Series: Computer Networking from Absolute Basics — Part 2 This is the part 2 of my series “Computer Networking from Absolute Basics”. If you haven’t read part 1 yet, I’d really appreciate it if you check that out first. It mainly covers what the internet is, how we access it, how data travels from one end system to the other end system, and more. Part 1 was published in MeetCyber and can be read here: Click Here That said, if you’re already familiar with these basics and want to jump straight into access networks , feel free to continue reading. Access Networks Photo by Conny Schneider on Unsplash Access network is the part of the network that connects end devices to the ISP’s first router, also called edge router . An ISP (Internet service provider) is a company that provides access to the internet. Everything from your home router or modem up to the ISP’s first router falls under the access network. This includes all the network equipments and physical links between your home router or modem and the ISP’s first router. The access network doesn’t include the end device itself. Now that we understand what an access network is, the next question is: how do we actually connect our homes to the ISP? The answer isn’t the same for everyone. Depending on where you live and the infrastructure available, your internet connection may use telephone lines, cable TV lines, or optical fibre. These different way of connecting end users to the ISP are called access technologies . In the next sections, we’ll look at common access technologies used today. ACCESS TECHNOLOGIES Home Access: DSL ( Digital Subscriber Line ): It is a technology that allows you to get a high speed internet over your existing telephone lines. How does DSL work? A telephone line can carry signals at different frequencies. Low frequencies are used for voice calls while, high frequencies are used to carry internet data. Because of this frequency separation, a telephone call and an internet connection can share the same DSL line at the same time without interfering with each other. Now, let’s take a look at a diagram to make everything crystal clear. DSL internet access technology Types of DSL: ADSL ( Asymmetric Digital Subscriber Line ) : Downstream (download) speeds are higher than upstream (upload) speeds. SDSL ( Symmetric Digital Subscriber Line ) : Downstream (download) speeds are equal to upstream (upload) speeds. 2. Cable Internet access : Cable Internet uses the cable TV wires that are already installed in many homes. A residence usually gets cable internet access from the same company that provides its cable television service. From the ISP’s side, fiber optic cables are used because they are very fast. The fiber reaches a junction point in your neighbourhood and from there, coaxial cable runs to individual houses or apartments. Since both fiber and coaxial cables are used in this setup, it is referred to as hybrid fiber coax (HFC). Cable internet access requires a cable modem, a cable modem is usually connected to a home router through an Ethernet port, and the router then connects to computing devices such as laptops and smartphones. We’ll discuss Ethernet later in the series. At ISP’s central location, called the head end. CMTS manages communication between multiple cable modems and the ISP’s network. The CMTS receives data from cable modems on the upstream channel and sends data back to them on the downstream channel. In simple terms, it acts as the central control point for cable internet, performing a role similar to what a DSLAM does in DSL networks. Cable modems divide the HFC network into two channels, a downstream and an upstream channel. Hybrid fiber-coaxial cable One important point to note is that cable internet access is a shared broadcast medium . This means that data sent by the ISP is broadcast to everyone in the neighbourhood, and each cable modem picks only the data meant for it . Because the medium is shared, if several users in the same neighbourhood download large files or stream videos at the same time, they all use the same downstream channel . As a result, the actual data rate received by each user becomes lower than the total (aggregate) downstream capacity of the cable network. The same idea applies to the upstream channel as well. When multiple users upload data simultaneously, such as sending files, joining video calls, or backing up data to the cloud, they must share the available upstream bandwidth , which can reduce individual upload speeds. A simple way to understand this is through an analogy. Imagine a single large water pipe supplying water to many houses in a neighbourhood. When only a few houses are using water, everyone gets good water pressure. But when many houses turn on their taps at the same time, the water pressure at each house drops . In the same way, cable internet users share a common communication channel, and heavy usage by many users at the same time can reduce the speed experienced by each individual user. 3. FTTH ( Fiber to the home ) : FTTH (Fiber to the Home) is an access technology in which optical fiber cables run from the ISP to the user’s home . Unlike DSL or cable internet, FTTH does not rely on copper or coaxial cables for the last part of the connection. Instead, it uses optical fiber cables that carry data as light signals directly to the home. At the ISP’s central office, a device called the Optical Line Terminal (OLT) is responsible for managing communication with many homes. Think of the OLT as a traffic controller : Downstream : sends data to everyone Upstream : tells each home when to speak and for how long A single optical fiber leaves the OLT and travels toward a neighbourhood. When this fiber reaches very close to homes , it is split using a passive optical splitter , and individual fiber strands then go to each house or apartment. Downstream communication When the OLT sends data downstream, the optical splitter simply copies the same light signal and forwards it to every connected home . As a result, every ONT receives all downstream data . Now you might wonder what an ONT is. ONT ( Optical Network Terminator ) acts like a fiber modem by converting light signals to electric signals and vice-versa. However, this does not mean users can see each other’s data. Each packet is encrypted , and an ONT at the user’s home can only decrypt the packets meant for that specific user . All other packets are discarded. Upstream communication Upstream communication works differently. Since multiple homes share the same fiber toward the OLT, transmissions must be carefully coordinated . Each home is assigned specific time slots during which it is allowed to transmit data. This prevents signals from different homes from colliding on the shared fiber. Simplified FTTH (PON-based) 4. 5G fixed wireless 5G Fixed Wireless Access (FWA) is an access network technology that delivers high-speed broadband connectivity using 5G wireless signals instead of traditional wired connections like fiber or DSL. It provides homes and businesses with low-latency, high-capacity internet through radio links, often serving as a cost-effective alternative to laying physical cables. Essentially, it brings 5G mobility performance to fixed locations, enabling ultra-fast internet without extensive infrastructure deployment. Access in the Enterprise and the Home: Ethernet Ethernet is a wired access technology widely used to connect end devices like computers and routers to a local area network (LAN). It provides reliable, high-speed, and low-latency connectivity, typically using twisted-pair or fiber-optic cables, and is the backbone for enterprise and home networking. 2. WiFi Wi-Fi is a wireless access technology that allows devices to connect to a network over radio waves. It offers flexibility and mobility within homes, offices, and public areas, supporting high-speed internet without physical cables, though speeds and reliability can vary depending on distance, interference, and network congestion. How the Internet Reaches Your Home (Summary): Imagine the Internet as a stream of information flowing from your ISP to your home. It travels over an access network like DSL (telephone lines), cable (TV cables), or FTTH (optical fiber) until it reaches your router. Inside the router is a built-in access point (AP) , which acts like a translator — turning this digital stream into Wi-Fi radio signals that your phones, laptops, and smart devices can understand. Devices that prefer a wired connection can still tap into the Internet through Ethernet cables . In essence, the access point is the bridge that brings the wired Internet to life wirelessly inside your home. Wide Area Wireless Access and Base Station: Wide Area Wireless Access (WWA) delivers Internet connectivity over large geographic areas using cellular or radio networks, enabling devices to stay connected across cities, towns, or even remote locations. Technologies like 4G, 5G, and LTE provide broad coverage far beyond what Wi-Fi can reach. At the heart of this network are base stations (cell towers), which act as communication hubs. Each base station transmits and receives radio signals within a specific area, manages multiple device connections, and links users to the core network, effectively bridging mobile devices to the Internet while on the move. That’s it for Part 2! We’ll continue exploring more in the next part of this series. I’m still learning, so if you notice any mistakes or have suggestions, I’d love to hear them. This series is based on what I’m reading in the book Computer Networking: A Top-Down Approach by James F. Kurose and Keith W. Ross, and I’m sharing it here as I understand it. Next up: the network core — let’s explore it together in the next post!” References James F. Kurose & Keith W. Ross, Computer Networking: A Top-Down Approach , 8th Edition, Pearson. Deep Dive into Access Networks was originally published in InfoSec Write-ups on Medium, where people are continuing the conversation by highlighting and responding to this story.