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Versions: (draft-wu-multimob-igmp-mld-tuning) 00 01 02 03 04 05 06 RFC 6636

MULTIMOB Working Group                                         H. Asaeda
Internet-Draft                                           Keio University
Expires: November 28, 2011                                        H. Liu
                                                                   Q. Wu
                                                     Huawei Technologies
                                                            May 27, 2011


    Tuning the Behavior of IGMP and MLD for Mobile Hosts and Routers
                 draft-ietf-multimob-igmp-mld-tuning-00

Abstract

   IGMP and MLD are the protocols used by hosts to report their IP
   multicast group memberships to neighboring multicast routers.  This
   document describes the ways of IGMPv3 and MLDv2 protocol optimization
   for mobility, and aims to become a guideline for query and other
   timers tuning.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on November 28, 2011.

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Explicit Tracking of Membership Status . . . . . . . . . . . .  5
   4.  Tuning IGMP/MLD Timers and Values  . . . . . . . . . . . . . .  6
     4.1.  Tuning IGMP/MLD General Query Interval . . . . . . . . . .  6
     4.2.  Tuning IGMP/MLD Query Response Interval  . . . . . . . . .  6
     4.3.  Tuning Last Member Query Timer (LMQT) and Last
           Listener Query Timer (LLQT)  . . . . . . . . . . . . . . .  7
     4.4.  Tuning Startup Query Interval  . . . . . . . . . . . . . .  8
     4.5.  Tuning Robustness Variable . . . . . . . . . . . . . . . .  8
   5.  Destination Address of Specific Query  . . . . . . . . . . . .  9
   6.  Interoperability . . . . . . . . . . . . . . . . . . . . . . . 10
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 13
   Appendix A.  Unicasting General Query  . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15














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1.  Introduction

   The Internet Group Management Protocol (IGMP) [2] for IPv4 and the
   Multicast Listener Discovery Protocol (MLD) [3] for IPv6 are the
   standard protocols for hosts to initiate joining or leaving multicast
   sessions.  These protocols must be also supported by multicast
   routers or IGMP/MLD proxies [10] that maintain multicast membership
   information on their downstream interfaces.  Conceptually, IGMP and
   MLD work on wireless networks.  However, wireless access technologies
   operate on a shared medium or a point-to-point link with limited
   frequency and bandwidth.  In many wireless regimes, it is desirable
   to minimize multicast-related signaling to preserve the limited
   resources of battery powered mobile devices and the constrained
   transmission capacities of the networks.  A mobile host may cause
   initiation and termination of a multicast service in the new or the
   previous network upon its movement.  Slow multicast service
   activation following a join may degrade reception quality.  Slow
   service termination triggered by IGMP/MLD querying or by a rapid
   departure of the mobile host without leaving the group in the
   previous network may waste network resources.

   To create the optimal multicast membership management condition, IGMP
   and MLD protocols could be tuned to "ease a mobile host's processing
   cost or battery power consumption by IGMP/MLD Query transmission
   timing coordination by routers" and "realize fast state convergence
   by successive monitoring whether downstream members exist or not".

   This document describes the ways of tuning the IGMPv3 and MLDv2
   protocol behavior for mobility, including query and other timers
   tuning.  The selective optimization that provides tangible benefits
   to the mobile hosts and routers is given by keeping track of
   downstream hosts' membership status and varying IGMP/MLD Query types
   and values to tune the number of responses.  The proposed behavior
   interoperates with the IGMPv3 and MLDv2 protocols.

















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2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
   NOT","SHOULD", "SHOULD NOT", "RECOMMENDED","MAY", and "OPTIONAL" in
   this document are to be interpreted as described in RFC 2119 [1].














































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3.  Explicit Tracking of Membership Status

   Mobile hosts use IGMP and MLD to request to join or leave multicast
   sessions.  When the adjacent upstream routers receive the IGMP/MLD
   Report messages, they recognize the membership status on the link.
   To update the membership status, the routers send IGMP/MLD Query
   messages periodically as a soft-state approach does, and the member
   hosts reply IGMP/MLD Report messages upon reception.  IGMP/MLD Query
   is therefore necessary to obtain the up-to-date membership
   information, but a large number of the reply messages sent from all
   member hosts may cause network congestion or consume network
   bandwidth.

   The "explicit tracking function" [9] is the possible approach to
   reduce the transmitted number of IGMP/MLD messages and contribute to
   mobile communications.  It enables the router to keep track of the
   membership status of the downstream IGMPv3 or MLDv2 member hosts.

   The explicit tracking function reduces the chance of Group-Specific
   or Group-and-Source Specific Query transmission.  Whenever a router
   that does not enable the explicit tracking function receives the
   State-Change Report and the router's membership state is changed to
   block some source or group, it sends the corresponding Group-Specific
   or Group-and-Source Specific Query messages to confirm whether the
   Report sender is the last member host or not.  However, if a router
   enables the explicit tracking function, it does not always need to
   ask Current-State Report message transmission to the receiver hosts
   since the router recognizes the (potential) last member host when it
   receives the State-Change Report.  The router can therefore send
   IGMP/MLD Group-Specific and Group-and-Source Specific Queries LMQC/
   LLQC times (see Section 4.3 for LMQC/LLQC) only when it recognizes
   the last member has left from the network.  This reduces the
   transmitted number of Current-State Report messages.

   Enabling the explicit tracking function is advantageous for mobile
   multicast, but the function requires additional processing capability
   and a possibly large memory for routers to keep all membership
   status.  Especially when a router needs to maintain a large number of
   receiver hosts, this resource requirement may be potentially-
   impacted.  Therefore, in this document, we propose that adjacent
   upstream multicast routers SHOULD enable the explicit tracking
   function for IP multicast communications on wireless networks, if
   they have enough resources.  If operators think that their routers do
   not have enough resources, they MAY decide to disable this function
   on their routers.  Note that whether routers enable the explicit
   tracking function or not, they need to maintain downstream membership
   status by sending IGMPv3/MLDv2 General Query messages as some IGMPv3/
   MLDv2 messages may be lost during transmission.



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4.  Tuning IGMP/MLD Timers and Values

4.1.  Tuning IGMP/MLD General Query Interval

   IGMP and MLD are non-reliable protocols; to cover the possibility of
   a State-Change Report being missed by one or more multicast routers,
   "hosts retransmit the same State-Change Report messages [Robustness
   Variable] - 1 more times", at intervals chosen at random from the
   range (0, [Unsolicited Report Interval]) [2][3].  Although this
   behavior increases the protocol robustness, it does not guarantee
   that the State-Change Report is reached to the routers.  Therefore,
   routers still need to refresh the downstream membership information
   by receiving Current-State Report periodically solicited by IGMP/MLD
   General Query sent in the [Query Interval] period, in order to be
   robust in front of host or link failures and packet loss.  It also
   supports the situation that mobile hosts turn off or move from the
   wireless network to other wireless network managed by the different
   router without any notification (e.g., leave request).

   The [Query Interval] is the interval between General Queries sent by
   the regular IGMPv3/MLDv2 querier, and the default value is 125
   seconds [2][3].  By varying the [Query Interval], multicast routers
   can tune the number of IGMP/MLD messages on the network; larger
   values cause IGMP/MLD Queries to be sent less often.

   This document proposes 150 seconds for the [Query Interval] value by
   changing the Querier's Query Interval Code (QQIC) field specified in
   the IGMP/MLD Query message, for the case that a router enabling the
   explicit tracking function sends General Query and potentially
   operates a large number of member hosts such as more than 200 hosts
   on the wireless link.  This longer interval value contributes to
   minimizing traffic of Report messages and battery power consumption
   for mobile hosts.

   On the other hand, this document also proposes 60 to 90 seconds for
   the [Query Interval] value for the case that a router enabling the
   explicit tracking function attaches to a wireless link having higher
   capacity of the resource.  This shorter interval contributes to quick
   synchronization of the membership information tracked by the router
   but may consume battery power of mobile hosts.

   If a router does not enable the explicit tracking function, the
   [Query Interval] value would be its default value, 125 seconds.

4.2.  Tuning IGMP/MLD Query Response Interval

   The [Query Response Interval] is the Max Response Time (or Max
   Response Delay) used to calculate the Max Resp Code inserted into the



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   periodic General Queries.  Its default value is 10 seconds expressed
   by "Max Resp Code=100" for IGMPv3 [2] and "Maximum Response
   Code=10000" for MLDv2 [3].  By varying the [Query Response Interval],
   multicast routers can tune the burstiness of IGMP/MLD messages on the
   network; larger values make the traffic less bursty as host responses
   are spread out over a larger interval, but will increase join latency
   when State-Change Report is missing.

   According to our experimental analysis, this document proposes two
   tuning scenarios for tuning the [Query Response Interval] value in
   different wireless link conditions; one scenario is for a wireless
   link with a lower capacity of network resource or a lossy link, and
   the other scenario is for a wireless link with enough capacity or
   reliable condition for IGMP/MLD message transmission.

   Regarding the first scenario, for instance, when a multicast router
   attaches to a bursty IEEE 802.11b link, the router configures the
   longer [Query Response Interval] value, such as 10 to 20 (sec).  This
   configuration will reduce congestion of the Current-State Report
   messages on a link but may increase join latency and leave latency
   when the unsolicited messages (State-Change Record) are lost on the
   router.

   The second scenario may happen for a multicast router attaching to a
   wireless link having higher capacity of the resource or a point-to-
   (multi-)point link such as an IEEE 802.16e link, because IGMP/MLD
   messages do not seriously affect the link condition.  The router can
   seek Current-State Report messages with the shorter [Query Response
   Interval] value, such as 5 to 10 (sec).  This configuration will
   contribute to quickly (at some level) discovering non-tracked member
   hosts and synchronizing the membership information.

4.3.  Tuning Last Member Query Timer (LMQT) and Last Listener Query
      Timer (LLQT)

   Shortening the Last Member Query Timer (LMQT) for IGMPv3 and the Last
   Listener Query Timer (LLQT) for MLDv2 contributes to minimizing leave
   latency.  LMQT is represented by the Last Member Query Interval
   (LMQI), multiplied by the Last Member Query Count (LMQC), and LLQT is
   represented by the Last Listener Query Interval (LLQI), multiplied by
   the Last Listener Query Count (LLQC).

   While LMQI and LLQI are changeable, it is reasonable to use the
   default values (i.e., 1 second) for LMQI and LLQI in a wireless
   network.  LMQC and LLQC, whose default value is the [Robustness
   Variable] value, are also tunable.  Therefore, LMQC and LLQC MAY be
   set to "1" for routers enabling the explicit tracking function, and
   then LMQT and LLQT are set to 1 second.  However, setting LMQC and



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   LLQC to 1 increases the risk of missing the last member; LMQC and
   LLQC SHOULD be set to 1 only when network operators think that their
   wireless link is stable enough.

   On the other hand, if network operators think that their wireless
   link is lossy (e.g., due to a large number of attached hosts or
   limited resources), they MAY set LMQC and LLQC to "2" for their
   routers enabling the explicit tracking function.  Although bigger
   LMQC and LLQC values may cause longer leave latency, the risk of
   missing the last member will be reduced.

4.4.  Tuning Startup Query Interval

   The [Startup Query Interval] is the interval between General Queries
   sent by a Querier on startup.  The default value is 1/4 of [Query
   Interval]; however, this document recommends the use of its shortened
   value such as 1 second since the shorter value would contribute to
   smooth handover for mobile hosts using, e.g., PMIPv6 [11].  Note that
   the [Startup Query Interval] is a static value and cannot be changed
   by any external signal.  Therefore operators who maintain routers and
   wireless links must properly configure this value.

4.5.  Tuning Robustness Variable

   To cover the possibility of unsolicited reports being missed by
   multicast routers, unsolicited reports are retransmitted [Robustness
   Variable] - 1 more times, at intervals chosen at random from the
   defined range [2][3].  The QRV (Querier's Robustness Variable) field
   in IGMP/MLD Query contains the [Robustness Variable] value used by
   the querier.  The default [Robustness Variable] value defined in
   IGMPv3 [2] and MLDv2 [3] is "2".

   This document proposes "2" for the [Robustness Variable] value for
   mobility, when a router attaches to a wireless link having lower
   capacity of the resource or a large number of hosts.  For a router
   that attaches to a wireless link having higher capacity of the
   resource or reliable condition, it is not required to retransmit the
   same State-Change Report message; hence the router sets the
   [Robustness Variable] to "1".  Note that whether the explicit
   tracking function is enabled or not, the [Robustness Variable] value
   SHOULD NOT be bigger than "2".










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5.  Destination Address of Specific Query

   IGMP/MLD Group-Specific and Group-and-Source Specific Queries defined
   in [2][3] are sent to verify whether there are hosts that desire
   reception of the specified group or a set of sources or to rebuild
   the desired reception state for a particular group or a set of
   sources.  These specific Queries build and refresh multicast
   membership state of hosts on an attached network.  These specific
   Queries should be sent to each desired hosts with specific multicast
   address (not the all-hosts/all-nodes multicast address) as their IP
   destination addresses, because hosts that do not join the multicast
   session do not pay attention to these specific Queries, and only
   active member hosts that have been receiving multicast contents with
   the specified address reply IGMP/MLD reports.





































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6.  Interoperability

   IGMPv3 [2] and MLDv2 [3] provide the ability for hosts to report
   source-specific subscriptions.  With IGMPv3/MLDv2, a mobile host can
   specify a channel of interest, using multicast group and source
   addresses in its join request.  Upon its reception, the upstream
   router that supports IGMPv3/MLDv2 establishes the shortest path tree
   toward the source without coordinating a shared tree.  This function
   is called the source filtering function and required to support
   Source-Specific Multicast (SSM) [8].

   Recently, the Lightweight-IGMPv3 (LW-IGMPv3) and Lightweight-MLDv2
   (LW-MLDv2) [4] protocols have been proposed in the IETF.  These
   protocols provide protocol simplicity for mobile hosts and routers,
   as they eliminate a complex state machine from the full versions of
   IGMPv3 and MLDv2, and promote the opportunity to implement SSM in
   mobile communications.

   This document assumes that both multicast routers and mobile hosts
   MUST be IGMPv3/MLDv2 capable, regardless whether the protocols are
   the full or lightweight version.  And this document does not consider
   interoperability with older version protocols.  The main reason not
   being interoperate with older IGMP/MLD protocols is that the explicit
   tracking function does not work properly with older IGMP/MLD
   protocols.


























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7.  Security Considerations

   This document neither provides new functions or modifies the standard
   functions defined in [2][3][4].  Therefore there is no additional
   security consideration provided.














































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8.  Acknowledgements

   Marshall Eubanks, Gorry Fairhurst, Behcet Sarikaya, Yogo Uchida, Stig
   Venaas, Jinwei Xia, and others provided many constructive and
   insightful comments.














































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9.  References

9.1.  Normative References

   [1]   Bradner, S., "Key words for use in RFCs to indicate requirement
         levels", RFC 2119, March 1997.

   [2]   Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
         Thyagarajan, "Internet Group Management Protocol, Version 3",
         RFC 3376, October 2002.

   [3]   Vida, R. and L. Costa, "Multicast Listener Discovery Version 2
         (MLDv2) for IPv6", RFC 3810, June 2004.

   [4]   Liu, H., Cao, W., and H. Asaeda, "Lightweight IGMPv3 and MLDv2
         Protocols", RFC 5790, February 2010.

   [5]   Deering, S., "Host Extensions for IP Multicasting", RFC 1112,
         August 1989.

   [6]   Fenner, W., "Internet Group Management Protocol, Version 2",
         RFC 2236, July 1997.

   [7]   Deering, S., Fenner, W., and B. Haberman, "Multicast Listener
         Discovery (MLD) for IPv6", RFC 2710, October 1999.

   [8]   Holbrook, H. and B. Cain, "Source-Specific Multicast for IP",
         RFC 4607, August 2006.

   [9]   Asaeda, H. and Y. Uchida, "IGMP/MLD-Based Explicit Membership
         Tracking Function for Multicast Routers",
         draft-asaeda-mboned-explicit-tracking-01.txt (work in
         progress), October 2010.

9.2.  Informative References

   [10]  Fenner, B., He, H., Haberman, B., and H. Sandick, "Internet
         Group Management Protocol (IGMP) / Multicast Listener Discovery
         (MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")",
         RFC 4605, August 2006.

   [11]  Gundavelli, S, Ed., Leung, K., Devarapalli, V., Chowdhury, K.,
         and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.








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Appendix A.  Unicasting General Query

   IGMPv3 and MLDv2 specifications [2][3] describe that a host MUST
   accept and process any Query whose IP Destination Address field
   contains any of the addresses (unicast or multicast) assigned to the
   interface on which the Query arrives.  In general, the all-hosts
   multicast address (224.0.0.1) or link-scope all-nodes multicast
   address (FF02::1) is used as the IP destination address of IGMP/MLD
   General Query.  On the other hand, according to [2][3], a router MAY
   be able to unicast General Query to tracked member hosts in [Query
   Interval], if the router keeps track of membership information
   (Section 3).

   Unicasting IGMP/MLD General Query would reduce the drain on battery
   power of mobile hosts as only the active hosts that have been
   receiving multicast contents respond the unicast IGMP/MLD General
   Query messages and non-active hosts do not need to pay attention to
   the IGMP/MLD messages.  This also allows the upstream router to
   proceed fast leaves (or shorten leave latency) by setting LMQC/LLQC
   smaller, because the router can immediately converge and update the
   membership information, ideally.

   However, there is a concern in unicast General Query.  If a multicast
   router sends General Query "only" by unicast, it cannot discover
   potential member hosts whose join requests were lost.  Since the
   hosts do not retransmit the same join requests (i.e., unsolicited
   Report messages), they loose the chance to join the channels unless
   the upstream router asks the membership information by sending
   General Query by multicast.  It will be solved by using both unicast
   and multicast General Queries and configuring the [Query Interval]
   timer value for multicast General Query and the [Unicast Query
   Interval] timer value for unicast General Query.  However, using two
   different timers for General Queries would require the protocol
   extension this document does not focus on.  If a router does not
   distinguish the multicast and unicast General Query Intervals, the
   router should only use and enable multicast General Query.

   Also, unicasting General Query does not remove multicasting General
   Query.  Multicast General Query is necessary to update membership
   information if it is not correctly synchronized due to missing
   Reports.  Therefore, enabling unicast General Query SHOULD NOT be
   used for the implementation that does not allow to configure
   different query interval timers as [Query Interval] and [Unicast
   Query Interval] (See Appendix A for the detail).  If a router does
   not distinguish these multicast and unicast General Query Intervals,
   the router SHOULD only use and enable multicast General Query.





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Authors' Addresses

   Hitoshi Asaeda
   Keio University
   Graduate School of Media and Governance
   5322 Endo
   Fujisawa, Kanagawa  252-0882
   Japan

   Email: asaeda@wide.ad.jp
   URI:   http://www.sfc.wide.ad.jp/~asaeda/


   Hui Liu
   Huawei Technologies Co., Ltd.
   Huawei Bld., No.3 Xinxi Rd.
   Shang-Di Information Industry Base
   Hai-Dian Distinct, Beijing  100085
   China

   Email: helen.liu@huawei.com


   Qin Wu
   Huawei Technologies Co., Ltd.
   Site B, Floor 12F, Huihong Mansion
   No.91 Baixia Rd.
   Nanjing, Jiangsu  21001
   China

   Email: Sunseawq@huawei.com




















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