realm 150 from DR device (directly connected to the Source) to IGMP/MLD 151 Querier device (directly connected to the Receiver). 153 2. Discussion 155 Global IPv4 address depletion inevitably challenges service providers 156 who must guarantee IPv4 service continuity during the forthcoming 157 transition period. In particular, access to IPv4 contents that are 158 multicast to IPv4 receivers becomes an issue when the forwarding of 159 multicast data assumes the use of global IPv4 addresses. 161 The rarefaction of global IPv4 addresses may indeed affect the 162 multicast delivery of IPv4-formatted contents to IPv4 receivers. For 163 example, the observed evolution of access infrastructures from a 164 service-specific, multi-PVC scheme towards a "service-agnostic", 165 single PVC scheme, assumes the allocation of a globally unique IPv4 166 address on the WAN interface of the CPE (or to a mobile terminal), 167 whatever the number and the nature of the services the customer has 168 subscribed to. 170 During the transition period, the usage of the remaining global IPv4 171 address blocks will have to be rationalized for the sake of IPv4 172 service continuity. The current state-of-the-art suggests the 173 introduction of NAT capabilities (generally denoted as CGN, for 174 Carrier-Grade NAT) in providers networks, so that global IPv4 175 addresses will be shared between several customers. As a 176 consequence, CPE or mobile UE devices will not be assigned a 177 dedicated global IPv4 address anymore, and IPv4 traffic will be 178 privately-addressed until it reaches one of the NAT capabilities 179 deployed in the network. From a multicast delivery standpoint, this 180 situation suggests the following considerations: 182 o The current design of some multicast-based services like TV 183 broadcasting often assumes that IPv4 multicast forwarding relies 184 upon the use of a private IPv4 addressing scheme because of a 185 walled garden approach. Privately-addressed IGMP [RFC2236] 186 [RFC3376] traffic sent by IPv4 receivers is generally forwarded 187 over a specific (e.g. "IP TV") PVC towards an IGMP Querier 188 located in the access infrastructure, e.g.- hosted by a BRAS 189 device that is the PPP session endpoint and which may also act as 190 a PIM DR [RFC4601] router. This design does not suffer from 191 global IPv4 address depletion by definition. But it will be 192 questioned when migrating the access infrastructure towards a 193 publicly-addressed single PVC design scheme. 195 o The progressive introduction of IPv6 as the only perennial 196 solution to global IPv4 address depletion does not necessarily 197 assume that multicast-based IPv4 services will be migrated 198 accordingly. Access to IPv4 multicast contents raises several 199 issues: (1) The completion of the IGMP-based multicast group 200 subscription procedure, (2) The computation of the IPv4 multicast 201 distribution tree, and (3) The IPv4-inferred addressing scheme to 202 be used in a networking environment which will progressively 203 become IPv6-enabled, but not necessarily IPv6 multicast enabled. 205 o In any case, contents should not be multicast twice (using both 206 versions of IP) for the sake of bandwidth optimization. Injecting 207 multicast content using both IPv4 and IPv6 raises some 208 dimensioning issues that should be carefully evaluated by service 209 providers during network planning. For instance, if only few 210 IPv6- enabled receivers are in use, it can be more convenient to 211 convey multicast traffic over IPv4 rather than doubling the 212 consumed resources for few users. 214 There are at least several options that can deal with the 215 aforementioned considerations. 217 1. Stick to a walled garden design that relies upon a private IPv4 218 addressing scheme. But this approach jeopardizes the evolution 219 of access networking infrastructures towards the use of a unique, 220 per-customer, globally-addressed, service-wise PVC design scheme. 221 And it also delays migration towards IPv6 instead of encouraging 222 it. 224 2. Use AMT (Automatic Multicast without explicit Tunnels, 225 [I-D.ietf-mboned-auto-multicast]), to encapsulate IGMP traffic 226 into UDP packets that will be sent to an AMT Relay located 227 upstream in the network. This approach may not be suitable for 228 the delivery of IP TV content in operational networks mainly due 229 to delays which may be experienced for zapping. 231 Note that unicast IP addresses are used for communicating with 232 service platforms to get control information (e.g., channel lists) 233 and, as the identification of customers for management, traffic 234 engineering, etc. 236 The following sections elaborate more on the use cases, issues and 237 requirements. 239 3. Use Cases 241 3.1. Purpose 243 This section describes a set of use cases which need to be 244 considered. 246 As mentioned above, the walled garden scheme where private IPv4 247 addresses are used for the delivery of multicast-based service 248 offerings is out of scope. 250 3.2. Context 252 During transitioning, there might be a mix of multicast receivers, 253 sources, and networks running in different address families. 254 However, the operator should continue to deliver the multicast 255 service to both IPv4 and IPv6 receivers. Since there is mis-match of 256 IP address family of sources, receiver, and delivery network, the 257 operator should plan carefully and choose the right transition 258 technique that could efficiently utilize the network resources to 259 deliver the services. 261 Both fixed (Figure 1) and mobile networks (Figure 2, which reflects 262 the current status of the IPv6 Study Item conducted within 3GPP and 263 some public plans for the LTE deployment) have been considered. 265 +------------+-----------+-------------+-----------+----------------+ 266 | Deployment | Legacy | CPE | Legacy | Underlying IP | 267 | Model | Receiver | | Source | capabilities | 268 +------------+-----------+-------------+-----------+----------------+ 269 | DS | IPv4-only | IPv4-only | IPv4-only | IPv4 and IPv6 | 270 | | | and DS | | | 271 +------------+-----------+-------------+-----------+----------------+ 272 | DS-Lite | IPv4-only | IPv4-only | IPv4-only | IPv4 and IPv6 | 273 | | | and DS-Lite | | | 274 +------------+-----------+-------------+-----------+----------------+ 275 | Greenfield | -- | IPv6-only | --- | IPv6 | 276 | IPv6 | | | | | 277 +------------+-----------+-------------+-----------+----------------+ 278 | Hybrid | IPv4-only | IPv4-only, | IPv4-only | IPv4 and IPv6 | 279 | (*) | | DS and | | | 280 | | | DS-Lite | | | 281 +------------+-----------+-------------+-----------+----------------+ 283 (*) Hybrid is used to denote a network where customers may be 284 IPv4-only DS and/or DS-Lite serviced. 286 Figure 1: IPv6 integration scenarios in fixed networks. 288 +----------------+-----------+---------------+--------------------+ 289 |Deployment Model| Legacy UE | Legacy source |Network Capabilities| 290 +----------------+-----------+---------------+--------------------+ 291 | DS PDP | IPv4-only | IPv4-only | IPv4 and IPv6 | 292 +----------------+-----------+---------------+--------------------+ 293 |IPv6-only PDP | IPv4-only | IPv4-only | IPv4 and IPv6(*) | 294 +----------------+-----------+---------------+--------------------+ 296 (*) The underlying network is likely to be dual-stack except for 297 IPv6 greenfield deployments. 299 Figure 2: IPv6 integration scenarios in mobile networks (PDP 300 Activation). 302 There are three variables to be considered when analyzing the 303 multicast use cases, "Source", "Receiver" and the "Multicast Delivery 304 Infrastructure" (denoted for short as "Network"). 306 To simplify the analysis, one of the variables: "Network", is hold. 307 So based on the capabilities of the underlying multicast delivery 308 infrastructure. According to the above figures, two use cases can be 309 considered: 311 o Dual-Stack: Both IPv4 and IPv6 multicast delivery function are 312 wholly enabled; 314 o Mono-Stack: Not wholly dual-stack enabled but for example, is 315 either IPv4-only or IPv6-only, or may be a hybrid of IPv4 portion 316 and IPv6 portion (refer to Hybrid cases in Figure 5). 318 3.3. Dual-Stack Multicast Delivery Infrastructure 320 Dual-stack model is supposed to be the most straight forward 321 deployment model where the network is dual-stack and the same content 322 is sourced into both IPv4 and IPv6 multicast stream. Depending on 323 the receiver, it could choose to listen to either stream. 325 [NOTE: if the source is framed in single stack (i.e., IPv4-only or 326 IPv6-only) or the network is not wholly dual-stack enabled, even 327 there are both IPv4 and IPv6 receivers, it should not be regarded 328 as the Dual-Stack Model use case. 330 In this case, since the stream from source to receivers of the 331 same address family can be natively delivered without any new 332 functions, the native delivery portion is not taken into account. 333 Then this is regarded as one of Mono-Stack Model cases. For 334 example, the case where the source is IPv4 framed while the 335 network is wholly dual-stack enabled and there are both IPv4 and 336 IPv6 receivers, is simply regarded as the Case 1 in Mono-Stack 337 Model; Or for example, the case where the source and receivers are 338 dual-stack, and the network is IPv6-only, is regarded as Case 6, 339 also refer to Section 3.4.2.] 341 This model assumes the multicast content and delivery infrastructure 342 is dual-stack. This assumption may not be valid because the dual- 343 stack formatted source may not always be available since numerous 344 players intervene in the delivery of multicast-based service: content 345 providers and the network provider. The content may not be 346 controlled by the underlying network providers. 348 For this scenario, legacy IPv4 receivers will continue to access to 349 IPv4-formatted multicast content. 351 Figure 3 summarizes the issues encountered if this option is used. 353 +-----------------+----------------------------------------------+ 354 | Deployment Model| Comments | 355 +-----------------+----------------------------------------------+ 356 | DS | No issue is encountered | 357 +-----------------+----------------------------------------------+ 358 | DS-Lite | For IPv4-only receivers, extra functions are | 359 | | required to deliver the multicast service | 360 +-----------------+----------------------------------------------+ 361 | Hybrid | Idem as per DS-Lite case | 362 +-----------------+----------------------------------------------+ 364 Figure 3: Impact analysis. 366 From a bandwidth perspective, it is not viable to duplicate the same 367 content in IPv4 and IPv6. Indeed, injecting multicast content using 368 both IPv4 and IPv6 raises dimensioning issues that should be 369 carefully evaluated by service providers (in particular in the access 370 network). For instance, if only few IPv6-enabled receivers are in 371 use, it is more convenient to convey multicast traffic over IPv4 372 rather than doubling the consumed network resources for few users. 374 Figure 4 summarizes the main characteristics of this use case: 375 +--------+----------------------------------------------------------+ 376 | Pros | Limitations | 377 +--------+----------------------------------------------------------+ 378 | Simple | * CAPEX (e.g., bandwidth cost) | 379 | | * Requires coordination between the content and the | 380 | | network providers | 381 | | * Despite DS-formatted content, extensions are still | 382 | | required to deliver the content to IPv4-only receivers | 383 | | when DS-Lite is deployed. | 384 +--------+----------------------------------------------------------+ 386 Figure 4: Main Characteristics. 388 3.4. Mono-Stack Multicast Delivery Infrastructure 390 Consider now the case where the multicast content is reachable only 391 with one single address family (i.e., IPv4 or IPv6). Depending on 392 transition steps, the source could stay in IPv4 or move to IPv6. And 393 the legacy receivers are IPv4-reachable while the new receivers may 394 be IPv6-enabled. 396 +-------+------------+------------+------------+-------------+ 397 | Use | Network | Source | Receiver | Use Case | 398 | Cases |Capabilities| | | Categories | 399 +-------+------------+------------+------------+-------------+ 400 | 1 | | IPv4 | IPv6 | | 401 +-------+ +------------+------------+ Translation | 402 | 2 | IPv4 | IPv6 | IPv4 | | 403 +-------+ +------------+------------+-------------+ 404 | 3 | | IPv6 | IPv6 | Traversal | 405 +-------+------------+------------+------------+-------------+ 406 | 4 | | IPv4 | IPv6 | | 407 +-------+ +------------+------------+ Translation | 408 | 5 | IPv6 | IPv6 | IPv4 | | 409 +-------+ +------------+------------+-------------+ 410 | 6 | | IPv4 | IPv4 | Traversal | 411 +-------+------------+------------+------------+-------------+ 412 | | | IPv4, IPv6 | IPv4, IPv6 | | 413 |Hybrid*| IPv4, IPv6 +------------+------------+ Hybrid | 414 | | | IPv4, IPv6 | IPv4, IPv6 | | 415 +-------+------------+------------+------------+-------------+ 417 Figure 5: Mono-stack use cases 419 * In Hybrid cases, the network is partially IPv4 and partially IPv6. 421 See below: 423 --------------- 424 // R4 S4 \\ S6 = v6 Source 425 / +----+ | R6 = v6 Receiver 426 +----+ IPv4 | DR |----| S4 = v4 Source 427 R6 ---| QR | Network +----+ |- S6 R4 = v4 Receiver 428 +----+ / | DR = Designated Router 429 \\ // QR = IGMP/MLD Querier 430 --------------- 432 Figure 6: IPv4 Delivery Network 434 --------------- 435 // R6 S6 \\ S6 = v6 Source 436 / +----+ | R6 = v6 Receiver 437 +----+ IPv6 | DR |----| S4 = v4 Source 438 R4 ---| QR | Network +----+ |- S4 R4 = v4 Receiver 439 +----+ / | DR = Designated Router 440 \\ // QR = IGMP/MLD Querier 441 --------------- 443 Figure 7: IPv6 Delivery Network 445 --------------- -------------- 446 // R6 S6 \\ // R4 S4 \\ 447 / IPv6 +------+ IPv4 \ 448 | Network | MR | Network | 449 \ +------+ / 450 \\ // \\ // 451 -------------- --------------- 452 S6 = v6 Source 453 R6 = v6 Receiver 454 S4 = v4 Source 455 R4 = v4 Receiver 456 MR = Multicast Router, could be border router connecting 457 IPv4 and IPv6 network, or DR connecting the source, 458 or QR connecting the receiver 460 Figure 8: Hybrid Delivery Network 462 3.4.1. Translation Cases 464 If the multicast source and receiver are belonging to different 465 address families, translation happens. The locations of translation 466 functions defers according to the address family of delivery network. 468 The translation can happen either close to the source or close to the 469 receiver. Depending on the deployment model, this decision may 470 result a different transition technology being selected. Only a 471 single distribution tree is required if only one address family is 472 serviced by a given transport network. 474 The content will be delivered once which is better utilized the 475 network bandwidth. However if the application relies on the IP 476 information stored in the payload (e.g., SDP), then translation will 477 break the application. 479 +-----------------------+-------------------------------------------+ 480 | Pros | Limitations | 481 +-----------------------+-------------------------------------------+ 482 | Bandwidth utilization | * Receivers have to know the translated | 483 | | source address in the context SSM | 484 | | * Receivers would have to know the | 485 | | translated multicast group address | 486 | | * The information loss during the | 487 | | translation operations | 488 | | * The burden and necessary coordinations | 489 | | are involved if stateful translations are | 490 | | employed | 491 | | * ALGs may be required to assist the | 492 | | discovery of source address and multicast | 493 | | group address | 494 +-------------------------------------------------------------------+ 496 Figure 9: Main Characteristics of translation-based schemes. 498 [NOTE: Access to IPv6-only multicast content by legacy customers 499 is not seen as a valid scenario; especially in the context of IP 500 TV service offering. Whenever this configuration is met by an 501 operator, it MAY consider the following mitigation alternatives: 503 * Enable IPv4-IPv6 interconnection functions to allow the 504 successful delivery of IPv6-only multicast content to IPv4-only 505 receivers 507 * Or swap the receiver device (e.g., STB) with a new dual-stack 508 one if the provider controls STB and/or CP router devices.] 510 3.4.2. Traversal Cases 512 If the multicast source and receiver are belonging to the same 513 address family, while the delivery network is not. 515 A viable scenario for this use case is DS-Lite Model: Customers with 516 legacy receivers must continue to access the IPv4-enabled multicast 517 services. This means the traffic should be accessed over IPv4. The 518 following cases should be covered by any candidate solution to the 519 issue of forwarding IPv4 multicast traffic in DS-Lite environment: 520 (1) IPv4-only multicast receiver; (2) Dual-Stack multicast receiver. 521 As for the content, two scenarios are considered as valid ones: (1) 522 IPv4-only content; (2) Dual-Stack content (i.e., content reachable in 523 both IPv4 and IPv6). 525 Note that: 527 1. The legacy IPv4 receiver can access dual-stack and IPv4-only 528 content. No issue is induced by this scenario. Multicast flows 529 will be delivered using native IPv4 transfer mode. 531 2. An IPv4-only receiver behind a DS-Lite CGN: Additional functions 532 are required to deliver the content to the receiver; 534 3. A dual stack receiver should access a dual stack content using 535 IPv6. No extra function is required to implement this scenario; 537 4. Dual-Stack receiver accessing IPv4-only content: This scenario is 538 similar to the IPv4-only receiver accessing the IPv4-only content 539 (2nd bullet). Additional functions are required. 541 In order to deliver IPv4 multicast flows to DS-Lite serviced users, 542 two solution flavors can be envisaged: 544 +---------------+---------------------------------------------------+ 545 | Solution | Characteristics | 546 | Flavor | | 547 +---------------+---------------------------------------------------+ 548 | Translation | For IPv4 content, introduce an IPv4-IPv6 | 549 | | translator in the provider's network. Multicast | 550 | | streams will then be delivered to the receivers | 551 | | using IPv6 until the CPE. A second level of NAT | 552 | | can then be enforced if the receiver is | 553 | | IPv4-only | 554 | +---------------------------------------------------+ 555 | | This solution may require two | 556 | | translation levels, can impact the overall | 557 | | performance of the CPE, may alter the perceived | 558 | | quality of experience, etc. This solution may be | 559 | | the source of service disruption (especially for | 560 | | live TV broadcasting). This is not desirable | 561 | +---------------------------------------------------+ 562 | | For IPv6 content, all streams are delivered to | 563 | | the DS-Lite CPE using IPv6; an IPv4-IPv6 | 564 | | translator can be enabled in the CPE to forward | 565 | | the streams to an IPv4-only receiver. The | 566 | | IPv4-IPv6 translation function may impact the | 567 | | performance of the CPE | 568 +---------------+---------------------------------------------------+ 569 | Encapsulation | To access IPv4 content from an IPv4-only or | 570 | | dual-stack receiver: If the receiver encapsulates | 571 | | the multicast signaling, it will result packet | 572 | | replication per tunnel interface. If the | 573 | | underneath network is not aware of the multicast | 574 | | topology, it will deliver the encapsulated | 575 | | multicast packets as unicast packets. The | 576 | | replication will happen at the encapsulator | 577 | | rather than the edge multicast router. This | 578 | | would poorly utilize the network bandwidth | 579 | +---------------------------------------------------+ 580 | | This problem could be mitigated. If the | 581 | | encapsulator translates the multicast group | 582 | | address to another address family and uses it for | 583 | | the multicast signaling, the underneath network | 584 | | could build a multicast distribution tree using | 585 | | the translated multicast address. Thus, the | 586 | | network could deliver the encapsulated packets in | 587 | | the standard multicast fashion using the | 588 | | multicast delivery tree built by the translated | 589 | | multicast address group. In other words, the | 590 | | encapsulator bridges two multicast trees at the | 591 | | control plane but performs encapsulation at the | 592 | | data plane. This is a hybrid of translation and | 593 | | encapsulation mechanisms | 594 | +---------------------------------------------------+ 595 | | Since legacy IPv4-only receivers are predominant, | 596 | | it is optimal to enable the IPv4-IPv6 | 597 | | encapsulation function closer to the receivers | 598 | | (e.g., first IP node). Doing so, would lead to a | 599 | | single core multicast tree and flow replication | 600 | | to DS-Lite serviced devices will occur upon | 601 | | request. Multicast flows are not replicated in | 602 | | the core and aggregation network | 603 | +---------------------------------------------------+ 604 | | If the IPv4-IPv6 encapsulation function is | 605 | | implemented deeper in the network, and since | 606 | | legacy customers need to be serviced in IPv4, | 607 | | multicast flows are likely to be duplicated | 608 | | (native, encapsulated) which is not optimal | 609 | +---------------------------------------------------+ 610 | | The IPv4-in-IPv6 encapsulated multicast flows | 611 | | destined to IPv4-embedded IPv6 group address are | 612 | | treated as any IPv6 multicast flows, and can be | 613 | | replicated within Multicast VLANs. | 614 | | Mechanisms such as MLD Snooping or MLD Proxying | 615 | | can be introduced into the distributed | 616 | | Access Network Nodes which could behave as MLD | 617 | | Queriers and replicate multicast flows as | 618 | | appropriate | 619 | +---------------------------------------------------+ 620 | | To access IPv6 content from a dual-stack | 621 | | receiver: No new function is required since | 622 | | native multicast IPv6 functions can be used | 623 +---------------+---------------------------------------------------+ 625 4. Issues and Required Functions 627 It is not so easy to provide a single solution which will be 628 convenient for all Service Providers. This is even complex if we 629 consider real deployments where the network is a collection of: 630 Legacy, DS, DS-Lite, PPP, DHCP, GE, ATM, PIM-SM, SSM, P2MP LSP, mVPN, 631 etc. However, the following requirements should be taken into 632 account. 634 4.1. Fast Zapping 636 The IGMP Leave latency may be an issue when considering channel 637 zapping. In current IPv4-based TV service offerings, when a user 638 changes a TV channel, an IGMP Leave message is sent followed by an 639 IGMP Report to join a new channel. This may lead to two channels to 640 be sent to the receiver and as a consequence a traffic peak which may 641 cause congestion on access links is experienced. 643 A procedure called IGMP fast-leave is commonly used to avoid this 644 problem and to immediately stop the multicast stream as soon as the 645 IGMP Leave is received. In current deployments, IGMP fast-leave 646 requires activation of the IGMP Proxy in DSLAM. 648 Fast zapping issues MUST be taken into account when dealing with 649 IPv4-IPv6 multicast delivery. 651 4.2. Group and Source Discovery Considerations 653 An ALG is required to help an IPv6 receiver to select the appropriate 654 IP address when only the IPv4 address is advertised (e.g., using 655 SDP); otherwise the access to the IPv4 multicast content can not be 656 offered to the IPv6 receiver. 658 The ALG may be located downstream the receiver. As such, the ALG 659 does not know in advance whether the receiver is dual-stack or IPv6- 660 only. 662 The ALG may be tuned to insert both the original IPv4 address and 663 corresponding IPv6 multicast address using for instance the ALTC SDP 664 attribute [I-D.boucadair-mmusic-altc]. 666 In order to avoid involving an ALG in the path, an IPv4-only source 667 can advertise both its IPv4 address and IPv4-embedded IPv6 multicast 668 address using for instance the ALTC SDP attribute. However, a dual- 669 stack receiver may prefer to use the IPv6 address to receive the 670 multicast content. This address selection would require multicast 671 flows to cross an IPv4-IPv6 interconnection function. 673 4.3. Subscription 675 Multicast distribution trees are receiver-initiated. IPv4 receivers 676 that wish to subscribe to an IPv4 multicast group will send the 677 corresponding IGMP Report message towards the relevant IGMP Querier. 678 In case the underlying network is IPv6, the information conveyed in 679 IGMP messages should be relayed into corresponding MLD messages. 681 4.4. Multicast Tree Computation 683 Grafting to an IPv4 multicast distribution tree through an IPv6 684 multicast domain suggests that IPv4 multicast traffic will have to be 685 conveyed along an "IPv6-equivalent" multicast distribution tree. 686 That is, part of the multicast distribution tree along which IPv4 687 multicast traffic will be forwarded SHOULD be computed and maintained 688 by means of the PIMv6 machinery, so that the distribution tree can be 689 terminated as close to the IPv4 receivers as possible for the sake of 690 the multicast forwarding efficiency. This assumes a close 691 interaction between the PIM designs enforced in both domains. Such 692 interaction may be further complicated by different combinations: the 693 IPv4 multicast domain is SSM-enabled (with no RP routers), while the 694 IPv6 multicast domain may support both ASM and SSM [RFC3569] modes. 696 For instance, the ASM mode would be used to optimize the forwarding 697 of IPv4 multicast data sent by different sources into the IPv6 698 multicast domain by selecting privileged RP routers that could be 699 located at the border between the IPv6 and the IPv4 multicast 700 domains. 702 4.5. SLA Considerations 704 Some contract agreements may prevent a network provider to alter the 705 content as sent by the content provider, in particular for copyright, 706 confidentiality and SLA assurance reasons. 708 The streams should be delivered without alteration to requesting 709 users. Crossing a NAT or enforcing an encapsulation may lead to 710 fragmentation or extra delays and therefore impact the perceived 711 quality of service. 713 4.6. Load Balancing 715 In some operational network, a source-based NAT function is used for 716 load-balancing purposes. Because of some operational issues induced 717 by this NAT function, plans to remove the stateful NAT function are 718 adopted by some operators. 720 Since the same concern apply for stateful IPv4-IPv6 translation 721 function, stateless interconnection function SHOULD be privileged. 723 [To be further elaborated] 725 4.7. Bandwidth Consumption 727 As a reminder, to optimize the usage of network resources, all 728 multicast streams are conveyed in the core network while only popular 729 ones are continuously conveyed in the aggregation/access network 730 (static mode). Non-popular streams are conveyed in the access 731 network upon request (dynamic mode). 733 [To be further elaborated] 735 4.8. ASM-SSM Considerations 737 PIM-SSM is currently used in IP TV service offerings. 739 [To be further elaborated: ASM with unicast-based prefix can be used 740 in the IPv6 realm while SSM is used in the IPv4 domain.] 742 4.9. Interconnection Functions 744 As mentioned above, several interconnection functions are required. 745 These functions can be divided into: 747 1. Interworking functions for control messages 749 2. Interconnection function for data flows. 751 4.9.1. Interworking Functions for Control Flows 753 The following sub-sections describes some interworking functions 754 which may be required. 756 4.9.1.1. IGMP-MLD Interworking 758 IGMP-MLD Interworking Function combines the IGMP/MLD Proxying 759 function specified in [RFC4605] and the IGMP/MLD adaptation function 760 which is meant to reflect the contents of IGMP messages into MLD 761 messages, vice versa. 763 For example, when an IGMP Report message is received from a receiver 764 to subscribe to a given multicast group G (and optionally associated 765 to a source if SSM mode is used), the IGMP-MLD Interworking Function 766 MUST send an MLD Report message to subscribe to the corresponding 767 IPv6 group. 769 4.9.1.2. IPv4-IPv6 PIM Interworking 771 [RFC4601] allows the computation of PIM-based IPv4 or IPv6 772 distribution trees; PIM is IP version agnostic. There is no specific 773 IPv6 PIM machinery that would work differently than an IPv4 PIM 774 machinery. The new things needed for the IPv4-IPv6 PIM Interworking 775 Function are just to allow the PIM message received from one address 776 family to correspondingly trigger the operation of the other address 777 family per PIM machinery specified. 779 The address mapping MUST performed similarly to that of the IGMP-MLD 780 Interworking Function. 782 4.9.1.3. MLD-IPv4 PIM Interworking 784 This function is required when the MLD Querier is connected to an 785 IPv4 PIM realm and not an IPv6 one. 787 The address mapping MUST performed similarly to that of the IGMP-MLD 788 Interworking Function. 790 4.9.1.4. IGMP-IPv6 PIM Interworking 792 Similar to the previous sub-section. 794 The address mapping MUST performed similarly to that of the IGMP-MLD 795 Interworking Function. 797 4.9.1.5. PIMv6-IGMP or PIMv4-MLD Interworking 799 [To be further elaborated] 801 4.9.2. Interconnection Function for Traffic Flows 803 According to different scenarios, translation or encapsulation 804 mechanism can be used for traffic flows interconnection. 806 The behaviour of this interconnection function MUST be specified. 808 5. Conclusions 810 The analysis above has shown: 812 1. Operational networks are complex environments; these networks are 813 likely to be hybrid ones. 815 2. Some issues are deployment-specific (e.g., density of IPv6- 816 enabled customers attached to an access network, if only few 817 IPv6-enabled receivers are in use it is more convenient to convey 818 multicast traffic over IPv4 rather than doubling the consumed 819 network resources for few users, etc.); 821 3. For all use cases, a solution is required for the delivery of 822 multicast-based services to DS-Lite serviced customers. 824 4. For DS-Lite, encapsulation and translation solutions rely on the 825 same control functions; the only difference is in the treatement 826 of data flows. 828 5. Standardizing the algorithms for IPv4-IPv6 Interworking functions 829 should be undertaken for both encapsulation and translation. 831 6. Some performance analysis are required to assess the impact of 832 activating some extra functions on the CP routers (e.g., assess 833 the impact of de-capsulation fucntion compared to transalation 834 function, evaluate the impact on CP router when several receiers 835 are behind the same CP router, etc.). 837 6. IANA Considerations 839 This document makes no request of IANA. 841 Note to RFC Editor: this section may be removed on publication as an 842 RFC. 844 7. Security Considerations 846 Access to contents in a multicast-enabled environment raises 847 different security issues that have been already documented. This 848 draft does not introduce any specific security issue. 850 8. References 852 8.1. Normative References 854 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 855 Requirement Levels", BCP 14, RFC 2119, March 1997. 857 [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. 858 Thyagarajan, "Internet Group Management Protocol, Version 859 3", RFC 3376, October 2002. 861 [RFC3569] Bhattacharyya, S., "An Overview of Source-Specific 862 Multicast (SSM)", RFC 3569, July 2003. 864 [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 865 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 866 Protocol Specification (Revised)", RFC 4601, August 2006. 868 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 869 "Internet Group Management Protocol (IGMP) / Multicast 870 Listener Discovery (MLD)-Based Multicast Forwarding 871 ("IGMP/MLD Proxying")", RFC 4605, August 2006. 873 8.2. Informative References 875 [I-D.boucadair-mmusic-altc] 876 Boucadair, M., Kaplan, H., Gilman, R., and S. 877 Veikkolainen, "Session Description Protocol (SDP) 878 Alternate Connectivity (ALTC) Attribute", 879 draft-boucadair-mmusic-altc-01 (work in progress), 880 September 2010. 882 [I-D.ietf-mboned-auto-multicast] 883 Thaler, D., Talwar, M., Aggarwal, A., Vicisano, L., and T. 884 Pusateri, "Automatic IP Multicast Without Explicit Tunnels 885 (AMT)", draft-ietf-mboned-auto-multicast-10 (work in 886 progress), March 2010. 888 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 889 2", RFC 2236, November 1997. 891 Authors' Addresses 893 Christian Jacquenet 894 France Telecom 896 Email: christian.jacquenet@orange-ftgroup.com 897 Mohamed Boucadair 898 France Telecom 899 Rennes 35000 900 France 902 Email: mohamed.boucadair@orange-ftgroup.com 904 Yiu Lee 905 Comcast 906 US 908 Email: Yiu_Lee@Cable.Comcast.com 910 Jacni Qin 911 ZTE 912 China 914 Email: jacniq@gmail.com 916 Tina Tsou 917 Huawei Technologies (USA) 918 2330 Central Expressway 919 Santa Clara, CA 95050 920 USA 922 Phone: +1 408 330 4424 923 Email: tena@huawei.com