MODELS FOR SETTING ATM PARAMETER VALUES

In ATM networks, a user should negotiate at connection set-up a traffi c contract which includes traffic characteristics and requested QoS. T he traffic characteristics currently considered are the Peak Cell Rate , the Sustainable Cell Rate, the Intrinsic Burst Tolerance and the Cel l Delay Variation (CDV) tolerance(s). The values taken by these traffi c parameters characterize the so-called ''Worst Case Traffic'' that is used by CAC procedures for accepting a new connection and allocating resources to it. Conformance to the negotiated traffic characteristics is defined, at the ingress User to Network Interface (UNI) and at sub sequent Inter Carrier Interfaces (ICIs), by algorithmic rules based on the Generic Cell Rate Algorithm (GCRA) formalism. Conformance rules a re implemented by policing mechanisms that control the traffic submitt ed by the user and discard excess traffic. It is therefore essential t o set traffic characteristic values that are relevant to the considere d cell stream, and that ensure that the amount of non-conforming traff ic is small. Using a queueing model representation for the GCRA formal ism, several methods are available for choosing the traffic characteri stics. This paper presents approximate methods and discusses their app licability. We then discuss the problem of obtaining traffic character istic values for a connection that has crossed a series of switching n odes. This problem is particularly relevant for the traffic contract c omponents corresponding to ICIs that are distant from the original sou rce.