What is DOCSIS and How Does It Make Gigabit-Speed Cable Internet a Reality?

This is the age of gigabit-speed Internet, but with over 90% of the U.S. currently wired for coaxial Internet and only 25% with potential access to fiber, it doesn’t feel like we’re all there yet. Since late 2015, however, some existing cable connections have been getting serious speed upgrades (multiple gigabits per second!) by just changing a few pieces of hardware – no new wiring required. This standard, DOCSIS 3.1, has been around since 2013, but with more ISPs updating their equipment, it’s possible that in a few more years most users won’t need to wait for actual fiber to get fiber speeds.

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Data Over Cable Service Interface Specification (DOCSIS) is a long way to say “how cable Internet works.” DOCSIS 1.0 was developed by Cable Labs in 1997, and it’s been under development since, getting faster and more power-efficient with each incarnation.

Without getting too much into the physics of it, the DOCSIS standard works this way: a cable box gets signals from an ISP’s fiber optic network, translates them into signals that coaxial cables can carry, and relays those signals over the “last mile” of coax cable to users. These signals end up in the user’s cable modem, from which the user can send data back to the box for retranslation. Within the cable itself, the DOCSIS standard governs which frequencies are used to send data upstream and downstream.

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Think of the whole thing as a highway (the cable) with lanes (frequency ranges) running in two directions. DOCSIS is the set of rules that govern how many lanes go in each direction (the physical frequency layer) and how traffic flows onto them (media access control or software layer). With each new version, the highway gets organized more efficiently, and the vehicles on it can fit more passengers (data). Because the highway is always located in the same physical space (the coax cable), you only need to upgrade a few key points, mostly at the entry and exit ramps, to change the traffic patterns (the flow of bits) for the better.

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Of course, the main point of these new standards is getting better speeds, so how has DOCSIS gotten faster over the past few generations?

VersionDownload SpeedUpload SpeedYear
140 Mbit/s10 Mbit/s1997
240 Mbit/s30 Mbit/s2002
31.2 Gbit/s200 Mbit/s2006
3.110 Gbit/s1-2 Gbit/s2013
3.1 Full Duplex10 Gbit/s10 Gbit/s2017

After its release in 2013, DOCSIS took a few years before it started rolling out to users in late 2015. As of 2018, though, it is still in very early stages worldwide. However, it represents a huge potential leap in terms of performance due to several key improvements. In non-technical terms, 3.1 can get more passengers onto the highways at once and can add more lanes to the highway. In slightly more technical terms, it uses higher frequencies with more room on them, splits streams of data into multiple streams so it can use more of each frequency band, and improves packet queuing, meaning that data doesn’t have to wait as long before entering the cable, which reduces latency. Simply put, DOCSIS 3.1 and onward can fit more data into the same amount of space, giving you better up and downstream speeds.

As a bonus, DOCSIS 3.1 is backwards-compatible, meaning that moving from 3.0 to 3.1 can be a gradual process. You can change the ISP’s equipment to 3.1 while leaving the user’s equipment on the 3.0 standard until they want to upgrade.

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Even though DOCSIS 3.1 hasn’t really made it into the mainstream yet, Cable Labs is already finalizing the DOCSIS 3.1 Full Duplex standard, which may be released by 2019. There has also been some noise about DOCSIS 4.0, though this is a long way off.

As the name implies, Full Duplex allows the upstream and the downstream to both use the entire range of available frequencies. A telephone is a good example of duplex communication: two people can talk at the same time and hear each other on both ends of the phone, rather than only one person being able to transmit at a time, like a walkie-talkie. This essentially means that rather than dividing the coax cable into upstream and downstream channels, any channel will be able to carry data in any direction, making it possible for upload speeds to match download speeds, with (very) theoretical maximums of ten Gbps both ways.

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Unfortunately, DOCSIS 3.1 is still in its early stages, as many ISPs are transitioning slowly and charging high prices. Where it is available, you can get 1-2 Gbps download, with up to 1 Gbps upload, making it a real competitor to fiber. However, the speed doesn’t come cheap: cable companies are trying to maximize their return while they can, so the fees are currently equal to or greater than fiber in most areas. Given that cable hardware already exists for many users, though, it’s likely that DOCSIS 3.1 will eventually be serving more users than fiber, and prices may fall as higher speeds become the norm.

Regardless of how soon the world gets DOCSIS 3.1, living in the DOCSIS 3.0/early fiber era is nice. Most places that have broadband can’t complain too much about download speeds, and faster upload is on its way. As with any technological evolution, it may take some time to come together, but between fiber, DOCSIS 3.1, and low-earth-orbit satellite Internet, the future of connectivity looks pretty good.

Image credit: BROADBANDNOW

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