Paper review: IP Multicast Channels: EXPRESS Support for Large-scale Single-source Applications

Reviewer: Mike Liu

  1. State the problem the paper is trying to solve.
  2. The main problem the paper is trying to design a system for extending IP multicast to support a channel mode of multicast.
  3. State the main contribution of the paper: solving a new problem, proposing a new algorithm, or presenting a new evaluation (analysis). If a new problem, why was the problem important? Is the problem still important today? Will the problem be important tomorrow?  If a new algorithm or new evaluation (analysis), what are the improvements over previous algorithms or evaluations? How do they come up with the new algorithm or evaluation? 
  4. The main contribution of this paper is that it presents a specific realization of a channel model of multicast called EXPlicitly REquested Single-Source (EXPRESS) multicast. The problem of designing a channel mode of multicast is relatively new extension of the challenges of multicast on the Internet and is important for several new applications on the verge of arriving on the Internet. These new applications include Internet TV, distance learning, file distribution, and other emerging large-scale multicast applications that strain the current model of multicast, which lacks a basis for charging, lacks access control, and is difficult to scale.
  5. Summarize the (at most) 3 key main ideas (each in 1 sentence.) 
  6. The three 3 key main ideas are: (1) EXPlicitly REquested Single-Source (EXPRESS) multicast channels can be provided through a series of simple modifications: (a) First, using a small portion of the class D address space in the IP multicast model, EXPRESS provides orders of magnitude more multicast channels per host than available in the group model, and address can be allocated by each host and without global coordination; (b) Second, EXPRESS channels can be implemented using a single simple protocol that requires no change to the current fast-path mechanisms in routers (2) Counting support in EXPRESS can be implemented efficiently using a method of proactive counting, and provides a simple but powerful extension for many-to-one communication. (3) Large-scale multicast applications that are almost single-source can be implemented on top of EXPRESS channels with a modest amount of middleware using application-selected and controlled session relay nodes; scalable multicast applications that we are aware of can be implemented efficiently and robustly using the EXPRESS service model.
  7. Critique the main contribution
  8. What lessons should researchers and builders take away from this work. What (if any) questions does this work leave open?
  9. The lessons that researchers should take away is that the EXPRESS channel model seems to be a good solution for solving the limitations of the current IP multicast group model with its provisions for charging, access control, and scalability. The questions it leaves open are whether their are further bugs that need to be worked out in EXPRESS, whether it fares well in its actual implementation, and how well it can be pervasively deployed.