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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MULTIMOB Working Group H. Asaeda 3 Internet-Draft Y. Uchida 4 Expires: August 27, 2011 Keio University 5 H. Liu 6 Q. Wu 7 Huawei Technologies 8 February 23, 2011 10 Tuning the Behavior of IGMP and MLD for Mobile Hosts and Routers 11 draft-asaeda-multimob-igmp-mld-optimization-05 13 Abstract 15 IGMP and MLD are the protocols used by hosts to report their IP 16 multicast group memberships to neighboring multicast routers. This 17 document describes the ways of IGMPv3 and MLDv2 protocol optimization 18 for mobility, and aims to become a guideline for query and other 19 timers tuning. 21 Status of this Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at http://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on August 27, 2011. 38 Copyright Notice 40 Copyright (c) 2011 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (http://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 This document may contain material from IETF Documents or IETF 54 Contributions published or made publicly available before November 55 10, 2008. The person(s) controlling the copyright in some of this 56 material may not have granted the IETF Trust the right to allow 57 modifications of such material outside the IETF Standards Process. 58 Without obtaining an adequate license from the person(s) controlling 59 the copyright in such materials, this document may not be modified 60 outside the IETF Standards Process, and derivative works of it may 61 not be created outside the IETF Standards Process, except to format 62 it for publication as an RFC or to translate it into languages other 63 than English. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 68 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 69 3. Explicit Tracking of Membership Status . . . . . . . . . . . . 5 70 4. Tuning IGMP/MLD Timers and Values . . . . . . . . . . . . . . 6 71 4.1. Tuning IGMP/MLD General Query Interval . . . . . . . . . . 6 72 4.2. Tuning IGMP/MLD Query Response Interval . . . . . . . . . 6 73 4.3. Tuning Last Member Query Timer (LMQT) and Last 74 Listener Query Timer (LLQT) . . . . . . . . . . . . . . . 7 75 4.4. Tuning Startup Query Interval . . . . . . . . . . . . . . 8 76 4.5. Tuning Robustness Variable . . . . . . . . . . . . . . . . 8 77 5. Destination Address of Specific Query . . . . . . . . . . . . 9 78 6. Interoperability . . . . . . . . . . . . . . . . . . . . . . . 10 79 7. Security Considerations . . . . . . . . . . . . . . . . . . . 11 80 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 81 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 82 9.1. Normative References . . . . . . . . . . . . . . . . . . . 13 83 9.2. Informative References . . . . . . . . . . . . . . . . . . 13 84 Appendix A. Unicasting General Query . . . . . . . . . . . . . . 14 85 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 87 1. Introduction 89 The Internet Group Management Protocol (IGMP) [2] for IPv4 and the 90 Multicast Listener Discovery Protocol (MLD) [3] for IPv6 are the 91 standard protocols for hosts to initiate joining or leaving multicast 92 sessions. These protocols must be also supported by multicast 93 routers or IGMP/MLD proxies [11] that maintain multicast membership 94 information on their downstream interfaces. Conceptually, IGMP and 95 MLD work on wireless networks. However, wireless access technologies 96 operate on a shared medium or a point-to-point link with limited 97 frequency and bandwidth. In many wireless regimes, it is desirable 98 to minimize multicast-related signaling to preserve the limited 99 resources of battery powered mobile devices and the constrained 100 transmission capacities of the networks. A mobile host may cause 101 initiation and termination of a multicast service in the new or the 102 previous network upon its movement. Slow multicast service 103 activation following a join may degrade reception quality. Slow 104 service termination triggered by IGMP/MLD querying or by a rapid 105 departure of the mobile host without leaving the group in the 106 previous network may waste network resources. 108 To create the optimal multicast membership management condition, IGMP 109 and MLD protocols could be tuned to "ease a mobile host's processing 110 cost or battery power consumption by IGMP/MLD Query transmission 111 timing coordination by routers" and "realize fast state convergence 112 by successive monitoring whether downstream members exist or not". 114 This document describes the ways of tuning the IGMPv3 and MLDv2 115 protocol behavior for mobility, including query and other timers 116 tuning. The selective optimization that provides tangible benefits 117 to the mobile hosts and routers is given by keeping track of 118 downstream hosts' membership status and varying IGMP/MLD Query types 119 and values to tune the number of responses. The proposed behavior 120 interoperates with the IGMPv3 and MLDv2 protocols. 122 2. Terminology 124 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL 125 NOT","SHOULD", "SHOULD NOT", "RECOMMENDED","MAY", and "OPTIONAL" in 126 this document are to be interpreted as described in RFC 2119 [1]. 128 3. Explicit Tracking of Membership Status 130 Mobile hosts use IGMP and MLD to request to join or leave multicast 131 sessions. When the adjacent upstream routers receive the IGMP/MLD 132 Report messages, they recognize the membership status on the link. 133 To update the membership status, the routers send IGMP/MLD Query 134 messages periodically as a soft-state approach does, and the member 135 hosts reply IGMP/MLD Report messages upon reception. IGMP/MLD Query 136 is therefore necessary to obtain the up-to-date membership 137 information, but a large number of the reply messages sent from all 138 member hosts may cause network congestion or consume network 139 bandwidth. 141 The "explicit tracking function" [9] is the possible approach to 142 reduce the transmitted number of IGMP/MLD messages and contribute to 143 mobile communications. It enables the router to keep track of the 144 membership status of the downstream IGMPv3 or MLDv2 member hosts. 146 The explicit tracking function reduces the chance of Group-Specific 147 or Group-and-Source Specific Query transmission. Whenever a router 148 that does not enable the explicit tracking function receives the 149 State-Change Report and the router's membership state is changed to 150 block some source or group, it sends the corresponding Group-Specific 151 or Group-and-Source Specific Query messages to confirm whether the 152 Report sender is the last member host or not. However, if a router 153 enables the explicit tracking function, it does not always need to 154 ask Current-State Report message transmission to the receiver hosts 155 since the router recognizes the (potential) last member host when it 156 receives the State-Change Report. The router can therefore send 157 IGMP/MLD Group-Specific and Group-and-Source Specific Queries LMQC/ 158 LLQC times (see Section 4.3 for LMQC/LLQC) only when it recognizes 159 the last member has left from the network. This reduces the 160 transmitted number of Current-State Report messages. 162 Enabling the explicit tracking function is advantageous for mobile 163 multicast, but the function requires additional processing capability 164 and a possibly large memory for routers to keep all membership 165 status. Especially when a router needs to maintain a large number of 166 receiver hosts, this resource requirement may be potentially- 167 impacted. Therefore, in this document, we propose that adjacent 168 upstream multicast routers SHOULD enable the explicit tracking 169 function for IP multicast communications on wireless networks, if 170 they have enough resources. If operators think that their routers do 171 not have enough resources, they MAY decide to disable this function 172 on their routers. Note that whether routers enable the explicit 173 tracking function or not, they need to maintain downstream membership 174 status by sending IGMPv3/MLDv2 General Query messages as some IGMPv3/ 175 MLDv2 messages may be lost during transmission. 177 4. Tuning IGMP/MLD Timers and Values 179 4.1. Tuning IGMP/MLD General Query Interval 181 IGMP and MLD are non-reliable protocols; to cover the possibility of 182 a State-Change Report being missed by one or more multicast routers, 183 "hosts retransmit the same State-Change Report messages [Robustness 184 Variable] - 1 more times", at intervals chosen at random from the 185 range (0, [Unsolicited Report Interval]) [2][3]. Although this 186 behavior increases the protocol robustness, it does not guarantee 187 that the State-Change Report is reached to the routers. Therefore, 188 routers still need to refresh the downstream membership information 189 by receiving Current-State Report periodically solicited by IGMP/MLD 190 General Query sent in the [Query Interval] period, in order to be 191 robust in front of host or link failures and packet loss. It also 192 supports the situation that mobile hosts turn off or move from the 193 wireless network to other wireless network managed by the different 194 router without any notification (e.g., leave request). 196 The [Query Interval] is the interval between General Queries sent by 197 the regular IGMPv3/MLDv2 querier, and the default value is 125 198 seconds [2][3]. By varying the [Query Interval], multicast routers 199 can tune the number of IGMP/MLD messages on the network; larger 200 values cause IGMP/MLD Queries to be sent less often. 202 This document proposes 150 seconds for the [Query Interval] value by 203 changing the Querier's Query Interval Code (QQIC) field specified in 204 the IGMP/MLD Query message, for the case that a router enabling the 205 explicit tracking function sends General Query and potentially 206 operates a large number of member hosts such as more than 200 hosts 207 on the wireless link. This longer interval value contributes to 208 minimizing traffic of Report messages and battery power consumption 209 for mobile hosts. 211 On the other hand, this document also proposes 60 to 90 seconds for 212 the [Query Interval] value for the case that a router enabling the 213 explicit tracking function attaches to a wireless link having higher 214 capacity of the resource. This shorter interval contributes to quick 215 synchronization of the membership information tracked by the router 216 but may consume battery power of mobile hosts. 218 If a router does not enable the explicit tracking function, the 219 [Query Interval] value would be its default value, 125 seconds. 221 4.2. Tuning IGMP/MLD Query Response Interval 223 The [Query Response Interval] is the Max Response Time (or Max 224 Response Delay) used to calculate the Max Resp Code inserted into the 225 periodic General Queries. Its default value is 10 seconds expressed 226 by "Max Resp Code=100" for IGMPv3 [2] and "Maximum Response 227 Code=10000" for MLDv2 [3]. By varying the [Query Response Interval], 228 multicast routers can tune the burstiness of IGMP/MLD messages on the 229 network; larger values make the traffic less bursty as host responses 230 are spread out over a larger interval, but will increase join latency 231 when State-Change Report is missing. 233 According to our experimental analysis, this document proposes two 234 tuning scenarios for tuning the [Query Response Interval] value in 235 different wireless link conditions; one scenario is for a wireless 236 link with a lower capacity of network resource or a lossy link, and 237 the other scenario is for a wireless link with enough capacity or 238 reliable condition for IGMP/MLD message transmission. 240 Regarding the first scenario, for instance, when a multicast router 241 attaches to a bursty IEEE 802.11b link, the router configures the 242 longer [Query Response Interval] value, such as 10 to 20 (sec). This 243 configuration will reduce congestion of the Current-State Report 244 messages on a link but may increase join latency and leave latency 245 when the unsolicited messages (State-Change Record) are lost on the 246 router. 248 The second scenario may happen for a multicast router attaching to a 249 wireless link having higher capacity of the resource or a point-to- 250 (multi-)point link such as an IEEE 802.16e link, because IGMP/MLD 251 messages do not seriously affect the link condition. The router can 252 seek Current-State Report messages with the shorter [Query Response 253 Interval] value, such as 5 to 10 (sec). This configuration will 254 contribute to quickly (at some level) discovering non-tracked member 255 hosts and synchronizing the membership information. 257 4.3. Tuning Last Member Query Timer (LMQT) and Last Listener Query 258 Timer (LLQT) 260 Shortening the Last Member Query Timer (LMQT) for IGMPv3 and the Last 261 Listener Query Timer (LLQT) for MLDv2 contributes to minimizing leave 262 latency. LMQT is represented by the Last Member Query Interval 263 (LMQI), multiplied by the Last Member Query Count (LMQC), and LLQT is 264 represented by the Last Listener Query Interval (LLQI), multiplied by 265 the Last Listener Query Count (LLQC). 267 While LMQI and LLQI are changeable, it is reasonable to use the 268 default values (i.e., 1 second) for LMQI and LLQI in a wireless 269 network. LMQC and LLQC, whose default value is the [Robustness 270 Variable] value, are also tunable. Therefore, LMQC and LLQC MAY be 271 set to "1" for routers enabling the explicit tracking function, and 272 then LMQT and LLQT are set to 1 second. However, setting LMQC and 273 LLQC to 1 increases the risk of missing the last member; LMQC and 274 LLQC SHOULD be set to 1 only when network operators think that their 275 wireless link is stable enough. 277 On the other hand, if network operators think that their wireless 278 link is lossy (e.g., due to a large number of attached hosts or 279 limited resources), they MAY set LMQC and LLQC to "2" for their 280 routers enabling the explicit tracking function. Although bigger 281 LMQC and LLQC values may cause longer leave latency, the risk of 282 missing the last member will be reduced. 284 4.4. Tuning Startup Query Interval 286 The [Startup Query Interval] is the interval between General Queries 287 sent by a Querier on startup. The default value is 1/4 of [Query 288 Interval]; however, this document recommends the use of its shortened 289 value such as 1 second since the shorter value would contribute to 290 smooth handover for mobile hosts using, e.g., PMIPv6 [12]. Note that 291 the [Startup Query Interval] is a static value and cannot be changed 292 by any external signal. Therefore operators who maintain routers and 293 wireless links must properly configure this value. 295 4.5. Tuning Robustness Variable 297 To cover the possibility of unsolicited reports being missed by 298 multicast routers, unsolicited reports are retransmitted [Robustness 299 Variable] - 1 more times, at intervals chosen at random from the 300 defined range [2][3]. The QRV (Querier's Robustness Variable) field 301 in IGMP/MLD Query contains the [Robustness Variable] value used by 302 the querier. The default [Robustness Variable] value defined in 303 IGMPv3 [2] and MLDv2 [3] is "2". 305 This document proposes "2" for the [Robustness Variable] value for 306 mobility, when a router attaches to a wireless link having lower 307 capacity of the resource or a large number of hosts. For a router 308 that attaches to a wireless link having higher capacity of the 309 resource or reliable condition, it is not required to retransmit the 310 same State-Change Report message; hence the router sets the 311 [Robustness Variable] to "1". Note that whether the explicit 312 tracking function is enabled or not, the [Robustness Variable] value 313 SHOULD NOT be bigger than "2". 315 5. Destination Address of Specific Query 317 IGMP/MLD Group-Specific and Group-and-Source Specific Queries defined 318 in [2][3] are sent to verify whether there are hosts that desire 319 reception of the specified group or a set of sources or to rebuild 320 the desired reception state for a particular group or a set of 321 sources. These specific Queries build and refresh multicast 322 membership state of hosts on an attached network. These specific 323 Queries should be sent to each desired hosts with specific multicast 324 address (not the all-hosts/all-nodes multicast address) as their IP 325 destination addresses, because hosts that do not join the multicast 326 session do not pay attention to these specific Queries, and only 327 active member hosts that have been receiving multicast contents with 328 the specified address reply IGMP/MLD reports. 330 6. Interoperability 332 IGMPv3 [2] and MLDv2 [3] provide the ability for hosts to report 333 source-specific subscriptions. With IGMPv3/MLDv2, a mobile host can 334 specify a channel of interest, using multicast group and source 335 addresses in its join request. Upon its reception, the upstream 336 router that supports IGMPv3/MLDv2 establishes the shortest path tree 337 toward the source without coordinating a shared tree. This function 338 is called the source filtering function and required to support 339 Source-Specific Multicast (SSM) [8]. 341 Recently, the Lightweight-IGMPv3 (LW-IGMPv3) and Lightweight-MLDv2 342 (LW-MLDv2) [4] protocols have been proposed in the IETF. These 343 protocols provide protocol simplicity for mobile hosts and routers, 344 as they eliminate a complex state machine from the full versions of 345 IGMPv3 and MLDv2, and promote the opportunity to implement SSM in 346 mobile communications. 348 This document assumes that both multicast routers and mobile hosts 349 MUST be IGMPv3/MLDv2 capable, regardless whether the protocols are 350 the full or lightweight version. And this document does not consider 351 interoperability with older version protocols. The main reason not 352 being interoperate with older IGMP/MLD protocols is that the explicit 353 tracking function does not work properly with older IGMP/MLD 354 protocols. 356 7. Security Considerations 358 This document neither provides new functions or modifies the standard 359 functions defined in [2][3][4]. Therefore there is no additional 360 security consideration provided. 362 8. Acknowledgements 364 Marshall Eubanks, Gorry Fairhurst, Behcet Sarikaya, Stig Venaas, 365 Jinwei Xia, and others provided many constructive and insightful 366 comments. 368 9. References 370 9.1. Normative References 372 [1] Bradner, S., "Key words for use in RFCs to indicate requirement 373 levels", RFC 2119, March 1997. 375 [2] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. 376 Thyagarajan, "Internet Group Management Protocol, Version 3", 377 RFC 3376, October 2002. 379 [3] Vida, R. and L. Costa, "Multicast Listener Discovery Version 2 380 (MLDv2) for IPv6", RFC 3810, June 2004. 382 [4] Liu, H., Cao, W., and H. Asaeda, "Lightweight IGMPv3 and MLDv2 383 Protocols", RFC 5790, February 2010. 385 [5] Deering, S., "Host Extensions for IP Multicasting", RFC 1112, 386 August 1989. 388 [6] Fenner, W., "Internet Group Management Protocol, Version 2", 389 RFC 2236, July 1997. 391 [7] Deering, S., Fenner, W., and B. Haberman, "Multicast Listener 392 Discovery (MLD) for IPv6", RFC 2710, October 1999. 394 [8] Holbrook, H. and B. Cain, "Source-Specific Multicast for IP", 395 RFC 4607, August 2006. 397 [9] Asaeda, H. and Y. Uchida, "IGMP/MLD-Based Explicit Membership 398 Tracking Function for Multicast Routers", 399 draft-asaeda-mboned-explicit-tracking-01.txt (work in 400 progress), October 2010. 402 9.2. Informative References 404 [10] Asaeda, H. and T. Schmidt, "IGMP and MLD Protocol Extensions 405 for Mobility", 406 draft-asaeda-multimob-igmp-mld-mobility-extensions-04.txt (work 407 in progress), March 2010. 409 [11] Fenner, B., He, H., Haberman, B., and H. Sandick, "Internet 410 Group Management Protocol (IGMP) / Multicast Listener Discovery 411 (MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")", 412 RFC 4605, August 2006. 414 [12] Gundavelli, S, Ed., Leung, K., Devarapalli, V., Chowdhury, K., 415 and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008. 417 Appendix A. Unicasting General Query 419 IGMPv3 and MLDv2 specifications [2][3] describe that a host MUST 420 accept and process any Query whose IP Destination Address field 421 contains any of the addresses (unicast or multicast) assigned to the 422 interface on which the Query arrives. In general, the all-hosts 423 multicast address (224.0.0.1) or link-scope all-nodes multicast 424 address (FF02::1) is used as the IP destination address of IGMP/MLD 425 General Query. On the other hand, according to [2][3], a router MAY 426 be able to unicast General Query to tracked member hosts in [Query 427 Interval], if the router keeps track of membership information 428 (Section 3). 430 Unicasting IGMP/MLD General Query would reduce the drain on battery 431 power of mobile hosts as only the active hosts that have been 432 receiving multicast contents respond the unicast IGMP/MLD General 433 Query messages and non-active hosts do not need to pay attention to 434 the IGMP/MLD messages. This also allows the upstream router to 435 proceed fast leaves (or shorten leave latency) by setting LMQC/LLQC 436 smaller, because the router can immediately converge and update the 437 membership information, ideally. 439 However, there is a concern in unicast General Query. If a multicast 440 router sends General Query "only" by unicast, it cannot discover 441 potential member hosts whose join requests were lost. Since the 442 hosts do not retransmit the same join requests (i.e., unsolicited 443 Report messages), they loose the chance to join the channels unless 444 the upstream router asks the membership information by sending 445 General Query by multicast. It will be solved by using both unicast 446 and multicast General Queries and configuring the [Query Interval] 447 timer value for multicast General Query and the [Unicast Query 448 Interval] timer value for unicast General Query. However, using two 449 different timers for General Queries would require the protocol 450 extension this document does not focus on. If a router does not 451 distinguish the multicast and unicast General Query Intervals, the 452 router should only use and enable multicast General Query. 454 Also, unicasting General Query does not remove multicasting General 455 Query. Multicast General Query is necessary to update membership 456 information if it is not correctly synchronized due to missing 457 Reports. Therefore, enabling unicast General Query SHOULD NOT be 458 used for the implementation that does not allow to configure 459 different query interval timers as [Query Interval] and [Unicast 460 Query Interval] (See [10] for the detail). If a router does not 461 distinguish these multicast and unicast General Query Intervals, the 462 router SHOULD only use and enable multicast General Query. 464 Authors' Addresses 466 Hitoshi Asaeda 467 Keio University 468 Graduate School of Media and Governance 469 5322 Endo 470 Fujisawa, Kanagawa 252-0882 471 Japan 473 Email: asaeda@wide.ad.jp 474 URI: http://www.sfc.wide.ad.jp/~asaeda/ 476 Yogo Uchida 477 Keio University 478 Graduate School of Media and Governance 479 5322 Endo 480 Fujisawa, Kanagawa 252-0882 481 Japan 483 Email: uchida@sfc.wide.ad.jp 485 Hui Liu 486 Huawei Technologies Co., Ltd. 487 Huawei Bld., No.3 Xinxi Rd. 488 Shang-Di Information Industry Base 489 Hai-Dian Distinct, Beijing 100085 490 China 492 Email: helen.liu@huawei.com 494 Qin Wu 495 Huawei Technologies Co., Ltd. 496 Site B, Floor 12F, Huihong Mansion 497 No.91 Baixia Rd. 498 Nanjing, Jiangsu 21001 499 China 501 Email: Sunseawq@huawei.com