How to mitigate BufferBloat on an ADSL connection?

Question

I've had interesting networking experience before. Before I moved, I've had a VDSL connection, with 3mb uplink. (The down speed was around 30mb but is not relevant at this moment). Whenever I saturated the uplink (CrashPlan backup), I could see a slowdown in general latency and responsiveness, but I could still use the internet without any major issue.

Now, I've moved to a place further away, where I only get normal ADSL+. The speed is 10mb downlink with 1mb uplink. The problem is, however, that whenever I saturate the uplink almost everything grinds to a halt - ping times are climbing to tens of seconds and the general experience is pretty bad. Even if I utilise only 50% of the upload speed, the latency grows to 500-800ms.

At first, I attributed the problem to the decreased connection quality - however, now I think that it's a configuration/networking problem on my provider side and has nothing to do with the quality of the copper coming my way. What further re-assured this belief is that a friend of mine has a connection with similar parameters (another area but similar distance to the exchange) and he can happily saturate the upload without compromising the overall connectivity!

So, what could be the problem? Is this the famous Bufferbloat problem? If so, is there a way to mitigate it? The tech support just tells me to make sure I am not using the upload too much in order to ensure connectivity... which is weak in my book.

I was also looking into some of the tomato firmware router, any advice on this? I've tried all possible QoS settings to give the backup software lower priority but this only fixes the issue partially.

So, to sum up - do you think it is a bufferbloat and if so, how to fix it? (other than changing providers)

Answer 1

There's no reason using 50% upload and 0% download should cause significant ping increases. Something else is going on here. I don't know if that's what bufferbloat is. I suspect it's just a physical issue with your modem or line. Badly congested connections should still be able to maintain pings under 1 second. I would troubleshoot with the ISP and/or check out modem stats if your modem supports it (your ISP can check if your modem doesn't). I'm guessing the the signal to noise ratio is below 6 on the upload or the attenuation is too high (greater than 55db)

Lack of bandwidth management doesn't help either (but should never cause things to be as bad as you describe) You should implement a QoS Solution; the only thing that works properly for aDSL connections is one with the TC-ATM patch. I would recommend Tomato Toastman or Shibby , recent versions. My "mini-guide" to configure this is here: http://www.dslreports.com/forum/r28371690-Cable-Help-Configuring-Tomato-QoS- . The only difference with your setup is you put the "settings for DSL modems only" to something like 32-bytes instead of "none".

Bufferbloat test: http://netalyzr.icsi.berkeley.edu/

Answer 2

It is probably bufferbloat. Tomato has no fixes for that.

Try openwrt, dd-wrt, or cerowrt's qos system, they all use fq_codel now.

I note that some forms of DSL use ATM encapsulation, accurate compensation for which was broken until very recently (fixed in linux 3.10.12 or later, current openwrt barrier breaker head, cerowrt head)

Answer 3

The way to fix "buffer bloat" is to disable your ISPs buffer entirely by limiting your incoming and outgoing bandwidth to just under their respective limits. This way the buffer on your ISP's side never gets used and you experience an improvement in latency at a small cost in throughput.

tc is the Linux/DD-WRT/Tomato tool for this. A script exists called "Wondershaper" that implements this on PCs, perhaps you could adapt it for Tomato.