On service models for multicast transmission in heterogeneous environments

We examine in this paper the tradeoff between application complexity, network complexity, and network efficiency. We argue that the design of the current Internet reflects a tradeoff between lower network complexity (no state in the network, no signalling) and higher application complexity (rate and error control mechanisms to obtain an adaptive application) assuming a unicast service model. For such a service model, a design methodology that leans heavily towards application complexity has proven very successful. However, we also argue that this tradeoff changes radically for a multicast/multilayer service model. These insights motivate a new service model which slightly departs from the best-effort model, and which trades off a slightly higher network complexity for much lower application complexity and higher network efficiency. We describe this service model and the associated network protocols. The protocol complexity is only marginally higher than that of a simple multicast routing protocol with receiver-initiated join/leave capabilities. The dependencies between multilayer flows are established and maintained as soft state; therefore, no explicit session signalling to establish and tear down the flow dependence state is necessary