OSI Model Layer 5, 6, and 7 -- Session, Presentation, & Application Layers -- what they actually do

Summary

This video explores the often-overlooked layers 5, 6, and 7 of the OSI model, emphasizing their practical importance in networking. The speaker demystifies how these layers contribute to the functionality of the internet, from managing user sessions (layer 5), interpreting data (layer 6), to defining application commands (layer 7). Using relatable examples like HTTP cookies, the video shows how these layers work in harmony. It also highlights why the TCP/IP model combines these layers into a single application layer, encouraging viewers to see networking models as tools for understanding abstraction in computer networks.

Takeaways

• 💡 The OSI model is often misunderstood and seen as something just to memorize, but it's crucial for understanding how the internet works.
• 📶 Layers 5, 6, and 7 are often called the 'Forgotten Layers' because they're not as well covered as Layers 1 through 4.
• 🌍 The goal of networking is to allow data sharing between two users via computers, with each OSI layer playing a role in achieving this.
• 🖥️ Layer 5, the session layer, distinguishes between different user sessions, even if Layer 2, 3, or 4 information is the same.
• 🍪 HTTP cookies are an example of Layer 5, allowing users to maintain their session across different networks without logging in repeatedly.
• 🔢 Layer 6, the presentation layer, interprets the ones and zeros in a packet, converting them into characters or data formats like ASCII or Base64.
• 🌐 HTTP uses extended ASCII encoding at Layer 6 to translate binary data into readable characters.
• 🔎 Layer 7, the application layer, defines how the interpreted data is used, such as executing commands in HTTP to request a webpage.
• ⚙️ Different protocols (like FTP and HTTP) implement Layers 5, 6, and 7 differently based on their application needs.
• 📊 While OSI has seven layers, the TCP/IP model often combines Layers 5, 6, and 7 into one 'application layer' for simplicity, as protocols may handle these layers uniquely.

Q & A

What is the main focus of the video script?

The video focuses on explaining layers 5, 6, and 7 of the OSI model, which are often overlooked or combined into a single application layer in other models like TCP/IP.

Why are layers 5, 6, and 7 of the OSI model referred to as the 'Forgotten layers'?

They are referred to as 'Forgotten layers' because most resources and discussions on the OSI model focus on layers 1 through 4, and the TCP/IP model combines layers 5, 6, and 7 into a single application layer.

What problem does layer 5 of the OSI model solve?

Layer 5, the session layer, solves the problem of distinguishing between different user sessions. It allows networking protocols to keep track of user-specific data and separate different sessions, even if the underlying layer 2, 3, or 4 addresses are the same.

Can you provide an example of how layer 5 functions in modern computing?

An example of layer 5's function is HTTP cookies. These cookies store user-specific information that allows websites to identify users independently from changes in layer 2, 3, or 4 information, such as IP addresses, when switching networks.

What role does layer 6, the presentation layer, play in the OSI model?

Layer 6 determines how to interpret the ones and zeros received by a network. It manages tasks like data encoding, compression, and encryption by deciding how data should be formatted or interpreted, such as using Base64, hexadecimal, or ASCII encoding.

How does layer 7, the application layer, function in the OSI model?

Layer 7, the application layer, defines the application commands that are carried out after the data is processed and interpreted. For example, in HTTP, the 'GET' command is used to request web pages, making layer 7 responsible for executing such high-level functions.

Why are layers 5, 6, and 7 combined into a single application layer in the TCP/IP model?

Layers 5, 6, and 7 are combined in the TCP/IP model because each protocol or application handles these layers' responsibilities (session, presentation, and application) in its own way. Since there's no strict need to separate them, they are grouped as a single 'application layer' for simplicity.

How do different protocols like HTTP and FTP implement layers 5, 6, and 7 differently?

Different protocols implement these layers based on their specific needs. For example, HTTP uses cookies for session management (layer 5), extended ASCII encoding for data (layer 6), and commands like 'GET' for application operations (layer 7). In contrast, FTP may not have session management (layer 5) and uses its own set of application commands in layer 7.

What is the significance of understanding the OSI model in layers of abstraction?

Understanding the OSI model in layers of abstraction allows you to see how different networking responsibilities are divided among layers. Each layer focuses on a specific function, making networking more manageable by ensuring that higher layers do not have to worry about the details handled by lower layers.

Why is it important not to try to fit all networking knowledge strictly into the OSI model?

The OSI model and TCP/IP models are abstractions meant to teach networking concepts. Networking in practice can be more complex, and it's not always necessary to fit everything into one of these layers. These models serve as guidelines rather than strict rules.