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.