Facebook’s Terragraph lands under SRG’s microscope: Pass or fail?

Facebook’s desire to connect more people to the internet is well known, and its Terragraph initiative is one way to achieve that. But how does Terragraph perform outside a trial situation? Signals Research Group (SRG) decided to take a look. 

Terragraph is a fixed wireless access (FWA) platform that uses 60 GHz spectrum. It’s unlicensed, so other applications can use the spectrum, creating interference concerns. It’s also high enough to fall into the millimeter wave (mmWave) camp, where coverage is limited and performance is degraded in non-line-of-sight conditions.

On the other hand, 60 GHz is ideal in many respects because it provides ample bandwidth, and there’s a lot of it. Plus, those oxygen absorption issues that make it particularly susceptible to rain appear to be a thing of the past.

SRG was tapped to perform benchmark testing of Facebook’s Terragraph network at its Menlo Park, California, campus. Although Terragraph has been commercially deployed since at least 2019, SRG believes its study is the first third-party benchmark report on the platform.

“We’re accustomed to high data speeds with millimeter wave radio systems given our experience with testing and analyzing 5G NR. With Terragraph we observed sustained bidirectional data speeds in the range of 1.7 to 1.8 Gbps between two nodes, with the throughput only slightly lower with a three-hop link, or 1.6 to 1.7 Gbps,” SRG wrote. “For us, the most impressive performance attributes from a radio access perspective were the low latency and jitter associated with the FWA system.”

Emil Olbrich, VP of Networks at SRG, said he was especially impressed by the work done in the Layer 2 and Layer 3 routing. In addition to being an open source solution, Facebook’s Terragraph uses the Open/R platform, which is really good at sending data across multiple nodes of a network and then reassembling with the ability to get better reliability, according to Olbrich.

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Nowadays, routers in Facebook data centers – which power everyday things like Instagram and Facebook – use Open/R even though it was originally developed for the wireless Terragraph platform, he noted.

In addition, the ability in the 60 GHz band to mitigate interference was impressive. “I think that speaks a lot to their antenna technology and the RF front end that they’ve deployed on the Terragraph solution,” Olbrich added.  

Bear in mind, all of these tests were happening on the Facebook campus, which is a sprawling place with dozens of buildings alongside plenty of foot and vehicle traffic during normal times. However, that wasn’t the case during the month of May 2021.

About the only folks on campus were the SRG personnel and some Facebook engineers, so it was a fairly deserted place thanks to the Covid pandemic. “It actually provided us a great opportunity,” Olbrich said. “We were able to utilize the situation to our advantage.”

Props to 1564

It’s worth noting that they used the ITU-T Y.1564 standard to evaluate Terragraph performance. It’s something that’s normally used in a wireline environment, but Obrich said he thought it would be worthwhile to test using the 1564, and “they passed.”

The results are in the report, but in short: “Their latency was extremely good. Their frame loss was negligible, and jitter wasn’t that much. It met all the requirements of 1564.” So if someone says it’s “fiber-like,” they have some real substance to back that up.

That said, “you have to design your link properly,” and have the proper link budget to meet the atmospheric conditions, whether it be heavy rain or snowfall, he added.

Facebook offers Terragraph reference designs so that other companies can use them, thereby providing broadband to more hard-to-reach or under-served areas of the U.S. – or the world, for that matter. Terragraph licensees cited in the report include Cambium Networks, Edgecore Networks, MikroTik, Radwin and Siklu.

If you’re a municipality in the U.S., for example, that doesn’t want to spend money on spectrum and just wants connectivity, “this is a great way to do that so you don’t have to dig up a street and put fiber in there,” he said.  

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Terragraph doesn’t change the laws of physics, meaning that providing extended coverage with 60 GHz spectrum will always be challenging, SRG stated in its report. “However, we also found the perceived interference issues associated with using an unlicensed radio platform do not exist since the Terragraph scheduling algorithms intelligently adjust the routing of packets if external sources of interference are detected or if obstructions along the transmission path develop.”

SRG conducted its tests after Facebook reached out in late 2020 about doing a benchmark study. In some instances, Facebook Connectivity engineers executed tests on behalf of SRG, which cited security-related hurdles facing non-Facebook employees and a general unfamiliarity with the Facebook Network Management System.