Comcast, the largest provider of cable-based broadband service in the U.S., will limit residential customers to 250 gigabytes of bandwidth a month beginning Oct. 1, the company announced late Thursday.

Comcast will contact customers who go above the 250G byte limit and ask them to curtail their use, Comcast said. If a customer goes over the monthly limit again during the following six months, Comcast will suspend service for a year.

Currently, Comcast contacts high-bandwidth customers and will suspend their accounts if they don't curb their use, but it has not set a firm bandwidth limit until now. Most customers contacted about their bandwidth usage agree to limit their activity, according to Charlie Douglas, Comcast's director of communications.

Earlier this month, the U.S. Federal Communications Commission struck down Comcast's past network management practice of slowing BitTorrent peer-to-peer traffic in an effort to reduce congestion. The FCC ruled that Comcast was violating so-called net neutrality principles by targeting a certain kind of Internet traffic.

The new bandwidth cap will affect less than 1 percent of Comcast customers, Douglas said. Those customers "are using so much bandwidth that they are degrading the experience of other users," he added. "Two-hundred-and-fifty gigabytes is an extremely large amount of data."

Some high-bandwidth users have asked Comcast to identify a specific cap so they know where the line is, Douglas added. Some other broadband providers also warn customers about excessive bandwidth use.

An average Comcast customer uses two to three gigabytes of bandwidth a month, Comcast said. To reach the 250G-byte limit, a customer would have to do one of the following: send 50 million e-mails, download 62,500 songs or download 125 standard-definition movies, the company said in its announcement.

Comcast has also looked at charging high-bandwidth users additional fees, and it still has not ruled out doing so in the future, Douglas said.

Comcast is also looking at "de-prioritizing" heavy users' traffic during times of network congestion. The plan Comcast is considering would slow heavy users' traffic for up to 20 minutes during times of the most congestion.

Comcast will notify customers of the new bandwidth limits using several methods, including banner ads at Comcast.net and notices sent with monthly bills, the company said. Some net neutrality advocates criticized Comcast for not telling customers of its previous network management plan to slow P-to-P traffic at times.

The IDG News Service is a Network World affiliate.