Initiating an ISC VTAM session

A session must be established before data can be transmitted between another logical unit type 6.1 and IMS. If message resynchronization is required, it is performed after the bind.

IMS can be requested to initiate a session in one of the following ways:
  • An ISC logical unit requests session initiation by sending the initiate-self command. VTAM® verifies the command and passes the request to IMS.
  • An ISC logical unit sends BIND to initiate a session with IMS.
  • The z/OS® VTAM network operator requests session initiation on behalf of the logical unit by using the z/OS VARY command with the LOGON option. VTAM processes the request and passes it to IMS. The VARY command cannot be used to initiate parallel sessions.
  • VTAM passes to IMS a logon or BIND SCIP request for each logical unit defined to VTAM as belonging to IMS. (This method cannot be used to initiate parallel sessions.)
  • An authorized IMS terminal operator requests session initiation for an ISC logical unit by entering the IMS /OPNDST command.  
IMS can initiate (send BIND) or accept (receive BIND) a session if all the following conditions are met:
  • The IMS master terminal operator has issued a /START DC command.
  • The logical unit name is known by IMS.
  • The logical unit is not stopped (/STOP command) within IMS.
  • The logical unit has not reached the maximum allowable sessions defined to IMS. (This applies to statically defined terminals only.)
  • If the session is to be parallel, the CINIT or BIND session qualifier field must contain a valid LTERM subpool name that defines the message queue set to be used. A valid subpool name is one that is not stopped or allocated (except during session restart). The session qualifier fields must not be supplied when requesting session initiation with a logical unit defined to IMS as single session.
  • For statically defined terminals, the MSGDEL option for the LTERM subpool as specified on the SUBPOOL macro does not conflict with the MSGDEL option specified for the session on the TERMINAL macro.
  • No invalid or conflicting parameters are indicated on either a CINIT, BIND, or negotiable BIND reply.