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Enhancing Source Mobility in Multimedia Applications: Evaluation of the Tree Morphing Protocol

This paper evaluates the Tree Morphing Protocol, designed to improve seamless handovers for mobile Source-Specific Multicast (SSM) sources. Traditional SSM systems face challenges with mobile sources, particularly in maintaining real-time constraints and effective routing. The Tree Morphing Protocol addresses these issues by morphing existing delivery trees during handover, preserving connectivity and reducing packet loss. This study presents simulations conducted on OMNeT++ to assess the protocol's performance in both ideal and real-world scenarios, ultimately highlighting its benefits and future enhancements for practical applications.

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Enhancing Source Mobility in Multimedia Applications: Evaluation of the Tree Morphing Protocol

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  1. Olaf Christ, Thomas C. Schmidt, Matthias Wählisch christ_o@informatik.haw-hamburg.de {t.schmidt, waehlisch@ieee.org} HAW Hamburg & link-lab Towards Seamless Handovers in SSM Source Mobility – An Evaluation of the Tree Morphing Protocol

  2. Agenda • Mobile SSM Sources: What is the problem? • Tree Morphing: Routing for mobile SSM Sources • Design of the Tree Morphing Protocol • Simulation & Evaluation • Conclusion & Outlook

  3. Source Specific Multicast • Listeners subscribe to source-specific (S,G) channels • Typically used for real-time applications • WebTV / IPTV • VoIP / VCoIP • Collaborative applications • Massive Multiplayer Games • Immediate shortest path trees • Routing simplified (in contrast to ASM) • Easy to deploy, domain transparent

  4. Problem: Mobile SSM Sources • Real-time constraints (50 – 100 ms) • SSM was designed for known, fixed sources • On source handover, the delivery tree rooting at the source invalidates • Address duality: Source filtering in routers and receivers • Logical Group Identifier: Home Address • Topological Tree Locator: Care-of Address • Decoupling: Source cannot Control Receiver Initiated Updates • May loose receivers on handover

  5. Solutions • Statically Rooted Distribution Trees • Handover compliant to Mobile IPv6 • Packets are tunneled via the Home Agent • Additional undesired latencies • Single Source of Failure • Reconstruction of Distribution Trees • Separate multicast control tree with information about source address changes or • Bicasting data into an old and a new tree via anchor points (APs) • Tree Modification Schemes • Attempt to re-use established states

  6. Multicast Forwarding States: Change of Distribution Trees under Mobility 75 – 95 % Coincidence for a mobility ‘step-size’ of 5 and100 Receivers

  7. Tree Morphing:Routing for mobile SSM sources • Preserve previous trees: • Keep contact subsequent to handover • Idea: Morph previous into next tree: • Elongate root (modify RPF-Check) • Send packets to previous root of delivery tree • Discover shortcuts, but re-use common parts of trees • Dismiss unneeded branches • A new SPT is generated • Need to change routing • Extend (CoA,G) states to (CoA,G,HoA)

  8. Mobile Source Specific Multicast:Tree Morphing Protocol

  9. Root Elongation Phase

  10. First Shortcut

  11. Optimized Tree

  12. Design of the Tree Morphing Protocol • State update - necessary information • Group context (HoA, G) • Tree topology (nCoA, G) • “Piggy-backing” of update information • Eliminates additional update packets • Minimum extension to existing mobility messages • Re-use of existing headers (see next slides) • Security and robustness of updates

  13. Tree Morphing: State Update Message • Combination of a Binding Update with CGA headers, a Router Alert Option and a Routing Header • Routing Header directs packets from nDR to pDR (source routing) • Router Alert Option instructs routers, to further inspect the packet (RFC 2711) • CGA authenticates these updates

  14. Benefits of Tree Morphing Protocol • Signaling of updates by combining existing IPv6 headers • Router Alert Option is slight addition to existing Mobile IPv6 Binding Update • Packet processing is well-defined and already well tested • Inserting the update message into the data stream does not introduce additional packets

  15. Simulation • OMNeT++ • IPv6Suite

  16. First Step: Test Topologies Net 1 Net 2

  17. Delay Stretch Net 1 Net 2

  18. Convergence Time

  19. Packet Loss

  20. Second Step: Real-world TopologiesSCAN + Lucent (1.540 Core Routers)

  21. Conclusion & Outlook • Benefits of Tree Morphing • Algorithm enables smooth source handover with state re-use • Protocol signaling realized as compact combination with Mobile IPv6 headers • Evaluation: Full protocol implementation on OMNeT++ • Test topologies reveal strengths and weaknesses • Real-world topologies smoothly mix effects • Packet loss too high • Current work and outlook • Protocol improvement: decouple signaling, eleminate source routing • Heals performance deficits (loss in particular) • Optimized versions for Fast MIPv6 & Multihoming

  22. Do you have any questions? Thank you very much for your attention!

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