Patent ID: 8312189

Claim:
A computer program product for processing communications between a control unit and a channel subsystem in an input/output processing system, comprising a non-transitory tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method comprising: sending a command from the channel subsystem to the control unit to initiate an input/output operation, the sending of the command for opening a first exchange with the control unit, the first exchange identified by a first identifier, the command including a transport command control block (TCCB), the TCCB including at least one device control word (DCW) and the TCCB being obtained by a location identified by a transport control word (TCW); setting a time period for completion of the input/output operation; and based on the input/output operation not completing within the time period, sending a message to determine whether the control unit has the first exchange, identified by the first identifier, open for the command, the sending of the message for opening a second exchange, the second exchange identified by a second identifier, wherein the message interrogates the control unit to determine whether the control unit has received the command.