The international telecommunication network in Iran is currently based on two digital International Switching Centers (ISCs). Iran's second ISC with a capacity of 12,260 ports was established in 1996 in Tehran (the first ISC is also in Tehran). According to TCI's annual report, in 1997, the two ISCs had a total capacity of about 22,000 ports, 7,600 incoming trunks from the national network, and 3,900 both-way outgoing trunks. A third ISC is expected to be established in Shiraz in the near future which would increase the total capacity by about 9,840 ports.
Through the development and expansion of ISCs, the number of international circuits has clearly increased. In 1991, there were only about 1,854 international circuits in Iran. This number reached 7,021 in 1996, which shows about 279% increase in the period of five years. The total number of international circuits by March 1999 (end of the Iranian year 1377) was 7,937. Table 3.6 shows the number of international circuits in Iran.
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Moreover the number of network centers with international channels was 604 in 1997, which increased by about 24% to reach 750 centers in 1998.
Iran currently uses No. 5 and CCS7 (Common Channel Signaling System No. 7, also known as C7) signaling systems to establish direct and transit routes with different countries. These routes are established through Shahid Ghandi, Isfahan and Boumehen satellite earth stations, Iran-UAE submarine cable, Trans-Asia-Europe (TAE) optical fiber lines and terrestrial microwave links.