Suppose an error is suspected in communication between System A and System B. The problem can be determined by looking at either system. The following procedure applies to System A, but could equally well apply to System B. The first step is to look at the field CSACRBA in the CSA optional features list in System A. If CSACRBA is zero, the interregion communication routine is not active in that system.
If CSACRBA is not zero, examine the TCTSEs in System A and find the TCTSE for System B. In this TCTSE, TCSEIRCF is the flag byte that indicates the state of communication between the two systems. If bit TCSEIRNC in this byte is on, there is no communication between System A and System B. This is either because System B has not started interregion services, or because System A is out of service with respect to System B, or because System B is out of service with respect to System A.
If bit TCSEIRNC is off, a session should exist. The next step is to inspect the primary and secondary session(s) between the systems. The first primary session is pointed to by field TCSEVC1 in the TCTSE, and the first secondary session is pointed to by TCSEVC2. If System A initiated the session, look at secondary sessions, otherwise look at primary sessions.
Each session is defined by a TCTTE. The field TCTESCCB in TCTTE is zero if the session is not connected to the other system, otherwise it contains the address of the subsystem connection control block (SCCB) that the interregion SVC routine uses to represent that end of the connection.
Assuming the session is connected, TCTTECA is zero if no task is using the session. Otherwise, TCTTECA points to the TCA of the task that uses the session.
The protocol for interregion SVC transfer is similar to that for VTAM® SNA data flow control. Field TCTEIRF1 contains information on the state of the session, field TCTESBRS gives the bracket status, field TCTESRHI is the inbound request header, and field TCTESRHO is the outbound request header.
The field TCTENIBA points to the TCTTE extension for the NIB descriptor. Within this TCTTE extension, TCTEPSQ contains the primary name, and TCTESSQ contains the secondary name. Thus a session in System A can be related to a session in System B.