DFSAPPC message switch

DFSAPPC is an LU 6.2 descriptor that provides an IMS system service.

It allows LU 6.2 application programs to send messages to the following:

Application programs (transactions)
IMS-managed local or remote LTERMs (message switches)
LU name and TP name

Messages sent with the LTERM= option are directed to IMS-managed local or remote LTERMs. Messages sent without the LTERM= option are sent to the appropriate LU 6.2 application or IMS application program.

Because the LTERM can be an LU 6.2 descriptor name, the message is sent to the LU 6.2 application program as if an LU 6.2 device had been explicitly selected.

With DFSAPPC, message delivery is asynchronous. If a message is allocated and the allocate fails, the message is held on the IMS message queue until it can be successfully delivered.

Example: In the LU 6.2 conversation example, an IMS application issues a DFSAPPC message switch to its partner with the LU name FRED and TPN name REPORT. REPI is the user data.

DFSAPPC  (TPN=REPORT LU=FRED) REP1

You can use a 17-byte network-qualified name in the LU= field.

Restriction: LU 6.2 architecture prohibits the use of the ALTRESP PCB on a CHNG call in an LU 6.2 conversation. The LU 6.2 conversation can only be associated with the IOPCB. The application sends a message on the existing LU 6.2 conversation (synchronous) or has IMS create a new conversation (asynchronous) using the IOPCB. Since there is no LTERM associated with an LU 6.2 conversation, only the IOPCB represents the original LU 6.2 conversation.

Related Reading: For more information about DFSAPPC, see IMS Version 15.5 Communications and Connections.