1. Reliable Multicasting –IP-multicast is unreliable. Need a reliable multicast layer to simplify the software design. –Like in reliable unicast (PAR), we need to add acknowledgement to ensure 100% reliability. Sender makes sure that a packet is acknowledged by all receivers before removing it from the buffer. Receiver makes sure that duplicated packets will not be passed to the upper layer. Many variations in terms of how acknowledgements and retransmissions are organized.

2. Reliable multicast protocols : –ACK-based –NAK-based –Ring-based –Tree-based

3. ACK based protocols ACK-based protocols Straight-forward extension of the reliable unicast protocol. Ack-implosion problem, not scalable.

4. NAK-based protocols A receiver responses only when something is wrong. More scalable compared to the ACK-based scheme Other mechanism must be incorporated to ensure the reliability.

5. Ring-based protocols Receivers take turn to ACK. Each data packet has only one acknowledgement packet. Implementation is fairly complicated.

6. Tree-based protocols Receivers are divided into groups. Each group has a group leader. Sender interacts with the group leaders. Group leaders interact with group members.

8. Reliable multicast over Ethernet connected clusters: –Multicasting over Ethernet is different from multicasting in the general Internet Environment Broadcast Short propagation delay. Shared media network. Low error rate. Reliable multicast over the Internet: –Very difficult because of the heterogeneous nature in the Internet. –10 years research still cannot come to a conclusion IP multicast model may need to change to support reliable multicast over the Internet!!!

9. Scalability of an ACK-based protocol

10. –Performance of the reliable multicast protocols: Small message: ACK-based, NAK-based and Ring-based are better than tree-based.

11. –Performance of the reliable multicast protocols: Large message: NAK-based is the best.

12. Reference: –Ryan Lane, Scott Daniels and Xin Yuan An Empirical Study of Reliable Multicast Protocols over Ethernet- Connected Networks. International Conference on Parallel Processing, 2001. Available at http://www.cs.fsu.edu/~xyuan/cop5570/icpp01.ps