An improved CSMA/CD protocol for the packet-switched channel of the integrated services terminal bus

The Integrated Services Terminal (IST) bus is a low-cost, ISDN (integrated-services-digital-network)-compatible LAN that carries eight 64 kb/s circuit-switched channels and one 64 kb/s packet-switched channel. An improved CSMA-CD (carrier-sense multiaccess with collision detection) protocol on the latter channel guarantees access even with 100% load. The results of a computer-based investigation into the performance of this protocol are presented. With heavy loads and moderate message lengths, it is observed that the mean channel occupation saturates. In this saturation region, the mean message delay rapidly increases. The individual message delay can be found in a fairly long interval, the length of which depends on the variance of the message delay. For light loads, the mean message delay is independent of the number of terminals