– 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. There are several reasons for this. First, implementing a multicast/multilayer service requires per-flow state. The incremental cost of deploying a slightly more elaborate service model that takes into account flow dependence is much smaller than in the case of unicast. Second, several end-to-end functions, such as channel estimation and error control, are considerabl...