International Business Machines Corporation

Werner K Bux

Daniel Manuel Dias

Parviz Kermani

Ambuj Goyal

Wolfgang B Kleinoeder

In the Checkpoint Mode Protocol (CPM), checkpoint frames are transmitted at regular intervals for acknowledging received information frames and individually requesting retransmission of missing information frames. The disclosed invention reduces the flow of checkpoint frames in situations where their information is not required. This is achieved by either sending a Stop Checkpointing frame from sender to receiver in particular situations, or by inserting, in the case of duplex transmission (i.e. both stations are sending and receiving), Request-Reply bits into normal checkpoint frames for suppressing the flow of checkpoint frames when they are not necessary. In each case, provisions are made to resume the transmission of checkpoint frames as soon as they are required again.

Control flow reduction in selective repeat protocols

In a communication system comprising several stations, access to the ring is granted to one station at a time by circulating a token on the ring and updating the priority of the token is disclosed. This invention provides for a first station to transmit a token immediately after it has finished transmitting a frame containing a packet(s) needed to be transmitted from the first station without waiting for the header of the frame to return to the first station. A priority signalling packet is then transmitted on the ring from the first station after the first station transmits the token on the ring. This priority signalling packet contains information as to the particular priority level that the token should be updated to. Finally, the priority level of the token is updated to correspond to the particular priority level when the priority signalling packet reaches the station that holds the token.

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Richterswil, Germany

Werner K Bux