Netgear XM128 ISDN User Manual Page 64

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Reference Guide for the Model XM128 ISDN Digital Modem
6-16 ISDN Overview
Because the V.42bis algorithm needs an error-free transmission channel between the compression
and decompression processes, it can only work with a protocol that has error control competence.
The X.75 and V.120 protocols can be used together with V.42bis data compression. The V.110
protocol, on the other hand, is just an R-interface layer 1 adaptation protocol without error-control
and is thus inadequate for V.42bis.
X.75 ISDN Communications (Europe)
This section describes how to set up and configure your Model XM128 modem with X.75
protocols. Refer to Table 6-5 for the X.75 protocol specifications for Europe.
The X.75 protocol was originally designed for packet-switched signaling systems in public
networks to provide data transmission services. Now, however, it is also used as the link layer for
telematic services (as defined in T.90) in ISDN. These services include both the ISDN
circuit-switched mode (DTE-DTE communication) and the ISDN packet-switched mode
(DTE-DCE communication).
Answering an X.75 Call
There is no need to configure the ISDN mode to the protocol of an incoming call. The Model
XM128 modem is able to determine the correct protocol to use by examining the data coming in
from the remote site. Protocol determination takes place if the device is set to auto-answer or after
an answering command is issued.
One exception to this process is when the ISDN data call is carried through speech bearer. In this
case, you need to make an MSN entry for the phone number from which you are expecting the
data-over-speech-bearer call to be coming for the X.75 protocol. Use AT&ZI0=n. Refer to
Data
over Speech Channel” on page 6-7 for further information.
To allow the Model XM128 modem to answer the incoming call, you need to set S0 to a value
greater than 0 (for example, ATS0=1). The Model XM128 modem answers the call and uses
asynchronous-to-synchronous conversions to and from the DTE. If S0 is not set (S0=0), the DCE
reports RING and also makes an audible ring notification.
Making an X.75 Call
The default data protocol of the Model XM128 modem is ATB20 (V.120). the X.75 protocols can
be chosen using the following AT commands:
ATB00
(for X.75 with transparent layer 3)
ATB01
(for
X.75 with T.70 NL)
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