Method and apparatus for reliable descriptor chaining in a media access control/host system interface unit

Claim 1

An interface system adapted for connection between a local area network communications medium and a network station, the interface system comprising: a bus interface unit adapted for connection to the network station for receiving information objects stored in a memory system associated with the network station, each information object stored in the memory system consisting of a sequence of one or more parts, each part having a descriptor associated therewith, the desciptor identifying the associated part as either a "first" part which is the first part in the sequence, a "last" part which is the last part in the sequence, a "middle" part that occurs between a first part and a last part, or an "only" part wherein the sequence consists of only one part, such that transfer of a correct information object from the memory system to the interface system will meet consistency criteria as follows: a "first" part must follow either a "last" part or an "only" part; an "only" part must follow either a "last" part or an "only" part; a "first" part or a "middle" part must precede a "last" part; request circuitry connected to the bus interface unit and adapted for connection to the communications medium for transferring information objects received by the interface system from the memory system via the bus interface unit to the communications medium; and detection circuitry connected to monitor each information object received by the interface system to determine if said information object meets the consistency criteria, the detection circuitry including an interrupt generator that provides an interrupt signal to the network station if the consistency criteria is not met for said information object, whereby incorrect information objects are prevented from being transferred from the memory system to the communications medium.