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Do congestion problems stem from a bit of 1987 code?
Wednesday 26 March 2008 14:08:08 by Andrew Ferguson

We all know that broadband providers have a tendency to blame P2P traffic for many woes and a lot of time this goes hand in hand with comments about illegal traffic in the form of pirated software and copyrighted material being transmitted without appropriate permissions.

There are some very good reasons behind why P2P traffic is the problem that it is, and anyone in a shared household will be all too aware that one person running a P2P app can easily swamp the connection and even if others try to grab some traffic space they find it very hard. This is often down to the nature of the TCP stack that includes algorithms on how traffic is handled. At its simplest level it means the software that opens the most connections will get the lions share of the available bandwidth. A blog on ZDNet titled Fixing the unfairness of TCP congestion control describes the issue in some length and provides a potential solution.

Back in the days before web browsers existed the Internet did exist and around October 1986 the Internet, which measured some 30,000 computers, started to grind to a halt and Van Jacobson created a patch in 1987 that resolved this problem. This patch is still at the core of TCP stacks today. In a day when computers would generally only have one TCP stream open at a time this worked, but once P2P, which may use 10 to 100 simultaneous connections, has become popular the congestion control mechanism is working against the average user who by and large is still using interactive bursty applications such as web browsing.

The problems in Japan where the 100Mbps connections are described as a traffic jam will sound familiar to UK users, and perhaps be a surprise to some, as many believe the Japanese market to provide cheap fast broadband. Of course providers have come up with various solutions, such as usage limits, pay as you go services, and traffic management techniques. The latter can be unfair since it will often impact the occasional user as much as those looking to fill as many hard disks as they can afford. Traffic management can also lead to unexpected results, breaking some games for example that use P2P to distribute patches. The net neutrality debate centers mostly around concerns that a company may throttle external services such as video while prioritising its own video service and does little to address the issues of congestion other than forcing providers to upgrade networks which, unless the customer pays more, will eventually bankrupt companies.

The proposed solution of a Weighted TCP algorithm whereby single stream apps tag their stream with a higher weight than an application with eleven streams would seem to offer a solution. The method sounds not unlike some traffic tagging and control systems whereby one piece of hardware is used to tag the traffic and a second bit of hardware actually adjusts the amount of capacity given to that traffic stream. The advantage of embedding this into the TCP stack is that it would become part of all hardware, thus helping to manage traffic even at the home router level.

One other solution that has been around since 2001 is Explicit Congestion Notification (ECN). This is already in the Linux, Windows Vista and Windows Server 2008 TCP stacks but is disabled by default. If enabled, people may find it works but if older routers are encountered, packets may be dropped. As older kit is removed from networks and more TCP stacks support ECN we may see the mechanism exploiting its better signaling method, which at its heart is the fact that packets are not dropped when a network gets busy.

The P2P and network congestion debates are a minefield as many bodies are voicing just their own interests rather than looking at a larger much more technical picture. With luck an engineering solution can be arrived at rather than the bean counter solutions which often see excess usage charges or traffic throttling being applied.

Comments

Posted by nervous over 9 years ago
Sounds fair and wise to me!
Posted by Dixinormous over 9 years ago
The only issue being that a zealous coder will take exception to their P2P not being treated as gold standard traffic and mess with it so that it tags its' streams with maximum weight, that gets stopped, coders obfuscate streams, obfuscation is broken and round and round it goes.
Posted by comnut over 9 years ago
Yeah like a road hog who never obeys the signs, cuts up other drivers, and then wonders why the police always accuse him...
Posted by Dawn_Falcon over 9 years ago
With the current state of the market, if my app didn't claim maximum priority regardless it'd be negligent. Moreover, current "soloutions" add considerable latency, which shafts a lot of appliations...
Posted by CARPETBURN over 9 years ago
quote"The problems in Japan where the 100Mbps connections are described as a traffic jam will sound familiar to UK users"
Not this old chestnut again, ive used 100Mbps services in other parts of Europe (obviously thatsnot including Japan) and never had issues maxing speed withthe connection, like wise here at home i have no issues maxing my LLU connection, and it seems others with the same LLU service have no issues either. I spose everyone that uses my ISP and everyone that uses 100Mbps services in the country i was in are just lucky are they?
Posted by CARPETBURN over 9 years ago
This is nothing more than more diatribe to try to bash P2P... Why people cant just realise its here and like good old FTP its not going to stop i dont know, but P2P aint gonna go anywhere and blaming users is just pathetic.
Why aint they blaming newsgroup or FTP users that have many connections going at once huh????
Truely pathetic some of these dreamers and their its all P2Ps fault mentality
Posted by Dixinormous over 9 years ago
CARPETBURN there is a lot of contention on the higher bandwidth services in Japan, that was what was referred to. Some contention within the ISP but as soon as you leave it it gets a bit hairy.

Likewise higher speed solutions in Europe.

http://www.dslreports.com/archive

Neither FTP nor newsgroups go near the amount of open connections some P2P does, not anti-P2P that's fact.
Posted by Dixinormous over 9 years ago
FYI CARPETBURN Bredbandsbolaget go up to 100Mbit downstream 10Mbit upstream. Note the results below:

http://www.dslreports.com/archive?cid=8

Lower average speed than Beunlimited. If you think LLU is immune to congestion you're wrong as well. LLU is losing money hand over fist staying congestion free (relatively) and there have been occasions where Be have congested.
Posted by c_j_ over 9 years ago
Cor, who'd have thunk it? End to end TCP flow control is broken, and needs fixing.

I got news for folk. If folk want end to end flow control and guaranteed delivery and guaranteed bandwidth folk can have it right now, but won't like the price.

If folk want "fair", better read the small print: one person's view of "fair" isn't the same as another's.

1) Good, fast, cheap. Pick two.
2) Bandwidth costs money. IP bandwidth cost less than ATM bandwidth while IP congestion wasn't a problem. IP congestion arrives, punters unhappy, fix = spend more.
Posted by c_j_ over 9 years ago
One other thing re packet loss (closely related to flow control): in a DSL broadband network, packet loss can occur in various places, e.g. in the core network eg due to transient congestion, or on the "last mile" due to transient signal quality issues due to too-low SNR due to (eg) MaxDSL. Has anyone done any analysis of whether packet loss due to line errors is significant in this picture ? BTw/ISPs have line error info in DSLAMs, and any decent DSL modem/router also offers that info to the end user.
Posted by kamelion over 9 years ago
Carpetburn as usual you are wrong. My newsgroup access is limited to 10 open connections far less than torrent access which can use in excess of 400 half open connections. The same goes for FTP.

Lately your posts have started to become even more bizarre than usual. Time to open your eyes as well as your mind.
Posted by CARPETBURN over 9 years ago
quote"FYI CARPETBURN Bredbandsbolaget go up to 100Mbit downstream 10Mbit upstream. Note the results below:

http://www.dslreports.com/archive?cid=8"

FYI its clear not even a small percent of those are subbed to a 100Mb service, one look at the uprates shows that. Ive used 100Mb in europe... you dont end up with uprates under 1Mb from it.

quote"LLU is losing money hand over fist"
and your point is what??? Who cares!
Posted by CARPETBURN over 9 years ago
quote"Carpetburn as usual you are wrong. My newsgroup access is limited to 10 open connections far less than torrent access which can use in excess of 400 half open connections. The same goes for FTP."

Re-read the story, doesnt matter if its 10 connections or several hundred.
I didnt even mention download managers which can leech from multi locations, multiple files, with multiple connections... I stand by what i said this is just another P2P bashing story. Using flashget with a small patch i could download with far more connections that any torrent client is likely to have per file.
Posted by CARPETBURN over 9 years ago
quote"Lately your posts have started to become even more bizarre than usual. Time to open your eyes as well as your mind."

My eyes are fully open...... P2P aint going nowhere, doesnt matter how much people whinge about it, its here, get use to it.
Posted by andrew (Favicon staff member) over 9 years ago
Sorry but the difference between 10 and say 400 connections does matter. That is a significant difference under the current algorithms.

Someone is trying to point out the flaws in how traffic is handled and that it may need updating. If people bothered to read the blog fully it would clearer that this is not an anti P2P rant but an attempt to improve things fro all.
Posted by Dixinormous over 9 years ago
CARPETBURN the BBB.se / B2 10Mbit FTTH service is symettrical, it's 10/10. If you see bad upstream rates it's probably congestion as proportionately upstream use is higher than down.

Also it does matter that LLU is losing money like crazy, sadly in this world someone has to pay these bills. We had good IPStream for a while due to people losing money on it, then times changed. LLU will probably follow.

The only ranting is pro-P2P from you my good man. Bandwidth is limited in places and there are other apps that might want it.
Posted by Dawn_Falcon over 9 years ago
There is zero evidence that the LLU providers are losing massive amounts of cash. And there were plenty of profitable ISP's under the old IPStream providers - there was (shock, horror) more than the current one viable business model as well!
Posted by CARPETBURN over 9 years ago
quote"CARPETBURN the BBB.se / B2 10Mbit FTTH service is symettrical, it's 10/10."

And as i said few of them are on that service, the ISP you are talking about does also provider slower speed services you know??
To suggest someone in sweeden subbing to a 10Mb or 100Mb will get upstreams like your prior link showed (IE 256k and some not much higher) is ridiculous. You only have to download a largish torrent file and connect to a user of that ISP subbing to their fast services to show they will happily up at rates over 10Mb
Posted by CARPETBURN over 9 years ago
quote"Also it does matter that LLU is losing money like crazy, sadly in this world someone has to pay these bills. We had good IPStream for a while due to people losing money on it, then times changed. LLU will probably follow."
Firstly if they are losing so much cash why do they keep expanding??? Secondly no one from a customer view point cares, if the service degrades people will just change ISP. Thirdly most LLU providers have fingers in other pies and make money from other areas, i dont suddenly see the services stopping or degrading.
Posted by CARPETBURN over 9 years ago
quote"The only ranting is pro-P2P from you my good man. Bandwidth is limited in places and there are other apps that might want it."
Im neither pro or anti P2P but i do have the sense to realise its going to be here for a while. Sick of oh this and that problem is because of P2P... An ISP grabs my cash quick enough, pity SOME ISPS dont make things work as they should just as quick. Instead of blaming some protocol thats been around years.
Posted by andrew (Favicon staff member) over 9 years ago
If people read the article linked to they would see the proposal is not for P2P to be removed but a way in which it will co-exist with other traffic and still give the other traffic a chance.

Posted by Dawn_Falcon over 9 years ago
They're dreaming if they think p2p apps will willingly do it though - people will just set the priorities high of it's left down to the application level.

This shafts other apps more at that level, so looking on this with a...future agenda...from the ISP side in mind makes sense, andrew.
Posted by CARPETBURN over 9 years ago
andrew and dawn its obviously a P2P whinge and P2P user whinge like so many other storys before it, rather than blame an app or a certain type of user, they should just make things work properly.
P2P and users are not going to comply with a few ideas to make an ISPs life easier and why should they, customers pay them to provide a service, not moan at the way you use a service.
If the current system and the way it works is no longer cutting the mustard, maybe they should make it better rather than try the shortcut and hope method.
Posted by chrysalis over 9 years ago
I find it ironic coming from BT I would say they are a large obstacle themselves with their obscene traffic costs which alone causes congestion. The prioritising single threads has some flaws for example downloading a web page often uses multiple threads.
Posted by CARPETBURN over 9 years ago
Not to mention chrysalis BT throttle other traffic which is not even P2P based so why they are saying P2P causes issue makes the story even more bizarre... If its just P2P why not just ban that on your network all together rather than punish (throttle) users that dont even touch P2P. It Makes no sense. Its just a whine like most of these type of storys are... Thinking about how full the pockets are rather than making the service better... AS USUAL.
Posted by mr_chris over 9 years ago
@CARPETBURN - I have to disagree - it's not 'obviously a P2P whinge'. In fact it's obvious you haven't either read or understood the article at all. If you had, you'd see it was mainly focussed on a problem which occurs with a lot of TCP streams open at once - citing P2P as a real-world example that I think most people reading this article would understand as an example of an application that uses a large number of connections.

I certainly didn't see it as an excuse to write a P2P bashing article.
Posted by CARPETBURN over 9 years ago
quote"it's not 'obviously a P2P whinge'. In fact it's obvious you haven't either read or understood the article at all. If you had, you'd see it was mainly focussed on a problem which occurs with a lot of TCP streams open at once - citing P2P as a real-world example"
Why only mention P2P then??? I can name several things which would use more connections than a p2p app (CONT)
Posted by CARPETBURN over 9 years ago
The linked story mentions how in the 80s they had to come up with new ideas due to the huge amount of people that were starting to go online and basically halt the network in its tracks.... How about instead of blaming P2P about todays situation they spend some of the cash they have fleeced in the last 20 years and now come up with a new idea... I believe its called upgrading and adapting your business model, to make your service better.... Opps how silly of me that would cost them money!
Posted by CARPETBURN over 9 years ago
Companys like BT want it both ways..... They want all the profit, but not the expense to supply the service... sick and tired of their tales of woe. If you are going to sell a service and you cant provide the service you promise to everyone for whatever reasons, you shouldnt be taking their money in the first place... Fix it or stop taking the cash... Dont pass the buck and blame a few users or their use of an application.
Posted by mr_chris over 9 years ago
quote "How about instead of blaming P2P about todays situation..."

Sorry, I think you're still blinkered about the P2P thing. The article is about ways of trying to make multi-connection apps coexist with other applications. In fact you've gone off on a complete rant that's nothing whatsoever to do with the article!!
Posted by Kaufhof over 9 years ago
Do those who think this story is some kind of an "excuse", seized upon by ISPs, not realise that today's use of the internet was never even remotely envisaged by its "ceeators"?

It would be sueprising (to me anyway) if there were not problems which had been overlooked.
Posted by CARPETBURN over 9 years ago
quote"The article is about ways of trying to make multi-connection apps coexist with other applications."

As said they need to stop blaming modern day use and applications, and just fix it, or stop taking money, you wouldnt be happy if i promised you something, took your money and then could not deliver it.
Posted by Dixinormous over 8 years ago
Good idea, let's hike the bills back up in a huge way. See if you like the idea of paying double what you are now to leech so that you can do it without fear of having to share bandwidth fairly with other applications.

Maybe even an ISP dedicated to P2P, to run properly though it'd cost a fortune without those lovely lighter users and shaping to keep it running properly mind you.

No this story isn't an excuse, it's quite reasonable and pragmatic approach to networks where bandwidth is not unlimited.
Posted by Zeeko over 8 years ago
Is there a modified Linux Weighted TCP stack we can try out or do both ends of the connection need to be using a modified stack similar to the ECN flag ?
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