This story appeared on Network World at


Comcast: Unexplained bandwidth caps


Comcast isn't saying why it's implementing bandwidth caps on its high-speed Internet service


'Net Insider By Scott Bradner , Network World , 09/02/2008


Comcast is in the news again. Over the last few months it seems like a new Comcast-related story has broken every few weeks -- all of them quite bad news for the service provider. The PR people over there sure must be busy.


A few days ago Comcast let it be known that it was testing a mechanism that "slowed down" the traffic of heavy users of its high-speed Internet service. Around the same time, Comcast settled with the Florida Attorney General who had charged the service provider with not properly disclosing information, for example, customer data usage caps.


Neither of these stories received much press coverage. But in the middle of these stories came another about Comcast that did receive a lot of attention -- Comcast announced that it was going to put a usage cap of 250GB per month on all residential users. Repeated violations of the cap could get a customer disconnected for a year.


After a bunch of fervor, it turned out that Comcast had been doing this all along. But this was the first time it was actually willing to tell anyone what the limit was (this willingness just might be related to the Florida case).


Comcast has not actually said just why it has a usage cap, at least not anyplace I've seen. For example, its FAQ on the limits
does not include a "why" question and its announcement of the feature does not say why it is doing this. Comcast has implied
that it has something to do with fighting congestion and most of the press coverage seems to assume that is the goal. But, as I've written about before, usage caps or usage-based fees do not, and cannot, have anything to do with fighting congestion.


The "slowing" mechanism that Comcast is testing is directly related to fighting the effects of congestion. According to published reports, Comcast is not actually slowing traffic (as the headlines would have you believe). Instead, in times of congestion, they are temporally setting a lower priority on traffic from customers which have been judged to be receiving or sending too much traffic in the proceeding few minutes.


This will slow traffic if the congestion persists because some of the lower-priority traffic will likely be dropped when the router buffers overflow and will have to be retransmitted, which takes longer.


If a usage cap is unrelated to fighting congestion then we must look at other reasons for Comcast maintaining such a cap. It is possible that the corporate powers-that-be are not technically cluefull, acceptable lingo enough to understand that a cap does not help reduce congestion. But Comcast has some very smart people working for it that I'm sure understand the technology, so the powers would have to be ignoring their own people, which I hope is not the case.


It's far more likely that the cap is in place to make sure that Comcast's network cannot be relied upon by competitors for high quality video delivery. Comcast's current cap of 250GB per month, which the company could change any time it wants to, works out to a few hours per day of HD video, not very much. A couple of people in a household could easily exceed that on a regular basis, at least until Comcast pulled the plug.


It sure looks to me like Comcast is engaging in anticompetitive behavior. Considering the current FCC bias against cable companies, I'm more than a bit surprised that the FCC has not started to nose around. Maybe the rumors about AT&T and other telephone companies considering usage-based fees is keeping the FCC at bay.


Disclaimer: Harvard employs usage-based fees for some things like food but, as far as I know, most of the rest of the student fees are flat rate. In any case, the above represents my own views, not those of the university.


All contents copyright 1995-2009 Network World, Inc.