Hogging the Trough: The EFF Strikes Back

So let's recap the argument. I say BitTorrent causes problems for Comcast's DOCSIS network that can't be healed economically by randomly dropping packets. Packet drop applies back-pressure to conventional TCP sessions, but it does nothing to the data queued inside Comcast users' cable modems, where it contends for scarce upstream bandwidth with other users.

Packet-drop also does nothing to affect the rate at which new connect requests come into the Comcast network from BitTorrent users across the Internet. Random packet-drop has profound effects on conventional applications, but very little on BitTorrent, and the routers to do packet-drop in real-time are more expensive than the aynchronous Sandvine system.

Therefore, it's acceptable for Comcast, as a matter of reasonable network management, to employ TCP Resets to prevent BitTorrent doing harm to the web browsing, standard file downloading, and VoIP sessions that are the typical behavior of the Comcast customer.

My claim is borne out by Professor Martin's analysis of TCP's interaction with the DOCSIS Medium Access Control protocol, and by his analysis of BitTorrent's side effects on web browsing. It's further borne out by observations of BitTorrent's cycling behavior, and the well-known weakness in packet drop in terms of cycling and fairness which I addressed on the last article.

Confronted with all this evidence, the EFF and Eckersley would be wise to admit their confusion and vow to devote further study to the topic, in particular to wait for the FCC's analysis of the complaint.

To the cable company's credit, it has announced plans to begin a major network upgrade starting in the fourth quarter, resulting in a nearly symmetric 130/100 Mbit/s network with the kind of traffic controls that the EFF dreams about.

(When it's not lobbying for usage-based pricing. Eckersley cites Australian ISP Whirlpool's pricing plans as exemplary.)

With such a system on the drawing board, it's not hard to fathom why Comcast doesn't want to lay in the collection of the expensive routers (Sandvine runs on PC hardware and processes packets out-of-band) the EFF would have them buy to patch their current network into EFF-approved shape; all it takes is a willingness to see reality as it is and an ability to put the holy books aside. That may be a hard slog for a Net-Utopian advocacy group harboring delusions of conspiratorial persecution, but it's the right thing to do.

Conclusion

Everyone who's argued with religious fanatics has seen them dig in their heels and flail when confronted with challenges to their belief systems. Point out the inconsistencies in the Genesis account of creation or the implausibility of Noah's Ark and you'll get some creative sputtering followed by affirmations of faith at a high volume level.

The EFF's response is over-heated religious rhetoric that ignores both the economic constraints that bind network operators, and the ineffectiveness of the Internet's inherited methods at dealing with challenges created by new protocols and applications. The literature on packet-drop in particular suggests a dozen variations, none of which applies across the scope of a single BitTorrent user's communications.

While the Internet's end-to-end architecture makes it a fertile testbed for the implementation of new protocols, each brings with it new traffic patterns that must be dealt with in ways that prevent others from starving. Hogging the trough is simply not acceptable network behavior.®

Richard Bennett is a network architect and occasional activist in Silicon Valley. He wrote the first standard for Ethernet over twisted-pair wiring and contributed to the standards for WiFi and the Ultra-Wideband wireless networks. His eleven-year old blog is at bennett.com. He will debate these issues on a panel at the Toll Roads Symposium in San Francisco on Saturday.

Related links

Dismantling a Religion: The EFF's Faith-Based Internet

Copyright specialist Peter Eckersley's response - Scrutinizing Comcast's Apologists