BT Infinity 1 speed drop

I have a long line to the exchange and used to get 1.25Mbps on ADSL2+. FTTC finally arrived and BT forecast 27Mbps even though I am over 1km from the cabinet. I ordered Infinity 1 and the day of installation came and the BT engineer showed me that the speed was in fact 27Mbps as forecast. Later that day I did a test on Speedtest.net and the download speed was around 26Mbps, and upload was around 1.2Mbps.

A day after the installation the download speed had dropped to 15Mbps and 9 days later it is still around 15Mbps and the upload speed has fallen to 0.7Mbps, slower than when on ADSL2+. No changes have been made to any wiring or sockets.

I realise there is a settling in period but can anyone offer any advice re:

Is it normal for the speed to drop so much after the first day?
Why is the upload speed so slow?
FTTC has only just become available in our area so a lot of people are being connected. Could this have an effect?
Is the target noise margin 6db as with standard ADSL?
Should I take this up with BT?

===========================================================
Stats as follows

3. Firmware version: Software version 4.7.5.1.83.8.173.1.4 (Type A) Last updated Unknown
4. Board version: BT Hub 5A
5. VDSL uptime: 0 days, 03:12:33
6. Data rate: 797 / 15217
7. Maximum data rate: 1092 / 15808
8. Noise margin: 6.4 / 6.2
9. Line attenuation: 0.0 / 27.5
10. Signal attenuation: 0.0 / 22.1
11. Data sent/received: 3.1 GB / 2.1 GB
===========================================================

Thanks in anticipation.

Is it normal for the speed to drop so much after the first day?
No
Why is the upload speed so slow?
Because the upstream and downstream are weaved together so upstream drops off over distance more than it used to with ADSL2+ and the DLM will have eaten a chunk.
FTTC has only just become available in our area so a lot of people are being connected. Could this have an effect?
Yes
Is the target noise margin 6db as with standard ADSL?
The DLM works differently, tends to cap/band speeds rather than work to target margins.
Should I take this up with BT?
Maybe, but if you think line length is closer to 1.5km, then your speeds are what I'd expect once cross talk kicked in.

The fact the maximum rate is close to the data rate suggests you were the first in your bundle, and its the next couple of people in your cable bundle that will have killed your speed I suspect.

Thank-you so much for your prompt and informative answer. I think my main problem is that it started out at 27mbps. If it had started at 15Mbps and stayed there, I would have been happy. Should I assume that at 27Mbps it would have been unstable and therefore I'm better off where I am? Think I'll still contact BT to see what they say. Thank-you.

Near impossible to say for sure, but the cross talk theory is that it can cause this sort of drop and combine this with a DLM that aims for an error free line then feasible.

If it was me, and I knew for sure line was 1km long I'd moan more at ISP, if I knew line was likely to be over 1250m then I'd just take it as the way VDSL2 works...i.e. first user goes great for a while.

So best way to avoid wasting hours on the phone getting no where, is to check the distance using a walking route via Google Maps.

Google maps indicates 1500m along the road and the line distance cannot be significantly shorter than this, assuming there's not a cabinet somewhere that I don't know about.

In which case you look to have settled down at the speed expected with some cross talk involved

This is very worrying. Presumably this also applies to superfast broadband from other providers. The poor upload performance probably makes cloud storage and computing unviable.

In this case, the Noise Margin is above the target indicating the presence of noise which may have reduced the sync speed.
This indicates there is possibly something wrong with the install.

This has now got a lot worse. The speed gradually got worse until it was around 10mb. BT came out at the end of December and said it was impossible to synch at 27mb ( as it had done on day 1) and I would have to settle for 14 / 15 mb and they would not respond to any further complaints at this speed. Bearing in mind the advice received here I was happy to accept this. They said the reason for it being 10mb was because I had switched off the router once, for 3 days when I was away over Christmas and that it would recover to 15mb.

Router stats at that time were as below although I noticed that the maximum data rate varied a lot from day to day.

4.Board version: BT Hub 5A
5. VDSL uptime: 1 days, 18:30:45
6. Data rate: 579 / 11741
7. Maximum data rate: 661 / 12871
8. Noise margin: 8.4 / 6.7
9. Line attenuation: 0.0 / 29.0
10. Signal attenuation: 0.0 / 22.7

As of today thing have not improved, although the maximum data rate has halved.

5. VDSL uptime: 7 days, 01:01:49
6. Data rate: 579 / 11741
7. Maximum data rate: 622 / 6440
8. Noise margin: 7.2 / 7.1
9. Line attenuation: 0.0 / 29.0
10. Signal attenuation: 0.0 / 22.7

I am in contact with someone from with BT Broadband Digital Care who are has been helpful and is looking into this but I wondered if anyone here would care to comment. Also could anyone explain the difference between Data Rate and Maximum data rate and how the maximum can be less than the Data rate?

Thanks for all your advice and comments so far.

Who ever you spoke to has mis informed you, because for one thing switching off your router/modem for several days even hrs or 10-15 minutes would not normally cause DLM to intervene and lower your IP profile But if you repeated the switching it off and on in quick succession it would cause DLM to think there was an issue,

What is your IP profile? if you don't know go to
Bt performance tester

Run the speed test and then it will give you the option to do further checks, enter you number in the dialog box, and run it will eventually display details of your ip profile and what throughput speeds you achived , if you can copy &paste those results here it may help us help you further ,

The maximum data rate has halved because of the Noise margin. The noise margin are often a lot lower at night, your best bet is to check in the afternoon at the same time intervals.

Data rate is the speed your modem and the MSAN are synced at, this is the amount of bandwidth the MSAN will send to your house.

Maximum Data rate is an estimate of what you could achieve, this is done upon the Noise Margin. The target margin for an FTTC connection is 6db. If the noise margin is above the target margin (6db) the Maximum Data rate is likely to be higher than the Data rate, though this isn't always the case. If it's below it's typical that the Maximum Data Rate will be less than the actual Data Rate.

Though I would think your connection is where it should be considering your distance from the cabinet, also with some Crosstalk in effect.

Edited by deleted (Sun 19-Jan-14 19:01:51)

In reply to a post by ryant704:

The maximum data rate has halved because of the Noise margin.

Rubbish, the NM's hardly moved!

In reply to a post by ryant704:

The target margin for an FTTC connection is 6db. If the noise margin is above the target margin (6db) the Maximum Data rate is likely to be higher than the Data rate, though this isn't always the case. If it's below it's typical that the Maximum Data Rate will be less than the actual Data Rate.

I believe this is a load of drivel. There is no such relationship and is belied by the OP's reported stats.

Thanks for your comments. I was suspicious about the info re switching off of the router but it came from the engineer who visited after being on the phone to his help desk people.

Here is the result of a speed test earlier today. It has lost some formatting but you can get the general idea.
=================================================
1. Best Effort Test: -provides background information.

Download Speed
10.77 Mbps

0 Mbps 11.36 Mbps
Max Achievable Speed

Download speedachieved during the test was - 10.77 Mbps
For your connection, the acceptable range of speedsis 20 Mbps-11.36 Mbps .
Additional Information:
IP Profile for your line is - 11.36 Mbps

2. Upstream Test: -provides background information.

Upload Speed
0.51 Mbps

0 Mbps 10 Mbps
Max Achievable Speed

Upload speed achieved during the test was - 0.51Mbps
Additional Information:
Upstream Rate IP profile on your line is - 10 Mbps


The test result has indicated that you should contact your ISP for further assistance.

All you can do is keep on complaining to your isp. What you have for what you are paying just isn't worth the money, less than 1mbps upload sync there has to be some kind of fault with the line, or part of it is aluminium , how far are you from the exchange, more than 2miles? BT should be allowing you to leave without penalty if they cannot provide the service that you are paying for and IMO for a FTTC service you should be getting at least a better upload speed if not a bit more from the downstream as well

Edited by tommy45 (Mon 20-Jan-14 00:52:31)

BT did offer to allow me to cancel my contract but that would mean going back to ADSL at 1.25 mb because I am 6 or 7 km from the exchange.

When I was on ADSL I used routerstats to display a graph of my noise margin and whereas in the past this had been fairly smooth, I had noticed that more recently the graph had shown the margin to vary quite widely over a short period of time. I don't know how to display the same information with VDSL as routerstats says it does not work with VDSL.

Part of the problem, I think, is that the overhead wires go through some trees and it is very difficult to get to the junctions on the poles so no-one can or wants to do it.

In reply to a post by philflyer:

I don't know how to display the same information with VDSL as routerstats says it does not work with VDSL.

Basic RouterStats or RouterStats Lite does not, but RouterStatsHub does interface to the HH5 and will display the data.

Wow! Thanks for that. I hadn't seen the reference to RouterStatsHub. Now graphing!

What do the first results look like.

The downstream noise margin is more or less steady at 7.2db. The upstream is constantly fluctuating by about 0.75db at first centred around 7.5 db then half an hour later around 8.0 db then half an hour later around 7.1db. Speed is 11741 down, 519 up. Engineer coming tomorrow.

That isn't really much of a fluctuation - if it was more than 3 or 4dB it might be cause for concern but that isn't really conclusive of anything but a potentially normal line (although I wouldn't consider 519 up to be normal for a line with that downstream).

I thought I would give an update on this as things have changed recently.

To cut a long story short, at the beginning of the year I was told that nothing could be done and I would have to put up with speeds of 12Mb down 0.5 Mb up so I took no more action.

A couple of weeks ago I rang BT just to check when my contract ended so that I could look at alternative suppliers. That really set things moving and I was passed to an extremely helpful lady, who was horrified to see the speed I was getting and said that she would do something about it. A couple of the usual obligatory missed BT engineer appointments then followed, interspersed with one engineer who said there was a fault where the line went underground but someone else would have to fix it. Another engineer then came and said there was no fault but he would try and find a different pair of wires to use. When he did this the speed immediately shot up significantly and after a reset it is now 23mb download (was 12mb) and 2mb (was 500kb) upload.The noise margins are both really steady at 6db whereas before the upstream margin was constantly fluctuating. Speedtest.net gives 21.67 down, 1.98 up.The engineer warned that the speed might drop again during the 10 day settling in period but after a day and a half the speeds are still holding. If the connection is sound and the noise margins are steady, is there any reason why the system should want to reduce the speed now? Full marks to the lady at BT who phoned me regularly with updates and was determined to get something done.

In reply to a post by philflyer:

If the connection is sound and the noise margins are steady, is there any reason why the system should want to reduce the speed now?

DLM will cap your sync speed to raise your noise margin if it sees a high number of disconnections.

The engineer warned that the speed might drop again during the 10 day settling in period

It's a bit sad when even an Openreach engineer believes this .

Re my comment just now to BatBoy, there is no ten-day period on FTTC, despite what BT Wholesale say. Even on ADSL2+ the ten days did not do what they believe, and that was under their control.

On FTTC the line speed is controlled by the Openreach DLM running in the FTTC cabinet, not the BT Wholesale one running in the exchange which merely jumps in and adds the IP Profile at the point where Openreach hand your connection over to them at the exchange.

There is a document SIN 498. Here is the relevant extract:-

2.2 User Network Interface - General

2.2.1 Dynamic Line Management

Dynamic Line Management (DLM) is employed in GEA-FTTC. DLM constantly manages lines to maintain a target link quality (speed and stability). It does this for as long as the product exists.

At provision, the line is put on �wide open� VDSL2 line profiles allowing the upstream and downstream line speeds to run at the upper limit of the product option selected.

On the first day of operation, DLM will intervene if severe instability is detected. Otherwise, DLM will wait until the day after provision before deciding if it must intervene, provided that the line has been trained up for at least 15 minutes during the preceding day.

In essence/practice that means if anything is going to change a lot it will normally be some time during the second night since installation and use.

As with BT Wholesale based ADSL2+ the DLM does run for ever. The most common intervention is to add interleaving if there are bursts of noise. Whereas on ADSL2+ speed wasn't really affected by interleaving, on FTTC it is quite dramatic. The initial intervention normally loses you about 10Mbps and the latency increases by 8ms.

The good news is that if the noise was something unusual such as a thunderstorm, after a fair while it will be automatically removed again. That was very rare, if at all, on ADSLx.

Edited by RobertoS (Wed 22-Oct-14 20:24:34)

Thank-you both for your interesting and informative comments. I have left my PC running continuously with Routerstats. At 2.30 am this morning it reconnected even though the noise margin had remained steady at 6.0. This resulted in a a small speed drop to 22.9 / 1.8. So all appears to be well and I just hope it stays there.

Looks good.

The engineer will have requested a DLM reset when he did the job, so you should be OK now. From your earlier post I gather Wed night was the second since the pair change so this would be DLM altering something. Quite what is hard to know, as that looks like a drop in sync simply due to night-time connection.

Have you got a separate modem, or just the HomeHub?

Yes - Wed night was the second night and so now we have gone through the third night which had no reconnect even though the margin seemed to drop fractionally below 6.0. To answer your question I have the homehub 5A.
So after 11 months of half speed I wonder if BT might offer me any special price to tempt me to stay with them?

They may offer you a tenner off a month, but isn't the lure of BT Sport enough?

I think the lure of a considerably cheaper phone and broadband package from Plusnet is much greater - unless they get Formula 1 on BT sport which is highly unlikely.