024.1 Lesson 1

Wired networks use physical cables to connect devices, much like how a charger connects your phone to a power outlet. The most common types of wired connections are Ethernet and fiber optic.

Ethernet is widely used in homes and offices because it can send data quickly, similar to how a water hose delivers water at high pressure. It works well over both short distances, like between your computer and a nearby router, and longer distances within a building.

Fiber optic cables, on the other hand, are like the superhighways of the internet. Instead of using electrical signals like Ethernet, they use light to transfer data, making them much faster and capable of carrying data over much longer distances — think of fiber optics as delivering information at the speed of light. However, just as building a highway is more expensive than laying a regular road, fiber optics are more costly and complex to install, so they’re most often found in large companies or for internet connections between cities.

In contrast, Wi-Fi networks use radio waves to send data, similar to how your car radio picks up music from a station without needing any wires. Wi-Fi is incredibly popular because it lets your devices, like smartphones and laptops, connect to the internet without the hassle of plugging in any cables. This flexibility makes it great for moving around the house while staying connected.

Wi-Fi typically operates on two “channels” or frequency bands: 2.4 GHz and 5 GHz. Think of these like lanes on a road. The 2.4 GHz band is like a wider road that reaches farther — allowing you to connect even in rooms far from the router — but the speed is slower, like driving on a busy highway. On the other hand, the 5 GHz band is like a faster but narrower lane. It gives you quicker speeds for things like streaming or gaming, but you need to be closer to the router, just like how speeding is easier on a short, clear road.

However, while Wi-Fi is super convenient, it can be more easily disrupted, much like how radio signals can be affected by walls or other electronic devices. It’s also more exposed to security risks, so measures such as strong passwords and encryption are important to keep your network safe from unwanted visitors.

Cell networks, including 3G, 4G, and now 5G, employ tall cell towers to send and receive data from your mobile phone. These towers send out signals that your phone picks up so you can access the internet without needing Wi-Fi or any cables. These networks are what allow you to use apps, browse the web, or stream music while you’re out and about, even when you’re far from home.

Each generation — 3G, 4G, and 5G — represents a leap in how fast and powerful these networks are. 3G is like an old, slower road that used to be great for simple activities like sending texts or loading basic websites. 4G came along and made everything faster, allowing for activities such as video streaming and quicker downloads. 5G is the newest and fastest, like a high-speed bullet train that can handle even more data at once, making it ideal for activities such as virtual reality and smart devices.

However, just as some areas have better road conditions than others, the speed and strength of your cell network depend on where you are. In some places, you might have great 4G or 5G coverage, giving you fast speeds, whereas in other areas, the signal might be weaker, resulting in slower internet connections.

To understand how network devices communicate, it’s crucial to grasp how they identify and recognize each other within different types of network media, such as Wi-Fi, Ethernet, fiber optic, or cell networks.

This identification is essential because when one device makes a request to another, it must be possible to determine where the data packet originated and which computer the intended recipient is on.

On a local network level, this addressing is handled by a convention known as the MAC address (Media Access Control). The MAC address acts like a unique “fingerprint” for each device on the network, ensuring that data is properly directed and delivered to the correct device. Without this type of addressing, it would be impossible to manage data traffic between multiple connected devices, leading to confusion and data loss.

Every device connected to a network has its own MAC address, making the addresses essential for communication within that network. Each MAC address consists of six pairs of hexadecimal characters or bytes, where the first three pairs typically identify the manufacturer of the device, and the last three pairs are specific to that particular device.

The Institute of Electrical and Electronics Engineers (IEEE) maintains the standard for MAC addresses. The standard defines that the first three bytes, known as the Organizationally Unique Identifier (OUI), identify the manufacturer — Cisco, Intel, etc. The OUIs are assigned to manufacturers by the IEEE. The remaining three bytes are determined by the manufacturer, who is responsible for managing the numbering of each device they produce.

An example of a MAC address is:

00:1A:2B identifies the manufacturer. This particular OUI refers to a certain small manufacturer of communications products. 3C:4D:5E` is the unique identifier for that specific device produced by the manufacturer.

Although a MAC address is unique and embedded in the hardware, it can be modified through various techniques, allowing it to be changed when necessary.

To manage and direct the flow of data within networks, several important devices are used, each with a specific role. These are described in the following sections.

An IP network is a network that uses the Internet Protocol (IP) to send and receive data between devices. Every device on an IP network — whether it’s a computer, smartphone, or server — has a unique identifier known as an IP address. This address functions like a home address for your device, allowing data to find its way to the correct destination.

There are two primary versions of IP addresses, each with its own format and purpose.

Internet Protocol version 4 (IPv4) is the most widely used version of IP addressing. It consists of four groups of numbers, each ranging from 0 to 255, separated by periods (e.g., 192.168.1.1). The total number of available IPv4 addresses is around 4.3 billion, which may seem like a lot, but due to the exponential growth of internet-connected devices (smartphones, computers, IoT devices, etc.), IPv4 addresses have become increasingly scarce. To address this shortage, techniques like Network Address Translation (NAT) were implemented to extend the usefulness of IPv4, but this was only a temporary fix.

Internet Protocol version 6 (IPv6) solves the limitations of IPv4. This version uses a much longer and more complex format, consisting of eight groups of four hexadecimal digits separated by colons (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334). IPv6 provides an almost limitless pool of addresses — approximately 340 undecillion — enough to support the growing demand for internet-connected devices far into the future. Beyond just offering more addresses, IPv6 also improves efficiency, simplifies routing, and enhances security with features such as built-in encryption and improved device authentication.

IP networks are incredibly flexible. They can be small, such as a Local Area Network (LAN) that connects devices in a home or office, or they can be vast and complex, such as a Wide Area Network (WAN) that spans multiple cities or countries. However, all IP networks rely on the same fundamental principles of addressing and packet forwarding to function.

When data is sent across an IP network, it is broken into small units called packets. Each packet is tagged with the source and destination IP addresses and then routed across the network. Routers, which were discussed earlier, are responsible for directing these packets to the correct destination, using the IP addresses as a guide.

The internet is essentially the largest IP network in the world, connecting billions of devices globally. It works by interconnecting multiple smaller networks, allowing them to communicate with one another. When you visit a website, send an email message, or stream a video, your device communicates with servers located all around the world via the internet.

The internet is based on a collection of protocols, the most important of which is Transmission Control Protocol/Internet Protocol (TCP/IP). This suite of protocols ensures that data is transmitted reliably across different networks. The IP part, already discussed, handles addressing and routing, while the TCP part ensures that data arrives intact and in the correct order, even if it’s sent in multiple packets.

One of the key aspects of the internet is decentralization. No single entity controls the entire internet; instead, it is made up of many interconnected networks, each managed by different organizations, companies, and governments. This decentralized structure makes the internet highly resilient but also introduces challenges in regulation, security, and privacy.

At the core of internet communication is routing — the process of determining the best path for data to travel from one device to another across different networks. Think of it like GPS for the internet. When you send a request to load a website, your data is broken down into small packets, which need to find their way from your device to the server hosting that website. As mentioned before, routers are specialized devices that direct traffic between networks and determine the most efficient route for these packets.

Routers make decisions based on IP addresses. They forward data based on the destination IP address, hopping from one network to another until the data reaches its final destination. Just as a package in the mail might pass through several distribution centers before reaching your home, data packets travel through multiple routers across different networks.

Routing happens at the Network Layer (Layer 3) of the OSI model, and routers use protocols such as IP to guide packets.

One important concept in routing is the default router, often referred to as the default gateway, which plays a crucial role in how devices communicate both within a local network and with the wider internet. Simply put, a default router acts as a bridge between a local network (such as the one in your home) and external networks, most commonly the internet.

A default router is the device that your computer or other devices use to access external networks. When a device on a local network needs to send data to another device that is not part of the same network — such as accessing a website or connecting to a cloud service — it sends the data to the default router. The router then forwards this data to the appropriate destination on the internet or another external network.

In most home or small office setups, the default router is the same device as your wireless router, which connects your home to the internet via an ISP.

Your connection to the internet is made possible by ISPs, which are companies that provide access to the internet for homes, businesses, and organizations. They operate large networks of routers, cables, and servers that connect smaller local networks (like your home Wi-Fi) to the global internet.

An ISP assigns your home or business a unique public IP address, which allows your router to communicate with other devices on the internet. When you type in a web address, your device first contacts your ISP, which directs your request to the appropriate destination on the internet. The ISP acts as a “middleman,” routing your data to its destination, and sending the responses back to you.