The low-cost system, based on IIT's wireless in local loop (WLL) technology, uses radio frequency waves instead of cables to send and receive signals. It has already been shown to provide high-quality phone services in Chennai.

The WLL system is cheaper than wired lines and provides Internet access at 35 kilobytes per second (KBPS). It can be upgraded to provide access at 70 KBPS and does away with the problem of telecom network congestion, professor at IIT's department of electrical engineering, Ashok Jhunjhunwala, said.

The system was unveiled during the science congress in Chennai in January where it provided instant telephone and Internet access to the participants over the entire Anna University campus. Its details were reported at recent conference on communications technologies here.

TheMahanagar Telephone Limited (MTNL) has placed orders for two trial systems in Delhi and Mumbai, according to scientists who demonstrated the system.

It allows the subscriber to connect to any telephone or fax machine. Internet access is provided without the need for a modem by directly connecting the personal computer (PC) to WLL subscriber terminal.

The system incorporates a remote access switch (RAS) which helps reduce congestion in the network and call charges while the net is being accessed.

In current systems, an Internet user blocks the line from the time he connects and browses the net to the time he downloads the required text.

Internet calls are of long duration, and each of them holds up the circuit from the subscriber all the way to the Internet service provider (ISP), Jhunjhunwala explained.

This results in congestion in the trunk route between the subscriber's exchange and ISP's exchange which is designed for short-duration voice (telephone) traffic.

Also, the subscriber pays thetelecom charges for the duration of the call. In the WLL system, the subscriber is connected to the RAS which is linked to the Internet service provider. All calls from the Internet subscribers terminate at the RAS which is placed at the subscriber's exchange.

The RAS multiplexes or simultaneously transmits several data over a single carrier, reducing the trunk network congestion considerably.

Since the trunk network is not used by the subscriber and the call terminates at the RAS itself, the call charges for Internet access can be reduced, Jhunjhunwala said. An additional advantage with the IIT's WLL system is that the line is free to make and receive telephone calls even when the Internet is being accessed, he said.

However, if the RAS is used with conventional wired lines, voice calls cannot be made or received when Internet access is going on. IIT's indigenous RAS costs far less than imported products available today, Jhunjhunwala said.

He said the IIT system can be deployed in urban areas withhigh subscriber density, as well as sparsely populated rural areas with low subscriber density. It is weather-proof and easy to instal and maintain.

IIT's WLL system is based on digital European cordless phone technology devised by the European Telecommunications Standards Institute.

It comprises a control system called DECT interface unit (DIU) that interfaces with the local exchange; base stations that transmit signals; wall sets that receive signals from the base station; and the suer hand sets. The telephone, fax or modem can be connected to the wall set.

Each system consists of one DIU linked to up to 20 base stations, which are in turn connected to 1000 wall sets. For Internet connection, each DIU is linked to two RAS which are connected to four or five subscribers. The RAS maintains a consolidated link with the ISP.