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uTorrent shifts towards UDP to make it work better
Wednesday 03 December 2008 10:39:54 by Andrew Ferguson

Peer to peer applications are changing it seems. uTorrent is running experiments that may see it shift a lot of data from TCP to UDP. In the short term this would benefit some torrent users since providers that have simply rate limited the TCP ports used by BitTorrent will have to play catch up, and UDP by its connectionless nature may prove to be harder to traffic manage, but given providers can identify UDP gaming traffic it will only be a matter of time before any limits kick back in.

The Register has an article by Richard Bennett that tells us that Gamers, VoIP users and video conference users need to beware. Now if a provider has allocated just 20% of its available bandwidth to UDP traffic at peak times, and P2P starts to shift into this area, then yes packet loss may rise and jitter, when the packets arrive with variable delay, will increase. Simon Morris who is a BitTorrent Product Manager has countered The Register's article on

uTP is our UDP-based implementation of the BitTorrent protocol. Normally BitTorrent is implemented on top of TCP which is the standard congestion control mechanism for the internet. It so happens that the congestion control mechanism inside TCP is quite crude and problematic. It only detects congestion on the internet once “packet loss” has occurred – i.e. once the user has lost data and (probably) noticed there is a problem. The problems of TCP are fairly well known in technical circles, but it doesn’t get fixed as TCP is one of those protocols that is implemented in every OS, client and server, on the internet. Co-ordinating a giant upgrade is a very long process.

Because BitTorrent publishes the world’s most popular BitTorrent clients AND because these clients are talking mostly to each other (not to web servers), then we have an opportunity to detect end-to-end congestion and implement a protocol that can detect problems very quickly and throttle back accordingly so that BitTorrent doesn’t slow down the internet connection and Gamers and VOIP users don’t notice any problems. This is our objective.

Simon Morris BitTorrent Product Manager

So it seems they are claiming that the new uTP layer they've added will throttle the UDP packets back when congestion is seen, but it is not clear whether we are talking congestion on an individuals connection, or congestion at any point between two peers? If peer to peer is trying to behave better and be more traffic friendly then that is perhaps to be welcomed, but gamers are often some of the first to notice problems, and any packet loss or jitter that this causes can ruin a game.


Posted by chrysalis over 8 years ago
apperently the register have knee jerked and got it wrong, the main reason for this change is supposedbly that if p2p utilises udp then it wont affect latency senstive applications so much as tcp will take priority over it. Meaning in simple terms someone can be downloading on utorrent and they wont notice so much slowdown as they do now.
Posted by CARPETBURN over 8 years ago
Indeed, also should in theory mean anyone thats ever had trouble browsing the web (EVEN AFTER TWEAKING UTORRENTS SETTINGS) will or should now be able to.
Posted by Dawn_Falcon over 8 years ago
No Chrysalis, it's both. It's bypassing TCP flow, and implimenting its own which may or may not make it a good netizen.

Andrew - "Identifying" game traffic, right. You mean knowingly crippling their subscribers ability to play games via DPI methods which add considerable latency.
Posted by CARPETBURN over 8 years ago
Oh please lets not start on the merrits of game copying and downloading again, maybe if publishers could make a game which works instead of turning its nose up just cos you may have say Nero or similar installed they then can have a pat on the back and feelings of regret at what occurs with P2P in this day and age.
Posted by Dawn_Falcon over 8 years ago
Copying and downloading? Who mentioned those? I think you have a guilty concience, Carpet.

No, I was refering to *playing* games.
Posted by CARPETBURN over 8 years ago
Only thing im guilty of is not even bothering with poorly programmed churned out gaming poop the PC sees nowadays. If i had a gun licence id like to pay some gaming companies a visit and show them what a real FPS game is... that should make them think what real "immersion" and other cack terms they spout truely means.
Posted by Dawn_Falcon over 8 years ago
Ah, just death threats then.
Posted by CARPETBURN over 8 years ago
LOL.... ME.... Threats... LOL I aint the chief clown threatning to sue people every second of the day
Posted by fox-uk over 8 years ago
"make it a good netizen."

Let's see...
I pay for a computer
I pay for broadband
This allows me to legaly use the internet.

Now I'm expected to act like a 'good netizen'

Sorry, I left kindergarten over 50 years ago and expect to get what I pay for.

I don't get what I was sold so I will take what I can (in bandwidth etc.) when I am allowed to use it.

Just because the sellers have been doing this for many years doesn't make them right and their customers 'bad' anything.

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