Sunday, August 14, 2011

Osi Layers

Open system Interconnection-Created by ISO(International Organization for Standardization) in 1970 .

* OSI layer helps to communicate two different vendor network devices using common set of rules.
*That rules are very difficult to understand vendors.So that rules are separate seven groups,each group called    layers. In this method is called layered approach model.
* Types of Seven Layers: Application,Presentation,Session,Transport,Network,Data link,Physical.
* First three top layers(Application,Presentation and Session) managed application process(host layers) and bottom  four layers(Transport,Network,Data link,Physical) are manged communication process(media layers)

Application Layers:

* Application layer provides interface between user and that particular application.
* Application layer responsible for establishing and identifying intended communication partner(User).
*Application layer choose actual  application (using port no) and  give to next  layer using protocol stack. 
* Application layer acting to network related applications and also desktop related applications.

                   * In my system,i removed my NIC card and TCP/IP settings,network drivers.At a time open my Internet explore the html web page document opened and retrieve HTTP protocol and getting some error message.In these case user opened html page and using http protocol and create Application layer PDU (Protocol data unit)and give to next layer using via port no(HTTP port no-80).And also added Presentation and Session layer PDU's finally comes to network layer finding source and destination ip address,But system don't have NIC card so encapsulation failed and lost the data  finally getting some error message.In this cause user connected to application and getting replay message.

Presentation Layer:

* Presentation layer  responsible present the data and data translation and code formatting for Application  layer entities(Application layer PDU).
*Presentation layer also responsible for data compression,decompression and data encryption,decryption.  
*Presentation layer responsible for general format to ASCII format.It means sender data to translate to any format and then re translate to that format in destination system. 

Session Layer: 

*Transport layer responsible for  setting up (connecting)and managing and tear down (disconnect)session between presentation layer entities.
*Transport layer dialog control (end to end connection control)between two devices or end to end nodes and also organize the server to client or between two nodes using different modes.
Simplex-This is one way communication.(sender transmit the data and receiver received that data but receiver can't communicate to sender)
Half duplex- In this method sender to send the data to receiver after received the data then receiver replay back(At the same time can't communicate sender and receiver)
Full duplex-In this method at the same time communicate sender and receiver.
* And the main work for session layer different application data keeps and communicate to that exact that application for destination. 

Transport Layer: 

* Transport layer responsible create segments(break the big data to small small segments) for session layer data entries and reassemble the segments to data and give to session layer.
*Transport layer gives End to End Transport services and create logical connection between sending host to receiving host. 
*Transport layer works with TCP and UDP protocols. 
TCP(Transmission control protocol)