Ever been sitting around waiting for the latest wacky cat video to finish buffering, wondering what the holdup is? In these days of high speed Internet access, it seems like we shouldn’t ever have to wait for such important things, yet we still do, at least every now and again. Recently, researchers looked at data on Internet congestion in an effort to better understand where the slowdowns occur, and their work has provided some interesting findings.
The study, Where in the Internet is congestion? by Daniel Genin and Jolene Splett of the National Institute of Standards and Technology, was released last week. It’s based on publicly available data from the FCC’s ongoing Measuring Broadband America study, which was begun in 2010. The study has deployed more than 10,000 wireless routers with custom firmware in homes and businesses, spanning 16 ISPs. These routers collect performance data hourly and send them to a handful of geographically distributed servers.
Genin and Splett looked at two metrics to evaluate Internet congestion: a download throughput benchmark (based on multi-threaded TCP download speed tests) and website download speed (based on the time to download the homepages, including all code and images, of ten of the most popular websites). While the authors were primarily concerned with finding where the congestion occurs (i.e., closer to home or farther upstream), they had some interesting findings, particularly relating to the performance of cable via DSL networks.
Looking at data on roughly 3,000 Internet connections via cable or DSL ISPs between March and June of 2011, Genin and Splett found that your slow access may be because:
You’re using DSL
On average, people using cable had faster download speeds than those on DSL; the average measured download throughput speed for cable was 13.5 Mbps, while it was 5.4 Mbps for DSL.
You’re using cable
While cable ISPs offered higher average download speeds than DSL, there was also more congestion on their networks. Specifically, roughly 30% of cable connections experienced “recurrent congestion,” defined as failing to reach 80% of the measured average download speed more than 20% of the time. On the other hand, only about 10% of DSL connections experienced recurrent congestion.
You’re using the wrong ISP
While Genin and Splett found that congestion rates were similar across DSL ISPs, they found that they varied greatly among cable providers. Unfortunately, individual ISPs were not identified, so we can’t say which ones to avoid.
There’s congestion far away from your house
In determining where along the path of content delivery congestion occurred, the researchers found that, in the majority of instances, it was happening before the “last mile” of the trip. That is, most congestion doesn’t happen at the edge of the network (i.e., close to the house or business), but rather closer to the core, such as where the ISP connects to the public Internet.
The whys of all this congestion, and the differences between cable and DSL networks, remain to be determined. More information should be forthcoming as the FCC’s study continues and, hopefully, as ISPs decide to be more open about sharing their traffic data so the patterns and causes of congestion can be better understood. In the meantime, you’ll just have to patient while that video of skydiving cats buffers. Oh well.
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