Glasnost: Results from tests for BitTorrent traffic blocking

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More than 8,000 users from locations around the world have used our tool, Glasnost, to test whether their BitTorrent traffic is being manipulated. On this page, we present preliminary results from these tests. The tests were conducted between March 18th and July 25th 2008.

We will update this page with more detailed results as we get more data from the tests. We also hope to uncover more cases of blocking as we refine our measurement tool and our analysis. So make sure to check back later. Alternately, you can stay up-to-date on our findings by subscribing to the glasnost-updates mailing list.

We have released the source code of our tool. You are welcome to download and inspect the code. Please contact us if you find any bugs or have questions, comments, or suggestions.

We published a paper on this work in the ACM Internet Measurement Conference 2008. It contains updated results up to May 7th, 2008 from more than 47,300 end users. You can download the paper in pdf format here.


How do we detect BitTorrent blocking by ISPs?

At a high-level, our test sets up a series of BitTorrent flows between an end user's host and our Glasnost test servers. We collect the packet trace for each flow on the server side, and we closely monitor both end points for any error conditions that might cause a flow to be aborted. If a flow is aborted by a control (RST) packet that was not sent by either of the end points, we report the flow as being blocked by some ISP along its path.

For more details on how we detect BitTorrent blocking, please click here.


Are ISPs blocking BitTorrent traffic?

Location of tested nodes

Note: This product includes GeoLite data created by MaxMind, available from

The map plots the geographic location of the 8,175 nodes that ran our BitTorrent tests. These hosts are distributed across 90 countries and 1224 access ISPs. Hosts that found their BitTorrent transfers being blocked are marked in red.

Note: ISPs may throttle (rate-limit) BitTorrent traffic without blocking it. The results we present here are limited to hosts whose BitTorrent transfers to our servers are blocked, i.e., interrupted by RST packets generated by some ISP along the path. We are still actively investigating techniques to accurately detect throttling. So we do not report any results on rate-limiting BitTorrent traffic at this time and we do not mark such throttled hosts in red.

The table below shows for each country (a) the number of hosts that ran our test, (b) the number of hosts for which we detected BitTorrent blocking, (c) the number of distinct access ISPs from which our test was run, and (d) the number of these ISPs that contained one or more hosts for which we detected BitTorrent blocking.


Details of blocked BitTorrent transfers

1. All hosts which observed blocking did so in the upstream direction (i.e., when the client host attempted to upload data to one of our Glasnost servers). Only a handful of hosts observed blocking for downstream BitTorrent transfers.

2. We found widespread blocking of BitTorrent transfers only in the U.S. and Singapore. Interestingly, even within these countries, most of the hosts that observed blocking belonged to a few large ISPs.

3. Both in the U.S. and in Singapore, all hosts that suffered BitTorrent blocking are located in cable ISPs. We did not see any blocking of BitTorrent transfers from DSL hosts in these countries.

Most (573 of 599) U.S. hosts that observed blocking are located in Comcast and Cox networks. In Singapore, all blocked hosts are connected using the StarHub network. While we did observe blocking for hosts in 10 other ISPs (7 of which are in the U.S.), we did not see widespread blocking of BitTorrent traffic for hosts in those ISPs.

The table below shows the details of BitTorrent blocking for Comcast, Cox, and StarHub. For each ISP, we show (a) the number of distinct hosts we measured, and (b) the number of these hosts for which we detected BitTorrent blocking.


Is BitTorrent blocked only during periods of peak network congestion?

Recently it has been reported that Comcast defended its BitTorrent blocking before FCC as a necessary practice that is done only during periods of heavy network traffic. It is widely known that network traffic exhibits a strongly diurnal pattern. So we analyzed our data to see if hosts in Comcast and Cox networks see fewer of their upstream transfers blocked during early morning or weekends (when network load is generally low) than during other times of the day.

The graphs below show (a) the number of measurements to Comcast hosts at different hours of the day and (b) the percentage of these measurements for which we observed BitTorrent blocking. The percentage of blocked connections remains high at all times of the day. Our data suggests that the BitTorrent blocking is independent of the time of the day.

comcast comcast

The graphs below show that the percentage of blocked BitTorrent connections remains fairly high even during the weekends for Comcast hosts.

comcast comcast

Similarly, the graphs below show that Cox hosts suffer BitTorrent blocking at all times of the day. Note that the data for Cox is more noisy than Comcast, due to the smaller number of measured hosts.

cox cox

The graphs below show that the percentage of blocked BitTorrent connections remains fairly high even during the weekends for Cox hosts.

cox cox



We are researchers at the Max Planck Institute for Software Systems. Our research focuses on characterizing residential broadband networks and understanding their implications for the designers of future protocols and applications. In case you have questions about this tool or our research, please visit our network transparency project webpage or contact us via e-mail: broadband @at@ mpi-sws mpg de

Faculty   Students
* Krishna P. Gummadi
  * Marcel Dischinger
* Andreas Haeberlen
* Alan Mislove