| The Point-to-Point Protocol (PPP) provides a standard method for transporting multi-protocol datagrams over point-to-point links. PPP was originally emerged as an encapsulation protocol for transporting IP traffic between two peers. It is a data link layer protocol (layer 2 in the OSI model) in the TCP-IP protocol suite over synchronous modem links, as a replacement for the non-standard layer 2 protocol SLIP. However, other protocols other than IP can also be carried over PPP, including DECnet and Novell"s Internetwork Packet Exchange (IPX).
PPP is comprised of the following main components:
In order to establish communications over a point-to-point link, each end of the PPP link must first send LCP packets to configure and test the data link. After the link has been established and optional facilities have been negotiated as needed by the LCP, PPP must send NCP packets to choose and configure one or more network-layer protocols. Once each of the chosen network-layer protocols has been configured, datagrams from each network-layer protocol can be sent over the link. The link will remain configured for communications until explicit LCP or NCP packets close the link down, or until some external event occurs (an inactivity timer expires or network administrator intervention). |
| Protocol Structure - PPP (Point to Point Protocol) Frame |
| The LAPF is the same as the LAPD with the following address field: |
| 8 bits | 12 bits | 24 bits | 40 bits | Variable | 16-32 bits |
| Flag | Address | Control | Protocol | Information | FCS |
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Related protocols:PPPoE, PPPoA, SLIP, CHAP, PAP, HDLC, LCP, NCP, IPCP, L2TP, IP, IPX, DECnet
Sponsor Source:PPP is defined by IETF (http://www.ietf.org) RFC1661 with an update RFC2153.
Reference:http://www.javvin.com/protocol/rfc1661.pdf: The Point-to-Point Protocol (PPP)
http://www.javvin.com/protocol/rfc2153.pdf: PPP Vendor Extensions
