Check my latest piece in The Register on the Comcast/BitTorrent detente.
Analysis So Comcast will stop shaping peer-to-peer seeding sessions with spoofed TCP RST commands. I caught up with the cable giant’s CTO Tony Werner on Thursday for more details.
The move should delight the company’s critics. These innocent control packets have been compared to identity theft, to collusion with dictatorial regimes, and outright hacking of customer systems. BitTorrent may not be an IETF-sanctioned RFC protocol in its own right, but Comcast has decided to bind itself to traffic management practices that don’t produce obviously non-standard packets. Instead, they’re going to install additional equipment that will do real-time traffic accounting by user, feeding back information to the cable infrastructure that will equitably distribute opportunities to offer upstream traffic. In essence, this system makes the cable standard DOCSIS much more sophisticated; now it will behave just like DSL, only faster.
In DSL systems, each customer typically has a dedicated physical cable to a DSLAM, a type of concentrator. The DSLAM aggregates customer data onto a common upstream link according to a fairness algorithm that picks frames for from buffers at the heads of these dedicated links in a manner that minimizes bandwidth hogging. In the new Comcast system, the fairness algorithm is deployed in the CMTS (the cable equivalent of a DSLAM), and acts on buffers in each customer’s cable modem. The CMTS is able to do this because DOCSIS data transfers from customer to network are preceded with brief requests for bandwidth. Armed with intelligence about each user’s recent traffic history and the state of the network generally, the newly-intelligent CMTS will schedule bandwidth by customer according to a fairness algorithm of its own, with the same range of choices that exist for DSLAMs.
This was fun to write, and the reaction has so far been very positive, which is unusual among the crowd that comments at The Reg.