The authors propose a MAC-level protocol with bounded packet delay time for Ethernet-type networks. The proposed protocol, named Virtual Token, aims at improving the performance of CSMA/CD under heavy load, retaining its good characteristics for light and moderate traffic conditions. The improvement is achieved by passing an implicit token. Collision-free protocols based on passing explicit tokens are known to perform well under heavy traffic conditions, but they are outperformed by collision protocols for lighter loads. Unfortunately, the maximum packet delay in pure collision protocols is not bounded which is unacceptable in certain applications. The authors prove that the Virtual Token protocol guarantees packet delivery in a bounded time, and report results of numerous simulation experiments carried out to investigate its performance.
