Non-Saturating Fairness Protocol and Method for NACKing Systems

Processing transaction requests in a shared memory multi-processor computer network is described. A transaction request is received at a servicing agent from a requesting agent. The transaction request includes a request priority associated with a transaction urgency generated by the requesting agent. The servicing agent provides an assigned priority to the transaction request based on the request priority, and then compares the assigned priority to an existing service level at the servicing agent to determine whether to complete or reject the transaction request. A reply message from the servicing agent to the requesting agent is generated to indicate whether the transaction request was completed or rejected, and to provide reply fairness state data for rejected transaction requests.