Question 1 (PIM)
Assume you have a source S, and assume that some receivers have joined the shortestpath
tree of S, while other receivers have joined only the shared tree. Prove that, if the
network is in a steady state (no routing table changes, no receivers leaving or joining
either tree), then multicast packets will traverse each link of both trees once and only
once. That is, packets cannot keep going from one tree to the other and back again.
Question 2 (PIM)
Instead of PIM, consider an alternative receiver-oriented multicast protocol, where
instead of the root of the shared tree being a single router, let the root of the shared tree
be a LAN (not a router). What changes would you make to PIM to make this work? Or if
it can’t be done, explain why.