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Network and Engineering 

The Road to 10G: Using Prisms and Sonars to Increase Network Reliability

By Elad Nafshi
The Road to 10G: Using Prisms and Sonars to Increase Network Reliability

Key Takeaways

XMF, a new network technology, reduces the amount of time it takes for a technician to find and isolate a fiber cut from 2 hours down to one-and-a-half minutes.
Technicians are using XMF to discover and repair degraded fiber performance before customers ever notice something is wrong.
Technologies like XMF and Comcast Octave help to ensure that our network reaches new heights of speed, capacity, security, and reliability.

Venk Mutalik – an engineer on our Next Generation Access Network team – was working late one night in 2019 when he had an inspiration to use a well-known technology component in an entirely new way to keep our networks running smoothly for customers.  

Today, the innovation that Mutalik and his team built from that idea is giving our network engineering teams unprecedented visibility into network performance and allowing them to detect and fix issues faster than ever before. This technology is just one of many innovations Comcast is deploying to prepare our network for 10G.

The long-haul fiber optic network equipment that connects cities and towns across the United States rely on thousands of highly specialized devices called “ROADMs” (reconfigurable add-drop multiplexers) that ensure trillions of bytes of information get to their intended destinations. ROADMs contain ‘optical spectrum analyzer’ chips that are essentially ultra-smart prisms, splitting fiber optic laser light into smaller and smaller beams and pointing them reliably to the right destinations, all in milliseconds. 

Every year or so, manufacturers release a newer generation of more powerful and higher resolution optical spectrum analyzer chips, and network operators replace the previous versions of the devices in their networks. The same is true for other components like the optical time domain reflectometers, optical SONAR-like components that use “optical echoes” to pinpoint fiber imperfections.

That’s what got Mutalik thinking. He knew that previous-generation optical spectrum analyzers and other such components were incredibly powerful devices designed to manage fiber-optic traffic over thousands of miles. What would happen if we repurposed these mature opto-electronic chips to monitor traffic traveling thousands of feet?

Comcast’s local fiber optic networks in cities, towns and neighborhoods cover shorter distances than the long-haul networks connecting cities. Mutalik reasoned that optical components such as optical spectrum analyzers, which are designed to perform pinpoint measurements over thousands of miles, would be that much more effective managing an optical network that powers a single neighborhood.

His team got together and built a prototype for a system called the XMF. By installing these optical spectrum analyzers in our local fiber networks and developing software to leverage the devices’ capabilities in new ways, the team was able to gain unprecedented visibility into performance along every millimeter of those networks.

And because XMF leverages previous-generation technology for a new purpose, it makes it more cost effective to install ultra-precise fiber diagnostic tools at many points throughout our local fiber networks, creating significantly more visibility for technical teams, and delivering higher reliability to customers.  

The XMF platform continuously monitors hundreds of thousands of local broadband optical links every minute across the Comcast network, measuring both the optical spectrum and testing the length and quality of the fiber links. In practical terms, that means that with XMF installed, network engineers can now pinpoint the exact point at which a local fiber network is experiencing an issue and share the precise geolocation with local technicians. When installed, XMF reduces the amount of time it takes for a technician to find and isolate a fiber cut from 2 hours down to one-and-a-half minutes.

The system is so fast, that in many cases technicians are using XMF to discover and repair degraded fiber performance before customers ever notice something is wrong. 

The XMF team is now rolling out a handheld version of the XMF platform that technicians can use in the field to identify fiber link issues in seconds and even diagnose and repair those issues on the spot. And as the team works to refine the handheld platform, they are beginning to scale the rack-mounted original version more broadly across the Comcast network.

XMF is both a tremendous example of the sort of innovation that takes place every day among our engineering teams, and a critical development for the forthcoming deployment of 10G technology.

Even as we develop, test and deploy technology to deliver even faster speeds to our customers, we know we have to work equally hard to ensure that those fast speeds are coupled with tremendous security and reliability. Technologies like XMF and Comcast Octave help to ensure that even as our network reaches new heights of speed and capacity, it will also be more secure and reliable than ever for the customers who depend on it.

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