Admission Control for Speech Traffic in the Presence of Overbooking

ABSTRACT

Voice codecs use silence detection to reduce their average output rate and produce on/off packet streams. When several of such on/off packet streams are multiplexed onto a single link, the packets face both packet scale and burst scale congestion. If the sum of the peak rates of the flows does not exceed the link bandwidth, the distribution of the packet waiting time resulting from packet scale queuing can be calculated by a weighted n·D/D/1 formula [1, 2]. However, advantage can be taken of the reduced flow rates by overbooking the link bandwidth in the sense that the sum of their mean rates is below the link bandwidth, but the sum of their peak rates exceeds the link bandwidth. Then, the well-known formula cannot be applied, but this is the most frequent application scenario. Therefore, we change the weighted formula by a simple adaptation and show by means of simulation that it well approximates the distribution of the packet waiting times in an overbooked system. We also clarify the relation of our new method to the well-known AMS [3] solution for on/off fluid flows. The simplicity of our approximation makes it attractive for engineers and applicable for admission control purposes in switching devices.