On ATM cell batching and its effects on bus arbitration in a conventional multimedia server

In earlier work, we proposed ATM cell batching as an effective technique to reduce system bus utilisation of ATM controllers for high-volume data streaming. Cell batching introduces small on-board data buffers, thus enabling longer burst transfers on the system bus. The effects of cell batching on other server components are investigated. In particular, cell batching alters the temporal relationship of bus accesses initiated by ATM controllers, and can thus affect the performance of arbitration in terms of access latency. We use extensive simulations of a traditional multimedia server architecture in a streaming scenario to evaluate a number of widely used arbitration protocols. Simulation results suggest that cell batching can increase average and maximum access latency of I/O devices, and that it reduces fairness. These results are consistent across the considered range of arbitration protocols. Compared with results for a system without cell batching, however overall level of service is improved by up to 20%. Moreover, cell batching tends to obliterate the difference between arbitration protocols.