Why BitTorrent Causes Latency and How To Fix It

Sivar recommends an article by George Ou examining why BitTorrent affects performance so much more than other types of file transfer and a recommendation on how to fix it. The suggestion is to modify P2P clients so that, at least on upload, they space their traffic evenly in time so that other applications have a chance to fit into the interstices. "[Any] VoIP [user] or online gamer who has a roommate or a family member who uses BitTorrent (or any P2P application) knows what a nightmare it is when BitTorrent is in use. The ping (round trip latency) goes through the roof and it stays there making VoIP packets drop out and game play impossible."

Re:QoS?

[ILuvRamen]

yeeeeeah or for free, you could just cap the bandwidth your client uses. I cap it at 25KBps up and 400 down out of my approximate 70 up and 850 down (Road Runner) and I play MMORPGs under those conditions just fine.

Simpler solution

[Frozen-Solid]

Use the bandwidth capping abilities in all modern P2P clients. If you're trying to torrent, max it's upload and download capabilities below your total network bandwidth. I have a 1Mbit up and 10Mbit connection. Capping my total upload in KTorrent to 100KByte/s and my down to 900KByte/s allows me to do anything else on the internet without issue. Very few online games or other uses of the internet require more than a 100KB down and 30KB or so up. Learn to properly manage your P2P programs and you won't have a problem.

Wait, wait wait!

[drolli]

So, if the ISPs do traffic shaping "to improve the service" it's bad, but we admit that on the small scale (when it affects ourselfs) there is a real need for traffic shaping! Thats interesting....

Uh, yeah?

[Anonymous Coward]

And we admit that on a small scale, we need to control our eating, but we don't want the grocery store telling us how much of things we can buy.

Re:Wait, wait wait!

[rossz]

What ISPs are doing is not traffic shaping. They are doing traffic elimination. I don't have a problem with traffic shaping. It's often necessary to get different things to play nice with each other.

Re:Simpler solution

[flerchin]

Read the bloody article. He shows that bittorent traffic capped to 10% of total bandwidth still causes more latency than an http download using 90% of the pipe. The total latency hit is small, but still significant for VOIP or high intensity gaming.

Re:QoS?

[cgdiaz]

Well, since the article is about how to stop other users on the network from ruining your net experience, I think we assume they will be on a router of some sort.

Re:QoS, but only on the Telco Side

[wintermute000]

Hear, hear

I love these home geek "i know how to flash DD-WDT and click on a GUI" networking experts, who fail to grasp your point above (i.e. QoS = OUTBOUND).

Since downstream QoS from telco aggregation router is not practical to implement, the best fix is to throttle the clients on the end user PCs, free and just a few clicks away.

Or if you want to be really advanced, QoS outbound from a second router (or linux gateway or firewall etc.) behind your WAN router but really that's overkill for 99% of users.

Re:QoS?

[WhatAmIDoingHere]

It's called a "Mac." They come from this new start-up company in California called "Apple." A silly name, I know, but you'd be surprised at how secure their OS is!

Re:QoS?

[schnipschnap]

You should have taken a quick look at the article first. The author basically experienced excessive lag even though he did cap his upload rate, compared to what an upload or download via a different protocol (FTP, HTTP, VoIP) would cause. This is because the BT client fires or receives packets whenever they are available, while the others receive or send packets in a spaced manner (unless they saturate the pipe). That means that even though your upload rate may be limited to 10 KB/s, if your total upload is 20 KB/s, you might experience a maximum lag of 0.5 seconds. The guy put up a lot of graphs to illustrate that it happens quite often actually. It seems that he got those patterns with the "official" client and with Azureus.

Re:From the Great Geek Philosopher Hypocrates

[the brown guy]

Yeah, but the action that the ISPs take to correct the negative effects caused by millions of people actually using their allotted bandwidth is unfair (and possibly illegal, IANAL and I have no issues w/throttling so haven't been following closely.)
There is a huge difference between a corporation not giving customers what they have paid for, and the customers using that bandwidth how they see fit.
Just my 0,02

Re:From the Great Geek Philosopher Hypocrates

[chubs730]

When are ethical issues not directly derived from self interest? The issue with throttling at an ISP level is receiving the service one pays for. Bandwidth shaping for a personal network, deciding what one would like to do with the service they purchased, is an entirely separate issue.

Re:From the Great Geek Philosopher Hypocrates

[thedbp]

I would say that a network is, by design, a shared interdependancy. Selfish network behavior, regardless of that activity's legality, is a detriment to the entire system, while simultaneously making it harder to maintain, support, and manage.

Look, I'm not for legislation, but a little common sense will tell you that it simply isn't right for a small minority of the customers to use a massive percentage of available bandwidth, using applications that they themselves say wreak havok on their local network.

You speak of not providing people with what they've paid for. How about all those next gen services we want rolled out, how will they ensure they can manage network traffic fairly when all users need a much bigger chunk of bandwidth for standard services? If P2P users can't keep in mind the rights of those not using the same torrent, or their responsibility to be good network neighbors when they KNOW their activity disrupts others, they have no reason to expect the same courtesy. A free Internet only works if there's respect.

If there's no respect, that's when you wind up with silly things like legislation.

Re:From the Great Geek Philosopher Hypocrates

[evilviper]

The geeks of slashdot acknowledge that P2P use strangles traffic on their LAN, and feel that some modification needs to happen to address this.

However, when service providers complain about the negative effects of millions of people using P2P on their backbones, and take action to correct this, same said slashdot geeks get their panties in a bunch and cry fowl.

There's nothing wrong with reasonable traffic shaping. ISPs, however, DON'T want to do that. They want to damn near cut-off Bittorrent traffic entirely, even though reducing it by, say, 1/4th would have the desired effect.

What's more, with network non-neutrality, what they really want, and what their QoS policies are set to enforce, is to drastically throttle all applications that COMPETE with their own... You can see this most dramatically with VoIP services, but also with P2P you can see that the ISP's own applications and services that use up bandwidth just a badly do NOT get throttled.

Those issues are why there is "moral outrage". People aren't angrily upset that their torrents were just slightly slowed down...

Re:QoS?

[dmsuperman]

I have a 15mbps connection with 500 up (also not sure advertised). Even with all of that bandwidth, as soon as my single roommate starts his bittorrent client up the whole internet connection goes to shit.

Re:QoS?

[X0563511]

I need to come up with a greasemonkey script that automatically hides any posts containing "apple" or "mac". I'm sick of having to bother reading this tripe. I don't care what Apple comes up with, I'm not purchasing any of their products. Their philosophies of product design/use directly oppose mine, and hence all of their products are going to fit me like a pair of pants with an extra/missing leg.

It's about control.

[SanityInAnarchy]

It's very, very simple:

The geeks of slashdot acknowledge that P2P use strangles traffic on their LAN, and feel that some modification needs to happen to address this.

And when we do this, we're doing it to our own LAN. And it affects our own bandwidth, and the bandwidth of any roommates -- who most likely know what's going on, and agree to it. (After all, it's not as though it's going to slow the torrent by much.)

However, when service providers complain about the negative effects of millions of people using P2P on their backbones, and take action to correct this, same said slashdot geeks get their panties in a bunch and cry fowl.

Cry "bird"? WTF?

More seriously: Me shaping my own traffic is very different from someone else shaping my traffic against my will.

To borrow another poster's analogy:

I have no problem with choosing what kind of food I eat. If I had kids, I'd have no problem choosing what kind of food they eat.

I would very much not like the grocery store to choose what kind of food is best for everyone.

Fortunately, it's in the grocery store's best interest to give customers what they want. For some reason, ISPs think it's not in their best interest to do the same.

Re:QoS?

[h3llfish]

Ah yes... security through obscurity. You better hope that this "apple" stuff never catches on, or someone might decide it's worth the trouble to write a virus to go after the smug snotty douchebags of the world.