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Highspeed Fiber vs Cable Internet: ONT vs Modem, and What is DOCSIS, Anyway?

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

This post will explain the two briefly and give some suggestions on how to handle each.

By the way, if you live in areas with both options, you can use them together. All you need is a router that features Dual-WAN, plus two broadband connections (preferably of similar speeds), but that’s probably a topic of another post.

Dong’s note: Part of this post was initially published as the introduction in the piece on how to replace the ISP-supplied equipment with your own. I moved it out on December 28, 2021, to further clarify the topic.

Cable Modem vs Fiber ONT
Fiber vs Cable Internet: Here, we have 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 been significantly declining due to slow speeds and unreliability in the past couple of 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 made initially 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 both 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 ourselves the Cable modem.

To carry data signals, Cable modems use a standard called DOCSIS, which is an acronym for data over cable service interface specifications. That’s about 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.

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

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.

Originally, 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 the need to get 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.

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.

Fiber Internet

Fiber-optic has a ton of confusing terms.

Technically, the name is GPON, short for Gigabit passive optical networks. GPON itself 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 in mind, Fiber doesn’t require a modem. Instead, it uses an ONT, short for Optical Network Terminal, at each endpoint.

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

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

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.

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.

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.

That said, Fiber is the only wiring needed and the preferred one 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 a lot of Cable providers actually use fiber as their main data lines connecting different existing Cable networks. This is why sometimes, you have Cable Internet outages in large areas — likely the main fiber line is broken.

Fiber ONT 2 Fiber ONT 1
Here's a Fiber ONT from AT&T. Note its data port which is almost always a 10Gbps Multi-Gig port to connect to a Wi-Fi router's WAN port.

Notes 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.

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

And that’s the only thing you need to keep in mind 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 they do in the EU.

Also, it involves many technicalities, like channels, streams, QAM, etc. I’m not getting into the details here, 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.

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

DOSIS3.0 vs DOCSIS 3.1: Which to get

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

The takeaway

Both Cable Internet 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 upload speed, and might be the only choice for many regions.

In the meantime, those with an existing Cable TV network 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 just the terminal device (modem or ONT) and not a gateway — that’s a combo device that has a Wi-Fi router and the modem/ONT built-in — when possible.

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

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28 thoughts on “Highspeed Fiber vs Cable Internet: ONT vs Modem, and What is DOCSIS, Anyway?”

  1. Thanks for the article – very informative. Our home was built 5 years ago with an in-wall distribution hub – cable modem, router, switches, etc. – and of course wired Ethernet to every room. For Wi-Fi, we have multiple wireless access points powered by POE. Fiber is being added by our utility dept and will soon be available at our home. We would love to have the higher speeds, and the cost is going to be cheaper monthly that what we have paid for Comcast. However, we have concerns about integration to our robust existing system, how we will get the fiber module run in the wall to replace the current cable modem, etc. With all this relatively new, and fiber optic’s inability to be bent/manhandled by running through walls like RG6, what advice would you have for us?

    Reply
    • Running Ethernet cable isn’t much different then running coax. Just make sure you use the right cable for the right application. For in wall installations most electricians use Cat6 CMR (riser) rated cable Cat6 or 6a CMX rated cable is recommended for outdoor residential applications. Both use solid core copper and can be bent, but not like patch cable which uses stranded cooper and is more flexible. If the installation is done professionally, running Ethernet through walls or outdoors shouldn’t be an issue.

      Reply
        • Hi Dong! With fiber yes.
          Actually, I was referring to the installation, not the performance of coax. However, with a Docsis 3.1 cable system, coax speeds can match maximum cat6 download speeds of 10MBPS (rated at 240 MHz). Where as cat5e (rated at 100 MHz) is limited to about 1Gig. That is why I use, and always recommend, cat6 or 6a Ethernet cable for fiber.

          Reply
      • I appreciate that Ian, however house is already wired. I ran RG6 and Cat6 to each room, some multiple runs in a few rooms. My concern had to do with replacing the cable modem with a new fiber system, but incorporating into the existing β€œsmart home” type setup. With the switches and modem in a wall cabinet, I had concern that fiber could not be bent or ran through the wall to enter the existing cabinet. If it can’t be incorporated as is, then I would probably just stay with cable due to aesthetics. Thanks again

        Reply
  2. Hi, are there any ONT’s that you recommend? My ISP allowed me to do that, I only need to provide them my new ONT MAC adress to authorize it. I currently have ZTE F680, but it often drops connection. Maybe I would ask them for F601 but I’m worried about stability. I also found on internet Ubiquiti UF Loco, I trust more Ubiquiti than ZTE but it’s a bit expensive and works with ZTE OLT’s.

    Reply
  3. I currently have cable internet and each room in my house also has a coax wall outlet for cable TV that are not being used. Is it possible to have a cable modem in each room so that each room can have a wired connection? Love your articles!

    Reply
    • No, Steve, you can only use one modem per a Cable Internet plan. But you can move the modem around the house and place your router there for the best coverage.

      Reply
  4. I have a Motorola cable modem, which I bought about four years ago. No problems with it whatsoever and Comcast didn’t blink at my using it instead of their cable box. They did do some harassment when I switched from their TV service to Sling, but that stopped suddenly when it became clear that a change in federal administration suggested that there might be tougher oversight.

    Reply
    • Yeap. You should be able to replace the equipment with your own, M. Considering the modem is relatively old, you might want to get a new one if you have already upgraded the speed.

      Reply
  5. Dong there is a 3rd option I am just trying out 5G cellular WiFi. I Just got the T-Mobile Home WiFi unit. I am gettin as high as 400 Mbps directly off the box. I connected my Asus mesh setup via Ethernet and it works fine. I was getting 1 Gig with cable but this is allowing me to ditch my cable company and it’s plenty fast for streaming 4k and multiple devices. The only problem is latency which is no where near as good cable.

    Reply
      • High density areas like NYC metro currently receive 5G mmWave to boost bandwidth with services like T-mobile. The objective is to eventually offer gibibyte speeds on these systems. Hopefully, they will become more common and therefore offer more competition with Fios and cable systems in the future.

        Reply
        • As Fiber becomes more popular and cheaper, Cable will get even cheaper. I don’t think Cable will go away any time soon, if at all. It’s plenty fast and reliable.

          Reply
          • Just my two cents as a member of the Fair Internet Coalition lol. You’re assuming that the ISP’s will continue to maintain their cable systems properly. There have been major complaints here in the North East and other parts of the US, about subpar cable service issues. Since the FCC is considering defining broad band as at least 100 MBPS down and 100 MBPS up, I’m wondering just how long it will take for many of them to upgrade to Docsis 3.1. Altice, a telecommunication company, purchased Cablevision here in the tri-state area, with the intent to convert it to fiber. It was an aggressive 5 year plan which was interrupted by Covid in 202O. Now that they have restarted the program, most of their ads are promoting their new fiber network. Most of the cable techs and IT engineers that I know in the industry believe that cable has become antiquated. IMO, at some point in the not too distant future, cable will be riding off into the sunset and replaced by these newer more competitive technologies which offer better performance, and less maintenance.

          • I think it’s better to have both, Ian. It’s good to have competitions. Where I am Cable is quite good and reasonable in costs while Fiber is limited in availability and still quite expensive. My guess is this is case by case. Most of us can live with 20Mbps upload speed if the download is Gigabit or higher.

          • I agree Dong that the more competition the better and as long as cable can produce a service that meets consumer needs so be it. However, the trend now is to replace copper with fiber which is why many cable customers are starting to experience more service issues. It’s not financially feasible for a cable company to continue to invest in a antiquated system and until that system is replaced, maintenance suffers. You will find that most new construction areas these days are now receiving fiber nodes, not coax.

          • Yeap, but existing houses are not going anywhere. In many, cable is the only option. Don’t forget many still use it for their TV service. I’m not against Fiber, but the transition will take longer than you think. At least in certain regions.

      • Maybe in a future article you could comment on 5G mmWave wireless, currently being used by T-mobile in high density areas like NYC. Thanks.

        Reply
    • You must live in a place like NYC near a tower. According to the Fair Internet Coalition, most people who have T-Mobile home service, experience an average between 35 and 100 MBPS which is dependent on location and weather conditions that don’t usually have an impact on Fios and Cable. Latency averages between 25 and 50 MS. However, upload speeds are usually higher then cable, but can’t compete with Fios.

      Reply
  6. Nice article Dong!

    Just curious if there is a difference in latency at all between cable and fiber. Get back when you can!

    Reply
    • They are about the same, Allen, and should be around 10ms to 15ms. That’s good enough for anything, lower make no or little difference.

      Reply
  7. I have an Arris 3.0 modem. Oddly enough it’s specifications claim a maximum data rate of 960 mbps with 24 download channels which my ISP is currently using. It also shows that my hybrid (Optimum) cable system is only using 2.0 docis with four upload channels. My average upload speed is close to 40 mbps. Verizon just installed Fios in my town home complex and I will be going that route sooner then later.

    Reply

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