Performance evaluation of d-channel access protocols in ISDN

Abstract

Chapter One introduces the concept of Integrated Services Digital Networks (ISDN). A brief outline of the integration of voice and data services is given, indicating the different characteristics of these two services. Evolution from the existing telephone networks towards the full ISDN is mentioned, emphasizing the transition from analog to all digital in the transmission facilities. The ISDN emphasizing and customer access are discussed together with the access protocol architecture.

Chapter Two surveys the modelling and evaluation techniques in the study of communication and computer systems. These include the analytical, simulation and direct measurement methods. Common approaches to model queueing systems are described, with particular interest in the modelling of multiple classes priority queues. Event-oriented simulation methodology is presented, including techniques to establish the credibility of the simulation models.

Chapter Three describes the access protocols that are suitable for the ISDN. Queueing and simulation models, based on the approaches mentioned in Chapter Two, are used in the performance studies and numerical comparisons. In particular, the pre-emptive access procedures are suggested as alternatives to improve the signalling delay.

Chapter Four derives an appropriate queueing model for the analysis of the 95 percentile of the s-delay in ISDN, from which the Laplace Transform of the s-delay is obtained. Inversion of the Laplace Transform can only be obtained by using numerical methods. Comparison with simulation results is made to validate the queueing model.

Chapter Five presents a new access protocol based on the packet-switching technology. Each station is assumed to generate messages consisting of an arbitrarily distributed, random number of fixed size packets. The channel is time-slotted with a slot time equal to a packet transmission time. The protocol ensures that an ongoing message transmission can not be preempted by any messages of the same class, but can be pre-empted at the beginning of the next slot by a higher priority message. Study of this protocol is based on simulation and analytical techniques. From the mean signalling delay formula derived, the optimal packet size is obtained. With the optimal packet size, the performance of the mean signalling delay of the Packet Switching protocol is found to be as good as those preemptive ones. Comparisons between various priority protocols are presented to indicate the delay-throughput characteristics among them.

Chapter Six discusses the fairness of the access protocols in ISDN. The fairness measure is according to the average end-to-end message delay for each station. This issue is studied through the design aspects of the scheduling disciplines. A Random Number Prefix scheme is proposed to improve the fairness measure.

Chapter Seven summarises the major conclusions reached from the investigations. Further researches are suggested and discussed.