How Does Dial Up Work?
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The Dial-Up Service Provider Sets up a Server
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Dial-up servers can be set up in a variety of configurations, ranging from small, one- or two-line community servers to commercial-grade servers that support hundreds of simultaneous connections. Because multiple customers will be passing considerable traffic at the same time, servers generally require substantial amounts of memory and processor cycles. Special server software answers incoming customer calls and binds the customer connection to an Internet connection.
The Dial-Up Server is Connected to the Internet
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When the dial-up server is set up, it must maintain a constant connection to the Internet so that connected customers may access the network at any time. These connections are generally established through a commercial-grade T1 or higher bandwidth Internet connection, commonly known as a "dedicated Internet" service line. Depending on the number of customers the dial-up company expects, multiple dedicated connections may be available to each server, and several servers may be active at the same time.
The Dial-Up Server is Configured to Answer Incoming Calls
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Once the server is set up, properly configured and connected to the Internet, it is ready to begin accepting incoming dial-up connections. The Internet service provider (ISP) who runs the servers purchases a special "hunt group" telephone service from the local telecommunication provider; this configuration allows customers to dial one telephone number and have the call routed to any available incoming telephone line. The number is distributed to customers who dial in to the servers with dial-up networking software.
Dial-Up Connections are Bound to the Internet
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When a customer uses dial-up networking software to connect to the Internet, the computer establishes a connection using a modem. The modem dials the service number provided and waits for an answer; when the server answers, the modem establishes a connection (using a process known as a "handshake") and obtains an Internet protocol (IP) address. The server software then binds--or connects--this address to the upstream Internet connection, allowing data packets sent from the dial-up customer's computer to reach the Internet and return to the correct computer.
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