September 24, 2023

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Cable Modem vs Fiber ONT

Fiber vs Cable Internet 101: The Best Tips

When it comes to land-based high-speed broadband connections, there are currently two competing technologies: Cable vs Fiber-optic, or Fiber, for short.

This post will briefly explain the two and give some tips on handling each. Among other things, you’ll walk away confident about what equipment to get the next time you upgrade or change your Internet service.

I wrote this based only own experience as someone who has recently kinda moved to 10Gbps Fiber-optic after years of using Cable. “Kinda” because I’ve kept both.

Dong’s note: I first published this piece on December 28, 2021, and updated it on September 14, 2022, to add relevant, up-to-date information.

Cable Modem vs Fiber ONT
Fiber vs Cable Internet: Pictured here are both in action. The Cable modem (top) is connected to a cable line, and the ONT is live with Fiber-optic signals. Both will deliver the Internet to a single wired device — that’s where you plug in your Wi-Fi router’s WAN port. In this particular setup, you need two routers or one that supports Dual-WAN.

Fiber vs Cable Internet, or ONT vs modem

Before continuing, though, let’s address the elephant in the room: your beloved DSL. Yes, I’m aware of it.

Short for digital subscriber line, DSL uses the existing phone line — that same wire we once used for the good old Dial-up connection — to deliver modest broadband connections.

DSL has declined significantly due to slow speeds and unreliability in the past few years. Most DSL providers have been slowly moving to Fiber as the replacement.

But in a way, as far as the Internet net is concerned, DSL is similar to Cable.

Cable Internet

As the name suggests, Cable Internet is the broadband connection via the coaxial copper wires used originally for Television or Cable TV.

Since the wiring was initially made for a different purpose, there needs to be a modem to make it work for the Internet, like the case of DSL.

A modem is a device that works as a modulator and a demodulator. It converts service signals into computer data signals and vice versa. Since the service in question here is cable TV, we have the Cable modem.

Cable modems use a standard DOCSIS to carry data signals, an acronym for data over cable service interface specifications. That’s the only acronym you need to know in the world of Cable Internet.

DOCSIS helps make broadband affordable since it leverages the existing copper wiring for cable TV — the infrastructure is already there.

And since coaxial wiring works like a cobweb, DOCSIS is resilient. When a cable breaks, that affects only a few families, if at all. (In return, Cable can also be hard to maintain since it can take a long time to locate and fix a broken line.)

The biggest shortcoming of DOCSIS is that it has lopsided connection speeds — the upload tends to be one-tenth (or even lower) of the download — known as asynchronous Internet. That’s the case with all cable connections.

The curious case of Cable Internet’s fast download vs slow upload speeds

In case you’re wondering why Cable Internet’s upload speed is always much slower than download, the reason is quite simple.

Initially, the network of coaxial copper wires was built to deliver a ton of data — the video and audio signals of Cable TV — to each household without needing anything in return. For the most part, TV viewers don’t send anything back to the provider.

When provisioned to deliver data, the same concept applies to the wiring, but this time that’s because the provider can lower the investment and maintenance costs by not providing fast upload speeds. So only lopsided modems are manufactured, and the rest is history.

And that has generally worked out fine since, in practice, consumers receive much more data (download) than they send (upload).

Presently, there are two main versions of DOCSIS in use, including DOCSIS 3.0 and DOCSIS 3.1 — there will be DOCSIS 4.0 at some point. Consequently, picking a suitable modem can be quite a task. It’s so much so that it needs a different section entirely — more below after we’re done with Fiber.

ARRIS Surfboard S33 Next to SB6141
A top-notch ARRIS DOCSIS 3.1 (Surfboard S33) next to a once-popular but modest DOCSIS 3.0 (ARRIS SB6141) counterpart

Fiber Internet

Fiber-optic has a ton of confusing terms.

Technically, the name is GPON, short for Gigabit passive optical networks. GPON is part of the Fiber to the Premises (FTTP), a.k.a Fiber to the Homes (FTTH), broadband delivery approach.

Nowadays, it’s more often called PON since it can deliver Multi-Gig broadband.

Since the wiring is designed for data connections, Fiber doesn’t require a modem. Instead, it uses an ONT at each endpoint, which is short for Optical Network Terminal.

In other words, an ONT is an Internet outlet that links to an Internet service provider (ISP) to deliver Internet to a home or an office. Each ONT has (at least) a network port to connect to a router’s WAN port.

ONT vs Cable Modem in a nutshell

Though totally different in technologies, an ONT to a Fiber-optic service is similar to a modem to a Cable Internet plan.

They are both terminal devices that bring the Internet into a particular location — a home or an office. Specifically, they’re designed to connect to the WAN port of a router.

A modem converts the signals between those of the service line and data. An ONT sends infrared light pulses to the ISP’s server to send and receive data.

Both get you connected at high speeds. How high? That depends on the Internet plan you have.

But the two share one thing in common: They need to be supported by the provider to work. Each ONT or modem might work with multiple ISPs, but an ISP can dictate which modems or ONTs it supports.

The point is that if you want to get your own terminal device, make sure you get one that your Internet service provider supports.

The messy acronyms aside, Fiber-optic gives you “high-quality” Internet thanks to the fact that the modern optical data line runs (almost) directly from the provider to your home.

Among other things, this type of broadband delivers high speeds in both directions (upload and download) — that’s synchronous Internet — currently up to 10Gbps and even faster.

On the downside, Fiber is expensive — it requires new wiring — and generally has a single point of failure. If a line is cut or broken, the Internet can be down for a large population. But it’s also much faster to locate and fix a broken line.

Fiber vs Cable Internet: The future is in the former

Generally, Fiber is the way of the future. It’s clean, fast, versatile, and built purposely for a high-speed data network. It’s simply far superior to the old copper wiring of Cable.

On top of that, with TV services moving slowly to streaming, there’s no longer a need for new coaxial development.

Cable Internet is just a matter of leveraging existing infrastructure until it’s no longer suitable or worth the maintenance, which is still far in the future.

Fiber ONTFiber ONT
Here’s a Fiber ONT from AT&T. Note its black Ethernet (Data) port, which is either a Gigabit or 10GbE Multi-Gig port to connect to a Wi-Fi router’s WAN port.

That said, Fiber is the only, and preferred, wiring needed for new real-estate and technology developments. In other words, if your area doesn’t have Cable or Fiber right now, it’ll get the latter, if at all.

Another thing to note is that many Cable providers use fiber as their primary data lines connecting existing Cable networks. Consequently, sometimes, we also have Cable Internet outages in large areas — likely the main fiber line is broken.

Tips on getting Fiber-optic hardware

When you order Fiber Internet, you’ll get an ONT — your provider will install one in your home.

The ONT might come as a standalone unit, like the one in the picture you see above, or a combo device that is a Wi-Fi router with a built-in ONT (often called an ONR or Optical Network Router.)

For flexibility, it’s always best to get just a standalone ONT when possible. That gives you the freedom to get a Wi-Fi solution of your choosing.

If you get a combo device, just like the case of a Cable gateway, you will likely have to do some tweaking to avoid double NAT.

Double NAT vs Single NAT: How to best use that ISP-provided gateway

Some Fiber-optic provider installs an ONT and then offer to lend you a Wi-Fi device. In this case, say no and get your own router or mesh system.

Sonic Fiber optic ONTAsus RT AX89X Fully Loaded
Here’s a Sonic Fiber ONT in action. Note the green service line and the white network cable connected to its 10GbE port. This ONT is the only thing you’d need from the ISP. You can use any route or mesh system on the other end of the white cable. In my case, it’s the Asus RT-AX89X.

And that’s the only thing you need to remember when getting Fiber. On the other hand, getting a Cable modem can be pretty complicated.

Cable modem (further) explained: DOCSIS 3.0 vs DOCSIS 3.1

Again, currently, the world uses versions 3.0 and 3.1 of the DOCSIS standard. (There’s no need to worry about the earlier revisions — thank goodness!)

DOCSIS’s specifications can be very confusing. For one, it changes depending on the region. For example, a set of particular modem specs might mean different speeds in the US than in the EU.

Also, it involves many technicalities, like channels, streams, QAM, etc. I’m not getting into the details, nor should you care about them. Instead, let’s focus on the two standards and what they mean.

DOCSIS 3.0: Stream channels matter

In a simplified way, with DOCSIS 3.0, you can grade a cable modem’s speeds via the number of stream channels it can handle.

There are downstream channels (for download) and upstream channels (for upload). More stream channels, or channels for short, translate into faster speeds.

Each modem comes with an indicator of the number of channels it can handle via a pair of digits. For example, the Netgear CM600 is a 24×8 modem. It has 24 downstream channels and 8 upstream channels.

In the US, the DOCSIS 3.0 standard delivers about 40Mbps per channel for download and 4Mbps for upload — again, these are ballpark numbers that vary from one provider to another. As a result, the CM600 caps at 960Mbps download and 32Mbps upload.

Generally, DOCSIS 3.0’s number of channels max out at 32×8. So a top-notch modem of this standard has cap speeds of some 1.3Gbps download. And that’s DOCSIS 3.0’s maximum bandwidth.

It’s important to note that just because a modem supports a specific performance grade (represented by the number of stream channels) doesn’t mean it will work at that grade. That depends on the service provider’s end (and the Internet plan you pay for).

And a provider generally loves to use as few channels as possible. The more stream channels, the more expensive equipment they need.

And that brings us to DOCSIS 3.1. This standard delivers a higher speed per stream channel. This version needs fewer channels to provide the same bandwidth and now has the cap of some 10Gbps in theory — that’s some 10x of version 3.0.

Fiber optic Ont vs Cable Modem
Here is another setup of a Cable modem and a Fiber-optic ONT in a live Dual-WAN setup. Pictured here are the Sonic 10GbE ONT and the Netgear CM2000 Multi-Gig modem.

DOCSIS 3.1: Top-tier DOCSIS 3.0 is the base

Though the actual speed varies from one vendor to another, a low-end DOCSIS 3.1 modem can generally deliver at least the same download speed as a top-tier 32×8 DOCSIS 3.0 counterpart.

DOCSIS 3.1 is so fast that vendors now omit the stream channel numbers. Instead, they call the modem DOCSIS 3.1 and its cap speed, Gigabit or Multi-Gig. The Netgear CM2000, for example, is a DOCSIS 3.1 2.5Gbps modem.

In other words, the stream channel numbers, such as 32×8 or 24×8, are only relevant in DOCSIS 3.0, where most modems cannot deliver Gigabit Internet. Starting with 3.1, Gigabit is the minimum, and Multi-Gig is a new norm.

Or you can safely assume that DOCSIS 3.1 starts at the place where DOCSIS 3.0 maxes out. And generally, most, if not all, DOCSIS 3.1 modems can function as 32×8 DOCSIS 3.0 ones. But it’s ultimately the Internet provider that decides which modem works and at what speed.

(DOCSIS 3.1 includes other benefits, but they are generally irrelevant from the consumers’ end.)

Real-world cable (download) speeds

No matter how fast a cable modem’s advertised speed is, its actual ceiling speed is always its LAN port — the one you connect to a router’s WAN port.

Speed testing: How to get the correct Internet or Wi-Fi numbers

That said, all cable modems with a Gigabit LAN port will cap at 1Gbps or lower.

Some modems can deliver Multi-Gig broadband speeds. In this case, they must have a Multi-Gig port (be it 2.5Gbps, 5Gbps, or 10Gbps) or features WAN Link Aggregation where you can combine two 1Gbps ports into a single 2Gbps WAN connection.

And, of course, to enjoy Multi-Gig broadband, you need to have a router supporting similar speed grades on the WAN side. After that, the speed must be available from the provider’s end. And, finally, you’re willing to pay for it.

The point is, there’s no need to get a modem that can deliver a faster speed than your current subscription. However, it never hurts to have a top-tier modem if you want to upgrade your broadband later.

Multi-Gig Wi-Fi routers: Get ahead of the speed curve today

Tips on getting a Cable modem: DOSIS3.0 or DOCSIS 3.1?

First of all, again, when applicable, you should get just the modem itself instead of a combo device which is a Wi-Fi router with a Cable modem built-in.

(The former gives you the flexibility in handling the hardware — you’re not stuck with a combo that’s lacking in either the modem or the Wi-Fi portion or both.)

If you have a sub-Gigabit Cable Internet plan, in most cases, it doesn’t matter which modem you get.

However, keep in mind that if your broadband is slower than 300Mbps, it might require a DOCSIS 3.0 modem. So check with your provider.

On the other hand, with a Gig+ and Multi-Gig Internet plan, DOCSIS 3.1 is a must. On top of that, you might want to get a cable that supports Link Aggregation if that’s how your provider delivers Multi-Gig.

Here’s my simple rule to determine which type of modem to get based on your Internet download speed:

  • 500Mbps or slower: Get a DOCSIS 3.0 modem. A DOCSIS 3.1 one is not necessary and might not work.
  • 500Mbps to sub-Gigabit: Either will do, but it’s a better idea to go with DOCSIS 3.1.
  • Gigabit for faster (Gig+, Multi-Gig): DOCSIS 3.1.
Internet and Wi-Fi: Netgear CM600 Cable Modem
Fiber vs Cable Internet: Here’s a modem connected to a service line and a Wi-Fi router’s WAN port.

The takeaway

Both Cable and Fiber will be able to give you faster broadband than any current application would ever need, providing you don’t mind paying.

But in more ways than one, Fiber is the way of the future. It has a much higher ceiling speed, especially the upload, much lower latency, and might be the only choice for many regions.

In the meantime, those with an existing Cable TV cable can benefit from the evolution of coaxial copper wiring. This infrastructure is still more than enough for anyone’s broadband needs for the foreseeable future.

No matter which you opt for, make sure you get only the bare necessity from the Internet provider, namely the terminal device (modem or ONT). When possible, avoid getting the gateway — that’s a combo device that has a Wi-Fi router and the modem/ONT built-in –, or any Wi-Fi equipment from the provider.

It’s always best to get a separate Wi-Fi solution for your home, be it a single router or a mesh system.

Besides not having to pay for equipment rent, better performance, and more features, you’ll be able to control your privacy to a much higher degree.