WORTH READING BitTorrent net meltdown delayed

[David Farber <dave () farber net>]

Begin forwarded message:

From: dewayne () warpspeed com (Dewayne Hendricks)
Date: December 5, 2008 3:25:07 PM EST
To: Dewayne-Net Technology List <xyzzy () warpspeed com>
Subject: [Dewayne-Net] BitTorrent net meltdown delayed

Original URL: <http://www.theregister.co.uk/2008/12/05/richard_bennett_bittorrent_udp/ 
>

BitTorrent net meltdown delayed

But is UTP the best approach?

By Richard Bennett

Posted in Telecoms, 5th December 2008 13:48 GMT

The internet's TCP/IP protocol doesn't work very well. As the  
internet's traffic cop, it's supposed to prevent applications from  
overloading the network, but it's at a loss when it comes to managing  
P2P applications. This deficiency, generally known to network  
engineers but denied by net neutrality advocates, has been a central  
issue in the net neutrality debate. BitTorrent Inc has now weighed in  
on the side of the TCP/IP critics.

The next official release of the uTorrent client – currently in alpha  
test – replaces TCP with a custom-built transport protocol called uTP,  
layered over the same UDP protocol used by VoIP and gaming. According  
to BitTorrent marketing manager Simon Morris, the motivation for this  
switch (which I incorrectly characterized in The Register earlier this  
week as merely another attempt to escape traffic shaping) is to better  
detect and avoid network congestion.

Morris also told the media this week that TCP only reduces its sending  
rate in response to packet loss, a common but erroneous belief. Like  
uTP, Microsoft's Compound TCP (http://research.microsoft.com/~kuntan/index_files/Page315.htm 
) begins to slow down when it detects latency increases. Even though  
TCP is capable of being just as polite as BitTorrent wants uTP to be,  
the fact that it hides its delay measurements from applications makes  
it troublesome for P2P clients with many paths to choose from. But  
it's sensible to explore alternatives to TCP, as we've said on these  
pages many times, and we're glad BitTorrent finally agrees.

It remains to be seen whether uTP is the best approach. The company  
has touted its close relationships with ISPs and the IETF's LEDBAT  
task group, but has so far shared none of the specifics of uTP  
operation in public fora. The PowerPoints they've shared with the IETF  
are encouraging, but they're a long way from the source code,  
simulations, and hard data from impartial sources that are  
prerequisite to any new protocol standard.

One thing that is certain is that uTP will not reduce the volume of  
traffic that P2P moves across the internet, something that would be  
commercial suicide for a company that depends heavily on aggressive  
file sharers, and pirates, for its popularity. But it does try to find  
the nooks and crannies of the internet where its content, legal and  
otherwise, can be gathered with the least impact on other users. If  
successful, this will make the internet more stable.

The stakes in the competition to replace TCP are considerable for a  
struggling company that recently had to lay off half its staff.  
BitTorrent lives at the intersection of three groups with sharply  
opposing interests: P2P users, most of them pirates; internet service  
providers with traffic and legacy equipment issues; and major  
television and movie studios who want wide distribution but no piracy.  
These interests have clashed in the past, particularly when a  
licensing deal with the MPAA raised the shackles of private P2P  
trackers, causing them to temporarily ban uTorrent clients until they  
could be satisfied that the privacy of those trafficking in stolen  
content wouldn't be compromised.

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