Impact on conversation initiation

The requests issued to start a conversation differ depending on whether an application program requires explicit control of the SNASVCMG session. The application program can control the activation and deactivation of the SNASVCMG session through the APPCCMD CONTROL=OPRCNTL, QUALIFY=CNOS request, or it can let VTAM® automatically activate the SNASVCMG session. VTAM activates the SNASVCMG session if all of the following conditions are met.

The application program issues APPCCMD CONTROL=OPRCNTL, QUALIFY=CNOS for a mode name other than SNASVCMG.
The SNASVCMG session is not active.
The application program has not specified on the CNOS request that the partner LU is single-session capable.

When the application program controls the activation of the SNASVCMG session, the first APPCCMD CONTROL=OPRCNTL, QUALIFY=CNOS (where LOGMODE=SNASVCMG) for a partner LU indicates that the partner LU should support parallel sessions. VTAM does not negotiate the activation with the partner LU. If a subsequent BIND is received from the partner LU indicating single-session capability, VTAM rejects the BIND.

Application programs cannot issue APPCCMD CONTROL=OPRCNTL, QUALIFY=CNOS for the SNASVCMG mode name if the partner LU is not parallel-session capable. Partner-LU parallel-session capability cannot be changed once it is established by VTAM.