NETGEAR XM128 ISDN - Manual (Page 63)

Reference Guide for the Model XM128 ISDN Digital Modem
ISDN Overview 6-15
128 Kbps Speeds
BRI ISDN consists of three (2B+D) logical channels. Each B channel can be used independently
for a dial-up connection running at 56 Kbps or 64 Kbps (bits per second).
The two B channels can be used together for a single data connection to provide 112K (with
In-Band Signaling) or 128K (when Out-of-Band Signaling is used). It is called a Bundle
Connection (different from BONDING).
The type of channel bundling described in the V.120 section is supported only between the
following NETGEAR products: Model XM128 modem. Dialing Prestored Phone Numbers
Use ATDSn, n=0,1,...,39, to dial the (n+1)th phone number twice for both the bundle connections.
Use ATDSn+Sm, (n and n=0,1,...,39) to dial the (n+1)th phone number for the first connection and
the (m+1)th phone number for the second connection.
For example, ATDIS0+S1[Enter] dials the number stored in location 0, and the number stored in
location 1 for the bundle connection.
Error Correction and Data Compression with V.120
With V.120, the default setting is for Link Access Protocol Digital (LAPD) error correction only.
No data compression is negotiated. The following AT commands are used to switch the V.42bis
data compression on or off for ISDN data calls when using V.120 protocol:
• AT&K44 (enable V.42bis on ISDN call)
• AT&K00 (disable V.42bis on ISDN call)
With the &K44 setting, the Model XM128 modem tries to connect using V.42bis data
compression. If the remote device does not support V.42, then LAPD error correction can be used.
When a connection is made using V.42bis compression, the following connect message is
displayed:
CONNECT 115200/V120 56000/LAPD/V42b.
It takes extra time for the calling ISDN device to negotiate V.42bis. If you know in advance that the
called site has no V.42bis capability, it would be better to issue the AT&K00 command beforehand
in order to get a quick connection.
V.42bis is an international data compression standard commonly used in modem communications.
This standard provides real-time data compression. The NETGEAR expertise in data compression
has been brought into its ISDN applications, which are much higher in speed than modem
communications.