Functions available to an ISC TCP/IP session

CICS® supports ISC TCP/IP sessions with a private IP interconnectivity (IPIC) protocol and an asynchronous command level (EXEC) application programming interface (API).

The asynchronous API provided by CICS for ISC TCP/IP sessions uses the START and RETRIEVE EXEC commands. When used within the context of a CICS application program, the START and RETRIEVE EXEC commands create the IPIC data flow control protocols for the asynchronous processing that is associated with messages on the session.

A START command causes an IPIC header to be issued with the message. Messages sent to IMS with the START command can be only one chain in length and are sent with BB/EB. CICS uses the RETRIEVE command to obtain asynchronous messages from the session for CICS transaction processing. The other IPIC data flow control protocols issued with an asynchronous message depend upon the type of message issued.

The use of the CICS asynchronous START and RETRIEVE EXEC commands with ISC TCP/IP sessions precludes the use of any function for which CICS requires a synchronous flow. For example, the START and RETRIEVE EXEC commands support only single-chain messages. Additionally, certain functions that are supported by ISC VTAM® sessions are not supported by ISC TCP/IP sessions.

The following tables show the functions available on ISC TCP/IP sessions with CICS.

The tables do not take into consideration the recovery aspects of any of the listed combinations. A Yes indicates only that the approach is possible. However, a system designer should take into account the need for ease of recovery and restart.

Table 1. Functions available to an ISC TCP/IP session with CICS: CICS front end
Functions ISC TCP/IP support
Nonresponse or nonconversational mode IMS input transaction Yes
Nonresponse or nonconversational mode IMS output transaction Yes
Response mode IMS transaction (including Fast Path) No
Conversational mode nonlast IMS input transaction No
Conversational mode last IMS input transaction No
Recoverable1 IMS transaction N/A
Nonrecoverable1 IMS transaction N/A
IMS message switch Yes
Front-End Switch (FES) exit routine (DFSFEBJ0) No
IMS operator commands /DISPLAYand /RDISPLAY only
Message Format Service (MFS)2 No
Single-segment input/output IMS transaction Yes
Multi-segment input/output IMS transaction No
Table 2. Functions available to an ISC TCP/IP session for CICS EXEC commands: IMS front end
Functions ISC TCP/IP support
CICS transaction Yes
CICS operator command (system transaction) No
MFS2 No
Notes for CICS EXEC tables:
  1. A transaction is defined as recoverable or nonrecoverable during IMS system definition and is acceptable to IMS only when the sync point protocols and transaction definitions are consistent. See Relationship of ISC and IMS execution modes and Keeping half sessions synchronized for more information.
  2. MFS maps data between the session and the IMS application program. In CICS, basic mapping support (BMS) maps data at the request of the CICS application program. BMS does not interact with the session, but can be used to handle mapping of data to and from IMS. IMS MFS and CICS BMS do not communicate.