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No sign yet of BT Wholesale congestion improving
Tuesday 18 March 2014 11:38:45 by Andrew Ferguson

Generally the 21CN WBC platform operated by BT Wholesale that has been rolled out over a number of years has been vastly superior to the old ATM based network, but for some weeks now there has been a growing number of people complaining of peak time congestion issues.

One of the most worrying comments to come out of BT Wholesale has been the level of packet loss that is considered acceptable within BT Wholesale, which is a massive 3% and this is actual packet loss apparently not just packets delayed for 500ms.

The problem appears to be affecting multiple broadband providers, and is not consistent across the United Kingdom. We all know that broadband usage is climbing rapidly as more people switch to OTT TV platforms for their viewing, but as the billing on the WBC network is based around the peak utilisation it is in the interest of BT Wholesale to carry as much traffic as possible, rather than allow congestion.

Example speed tests showing what congestion looks like
Sample speed tests reflecting BT Wholesale congestion
Click image for larger version

Spotting congestion is fairly easy using our speed test, which carries out a single thread test that can reveal widely varying speeds when a line is affected by congestion or if your TCP RWIN value is holding back your connection (seen as a slow ramp to a maximum speed). Low levels of congestion should not affect the HTTPx6 test, which uses six threads to try and overcome any congestion, but when congestion is bad this may start to vary in speed over time too.

Ping tool graph showing BT Wholesale packet loss
BQM graph from an otherwise idle FTTC connection on a BT Wholesale based service
Click image for larger version

Another tool is our broadband quality monitor tool, and the above graph is from Saturday 15th and the connection was actually idle for the whole day (just 0.2GB of data usage recorded). This shows packet loss creeping in at peak times (red lines at top of graph) and an unusual pattern for maximum latency that seems to suddenly correct itself (yellow spikes).

Update Thursday 20th March 2014 BT Wholesale has supplied a statement regarding the backhaul capacity issues

BT Wholesale continues to invest in adding new capacity to its next generation broadband network to meet the growing bandwidth requirements of its communications provider customers and their broadband users. According to Ofcom's measures, our network performs strongly in terms of throughput and minimising packet loss, jitter and delay.

However, we recently encountered some technical issues along the way when rolling out extra capacity. This may be affecting network performance for some ISPs across a small number of exchanges.

We have planned fixes in place for these issues and whilst some will be resolved very rapidly, others are more complex and may take longer to fix.

We continue to work hard to fully resolve these problems. In the meantime, we would urge communications providers to contact us should they have any concerns around bandwidth and network performance."

BT Wholesale statement on capacity issues


Posted by Dixinormous over 3 years ago
Very useful, both in terms of assisting with spotting congestion, and in terms of spotting people who appear to mistake a saturated line with congestion, or need some attention.
Posted by adslmax over 3 years ago
BTw are no way to get away with it
Posted by GeeTee over 3 years ago
Is this really a BTW overall platform problem, or is it that ISPs are not buying sufficient bandwidth from BTW?
Posted by timmay over 3 years ago
Interesting to see that of the two non-llu lines I monitor the eclipse one shows increased packet loss in the evenings and the XLN one shows increased latency but packet loss has not increased from 0% or very near. FYI Sky LLU has no issues at all with :-D
Posted by Kper over 3 years ago
What does it indicate when the tbbx1 line is more or less straight and line speed, whilst the httpx6 line is about half as fast and all over the place?

It's been a puzzle for a long time.

Curiously, this current WBC congestion has had the effect of bringing the two lines together to a similar average with more similar variability...
Posted by andrew (Favicon staff member) over 3 years ago
If the tbbx1 is stuck at 12 Mbps and its OSX then a flash implementation issue.

Best to post the link, as what one person calls flat is wobbly line to some.
Posted by Kper over 3 years ago
WinXP on FTTP.

tbbx1 not quite as flat as normal (- the congestion?)

Could be flash (3rd graph looks anomalous,) but I suspect the BRAS.

The router has been tested to much a higher throughput, but the effect is the same with a HH4 in any case, and on other PCs too... The most interesting clue to me is that this current bout of congestion seems to bring the graph lines together.
Posted by andrew (Favicon staff member) over 3 years ago
No need to use tinyurl you can copy/paste the URL given on the page it reveals nothing private about you.

If using Firefox take a look at

Looks more like a software issue most of the time.
Posted by Kper over 3 years ago
OK, cheers, I'll take a look. The URL shortener (and clipped grammar) was just because I ran out of characters in the comment with the full ones!
Posted by Kper over 3 years ago
Looks like you could be right about the software issue, Andrew.

This is using Firefox with the Plugin Container disabled:

And this is Chrome for comparison:

So maybe my comment should be "Congestion? What congestion?!" :)

Thanks for the insight into an age-old mystery, anyway.
Posted by andrew (Favicon staff member) over 3 years ago
Suspect if we just published the figures no-one would be any the wiser to the variations over time that different things create.
Posted by Kper over 3 years ago
Suspect you're correct in that suspicion!
Posted by cick4internet over 3 years ago
Well.. do you really think your gonna get a dedicated 75mbps for £30 per month???

Somethings gotta give out some time :-) The math just don't add up!!
Posted by Kper over 3 years ago
Lacking sufficient nous, I don't really know whether or not something has to give at that price point.

I did try looking at my connection using Firefox in Linux Mint instead, though, and it seems to think something has given:

Very likely still a software issue rather than congestion, since the tbbx1 line is so flat, but I'm not wholly sure yet whether my comment is "Congestion? What congestion?" or "This congestion is terrible!"

Maybe it would be better not to comment at all, since cat videos still work OK :)
Posted by andygegg over 3 years ago
I've never seen a graph that looked even remotely that flat!
Posted by chrysalis over 3 years ago
andrew please reveal the isp's affected, as the reprots seem centered around plusnet with the exception of ignition who says he has it also on BT retail, but I cant find any other BT retail, zen etc. AAISP have on their blogs but their indiciations are it isnt anywhere near as widespread as it is on plusnet.
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