Switching in India

In India, the first private telephone line was set up in 1875, between the post office at Steam Navigation Company at the Mazgaon dockyard and the Fort Area office in Bombay. The instrument was operated through alphabets instead of numerals. In November 1881, licences were granted to private companies to operate telephone systems in Madras, Calcutta, Bombay, and Rangoon. Calcutta was the first city to have a telephone exchange in India, when in 1882, a 50-lines Siemens exchange was installed in the city. The Bombay telephone exchange was opened later. By that year, there were five telephone exchanges connecting 244 phones.

By 1899, there were about 50 telephone exchanges with 33,000 lines owned by private companies and the government. The first automatic exchange was commissioned at Shimla in 1913 with a capacity of 700 lines with 400 working connections. By 1890, the telegraph and the telephone started serving the needs of the Railways. In 1943, the government exercised its option to purchase the assets of the telephone companies. At the dawn of independence, there were only 321 exchanges with a capacity of about 0.1 million lines with 86,000 working connections.

Common control switching was introduced in India in the mid-1960s. Crossbar accounted for 15 percent of the local network. The imported Penta Conta crossbar system in India did not give satisfactory performance. Basically, the system was designed for traffic conditions in Europe, where calling rates are low in view of the large number of telephones. A task force of telecommunication experts, set up in 1971 (when about 1,00,000 lines of crossbar exchanges had been commissioned in the network), found various defects in the system and suggested solutions to improve the performance. The task force found solutions to all the problems. The equipment produced in ITI from 1974 incorporated the improvements. It was also decided to upgrade all crossbar exchanges on the line suggested. This was a slow process, as work had to be done while the exchanges were in operation. To assess the solutions, a 2,000-line exchange was built incorporating the improvements and was commissioned in Delhi in 1975. Known as Janpath-IV it has functioned in a busy area, with a 3 percent failure rate as against 30 percent failure of local calls occurring earlier in a similar exchange.

However, re-design of the system itself was called for. It was found that the Penta Conta crossbar system was highly vulnerable to traffic overload and tended to break down under its impact. There were inadequacies in the interworking of the various devices of the common control equipment. For example, the rated capacity of a pair of line markers in a Penta Conta exchange to put through calls was only 600. But in practice, 16,000 calls were to be handled by a pair of line markers. With a view to re-designing the system, the Indian Crossbar Project (ICP) was set up in 1974 with a term of four years. It was to design a local exchange and a trunk automatic exchange suitable for Indian conditions. A 2,000-line local exchange of ICP design and a 1,000-line trunk automatic exchange were developed.

In India, the first experimental Stored Programme Control (SPC) electronic exchange was put into service in Delhi in November 1974. The first public local exchange known as SPC-1 switching system was set up in New Delhi in the late 1970s to evaluate the new system. The SPC makes a telephone exchange “think”. In other words, the SPC system is similar to the manual exchange, except that a machine that can perform superhuman feats has replaced the operator. Just one unit performs the function of digit storage, path selection, and translation for the entire exchange.

The country’s first factory to make digital electronic switching equipment has been set up at Mankapur in Gonda district in Uttar Pradesh, as a branch of the Indian Telephone Industries Ltd (ITI). The factory, which had an annual capacity of 5,00,000 lines, was built in technical collaboration with a French firm, Alcatel-Thomson. The Indian factory was based on the firm’s fully digital E-10 B design and the software of the system was adapted to Indian conditions and traffic demands. 

The Centre for Development of Telematics (C-DOT) was set up in India to develop advanced communication technology and products indigenously, to digitize India’s telephone network and prepare for the Integrated Service Digital Network (ISDN). C-DOT has designed and developed a family of digital electronic switching systems for a variety of telecommunication

applications–local, trunk tandem, and a combination of them for rural as well as urban areas. The systems focus on typical Indian conditions such as high-traffic loads and low-telephone density, busy-hour attempts, high-temperature and dusty environment, and power supply problem. C-DOT’s PABX technology was made available to local manufacturers making MAX-M and MAX-L switches. The ITI marked the XL and other exchanges. C-DOT switches handle over a third of the country’s telecommunication network including PABXs. C-DOT’s rural automatic exchanges have been installed in Bangladesh, Vietnam, Russia, Yemen, Nigeria, and Nepal.