Exchange upgraded to ADSL2+, now speed slower!

Had a email from bt saying they have upgraded my exchange to give me a faster and more reliable service. My modem has been synced at 2856kbps for 47 days with a noise margin of 9dB, and the letter stated that they disconnected my service for a few minutes while they upgrade my line! It has now synced at 1856kbps with a noise margin of 6dB! Download speed thus dropped from 2.5Mb to 1.5Mb and the video quality has dropped from 720P netflix down to 480i, and the picture is horrid! What can I do? Why has my speed dropped so much? Fuming!

Were you on ADSL rather than ADSL2+ before?

If so, find the page in your router GUI that specifies the G.DMT/ADSL/ADSL2/ADSL2+ settings. Try disabling ADSL2+ but retain ADSL2 and G.DMT/ADSL. Do this well inside daylight hours.

If that doesn't give as much as you expect, an hour later disable ADSL2 as well.

You could try it now and maybe get a slight improvement, as long as you haven't just done a load of re-sync's and it may help. Then tomorrow some time between 10am and 2pm at this time of year should give best possible.

In the summer 9-5 is safe, and wider than that fairly safe.

You should be able to get them to regrade your line back to regular ADSL. It might need to go through a specialst team though so be prepared to escalate the issue.

In reality it's super easy to do and the change will go through within 24-48 hours depending on when the order is placed.

Easily done in the way I described, and ADSL2 may be best as it normally lowers the attenuation by 3dB. Given his low earlier ADSL speed it's a toss-up between ADSL and ADSL2 - only trying each will tell.

I have a 2-Wire modem, can those methods of connecting be disabled on them?

Never had one, but almost certainly. You can look without connecting it to the line. Just power it up and connect a computer to it.

There will probably be a menu possibly labelled WAN, or DSL.

Left the modem off since I posted this thread overnight, and switched it back on at 9:30am Speed jumped up to 3104Kbps, and download speed now at 2.7Mb! Faster than ive ever had! This a good speed for my attenuation?

DSL Details

Modem Type: Built in modem - ADSL
DSL Line (Wire Pair): Line 1 (inner pair)
Current DSL Connection:
Down Up
Rate: 3104 kbs 448 kbs
Max Rate: 2756 kbs 948 kbs
Noise Margin: 7.0 dB 22.0 dB
Attenuation: 57.1 dB 31.5 dB
Output Power: 17.9 dBm 11.9 dBm

Protocol: G.DMT Annex A
Channel: Interleaved
DSLAM Vendor Information Country: {46336} Vendor: {BDCM} Specific: {42915 }
ATM PVC: 0/38

Rate Cap: 2756 kbs
Attenuation @ 300kHz: 57.1 dB
Uncanceled Echo: -14.1 dB Ok
VCXO Frequency Offset: -2.2 ppm Ok
Final Receive Gain: 34.5 dB Ok
Excessive Impulse Noise: 0 Ok

Edited by 8skellerns (Wed 27-Jan-16 20:22:37)

Weird stats but good to see.

You are still on ADSL, but probably on IPStream Connect, which runs it through the ADSL2+ system once it gets past the DSLAM. Alternatively you are now on an ADSL2+ DSLAM and your circuit configured down to ADSL.

With that attenuation you might get a bit more on ADSL2.

I've a feeling your bad speeds might have been on ADSL2+, which frequently results in a 3dB increase in attenuation. In most cases modem and MSAN software designers have failed to compensate for that, as it's rubbish.

I say that because what we see is an average attenuation across all the frequencies, and given the extra range of frequencies on ADSL2+ and the higher ones attenuate more, of course the average rises. The sync negotiation clearly takes the average into account somewhere, but if there is no way you will be able to use any of those higher frequencies then the average of the ones you can use should be taken instead. Or at least, the average of the ADSL ones.

ADSL2 uses the same frequencies as ADSL but better, and the attenuation is the same as on ADSL. On your attenuation I'd expect the resultant sync to be roughly the same, but as I think I said in my earlier post the only way to see is to try. However if your line has been configured to ADSL (G.DMT) then you won't be able to try ADSL2. At your end you can only force a lower level, not a higher one.

That is a 2-wire modem - I recognise the format and have played with quite a few. The best time to sync is during daylight hours and then from experience I have found that around 1/2 to 1 hour after sunrise, so around 8:30 (in London).

Keep it running with minimal reboots and then after a couple of week, do a managed power down, reboot and resync. IF the line has been behaving itself, you may well see the target SNR set to 3dB - nothing that you can do and that will give you a little more speed.

On a reasonable line the 2700 will hold sync even when the SNR drops to around zero.

The figures for Uncanceled Echo, VCXO Freq Offset are fine and suggests you have a fairly good, albeit long, line. On the same page there is a Training History - one column there is headed MODE, what does it give there? That will confirm ADSL, ADSL2, ADSL2+ ...

Router stats lite works well on the 2700, so worth installing and running for a day to see how the SNR varies over a 24 hour period.

He is currently on ADSL, whatever the history. Though it would be nice to know what he was on when his speeds were bad.