Cable Internet: Fast Until the Neighborhood Wakes Up

Getting the Internet Right: Part 4 of 12

Cable internet is probably the most common type of business internet in the country right now, and for understandable reasons. It's widely available, the speeds are high, the pricing is reasonable, and for many businesses it works well enough that they never have a reason to look deeper. But "well enough" and "right for your situation" aren't always the same thing, and cable has some characteristics that are worth understanding, especially if you're running phones or video over it.

How cable internet works

Cable internet uses the same coaxial cable network that delivers cable television. That's the thick round cable with the threaded connector that you've probably screwed into the back of a TV at some point. The technology that makes internet work over these cables is called DOCSIS, which has gone through several generations. The current version, DOCSIS 3.1, is what most cable providers have deployed, and while the DOCSIS 3.1 spec supports up to 10 Gbps downstream, most cable providers deploy it at speeds up to about a gigabit download.

The coaxial cable runs from your building to a neighborhood node, which is typically a cabinet or box mounted on a utility pole or in a ground enclosure somewhere in your area. That node converts the signal and sends it to the cable company's headend facility, usually over fiber. From the headend, you reach the cable company's backbone and then the broader internet.

That neighborhood node is the key piece to understand. Unlike DSL, where each customer has their own dedicated copper pair, cable internet shares the coaxial cable between your building and the node with other customers in your area. Everyone connected to the same node is sharing the same pool of bandwidth.

The shared bandwidth problem

This is cable's defining characteristic, and it's the source of most of the complaints that people have about it, even if they don't realize it.

When the cable company says you have a "500 Mbps" connection, what they mean is that you can use up to 500 Mbps of the total capacity available at your node. But the total capacity at the node is split among all the customers connected to it. If there are 200 homes and businesses on your node and nobody else is doing anything, you might actually see speeds close to 500 Mbps. If it's midday and half of those connections are active, you're all sharing the same capacity.

In practice, this means your cable internet speeds vary throughout the day. Early morning and late night tend to be fast. The middle of the workday is typically slower. And the worst period, somewhat counterintuitively, is often early evening when residential customers come home and start streaming video, because many business cable connections share infrastructure with the residential network in the same area.

For web browsing and file downloads, this variability is usually just an annoyance. Pages load a little slower, downloads take a bit longer. You probably wouldn't even notice unless you were running a speed test at different times of day.

For voice and video, the story is different. It's not the speed reduction itself that causes problems. As we discussed in How Internet Connections Actually Work, voice calls don't need much bandwidth. The issue is that congestion at the node doesn't just reduce speed. It also increases latency, increases jitter, and can cause packet loss. These are exactly the three things that voice traffic cannot tolerate.

A cable connection that tests at 300 Mbps during off peak hours and 100 Mbps during peak hours might still have plenty of raw speed for your calls at both times. But the congestion that caused the speed to drop from 300 to 100 may also have pushed your jitter from 5 milliseconds to 40 milliseconds, and that's the difference between crystal clear calls and calls that sound choppy or robotic.

The upload asymmetry

Cable internet is asymmetrical by design, and severely so. A typical cable business plan might offer 500 Mbps download and 20 to 35 Mbps upload. Some plans are even more lopsided than that.

DOCSIS 3.1 allocates the majority of the available spectrum to the download direction because the technology was designed primarily for content consumption, delivering TV and video. The upload allocation is a fraction of the download, and it's shared among all customers on the node just like the download is.

For businesses running VoIP, this matters a lot. Your calls need upload bandwidth for the outgoing audio, and if you've got ten people on calls simultaneously, that's roughly 1 Mbps of steady upload traffic just for voice. Add in video calls, cloud backup, email with attachments, and anything else that sends data outbound, and that 20 Mbps upload can get tight faster than you'd expect.

This is one of the more common scenarios we see when businesses have intermittent call quality problems. The download speeds look great, the connection seems fast, speed tests come back impressive, but the upload is congested during business hours because there simply isn't enough upload capacity for everything that needs it. Our Bandwidth Calculator can help you estimate whether your upload capacity is sufficient for your actual call volume and cloud usage. And since most speed test tools emphasize download speed, the upload bottleneck often goes undiagnosed until someone specifically looks for it.

Business cable versus residential cable

Most cable companies offer both residential and business internet plans. The business plans are more expensive, often significantly so. What do you get for the extra money?

The answer varies by provider, but typically a business cable plan includes a static IP address (important for some business applications), a service level agreement that promises faster response times for outages, the option for a phone line bundled with the service, and sometimes slightly higher upload speeds. Some providers also claim that business customers are on a less congested node, though this isn't always verifiable.

What you generally don't get is a fundamentally different network experience. Business cable still uses the same coaxial infrastructure, the same DOCSIS technology, and in many cases the same neighborhood nodes as the residential service. The shared bandwidth characteristic is still there. You're paying more for better support and better terms, which have real value, but the underlying connection technology is the same.

This is an important distinction. When a cable company tells you they offer "business grade" cable internet, they're not wrong. But they're not describing the same thing as what the telecom industry means by "business grade" in the context of dedicated connections. It's a marketing term being applied to a shared infrastructure product. That doesn't make it bad. It makes it something you should understand clearly before you buy.

Where cable internet works well

For small to medium businesses with moderate phone usage and good availability in their area, cable internet is a perfectly viable primary connection. If your office has under 15 or 20 people, you're not running a call center, and you're in an area where the cable infrastructure is well maintained and not overly congested, cable can deliver a good experience at a reasonable price.

Cable is also very widely available, which is a real advantage. In many suburban and urban areas, you can get cable internet at locations where fiber isn't available yet. The installation is typically straightforward and fast compared to dedicated connections, which can take weeks or months to provision.

If you're on cable and your experience is consistently good, there may be no reason to change. The important thing is to understand what you have and what its limitations are, so that if problems develop, you know where to look.

Where cable internet falls short

Cable becomes a harder sell as your office grows, as your dependency on phones and video increases, or as you move into applications that need reliable upload bandwidth. The shared nature of the connection means that problems can appear that are entirely outside your control. A new business moving into the building next door, or a shift in usage patterns in your neighborhood, can change your internet experience overnight without anything on your end changing.

Call centers or any business where phones are a primary tool should think carefully about relying on cable as their sole connection. The variability in quality during peak hours, combined with the upload constraints, creates a risk that dedicated connections simply don't have.

If you're already experiencing intermittent call quality issues on a cable connection, especially if they tend to happen at consistent times of day, congestion on your node is a strong possibility. Running a VoIP quality test at different times of day can help you see exactly when jitter and packet loss spike, which is strong evidence to bring to your cable provider. Your cable provider may be able to tell you how loaded your node is, though getting that information sometimes requires persistence. If the node is heavily loaded, the only real fix on the provider's side is a node split, where they divide the customers on an overloaded node into two separate nodes. Providers do this regularly, but it's on their timeline, not yours.

The DOCSIS 4.0 question

DOCSIS 4.0 is the next generation of cable technology, and it promises to address some of cable's current weaknesses, particularly on the upload side. The new standard supports symmetrical speeds, meaning upload could finally match download. Some cable companies have announced rollout plans, though widespread deployment is still in its early stages.

If and when DOCSIS 4.0 becomes widely available, it could significantly change the calculus for business cable internet. Symmetrical speeds on a cable connection would remove one of the biggest complaints about the technology for business use. However, the shared bandwidth characteristic would still be there, so congestion during peak hours would still be a factor even with higher upload speeds.

For now, buying decisions should be based on what's actually available and deployed at your address today, not on roadmap promises. When DOCSIS 4.0 is real and in the ground at your location, it'll be worth another look.

Next up: Fiber Internet: Not All Fiber Is the Same, the connection type everyone wants, and the details that determine whether you're actually getting what you think you're getting.