Controls whether or not a CV64 structure is provided to the VTAM application.
This parameter is applicable to the SYSTEM control statement (see SYSTEM statement).
When a VTAM application is accessed by a TN3270 client directly through the z/OS Communication Server TN3270 Server, the application receives a CV64 structure in the VTAM session's CINIT. The CV64 structure contains the TN3270 client's IP address and port which can be used by the application to help identify the origin of the TN3270 Client. Prior to use of the CV64 parameter in IBM Session Manager, if any IBM Session Manager was placed between the TN3270 Server and the VTAM application, then no CV64 structure was supplied to the application in the session's CINIT. Providing z/OS is at Release 12 or higher and the CV64 parameter is specified, IBM Session Manager will supply a CV64 structure to the VTAM application in the session's CINIT.
The CV64 structure is associated with the VTAM ACB used to access the application. This association is constructed when the ACB is opened. The association is lost when the ACB is closed. Therefore you should ensure your configuration provides an ACB that is not used by any other user whilst this association between the TN3270 client and the ACB exists. Consider using the SYSTEM parameter CLOSEACBINACT to close an ACB when the last user's session using an ACB has terminated.
So if a user accesses an application with an ACB that was opened by another user (and not subsequently closed then re-opened), the original user's CV64 structure will be passed to the application. This is also the case for parallel session applications, for example TSO, that allow multiple users to access the application through the same ACB. If the CV64 facility is required for parallel session applications then these applications must be defined with a range of ACBs, with enough ACBs in the defined range for the total number of concurrent users. See 'RANGE statement' in the Technical Reference manual; this statement must be specified with RRA=YES.
If the CV64 parameter is specified then TN3270 users who access IBM Session Manager directly through its TN3270 Server will also provide a CV64 structure to their VTAM applications.
If the CV64 parameter is not specified or CV64 No or OFF is specified then no CV64 structure is provided to the VTAM application.