After opening its ACB and establishing sessions with one or more LUs, the application program can communicate on each session by issuing SEND, RECEIVE, SESSIONC, and RESETSR macroinstructions. VTAM® obtains the name of the application program that made the request and the identity of the session (if a specific session is being addressed) from the RPL. The communication macroinstruction specifies an RPL; the RPL contains the address of an ACB and the identity of the session.

The SEND and RECEIVE macroinstructions write and read requests and responses. A request contains data or control information or both. A response contains information that tells whether a request requiring a response arrived at the destination LU and was processed successfully or unsuccessfully.

Only data is written from or read into an application program data area. Control information is sent by being specified symbolically in a SEND macroinstruction or its associated RPL. Control information and responses that are received are not read into a data area, but are detected by analyzing fields in the RPL associated with a RECEIVE macroinstruction or in an RPL associated with the scheduling of a special exit routine that handles the receipt of responses and control requests.

SESSIONC is used to send session control requests and responses. The RESETSR macroinstruction is used to control the continue-any and continue-specific modes of a session. Both macroinstructions use the RPL and ACB control blocks in the same way as SEND and RECEIVE to identify the session and application program LU.