Re: [ledbat] "Oh Noes, the Internetz will Melt Down..."

Stanislav Shalunov <shalunov@shlang.com> Tue, 02 December 2008 08:30 UTC

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From: Stanislav Shalunov <shalunov@shlang.com>
To: Lars Eggert <lars.eggert@nokia.com>
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Subject: Re: [ledbat] "Oh Noes, the Internetz will Melt Down..."
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Some clarification of terminology --

uTP is, technically, a transport framing over UDP.  Congestion control  
used is, indeed, what I described in Minneapolis.

DNA is the BitTorrent Inc commercial product for content delivery.   
The protocol is BitTorrent, but DNA is a closed system with only one  
tracker and only one client implementation.  It uses only uTP for  
transport.

uTorrent is a free implementation of the BitTorrent protocol  
distributed by BitTorrent Inc.  The new version, 1.9, uses uTP along  
with TCP.

So the new version of uTorrent more widely deploys the transport, and  
the congestion control (both referred to as uTP in the quote below),  
already used in DNA.  It is designed to be less aggressive than TCP  
and has been useful to reduce latency in DNA.

-- Stas



On Dec 1, 2008, at 8:23 AM, Lars Eggert wrote:

> On 2008-12-1, at 17:56, Nicholas Weaver wrote:
>> The typical Fear Mongering "UDP Death Uhz Da Internetz":
>> http://www.theregister.co.uk/2008/12/01/richard_bennett_utorrent_udp/
>
> Wow. Talk about jumping to conclusions. That is quite an "article".
>
>> However, the question is, does anyone have insight into the "uTP"
>> congestion control protocol and what it is actually doing?
>
> See http://forum.utorrent.com/viewtopic.php?id=49813
>
> "What is in 1.9:
> uTP, the micro transport protocol. This UDP-based reliable transport  
> is designed to minimize latency, but still maximize bandwidth when  
> the latency is not excessive. We use this for communication between  
> peers instead of TCP, if both sides support it. In addition, we use  
> information from this transport, if active, to control the transfer  
> rate of TCP connections. This means uTorrent, when using uTP, should  
> not kill your net connection - even if you do not set any rate limits.
>
> What was in 1.8.1:
> uTP, but connection attempts were not initiated by default, and  
> there was no control over TCP as described above. You can enable it,  
> but likely you will see the uTP connections not transfering much  
> data, because they are pushed out of the way by TCP."
>
> This last bit sounds a lot like if uTP is is using some sort of less- 
> than-best-effort CC. (I believe someone mentioned in Minneapolis  
> that utorrent would implement BitTorrent's DNA - maybe this is it?
>
> Lars
>
>
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--
Stanislav Shalunov



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