Wierd one

[Chronos]

Mystery Problem...

At least it has BT Openreach and Sky beaten.....

I am barely 1km from my local exchange on Sky LLU.
This is the actual distance by cable length.

4 weeks ago my Broadband stopped, with no synch.

After many weeks and much line checking and some new splices we now have Broadband, but despite the line being "clean" ( B.T comment) my stats are as follows:-

ADSL Link Downstream Upstream
Connection Speed 16027 kbps 765 kbps
Line Attenuation 21 db 8 db
Noise Margin 7 db 15 db

THe line attenuation on ADSL2 is only 21db, but the noise margin is only 7db at best.

Even on ADSL 1 I can only achieve 6440 download connect...
The line attenuation drops to 16db but I cannot achieve the full 8128 connect.

I have a filtered faceplate on my master socket.

BT Openreach have been out 3 times to my home, and can find no problems with the wiring inside or out to the pole. The drop cable was also replaced.

Any ideas why the maximum attainable synch is lower than I should be achieving?

The BT engineer has confirmed I am not on anything other than copper as far as he can tell.

One BT engineer did achieve just over 17mb with his router though.

5 netgear DG 934s have been tested to rule out a router problem.

Everyone is baffled.

Any thoughts anyone?

[Isitme]

I don't really understand your problem, you are syncing at 16027 kbps. That is twice as fast as the 8128 you quote. If your PC is in good order and properly set up you should attain an actual download speed of around 1700 kilobytes/sec(1.66MB/s) allowing for overheads. Go here http://www.skyuser.co.uk/speedtester/ and do a speed test then post the results. Do this using ADSL2+ as you should be doing, adsl1 has a maximum speed of 8Mb.

[Chronos]

Hi ,
I don't think you quite grasp the problem, but thanks for trying to answer.



I am on ADSL2, and the stats reflect that.

When SKY have try to connect me by placing me on ADSL1 ( for testing purposes only), I still then cannot synch at the full 8128, even though my line attenuation is only 16/17db, approx 3db less than on ADSL2 which is normal.

Even with a line attenuation of, say, 25 db I ought to be able to synch at 8128 with a good line.

What is NOT normal is the fact that the target SNR is only 7db given the line quality, which is excellent..

THAT is the problem.

With the good quality line that I have, I should be synching at the full 20mb, with a much better SNR.

[Isitme]

With the good quality line that I have, I should be synching at the full 20mb, with a much better SNR.

I have been on this forum for a long time and I don't think I have ever seen a line with an attenuation of 21dbs, syncing at the full 20Mbs. Those that do are normally in the low teens. I think you are using theoretical values, rather than real life ones to make your calculations. I would be more worried about your upload, which is very low. You should ask Sky to up this.

[Chronos]

OK, you may be right.

Having read the sticky about speeds and SVBN, I believe it is probably the Sky equipment causing problems, possibly some lack of compatibility with the chipsets?

I do know Sky are no longer sourcing Netgear modems.

I wonder how a Sagem would perform, as it has a Broadcom chipset I believe?

[IWasNotTheEnemy]

Just cause you say the line is 'excelent', 'clean' etc. it could be far from it. Do you have line rental with Sky? If you ring 1571 does it Sky Answerphone or BT answerphone? If it says BT answerphone then you're not on the SVBN and this is going to be the best you can get...

And to reinterate what Tom said - you'll rarely see anyone over 20dB att. on 20Mbps...

[Chronos]

Just cause you say the line is 'excelent', 'clean' etc. it could be far from it. Do you have line rental with Sky? If you ring 1571 does it Sky Answerphone or BT answerphone? If it says BT answerphone then you're not on the SVBN and this is going to be the best you can get...

And to reinterate what Tom said - you'll rarely see anyone over 20dB att. on 20Mbps...

I am on SVBN.

BT say the line is "excellent with no errors".
So do Sky.

I cannot achieve 8.128mb synch on g.dmt (when it is tried by Sky) with a 16db line attenuation.

The best it will achieve on g.dmt is 6.4mb.

I am not a novice.
I am experienced, and I am sure the guys at Sky Networking and BT are not fobbing me off with waffle about line quality.

I am after any expert advice on what could possibly be wrong to cause these problems with speed, given my comments.

I am less than 1000m from my exchange by road.

The fact that a line with a 16db attenuation on g.dmt cannot achieve an 8128mb synch is indicative of something, particularly as it is a line not showing any CRCs or FECs.

Thanks for attempting to answer the question however.

[IWasNotTheEnemy]

try a different router, worth a go

[Chronos]

try a different router, worth a go

It's looking to be the only option left.