IP multicast Advisor: Prof. Wanjiun Liao Instructor: De-Nian Yang e-mail: tony@kiki.ee.ntu.edu.tw

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?

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

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

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.

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)

DVMRP(cont’d) Receiver Sender SPT branch data

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

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

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

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

MOSPF(con’t) Group-membership LSA Receiver

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

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

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.

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.

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

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.

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.

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.

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

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.

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

Reference MBONE Related protocols can be found on http://www.ietf.org http://www.cs.columbia.edu/~hgs/internet/mbone-faq.html http://www.savetz.com/mbone/ Related protocols can be found on http://www.ietf.org