Netgear XM128 ISDN User Manual download pdf (Page 147)

Reference Guide for the Model XM128 ISDN Digital Modem

ISDN Reference G-3

The B channels are used for carrying user communication information, which can be data,

voice, or fax. Voice and analog data must be sent on the B channels. Unlike the asynchronous

communications between most PCs and your Model XM128 modem, the B channel operates

in synchronous mode. In order to convert the asynchronous communication to synchronous

communication, it is necessary to use a Rate Adaption Protocol.

In North America, the V.120 Protocol is the most popular Rate Adaptation Protocol used. The

V.120 Protocol is an ITU-T protocol that supports synchronous and asynchronous rate adaption

and provides link-layer error control. NETGEAR also implements V.42bis data compression on

top of V.120, allowing the user to achieve even higher data communication throughput.

The Model XM128 modem also supports high-level data link control (HDLC) asynchronous to

synchronous conversion from Point-to-Point Protocol (PPP). This protocol is very popular for

Internet access and remote access applications.

Currently, most of us still use plain old telephone service (POTS) for our regular communication

needs. The Model XM128 modem provides two POTS ports (PHONE 1 and PHONE 2) for you to

connect analog devices; this feature lets you continue to use analog communications. You can

connect phones, fax machines, or analog modems to the PHONE 1 and PHONE 2 ports, while

using one of the idle B channels (even if the Model XM128 modem is busy doing data

communications).

Terminal Adapter or Digital Modem

A terminal adapter (TA) allows users to send and receive data over the ISDN network. You can

send and receive both data and voice simultaneously by using both B channels. The PHONE 1 and

PHONE 2 ports in the Model XM128 modem allow you to connect analog devices to the modem

to make outgoing calls as well as to receive incoming calls. With its auto-detect feature, the

Model XM128 modem monitors incoming calls from both analog and digital devices. It monitors

these calls without user intervention and makes connections accordingly.

ISDN Basic Rate Interface Points

In the interest of supporting deregulated Customer Premises Equipment (CPE), the exchange

Carrier Standard Association in the United States established a basic rate transmission standard for

CPE. The standards are defined for equipment to connect to different reference points of the ISDN

link. Some of these reference points are S, T, and U. They have very specific definitions and

provide standard interfaces for equipment connected to them.

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Netgear XM128 ISDN User Manual Page 147