Point-to-Point Protocol - A Brief Introduction

Promoted by Internet Engineering Task Force (IETF) in 1994, PPP i.e. Point-to-Point-Protocol is a protocol that is used in computer world to establish a connection between two peers or nodes facilitating transmission of IP packets i.e. datagrams over serial communication lines. This protocol is mainly related to the Data Link layer (second layer) of OSI-ISO Model and is also designed and developed in a generic manner to support the Network Layer (third layer) of OSI Model.

This protocol provides connection over both synchronous and asynchronous data communication lines. PPP protocol was developed to incorporate almost all the points/facilities provided by the earlier protocols like SLIP, HDLC (High-Level Data Link Control Protocol), X.25 etc. along with which it also included few more new features.

The Point-to-Point-Protocol mainly cover/support the following main components:
1) Link Control Protocol, which is developed in a generic way with compatibility with wide range of environment. Link Control Protocol can handle various types and sizes of datagram packets and manage the link with facilities such as testing, error-correction in links, authentication and operation verification intelligence.
2) Network Control Protocols (extensible Link Control Protocol) such as Ipv6CP, MUXCP, and IPXCP etc. for establishing, configuring and managing the connections.
3) Encapsulation intelligence for encapsulating datagrams.

First, the Link Control Protocol packets are sent in order to establish and configure the data link between the systems that want to establish Point-to-Point link. Once the necessary setting for LCP is done, Network Control Protocol packet is sent to configure the network-layer protocols, after which the link gets established and systems can start communication. In order to close the link, either LCP or NCP packet should be sent.

Point-to-Point-Protocol Structure:

Flag bits - 8
Address - 16
Control Binary Sequence - 24
Protocol - 40
Data/Information (Variable Bits) - Variable bits
Frame Check Sequence - 16-32 Bits

* Flag field contains a binary sequence (1 byte) that indicates beginning/end of a frame.
* Address field contains a binary sequence (1 byte) as a standard broadcast address.
* Control field contains a binary sequence (1 byte).
* Protocol field is around 1-2 bytes and contains setting for the protocol in data field.
* Information field may or may not contain data in it.
* FCS i.e. Frame Check Sequence is of a length from 2 to 4 bytes and is used for error detection and correction.

Basic Features of Point-to-Point-Protocol:
1) It is very easy to configure and manage. Point-to-Point-Protocol has intelligent self-configuration mechanisms, which use Link Control Protocol.
2) Multilink Point-to-Point-Protocol is used to provide extra bandwidth between the systems using multiple links.
3) Point-to-Point-Protocol is compatible and can run on any full-duplex link.
4) PPP can be used to multiplex various protocols over the same line.
5) PPP supports (or is compatible with) various other protocols and environment such as Ethernet (Point-to-Point Protocol over Ethernet - PPPoE), ATM (Point-to-Point Protocol over ATM - PPPoATM) and Packet over SONET/SDH - PoS.
6) PPP supports various Compression methods.
7) Point-to-Point Protocol supports Encapsulation of packets.
8) PPP has features like automatic self-configuration, looped link detection, authentication, error detection and correction etc.

(Please NOTE: Above enlisted features is not the complete list of features of Point-to-Point Protocol, but a list of prominent features of the same.)