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

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
Fall, 2001
CS 640

3. Protocol types Dense mode protocols Sparse mode protocol
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
Fall, 2001
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 (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
Fall, 2001
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)
Fall, 2001
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
Fall, 2001
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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
Fall, 2001
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8. PIM-SM(1) S A B RP D C E R2 R1 Source Receiver 1 Receiver 2 Fall, 2001
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9. PIM-SM(2) S
Receiver 1 Joins Group G C Creates (*, G) State, Sends (*, G) Join to the RP
Source A B RP D
Join C E R2 R1
Receiver 1
Receiver 2
Fall, 2001
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10. PIM-SM(3) S A B RP D C E R2 R1 RP Creates (*, G) State Source
Receiver 1
Receiver 2
Fall, 2001
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11. PIM-SM(4) S
Source Sends Data A Sends Registration to the RP
Source
IP tunnel between A and RP since
multicast tree is not established
Register
Data A B RP D C E R2 R1
Receiver 1
Receiver 2
Fall, 2001
CS 640

12. PIM-SM(5) S
RP decapsulates Registration Forwards Data Down the Shared Tree Sends Joins Towards the Source
Source
join
join A B RP D C E R2 R1
Receiver 1
Receiver 2
Fall, 2001
CS 640

13. PIM-SM(6) S
RP Sends Register-Stop Once Data Arrives Natively
Source
Register-Stop A B RP D C E R2 R1
Receiver 1
Receiver 2
Fall, 2001
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14. PIM-SM(7) SPT Switchover
C Sends (S, G) Joins to Join the Shortest Path Tree (SPT)
Source A B RP D
join C E R2 R1
Receiver 1
Receiver 2
Fall, 2001
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15. PIM-SM(8) S A B RP D C E R2 R1 C starts receiving Data natively Source
Receiver 1
Receiver 2
Fall, 2001
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16. PIM-SM(9) S
C Sends Prunes Up the RP tree for the Source. RP Deletes (S, G) OIF and Sends Prune Towards the Source
Source
Prune
Prune A B RP D
Prune C E R2 R1
Receiver 1
Receiver 2
Fall, 2001
CS 640

17. PIM-SM(10) S A B RP D C E R2 R1 B, RP pruned Source Receiver 1
Fall, 2001
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18. PIM-SM(11) S A B RP D C E R2 R1 Source
New receiver2 joins E Creates State and Sends (*, G) Join A B RP D C E
join R2 R1
Receiver 1
Receiver 2
Fall, 2001
CS 640

19. PIM-SM(12) S A B RP D C E R2 R1 Source
C Adds Link Towards E to the OIF List of Both (*, G) and (S, G) Data from Source Arrives at E A B RP D C E R2 R1
Receiver 1
Receiver 2
Fall, 2001
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”)
Fall, 2001
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)
Fall, 2001
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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
Fall, 2001
CS 640

23. Multicast Routers mrouted (Xerox PARC) : DVMRP
GateD (Merit) : DVMRP, PIM-DM, PIM-SM
Cisco IOS : DVMRP, PIM-DM, PIM-SM
Fall, 2001
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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:
Fall, 2001
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25. Session Directory
Fall, 2001
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26. Example Session
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27. M-BONE in 1994
Fall, 2001
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28. M-BONE in 1996
Fall, 2001
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29. M-BONE in 1998
Fall, 2001
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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.
Fall, 2001
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
Fall, 2001
CS 640