From: Michelle Liu (liujing@u.washington.edu)
Date: Tue Nov 09 2004 - 19:58:43 PST
Review of "The PIM Architecture for Wide-Area Multicast Routing"
Jing Liu
This paper proposes a multicast routing architecture PIM particularly suitable in the scenario of wide area internets, where many groups will be sparsely represented. In the paper, the limitation of both link-state multicast and distance-vector multicast are discussed. Broadcasting of membership information is one major factor preventing link-state multicast from scaling to larger, wide-area networks. In the case of distance-vector multicast, routers that are not on the multicast delivery tree still have to carry the periodic truncated-broadcast of packets, and process the subsequent pruning of branches for all active groups. Thus, Existing link-state and distance-vector multicast routing schemes have good scaling properties only when multicast groups densely populate the network of interest. The proposed PIM have the following characteristics. First, it maintains the traditional IP multicast service model of receiver initiated membership. Second, it supports both shared and source-specific (shortest-path) distribution trees. Third, PIM is not dependent on a specific unicast routing protocol. Fourth, it uses soft-state mechanisms to adapt to underlying network conditions and group dynamics.
PIM differs from existing IP multicast schemes in two fundamental ways. First, the routers with local members join a PIM sparse mode distribution tree by sending explicit join messages. Second, PIM use per-group Rendezvous points (RP) for receivers to "meet" new sources. Both mechanisms take the scenario of sparsely distributed multicast groups into consideration. Moreover, PIM supports both shared and shortest path tree types. The paper shows the efficiency low cost of PIM.
It would be nice if the author could provide simulation or experimental data to prove the efficiency of the new architecture, especially the comparison of PIM with existing IP multicasting schemes.
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