Performance modeling of video teleconferencing in ATM networks

Results are presented of a simulation study of the potential multiplexing gains from using variable-bit-rate (VBR) encoding to multiplex video teleconferencing traffic over an asynchronous transfer mode (ATM) network. Simulated traffic from several video teleconferences is fed into a buffer and multiplexed onto a higher-speed output line. The cell loss resulting from buffer overflow is observed. The major results are as follows: (1) the spacing between cells has a large role in determining the aggregate cell loss rate seen by a collection of calls. The cell loss rate is reduced when either the frame start times are evenly spaced or cells are evenly distributed in the video frame. (2) After the cell loss rate becomes nonnegligible, it grows rapidly as a function of the number of access lines. (3) The cell losses are not distributed uniformly over time but are clustered. A consequence is that the average time between clusters of cell loss and the time to first loss is greater than if the losses were spaced uniformly. (4) A simple model is found to describe when a cluster of cell losses occurs, the duration of the cluster, and how many cells are lost in the cluster