Using MSC in an APPC/IMS environment
APPC/IMS uses the services of APPC/MVS™ and MSC to provide the communication interface for an MSC configuration.
- LU 6.2 programs to use the TP name of an IMS remote standard application program or an IMS remote modified application program. (The transaction is sent to the remote IMS and executes. The transaction's reply is sent across the MSC links to the local IMS and then on to the LU 6.2 application program.)
- A message switch to a remote logical terminal (LTERM) through the DFSAPPC System Service.
- Use of DFSAPPC for sending IMS remote transactions and data.
- Immediate or deferred program-to-program switching to an MSC-routed remote application program.
CPI Communications driven application programs cannot include transactions that execute on remote IMS systems.
All IMS transaction types except Fast Path are supported: conversational, nonconversational, response mode, and nonresponse mode.
IMS adds a prefix to the LU 6.2 message when the message is sent over an MSC link. The minimum size of this prefix is 480 bytes. The buffer sizes defined for MSC links should be large enough to hold at least one complete message. Valid MSC buffer sizes are 1024 bytes to 65536 bytes.
To change the input message destination to any IMS local or remote destination after a message is received but before it is processed, use the TM and MSC Message Routing and Control user exit (DFSMSCE0).
Definitions: Using MSC with APPC/IMS requires you to understand the terminology used for the different MSC systems:
- The originating system (local) is the system from which the LU 6.2 program enters the IMS transaction.
- The remote system is the system in which the remote transaction executes.
- The intermediate system is the IMS that routes messages between the local and remote systems.
At any time, any of these three systems can receive LU 6.2 transactions.