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OSI(Open System Interconnection)

  what is OSI ?

  -OSI model was first proposed by International Standards Organization(ISO) to solve the multiple problems faced in telecommunication.

 It is conceptual model of telecommunication networking where the whole process is divided into seven effective layers. It synchronizes the whole process and helps one understand the interoperation of the diverse communication system under the standard protocol.

7 layer as following -

7.Application Layer - This is the last layer of OSI system  and this layer represents the data that is  understood by the user. The application layer supplies network services to end user applications . protocols works in this layer are HTTP,FTP,SMTP.


6.Presentation Layer - The presentation layer is the simplest in a function of any piece of the OSI model. It handles syntax processing of message data such as format conversations and encryption / decryption needed to support application layer above it. protocols works in this layer are JPEG,GIF,MPEG.


5.Session Layer -  In this session layer, communication and connection between computers is controlled in a managed environment . It has the sole capacity  of managing and terminating connection and helping in establishing connections between local and remote applications. protocols works in this layer are AppleTalk, WinSock.


4.Transport Layer - In the fourth layer , variable length data sequence has to be transferred from source to destination host through one or more network. This transport layer delivers data across network connections. The transport layer is to be delivered the entire message from source to destination, and receiving data  without any errors. protocols works in this layer are TCP, UDP, SPX.


3.Network Layer -  The network layer adds the concept of routing above the data link layer , when data arrives at the network layer the source and destination addresses contained inside each frame are examined to determine if the data has reached its final destination. addressing, routing, and forwarding are the three major functions at this layer. protocols works in this layer are IP, ICMP, IPX. Device works in this layer is ROUTER.


2.Data Link Layer - Data link layer encodes and decodes data packet into bits and using its transmission protocol it handles the errors in the physical layer. It also controls flow and synchronization of the frames and at the same time it manages controlling access of the physical layer network devices. protocols works in this layer are Switch, Bridge, Ethernet cable. 


1.Physical Layer -  This layer is the primary layer of the OSI model and consist of connecting devices such as ethernet cable, token ring, hubs and electrical specifications for data connection. This layer is responsible for connecting the device to physical transmission medium such as copper or optical cable or radio frequency or pulses of infrared. protocols works in this layer are Hub, Repeater, Ethernet, Token Ring.

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