OSI Model

By

Sagar

 

OSI stands for (Open System Interconnection) model defines a networking framework to implement protocols in seven layers. Use this handy guide to compare the different layers of the OSI model and understand how they interact with each other.
It is also called as “Model for Open System Interconnection” and it is normally referred as “OSI reference Model”.
OSI Model mainly contains seven layers in it where the lowest layer is Physical Layer and the highest layer is called as Application Layer.

Seven layers of OSI Model are as follows:

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

1. Physical Layer
Physical Layer is the first layer of the OSI Model i.e. Lowest layer in the model This layer is mainly used to maintain, activate and to deactivate the physical connections.
It is also used to convert digital bits(i.e 0 or 1) into electrical signal.
This layer fails to perform some operations those are
1.It does not detect or correct errors.

2. Data Link Layer
Data Link layer is responsible for reliable node or node delivery of data. It accepts packets from the network layer and forms frames and gives it to the physical layer.

3. Network Layer
This layer delivers the packets from source to destination across multiple networks.
If some hoe two systems are connected on same link, them there is no need for network layer.

4.Transport Layer
Transport layer is responsible for source to destination delivery of entire message, it ensures that the whole message arrives intact in order , ensuring both error control and flow control at the source- to destination level.

5. Session Layer
Session layer establishes , maintains and synchronises the interaction between communicating systems. It controls logging on and off, user identification , billing and session management.

6. Presentation Layer
Presentation layer mainly takes care of syntax and semantics of the information exchanged between communication systems.
Presentation layer basically functions as a pass through device. It receives premitives from application layer and issue duplicate primitives to the session layer below it, using the Presentation Service Access Point(PSAP) and Session Service Access Point(SSAP)

7. Application Layer
Application Layer is the last layer of OSI Model, it is the highest layer of in OSI model, Application layer provides services that directly support users application such as database access, e-mail and file transfer.