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Towards Seamless Handovers in

SSM Source Mobility – An Evaluation

of the Tree Morphing Protocol

Olaf Christ, Thomas C. Schmidt, Matthias Wählisch

christ_o@informatik.haw-hamburg.de{t.schmidt, waehlisch@ieee.org}

HAW Hamburg & link-lab

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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

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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

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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

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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

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Multicast Forwarding States: Change of Distribution Trees under Mobility

75 – 95 % Coincidencefor a mobility ‘step-size’ of 5 and100 Receivers

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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

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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

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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

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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

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Simulation

• OMNeT++

• IPv6Suite

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First Step: Test Topologies

Net 1 Net 2

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Delay Stretch

Net 1 Net 2

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Convergence Time

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Packet Loss

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

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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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Thank you very much for your attention!

Do you have any questions?