The communication between z/OS CICS and MFA Server uses standard LU6.2 ISC protocol as implemented by CICS. The SNA logical unit names used in the MFA Server configuration are the key to this communication. In the example, the target z/OS CICS system is identified as CICSSYSA (LUNAME="CICSSYSA") and the target ES/MSS server is identified as MFAMTO1 (ACBNAME= "MFAMTO1").
Our target z/OS CICS initiates work to ES/MSS when a request is directed to an external CICS SYSID that is associated with the MFAMTO1 LU name by CICS definitions. A CICS CONNECTION defines the MFAMTO1 LU name and assigns an external SYSID. A CICS SESSIONS definition for that connection defines the SNA logmode to be used for the ISC conversations. It is important to note that the SYSID values known to z/OS CICS do not have to match the SYSID values known to MFA Server and ES/MSS, however, MFA Server and ES/MSS must agree in their definitions. Although the SYSID values known to CICS can be different from the ES/MSS and MFA Server definitions, we recommend that the same SYSID values be used throughout the definitions.
CICS handles the request to the external SYSID by establishing the LU6.2 sessions that support the ISC exchanges, if they are not already established. CICS then sends the initial FMH-5 Attach request for the conversation to MFAMTO1. MFA Server recognizes this request as a conversation for ES/MSS because CICS used the MFAMTO1 LU name. MFA Server also checks that the request originated in a defined CICS server by locating the definition for the originator's LU name (CICSSYSA) and logmode name (#INTER) combination. Having located the two sets of definitions, MFA Server can forward the request on to the target ES/MSS server. If there is currently no socket connection to ES/MSS, MFA Server has the IP address and port number needed to contact ES/MSS's ISC listener. Now the request can be forwarded to ES/MSS over the socket connection associated with the MTO1-CICA SYSID combination.