updated 06:15 pm EST, Thu November 5, 2009
Comcast two-tier throttling now active
(Update clarifying timing) Comcast in a new FCC notice (PDF) revealed that it has already begun implementing a new throttling system. The approach is now service-agnostic and will lower the priority of any data packets if a user's cable modem either tops 70 percent of download or upload bandwidth for more than 15 minutes or else is flagged as bogging down the CMTS node, which manages a neighborhood's cable modem traffic.
When throttling is active, local routers will either reduce the priority of the connection altogether for 15 minutes or until average bandwidth use falls below 50 percent during a similar span. The throttling could lead to packet loss in "extreme" cases where enough priority information exists to flood out that data, Comcast says. Certain traffic won't be completely throttled, however, as a node facing little to no congestion will send low-priority traffic through at a similar rate to normal data.
The update fulfills a promise made by the company to drop format-specific throttling following an FCC ruling that barred it from discriminating against BitTorrent and other specific protocols. The decision followed the establishment of a non-binding net neutrality principle and the eventual discovery that Comcast had masked its behavior by publicly denying its throttling even as tests confirmed the practice. Moves are underway at the FCC to formally ban such earlier tactics but likely won't take effect until 2010 at the earliest. [via The Inquirer]
Update: Although the FCC filing is new and provided significant added detail regarding the throttling method, the system reflects what was implemented in late 2008.