Operating an IMS network

Operating a basic IMS network involves several tasks.

Operating tasks include:
  • Establishing a communication session between a logical unit and IMS
  • Sending data between a logical unit and IMS
  • Terminating the session between a logical unit and IMS
  • Restarting the session after a failure

Operating the network with APPC/IMS

APPC/IMS supports IMS commands for network operation, but the LU 6.2 device handles normal operations such as session startup, transaction initiation, and error handling that does not require master terminal operator (MTO) intervention.

Initiating a session with IMS

A session can be initiated by a logical unit, by the VTAM® network operator, by the IMS master terminal operator (MTO), automatically by VTAM, or by IMS itself. After a logical unit connects to IMS, it remains connected until one of the following actions occurs:
  • The logical unit itself requests disconnection.
  • The IMS MTO requests disconnection.
  • Another VTAM application program requests connection to the terminal.
  • IMS, VTAM, NCP, the logical unit, or the entire network is stopped.

After the physical connection between the controller and VTAM is established, an LU-to-LU session is initiated. The LU that is requesting the session informs VTAM that it wants to communicate with IMS. VTAM notifies IMS of the request through the VTAM Logon exit routine. IMS indicates that it will accept the request, and VTAM then logically connects the LU to IMS. A session is required before communication between the LU and IMS can be accomplished. To open a session, all nodes in the communication path (IMS, NCP, line, and station) must be in active status. After a session is established, VTAM directs all data between the logical unit and IMS.

IMS also supports SNA communication links in an Extended Recovery Facility (XRF) complex.

Logging on and signing on to IMS

The following definitions apply to logging onto IMS and signing onto IMS:

Definitions: 
  • Logging on to a terminal establishes a session with IMS for that terminal.
  • Signing on to a terminal identifies a user to IMS.

Logging off and signing off from IMS

The following definitions apply to logging off from IMS and signing off from IMS:

Definitions: 
  • Logging off from a terminal ends a session with IMS for that terminal.
  • Signing off from a terminal ends an identification of a user to IMS.