Application programs have little explicit control over whether sessions are initiated. They use CNOS requests to control session limits. These requests cause VTAM® to activate or deactivate sessions.

Application programs can explicitly accept or reject session establishment requests in the LOGON and SCIP exit routines by using CONTROL=OPRCNTL, QUALIFY=ACTSESS or CONTROL=OPRCNTL, QUALIFY=DACTSESS. These exits must be present in the application program for this capability to exist. The LOGON and SCIP exits also enable the application program to change session parameters by specifying an alternate BIND or BIND response.

A session partner that does not support parallel sessions can initiate a 6.2 session as an SLU. The mode entry used must specify that parallel sessions and CNOS are not supported. Reference the byte 'BINFLG2' at hex offset 17 in the BIND DSECT. (Refer to z/OS Communications Server: SNA Programmer's LU 6.2 Reference for this byte.)

After VTAM establishes the session, the application program can request rejection termination of the session by issuing the APPCCMD CONTROL=REJECT, QUALIFY=SESSION macroinstruction. See Managing sessions for more details on controlling session limits.