VTAM® maintains a set of session limits for partner logical units for each mode name used. These session limit values are used if a partner LU attempts to negotiate a change in the current number of sessions. If VTAM receives a request from the other partner LU to change the number of sessions for its LU 6.2 logical unit, VTAM uses the session limit values to determine whether to accept or reject the requested change. Note that the partner LU may be unable to accept increases in the session limits. Therefore, the end result of any change requests can still mean that the session limits do not increase.

If a session is available for use by a conversation, the process of starting and ending a conversation requires fewer system resources than starting and ending a session. Ideally, therefore, application programs should set up their session limits so that VTAM can establish a number of sessions with other LUs that will be relatively long-lived. Applications can then treat these sessions as resources that support conversations.