Comcast taps long-haul tech to monitor expanding fiber access network

Comcast is pushing fiber deeper into its network with a new distributed access architecture (DAA) and deploying fiber-to-the-premises (FTTP) in a more targeted fashion. While the rollout will add critical capacity to Comcast's network as it pursues a broader "10G" initiative that will enable symmetrical speeds of 10 Gbit/s, it also presents the operator with some new challenges, namely in the area of fiber network monitoring.

"Speed's great, but how do we make sure it's really up to the reliability expectation of our customers?," explains Elad Nafshi, Comcast's SVP of next generation access networks. "If it gets cut, you need to find where it is, and you need to fuse it together." The challenge therein, he said, was to achieve uniform, real-time visibility across all parts of Comcast's access network, including the coax and fiber elements.

Up to now, pinpointing the location of a fiber cut has typically been a time-consuming exercise, on the order of two hours, according to Comcast's estimates. However, the operator has been able to reduce that time to about a minute-and-a-half using "XMF," a new monitoring platform for Comcast's fiber access network that was developed by Venk Mutalik, an engineer on Comcast's Next Generation Access Network team.

What's old becomes new (and useful) again

XMF, it turns out, is a classic case of morphing an older technology into something that's new, useful and scalable.

Mutalik's idea, inspired in 2019, was to tap the capabilities of previous-generation optical spectrum analyzer (OSA) chips used in reconfigurable add-drop multiplexers (ROADMs) for long-haul fiber transport networks, and adapt and redeploy them to Comcast's growing fiber access network. Instead of using those OSA chips to monitor fiber traffic travelling thousands of miles on the long-haul network, engineers could now use them to keep close tabs on traffic traveling thousands of feet on the fiber access network.

Comcast, Mutalik explained, has great visibility into those long-distance fibers. But, he noted, the operator lacked similar visibility into a fiber access network that now represents more miles of fiber than what makes up the company's long-distance, coast-to-coast connections.

"We don't have as much visibility into that access plant that we would like to have," Mutalik explained, noting that it has been traditionally difficult to rapidly locate fiber cuts on the access network. Inference-based technologies that, for example, tell an operator if a power outage was the cause of a node outage, simply isn't enough in this instance. "With fiber, we need direct observation," he explained. "Inference is not going to cut it because we need to not only know it's a fiber that is cut, we also need to know where the fiber was cut … We can't predict when a fiber gets cut, so those fibers have to be monitored 24/7, 365."

XMF is designed to eliminate that guesswork. Comcast can gather that direct information, lay it into a GIS (geographic information system) system and recover the fiber with the right fix agents before needing to understand everything that is going on below the surface.

Mutalik said the system also provides Comcast with proactive network maintenance capabilities on optical cables that it already has on the RF part of the HFC network. That effectively gives the operator a heads-up on fiber cuts and alerts when degradation is underway. "That's a pretty important attribute, which we are only now starting to understand," he said.

Nafshi estimates that Mutalik took the idea from a PowerPoint to a prototype within weeks. Comcast has already deployed these optical spectrum analyzers in rack-mounted units to a broad portion of its fiber access network, and paired that with new XFM handheld monitoring/troubleshooting devices for field technicians. He expects to expand the deployment through the rest of 2021.

Nafshi said XMF applies to any Comcast fiber installation, not just those for hybrid fiber/coax (HFC) networks that have implemented DAA.

Comcast has also stitched XMF into its core software platforms and care and dispatching tools. "That's where the magic really happens," Nafshi said.

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— Jeff Baumgartner, Senior Editor, Light Reading