How an application program interrogates VTAM

To determine the capability of a potential session partner, the application program can issue the APPCCMD CONTROL=OPRCNTL, QUALIFY=DISPLAY macroinstruction with a mode name of X'0' and specify the DISPLAY control block. The returned SLDSCAP field in the DISPLAY control block indicates whether the partner LU supports parallel sessions. (The AREA field in the RPL points to the DEFINE/DISPLAY control block.) This method can be used only after a CNOS request that involves the partner LU has completed.

Note:

Even if parallel sessions are not going to be used by an application program, an entry for the SNASVCMG mode should be included in an installation's logon mode table. VTAM® can use this mode internally as part of its processing for session limits with single-session partners if VTAM does not already know the session capability of the partner LU.
If a CNOS request other than (1,1,0) is specified to a partner LU that is only single-session capable, a session will not be started automatically regardless of the setting of AUTOSES.