HP Advanced Communications Controllers (ACC) manual Outbound Multiplexing

ZCOM Message Handling

Multiplexing

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

	Logical Terminal #1
TZLU1		LTZMXP-PZLU

	Logical Terminal #2
TZLU2		LTGZLK=TZLU2

PZLU

Physical Terminal

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