<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">Hello Martin,<div><br></div><div>thanks a lot.</div><div><br>On Jul 25, 2014, at 18:32 , Martin Geddes <<a href="mailto:mail@martingeddes.com">mail@martingeddes.com</a>> wrote:<br><br><blockquote type="cite">So what is ΔQ and how do you "compute" it (to the extent it is a "computed" thing)?<br><br>Starting point: the only observable effect of a network is to lose and delay data -- i.e. to "attenuate quality" by adding the toxic effects of time to distributed computations. ΔQ is a morphism that relates the "quality attenuation" that the network imposes to the application performance, and describes the trading spaces at all intermediate layers of abstraction. It is shown in the attached graphic.<br><br>Critically, it frames quality as something that can only be lost ("attenuated"), both by the network and the application. Additionally, it is stochastic, and works with random variables and distributions.<br><br>At its most concrete level, it is the individual impairment encountered by every packet when the network in operation. But we don't want to have to track every packet - 1:1 scale maps are pretty useless. So we need to abstract that in order to create a model that has value.<br><br>Next abstraction: an improper random variable. This unifies loss and delay into a single stochastic object.<br>Next abstraction: received transport, which is a CDF where we are interested in the properties of the "tail".<br><br>Next abstraction, that joins network performance and application QoE (as relates to performance): relate the CDF to the application through a Quality Transport Agreement. This "stochastic contract" is both necessary and sufficient to deliver the application outcome.<br><br>Next concretisation towards QoE: offered load of demand, as a CDF.<br>Next concretisation towards QoE: breach hazard metric, which abstracts the application performance. Indicates the likelihood of the QTA contract being broken, and how badly.<br>Final concretisation: the individual application performance encountered by every user. Again, a 1:1 map that isn't very helpful.<br><br>So as you can see, it's about as far away from a single point average metric as you can possibly get. A far richer model is required in order to achieve robust performance engineering.<br><br>It is "computed" using multi-point measurements to capture the distribution. The G/S/V charts you see are based on processing that data to account for various issues, including clock skew.<br><br>I hope that helps. We need to document more of this in public, which is an ongoing process. <br></blockquote><div><br></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>You lost me, I think what I should have asked for is a real example with numbers and the formulas ;) I guess that is deep in “secret sauce” territory. Alas, if that should be true it also means that deltaQ is not going to help me understand my network any better …</div><div><br></div><div>Best Regards</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>Sebastian</div><div><br></div><br><blockquote type="cite"><br>Martin<br><br>On 25 July 2014 16:58, Sebastian Moeller <<a href="mailto:moeller0@gmx.de">moeller0@gmx.de</a>> wrote:<br>Hi Martin,<br><br>thanks for the pointers,<br><br><br>On Jul 25, 2014, at 16:25 , Martin Geddes <mail@martingeddes.com> wrote:<br><br>> You may find the following useful background reading on the state of the art in network measurement, and a primer on ΔQ (which is the property we wish to measure).<br>><br>> First, start with this presentation: Network performance optimisation using high-fidelity measures<br>> Then read this one to decompose ΔQ into G, S and V: Fundamentals of network performance engineering<br>> Then read this one to get a bit more sense on what ΔQ is about: Introduction to ΔQ and Network Performance Science (extracts)<br>><br>> Then read these essays:<br>><br>> Foundation of Network Science<br>> How to do network performance chemistry<br>> How to X-ray a telecoms network<br>> There is no quality in averages: IPX case study<br><br> All of this makes intuitively sense, but it is a bit light on how deltaQ is to be computed ;).<br> As far as I understand it also has not much bearing on my home network; the only one under my control. Now, following the buffer bloat discussion for some years, I have internalized the idea that bandwidth alone does not suffice to describe the quality of my network connection. I think that the latency increase under load (for unrelated flows) is the best of all the bad single number measures of network dynamics/quality. I should be related to what I understood deltaQ to depend on (as packet loss for non real time flows will cause an increase in latency). I think that continuous measurements make a to n of sense for ISPs, backbone-operators, mobile carriers … but at home, basically, I operate as my own network quality monitor ;) (that is I try to pin point and debug (transient) anomalies).<br><br>><br>> Martin<br>><br>> For fresh thinking about telecoms sign up for my free newsletter or visit the Geddes Think Tank.<br>> LinkedIn Twitter Mobile: +44 7957 499219 Skype: mgeddes<br>> Martin Geddes Consulting Ltd, Incorporated in Scotland, number SC275827 VAT Number: 859 5634 72 Registered office: 17-19 East London Street, Edinburgh, EH7 4BN<br>><br>><br>><br>> On 25 July 2014 15:17, Sebastian Moeller <moeller0@gmx.de> wrote:<br>> Hi Neil,<br>><br>><br>> On Jul 25, 2014, at 14:24 , Neil Davies <Neil.Davies@pnsol.com> wrote:<br>><br>> > Rich<br>> ><br>> > I have a deep worry over this style of single point measurement - and hence speed - as an appropriate measure.<br>><br>> But how do you propose to measure the (bottleneck) link capacity then? It turns out for current CPE and CMTS/DSLAM equipment one typically can not relay on good QoE out of the box, since typically these devices do not use their (largish) buffers wisely. Instead the current remedy is to take back control over the bottleneck link by shaping the actually sent traffic to stay below the hardware link capacity thereby avoiding feeling the consequences of the over-buffering. But to do this is is quite helpful to get an educated guess what the bottleneck links capacity actually is. And for that purpose a speediest seems useful.<br>><br>><br>> > We know, and have evidence, that throughput/utilisation is not a good proxy for the network delivering suitable quality of experience. We work with organisation (Telco’s, large system integrators etc) where we spend a lot of time having to “undo” the consequences of “maximising speed”. Just like there is more to life than work, there is more to QoE than speed.<br>> ><br>> > For more specific comments see inline<br>> ><br>> > On 25 Jul 2014, at 13:09, Rich Brown <richb.hanover@gmail.com> wrote:<br>> ><br>> >> Neil,<br>> >><br>> >> Thanks for the note and the observations. My thoughts:<br>> >><br>> >> 1) I note that speedof.me does seem to overstate the speed results. At my home, it reports 5.98mbps down, and 638kbps up, while betterspeedtest.sh shows 5.49/0.61 mbps. (speedtest.net gives numbers similar to the betterspeedtest.net script.)<br>> >><br>> >> 2) I think we're in agreement about the peak upload rate that you point out is too high. Their measurement code runs in the browser. It seems likely that the browser pumps out a few big packets before getting flow control information, thus giving the impression that they can send at a higher rate. This comports with the obvious decay that ramps toward the long-term rate.<br>> ><br>> > I think that its simpler than that, it is measuring the rate at which it can push packets out the interface - its real time rate is precisely that - it can not be the rate being reported by the far end, it can never exceed the limiting link. The long term average (if it is like other speed testers we’ve had to look into) is being measured at the TCP/IP SDU level by measuring the difference in time between the first and last timestamps of data stream and dividing that into the total data sent. Their “over-estimate” is because there are packets buffered in the CPE that have left the machine but not arrived at the far end.<br>><br>> Testing from an openwrt router located at a high-symmetric-bandwidth location shows that speedof.me does not scale higher than ~ 130 Mbps server to client and ~15Mbps client to server (on the same connection I can get 130Mbps S2C and ~80Mbps C2S, so the asymmetry in the speedof.me results is not caused by my local environment).<br>> @Rich and Dave, this probably means that for the upper end of fiber and cable and VDSL connections speed of.me is not going to be a reliable speed measure… Side note www.sppedtest.net shows ~100Mbps S2C and ~100Mbps C2S, so might be better suited to high-upload links...<br>><br>> ><br>> >><br>> >> 3) But that long-term speed should be at or below the theoretical long-term rate, not above it.<br>> ><br>> > Agreed, but in this case knowing the sync rate already defines that maximum.<br>><br>> I fully agree, but for ADSL the sync rate also contains a lot of encapsulation, so the maximum achievable TCP rate is at best ~90% of link rate. Note for cerowrt’s SQM system the link rate is exactly the right number to start out with at that system can take the encapsulation into account. But even then it is somewhat unintuitive to deduce the expected good-put from the link rate.<br>><br>> ><br>> >><br>> >> Two experiments for you to try:<br>> >><br>> >> a) What does betterspeedtest.sh show? (It's in the latest CeroWrt, in /usr/lib/CeroWrtScripts, or get it from github: https://github.com/richb-hanover/CeroWrtScripts )<br>> >><br>> >> b) What does www.speedtest.net show?<br>> >><br>> >> I will add your question (about the inaccuracy) to the note that I want to send out to speedof.me this weekend. I will also ask that they include min/max latency measurements to their test, and an option to send for > 10 seconds to minimize any effect of PowerBoost…<br>><br>> I think they do already, at least for the download bandwidth; they start with 128Kb and keep doubling the file size until a file takes longer than 8 seconds to transfer, they only claim to report the numbers from that last transferred file, so worst case with a stable link and a bandwidth > 16kbps ;), it has taken at least 12 seconds (4 plus 8) of measuring before the end of the plot, so the bandwidth of at least the last half of the download plot should be representative even assuming power boost. Caveat, I assume that power boost will not be reset by the transient lack of data transfer between the differently sized files (but since it should involve the same IPs and port# why should power boost reset itself?).<br>><br>> Best Regards<br>> Sebastian<br>><br>><br>><br>> >><br>> >> Best regards,<br>> >><br>> >> Rich<br>> >><br>> >><br>> >><br>> >> On Jul 25, 2014, at 5:10 AM, Neil Davies <neil.davies@pnsol.com> wrote:<br>> >><br>> >>> Rich<br>> >>><br>> >>> You may want to check how accurate they are to start.<br>> >>><br>> >>> I just ran a “speed test” on my line (which I have complete control and visibility over the various network elements) and it reports an average “speed” (in the up direction) that is in excess of the capacity of the line, it reports the maximum rate at nearly twice the best possible rate of the ADSL connection.<br>> >>><br>> >>> Doesn’t matter how pretty it is, if its not accurate it is of no use. This is rather ironic as the web site claims it is the “smartest and most accurate”!<br>> >>><br>> >>> Neil<br>> >>><br>> >>> <speedof_me_14-07-25.png><br>> >>><br>> >>> PS pretty clear to me what mistake they’ve made in the measurement process - its to do with incorrect inference and hence missing the buffering effects.<br>> >>><br>> >>> On 20 Jul 2014, at 14:19, Rich Brown <richb.hanover@gmail.com> wrote:<br>> >>><br>> >>>> Doc Searls (http://blogs.law.harvard.edu/doc/2014/07/20/the-cliff-peronal-clouds-need-to-climb/) mentioned in passing that he uses a new speed test website. I checked it out, and it was very cool…<br>> >>>><br>> >>>> www.speedof.me is an all-HTML5 website that seems to make accurate measurements of the up and download speeds of your internet connection. It’s also very attractive, and the real-time plots of the speed show interesting info. (screen shot at: http://richb-hanover.com/speedof-me/)<br>> >>>><br>> >>>> Now if we could get them to a) allow longer/bigger tests to circumvent PowerBoost, and b) include a latency measurement so people could point out their bufferbloated equipment.<br>> >>>><br>> >>>> I'm going to send them a note. Anything else I should add?<br>> >>>><br>> >>>> Rich<br>> >>>> _______________________________________________<br>> >>>> Bloat mailing list<br>> >>>> Bloat@lists.bufferbloat.net<br>> >>>> https://lists.bufferbloat.net/listinfo/bloat<br>> >>><br>> >><br>> ><br>> > _______________________________________________<br>> > Bloat mailing list<br>> > Bloat@lists.bufferbloat.net<br>> > https://lists.bufferbloat.net/listinfo/bloat<br>><br>> _______________________________________________<br>> Bloat mailing list<br>> Bloat@lists.bufferbloat.net<br>> https://lists.bufferbloat.net/listinfo/bloat<br>><br><br><br><img name="ΔQ morphism.png" apple-inline="yes" id="99FB2770-AE75-48F7-8294-A46BE82CC859" height="540" width="720" apple-width="yes" apple-height="yes" src="cid:E3F9FCD4-1AA3-4B8F-804B-889A9D016665@lan"><br></blockquote><br></div></body></html>