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OSI Layer Model Overview

OSI Layer Model Overview :- OSI Layers or Model means is open system interconnect and OSI model tell that how to data travel in digital world (network). OSI developed by the International Organization for Standardization (ISO) in 1974.

OSI have Seven Layer:-
OSI Layer Model Overview - 1
1) Application Layer, 2) presentation Layer and 3) Session Layer - These Layers known as upper layer or Software Layer.

4) Transport Layer - It is Heart of OSI.

5) Network Layer, 6) Data link Layer, 7) Physical Layer - These Layers known as Lower Layer or Hardware Layer.

1) Application Layer:- Application Layer is responsible for providing Networking services to the user it means this layer is closest to the end user. It is also know as desktop layer. Identification of services is done using port number. Data Flow From Application Layer Data will be Data.

Total Number of Ports are 0 to 65535.
Reserved Ports 0 to 1023.
Open client Ports 1024 to 65535.

2) Presentation Layer:- Presentation Layer is responsible for converting data into standard format. Data Flow From Presentation Layer Data will be Data.
Example ASII, JPEG, MP3 etc.

Following Tasks are Preform at Presentation Layer:
# Encryption – Decryption
# Encoding – Decoding
# Compression – Decompression

3) Session Layer:- Session Layer is responsible for establishing maintaining and terminating session. Data Flow From Session Layer Data will be Data.

4) Transport Layer:- Transport Layer is responsible for end to end connectivity. It is also know as the heart of OSI Layers. Data Flow From Transport Layer Data will be Segment.

Following Tasks are Performed by the Transport Layer:
# Identifying Service
# Multiplexing & De-multiplexing
# Segmentation
# Sequencing & Reassembling
# Error Correction
# Flow Control

5) Network Layer:- Network Layer is responsible for providing best path for data to reach the destination. Logical Addressing works on this layer and Router is a Network layer device. Data Flow From Network Layer Segment will be Packet.

It is divided into two parts:
# Routed Protocols
# Routing Protocols

6) Data Link Layer:- Data Link Layer is divided into two sub layers. Data Flow From Data Link Layer Packet will be Frame.

# LLC-(Logical Link Control) it talk about WAN protocols e.g PPP, HDLC, Frame-Relay.
# MAC-(Media Access Control) it talks about physical Address. It is a 48 bit address i.e. 12 digit Hexadecimal Number.

It is also responsible for Error detection.
Devices Working on Data Link Layer are Switch, Bridge, NIC

7) Physical Layer:- Physical Layer is responsible for electrical, mechanical and procedural checks. Data will be converted into Binary i.e 0 & 1. Data will be in the form of electrical pulses if it is Coaxial or twisted pair cable and in the form of light if it is fiber optic cable. Data Flow From Physical Layer Frame will be Bits.

Devices working at Physical Layer are Hubs, Repeater, Modems etc.
OSI Layer Model Overview - 2

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