The Point-to-Point Protocol (PPP) is a data link protocol generally used in establishing a direct connection between two networking systems. It can give connection authentication, compression, and transmission encryption (having ECP, RFC 1968).
PPP is used over many kinds of physical networks adding serial cable, trunk line, phone line, cellular telephone, specialized radio fiber optic, and links such as SONET. PPP is also used over Internet access connections. Internet service providers (ISPs) have needed PPP for customer dial-up access to the Internet, since IP messages cannot be transmitted over a modem line on their own, without message data link protocol. Two encapsulated parts of PPP, Point-to-Point Protocol over ATM (PPPoA) and, Point-to-Point Protocol over Ethernet (PPPoE) are used most generally by Internet Service Providers (ISPs) to connect a Digital Subscriber Line (DSL) Internet service connection with users.