Toward a Time-scale Based Framework for Abr Traac Management

This paper discusses some issues and possibilities for more eeective ABR (Available Bit Rate) traac management which arise from a careful consideration of various time scales present in an ATM networking environment. Since the ABR applications will typically use the remaining resources after CBR (Constant Bit Rate) and VBR (Variable Bit Rate) applications have been accommodated, the ABR rate should be controlled through a feedback based ow control scheme to avoid excessive losses. It is well known that the increased propagation delay between the (controlled) ABR source and the network node leads to increased time horizons over which the source rate is based on outdated information, resulting in increased amount of bandwidth mismatch and, thus, cell losses. For this reason, the eeectiveness of feedback based ow control schemes reduces with increased propagation delay. Besides the physical distance, some other system parameters-namely the network, ABR and VBR time scales-may also impact considerably on the eeectiveness of feedback based ow control schemes. In this paper, the impact of these time scales is considered. In addition, a proactive feedback based ow control scheme is described, aiming to reduce the amount of bandwidth mismatch by generating early feedbacks.