Integrated Services Digital Network (ISDN) is a set of communication standards which is used for digital transmission of voice and data over a digital line. These digital lines are commonly telephone lines and exchanges which are established by the government. This was a common high-end Internet service in 1990’s and in early 2000’s. It was offered by many ISPs as an alternative to dial-up Internet access. The first ISDN was defined by the CCITT organization, now called as ITU-T (International Telegraph and Telephone Consultative Committee) in 1988.