IIT Madras develops direct Internet access system
The Times of India, December 18, 1999

The Telecommunications and Computer Networking Group (TeNeT) at IIT, Madras, in association with Chennai-based Banyan Networks, has developed a direct Internet access system (DIAS) that allows telecom service providers to provide high-bandwidth Internet access, simultaneously with voice services, without any changes to the existing cabling infrastructure.

And unlike current residential PSTN (public switched telephone network) and ISDN (integrated switched digital network) dial-up access, the DIAS provides an always-on Internet access that is permanently available at the customer's premises.

``We used digital subscriber loop (DSL) techniques to provide seamless voice and data connectivity to the customer over the same pair of copper wires,'' says Ashok Jhunjhunwala, head of TeNeT, as also the head of IIT Madras' department of electrical engineering.

Currently, an Internet subscriber has to use a modem to place a call over the telephone line to connect to the ISP. Besides, the system does not enable simultaneous use of the Internet and the telephone, and supports a maximum connection speed of about 56 kbps.

DIAS, on the other hand, obviates a modem. What it requires is a digital subscriber unit (DSU) at the customer's premises, which combines voice and Internet data packets on a single twisted-pair wire. And an integrated access node (IAN) at the service provider's premises, which separates the voice and data traffic from a number of subscribers and routes them independently to the PSTN and the Internet respectively.


The basic DSU, designed for the small office and residential Internet user, provides a permanent Internet connection at a maximum data bandwidth of 144 kbps, which drops to 80 kbps when the telephone is in use. The high bit-rate DSU, designed for corporate subscribers, provides voice connectivity for upto eight telephones and a permanent data bandwidth of upto 2 mbps, which drops by 64 kbps for each telephone that's in use.

According to Jhunjhunwala, the system is highly cost effective. It also avoids congestion in the trunk network of the PSTN that could be caused by long duration Internet calls. And what's more, if the ISP is in a distant city, the subscriber does not have to pay long distance call charges, as he does currently.

What's the principle on which DIAS works? Jhunjhunwala explains: Internet sessions are usually of a long duration, but do not generate continuous traffic. The data traffic is bursty and for most of the connection time, no data is transmitted or received. And even when data is transmitted, it rarely uses more than 10-15 per cent of the available bandwidth. Nonetheless, the PSTN connection is always on, utilising the resources continuously.

What DIAS does is to occupy the PSTN resources only to the extent that is required by the subscriber data. It first separates Internet data traffic from voice traffic and then, through a technique called traffic aggregation, combines and concentrates Internet data from multiple subscribers. This concentrated data is then carried to the ISP through leased or switched circuits.

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