DOCSIS 3.1: Begin Preparing Now

BTR_Feature_Art_DOCSIS_9_9_13 Experts believe that DOCSIS 3.1 is few years off. The specification has not yet been finalized. After that, test and early customer premise equipment (CPE) and corresponding CMTS and CCAP line cards will be sprinkled through systems. The bottom line is that it will be a long time until DOCSIS 3.1 is an element of everyday cable operations.

So preparations should start now.

The industry has been down this road before. What seems like a long road, with plenty of cushion for adjustment, is deceptively short: The great change that the new technology brings demands equally great preparation to the plant, which must be in top shape when the first modems appear.

There are a couple of reasons that DOCSIS 3.1 requires operators to start preparing their plant early in the process:

  • The new protocol's two modulation schemes - orthogonal frequency division multiplexing in the downstream and orthogonal frequency division multiple access in the upstream - are more robust than the QAM and QPSK techniques used in DOCSIS 3.0. This ruggedness makes higher orders of modulation possible. These streams, which can offer densities of 512-QAM, 1024-QAM, 2048-QAM and even 4096-QAM, are increasingly sensitive. Problems such as packet errors are increasingly likely to occur, especially if the plant isn't in great shape. In some cases, a poor platform will totally disrupt service. In others - perhaps most - DOCSIS 3.1 will fail back to a previous version of the standard.

  • DOCSIS 3.1, as all DOCSIS protocols, will be backward compatible to earlier iterations specification. Thus, the amount of DOCSIS traffic will build. Poorly maintained systems will be hard pressed to support this gradually increasing traffic.

Brady Volpe, the principal of The Volpe Firm, suggests that a great deal of preparatory work for DOCSIS 3.1 is the type of block-and-tackling that operators have been doing since the industry was born. "A lot of networks today may be using 256-QAM, but if you look at the spread, you see a bunch of cable modems that have low MER (modulation error ratio) and are just on the edge of staying online," he said. "Cable operators need to tighten up the plant to get the modems on the low side onto the Six Sigma curve."

Volpe sees the way of setting up the infrastructure to succeed when  DOCSIS 3.1 arrives as doing the basics. "We need to replace Fabry-Perot lasers with DFBs (distributed feedback lasers) and eliminate ingress noise. Today in DOCSIS 3.0, we are starting to do more channel bonding and are having problems. If operators think that DOCSIS 3.1 will make this better, they are very, very wrong. It is only going to make them worse."

Daniel Howard, the SCTE's CTO and senior vice president of engineering, also sees lasers as an important element of DOCSIS 3.1 readiness. Maintaining linearity always has been an aim of cable operators, of course. Howard paints a picture of a landscape that is more sensitive than in the past and therefore more liable to non-linearities. "As you load up an RF system to the max, you run into the limits of existing laser technology," he said. "So it is important to manage the process of loading it just enough. You want have maximum capabilities but don’t want to overload [lasers] to the point where you cause distortions. That's something that always is done, but operators must take it to the next level."

Don’t Forget the Amps

Amplifier technology also is more exacting and demanding in a DOCSIS 3.1 world. James Martin, the director of business development for the infrastructure business unit of chip maker Anadigics, suggested that a lot of work has to be done on the amplifiers that are currently deployed in order to make them seamlessly fit into a DOCSIS 3.1 landscape.

The issue is that the wider upstream path that DOCSIS 3.1 demands - which starts at the floor of the existing upstream and extends to the new higher ceiling created by dedicating 1.2 GHz - demands one of two things: amplifiers with higher power and higher gain or the re-spacing of the amps that already are in place.

Obviously, the former is preferable. "The industry needs to deploy amplifiers in their HFC networks that can eventually be switched to the higher frequencies," Martin said. He added that new semiconductors based on gallium nitride can be used to create the next generation of amplifiers.

Longer term preparation for DOCSIS 3.1 obviously is on the minds of engineers at the SCTE and CableLabs, which are co-sponsoring a symposium on Oct. 21, the day before the start of Cable-Tec Expo in Atlanta. The SCTE's Howard said the industry - as represented by the two organizations - learned a lesson from the rollout of DOCSIS 3.0. That spec includes synchronous code division multiple access (S-CDMA) modulation. "Nobody deployed it, with a few exceptions," Howard said. "One of the challenges was its complexity."

Howard said the SCTE perhaps wasn't as involved in training the cable tech community for S-CDMA as it should have been. That problem won't recur, he said, because of a recognition by SCTE and CableLabs that training is key. "We are joined at the hip on DOCSIS 3.1," he said.

The bottom line is that DOCSIS 3.1 puts new demands on the underlying plumbing of cable systems. Observers say that work must start today on improving that infrastructure. The good news is that once DOCSIS 3.1 is operational, engineers will have access to a new world of diagnostic data and telemetry that is baked into the standard. The challenge to the industry, however, is to make sure that DOCSIS 3.1 works on day one.

Carl Weinschenk is Senior Editor of Broadband Technology Report. Contact him at

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