10Gbps symmetrical cable broadband trials will begin next year

Symmetrical 10Gbps cable broadband trials will begin in the next year, according to CableLabs, the shepherd of the DOCSIS standard. DOCSIS, and a (clearly superior) permutation called EuroDOCSIS, is used by all of the world's major cable Internet providers, including Virgin Media, Comcast, and Verizon.

Most of the world's high-speed cable providers currently use DOCSIS 3.0, which was standardised in 2006. It has a max upstream throughput of 220Mbps, and downstream capacity of about 1.2Gbps in the US or 1.6Gbps in Europe. (Funnily enough, PAL's wider channel width than NTSC—8MHz vs. 6MHz—means we get higher bandwidth DOCSIS links.)

In 2013, DOCSIS 3.1 bumped the max downstream throughput to 10Gbps and upstream to about 2Gbps. In September this year, CableLabs announced that it was working on an update to the spec called Full Duplex DOCSIS 3.1, which is exactly what it sounds like: 10Gbps in both directions. Now, following some positive results in the R&D lab, the not-for-profit consortium has announced that it expects to trial the tech in "about a year."

DOCSIS has always been heavily asymmetrical, and some of you will painfully remember the olden days of sharing 10 megabits of upload bandwidth across an entire neighbourhood. Full Duplex DOCSIS 3.1 will be the first time that the spec has allowed for symmetrical throughput—and according to the limited info released by CableLabs, the tech being used is pretty interesting.

DOCSIS 3.1 has access to about 1.2GHz of spectrum, from 0MHz to 1.2GHz. Usually, the lion's share of that spectrum (about 80 percent) is allocated to downstream traffic. It would be more effective, of course, if both upstream and downstream could use the same big block of spectrum. That's how modern wireless technologies such as LTE do it, with methods such as TDD—time division duplexing, where users take it in turns (i.e. a time slot) to use the same spectrum.

CableLabs is going one step further with Full Duplex DOCSIS 3.1, though: it will let the client and the server speak at the same time into the same block of spectrum using a technique called self-interference cancellation. With two devices transmitting at the same time there is a ton of interference on the line, but because the cable modem termination system (CMTS)—the hardware that your cable modem connects to—knows what signal it sent into the cable, it can automatically subtract its own transmission from the line, and be left with just the signal sent by your modem. This technique is somewhat comparable to vectoring, which has played a key role in boosting DSL speeds over the years.

This noise-cancellation tech will initially only be required at the CMTS to achieve 10Gbps upstream, according to CableLabs, but in the future it could be put into the modem as well, which would likely realise yet another throughput boost. Curiously, one of the possible issues that may interfere with the rollout of symmetrical 10Gbps cable broadband is the huge amount of power (i.e. electricity) required by the CMTS to transmit a strong 1.2GHz signal to every customer in the neighbourhood, and to perform the noise cancellation operation for dozens of 10Gbps streams simultaneously, which is computationally very demanding.

Some networks have started to deploy the original (10Gbps down, 2Gbps up) DOCSIS 3.1 spec—Comcast in the US, Videotron in Canada—but generally, cable ISPs don't seem to be rushing towards the faster speeds; they're happy to keep gradually bumping speeds up as needed. Virgin Media is trialling DOCSIS 3.1 in the UK and has indicated that a wider rollout could be on the cards, but I doubt anything will happen until other ISPs start to roll out G.fast (300Mbps+ over telephone wires). Maybe we'll get some DOCSIS 3.1 in the second half of 2017.

Listing image by Fox Photos/Getty Images