Robert P Leo

US Patent:

49998340, Mar 12, 1991

Filed:

Mar 20, 1989

Appl. No.:

7/326136

Inventors:

Robert P. Leo - Charlotte NC
Mark W. McColgan - Concord NC
James E. Stockman - Charlotte NC
Jeffrey H. Young - Charlotte NC

Assignee:

International Business Machines Corporation - Armonk NY

International Classification:

H04J 326

US Classification:

370 941

Abstract:

A method of communicating between a primary station and a secondary station wherein variable sized packets of information are transferred asynchronously (or in start/stop mode) between the primary station and the secondary station. A communication control (e. g. , "BREAK" in the preferred embodiment) indicates the end of each packet. To permit the high speed transfer of data, the secondary station receives a high-speed clocking signal externally, from the primary in the preferred embodiment. The primary station generates and transmits a sequence number in connection with each packet, and the secondary responds to each packet with a status, but without generating a sequence number of its own or transmitting a sequence number. The primary station responds to the lack of a response from the secondary station by resending a transmission, while the secondary station responds to a duplicate transmission by ignoring the second transmission, and responds by resending the status from the previous transmission (which may not be the current status). This method using a minimum of overhead insures that the secondary station only proceeds after it has successfully transmitted its last status to the primary, thus guaranteeing that dynamically changing status will not be lost.