NETGEAR XM128 ISDN - Manual (Page 59)

Reference Guide for the Model XM128 ISDN Digital Modem
ISDN Overview 6-11
The highest asynchronous V.110 user rate depends on bit 4 of S119 as follows:
• S119.4=0 (19.2 Kbps)
• S119.4=1 (38.4 Kbps for areas other than Japan)
• S119.4=1 (57.6 Kbps for Japanese version)
If the DTE speed is higher than what has been set, the user rate in Table 6-6 is used.
The X bits in the 80-bit frame are used for remote flow control.
V.120 ISDN Communications
This section describes how to set up and configure your Model XM128 modem with the V.120
ISDN protocol. Refer to
Table 6-5 on page 6-9 for the ISDN protocol specifications.
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 do not deliver the LLC.
Other switches do deliver the LLC, but the V.120 selection is discarded midway.
If the called modem does not get any B channel protocol information from the incoming setup
message and the remote device is a NETGEAR ISDN device, the Model XM128 modem can
identify the V.120 protocol automatically with the Multi Auto-answer Routine. Otherwise, the
handshake fails.
Selecting V.120 for German National ISDN (1TR6)
With a 1TR6 switch, data connections are achieved by setting the Service Indicator to 7
(Daten_bertragung 64Kbps) and using the Additional Information octet to select B channel
protocols. Because there is no predefined code for asynchronous V.120, the Model XM128 modem
uses the synchronous V.120 code to fill in the additional information octet. This approach might
not work all the time.