What is a Multicast Mesh?

Answer 1

A multicast mesh is a type of routing for ad hoc networks. Imagine a collection of say, 1000 laptops and smart-phones. Now, imagine that we want to send a message from any one device to any other. There are two routing types that immediately come to my mind: multicast tree and multicast mesh.

multicast tree: a device will only accept and forward a message from sender to receiver IF that router is on the shortest path from sender to receiver (basically, there are some more details). This routing protocol eliminates multicast loops (good) and nearly optimally provides the shortest route from sender to receiver. However, since this is an ad hoc network, a device on that path can turn off. When this happens (and it will), the entire ad hoc network has to send control messages to every device so that they know what tree they are on. This sucks, because it is a lot of overhead, and will happen frequently.

multicast mesh: Each device accepts messages even if the device is not on the shortest path from sender to receiver. This provides richer connectivity, and is robust when devices come and go. However, there is a problem, richer connectivity also means poor bandwidth utilization (there are duplicate messages in the network). Also, a purely multicast mesh network does not scale well (control messages + duplicate messages mire the network as nodes increase).