OSI Model , OSI Modeling , Layers of OSI Model

OSI Model | OSI Modeling | Design Principle | Reference model | Layers of OSI model | 
                       OSI MODEL 
              ( Open System Interconnection)

        To make the system compatible to communicate with each other ISO( International Organization of Standard) has developed standard so that standard we called it as OSI model and the process is known as OSI modeling. OSI is a seven layer architecture system.
Design principle of OSI reference model:- 

1- Where a different abstractions are needed  a layer has to be created .

2- Each layer should perform a well defined function.

3- Function of layer should be follow the international standard.

4- To  minimize the into flow across the interface.


              Features Of Reference Model 

 1- Big  picture of communication over network is understandable through this OSI.

2- How hardware and software are work together.

3- Trouble shorting is easier. It can be used to compare basic functional relationships on different network . 

              -:  Layers Of OSI Model :- 
There are seven layers in OSI model are given as - 

1- Physical layer 
2- Data Link Layer 
3- Network Layer 
4- Transport Layer 
5- Session Layer 
6- Presentation Layer
7- Application Layer 

1- PHYSICAL LAYER - (a) It is responsible for moving individual bits from one node to the other node .
(b)  This layer is used to establish or terminate a connection to communication media.
(c)   It converts the received data into bit stream.

   Function- (i)-  Defines the transmission media.
        (ii)- It defines the type of encoding.
        (iii)- It decides the data rate ( no. of bits  send each second).
        (iv) - Defines different types of topology.
        (v)- Transmission mode.
         (vi)- Line configuration multi-point.

2-  Data link layer - It transform the physical layer into reliable link .

   Function- 

   
(a)  Framing-  Conversion of bits into frame ( bits are grouped into frames ).
(b) Physical Addressing-  A header is added to frame .
(c) Flow control-  A rate  at which data is send in flow control.
 (d) Error control-  From different different mechanisms error is controlled.
  (e) Access control-  Which device is having control on access.


    3- Network Layer - Responsible for source to destination delivery of packets.

   Function- 

 (a) Logical addressing- Header to the packet coming from upper layer.


4- Transport Layer-  Responsible for process to process delivery. Process is application running on the system.


Function-  Service point addressing port address. It is port number at which that particular application is running. Each application is given a port number in a system.

5- Session Layer - This layer establishes manages synchronizes and terminates connection between the computer.

Function-  

(a)  Dialog  Control- Keeping control track of whose turn is to transmit.
       
       Dialog Control    Half duplex 
                                        Full duplex 

(b) Token management-  Preventing two parties from attempting the same critical operation at the same time.
(c) Synchronization-  Check pointing long transmission to allow them to continue from where they where after a crash .


6- Presentation Layer - It deals  with the syntax and semantic of the information exchange between two systems.

Function-  


(a)  Translation - Converting a message to compatible bit system.
(b) Encryption- Converting plain text to cliphor text.
 Compression- Reducing no.of bits contained in the information.

7- Application Layer - It enabled the users human software to access the hardware.

Function- 

Network virtual  terminal- (a)  Software version of physical terminal ( remote host login is faulitated) .


 (b)  File transfer, access and management.
(c)   E- mail services.
 (d)  Directory services.

       

     In short form 

   A( Network Access )
   P( Encryption , compress)
    S( Manage session)
    T( Process to process delivery)
    N( Source to destination, routing)
    D( Frame, flow chart,error)
    P( Data rate media mode)