Stubborn: a medium access protocol for expert assistants in distributed control systems

A novel implementation is presented, the Stubborn protocol, which provides the right compromise to obtain a balanced and near-optimal performance under both normal (control) operation and transient (emergency) conditions. It is based on the following simple principle: stations make access attempts as in the usual 1-persistent CSMA/CD (carrier-sense multiple-access with collision detection). In case of collision, a station with priority higher than zero will not interrupt transmission, but will exercise its right to extend the collision for a period proportional to its priority level. The station that persists longer will be able to start 'clean' transmission as soon as all others have desisted. The algorithm is complemented with tie-breaking procedures.<>