Internet Research Task Force (IRTF)                           T. Schmidt
Request for Comments: 5757                                   HAW Hamburg
Category: Informational                                     M. Waehlisch
ISSN: 2070-1721                                                 link-lab
                                                            G. Fairhurst
                                                  University of Aberdeen
                                                           February 2010
Internet Research Task Force (IRTF)                           T. Schmidt
Request for Comments: 5757                                   HAW Hamburg
Category: Informational                                     M. Waehlisch
ISSN: 2070-1721                                                 link-lab
                                                            G. Fairhurst
                                                  University of Aberdeen
                                                           February 2010

Multicast Mobility in Mobile IP Version 6 (MIPv6): Problem Statement and Brief Survey




This document discusses current mobility extensions to IP-layer multicast. It describes problems arising from mobile group communication in general, the case of multicast listener mobility, and problems for mobile senders using Any Source Multicast and Source-Specific Multicast. Characteristic aspects of multicast routing and deployment issues for fixed IPv6 networks are summarized. Specific properties and interplays with the underlying network access are surveyed with respect to the relevant technologies in the wireless domain. It outlines the principal approaches to multicast mobility, together with a comprehensive exploration of the mobile multicast problem and solution space. This document concludes with a conceptual road map for initial steps in standardization for use by future mobile multicast protocol designers. This document is a product of the IP Mobility Optimizations (MobOpts) Research Group.


Status of This Memo


This document is not an Internet Standards Track specification; it is published for informational purposes.


This document is a product of the Internet Research Task Force (IRTF). The IRTF publishes the results of Internet-related research and development activities. These results might not be suitable for deployment. This RFC represents the consensus of the MobOpts Research Group of the Internet Research Task Force (IRTF). Documents approved for publication by the IRSG are not a candidate for any level of Internet Standard; see Section 2 of RFC 5741.

本文件是互联网研究工作组(IRTF)的产品。IRTF发布互联网相关研究和开发活动的结果。这些结果可能不适合部署。本RFC代表了互联网研究工作组(IRTF)MobOpts研究小组的共识。IRSG批准发布的文件不适用于任何级别的互联网标准;见RFC 5741第2节。

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at


Copyright Notice


Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved.

版权所有(c)2010 IETF信托基金和确定为文件作者的人员。版权所有。

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents ( 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.

本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(自本文件出版之日起生效。请仔细阅读这些文件,因为它们描述了您对本文件的权利和限制。

Table of Contents


   1. Introduction and Motivation .....................................4
      1.1. Document Scope .............................................5
   2. Problem Description .............................................6
      2.1. General Issues .............................................6
      2.2. Multicast Listener Mobility ................................9
           2.2.1. Node and Application Perspective ....................9
           2.2.2. Network Perspective ................................10
      2.3. Multicast Source Mobility .................................11
           2.3.1. Any Source Multicast Mobility ......................11
           2.3.2. Source-Specific Multicast Mobility .................12
      2.4. Deployment Issues .........................................13
   3. Characteristics of Multicast Routing Trees under Mobility ......14
   4. Link Layer Aspects .............................................15
      4.1. General Background ........................................15
      4.2. Multicast for Specific Technologies .......................16
           4.2.1. 802.11 WLAN ........................................16
           4.2.2. 802.16 WIMAX .......................................16
           4.2.3. 3GPP/3GPP2 .........................................18
           4.2.4. DVB-H / DVB-IPDC ...................................19
           4.2.5. TV Broadcast and Satellite Networks ................19
      4.3. Vertical Multicast Handovers ..............................20
   5. Solutions ......................................................20
      5.1. General Approaches ........................................20
      5.2. Solutions for Multicast Listener Mobility .................21
           5.2.1. Agent Assistance ...................................21
           5.2.2. Multicast Encapsulation ............................22
           5.2.3. Hybrid Architectures ...............................23
           5.2.4. MLD Extensions .....................................23
      5.3. Solutions for Multicast Source Mobility ...................24
           5.3.1. Any Source Multicast Mobility Approaches ...........24
           5.3.2. Source-Specific Multicast Mobility Approaches ......25
   6. Security Considerations ........................................26
   7. Summary and Future Steps .......................................27
   Appendix A. Implicit Source Notification Options...................29
   Informative References.............................................29
   1. Introduction and Motivation .....................................4
      1.1. Document Scope .............................................5
   2. Problem Description .............................................6
      2.1. General Issues .............................................6
      2.2. Multicast Listener Mobility ................................9
           2.2.1. Node and Application Perspective ....................9
           2.2.2. Network Perspective ................................10
      2.3. Multicast Source Mobility .................................11
           2.3.1. Any Source Multicast Mobility ......................11
           2.3.2. Source-Specific Multicast Mobility .................12
      2.4. Deployment Issues .........................................13
   3. Characteristics of Multicast Routing Trees under Mobility ......14
   4. Link Layer Aspects .............................................15
      4.1. General Background ........................................15
      4.2. Multicast for Specific Technologies .......................16
           4.2.1. 802.11 WLAN ........................................16
           4.2.2. 802.16 WIMAX .......................................16
           4.2.3. 3GPP/3GPP2 .........................................18
           4.2.4. DVB-H / DVB-IPDC ...................................19
           4.2.5. TV Broadcast and Satellite Networks ................19
      4.3. Vertical Multicast Handovers ..............................20
   5. Solutions ......................................................20
      5.1. General Approaches ........................................20
      5.2. Solutions for Multicast Listener Mobility .................21
           5.2.1. Agent Assistance ...................................21
           5.2.2. Multicast Encapsulation ............................22
           5.2.3. Hybrid Architectures ...............................23
           5.2.4. MLD Extensions .....................................23
      5.3. Solutions for Multicast Source Mobility ...................24
           5.3.1. Any Source Multicast Mobility Approaches ...........24
           5.3.2. Source-Specific Multicast Mobility Approaches ......25
   6. Security Considerations ........................................26
   7. Summary and Future Steps .......................................27
   Appendix A. Implicit Source Notification Options...................29
   Informative References.............................................29
1. Introduction and Motivation
1. 介绍和动机

Group communication forms an integral building block of a wide variety of applications, ranging from content broadcasting and streaming, voice and video conferencing, collaborative environments and massive multiplayer gaming, up to the self-organization of distributed systems, services, or autonomous networks. Network-layer multicast support will be needed whenever globally distributed, scalable, serverless, or instantaneous communication is required.


The early idea of Internet multicasting [1] soon led to a wide adoption of Deering's host group model [2]. Broadband media delivery is emerging as a typical mass scenario that demands scalability and bandwidth efficiency from multicast routing. Although multicast mobility has been a concern for about ten years [3] and has led to numerous proposals, there is as yet no generally accepted solution. Multicast network support will be of particular importance to mobile environments, where users commonly share frequency bands of limited capacity. Reception of "infotainment" streams may soon require wide deployment of mobile multicast services.


Mobility in IPv6 [4] is standardized in the Mobile IPv6 RFCs [5][6], and it addresses the scenario of network-layer changes while moving between wireless domains. MIPv6 [5] only roughly defines multicast mobility for Mobile Nodes (MNs) using a remote subscription approach or through bidirectional tunneling via the Home Agent (HA). Remote subscription suffers from slow handovers relying on multicast routing to adapt to handovers. Bidirectional tunneling introduces inefficient overhead and delay due to triangular forwarding, i.e., instead of traveling on shortest paths, packets are routed through the Home Agent. Therefore, these approaches have not been optimized for a large scale deployment. A mobile multicast service for a future Internet should provide "close-to-optimal" routing at predictable and limited cost, offering robustness combined with a service quality compliant to real-time media distribution.

IPv6[4]中的移动性在移动IPv6 RFCs[5][6]中进行了标准化,它解决了在无线域之间移动时网络层发生变化的情况。MIPv6[5]仅粗略定义了使用远程订阅方法或通过家乡代理(HA)的双向隧道的移动节点(MN)的多播移动性。远程订阅存在依赖多播路由以适应切换的缓慢切换问题。由于三角转发,双向隧道引入了低效的开销和延迟,即,数据包不是在最短路径上传输,而是通过归属代理进行路由。因此,这些方法尚未针对大规模部署进行优化。未来互联网的移动多播服务应以可预测且有限的成本提供“接近最优”的路由,提供健壮性和符合实时媒体分发的服务质量。

Intricate multicast routing procedures are not easily extensible to satisfy the requirements for mobility. A client subscribed to a group while performing mobility handovers requires the multicast traffic to follow to its new location; a mobile source needs the entire delivery tree to comply with or to adapt to its changing position. Significant effort has already been invested in protocol designs for mobile multicast receivers; only limited work has been dedicated to multicast source mobility, which poses the more delicate problem [65].


In multimedia conference scenarios, games, or collaborative environments, each member commonly operates as a receiver and as a sender for multicast group communication. In addition, real-time communication such as conversational voice or video places severe temporal requirements on mobility protocols: Typical seamless handover scenarios are expected to limit disruptions or delay to less than 100 - 150 ms [7]. Jitter disturbances should not exceed 50 ms. Note that 100 ms is about the duration of a spoken syllable in real-time audio. This problem statement is intended to also be applicable to a range of other scenarios with a range of delivery requirements appropriate to the general Internet.


This document represents the consensus of the MobOpts Research Group. It has been reviewed by the Research Group members active in the specific area of work. In addition, this document has been comprehensively reviewed by multiple active contributors to the IETF MEXT, MBONED, and PIM Working Groups.

本文件代表了MobOpts研究小组的共识。该报告已由活跃于特定工作领域的研究小组成员审查。此外,IETF MEXT、MBONED和PIM工作组的多个积极参与者对本文件进行了全面审查。

1.1. Document Scope
1.1. 文件范围

This document defines the problem scope for multicast mobility management, which may be elaborated in future work. It is subdivided to present the various challenges according to their originating aspects, and identifies existing proposals and major bibliographic references.


When considering multicast node mobility, the network layer is complemented by some wireless access technology. Two basic scenarios are of interest: single-hop mobility (shown in Figure 1.a) and multi-hop mobility (shown in Figure 1.b). Single-hop mobility is the focus of this document, which coincides with the perspective of MIPv6 [5]. The key issues of mobile multicast membership control and the interplay of mobile and multicast routing will be illustrated using this simple scenario.


Multi-hop network mobility is a subsidiary scenario. All major aspects are inherited from the single-hop problem, while additional complexity is incurred from traversing a mobile cloud. This may be solved by either encapsulation or flooding ([8] provides a general overview). Specific issues arising from (nested) tunneling or flooding, especially the preservation of address transparency, require treatment analogous to MIPv6.


                                       +------+           +------+
                                       |  MN  |  =====>   |  MN  |
                                       +------+           +------+
                                          |                  .
                                          |                  .
                                          |                  .
                                       +-------+          +-------+
                                       | LAR 1 |          | LAR 2 |
                                       +-------+          +-------+
                                                \        /
                                            ***  ***  ***  ***
                                           *   **   **   **   *
   +------+           +------+            *                    *
   |  MN  |  =====>   |  MN  |             *  Mobile Network  *
   +------+           +------+            *                    *
      |                  .                 *   **   **   **   *
      |                  .                  ***  ***  ***  ***
      |                  .                  |                 .
   +-------+          +-------+         +-------+          +-------+
   | AR 1  |          | AR 2  |         | AR 1  |  =====>  | AR 2  |
   +-------+          +-------+         +-------+          +-------+
       |                |                   |                |
       ***  ***  ***  ***                   ***  ***  ***  ***
      *   **   **   **   *                 *   **   **   **   *
     *                    *               *                    *
      *  Fixed Internet  *                 *  Fixed Internet  *
     *                    *               *                    *
      *   **   **   **   *                 *   **   **   **   *
       ***  ***  ***  ***                   ***  ***  ***  ***
                                       +------+           +------+
                                       |  MN  |  =====>   |  MN  |
                                       +------+           +------+
                                          |                  .
                                          |                  .
                                          |                  .
                                       +-------+          +-------+
                                       | LAR 1 |          | LAR 2 |
                                       +-------+          +-------+
                                                \        /
                                            ***  ***  ***  ***
                                           *   **   **   **   *
   +------+           +------+            *                    *
   |  MN  |  =====>   |  MN  |             *  Mobile Network  *
   +------+           +------+            *                    *
      |                  .                 *   **   **   **   *
      |                  .                  ***  ***  ***  ***
      |                  .                  |                 .
   +-------+          +-------+         +-------+          +-------+
   | AR 1  |          | AR 2  |         | AR 1  |  =====>  | AR 2  |
   +-------+          +-------+         +-------+          +-------+
       |                |                   |                |
       ***  ***  ***  ***                   ***  ***  ***  ***
      *   **   **   **   *                 *   **   **   **   *
     *                    *               *                    *
      *  Fixed Internet  *                 *  Fixed Internet  *
     *                    *               *                    *
      *   **   **   **   *                 *   **   **   **   *
       ***  ***  ***  ***                   ***  ***  ***  ***

a) Single-Hop Mobility b) Multi-Hop Mobility

a) 单跳移动b)多跳移动

Figure 1: Mobility Scenarios - A Mobile Node (MN) Directly Attaching to Fixed Access Routers (ARs) or Attached via Local Access Routers (LARs)


2. Problem Description
2. 问题描述
2.1. General Issues
2.1. 一般问题

Multicast mobility is a generic term, which subsumes a collection of distinct functions. First, the multicast communication is divided into Any Source Multicast (ASM) [2] and Source-Specific Multicast (SSM) [9][10]. Second, the roles of senders and receivers are distinct and asymmetric. Both may individually be mobile. Their interaction is facilitated by a multicast routing protocol such as the Distance Vector Multicast Routing Protocol (DVMRP) [11], the


Protocol Independent Multicast - Sparse Mode / Source-Specific Multicast (PIM-SM/SSM) [12][13], the Bidirectional PIM [14], or the inter-domain multicast prefix advertisements via Multiprotocol Extensions for BGP-4 (MBGP) [15]. IPv6 clients interact using the multicast listener discovery protocol (MLD and MLDv2) [16][17].


Any solution for multicast mobility needs to take all of these functional blocks into account. It should enable seamless continuity of multicast sessions when moving from one IPv6 subnet to another. It is desired to preserve the multicast nature of packet distribution and approximate optimal routing. It should support per-flow handover for multicast traffic because the properties and designations of flows can be distinct. Such distinctions may result from differing Quality-of-Service (QoS) / real-time requirements, but may also be caused by network conditions that may differ for different groups.


The host group model extends the capability of the network-layer unicast service. In common with the architecture of fixed networks, multicast mobility management should transparently utilize or smoothly extend the unicast functions of MIPv6 [5], its security extensions [6][18], its expediting schemes FMIPv6 [19] and Hierarchical Mobile IPv6 Environment (HMIPv6) [20], its context transfer protocols [21], its multihoming capabilities [22][23], emerging protocols like PMIPv6 [62], or future developments. From the perspective of an integrated mobility architecture, it is desirable to avoid multicast-specific as well as unicast-restricted solutions, whenever general approaches can be derived that can jointly support unicast and multicast.


Multicast routing dynamically adapts to the network topology at the locations of the sender(s) and receiver(s) participating in a multicast session, which then may change under mobility. However, depending on the topology and the protocol in use, current multicast routing protocols may require a time close to seconds to converge following a change in receiver or sender location. This is far too slow to support seamless handovers for interactive or real-time media sessions. The actual temporal behavior strongly depends on the multicast routing protocol in use, the configuration of routers, and on the geometry of the current distribution tree. A mobility scheme that readjusts routing, i.e., partially changes or fully reconstructs a multicast tree, is forced to comply with the time scale for protocol convergence. Specifically, it needs to consider a possible rapid movement of the mobile node, as this may occur at much higher rates than common protocol state updates.


The mobility of hosts using IP multicast can impact the service presented to the higher-layer protocols. IP-layer multicast packet distribution is an unreliable service that is bound to a


connectionless transport service. Where applications are sensitive to packet loss or jitter, countermeasures need to be performed (loss recovery, content recoding, concealment, etc.) by the multicast transport or application. Mobile multicast handovers should not introduce significant additional packet drops. Due to statelessness, the bi-casting of multicast flows does not cause degradations at the transport layer, and applications should implement mechanisms to detect and correctly respond to duplicate datagrams. Nevertheless, individual application programs may not be robust with respect to repeated reception of duplicate streams.


IP multicast applications can be designed to adapt the multicast stream to prevailing network conditions (adapting the sending rate to the level of congestion, adaptive tuning of clients in response to measured delay, dynamic suppression of feedback messages, etc.). An adaptive application may also use more than one multicast group (e.g., layered multicast in which a client selects a set of multicast groups based on perceived available network capacity). A mobility handover may temporarily disrupt the operation of these higher-layer functions. The handover can invalidate assumptions about the forwarding path (e.g., acceptable delivery rate, round-trip delay), which could impact an application and level of network traffic. Such effects need to be considered in the design of multicast applications and in the design of network-layer mobility. Specifically, mobility mechanisms need to be robust to transient packet loss that may result from invalid path expectations following a handover of an MN to a different network.


Group addresses, in general, are location transparent, even though they may be scoped and methods can embed unicast prefixes or Rendezvous Point addresses [24]. The addresses of sources contributing to a multicast session are interpreted by the routing infrastructure and by receiver applications, which frequently are aware of source addresses. Multicast therefore inherits the mobility address duality problem of MIPv6 for source addresses: addresses being a logical node identifier, i.e., the home address (HoA) on the one hand, and a topological locator, the care-of address (CoA), on the other. At the network layer, the elements that comprise the delivery tree, i.e., multicast senders, forwarders, and receivers, need to carefully account for address duality issues, e.g., by using binding caches, extended multicast states, or signaling.


Multicast sources, in general, operate decoupled from their receivers in the following sense: a multicast source sends packets to a group of receivers that are unknown at the network layer and thus operates without a feedback channel. It neither has means to inquire about the properties of its delivery trees, nor the ability to learn about the network-layer state of its receivers. In the event of an inter-


tree handover, a mobile multicast source therefore is vulnerable to losing connectivity to receivers without noticing. (Appendix A describes implicit source notification approaches). Applying a MIPv6 mobility binding update or return routability procedure will similarly break the semantic of a receiver group remaining unidentified by the source and thus cannot be applied in unicast analogy.


Despite the complexity of the requirements, multicast mobility management should seek lightweight solutions with easy deployment. Realistic, sample deployment scenarios and architectures should be provided in future solution documents.


2.2. Multicast Listener Mobility
2.2. 多播侦听器移动性
2.2.1. Node and Application Perspective
2.2.1. 节点和应用程序透视图

A mobile multicast listener entering a new IP subnet requires multicast reception following a handover in real-time. This needs to transfer the multicast membership context from its old to its new point of attachment. This can either be achieved by (re-)establishing a tunnel or by transferring the MLD Listening State information of the MN's moving interface(s) to the new upstream router(s). In the latter case, it may encounter any one of the following conditions:


o In the simplest scenario, packets of some, or all, of the subscribed groups of the mobile node are already received by one or several other group members in the new network, and thus multicast streams natively flow after the MN arrives at the new network.

o 在最简单的场景中,移动节点的订阅组的一些或全部的分组已经由新网络中的一个或多个其他组成员接收,并且因此多播流在MN到达新网络之后本机地流动。

o The requested multicast service may be supported and enabled in the visited network, but the multicast groups under subscription may not be forwarded to it, e.g., groups may be scoped or administratively prohibited. This means that current distribution trees for the desired groups may only be re-joined at a (possibly large) routing distance.

o 所请求的多播服务可以在所访问的网络中得到支持和启用,但是订阅下的多播组可能不会被转发给它,例如,组可能被限定范围或管理禁止。这意味着所需组的当前分布树只能在(可能较大的)路由距离处重新连接。

o The new network may not be multicast-enabled or the specific multicast service may be unavailable, e.g., unsupported or prohibited. This means that current distribution trees for the desired groups need to be re-joined at a large routing distance by (re-)establishing a tunnel to a multicast-enabled network node.

o 新网络可能未启用多播,或者特定多播服务可能不可用,例如,不支持或禁止。这意味着需要通过(重新)建立到支持多播的网络节点的隧道,在较大的路由距离处重新连接所需组的当前分发树。

The problem of achieving seamless multicast listener handovers is thus threefold:


o Ensure multicast reception, even in visited networks, without appropriate multicast support.

o 确保多播接收,即使在访问过的网络中,也没有适当的多播支持。

o Minimize multicast forwarding delay to provide seamless and fast handovers for real-time services. Dependent on Layer 2 (L2) and Layer 3 (L3) handover performance, the time available for multicast mobility operations is typically bound by the total handover time left after IPv6 connectivity is regained. In real-time scenarios, this may be significantly less than 100 ms.

o 最小化多播转发延迟,为实时服务提供无缝快速切换。根据第2层(L2)和第3层(L3)切换性能,多播移动操作的可用时间通常受恢复IPv6连接后剩余的总切换时间的限制。在实时场景中,这可能明显小于100毫秒。

o Minimize packet loss and reordering that result from multicast handover management.

o 最大限度地减少多播切换管理导致的数据包丢失和重新排序。

Moreover, in many wireless regimes, it is also desirable to minimize multicast-related signaling to preserve the limited resources of battery-powered mobile devices and the constrained transmission capacities of the networks. This may lead to a desire to restrict MLD queries towards the MN. Multihomed MNs may ensure smooth handoffs by using a "make-before-break" approach, which requires a per-interface subscription, facilitated by an MLD JOIN operating on a pre-selected IPv6 interface.


Encapsulation on the path between the upstream router and the receiver may result in MTU size conflicts, since path-MTU discovery is often not supported for multicast and can reduce scalability in networks with many different MTU sizes or introduce potential denial-of-service vulnerabilities (since the originating addresses of ICMPv6 messages cannot be verified for multicast). In the absence of fragmentation at tunnel entry points, this may prevent the group from being forwarded to the destination.


2.2.2. Network Perspective
2.2.2. 网络透视

The infrastructure providing multicast services is required to keep traffic following the MN without compromising network functionality. Mobility solutions thus have to face some immediate problems:


o Realize native multicast forwarding, and where applicable, conserve network resources and utilize link-layer multipoint distribution to avoid data redundancy.

o 实现本机多播转发,并在适用的情况下,节约网络资源,利用链路层多点分布避免数据冗余。

o Activate link-multipoint services, even if the MN performs only a L2/vertical handover.

o 激活链路多点服务,即使MN仅执行L2/垂直切换。

o Ensure routing convergence, even when the MN moves rapidly and performs handovers at a high frequency.

o 确保路由收敛,即使在MN快速移动并以高频率执行切换时也是如此。

o Avoid avalanche problems and stream multiplication (n-casting), which potentially result from replicated tunnel initiation or redundant forwarding at network nodes.

o 避免雪崩问题和流倍增(n-casting),这可能是由网络节点上的复制隧道启动或冗余转发引起的。

There are additional implications for the infrastructure: In changing its point of attachment, an exclusive mobile receiver may initiate forwarding of a group in the new network and termination of a group distribution service in the previous network. Mobility management may impact multicast routing by, e.g., erroneous subscriptions following predictive handover operations, or slow traffic termination at leaf nodes resulting from MLD query timeouts, or by departure of the MN from a previous network without leaving the subscribed groups. Finally, packet duplication and reordering may follow a change of topology.


2.3. Multicast Source Mobility
2.3. 多播源移动性
2.3.1. Any Source Multicast Mobility
2.3.1. 任意源多播移动性

A node submitting data to an ASM group either forms the root of a source-specific shortest path tree (SPT), distributing data towards a rendezvous point (RP) or receivers, or it forwards data directly down a shared tree, e.g., via encapsulated PIM Register messages, or using bidirectional PIM routing. Native forwarding along source-specific delivery trees will be bound to the source's topological network address, due to reverse path forwarding (RPF) checks. A mobile multicast source moving to a new subnetwork is only able to either inject data into a previously established delivery tree, which may be a rendezvous-point-based shared tree, or to (re-)initiate the construction of a multicast distribution tree for its new network location. In the latter case, the mobile sender will have to proceed without knowing whether the new tree has regained ability to forward traffic to the group, due to the decoupling of sender and receivers.


A mobile multicast source must therefore provide address transparency at two layers: To comply with RPF checks, it has to use an address within the source field of the IPv6 basic header, which is in topological agreement with the employed multicast distribution tree. For application transparency, the logical node identifier, commonly the HoA, must be presented as the packet source address to the transport layer at the receiver side.


The address transparency and temporal handover constraints pose major problems for route-optimizing mobility solutions. Additional issues arise from possible packet loss and from multicast scoping. A mobile source away from home must respect scoping restrictions that arise from its home and its visited location [5].


Intra-domain multicast routing may allow the use of shared trees that can reduce mobility-related complexity. A static rendezvous point may allow a mobile source to continuously send data to the group by encapsulating packets to the RP with its previous topologically correct or home source address. Intra-domain mobility is transparently provided by bidirectional shared domain-spanning trees, when using bidirectional PIM, eliminating the need for tunneling to the corresponding RP (in contrast to IPv4, IPv6 ASM multicast groups are associated with a specific RP/RPs).

域内多播路由可以允许使用共享树,从而降低与移动性相关的复杂性。静态集合点可允许移动源通过使用其先前拓扑正确的或归属源地址将分组封装到RP来连续地向组发送数据。当使用双向PIM时,通过双向共享域生成树透明地提供域内移动性,消除了到相应RP的隧道的需要(与IPv4相比,IPv6 ASM多播组与特定RP/RPs相关联)。

Issues arise in inter-domain multicast, whenever notification of source addresses is required between distributed instances of shared trees. A new CoA acquired after a mobility handover will necessarily be subject to inter-domain record exchange. In the presence of an embedded rendezvous point address [24], e.g., the primary rendezvous point for inter-domain PIM-SM will be globally appointed, and a newly attached mobile source can contact the RP without prior signaling (like a new source) and transmit data in the PIM register tunnel. Multicast route optimization (e.g., PIM "shortcuts") will require multicast routing protocol operations equivalent to serving a new source.


2.3.2. Source-Specific Multicast Mobility
2.3.2. 源特定组播移动性

Source-Specific Multicast has been designed for multicast senders with static source addresses. The source addresses in a client subscription to an SSM group is directly used to route identification. Any SSM subscriber is thus forced to know the topological address of the contributor to the group it wishes to join. The SSM source identification becomes invalid when the topological source address changes under mobility. Hence, client implementations of SSM source filtering must be MIPv6 aware in the sense that a logical source identifier (HoA) is correctly mapped to its current topological correspondent (CoA).


As a consequence, source mobility for SSM requires a conceptual treatment beyond the problem scope of mobile ASM. A listener subscribes to an (S,G) channel membership and routers establish an (S,G)-state shortest path tree rooted at source S; therefore, any change of source addresses under mobility requires state updates at all routers on the upstream path and at all receivers in the group. On source handover, a new SPT needs to be established that will share paths with the previous SPT, e.g., at the receiver side. As the principle of multicast decoupling of a sender from its receivers holds for SSM, the client updates needed for switching trees become a severe burden.


An SSM listener may subscribe to or exclude any specific multicast source and thereby wants to rely on the topological correctness of network operations. The SSM design permits trust in equivalence to the correctness of unicast routing tables. Any SSM mobility solution should preserve this degree of confidence. Binding updates for SSM sources thus should have to prove address correctness in the unicast routing sense, which is equivalent to binding update security with a correspondent node in MIPv6 [5].


The above methods could add significant complexity to a solution for robust SSM mobility, which needs to converge to optimal routes and, for efficiency, is desired to avoid data encapsulation. Like ASM, handover management is a time-critical operation. The routing distance between subsequent points of attachment, the "step size" of the mobile from previous to next designated router, may serve as an appropriate measure of complexity [25][26].


Finally, Source-Specific Multicast has been designed as a lightweight approach to group communication. In adding mobility management, it is desirable to preserve the leanness of SSM by minimizing additional signaling overhead.


2.4. Deployment Issues
2.4. 部署问题

IP multicast deployment, in general, has been slow over the past 15 years, even though all major router vendors and operating systems offer implementations that support multicast [27]. While many (walled) domains or enterprise networks operate point-to-multipoint services, IP multicast roll-out is currently limited in public inter-domain scenarios [28]. A dispute arose on the appropriate layer, where group communication service should reside, and the focus of the research community turned towards application-layer multicast. This debate on "efficiency versus deployment complexity" now overlaps the mobile multicast domain [29]. Garyfalos and Almeroth [30] derived from fairly generic principles that when mobility is introduced, the performance gap between IP- and application-layer multicast widens in different metrics up to a factor of four.


Facing deployment complexity, it is desirable that any solution for mobile multicast does not change the routing protocols. Mobility management in such a deployment-friendly scheme should preferably be handled at edge nodes, preserving a mobility-agnostic routing infrastructure. Future research needs to search for such simple, infrastructure-transparent solutions, even though there are reasonable doubts as to whether this can be achieved in all cases.


Nevertheless, multicast services in mobile environments may soon become indispensable, when multimedia distribution services such as Digital Video Broadcasting for Handhelds (DVB-H) [31][32] or IPTV develop a strong business case for portable IP-based devices. As IP mobility becomes an important service and as efficient link utilization is of a larger impact in costly radio environments, the evolution of multicast protocols will naturally follow mobility constraints.


3. Characteristics of Multicast Routing Trees under Mobility
3. 移动环境下组播路由树的特性

Multicast distribution trees have been studied from a focus of network efficiency. Grounded on empirical observations, Chuang and Sirbu [33] proposed a scaling power-law for the total number of links in a multicast shortest path tree with m receivers (proportional to m^k). The authors consistently identified the scale factor to attain the independent constant k = 0.8. The validity of such universal, heavy-tailed distribution suggests that multicast shortest path trees are of self-similar nature with many nodes of small, but few of higher degrees. Trees consequently would be shaped tall rather than wide.


Subsequent empirical and analytical work [34][35] debated the applicability of the Chuang and Sirbu scaling law. Van Mieghem et al. [34] proved that the proposed power law cannot hold for an increasing Internet or very large multicast groups, but is indeed applicable for moderate receiver numbers and the current Internet size of N = 10^5 core nodes. Investigating self-similarity, Janic and Van Mieghem [36] semi-empirically substantiated that multicast shortest path trees in the Internet can be modeled with reasonable accuracy by uniform recursive trees (URTs) [37], provided m remains small compared to N.

随后的实证和分析工作[34][35]讨论了庄和Sirbu标度定律的适用性。Van Mieghem等人[34]证明,所提出的幂律不能适用于不断增加的互联网或非常大的多播组,但确实适用于中等接收器数量和当前互联网大小的N=10^5个核心节点。Janic和Van Mieghem[36]通过对自相似性的研究,半经验地证明了互联网中的多播最短路径树可以通过均匀递归树(URT)[37]以合理的精度进行建模,前提是m比N小。

The mobility perspective on shortest path trees focuses on their alteration, i.e., the degree of topological changes induced by movement. For receivers, and more interestingly for sources, this may serve as a characteristic measure of the routing complexity. Mobile listeners moving to neighboring networks will only alter tree branches extending over a few hops. Source-specific multicast trees subsequently generated from source handover steps are not independent, but highly correlated. They most likely branch to identical receivers at one or several intersection points. By the self-similar nature, the persistent sub-trees (of previous and next distribution tree), rooted at any such intersection point, exhibit again the scaling law behavior, are tall-shaped with nodes of mainly low degree and thus likely to coincide. Tree alterations under mobility have been studied in [26], both analytically and by


simulations. It was found that even in large networks and for moderate receiver numbers more than 80% of the multicast router states remain invariant under a source handover.


4. Link-Layer Aspects
4. 链接层方面
4.1. General Background
4.1. 一般背景

Scalable group data distribution has the highest potential in edge networks, where large numbers of end systems reside. Consequently, it is not surprising that most LAN network access technologies natively support point-to-multipoint or multicast services. Wireless access technologies inherently support broadcast/multicast at L2 and operate on a shared medium with limited frequency and bandwidth.


Several aspects need consideration: First, dissimilar network access radio technologies cause distinct group traffic transmissions. There are:


o connection-less link services of a broadcast type, which mostly are bound to limited reliability;

o 广播类型的无连接链路服务,其可靠性通常有限;

o connection-oriented link services of a point-to-multipoint type, which require more complex control and frequently exhibit reduced efficiency;

o 点对多点类型的面向连接的链路服务,需要更复杂的控制,并且经常表现出降低的效率;

o connection-oriented link services of a broadcast type, which are restricted to unidirectional data transmission.

o 广播类型的面向连接的链路服务,仅限于单向数据传输。

In addition, multicast may be distributed via multiple point-to-point unicast links without the use of a dedicated multipoint radio channel. A fundamental difference between unicast and group transmission arises from power management. Some radio technologies adjust transmit power to be as small as possible based on link-layer feedback from the receiver, which is not done in multipoint mode. They consequently incur a "multicast tax", making multicast less efficient than unicast unless the number of receivers is larger than some threshold.


Second, point-to-multipoint service activation at the network access layer requires a mapping mechanism from network-layer requests. This function is commonly achieved by L3 awareness, i.e., IGMP/MLD snooping [70] or proxy [38], which occasionally is complemented by Multicast VLAN Registration (MVR). MVR allows sharing of a single multicast IEEE 802.1Q Virtual LAN in the network, while subscribers remain in separate VLANs. This L2 separation of multicast and unicast traffic can be employed as a workaround for point-to-point link models to establish a common multicast link.

其次,网络接入层的点对多点服务激活需要来自网络层请求的映射机制。此功能通常通过L3感知来实现,即IGMP/MLD窥探[70]或代理[38],偶尔通过多播VLAN注册(MVR)来补充。MVR允许在网络中共享单个多播IEEE 802.1Q虚拟LAN,而订户保留在单独的VLAN中。这种多播和单播通信量的L2分离可以作为点到点链路模型建立公共多播链路的解决方法。

Third, an address mapping between the layers is needed for common group identification. Address resolution schemes depend on framing details for the technologies in use, but commonly cause a significant address overlap at the lower layer (i.e., more than one IP multicast group address is sent using the same L2 address).


4.2. Multicast for Specific Technologies
4.2. 针对特定技术的多播
4.2.1. 802.11 WLAN
4.2.1. 802.11无线局域网

IEEE 802.11 Wireless Local Area Network (WLAN) is a broadcast network of Ethernet type. This inherits multicast address mapping concepts from 802.3. In infrastructure mode, an access point operates as a repeater, only bridging data between the Base (BSS) and the Extended Service Set (ESS). A mobile node submits multicast data to an access point in point-to-point acknowledged unicast mode (when the ToDS bit is set). An access point receiving multicast data from an MN simply repeats multicast frames to the BSS and propagates them to the ESS as unacknowledged broadcast. Multicast frames received from the ESS receive similar treatment.

IEEE 802.11无线局域网(WLAN)是一种以太网类型的广播网络。这继承了802.3中的多播地址映射概念。在基础设施模式下,接入点作为中继器运行,仅在基站(BSS)和扩展服务集(ESS)之间桥接数据。移动节点以点对点确认单播模式(设置ToDS位时)向接入点提交多播数据。从MN接收多播数据的接入点只是将多播帧重复到BSS,并将其作为未确认广播传播到ESS。从ESS接收的多播帧接受类似的处理。

Multicast frame delivery has the following characteristics:


o As an unacknowledged service, it offers limited reliability. The loss of frames (and hence packets) arises from interference, collision, or time-varying channel properties.

o 作为未确认的服务,它提供的可靠性有限。帧(以及数据包)的丢失是由干扰、冲突或时变信道特性引起的。

o Data distribution may be delayed, as unicast power saving synchronization via Traffic Indication Messages (TIM) does not operate in multicast mode. Access points buffer multicast packets while waiting for a larger Delivery TIM (DTIM) interval, whenever stations use the power saving mode.

o 数据分发可能会延迟,因为通过业务指示消息(TIM)的单播节能同步不能在多播模式下运行。当站点使用省电模式时,接入点会在等待更大的传输TIM(DTIM)间隔时缓冲多播数据包。

o Multipoint data may cause congestion, because the distribution system floods multicast, without further control. All access points of the same subnet replicate multicast frames.

o 多点数据可能会导致拥塞,因为分发系统会淹没多播,而无需进一步控制。同一子网的所有接入点都复制多播帧。

To limit or prevent the latter, many vendors have implemented a configurable rate limit for forwarding multicast packets. Additionally, an IGMP/MLD snooping or proxy may be active at the bridging layer between the BSS and the ESS or at switches interconnecting access points.


4.2.2. 802.16 WIMAX
4.2.2. 802.16 WIMAX

IEEE 802.16 Worldwide Interoperability for Microwave Access (WIMAX) combines a family of connection-oriented radio transmission services that can operate in single-hop point-to-multipoint (PMP) or in mesh

IEEE 802.16全球微波接入互操作性(WIMAX)结合了一系列面向连接的无线传输服务,可在单跳点对多点(PMP)或网状网络中运行

mode. The latter does not support multipoint transmission and currently has no deployment. PMP operates between Base and Subscriber Stations in distinguished, unidirectional channels. The channel assignment is controlled by the Base Station, which assigns channel IDs (CIDs) within service flows to the Subscriber Stations. Service flows may provide an optional Automatic Repeat Request (ARQ) to improve reliability and may operate in point-to-point or point-to-multipoint (restricted to downlink and without ARQ) mode.


A WIMAX Base Station operates as a full-duplex L2 switch, with switching based on CIDs. Two IPv6 link models for mobile access scenarios exist: A shared IPv6 prefix for IP over Ethernet Circuit Switched (CS) [39] provides Media Access Control (MAC) separation within a shared prefix. A second, point-to-point link model [40] is recommended in the IPv6 Convergence Sublayer [41], which treats each connection to a mobile node as a single link. The point-to-point link model conflicts with a consistent group distribution at the IP layer when using a shared medium (cf. Section 4.1 for MVR as a workaround).

WIMAX基站作为全双工L2交换机运行,基于CID进行切换。存在两种用于移动接入场景的IPv6链路模型:用于IP over Ethernet Circuit Switched(CS)[39]的共享IPv6前缀在共享前缀内提供媒体访问控制(MAC)分离。第二种点对点链路模型[40]建议在IPv6聚合子层[41]中使用,该模型将移动节点的每个连接视为单个链路。当使用共享介质时,点到点链路模型与IP层的一致组分布冲突(参考第4.1节MVR作为解决方法)。

To invoke a multipoint data channel, the base station assigns a common CID to all Subscriber Stations in the group. An IPv6 multicast address mapping to these 16-bit IDs is proposed by copying either the 4 lowest bits, while sustaining the scope field, or by utilizing the 8 lowest bits derived from Multicast on Ethernet CS [42]. For selecting group members, a Base Station may implement IGMP/MLD snooping or proxy as foreseen in 802.16e-2005 [43].


A Subscriber Station multicasts IP packets to a Base Station as a point-to-point unicast stream. When the IPv6 CS is used, these are forwarded to the upstream access router. The access router (or the Base Station for IP over Ethernet CS) may send downstream multicast packets by feeding them to the multicast service channel. On reception, a Subscriber Station cannot distinguish multicast from unicast streams at the link layer.

用户站将IP数据包作为点对点单播流多播到基站。当使用IPv6 CS时,这些将转发到上游接入路由器。接入路由器(或以太网上IP CS的基站)可以通过将下行多播分组馈送到多播服务信道来发送下行多播分组。在接收时,用户站无法在链路层区分多播和单播流。

Multicast services have the following characteristics:


o Multicast CIDs are unidirectional and available only in the downlink direction. Thus, a native broadcast-type forwarding model is not available.

o 多播CID是单向的,仅在下行链路方向可用。因此,本机广播类型转发模型不可用。

o The mapping of multicast addresses to CIDs needs standardization, since different entities (Access Router, Base Station) may have to perform the mapping.

o 多播地址到CID的映射需要标准化,因为不同的实体(接入路由器、基站)可能必须执行映射。

o CID collisions for different multicast groups may occur due to the short ID space. This can result in several point-to-multipoint groups sharing the same CID, reducing the ability of a receiver to filter unwanted L2 traffic.

o 由于ID空间较短,可能会发生不同多播组的CID冲突。这可能导致多个点对多点组共享相同的CID,从而降低接收器过滤不需要的L2通信量的能力。

o The point-to-point link model for mobile access contradicts a consistent mapping of IP-layer multicast onto 802.16 point-to-multipoint services.

o 移动接入的点对点链路模型与IP层多播到802.16点对多点服务的一致映射相矛盾。

o Multipoint channels cannot operate ARQ service and thus experience a reduced reliability.

o 多点信道无法运行ARQ服务,因此可靠性降低。

4.2.3. 3GPP/3GPP2
4.2.3. 3GPP/3GPP2

The 3rd Generation Partnership Project (3GPP) System architecture spans a circuit switched (CS) and a packet-switched (PS) domain, the latter General Packet Radio Services (GPRS) incorporates the IP Multimedia Subsystem (IMS) [44]. The 3GPP PS is connection-oriented and based on the concept of Packet Data Protocol (PDP) contexts. PDPs define point-to-point links between the Mobile Terminal and the Gateway GPRS Support Node (GGSN). Internet service types are PPP, IPv4, and IPv6, where the recommendation for IPv6 address assignment associates a prefix to each (primary) PDP context [45].


In Universal Mobile Telecommunications System (UMTS) Rel. 6, the IMS was extended to include Multimedia Broadcast and Multicast Services (MBMS). A point-to-multipoint GPRS connection service is operated on radio links, while the gateway service to Internet multicast is handled at the IGMP/MLD-aware GGSN. Local multicast packet distribution is used within the GPRS IP backbone resulting in the common double encapsulation at GGSN: global IP multicast datagrams over Generic Tunneling Protocol (GTP) (with multipoint TID) over local IP multicast.

在通用移动通信系统(UMTS)中。6、IMS扩展到包括多媒体广播和多播服务(MBMS)。点对多点GPRS连接服务在无线链路上运行,而互联网多播网关服务在支持IGMP/MLD的GGSN上处理。在GPRS IP主干网内使用本地多播数据包分发,从而在GGSN实现常见的双重封装:通用隧道协议(GTP)上的全局IP多播数据报(具有多点TID)本地IP多播。

The 3GPP MBMS has the following characteristics:

3GPP MBMS具有以下特征:

o There is no immediate Layer 2 source-to-destination transition, resulting in transit of all multicast traffic at the GGSN.

o 没有立即的第2层源到目的地转换,导致所有多播流量在GGSN传输。

o As GGSNs commonly are regional, distant entities, triangular routing and encapsulation may cause a significant degradation of efficiency.

o 由于GGSN通常是区域性的、遥远的实体,三角形路由和封装可能会导致效率显著降低。

In 3GPP2, the MBMS has been extended to the Broadcast and Multicast Service (BCMCS) [46], which on the routing layer operates very similar to MBMS. In both 3GPP and 3GPP2, multicast can be sent using either point-to-point (PTP) or point-to-multipoint (PTM) tunnels, and


there is support for switching between PTP and PTM. PTM uses a unidirectional common channel, operating in unacknowledged mode without adjustment of power levels and no reporting on lost packets.


4.2.4. DVB-H / DVB-IPDC

Digital Video Broadcasting for Handhelds (DVB-H) is a unidirectional physical layer broadcasting specification for the efficient delivery of broadband and IP-encapsulated data streams, and is published as an ETSI standard [47] (see This uses multiprotocol encapsulation (MPE) to transport IP packets over an MPEG-2 Transport Stream (TS) with link forward error correction (FEC). Each stream is identified by a 13-bit TS ID (PID), which together with a multiplex service ID, is associated with IPv4 or IPv6 addresses [48] and used for selective traffic filtering at receivers. Upstream channels may complement DVB-H using other transmission technologies. The IP Datacast Service, DVB-IPDC [31], specifies a set of applications that can use the DVB-H transmission network.

用于手持设备的数字视频广播(DVB-H)是一种单向物理层广播规范,用于高效传送宽带和IP封装数据流,并作为ETSI标准发布[47](参见 这使用多协议封装(MPE)在具有链路前向纠错(FEC)的MPEG-2传输流(TS)上传输IP数据包。每个流由13位TS ID(PID)标识,该ID与多路复用服务ID一起与IPv4或IPv6地址相关联[48],并用于在接收器处进行选择性流量过滤。上行信道可以使用其他传输技术来补充DVB-H。IP数据广播服务DVB-IPDC[31]指定了一组可以使用DVB-H传输网络的应用程序。

Multicast distribution services are defined by a mapping of groups onto appropriate PIDs, which is managed at the IP Encapsulator [49]. To increase flexibility and avoid collisions, this address resolution is facilitated by dynamic tables, provided within the self-contained MPEG-2 TS. Mobility is supported in the sense that changes of cell ID, network ID, or Transport Stream ID are foreseen [50]. A multicast receiver thus needs to relocate the multicast services to which it is subscribed during the synchronization phase, and update its service filters. Its handover decision may depend on service availability. An active service subscription (multicast join) requires initiation at the IP Encapsulator / DVB-H Gateway, which cannot be signaled in a pure DVB-H network.

多播分发服务通过将组映射到适当的PID来定义,PID由IP封装器管理[49]。为了增加灵活性并避免冲突,这种地址解析通过在自包含的MPEG-2 TS中提供的动态表来实现。在预见小区ID、网络ID或传输流ID变化的意义上支持移动性[50]。因此,多播接收器需要在同步阶段重新定位其订阅的多播服务,并更新其服务过滤器。其切换决策可能取决于服务可用性。主动服务订阅(多播加入)需要在IP封装器/DVB-H网关处启动,而在纯DVB-H网络中无法发出信号。

4.2.5. TV Broadcast and Satellite Networks
4.2.5. 电视广播和卫星网络

IP multicast may be enabled in TV broadcast networks, including those specified by DVB, the Advanced Television Systems Committee (ATSC), and related standards [49]. These standards are also used for one-and two-way satellite IP services. Networks based on the MPEG-2 Transport Stream may support either the multiprotocol encapsulation (MPE) or the unidirectional lightweight encapsulation (ULE) [51]. The second generation DVB standards allow the Transport Stream to be replaced with a Generic Stream, using the Generic Stream Encapsulation (GSE) [52]. These encapsulation formats all support multicast operation.


In MPEG-2 transmission networks, multicast distribution services are defined by a mapping of groups onto appropriate PIDs, which is managed at the IP Encapsulator [49]. The addressing issues resemble


those for DVB-H (Section 4.2.4) [48]. The issues for using GSE resemble those for ULE (except the PID is not available as a mechanism for filtering traffic). Networks that provide bidirectional connectivity may allow active service subscription (multicast join) to initiate forwarding from the upstream IP Encapsulator / gateway. Some kind of filtering can be achieved using the Input Stream Identifier (ISI) field.


4.3. Vertical Multicast Handovers
4.3. 垂直多播切换

A mobile multicast node may change its point of Layer 2 attachment within homogeneous access technologies (horizontal handover) or between heterogeneous links (vertical handover). In either case, a Layer 3 network change may or may not take place, but multicast-aware links always need information about group traffic demands. Consequently, a dedicated context transfer of multicast subscriptions is required at the network access. Such Media Independent Handover (MIH) is addressed in IEEE 802.21 [53], but is relevant also beyond IEEE protocols. Mobility services transport for MIH are required as an abstraction for Layer 2 multicast service transfer in an Internet context [54] and are specified in [55].

移动多播节点可在同质接入技术(水平切换)内或异质链路(垂直切换)之间改变其第2层连接点。在这两种情况下,第3层网络的变化可能会发生,也可能不会发生,但多播感知链路始终需要有关组流量需求的信息。因此,在网络访问时需要多播订阅的专用上下文传输。这种媒体独立切换(MIH)在IEEE 802.21[53]中有论述,但也与IEEE协议无关。MIH的移动服务传输需要作为互联网上下文中第2层多播服务传输的抽象[54],并在[55]中规定。

MIH needs to assist in more than service discovery: There is a need for complex, media-dependent multicast adaptation, a possible absence of MLD signaling in L2-only transfers, and requirements originating from predictive handovers. A multicast mobility services transport needs to be sufficiently comprehensive and abstract to initiate a seamless multicast handoff at network access.


Functions required for MIH include:


o Service discovery. o Service context transformation. o Service context transfer. o Service invocation.

o 服务发现。o服务上下文转换。o服务上下文传输。o服务调用。

5. Solutions
5. 解决
5.1. General Approaches
5.1. 一般方法

Three approaches to mobile multicast are common [56]:


o Bidirectional Tunneling, in which the mobile node tunnels all multicast data via its home agent. This fundamental multicast solution hides all movement and results in static multicast trees. It may be employed transparently by mobile multicast

o 双向隧道,其中移动节点通过其归属代理隧道所有多播数据。这个基本的多播解决方案隐藏了所有的移动,并导致静态多播树。它可以被移动多播透明地使用

listeners and sources, at the cost of triangular routing and possibly significant performance degradation from widely spanned data tunnels.


o Remote Subscription forces the mobile node to re-initiate multicast distribution following handover, e.g., by submitting an MLD listener report to the subnet where a receiver attaches. This approach of tree discontinuation relies on multicast dynamics to adapt to network changes. It not only results in significant service disruption but leads to mobility-driven changes of source addresses, and thus cannot support session persistence under multicast source mobility.

o 远程订阅强制移动节点在切换后重新启动多播分发,例如,通过向接收器连接的子网提交MLD侦听器报告。这种树中断方法依赖于多播动态来适应网络的变化。它不仅会导致严重的服务中断,而且会导致移动驱动的源地址更改,因此无法支持多播源移动下的会话持久性。

o Agent-based solutions attempt to balance between the previous two mechanisms. Static agents typically act as local tunneling proxies, allowing for some inter-agent handover when the mobile node moves. A decelerated inter-tree handover, i.e., "tree walking", will be the outcome of agent-based multicast mobility, where some extra effort is needed to sustain session persistence through address transparency of mobile sources.

o 基于代理的解决方案试图平衡前两种机制。静态代理通常充当本地隧道代理,允许在移动节点移动时进行一些代理间切换。减速树间切换,即“树行走”,将是基于代理的多播移动的结果,其中需要一些额外的努力来通过移动源的地址透明性来维持会话持久性。

MIPv6 [5] introduces bidirectional tunneling as well as remote subscription as minimal standard solutions. Various publications suggest utilizing remote subscription for listener mobility only, while advising bidirectional tunneling as the solution for source mobility. Such an approach avoids the "tunnel convergence" or "avalanche" problem [56], which refers to the responsibility of the home agent to multiply and encapsulate packets for many receivers of the same group, even if they are located within the same subnetwork. However, this suffers from the drawback that multicast communication roles are not explicitly known at the network layer and may change unexpectedly.


None of the above approaches address SSM source mobility, except the use of bidirectional tunneling.


5.2. Solutions for Multicast Listener Mobility
5.2. 多播侦听器移动性解决方案
5.2.1. Agent Assistance
5.2.1. 代理协助

There are proposals for agent-assisted handover for host-based mobility, which complement the unicast real-time mobility infrastructure of Fast MIPv6 (FMIPv6) [19], the M-FMIPv6 [57][58], and of Hierarchical MIPv6 (HMIPv6) [20], the M-HMIPv6 [59], and to context transfer [60], which have been thoroughly analyzed in [25][61].

有针对基于主机的移动性的代理辅助切换的建议,补充了Fast MIPv6(FMIPv6)[19]、M-FMIPv6[57][58]和分层MIPv6(HMIPv6)[20]、M-HMIPv6[59]的单播实时移动性基础设施以及上下文传输[60],这些已在[25][61]中进行了深入分析。

All these solutions presume the context state was stored within a network node that is reachable before and after a move. But there could be cases were the MN is no longer in contact with the previous network, when at the new location. In this case, the network itself cannot assist in the context transfer. Such scenarios may occur when moving from one (walled) operator to another and will require a backwards compatible way to recover from loss of connectivity and context based on the node alone.


Network-based mobility management, Proxy MIPv6 (PMIPv6) [62], is multicast transparent in the sense that the MN experiences a point-to-point home link fixed at its (static) Local Mobility Anchor (LMA). This virtual home link is composed of a unicast tunnel between the LMA and the current Mobile Access Gateway (MAG), and a point-to-point link connecting the current MAG to the MN. A PMIPv6 domain thereby inherits MTU-size problems from spanning tunnels at the receiver site. Furthermore, two avalanche problem points can be identified: the LMA may be required to tunnel data to a large number of MAGs, while an MAG may be required to forward the same multicast stream to many MNs via individual point-to-point links [63]. Future optimizations and extensions to shared links preferably adapt native multicast distribution towards the edge network, possibly using a local routing option, including context transfer between access gateways to assist IP-mobility-agnostic MNs.


An approach based on dynamically negotiated inter-agent handovers is presented in [64]. Aside from IETF work, numerous publications present proposals for seamless multicast listener mobility, e.g., [65] provides a comprehensive overview of the work prior to 2004.


5.2.2. Multicast Encapsulation
5.2.2. 多播封装

Encapsulation of multicast data packets is an established method to shield mobility and to enable access to remotely located data services, e.g., streams from the home network. Applying generic packet tunneling in IPv6 [66] using a unicast point-to-point method will also allow multicast-agnostic domains to be transited, but does inherit the tunnel convergence problem and may result in traffic multiplication.


Multicast-enabled environments may take advantage of point-to-multipoint encapsulation, i.e., generic packet tunneling using an appropriate multicast destination address in the outer header. Such multicast-in-multicast encapsulated packets similarly enable reception of remotely located streams, but do not suffer from the scaling overhead from using unicast tunnels.


The tunnel entry point performing encapsulation should provide fragmentation of data packets to avoid issues resulting from MTU-size constraints within the network(s) supporting the tunnel(s).


5.2.3. Hybrid Architectures
5.2.3. 混合控制方式

There has been recent interest in seeking methods that avoid the complexity at the Internet core network, e.g., application-layer and overlay proposals for (mobile) multicast. The possibility of integrating multicast distribution on the overlay into the network layer is also being considered by the IRTF Scalable Adaptive Multicast (SAM) Research Group.


An early hybrid architecture using reactively operating proxy-gateways located at the Internet edges was introduced by Garyfalos and Almeroth [30]. The authors presented an Intelligent Gateway Multicast as a bridge between mobility-aware native multicast management in access networks and mobility group distribution services in the Internet core, which may be operated on the network or application layer. The Hybrid Shared Tree approach [67] introduced a mobility-agnostic multicast backbone on the overlay.


Current work in the SAM RG is developing general architectural approaches for hybrid multicast solutions [68] and a common multicast API for a transparent access of hybrid multicast [69] that will require a detailed design in future work.

SAM RG的当前工作是为混合多播解决方案[68]开发通用架构方法,并为混合多播的透明访问开发通用多播API[69],这将需要在未来工作中进行详细设计。

5.2.4. MLD Extensions
5.2.4. MLD扩展

The default timer values and Robustness Variable specified in MLD [17] were not designed for the mobility context. This results in a slow reaction of the multicast-routing infrastructure (including L3-aware access devices [70]) following a client leave. This may be a disadvantage for wireless links, where performance may be improved by carefully tuning the Query Interval and other variables. Some vendors have optimized performance by implementing a listener node table at the access router that can eliminate the need for query timeouts when receiving leave messages (explicit receiver tracking).


An MN operating predictive handover, e.g., using FMIPv6, may accelerate multicast service termination when leaving the previous network by submitting an early Done message before handoff. MLD router querying will allow the multicast forwarding state to be restored in the case of an erroneous prediction (i.e., an anticipated move to a network that has not taken place). Backward context transfer may otherwise ensure a leave is signaled. A further optimization was introduced by Jelger and Noel [71] for the special case when the HA is a multicast router. A Done message received


through a tunnel from the mobile end node (through a point-to-point link directly connecting the MN, in general), should not initiate standard MLD membership queries (with a subsequent timeout). Such explicit treatment of point-to-point links will reduce traffic and accelerate the control protocol. Explicit tracking will cause identical protocol behavior.


While away from home, an MN may wish to rely on a proxy or "standby" multicast membership service, optionally provided by an HA or proxy router. Such functions rely on the ability to restart fast packet forwarding; it may be desirable for the proxy router to remain part of the multicast delivery tree, even when transmission of group data is paused. To enable such proxy control, the authors in [71] propose an extension to MLD, introducing a Listener Hold message that is exchanged between the MN and the HA. This idea was developed in [59] to propose multicast router attendance control, allowing for a general deployment of group membership proxies. Some currently deployed IPTV solutions use such a mechanism in combination with a recent (video) frame buffer, to enable fast channel switching between several IPTV multicast flows (zapping).


5.3. Solutions for Multicast Source Mobility
5.3. 多播源移动性解决方案
5.3.1. Any Source Multicast Mobility Approaches
5.3.1. 任何源组播移动性方法

Solutions for multicast source mobility can be divided into three categories:


o Statically Rooted Distribution Trees. These methods follow a shared tree approach. Romdhani et al. [72] proposed employing the Rendezvous Points of PIM-SM as mobility anchors. Mobile senders tunnel their data to these "Mobility-aware Rendezvous Points" (MRPs). When restricted to a single domain, this scheme is equivalent to bidirectional tunneling. Focusing on inter-domain mobile multicast, the authors designed a tunnel- or SSM-based backbone distribution of packets between MRPs.

o 静态根分布树。这些方法遵循共享树方法。Romdhani等人[72]建议使用PIM-SM的交会点作为机动锚。移动发送者通过隧道将数据传输到这些“移动感知交会点”(MRP)。当仅限于单个域时,该方案相当于双向隧道。针对域间移动组播,作者设计了一种基于隧道或SSM的MRP间数据包骨干分发方案。

o Reconstruction of Distribution Trees. Several authors have proposed the construction of a completely new distribution tree after the movement of a mobile source and therefore have to compensate for the additional routing (tree-building) delay. M-HMIPv6 [59] tunnels data into a previously established tree rooted at mobility anchor points to compensate for the routing delay until a protocol-dependent timer expires. The Range-Based Mobile Multicast (RBMoM) protocol [73] introduces an additional Multicast Agent (MA) that advertises its service range. A mobile source registers with the closest MA and tunnels data through it. When moving out of the previous service range, it

o 重建分布树。几位作者提出在移动源移动后构建一个全新的分发树,因此必须补偿额外的路由(树构建)延迟。M-HMIPv6[59]将数据隧道到先前建立的树中,该树以移动性锚点为根,以补偿路由延迟,直到协议相关计时器过期。基于范围的移动多播(RBMoM)协议[73]引入了一个额外的多播代理(MA),用于宣传其服务范围。移动源使用最近的MA注册,并通过它传输数据。当移出以前的服务范围时,它

will perform MA discovery, a re-registration and continue data tunneling with a newly established Multicast Agent in its new current vicinity.


o Tree Modification Schemes. In the case of DVMRP routing, Chang and Yen [74] propose an algorithm to extend the root of a given delivery tree for incorporating a new source location in ASM. The authors rely on a complex additional signaling protocol to fix DVMRP forwarding states and heal failures in the reverse path forwarding (RPF) checks.

o 树修改方案。在DVMRP路由的情况下,Chang和Yen[74]提出了一种算法来扩展给定传递树的根,以便在ASM中合并新的源位置。作者依靠一个复杂的附加信令协议来修复DVMRP转发状态并修复反向路径转发(RPF)检查中的故障。

5.3.2. Source-Specific Multicast Mobility Approaches
5.3.2. 源特定组播移动方法

The shared tree approach of [72] has been extended to support SSM mobility by introducing the HoA address record to the Mobility-aware Rendezvous Points. The MRPs operate using extended multicast routing tables that simultaneously hold the HoA and CoA and thus can logically identify the appropriate distribution tree. Mobility thus may reintroduce the concept of rendezvous points to SSM routing.


Approaches for reconstructing SPTs in SSM rely on a client notification to establish new router state. They also need to preserve address transparency for the client. Thaler [75] proposed introducing a binding cache and providing source address transparency analogous to MIPv6 unicast communication. Initial session announcements and changes of source addresses are distributed periodically to clients via an additional multicast control tree rooted at the home agent. Source tree handovers are then activated on listener requests.


Jelger and Noel [76] suggest handover improvements employing anchor points within the source network, supporting continuous data reception during client-initiated handovers. Client updates are triggered out of band, e.g., by Source Demand Routing (SDR) / Session Announcement Protocol (SAP) [77]. Receiver-oriented tree construction in SSM thus remains unsynchronized with source handovers.


To address the synchronization problem at the routing layer, several proposals have focused on direct modification of the distribution trees. A recursive scheme may use loose unicast source routes with branch points, based on a multicast Hop-by-Hop protocol. Vida et al. [78] optimized SPT for a moving source on the path between the source and first branching point. O'Neill [79] suggested a scheme to overcome RPF check failures that originate from multicast source address changes with a rendezvous point scenario by introducing extended routing information, which accompanies data in a Hop-by-Hop option "RPF redirect" header. The Tree Morphing approach of Schmidt

为了解决路由层的同步问题,有几项建议侧重于直接修改分发树。递归方案可以基于逐跳多播协议使用带有分支点的松散单播源路由。Vida等人[78]在源和第一个分支点之间的路径上优化了移动源的SPT。O'Neill[79]提出了一种方案,通过引入扩展路由信息(随逐跳选项“RPF redirect”报头中的数据)来克服因多播源地址更改而导致的RPF检查失败,该信息来自集合点场景。Schmidt的树变形方法

and Waehlisch [80] used source routing to extend the root of a previously established SPT, thereby injecting router state updates in a Hop-by-Hop option header. Using extended RPF checks, the elongated tree autonomously initiates shortcuts and smoothly reduces to a new SPT rooted at the relocated source. An enhanced version of this protocol abandoned the initial source routing and could be proved to comply with rapid source movement [81]. Lee et al. [82] introduced a state-update mechanism for reusing major parts of established multicast trees. The authors start from an initially established distribution state, centered at the mobile source's home agent. A mobile source leaving its home network will signal a multicast forwarding state update on the path to its home agent and, subsequently, distribution states according to the mobile source's new CoA along the previous distribution tree. Multicast data is then intended to flow natively using triangular routes via the elongation and an updated tree centered on the home agent. Based on Host Identity Protocol identifiers, Kovacshazi and Vida [83] introduce multicast routing states that remain independent of IP addresses. Drawing upon a similar scaling law argument, parts of these states may then be reused after source address changes.


6. Security Considerations
6. 安全考虑

This document discusses multicast extensions to mobility. It does not define new methods or procedures. Security issues arise from source address binding updates, specifically in the case of source-specific multicast. Threats of hijacking unicast sessions will result from any solution jointly operating binding updates for unicast and multicast sessions.


Multicast protocols exhibit a risk of network-based traffic amplification. For example, an attacker may abuse mobility signaling to inject unwanted traffic into a previously established multicast distribution infrastructure. These threats are partially mitigated by reverse path forwarding checks by multicast routers. However, a multicast or mobility agent that explicitly replicates multicast streams, e.g., Home Agent that n-casts data, may be vulnerable to denial-of-service attacks. In addition to source authentication, a rate control of the replicator may be required to protect the agent and the downstream network.


Mobility protocols need to consider the implications and requirements for Authentication, Authorization, and Accounting (AAA). An MN may have been authorized to receive a specific multicast group when using one mobile network, but this may not be valid when attaching to a different network. In general, the AAA association for an MN may change between attachments, or may be individually chosen prior to network (re-)association. The most appropriate network path may be


one that satisfies user preferences, e.g., to use/avoid a specific network, minimize monetary cost, etc., rather than one that only minimizes the routing cost. Consequently, AAA bindings may need to be considered when performing context transfer.


Admission control issues may arise when new CoA source addresses are introduced to SSM channels [84]. Due to lack of feedback, the admission [85] and binding updates [86] of mobile multicast sources require autonomously verifiable authentication. This can be achieved by, for instance, Cryptographically Generated Addresses (CGAs).


Modification to IETF protocols (e.g., routing, membership, session announcement, and control) as well as the introduction of new entities, e.g., multicast mobility agents, can introduce security vulnerabilities and require consideration of issues such as authentication of network entities, methods to mitigate denial of service (in terms of unwanted network traffic, unnecessary consumption of router/host resources and router/host state/buffers). Future solutions must therefore analyze and address the security implications of supporting mobile multicast.


7. Summary and Future Steps
7. 总结和今后的步骤

This document is intended to provide a basis for the future design of mobile IPv6 multicast methods and protocols by:


o providing a structured overview of the problem space that multicast and mobility jointly generate at the IPv6 layer;

o 提供多播和移动在IPv6层共同产生的问题空间的结构化概述;

o referencing the implications and constraints arising from lower and upper layers and from deployment;

o 参考下层和上层以及部署产生的影响和限制;

o briefly surveying conceptual ideas of currently available solutions;

o 简要调查当前可用解决方案的概念想法;

o including a comprehensive bibliographic reference base.

o 包括一个全面的参考书目库。

It is recommended that future steps towards extending mobility services to multicast proceed to first solve the following problems:


1. Ensure seamless multicast reception during handovers, meeting the requirements of mobile IPv6 nodes and networks. Thereby addressing the problems of home subscription without n-tunnels, as well as native multicast reception in those visited networks, which offer a group communication service.

1. 在切换过程中确保无缝多播接收,满足移动IPv6节点和网络的要求。从而解决了没有n隧道的家庭订阅问题,以及在提供组通信服务的访问网络中的本地多播接收问题。

2. Integrate multicast listener support into unicast mobility management schemes and architectural entities to define a consistent mobility service architecture, providing equal support for unicast and multicast communication.

2. 将多播侦听器支持集成到单播移动性管理方案和体系结构实体中,以定义一致的移动性服务体系结构,为单播和多播通信提供同等支持。

3. Provide basic multicast source mobility by designing address duality management at end nodes.

3. 通过在终端节点设计地址二元性管理,提供基本的多播源移动性。

Appendix A. Implicit Source Notification Options

An IP multicast source transmits data to a group of receivers without requiring any explicit feedback from the group. Sources therefore are unaware at the network layer of whether any receivers have subscribed to the group, and unconditionally send multicast packets that propagate in the network to the first-hop router (often known in PIM as the designated router). There have been attempts to implicitly obtain information about the listening group members, e.g., extending an IGMP/MLD querier to inform the source of the existence of subscribed receivers. Multicast Source Notification of Interest Protocol (MSNIP) [87] was such a suggested method that allowed a multicast source to query the upstream designated router. However, this work did not progress within the IETF mboned working group and was terminated by the IETF.

IP多播源向一组接收器发送数据,而不需要该组的任何明确反馈。因此,源在网络层不知道是否有任何接收器订阅了该组,并且无条件地将在网络中传播的多播分组发送到第一跳路由器(在PIM中通常称为指定路由器)。已经有人试图隐式地获取关于监听组成员的信息,例如,扩展IGMP/MLD查询器以通知来源存在订阅的接收者。多播源兴趣通知协议(MSNIP)[87]就是这样一种建议的方法,允许多播源查询上游指定的路由器。然而,这项工作在IETF mboned工作组内没有进展,并被IETF终止。

Multicast sources may also be controlled at the session or transport layer using end-to-end control protocols. A majority of real-time applications employ the Real-time Transport Protocol (RTP) [88]. The accompanying control protocol, RTP Control Protocol (RTCP), allows receivers to report information about multicast group membership and associated performance data. In multicast, the RTCP reports are submitted to the same group and thus may be monitored by the source to monitor, manage and control multicast group operations. RFC 2326, the Real Time Streaming Protocol (RTSP), provides session layer control that may be used to control a multicast source. However, RTCP and RTSP information is intended for end-to-end control and is not necessarily visible at the network layer. Application designers may chose to implement any appropriate control plane for their multicast applications (e.g., reliable multicast transport protocols), and therefore a network-layer mobility mechanism must not assume the presence of a specific transport or session protocol.

还可以使用端到端控制协议在会话或传输层控制多播源。大多数实时应用程序采用实时传输协议(RTP)[88]。随附的控制协议RTP控制协议(RTCP)允许接收方报告有关多播组成员身份和相关性能数据的信息。在多播中,RTCP报告被提交到同一组,因此可以由源监控,以监控、管理和控制多播组操作。实时流协议(RTSP)RFC 2326提供了可用于控制多播源的会话层控制。但是,RTCP和RTSP信息用于端到端控制,不一定在网络层可见。应用设计者可以选择为其多播应用实现任何适当的控制平面(例如,可靠的多播传输协议),因此网络层移动机制不得假定存在特定的传输或会话协议。

Informative References


[1] Aguilar, L. "Datagram Routing for Internet Multicasting", In ACM SIGCOMM '84 Communications Architectures and Protocols, pp. 58-63, ACM Press, June, 1984.

[1] Aguilar,L.“因特网多播的数据报路由”,载于ACM SIGCOMM'84《通信体系结构和协议》,第58-63页,ACM出版社,1984年6月。

[2] Deering, S., "Host extensions for IP multicasting", STD 5, RFC 1112, August 1989.

[2] Deering,S.,“IP多播的主机扩展”,STD 5,RFC 1112,1989年8月。

[3] G. Xylomenos and G.C. Plyzos, "IP Multicast for Mobile Hosts", IEEE Communications Magazine, 35(1), pp. 54-58, January 1997.

[3] G.Xylomenos和G.C.Plyzos,“移动主机的IP多播”,IEEE通信杂志,35(1),第54-58页,1997年1月。

[4] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998.

[4] Deering,S.和R.Hinden,“互联网协议,第6版(IPv6)规范”,RFC 2460,1998年12月。

[5] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in IPv6", RFC 3775, June 2004.

[5] Johnson,D.,Perkins,C.,和J.Arkko,“IPv6中的移动支持”,RFC 37752004年6月。

[6] Devarapalli, V. and F. Dupont, "Mobile IPv6 Operation with IKEv2 and the Revised IPsec Architecture", RFC 4877, April 2007.

[6] Devarapalli,V.和F.Dupont,“使用IKEv2的移动IPv6操作和修订的IPsec架构”,RFC 4877,2007年4月。

[7] ITU-T Recommendation, "G.114 - One-way transmission time", Telecommunication Union Standardization Sector, 05/2003.

[7] ITU-T建议,“G.114-单向传输时间”,电信联盟标准化部门,2003年5月。

[8] Akyildiz, I and Wang, X., "A Survey on Wireless Mesh Networks", IEEE Communications Magazine, 43(9), pp. 23-30, September 2005.

[8] Akyildiz,I和Wang,X.,“无线网状网络的调查”,《IEEE通信杂志》,43(9),第23-30页,2005年9月。

[9] Bhattacharyya, S., Ed., "An Overview of Source-Specific Multicast (SSM)", RFC 3569, July 2003.

[9] Bhattacharyya,S.,Ed.“源特定多播(SSM)概述”,RFC 3569,2003年7月。

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

[10] Holbrook,H.和B.Cain,“IP的源特定多播”,RFC 4607,2006年8月。

[11] Waitzman, D., Partridge, C., and S. Deering, "Distance Vector Multicast Routing Protocol", RFC 1075, November 1988.

[11] Waitzman,D.,Partridge,C.和S.Deering,“距离向量多播路由协议”,RFC 1075,1988年11月。

[12] Estrin, D., Farinacci, D., Helmy, A., Thaler, D., Deering, S., Handley, M., Jacobson, V., Liu, C., Sharma, P., and L. Wei, "Protocol Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification", RFC 2362, June 1998.

[12] Estrin,D.,Farinaci,D.,Helmy,A.,Thaler,D.,Deering,S.,Handley,M.,Jacobson,V.,Liu,C.,Sharma,P.,和L.Wei,“协议独立多播稀疏模式(PIM-SM):协议规范”,RFC 2362,1998年6月。

[13] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", RFC 4601, August 2006.

[13] Fenner,B.,Handley,M.,Holbrook,H.,和I.Kouvelas,“协议独立多播-稀疏模式(PIM-SM):协议规范(修订版)”,RFC 4601,2006年8月。

[14] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, "Bidirectional Protocol Independent Multicast (BIDIR-PIM)", RFC 5015, October 2007.

[14] Handley,M.,Kouvelas,I.,Speakman,T.,和L.Vicisano,“双向协议独立多播(BIDIR-PIM)”,RFC 50152007年10月。

[15] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, "Multiprotocol Extensions for BGP-4", RFC 4760, January 2007.

[15] Bates,T.,Chandra,R.,Katz,D.,和Y.Rekhter,“BGP-4的多协议扩展”,RFC 4760,2007年1月。

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

[16] Deering,S.,Fenner,W.和B.Haberman,“IPv6的多播侦听器发现(MLD)”,RFC 2710,1999年10月。

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

[17] Vida,R.,Ed.,和L.Costa,Ed.,“IPv6的多播侦听器发现版本2(MLDv2)”,RFC 3810,2004年6月。

[18] Arkko, J., Vogt, C., and W. Haddad, "Enhanced Route Optimization for Mobile IPv6", RFC 4866, May 2007.

[18] Arkko,J.,Vogt,C.,和W.Haddad,“移动IPv6的增强路由优化”,RFC 4866,2007年5月。

[19] Koodli, R., Ed., "Mobile IPv6 Fast Handovers", RFC 5568, July 2009.

[19] Koodli,R.,Ed.,“移动IPv6快速切换”,RFC 5568,2009年7月。

[20] Soliman, H., Castelluccia, C., ElMalki, K., and L. Bellier, "Hierarchical Mobile IPv6 (HMIPv6) Mobility Management", RFC 5380, October 2008.

[20] Soliman,H.,Castelluccia,C.,ElMalki,K.,和L.Bellier,“分层移动IPv6(HMIPv6)移动性管理”,RFC 53802008年10月。

[21] Loughney, J., Ed., Nakhjiri, M., Perkins, C., and R. Koodli, "Context Transfer Protocol (CXTP)", RFC 4067, July 2005.

[21] Loughney,J.,Ed.,Nakhjiri,M.,Perkins,C.,和R.Koodli,“上下文传输协议(CXTP)”,RFC 4067,2005年7月。

[22] Montavont, N., Wakikawa, R., Ernst, T., Ng, C., and K. Kuladinithi, "Analysis of Multihoming in Mobile IPv6", Work in Progress, May 2008.

[22] N.Montavont、R.Wakikawa、T.Ernst、T.Ng、C.和K.Kuladinhi,“移动IPv6中的多宿分析”,正在进行的工作,2008年5月。

[23] Narayanan, V., Thaler, D., Bagnulo, M., and H. Soliman, "IP Mobility and Multi-homing Interactions and Architectural Considerations", Work in Progress, July 2007.

[23] Narayanan,V.,Thaler,D.,Bagnulo,M.,和H.Soliman,“IP移动性和多主交互与架构考虑”,正在进行的工作,2007年7月。

[24] Savola, P. and B. Haberman, "Embedding the Rendezvous Point (RP) Address in an IPv6 Multicast Address", RFC 3956, November 2004.

[24] Savola,P.和B.Haberman,“将集合点(RP)地址嵌入IPv6多播地址”,RFC 3956,2004年11月。

[25] Schmidt, T.C. and Waehlisch, M. "Predictive versus Reactive - Analysis of Handover Performance and Its Implications on IPv6 and Multicast Mobility", Telecommunication Systems, 30(1-3), pp. 123- 142, November 2005.

[25] Schmidt,T.C.和Waehlisch,M.“预测与反应-切换性能分析及其对IPv6和多播移动性的影响”,电信系统,30(1-3),第123-142页,2005年11月。

[26] Schmidt, T.C. and Waehlisch, M. "Morphing Distribution Trees - On the Evolution of Multicast States under Mobility and an Adaptive Routing Scheme for Mobile SSM Sources", Telecommunication Systems, 33(1-3), pp. 131-154, December 2006.

[26] Schmidt,T.C.和Waehlisch,M.“变形分布树——移动和移动SSM源自适应路由方案下多播状态的演变”,电信系统,33(1-3),第131-154页,2006年12月。

[27] Diot, C. et al. "Deployment Issues for the IP Multicast Service and Architecture", IEEE Network Magazine, spec. issue on Multicasting, 14(1), pp. 78-88, 2000.

[27] Diot,C.等人,“IP多播服务和架构的部署问题”,《IEEE网络杂志》,关于多播的规范问题,14(1),第78-88页,2000年。

[28] Eubanks, M., 2008.

[28] 尤班克斯,M。, 2008.

[29] Garyfalos, A, Almeroth, K. and Sanzgiri, K. "Deployment Complexity Versus Performance Efficiency in Mobile Multicast", Intern. Workshop on Broadband Wireless Multimedia: Algorithms, Architectures and Applications (BroadWiM), San Jose, California, USA, October 2004. Online:

[29] Garyfalos,A,Almeroth,K.和Sanzgiri,K.“移动多播中的部署复杂性与性能效率”,实习生。宽带无线多媒体研讨会:算法、架构和应用(BroadWiM),美国加利福尼亚州圣何塞,2004年10月。在线:

[30] Garyfalos, A, Almeroth, K. "A Flexible Overlay Architecture for Mobile IPv6 Multicast", IEEE Journ. on Selected Areas in Comm., 23(11), pp. 2194-2205, November 2005.

[30] Garyfalos,A,Almeroth,K.“移动IPv6多播的灵活覆盖架构”,IEEE期刊。关于Comm中的选定区域,第23(11)页,第2194-2205页,2005年11月。

[31] "Digital Video Broadcasting (DVB); IP Datacast over DVB-H: Set of Specifications for Phase 1", ETSI TS 102 468;

[31] “数字视频广播(DVB);DVB-H上的IP数据广播:第1阶段规范集”,ETSI TS 102 468;

[32] ETSI TS 102 611, "Digital Video Broadcasting (DVB); IP Datacast over DVB-H: Implementation Guidelines for Mobility)", European Standard (Telecommunications series), November 2004.

[32] ETSI TS 102 611,“数字视频广播(DVB);DVB-H上的IP数据广播:移动性实施指南”,欧洲标准(电信系列),2004年11月。

[33] Chuang, J. and Sirbu, M. "Pricing Multicast Communication: A Cost- Based Approach", Telecommunication Systems, 17(3), 281-297, 2001. Presented at the INET'98, Geneva, Switzerland, July 1998.

[33] Chuang,J.和Sirbu,M.“定价多播通信:基于成本的方法”,电信系统,17(3),281-2972001。在1998年7月于瑞士日内瓦举行的INET'98上提交。

[34] Van Mieghem, P, Hooghiemstra, G, Hofstad, R. "On the Efficiency of Multicast", IEEE/ACM Trans. Netw., 9(6), pp. 719-732, Dec. 2001.

[34] Van Mieghem,P,Hooghiemstra,G,Hofstad,R.“关于多播的效率”,IEEE/ACM Trans。《网络》,第9(6)页,第719-732页,2001年12月。

[35] Chalmers, R.C. and Almeroth, K.C, "On the topology of multicast trees", IEEE/ACM Trans. Netw., 11(1), 153-165, 2003.

[35] Chalmers,R.C.和Almeroth,K.C.“关于多播树的拓扑”,IEEE/ACM Trans。《网络》,第11(1)页,第153-165页,2003年。

[36] Janic, M. and Van Mieghem, P. "On properties of multicast routing trees", Int. J. Commun. Syst., 19(1), pp. 95-114, Feb. 2006.

[36] Janic,M.和Van Mieghem,P.“关于多播路由树的性质”,国际公共杂志。《系统》,第19(1)页,第95-114页,2006年2月。

[37] Van Mieghem, P. "Performance Analysis of Communication Networks and Systems", Cambridge University Press, 2006.

[37] Van Mieghem,P.“通信网络和系统的性能分析”,剑桥大学出版社,2006年。

[38] 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.

[38] Fenner,B.,He,H.,Haberman,B.,和H.Sandick,“基于Internet组管理协议(IGMP)/多播侦听器发现(MLD)的多播转发(“IGMP/MLD代理”)”,RFC 46052006年8月。

[39] Jeon, H., Jeong, S., and M. Riegel, "Transmission of IP over Ethernet over IEEE 802.16 Networks", RFC 5692, October 2009.

[39] Jeon,H.,Jeong,S.,和M.Riegel,“通过IEEE 802.16网络通过以太网传输IP”,RFC 5692,2009年10月。

[40] Shin, M-K., Ed., Han, Y-H., Kim, S-E., and D. Premec, "IPv6 Deployment Scenarios in 802.16 Networks", RFC 5181, May 2008.

[40] Shin,M-K.,Ed.,Han,Y-H.,Kim,S-E.,和D.Premec,“802.16网络中的IPv6部署场景”,RFC 5181,2008年5月。

[41] Patil, B., Xia, F., Sarikaya, B., Choi, JH., and S. Madanapalli, "Transmission of IPv6 via the IPv6 Convergence Sublayer over IEEE 802.16 Networks", RFC 5121, February 2008.

[41] Patil,B.,Xia,F.,Sarikaya,B.,Choi,JH.,和S.Madanapalli,“通过IEEE 802.16网络上的IPv6聚合子层传输IPv6”,RFC 51212008年2月。

[42] Kim, S., Jin, J., Lee, S., and S. Lee, "Multicast Transport on IEEE 802.16 Networks", Work in Progress, July 2007.

[42] Kim,S.,Jin,J.,Lee,S.,和S.Lee,“IEEE 802.16网络上的多播传输”,正在进行的工作,2007年7月。

[43] IEEE 802.16e-2005: IEEE Standard for Local and metropolitan area networks Part 16: "Air Interface for Fixed and Mobile Broadband Wireless Access Systems Amendment for Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands", New York, February 2006.

[43] IEEE 802.16e-2005:IEEE局域网和城域网标准第16部分:“固定和移动宽带无线接入系统的空中接口——许可频带内固定和移动组合操作的物理和介质接入控制层修正案”,纽约,2006年2月。

[44] 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; "IP Multimedia Subsystem (IMS)"; Stage 2, 3GPP TS 23.228, Rel. 5 ff, 2002 - 2007.

[44] 第三代伙伴关系项目;技术规范组服务和系统方面;“IP多媒体子系统(IMS)”;第2阶段,3GPP TS 23.228,Rel。5日以后,2002-2007年。

[45] Wasserman, M., Ed., "Recommendations for IPv6 in Third Generation Partnership Project (3GPP) Standards", RFC 3314, September 2002.

[45] Wasserman,M.,Ed.“第三代合作伙伴项目(3GPP)标准中的IPv6建议”,RFC 3314,2002年9月。

[46] 3GPP2,, "X.S0022-A, Broadcast and Multicast Service in cdma2000 Wireless IP Network, Rev. A.",, February 2007.

[46] 3GPP2,,“X.S0022-A,cdma2000无线IP网络中的广播和多播服务,Rev.A.”,,2007年2月。

[47] ETSI EN 302 304, "Digital Video Broadcasting (DVB); Transmission System for Handheld Terminals (DVB-H)", European Standard (Telecommunications series), November 2004.

[47] ETSI EN 302 304,“数字视频广播(DVB);手持终端传输系统(DVB-H)”,欧洲标准(电信系列),2004年11月。

[48] Fairhurst, G. and M. Montpetit, "Address Resolution Mechanisms for IP Datagrams over MPEG-2 Networks", RFC 4947, July 2007.

[48] Fairhurst,G.和M.Montpetit,“MPEG-2网络上IP数据报的地址解析机制”,RFC 4947,2007年7月。

[49] Montpetit, M.-J., Fairhurst, G., Clausen, H., Collini-Nocker, B., and H. Linder, "A Framework for Transmission of IP Datagrams over MPEG-2 Networks", RFC 4259, November 2005.

[49] Montpetit,M.-J.,Fairhurst,G.,Clausen,H.,Collini Nocker,B.,和H.Linder,“通过MPEG-2网络传输IP数据报的框架”,RFC 4259,2005年11月。

[50] Yang, X, Vare, J, Owens, T. "A Survey of Handover Algorithms in DVB-H", IEEE Comm. Surveys, 8(4), pp. 16-24, 2006.

[50] Yang,X,Vare,J,Owens,T.“DVB-H中切换算法的调查”,IEEE Comm.Surveys,8(4),第16-242006页。

[51] Fairhurst, G. and B. Collini-Nocker, "Unidirectional Lightweight Encapsulation (ULE) for Transmission of IP Datagrams over an MPEG-2 Transport Stream (TS)", RFC 4326, December 2005.

[51] Fairhurst,G.和B.Collini Nocker,“通过MPEG-2传输流(TS)传输IP数据报的单向轻量封装(ULE)”,RFC 4326,2005年12月。

[52] Fairhurst, G. and B. Collini-Nocker, "Extension Formats for Unidirectional Lightweight Encapsulation (ULE) and the Generic Stream Encapsulation (GSE)", RFC 5163, April 2008.

[52] Fairhurst,G.和B.Collini Nocker,“单向轻量级封装(ULE)和通用流封装(GSE)的扩展格式”,RFC 51632008年4月。

[53] "Draft IEEE Standard for Local and Metropolitan Area Networks: Media Independent Handover Services", IEEE LAN/MAN Draft IEEE P802.21/D07.00, July 2007.

[53] “局域网和城域网IEEE标准草案:媒体独立切换服务”,IEEE LAN/MAN草案IEEE P802.21/D07.00,2007年7月。

[54] Melia, T., Ed., "Mobility Services Transport: Problem Statement", RFC 5164, March 2008.

[54] Melia,T.,编辑,“移动服务运输:问题陈述”,RFC 51642008年3月。

[55] Melia, T., Ed., Bajko, G., Das, S., Golmie, N., and JC. Zuniga, "IEEE 802.21 Mobility Services Framework Design (MSFD)", RFC 5677, December 2009.

[55] 梅里亚,T.,Ed.,巴伊科,G.,达斯,S.,戈尔米,N.,和JC。Zuniga,“IEEE 802.21移动服务框架设计(MSFD)”,RFC 5677,2009年12月。

[56] Janneteau, C, Tian, Y, Csaba, S. et al. "Comparison of Three Approaches Towards Mobile Multicast", IST Mobile Summit 2003, Aveiro, Portugal, 16-18 June 2003.

[56] Janneteau,C,Tian,Y,Csaba,S.等人,“移动多播三种方法的比较”,IST移动峰会2003年,葡萄牙阿维罗,2003年6月16-18日。

[57] Suh, K., Kwon, D.-H., Suh, Y.-J. and Y. Park, "Fast Multicast Protocol for Mobile IPv6 in the fast handovers environments", Work in Progress, January 2004.

[57] Suh,K.,Kwon,D.-H.,Suh,Y.-J.和Y.Park,“快速切换环境中移动IPv6的快速多播协议”,正在进行的工作,2004年1月。

[58] Xia, F. and B. Sarikaya, "FMIPv6 extensions for Multicast Handover", Work in Progress, March 2007.

[58] Xia,F.和B.Sarikaya,“多播切换的FMIPv6扩展”,正在进行的工作,2007年3月。

[59] Schmidt, T. and M. Waehlisch, "Seamless Multicast Handover in a Hierarchical Mobile IPv6 Environment (M-HMIPv6)", Work in Progress, November 2005.

[59] Schmidt,T.和M.Waehlisch,“分层移动IPv6环境中的无缝多播切换(M-HMIPv6)”,正在进行的工作,2005年11月。

[60] Miloucheva, I. and K. Jonas, "Multicast Context Transfer in mobile IPv6", Work in Progress, June 2005.

[60] Miloucheva,I.和K.Jonas,“移动IPv6中的多播上下文传输”,正在进行的工作,2005年6月。

[61] Leoleis, G, Prezerakos, G, Venieris, I, "Seamless multicast mobility support using fast MIPv6 extensions", Computer Comm., 29(18), pp. 3745-3765, 2006.

[61] Leoleis,G,Prezerakos,G,Venieris,I,“使用快速MIPv6扩展的无缝多播移动性支持”,计算机通讯,29(18),第3745-37652006页。

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

[62] Gundavelli,S.,Ed.,Leung,K.,Devarapalli,V.,Chowdhury,K.,和B.Patil,“代理移动IPv6”,RFC 5213,2008年8月。

[63] Deng, H., Chen, G., Schmidt, T., Seite, P., and P. Yang, "Multicast Support Requirements for Proxy Mobile IPv6", Work in Progress, July 2009.

[63] Deng,H.,Chen,G.,Schmidt,T.,Seite,P.,和P.Yang,“代理移动IPv6的多播支持要求”,正在进行的工作,2009年7月。

[64] Zhang, H., Chen, X., Guan, J., Shen, B., Liu, E., and S. Dawkins, "Mobile IPv6 Multicast with Dynamic Multicast Agent", Work in Progress, January 2007.

[64] Zhang,H.,Chen,X.,Guan,J.,Shen,B.,Liu,E.,和S.Dawkins,“使用动态多播代理的移动IPv6多播”,正在进行的工作,2007年1月。

[65] Romdhani, I, Kellil, M, Lach, H.-Y. et. al. "IP Mobile Multicast: Challenges and Solutions", IEEE Comm. Surveys, 6(1), pp. 18-41, 2004.

[65] Romdhani,I,Kellil,M,Lach,H.-Y.等人,“IP移动多播:挑战和解决方案”,IEEE通信调查,6(1),第18-412004页。

[66] Conta, A. and S. Deering, "Generic Packet Tunneling in IPv6 Specification", RFC 2473, December 1998.

[66] Conta,A.和S.Deering,“IPv6规范中的通用数据包隧道”,RFC 2473,1998年12月。

[67] Waehlisch, M., Schmidt, T.C. "Between Underlay and Overlay: On Deployable, Efficient, Mobility-agnostic Group Communication Services", Internet Research, 17(5), pp. 519-534, Emerald Insight, Bingley, UK, November 2007.

[67] Waehlisch,M.,Schmidt,T.C.“在底层和覆盖层之间:关于可部署、高效、机动性不可知的群体通信服务”,互联网研究,17(5),第519-534页,Emerald Insight,宾利,英国,2007年11月。

[68] J. Buford, "Hybrid Overlay Multicast Framework", Work in Progress, February 2008.

[68] J.Buford,“混合覆盖多播框架”,正在进行的工作,2008年2月。

[69] Waehlisch, M., Schmidt, T., and S. Venaas, "A Common API for Transparent Hybrid Multicast", Work in Progress, October 2009.

[69] Waehlisch,M.,Schmidt,T.,和S.Venaas,“透明混合多播的通用API”,正在进行的工作,2009年10月。

[70] Christensen, M., Kimball, K., and F. Solensky, "Considerations for Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) Snooping Switches", RFC 4541, May 2006.

[70] Christensen,M.,Kimball,K.,和F.Solensky,“互联网组管理协议(IGMP)和多播侦听器发现(MLD)窥探交换机的注意事项”,RFC 4541,2006年5月。

[71] Jelger, C, Noel, T. "Multicast for Mobile Hosts in IP Networks: Progress and Challenges", IEEE Wirel. Comm., 9(5), pp 58-64, Oct. 2002.

[71] Jelger,C,Noel,T.“IP网络中移动主机的多播:进展和挑战”,IEEE Wirel。Comm.,9(5),第58-64页,2002年10月。

[72] Romdhani, I, Bettahar, H. and Bouabdallah, A. "Transparent handover for mobile multicast sources", in P. Lorenz and P. Dini, eds, Proceedings of the IEEE ICN'06, IEEE Press, 2006.

[72] Romdhani,I,Bettahar,H.和Bouabdallah,“移动多播源的透明切换”,载于P.Lorenz和P.Dini,编辑,IEEE ICN'06会议录,IEEE出版社,2006年。

[73] Lin, C.R. et al. "Scalable Multicast Protocol in IP-Based Mobile Networks", Wireless Networks, 8 (1), pp. 27-36, January, 2002.

[73] Lin,C.R.等人,“基于IP的移动网络中的可扩展多播协议”,无线网络,8(1),第27-36页,2002年1月。

[74] Chang, R.-S. and Yen, Y.-S. "A Multicast Routing Protocol with Dynamic Tree Adjustment for Mobile IPv6", Journ. Information Science and Engineering, 20(6), pp. 1109-1124, 2004.

[74] Chang,R.-S.和Yen,Y.-S.“移动IPv6中具有动态树调整的多播路由协议”,Journ。《信息科学与工程》,20(6),第1109-11242004页。

   [75]  Thaler, D. "Supporting Mobile SSM Sources for IPv6",
         Proceedings of ietf meeting, Dec. 2001.
   [75]  Thaler, D. "Supporting Mobile SSM Sources for IPv6",
         Proceedings of ietf meeting, Dec. 2001.

[76] Jelger, C. and T. Noel, "Supporting Mobile SSM sources for IPv6 (MSSMSv6)",Work in Progress, January 2002.

[76] Jelger,C.和T.Noel,“支持IPv6移动SSM源(MSSV6)”,正在进行的工作,2002年1月。

[77] Handley, M., Perkins, C., and E. Whelan, "Session Announcement Protocol", RFC 2974, October 2000.

[77] Handley,M.,Perkins,C.,和E.Whelan,“会话公告协议”,RFC 29742000年10月。

[78] Vida, R, Costa, L, Fdida, S. "M-HBH - Efficient Mobility Management in Multicast", Proc. of NGC '02, pp. 105-112, ACM Press 2002.

[78] Vida,R,Costa,L,Fdida,S.“M-HBH-多播中的高效移动性管理”,Proc。《NGC'02》第105-112页,ACM出版社2002年。

[79] A. O'Neill "Mobility Management and IP Multicast", Work in Progress, July 2002.

[79] A.O'Neill“移动性管理和IP多播”,正在进行的工作,2002年7月。

[80] Schmidt, T. C. and Waehlisch, M. "Extending SSM to MIPv6 - Problems, Solutions and Improvements", Computational Methods in Science and Technology, 11(2), pp. 147-152. Selected Papers from TERENA Networking Conference, Poznan, May 2005.

[80] Schmidt,T.C.和Waehlisch,M.“将SSM扩展到MIPv6——问题、解决方案和改进”,《科学和技术中的计算方法》,第11(2)页,第147-152页。特蕾娜网络会议论文选集,波兹南,2005年5月。

[81] Schmidt, T.C., Waehlisch, M., and Wodarz, M. "Fast Adaptive Routing Supporting Mobile Senders in Source Specific Multicast", Telecommunication Systems, 43(1), pp. 95-108, 2009,

[81] Schmidt,T.C.,Waehlisch,M.和Wodarz,M.“在源特定多播中支持移动发送者的快速自适应路由”,电信系统,43(1),第95-108页,2009年,

[82] Lee, H., Han, S. and Hong, J. "Efficient Mechanism for Source Mobility in Source Specific Multicast", in K. Kawahara and I. Chong, eds, "Proceedings of ICOIN2006", LNCS vol. 3961, pp. 82-91, Springer-Verlag, Berlin, Heidelberg, 2006.

[82] Lee,H.,Han,S.和Hong,J.“源特定多播中源移动性的有效机制”,K.Kawahara和I.Chong主编,“2006年ICOO2006年会议记录”,LNCS第3961卷,第82-91页,Springer Verlag,柏林,海德堡,2006年。

[83] Kovacshazi, Z. and Vida, R. "Host Identity Specific Multicast", Third International Conference on Networking and Services ICNS, IEEE Press, pp. 1-1, June 2007.

[83] Kovacshazi,Z.和Vida,R.“特定于主机身份的多播”,第三届网络和服务ICN国际会议,IEEE出版社,第1-1页,2007年6月。

[84] Kellil, M, Romdhani, I, Lach, H.-Y, Bouabdallah, A. and Bettahar, H. "Multicast Receiver and Sender Access Control and its Applicability to Mobile IP Environments: A Survey", IEEE Comm. Surveys & Tutorials, 7(2), pp. 46-70, 2005.

[84] Kellil,M,Romdhani,I,Lach,H.-Y,Bouabdallah,A.和Bettahar,H.“多播接收器和发送器访问控制及其对移动IP环境的适用性:调查”,IEEE Comm.Surveys&Tutorials,7(2),第46-702005页。

[85] Castellucia, C, Montenegro, G. "Securing Group Management in IPv6 with Cryptographically Based Addresses", Proc. 8th IEEE Int'l Symp. Comp. and Commun, Turkey, July 2003, pp. 588-93.

[85] Castellucia,C,黑山,G.“使用基于加密的地址在IPv6中保护组管理”,Proc。第八届IEEE国际研讨会。公司。土耳其公社,2003年7月,第588-93页。

[86] Schmidt, T.C, Waehlisch, M., Christ, O., and Hege, G. "AuthoCast - a mobility-compliant protocol framework for multicast sender authentication", Security and Communication Networks, 1(6), pp. 495-509, 2008.

[86] Schmidt,T.C,Waehlisch,M.,Christ,O.,和Hege,G.“AuthoCast-一种适用于多播发送方身份验证的移动性兼容协议框架”,安全与通信网络,1(6),第495-5092008页。

[87] Fenner, B., Holbrook, H., and I. Kouvelas, "Multicast Source Notification of Interest Protocol (MSNIP)", Work in Progress, November 2001.

[87] Fenner,B.,Holbrook,H.,和I.Kouvelas,“多播源兴趣通知协议(MSNIP)”,正在进行的工作,2001年11月。

[88] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003.

[88] Schulzrinne,H.,Casner,S.,Frederick,R.,和V.Jacobson,“RTP:实时应用的传输协议”,STD 64,RFC 35502003年7月。



Work on exploring the problem space for mobile multicast has been pioneered by Greg Daley and Gopi Kurup within their early document "Requirements for Mobile Multicast Clients".

格雷格·戴利(Greg Daley)和戈皮·库鲁普(Gopi Kurup)在其早期文件《移动多播客户端的需求》中率先探索了移动多播的问题空间。

Since then, many people have actively discussed the different issues and contributed to the enhancement of this memo. The authors would like to thank (in alphabetical order) Kevin C. Almeroth, Lachlan Andrew, Jari Arkko, Cedric Baudoin, Hans L. Cycon, Hui Deng, Marshall Eubanks, Zhigang Huang, Christophe Jelger, Andrei Gutov, Rajeev Koodli, Mark Palkow, Craig Partridge, Imed Romdhani, Hesham Soliman, Dave Thaler, and last, but not least, very special thanks to Stig Venaas for his frequent and thorough advice.

自那时以来,许多人积极讨论了不同的问题,并为加强这份备忘录作出了贡献。作者要感谢(按字母顺序排列)凯文·C·阿尔梅罗斯、拉克兰·安德鲁、贾里·阿尔科、塞德里克·波多恩、汉斯·L·赛康、惠登、马歇尔·尤班克斯、黄志刚、克里斯托夫·杰尔格、安德烈·古托夫、拉吉夫·库德利、马克·帕尔科夫、克雷格·帕特里奇、伊德·隆达尼、赫萨姆·索利曼、戴夫·泰勒,最后但并非最不重要的是,非常特别地感谢Stig Venaas经常提供的全面建议。

Authors' Addresses


Thomas C. Schmidt Dept. Informatik Hamburg University of Applied Sciences, Berliner Tor 7 D-20099 Hamburg, Germany Phone: +49-40-42875-8157 EMail:

Thomas C. Schmidt汉堡应用科学汉堡大学,柏林大学7 D-200 99汉堡,德国电话:+4940-428 75-8157电子邮件:schmidt@informatik.haw-汉堡

Matthias Waehlisch link-lab Hoenower Str. 35 D-10318 Berlin, Germany EMail:

Matthias Waehlisch link lab Hoenower Str.35 D-10318德国柏林电子邮件:mw@link-实验室网络

Godred Fairhurst School of Engineering, University of Aberdeen, Aberdeen, AB24 3UE, UK EMail:

阿伯丁大学GoRead FelHurt工程学院,英国,阿伯丁,AB24 3UE,电子邮件