We deal with communication networks whose topology changes arbitrarily subject to the restriction that no edge-cut in the network persists forever. Up to now, no formal-ground rules have been proposed for such networks, and no protocol has been proved to possess any desirable property. We introduce a new proof methodology, in the sense that link-behavior in such networks is axiomatized.

Our methodology is exemplified on broadcast protocols. A reliable broadcast protocol must deliver copies of a message to all nodes in a communication network, in finite time and in the correct order. No existing broadcast protocol with a reasonable cost is reliable, and in fact, one is inclined to believe that a communication protocol cannot be reliable, unless it knows in advances which links will fail in the future, or sends the information along all links. However, we present a new broadcast protocol which does achieve reliability with minimum cost. Moreover, in stable networks, minimum delay is achieved, too. As a by-product, we achieve a new reliable routing protocol. The main idea of our protocol is to perform the broadcast along a dynamic tree, such that the father of each node is the neighbor which has received the maximum number of messages. This guarantees that the tree will eventually reconnect each sub-network to its complement.