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What is the OSI model?

OSI model 
OSI stands for open system interconnection .OSI model is a reference model developed by ISO in 1984 ,which defines how data is transferred from one computer network to another computer network .OSI model consists of 7 layers .These are follows- 
(1) Application later- 
- Application layer is the top-most layer of the OSI model .
- Application layer is used by network applications .It means computer application that use internet .Like -Google chrome,Safari etc.
- It allows application to communicate with other application. 
- Protocols like Http,ftp, telnet,smtp etc, are worked in this layer .
(2) Presentation layer-
-The presentation layer is also known as Syntax layer .
- The presentation layer translates data between the format the network require and the format the computer expects.It means ,it does encryption at sender side and decryption at receiver side.Encryption means changing the plain text into cipher text and decryption means changing the cipher to plain text .
(3) Session layer- 
- When two stations need to communicate with each other ,a session is need to be created ,this is done by session layer .
- The function of session layer is setup, coordination and termination between applications at each end.
(4) Transport layer- 
-Transport layer provides connectivity to both software layer and hardware layer .
-Software layer consists of 3 layers i.e, Application layer, presentation layer and session layer .
-Hardware layer consists of Network layer ,data link layer and physical layer .
-segmentation occurs at transport layer .
-Two major protocols are used in this layer i.e, TCP and UDP for data transmission.
-Tcp(transmission control protocol) is generally used to retransmit data and it provides acknowledgement of data .
-UDP(user datagram protocol) is used for fast data transmission.Does not the data will be lost or not .but UDP is faster than TCP .UDP doesn't provide the acknowledgement of the data .
(5) Network layer- 
-The main function of Network layer is logical addressing , Routing and path determination.
-Data unit in network layer is called packets.
-IP addressing is done in network layer is called logical addressing. In logical addressing senders and receivers IP addresses are assigned to each segment to form a data packet .
-Routing is the method of moving data packets from source to destination.
- Choosing the best path out of the available path for data delivery is called path determination.
-Protocols like ARP, ICMP etc. are used in Network layer .
(6)Data link layer- 
- Physical addressing is done at data link layer ,where senders and receivers IP(internet protocol) addresses are assigned to each data packets to form a frame .
-Data unit in data link layer is called Frame.
-Data link layer with MAC method control data transmission. 
-The main function of data link layer is error control,flow control and it also provides a well defined interface to Network layer .
(7) Physical layer - 
-It is the lowest layer of the OSI model .
-It is the lowest layer of the OSI model.
-It establishes the actual physical connection between the devices.
-The main function of physical layer is transforming of bits into signal .




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