2008-05-19

US ISPs are generally perceived by users here to offer unlimited and fairly neutral connections to the 'Net for a monthly fee. Or they were, anyway, until Comcast admitted that it was "delaying" P2P traffic at peak times. New research from Germany now demonstrates that it's not just Comcast; Cox is getting a piece of the P2P blocking action, too. What's more, neither company blocks only at peak usage times. Paging the FCC!

Researchers from the Max Planck Institute for Software Systems have just released results of their own tests into BitTorrent blocking from around the world, and the results are startling: almost no one does it. In fact, out of 1,224 measured ISPs, only 13 were found to block BitTorrent traffic out. And where are the blocks coming from? Predominantly from the USA, where nine of the 13 ISPs were located.

Singapore, Malaysia, Canada, and Ireland each had one ISP apiece that engaged in blocking, though only Singapore's StarCom did so with regularity (26 out of the 45 tests that used its network were blocked with TCP reset packets).

Of the nine ISPs in the US found to block BitTorrent, Comcast and Cox were far and away the most aggressive. Both blocked more than half of all attempted BitTorrent tests on their networks (82 of 151 tests on Cox were blocked, while 491 of 788 tests on Comcast met the same fate).

The tests were done using a piece of open source software called Glasnost that users around the world downloaded and installed on their machines. 8,000 users took part in the test, which used Glasnost to establish BitTorrent sessions with a set of test servers in Germany. Since the researchers can collect information about both sides of the connection, they can determine when a connection is artificially broken using TCP reset packets (Comcast's preferred method).

One limit of such testing is that it can't uncover throttling or shaping of any kind, so the Max Planck researchers are clear to note that their work represents a strongly conservative estimate of the number of ISPs who interfere with P2P traffic.

Only at peak hours?

The researchers also took a look at time of day to see if the blocks occurred only during times of peak usage (generally in the evenings). They did not. Blocks, in fact, were pretty consistent throughout the day, as the Comcast chart below shows.

Free Press, one of the groups pressuring the FCC to take action in the current proceeding involving Comcast, responded with even more than its usual outrage to the news.

Ben Scott, the group's policy director, said in a statement, "Consumers have no reason left to trust their cable company. These Internet experts have also unequivocally demonstrated that blocking is not limited to times of supposed congestion. Their sophisticated testing shows that Comcast and Cox block BitTorrent applications at all times of the day—not just at times of peak traffic. This research proves beyond a shadow of a doubt that consumers, Congress and the FCC must urgently pursue the complaints against network providers."
Methodology

Previous research into TCP reset packets by Vuze drew the wrath of AT&T, which said that it does not use reset packets as a network management tool and that simply seeing resets on its network meant nothing. Vuze admitted that its methodology generated inconclusive results, but the new research appears much more rigorous.

The Max Planck Institute has published its methodology for inspection. The Glasnost program establishes several TCP streams before and after the BitTorrent connection; if none of these experience reset packets or other network problems, but the BitTorrent stream does get blocked, the researchers conclude that it was BitTorrent specifically that triggered a reset from a machine in the middle. In addition, the researchers only counted a reset packet as a block if it was generated just after protocol-specific "bitfield" messages but before any actual data transfer.

Requests for comment to both Cox and Comcast were not returned by press time.
Update:

Comcast comments to Ars. Parse this as you will:

"Comcast does not, has not, and will not block any websites or online applications, including peer-to-peer services like BitTorrent. We have acknowledged that we manage peer-to-peer traffic in a limited manner to minimize network congestion. While we believe our current network management approach was a reasonable choice, we are now working with a variety of companies including BitTorrent and confirm our March announcement that we will move to a protocol-agnostic network management technique no later than December 31, 2008."

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