At its core, Digital Subscriber Line (DSL) technology was created to solve the “last mile” problem—the final stretch of wiring that connects a service provider’s network to your home. For decades, this last mile consisted of simple copper telephone lines, which created a bottleneck for the high-speed data of the burgeoning internet.

Think of your phone line as a road. Originally, it was a single, slow lane designed for just one purpose: carrying the low-frequency signals of voice calls. DSL technology was the breakthrough that figured out how to add multiple, high-speed lanes to that very same road. It achieved this by using a much wider range of frequencies on the copper wire, allowing massive amounts of data to travel alongside the original voice lane without causing a traffic jam.

However, not all DSL is created equal. Over the years, engineers developed several “flavors” of this technology, each optimized for different speeds, distances, and purposes. This guide will demystify these different types and explain how they work to bring the internet to you.