Multicast routing in dense and sparse modes: simulation study of tradeoffs and dynamics

PIM (protocol independent multicast) is capable of supporting sparse mode (SM) and dense mode (DM) operations. In sparse mode, PIM can use shared trees (RPT) or shortest path trees (SPT) to deliver data packets. The availability of these various modes opens questions regarding when each should be used, and the consequences of switching among them dynamically. This paper reports on two specific issues: (1) the overhead tradeoffs between dense mode operations and sparse mode operations, (2) the behaviors of PIM when receivers transition from RPT to SPT. Our results illustrate the cross-over point of sparse mode and dense mode overheads, which gives a hint for selecting protocol modes according to the group density metric. We also show that the conditions under which packet losses occur due to SPT switch are rare