This indigenous telecom technology has been developed by researchers at the Telematics and Optical Communication laboratory at the IIT jointly with the Chennai-based Midas Communication Technologies Limited and the US firm Analog Devices. It eliminates the need for copper wire in the local loop, bringing substantial savings in rendering a telephone connection.

Based on the digital enhanced cordless telecommunications (DECT) standard, the state-of-the-art system operates in the bandwidth of 1800 MHz to 1900 MHz. For urban, suburban or rural applications, it offers wireline voice quality and integrates seamlessly with the existing public switched telephone network (PSTN). The system serves subscriber densities from one to 10,000 subscribers per square kilometre. It can be upgraded to 64 kb/s data transmission and is capable of being integrated to digital network. The prices range from Rs.11,000 to Rs.16,000 per line compared to the Rs.35,000 per line cost of a wired system.

According to Prof. Ashok Jhunjhunwala, head of the Telematics department at IIT and a driving force behind the technology, every telecom network has three parts -- backbone network, the exchange and the local loop (cabling from exchange to receiver). Together, these three components cost around Rs 28,000 (at Rs 5,000, Rs 8,000 and Rs 15,000 respectively). "If infrastructure costs (estimated at about Rs 4,000) are added, we get a figure of around Rs 32,000," he says. The coverage area of CorDECT ranges from 5 kilometres to 10.5 kilometres line-of-sight. It can also be configured to cover a range of more than 25 kilometres in sparsely populated areas. "This totally indigenous design and development can help India catch up with the rest of the globe in the telecom area," says a confident Prof. Jhunjhunwala.

Explaining each segment of the telecom network, the IIT professor says costs in both backbone network and exchange technology has come down substantially, thanks to breath-taking advances in telecom technology. The cost of providing a local loop, however, remains quite high, particularly because of the expensive copper wire, which is getting dearer every year. The solution, the IIT team has to offer is the total replacement of copper wireline in the local loop by radio signals, which will carry data and voice over a reasonable distance.

"This can be done by fixing a base station, either on top of a building or on a street pole. The station is still connected by wire to the exchange but the station transmits on wireless to the subscriber. Around 150-200 subscribers can be served by the station this way. Each telephone line of this sort would cost around Rs.10,000."

The professor observes that if a goal of, say, 100 million telephone subscribers was to be met so that India could keep abreast with the communications revolution, it was essential that more economical means of installing a telephone line be found. This exciting work of Prof. Jhunjhunwala has already been noticed and has fetched him the Shanti Swarup Bhatnagar Prize for 1998.

"In the West, installing a line costs about $800, which is not too expensive for them. So they do not have to bother about such technology. But the tragedy in India is that we think that because no one in the West has done anything about it, nothing need be or can be done," he says. The experimental telephone exchange launched at Adayar, a Chennai suburb, has, by all accounts, vindicated Prof. Jhunjhunwala and his team; they have already shipped the technology to France, China, Brazil and Indonesia, among other countries.

Each CorDECT system comprises one DECT interface unit (DIU), 20 compact base stations (CBSs) and up to 1000 wall or hand sets, with each CBS serving 30 to 70 subscribers. The DIU interfaces with the PSTN via E-1 digital links on one side and the CBSs or base station distributor (BSD) via twisted pair copper on the other. The network management system (NMS) manages the DIUs and subscribers connected to them. The NMS connects to the PSTN via an E-1 link, which provides an X.25 64 kb/s channel for every DIU that it manages.

"CorDECT is based on a microcellular architecture," says a senior director at Midas. "The major difference between GSM, Japan's personal handphone system or DECT systems and CorDECT is that CorDECT is extremely cost-effective and can be deployed in different scenarios. More than anything else, it can offer high-speed data transmission facilities, Internet access, ISDN services, all at very reasonable rates."

To expand an existing urban telephone network, an operator can customise the configuration of CorDECT depending on whether the operator wishes to add a few hundred subscribers in a radius of 4 kilometres to 5 kilometres or cover a larger area. A cluster of about eight CBSs are placed on a tower on top of a tall building, and they are connected through copper cables with the DIU located in the same building.

The wall-sets can be mounted with antennas on the window or rooftop to serve subscribers in the required radius. Similarly, new operators can cover a large area by linking clusters of CBSs with four or five DIUs through fibre-optic cable or point-to-point 8-Mb/s radio links. In sparsely populated areas, the CorDECT can be economically deployed using the relay base station (RBS), which is an IIT-patented technique. A DIU and a CBS cluster could serve subscribers in a 30-kilometre radius using the RBS. Like any digital switch, the system also supports supplementary services such as pay phones, call identification, ringback facility and group hunting.

Together with Midas, Banyan and Vembu – three technology firms launched by IIT alumni, the IIT team is also doing extremely interesting work in areas like Digital Internet Access Systems (DIAS). Those who do not have a leased line are painfully aware of the glitches in dialling up the Internet Service Provider (ISP).

According to Prof. Jhunjhunwala, widespread deployment of Fibre in the Local Loop (FiLL) network "holds the promise of providing permanent Net access at affordable cost". Banyan has also developed a solution to multiplex calls from subscriber to the ISP. This reduces line congestion, he said.

"We have the people who can come up with the necessary hardware and software for work of this sort. They are already doing it for companies abroad. If they can do it for India, we can really make telecom technology cost-effective, something that is very important in India," the professor says.