A proposed adaptive control method for packet transmission delay in packet speech system

There are two basic problems in speech packet switching systems. One is how to guarantee the synthesized speech quality against fluctuation of the mean and variance of packet transmission delay in the network due to traffic fluctuation in packet switching. the other is the problem of deciding the beginning time of the talkspurt synthesis (i.e., when to begin talkspurt synthesis at the receiver side). Under the assumption that the packet transmission delay time is approximated by an exponential function, it is shown that the jitter absorbing time for each talkspurt can be calculated by observation of the packet arrival time at the receiver side. Using this result, an adaptive control method is presented to cope with the above two problems, where the jitter absorbing time is changed according to network traffic changes and the talkspurt synthesis time is determined from several packet arrival times. It is shown from simulation and numerical calculation that application of this control method to a speech packet switching system permits guaranteeing the voice quality in spite of traffic fluctuation in the network and reducing the probability of late beginning of talkspurt synthesis.