Remote PHY – Lessons From the Field

Cable's remote PHY era is in the early phases, but Comcast has been taking heed of the lessons it has learned from the field as it prepares to scale up deployments that will lead to distributed access architectures and lay the groundwork for Full Duplex DOCSIS.

A "huge" lesson learned centers on the all-important area of power, Jorge Salinger, VP of access architecture at Comcast Corp. (Nasdaq: CMCSA, CMCSK), said Thursday, September 27, during a webinar on remote PHY hosted by Light Reading and sponsored by Viavi Solutions Inc. (See Comcast Eyes 'Scale Deployments' of Remote PHY in 2018.)

In a remote PHY scenario, "a short power outage in the node is a long power outage for a customer," Salinger said.

In traditional, non-remote PHY settings, when power is removed from a node for a few seconds, it could turn into a 30-second disruption of service as power is quickly restored. However, if power is removed for just one second in a newer remote PHY device (RPD), the service disruption can last about five minutes because the RPD must endure a lengthier reconfiguration process and also resynch with the servers when power is returned.

Salinger said Comcast has also learned that turning up a new line card or CCAP (Converged Cable Access Platform) device is a much more complicated process when the PHY is distributed out toward the node rather than back in the core.

"That process has to get optimized for remote PHY deployment," he said. He added later that getting techs trained up for this new architecture is another key challenge that will need to be addressed.

And they'll have to be addressed soon, as Comcast looks to start "scale deployments" of remote PHY by the end of this year.

Comcast already has remote PHY equipment deployed for its initial trial locations that are already 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 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.

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.

For more about this topic and other opportunities and challenges ahead for remote PHY and DAA, please turn to the story posted at our sister site, Light Reading. (See As Remote PHY Nears, No Time to Spare.)

— Jeff Baumgartner, Senior Editor, Light Reading