The document describes the OSI model, which is a conceptual framework that standardizes network communication functions into seven layers. Each layer is responsible for specific protocols and functions. The layers work together to allow data transmission between devices on different networks, with the physical layer transmitting bits and the application layer allowing user interaction with network services.

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OSI MODEL
Open System Interconnection
1st Year ICS: Chapter 2

2. Connectivity of Devices

3.  A conceptual framework
 Standardizes and describes the functions of a
telecommunications or networking system.
 It divides network communication into seven
distinct layers
 Each responsible for specific functions and
protocols.
Introduction of OSI
PART
1

4.  It was developed by International Standard
Organization(ISO) in 1983.
 It was develop to allow different network to
communication with each other even their
architecture are different.
Introduction of OSI
(Cont…)

5. Working of Layers

7.  Physical to Application
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 Please Do Not Teach Stupid People Acronyms
 Application to Physical
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 A Penguin Said That Nobody Drinks Pepsi
Way to remember names of
layer

8.  Provides network services directly to end-users
and applications.
 Includes various application protocols for
specific functions (e.g., HTTP for web
browsing).
 Allows users to interact with network services
like email, file transfer, and remote access.
 Responsible for user interface and data
presentation.
 Skype, Whatsapp, Instagram, Gmail etc
Application Layer

9.  FTP:
 File Transfer protocol: use to transfer files
 SMTP:
 Simple mail transfer protocol: use to forward
email from one device to another.
 HTTP or HTTPS:
 hyperText Transport Protocol Secured: it is used
in connecting server and client.
Protocols in Application
Layer

11.  In this layer data is represented in the stream of
bits (set of bits).
 Functions of Presentation Layer
 Data Reformatting: Data reformatting in the
Presentation Layer involves the transformation
of data into a format that is suitable for
transmission or for the recipient system to
understand.
Presentation Layer

12.  Encryption/Decryption:
 Data is encrypted before transfer, sender
computer change the original format of data into
another format is called Encryption.
 At receiving side data is again change back into
the original format from other format is called
Decryption.
 Compression:
 Process of reducing the size of data which is to
be sent over the network.
Presentation Layer

13.  Session is an exchange of messages between
computer.
 Establishes, Control and manages user
connection.
 It synchronize the data transfer with
checkpoints.
 It check the data after each checkpoints. If
failure occurs, it retransmit data from last check
point.
Session Layer

14.  If the checkpoint is set to 10 pages. A computer
sending 100 pages. If a failure occurs at 55
pages. It will retransmit data from page 51,
because last checkpoint was set to page 50.
Session Layer

15.  Is responsible for end-to-end connection
between two devices.
 Take data from session layer and divide them
into smaller chunks, these chunks called
“packets”.
 In transport layer, the process of dividing data
in the form of small packets to transfer data
effectively is called “Packet Switching”
 These packets are again reassembled at
receiving side and become a file.
 The TCP works in the Transport layer.
Transport Layer