Multicasting. CSE 6590 Winter 2012. Internet Multicast Service Model. 126.96.36.199. 188.8.131.52. multicast group 184.108.40.206. 220.127.116.11. 18.104.22.168. Multicast group concept: use of indirection a host “sends” IP datagrams to multicast group.
Multicast group concept: use of indirection
Receivers: multicast group ID G, a class-D address
Both cases need filtering at IP layer.
1. Link-layer (Ethernet) broadcast
2. Link-layer (Ethernet) multicast
IGMP-2: hosts send explicit host-membership leave messages to reduce leave latency.
IGMP-3: filtering and blocking
Extends OSPF for multicasting.
Every router has the complete topology of its own network.
A receiver joins a multicast group G by exchanging IGMP messages with its end-router R.
The end-router R broadcasts its group membership to the whole network in the form (G, R).
Every router in the network maintains a group membership table with each entry being a tuple [S, G, <R1, R2, …>].
A sender simply sends data packets as they are available.
Each router uses the network topology, the group membership table, and the multicast group ID in the data packets to compute the route(s) to the destination(s).
if (multicast datagram received on incoming link on shortest path back to sender)
then flood datagram onto all outgoing links
else ignore datagram