Quick Start Manual

Reference Guide for the Model XM128 ISDN Digital Modem
G-2 ISDN Reference
Basic Rate Interface
When you order a Basic Rate Interface (BRI) ISDN line, you receive what is known as the 2B+D
service. This service provides two B channels that can transmit at 64 Kbps per channel for user
information and a D channel that can communicate between the user and the ISDN network at
16 Kbps.
The D channel is used to manage communication between the equipment and the switch. It is used
mainly to exchange signal messages with the switch and to set up and release calls. In most cases,
if there is any incompatibility issue raised, it is the D channel signaling protocol that is causing the
problem. The Model XM128 modem does not allow the user to use the D channel for sending and
receiving user data.
Out-of-Band Signaling
Some switches transmit all the network signals through the D channel, freeing both B channels to
be used exclusively for your communication. This arrangement allows a throughput of 128 Kbps
(64 Kbps per channel). However, not all switches support out-of-band signaling at this time. For
the switches that do not support out-of-band signaling, network signals are transmitted through B
channels only, which reduces the bandwidth to 56 Kbps.
The Model XM128 modem currently supports the following switch types and D channel protocols:
• DSS1
• 1TR6
• AT&T 5ESS Custom and National ISDN-1 protocol
• Northern Telecom DMS-100 Custom and National ISDN-1 protocol
• Siemens EWSD National ISDN-1 protocol
• Rate Adaption & B channel protocol
The Model XM128 modem currently supports the following protocols:
• V.120
•X.75
• V.110
• Asyn-to-sync PPP and PPP/MP