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 An organization has deployed a campus network using cellular IP

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 An organization has deployed a campus network using cellular IP. The cellular IP network extends the wired infrastructure of the campus as shown in the figure 1 below. The gateways in cellular IP connect their respective wireless segments to the wired segment. Each Base Station in the wireless segment provides layer 3 functionality (in other words, they act as IP forwarding engines). The campus network supports multicast routing. All the components in the wireless part strictly adhere to cellular IP standard. Assume that this campus network deploys Source Based Multicast Routing scheme - a protocol that builds source-based multicast distribution trees

A visiting mobile node MN enters the wireless network and initially gets registered to its home network via BS1-G1 and acquires a Care of Address (CoA - an address from the campus network address space). The CoA assigned to the MN remains unchanged irrespective of MN's movements within the campus network. In other words, MN does not need to acquire a new CoA upon moving to a wireless segment under the same or under a different gateway. 

While initially at BS1, the MN joins a multicast group G whose scope is local to this campus network (all sources, and members reside in the campus network). Assume that hosts H1, H3, H5, and H7 are members of this group with H1, H7, and MN also acting as Multicast sources. In this scenario, explain what problems can arise in multicast communication when:

•     MN is mobile and is a recipient of multicast packets.

•     MN is mobile and is a source of multicast traffic.  

 

 

 

 

Appendix

Source Based Multicast Routing

Consider a single sender. In a source-based multicast Routing scheme, the routing process builds shortest path trees rooted at the sender. The router delivers packets to each receiver along the shortest path. In a nutshell, it builds a shortest path spanning tree routed at source to all intended destinations.

 

Source Based Multicast Routing (SBMR)

The SBMR techniques implement the Reverse Path Multicast (RPM) algorithm. The RPM constructs an implicit spanning tree for each source.

 

? It accepts a packet from a source S, on link L, if L is the shortest path toward S. (Reverse Path Check)

? Uses unicast routing table which contains shortest paths to each node in the network.

 

In this technique, the first packet flooded across the internetwork. The packet scope is restricted by a TTL value. Due to flooding, all routers in the network get a copy of the packet. Routers not having any downstream router in multicast tree are called leaf routers. If a leaf router has no group members on its sub-networks, a Prune message is sent upstream to parent router (one hop up). The prune state is maintained in every router. This process is repeated every hop upwards. These cascaded prune messages create/truncate the original RPM tree. Prune information only held for a certain lifetime (soft state). A Graft message is sent to quickly recover back a previous pruned branch. It cancels out the previously received prune message. Graft cascades reliably hop by hop toward the source.