dial up connections
A dial-up connection is a fixed Internet connection that uses a voice band modem and telephone lines to transport data between your computer and your ISP. When you used dial-up connection, your computer's modem places a regular telephone call to your ISP. When the ISP's computer answers your call, a dedicated circuit is established between you and your ISP- just as though you had made a voice call and someone at the ISP had picked up the phone and answered it. The circuit remains connected for the duration of your call and provides a communications link that carries data between your computer and the ISP. As your data arrives at the ISP, a router sends it out over the Internet.
When your computer is connected to your ISP over a dial-up connection, data is transmitted over the same frequencies normally used for voice conversations. If you have only one telephone line, you cannot up your telephone receiver, dial your friend, and carry on a voice conversation while you are sending data. Some modems use technologies similar to call waiting that allows you to remain connected to you ISP and temporarily suspend data transfers while answering a voice call.