Performance of the Expressnet with voice/data traffic

Abstract

In the past few years, local area networks have come into widespread use for the interconnection of computers. Together with the trend towards digital transmission in voice telephony, this has spurred interest in integrated voice/data networks. The Expressnet, an implicit-token round-robin scheme using unidirectional busses, achieves high performance even at bandwidths of 100 Mb/s. Other features that make the protocol attractive for voice/data traffic are bounded delays and priorities. The latter is achieved by devoting alternate rounds to one or the other of the two traffic types. By the use of accurate simulation, the performance of the Expressnet with voice/data traffic is characterized. It is shown that the Expressnet satisfies the real-time constraints of voice traffic adequately even at bandwidths of 100 Mb/s. Data traffic is able to effectively utilize bandwidth unused by voice traffic. The trade-offs in the alternating round priority mechanism are quantified. Loss of voice samples under overload is shown to occur regularly in small, frequent clips, subjectively preferable to irregular clips. In a comparison of the Expressnet, the contention-based Ethernet and the round-robin Token Bus protocols, the two round-robin protocols are found to perform better than the Ethernet under heavy load owing to the more deterministic mode of operation. The comparison of the two round-robin protocols highlights the importance of minimizing scheduling overhead at high bandwidths.