OSI Models

 OSI Is Stand for Open System Interconnection. the OSI Models defines a networking for implanting protocol in seven layers by the     international organisation for standard(iSO) .the oSI reference model is based on protoco develop by iSO so the model is also called ISO OSI reference model.
 It was develop in  1984 .it has seven layer.there are following seven layer.

7.  application layer.  

6. presentation layer.  

5. Session layer.  

4, transport layer.  

3.Network layer.

2.Datalink layer.

1.Physical layer.

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 Benefite and reason.

1.  To divide the interrelated aspects of network operation into less complex operations.
2.  To define standard interfaces to achieve compatibility and multivendor integration.
 3. To achieve a modular approach to networking protocols so new applications and services can be deployed   without redesigning other layers.
 4. To keep changes in one area from affecting other layers.
 5. To ease troubleshooting using data packets which will have specific information about each layer.

 

Application layer /layer7

  1. the application layer is top  most layer in osi model.also known as layer 7.

2. by thi layer user communicate to the computer server.the application used in communication is email,chrome,skype etc.

3. Provides interface between OSI RM and end user applications

4. Provides network services to user client/server-based applications

5, Establishes and defines program-to-program communication

      6. Identifies availability of intended communication partner

      Examples  include ftp, tftp, http, www browsers, DNS, SMTP, telnet .

Presentation layer/layer6.

1.  Defines data format for transmission .

 2. Ensures arriving data from the network can be used by the application and information sent by the application can be transmitted on the network .

3.  Performs encryption and decryption .

 Example:   representations include ASCII, EBCDIC, JPEG, TIFF, PICT, MPEG, MIDI, HTML.

Session layer/layer 5.

 

1. Session layer is a layer5 that controls /manage mainly session time of website/networks.

 2. Defines how to start, control and end sessions

 3. RPCs operate at this layer Logon Validation happens at this layer.

 4. Named Pipes defined at this layer – Named Pipes use TCP to guarantee communications, example – NetLogon 5.  Session layer organizes communication through simplex, halfduplex or full-duplex

Example:    protocols include SQL, RPC, NetBIOS, Named Pipes .

Transport layer/layer 4

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1. It is a main types of layers in OSI Model because it's functions works is provide data dealing mechanism between the application in the networks.

2.   Segments data to be passed down to the Network layer and reassembles data for the Session and upper layers 3.    Provides the choice of connection-oriented and guaranteed (TCP) or connectionless and non-guaranteed (UDP) delivery of data

 4.    Provides end-to-end transport services

 5.  Provides flow control to overcome congestion in the receiving host’s buffers

6.  TCP uses port numbers to multiplex from the Transport layer through to the Application layer

[multiplex = ability to send different data from a number of applications in the same transport connection]           7.  3 flow control mechanisms

Network layer/layer 3.

 

1. It is responsible for communication network.it recognise network with help of networks address.Network address is logical address like IP Address IPX.it is a commmon for a computer .

2. The determination or routing is performed at this layer.Router is worked on this layer.

3. Network layer maintains routing table .

Data-link layer/layer 2.

1. Provides error-free link between 2 devices – CRC used for error checking .

 2. Packets from the Network layer are placed into frames .

3. Data Link layer handles physical transmission of data from one node to another

 4. Handles error notification

5. IEEE subdivided this layer into 2 sublayers

Physical layer/layer 1.

 

1.Defines connections – RJ-45, RJ-11, BNC, HSSI, RS-232

2.Places frames, represented as bits, onto media as electric signals or pulses of light

3.  Hubs and repeaters operate at this layer .