OSI Model Explained | Real World Example

Summary

In this video, Ser Bros explains the OSI model, a seven-layer framework used to understand how networks function. It details each layer, from the physical layer (Layer 1) to the application layer (Layer 7), and how data is processed through them. The video highlights the real-world example of sending an email, showing how the data is encapsulated at each layer. The video also covers how the OSI model can help with troubleshooting network issues, by pinpointing problems at specific layers. Despite the OSI model being less commonly used today, its concepts remain essential in network management and troubleshooting.

Takeaways

• 😀 The OSI model is a seven-layer theoretical stack used as a reference to understand how networks operate.
• 😀 The OSI model was created to standardize networks and enable multi-vendor systems to communicate.
• 😀 Although the OSI model is not used directly in practice, it remains important for troubleshooting and describing network operations.
• 😀 The seven layers of the OSI model are: Physical, Data Link, Network, Transport, Session, Presentation, and Application.
• 😀 Layer 1 (Physical) handles the transmission of raw data over physical hardware like Ethernet cables.
• 😀 Layer 2 (Data Link) adds physical addresses (MAC addresses) and is where switches operate.
• 😀 Layer 3 (Network) deals with IP addressing and routing, with routers operating at this layer.
• 😀 Layer 4 (Transport) is responsible for transport protocols like TCP and UDP, ensuring data delivery through error handling and sequencing.
• 😀 Layer 5 (Session) manages the establishment and termination of connections between devices.
• 😀 Layer 6 (Presentation) formats data for the receiving device and handles encryption/decryption when necessary.
• 😀 Layer 7 (Application) is where user communication occurs, utilizing application-specific protocols like SMTP for email sending.
• 😀 Encapsulation describes how data moves through each OSI layer, adding necessary information at each stage (e.g., addresses, protocols).
• 😀 Troubleshooting network issues can involve checking each OSI layer, identifying problems at specific layers such as Layer 1 (hardware) or Layer 3 (IP addressing).

Q & A

What is the OSI model?

The OSI model is a theoretical stack of seven layers that help explain how networks operate. It was introduced to standardize networks and ensure multi-vendor systems could communicate with each other.

Why don't we use the OSI model in practice?

Although we don't use the OSI model in practice, we use the TCP/IP model. The concepts of both models are similar, but the layers are slightly different. The OSI model is still referenced in troubleshooting and explaining network operations.

What is the purpose of the physical layer in the OSI model?

The physical layer is responsible for carrying data across physical hardware, such as ethernet cables. It is the lowest layer of the OSI model.

What happens at the data link layer?

At the data link layer, physical addresses (such as MAC addresses) are added to the data. This is where devices like switches operate.

What is the role of the network layer in the OSI model?

The network layer handles IP addressing and routing. At this stage, source and destination IP addresses are added, and routers operate at this layer.

How does the transport layer function?

The transport layer adds transport protocols such as TCP and UDP. TCP, for instance, ensures error handling and sequencing to guarantee no data is lost. It also adds source and destination port numbers.

What is the responsibility of the session layer?

The session layer is responsible for establishing, managing, and terminating connections between devices.

What happens at the presentation layer?

The presentation layer formats the data so that the receiving application can understand it. It can also encrypt and decrypt data if necessary.

What does the application layer do?

The application layer is where users and applications interact. It uses application-specific protocols, such as SMTP for sending emails, to facilitate communication.

How does the OSI model help in troubleshooting network issues?

When troubleshooting a network issue, the OSI model can be used to check each layer to identify where the problem is occurring. For example, checking Layer 1 for hardware issues, Layer 2 for switch issues, or Layer 3 for IP address problems.