OSI Reference model<br /><ul><li>OSI: OPEN SYSTEM INTERCONNECTION
The purpose of the OSI model is to open communication between different systems without requiring changes to the logic of the hardware and software.
Is a set of protocols that allows any two difference system to communicate regardless of their underlying architecture. </li></li></ul><li>4<br />The OSI model is a layered framework for the design of network systems that allows for communication across all types of computer systems. <br />It consists of seven separate but related layers, <br />APPLICATION LAYER<br />PRESENTATION LAYER<br /> SESSION LAYER<br />TRANSPORT LAYER<br />NETWORK LAYER<br />DAT LINK LAYER<br />PHYSICAL LAYER<br />
INTRODUCTION TO PPP:<br /><ul><li>In networking, the Point-to-Point Protocol, or PPP, is a data link protocol.
PPP is commonly used in establishing a direct connection between two networking nodes. It can provide connection authentication, transmission encryption privacy, and compression.</li></ul>WHY POINT TO POINT:<br />When computer is connected to ISP via the modem, the<br />ISP and the computer made the two common points on<br />the network and hence the protocol which operates<br />between these 2 points is called Point to Point protocol. <br />5<br />
SLIP (Serial Line IP) v/s PPP:<br /><ul><li>SLIP was used as framing protocol over serial lines before the advent of PPP.</li></ul>SLIP has some deficiencies:<br /> SLIP does not have error detection mechanism (left to TCP to detect and recover from errors<br /> on the transmission line).<br />SLIP only supports IP (no other layer 3 protocols).<br />SLIP does not provide dynamic IP address assignment.<br />4. SLIP does not provide authentication.<br />6<br />
<ul><li>PPP was devised in order to overcome the deficiencies of SLIP.</li></ul>PPP features:<br />PPP affords error detection (checksum).<br />PPP allows to dynamically assign an IP address (NCP).<br />PPP provides authentication (PAP / CHAP)<br />PPP is a symmetric protocol: The 2 parties in a PPP session are the initiator (I, usually client) and the responder (R, usually server).<br />7<br />
Functions of PPP:<br />PPP is widely used , especially in analog modem<br />access to ISP, where one end is PC and another end<br />is ISP router the functions performed are:<br />The PPP was designed to transport multi-protocol packets between two peers connected by simple links.<br />These links provide Full-Duplex simultaneous bi-directional operation.<br />8<br />
The PPP allows different types of protocols to function<br />on its platform and on the same link. <br />They are:<br />LCP(Link Control Protocol)<br /><ul><li> Used for establishing the link.
Allows to negotiate link options:</li></ul> >Authentication protocol to be used.<br /> >Header compression / address field compression.<br /> > MRU (maximum receive unit).<br /><ul><li> Periodically test the link (LCP Echo request / reply).
Bring down the link gracefully when no longer in use. </li></ul>9<br />
2. NCP(Network Control Protocol)<br /><ul><li> Dynamic assignment of IP address.
Dynamic assignment of DNS primary and secondary server.
The host must set a default route to the PPP interface since there is no default gateway IP address (the link is point-to-point with no IP address = unnumbered).</li></ul>10<br />
The PPP provides three methods of authentication:<br />Password Authentication Protocol(PAP):<br /> Uses a password to authenticate.<br />2. Challenge Handshake Authentication Protocol(CHAP): Which uses the handshake of the server with the dial up as an authentication. <br />3. Extensible Authentication Protocol (EAP): <br /> Is most commonly used for authentication on wireless networks.<br />11<br />
Difference between PAP and CHAP:<br />12<br />
Flag - Indicates the beginning or end of a frame, consists of the binary sequence 01111110.<br />Address - Contains the binary sequence 11111111, the standard broadcast address. (Note: PPP does not assign individual station addresses.)<br />Control - Contains the binary sequence 00000011, which calls for transmission of user data in an unsequenced frame.<br />Protocol - Identify the protocol encapsulated in the information field of the frame.<br />Information - Zero or more octet(s), contain the datagram for the protocol specified in the protocol field.<br />FCS - Frame Check Sequence (FCS) Field, normally 16 bits. By prior agreement, consenting PPP implementations can use a 32-bit FCS for improved error detection.<br />14<br />
Byte Stuffing<br /><ul><li>For “data transparency”, the data field must be allowed to include the pattern <01111110> ; ie, this must not be interpreted as a flag.
To alert the receiver, the transmitter “stuffs” an extra < 01111101> byte after each < 01111110> data byte.
The receiver discards each 01111101 after 01111110, and continues data reception .</li></li></ul><li>PPP Operation:<br />16<br />UP<br />OPENED<br />DEAD<br />ESTABLISH<br />AUTHENTICATE<br />FAIL<br />FAIL<br />SUCCESS<br />TERMINATE<br />NETWORK<br />CLOSING<br />
Sequence Of Operations Is Shown Below:<br /> USER<br />17<br />ROUTER<br />CONFIGURE - REQUEST(LCP)<br /> CONFIGURE - ACK(LCP)<br />CONFIGURE – REQUEST IP(NCP)<br /> CONFIGURE – ACK IP(NCP)<br /> IP DATA PACKETS<br /> TERMINATE REQUEST(LCP)<br /> TERMINATE – ACK(LCP)<br />
Application of PPP:<br />PPP (Point to Point Protocol) is very popular: used in dial up connection between residential Host and ISP; <br />On SONET/SDH connections.<br />PPP is extremely simple (the simplest in the Data Link protocol family) and very streamlined. <br />18<br />