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Point-to-point protocol (PPP) is a computer networking method for transmitting data between two computers or devices. PPP and its companion protocols are designed to bridge the gap between physical connections and more abstract network protocols like the Internet Protocol. It has advanced features designed to ensure quality, security, and performance. PPP is most commonly used for dial-up Internet connections, but can be used for other types of connections as well.
The most widespread computer networking protocols, the Transmission Control Protocol and the Internet Protocol (TCP/IP), rely on a lower physical networking layer for connectivity. These protocols were designed with traditional computer network technology like Ethernet in mind. This became a issue when computers began to be connected to one another in other ways. Unlike traditional networks where many computers are interconnected, serial connections and point-to-point links provide direct bridges between two machines. TCP/IP was not designed for this type of environment.
The point-to-point protocol solves this problem and allows TCP/IP to be used over point-to-point links. PPP “encapsulates” the individual units of data, called datagrams, produced by other network protocols. In their encapsulated form, datagrams travel over a point-to-point link and are then converted back to standard TCP/IP datagrams for travel across traditional networks. A common example is a dial-up Internet connection, where a customer’s computer generates standard TCP/IP traffic, encapsulates it using PPP and sends it across standard phone lines to an Internet Service Provider (ISP) server. At the ISP’s end, the encapsulated data becomes a standard datagram once more and can travel across the Internet.
Although the name implies a single protocol, the point-to-point protocol is reliant upon several companion protocols to operate. The Link Control Protocol (LCP) initiates and maintains PPP connections. Several protocols can be used for user authentication, including the Password Authentication Protocol (PAP), Challenge-handshake authentication protocol (CHAP), and the newer Extensible Authentication Protocol (EAP). Other protocols can enable encryption over a PPP connection or compress data to make the link more efficient. Two connections can even be joined together for greater bandwidth using the PPP Multilink Protocol.
As noted, dial-up Internet connections frequently use the point-to-point protocol as the basis for their operation. PPP was, however, designed to be flexible and can be used with other types of point-to-point connections. Internet connections over Integrated Services Digital Network (ISDN) systems sometimes use PPP, and Digital Subscriber Line (DSL) services uses a slightly modified version known as point-to-point protocol over Ethernet (PPPoE). PPP isn’t limited to TCP/IP either; it can encapsulate datagrams from many other networking protocols, enabling more advanced connections used in enterprise settings.