Over the past several days, there have been a number of rumors and lots of discussion about the issue of bandwidth caps and Comcast. There have been a number of reports of users having reached some sort of bandwidth limit—reportedly 90GB—and having their service cut off by America's largest cable ISP. Ars spoke to Comcast today in an attempt to find out what's going on.

Surprisingly, Comcast's Acceptable Use Policy, to which all of its subscribers must agree, is somewhat vague when it comes to bandwidth limits. There are no hard numbers, just an admonition that Comcast's high-speed Internet subscribers are not allowed to "restrict, inhibit, or otherwise interfere with the ability of any other person, regardless of intent, purpose or knowledge, to use or enjoy the Service, including... generating levels of traffic sufficient to impede others' ability to send or retrieve information."

It's only when that last factor comes into play that Comcast will take action, Charlie Douglas, Comcast's director of corporate communications for online and voice services, told Ars. Douglas also said that those customers are an extremely small minority. "More than 99.99% of our customers use the residential high-speed Internet service as intended, which includes downloading and sharing video, photos and other rich-media," he told Ars.

Douglas said that Comcast customers whose Internet use causes issues for others on the network can expect a call from the company. "[Our] policy is to proactively contact the customer via phone to work with them and address the issue," he said. In some cases, addressing the issue involves determining whether their PC has been compromised and is now part of a spam- and malware-spewing botnet. If that is the case, Douglas says that Comcast will work with the customer to fix the problem.

In other cases, Comcast will suggest to the user that he or she move to a different Internet plan, often a "commercial-grade" product. Those include Standard and Enhanced packages that offer much the same speeds as the consumer packages, but come with extra niceties such as 24/7 support, domain name services, and static IP addresses. The Standard package starts at $95 per month and the Enhanced plan goes for $160.

Douglas was careful to emphasize that bandwidth abusers are a very small minority of Comcast's customers, reiterating that the issue is confined to less than 0.01 percent of the company's subscribers. "In fact, 95 percent of our users could increase their bandwidth usage a hundred-fold and still be in compliance," he said.

When asked whether Comcast would be better off with a proactive policy that spells out the limits in advance, Douglas defended the company's current stance. "We think it's a very proactive policy," he argued. "We actively monitor and look for patterns of repeated and consistent use with the goal of ensuring our customers have the best network possible." Most of the users contacted by Comcast ratchet their usage back significantly when they're done, according to the company.

Although Comcast is at the forefront of recent discussion around the issue of bandwidth caps, the company is by no means the only ISP with a cap. Much to the dismay of broadband users around the world, ISPs have begun turning to bandwidth caps in an attempt to cut down on the amount and type of traffic flowing through their networks. Many of those have actually relaxed over the past few years: in 2002, Canadian ISP Sympatico had a 5GB bandwidth cap. Users now indicate that the cap has been raised to 60GB for many users, while some have an unlimited bandwidth allowance.

Comcast's biggest problem may not be the fact that the bandwidth caps exist but that the company isn't transparent about how they work and at what level users will run into trouble. The situation is magnified by the fact that there appears to be a strong overlap between two populations: those who have run afoul of the ISP's limits and those who are likely to complain loudly when they feel they are being treated unfairly by their ISP.

It may very well be that a minute proportion of Comcast users are affected by the caps—although using Douglas' 99.99 percent figure, that still works out to around 1,150 users based on Comcast's 11.5 million subscribers as of the end of 2006—and it's great that Comcast calls users who are going overboard on bandwidth instead of merely pulling the plug once the mystery number is reached. But it seems that Comcast and its users could be spared a lot of pain if that number wasn't such a big mystery.