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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
[email protected]{t.schmidt, [email protected]}
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?