At issue is Comcast Corp. and peer-to-peer file-sharing applications. Comcast says it doesn’t block access to P2P software clients. However, Associated Press nationwide tests suggest otherwise, and that the ISP is actively blocking BitTorrent downloads.

Of course, P2P carries a lot of baggage. Long the scorn of the recording, film and TV industries, P2P is often cited by those industries as the major conduit of copyright-infringing material.

But those same industries blaming P2P for piracy are also looking at file-sharing as a low-coast distribution channel. Having thousands of P2P-connected computers hosting your content for distribution is a lot cheaper than posting your song, film or software product on your own server and making people line up for the download.

The issue isn’t just about ISPs hindering P2P downloading and uploading. It’s also about “Net neutrality,” the concept that all traffic should be treated equally and no individual, company or organization should have a fast track to the information superhighway.

Net neutrality became an issue when tentative plans were drawn up in 2005 that would, if initiated, result in major Web sites paying for a fast lane on which to ship their data. Under these plans, a heavily trafficked site (Google, for example) could pay extra for the privilege of having a faster channel for its services.

While not actually a law, the Net neutrality concept calls for all data to be treated as equal, and that digital stream from Rhapsody should be treated no differently than a video clip from CNN or a download from a major gaming site. However, there are signs that all data is not being treated equally when it passes through Comcast’s network.

Comcast, the No. 2 Internet provider in the United States, says it “does not block access to any applications, including BitTorrent,” one of the most popular P2P software applications.

But a series of tests conducted by The Associated Press discovered that, while Comcast doesn’t necessarily block downloads via BitTorrent, it does block or limit uploads. And since one person’s download is another person’s upload, blocking that upload could be considered a hindrance for BitTorrent.

According to AP, Comcast’s blockage of BitTorrent trading is inconsistent and only happens when one BitTorrent user tries to share a complete file with another. Since BitTorrent is based on several users uploading only a small portion of any given file, the single person-to-person sharing scenario described in the tests is not descriptive of all BitTorrent traffic.

But when a single user shares that file with a single downloader, AP’s tests showed that Comcast sends a message to each user, and that each message claims to be the other P2P participant. So the downloader thinks he’s getting a message from the uploader and visa-versa.

And the content of that message? It tells the other computer to stop communicating. The Associated Press likens it to a telephone conversation where the operator cuts in on a conversation, telling each person on the phone in the voice of the other participant, “Sorry, I have to hang up. Goodbye.”

Why is Comcast doing this? AP says it’s a traffic issue for the ISP as it tries to keep P2P users from gulping too much bandwidth. That shouldn’t surprise anyone since P2P applications can account for anywhere from 50 to 90 percent of Net traffic.

However, other ISPs do make an effort to manage Internet data as it flows through their systems. It’s called “traffic shaping” and it can mean giving a higher priority to some data, such as e-mail or Instant Messaging, while giving file-sharing apps a lower priority.

Comcast is being taken to task because its method of blocking BitTorrent usage affects only one kind of traffic. Furthermore, that method affects everyone relying on BitTorrent, including content companies, bands, artists, TV and film makers using BitTorrent for legitimate data distribution.

What does BitTorrent, Inc., which has partnered with several high-profile media companies to distribute their content, have to say about all this?

“They’re using sophisticated technology to degrade service, which probably costs them a lot of money,” BitTorrent Inc. co-founder Ashwin Navin said. “It would be better to see them use that money to improve service.”