Reference Guide

ZCOM Message Handling
Multiplexing
Chapter 2 31
Outbound Multiplexing
The multiplexing program uses the zread call to determine the origin of
the message, after which, the program would normally attach a protocol
header and forward the message to the destination physical terminal.
MZAUXL in the message header (see the chapter on Tables and Data
Structures) can be used to save the originating source node and ZLU on
the outbound message. The MZSRCE field in the message header is then
overridden with the multiplexing program’s primary ZLU, hence status
and response messages may be routed to the multiplexing program
instead of the sender. Routine zsend writes to the physical terminal (with
bit ZCOM_ZSEND_NOMX set in the mode parameter). Routine zsend
with user header (mode bit ZCOM_ZSEND_MHD) must also be used.
The responses to the outbound messages are received by the
multiplexing program as type 6 (ZCOM_MSTYPE_RSLT) messages
(request code ZCOM_MRQCODE_WRITE [2]). The multiplexing
program has to strip the protocol header which it had previously added
and forward the response to the ZLU number saved in MSPARE (using
zsend with bits ZCOM_ZSEND_MHD and ZCOM_ZSEND_NOMX both
set).
Figure 2-3 Outbound Multiplexing
TZLU1
TZLU2
Logical Terminal #1
Logical Terminal #2
LTZMXP-PZLU
LT GZ LK =T Z LU 2
PZLU
Physical
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