Source Models for Speech Traffic Revisited
Michael Menth, Andreas Binzenhöfer, and Stefan Mühleck.
Research Report 426
Abstract
In this paper, we analyze output traces of different voice codecs
and present analytical models to describe them by stochastic
processes. Both the G.711 and the G.729.1 codec yield constant bit
rate traffic, the G.723.1 as well as the iLBC codec use silence
detection leading to an on/off process, and the GSM AMR and the
iSAC codec produce variable bit rate (VBR) traffic. We apply all
codecs to a large set of typical speech samples and provide
quantitative models that are based on standard and modified on/off
processes as well as memory Markov chains. Our models are in good
accordance with the original traces as they capture the
complementary cumulative distribution function (CCDF) of the
on/off phase durations and the packet sizes, the autocorrelation
function (ACF) of consecutive packet sizes, and the queuing
properties of the original traces. In addition, they are rather
simple which makes them especially useful for application in
analytical and simulative studies. The durations of the on/off
phases in our model are an order of magnitude larger than those
found by previous work and to the best of our knowledge this is
the first paper presenting a model for VBR voice.