Application programming interface for LU type 6.2

IMS application programs can use the IMS implicit LU 6.2 API to access LU 6.2 devices. This API provides compatibility with non-LU 6.2 device types so that the same application program can be used from both LU 6.2 and non-LU 6.2 devices.

The API adds to the APPC interface by supplying IMS-provided processing for the application program. You can use the explicit CPI Communications interface for APPC functions and facilities for new or rewritten IMS application programs.

Implicit API

The implicit API accesses an APPC conversation indirectly. This API uses the standard DL/I calls (GU, ISRT, PURG) to send and receive data. It allows application programs that are not specific to LU 6.2 protocols to use LU 6.2 devices.

The API uses new and changed DL/I calls (CHNG, INQY, SETO) to utilize LU 6.2. Using the existing IMS application programming base, you can write specific applications for LU 6.2 using this API and not using the CPI Communications calls. Although the implicit API uses only some of the LU 6.2 capabilities, it can be a useful simplification for many applications. The implicit API also provides function outside of LU 6.2, like message queueing and automatic asynchronous message delivery.

IMS generates all CPI Communications calls under the implicit API. The application interaction is strictly with the IMS message queue.

The remote LU 6.2 system must be able to handle the LU 6.2 flows. APPC/MVS generates these flows from the CPI Communications calls issued by the IMS application program using the implicit API. An IMS application program can use the explicit API to issue the CPI Communications directly. This is useful with remote LU 6.2 systems that have incomplete LU 6.2 implementations, or that are incompatible with the IMS implicit API support.

The existing API is extended so that:

  • Asynchronous LU 6.2 output is created by using alternate PCBs that reference LU 6.2 destinations. The DL/I CHNG call can supply parameters to specify an LU 6.2 destination. Default values are used for omitted parameters.
  • An application program can retrieve the current conversation attributes such as the conversation type (basic or mapped), the sync_level (NONE, CONFIRM, or SYNCPT), and asynchronous or synchronous conversation.
  • A terminal message switch can be used to and from LU 6.2 devices.

Explicit API

The explicit API (the CPI Communications API) can be used by any IMS application program to access an APPC conversation directly.

IMS resources are available to the CPI Communications driven application program only if the application issues the APSB (Allocate PSB) call. The CPI Communications driven application program must use the CPI-RR SRRCMIT and SRRBACK verbs to initiate an IMS sync point or backout, or if SYNCLVL=SYNCPT is specified, to communicate the sync point decision to the z/OS® Resource Recovery Services sync point manager.

Related Reading: For a description of the SRRCMIT and SRRBACK verbs, see SAA CPI Resource Recovery Reference.