Optimal control approach to dynamic bandwidth allocation in B-ISDN

Abstract

Asynchronous Transfer Mode (ATM) will be the transfer mode for implementing Broadband-ISDN (B-ISDN). 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. Continuous as well as variable bit rates will be serviced. The bandwidth allocated to 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. We consider the problem of dynamically allocating bandwidth in B-ISDN 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 cell rate allocation and yields a simple controller of feedback form. The problem is treated by Hamilton-Jacobi arguments, to formulate an optimal cell rate allocation strategy for the equilibrium costate case. The behaviour of the optimal solution is demonstrated using simulation, which shows a dynamic tradeoff between cell rate and buffer allocations.