A priority leaky-bucket regulator for virtual path traffic in ATM networks

Abstract

In integrated services networks (B-ISDN/ATM) incoming traffic streams with different Quality of Service (QoS) requirements, sharing a single contract for use of a policed virtual path, may be jointly regulated on the basis of their type and QoS requirements to make the best use of available bandwidth in the path. The shaping/policing mechanism may use the information about the network policer located at the User-Network Interface (UNI) to perform policing with a form of priority service to ensure satisfactory levels of cell loss and delay for both real-time and non-real time traffic. This paper proposes and analyzes such a priority, buffered leaky-bucket mechanism for shaping/policing high-priority and low-priority sources, which share an ATM virtual path under a single, common user-network connection contract. The proposed priority traffic regulator maintains a dedicated cell buffer for each type of traffic to be able to trade off cell delay and loss (or tagging) on the basis of the QoS requirements for each priority class. The analysis adopts a Discrete Batch Markovian Arrival Process (D-BMAP) model for both high-priority and low-priority sources. It is shown that the system model has an M/G/1 type queuing structure, which is exploited for the computation of the joint buffer content distribution and cell loss probabilities of the high-priority and low-priority traffic streams. The obtained numerical results capture the effect of the shaper/policer and source parameters on the cell loss performance, and may be used for design optimization. A comparison of the priority leaky-bucket with the classical single buffer leaky-bucket regulator is carried out to quantify the improvement in terms of bandwidth utilization.