We analyze teleconference traffic, with moderate motion and scene changes, generated by different video codecs. These codecs differ in several aspects of coding, such as in the use of DCT and motion compensation. Our results are that, even when traffic is generated using different coding schemes, the number of cells per frame can be described by a gamma (or equivalently negative binomial) distribution and a DAR( 1) model determined by three traffic parameters (the mean, variance, and correlation) can be used to accurately model the source. The main contribution of this paper is in showing that our previously published results on source modeling and marginal distributions, which were based on analysis of traffic generated by one type of coder, hold for coders which differ in various ways and particularly differ in the use of motion compensation.

No abstract

Asynchronous transfer mode (ATM) broadband networks will support variable bit rate video codecs, which are capable of maintaining a constant picture quality. To demonstrate this capability, a prototype hardware video coder has been developed in the Siemens Central Communications Laboratories. The prototype uses interframe coding, combined with a discrete cosine transform, and is able to reproduce the original picture quality, independent of signal sources or picture material used.A gain in transmission efficiency is expected when several video sources share a common ATM channel ('statistical multiplexing'). This paper reports on a series of measurements that have been performed using this coder for a large variety of video sources to determine the possible gain in transmission efficiency.The main results are: for realistic video phone scenes, up to about three times the number of signals can be transmitted compared to transmision with constant rate and the same picture quality, if the output signal of the coder has been smoothed over a period of one frame. Smoothing over shorter periods reduces the potential gain substantially. The statistical multiplexing gain increases with the duration of the picture sequences due to the criterion of constant picture quality. It varies very little with the acceptable packet loss rate.