Each side of a channel-to-channel adapter (CTCA) is represented by a cross-channel node control block (XCNCB). In addition, each side has a physical unit service I/O (PIO) control block and a station control block (SCB). The PIO is used for exchange ID (XID) channel programs (the physical unit services I/O that occurs before the link is active). The PIO is mapped by ISTPIO. The SCB is a station work area where CCWs for normal data transfer are built. It is not mapped, and is not described in z/OS Communications Server: SNA Data Areas Volume 1 or z/OS Communications Server: SNA Data Areas Volume 2.

A series of channel programs are issued when the operator activates the CTC connection. These I/O exchanges are used by the hosts to communicate various capabilities to the other host. The capabilities are transferred via the XID channel program.