Elad Nafshi Comcast

Comcast EVP and Chief Network Officer Elad Nafshi always seems to have a welcoming smile with just a bit of a smirk. And why not?

He’s been directing the company’s ambitious network upgrade plans that have been gradually but still not fully revealed over the last few years.

The cable industry uses the broad term 10G to encompass these network upgrades, the sum total of which is aimed at eventually supporting speeds of 10 Gbps downstream and 6 Gbps upstream.

Comcast is unlikely to support those speeds in the near term. Nevertheless, the company aims to offer symmetrical multi-gigabit speeds before the end of 2023 to some customers, with the company’s entire 50-million location footprint targeted for upgrades by 2025.

I talked to Nafshi about those plans last week and got some additional information about what the company already has done and what it has yet to do.

Topics ranged from the company’s recent 2 Gbps upgrade, to what’s entailed in deploying DOCSIS 4.0, to the company’s rural deployments and more.

2 Gbps Upgrades Pave the Way for DOCSIS 4.0

Comcast announced last fall that it would be offering 2 Gbps service in parts of its Northeast service territory by the end of 2022. Upstream speeds are as high as 200 Mbps and, according to Nafshi, are underpinned by DOCSIS 3.1, distributed access architecture (DAA) and mid-splits.

DOCSIS 3.1 is the current generation of broadband technology for cable company hybrid fiber coax (HFC) networks.

Mid-splits are a cable industry term for expanding the spectrum within the coaxial portion of the HFC network and increasing the amount of spectrum that can be used for upstream communications. Moving to a mid-split approach requires replacing diplex filters at each amplifier in the network.

(Comcast 10G plans include upgrading to a full-duplex approach to allocating the spectrum within the coax portion of the link. Doing so enables a large portion of the spectrum to be used for upstream or downstream communications.)

DAA involves virtualizing the cable modem termination system (CMTS) and distributing that functionality throughout the network. It also involves converting the fiber portion of the HFC connection to IP communications which, among other things, improves the signal-to-noise ratio.

Deploying DAA boosts the speeds that the HFC infrastructure can support. The deployment involves installing either remote PHY or remote MAC-PHY devices at the node where signals from the fiber connection are converted for transmission over coax.

According to Nafshi, Comcast chose remote PHY devices (RMDs) because they provide more sustainable power savings and “ultimately better reliability driven by a simpler software implementation.” He added, though, that a MAC-PHY approach may work fine for some network operators.

The RMD is also the device that needs to be upgraded to support DOCSIS 4.0, the next generation of cable modem technology. That means that wherever Comcast already has deployed RMDs, it can implement DOCSIS 4.0 through a software upgrade and by installing a DOCSIS 4.0 device at the customer premises when the DOCSIS 4.0 equipment is commercially available – a milestone that the industry expects to reach later this year.

Nafshi declined to reveal how extensively Comcast has deployed DAA or what percentage of its service territory has had spectrum expanded within the coax portion of the connection, however.

Rural Deployments

Nafshi and I talked a bit about Comcast’s rural deployments. The company has been winning a substantial amount of funding to cover some of the costs of those deployments through various state programs, including in Florida, Indiana, South Carolina, Alabama, Minnesota, and Georgia.

Traditionally cable companies haven’t pursued government funding, but that changed when Charter was one of the biggest winners in the Rural Digital Opportunity Fund, winning over $1 billion to cover some of the costs of deployments in multiple states. Charter will be deploying fiber broadband to those locations, but when we asked if Comcast would be doing the same, Nafshi’s answer was different.

“In rural deployments, we have the optionality to build fiber or coax cable depending on the location,” said Nafshi. “Our architecture enables us to build both and ultimately deliver multi-gig symmetrical services over the same DAA architecture powered by the same vCMTS.”

The latter is a reference to the modularized nature of DAA. Operators can deliver service from the node to the customer by either coax or fiber, depending on the module installed in the vCMTS.

When Comcast deploys fiber, it uses 10G EPON, Nafshi said.

A Pet Project

Nafshi was eager to talk about one other element of Comcast’s 10G, DOCSIS 4.0 and related plans – the Octave technology that the company uses to gather and sift through enormous amounts of performance data from its network, enabling the company to optimize and troubleshoot the network.

The company used the technology during the COVID-19 pandemic to increase network efficiency, which helped the company gain capacity at a time when it was badly needed.

The same platform will be “critical in the launch of 10G and DOCSIS 4.0,” Nafshi said, because “it enables us to optimize the delivery of the upstream traffic,” which is critical to supporting symmetrical speeds.

Octave already helps support the 200 Mbps upstream speeds available in certain areas using DOCSIS 3.1, and it will be even more important for DOCSIS 4.0, as Comcast aims to deliver even faster upstream speeds, Nafshi said.

A key takeaway from our interview: There are loads of pieces to cable company upgrades, with each piece having multiple deployment options and providing incremental benefits that the cable industry hopes will add up to something big.

If the cable industry’s bet on 10G and DOCSIS 4.0 is right, it could yield big benefits to companies like Comcast, while also providing a relatively seamless path to upgrade to fiber broadband in the future.

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