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FTTC Speeds - Restricted after 12 Midday?

Community Veteran
Posts: 1,412
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Registered: 29-01-2009

FTTC Speeds - Restricted after 12 Midday?

Our FTTC connection finally went in today, but I'm seeing some strange speed behaviour...
The first tests (to Speedtest.net) showed we were limited to the old ADSL speed. Adam soon changed that...
The next batch of tests (Speedtest.net and mybroadbandspeed.co.uk) all showed speeds of around 33-35Mbps. Not quite what I'd expect for a full sync of 40Mbps, but certainly decent.
The first problem showed with the BT speed tester.: The pages there were increadibly slow to load - even the relatively static non-testing part of the site! The data showed while waiting for the test did confirm an IP profile of 38717, matching the full sync speed, but a proper test never executed.
Since 12 Midday however, I've had much worse results. Both speedtest.net and mybroadbandspeed.co.uk tell me the speed is roughly 9-10Mbps. For example:

The BT speed tester is still not playing ball at all. The member centre reports a speed of 37Mbps, so that doesn't seem to be a factor.
Any ideas of the cause? Is this a traffic management issue?
And yes - it is ironic that I have been trying to help someone else out on here whose speeds seem to keep getting stuck at 9Mbps (I don't think that was an FTTC case, though). I'm using a wired connection to the router, but via a pair of Gigabit switches. The connection has negotiated at 1Gbps too.
Plusnet Customer
Using FTTC since 2011. Currently on 80/20 Unlimited Fibre Extra.
10 REPLIES
jojopillo
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Registered: 16-06-2010

Re: FTTC Speeds - Restricted after 12 Midday?

HI WWWombat,
Looks like it may be the traffic management profile. Just looking in to getting that sorted for you. Also, Adam said to let you know he's doing your regrade at the moment.
Jojo Smiley
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Re: FTTC Speeds - Restricted after 12 Midday?

Give things another go now...

Bob Pullen
Plusnet Product Team
If I've been helpful then please give thanks ⤵

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Re: FTTC Speeds - Restricted after 12 Midday?

I just got back in, and tried some more tests. At first it didn't look very promising, but there was one reasonable result:
Speedtest.net London: 9Mbs down, 1.7Mbps up
Speedtest.net Maidenhead: 6.6Mbs down, 1.7Mbps up
Speedtest.net Milton Keynes: 6.4Mbs down, 1.7Mbps up
Speedtest.net Hull: 8.2Mbs down, 1.7Mbps up
MyBroadbandspeed.co.uk: 12Mbps down, 1.6mbps up

But this time, the BT tester was responding well to the basic pages, and managed to run the tests:
  Down:  32664
  Profile: 38717
  Up:        1554
  Profile:  2000
Still not quite at top speed for the profile, but a sight better than the other testers.
So Uplink seems to be going just fine, for the spec, but download is a rather strange mix.
I also left my stats package running more download tests than normal (hang the bandwidth!): these were 5MB tests from the TBB download page on port 80, running every 15 mins.
The graph is attached, showing that the speed sat nearer 6Mbps until 3PM, and then switched to average 10Mbps - perhaps with Bob's change.
The daytime speeds used to be a very consistent 6.1Mbps on 20CN ADSL.
The stats tests are sourced from a different local machine than the interactive tests. I'm going to test the throughput on my internal network, to see if I have some other choke point.
Plusnet Customer
Using FTTC since 2011. Currently on 80/20 Unlimited Fibre Extra.
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Re: FTTC Speeds - Restricted after 12 Midday?

About to investigate the internal network, but I thought I'd check my TBB ping latency graphs. I thought these were interesting...
Last day of ADSL (31st):

And 1st:

First day of Fibre (3rd):

That is a significant change in packet loss - that background level of 5% loss.
Will that loss be over the VDSL leg? I'm guessing ICMPs are not retried at the IP level (ie in routers), so can be discarded there. But if the blocks get CRC errors over the VDSL link, they *would* get retried, wouldn't they?
Is anyone else seeing behaviour like this over FTTC?
Plusnet Customer
Using FTTC since 2011. Currently on 80/20 Unlimited Fibre Extra.
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Re: FTTC Speeds - Restricted after 12 Midday?

OK, while investigating my LAN, I've found I'm getting weird behaviour here.
Machine A, directly connected to router at 100Mbps, can get speed tests of 32/1.0
Machine B, connected to a gigabit switch at 1Gbps, can get speed tests of 34/1.7
Machine C, connected to a gigabit switch at 1Gbps, can get speed tests of 10/1.4, and can do other downloads at 13 Mbps.
Machine D, connected to a gigabit switch at 1Gbps, can't do speedtests right now, but can do other downloads between 6 and 14 Mbps.
Naturally, my worryingly slow results in the OP were from machines C and D.
That suggests something wrong with machines C and D, but I have them transferring internally at anywhere between 250 Mbps and 800Mbps.
Strange. I'm playing with network topologies now, to see if i can coax C and D into better behaviour...
Plusnet Customer
Using FTTC since 2011. Currently on 80/20 Unlimited Fibre Extra.
Superuser
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Re: FTTC Speeds - Restricted after 12 Midday?

Surely can't make a difference, but…
If you plug Machine C into the port currently used by B, and vice-versa, does the behaviour change?
David
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Re: FTTC Speeds - Restricted after 12 Midday?

They're on different switches (I have 3 gigabit switches) - and to swap ports like that means going into the loft, so I'll leave that for later. I was trying to find my longest ethernet cable, to bypass everything, but I can't find that right now.
However, I *do* now have an explanation for machine C:

  • It is Windows 7, 64-bit. I use firefox by default - and this gives me the speeds of 9-12Mbps.

  • I tried bypassing the switch next to C, so it connected direct to the switch in the loft (so was connected like machine B) - no change.

  • I tried using IE9 in 64-bit mode. Speedtest.net didn't like the version of flashplayer.

  • I tried IE9 in 32-bit mode. Hey presto: Speeds of 33-34/1.7. Obviously the problem was in Firefox and/or its version of flash.

  • I re-installed flash (not sure if it was actually an upgrade), and ran the tests from firefox: No change.

  • I then started disabling firefox add-ons, until I found the one that limited the speeds. It was the "Firebug" add-on.


So, for machine C, it was a Firefox add-on that was causing the problems.
New results:

That gets it up to the speeds of the other boxes. Still not quite top-drawer - but the packet-loss problem is still there, and will be taking away some throughput.
Now for machine D...
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Re: FTTC Speeds - Restricted after 12 Midday?

There have been a couple of significant changes today.


First, at about 9:30am, the 5% packet loss disappeared, but we gained a higher latency:


I was wondering why DLM didn't act on that packet loss - but it seemed to wait until 48 hours after we were first activated.
A BT speedtest mid-morning showed that DLM had only changed the latency. The IP profile was still 38717, suggesting that the sync was still 40000.
However, the speeds returned were still of the order of 32Mbps (for the BT tester), and 34Mbps (for mybroadbandspeed and speedtest.net).



The effect on my "faulty" Machine D were instantly noticeable: Where it downloaded in the region of 6-10Mbps before 9:30am, those speeds jumped to the 14-18Mbps range, and have stayed there since. It appears that some of the degrade was because of packet loss, while the rest now appears to be down to the raw speed that the download (using Perl's LWP) could work at. The graph demsontrating the effect is attached.
Even when getting the top speeds, I think there's more in the tank - from comparison with non-Plusnet results - and I think it is being masked by the Plusnet profile of 37Mb - someone reminded me that the 20Mb profile actually gives faster speeds. I suspect that the Plusnet 37Mbps is overly restrictive by around 2Mbps.


Second - as can also be seen on the graph above - DLM seems to have triggered a new "sync/login" at 7:30pm. A BT speedtest this evening shows we now have an IP Profile of 34799, and a download speed of 31.3Mbps; MBS also shows 31Mbps. Speedtest.net will only give results in the region of 20-23Mbps for a range of servers - I suspect they're being managed under the evening "20Mbps" browsing restriction, so I'll have to try again later.
Edit: Now it has gone 11PM, I can get a result from Speedtest.net: 33.7Mbps.



The loss of 4Mbps off the IP Profile, but only losing 1-2Mbps off the actual download speeds (to BT and MBS) also suggests that the Plusnet profile of 37Mbps is overly restrictive.


Third, my "faulty" machine D, using an old version of Fedora Linux:
I was testing this afternoon with command-line "wget" commands to download 10, 20 and 50MB files. A single download would be limited to around 24Mbps, but I could get 3 downloads in parallel to give close to 36Mbps.
It looks like the results on Friday were caused by both the packet loss and by some software perrformance problems within Perl/LWP.
After that, I booted into a recent Ubuntu Live CD, and tried again. But by that time, we were into the evening "20Mbps" browsing restriction (and hitting it), so I gave up, and will try again when line speeds are available again.
BTW - Only having line speeds available between 1am and 7am for many protocols makes it really hard to run tests to see what the actual line speed is!
Plusnet Customer
Using FTTC since 2011. Currently on 80/20 Unlimited Fibre Extra.
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Re: FTTC Speeds - Restricted after 12 Midday?

This is getting to be a right saga, eh?
As we went past 1am, I thought I'd try some tests to see if we'd lost any of the management traits.... and that showed that Adam's regrade had gone through just fine:



BT's speedtester shows the new speeds, but right now thinks I have the old profile. I'm sure it will change in the next few hours.
So yeah - thanks Adam. I don't think I've said that enough - so really ... THANKS ADAM!

I then took a look at the TBB ping graph... and found that DLM had triggered again - this time, just after midnight, it took away the interleaving, reduced latency, and put back the 5% packet loss.
The IP profile hasn't (yet) changed on the BT speedtest results.


  • This image will update throughout tomorrow, so who knows what extra DLM tricks it will show before I look again


I hope someone is learning lots about how the FTTC DSLAM goes about its work here ;-)
For those reading after the weekend off, what I'm left most concerned about is the packet loss/DLM intervention - but this is a new installation, so I guess I do need to leave it to settle down.
Once it has settled, then I'll be most concerned about why the 37Mb profile seems to lose around 2Mb of performance... if I get a profile back up at that level again.
Plusnet Customer
Using FTTC since 2011. Currently on 80/20 Unlimited Fibre Extra.
phil4
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Registered: 13-12-2007

Re: FTTC Speeds - Restricted after 12 Midday?

My understanding is that the interleaving isn't controllable by PN on FTTC....
Indeed it seems the DSLAM turns the interleaving on and off when it feels like it.  It is a bit strange it dropped your profile too, but I guess that's what the training period is for.
So the one thing you might want to push more, the thing that is definitely under PN's control, is the 37Mbps profile, which regardless of your BT profile, you always seem to be 2-3Mbps away from (let alone 38717 BT profile).