A Variation on CSMA/CD That Yields Movable TDM Slots in Integrated Voice/Data Local Networks

Abstract

A variation on the carrier-sense, multiple-access/collision-detection (CSMA/CD) protocol for local-area, random-access broadcast networks is presented. The new protocol supports any mix of voice and data traffic, and has an upper bound on the delay of periodic traffic. In conventional CSMA/CD systems, statistical fluctuations in the transmission delay may cause disruptions in reconstructed voice waveforms. This does not occur with the new protocol. With this protocol, data sources use conventional CSMA/CD techniques to access the channel, while voice sources use a subset of these protocols, and appear to acquire a time-division multiplexed (TDM) slot. As in TDM systems, the entire system capacity can be used by the periodic sources. Unlike TDM systems, periodic slots are repositioned when other transmissions interfere with them, timing discrepancies between sources can be tolerated, and a centralized controller is not required to assign slots. Simulations are used to compare the delays in this system with those in conventional CSMA/CD systems. It is shown that at link utilizations of 0.9, voice sources can operate in a time-assignment, speech-interpolation mode. The effect of periodic traffic on conventional CSMA/CD protocols is also determined.