DSL Network Guide Chapter 10: Authentication

Authentication is done through various kinds of protocols. A protocol is a set of rules a system excpects. If I were writing a video game that saves the characters information I might write a protocol that dictates the save file look like this: name, hit points, class, items. So the save file might say Golthar, 145/205, barbarion, aegis. As long as the save file follows my protocol then the game will be able to load up the profile correctly.
The most common form of authentication used with DSL is through a protocol called PPPoE, point-to-point protocol over ethernet. PPPoE is an extension of the PPP protocol used for dial-up. I think to better understand PPPoE it help to understand PPP a little bit.
Windows 95 and above had PPP built into via dial-up networking. A dial-up networking connection needed three pieces of information, your username, password, and phone number to dial. The phone number was dialed via the phone lines. On the other end of the phone was another modem connected to a computer. Once the call was completed the two modems would negotiate what was going on via the PPP protocol. This is reffered to as the handshake is what all those screaching noises is about. Once the two have agreed on how to communicate your computer hands over your username and password passed through the modem to the other computer. Once that is verified as correct you are online.
PPPoE is very similair to this. The "handshake" is done when you turn on your modem. The modem and the LT card in the CO establish a connection together. Now here's where PPPoE comes in. Windows 95 - Windows ME do not have PPPoE built into it so more software needs to be installed. This usually comes in the form of RASPPPoE, Enternet 300, or others. Windows XP has this built in as part of dial-up networking. All the PPPoE client needs is your username and password. It passes this through the modem on to the servers on the other end. If they are validated then the machine running the PPPoE software is given an IP address. DSL connections with PPPoE are not a true always on connection.
DHCP is usually used for static customers. With this format the NIC card or router has your static IP information programmed into it. It hands this off and the servers then assign you your static IP.
Other forms such as PPPoA are used also but are not common and are usually being fazed out.

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