Selecting V.120 For European Isdn (Dss1) Switch; Selecting V.120 For Germany National Isdn (1Tr6) - ZyXEL Communications Omni TA128 User Manual

Chapter 7 - V.120 ISDN Communications

Selecting V.120 for European ISDN (DSS1) switch

With European ISDN, V.120 is an option in the Bearer Capability (BC) information
element, which is a mandatory information element in the SETUP message. Although we
can specify V.120 in the Low-Layer-Compatibility (LLC) information element, some
switches just don't deliver the LLC. Other switches do deliver the LLC, but the V.120
selection will be discarded mid way.
If the called TA doesn't get any B channel protocol information from the incoming
SETUP message and the remote device is a ZyXEL ISDN device, the Omni TA128 will
be able to identify the V.120 protocol automatically with the Multi Auto-answer routine.
Otherwise, the handshake will fail.

Selecting V.120 for Germany National ISDN (1TR6)

With 1TR6 switch, data connections are achieved by setting the Service Indicator to 7
(Daten_bertragung 64Kbps) and the Additional Information octet is used to select B
channel protocols. Since there is no pre-defined code for asynchronous V.120, Omni
TA128 uses the synchronous V.120 code to fill in the additional information octet. This
approach might not work all the time.
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