Advanced traffic-policing mechanisms for VBR traffic over ATM networks

One major function of the ATM (Asynchronous Transfer Mode) networks is to provide real-time, low-loss, and minimum- delay transmission of VBR (variable bit rate) video traffic. The Leaky Bucket (LB) mechanism has been proposed and adopted at the ATM Forum to police network traffic. In this work, we enhance and integrate the ideas of (1) soft multiplexing and (2) multi-level rate policing, to design an advanced traffic policing mechanism: the Multi-Level Leaky Bucket with Token Passing. The new mechanism has an efficient mechanism to estimate the current bit-rate and burst-duration of a VBR source. Based on the estimation, it allows sources to transmit at different bit rates for restricted amounts of time. It also allows interactions among the Leaky Buckets of the input streams of the same virtual path. We use simulation to evaluate the performance of the new mechanism and to compare it with three existing methods. Two VBR traffic source models are used: (1) Markov Modulated Poisson Process with parameters set according to a HDTV model, and (2) an Autoregressive Markovian model of order 2, AR. We compare bandwidth utilization, cell-loss probability, and queuing delay for all methods, by varying the offered traffic load and the size of cell buffers and token buckets. We found that, due to different traffic characteristics possessed by different VBR sources, using token passing or multi-rate policing alone does not improve the original LB on certain VBR sources. We found that the new mechanism achieves better performance than the three existing schemes in all the scenarios.