"If they are going to put caps, then they need to give us what I think is an acceptable expectation: a meter," Malik wrote Thursday. "Figure out a way to tell us what is our monthly usage, and let us know if we are running up against a 250 GB cap, we know when to stop ..."

Malik also questioned Comcast's estimates about how many e-mails a subscriber would have to send, songs they'd have to download, or movies they'd have to download to reach the cap. On one Comcast Web page explaining the caps, the company gives two different sets of numbers, Malik pointed out. On one part of the page, Comcast says a user would have to send 40 million e-mails or download 50,000 songs to reach the cap, and further down the numbers change to 50 million e-mails and 62,500 songs.

The 50 million e-mails is based on an estimate of 0.5 kilobytes per e-mail. "If you believe the 0.05 kb/e-mail then you also believe in the Tooth Fairy," Malik wrote.

Some critics raised concerns that the 250G-byte limit may be generous at the moment, but broadband users' bandwidth needs will continue to increase.

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.

"It remains unclear how the cap announced today helps solve Comcast's supposed congestion problems," said S. Derek Turner, research director of Free Press, another digital rights group critical of Comcast's past network management. "Though the proposed cap is relatively high, it will increasingly ensnare more users as technology continues its natural progression."

Turner applauded Comcast for being open about its caps. Well-disclosed caps are a better short-term solution than "Comcast's current practice of illegally blocking Internet traffic," he said.

Comcast will review the broadband caps periodically and look at whether they need to be increased, Douglas said.

Some Internet posters also questioned if the bandwidth caps violate customer agreements offering unlimited service. Comcast in past years has advertised that subscribers have unlimited downloads.

But Comcast doesn't have contracts with most customers that promise unlimited bandwidth, Douglas said. Comcast's terms of service allow the provider to change those terms, and generally focus on acceptable use, he said.