This week our focus is on multicast in the network. Both papers were on application level overlay networks that are used for multicast. This paper takes the approach of building a generic framework protocol used for multicast. The analogy they used was like TCP for unicast, they wanted a framework for reliable delivery (but it's also best effort with eventual delivery of the message). It starts by stating several unicast methods that are bad suited for multicast networks. These networks include ACKs used for reliable delivery. Bad idea for multicast because of ACK explosion and the sender doesn't necessarily know all the receivers and participants involved. Another bad method is the state tracking of communication channels. These include sequence numbers, because participants can leave and join at any time. So the multicast is better suited using application data units. The paper implements it multicast framework using a whiteboard program, which allows users to have online conferencing and see the same whiteboard or presentation.
From what i read, the protocol involves a lot of random backoff timers to ensure that only one copy of repair and recover request is received, and all other receivers will not send out requests for the same data. Also, data is synced by page (for the whiteboard program), but the paper also mentions that you can request old pages, but they don't give any specifics. It seems like this protocol/framework was designed to work with different network topologies, as the paper tries to compare the different network topologies, but it seems that it still has some assumptions about the underlying topology. The next paper is more focused on maintaining an overlay topology for efficient delivery for multi cast networks.
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