Multicast

1. Multicast Outline Multicast revisited Protocol Independent Multicast - SM Future Directions

2. CS 640 2 Multicast Revisited Motivation: multiple hosts wish to receive the same data from one or more senders Multicast routing defines extensions to IP routers to support broadcasting data in IP networks Until now IP has only facilitated a point to point routing Multicast data is sent and received at a multicast address which defines a group Simple notion of a group is a TV channel Data is sent and received in multicast groups via routing trees from sender(s) to receivers. Protocols are principally concerned with setting up and maintaining trees Note: All multicast messaging is sent via unicast

3. CS 640 3 Protocol types Dense mode protocols assumes dense group membership Source distribution tree and NACK type DVMRP (Distance Vector Multicast Routing Protocol) PIM-DM (Protocol Independent Multicast, Dense Mode) Example: Company-wide announcement Sparse mode protocol assumes sparse group membership Shared distribution tree and ACK type PIM-SM (Protocol Independent Multicast, Sparse Mode) Examples: a Shuttle Launch

4. CS 640 4 PIM-SM overview (1) Developed due to scaling issues Flooding is generally a real bad idea Based on creating routing tree for a group with Rendezvous Point (RP) as a root for the tree RP is a focus for both senders and receivers Explicit join model Receivers send Join towards the RP Sender send Register towards the RP Supports both shared trees (default) and source trees RPF check depends on tree type For shared tree (between RP and receivers), uses RP address For source tree (between RP and source), uses Source address

5. CS 640 5 PIM-SM overview(2) Only one RP is chosen for a particular group RP statically configured or dynamically learned (Auto-RP, PIM v2 candidate RP advertisements) Data forwarded based on the source state (S, G) if it exists, otherwise use the shared state (*, G) (*,G) means all senders RFC2362 – “PIM Sparse Mode Protocol Spec” (experimental) Internet Draft: draft-ietf-pim-v2-sm-00.txt (October 1999)

6. CS 640 6 PIM-SM Basics PIM Neighbor Discovery PIM SM Forwarding PIM SM Joining PIM SM Registering PIM SM SPT-Swichover PIM SM Pruning PIM SM Bootstrap PIM SM State Maintenance

7. CS 640 7 PIM SM Tree Maintenance Periodic Join/Prunes are sent to all PIM neighbors Periodic Joins refresh interfaces in a PIM neighbor’s downstream list Periodic Prunes refresh pruned state of a PIM neighbor There is a designated router (DR) for each local network and all other routers get pruned Received multicast packets reset (S,G) entry expiration timers. (S,G) entries are deleted if timers expire

8. CS 640 8 PIM-SM(1)

9. CS 640 9 PIM-SM(2)

10. CS 640 10 PIM-SM(3)

11. CS 640 11 PIM-SM(4)

12. CS 640 12 PIM-SM(5)

13. CS 640 13 PIM-SM(6)

14. CS 640 14 PIM-SM(7)SPT Switchover

15. CS 640 15 PIM-SM(8)

16. CS 640 16 PIM-SM(9)

17. CS 640 17 PIM-SM(10)

18. CS 640 18 PIM-SM(11)

19. CS 640 19 PIM-SM(12)

20. CS 640 20 Inter-Domain Multicast Routing BGP4+ (Multicast BGP) for short-term solution Tweeks to BGP4 to support multicast Multicast Address Set and Claim (MASC) Hierarchical multicast address allocation at domain level Dynamic allocation (not permanent) of addresses by “set and claim with collision” Border Gateway Multicast Protocol (BGMP) Use a PIM-like protocol between domains (“BGP for multicast”)

21. CS 640 21 MASC Assume Addr(A) is allocated to domain A and domains B and C sit “below” A in a domain hierarchy B selects Addr(B) which is subset of Addr(A) and send claim (addr(B)) message to A and C A forwards claim to all children except B. If any of A’s children is already using Addr(B) they will report a collision to A. A will notify B of the collision and B will select other address space. Address space information is used to create distribution tree using BGMP. Stored in M-RIB (Multicast Routing Information Base)

22. CS 640 22 BGMP BGMP builds shared tree of domains for a group Uses a rendezvous mechanism at the domain level Shared tree is bidirectional Root of shared tree of domains is at root domain Runs in routers that border a multicast routing domain Runs over TCP Joins and prunes travel across domains Can build unidirectional source trees M-IGP (multicast Intra-Gateway Protocol) tells the borders about group membership

23. CS 640 23 Multicast Routers mrouted (Xerox PARC) : DVMRP GateD (Merit) : DVMRP, PIM-DM, PIM-SM Cisco IOS : DVMRP, PIM-DM, PIM-SM

24. CS 640 24 M-Bone Wide area IP multicast test bed using IP-in-IP tunneling Routing protocol DVMRP is used Transition to PIM (DM, SM) is ongoing Started in March 1992 for audio broadcasting of IETF meeting (San Diego) Latest tolopology ftp://ftp.parcftp.xerox.com/pub/net-research/mbone/maps/mbone-map-big.ps About 6000 (S,G) entries Discussion list: mbone@isi.edu

25. CS 640 25 Session Directory

26. CS 640 26 Example Session

27. CS 640 27 M-BONE in 1994

28. CS 640 28 M-BONE in 1996

29. CS 640 29 M-BONE in 1998

30. CS 640 30 Future Mulicast Service Current multicast service - latency and packet drop Research for “Reliable multicast” is actively going on for; large scale interactive gaming on the Internet Distributed databases large scale news distribution etc.

31. CS 640 31 Reliable multicast technology SRM ( Scalable Reliable Multicast) multicast with re-transmit (with random back-off) All nodes can re-transmit datagram (Multicast/Unicast) MTP (Multicast Transport Protocol: RFC1301) FEC (Forward Error Correction) error packet recovery by redundant packets