A hierarchical control structure for multimedia access networks

We consider the problem of multimedia service distribution over an integrated services broadband access network, based on the transport of fixed-size traffic units (ATM cells). In general, the presence of distributed access multiplexers is assumed, which are both geographically dispersed and hierarchically structured. Such multiplexers are intelligent devices with decision making capabilities that operate jointly, in order to make the best possible use of the transport capacity of the access network and to maintain the quality of service (QoS) requirements of different users and service classes. Following the physical system organization, a hierarchical control structure is defined, where each service class is served by an independent controller, parametrized by the bandwidth allocated to it, and a central agent, playing the role of a coordinator in the hierarchical control scheme, decides upon the bandwidth partitions. This decision aims at minimizing a global cost that captures QoS requirements both at the call-level (call blocking probability) for QoS-aware, connection-oriented services and at the cell-level (cell loss probability) for connectionless, best-effort, ones. The control architecture also reflects the multilayer hierarchy introduced by the presence of multiple teletraffic time scales, by essentially decoupling the above problem from that of ensuring QoS at the cell-level for services of the first type. The cost functions used in the optimization and the control strategies are described, and numerical results are reported, which indicate the effectiveness of the method.