DATA COMMUNICATION METHOD AND SYSTEM

摘要

A method of multipoint communications utilises a protocol in which data messages (10) sent by a primary source are multicast to a plurality of secondary receiving stations (S1..Sn). Each message packet contains a control field comprising a station identifier code (14) and an instruction for the specified station to acknowledge a predetermined number of messages. Each successive message packet comprises a station identifier code which differs in an alterable set cyclical sequence. Thus, acknowledgements of correct receipt of data are taken in a cycle of length L such that in a space of L messages each receiver must acknowledge at least once. In this way the primary source need only keep the L latest messages because all the stations have acknowledged correct receipt of at least up to the current message minus L. The multipoint communications method uses a protocol which can be applied to existing communications networks.