In Computing, the Point-to-Point Protocol, or PPP, is commonly used to establish a direct connection between two Node (networking). Its primary use has been to connect computers using a phone line, though it is also occasionally used over Broadband connections (as PPPoE or PPPoA). Many internet service providers use PPP when providing customers with dial-up access (e.g. to the Internet, where it has largely superseded an older protocol known as Serial Line Internet Protocol).

PPP is commonly used to act as a OSI model (the Data Link layer of the OSI model) protocol for connection over synchronous and asynchronous circuits. PPP was designed to work with several network layer protocols, such as Internet Protocol, IPX and AppleTalk, and as a replacement for the non-standard layer 2 protocol Serial Line Internet Protocol.

PPP was designed much later than the original HDLC specifications. As a result, the creators of PPP included many additional features that had not been seen in WAN data-link protocols up to that time.

=Enhanced error detection=

PPP uses Frame Check Sequence fields to determine if an individual frame has an error; however, PPP monitors the frequency with which frames are received in error,

=Looped link detection=

LCP (Link Control Protocol, an integral part of PPP and defined in the same RFC) notices looped links using a feature involving Magic number (programming). When using PPP, the endpoint sends PPP LCP messages; these messages include a magic number which is different on each end point. If a line is looped, the end point receives an LCP message with its own magic number instead of getting a message with the other peer s magic number. R

=Other PPP features=

PPP provides hooks for automatically configuring the network interfaces at each end (setting an IP address, default gateway etc.) and for authentication: Password authentication protocol and Challenge-handshake authentication protocol.

While both PPP and Dynamic Host Configuration Protocol offer support for automatic configuration of interfaces, DHCP is more widely used nowadays but lacks ability to authenticate users.

PPP is described by Internet Engineering Task Force 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 Challenge-handshake authentication protocol, the Challenge Handshake Authentication Protocol which is commonly used when establishing dialup connections with ISPs.

RFC 2516 describes PPPoE, a method for transmitting PPP over Ethernet which is sometimes used with Digital Subscriber Line.

RFC 2364 describes PPPoA, a method for transmitting PPP over Asynchronous Transfer Mode Adaptation Layer 5 (AAL5) known as or PPPoATM for PPP over ATM.

=PPP frame=

Name Number of bytes Description Flag 1 indicates frame s begin or end Address 1 broadcast address Control 1 control byte Protocol 2 setting of protocol in data field Data variable (0 or more) datagram FCS 2 (or 4) error correction sum

=Multilink PPP=

Multilink PPP can connect multiple links between two systems as needed to provide extra bandwidth. Remotely accessing resources through PPP Multilink allows for the increase in overall throughput by combining the bandwidth of two or more physical communication links such as analog modems, ISDN, and other analog/digital links. PPP Multilink is based on Internet Engineering Task Force (IETF) standard RFC 1990 (obsoletes RFC 1717).

=RFCs=

=See also=