Session limits for SNASVCMG mode name

Additional session limit considerations apply when changing the session limits for the SNASVCMG mode name. This is a special mode name that VTAM® uses to exchange information with other LUs in implementing the LU 6.2 architecture. (Issuing a CNOS request to change the session limits for the SNASVCMG mode name alters certain information only for the local LU. The partner LU is not notified of the changes.)

Application programs can issue commands to change the session limits for this mode name. However, the maximum number of sessions can only be 2 on this mode name, and the maximum number of contention-winner or contention-loser sessions can only be 1. Therefore, the session limits for the SNASVCMG mode are set to (2,1,1) when active and (0,0,0) when reset.

Note: If default session limits of (1,1,0) are set for a single-session capable LU and AUTOSES is nonzero, one contention winner session will be activated on behalf of the application.

The session limits for the SNASVCMG mode name can be 0 only if all other session limits with a partner LU are also 0. In addition, no queued conversation requests can be awaiting completion. (For information on how the application program can specify whether queued requests are honored, see Draining and session deactivation responsibility.)

VTAM allows CNOS requests for modes other than the SNASVCMG mode to be issued without requiring the application program to first issue a CNOS request for the SNASVCMG mode. If the application program does not issue a CNOS request for the SNASVCMG mode, VTAM:

Issues the CNOS request for the SNASVCMG mode on behalf of the application program
Adds the SNASVCMG mode to the LU-mode table
Updates the SNASVCMG mode session limit to a value of 2

This allows the successful completion of a CNOS without the additional overhead of issuing a CNOS request against the SNASVCMG mode.

If VTAM handles the CNOS request of the SNASVCMG mode, the results might be slightly different than when the application program issues the CNOS request. For example, if the application program issues the CNOS request for the SNASVCMG mode, the usage of the AUTOSES operand immediately becomes applicable for the SNASVCMG mode. If VTAM handles the CNOS request, the AUTOSES operand is not immediately activated for the SNASVCMG mode; VTAM starts only the sessions it needs for the SNASVCMG.