1 Towards Seamless Handovers in SSM Source Mobility – An Evaluation of the Tree Morphing Protocol Olaf Christ, Thomas C. Schmidt, Matthias Wählisch {t.schmidt, HAW Hamburg & link-lab

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 and 100 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)

Mobile Source Specific Multicast: Tree Morphing Protocol

Root Elongation Phase

First Shortcut

Optimized Tree

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

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

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

Simulation OMNeT++ IPv6Suite

First Step: Test Topologies Net 1Net 2

Delay Stretch Net 1Net 2

Convergence Time

Packet Loss

Second Step: Real-world Topologies SCAN + Lucent (1.540 Core Routers)

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

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