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OSI Model and Its Seven Layers

OSI Model and Its Seven Layers



OSI Model – Definition - What are the Seven Layer of OSI Model? The OSI (Open System Interconnection) model is developed by (International Standard Organisation) ISO in 1984 to provide a virtual / conceptual model for the aspects context to network communication. It divides the vary services and functions provided by network hardware and software in seven layers. A layer serves the layer above it and is served by the layer below it. It has seven layers, where each layer describe a different functions of data traveling through the network. The more regarding OSI Model and Its Seven Layers is discussed below.

The Application, Presentation and Session layer are known as the Upper Layer and are implemented in software applications. The Transport and Network layer are concerned with protocols for delivery and routing of packets to a destination and are implemented in software. The Data Link is implemented in hardware & software, the Physical layer is implemented in hardware only.

The diagram below shows the 7 layers of the OSI Model, in correct order to understand all the virtual and conceptual definitions of OSI Model. The name of the layers are Application layer, Presentation layer, Session layer, Transport layer, Network layer, Data Link layer and physical layer. They works as peer to peer model, which acts in each of the layers of OSI model.

WHAT IS FUNCTION OF PHYSICAL LAYER IN OSI MODEL?

PHYSICAL LAYER

The Physical layer communicates directly with the physical media, it is responsible for activating, maintaining the physical link. The physical layer handles a raw bits stream and places it on the wire to be picked up by the Physical layer at the receiving node. The Physical layer is responsible for electrical and optical signalling, voltage levels, data transmission rates and distances as well as mechanical specifications such as cable lengths and connectors, the amount of pins and their uses. The devices that operate on physical layer are HUBs, repeaters, NICs, RS-232, OC-3, BRI, V.24, V.35, etc.

WHAT IS THE FUNCTION OF DATA LINK LAYER IN OSI MODEL?

DATA LINK LAYER


The Data Links provides abstract network services to the Network layer so the layer can be ignorant about the physical network topology and provides access to the physical networking media. It is responsible for reassembling bits taken from the wire by the Physical layer to frames, makes sure they are in the correct order and no error occurs. It Provides error checking by adding a CRC to the frame and flow control. Examples of devices that operate on this layer are switches, bridges, WAPs. and What are the Seven Layer of OSI Model? is continued... OSI Model and Its Seven Layers also continued..

WHAT IS THE FUNCTION OF NETWORK LAYER IN OSI MODEL ?

NETWORK LAYER


This layer converts the segments from the Transport layer into packets (or datagrams) and is responsible for path determination, routing, and the delivery of these individual packets across multiple networks without guaranteed delivery. The network layer treats these packets independently, without recognizing any relationship between those packets, it relies on upper layers for reliable delivery and sequencing.
Also this layer is responsible for logical addressing. For example - IP addresses.
Examples of protocols used in this layer are: IP, IPX, AppleTalk, ICMP, RIP, OSP and others. Devices that operate on this layer: Routers etc.

WHAT IS THE FUNCTION OF TRANSPORT LAYER IN OSI MODEL?

TRANSPORT LAYER


This layer converts the data received from the upper layers into segments. Used for flow control and data recovery. The Transport layer is responsible for end-to-end (also called source-to-destination) delivery of entire messages. Provides end-to-end connectivity, it allows data to be transferred reliably and sequencing to guarantee that it will be delivered in the same order that it was sent. Provides services such as error checking and flow control (software). Protocols that operate on this layer: TCP, UDP etc.

WHAT IS THE FUNCTION OF SESSION LAYER IN OSI MODEL?

SESSION LAYER


It defines how to establish and terminate a session between the two systems. It establishes, maintains and terminates end-to-end connections (sessions) between two applications on two network nodes. It controls the dialogue between the source and destination node, which node can send when and how long. Also provides error reporting for the Application, Presentation and Session layer. Protocols/API's that operate on this layer include: RPC, SQL and NETBIOS.


WHAT IS THE FUNCTION OF PRESENTATION LAYER IN OSI MODEL?

PRESENTATION LAYER


This layer represents/ facilitate data in a particular format to the Application layer. It defines encryption, compression, conversion and various coding functions. The properties which is seen in this layer are: MIME, ASCII, GIF, TIFF, JPEG and MPEG. Compression and encryption are defined at this layer.

WHAT IS THE FUNCTION OF APPLICATION LAYER IN OSI MODEL?

APPLICATION LAYER


The Application layer provides services directly to the user's application such as a web browser, email software, web applications and Windows Explorer. It enables network applications to communicate with other network applications. This layer is said to be "Nearest to the User". Protocols that operate on this layer include: SMTP, NTP, SNMP and EDI, TELNET, HTTP and FTP.

This is short and simple description about What are the Seven Layer of OSI Model? and OSI Model and Its Seven Layers. In next article we will talk about TCP/IP protocol and differnce between OSI model and TCP/IP protocol.


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