On the Usage of Virtual Paths, Virtual Channels, and Bu ers in ATM Tra c Management

Tra c in ATM networks can be described by numerous parameters. On a per session basis, one may use peak rate, average rate, sustainable rate, average burst duration, average silence duration, and others. In a longer time scale, parameters like the average and peakedness of connection request interarrival times, the average and variance of session holding times, and so on are proposed. Theoretically, users should provide the former parameters and network operators the latter. In reality, however, few users can be expected to provide all sorts of statistical information about their tra c in advance, and operators do not have enough experience to prepare tra c forecasts for new services and applications. Moreover, even if the information could be provided, the lack of simple yet valid tra c models for ATM networks means that it is far from clear how such information should be used. Realising that ATM networks, which are already being built, at least for the next few years will have to operate under these uncertain conditions, we propose a robust and forgiving network design and tra c management strategy. The idea is to use only little information about o ered tra cs and then dynamically control resource allocations, so as to provide acceptable quality of service combined with high utilisation. The network design is based on the idea of keeping congestion at the edges of the network, so that the operating areas of fast congestion control mechanisms are minimised. Tra c variations are characterised by a model of six layers, each of which is assigned a corresponding layer in a tra c management model. We de ne the functionalities of each level in the latter modell and review possible implementations. In particular, we report on an implementation of two of these layers and discuss in some detail how a third one could be added.