nanog mailing list archives
Re: BitTorrent swarms have a deadly bite on broadband nets
From: "Steven M. Bellovin" <smb () cs columbia edu>
Date: Sun, 21 Oct 2007 23:46:20 +0000
On Sun, 21 Oct 2007 13:03:11 -0400 (EDT) Sean Donelan <sean () donelan com> wrote:
http://www.multichannel.com/article/CA6332098.html The short answer: Badly. Based on the research, conducted by Terry Shaw, of CableLabs, and Jim Martin, a computer science professor at Clemson University, it only takes about 10 BitTorrent users bartering files on a node (of around 500) to double the delays experienced by everybody else. Especially if everybody else is using "normal priority" services, like e-mail or Web surfing, which is what tech people tend to call "best-effort" traffic. Adding more network bandwidth doesn't improve the network experience of other network users, it just increases the consumption by P2P users. That's why you are seeing many universities and enterprises spending money on traffic shaping equipment instead of more network bandwidth.
This result is unsurprising and not controversial. TCP achieves fairness *among flows* because virtually all clients back off in response to packet drops. BitTorrent, though, uses many flows per request; furthermore, since its flows are much longer-lived than web or email, the latter never achieve their full speed even on a per-flow basis, given TCP's slow-start. The result is fair sharing among BitTorrent flows, which can only achieve fairness even among BitTorrent users if they all use the same number of flows per request and have an even distribution of content that is being uploaded. It's always good to measure, but the result here is quite intuitive. It also supports the notion that some form of traffic engineering is necessary. The particular point at issue in the current Comcast situation is not that they do traffic engineering but how they do it. --Steve Bellovin, http://www.cs.columbia.edu/~smb
Current thread:
- BitTorrent swarms have a deadly bite on broadband nets Sean Donelan (Oct 21)
- Re: BitTorrent swarms have a deadly bite on broadband nets Marshall Eubanks (Oct 21)
- Re: BitTorrent swarms have a deadly bite on broadband nets Steven M. Bellovin (Oct 21)
- Re: BitTorrent swarms have a deadly bite on broadband nets Joel Jaeggli (Oct 21)
- Re: BitTorrent swarms have a deadly bite on broadband nets Mark Smith (Oct 22)
- RE: BitTorrent swarms have a deadly bite on broadband nets Frank Bulk (Oct 22)
- RE: BitTorrent swarms have a deadly bite on broadband nets Crist Clark (Oct 22)
- RE: BitTorrent swarms have a deadly bite on broadband nets Buhrmaster, Gary (Oct 22)
- Re: BitTorrent swarms have a deadly bite on broadband nets Majdi S. Abbas (Oct 22)
- Re: BitTorrent swarms have a deadly bite on broadband nets Sean Donelan (Oct 22)
- Re: BitTorrent swarms have a deadly bite on broadband nets Adrian Chadd (Oct 22)
- Rack space and bandwidth in Joran Leigh Porter (Oct 22)
- Message not available
- Re: BitTorrent swarms have a deadly bite on broadband nets Adrian Chadd (Oct 23)
- Re: BitTorrent swarms have a deadly bite on broadband nets Joel Jaeggli (Oct 21)