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Feedback on FTTC - Performance

Community Veteran
Posts: 1,411
Thanks: 4
Registered: 29-01-2009

Feedback on FTTC - Performance

Here's my feedback on the initial performance I experienced with FTTC.
I've correlated results from a number of places, so it should help for anyone who needs to compare in the future too.
Summary
My line first came in with a profile of 38717, indicating top speed, with 13ms latency - so we let the engineer go on his way.
However, it turns out that it suffered from 4% packet loss for the first 48 hours, when DLM intervened and added interleaving, which increased latency to ~ 20ms
The packet loss stopped immediately, but that didn't stop DLM intervening again some 12 hours later - this time dropping the speed by about 4Mbps.
Speed checkers only saw a drop of around 1Mbps.
As this was a trial order, it was then regraded to a 10000 uplink. That caused DLM to get reset, and speeds (and packet loss) restored - but it went through an almost identical DLM process.
This means I have some good speedtest results of a line running at 40Mbps against one running at 36Mbps, twice over. Some are manual tests, and some from the SamKnows measurement box.
The 2 questions out of this are
- Did I send the engineer away too quickly? Is there something that could have been done to the line?
- Why does a drop in profile of 4Mbps only cause a drop of 1-2Mbps in speed tests? Is Plusnet's "37Mb" profile too conservative?
I've not added any graphs to this report, but if anyone wants to see anything, just let me know...
Day 1 AM - The Raw Speeds
The DSL checker estimated 30.1Mbps down and 6.2 Up. However, with a distance of around 500m, I was being optimistic that I would get much nearer the full 40000 sync. Other people on this distance seems to see those speeds.
The engineer & his box reported the following line conditions:

  • length 550-600m

  • downstream sync around 36500

  • upstream sync 2000

  • noise margin 7.7dB

  • attenuation 17dB


If it were left at that, I'd have got him to check the connections, as I'd have expected a 40000 sync; I've certainly seen that on those distance & attenuation values. Another cause for local suspicion was that an engineer installing the neighbour's FTTC connection a couple of weeks ago *did* encounter line problems, and was out fiddling in the DP outside.
However, my engineer went on to run further tests (that send the results back via text message)... which then reported a 40,000 sync.
OK, I thought, and went on to do some of my own tests...
The BT speedtester was reporting a 38717 profile - suggesting a 40000 sync - and Speedtest.net gave 35.04Mbps: it is the best I've yet managed, and was the first test after my FTTC profile was set up.
Upstream tests were around 1.7Mbps.
So all seemed perfect at this point.
Day 1 PM - Mea Culpa
After this came the little debacle, where my speeds tumbled on various testers. It turned out to be software in both cases (Perl on a Linux box, and a Firefox plugin on a Windows box).
Lets ignore this bit, shall we ;-)
Day 2 - Packet Loss
Speeds continued being pretty good, on the systems that worked correctly anyway. Speedtests arund 34.5Mb.
However, I now discovered (via my TBB graphs) that i was suffering around 4% packet loss all the time.
Day 3 - DLM intervenes twice
After exactly 48 hours, DLM added interleaving, which increased the latency. This was visible on the TBB graphs, but they also showed that the packet loss disappeared.
This happened without a resync, and the BT speedtester continued to report a profile of 38717, and speedtest.net results were of the order of 34.7Mbps
Then around 7PM there was a resync on the line, again visible on the TBB graphs. After this time, BT speedtester reports on the profile were 34799, a drop of almost 4Mbps. Speedtest.net results were then around 33.7Mbps, a drop of only 1Mbps.
Day 4 - Upstream Regrade
Shortly after midnight was another resync. This went along with the regrade of the upstream to 10Mbps, and an obvious reset of DLM: The packet loss was back, along with the lower latency. The BT speedtester said the profile was back at 38717.
Speedtest.net results were back up to around 34.7 Mbps
Day 5 - Packet Loss
Just like day 2, things continued with the higher speeds, low latencies, and with continuous packet loss on the TBB graphs.
One curious thing happened: I downloaded a Fedora Linux DVD in the early hours, and while the download took place (for an hour or so) the packet losses almost disappeared.
I also deliberately switched off the modem & router in the evening, as I re-arranged the network to plug in my SamKnows measurement box.
Even after that, the packet loss continued, and the profile was still 38717. But now I could see the performance on the SamKnows graphs...
For that evening, SamKnows reports latency of 11ms, loss of 4%, and come 23:00, a multi-threaded download speed of 34.6mbps.
Day 6 - DLM intervenes once
For this day, the TBB graph shows increased latencies, and the packet loss disappears, at around 10am. There is a funny blip for a while beforehand, around 9am, where the latency increases a bit, but there is no change to packet loss figures. The latency goes back down to its lower value for 30 minutes before the "proper" fix happens.
Again, there is no obvious resync associated with the change in latency, and the BT speedtester continued to report a profile of 38717.
In fact, I was curious to see if DLM had decided to keep the speed - so in the evening I power-cycled everything, to force a resync.
BT speedtests after this point continued with a profile of 38717.
SamKnows confirms the change in latency, from 11ms to 19ms, along with the end of the packet loss. Downloads were at 34.6Mbps at 4pm and 33.8Mbps at 11pm, but were more like 24-26Mbps in the evening management period.
Day 7 AM - DLM intervenes once again
The overnight download test by SamKnows return a result of 35.6Mbps - its highest one in my records.
At this point, things were looking good. The packet loss had gone, but we'd managed to keep the higher sync level. Excellent...
Then in the middle of the day, I powered things down for a while, so I could sort out more permanent power arrangements for all these boxes.
When I bring everything back up, the subsequent BT speedtester results confirm that the profile has gone back down to the 34800 region - pretty much like day 3. A drop of 4Mbps again.
Day 7 PM through to Day 15
From this point onwards, Speedtest.net results have tended to be in the region of 33.2-33.7Mbps outside management time. Spookily consistent.
Samknows download tests are usually between 33-34Mbps when not managed.
The BT speedtester can be anywhere in the region of 28-31Mbps, very occasionally up to nearly 32Mbps.
Upstream tests, from Speedtest.net, seem to be consistently either around 7.7Mbps or 8.2Mbps. BT's tests usually returns anywhere in the range of 7.5-8.2Mbps.
I've also caused 2 or 3 additional resyncs, and they're all result in profile between 34770 and 34900. I plan on leaving the modem alone for a while now, an opinion reinforced after reading ashgeo's post.
General Speedtest Results
I've found that:
- Speedtest.net is the most consistent tester, so long as it is done outside management hours.
  London, Milton Keynes, Maidenhead & Newbury all give similar results
- The BT speedtester tends to be 2 or 3 Mbps below the Speedtest.net figure for downstream at best, but about the same for upstream. It is much less consistent.
- The SamKnows box reports speeds almost 34Mbps for unmanaged hours, and in the 21-26 region when managed.
- MyBroadbandSpeed and the TBB speed tester are hopelessly inconsistent.
- The SamKnows latency & loss tests match well with the results on the TBB quality graphs
Speeds & Traffic Management
We're on the "Extra Fibre" package, which notionally gets some level of management throughout the day. With one small exception, the management hasn't been noticeable at all, nor has any sign of exchange congestion. We have had absolutely perfect behaviour when downloading, browsing, or streaming of YouTube and iPlayer - even to watch the Canadian Grand Prix last weekend.
The exception? Obviously I've done a lot of speed-testing above, trying to see what was happening. Its a bit annoying that the Speedtest.net data gets managed in the 6PM-11PM slot. It makes a big chunk where I can't run worthwhile comparisons.
Conclusions & Questions
Initially the line suffers from packet loss - and DLM seems to do the right thing in turning interleaving on to fix this.
I do wonder what kind of interference I am suffering to see a relatively consistent 3-4% packet loss throughout the day. The only exception was for an hour when a long download took place!
It then seems strange that, having turned interleaving on, and the line seemingly working fine, DLM then chose to also drop the profile/sync speed by around 4Mbps.
Also strange is the fact that, once the sync speed has been dropped by that 4Mbps, I see drops in speed test results in both of my most consistent testers - Speedtest.net and the Samknows box: but only by about 1Mbps.
That result suggests that I'm not really running at full speed when the BT profile is 38717.
I've seen on the forum mention that the "37Mb" profile behave slower than the "20Mb" profile used to (back, earlier in the trials).
This result suggests that the profile may well indeed be overly restrictive.
So my overriding questions have to be:
Is there anything I can do about that 4% loss? Or should I accept that the use of interleaving is the right way to fix it?
Equally, should I accept the drop of 4Mbps, even though it seems to be needless?
And finally, is Plusnet's 37Mb profile really giving us the pinnacle of performance?
Plusnet Customer
Using FTTC since 2011. Currently on 80/20 Unlimited Fibre Extra.
13 REPLIES
phil4
Grafter
Posts: 244
Registered: 13-12-2007

Re: Feedback on FTTC - Performance

I think I once mentioned my puzzlement over the 40 -> 38171 -> 37 speeds.
I appreciate that we'll lose some bits due to protocol overheads and the like, but this still leaves me wondering why BT have a profile of 38171, and PN 37.
Of course the PN profile could just be named 37, even though it's 38717, but if that were the case, I'd expect the Marketeers to have called it "40"!
There something odd that doesn't add up with the above, but I'm so relieved I'm getting so much better than my old 1.5, and more stability and better support than my old Virgin connection, I don't want to be rocking any boats.
Epyon
Grafter
Posts: 285
Registered: 31-03-2011

Re: Feedback on FTTC - Performance

About speedtest.net getting a better result than BT speedtester i don't think its just FTTC i also like 2mbps less.
Community Veteran
Posts: 1,411
Thanks: 4
Registered: 29-01-2009

Re: Feedback on FTTC - Performance

No answers?
Anyway, I've been monitoring the connection since my first post 12 days ago, and have left the fibre modem connected untouched since then.
In that time, my TBB BQM "Ping Latency" graph has shown only a single time that the modem appears to have resynced:
- I last power-cycled the modem (& router) at 6pm on the 15th
- The BQM graph shows a break at 10pm on the 27th; this seems to have been a break at the modem, as the router continued to count up the "connection time" of the PPPoE session. Perhaps the router didn't notice.
- The BQM graph then shows a break at 4pm on the 28th, which was a manual disconnect/reconnect at the PPPoE router (not modem). The router's "connection status" page shows a connection time reset to zero, but the "statistics" page shows the uptime to be counting on (now up to 14 days+).
27th:

28th:

My BT speedtests continue to show an IP Profile of 34799 - so whatever caused the modem resync did NOT allow it to sync higher. I then did the manual disconnect of the PPPoE session in case the previous resync *had* changed speeds, but the non-negotiation of a new PPPoE session had left me running on "old" speeds... but it seems not.
Other than that, my experience is fine - and continues the behaviour I reported last time. All measurements show everything working exactly as expected, with regular slowdowns of browser traffic between 6pm and 11pm. The slowdown is often down to 24-26Mbps, rather than as low as 20Mbps.
@phil4 - I think the "37" profile is indeed just a name... and I think it is relatively meaningless to us now, because Plusnet's profile doesn't seem to alter when the BT side varies. Of course, I've seen mine go from 38717 to 34799 twice, and then vary perhaps 100-200 around the 34800 level. It might not be enough to trigger anything on PN's side yet...
@Epyon - I hadn't really made much of a note of the BT tester's results before FTTC. I use it a lot more now, simply because it is the only way to get hold of the IP Profile value.
Plusnet Customer
Using FTTC since 2011. Currently on 80/20 Unlimited Fibre Extra.
knowdice
Grafter
Posts: 328
Registered: 25-04-2008

Re: Feedback on FTTC - Performance

I think you are right about the Plusnet profile being "just a name" as I'm still showing as 20mb which is the "old" trial profile but I certainly do get full FTTC speed at about 34mbs being 600-650metres from the cabinet.
As far as physical layer testing goes, you are really not going to get very far with the BT modem as you don't have access to its stats...maybe consider changing to a Draytek or Fritz!box modem/router where you have complete control & access.
Community Veteran
Posts: 1,411
Thanks: 4
Registered: 29-01-2009

Re: Feedback on FTTC - Performance

Right - loss of those stats is very frustrating. It means you can't get any real feedback as to how your line is behaving, or how any changes affect things. A 1-hour delay between BT tests makes a judgement via the IP Profile a very slow process too.
Plusnet Customer
Using FTTC since 2011. Currently on 80/20 Unlimited Fibre Extra.
Community Veteran
Posts: 1,411
Thanks: 4
Registered: 29-01-2009

Re: Feedback on FTTC - Performance

An update on overnight behaviour:
I've updated my "cacti" script, so that it can capture the throughput available on FTTC, and been running it for the last week.
For the first 4 days, this has given perfectly expected results - showing a ceiling level of 32Mbps down & 8.3Mbps up outside peak hours, and something in the 20-25 Mbps region for the evening peak.
However, from the graphs over the last 3 days, I've noticed some obvious slowdowns in the 12PM - 8AM periods - obvious when compared to the previous days, anyway. They are highlighted in the attached graph.
There's nothing going on in-house to cause these, which suggests that we're hitting some congestion elsewhere. Is there anything on the PN side that can correlate to this? Or is it more likely to be a cabinet-level or exchange-level issue?
Plusnet Customer
Using FTTC since 2011. Currently on 80/20 Unlimited Fibre Extra.
knowdice
Grafter
Posts: 328
Registered: 25-04-2008

Re: Feedback on FTTC - Performance

Is this just "traffic management" relating to whatever Plusnet package you are on?
Community Veteran
Posts: 1,411
Thanks: 4
Registered: 29-01-2009

Re: Feedback on FTTC - Performance

We're on the "Extra Fibre" package, where browsing activities are managed between 6pm and 11pm, limited to 20Mbps.
Those periods are indeed limited - usually to about 24Mbps - and can be seen on the graph too. But I was expecting those.
The overnight bit, between midnight & 8AM, just stood out. Up to the 28th, my tests were a straight line - consistent maximum performance. But on the 29th and after, the same period shows lower speeds and considerably less consistency. It looks like there's a touch of congestion somewhere.
One night wouldn't have meant a lot - but the same thing 3 nights in a row looks a little suspicious. The timing certainly suggests that I'm being hit by someone transferring lots of traffic overnight - my guess being P2P. Unfortunately, Plusnet's http://usage graphs have been broken for a while, so we can't see if there has been much of a problem there.
Strangely, my TBB ping monitors don't show any hint of additional latencies in the same slots. Maybe there's some other explanation...
Plusnet Customer
Using FTTC since 2011. Currently on 80/20 Unlimited Fibre Extra.
Dev
Grafter
Posts: 198
Registered: 01-08-2007

Re: Feedback on FTTC - Performance

My profile seems to be stuck on 21, hope someone at PN can have a look.
Community Veteran
Posts: 1,411
Thanks: 4
Registered: 29-01-2009

Re: Feedback on FTTC - Performance

I think I've figured out the "midnight-8AM" behaviour I reported in posts #6 and #8:
The simple answer is that it was dependent on the gateway I was connected to.
I realised that, on the day before i could see the different speeds, I had reconnected to Plusnet. I'd gone from pcl-ag2 to ptn-ag1.
Last night I reconnected, and went to thn-ag1, which improved behaviour in the midnight-8AM slot. Unfortunately, it also took my latency from 18.5ms to 21.5ms.
Plusnet Customer
Using FTTC since 2011. Currently on 80/20 Unlimited Fibre Extra.
Plusnet Help Team
Plusnet Help Team
Posts: 12,718
Thanks: 102
Fixes: 31
Registered: 27-04-2007

Re: Feedback on FTTC - Performance

Hi WWWombat,
I'm sorry for a delayed response from the staff side of things. Can I ask you to complete the fault checker at https://portal.plus.net/apps/kbdfaults
Reply back here once you've done that, it will help me gather some extra info and get some diagnostics done. I'll give you a call (most likely tomorrow) after that.
If this post resolved your issue please click the 'This fixed my problem' button
 Adam Walker
 Plusnet Help Team
Community Veteran
Posts: 1,411
Thanks: 4
Registered: 29-01-2009

Re: Feedback on FTTC - Performance

Right, that's done. It said its gone to the Faults team.
No surprises from the BT Speedtester; I have lots of images saved from different tools, if you want to see them.
Plusnet Customer
Using FTTC since 2011. Currently on 80/20 Unlimited Fibre Extra.
markg140
Grafter
Posts: 71
Registered: 11-05-2011

Re: Feedback on FTTC - Performance

500m of copper is still a fair bit for speed to degrade to be quite honest.
And that is assuming it's a decent grade copper and not alimunium.

Can't wait for BT to upgrade to an 80MB package, hoping Plusnet follow suit.
Judging from BT's speedtester I can get upto 75MBps down my line YAY Smiley