OSI Model & Its Layers

What is OSI Model?

 OSI stand for Open System Interconnection Model. OSI Model published in 1984 by International Organization for Standardization IOS This model tells you, how data travels in a network in complete details theoretically. OSI model helps you to understand the network in better way.

OSI model is a framework used to describe the functions of a networking system.

OSI model characterize computing functions into a universal set of roles and requirements in ordered to support interoperability between different products and software’s.

OSI Model Layers

These are following 7 layers are in OSI Model.

                                            i   Application Layer:

Application layers is the first layer of OSI Model.

This is the only layer where user can directly interact with the data.

This layer provides user interface, and supports services such as mail access, file transfer, browsing internet, remote desktop connection etc.

This layer use FTP, TELNET, DHCP, HTTP, DNS, POP3, SMTP protocols.

                                        ii.   Presentation Layer:

Presentation layer is the second layer of OSI model.

This layer is responsible for translation, encryption and compression.

Protocols work under this layer is SSL.

                                   iii.   Session Layer:

Session layer is the third layer of OSI Model.

It is responsible for dialog control and synchronization.

This layer also control duplexing, termination and restart.

                                    iv.  Transport Layer:

Transport layer is fourth layer of OSI model.

It converts packets into segments and forward it to the session layer.

This layer responsible for segmentation, connection control, flow control and error control.

Protocols works under this layer are: TCP & UDP.

Datagram at Transport layer called segments.

                                     v.  Network Layer:

This Fifth 5th layer of OSI Model. It provides connection between hosts on different network.

It converts frames into packages and forward it to the Transport layer.

This layer is responsible for logical addressing, routing etc.

Devices works under this layer are Router etc.

                                   vi.   Data Link Layer:

Data link layer is the sixth layer of OSI Model. It provides connection between hosts on same network.

It converts bits into frames and forward it to the network layer.

This layer is responsible for framing, physical addressing, flow control, error control and access control.

Devices works under this layer are: switch and Bridge and NIC.

Protocols used under this layer are: PPP, PPTP etc.

Datagram at Data Link layer called frames.

                                 vii.  Physical Layer:

This is Last layer of OSI Model.

In this layer all the physical connectivity of a network, such as connectivity of devices using wires takes place.

It converts data into bits and forward it to a data link layer.

Devices works under this layer are: HUB, Repeaters, cables etc.

Datagram at Physical Layer called bits.

                  ______________________The End____________________

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