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 tra c and real-time tra c. The protocol provides predictable packet-delivery bounds for real-time tra c. It does not require changes to existing Ethernet controllers for datagram tra c. 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 tra c, and no failures to meet deadlines for periodic tra c. This research was supported in part by the National Science Foundation Grant No. NCR-9111323 and by the Center for Advanced Manufacturing and Industrial Automation of the University of Kentucky.