VTAM facilities used

The physical transmission of data between IMS and a SLU P system is controlled by VTAM®.

Related reading: For more information on the communication facilities that govern data transmission between IMS (a VTAM application program) and the controller, see Network Program Products General Information and z/OS® Communications Server: SNA Programming.

The VTAM facilities that IMS uses, particularly for a SLU P system, include:
  • Connection, disconnection, and establishing logon mode
  • Messages and responses
  • Definite response 1 and definite response 2 (All data transmitted between IMS and a workstation must request a definite response 1, definite response 2, definite response 1 and 2, or exception definite response 1 or 2. VTAM commands must request definite response 1.)
  • Sequencing and chaining
  • Quiescing
  • Facilities for ensuring orderly communication, including the use of brackets and change-direction indicators. In SNA protocol, a bracket is one or more chains of request units (RU) and the responses that are exchanged between two LU-to-LU half sessions that represent a transaction. In VTAM, a change-direction indicator means that the sender has finished sending and is prepared to receive.
  • Sequence-number recovery
  • Receiving input, sending messages
  • Unconditional bracket termination
  • Primary Error Recovery Procedure (ERP)

    The ERP is terminated by an IMS output error message sent to the workstation.

IMS also supports the class of service (COS) and session outage notification (SON) facilities.