DSL vs Cable vs Fiber Looking at the Big Picture of DSL, Cable, and Fiber Internet Service Technologies.

While politicians and media might have you believe that the Internet is delivered by “a series of tubes,” [1] anybody who’s gone through the process of configuring their DSL, cable, or fiber-optic connection knows that the truth is a little more nuanced.

For consumers, Fiber is the top choice. Cable is a runner up, with DSL coming in slightly behind on overall performance. Image via Martinelle/Pixabay.

In this post I’ll break down the differences between the most common methods of connecting to the Internet — DSL, cable, and fiber — to help you understand how these systems work and which makes the most sense for your Internet needs.

Part I: the basics

The Internet is an opportunist. It can travel by radio waves, phone line, cable networks, and even the electrical wiring in your house. For the most part, data travels between computers using physical wires.

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Because wires are so efficient (and widely available), most Internet connections come via some sort of cable. The prevalent options are: phone lines (DSL), cable lines (cable), and fiber-optic cables (fiber).

Cables that carry broadband: copper & fiber

There are differences in how data travels by each type of cable, but the big picture is the same: data traveling back and forth between computers. (In the context of surfing the web, that means data flowing between your computer and the computers that serve websites, called servers.)

In the case of DSL, the data travels as waves over copper phone lines (you know, the ones that fall down during storms). With cable connections, the data travels on coaxial copper cables buried underground, originally intended for television. Fiber connections, on the other hand, transmit data as bursts of light through strands of glass or plastic.

For most of us, understanding the technical specs of DSL vs cable vs Fiber isn’t important. What’s important is understanding the basics of how each Internet connection delivers data to your home or office. (For more nitty-gritty details about each DSL, cable, and fiber Internet systems, skip down to section II.)

The “backbone” of the Internet

To understand where the Internet is coming from, you can imagine the Internet as a tree. Your neighborhood is a twig, and the core of the tree is the “backbone” of the Internet.

The backbone of the Internet (the part that transmits data between cities, countries, and continents) is mostly made of fiber-optic cables. These networks are sprawling and complex, but the main thing to understand is that they’re basically bundles of fiber-optic cable that carry data over huge distances — across continents and under oceans between them.

“Last mile” technologies: ISPs connect you to the backbone

DSL, cable, and fiber connections all have one thing in common — connecting consumers to the “backbone.” For this reason, Internet services sold from ISPs to consumers are called “last mile” technologies. Even with a lowly dial-up connection, most of the journey data travels between your computer and remote servers happens over fiber on the Internet backbone or carrier fiber networks — but those last couple miles between your house and the ISP can slow things down considerably, when the data switches over to older copper cables.

DSL, cable, fiber: big picture overview

Here’s a quick overview of the pros, cons, and stats of the primary “last mile” technologies: DSL, cable, and fiber.

DSL

  • Delivers Internet via copper phone lines
  • 90% coverage nationwide
  • Segregates bandwidth within phone line to share with landline
  • Direct ISP-to-residence connection
  • Higher latency & lower bandwidth than cable
  • Speeds slower for users farther from ISP office

Cable

  • Delivers Internet via copper coaxial television cable
  • 89% coverage nationwide
  • Bandwidth generally shared with neighbors
  • Higher bandwidth & lower latency than DSL in most cases
  • Speeds not substantially affected by distance from ISP office

Fiber

  • Delivers Internet via fiber-optic cable
  • 25% coverage nationwide
  • usually uses cable connection between residence and fiber line
  • Next-generation speeds of up to 1Gbps up/down
  • Speeds not affected by distance from ISP

Section 2: let’s get technical

Advanced Guides

For readers with more technical background, please see our dedicated technical guides for cable, DSL, and fiber:

Terminology

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Internet infrastructures gets more complicated the closer you look at it. We’ll try to keep the jargon limited in this post, but there are a few critical terms important for understanding DSL, cable, and fiber Internet connections.

Bits vs. Bytes:

Bits and bytes both measure computer data. Unfortunately, they’re often confused by the average Internet user, thanks to the fact that they sound the same and both start with “b.”

Bits are the smallest piece of data possible, used to “encode” letters, numbers, code, and everything else that makes up the digital world. Each bit is either a zero or a one, with no in-between.

Similar to Morse Code, data travels as bits because it’s simple for wires and airwaves to transmit — on, off, on, on, off — however, it’s the ordering of bits that gives the data meaning.

Bits express data by arranging into meaningful eight-part patterns called bytes. Because bytes are the smallest chunk of data with real meaning, they’re commonly used to express storage capacity and file size. Bits, on the other hand, are more often used to describe Internet speed (mostly because 10 Megabits per second sounds way more impressive than 1.3 Megabytes per second).

Bits are expressed as a lowercase “b” in print, while bytes are expressed with an uppercase “B.” Because it takes so many bits and bytes to express even a simple file or package of data (millions of bytes in an mp3 file alone), metric prefixes are commonly used to express size:

  • 1,000 bytes = 1 kilobyte (1 KB)
  • 1,000,000 bytes = 1 megabyte (1 MB)
  • 1,000,000,000 bytes = 1 gigabyte (1 GB)

Upload/download & asymmetric/symmetric connections:

There are only two things you can do with data on the Internet: download it or upload it. Depending on your needs, the ratio between how much data you download and upload will differ. Because of this, Internet connections come in two flavors: asymmetric and symmetric.

Asymmetric connections can receive data faster than they send it — common for household connections, with the assumption that users spend more time watching YouTube videos than uploading them. (With the rise of gaming and real-time video communications like Skype, this assumption is becoming less relevant).

Symmetric connections, as the name suggests, send and receive data at the same speed.

DSL: technical overview

DSL stands for Digital Subscriber Line. Like cable, DSL uses copper cables to transmit data as waveforms. In the case of DSL, the cables are copper telephone wire, sharing the connection with your landline phone (if you still have a landline phone, that is).

DSL replaced dial-up Internet connections because the technology behind it (DSL modems, primarily) uses the phone cable much more efficiently. Dial-up connections had to effectively place a call to a modem at your Internet Service Provider(ISP), communicating data through waveforms on the same frequency as analog voice communications. This is why you couldn’t use your phone while connected to dial-up Internet.

DSL maintains an “always on” connection by utilizing a much higher frequency within the wire (4000Hz-4MHz, contrasted with the 300-3400Hz used for voice signal) to essentially segregate voice and digital communications in the same wire.

Telephone with cable.

DSL connections are delivered over twisted copper telephone networks. Image via Negative Space.

The technology that makes this possible is the humble DSL modem. DSL Modems modulate the signal at the sending end and demodulating it at the receiving end to decipher analog waveforms into clear-cut digital signal — think of DSL (and cable) modems as analog-to-digital translators.

Types of DSL connections

To complicate matters further, there are actually 14 different types of DSL service. The most common by far is ADSL (asymmetric digital subscriber line), deployed to most consumers based on the assumption that download speed should take priority of upload speeds.

Pros & cons of DSL

So what does this mean for the consumer? Well, DSL Internet has a few advantages and disadvantages in comparison with cable and fiber. The main selling point of DSL is widespread availability; telephone infrastructure is already deployed basically everywhere, so it doesn’t take much setup to get most folks connected by DSL, especially in rural areas where cable is less likely to be an option.

The second advantage is in how the connection reaches the end user: while cable connections are essentially shared within neighborhoods, DSL connects directly from ISP to consumer. While cable provides faster speeds, it can get bogged down at peak times (e.g. 6-9pm, when everyone in the neighborhood wants to stream Game of Thrones while their kids broadcast on Twitch upstairs). Because of this, the DSL connections can seem more consistent, even if they are overall slower than cable. .

The big con of DSL is the phone cable itself; telephone cables usually top out at around 40 Mbps down, while cable can deliver closer to 100 Mbps under ideal conditions. (However, shared bandwidth and unmaintained infrastructure often results in equivalent effective speeds for either technology much lower than 40 Mbps).

Distance between ISP office and residence is also a factor with DSL connections, as residences farther from the central office generally receive slower speeds and higher latency than those closer to the office. Because telephone cable is thinner in diameter than coaxial television cable or fiber, it requires “repeaters” every couple miles to keep the signal from degrading more than 3-5 miles from the ISP office where the fiber “backbone” meets the copper “last mile.”

Cable: technical overview

Behind DSL, cable is the most common type of home Internet access. Like DSL, cable Internet transmits data via copper wires — the difference is that cable uses higher-bandwidth coaxial cables laid underground, originally purposed for cable television service. Cable modems also differ somewhat from DSL modems, although the concept (modulating and demodulating analog signals at either end of the copper cable) is the same.

Like DSL, cable is a “last mile” technology that piggybacks on pre-existing networks to bridge the gap between ISPs and consumers.

Cable network diagram.

Cable bandwidth is often shared between houses in a neighborhood, but the coaxial cables it’s based on provides better overall performance than DSL.

The main difference from the consumer’s perspective is how the signal reaches their house once it’s in a neighborhood’s coaxial cable network. Although coaxial cable has a higher bandwidth capacity than telephone wires, that bandwidth is shared from a central “node” where the ISP “backbone” meets the local coaxial network. Anywhere from 100-2000 homes can share bandwidth through a single node [2], and the number of homes connected vary’s greatly depending on a combination of available infrastructure weighed against user subscription rate.

So long as the node can handle the bandwidth needs of its network, this system works well and saves on the cost of a direct ISP-to-residence connection. When improperly managed, however, it results in low speeds during peak use hours and “throttling” to ensure that “bandwidth hogs” don’t bog down the system. ISPs have recently started capping data usage to offset infrastructure difficulties.

ISPs have also been known to market hybrid fiber-coaxial networks in which the fiber switches to cable at a local cabinet as “fiber connections.” Because virtually all connections switch from fiber to copper at some point between the ISP office and the consumer, it’s important that Internet users check what technical definition their cable or fiber connection falls under; a full list is provided below.

Pros and cons of cable

Cable solves some of the problems associated with DSL service (low bandwidth, outdated infrastructure) but comes with its own host of potential failure points.

The biggest con when it comes to cable is higher cost, largely a product of lack of competition among cable providers — cable infrastructure is more expensive than telephone, so many Americans only have access to one provider if they want true broadband Internet.

The other problem point with cable is bandwidth sharing. Since bandwidth is shared within neighborhoods, oftentimes cable will be slowed to the same speed (or lower) than DSL during peak use times.

Fiber-optic: technical overview

Inside of light filled tube.

Fiber uses light, versus cable and DSL which use RF frequencies. Think of it as the difference between analog and digital. Image via Mathew Schwartz

Fiber optics are the fastest form of broadband currently available. Fiber optic cables transmit signal with light itself, making them a different beast altogether from copper-based technologies like DSL and cable.

The cable itself is made of densely-packed silica glass strands. Light is transmitted into each strand using laser transmitters, and the transmitted light particles “bounce” through the tube. In practice these tubes are very long (literally crossing oceans), so in practice communication companies employ repeaters to boost the signal; while copper telephone cables require repeaters every couple miles, fiber cables can go transmit a signal over as many as 80-100km without amplification; however, in practice, repeaters are usually installed every 20km or so.

Copper can technically conduct at close to the same speed; however, light bursts in glass are easier to interpret at either end than waveforms in copper, making fiber much, much faster in practice. (You can visualize fiber delivering clear-cut dots and dashes to your modem while cable delivers sloppy, ambiguous vibrations.) While cable bandwidth tops out at around 100 Mbps, services like Google Fiber can transmit signal at approximately 200,000 Km/s, enabling Internet speeds of up to 1 Gbps.

…Upload and download. That’s huge — around 10x what cable and DSL offer.

Additionally, fiber optic cable can transmit different wavelengths (colors) of light, allowing signal to be “split” at either end to multiply data capacity.

Fiber cable diagram.

Fiber cables transmit data as pulses of light rather than as RF transmissions.

The catch with fiber is availability; installing the cable is expensive, the cable itself is expensive, and ISPs and consumers generally don’t like to do expensive stuff. (We have this to thank for the “if it ain’t broke don’t fix it” situation with DSL and cable throughout the US.) Check our report on fiber availability in the US if you want to see what’s in your area.

Fortunately, this is starting to change as consumers get accustomed to bandwidth simply unavailable from traditional infrastructure and ISPs begin to realize that the cost per capacity of copper vs. fiber can lose them money in the long run. Since fiber cables are much smaller than copper while delivering many times the bandwidth, fiber installation can in some cases trump the high cost of the fiber cable itself from the ISP’s perspective.

Types of fiber connections

Diagram of fiber connection types.

Consumer “fiber” connections are described in terms of how close to the subscriber’s building the fiber line runs. FTTH (Fiber to the Home) is the optimum connection.

As it stands, not all fiber connections are created equal — and not all connections marketed as “fiber” are truly fiber all the way to your home network — leading to much confusion as some ISPs market “fiber” internet connections that are actually hybrid fiber-coaxial networks.

Fiber connections currently available fall under several categories, with each denoting at what point the fiber terminates. Here are the main categories you’re likely to see, in order of distance:

  • FTTP (fiber to the premises, including FTTH (home) and FTTD (desktop))
  • FTTB (fiber to the building, then shared between apartments via another technology)
  • FTTC (fiber to the cabinet, typically within 300 meters of residence)
  • FTTN (fiber to the node, typically within a 3 miles of residence)

Pros and cons of fiber

From the consumer’s perspective, fiber’s big advantage is simply speed and resilience. Fiber is by nature unaffected by electromagnetic interference like copper, making it much more resilient to outside factors — like proximity to other infrastructure and weather.

Overall, fiber has few faults outside of cost and limited availability. For the time being, it’s the most advanced form of data transmission available (outside quantum mechanics) and represents the future of Internet access in the developed world.

The Internet is a network of networks

While fiber has yet to be readily available to consumers on the same scale as cable and DSL, it’s already the dominant Internet infrastructure from a “big picture” perspective, handling the majority of data traffic outside the “last mile” familiar to broadband customers.

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The Internet is a “network of networks,” and improvisational use of outdated technologies has always been a part of broadband deployment.

We can expect that fiber will continue to grow alongside increasing reliance on high-speed broadband Internet for work, play, and communications. However, so long as copper remains viable for consumer’s bandwidth needs, ISPs are sure to continue using it to deliver Internet “on a budget.”

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