On-demand multicast in mobile wireless networks

We propose an “on-demand” multicast routing protocol for a wireless, mobile, multihop network. The proposed scheme has two key features: (a) it is based on the forwarding group concept (i.e., a subset of nodes is in charge of forwarding the multicast packets via scoped flooding) rather than on the conventional multicast tree scheme (b) it dynamically refreshes the forward group members using a procedure akin to on-demand routing (hence the name). “On-demand” multicast is well suited to operate in an on-demand routing environment where routes are selectively computed as needed between communicating node pairs instead of being maintained and updated globally by a routing “infrastructure” (like in distance vector or link state, for example). On-demand multicast is particularly attractive in mobile, rapidly changing networks, where the traffic overhead caused by routing updates and tree reconfigurations may become prohibitive beyond a critical speed; and in large network with sparse traffic requirements, where the traffic, processing and storage overhead of the routing infrastructure solution compromises scalability. Via simulation, we compare on-demand multicast with a traditional tree multicast scheme, DVMRP, and with a version of forwarding group multicast which uses conventional distance vector routing instead of on-demand routing. This allows us to assess the penalty of the tree and of the global routing infrastructure as a function of mobility and sparseness