

Changing the game with μTP - moriarty
http://blog.bittorrent.com/2009/10/05/changing-the-game-with-%ce%bctp/

======
wmf
What's unsaid here is that uTP is an undocumented protocol that isn't
available to other BitTorrent implementations like Azureus/Vuze, potentially
making them second-class citizens.

~~~
dschobel
from the bittorrent.com comments, a quote from a high-up at BT:

Simon Morris

Posted October 8, 2009 at 5:52 pm

As a matter of fact µTP is indeed a replacement for TCP, so we think the name
is appropriate. _You can check out standardization work which we’re chairing
at the IETF called the LEDBAT working group_

~~~
wmf
LEDBAT is only standardizing a small subset of uTP:

"Framing is not on the WG's charter."

[http://www.ietf.org/mail-
archive/web/ledbat/current/msg00117...](http://www.ietf.org/mail-
archive/web/ledbat/current/msg00117.html)

------
jws
This new protocol uses packet latency based throttling instead of the packet
loss based throttling of TCP.

I don't think the article documents any details. Maybe I missed a link.

~~~
dschobel
Latency based congestion control already exists for TCP[1].

So my question is, why wouldn't you get the same effect by running BT on top
of a network stack using Vegas?

Someone flash the tptacek signal!

[1] <http://en.wikipedia.org/wiki/TCP_Vegas>

~~~
jws
It appears to me that if you use Vegas on your Linux machine then all of your
TCP connections use Vegas, which will make you a second class citizen to all
the Reno folk out there on the internet.

If you assume that your own uplink is the only bottleneck to be dealt with
(say you are serving torrents over a DSL line) then this is reasonable, but I
don't think I'd want to yield to all TCP users everywhere with all of my
outgoing traffic.

There are also some scary comments in the notes from before it was rolled into
the kernel, like the code doesn't handle route changes.

I can see why a vendor would choose something over which they have control.

------
tybris
[http://research.microsoft.com/en-
us/um/people/costa/papers/s...](http://research.microsoft.com/en-
us/um/people/costa/papers/slot09zeroday.pdf) might be an interesting
alternative/complement.

~~~
wmf
OTOH,
[http://conferences.sigcomm.org/hotnets/2009/papers/hotnets20...](http://conferences.sigcomm.org/hotnets/2009/papers/hotnets2009-final115.pdf)
suggests that localization doesn't help that much.

------
known
Isn't <http://en.wikipedia.org/wiki/Precision_Time_Protocol> better than uTP?

