Paper Review: <FJML+95 >>
A Reliable Multicast Framework for Light-weight Sessions and Application Level Framing

Reviewer: Oleg Elkhunovich

Problem

Unicast has been studies greatly and very well understood. Multicast however offers many new problems. For example, ACK's can create implosion effect in multicast. Reliability is difficult and sender is responsible which makes it a huge burden. There are many other problems with the multicast that authors address with their framework.

Contribution

This paper presents SRM - Scalable Reliable Multicast - new multicast framework. The framework is developed with the needs of wb in mind. wb is a whiteboard conferencing tool.

Main Ideas

  • To prevent an implosion of control packets sebt back to the sender, the packets are sent multicast so that other receivers do not send the packets if they already received an identical one by another receiver. Receivers send packets after waiting for some random time dependent on the distance from the sender in seconds.
  • There is a tradeoff between duplicate requests and the length of the delay before a request is send and fullfilled.
  • The best way to meet diverse application requirements is to leave as much functionality and flexibility as possible to the application.

    Critique

    Significance: 4
    The framework that the authors purpose is significant for development of applications using multicast. It gives a lot of flexibility and leaves a lot of decision to the applications which is a big plus. The model is pretty efficient.
    Methodology:
    Methodology is convincing. SRM has been implemented in wb is presented in that context which shows that it works. It would be better if more of the experiments we performed in reality and not using simulations. However, authors communicate a lot of information using their experiments nevertheless.
    Limitation:
    SRM is largely base on the requirements of wb and other applications are not examined enough. It would be interesting to see it adopted and implemented in other applications. Future work is needed on scalable session messages, local recovery, and congestion control

    Lessons:
    Interesting and valuable standards can emerge from the necessassity when building a particular application.