OSI model with examples

Let's go through each layer of the OSI model with examples:

1.    Physical Layer:

·       Example: Ethernet cables, fiber optic cables, wireless transmission (Wi-Fi), hubs.

2.    Data Link Layer:

·       Example: Ethernet frames, PPP (Point-to-Point Protocol), MAC addresses.

·       Sub-layers: LLC (Logical Link Control) and MAC (Media Access Control).

3.    Network Layer:

·       Example: IP (Internet Protocol), ICMP (Internet Control Message Protocol), routing protocols (e.g., OSPF, BGP).

·       Concerned with logical addressing and routing.

4.    Transport Layer:

·       Example: TCP (Transmission Control Protocol), UDP (User Datagram Protocol).

·       Manages end-to-end communication, flow control, and error detection.

5.    Session Layer:

·       Example: NetBIOS (Network Basic Input/Output System), RPC (Remote Procedure Call).

·       Manages sessions, establishes, maintains, and terminates connections.

6.    Presentation Layer:

·       Example: JPEG, GIF, encryption/decryption.

·       Deals with data format translation, encryption, and compression.

7.    Application Layer:

·       Example: HTTP/HTTPS (Hypertext Transfer Protocol/Secure), FTP (File Transfer Protocol), SMTP (Simple Mail Transfer Protocol), DNS (Domain Name System).

·       Provides network services directly to end-users or applications.

Let's take an example to illustrate how the OSI model works in a real-world scenario:

Suppose you want to access a website using your web browser:

• Application Layer: Your web browser uses the HTTP or HTTPS protocol to request the web page from the server.
• Presentation Layer: If the data needs to be encrypted (as in the case of HTTPS), this layer would handle encryption and decryption. It also ensures that the data is presented in a format that both the sender and receiver understand.
• Session Layer: Manages the session between your browser and the web server. It establishes the connection, maintains it while you're browsing, and terminates the connection when you close the browser.
• Transport Layer: If using HTTP, the browser may use TCP to ensure reliable delivery of data. TCP manages the flow of data and provides error checking.
• Network Layer: The request is broken into packets, and each packet is assigned an IP address. Routers at this layer determine the best path for these packets to reach the destination server.
• Data Link Layer: Each packet is encapsulated into a frame, and the MAC addresses (hardware addresses) of the source and destination devices are added. Ethernet is an example of a data link layer protocol.
• Physical Layer: The frames are transmitted over the physical medium, such as Ethernet cables or Wi-Fi signals.

At the destination, the process is reversed, with each layer handling its specific responsibilities until the data reaches the application layer of the server.

Understanding the OSI model helps in troubleshooting network issues, designing networks, and comprehending how different protocols and technologies interact in a networked environment.