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.<>