See Comparing normal information to expedited information for more information about normal and expedited information.

The APPCCMD CONTROL=SENDEXPD, QUALIFY=DATA macroinstruction is used to send expedited data to a partner application over a conversation allocated on a full-duplex-capable session. The amount of expedited data specified by the application should be in the range of 1 - 86 bytes.

The APPCCMD CONTROL=SENDEXPD, QUALIFY=DATA macroinstruction causes expedited data to be sent to the partner. This macroinstruction is posted complete immediately without waiting for a response from the partner LU. If the macroinstruction is issued and the response to a previous SENDEXPD request has not been received, a nonzero return code is returned to the application. The response from the partner LU is not sent until the expedited data has been received by the partner application.

For more information, refer to z/OS Communications Server: SNA Programmer's LU 6.2 Reference.

The APPCCMD CONTROL=SEND, QUALIFY=RQSEND macroinstruction causes a request-to-send indicator to be sent to the partner. This macroinstruction is posted complete after a response has been received from the partner LU. If the macroinstruction is issued and the response to a previously issued APPCCMD CONTROL=SENDEXPD request has not been received, a nonzero return code is returned to the application. For more information, refer to z/OS Communications Server: SNA Programmer's LU 6.2 Reference.

When sending expedited data, ensure that the partner transaction program supports the receipt of expedited data. In some circumstances, the APPCCMD CONTROL=SENDEXPD, QUALIFY=DATA macroinstruction completes successfully even when expedited data does not reach the partner. This can occur when a half-duplex transaction program has allocated a conversation on a full-duplex session and the partner transaction program does not support the receipt of expedited data.

For example, assume there are two existing half-duplex transaction programs. If the LUs upon which the transaction programs operate are upgraded to support full-duplex, then the sessions between the half-duplex transaction programs may begin to have full-duplex capability. Now assume one of the transaction programs is upgraded to exploit the sending of expedited data, which is allowed on a half-duplex conversation on a full-duplex session. If the other transaction program is not upgraded at the same time, a problem can occur.

The problem occurs when the upgraded transaction program sends expedited data to the partner. The first time the macroinstruction completes successfully, however, the downlevel partner will never receive the expedited data.

If the upgraded transaction program sends more expedited data to the partner, then that macroinstruction completes with an RCPRI, RCSEC of X'00A0', X'0005', REQUEST_NOT_ALLOWED— RSP_TO_PREVIOUS_SENDEXP_REQUEST_NOT_RECEIVED.