4. The method of claim 3 , wherein the I/O operation is a transport mode operation, and obtaining information includes obtaining a transport command word (TCW) at the channel subsystem, the TCW including a transport command control block (TCCB) address field including an address of a TCCB, the TCCB including a plurality of device command words (DCW) that each includes an I/O command.
5. The method of claim 4 , wherein the data transfer request is a request for information including the TCCB for transmission by the network interface to the control unit in a Transport Command Information Unit (IU), and the at least one data check word is generated using the initial value from the Data Check Word Seed field of a Transport Command ACW data length information from the TCW and the TCCB.