The document describes the 7-layer Open Systems Interconnection (OSI) model. The 7 layers are the physical, data link, network, transport, session, presentation, and application layers. Each layer has a specific role, with the physical layer concerned with physical connections and signals and the application layer providing protocols for user software. The OSI model was developed by ISO to allow devices with different internal systems to communicate by standardizing network communication.

1. Submitted to:
Pranab Bandhu Nath
Senior Lecturer
Department of Computer Science & Engineering
Submitted By:
Sujon Kumar Dey
ID No: 1834902519
Section B
Program: CSE (Day)
Class Note: 08
Course: Computer Networks
Course Code: CSE 317
Date of Submission: 29/05/2021
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2. OSI MODEL
OSI MODEL:
OSI Model stands for Open System Interconnection Model. We will cover all thing
about the OSI model in this content.
What is OSI Model?
Let, you have a laptop. You using windows as an operating system. Now you want
to send data to your friend from your laptop. Both of you have a LAN connection
between two laptops. The problem is your friend is using MAC as an operating
system. So how you can send the data? Because both of you have using different
internal systems.
For this type of problem-solving, OSI was invented by ISO in 1984.
OSI contains 7 layers. These 7 layers are:
Application Layer
Presentation Layer
Session Layer
Transport Layer
Network Layer
Data Link Layer
Physical Layer
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3. Work of the Different Layers:
Application Layer: Application layer is used by user end software, like web
browser, email, web application, etc. This layer provides a protocol for the
software to receive and send data. The common protocol of the application layer is
HTTP, HTTPS, FTP, SMTP, DNS, etc.
Presentation Layer: The presentation layer receives data from application layer
and it’s doing 3 works.
1. Translation
2. Data Compression
3. Encryption/Decryption
Translation: Presentation layer receives data as characters and numbers from the
application layer. Then it converts it as machine-understandable code like - ASCII.
It’s called translation.
Data Compression: After translation, there are many unnecessary bits. Before
transmitting this, the presentation layer also removes the unnecessary bits. This
helps to store and transmit it more fastly. It’s called data compression.
Encryption/Decryption: To protect, and keep the data integrity presentation layer
also perform the encryption and decryption. Before transmitting, the transmitter
encrypts it and, from the receiver end, it’s will decrypt. SSL(Secure Socket Layer)
is performing this encrypt and decrypt task.
Session Layer: The session layer is responsible for authorization and
authentication. Authentication or authorization is a process before connection
between server and user. Session layer also helpers of API (Application
Programming Interface).
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4. Transport Layer: Transport layer working for communication through flow
control, error control, and segmentation. This layer used TCP(Transport Control
Protocol) and UDP(User Datagram Protocol) protocol. UDP is faster than TCP.
Because UDP doesn’t provide any feedback during the communication. So UDP
can’t restore failed data. Another hand TCP can restore, but slower than UDP.
Network Layer: Network layer received data from the transport layer. Here data is
sent from one computer to another using data units. Data packets are the units of
the network layer.
Also, logical addressing, routing, and path determination is the function of network
layer.
Data Link Layer: Data link layer receives data packets from the network layer.
This data pack also contains the address of the sender and receiver. There are two
types of addresses are located.
Logical Addressing
Physical Addressing
The logical address contains the IP address in the data packets. And MAC address
is contained by Physical addressing.
Physical Layer:
The physical layer is responsible for physical connections like cable, wireless.
When it’s a cable, the physical layer transmits the electrical signal. When it’s
wireless, the physical layer transmits the radio signal. Finally, it’s moving the
signal to the application layer, then it’s visible to the user’s computer screen.
Reference:
https://www.youtube.com/watch?v=vv4y_uOneC0
https://www.imperva.com/learn/application-security/osi-model/#:~:text=The%20ap
plication%20layer%20is%20used,present%20meaningful%20data%20to%20users.
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