Performance analysis of an ATM multiplexer loaded with VBR trafficgenerated by multimode speech coders

摘要

Multimode coders are able to exploit the different characteristicsnof the speech waveform and to take into account the differentnpeculiarities of background noise, thus allowing improvements in bothnsignal reconstruction and network-offered load. In this context thenvariable rate code excited linear prediction (VR-CELP) coding, that is,na multimode variable bit rate (VBR) coding based on the CELP technique,nhas been introduced in the literature and is currently being considerednfor use in various applications, especially in the third-generation UMTSncellular systems. The target of the paper is to introduce an efficientnand accurate framework allowing a network designer to analyze the impactnof multimode VBR speech coding on the quality of service (QoS) providednby a wireless/wired ATM network. In order to capture the coder outputncharacteristics, we propose to model a VR-CELP voice source by using answitched batch Bernoulli process (SBBP). More specifically, three modelsnare introduced and compared in terms of accuracy and simplicity inndetermining network performance. As a result of the comparison, anfour-state model has been chosen as the best tradeoff. The model is thennused to analytically derive the loss probability and the jitternprobability density function of an ATM multiplexer loaded by a number ofnVR-CELP sources. Finally, the proposed paradigm has been assessed in ancase study where we demonstrate that, for a given output ATM linkncapacity and for a number of telecommunication services involving voicentransmission, VR-CELP coding performs better than traditional on-offncoding