With cable operators facing challenges in the upstream return path, many are turning to Full Duplex DOCSIS (FDX) to address the issue. However, FDX likely won't be available until 2019 and will face its own challenges along the way, leaving the industry to make do until relief is available.

Craig Leddy

January 10, 2017

3 Min Read
How Cable Plans Symmetrical Gigabit via FDX

As 2017 promises to be "the Year of DOCSIS 3.1" for cable, the industry is working to supercharge its Internet delivery upstream. While DOCSIS 3.0 and 3.1 have set the stage for downstream speeds at gigabit levels, the upstream return path has been limited, putting cable at a potential competitive disadvantage as cloud, video, business services, Internet of Things (IoT) and other rich applications eat up upstream capacity.

According to a new Heavy Reading report, Cable Bets On Full Duplex for Symmetrical Broadband, the cable industry is rallying around Full Duplex DOCSIS (FDX) to overcome its upstream limitations and enable symmetrical Internet service at multiple gigabit speeds. As an extension of DOCSIS 3.1, FDX relies upon cable's existing hybrid fiber-coaxial (HFC) architecture and uses unique tricks to share downstream and upstream bandwidth without causing signal interference.

However, the report says, FDX requires significant changes in cable's last-mile plant and is unlikely to move into the marketplace until 2019. The growing requirements for upstream capacity beg the nagging question of whether cable providers need to build fiber to the home, as Altice 's US division has already decided to do.

Comcast Corp. (Nasdaq: CMCSA, CMCSK), Cox Communications Inc. and other MSOs foresee FDX as a way to provide multi-gigabit symmetrical services, with downstream and upstream access available at the same speed.

"We have an awful lot of homes connected to coaxial cable in this country and we'd like to see that all of those homes have symmetrical services as quickly as we can," said Robert Howald, VP, Network Architecture for Comcast, during a recent Light Reading webinar, Betting on Full Duplex DOCSIS.

The Heavy Reading report explores FDX's challenges and opportunities and includes an update on DOCSIS 3.1 activity. On the upside, increasing upstream can support revenue opportunities, including upselling higher-speed tiers, attracting larger business customers and supporting richer interactive applications that take advantage of cloud, virtualization, the IoT and virtual reality.

But FDX will not arrive quickly and it faces challenges. CableLabs' specifications for the technology are not expected to be completed until the end of 2017, with trials and rollouts to follow in 2018 and 2019. During that time, upstream traffic will grow and cable competitors -- including Google Fiber Inc. , Verizon Communications Inc. (NYSE: VZ), AT&T Inc. (NYSE: T) and CenturyLink Inc. (NYSE: CTL) -- will continue to push their gigabit services, the report says.

As currently envisioned, FDX requires architectural changes in cable's last mile, including running fiber deep, removing amplifiers from the node (known as node+0) and putting taps on the side of homes or new gateway devices inside. Cable providers will have to weigh the potential capital and operations expenses versus the value of ramping up upstream capacity, the report says.

By using the same bandwidth that is used for downstream, FDX upstream delivery is like a high-speed train going in one direction, sharing a track with a high-speed train traveling in the opposite direction. To avoid a collision, FDX employs echo-cancelling technology and unique techniques to eliminate interference.

It was only a couple of years ago that the cable and broadband industry was debating the need to provide gigabit Internet service at all. Today 1 gigabit of downstream speed is a widely assumed goal, multiple gigabit speeds are in the offing and now symmetrical, multi-gigabit upstream capability is being developed. Go figure.

— Craig Leddy, Contributing Analyst, Heavy Reading

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