RELIABLE BROADCAST PROTOCOL FOR A TOKEN PASSING BUS NETWORK

摘要

RELIABLE BROADCAST PROTOCOL FOR A TOKEN PASSING BUS NETWORK In a communications system with a plurality of stations coupled to a single communications path, it becomes desirable for a transmitter to broadcast a packet message to a predefined broadcast group of receivers. For the system to operate reliably, it is also desirable that the system protocol assure that all stations, which are intended to receive the broadcast message, do indeed receive the broadcast message. The instant system, station apparatus and protocol contemplate a primary receiver, also called a token site. The primary receiver is adapted to receive and store information messages transmitted from a source station to a broadcast group. The source would continue to retransmit the broadcast message until it receives an acknowledgment control message from the primary receiver. In the event some receiver(s) in the broadcast group do not receive the broadcast message, such receiver(s) could request a retransmission of the message. The primary receiver, not the source station, would retransmit the broadcast message, thereby assuring a reliable broadcast system. The token site function can be rotated among the various receivers in the broadcast group to reduce storage costs. The possible token sites are identified in a token list to which stations may be added or from which stations may be deleted. The token list is transmitted to all stations in the broadcast group to assure that no more than one token site exists at any instant of time.