📢OSI Model — 7 Layers — Dataflow example 📧

OSI Model — illustration of data flow

OSI Model: The OSI (Open Systems Interconnection) model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven distinct layers. It was developed by the International Organization for Standardization (ISO) to ensure interoperability and compatibility between different network technologies and devices.

7 Layers of OSI Model:

1. Physical Layer:

• The Physical Layer is the lowest layer of the OSI model.
• It deals with the actual physical transmission and reception of raw data bits over a physical medium, such as cables or wireless signals.
• This layer defines the hardware characteristics, including voltage levels, data rates, and physical connectors.

2. Data Link Layer:

• The Data Link Layer is responsible for the reliable transfer of data frames between directly connected nodes on the same network segment.
• It detects and corrects errors that may occur in the Physical Layer and provides a mechanism for addressing devices on the local network (MAC — Media Access Control addresses).
• Switches operate at this layer, forwarding data based on MAC addresses.

3. Network Layer:

• The Network Layer deals with routing packets of data from the source to the destination across different networks or subnets.
• It handles logical addressing (IP — Internet Protocol addresses) and determines the best path for data to travel through the network.
• Routers operate at this layer, making decisions about how to forward data based on IP addresses.

4. Transport Layer:

• The Transport Layer is responsible for the reliable and error-checked delivery of data between end systems (e.g., computers).
• It segments data into smaller units (segments) and ensures they are correctly delivered to the destination. It also handles flow control and error recovery.
• Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) are common transport layer protocols.

5. Session Layer:

• The Session Layer establishes, maintains, and terminates communication sessions between applications on different devices.
• It allows applications to synchronize and manage their data exchange, ensuring that data is delivered in an orderly and manageable fashion.

6. Presentation Layer:

• The Presentation Layer is responsible for data translation, compression, encryption, and decryption. It ensures that data exchanged between applications is in a format they can understand.
• It abstracts the differences in data representation among various devices and systems.

7. Application Layer:

• The Application Layer is the topmost layer and interacts directly with end-user applications, providing network services directly to them.
• It includes various protocols and services used by applications, such as HTTP (for web browsing), SMTP (for email), and FTP (for file transfer).

💊Data flow in OSI Layers explained with an example:

📧 Sending an email to a friend involves passing through various layers of communication:

🔶 Application Layer: Email data is sent from your email software to the communication stack. The data passes through this layer to the next one.

🔶 Presentation Layer: Data compression takes place in this layer to optimize the email’s size.

🔶 Session Layer: Communication is initialized at this layer to establish a connection.

🔶 Transportation Layer: The data is segmented into smaller units for efficient transmission.

🔶 Network Layer: The segmented data is further broken down into packets with routing information.

🔶 Data Link Layer: Packets are encapsulated into frames for transmission over the network.

🔶 Physical Layer: The frames are converted into binary signals (0s and 1s) suitable for transmission over physical media like cables.

📧When the email reaches your friend:

- The data goes through the layers in the opposite order to be reconstructed and presented:

🔷 Physical Layer: The binary signals are converted back into frames.

🔷 Data Link Layer: Frames are reassembled into packets.

🔷 Network Layer: The packets are combined to form the original segmented data.

🔷 Transportation Layer: Segmented data is assembled into its complete form.

🔷 Session Layer: The communication session is concluded.

🔷 Presentation Layer: Any data decompression or format conversion occurs here.

🔷 Application Layer: The data is delivered to the email software in a human-readable format for your friend to read the email.

The OSI model serves as a guideline for designing and understanding network communication protocols, allowing devices to communicate with each other effectively.