ESnet Begins Testing TCP-BBR

Update to underlying internet protocol promises to improve data transmission performance

With Google’s Sept. 16 release of the new TCP congestion control algorithm, BBR (Bottleneck  Bandwidth and Round Trip Time/RTT), ESnet staff are gearing up to test this promising development.

According to early reports, Google engineers reported that the new algorithm “significantly increased throughput and reduced latency.” Google cited an increase in the speed of data transfers from three megabits per second (Mbps) to 9,150 Mbps on a test link with 1% packet loss and a latency of 100 milliseconds. Early testing by ESnet engineers has shown improvements from 10x to 100x on some international paths, but no improvements on other paths.

“I’m eager to work with our Google collaborators to understand the details of how BBR works and how it may benefit data-intensive science applications in the future,” said Brian Tierney, head of ESnet’s Advanced Network Technologies Group and co-creator of ESnet’s Fasterdata website. “This is potentially a great step forward for TCP, and we’re eagerly testing BBR TCP. We’ll post results as we get them.”

More technical details will be revealed when a description of BBR appears in the September-October 2016 issue of ACM Queue. Among the developers of BBR is Van Jacobson, who was a primary contributor to the original TCP in the 1980s when he worked at Lawrence Berkeley National Lab, where he led the Network Research Group.

Tierney said ESnet has begun testing BBR using the 2,000 instances of the perfSONAR network performance measurement hosts installed on research and public networks around the world. By using BBR to send data from one of ESnet’s test perfSONAR hosts, engineers can get details on the data transfer performance across 2,000 network paths with 2,000 different characteristics. “perfSONAR provides us with a really valuable test environment for new networking innovations like TCP BBR,” Tierney said.

Tierney said the old analogy of the Internet as an information highway really applies to the current version of TCP. As freeway traffic gets more congested, even the slightest event like a car with a flat tire can dramatically compound the situation as everyone slows down to rubberneck or go around.

With the current version of TCP, data traffic slows down when it hits congested stretches of a network and the problem gets worse the farther data travels. On some paths, BBR appears to help mitigate this slow-down.

ESnet is particularly interested in BBR as the network carries massive sets of data between 50 main sites in the U.S. and across four high-speed trans-Atlantic links.

“It looks like anyone who transfers big data over long distances could see huge improvements,” Tierney said. “The longer the path they are covering the bigger the difference will be.”

The announcement about BBR was posted on the Patchwork Linux network development website and can be found at

Watch the ESnet blog for updates as BBR tests are conducted. Results will also be shared on ESnet’s Fasterdata website where the organization houses best practices and a broad knowledgebase focused on high performance network engineering, performance testing and tuning, among other topics.