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DOCSIS 3.1: A Surgical Strike Weapon?

NEW ORLEANS -- DOCSIS 3.1 represents a huge gain in performance for cable broadband services, but after carving out precious bandwidth for the new platform, there will be relatively few D3.1-capable modems on the network to take advantage of that capacity early on.

Cable operators are now grappling with the question of how many DOCSIS 3.1 modems should be on a particular service group before they light up the spectrum that unlocks enormous horsepower for a new wave of D3.1-capable modems that will also support DOCSIS 3.0-based traffic. 

That’s just one issue Comcast has been studying as it continues to trial DOCSIS 3.1, said Jorge Salinger, the MSO’s vice president, access architecture, on Tuesday during a workshop titled: “DOCSIS 3.1 Readiness: To 1 Gig and Beyond.”

Salinger reiterated that Comcast has a “pretty aggressive plan for DOCSIS 3.1,” as field trials continue this year ahead of anticipated deployments in 2016, and talked up the 50% performance boost operators expect to get out of D3.1’s use of ODFM signals and the Low Density Parity Check forward error-correction scheme.

While DOCSIS 3.1 supports two 196-MHz blocks of spectrum, the specification allows operators to allocate a minimum of 24 MHz, Salinger pointed out, noting that it’s possible to proactively deploy DOCSIS 3.1 spectrum to the heaviest users, at least during the early phases of deployment.   

That approach could allow cable operators to supply new modems to that base of users and surgically free up DOCSIS 3.1 spectrum during the transition, he said, adding that Comcast and other operators still have other tools, such as moving to new, more efficient codecs, to create that can be applied to the new D3.1 platform.

Salinger also explained how Comcast might use DOCSIS 3.1 to deliver residential Gigabit broadband services. New hybrid modems, which will support both D3.0 and D3.1 traffic, could create bonded capacity of about 1.7 Gigabits per second, enabling Comcast to offer a “low penetration” 1-Gig service, he said, adding that DOCSIS 3.1 equipment is “developing at a very, very fast pace.”

But he allowed that testing and measuring DOCSIS 3.1-based services and evaluating capacity management with the new platform would provide “a new and different challenge.” DOCSIS 3.1, Salinger added, “will require some operational adjustment but can be deployed on existing plant.”

One company that’s trying to help cable meet the test and measurement challenge of DOCSIS 3.1 is Viavi (formerly JDSU).

Al Ruth, a product line manager at Viavi, presented on how the vendor is using current plant metrics to monitor the health and performance of OFDM-based DOCSIS 3.1 signals as they move through the cable network.

Viavi is currently weighing this in the form of a trial with an unnamed European cable operator in four markets that started with a node selection process, a plant data and analysis phase, and on to the current phase, which involves collecting and analyzing data in the home.

Those tests, Ruth said, involve several elements, including basic carrier-level measurements, modulation error ratio measurements, and ingress noise testing. 

While those trials are not yet complete, Ruth said Viavi has already concluded that it can review these key metrics to predict how DOCSIS 3.1 traffic will perform on the cable network.