Our main broadband speed checker is fairly unique in running two sets of download tests and by showing people the resulting throughput graph for the tests you can potentially spot whether a connection is suffering from congestion. An example of a connection suffering from congestion is shown below:

Sample WBC Speedtest showing congestion

With the vast number of tests that people are running we wondered if it was possible to get an idea for how a broadband provider behaves collectively. The spur for this has been the congestion problems hitting some parts of the UK on the BT Wholesale WBC network.

For those who do not know the background of our speed tester, the tbbx1 test is a simple single download using TCP port 8095 and the HTTPx6 test uses six simultaneous downloads which should saturate a connection. By running both tests you can see if settings like the TCP Receive Window (RWIN) size is too small (most operating systems now automatically tune the RWIN) or whether congestion is taking place, we generally cannot identify the source of the congestion, but by collectively analysing a big batch of tests you may be able to tell if the provider or wholesaler is having an effect. For OSX users there is an oddity where the flash tbbx1 test when using Safari will max out at around 12 Mbps – this is easy to spot as the tbbx1 line will be dead flat and investigation suggests it is a core flash issue that does not affect HTTP testing (hence why most other testers do not have the issue).

To assess the impact of congestion we are looking at the tests between 00:01 11th March 2014 and 09:00 24 March 2014 and are plotting the ratio between the HTTPx6 result and the tbbx1. Generally the closer the ratio is to one the better the result is. We have done this analysis for three providers, BT Retail, PlusNet (both who use the WBC network) and Sky who have their own full LLU network.

BT Speed Test Quality Graph

Beyond lots of pretty spikes, what you can see some days the ratio between the two tests is better than others. The rolling average used to plot the ratio does smooth out individual results, but this smoothing helps to reveal the peak periods on each day and identify that the evening of Friday 21st March looked to be a particularly bad evening.

Plusnet Speed Test Quality Graph

While PlusNet shares the same wholesale provider there are differences in how their services operate, and this seems to be demonstrated by the shape of the plot, but the Thursday 20th onwards looks to have been different to the usual patterns.  What is of interest is that the ratio between the two tests is closer with PlusNet, is their use of traffic management to help at peak times giving people a slightly better experience?

Sky Speed Test Quality Graph

Sky has been included here to act as a control and it was surprising to see the amount of variation, particularly for an operator that has the sales tagline ‘we will never slow you down’, which really means they won’t slow you down, but what other people are doing online will have an impact on your speeds. It is this shared nature of consumer broadband that actually makes it affordable.

So what have we learnt from spending a chunk of time collating all the data? Given the congestion issues are not affecting everyone on BT, PlusNet and other providers that use BT Wholesale it is not surprising that the spikes are not totally conclusive. Our feeling is that the real use for something like this is helping to back up the comments from users who are complaining about congestion when a provider denies it totally.

What we need now is a big streaming event to take place and then see what effect it had on the UK broadband infrastructure.

UPDATE Thursday 27th March 2014

fttc-adsl-speed-test-ratio-2

We wanted to see if there was any difference between ADSL2+ services on the BT Wholesale platform and the GEA-FTTC platform, in theory BT Wholesale congestion should affect ADSL2+ customers and GEA-FTTC users (where the provider uses BT Wholesale for backhaul), but if the congestion is widespread within the couple of miles for fibre optic cable between the cabinet and the exchange handover node it should only show up for the FTTC users.

We expected the ratios have different values, and as a general rule congestion impacts faster connections more, hence why when people post speed test results from South Korea we do not a massively high average speed.

So what do we make of the results, it is a varied bag, some days there are similar peaks and other days there are not. To pin down FTTC based congestion we need to concentrate on  a smaller area e.g. one exchange or even down to one cabinet but the problem then is of course getting enough people to run the tests so you can get statistically correct results.

We will keep an eye on our speed tests and see what over clever ways we can play with the data to try and produce some information. For now what is clear is that many speed tests mask the effects of contention and can lead to people getting a pleasing answer even when normal downloads and browsing may be hit or miss.

4 Responses


  1. Neil Blake on 07 Apr 2014

    Sunday afternoon 6 April saw my speed drop from 50+ to just 3 Mbps for a long period. Other local users have reported similar experiences, typically Fridays and Sundays. How do we monitor and report this phenomenon professionally in this small FTTC area?

    • andrew on 07 Apr 2014

      In terms of reporting, first stage is to the retail broadband providers, and between locals figuring out if it impacts all the providers, or just one of the wholesale platforms.

      Basically means doing a lot of leg work yourselves and learning the pattern. Our speed test is uniquely positioned to show this sort of variation, where as most others are setup to just provide numbers to make you feel happy.

  2. viccot on 20 Apr 2014

    My service with Plusnet was not as good as implied here and whenever I complained they blamed my equipment. I asked for a MAC code and my service mysteriously got better for three months then the problems started again. Switched to BT and service improved. Traffic management, which incidently plus net deny using, just evens out the misery. It does not solve the problem of inadequate bandwidth on the network.

  3. Simon on 25 Apr 2014

    im currently with BT and have nothing but problems with them, I’m on upto 16mb unlimited anytime calls package even tho my line is only rated upto 8mb and for the last 3 months im only receiving 1mb at peak times so I complained to them that in itself was a horrible experience, I was told im on a congested exchange and they would see if anything can be done, nothing has been done and since Wednesday morning this week I’ve had no broadband at all from them, so I spoke with a BT mod and he said he cant do anything until 9th may when a new update will take place, so I said I want to cancel my account then and he flatly refused to agree to it so im kind of stuck now and find it unbelievable that this can happen with-in the British law system.

    I understand that every area and exchange will differ in its output, but BT have spread themselves very thin and as a result there is a massive number of congested exchanges, so at peak times 6pm – 11pm and all weekends you will be in the slow lane.

    They are not easy to contact and once you do get through to someone you can understand they are bordering on being rude and sarcastic.

    If you try and be herd via their forums then forget it as they have that base covered also,
    They move your post around in their forums to suit themselves and to hide your complaints with-in a web of old post.

    They also use India call centres that will send you mad if you ever do have to phone them.

    The worse thing I ever did was to let this cowboy company be my isp. all they provided me with was a headache and frustration.


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