IRC uses two levels of control blocks:
- A CICS/MRO terminal control layer
- An interregion SVC layer interfaced by the DFHIR macro.
The CICS/MRO terminal control layer is shown in Figure 60.
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 61.
Notes:
- The first TCTTE on the chain is not necessarily the TCTTE for the task’s
primary terminal.
- A task has allocated MRO sessions to other systems.
- TCTTEs are described more fully in Terminal control.
- Primary TCTTEs relate to Receive sessions, and secondary TCTTEs relate
to Send sessions.
- TCSEVC1 is the label on the address of the TCTTE of the first primary
session. TCSEVC2 is that of the first secondary session.
- The primary and secondary sessions each have sets of TCTTEs. These are
found by using the DFHTC CTYPE=LOCATE macro.
- A TCTTE is allocated for a surrogate session in transaction routing.
The interregion SVC layer interfaced by the DFHIR macro is shown in Figure 62.
This layer uses the following control blocks, which, unless otherwise stated,
reside in subpool 241 in MVS™ storage:
- Global (that is, one per MVS system) housekeeping (used by DFHIRP)
- Subsystem control table extension (SCTE)
- The SCTE is dynamically created, and contains information about the
number of regions logged on to DFHIRP. It is used to locate the LACB. See
also Figure 74, which shows the subsystem interface control blocks,
including a pointer to the SCTE in the CICS subsystem anchor block (SAB).
- Logon address control block (LACB)
- The LACB contains entries to identify the regions that have logged on,
and contains the address of the region’s logon control block (LCB).
- Local housekeeping (used by DFHIRP)
- Logon control block (LCB)
- The LCB is created for each successful log on.
- Logon control block entry (LCBE)
- The LCBE contains the basic control information for each IRC system
with which this system communicates. It addresses the connection control
blocks (CCBs).
- Subsystem user definition block (SUDB)
- A SUDB provides access to IRC control blocks. There is one SUDB for
each TCB that is currently logged on (so each SUDB may have multiple LCBs
associated with it). The SUDB contains TCB-related data and working storage.
- Connection control block (CCB)
- A CCB is created for each IRC send-receive session, and contains information
controlling the connection to the other region. When the connection is in
use, it addresses the CSB.
- Connection status block (CSB)
- The CSB provides status information about the connection between two
regions.
- MVS transfer buffers (MVS SRB mode)
- The MVS transfer buffers are used to transfer IRC data between regions,
and reside in subpool 231 in MVS storage.
Figure 63 shows the control blocks that are accessed by both
the terminal control layer and the DFHIR layer. Figure 64 shows
the location of these control blocks in MVS virtual storage.
The following blocks are used by both the terminal control layer and the
DFHIR layer. These blocks are allocated at logon time within a single MVS
GETMAIN, and, unless otherwise stated, reside in subpool 251 of MVS storage.
- Subsystem logon control block (SLCB)
- The SLCB is used by the IRC SVC and region and contains the master ECB,
posted when the region has IRC activity. It is pointed to by the CRB and
LCB.
- Subsystem connection address control block (SCACB)
- The SCACB contains entries allowing the addressing of SCCBs from the
SLCB.
- Subsystem connection control block (SCCB)
- The SCCB is created for each IRC send-receive session, and is allocated
at logon. It contains the ECB, posted when input for the session is available.
Note:
There is a one-to-one relationship between TCTTEs and SCCBs when
they are in use.
The following is a summary of the MRO event control blocks (ECBs):
Name Location Who waits Who posts
Dependent ECB SCCB Application (TC WAIT) DFHIRP
LOGON ECB SLCB CICS (KCP, Op sys WAIT list) DFHIRP
Link ECB LCB DFHIRP (Op sys WAIT) DFHIRP
Work queue ECB QUEUE CSNC transaction DFHIRP
DFHZIS2
DFHZLOC
See the CICS Data Areas manual for a detailed description of the CICS control
blocks.
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