Zazzle Shop

Screen printing

Thursday, January 8, 2009

Comcast's New Network Throttling Now In Place

For the last few months, Comcast has been transitioning how it monitors and throttles broadband traffic. claims that this transition is now complete for all of Comcast's markets, meaning that Comcast users might see their connection speeds drop if they use too much sustained downstream throughput and they can even potentially lose their service if they exceed Comcast's monthly broadband cap.

Comcast previously received quite a bit of flack for throttling the throughput of users who were downloading certain types of data, such as torrent packets. While torrent traffic can often mean someone is downloading illegal content, that it not always the case--there is a growing amount of legitimate torrent content. Comcast decided to transition from this packet-inspection type of network monitoring to one that is content-agnostic.

Screenshot of a beta version of Comcast's bandwidth
usage meter tool (Credit:
The new system, which is now in place, monitors the amount of downstream traffic a user consumes and not what that traffic is actually composed of. The system first monitors the traffic on the cable modem termination system (CMTS) ports. If a particular CMTS port is deemed as "congested," any users on that port who are "identified as a primary reason why" that port is congested will have their traffic priority downgraded, which can potentially impact their throughput. By default, most users have a quality-of-service (QoS) traffic priority of "Priority Best-Effort" (PBE). However, if a user is flagged as causing congestion on a CMTS port, that user's priority changes to "Best-Effort" traffic (BE) for a period of time. states:

Comcast says that sustained use of 70% of your up or downstream throughput triggers the BE state, at which point you'll find your traffic priority lowered until your usage drops to 50% of your provisioned upstream or downstream bandwidth for "a period of approximately 15 minutes." A throttled Comcast user being placed in a BE state "may or may not result in the user's traffic being delayed or, in extreme cases, dropped before PBE traffic is dropped."

The downside is that if you are downloading a lot of data at a time when many of your neighbors are online, you might see your connection speeds slow down--or even drop out entirely--at least temporarily. The upside is that you can be as much of a bandwidth hog as you want at any given moment as long as the network can handle your traffic and your neighbors. This might act as an incentive for users to perform more of their large downloads during off hours.

But even if you never find your throughput temporarily throttled, you are still not out of the woods if you download and/or upload lots of large files. Don't forget that Comcast also has a monthly cap of 250GB of data--and that 250GB per month is an aggregate of both your downstream and upstream traffic. Users who go over the limit will receive a warning as well as a suggestion to upgrade their service from a residential to a commercial plan. Users who go over the 250GB per month twice in a six month period can have their service terminated. Comcast has promised a bandwidth usage meter tool so that Comcast users can keep track of their usage, but as of yet, the tool has not been released to Comcast customers.