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2mb Possible? 43db attenuation & 24db SNR

tumnus
Grafter
Posts: 104
Registered: 19-08-2007

2mb Possible? 43db attenuation & 24db SNR

I've searched all over the place for my specific case but haven't really come up with anything conclusive, so I'm asking directly here...

I've got a solid 1mb connection. My modem stats give a downstream attenuation of 43db and SNR of 24db. Having read up on this, even though the attenuation is borderline for 2mb, my SNR is so good, according to my modem at least, I thought I would be able to get a stable 2mb connection. At the end of the day, it is the SNR that is the important value, but they can only test attenuation remotely, no? Even if my modem is accurate to +/-5db and a regrade takes another 8db off the SNR, the worst case result would be 11db, which should still be stable.

When I first raised a ticket with PlusNet CS they were very quick and it took little convincing for them to do a Whoosh test. Lo and behold it confirmed my downstream attenuation is 43db. Anyway they gave me the choice of pushing it through to BT, with the warning that I may lose my regrade fee if I have to regrade back to 1mb. Fair enough "I'll take my chances" I said, so they put my support ticket in the 'BOT - DSL Regrades pool' whatever that is and they promptly replied "We have tested your line and it cannot support 2mb"!

I get the feeling they just did another Whoosh test and it never went to BT considering how quick it came back. Am I wasting my time chasing this? Has anyone else with similar or worse stats got a stable 2mb line through PlusNet?

I just moved to PlusNet from Pipex so it's still cheaper for unlimited 1mb, but 2mb would be even better....

TIA
8 REPLIES
Community Veteran
Posts: 14,469
Registered: 30-07-2007

2mb Possible? 43db attenuation & 24db SNR

The BOT team is within PlusNet and they are responsible for dealing with ADSL activations and regrades.

It does sound like they re-did the test and found the line attenuation to be >43dB - this can vary depending on whether conditions and time of day so with you being right on the limit, any degrading of your line will push you over.

That said... The most likely reason why your order did not go to BT is because BT are very strict on the limits for 2Mbs now (they have had a lot of line failures after upgrading lines with >43dB line attenuations) and if there is any doubt about you being over the 43dB strictly inforced limit, then BT would reject the order very quickly.

I suspect you won't get any further with this due to BTs strict inforcement of the limits now and you will have to wait for MaxDSL (due around April 2006) where the limits will no longer apply and your line will just sync at the best speed it can take.

Finally, it is only the line attenuation that is considered for speeds so having a high SNR makes no difference to the decisions BT now make for line suitability.
lingbob
Grafter
Posts: 734
Registered: 05-04-2007

2mb Possible? 43db attenuation & 24db SNR

Quote
It does sound like they re-did the test and found the line attenuation to be >43dB - this can vary depending on whether conditions and time of day so with you being right on the limit, any degrading of your line will push you over.

So, BT's limit for 2Mbps is 43db, do you know what their limits are for 4Mbps and 8Mbps.

Regards,
Martin
Community Veteran
Posts: 14,469
Registered: 30-07-2007

2mb Possible? 43db attenuation & 24db SNR

No-one knows what the limits will be for the higher speeds until the product is formally announced in April 2006.

In any case, once MaxDSL comes in in April, line limits will no longer be the determining factor for speeds, the line will sync at the highest reliable speed it can take, regardless of the line attenuation figure.
Community Veteran
Posts: 1,229
Thanks: 1
Registered: 12-04-2007

2mb Possible? 43db attenuation & 24db SNR

I wonder what the OP's attenuation was when they were on 512k??
Each jump in line speed increases line attenuation by a few dB or so as the OP said, therefore if the OP's attenuation figures were something sub 40 dB when they were on 512, then they would have been be put through for regrade without a second thought. Especially with such a good SNR!

I wonder what the actual figure that came back from woosh testing was.
Community Veteran
Posts: 14,469
Registered: 30-07-2007

2mb Possible? 43db attenuation & 24db SNR

Quote
Each jump in line speed increases line attenuation by a few dB or so

Line attenuation does not change when the speed changes. It is an indication of the quality of the signal (i.e. how much of the signal is lost) and is completely independent of the speed of the ADSL connection.

Only SNR changes when an increase in speed occurs because the faster speeds use a larger frequency range to supply the extra data and this in turn results in a higher noise level and thus SNR (signal to noise ratio) decreases. Normally SNR will decrease by 4->6dB for each jump in speed.

See ADSL: Understanding Line Loss and measurements for more details.
Community Veteran
Posts: 1,229
Thanks: 1
Registered: 12-04-2007

2mb Possible? 43db attenuation & 24db SNR

:? Oh! thx Peter

I thought I had read somewhere else on the forums a few times that attenuation went up with each speed upgrade. Oh well, I am getting old you know!
tumnus
Grafter
Posts: 104
Registered: 19-08-2007

2mb Possible? 43db attenuation & 24db SNR

Thanks for the feedback.

Does anyone have an official BT source for their attenuation limits? While PlusNet quotes 'less than 43db' for 2mb I've read more quotes from other ISP CS staff in my searches that say '43db OR less' and I'm sure they don't want the hassle of unstable lines anymore than PlusNet does.

Quote
I wonder what the actual figure that came back from woosh testing was.

The original Whoosh test gave an attenuation of 43db, which my modem is still showing, though it is now saying my SNR is 25db.

Hmmm, April isn't that far away for MaxDSL, but then again deadlines can slip.... :?
tumnus
Grafter
Posts: 104
Registered: 19-08-2007

2mb Possible? 43db attenuation & 24db SNR

Well, according the CS, the order did go to BT and got rejected Cry

The most frustrating thing about it is I could probably get a stable 2mb connection going off what others have said about the significance of the SNR and how much it drops per upgrade, but due to BT I can't have it....