OSI REFERENCE MODEL

BY SANTHOSH G

BEFORE WE KNOW …

What is NetworkingNetwork RequirementsWhat is TopologyTypes of Topologies

What is Networking?

Networking means interconnection of 2 or more autonomous pc’s in order to share the information & resources with security that they can have communication among themselves.

And there are many techniques for making pc’s networked and also there are many network hardware to make it possible.

Network requirements

There are four things that must be present in the network.

two or more individual systems

something to share (ex: data)

a physical pathway or transmission medium

rules of communication or protocols

Topology

The physical layout of the networkClassified in to the following.

1. Bus topology 2. Star topology 3. Ring topology 4. Mesh topology

Among these first 3 are the commonly used.

APPLICATION

PRESENTATION

SESSION

TRANSPORT

NETWORK

DATA LINK

PHYSICAL

OSI MODEL

THE OSI MODEL

The Open Systems Interconnection (OSI) model was developed by the International Organization for Standardization (ISO) in 1983 to provide a conceptual model on which networks could be based.

In the process of developing this framework, the ISO established a vocabulary that assisted engineers worldwide by giving them a common set of words to use to describe concepts they already understood and took for granted.

Physical Layer Functions

Physical Characteristics of interfaces & media (deals with electrical & mechanical specifications)

Representation of bits (electromagnetic or optical) Data Rate (bits per sec.) Synchronization (Sender & Reciever clock) Physical Topology (Star, Bus….) Transmission Mode (direction of transmission

between 2 devices; e.g Half, Full between devices)

Data Link Layer Functions

Framing Physical addressing (MAC of

sender/reciever as Header) Flow Control (Matching the Speed) Error Control (FCS Trailor ) Access control ( Which device uses the

media)

Network Player Functions

Logical Addressing (IP addressing used for

the communication out of the network)

Routing (Packets are routed in the internetwork

to the final destination)

Transport Layer Functions

Service- Point or Port addressing( Port no. as header to segment)

Segmentation & re-assembly (sequence no. to segments when sending & replace the missing packets when recieves)

Connection control ( connectionless or connection oriented)

Flow & error control( applied over entire message & error correction is through retransmission)

Session Layer Function

Dialog Control (half duplex or full duplex between application processes)

Synchronization (incertion of checkpoints in the stream of data for recovery)

Presentation Layer Funtions Translation(sender dependent format

- common format – Receiver dependent format)

Encryption & decryption Compression & decompression(for

multimedia information)

Application Layer Functions when you use your Web browser,

that actual software is an application running on your PC .It doesn't really “reside” at the application layer. Rather, it makes use of the services offered by a protocol that operates at the application layer, which is called the HTTP Other e.g FTP, E-Mail etc

RESOURECES

N/W Devices Vs Layers

Repeater Physical Bridge Data Link Router Network Brouter Data Link and

Network Gateway Transport, Session,

Presentation and Application

Multiplexer Physical Switch Data Link

THANK YOU