Network working group Q. Wu Internet Draft H. Liu Category: Informational Huawei Created: June 21, 2010 Expires: December 2010 Proposal for Tuning IGMPv3/MLDv2 Protocol Behavior in Wireless and mobile networks draft-wu-multimob-igmp-mld-tuning-02 Abstract This document proposes a variety of optimization approaches for tuning IGMPv3 and MLDv2 designed to provide useful guideline to allow wireless multicast communication in wireless networks using the current IGMP/MLD protocols. Conventions used in this document 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 [RFC2119]. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents Wu,et al Expires December 21, 2010 [Page 1] Internet-Draft Tuning IGMPv3/MLDv2 Protocol Behavior June 2010 at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on August 15, 2009. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Table of Contents 1. Introduction..................................................3 2. Evaluation of current versions of IGMP and MLD................4 3. Impact of wireless and mobility on IGMP/MLD...................6 3.1. Comparison analysis between wired and wireless multicast.6 3.2. Link models analysis for wireless multicast..............7 3.3. Characteristic requirements of wireless multicast........9 4. IGMP/MLD tuning optimization for Wireless or Mobile Network..10 4.1. Router behavior for tuning optimization.................10 4.1.1. Explicit Tracking of hosts.........................11 4.1.2. Report Suppression for the hosts...................13 4.1.3. Query Suppression for the routers..................13 4.1.4. Minimizing General Periodical Query Frequency by..... increasing interval each time......................14 4.1.5. Collecting membership by Using General Query with.... Unicast Query......................................14 4.1.6. Multiple Retransmission of Queries on packet loss..15 4.1.7. Avoiding packet bursts by tuning the scope........... of Queries.........................................15 4.1.8. Filtering unwanted multicast packets based.......... on link type.......................................15 Wu,et al Expires December 21, 2010 [Page 2] Internet-Draft Tuning IGMPv3/MLDv2 Protocol Behavior June 2010 4.1.9. Tuning Response Delay according to link type and status........................................15 4.1.10. Switching Between Unicast Query and Multicast...... Query.............................................16 5. Security Considerations.....................................17 6. Acknowledgement.............................................17 7. References..................................................17 7.1. Normative References...................................17 7.2. Informative Referencess................................18 Authors' Addresses.............................................19 1. Introduction Multicasting is more efficient a method of supporting group communication than unicasting. However, it has seen slow commercial deployment by ISPs and carriers for limited number of applications and the complexity of the architecture design [DEPLOY]. Along With the wide deployment of different wireless networks, multicast communication over wireless network comes to attract more and more interests from content and service providers, but still faces great challenges when considering it to keep up with node movement and frequent topology change and providing efficient service in the new wireless environment, e.g., dynamic group membership and constant update of delivery path due to node movement is highly required in the wireless network. On the other hand, unlike shared-medium wired LAN, some of wireless networks, e.g. Wireless 802.11 WLAN offer limited reliability and consume more power and cost more transmission overhead, in the worse case, it is more prone to cause congestion. Considering the existing multicast communications is designed only for fixed users using wired link, it does not work well for all the wireless link types. Therefore IGMP/MLD protocol should be enhanced or tuned to adapt to wireless environment to meet the reliability and efficiency requirements in the scenarios described in [REQUIRE]. This memo proposes a variety of optimization approaches for tuning IGMP/MLD protocols in wireless or mobile communication environment. It aims to make the minimum tuning without introducing obvious changes on the protocol behavior. These solutions can also be used in wired network when efficiency and reliability are required. They are discussed in detail in Section 4. Wu,et al Expires December 21, 2010 [Page 3] Internet-Draft Tuning IGMPv3/MLDv2 Protocol Behavior June 2010 2. Evaluation of current versions of IGMP and MLD As described in [RFC5757], the default timer values and counter values specified in IGMPv2/MLDv1[2236][2710] or IGMPv3/MLDv2 [RFC3376][RFC3810] were not designed for the mobility context. This may result in a slow reaction of the multicast-routing infrastructure following a client join or leave. This issue can be addressed by tuning these parameters for the expected packet loss on a link. IGMPv2 [RFC2236] and MLDv1 [RFC2710] only support ASM communication mode. They do not support SSM subscription, which may limit their widespread deployment in practical multicast network. IGMPv3 [RFC3376] and MLDv2 [RFC3810] and their lightweight version LW- IGMPv3/LW-MLDv2 [RFC5760] support all the features of ASM and SSM communication. Comparing with ASM mode, SSM [RFC4607] mode allows only sources specific multicast delivery and reduce the demand on the network and improve security by so limiting the source. Therefore SSM mode is much better to be candidates for wireless and mobile networks than their previous versions. IGMPv3/MLDv2 Explicit join and leave Reports are the messages sent unsolicitedly when a host intends to join or leave a group. They are beneficial for ensuring satisfactory user experience and must be guaranteed to improve service performance and to optimize resource use. Current IGMPv3 and MLDv2 provide the reliability for these messages by non responsive retransmission, which is not guaranteed the messages to be retransmitted is received and may be not adequate from both the robustness and efficiency aspects [ROBUST]. This issue could be enhanced by acknowledgement-retransmission in [ACK][IGMP- ACK]. In IGMPv2 [RFC2236] and MLDv1 [RFC2710], host suppression is used to suppress duplicated multicast listener reports on the link. In IGMPv3 and MLDv2, there is no such host suppression and explicit tracking of host membership is allowed, which can be used to decrease the number of unnecessary packets sent. Without host suppression, it is possible for a multicast router to explicitly keep track the membership of all multicast hosts in the access network using explicit tracking. And because the router has record of each user in its state database or listener node table, it is possible to eliminate the need for query timeouts when receiving leave messages and simplify the Query mechanism by reducing both the unnecessary Queries and reports generated on a network. Wu,et al Expires December 21, 2010 [Page 4] Internet-Draft Tuning IGMPv3/MLDv2 Protocol Behavior June 2010 On the other hand, without host suppression, the report count in response to a Query is not small, if the number of active receivers on the network is large. Even though the protocols enable the reports on an interface to be merged, further optimizations are still required to improve the efficiency and to reduce bandwidth consumption. In summary, it is desirable to choose IGMPv3/MLDv2 or LW- IGMPv3/MLDv2 as the basis for optimization of IGMP/MLD to adapt to wireless and mobile networks. But the performance still needs to be improved by carefully tuning the Query Interval and other variables to adapt to wireless and mobile scenarios. Also some enhanced mechanism with no protocol changes can be employed as well. Considering an enhancement in one direction might introduce side effects in another one, balances should be taken carefully to avoid defects and improve protocol performance as a whole, the comparison between IGMPv2/MLDv1 and IGMPv3/MLDv2 is illustrated in figure 2. +---------------------+----------------------+-------------------+ | Issues | IGMPv2/MLDv1 | IGMPv3/MLDv2 | +---------------------+----------------------+-------------------+ |Default Timer and | Not designed for | Not designed for| |Robustness Variable | Mobility context | Mobility context| | | Need to be tuned | Need to be tuned| +---------------------+----------------------+-------------------+ | | | | | Explicit Tracking | Not Support | Support | | | | | +---------------------+----------------------+-------------------+ | ASM and SSM | Only Support ASM | | | Subscription | Subscription | Both Support | +---------------------+----------------------+-------------------+ | | | | | Explicit Join | | | | and Leave | Support | Support | | | | | +---------------------+----------------------+-------------------+ | | | | |Host Suppression | Support | Not Support | +---------------------+----------------------+-------------------+ Figure 1. Comparison between IGMPv2/MLDv1 and IGMPv3/MLDv2 Wu,et al Expires December 21, 2010 [Page 5] Internet-Draft Tuning IGMPv3/MLDv2 Protocol Behavior June 2010 3. Impact of wireless and mobility on IGMP/MLD This section first evaluates the impact of wireless on mobility on IGMP/MLD by comparing wireless multicast with wired multicast and comparing different wireless link models. And then gives the characteristics requirement of wireless multicast. 3.1. Comparison analysis between wired and wireless multicast Existing multicast support for fixed user can be extended to mobile users in wireless environments. However applying such support to wireless multicast is difficult for the following five reasons. O Limited Bandwidth: In contrast with wired multicast, wireless multicast usually has limited bandwidth. Also the bandwidth available in upstream direction and downstream direction may not be equal. O Large packets Loss: In contrast with wired multicast, wireless multicast has large packet loss that range between 1%~30% based on the links. O Frequent Membership change: In the wired multicast, membership change only happens when a user leave or joins a group while in the wireless multicast, membership changes may also occur when a user changes the location. O Reliability: Due to possible unwanted interaction of protocols across layers and user movement, the wireless network may be overwhelmed with more excessive traffic than wired network. In worse case, this may lead to network performance degrading and network connection complete loss. O Increased Leave Latency: Unlike wired multicast, the leave latency in the wireless multicast will be increased with user movement. Wu,et al Expires December 21, 2010 [Page 6] Internet-Draft Tuning IGMPv3/MLDv2 Protocol Behavior June 2010 Figure 2 shows the details for the difference between wired multicast and wireless multicast. +--------------+---------------------+----------------------------+ | | Current wired | Wireless | | Issues | Multicast | multicast | +--------------+---------------------+----------------------------+ | | | Limited and variable | | Bandwidth | Plentiful | amount,possible asymmetric | | | | link | +--------------+---------------------+----------------------------+ | | | | | Loss of | Frequent(<1%) | Frequent and variable | | Packets | | (1%-30% based on links) | +--------------+---------------------+----------------------------+ | | | | | Membership | Only when a user | Also when a user moves | | Changes | leaves and joins | to another location | | | a group | | +--------------+---------------------+----------------------------+ | | | More complex due to | | | Possible use of a | wireless links and user | | Reliability | transport-layer | mobility; possible unwanted| | | protocol(such as the| interaction of protocols | | | Multicast File | at transport and link | | | Transfer Protocol) | layers | +--------------+---------------------+----------------------------+ | | | Increase due to | |Leave Latency | not changed by | user movement | | | user movement | and delayed or | | | | lost packet | -------------------------------------+---------------------------- Figure 2. Comparison between wired multicast and wireless multicast 3.2. Link models analysis for wireless multicast There are various type of wireless links. Each link type has different feature and performance, e.g., in various type links, Some link types provide better reliability for unicast than multicast, e.g., by unicast retransmission. In this document, we categorize the wireless link type into three typical link models: O PTP link model O PTMP link model Wu,et al Expires December 21, 2010 [Page 7] Internet-Draft Tuning IGMPv3/MLDv2 Protocol Behavior June 2010 O Broadcast link model Point to Point link model is the model with one dedicated link that connects exactly two communication facilities. In this model, each link has only one receiver and the bandwidth is dedicated for each receiver. Also one unique prefix or set of unique prefixes will be assigned to each receiver. Such link model can be accomplished by running PPP on the link or having separate VLAN for each receiver. PTMP link model is the model with multipoint link which consist of a series of receivers and one centralized transmitter. Unlike P2P link model, Bandwidth and prefix in this model are shared by all the receivers on the same link. Therefore Duplicate Address Detection (DAD) should be performed to check whether the assigned address is used by other receivers. Broadcast link model is the model with the link connecting two or more nodes and supporting broadcast transmission. Such link model is quite similar to PTMP link model. The obvious difference to the PTMP link model is Broadcast link model only provide downlink common channels for each user while P2MP link model also provide dedicated uplink channel for each user. Figure 3 shows the details for the difference between different wireless link models. +---------------+-----------------+---------------+---------------+ | Features | PTP | PTMP | Broadcast | | | link model | link model | link model | +---------------+-----------------+---------------+---------------| | | | Common | | | Shared link/ |Dedicated uplink | downlink | | | Dedicated link|and downlink | channels and |common downlink| | |channels for each| dedicated | Channel for | | |user | uplink |each user | | | | channels for | | | | | each | | | | | user | | +---------------+-----------------+---------------+---------------| | | | Prefix shared | Prefix shared | | Shared Prefix | Per Prefix for | by all | by all | | /Dedicated | each receiver | receivers | receivers | | Prefix | No need DAD |DAD is required|DAD is required| +---------------+-----------------+---------------+---------------| | | | | | |Shared Service | | | | Wu,et al Expires December 21, 2010 [Page 8] Internet-Draft Tuning IGMPv3/MLDv2 Protocol Behavior June 2010 | Support | Not Support | Support | Support | | | | | | +---------------+-----------------+---------------+---------------| | | Only one node | Link Layer | Broadcast | | | On the link | Multicast | Support | | | Forward | Support | at L2 | | link layer | multicast | using | using switch | | Broadcast | packets to | Backend | | | Multicast | the only | (e.g.,AR) | IGMP/MLD | | Support | receiver | IGMP/MLD | Snooping | | | on the | Snooping | at switch | | | link | at AR | | +---------------+-----------------+---------------+---------------| | | | | | | | | | Ethernet | | Ethernet | Not support | Not support | Support By | | link Support | | | Implementing | | | | | Bridge | | | | | | +---------------+-----------------+---------------+---------------+ Figure 3. Wireless Link Models Analysis 3.3. Characteristic requirements of wireless multicast Due to the impacts of wireless on IGMP/MLD described in the section 3.1, it is desirable for IGMP and MLD to have the following characteristics when used in wireless and mobile networks [REQUIRE]: o Adaptive to different link mode: IGMP and MLD are originally designed for wired multicast and some of their processing is not applicable to wireless multicast, e.g., asymmetrical link, limited bandwidth, larger packet loss rate, increased leave latency. Also Wireless and mobile network has various link types, each of them has different bandwidth and performance. Therefore IGMP/MLD protocol behavior should be tuned to adapt to different link model. o Minimal Join and Leave Latency: Fast join and leave of a subscriber helps to improve the user's experience during channel join and channel zapping. Fast leave also facilitates releasing of unused network resources quickly. Besides, mobility and handover may cause a user to join and leave a multicast group frequently, which also require fast join and leave to accelerate service activation and to optimize resource usages. o Robustness to packet loss: Wireless link has the characteristic that packet transmission is unreliable due to instable link Wu,et al Expires December 21, 2010 [Page 9] Internet-Draft Tuning IGMPv3/MLDv2 Protocol Behavior June 2010 conditions and limited bandwidth. For mobile IP network, packets sometimes have to travel between home network and foreign network and have the possibility of being lost due to long distance transmission. These network scenarios have more strict robustness requirement on delivery of IGMP and MLD protocol messages. o Minimum packet transmission: Wireless link resources are usually more precious and limited compared to their wired counterpart. Minimizing packet exchange without degrading general protocol performance should also be emphasized to improve efficiency and make good use of network capacity and processing capability. o Avoiding packet burst: Large number of packets generated within a short time interval may have the tendency to deteriorate wireless network conditions. IGMP and MLD when using in wireless and mobile networks should be optimized if their protocol message generation has the potential of introducing packet burst. 4. IGMP/MLD tuning optimization for Wireless or Mobile Network As mentioned in section 2, IGMPv3/MLDv2 or LW-IGMPv3/MLDv2 are recommended to be used as the basis for optimization of IGMP/MLD to adapt to wireless and mobile networks. In this section, taking these characteristics requirement into account, we will discuss several optimization approaches for tuning of IGMP and MLD in the wireless environment. The optimizations try to minimize the packet transmission for both the Reports and Queries, and at the meanwhile take the factor of improving reliability into account, with minimum cost. The different link types are also considered when varying behavior and parameters. 4.1. Router behavior for tuning optimization IGMPv3 and MLDv2 have three kinds of Queries: General Query periodically sent to all multicast receivers, Group Specific Query sent when a receiver leaves a (*,G) group, and Source-and-Group Specific Query sent when a receiver leaves an (S,G) group. These Queries have different functional scope. They are used to fetch and refresh the downstream membership information by being responded by solicited reports. This section lists the possible optimization approaches for Query messages. The solutions are not intended to be adopted altogether or simultaneously, but can be taken selectively according to the scale and conditions of the operating network. Wu,et al Expires December 21, 2010 [Page 10] Internet-Draft Tuning IGMPv3/MLDv2 Protocol Behavior June 2010 4.1.1. Explicit Tracking of hosts In the IGMPv2/MLDv1, the multicast listener reports are suppressed if the same report has already been sent by another host in the network which is also referred to as host suppression. As described in the A.2 of [RFC3810], the suppression of multicast listener reports has been removed in MLDv2 due to the following reasons: O Routers may want to track per-host multicast listener status on an interface. This enables the router to track each individual host that is joined to a particular group or channel and allow minimal leave latencies when a host leaves a multicast group or channel. o Multicast Listener Report suppression does not work well on bridged LANs. Many bridges and Layer2/Layer3 switches that implement MLD snooping do not forward MLD messages across LAN segments in order to prevent multicast listener report suppression. o By eliminating multicast listener report suppression, hosts have fewer messages to process; this leads to a simpler state machine implementation. o In MLDv2, a single multicast listener report now bundles multiple multicast address records to decrease the number of packets sent. In comparison, the previous version of MLD required that each multicast address be reported in a separate message. In these reasons, one important reason is for per-host tracking at the router which is also referred to as explicit tracking. Explicit tracking is used to explicitly keep track the membership of all multicast hosts in the access network which simplifies the Query mechanism by reducing both the unnecessary Queries and reports generated on a network. When explicit tracking is enabled on a router, the local replication can be used by the router to inspect incoming join and leave requests, record or refresh the membership state for each host on the interface, and take appropriate action to each received report. In the meanwhile, the router builds a table to track which channel being forwarded to each port. If the channel being requested to view is already being received at the router, it can replicate the stream and forward to this new requester which ensure good response time, but we should note that the router must ensure enough bandwidth available to service the request. Wu,et al Expires December 21, 2010 [Page 11] Internet-Draft Tuning IGMPv3/MLDv2 Protocol Behavior June 2010 By using the tracking table mentioned above, the router also has the capability to learn if a particular multicast address has any listeners on an attached link or if any of the sources from the specified list for the particular multicast address has any listeners on an attached link or not. Such capability can also be accomplished by using Group specific Query or Source-and-Group Specific Queries, i.e., the Group Specific and Source-and-Group Specific Queries, which are sent to query other members when a member leaves, are unnecessary because the router has already known who are active on the interface using explicit tracking. Therefore it is desirable that Group Specific Query is eliminated when explicit tracking is used. But this does not mean that explicit tracking can not be used with General periodical Query and current state report in response to General Query. In some cases (e.g., explicit join and leave message from hosts are lost), the Explicit tracking may depend on current state report to refresh the membership state by sending General Query. But different from using Group specific Query, General Query is periodical message sent by a router to all multicast receivers and used by the router to refresh the existing state at the router in each Query interval. Therefore explicit tracking may update membership state periodically by using periodical IGMP/MLD Query. The main benefits of using explicit tracking without Group specific Query or Source-and-Group Specific Queries are that it provides: O minimizing packet number and packet burst: Elimination of Group and Source-Group specific Queries in case a member leaves a group will reduce the great number of transmitted Group Specific Queries. And finally the total number of Reports in response to Group Specific Queries can be drastically reduced. O Minimal leave latencies: That is to say, a router configured with IGMPv3/MLDv2 and explicit tracking can immediately stop forwarding traffic if the last host to request to receive traffic from the router indicates that it no longer wants to receive traffic. O Faster channel changing: The channel change time of the receiver application depends on the leave latency, that is to say, single host can not receive the new multicast stream before forwarding of the old stream has stopped. O Reducing Power consumption: Due to elimination of the suppression of multicast listener reports, the host does not need to spend processing power to hear and determine if the same report has already been sent by another host in the network and therefore suppress the Wu,et al Expires December 21, 2010 [Page 12] Internet-Draft Tuning IGMPv3/MLDv2 Protocol Behavior June 2010 duplicated report message sent from itself, which is beneficial to mobile hosts that do not have enough battery power. However the router may need to increase power to process extra unnecessary report sent from the host due to elimination of the host suppression, which can be mitigated by aggregating the multicast group records in one single report message. On the other hand, when explicit tracking is enabled at the router, the router may consume more memory and processing overhead to store the membership state of all hosts on the interface, especially when explicit tracking is used with General Query. This issue can be optimized by separation of processing state changing report and current state report. That means the router with explicit tracking support will not send General Query to refresh membership state at this router and only take action to the state change report, e.g., explicit join report and explicit leave report which is beneficial to reduce leave latency. The current state report can be processed by another router who sends the period Query. 4.1.2. Report Suppression for the hosts The large number of Reports and bad link condition may result in packets burst. This packet burst can be mitigated by having the router aggregate the responses (membership reports) from multiple clients. The router can intercept IGMP/MLD reports coming from hosts, and forwards a summarized version to the router only when necessary. Typically this means that the router will forward IGMP/MLD membership reports as follows: - Unsolicited membership reports (channel change requests) are forwarded only the first subscriber joins a multicast group, or the last subscriber leaves a multicast group. This tells the router to begin or stop sending this channel to this router. - Solicited membership reports (sent in response to an query) are forwarded once per multicast group. The router may also aggregate multiple responses together into a single membership report. 4.1.3. Query Suppression for the routers The large number of Queries and bad link condition may result in packets burst. This packet burst can be mitigated by having the downstream router stop forwarding IGMP/MLD Queries packets sent to the hosts and respond with report as proxy to the upstream router. Typically this means that the router will: Wu,et al Expires December 21, 2010 [Page 13] Internet-Draft Tuning IGMPv3/MLDv2 Protocol Behavior June 2010 - Never send a specific query to any client, and - Send general queries only to those clients receiving at least one multicast group 4.1.4. Minimizing General Periodical Query Frequency by increasing interval each time As described in [RFC3376][RFC3810], General Queries is sent periodically by the Querier with fixed interval, to learn multicast address listener information from an attached link. This General Query can be slowed down when a router can not collect successfully all the members' report responses in the meanwhile the network congestion is going to happen [ADAPTIVE]. Its basic behavior is: the router after sending a Query, if acquires the response from the receiver, refreshes its state database and stop the querying retransmission process, or if after a time interval fails to get the report response, resends a Query with an increased (e.g. double) interval. This process can be repeated [Robustness variables] times, each time the retransmission is arranged in a prolonged time interval, till the router receives the response, or determines the receiver is unreachable and then stops the sending of the Query ultimately. This query retransmission with incremental interval enables the router to reduce the total packet retransmission times in the same time period comparing with retransmission for multiple times with fixed interval. Therefore it can be used to improve the robustness of the solicited report and of the Query in case of network congestion. The variable time interval and the termination condition should be configurable and could be set according to actual network condition. 4.1.5. Collecting membership by Using General Query with Unicast Query As described in [RFC3376] and [RFC3810], a node MUST accept and process any Query whose IP Destination Address field contains unicast address. That is to say, Unicast Query should be allowed in some cases which may benefit the battery power consumption on mobile terminals. It also can be used with General Query to improve the robustness of solicited reports when General Query that is used to collect membership information fails. Its basic behavior is: a router after sending a periodical Query collects successfully all the members' report responses except for one or two which are currently still valid in its database. This may be because the non- respondent ones silently leave the network without any notification, Wu,et al Expires December 21, 2010 [Page 14] Internet-Draft Tuning IGMPv3/MLDv2 Protocol Behavior June 2010 or because their reports are lost due to some unknown reason. The router in this case could choose to unicast a Query respectively to each non-respondent receiver to check whether they are still alive for the multicast reception, without affecting the majority of receivers that have already responded. Optionally, unicast Queries could be resent in incremental interval, as described in section 4.2.1. 4.1.6. Multiple Retransmission of Queries on packet loss As described in [RFC3376] and [RFC3810], Group specific Query and Group-and-Source specific Query, can be retransmitted several times within a given time interval. And also described in [RFC3376] and [RFC3810], General Query can be retransmitted [Startup Query Count] with [Startup Query Interval].In some case, a router which keeps track of all its active receivers, if after sending a Query, may fail to get any response from any receiver. And it may derive that this Query might have been lost before reaching the other end of the link. In such case, the router could choose to compensate this situation by sending another Query to solicit its active members and setting the retransmission times and one new timer for retransmission. When the retransmission timer expires and the response from receiver has not arrived, then another Query will be retransmitted. 4.1.7. Filtering unwanted multicast packets based on link type When the network needs to deliver packets to the receiver, the receiver may be in the dormant mode. In such case, Paging capability will be used to establish connection with the network when the receiver is waken up. Before the connection is established, packets destined to a receiver in dormant mode are buffered at the Access router. However the multicast capability within a link may cause for a receiver to wake up for unwanted multicast packet. This can be avoided by filtering the multicast packets and delivering the packets to only for receivers that are listening for particular multicast packets. As point-to-point link model has only one node on the link, they do not have any effect on the dormant mode. The broadcast link model and point to multipoint link model may have the multicast capability, which requires filtering at the access node to support the dormant mode for the receivers. 4.1.8. Tuning Response Delay according to link type and status As described in IGMPv3/MLDv2, a longer Maximum Response Delay will spread Report messages over a longer interval which can greatly Wu,et al Expires December 21, 2010 [Page 15] Internet-Draft Tuning IGMPv3/MLDv2 Protocol Behavior June 2010 reduce possibility of MLD traffic burstiness. However, a longer Maximum Response Delay in Multicast Address Specific and Multicast Address and Source Specific Queries extends the leave latency (the time between when the last listener stops listening to a source or multicast address and when the traffic stops flowing.) In order to avoid burstiness of MLD traffic and reduce leave latency, we can first use explicit tracking with Group Specific Query eliminated to minimize leave latency. And then the Response Delay may be dynamically calculated based on the expected number of Reporters for each Query and link type and link status. O If the expected number of Reporters is large and link condition is bad, the system administrator MUST choose the longer Maximum Response Delay; If the expected number of Reporters is small and the link condition is good, the administrator may choose the smaller Maximum response Delay. In this case, the MLD traffic burstieness can be reduced. o Another case is if the link type is PTP which means the resource is dedicated for one receiver on each link, then the Maximum Response Delay can be chosen smaller, if the link type is shared medium link or P2MP, then the Maximum Response Delay can be configured larger. 4.1.9. Switching Between Unicast Query and Multicast Query IGMP/MLD protocols define the use of multicast Queries whose destination addresses are multicast addresses and also allow use of unicast Queries with unicast destination. The unicast Query is sent only for one destination and has the advantages of not affecting other host on the same link. But in some cases(e.g., during the Queries on startup)using unicast Query instead of multicast Query ,the number the valid multicast receiver on the same link may be large, i.e., numerous Queries will be generated for each member, which will not be an efficient use of link resources. In this case the normal multicast Query will be a good choice because only one Query needs to be sent for the receivers. The router can choose to switch between unicast and multicast Query according to the practical network conditions. For example, if the receiver number is small, the router could send unicast Queries respectively to each receiver to solicit their membership states, without arousing other host which is in the dormant state. when the receiver number reaches a predefined level, the router could change Wu,et al Expires December 21, 2010 [Page 16] Internet-Draft Tuning IGMPv3/MLDv2 Protocol Behavior June 2010 to use multicast Queries. The router could make the switching flexibly according to practical conditions to improve the efficiency. 5. Security Considerations They will be described in the later version of this draft. 6. Acknowledgement The authors would like to thank WeeSan Lee, Imed Romdhani, Stig,Venaas, Gorry Fairhurst, Thomas C. Schmidt, Marshall Eubanks, Suresh Krishnan, J.William Atwood, Hitoshi Asaeda, Liu Yisong and Wei Yong for their valuable comments and suggestions on this document. 7. References 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to indicate requirement levels", RFC 2119, March 1997. [RFC1112] Deering, S. ''Host Extensions for IP Multicasting'', RFC1112, August 1989. [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 2", RFC 2236, November 1997. [RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast Listener Discovery (MLD) for IPv6", RFC 2710, October 1999. [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. Thyagarajan, "Internet Group Management Protocol, Version 3", RFC 3376, October 2002. [RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery Version 2(MLDv2) for IPv6", RFC 3810, June 2004. [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for IP", RFC 4607, August 2006. [RFC5790] Liu, H., Cao, W., and H. Asaeda, "Lightweight IGMPv3 and MLDv2 Protocols", RFC5790, February 2010. Wu,et al Expires December 21, 2010 [Page 17] Internet-Draft Tuning IGMPv3/MLDv2 Protocol Behavior June 2010 7.2. Informative Referencess [DEPLOY] C. Diot, B. Levine, B. Lyles, H. Kassem and D. Balensiefen. ''Deployment Issues for the IP Multicast Service and Architecture'' ,IEEE Networks Magazine's Special Issue on Multicast, January, 2000 [REQUIRE] H. Liu, Q. Wu, H. Asaeda and TM. Eubanks, "Mobile and Wireless Multicast Requirements on IGMP/MLD Protocols", draft-liu- multimob-igmp-mld-mobility-req-03.txt, March 2010. [ROBUST] A. Sen Mazumder, "Facilitating Robust Multicast Group Management", NOSSDAV'05, June 13-14, 2005, Stevenson, Washington, USA. [ACK] Nikaein, N. and Bonnet, C. "Wireless multicasting in an IP environment" In Proceedings of the 5th International Workshop on Mobile Multimedia Communication MoMuc'98 (Berlin, Germany, Oct. 12- - 14). IEEE Computer Society Press, 1998. [IGMP-ACK] H. Liu, Q, Wu, "Reliable IGMP and MLD Protocols in Wireless Environment", draft-liu-multimob-reliable-igmp-mld-00.txt, February 2010. [ADAPTIVE] I. Romdhani, J. Munoz, H. Bettahar, and A. Bouabdallah, "Adaptive Multicast Membership Management for Mobile Multicast Receivers", IEEE, 2006. [RFC5757] Schmidt, T., Waehlisch, M., and G. Fairhurst, "Multicast Mobility in Mobile IP Version 6 (MIPv6): Problem Statement and Brief Survey", RFC 5757, February 2010. Wu,et al Expires December 21, 2010 [Page 18] Internet-Draft Tuning IGMPv3/MLDv2 Protocol Behavior June 2010 Authors' Addresses Qin Wu Huawei Technologies Co., Ltd. Site B, Floor 12, Huihong Mansion,No.91 Baixia Rd. Nanjing, Jiangsu 21001 China Phone: +86-25-84565892 EMail: sunseawq@huawei.com Hui Liu Huawei Technologies Co., Ltd. Huawei Bld., No.3 Xinxi Rd. Shang-Di Information Industry Base Hai-Dian Distinct, Beijing 100085 China EMail: Liuhui47967@huawei.com Wu,et al Expires December 21, 2010 [Page 19]