The Point-to-Point Protocol, or PPP, is commonly used to establish a connection between two computers using a phone line. Many ISPs use PPP when providing customers with dial-up access, where it has largely superseded an older protocol known as SLIP.
PPP is a low-level communications protocol used between two connected hosts. PPP was designed to act as a layer 2 protocol for the TCP-IP protocol suite over synchronous modem links, as a replacement for the non-standard layer 2 protocol SLIP. However, other protocols can also be carried over PPP. (Layer 2 is the Data Link layer of the OSI model).
PPP also provides hooks for automatically configuring the network interfaces at each end (setting IP address, default gateway, etc.).
PPP is described by IETF RFC 1661. Numerous documents on PPP have been published through the RFC process since July 1990, including various authentication, encryption and compression methods and the use of PPP in conjunction with other network protocols
RFC 1994 describes CHAP, the challenge handshake authentication protocol which is commonly used when establishing dialup connections with ISPs.
See also HDLC