osi networking

Seven Layer of OSI Model

OSI reference model

Open System Interconnection (OSI) represents a generalization of concept of inter-process communication so that any open system may be technically able to communicate with another open system.

In the OSI reference model, the communication functions are divided into a hierarchy of seven layers. It also referred to as 7-layer model.

The transmission medium is not included in the seven layers and it can be regarded as 0th layer.

Layer Architecture of the OSI Reference Model

The Application Layer the seventh layer in

OSI network model.

Application Layer is the top-most layer of

the seven layered Open Systems

Interconnection (OSI) network model.

As the highest layer in the OSI model, the

application layer provides services to the

user of the OSI environment.

Application Layer•Login , password checking, file transfer

are some of the functions of the

application layer.

•. Real traffic data will be often

generated from the Application Layer.

This may be a web request generated

from HTTP protocol, a command from

telnet protocol, a file download request

from FTP protocol etc.

The purpose of the presentation layer is to present the information to communicating application entities in a way that preserves the meaning while resolving the syntax differences.

There are three syntactic version of data being transferred, the syntax used by the application entity of the originator of the data, the syntax used by the recipient of the data, and the “transfer” syntax used to transfer the data between presentation entities.

Application layer

Presentation layer

Transfer syntax

Local syntaxLocal syntax

Local and transfer syntax of the presentation layer

The purpose of the session layer is to

provide the means necessary for the

cooperating presentation entities to

organize and synchronize their data

exchange.

The session layer provides two-way

simulaneous, two-way alernate, and

one-way communication services.

Transport layer provides transparent

transfer of data between end systems,

or hosts, and is responsible for end-to-

end error recovery and flow control. It

ensures complete data transfer.

Layer 4 Transport examples include

SPX, TCP, UDP.

Network layer

Network layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing,internetworking, error handling, congestion control and packet sequencing.

Layer 3 Network examples include AppleTalk DDP, IP, IPX.

Data link layer

At this layer, data packets

are encoded and decoded into bits.

The data link layer is divided into two

sub layers: The Media Access Control

(MAC) layer and the Logical Link

Control (LLC) layer

Layer 2 Data Link examples include

PPP, FDDI, ATM, IEEE 802.5/ 802.2,

IEEE 802.3/802.2, HDLC, Frame

Relay.

Physical layer

Physical layer conveys the bit stream -

electrical impulse, light or radio

signal — through the network at the

electrical and mechanical level.

It provides the hardware means of

sending and receiving data on a

carrier, including defining cables,

cards and physical aspects.

Physical layer

Physical layer The bottom-most layer of the Seven

Layers of Open Systems

Interconnection (OSI) Model is

Physical Layer.

Fast Ethernet,RS232,

and ATM are protocols with physical

layer components.