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Bufferbloat is a common problem. It is not something your ISP is going to solve for you. If you are interested in where this grade comes from, what impact it can have, and what you can do about it, please read on.

The test continually checks latency from start to finish (not just at the beginning, like most other speed tests). If the latency rises dramatically during the download or upload section, it indicates your connection has become less responsive when fully loaded. This is bufferbloat. The degree of excess latency generates a bufferbloat grade between A+ (none) and F (heaps!).

Bufferbloat is undesirable latency caused by routers and cable/DSL modems buffering more data than necessary. It occurs at any bottleneck in a network: the most common place is the connection between your router/modem and your ISP.

Bufferbloat is undesirable because it interferes with the smooth operation of your network. You may have noticed it when, say, you run a backup to the cloud. Interactive applications become slow to respond. Web browsing, even to relatively uncomplicated pages (like gmail), is annoying. VOIP services may degrade or even stop working. Gamers can lag out. You may have become used to this, perhaps even considered it normal, but now that the problem is understood, there's a solution.

To fix bufferbloat, the router at the bottleneck must control the amount of data that's being sent so that it doesn't build a big queue. To do this, you can (a) turn on some kind of smart queue management (fq_codel, PIE, etc.) in your current router; (b) re-flash the router with new firmware that will do this, or (c) replace the equipment with a more suitable device. Although your ISP is unlikely to help fix any individual case of bufferbloat, they may (and should) be working to introduce better firmware and hardware to reduce the problem for all their customers.

You can read more about buffer bloat, and the various solutions available to you, at http://www.bufferbloat.net/projects/cerowrt/wiki/What_to_do_about_Bufferbloat




Feedback received on this FAQ entry:
  • BufferBloat on Optimum using Firefox/Chrome/Safari all came up with a "D"rating. I can get into the router through the Optimum site but have no idea how to turn on Smart Queue Management or re-flash the router firmware. I see the following Settings: Advanced Settings Advanced Wireless LAN Setup WAN Setup Port Management DNS Management I have no idea how to make adjustments here. Any suggestions would be greatly appreciated.

    2018-08-28 18:03:44 (zpasternak See Profile)

  • Bufferbloat goes crazy in Firefox (160+ ms) but never reaches more than 39 in Chrome. Latest version with both browsers, no addons enabled. macOS 10.13.2.

    2018-01-18 22:54:24

  • Interestingly my "bufferbloat" scores differs depending on the platform. I have a Windows 10 workstation and a macOS (High Sierra) workstation both connected directly to the FIOS Quantum Gateway (not wireless). When I run the speed test from the Windows 10 workstation using Chrome my scores are A+ (overall) A (bufferbloat) A+ (quality). From the macOS workstation (latest Mac Mini) the scores are worse: A (overall) C (bufferbloat) A+ (quality). Not sure what to make of this other than it appears the platform (hardware/OS) could have a significant impact on the score.

    2017-11-11 18:32:54 (wfleitz See Profile)

  • Changing my NIC port from Gigabit to 100mbps, which changed my bloat from an F to an A. It dropped my download from 134mbps to 95ish. I have an EVGA board w two NIC ports, so if I need more download speed for a big file, I can just switch the cable.

    2017-08-08 00:00:06

  • My Comcrap bufferbloat was below an "F" so I tried the QoS suggestions on my Ubiquity EdgeRouter. All is now an "A" with only minor tweaks. Except for Comcast "service"....of course......

    2017-04-27 11:47:33 (klay See Profile)

  • Yesterday (20170401) I placed a called to Charter to address bufferbloat on both my Ingress and egress paths. In the span of one hour I spoke with three representatives, and all of them stated Charter's position: "We can only guarantee the provisioned bandwidth, no packet loss, signals for downstream/upstream are in good spec, and ping is low from the cmts to the cm. They performed basic tests and seemed clueless about bufferbloat. I performed a speedtest at speedtest.charter.com and ran a ping test at the same time in terminal on my MAC. Charter said they cannot see the latency from their side and also that it's occuring because I'm maxing the line throughput. I even downloaded a 6MB file with them on the phone, direct to the modem, and still reached 150-190ms rtt above idle. ISP team members are positively uninformed of the issue. My expected provisionment (Slidell,LA area) and modem specificiations that Charter tests against: Downstream -14 to +14; Upstream: 22 SNR; 69Mb 5.6Mb up (Charter stated they purposely over provision my Cap of 60Mb 4Mb. *Measured speeds with direct modem & router are consistently 66.5 5.9 without cake/fq_codel sqm scripts. From the Charter Supervisor... "Charter has no control over residential modems nor can they adjustment any settings. All tier packages are preconfigured and cannot be altered unlike a business account which has a totally different system control system and software"

    2017-04-02 10:38:55 (mindwolf See Profile)

  • re: QoS - Some netgear routers run a speedtest. For slower connections, such as a 60/4 cable connection you will need to set the max rate for upload and download. I chose 55/3.5 manually and that worked much better. Also on a Netgear WNDR3700 with no option for downlink speed, flashing DD-WRT improved performance. I went from an F to a A on Bufferbloat.

    2016-12-10 19:23:37

  • http://www.bufferbloat.net/projects/cerowrt/wiki/What_to_do_about_Bufferbloat is a dead link

    2016-05-19 09:41:29 (maddawg See Profile)

  • Unless bufferbloat is really bad, I'm not sure it pays to fix it. For example on my speed tests I got a "C" for bufferbloat because my pings during uploads were 200 ms. I enabled QoS on my router which gave me an "A" for bufferbloat by dropping the pings to 10 ms, but it also dropped by download speeds from 90 Mbps to 45 Mbps and the upload speeds from 11 Mbps to 6 Mbps, dropping my speed to a "D". I don't think that's worth the trade off. It's likely I need a more powerful router to handle QoS at higher speeds, but is it really worth spending $400 on a router just to fix bufferbloat?

    2016-03-27 12:17:11 (Morac See Profile)

  • I was able to get an A rating by setting an upload bandwidth profile for all outbound traffic on my router, I started at my max registered speed and worked down by a few hundred kb at a time till the lag stopped ended up be 600kbps shy of max speed, but worth it in my opinion for that A rating. We'll see how it goes. Download was A rating to start with.

    2016-02-22 22:38:38

  • I read what another user said about changing his QoS settings. He didn't say what he tweaked but in my case, I enabled bandwidth controls and let the router figure it out for me. My down download Bloat stayed at 0 virtually, and my upload went into the tank... 1s+!!! I then turned that off and just enable Internet QoS. The Bloat remained about the same but the Mbps was cut in almost half. I think that maybe the Bloat parameter should be split into Up and Down. I don't really know where to go from here.

    2016-01-20 21:44:15 (Mofo See Profile)

  • Solved my bufferbloat problems by setting QOS settings. Went from F to A.

    2015-12-21 17:46:32 (davelister See Profile)

  • Well, it looks like my buffer is bloated. A big fat F every time. Maybe due to my being connected via a wireless bridged router?

    2015-07-24 08:32:36 (grimzly See Profile)

  • The DSLR Speed Test found more than 2s of buffer bloat latency on uploads but http://n2.netalyzr.icsi.berkeley.edu/summary said "We were not able to produce enough traffic to load the downlink buffer, or the downlink buffer is particularly small. You probably have excellent behavior when downloading files and attempting to do other tasks." The uplink buffer bloat numbers are in the ballpark. DSLR reports 259ms average, Netalyzr found 180ms.

    2015-06-05 13:26:46 (Eatmeingreek See Profile)

  • I think "Your ISP cannot help you fix Bufferbloat." is a bit too strong; the ISP is in a much better position to reduce buffer bloat on the downstream or ingress direction, as the bottleneck typically is the DSLAM/MSAN or the CMTS over which the ISP typically has control. Also for ISP-supplied the CPE (modem) the ISP should be in a position to implement buffer bloat fixes in the cPE for the upload or egress direction as well. And in due time, I am certain ISPs will help fix this issue, but only after management and marketing are as informed as the ISPs technical department tend to be. Now, waiting for this "enlightenment" to happen is not the best strategy in the short and intermediate term, so hurray for http://www.bufferbloat.net/projects/cerowrt/wiki/What_to_do_about_Bufferbloat .

    2015-05-06 08:11:24 (moeller0 See Profile)



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