End-station performance under leaky bucket traffic shaping

The shaping of traffic at its source is a prominent congestion control solution in ATM networks. The "leaky bucket" with a "cell spacer" is a very popular traffic-shaping approach. By sizing the leaky bucket and spacer parameters, an end station shapes its traffic to conform to a "good behaviour" contract with the network. The leaky bucket delays the transmission of a selected number of cells, while the spacer forces a minimum time distance between transmitted cells. When a contracted transmission rate is close to the traffic generation rate of the end station, this traffic stream will utilize most of the bandwidth available on its virtual connection. The high utilization of such a connection leads to large queues of frames and cells at the end station, with high adverse consequences for end-to-end delay and jitter. Based on the negotiated traffic parameters and source traffic characteristics, we study, through simulations, the contribution of the leaky bucket plus cell spacer subsystem to the delay and jitter in an end station. We also study the distribution of the size of the bursts of cells leaving the end station and entering the network. Finally, we derive the theoretical upper bound for the size of bursts of the cells.