1. IP multicast Advisor: Prof. Wanjiun Liao Instructor: De-Nian Yang

2. Multicast Why multicast? MBONE Internet’s Multicast Backbone
More than 2800 subnets in over 25 country by 1996 March
A semi-permanent IP multicast testbed
Use IP tunneling to send data
Multicast routing protocol: DVMRP, MOSPF, PIM
How to join MBONE?

3. Related protocols Group management protocol:
IGMP(Internet Group Management Protocol)
Multicast routing protocol:
Source-based tree
Multicast tree per (S,G)
DVMRP, MOSPF, PIM-DM
Shared tree
Multicast tree per (*,G)
CBT, PIM-SM

4. IGMP
The multicast router use IGMP to obtain the group-membership information of the LAN.
Periodically
Query
Query
Report
Report

5. Source-based tree A
Source B
．Source A and B use the same multicast address to send data.
．Intermediate routers use (S,G) to forward data.
．Intermediate routers create forward entry while receiving data.

6. DVMRP Distance vector multicast routing protocol
Rely on distance vector based unicast routing protocol(RIP)
For each (S,G), grow a shortest-path tree rooted on the source
Use distance vector routing algorithm to support reverse path multicasting(RPM)

7. DVMRP(cont’d)
Receiver
Sender
SPT branch
data

8. DVMRP(cont’d)
Receiver
Sender
SPT branch
data
Prune message

9. DVMRP(cont’d) Receiver Sender SPT branch data Prune message
．Data and Prune messages will be sent periodically.

10. DVMRP(cont’d) Receiver Sender SPT branch Graft message
．Receiver sends a graft message toward the to join the group
quickly.

11. MOSPF Multicast open shortest path first routing protocol
Rely on link state based unicast routing protocol(OSPF)
For each (S,G), grow a shortest-path tree rooted on the sources
Use Dijkstra’s algorithm and group-membership LSAs to compute shortest path tree

12. MOSPF(con’t)
Group-membership
LSA
Receiver

13. MOSPF(con’t)
．MOSPF creates tree without prune messages

14. Shared tree Sender Receiver Core
Source B
．Intermediate routers use (*,G) to forward data.
．Receivers join the multicast tree before receiving data.

15. CBT Core based trees multicast routing protocol
For each group, grow a shortest-path tree rooted on the core.
To join a group, the DR sends a Join_Request toward the core of the group.
Join_Ack is returned by an on-tree router or the core.

16. CBT(cont’d)
To leave a group, the DR sends a Quit_Notification to its parent router.
An on-tree router sends Echo_Requests and Echo_Replys to maintain the multicast tree.
If the sender doesn’t want to join the group, it encapsulates data packets and unicasts them to the core.

17. Comparison of source-based tree and shared tree
Source-based tree mechanisms scales worse than shared tree counterparts
Table size:
Source-based tree: group * source
Shared tree: group
Large overhead
DVMRP: periodically sending prune message if group density is low
MOSPF: periodically flooding link states

18. Comparison of source-based tree and shared tree
Shared tree mechanisms also have drawbacks
Core might be point of failure
Larger delay than source-based tree counterparts
Traffic concentration
PIM uses hybrid architecture to gain advantages of source-based tree and shared tree.

19. PIM-SM Data from S1 Data from S2 While the data rates of S1 and S2 are
both low, data travel through RP to
the receiver.

20. PIM-SM Data from S1 Data from S2
While the data rate of S2 is above some
threshold, DR of the receiver decides to
switch the traffic from shared tree to source-based tree.

21. PIM-SM Data from S1 Data from S2 DR of the receiver sends Join_Request
toward S2.

22. PIM-SM Data from S1 Data from S2 Prune message
While receiving data from S2 directly, the
intermediate router sends a prune message to
RP.

23. More about multicast Why shortest path tree? Is it reasonable?
Multicast with QoS
QoS routing
Multi-path reservation
IP multicast in MPLS and differentiated service network
QoS extension to legacy multicast routing protocols
Multicast with mobility
Reliable multicast
Secure Internet multicast

24. Reference MBONE Related protocols can be found on http://www.ietf.org
Related protocols can be found on