Comcast data usage meter accuracy measurement results

NetForecast just completed a report on the accuracy of Comcast’s Internet data usage meter. This is the third such independent audit report since 2010, and it details cumulative accuracy results based on more than a half million measurements at 55 Comcast service locations for the three-month period of January through March 2014. Comcast established an accuracy goal to measure traffic passing through a subscriber’s cable modem within plus or minus (+/-) 1% accuracy over a month. Our analysis validates that Comcast exceeded its goal, with actual month-end accuracy ranging between -0.75% to +0.36%.

Comcast has implemented continuous Internet data usage meter accuracy measurement aimed at validating and maintaining meter accuracy. NetForecast employs two types of accuracy audit approaches for Comcast: passive traffic measurements using real user traffic in subscribers’ homes, and active reference tests in which a NetForecast PC and server generate the only traffic on dedicated test lines. In combination, these two approaches identify potential meter accuracy issues and supply data needed to troubleshoot and resolve issues. 

For both approaches, NetForecast performs independent traffic measurements, obtains hourly usage meter records from Comcast for the locations, and compares the NetForecast data with Comcast’s records. Results from 50 passive and 5 reference locations are aggregated in the latest NetForecast report.

For the passive locations, we continuously count all traffic into/out of the Internet connections of volunteers who opt into the meter accuracy assessment program and self-install specially instrumented, off-the-shelf routers. Passive measurements take place under real-world conditions — i.e., they rely exclusively on the subscriber’s home traffic. This enables measurements to be performed at many locations, thus providing comprehensive geographical coverage. Passive traffic measurement provides data for every hour, enabling continuous insight into meter accuracy.

For the active reference test locations, NetForecast installs a test laptop PC running NetForecast software and the same specially instrumented router used for passive measurement on each Internet connection. We use FTP accounts on NetForecast servers on the Internet. Both downstream and upstream testing is performed under a variety of conditions.

Based on our measurement results, Comcast subscribers should be able to rely on Comcast’s meter accuracy. You can read our report here (PDF).

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