Routing and Switching

Assignment
OSI model layers and
it’s Protocols functionality
Beenish Maria
BSIT63S23S049
The OSI (Open Systems Interconnection) model is a conceptual framework used to understand
and standardize the functions of a communication system or network. It divides the process of
network communication into seven distinct layers, each responsible for a specific aspect of data
transfer. The OSI model helps to ensure that different types of hardware and software systems
can communicate and work together over a network, promoting interoperability between vendors
and systems.
The OSI model, with its seven layers, provides a structured approach to understanding how
network communication works. Each layer in the OSI model has a distinct role and
responsibility, from physically transmitting data to managing user applications, and these layers
work together to ensure smooth data exchange across a network.

The OSI Model

1. Physical Layer
 This layer is responsible for the actual physical connection between devices. It defines
the hardware elements such as cables, switches, and the electrical signals that pass
through them. It deals with raw data transmission in the form of binary (0s and 1s) over
physical mediums like coaxial cables, fiber optics, or wireless signals. The physical layer
focuses on data rates (refer to the speed at which data is transmitted over a
communication medium), voltage levels (in the physical layer represent the electrical
signals that carry the data. The voltage is used to encode bits (0s and 1s) for
transmission), and signal integrity (refers to the quality and accuracy of the electrical
signals as they travel across the communication medium).

Protocols:
 Ethernet: Specifies the physical and data link standards for LANs, including how
bits are transmitted across a medium.
 USB (Universal Serial Bus): Standard for connecting peripherals to a computer,
managing power supply, and data transfer.

2. Data Link Layer

The data link layer is responsible for node-to-node data transfer and error
detection/correction. It organizes data into frames and adds physical (MAC) addresses to
ensure that data is correctly sent between devices on the same network. This layer also
handles flow control and error checking, ensuring that frames are not corrupted during
transmission.

Protocols:
 Ethernet: Handles the formatting of frames, error checking, and MAC addressing
for devices on a LAN.
 Wi-Fi: A wireless LAN protocol that manages communication between devices
over a wireless medium.
 PPP (Point-to-Point Protocol): Used to establish direct connections over dial-up
lines, DSL, or VPNs, ensuring that data is transferred properly over point-to-point
links.

3. Network Layer
This layer is responsible for logical addressing (IP addresses) and routing data from the
source to the destination across multiple networks. It determines the best path through the
network and handles packet forwarding between different networks. The network layer
breaks down data into packets, adds the logical IP addresses of the source and
destination, and manages routing, ensuring that the packets reach their intended
destination even if they traverse multiple routers.

Protocols:
  IP (Internet Protocol): Responsible for routing packets across networks by
assigning IP addresses to devices and ensuring that packets are routed to their
correct destination.
 ICMP (Internet Control Message Protocol): Used by network devices to send
error messages, like when a service is unavailable or a packet cannot reach its
destination.
 RIP (Routing Information Protocol): Helps routers share information about the
best path to take for forwarding packets across a network.
 OSPF (Open Shortest Path First): A more advanced routing protocol that finds the
best path for data based on the shortest path first algorithm.

4. Transport Layer
The transport layer ensures that data is delivered error-free, in the correct order, and
without losses or duplications. It controls the reliability of communication by providing
services such as connection establishment, flow control, error correction, and
segmentation of large messages into smaller packets. It ensures end-to-end
communication between hosts.

Protocols:
 TCP (Transmission Control Protocol): Provides reliable, ordered delivery of data
between applications. It establishes a connection between the sender and receiver
and ensures that all data is received accurately.
 UDP (User Datagram Protocol): A connectionless protocol that provides fast,
best-effort delivery of data without guaranteeing that packets will arrive in the
correct order or at all.

5. Session Layer
The session layer is responsible for establishing, managing, and terminating
communication sessions between applications. It handles setting up, coordinating, and
terminating connections, ensuring that the data exchange continues smoothly and
consistently during a session. If there is a disruption, the session layer ensures recovery,
allowing applications to continue from where they left off.

Protocols:
 SMB (Server Message Block): Used for sharing files, printers, and serial ports
between computers on a network, maintaining a session during data transfers.
 NetBIOS (Network Basic Input/Output System): Provides services related to the
session layer, including establishing and maintaining connections between
applications over a network.
6. Presentation Layer
The presentation layer acts as a translator between the application and the network. It
ensures that data sent from the application layer is in a format that the recipient can
understand. This layer handles data encoding, compression, and encryption to ensure that
the data is readable by the receiving device and that sensitive information is secured
during transmission.

Protocols:
 SSL/TLS (Secure Sockets Layer/Transport Layer Security): Encrypts data to
provide secure communication between web browsers and servers.
 JPEG, PNG: Standard file formats for compressing and encoding images.
 MPEG: Used for compressing and encoding video and audio data for efficient
transmission.

7. Application Layer
The application layer is where users directly interact with the network. It provides various
network services like email, file transfers, web browsing, and database access. This layer
serves as the window for users and applications to access the network, allowing
communication between software applications and the lower OSI layers.

Protocols:
 HTTP/HTTPS (Hypertext Transfer Protocol): Used for communication between
web browsers and web servers. HTTPS adds security by encrypting the
communication.
 FTP (File Transfer Protocol): Allows users to transfer files from one host to
another over a network.
 SMTP (Simple Mail Transfer Protocol): Responsible for sending emails between
servers.
 DNS (Domain Name System): Translates domain names (like example.com) into
IP addresses so that browsers can load web pages.