Comcast Eyes 'Scale Deployments' of Remote PHY in 2018

Signaling a significant milestone in the pivot to a next-gen, more distributed access network, Comcast is gearing up for "scale deployments" of remote PHY by the end of this year, a top engineering exec at the cable operator said.

Following earlier testing, Comcast Corp. (Nasdaq: CMCSA, CMCSK) has already begun the "implementation phase" for remote PHY and an architecture that will move key elements such as the modulation/demodulation from the core network to the node, Jorge Salinger, VP of access architecture at Comcast, said Thursday in a webinar hosted by Light Reading and sponsored by Viavi Solutions Inc.

Comcast already has equipment in its initial trial locations serving customers. The MSO isn't revealing the size and scope of that work. It's far from spanning Comcast's entire footprint, but the current phase of the deployment is "quite big," Salinger said.

While some operators and vendors are also focused on remote MACPHY – where both the PHY and the MAC are distributed to the node -- Comcast's current focus is on remote PHY. (See As Remote PHY Nears, No Time to Spare, Remote PHY Moves Needle in Europe and Remote PHY Takes Early DAA Lead.)

While the anticipated benefits of remote PHY and Distributed Access Architecture (DAA) are wide-ranging, the reduction of headend space, power and cooling requirements was "the driver, in the end, that made us go as fast as possible and as deep into this development as we could," Salinger said.

Other benefits include improved maintenance of the outside plant, lower operational costs, and a boost in overall network capacity (thanks to a boost in modulation and bit rates) as fiber is pulled deeper into the network.

Another side benefit has to do with interoperability and the ability to mix and match remote PHY devices (RPDs) and network cores from multiple suppliers. Comcast has already been able to integrate RPDs from three vendors (not yet named) "without any major issues," Salinger said.

Salinger said the pivot to DAA and remote PHY will also aid "XNET," the label Comcast has applied to strategic focus on pulling fiber deeper into the network and migrating to a "node-plus-zero" architecture whereby the active components between the node and the home are eliminated and the company moves to service groups that are about one-tenth the size of what they used to be.

While XNET represents Comcast's primary HFC evolution tool, the "problem" with it, Salinger pointed out, is it presents Comcast with space, power and cooling challenges as those massive number of node splits occur. Though the density of equipment is improving, it's not happening fast enough to accommodate all of the equipment. The strategic pivot to remote PHY and DAA will remedy that issue, he said.

That combination is also leading Comcast to Full Duplex DOCSIS, an annex to DOCSIS 3.1 that will enable symmetrical gigabit speeds in part by allowing upstream and downstream transmission in the same block of spectrum. (See Charter Chief Puts Faith in Full Duplex DOCSIS and CableLabs Pushes Full Duplex Forward.)

"We plan to deploy Full Duplex extensively wherever we deploy remote PHY and XNET," Salinger said.

The shift to remote PHY also fits into grander virtualization plans at Comcast that will cover elements such as the cable modem termination system, the video engine, and the out-of-band engine (for legacy set-top box signaling).

"Our architecture is one that essentially changes everything," Salinger said.

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Other challenges on the horizon
And there are plenty of challenges ahead. DAA introduces increased complexity and the potential to disrupt the use of existing tools and processes.

As DAA moves from the lab into the field, "everyone is trying to figure it out…it's complex and there can be a lot of variations," Dave Hering, senior product line manager at Viavi, said, adding later that testing and maintenance needs and requirements are becoming more apparent as the work around DAA and remote PHY evolves.

Hering added that there's also a "demark disruption" to consider as more processes move from the headend out to the node. That, in turn, could give rise to more finger-pointing, as operators might be chasing down an HFC issue that might actually be linked to a metro network issue, he added.

Salinger said he's amazed at the amount of change that's occurring in the network as the industry moves toward DAA, Full Duplex DOCSIS and enables more wireless capabilities on the plant.

"The pace of innovation of the access network has never been as frantic as it is right now," he said.

Thursday's webinar was part one in a three-part series that Light Reading will host on the topic with Viavi.

The second, set for November 27, will dive into headend considerations and feature execs from Viavi, Arris Group Inc. (Nasdaq: ARRS) and Nokia Corp. (NYSE: NOK); and the third, set for Jan. 23, 2019, will discuss the cutover process, and feature execs from Viavi, Cisco Systems Inc. (Nasdaq: CSCO) and Harmonic Inc. (Nasdaq: HLIT).

— Jeff Baumgartner, Senior Editor, Light Reading

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