An application program SSCP-LU session uses TS profile 1 and FM profile 6.

For each destination PU, the application program must adhere to the request mode supported by that PU on the SSCP-PU session; otherwise, the request is rejected with a negative response (sense code = X'08510000'). For example, a PU that operates in immediate request mode should not be sent a new request until it has responded to the last request.

A procedure-related identifier (PRID) is available for use by the application program for request/reply correlation in some types of RUs. The PRID, if present, is contained in bytes 5–6, bits 4–15, in the CNM standard header (described in Standard CNM headers).

The application program generates a PRID if it is sending a Forward request that solicits a reply. The destination PU, which receives the request, saves the PRID (which was possibly translated by the SSCP) and returns it in all replies that correspond to the request. The PRID value (retranslated by the SSCP, if necessary) is returned to the application program within the embedded reply RU of the Deliver request.

The application program must determine (usually through use of its own timer) that the Deliver RU is not received for a PRID value. No notification is given to the application program if the PU to which the embedded NS RU was sent becomes inoperative before the reply RU can be sent by the PU.

A CNM application program is responsible for proper operation when a Deliver RU is not received for its corresponding Forward RU. A CNM application can cancel the correlation between the Deliver and Forward RUs. The Deliver RU that would have been correlated to the Forward RU is discarded.

A CNM RU (X'810814') with a subtype indicating cancel can be sent to VTAM® by a CNM application to cancel a Deliver RU. The Cancel RU contains the PRID assigned to the Forward RU, and the name of the destination used in the Forward RU. The CNM application must be able to receive the Deliver RU until the response to the CNM RU is received.

If the reply from the PU consists of multiple requests, the PU inserts the same PRID into each request. To handle this, each such reply has a “not last” bit defined as part of its format. This bit is used by the PU that is sending the requested data to indicate that at least one additional request RU is still to be sent. A flag is set in the Deliver RU by the SSCP when the embedded request contains a standard CNM header with a defined PRID field. A solicited flag is set in the CNM header by the replying PU whenever the PU generates a reply. Unsolicited Deliver requests have the solicited flag set off in the embedded RU. A PRID value can be reused after the application program receives the last reply RU using that PRID.