Reference Guide

ZCOM Message Handling
Multiplexing
Chapter 2 33
The inbound multiplexing program has the task of receiving all
messages from the physical terminal. It determines the origin of the
logical terminal from which the messages were sent. Then it processes
any of the control messages and forwards the data portion of any data
messages to the application receiver.
Figure 2-4 Inbound Multiplexing
Thus, to process an inbound message with multiplexing:
• zread (the message type will be type 1, ZCOM_MSTYPE_MSLT - a
message from a terminal ZLU).
• The source ZLU is obtained from PTZLU. PTZLU gives the ZLU of
one of the ZLUs in a multiplexed group.
• Decode the protocol header to extract the logical terminal address.
Use the ltfind routine to scan the multiplexed group to find a match
of the logical terminal address with LTADDR.
• Build a ZCOM message header where the source ZLU is the ZLU
found by ltfind, and the destination ZLU is taken from LTZRVR of
the logical terminal able.
•Use zsend (with bit ZCOM_ZSEND_MHD set) to send the message
and the ZCOM header to LTZRVR.
Logical
Terminal
TZLU
APPLICATION
LTZRVR
PZLU
Physical
Terminal
PTZLU
PTZRVR=PZLU