Control of multirate synchronous streams in hybrid TDM access networks

access multiplexer is considered, serving a TDM output channel with a hybrid structure, characterized by the presence of both isochronous (circuit-switched) and asynchronous (packet-switched) traffic. The isochronous traffic is, in turn, subdivided into several classes, which are distinguished according to their speed, in order to model a multirate, multitraffic environment. The aim of the paper is to define a control scheme for the allocation of the output link bandwidth, in order to realize two objectives: 1) minimize call blocking probability for the isochronous traffic and packet loss probability, and 2) meet quality of service requirements for both traffic types as closely as possible. The proposed scheme is based on a hierarchical control structure, where the description of the dynamics of the isochronous traffic is given in terms of continuous-time Markov chains and the packet rejection rate is approximated by means of the stationary distribution of an M/Pareto/l/K queue by exploiting the large difference in time scales between the isochronous flows and the asynchronous one. There are two control levels: 1) a "fast" one acting on the admission of isochronous calls by means of distributed decisional agents (one for each traffic class) which operate with the time scale of the connection request process dynamics, and 2) a slower one, playing the role of a coordinator in the hierarchical scheme, which periodically recomputes a set of parameters (related to the bandwidth allocation) by numerically solving a parametric optimization problem, where real-time information as well as traffic statistics are taken into account. Numerical results are provided, to investigate the performance of the control architecture.