Understanding Networking Layers

To really understand networking, we need to grasp all of the components involved. We're talking about everything from the cables that connect devices to each other to the protocols that these devices use to communicate. There are a bunch of models that help explain how network devices communicate, but in this course, we'll focus on a five-layer model. By the end of this lesson, you'll be able to identify and describe each layer and its purpose.

Physical Layer 📦🔌

Let's start at the bottom of our stack, where we have what's known as the physical layer. The physical layer represents the physical devices that interconnect computers. This includes the specifications for networking cables and connectors that join devices together, along with specifications describing how signals are sent over these connections.

Data Link Layer 🖧🔗

The second layer in our model is known as the data link layer. Some sources will call this layer the network interface or the network access layer. At this layer, we introduce our first protocols. While the physical layer is all about cabling, connectors, and sending signals, the data link layer is responsible for defining a common way of interpreting these signals so network devices can communicate. The most common protocol at this layer is known as Ethernet, although wireless technologies are becoming more popular.

Network Layer 🌐🌍

The third layer, the network layer, is also sometimes called the internet layer. It allows different networks to communicate with each other through devices known as routers. A collection of networks connected together through routers is an internetwork, with the most famous one being the internet. The network layer is responsible for getting data delivered across a collection of networks. The most common protocol used at this layer is known as IP (Internet Protocol), which is the heart of the internet and most small networks worldwide.

Transport Layer 🚚📦

The transport layer delivers data between two individual nodes and sorts out which client and server programs are supposed to receive that data. The transport layer protocol most commonly used is TCP (Transmission Control Protocol). It ensures that data is reliably delivered. Another protocol used at this layer is UDP (User Datagram Protocol), which does not provide reliability mechanisms like TCP. The transport layer, together with the network layer, ensures that data gets to the right applications running on those nodes.

Application Layer 💻📧

The fifth layer is known as the application layer. Protocols at this layer are application-specific and allow you to browse the web, send and receive email, and perform various other application-related tasks. The protocols in the application layer will be most familiar to you since you've probably interacted with them directly before, even if you didn't realize it.

You can think of these layers as different aspects of a package being delivered. The physical layer is the delivery truck and the roads. The data link layer is how the delivery trucks get from one intersection to the next. The network layer identifies which roads need to be taken to reach the destination. The transport layer ensures that the delivery driver knows how to knock on your door to inform you that your package has arrived. And finally, the application layer represents the contents of the package itself.

Now that you have a better understanding of these networking layers, you can delve deeper into each one and explore the intricacies of network communication.