Layers of the Internet

Have you ever wondered what happens when you look something up online? What happens in the background when you send a message or download a file? Behind every single online interaction like that lies a structured set of protocols that facilitate them. Those protocols enable data to flow smoothly across the networks upon networks that compose the Internet. Each of them has its own layers that handle the different processes that go on in the background during a connection.

These protocols are separated into two distinct models: the Internet Protocol Suite and the Open Systems Interconnection (OSI). They are the fundamental frameworks that describe how computers communicate over networks, which is what the Internet is basically: computers talking to each other. The Internet Protocol Suite is the model that is in active use today, while OSI is a more detailed guideline, or reference, for understanding network interactions. Read on as we examine their levels to understand the logic behind how things work online.

This post includes:

• The Internet Protocol Suite
• OSI

The Internet Protocol Suite

The Internet Protocol Suite is more colloquially known as TCP/IP. We will go into more detail about those abbreviations in a bit, but they are the two key protocols that the suite relies upon, that the Internet depends upon. That is why TCP/IP refers to the Internet Protocol Suite.

You can think of TCP/IP as a set of rules that define how computers communicate over the Internet. It is split into four layers, each of which performs a different function that ultimately enables computers to transfer data between each other. Without these four layers, we would not have the Internet as we know it today. So, let us take a look at each of these layers and explain them in detail, starting from the bottom.

1. Link Layer - This layer is the foundation of the Internet Protocol Suite (TCP/IP). It is responsible for moving data between devices on the same local network. It combines the physical aspect of data transmission (network wires, for example) and the organization of the data that is to be sent. Data is collected into ‘frames,’ which are the units of data the Link Layer uses. These ‘frames’ contain the data and the sender and receiver addresses – typically a MAC address. This layer ensures devices connected to the same local network can communicate directly without involving an outside network. The Ethernet protocol is a widely used protocol in this layer;
2. Internet Layer - Once the Link layer has to move data beyond a local network, it sends it to the Internet (Network) layer. That is the ‘routing’ layer of the Internet Protocol suite. There, it is broken down into smaller bits called ‘packets.’ When the packets are ready for sending, the Internet Protocol (IP) comes into play, essentially labeling each packet with the IP address of the recipient machine. Then, the protocol determines the shortest route to said recipient and sends the packets along. The receiving machine reassembles this chain of packets, and the data is received;
3. Transport Layer - While the Internet Layer ensures that data is sent to the correct recipient, the Transport layer ensures it is received. This layer is responsible for confirming that each piece of data is received and, if not, resending it until it is ready. The two primary protocols utilized here are TCP (Transmission Control Protocol) and UDP (User Datagram Protocol);
4. Application Layer - The top-most layer of the Internet Protocol Suite is where applications like web browsers operate. It is responsible for the delivery of data to the end user. Here, various protocols determine how software interfaces with the network to receive and transmit data. Some of the more common protocols are HTTP, SMTP, and FTP.

Now that we have elaborated on these layers, their responsibilities, and the protocols they use, the Internet makes much more sense, does it not? Each layer has its own job; we cannot send or receive data over the Internet without any of them. So, no YouTube or cat pictures!

The Internet Protocol Suite (TCP/IP) is the practical way that computers ‘speak’ to each other. This model has been used for decades now. There is a second model, however, that is more conceptual and not used nearly as much as TCP/IP but offers a detailed reference to each stage of data transfer.

OSI

The OSI model consists of almost twice as many layers as TCP/IP because it is a mostly conceptual framework for how communication between devices works. It is a comprehensive guide to network theory and how each step of the transmission process works.

As we go through the layers, from bottom to top, you will see why this more detailed breakdown of networking processes is a good idea to have on hand if you are trying to understand or troubleshoot a network connection within an application.

1. Physical Layer - This is where everything begins. The Physical layer is all about the hardware involved in data transfer. Cables, routers, network switches, etc. Here, data is converted into the necessary medium via which it will travel, like a fiber optic cable;
2. Data Link Layer - Here, data is organized in packets and then transmitted to other devices on the same network. Additionally, this layer checks for errors within these packets and resends them if necessary;
3. Network Layer - This is similar to the Data Link layer. However, it facilitates data delivery between different networks. Data is broken down into packets on the sender’s device, and the layer then determines the quickest physical route to the receiver’s device, where the packets will be reassembled. Typically, this is done via the Internet Protocol;
4. Transport Layer - This layer is responsible for reliable data transfer. It checks the data’s integrity and controls error recovery, flow, and retransmission of lost data. TCP and UDP are most commonly used here;
5. Session Layer - For two devices or applications to communicate and transmit data, a session must be created. This session is the ‘dialogue’ between the two devices, and the Session layer facilitates it. It opens, maintains, and closes the dialogue;
6. Presentation Layer - This layer is responsible for translating incoming data to a format readable by the application receiving it. It ensures that the recipient of the data gets it in a format it can process. The layer also encrypts data that leaves the application and decrypts data that arrives if the connection type is encrypted;
7. Application Layer - Finally, the Application layer is responsible for the protocols applications themselves use to interact with data. Some of those protocols include HTTP, SMTP, and FTP.

You can see for yourself how much more detailed this model is compared to TCP/IP. While TCP/IP is the model widely used in modern-day data transmission, OSI is a solid reference for how networking actually works.

Both models show how devices and applications communicate with each other, and understanding them is essential to grasp the underlying mechanics of the Internet. By familiarizing yourself with them, we hope you will have a better understanding and appreciation of the seamless connectivity that permeates our modern world.

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