2008
09.24

When the system ain’t happy, ain’t nobody happy

You may have seen my article a bit ago about Comcast instituting a 250GB per month cap on residential internet access as of October 1st. That date is now drawing near: next Wednesday.

The company has also said that they will throttle heavy users to “above DSL speeds” and, as of today, we know exactly what that means. Simply put, when Comcast’s network management software detects congestion on a cable channel (70% of available bandwidth being used up…download congestion is distinct from upload congestion but treated the same way) they turn on quality of service measures for that internet channel.

If it detects that a user is using more than 70% of their provisioned bandwidth for fifteen minutes straight, that user’s internet traffic is placed at a lower priority than everyone else’s. When bandwidth usage dips below 50% of the advertised service level for a fifteen minute period, this Quality of Service (QoS) sanction is lifted.

The practical application of this system is as follows: Comcast’s current cable channels, using DOCSIS 2.0 technology, can hold 38 Mbps of download traffic and 30 Mbps of upload traffic. Each channel is divided among around 275 subscribers. Before you wonder how such massive oversubscription works at all without bringing everyone’s internet to a crawl, realize that not everyone is going to be using, or max’ing out the bandwidth on, their connection at the same time, generally speaking. On the other hand, such recent developments as high definition internet video have rendered this much oversubscription a tenuous model. Hence the need to manage traffic when either a lot of customers go online (during “peak hours”, after school and work) or when a significant minority of customers want to watch online video.

The results of the QoS (Quality of Service) change? If the network is really congested and you get reassigned, gaming and voice or video chat may well become untenable propositions. Downloads may also slow down by a good bit, until you get out of the “time out” window. To be fair, satellite providers have been doing this foolishness for years, with 24-hour cap windows instead of 15-minute ones, but on the other hand they haven’t placed restrictions like these in addition to outright caps. Belt and suspenders, anyone?

The math works out this way: if you’re on the lower-tier connection (you’re on it if you have a regular bundle, or if you’re paying less than $60 for internet outside of your promotional period) your 15-minute limit, when the cable system is using more than 26.6 Mbps down or 21 Mbps up of traffic on your channel, is 472.5 MB for downloads, or just 78.75 MB for uploads. These may seem like large numbers, but a half-hour HD video show or a large application download can take out the download limit in under ten minutes (helped along by Comcast’s PowerBoost technology) and a video upload or even some photos will put you in the penalty box, though uploads have a much harder time being saturated at the cable system level than the more oversubscribed downloads. To get out of the QoS downgrade, you’d have to keep your traffic under 3 Mbps down or under 500 kbps up for 15 minutes, for a total transfer in that period of 337.5 MB or 56.25 MB uploaded. If you’re on the premium tier of service around here, your limit is 5.6 Mbps down, 1.4 Mbps up. Thresholds by those calculations run around 630 MB down (not quite enough for a Linux CD image, let alone a DVD image) and 157.5 MB uploaded (pick another time to upload your photos from that geology expedition you went on). To get back to normal, your thresholds are 450 MB downloaded and 112.5 MB uploaded in 15 minutes.

You’re reading this right: in congested time periods Comcast will go out of their way to penalize you for using the advertised speed of your connection for any extended period of time. Of course it’s convenient for them because they don’t have to mess with putting in new infrastructure, but it’s highly annoying, to say the least, for people who have paid good money for their internet, only to be capped and throttled (lesser of two evils, pick any two).

Of course, this throttling will be network-neutral…at least that’s what Comcst has to do to keep from getting into hot water with the FCC again…but on the other hand Comcast never seems to have a problem giving people all the cable TV they could possibly desire, provided you pay for it. Just goes to show that the current cable architecture wasn’t really made for internet, and Comcast isn’t willing…at all…to even try to put a solution to this problem.

One more thing: these network management processes won’t work all the time, especially in areas where plenty of people are streaming video online. A few dozen video streamers running at a megabit or two per second would fly under the radar for Comcast’s network management but still bring the cable node to the point of complete congestion. Or, taken from another angle, I could download a CD image at full speed, thus for whatever reason puting Comcast’s cable system beyond the “congested” threshold. I’m then knocked down a QoS level, so I can’t even do low-bandwidth stuff like VoIP reliably when the neighbors decide to start streaming HD video.

Fortunately, at the moment it looks as though generally my cable system isn’t reaching the congestion threshold, but during the daytime it gets close…and when it crosses below 11.4 Mbps of free bandwidth, effective soon, network management will make me that much less inclined to keep Comcast as my internet service. The problem? The alternatives: none at the speed Comcast is offering.

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