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Facebook walks on optical networking's wild side

The social network is using technologies that others may take years to adopt

By Stephen Lawson
March 10, 2014 10:02 PM ET

IDG News Service - As a company that draws more than 2 billion eyeballs per month, Facebook was a fitting harbinger of trends to come at an optical networking conference.

The social networking goliath is lighting up its own optical fiber, deploying 100Gbps links in its data centers and looking toward emerging silicon photonics technology, Facebook Director of Technical Operations Najam Ahmad said on Monday at an Optical Society of America meeting held alongside the annual OFC (Optical Fiber Communications) Conference in San Francisco.

Facebook's challenges mirror those of other enterprises and data center operators, with fast-growing data traffic and rapidly evolving network needs, but with 1.2 billion active monthly users, it's facing those issues sooner than some. Though his company is unique in some ways, Ahmad's comments in an on-stage interview may shed some light on the future of connectivity.

The biggest traffic at Facebook isn't in and out of its data centers but among the servers within them, Ahmad said. That's because every time a user logs in to the site, hundreds or thousands of servers are called into action to compute different parts of that customer's News Feed on the fly. This so-called "east-west" traffic is also growing faster as apps on Facebook grow more complex and user interactions become richer, he said.

So while many enterprises are deploying 10-Gigabit Ethernet today, that's already the minimum at Facebook.

"We haven't deployed anything less than a 10-Gig for about two years now," Ahmad said. Those are the links to servers themselves, and upstream from that, Facebook is using 40-Gigabit Ethernet and a few 100-Gigabit links. It's mostly on 40-Gigabit now because 100-Gigabit is still too expensive, he said. But within a year or two, Ahmad expects the company's fast pipes to become predominantly 100-Gigabit.

Facebook's computing needs are growing so quickly that the company no longer builds just one data center at a time, Ahmad said.

"Now what we do is we buy land, we build one building, and then a second, a third, and a fourth," he said. "All of a sudden, what we've done is build a campus. So our optical needs change slightly."

To link, say, four data centers spread across a campus of 10 to 20 acres, Ahmad would like to have a fiber technology that can span one or two kilometers and carry 100Mbps to start, then 200Mbps and 400Mbps as traffic grows over time. For that, he envisions connections using single-mode fiber rather than the multimode fiber most commonly used in data centers today, which has a shorter range.

Such a system is likely to use silicon photonics, an emerging technology that applies the world's most common semiconductor material to optical connectivity, Ahmad said. Facebook is also exploring silicon photonics because it wants to use so-called rack-level computing, in which computing, storage and memory are concentrated in separate racks and connected at high speed to form the equivalent of many servers. PCIe is another option for this, he added.

Reprinted with permission from IDG.net. Story copyright 2014 International Data Group. All rights reserved.
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