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CableLabs Kicks Off Pursuit of DOCSIS 4.0

Jeff Baumgartner
6/24/2019
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DOCSIS won't live forever, but it appears that the technology is nowhere near its last legs.

CableLabs is moving ahead on DOCSIS 4.0, a set of next-gen specifications for hybrid fiber/coax (HFC) networks that will repackage some recent annexes and enhancements made to DOCSIS 3.1 and tack on a few new, important capabilities, industry sources tell Light Reading.

The new 4.0 specs will include Full Duplex DOCSIS (FDX), a feature that enables both upstream and downstream traffic to run on the same block of spectrum, and a new Low Latency DOCSIS capability that is targeting sub-1 millisecond latencies.

A CableLabs official confirmed to Light Reading that the 4.0 effort is underway, noting that the organization is separating the current D3.1 family of specs into two families of specs -- DOCSIS 3.1 and DOCSIS 4.0.

"4.0 is the official version number now being given to the DOCSIS specifications that include Full Duplex DOCSIS functionality," the spokesperson said via email. "There is no change in functionality or in the requirements contained in the specification. We are implementing this update after finding that there are additional features being defined (e.g., Low Latency DOCSIS) that need to be clearly associated with a specific version of the DOCSIS specifications. Additionally, this provides clarification on the necessary energy efficiency allocations for both DOCSIS 3.1 and DOCSIS 4.0."

A greater spectrum of possibilities
CableLabs has not yet announced everything that will be packed into DOCSIS 4.0 and when the organization expects to complete the new specs.

In addition to adding some security enhancements, DOCSIS 4.0, sources said, will also add in a new Extended Spectrum DOCSIS (ESD) capability that will support HFC network traffic up to 1.8GHz, up from the 1.2GHz supported today by D3.1. That will allow cable operators to tap into 600MHz of additional usable spectrum and mine more capacity for various DOCSIS-based residential and business services, including high-speed Internet, IP video and wireless backhaul.

People familiar with the 4.0 effort believe that the bulk of the new specs could be wrapped before the end of 2019 (given that much of the specs for FDX and Low Latency DOCSIS are well downstream), and that the plant-related work for Extended Spectrum DOCSIS (to 1.8GHz) could be done before mid-2020. That could set the stage for products that support the full 4.0 specs to emerge in 2021.

In addition to cleaning up the additions and enhancements made to D3.1 in recent years, DOCSIS 4.0 should give vendors more clarity on what chips to develop, what products to build, and have improved visibility into what cable operators will end up buying. Some suppliers have complained that they needed more guidance in this area because cable operators have not been completely uniform concerning their next-gen network plans.

While Comcast pursues Full Duplex DOCSIS and distributed access architectures that use "node+0" designs (eliminating the amplifiers between the home and the node), most other MSOs are not nearly as committed to FDX or N+0, but are instead interested in Extended Spectrum DOCSIS and network designs that do not completely eliminate the amps between the home and the node -- they're looking at Node+1, Node+2, etc.

Under the new plan, FDX and Extended Spectrum DOCSIS are "must" components of DOCSIS 4.0, sources explained.

The new focus on DOCSIS 4.0 could delay Full Duplex DOCSIS a bit, as it seems likely that MSOs like Comcast would hold off until FDX products that support 1.8GHz enter the scene.

The renumbering under DOCSIS 4.0 will also help the cable industry meet the energy-consumption targets of industry-backed programs such as Energy 2020, people familiar with the project said.

DOCSIS 4.0 would mark the latest major, number-changing update to the platform since DOCSIS 3.1 was formally introduced in the fall of 2012. As part of an effort to boost the data efficiency of HFC networks, DOCSIS 3.1 altered the modulation of DOCSIS traffic by using blocks of OFDM subcarriers instead of the bonding of 6MHz- and 8MHz-wide QAM channels used in DOCSIS 3.0. D3.1 also changed the forward error correction technique from Reed-Solomon to low-density parity-check, a move that enables data transmissions to more easily shoot through plant noise.

But, wait, there's more!
DOCSIS 4.0 will specify how to raise usable spectrum to 1.8GHz on the HFC network, but CableLabs and its partners are already starting work on the next phase -- support for spectrum up to 3GHz, sources said.

3GHz is on the roadmap for a future, yet unnamed spec (DOCSIS 4.1?). Completion of that is considered to be at two or more years out, though some operators are already starting to spec-out 3GHz taps.

The approach, which would require a new generation of modems and other consumer premises equipment (CPE), would put the cable industry on a path to supporting downstream speeds of up to 25 Gbit/s and about 10 Gbit/s in the upstream. To do that, the operator would use a dedicated upstream up to 1GHz and dedicate 1GHz-3GHz for the downstream.

If that project were to bear fruit, it would enable cable operators to mine more capacity out of their DOCSIS platforms and HFC networks, and prolong a more expensive move to FTTP. Charter Communications execs have said that the upgrade to D3.1 cost the MSO just $9 per home passed for the network side of its DOCSIS 3.1 upgrade. It's not clear yet what the cost on a per home passed basis would cost under the proposed DOCSIS 4.0 specs.

Cable engineers have already been discussing the notion of expanding to 3GHz as a path beyond the industry's "10G" initiative that is eyeing symmetrical speeds of 10 Gbit/s using multiple types of access networks (HFC, FTTP and wireless/mobile).

At the recent Anga Com show in Germany, execs said industry technologists are already exploring ways to bring 25 Gbit/s capabilities to HFC.

Of note, John Chapman, CTO of cable access and a fellow at Cisco Systems, said he is co-authoring a paper to be presented with Intel Corp. at this fall's SCTE Cable-Tec Expo in New Orleans about how the HFC plant could support spectrum up to 3GHz.

"So there's a long road map for HFC ahead," Chapman said during a panel at Anga Com.

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— Jeff Baumgartner, Senior Editor, Light Reading

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