Optimal Bandwidth Allocation in Communication Networks

Broadband-ISDN (BISDN) will be implemented using Asynchronous Transfer Mode (ATM). This is prompted by the need to handle a variety of types of services, with diverse demands on the network in terms of the bit rate required and their holding times. Continuous as well as variable bit rates will be serviced. Services with holding times in the range of milliseconds to hours will be admitted to the network. The bandwidth required by a connection may vary over the lifetime of the connection, hence multiplexing and buffering within the network are provided (thus ATM) to allow more effective use of the resources. In this paper we consider the problem of dynamically allocating bandwidth in BISDN under nonstationary conditions using an optimal control approach. Our approach differs from the majority of existing literature on the optimal control of queuing systems which are based on the assumption of steady state queuing models. We use a state variable model to describe the dynamic behaviour of the virtual path for different traffic classes. Each link in a path is represented as a set of nonlinear differential equations describing the dynamics of the virtual path and the network traffic in terms of time-varying mean quantities. The optimisation objective is a tradeoff between buffer and bandwidth allocation and yields a controller of feedback form. The problem is treated by HamiltonJacobi arguments, to formulate an optimal bandwidth allocation strategy for the equilibrium costate case. The attainment of the costate equilibrium case is justified by using simulation. The behaviour of the (sub)optimal solution is demonstrated using simulation, which shows a dynamic tradeoff between bandwidth and buffer allocations.