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Adaptive Shared Tree Multicast in Mobile Wireless Networks

Adaptive Shared Tree Multicast in Mobile Wireless Networks. GLOBECOM 98 Ching-Chuan Chiang Mario Gerla Lixia Zhang Computer Science Department University of California, Los Angeles. Per-Source Tree Multicast. Like DVMRP and PIM-DM in wired net Each source supports own separate tree

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Adaptive Shared Tree Multicast in Mobile Wireless Networks

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  1. Adaptive Shared Tree Multicast in Mobile Wireless Networks GLOBECOM 98 Ching-Chuan Chiang Mario Gerla Lixia Zhang Computer Science Department University of California, Los Angeles

  2. Per-Source Tree Multicast • Like DVMRP and PIM-DM in wired net • Each source supports own separate tree • “Probing and Pruning” tree maintenance • Reverse Path Forwarding • “Fast Source” problem S2 S1 R2 R1

  3. RP-based Shared Tree Multicast • RP (Rendezvous Point)-based “Shared” tree • Similar to wired network PIM-SM, CBT • Tree maintenance: • hard state • soft state • Traffic concentration • “off-center” RP RP S1

  4. Shared Tree vs. Per-source Tree • Shared Tree: • scalability • less sensitive to fast source • longer path • traffic concentration • off center RP • Per-Source Tree: • shortest path • traffic distribution • no central node • scalability problem • fast source problem R2 R3 RP S2 R4 S1 R1

  5. Conclusions • Shared Tree scheme: • lower throughput in heavy load • lower control O/H • Adaptive scheme: • like a Per Source tree scheme in heavy load • like a Shared tree scheme in high mobility • Forwarding Group Multicast scheme: • more robust & lower O/H than shared tree

  6. RP Wireless Tree Multicasting (eg. Shared Tree) • In a mobile situation, tree is fragile: connectivity loss, multipath fading • Need to refresh paths very frequently • High control traffic overhead

  7. Forwarding Group FG FG FG FG FG Proposed solution: Forwarding Group Multicast • All the nodes inside the “bubble” forward the M-cast packets via “restricted” flooding • Flooding redundancy helps overcome displacements and fading • FG nodes selected by tracing shortest paths between M-cast members

  8. Key Concepts of ODMRP[5] • Mesh topology • Forwarding group concept • On-demand approach • Soft state

  9. Richer connectivity among multicast members Unlike trees, frequent reconfigurations are not needed Why a Mesh?

  10. A set of nodes in charge of forwarding multicast packets Supports shortest paths between any member pairs Flooding redundancy helps overcoming displacements and channel fading Forwarding Group Concept

  11. A sender periodically floods control messages when it has data to send All intermediate nodes set up route to sender Receivers update their Member Tables ; periodically broadcast Join Tables Nodes on path to sources set FG_Flag; FG nodes create and forward Join Tables to neighbors FG Maintenance (On-Demand Approach)

  12. Soft State Approach • No explicit messages required to join/leave multicast group (or FG) • An entry of a receiver’s Member Table expires if no Join Request is received from that sender entry during MEM_TIMEOUT • Nodes in the forwarding group are demoted to non-forwarding nodes if not refreshed (no Join Tables received) within FG_TIMEOUT

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