On worst case traffic in ATM networks

ATM networks allow for the input traffic from users to vary both from one call to another and within the call. ATM specifies a method for controlling the traffic flow across the user network interface (UNI). This involves each user negotiating call parameters with the network. Once these parameters have been decided then a contract is made between the user and network. The network must then enforce the contract in order to guarantee performance and quality of service to other users. What is of interest to the network is given a particular set of users and contracts what is the worst traffic that the users could input to the network while still abiding by their contracts. This type of input traffic would be called the worst case traffic as it would produce the lowest performance in the network. The reason why this is of importance is that for simulating network performance we would like to have the worst case traffic inputs. Furthermore, it´s important for the traffic controller of the network to know the possible worst case traffic so that it can assign parameters accordingly. The contract parameters have been decided upon by the standards organisations and what is needed now is to decide what type of traffic can pass these tests and produce the lowest network performance. This problem has been studied in the literature. We give some theoretical background to explain some of the results in the literature, and we further look at some examples of types of worst case traffic sources. We show that for the two most common types, the greedy on-off and the three state source that either can be worse, depending on the situation