Terminal control layer

The CICS/MRO terminal control layer is shown in Figure 1.

This layer uses the cross-region block (CRB). This is a global (that is, one per CICS® system) block that is created in the CICS dynamic storage area above the 16MB line (the ECDSA) when IRC is initialized, and provides information to communicate with the IRC SVC. See Figure 2.
Figure 1. CICS/MRO terminal control layer of control blocks
The first part of a diagram showing the CICS/MRO terminal control layer of control blocks.
The second part of a diagram showing the CICS/MRO terminal control layer of control blocks.
Notes:
  1. The first TCTTE on the chain is not necessarily the TCTTE for the task’s primary terminal.
  2. A task has allocated MRO sessions to other systems.
  3. TCTTEs are described more fully in Terminal control.
  4. Primary TCTTEs relate to Receive sessions, and secondary TCTTEs relate to Send sessions.
  5. TCSEVC1 is the label on the address of the TCTTE of the first primary session. TCSEVC2 is that of the first secondary session.
  6. The primary and secondary sessions each have sets of TCTTEs. These are found by using the DFHTC CTYPE=LOCATE macro.
  7. A TCTTE is allocated for a surrogate session in transaction routing.
Figure 2. Cross-region block (CRB)
Diagram illustrating the structure of the cross-region block (CRB).