The FCC’s broadband measurement group got more details...
The FCC’s broadband measurement group got more details Thursday on how it might determine whether a poky Internet experience is due to a bottleneck upstream, or interference in the house. The commission is planning on conducting a special study on…
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how what happens inside the home might affect Internet speeds (CD May 3 p1). Nick Feamster, an associate professor of computer science at Georgia Tech, led the group through how his “WTF” equipment -- standing for “Where’s the Fault” -- works. By looking at the “coefficient of variation” -- packet arrival times -- and seeing whether they are smooth or erratic on either side of the transmission, WTF can determine where the bottleneck is, Feamster said. When the wireless link is the bottleneck, the throughput is much more variable, he said: That’s caused by the variability in packet “interarrival” times. The equipment also looks at the MAC-layer retransmission rate and the wireless bitrate. If it sees a high wireless retransmission rate, or a bitrate that’s continually changing, “both of those things tend to be indicators of something shady going on in the wireless link,” Feamster said. The problem could also be caused by “contention” between several clients trying to access the access point, he said. FCC Office of Engineering and Technology Senior Attorney-Adviser James Miller reiterated that the purpose of this effort is not to compare ISP performance, but rather “to look at whether or not we could add to the consumer’s understanding” of where congestion lies.