The OSI Model

Presentation by: Shubham Pendharkar

Established in 1947, the International Standards Organization(ISO) is a multinational body dedicated to worldwide agreementon international standards. Almost three-fourths of countries in

the world are represented in the ISO. An ISO standard that

covers all aspects of network communications is the OpenSystem Interconnection (OSI) model. It was first introduced inthe late 1970s.

Open Systems Interconnection (OSI)

Each layer support the layers above it and offers services to

the layers below

Each layer performs unique and specific task

A layer only has knowledge of its neighbour layers only

Introduction to the OSI Model

Why OSI Model was created ?

An attempt to make a framework for developing

networking technologies.

A framework is helpful in the design of hardware and

software for communication.

ISO-OSI Model serves this purpose.

OSI became a tool for explaining the Networking in

general.

Division of Layers

Upper Layers

Lower Layers

Middle Layer

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link

1. Physical

7. Application

Application Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Aao

Pyar

Se

Tuhme

Networking

De

Padhaye

LAYER 7 –Application Layer

• The top layer of the OSI model

• Provides user layer interaction. Available in

the end user machine.

• Examples: Internet Explorer, Chrome

(Browsers) .

• Standards: FTP, HTTP, etc.

• PDU (Protocol Data Unit) is the data.

LAYER 6– Presentation Layer

• It ensures that data transferred from application layer of one system can be read by application layer of other system.

• Tasks which can be performed:* Compression* Decompression

* Encryption* Decryption

• PDU is the data.

LAYER 5 – Session Layer

• Session layer provides mechanism for

controlling the dialogue between the two

end systems. It defines how to start, control

and end conversations (called sessions)

between applications.

• Any necessary log-on or password validation

is also handled by this layer.

• PDU is the data.

LAYER 4 – Transport Layer

• It receives HUGE amount of data from upper layers and break them down into smaller parts called segments.

• Ensures that the data units are delivered error free.

• Ensures that data units are delivered in sequence.

• Provides connectionless (UDP) or connection oriented (TCP) service.

• Encapsulation starts from this layer.

• PDU is the Segment.

LAYER 3 – Network Layer

• It uses Logical Addressing (IP addressing).

• Makes ‘Best Path Determination’ decisions

based on Logical addressing.

• It receives SEGMENTS from the upper layer

and convert in into PACKETS.

• PDU is the Packet.

LAYER 2 – Data Link Layer

• It is responsible for Physical Addressing (MAC addressing).

• Handle errors by implementing an acknowledgement and retransmission scheme.

• It receives PACKETS from the upper layer and convert in into FRAMES.

• PDU is the Frames.

LAYER 1 – Physical Layer

• Provides physical interface for transmission of information.

• Covers all - mechanical, electrical, functional and procedural - aspects for physical communication.

• Such characteristics as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, physical connectors, and other similar attributes are defined by physical layer specifications.

Thank You