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OSI Seven-Layer Model : A Short Summarize Description of OSI Seven Layer Reference Model

Updated on June 2, 2011

OSI stands for Open Systems Interconnection Reference Model. In short it is termed as OSI model or OSI reference model or 7-layer model or Layered Model or OSI seven layer model. This is really an important topic topic of Network Engineer. Moreover, in your job life exam or interview exam, you must find some questions based on OSI model. If you sit for the exam or interview of networking related jobs or telecommunication jobs, it's quite sure there must be some questions related to it. Moreover, if your want to attend vendor exams like CCNA, you must find at least one question related to OSI reference model. So, it's very important to learn. OSI layer consists of seven layers: Physical layer, Data link layer, Network layer, Transport layer, Session layer, Presentation layer and Application layer. OSI layer model is really a big topic but for the exam or interview, you need to remember some of the basic things of OSI model. This page contains the summarized information of OSI reference model. If you really remember this page information, I'm sure it's really very helpful for you.

Definition of OSI model

OSI mode is a layered, abstract description for communications & computer network protocol design which consists of 7 layers and has two major components (i) an abstract model of networking (the Basic Reference Model) (ii) a set of concrete protocols

Layers of OSI reference model:

OSI reference model consists of seven layers. The layers name of OSI mode is given below:

7. Application
6. Presentation
5. Session
4. Transport
3. Network
2. Data link
1. Physical

The main summarize theme of this layer is described below very shortly but it will cover the required information to sit for the exam like CCNA or networking related job or networking job interview.

DATA untis of OSI model

Data unit..............LayerName
Data...................... Application layer
Data...................... Presentation layer
Data...................... Session layer
Segment................ Transport layer
Packet/Datagram.... Network layer
Frame ................... Data link layer
Bit......................... Physical layer

OSI seven layer model (image taken from
OSI seven layer model (image taken from

Summarize Description of OSI layers

In the following paragraphs, you will find summarize description of OSI layers:

Functionality of Application Layer

Application layer is the 7th layer of OSI model and sometimes referred as Layer Seven of OSI model. The functionality of  application layer is described below:

  • Network processes to applications.
  • Provides network services to application processes, such as e-mail, file transfer & terminal emulation.

Functionality of Presentation Layer

Presentation layer is the 6th layer of OSI model and sometimes referred as Layer Six of OSI model. The functionality of presentation layer is described below:

  • Data representation and encryption

  • Ensure data is readable by receiving system.

  • Format of data

  • Data structures

  • Negotiates data transfer syntax for application layer.

Functionality of Session Layer

Session Layer is the 5th layer of OSI model and sometimes referred as Layer Five of OSI model. The functionality of session layer is described below:

  • Interhost communication
  • Establish, manages & terminates session between appications.

Functionality of Transport Layer

Transport Layer is the 4th layer of OSI model and sometimes referred as Layer Four of OSI model. The functionality of transport layer is described below:

  • End-to-end connections and reliability (TCP)
  • Concerned with transportation issues between hosts.
  • Data transport reliability.
  • Establish, maintain, terminate virtual circuits.
  • Fault detection & recovery information flow control.
  • Controls the reliability of a given link through flow control, segmentation/desegmentation, and error control.

Functionality of Network Layer

Network Layer is the 3rd layer of OSI model and sometimes referred as Layer Three of OSI model. The functionality of Network layer is described below:

  • Path determination and logical addressing (IP)
  • Logical addressing
  • Best effort delivery

Functionality of Data link Layer

Data link layer is the 2nd layer of OSI model and sometimes referred as Layer Two of OSI model. The functionality of Data link layer is described below:

  • Physical addressing (MAC & LLC)
  • Provides reliable transfer of data across media
  • Physical addressing, network topology, line descipline, error notification, ordered delivery to frames, flow control

Functionality of Physical Layer

Physical Layer is the 1st layer of OSI model and sometimes referred as Layer One of OSI model. The functionality of physical layer is described below:

  • Media, signal and binary transmission

The above summarized information is really helpful to learn OSI reference model. This page is just the summarized information which is really need to remember. No detail description is provided here. For learning more or details you may follow the Related Articles/ References.

© Written by rancidTaste

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    • profile image


      2 years ago

      849944yv hbch

    • profile image

      Jimi Patel 

      4 years ago

      after this explaination i understand the base of osi model.this is the actual ans what i was looking for thanxxxxxxx...................

    • profile image


      5 years ago

      im feeling better now thanks a lot

    • profile image

      anees hassan 

      5 years ago

      osi model layers as a short qestion.

    • profile image


      6 years ago

      veryyyyyy gooddd

    • profile image


      7 years ago

      its very easy to understanding,thanks a lotttttttttttttttt

    • profile image

      Rabindra jha 

      7 years ago

      Its really helpful for me , its so easy way of understanding

    • profile image


      9 years ago

      Awesome post, very easy to learn,Thanks a lot..


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