(from
http://www.11alive.com/tech/article_...storyid=105115)
AP Tests Comcast's File-Sharing Filter
NEW YORK (AP) -- To test claims by users that Comcast Corp. was blocking
some forms of file-sharing traffic, The Associated Press went to the Bible.
An AP reporter attempted to download, using file-sharing program BitTorrent,
a copy of the King James Bible from two computers in the Philadelphia and
San Francisco areas, both of which were connected to the Internet through
Comcast cable modems.
We picked the Bible for the test because it's not protected by copyright and
the file is a convenient size.
In two out of three tries, the transfer was blocked. In the third, the
transfer started only after a 10-minute delay. When we tried to upload files
that were in demand by a wider number of BitTorrent users, those connections
were also blocked.
Not all Comcast-connected computers appear to be affected, however. In a
test with a third Comcast-connected computer in the Boston area, we were
unable to test with the Bible, apparently due to an unrelated error. When we
attempted to upload a more widely disseminated file, there was no evidence
of blocking.
The Bible test was conducted with three other Internet connections. One was
provided by Time Warner Inc.'s Time Warner Cable, and the other came from
Cablevision Systems Corp. The third was the business-class connection to the
AP's headquarters.
No signs of interference with file-sharing were detected in those tests.
Further analysis of the transfer attempt from the Comcast-connected computer
in the San Francisco area revealed that the failure was due to "reset"
packets that the two computers received, carrying the return address of the
other computer.
Those packets tell the receiving computer to stop communicating with the
sender. However, the traffic analyzer software running on each computer
showed that neither computer actually sent the packets. That means they
originated somewhere in between, with faked return addresses.
In tests analyzing the traffic received by a computer on Time Warner Cable
that was trying to download a file from a large "swarm" of BitTorrent users,
more than half of the reset packets received carried the return addresses of
Comcast subscribers, even though Comcast's 12.4 million residential
customers make up only about 20 percent of U.S. broadband subscribers. It
was the only U.S. Internet service provider whose subscribers consistently
appeared to send reset packets (which are occasionally generated
legitimately).
Comcast subscriber Robb Topolski, who discovered the blocking earlier this
year and traced it to reset packets, pointed out that a Canadian company
called Sandvine Inc. sells equipment that promises to save bandwidth for
Internet service providers by managing and redirecting file-sharing traffic.
BitTorrent Inc. President Ashwin Navin said that the interference method on
Comcast's network is consistent with Sandvine's technology. Sandvine did not
respond to a request for comment.
Comcast spokesman Charlie Douglas would not confirm that the company uses
Sandvine equipment.
"We rarely disclose our vendors or our processes for operating our network
for competitive reasons and to protect against network abuse," he said.
(Copyright 2007 by The Associated Press. All Rights Reserved.)
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