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   MobOpts Research Group                             Thomas C. Schmidt 
   Internet Draft                                           HAW Hamburg 
                                                     Matthias Waehlisch 
   Expires: September 2007                                     link-lab 
                                                             March 2007 
    
    
              Multicast Mobility in MIPv6: Problem Statement 
                <draft-schmidt-mobopts-mmcastv6-ps-02.txt> 
    
IPR Statement 
    
   By submitting this Internet-Draft, each author represents that any 
   applicable patent or other IPR claims of which he or she is aware 
   have been or will be disclosed, and any of which he or she becomes      
   aware will be disclosed, in accordance with Section 6 of BCP 79 [1]. 
    
Status of this Memo 
    
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   This document is a submission of the IRTF MobOpts RG. Comments should 
   be directed to the MobOpts RG mailing list, mobopts@irtf.org. 
    
    
    
Abstract 
    
   In this document we discuss mobility extensions to current IP layer 
   multicast solutions. Problems arising from mobile group communication 
   in general, in the case of multicast listener mobility and for mobile 
   Any Source Multicast as well as Source Specific Multicast senders are 
   documented. Characteristic aspects of multicast routing and 
   deployment issues are summarized. The principal approaches to the 
   multicast mobility problems are outlined subsequently. 
    

 
                         
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Table of Contents 
    

   1. Introduction and Motivation....................................3 

   2. Problem Description............................................4 
      2.1 Generals...................................................4 
      2.2 Multicast Listener Mobility................................5 
      2.3 Multicast Source Mobility..................................6 
         2.3.1 Any Source Multicast Mobility.........................6 
         2.3.2 Source Specific Multicast Mobility....................7 
      2.4 Deployment Issues..........................................8 

   3. Characteristics of Multicast Routing Trees under Mobility......8 

   4. Solutions......................................................9 
      4.1 General Approaches.........................................9 
      4.2 Solutions for Multicast Listener Mobility.................10 
      4.3 Solutions for Multicast Source Mobility...................10 
         4.3.1 Any Source Multicast Mobility Approaches.............10 
         4.3.2 Source Specific Multicast Mobility Approaches........11 

   5. Security Considerations.......................................12 

   6. IANA Considerations...........................................12 

   Appendix A. Implicit Source Notification Options.................12 

   7. References....................................................13 

   Acknowledgments..................................................17 

   Author's Addresses...............................................17 

   Intellectual Property Statement..................................18 

   Copyright Notice.................................................18 

   Disclaimer of Validity...........................................18 

   Acknowledgement..................................................18 

    
 
     
 


 
 
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1. Introduction and Motivation 
    
   Group communication forms an integral building block of a wide 
   variety of applications, ranging from public content distribution and 
   streaming over voice and video conferencing, collaborative 
   environments and gaming up to the self-organization of distributed 
   systems. Its support by network layer multicast will be needed, 
   whenever globally distributed, scalable, serverless or instantaneous 
   communication is required. As broadband media delivery more and more 
   emerges to be a typical mass scenario, scalability and bandwidth 
   efficiency of multicast routing continuously gains relevance. The 
   idea of Internet multicasting already arose in the early days [2], 
   its realization will be of particular importance to mobile 
   environments, where users commonly share frequency bands of limited 
   capacity. The rapidly increasing mobile reception of 'infotainment' 
   streams may soon require a wide deployment of mobile multicast 
   services. Multicast mobility consequently has been a concern for 
   about ten years [3] and led to innumerous proposals, but no generally 
   accepted solution. 
    
   The fundamental approach to deal with mobility in IPv6 [4] is stated 
   in the Mobile IPv6 RFCs [5,6]. MIPv6 [5] only roughly treats 
   multicast mobility, in a pure remote subscription approach or through 
   bi-directional tunneling via the Home Agent. Whereas the remote 
   subscription suffers from slow handovers, as it relies on multicast 
   routing to adapt to handovers, bi-directional tunneling introduces 
   inefficient overheads and delays due to triangular forwarding. 
   Therefore none of the approaches can be considered solutions for a 
   deployment on large scale. A mobile multicast service for a future 
   Internet should admit 'close to optimal' routing at predictable and 
   limited cost, robustness combined with a service quality compliant to 
   real-time media distribution.  
    
   Intricate multicast routing procedures, though, are not easily 
   extensible to comply with mobility requirements. Any client 
   subscribed to a group while in motion, requires delivery branches to 
   pursue its new location; any mobile source requests the entire 
   delivery tree to adapt to its changing positions. 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 [35]. 
    
   In multimedia conference scenarios each member commonly operates as 
   receiver and as sender for multicast based group communication. In 
   addition, real-time communication such as voice or video over IP 
   places severe temporal requirement on mobility protocols: Seamless 
   handover scenarios need to limit disruptions or delay to less than 
   100 ms. Jitter disturbances are not to exceed 50 ms. Note that 100 ms 
   is about the duration of a spoken syllable in real-time audio. 
 
 
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   It is the aim of this document, to specify the problem scope for a 
   multicast mobility management as to be refined in future work. The 
   attempt is made to subdivide the various challenges according to 
   their originating aspects and to present existing proposals for 
   solution, as well as major bibliographic references. 
    
    
2. Problem Description 
    
2.1 Generals 
    
   Multicast mobility must be considered as a generic term, which 
   subsumes a collection of quite distinct functions. At first, 
   multicast communication divides into Any Source Multicast (ASM) [7] 
   and Source Specific Multicast (SSM) [8,9]. At second, the roles of 
   senders and receivers are asymmetric and need distinction. Both may 
   individually be mobile. Their interaction is facilitated by a 
   multicast routing function such as DVMRP [10], PIM-SM/SSM [11,12], 
   Bi-directional PIM [13] or CBT [14] and the multicast listener 
   discovery protocol [15,16]. 
    
   Any multicast mobility solution must account for all of these 
   functional blocks. It should enable seamless continuity of multicast 
   sessions when moving from one IPv6 subnet to another. It should 
   preserve the multicast nature of packet distribution and approximate 
   optimal routing. It should support per flow handover for multicast 
   traffic, as properties and designations of flows may be of distinct 
   nature. 
    
   Multicast routing dynamically adapts to session topologies, which 
   then may change under mobility. However, depending on the topology 
   and the protocol in use, routing convergence arrives at a time scale 
   close to seconds, or even minutes and is far too slow to support 
   seamless handovers for interactive or real-time media sessions. The 
   actual temporal behavior strongly depends on the routing protocol in 
   use and on the geometry of the current distribution tree. A mobility 
   scheme that arranges for adjustments, i.e., partial changes or full 
   reconstruction of multicast trees is forced to make provision for 
   time buffers sufficient for protocol convergence. Special attention 
   is needed with a possible rapid movement of the mobile node, as this 
   may occur at much higher rates than compatible with protocol 
   convergence.  
    
   IP layer multicast packet distribution is an unreliable service, 
   which is bound to connectionless transport protocols. Packet loss 
   thus will not be handled in a predetermined fashion. Mobile multicast 
   handovers should not cause significant packet drops. Due to 

 
 
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   statelessness the bi-casting of multicast flows does not cause 
   foreseeable degradations of the transport layer.  
    
   Group addresses in general are location transparent, even though 
   there are proposals to embed unicast prefixes or Rendezvous Point 
   addresses [17]. Addresses of sources contributing to a multicast 
   session are interpreted by the routing infrastructure and by receiver 
   applications, which frequently are source address aware. Multicast 
   therefore inherits the mobility address duality problem for source 
   addresses, being a logical node identifier, i.e., the home address 
   (HoA) at the one hand and a topological locator, the care-of-address 
   (CoA) at the other. 
    
   Multicast sources in general operate decoupled from their receivers 
   in the following sense: A multicast source submits data to a group of 
   unknown receivers and thus operates without any feedback channel. It 
   neither has means to inquire on properties of its delivery trees, nor 
   will it be able to learn about the state of its receivers. In the 
   event of an inter-tree handover, a mobile multicast source therefore 
   is vulnerable to loosing receivers without taking notice. (Cf. 
   Appendix A for implicit source notification approaches). Applying a 
   mobility binding update or return routability procedure will likewise 
   break the semantic of a receiver group remaining unidentified by the 
   source and thus cannot be applied in unicast analogy. 
    
2.2 Multicast Listener Mobility 
    
   A mobile multicast listener entering a new IP subnet faces the 
   problem of transferring the multicast membership context to its new 
   point of attachment. It thereby may encounter either one of the 
   following conditions: The new network may not be multicast enabled or 
   the specific multicast service in use may be unsupported or 
   prohibited. Alternatively, the requested multicast service may be 
   supported and enabled in the new network, but the multicast groups 
   under subscription may not be forwarded to it. Then current 
   distribution trees for the desired groups may reside at large routing 
   distance. It may as well occur that data of some or all groups under 
   subscription of the mobile node are received by one or several local 
   group members at the instance of arrival and that multicast streams 
   flow natively. 
    
   The problem of achieving seamless multicast listener handovers is 
   thus threefold: 
     o Ensure multicast reception even in visited networks without  
       appropriate multicast support. 
     o Expedite primary multicast forwarding to comply with a seamless 
       timescale at handovers. 
     o Realize native multicast forwarding whenever applicable to  
       preserve network resources and avoid data redundancy. 
 
 
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   Additional aspects related to infrastructure remain. In changing its 
   point of attachment a mobile receiver may not have enough time to 
   leave groups in the previous network. Also, packet duplication and 
   disorder may result from the change of topology.  
    
2.3 Multicast Source Mobility 
    
2.3.1 Any Source Multicast Mobility 
    
   A node submitting data to an ASM group either defines the root of a 
   source specific shortest path tree (SPT), distributing data towards a 
   rendezvous point or receivers, or it forwards data directly down a 
   shared tree, e.g., via encapsulated PIM register messages. Aside from 
   tunneling or shared trees, forwarding along source specific delivery 
   trees will be bound to a topological network address due to reverse 
   path forwarding (RPF) checks. A mobile multicast source moving away 
   is solely enabled to either inject data into a previously established 
   delivery tree, which may be a rendezvous point based shared tree, or 
   to (re-)define a multicast distribution tree compliant to its new 
   location. In pursuing the latter the mobile sender will have to 
   proceed without control of the new tree construction due to 
   decoupling of sender and receivers. 
    
   A mobile multicast source consequently must meet address transparency 
   at two layers: In order to comply with RPF checks, it has to use an 
   address within the IPv6 basic header's source field, which is in 
   topological concordance with the employed multicast distribution 
   tree. For application transparency the logical node identifier, 
   commonly the HoA, must be presented as packet's source address to the 
   socket layer at the receiver side.  
    
   Conforming to address transparency and temporal handover constraints 
   will be major problems for any route optimizing mobility solution. 
   Additional issues arrive from possible packet loss and from multicast 
   scoping. A mobile source away from home must attend scoping 
   restrictions, which arise from its home and its visited location [5]. 
    
   Within intra-domain multicast routing the employment of shared trees 
   may considerably relax mobility related complexity. Relying upon a 
   static rendezvous point, a mobile source may continuously submit data 
   by encapsulating packets with its previous topologically correct or 
   home source address. Constraints even weaken, when bi-directional PIM 
   is used. Intra-domain mobility is transparently covered by bi-
   directional shared trees, eliminating the need for tunneling data to 
   reach the rendezvous point. 
    
   However, issues arise in inter-domain multicast scenarios, whenever 
   notification of source addresses is required between distributed 
 
 
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   instances of shared trees. A new CoA acquired after a mobility 
   handover will necessarily be subject to inter-domain record exchange. 
   In presence of embedded rendezvous point addresses [17], e.g., for 
   inter-domain PIM-SM, the primary rendezvous point will be globally 
   appointed and the signaling requirements obsolete. 
    
2.3.2 Source Specific Multicast Mobility 
    
   Fundamentally, Source Specific Multicast has been designed for static 
   addresses of multicast senders. Source addresses in client 
   subscription to SSM groups are directly used for route 
   identification. Any SSM subscriber is thus forced to know the 
   topological address of its group contributors. SSM source 
   identification invalidates, when source addresses change 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). 
    
   Consequently source mobility for SSM packet distribution requires a 
   dedicated conceptual treatment in addition to the problems of mobile 
   ASM. As a listener is subscribed to an (S,G) channel membership and 
   as routers have established an (S,G)-state shortest path tree rooted 
   at source S, any change of source addresses under mobility requests 
   for state updates at all routers and all receivers. On source 
   handover a new SPT needs to be established, which partly will 
   coincide with the previous SPT, e.g., at the receiver side. As the 
   principle multicast decoupling of a sender from its receivers 
   likewise holds for SSM, client updates needed for switching trees 
   turns into a severe problem. 
    
   An SSM listener subscribing to or excluding any specific multicast 
   source, may want 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]. 
    
   All of the above severely add complexity to a robust SSM mobility 
   solution, which should converge to optimal routes and, for the sake 
   of efficiency, should avoid data encapsulation, as well. Like in ASM 
   handover delays are to be considered critical. 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 [43,47]. 
    
   Finally, Source Specific Multicast has been designed as a light-
   weight approach to group communication. In adding mobility 
 
 
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   management, it is desirable to preserve the principle leanness of SSM 
   by minimizing additional signaling overheads. 
    
2.4 Deployment Issues 
    
   IP multicast deployment in general has been hesitant over the past 15 
   years, even though all major router vendors and operating systems 
   offer a wide variety of implementations to support multicast [44]. 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 into the mobile multicast 
   domain [45]. Hereunto Garyfalos and Almeroth [24] 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. 
    
   Therefore it is desirable that any solution to mobile multicast 
   should leave routing protocols unchanged. Mobility management in such 
   deployment-friendly schemes should preferably be handled at edge 
   nodes, preserving the routing infrastructure in mobility agnostic 
   condition. Facing the current state of proposals, the urge remains 
   open to search for such simple, infrastructure transparent solutions, 
   even though there are reasonable doubts, whether the desired can be 
   achieved in all cases.  
    
   Nevertheless, multicast services in mobile environments may soon 
   become indispensable, when multimedia distribution services such as 
   DVB will develop as a strong business case for IP portables. As IP 
   mobility will unfold dominance and as efficient link utilization will 
   show 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 
    
   Multicast distribution trees have been studied well under the focus 
   of network efficiency. Grounded on empirical observations Chuang and 
   Sirbu [38] proposed a scaling power-law for the total number of links 
   in a multicast shortest path tree with m receivers (prop. 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 rather tall than wide. 
    
   Subsequent empirical and analytical work, cf. [39,40], debated the 
   applicability of the Chuang and Sirbu scaling law. Van Mieghem et al. 
   [39] proved that the proposed power law cannot hold for an increasing 
   Internet or very large multicast groups, but is indeed applicable for 
 
 
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   moderate receiver numbers and the current Internet size N = 10^5 core 
   nodes. Investigating on self-similarity Janic and Van Mieghem [42] 
   semi-empirically substantiated that multicast shortest path trees in 
   the Internet can be modeled with reasonable accuracy by uniform 
   recursive trees (URT) [41], provided m remains small compared to N. 
    
   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 an outer measure for routing complexity. Source specific 
   multicast trees subsequently generated from mobility handover steps 
   are not independent, but highly correlated. They most likely branch 
   to the identical receivers at one or several intersection points. By 
   the self-similar nature, the persistent subtrees (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 [43], 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. Solutions 
    
4.1 General Approaches 
    
   Three approaches to mobile Multicast are commonly around [36]:  
    
    o Bi-directional Tunnelling guides the mobile node to tunnel all 
   multicast data via its home agent. This principle multicast solution 
   hides all movement and results in static multicast trees. It may be 
   employed transparently by mobile multicast listeners and sources, on 
   the price of triangular routing and possibly significant performance 
   degradations due to widely spanned data tunnels. 
    
    o Remote Subscription forces the mobile node to re-initiate 
   multicast distribution subsequent to handover by submitting an MLD 
   listener report within the subnet it newly attached to. This approach 
   of tree discontinuation relies on multicast dynamics to adapt to 
   network changes. It not only results in rigorous service disruption, 
   but leads to mobility driven changes of source addresses, and thus 
   disregards session persistence under multicast source mobility. 
    
    o Agent-based solutions attempt to balance between the previous two 
   mechanisms. Static agents typically act as local tunnelling proxies, 
   allowing for some inter-agent handover while the mobile node moves 
   away. A decelerated inter-tree handover, i.e. tree walking, will be 
   the outcome of agent-based multicast mobility, where some extra 

 
 
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   effort is needed to sustain session persistence through address 
   transparency of mobile sources. 
    
   MIPv6 [5] introduces bi-directional tunnelling as well as remote 
   subscription as minimal standard solutions. Various publications 
   suggest utilizing remote subscription for listener mobility, only, 
   while advising bi-directional tunnelling as the solution for source 
   mobility. Such approach suffers from the drawback that multicast 
   communication roles are not explicitly known at the network layer and 
   may change or mix unexpectedly. 
    
   It should be noted that none of the above approaches address SSM 
   source mobility, except the bi-directional tunnelling. 
    
    
4.2 Solutions for Multicast Listener Mobility 
    
   There are proposals of agent assisted handovers compliant to the 
   unicast real-time mobility infrastructure of Fast MIPv6 [18], the M-
   FMIPv6 [19,20], and of Hierarchical MIPv6 [21], the M-HMIPv6 [22], 
   and to context transfer [23], which have been thoroughly analyzed in 
   [43,49]. A hybrid architecture of reactively operating proxy-gateways 
   located at the Internet edges is introduced in [24]. An approach 
   based on dynamically negotiated inter-agent handovers is presented in 
   [25]. Aside from IETF work countless publications present proposals 
   for seamless multicast listener mobility, cf. [35] for a 
   comprehensive overview.  
    
4.3 Solutions for Multicast Source Mobility 
    
4.3.1 Any Source Multicast Mobility Approaches 
    
   Solutions for the multicast source mobility problem can be sorted in 
   three categories: 
    
    o Statically Rooted Distribution Trees:  
    
   Following a shared tree approach, Romdhani et al. [26] propose to 
   employ Rendezvous Points of PIM-SM as mobility anchors. Mobile 
   senders tunnel their data to these "Mobility-aware Rendezvous Points" 
   (MRPs), whence in restriction to a single domain this scheme is 
   equivalent to the bi-directional tunneling. Focusing on interdomain 
   mobile multicast, the authors design a tunnel- or SSM-based backbone 
   distribution of packets between MRPs. 
    
    o Reconstruction of Distribution Trees:  
    
   Several authors propose to construct a completely new distribution 
   tree after the movement of a mobile source and thereby have to 
 
 
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   compensate routing delays. M-HMIPv6 [22] tunnels data into previously 
   established trees rooted at mobility anchor points to compensate for 
   routing delays until a protocol dependent timer expires. The RBMoM 
   protocol [27] introduces additional Multicast Agents (MA), which 
   advertise their service range. The mobile source registers with the 
   closest MA and tunnels its data through it. When moving out of the 
   previous service range, it will perform a MA discovery, a re-
   registration and continue data tunneling with its newly established 
   Multicast Agent in its current vicinity. 
    
    o Tree Modification Schemes:  
    
   In the case of DVMRP routing, Chang and Yen [28] propose an algorithm 
   to extend the root of a given delivery tree for incorporating a new 
   source location in ASM. To fix DVMRP forwarding states and heal 
   reverse path forwarding (RPF) check failures, the authors rely on a 
   complex additional signaling protocol. 
    
4.3.2 Source Specific Multicast Mobility Approaches 
    
   The shared tree approach of [26] has been extended to SSM mobility by 
   introducing the HoA address record to Mobility-aware Rendezvous 
   Points. These MRPs operate on extended multicast routing tables, 
   which simultaneously hold HoA and CoA and are thus enabled to 
   logically identify the appropriate distribution tree. Mobility thus 
   re-introduces rendezvous points to SSM routing. 
    
   Approaches of reconstructing SPTs in SSM have to rely on client 
   notification for initiating new router state establishment. At the 
   same time they need to preserve address transparency to the client. 
   To account for the latter, Thaler [29] proposes to employ binding 
   caches and to obtain source address transparency analogous to MIPv6 
   unicast communication. Initial session announcements and changes of 
   source addresses are to be distributed periodically to clients via an 
   additional multicast control tree based at the home agent. Source 
   tree handovers are then activated on listener requests.  
   Jelger and Noel [30] suggest handover improvements by employing 
   anchor points within the source network, supporting a continuous data 
   reception during client initiated handovers. Client updates are to be 
   triggered out of band, e.g. by SDR. Receiver oriented tree 
   construction in SSM thus remains unsynchronized with source 
   handovers. 
    
   Addressing this synchronization problem at the routing layer, several 
   proposals concentrate on direct modification of distribution trees. 
   Based on a multicast Hop-by-Hop protocol, a recursive scheme of loose 
   unicast source routes with branch points, Vida et al [31] optimize 
   SPTs for moving sources on the path between source and first 
   branching point. O'Neill [32] suggests a scheme to overcome RPF check 
 
 
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   failures originating from multicast source address changes in 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 and Waehlisch 
   [33] uses 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. Lee et al. [34] introduce a state 
   update mechanism for re-using major parts of established multicast 
   trees. The authors start from initially established distribution 
   states centered at the mobile source's home agent. A mobile 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 are implemented along the 
   previous distribution tree. Multicast data then is intended to 
   natively flow in triangular routes via the elongation and updated 
   tree centered at the home agent. Consequently this mechanism refrains 
   from using shortest path trees. Unfortunately the authors do not 
   address the problem of RPF check failures in their paper. 
    
5. Security Considerations 
    
   This document discusses multicast extensions to mobility. 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. Admission control issues 
   may arise with new CoA source addresses being introduced to SSM 
   channels (cf. [37] for a comprehensive discussion). Future solutions 
   must address the security implications. 
    
6. IANA Considerations 
    
   There are no IANA considerations introduced by this draft. 
    
Appendix A. Implicit Source Notification Options 
    
   A multicast source will transmit data to a group of receivers without 
   any option of an explicit feedback channel. There are attempts though 
   to implicitly obtain information on listening group members. One 
   approach has been dedicated to inquire designated routers on the pure 
   existence of receivers. Based on an extension of IGMP, the Multicast 
   Source Notification of Interest Protocol (MSNIP) [48] was designed to 
   allow for the multicast source querying its designated router. 
   However, work on MSNIP has been terminated by IETF.  
    
   A majority of real-time applications employ RTP [50] as its 
   application layer transport protocol, which is accompanied by its 
 
 
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   control protocol RTCP. RTP is capable of multicast group distribution 
   and RTCP receiver reports are submitted to the same group in the 
   multicast case. Thus RTCP may be used to monitor, manage and control 
   multicast group operations, as it provides a fairly comprehensive 
   insight into group member statuses. However, RTCP information is 
   neither present at the network layer nor does multicast communication 
   presuppose the use of RTP. 
    
    
7. References 
 
Normative References 
                     
   1 S. Bradner "Intellectual Property Rights in IETF Technology", BCP 
      79, RFC 3979, March 2005. 
    
   2 Aguilar, L. "Datagram Routing for Internet Multicasting", In ACM 
      SIGCOMM '84 Communications Architectures and Protocols, pp. 58-63, 
      ACM Press, June, 1984. 
    
   3 G. Xylomenos and G.C. Plyzos "IP Multicast for Mobile Hosts", IEEE 
      Communications Magazine, pp. 54-58, January 1997. 
    
   4 R. Hinden and S. Deering "Internet Protocol Version 6 
      Specification", RFC 2460, December 1998. 
    
   5 D.B. Johnson, C. Perkins and J. Arkko "Mobility Support in IPv6", 
      RFC 3775, June 2004. 
    
   6 J. Arkko, V. Devarapalli and F. Dupont "Using IPsec to Protect 
      Mobile IPv6 Signaling Between Mobile Nodes and Home Agents", RFC 
      3776, June 2004. 
    
   7 S. Deering "Host Extensions for IP Multicasting", RFC 1112, August 
      1989. 
    
   8 S. Bhattacharyya "An Overview of Source-Specific Multicast (SSM)", 
      RFC 3569, July 2003. 
    
   9 H. Holbrook, B. Cain "Source-Specific Multicast for IP", RFC 4607, 
      August 2006. 
    
   10 D. Waitzman, C. Partridge, S.E. Deering "Distance Vector Multicast 
      Routing Protocol", RFC 1075, November 1988. 
    
   11 D. Estrin, D. Farinacci, A. Helmy, D. Thaler, S. Deering, M. 
      Handley, V. Jacobson, C. Liu, P. Sharma, L. Wei "Protocol 


 
 
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      Independent Multicast-Sparse Mode (PIM-SM): Protocol 
      Specification", RFC 2362, June 1998. 
    
   12 B. Fenner, M. Handley, H. Holbrook, I. Kouvelas: "Protocol 
      Independent Multicast - Sparse Mode PIM-SM): Protocol 
      Specification (Revised)", RFC 4601, August 2006. 
    
   13 M. Handley, I. Kouvelas, T. Speakman, L. Vicisano "Bi-directional 
      Protocol Independent Multicast (BIDIR-PIM)", draft-ietf-pim-bidir-
      09.txt, (work in progress), February 2007. 
    
   14 A. Ballardie "Core Based Trees (CBT version 2) Multicast Routing", 
      RFC 2189, September 1997. 
    
   15 S. Deering, W. Fenner and B. Haberman "Multicast Listener 
      Discovery (MLD) for IPv6", RFC 2710, October 1999. 
    
   16 R. Vida and L. Costa (Eds.) "Multicast Listener Discovery Version 
      2 (MLDv2) for IPv6", RFC3810, June 2004. 
    
   17 P. Savola, B. Haberman "Embedding the Rendezvous Point (RP) 
      Address in an IPv6 Multicast Address", RFC 3956, November 2004. 
    
   18 Koodli, R. "Fast Handovers for Mobile IPv6", RFC 4068, July 2004. 
    
   19 Suh, K., Kwon, D.-H., Suh, Y.-J. and Park, Y. "Fast Multicast 
      Protocol for Mobile IPv6 in the fast handovers environments", 
      Internet Draft - (work in progress, expired), February 2004. 
    
   20 Xia, F. and Sarikaya, B. "FMIPv6 extensions for Multicast 
      Handover", draft-xia-mipshop-fmip-multicast-00.txt, (work in 
      progress), September 2006. 
    
   21 Soliman, H., Castelluccia, C., El-Malki, K., Bellier, L. 
      "Hierarchical Mobile IPv6 mobility management", RFC 4140, August 
      2005. 
    
   22 Schmidt, T.C. and Waehlisch, M. "Seamless Multicast Handover in a 
      Hierarchical Mobile IPv6 Environment(M-HMIPv6)", draft-schmidt-
      waehlisch-mhmipv6-04.txt, (work in progress, expired), December 
      2005. 
    
   23 Jonas, K. and Miloucheva, I. "Multicast Context Transfer in mobile 
      IPv6", draft-miloucheva-mldv2-mipv6-00.txt, (work in progress, 
      expired), June 2005. 
    


 
 
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   24 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. 
    
   25 Zhang, H. et al "Mobile IPv6 Multicast with Dynamic Multicast 
      Agent", draft-zhang-mipshop-multicast-dma-03.txt, (work in 
      progress), January 2007. 
    
   26 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. 
    
   27 Lin, C.R. et al., "Scalable Multicast Protocol in IP-Based Mobile 
      Networks", Wireless Networks and Applications, 5, pp. 259-271, 
      2000. 
    
   28 Chang, R.-S. and Yen, Y.-S. "A Multicast Routing Protocol with 
      Dynamic Tree Adjustment for Mobile IPv6", Journ. Information 
      Science and Engineering 20, 1109-1124, 2004. 
    
   29 Thaler, D. "Supporting Mobile SSM Sources for IPv6", Proceedings 
      of ietf meeting Dec. 2001, individual.  
      URL: www.ietf.org/proceedings/01dec/slides/magma-2.pdf 
    
   30 Jelger, C. and Noel, T. "Supporting Mobile SSM sources for IPv6 
      (MSSMSv6)", Internet Draft (work in progress, expired), January 
      2002. 
    
   31 Vida, R., Costa, L., Fdida, S. "M-HBH - Efficient Mobility 
      Management in Multicast", Proc. of NGC '02, pp. 105-112, ACM Press 
      2002. 
    
   32 O'Neill, A. "Mobility Management and IP Multicast", draft-oneill-
      mip-multicast-01.txt, (work in progress, expired), July 2002. 
    
   33 Schmidt, T. C. and Waehlisch, M. "Extending SSM to MIPv6 - 
      Problems, Solutions and Improvements", Computational Methods in 
      Science and Technology 11(2), 147-152. Selected Papers from TERENA 
      Networking Conference, Poznan, May 2005. 
    
   34 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", Vol. 3961 of LNCS, pp. 82-
      91, Springer-Verlag, Berlin, Heidelberg, 2006. 
    
    
    

 
 
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Informative References 
    
   35 Romdhani, I., Kellil, M., Lach, H.-Y. et. al. "IP Mobile 
      Multicast: Challenges and Solutions", IEEE Comm. Surveys, 6(1), 
      2004. 
    
   36 Jannetau, C., Tian, Y., Csaba, S. et al "Comparison of Three  
      Approaches Towards Mobile Multicast", IST Mobile Summit 2003,  
      Aveiro, Portugal, 16-18 June 2003, online http://www.comnets.rwth- 
      aachen.de/~o_drive/publications/ist-summit-2003-IPMobileMulticast- 
      paperv2.0.pdf. 
    
   37 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. 
    
   38 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. 
    
   39 Van Mieghem, P., Hooghiemstra, G., Hofstad, R. "On the Efficiency  
      of Multicast", Transactions on Networking, 9, 6, pp. 719-732,  
      December 2001. 
    
   40 Chalmers, R.C. and Almeroth, K.C., "On the topology of multicast  
      trees", IEEE/ACM Trans. Netw. 11(1), 153-165, 2003. 
    
   41 Van Mieghem, P. "Performance Analysis of Communication Networks  
      and Systems", Cambridge University Press, 2006. 
    
   42 Janic, M. and Van Mieghem, P. "On properties of multicast routing 
      trees", Int. J. Commun. Syst. 19(1), pp. 95-114, 2006. 
    
   43 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. 
    
   44 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. 
    
   45 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: http://imj.ucsb.edu/papers/BROADWIM-
      04.pdf.gz 
 
 
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   46 Jelger, C., Noel, T. "Multicast for Mobile Hosts in IP Networks: 
      Progress and Challenges", IEEE Wireless Comm., pp 58-64, Oct. 
      2002. 
    
   47 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, Vol. 33, No. 1-3, pp. 131-154, Berlin Heidelberg:    
      Springer, December 2006. 
    
   48 Fenner, B. et al. "Multicast Source Notification of Interest  
      Protocol", draft-ietf-idmr-msnip-05.txt, (work in progress,  
      expired), March 2004. 
    
   49 Leoleis, G., Prezerakos, G., Venieris, I. "Seamless multicast  
      mobility support using fast MIPv6 extensions", Computer Comm. 29,  
      pp. 3745-3765, 2006. 
    
   50 Schulzrinne, H. et al. "RTP: A Transport Protocol for Real-Time  
      Applications", RFC 3550, July 2003. 
    
    
Acknowledgments 
    
   The authors would like to thank Mark Palkow (DaViKo GmbH) and Hans L. 
   Cycon (FHTW Berlin) for valuable discussions and a joyful 
   collaboration. They also thank Stig Venaas (UNINETT) for many 
   advices. 
    
    
Author's Addresses 
    
   Thomas C. Schmidt 
   HAW Hamburg, Dept. Informatik 
   Berliner Tor 7 
   D-20099 Hamburg, Germany 
   Phone: +49-40-42875-8157 
   Email: Schmidt@informatik.haw-hamburg.de 
     
    
   Matthias Waehlisch 
   link-lab 
   Hönowerstr. 35 
   D-10318 Berlin, Germany 
   Email: mw@link-lab.net 
    
    
    
 
 
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PAFTECH AB 2003-20262026-04-24 03:03:46