Efficient Signaling Algorithms for ATM Networks

ATM provides a connection-oriented model of communication. Each conversation between two end-points occurs over a virtual circuit. All cells for the same conversation flow along the same virtual circuit. For the circuit to be established, a call setup process is initiated by the source host and run over all intermediate switches in the path, as well as the destination. In the current ATM standard, signaling messages are carried between any pair of adjacent switches on a special reserved channel. Switch control software implement call setup protocols and the call setup algorithms defined by the protocols. Various such protocols exist, such as SPANS[5] and Q.2931[2]. We enumerate several properties that all ATM signaling algorithms must satisfy. With current signaling software and protocols, call setup time depends linearly on the number of switches in the setup path. As ATM network diameters grow larger, current standards result in large latencies in call setup time. When the call setup time dominates over the transmit time, the network throughput is low. To enable better signaling performance, we are exploring call setup algorithms in which physically non-adjacent switch controllers may communicate directly. ATM signaling topologies are essentially plastic and do not have to follow physical network topologies. The signaling channels between any two switch controllers may be hardware mapped through any intermediate switches; the intermediate switch controllers are not involved in the transmission of these signaling messages. Any arbitrary signaling topology can be overlaid on the physical network. A signaling overlay can be mapped onto an ATM network in the ATM meta-signaling phase. The simplest interconnection strategy is one where all the switch nodes are fully connected by virtual circuits. In this case, we demonstrate two algorithms which significantly improve performance. Performance is characterized in this paper by the number of messages and the number of rounds. Minimizing the number of messages in a signaling algorithm frees network bandwidth for carrying other data. Our enhanced linear algorithm achieves the minimum number of messages. Minimizing the number of rounds will have the greatest effect on call setup latency. Our multicast call setup algorithm achieves O(logn) performance in the number of rounds, where n is the number of switches.