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IP Multicast

IP Multicast. CS5248. Encoder. Decoder. Middlebox. Receiver. Sender. Network. You are Here. Communication Models. sender. receiver. Traditional Applications: One-to-One. Communication Models. sender. receivers. Media Applications: One-to-Many. Communication Models.

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IP Multicast

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  1. IP Multicast CS5248 Ooi Wei Tsang

  2. Encoder Decoder Middlebox Receiver Sender Network You are Here

  3. Communication Models sender receiver Traditional Applications: One-to-One

  4. Communication Models sender receivers Media Applications: One-to-Many

  5. Communication Models Media Applications: Many-to-Many

  6. Naïve Solution • Create M unicast connection for M clients NOT Scalable!

  7. Famous Example • Victoria’s Secret Spring Fashion Show • Live Broadcast in 1999 • Video bit-rate: 28 Kbps • Number of viewers: 1.5 Millions

  8. IP Multicast Ooi Wei Tsang

  9. New Model: IP Multicast sender receivers

  10. Group and Members

  11. Sending to a Group

  12. Joining and Leaving

  13. Anyone can Send

  14. Multicast Address • Group ID or “Multicast address” • 224.0.0.0 – 239.255.255.255

  15. Unicast S A A B Router C B Router Router Router C

  16. Multicast S G A Router B Router Router Router C

  17. Multicast S A Router G B Router Router Router G C

  18. Multicast S G A Router B Router Router G Router C

  19. Question 1 should I forward this packet to my subnet? Router ? G

  20. Question 2 which neighbors should I forward this packet? Router Router Router Router

  21. GroupManagement Ooi Wei Tsang

  22. Group Management • Routers maintain “local host group membership table” • “which group has a member in my subnet ?”

  23. IGMP v1.0 • JOIN messageA : “I want to join group G.” • QUERY messageR : “Which group have you joined ?”

  24. IGMP v1.0 • MEMBERSHIP ReportA : “I am a member of group G”A : “I am a member of group H”B : “I am a member of group G”

  25. Avoiding Implosion • Select random delay t • After time t, if nobody belongs to the same group, send membership report. • Resend the report after some delay just to be safe.

  26. Leave • If no one in group G after a few query messages, remove G from local host membership table. • Problem: Long leave latency (minutes)

  27. IGMP v2.0 • LEAVE message“I want to leave group G” • Group-Specific Query“Anybody else belongs to group G ?”

  28. IGMP v3.0 • Group-Source Inclusion“I want to listen to S from group G” • Group-Source Exclusion“I do not want to listen to S from group G”

  29. Question 2 which neighbors should I forward this packet? Router Router Router Router

  30. RoutingProtocols Ooi Wei Tsang

  31. Routing Protocols • Generic Methods : • Form a tree to all routers with members • Deliver the packets along the tree

  32. Shortest Path Tree • One tree for each source for each group

  33. Shared Tree • One tree for each group

  34. Routing Protocols • DVMRP • CBT • PIM

  35. DVMRP Distance Vector Multicast Routing Protocol Ooi Wei Tsang

  36. From S to G Q R P T

  37. Is R on the shortest path to S ? Q R P T

  38. If no.. ignore the packet Q R P T

  39. If yes.. continue Where should I forward it to ? Q R P T

  40. Forward to subnet? Q R P T

  41. Truncation • Router checks local host membership table. • Duplicate the packets only if there is a member in the subnet.

  42. Truncation Q R P T

  43. Forward to Neighbors? Q ? R P T ?

  44. Observation • If neighbor is going to ignore my packets, don’t need to send the packets to it.

  45. Exchanging Routing Tables Q R P T

  46. Flooding • Default : Always send to neighboring routers, unless told otherwise.

  47. Pruning • Routers who received a “useless” packet send a prune message back.“Don’t send me packets addressed to G anymore !”

  48. Q R P T

  49. Q R P T PRUNE

  50. Q R P T

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