C-DOT HDSL Modem

C-DOT, or the Center for Development of Telematics has

created an HDSL modem for high-speed communication. The modem has four RJ11

ports, each of which can support bandwidth of up to 2 Mbps, aggregating to a

maximum of 8 Mbps. One benefit of this modem is that it uses standard two-wire

copper telephone lines for communication, making it very cost effective.

Moreover, the maximum length of this cable can be 4 km without using a repeater

in between for amplifying the signal.

On the input side, the HDSL modem connects to an E1

Interface, which has to be of 2 Mbps bandwidth. There are four such ports on the

modem, which are also called PCM ports. One HDSL modem has to be configured as

the central unit. It then automatically communicates with the remote unit and

establishes a link. The modem has an RS-232 interface to configure it by

connecting it to a PC. Since there are four separate 2 Mbps links, it has LEDs

to indicate the status of each.

This modem can be used for communication in networks spanning

large distances such as telephone exchanges or campus area networks.

Communication over each link in the HDSL modem is full-duplex, meaning both ends

can transmit and receive data at the same time.

Anil Chopra in Bangalore