Dial-Up IP

Dial-Up IP

CSNET member sites that used the Internet infrequently could not justify the cost of a leased line connection. For such sites, CSNET developed a dial-up IF' system that worked as expected: whenever a connection was needed, software at the member's site used a modem to form a connection to the CSNET hub over the voice telephone network. A computer at the hub answered the phone call and, after obtaining valid authorization, began to forward traffic between the site and other computers on the Internet. Dialing introduced a delay after the first packet was sent. However, for automated services like electronic mail, the delay was unnoticeable.

Dialup internet access provides another example of a point-to-point network. From the TCP/IP view, dialing a telephone call is equivalent to running a wire. Once the call has been answered by a modem on the other end, there is a connection from one computer directly to another, and the connection stays in place as long as needed.