It sounds like something an overbearing customs officer would do with your airport bag. But deep packet inspection, or DPI - the practice of examining Internet transmissions to figure out what kind of content is being sent - is a hot-button issue in the online world.
Activists for a more open Internet say DPI limits freedom and innovation and threatens privacy. Big Internet service providers (ISPs) call it a reasonable way to keep costs and congestion down on their networks. Representatives from BCE Inc.'s Bell Canada unit and Rogers Communications Inc. will testify about the practice today at hearings of the Canadian Radio-television and Telecommunications Commission.
The controversy is about how and why Internet traffic in Canada is managed and controlled. If the CRTC chooses to get involved, it may swing that control away from the providers, which could signal that the regulator wants to have greater influence in the direction of the Internet than it has taken so far.
The key issue is peer-to-peer file sharing, a method of transmitting large files over the Internet. The format has attracted the ire of music, television, and movie industry associations, who allege that peer-to-peer makes it easy to share illegally obtained content. But ISPs worry too: because these transmissions can run all day and night, they say that a small number of users hog a disproportionate share of the bandwidth.
So while the ISPs continue to build network capacity, creating more room for transmission, they also use DPI to deal with Internet-clogging file-sharing.
Companies like Bell, Rogers and Shaw Communications Inc. employ DPI through the use of computer technology that makes an educated guess whether the information being sent is an e-mail, a picture, or a large video or software file being sent via a peer-to-peer application. They can then slow down the latter to avoid too much strain on their networks, or accord them a lower priority.
"We can't spend our way out of the peer-to-peer problem," said Ken Englehart, vice-president of regulatory affairs for Rogers Communications. "It can tie up a big part of the highway."
But activists say that the problems with peer-to-peer are exaggerated, and they call DPI a sledgehammer that isn't necessary to deal with a very limited problem.
Worrying about how much content is being transmitted over all is the wrong focus, activists say. Rather, "bursts of Internet traffic at specific times are what matter," said David Reed, a fellow at Hewlett-Packard Laboratories who testified this week on behalf of the Campaign for Democratic Media.
Those bursts don't necessarily involve peer-to-peer traffic. Last week's Michael Jackson memorial service was streamed by millions online, but most of that streaming used other applications, not peer-to-peer.
By using DPI, some say that ISPs threaten innovation. Technologies thrive on a sufficient number of users. But if DPI slows BitTorrent (a popular file-sharing application) and other applications, the people who write software might be less likely to use it.
DPI is intrusive because it is like the postal service "looking inside the envelope" that someone's mailed, Prof. Reed said. It can also make errors, wrongly labelling a transmission as peer-to-peer when it's really something else.
But the ISPs say it's reliable. "We find it highly accurate, and continuing to get better," said Matt Stein, vice-president of network services at Primus, which uses DPI to slow down file-sharing whenever there's too much traffic on the network. And they point to their policy to discard any information about the transmission after it's been analyzed.
Peer-to-peer technology is not just used to share pirated materials - the phone service Skype functions on similar principles - and none of the Canadian ISPs say they use DPI to determine whether content is legal or copyrighted.
But one point which is less debatable is that DPI can't catch everything. More users of file-sharing are starting to encrypt their transmissions, making it harder for ISPs to determine whether the transmissions are the Internet-clogging peer-to-peer ones.
Much of the fear on both sides comes from a high-profile U.S. case. In August, 2008, the Federal Communications Commission ordered Internet provider Comcast to end a "discriminatory" practice of actively blocking or slowing transmissions done through BitTorrent.
In Canada, the CRTC could use its power under the Telecommunications Act to regulate, through principles or very precise instructions. The Act says ISPs cannot "control the content or influence the meaning or purpose of their transmissions" or "unjustly discriminate toward any person." But the ISPs say the broader threats to which the activists allude - suppressing innovation, threatening privacy - are alarmist and exaggerated. And they are fighting the prospect of further regulation.
"Our customers would experience more delays and more inconsistent service, and possibly higher prices," if the CRTC were to regulate, said Mr. Englehart of Rogers.
Who peeks, and when
Deep Packet Inspection practices of some major Internet providers:
Bell, EastLink: Implement DPI during peak periods and slow down peer-to-peer applications for peak periods (for Bell, this is between 4:30 p.m. and 2 a.m.)
Rogers, Shaw, Cogeco: Implement DPI at all times for 'upstream' communications only (uploads from computer to the Internet), and slow down peer-to-peer applications.
Telus, MTS Allstream, Vidéotron, SaskTel: Don't use DPI.
Implements DPI at all times, giving lowest priority to peer-to-peer traffic whenever there is congestion on network.