OSI Model (Open Systems Interconnection Model)

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Networking Model –

Networking models categorize and provide a structure for networking protocols and standards.

Networking Protocols/standards –

A set of rules defining how network devices and software should work.


OSI Model –

1.      OSI stands for Open Systems interconnection model.

2.      A conceptual model that categorizes and standardizes the different functions in a network.

3.      Created by the “International Organization for Standardization” (ISO).

4.      Functions are divided into 7 layers.

5.      These layers work together to make the network work.

6.      Data is encapsulated at one end and de-encapsulated at other end with the help of OSI model layers.

7.      Upper layers (Application, presentation, and session) prepare data and lower layers (transport, network, data link, physical) sent it over the network.

 

7. Application

6. Presentation

5. Session

4. Transport

3. Network

2. Data link

1. Physical

 

Application layer –

1.      Application layer provides interface to end user, so that end user can interact with each other.

2.      Interacts with software application like web browser.

3.      HTTP and HTTPS are layer 7 protocols.

Presentation layer –

1.      Data in the application layer is in ‘application format’.

2.      It needs to be ‘translated’ to different format to be sent over the network.

3.      The presentation layer’s job is to translate between application and network formats.

4.      For example, encryption of data while sending, and decryption of data when receiving.

Session layer –

1.      Controls sessions between communicating hosts.

2.      Establishes, manages, and terminates connections between the local application (e.g., web browser) and the remote application. (e.g., YouTube)

Transport layer –

1.      Segments and resembles data for communications between end hosts.

2.      Breaks large pieces of data into smaller segments which can be more easily sent over the network and are less likely to cause transmission problems if errors occur.

3.      Provides host to host (end to end) communication.

Network layer –

1.      Provides connectivity between end hosts on different networks (i.e., outside of the LAN).

2.      Provides logical addressing (IP address).

3.      Provides path selection between source and destination.

4.      Routers operate at Layer 3.

Data link layer –

1.      Provides node to node connectivity and data transfer (for example, PC to switch, switch to router, router to router).

2.      Defines how data is formatted for transmission over a physical medium (e.g., copper UTP cables, fiber optic cables.)

3.      Detect and (possibly) corrects physical layer errors.

4.      Uses MAC addressing, separates from layer 3 addressing.

5.      Switches operate at layer 2.

Physical layer –

1.      Defines physical characteristics of the medium used to transfer data between devices.

2.      For example, voltage levels, maximum transmission distances, physical connectors, cable specifications etc.

3.      Digital bits are converted into electrical (for wired connections) or radio (for wireless connections) signals.

 





 

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