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Multicasting

Multicasting. Jean Walrand EECS. Outline. Definitions Broadcast, Multicast, Anycast Examples ARP, ICMP, Group Flooding Routing Multicast Tree of shortest paths; shortest tree Multicast Backbone Overlay Join Groups Soft State Reliable Multicast Nacks, Aggregation

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Multicasting

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  1. Multicasting Jean WalrandEECS

  2. Outline • Definitions • Broadcast, Multicast, Anycast • Examples • ARP, ICMP, Group • Flooding • Routing Multicast • Tree of shortest paths; shortest tree • Multicast Backbone • Overlay • Join Groups • Soft State • Reliable Multicast • Nacks, Aggregation • Multilayer Multicast

  3. Definitions • Broadcast • One to all • Multicast • One to all members of a group • Anycast • One to any member of a group

  4. Examples • ARP: • Broadcast to LAN (Note: VLANs) • 11…11 = “broadcast” address on Ethernet • ICMP: • Routers broadcast their link states in OSPF • Group: • Multicast of seminar to “subscribers” • Class-D IP addresses = group addresses

  5. A A [1; A] [1; A] [1] [1] B B C C {1} {1} [1] [1] [1; A, B] [1; A, C] Flooding • Send on all other ports: • Remember seen packets, or • Mark route on packets [1] [1] {1}

  6. 1 1 D1 2 2 1 2 S 2 D2 1 1 Routing Multicast • Simplest: Tree of shortest paths • Example

  7. 1 1 D1 2 2 1 2 S 2 D2 1 1 Routing Multicast (continued) • Optimal: Shortest tree • Example

  8. 1 1 1 1 D1 D1 2 2 2 2 1 1 2 2 S S 2 2 D2 D2 1 1 1 1 Routing Multicast (continued) • Comparison: Tree of shortest paths Sum of lengths = 9 Shortest tree Sum of lengths = 8

  9. 1 1 D1 2 2 1 2 S 2 D2 1 1 Routing Multicast (continued) • RPB: Reverse Path Broadcast Router R sends packet received from A if A is on the shortest path from R to S. Link AR A R

  10. 1 1 D1 Link RP 2 R 2 P 1 2 S 2 D2 1 1 Routing Multicast (continued) • RPM: Reverse Path Multicast RPB + Prune back if no member of Mcast group G Prune Prune Prune Not G

  11. 1 1 D1 2 2 Prune 1 2 S 2 D2 1 1 Routing Multicast (continued) • PIM-Dense Mode RPR + Prune + Graft (+ periodic RPR + Prune) G Prune Graft Graft Graft Join G

  12. Routing Multicast (continued) • PIM-Sparse Mode Periodic Join/Prune Messages from DR to RP Assumption: Relatively few group members

  13. 1 1 1 1 1 1 1 Reliable Multicast (continued) • ACKs do not scale • NACKs may implode • => NACK aggregation

  14. 2 2 2 2 Reliable Multicast (continued) • ACKs do not scale • NACKs may implode • => NACK aggregation

  15. 3 3 [Remember for T seconds] NACK2 3 3 3 3 3 Reliable Multicast (continued) • ACKs do not scale • NACKs may implode • => NACK aggregation

  16. [n] NACK n Reliable Multicast (continued) • Other idea: Designated Receivers Source DR DR

  17. Source Layer 1 Layer 2 Multilayer Multicast • Different channel bandwidths • => Multiple Layers Random “join” experiments

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