A reservation-based CSMA protocol for integrated manufacturing networks

This paper presents PCSMA, an extension to the CSMA/CD protocol (used in the Ethernet) to support both conventional datagram traffic and real-time traffic. The protocol provides predictable packet-delivery bounds for real-time traffic. It does not require changes to existing Ethernet controllers for datagram traffic. Under the new protocol, periodic sources follow a variation of the CSMA protocol that requires them to reserve transmission slots before they can begin transmission. This protocol is intended particularly for use in the integrated network in a manufacturing shop. Periodic sources include multiple sensors generating disparate types and rates of data. We have carried out an extensive performance evaluation of the protocol using a simulation model. The results are impressive: PCSMA shows fewer collisions than CSMA, equivalent delays for conventional traffic, and no failures to meet deadlines for periodic traffic