ADSL Speed anomalies

I have an ADSL link that for years has run at just over 6Mbps downstream, except when there are drop outs but these are rare. Over the last few days my speed dropped to less than 3Mbps.

Using Routerstats into my Technicolor router showed the RX Sync Speed as 7872Kbps and RX Noise Margin of 6.2dB. However, the Bits/Tone is really strange. Normally this would indicate most downstream tones in the region of 12 bits. But during this slow period I have about half the low end tones at only 1-2 bits; then a gap of about 40 tones with 0 bits, then the rest of the high end tones of 9 bits.

I spoke to John Lewis/Plusnet who ran lots of tests - supposedly - and found no problem and agreed with my sync speed. After some technical discussion in which I'd pointed out that I had tried another router on the master socket which showed the same problem they wanted to ship a new router. Again I pointed out that I had tried and alternate. Anyway they classified this as No Fault Found from their end and suggested an engineers visit with the caveat that should they not find any fault I would have to pay £65 if NFF. I wasn't totally happy as BT are constantly mucking about in our exchange but I agreed.

Now, is it a coincedence that a couple of minutes after I ended the call my downstream speed returned to the usualy +6Mbps. However, the bit loading still looks odd with the same pattern as previously.

Anybody care to comment on why I have my normal speed but poor bits/tone showing in Routerstats.

I cancelled the engineers visit just in time.

Thxs

Sounds like someone at Plusnet/John Lewis reset your IP profile on the line.

I think all ISP's do this...fact

I think if I put "fact" on the end of my post it makes it true and even more so if it's in capitals - FACT!

Over the 8 years I've been on this exchange and with three different ISPs, admittedly on top of BT, I've never had this problems before.

Here we are a couple of weeks on and now my speed has dropped to below 2Mbps. I'll give it a day or two before rattling someones cage again.

We constantly see BT Openreach messing about in our area and at the exchange. Its not unknown for them to screw things up for someone who hasn't a problem in the attempt to fix someone elses line.

Is the phone working correctly with no background noise?

I haven't done any tests on this latest round of issues but previously I plugged a laptop into the master socket and with two different routers still had the same problem.

The question about the phone is important. Preferably with a corded one into the test socket inside the master.

If it doesn�t work that means one wire of the pair is not connected somewhere between you and the MSAN. Broadband can work, but very slowly, on just one wire. Phone cannot. Similarly bad crackling on the phone can be down to a wire about to disconnect, though can have other causes.

Edited by RobertoS (Sat 13-Apr-19 10:34:27)

That's not the question I was asking! You need to plug a telephone handset in to the test socket inside the master socket and check you have a dial tone. If you have dial 17070 and pick option 2. The line should be quiet with no background noise or crackles. You could spend weeks trying to sort out your broadband, but if there's an unresolved issue with the telephone line you would still poor broadband. If this fails report it as a phone fault - when this is fixed it is more than likely the broadband will fix itself.

As RobertoS has said you should use a corded phone - if you don't have one borrow one from a friend or buy something like this: https://www.argos.co.uk/product/5529610

Until you upgrade to FTTP where it is fibre optic all the way to your home, a corded phone is an essential diagnostic tool for ADSL or FTTC.

Tested line with corded phone in master socket - no noise detected.

FWIW:
Rx Sync speed is 6240kbps when it usually runs just under 8000
RX SNR is 12.1 when it's usualy around 6
Line attenutation 31/16 - cant remember what it usually is.

Bit loading...

xdsl debug bitloadinginfo
Tone : # Bits per tone
0 : 0 0 0 0 0 0 0 2 4 5
10 : 6 7 7 8 8 7 8 7 7 8
20 : 7 7 7 7 7 7 7 6 5 4
30 : 4 0 31 -27 32 80 0 0 0 0
40 : 31 -27 63 -4 10 10 10 10 10 10
50 : 10 10 10 10 10 10 10 10 10 10
60 : 10 10 10 10 0 10 10 10 10 10
70 : 10 10 10 10 10 10 10 10 10 10
80 : 10 10 10 10 10 10 10 10 10 10
90 : 10 9 9 10 10 9 10 10 9 10
100 : 9 9 9 10 9 9 9 9 9 9
110 : 9 9 9 9 9 9 9 9 9 9
120 : 9 9 9 9 9 9 9 9 9 9
130 : 9 9 9 9 9 9 8 8 8 8
140 : 8 8 8 8 8 8 7 8 8 8
150 : 2 8 8 8 8 8 8 8 8 8
160 : 8 8 8 8 8 8 8 8 8 8
170 : 8 8 8 8 8 8 8 8 8 8
180 : 8 8 8 8 7 7 8 8 8 7
190 : 8 7 7 7 7 7 7 7 7 7
200 : 7 7 7 7 7 7 7 7 7 7
210 : 7 7 7 7 7 7 7 7 7 7
220 : 7 7 7 7 7 7 7 7 7 7
230 : 7 7 7 7 7 7 7 7 7 7
240 : 7 6 6 6 6 6 6 6 6 6
250 : 6 5 5 5 5 0

The do it yourself troubleshooter on the JL website doesn't work so I'll put in a call when I can.

Just for information my adsl is 20CN, which I'm told by the engineers is harder to setup than the later versions. But now its fixed.

Anyway, JL/Plusnet ran some more tests and confirmed that my sync speed was about 6300 and the SNRM was about 12.1. Also that my profile had been set to 5500. This didn't explain the poor throughput of about 2000 so they arranged for an engineer to visit.

He came this morning and tested the line and found no problems but confirmed the poor throughput and the same numbers I'd got as above.

He said the SNRM should have been 6 and since I was set to 12 this explained the lower sync speed and lower profile. He called BT and got this changed to 6, which took some time to do. I'm told its a manual process.

Once done the SNRM became 6 and the sync speed became 7840, which resulted in a higher profile so I should have got a throughput of about 6500. However, we were still seeing around 2000.

He then said that Plusnet also have their own profiles and contacted them and found it was set to about 3000. He requested this be changed but in the meantime he took my router to the exchange and set up a local connection there and eventually got the download speed of over 6500.

When he returned with my router the download speed when using his laptop was still around 2000 but he noticed that the ethernet cable connection to his laptop was a bit loose. We tried a wireless connection and he got the 6500 we were expecting. The cable connection problem was really a red herring because it's a spare and not one I was usiing for any of my tests.

I connected up my main machine and ran tests and its now back where it was three weeks ago - so a result.

There is no explanation of why the SNRM was dropped to 12 and no explanation of why Plusnet had dropped my profile to 3000.

In reply to a post by Spuriousfish:

There is no explanation of why the SNRM was dropped to 12 and no explanation of why Plusnet had dropped my profile to 3000.

(and from previous post)

In reply to a post by Spuriousfish:

FWIW:
Rx Sync speed is 6240kbps when it usually runs just under 8000
RX SNR is 12.1 when it's usualy around 6
Line attenutation 31/16 - cant remember what it usually is.

With ATTN like that, you should be getting sync of 7-8 Meg imo. While your SNR is usually at 6, if line quality allows for it, it can be dropped to 3. See my 'best effort' results image here:

http://www.camieabz.co.uk/broadband

Similar ATTN, but downstream SNR set to 3.

In addition, I would harass PN support to reset the profile, and have interleaving switched off (a.k.a. FastPath). When on older ADSL my profile would be 8192 or 8000. Forget which.

Worth nothing that restarting too often will result in slower connection, so request a profile reset, interleaving off, and if your router allows for it, set downstream SNR to 3. The reset might take a few days, and that will allow for things to settle. If your line isn't up to supporting 3db, it will reconnect at 6db.

Thanks for the reply.

As stated in my previous post, once BT and Plusnet reset noise margin and profiles my sync speed became 7936. This is giving me a download speed of approx 6200, which I'm quite happy with.