Cable Dreams of a Greater Upstream

The advent of DOCSIS 3.1 is once again raising the question of whether cable operators should extend the frequency range they use for upstream data traffic, or stick with what they've got.

Today, cable operators typically conduct upstream traffic within the spectrum range of 5MHz to 42MHz, but for many years there's been talk of extending the upper range to 85MHz (the so-called mid-split) or even 200MHz (the high-split) to gain more upstream bandwidth capacity. (See Comcast Hints Strongly at Upstream Mid-Split.)

From a marketing standpoint, upstream bandwidth has been cable's Achilles heel. Any operator deploying fiber to the home can advertise symmetrical broadband speeds, but cable operators using hybrid fiber-coaxial (HFC) networks are stuck right now with upstream maximums that struggle to hit the 50 Mbits/s mark. For the most part, consumers don't need higher upstream bandwidth, but marketing claims by FTTH operators can still drive demand, and there's always the possibility that the next big killer app will eat further into upstream margins.

Bob Greene, managing director of business development at Liberty Global Inc. (Nasdaq: LBTY), also sees signs that bandwidth usage trends may be changing.

"In Europe, all the operators, and specifically us, we've seen a huge increase in the upstream traffic," said Greene at Light Reading's Cable Next-Gen Technologies event. That increase, according to Greene, is led simply by the growing number of devices connecting to the Internet, and it has Liberty Global evaluating what capacity it might gain from eventually migrating to DOCSIS 3.1 in the upstream.

Casa Systems Inc. Director of Product Management Jeff Leung also confirmed that his company is getting interest from customers around upstream D3.1 trials.

"We are now seeing quite a bit of requests on the upstream as well in the US and also in Europe," said Leung. "We've been requested to get the upstream trials going on, and if you ask about the timeline, upstream is coming. It's probably going to be 2017, but trials [are] going to be this year for sure."

However, as Comcast Corp. (Nasdaq: CMCSA, CMCSK) VP of Access Architecture Jorge Salinger pointed out at the same event, the level of upstream capacity possible using DOCSIS 3.1 depends entirely on how much spectrum is allocated to the cause. Extracting the full potential out of D3.1 in the upstream means deploying the mid-split or the high-split. And that can be a painful proposition.

For more on cable technology trends, visit the cable channel here at Light Reading.

Robert Harris was vice president of network planning & architecture for more than a dozen years at Time Warner Cable Inc. (NYSE: TWC), and he's well aware of the difficulties involved in extending the frequency range available for upstream bandwidth. Asked about the possibility of the industry finally moving forward with a higher split, Harris was cautious, noting that companies "may be underestimating the challenges."

And there's another potential wrinkle in the debate: the industry's new investigation of Full Duplex DOCSIS 3.1. In theory if Full Duplex comes to fruition, operators will have a much broader range available for upstream bandwidth because upstream and downstream traffic will be able to share the same spectrum frequencies. (See What If Cable Does the Full Duplex?)

Could the potential for Full Duplex cause operators to hold off on a higher bandwidth split?

"No, I don't think so," said Salinger when the question was posed to him. "We're not sure exactly how complex it would be to implement... I don't think anybody would change their plans on not extending the upstream because of the expectation of Full Duplex."

Salinger didn't go so far as to say that Comcast is pursuing the mid-split, but that's a reasonable assumption given earlier statements and the operator's ambitious plans for DOCSIS 3.1. How quickly an implementation might happen, and whether others follow suit remains to be seen.

— Mari Silbey, Senior Editor, Cable/Video, Light Reading

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