Hitting the DOCSIS 'sweet spot'

SCTE/ISBE Cable-Tec Expo – It's not quite the 31 flavors of ice cream offered by Baskin-Robbins, but cable operators do have plenty of choices and technical options in hand with respect to today's DOCSIS 3.1 technology and, further down the road, with DOCSIS 4.0.

In a wide-ranging discussion at this week's all-virtual event, John Chapman, a fellow and chief technology officer for cable access at Cisco, took up the challenge of weighing and analyzing those options to determine which ones hit the "sweet spot" for cable operators.

DOCSIS 3.1 provides operators with a way to extend spectrum to 1.2GHz and pair it with a beefier swath of upstream spectrum – a "mid-split" to 85MHz or a "high split" up to 204MHz. Meanwhile, DOCSIS 4.0 has even more optionality – the use of Full Duplex DOCSIS (raising the spectrum ceiling to 1.2GHz with the ability to run upstream and downstream traffic in the same block of spectrum), or Extended Spectrum DOCSIS (lifting spectrum up to 1.8GHz, but keeping the downstream and upstream traffic separated, with the ability to raise the upstream as high as 684MHz).

Chapman noted that operators have ten choices with respect to frequency changes, so what's the right choice?

There is lots to factor into that question, but based on his analysis, the "sweet spot" for DOCSIS 3.1 is having the plant built out to 1.2GHz with a high-split upstream – offering 8.6 Gbit/s of downstream capacity and 1.4 Gbit/s of upstream (or 2.8 Gbit/s with two upstream ports), if the operator gets rid of its legacy QAM video and goes with all-DOCSIS and IP delivery for video. That setup would enable an operator to use DOCSIS 3.1 at its "maximum designed bandwidth," Chapman said.

The DOCSIS 3.1 "runner-up" is the 85MHz upstream design. That would give an operator the ability to deliver upstream capacity in the hundreds of Mbit/s, but not 1-Gig.

"The 204 [MHz high-split] option is really where the money and the opportunity is for DOCSIS 3.1," he said.

He argued that the sweet spot for DOCSIS 4.0 is having the plant built to 1.8GHz with an upstream set at 396MHz, providing 12 Gbit/s of downstream capacity and 3 Gbit/s of upstream capacity (or 6 Gbit/s with the aforementioned two-port upstream).

The runner-up for DOCSIS 4.0 is sticking with a 204MHz return, he said, noting that this option "shines" if an operator still has QAM video running on the plant.

Chapman also discussed in detail how DOCSIS 4.0 and the industry's move to a distributed access architecture – along with access to new CBRS spectrum – will position cable operators to become tomorrow's mobile operators and deliver on a future centered on service and network convergence. For his thoughts on that, please see this story: Cable's evolutionary path leads to mobile, convergence.

— Jeff Baumgartner, Senior Editor, Light Reading, special to Broadband World News