They’re showing off their work, which is still in the proof-of-concept stage, at OFC 2014, in San Francisco, this week.
Farrington, who won the coin toss and became CEO, worked on the Helios project, a hybrid electrical/optical switch, at U.C. San Diego with Amin Vahdat. Both got absorbed into the industry, Vahdat taking leave to work as a Google distinguished engineer, and Farrington joining Facebook — a job he left just weeks ago to run Packetcounter. (He and Huang had been pecking at the idea for months, so it’s not like they did too many tequila shots and woke up running a company.)
Packetcounter assigns optical, circuit-switched links to traffic flows in the data center. The “circuit-switched” part means the link stays open for as long as the data flow lives; it’s like the connection for an old-style telephone call.
These flows go through an all-optical switch such as Calient’s. These devices divert light from one port to another without examining the contents of the packets inside. Such a switch could fit into the aggregation layer of the data center, and that gives the top-of-rack switch a choice: Send traffic to other Ethernet switches (which is what normally happens) or into one of these optical circuits.
The latter is a lower-cost option compared with switch or router ports, and it’s better suited for the “elephant” flows — large, persistent flows. Optical switching is also useful for meeting low-latency requirements.
This packet/optical split is a routine part of the pitch for packet-optical equipment vendors such as Cyan and Infinera. The key is to pick which traffic would get the best benefit out of optical switching.
“To be able to make it work, you need to have some kind of management and control plane looking at the packet flows,” says Daniel Tardent, Calient vice president of marketing.
Control in the Optical Data Center
Packetcounter provides that control plane, applying concepts from Helios. The idea is to use Calient’s S320 Optical Circuit Switch (OCS) as an aggregation switch, accepting the 40-Gb/s uplinks coming from top-of-rack switches. The OCS becomes a rack-to-rack interconnect, in a sense, filling a role similar to the Cisco Nexus 7000’s, Farrington says.
Scanning the traffic matrix it’s constructed, Packetcounter figures out the best port usage for the optical links that run through the OCS. It can do this for multiple switches as well.
This can be useful even in not-so-extraordinary circumstances, Calient and Packetcounter argue. During the normal shifting of traffic patterns, if one switch starts getting overloaded, Packetcounter would detect the drop in performance. It could create new routes for the traffic and inform the top-of-rack switches of the new paths.
(What we’re talking about here is a reaction to ordinary changes in traffic, not a response to emergencies. The process can take 100 milliseconds to several seconds, Farrington says.)
Calient and Packetcounter are showing this setup on the OFC expo floor. It’s just a demo right now, “not a full closed-loop system,” Farrington says. “The commercialization of it is going to take a few more months.”
Still, Calient is hoping to get some small deployments going “toward the middle of the year,” Tardent says.
Not Necessarily That Optical Data Center
What Calient and Packetcounter are doing is distinct from Plexxi‘s work. Plexxi could do the same things (and in fact has worked with Calient), but it’s got a larger story about building an optical network around the data center, with traffic transported on topologies called rings. Packetcounter’s work and the Helios project are about dropping an optical switch into an otherwise ordinary data center — and operators really do think that can save them money.
“I don’t think I would have done that if people hadn’t asked for this kind of solution,” Farrington says of his decision to start a company. “People have a real need to make their budgets.”
He says “large operators” had been bugging him about commercializing Helios. He’s not saying whether Facebook was one of them.
Packetcounter doesn’t have any exclusive deal with Calient, so it’s possible Farrington and Huang could take the technology to other vendors.