[ale] to speed up your internet connection, slow it down (buffer bloat)

Sat Jul 7 13:54:12 EDT 2012

I was wondering if you had done any pre/post iperf (or something smiler)
testing? If so, can you share the results?

-Erik-

On Fri, Jul 6, 2012 at 5:13 PM, Ron Frazier (ALE) <
atllinuxenthinfo at techstarship.com> wrote:

> Hi all,
>
> I want to share some information about a phenomenon which can dramatically
> slow down your internet connection, or connections within a LAN some times.
> It's called buffer bloat. I first heard about it over on the NTP questions
> list. I don't remember why that came up, probably related to network
> latencies for NTP servers. Then, later, Steve Gibson discussed it on the
> Security Now podcast. I've provided several links below for those who wish
> to research it.
>
> For those not familiar, buffer refers to a memory queue in a router or
> other networking gear. The problem occurs when you go from a large
> bandwidth pipe to a smaller bandwidth pipe, such as the transition from
> your LAN to the internet WAN. At this point, you might go from 100 Mbps or
> 1 Gbps bandwidth to something like 3 Mbps or 20 Mbps or 50 Mbps or
> whatever. The point is, that it is a dramatic reduction in bandwidth.
>
> So, if you're trying to transmit to the internet at 100 Mbps and it can
> only take 20 Mbps, the link will become saturated. Without buffers or
> queues, about 4/5 of the packets will be dropped. The system will rapidly
> recognize that it cannot go that fast and it will scale down to something
> which the link can support.
>
> However, with large buffers, which many routers have, the problem becomes
> much worse. Let's say the router has a 4 M Byte or approximately 40 M bit
> ram buffer on it's outbound transmission channel. Your computer fills that
> buffer in about 4/10 sec, but, that buffer is going to take 2 sec to empty
> out sending the data to the internet. While I don't understand all the
> technical magic that happens, I do understand that the normal automatic
> throttling systems no longer work. So, your computer might be seeing a 2
> sec delay to get packets out on the internet while they meander through the
> buffer on a first in first out basis.
>
> There is a new intelligent packet dropping algorithm called CODEL that may
> be the solution. The bufferbloat site mentions it, and Steve did a podcast
> talking about it. It shows great promise, however, most routers don't
> implement the algorithm, and many probably never will get upgraded,
> including many home routers.
>
> So, here, as I understand it, is a way you can work around the problem.
>
> My wife works from home sometimes and uses a VPN back to work. Sometimes,
> here system locks up and says the connection is lost. I have as many as 7
> devices sharing the same internet connection, so her system may be
> experiencing congestion. I suspect that many times, the problem is on the
> other end at her office, but just in case, I decided to tweak the router. I
> turned on a QOS (quality of service) setting and told it to prioritize her
> data traffic over mine. I also made some changes to avoid any possible
> buffer bloat problem.
>
> The buffer bloat problem only shows up when the buffer fills. By the way,
> a clogged upstream buffer can shut down downloads too, since, during
> downloads, all tcp packets have to be acknowledged, and those
> acknowledgements must go upstream. A clogged buffer can essentially make
> your Internet connection almost unusable. I think this is what happens at
> many coffee shops. If you can't run CODEL or something like it, one way to
> prevent the problem is to make sure the buffer never fills up. One way to
> do that is to limit your upstream bandwidth to something less than what
> it's possible to do. In my case, the QOS menu of the router allows me to
> limit upstream bandwidth. I used speedtest.net to test the system. I was
> able to get a peak upstream bandwidth of 5.6 Mbps. So, I set the QOS
> controls on the router to limit the upstream bandwidth to 5 Mbps.
> Theoretically, this should mean that the outbound buffer on my router never
> will fill up because it's always emptying out faster than I'm putting data
> in. Theoretically, that should prevent the buffer bloat problem on my LAN.
> This, combined with prioritization of my wife's data, will hopefully solve
> her data problems.
>
> If you've had experience with this problem, please share what you learned
> and what you did about it.
>
> If you need info on the down and dirty operation of TCP/IP, ask some of
> the other wizards on the list.
>
> Hope this is helpful.
>
> Sincerely,
>
> Ron
>
> links below
>
> ----------------------
>
>
> http://en.wikipedia.org/wiki/Buffer_bloat
>
> http://www.bufferbloat.net/
>
> Steve Gibson discusses buffer bloat on the Security Now podcast episode
> 345.
> He introduces a potential solution, CODEL, developed by industry
> researchers, in episode 359.
>
> http://www.grc.com/securitynow.htm - Reference episodes 345 and 359.
>
> http://twit.tv/show/security-now/345
> http://media.grc.com/sn/sn-345.mp3
>
> http://twit.tv/show/security-now/359
> http://media.grc.com/sn/sn-359.mp3
>
>
>
> --
>
> Sent from my Android Acer A500 tablet with bluetooth keyboard and K-9 Mail.
> Please excuse my potential brevity.
>
> (To whom it may concern. My email address has changed. Replying to former
> messages prior to 03/31/12 with my personal address will go to the wrong
> address. Please send all personal correspondence to the new address.)
>
> (PS - If you email me and don't get a quick response, you might want to
> call on the phone. I get about 300 emails per day from alternate energy
> mailing lists and such. I don't always see new email messages very
> quickly.)
>
> Ron Frazier
> 770-205-9422 (O) Leave a message.
> linuxdude AT techstarship.com
>
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