[ NNSquad ] Re: Richard Bennett's Take on uTorrent / UDP / VoIP

[Brett Glass <nnsquad@brettglass.com>]

I have only one criticism of Richard's article: he understates his case.

In particular, because he neglects to mention one extremely 
important point. By switching to UDP, BitTorrent will not only 
compete with VoIP and some video and audio applications but also with DNS.

This could well be catastrophic (in fact, it could bring about the 
"Internet meltdown" that Lauren postulated some years back). Why? 
Because DNS (domain name service), as ISPs and network 
administrators know all too well, is a "critical path" protocol in 
virtually every application. If DNS is slow, EVERYTHING ELSE that 
users do will also be slow. Remember, most network applications, 
including Web browsers, have to stop and wait -- unable to do 
anything else -- until they resolve one or more domain names. So, 
they'll hang frustratingly if DNS packets are dropped due to 
congestion. And what underlying transport protocol does DNS use by 
default? UDP. (It can use TCP as well; however, it does so if, and 
only if, it has a lot of data to transfer. And TCP, due to its 
complex handshaking and "slow start" flow control, is much less 
efficient and much slower.)

So, what we're talking about is not just congestion but sand in the 
gears of the entire Internet.

Also, because uTP does not conform to any explicit congestion 
management protocol that could detect congestion BEFORE packets are 
dropped, the only way it would be able to detect congestion in the 
network would be after packets were dropped. Which means that by 
the time it did anything -- IF it did anything -- to mitigate the 
congestion it caused, it already would have damaged the network.

YMMV, but personally I wouldn't want to be on the same cable 
segment with someone using this new version of BitTorrent.

--Brett Glass