2700HGV not offering the performance over long line

[Polchraine]

I know, but at:

http://www.idnetters.co.uk/forums/index.php?topic=22013.msg530968#msg530968

the OP quotes 1152/288 as his sync speed, which would appear to be a fixed rate 1M service. 

If he has been moved to a fixed rate service then the OP should get reverted to an alternative as the line looks as though it will support more on the upstream.

[MisterW]

Yes, it will support more on the upstream but from these figures

Rate:               1152 kbs   288 kbs
Max Rate:       1272 kbs   788 kbs
Noise Margin:   4.0 dB   19.0 dB

The noise margin on the downstream is already below 6db. Reverting to a nonfixed connection will certainly increase the upstream but is just going to reduce the downstream since its going to try and maintain a 6db margin at least!.

[Polchraine]

Mine 2700 will sync at 3dB ... so choosing when to resync is vital.   It will drop overnight to around 0dB or maybe as low as -0.5 occasionally and then back up to 6, 7 or 8 dB during the day.     

On a non-fixed rate connection and at the speed the OP could now achieve, every dB or even 0.1dB can be vital in getting a few extra 10s of kbps.      Also, moving back would give a better upstream rate too.

[Rik]

Do you know if you have a 3db target noise margin?

[shpub]

I've been away for a couple of days but the experience with the new connection has not been good as the 2700 has been dropping the line a lot. Restarts every 45 minutes are not uncommon. The 2700 did a superb job of syncing onto the fixed rate but it is hanging on by the skin of its teeth. The amount of errors is high and the sync speeds have dropped significantly over the last few days. While downstream has dropped to 384, the upstream has gone to 484. 

I've tried all the normal tricks with test sockets etc and the conclusion I have come to is that for this particular line, ADSL Max with the NetGear forced into G.DMT mode gives the best combination of stability and speed so I've asked to go back to the original service. 

To be fair, and to quote IDNET... "the line is indeed very long - it is a miracle that it works at all!"

[Rik]

It's true to say that, for some people, ADSL2+ just doesn't work. Unfortunately, no-one can predict the results, it's a case of suck it and see. The good news is that you retain your ADSL2 bandwidth allowance when you re-modulate.

[shpub]

Just a quick update:

IDnet moved me to ADSLMax and the connection speeds with the 2700 went up. Unfortunately the 2700 decided to drop the SNR down to 3db to acheive them and the resulting errors etc caused the exchange to insist on a 15 db snr and a low sync rate: 288/288 was not uncommon.  Even leaving the 2700 connected for several days did nothing and the BT Speedtest results were very strange indeed. It often insisted that I had connected at 8k and my profile was 16k???

It seemed pretty obvious that I was in "BT Jail" without a get out of Jail card. I then got hold of a Billion 7300 which has the ability to override the exchange set SNR and that worked magic. 1024/488 at 7/11db SNR. Unfortunately the BT IP profile was still screwed up and I ended up with a 150k profile!

IDNet got BT to reset the line and the profile is now up at 750k which is what I expect for the sync rate. The line has been up for some 10 days now.


Conclusions:

• The 2700 is too good a modem in that it achieved sync rates that were frankly too high for the line. As a result, the link was not stable and I ended up with a 15db snr. There is no way of really controlling this from the 2700 which is a real pity.
• The 2700's insistence on syncing as high as possible when given a normal 6dB target really caused me problems as it seemed to throw the exchange into apoplexy!. 
• The 2700 data statistics are excellent and proved very useful.


• At 99p + postage of eBAY it certainly was worth trying. 


• If your line is bad - mine has measured 73db at best and 78 at worst attenuation - I think the 2700 is probably too good and without the control to rein it back, it can get you into a lot of trouble. I would suggest getting a modem with SNR control to force the situation into a known working sync rate and snr. I know this is supposed to happen but after my experiences it does appear that taking control from the modem end does provide a lot of benefit.

The end result is that I am reliably syncing at 1024/488, getting a good 750kb transfer rate which is at least 3 times the performance I was getting before. I am extremely happy. So thanks for everyone who guided me through this and I can't praise IDNet support high enough. 

For anyone else who has a really bad line... it does look like a bit of playing around with modems etc will reap benefits.

[Steve]

Whilst I understand overriding the dslam and setting your own margin, I'm still puzzled what happens with relationship between sync and IP profile when you've bypassed dslam margin control.

[Rik]

It's also perhaps worth mentioning that when the scheme to allow ISPs control of DLM parameters launches, you can get the best of both worlds, speed and stability.

[shpub]

Whilst I understand overriding the dslam and setting your own margin, I'm still puzzled what happens with relationship between sync and IP profile when you've bypassed dslam margin control.

So was I as the BT Speedtester results were all over the place. IDNet support were puzzled as well as their line stats were different to those reported by BTSpeedtest.

I think - and I am not totally sure of this - that the ip profile still gets adjusted to suit the sync rate but it doesn't necessarily get reported correctly. For some reason, the settings were screwed up as you can see from the Speedtest data.  It is very puzzling. I was very close to sacrificing a chicken or two over the modem as I could not make any sense of the BT figures I was seeing. Neither could James at IDNet so the chickens were saved. He suggested the reset.  Anyway the good thing is that it worked and I am enjoying a blissful and reliable 750k.

ISP control over the DSLAM... now there's an opportunity. I might just volunteer to try that out.


BT Speedtester results from 4th Sept when I first joined IDNET using Netgear 834G

Download speed achieved during the test was - 648 Kbps
The acceptable range of speeds is             200-1000 Kbps.
Your DSL Connection Rate :                    896 Kbps(DOWN-STREAM), 608 Kbps(UP-STREAM) Agrees with modem snr 6 db
IP Profile for your line is -                 750 Kbps
Best Efforts (BE) classes achieved during the test is - 14.42:23.82:61.76 (SBE:NBE:PBE)

BT Speedtester results from 18th Sept using Netgear 834G

Download speed achieved during the test was - 116 Kbps
The acceptable range of speeds is             1000-7150 Kbps.
Your DSL Connection Rate :                    256 Kbps(DOWN-STREAM), 448 Kbps(UP-STREAM) Agrees with modem but the snr was 15db not the normal 6db
IP Profile for your line is -                 3000 Kbps
Best Efforts (BE) classes achieved during the test is - 16.65:24.37:58.98 (SBE:NBE:PBE)
Upload speed  achieved during the test was -  364 Kbps
Upstream Rate IP profile on your line is -    448 Kbps

I could not get any higher sync rates. It was suggested that I used a modem that let me overide the target SNR, hence the change to the Billion.

BT Speed Tester from 21st Sept using  Billion 7300A with SNR overide on 

Download speed achieved during the test was - 119 Kbps
The acceptable range of speeds is             50-250 Kbps.
Your DSL Connection Rate :                    8124 Kbps(DOWN-STREAM), 888 Kbps(UP-STREAM) NB Modem reported 1024/448 snr 7db
IP Profile for your line is -                 274 Kbps
Best Efforts (BE) classes achieved during the test is - 11.95:35.68:52.38 (SBE:NBE:PBE)
Upload speed  achieved during the test was -  349 Kbps
Upstream Rate IP profile on your line is -    888 Kbps


BT Speedtester results from 22nd Sept using Billion 7300A with SNR overide on

Download speed achieved during the test was - 139 Kbps
The acceptable range of speeds is             1000-7150 Kbps.
Your DSL Connection Rate :                    1440 Kbps(DOWN-STREAM), 448 Kbps(UP-STREAM) NB Modem reported 1024/448 snr 6.5 db
IP Profile for your line is -                      2742 Kbps
Best Efforts (BE) classes achieved during the test is - 21.86:34.58:43.57 (SBE:NBE:PBE)
Upload speed  achieved during the test was -  363 Kbps
Upstream Rate IP profile on your line is -    448 Kbps

[Rik]

ISP control over the DSLAM... now there's an opportunity. I might just volunteer to try that out.

I already did.

[Tacitus]

It's also perhaps worth mentioning that when the scheme to allow ISPs control of DLM parameters launches, you can get the best of both worlds, speed and stability.

But does that apply both to 21CN AND Max?  My guess is that ISP control of DLM parameters won't apply to the 'old' system, but only to the new.....

[Rik]

It will, Tac, but it's a start. BT may be encouraged to spread it to 20CN if they are not upgrading.