\limitations" and \pitfalls" of Leaky Bucket a Study with Video Traac

The Leaky Bucket policing mechanism has been extensively studied in both the academic as well as the industrial communities, resulting in numerous publications. Recently, there has been much interest in solving the issues of admission control in High Speed Networks using parameters determined by the leaky bucket as the access control mechanism. In this paper, we demonstrate that the leaky bucket performs exceedingly poorly for a very important class of traac, namely correlated traac with real time constraints. An example of such traac is Variable Bit Rate (VBR) video. For VBR video traac we show that the leaky bucket policing mechanism acts as nothing more than a peak rate controller. We also show that malicious users could take advantage of this weakness, and hence gravely impact the Quality of Service (QOS) of honest users sharing the network resources. We use actual video sequences to demonstrate our results. Furthermore, we show that the cell loss rate for such traf-c is insensitive to the token buuer and data buuer sizes. All of our results use nite buuers.