- ✓The OSI model divides network communication into seven layers, each responsible for a specific aspect of data transmission.
- ✓TCP/IP is the practical protocol suite that underpins the internet, combining the transport and internet functions into a streamlined four-layer model.
- ✓Protocols such as HTTP, HTTPS, DNS, DHCP, and FTP each serve specific purposes and operate at defined layers of the network model.
- ✓Understanding how data is encapsulated as it travels down the protocol stack and de-encapsulated at the receiving end is fundamental to networking.
- ✓Network protocols are standardised by bodies such as the IETF and IEEE, ensuring interoperability between devices from different manufacturers.
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Start learning →Alex: Welcome back. We're starting Unit 2 today, which is all about Networking. And we're beginning with the fundamental principles and protocols. Sam, networking is a huge topic. Where do we start?
Sam: We start with the question of how any two devices on a network actually communicate. The answer involves layers. Networking is so complex that it was broken down into a layered model, where each layer handles a specific aspect of communication and relies on the layer below it. The most famous model is the OSI model, which has seven layers.
Alex: Can you run us through those layers?
Sam: The bottom layer is the Physical layer, which deals with the actual transmission of bits over a medium, whether that's electrical signals over copper cable, light pulses over fibre optic, or radio waves for wireless. Layer 2 is the Data Link layer, which handles error detection and frames data into packets for the physical medium. Layer 3 is the Network layer, which handles routing data between different networks, and that's where IP addresses live. Layer 4 is the Transport layer, which is where TCP and UDP operate, managing end-to-end communication between applications.
Alex: And the top three layers?
Sam: Layers 5 through 7, the Session, Presentation, and Application layers, deal with managing connections, data formatting, and the application-specific protocols respectively. In practice, the TCP/IP model, which is what the internet actually uses, condenses this into four layers: Network Access, Internet, Transport, and Application. Most practical networking knowledge focuses on the TCP/IP model.
Alex: What are the key protocols we need to know about?
Sam: HTTP and HTTPS are the protocols used for web browsing; the S in HTTPS indicates that the connection is encrypted using TLS. DNS, the Domain Name System, translates human-readable domain names like www.example.com into the IP addresses that routers use to route traffic. DHCP, Dynamic Host Configuration Protocol, automatically assigns IP addresses to devices when they join a network. FTP and SFTP are used for transferring files.
Alex: Why does it matter that these protocols are standardised?
Sam: Standardisation is what makes the internet work at all. A web server made by one manufacturer can communicate with a browser running on a device from a completely different manufacturer because both of them implement HTTP in the same way. Without these standards, every device would need custom software to communicate with every other type of device, which would be completely unworkable at scale.
Alex: Who is responsible for creating and maintaining these standards?
Sam: Several bodies. The Internet Engineering Task Force, or IETF, publishes standards called RFCs, Requests for Comments, which define internet protocols. The IEEE, the Institute of Electrical and Electronics Engineers, is responsible for many physical and data link layer standards including the 802.11 standards for Wi-Fi. Understanding that these standards bodies exist and how to look up their documentation is useful for any networking professional.
Alex: What's the most important concept from this lesson for a student to take away?
Sam: The layered model. Once you understand that networking is structured in layers and that each layer has a specific job, a huge amount of other networking knowledge starts to make sense. When you're troubleshooting a network problem, the OSI model gives you a structured way to diagnose which layer the problem might be at.
Alex: Brilliant. Thanks Sam. Next we're looking at the actual devices that make networks tick.