Patent ID: 8196149

Claim:
A computer program product for processing communications between a control unit and a channel subsystem in an input/output processing system, comprising a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method comprising: sending a Request Node Identification (RNID) message from the channel subsystem to the control unit in a Command mode, wherein the Command mode uses a Fibre Connectivity (FICON) protocol supporting Channel Command Words (CCWs); receiving a RNID response from the control unit, the RNID response comprising a Process Log-in (PRLI) indicator, the PRLI indicator indicating whether the control unit supports a PRLI message protocol; responsive to the received PRLI indicator indicating a PRLI message protocol is not supported by the control unit, continuing operation in the Command mode; responsive to the received PRLI indicator indicating the PRLI message protocol is supported by the control unit, sending a PRLI message to the control unit to determine whether the control unit supports a Transport mode, wherein the Transport mode supports Transport Command Control Blocks (TCCBs); and responsive to the PRLI message determining that the control unit supports the Transport mode, setting the operational parameters for the Transport mode for that control unit.