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55.5 db Attenuation high?

jim306
Grafter
Posts: 75
Registered: 31-10-2007

55.5 db Attenuation high?

Im trying to get my head around how attenuation affects line speed and wondering if my 55.5 db downstream is high considering im 2.87km from the exchange (straight line distance) compared to other people roughly the same distance from their exchange?
My upstream attenuation is 29.0 db, SNR margin 11.9 downstream and 20.0 up. My attainable rate is 3616 Kbps, line profile 2000kbps and actual throughput on bt speedtester 1790kbps Sad
If my attenuation is higher than what would be considered normal is there anything i can do to lower it? Im plugged directly into the master socket with the faceplate removed and there are no other telephones or extensions in the biulding.
6 REPLIES
James
Grafter
Posts: 21,036
Registered: 04-04-2007

Re: 55.5 db Attenuation high?

Hi Jim,
Attenuation doesn't directly affect line speed, but the synchronisation speed does.  However, synchronisation speed is directly linked to attenuation, as this is generally a good factor of determining how far away from the exchange you are.
There's a pretty lengthy guide on max broadband in my signature, which might well be worth a read.
Community Veteran
Posts: 14,469
Registered: 30-07-2007

Re: 55.5 db Attenuation high?

What James has said is correct for the fixed speed IPStream products where line attenuation determined whether tyou couls have 512Kbs, 1Mb or 2Mbs speeds.
With ADSL Max, it is the SNR that is the determining factor on what speed your will get as the exchange will adjust the sync speed up until it reaches a SNR of 6 (the BT default). Increasing sync speed decreases SNR whereas line attenuation stays constant.
Some info on the fixed speed product line attenuation / SNR can be found here: Understanding Line Loss and Measurements.
jim306
Grafter
Posts: 75
Registered: 31-10-2007

Re: 55.5 db Attenuation high?

My SNR margin has dropped to 9.1 today so hopefully i should start to see a speed increase in the next couple of days.
Community Veteran
Posts: 14,469
Registered: 30-07-2007

Re: 55.5 db Attenuation high?

That is not how it works.
Before you connect to the exchange, your line will have a certain SNR and line attenuation value. The higher your line attenuation, the weaker your signal is. The higher your SNR the better your signal can be distinguished from the background noise.
Thus to get a higher sync rate your SNR must be higher or line attenuation lower both of which result in a stronger signal.
When you connect to the exchange, the exchange tries to get the best sync rate but at the same time does not allow the SNR to go below a min threshold, which is 6dB in BTs case - not BT can increase this threshold to 9, 12 and 15dB on bad lines resulting in a lowering of sync rate..
The SNR you are seeing is after the exchange has established a sync rate and the SNR does fluctuate over the day with some days having a higher figure that others.
The only important SNR is the value you have when you connect to the exchange which you can't actually see as your router will only report SNR after it has connected.

However, in your case it looks like you have a stuck profile as the BT speedtest shows a sync rate of 3600 but an IP profile of 2000. The IP profile determines your data throughput rate and this should be at least 3000 fir a sync rate of 3600. You need to get this issue looked at by PlusNet support.
James
Grafter
Posts: 21,036
Registered: 04-04-2007

Re: 55.5 db Attenuation high?

It's not stuck.  It should rise tomorrow or the day after.
There was a recent low sync event.
jim306
Grafter
Posts: 75
Registered: 31-10-2007

Re: 55.5 db Attenuation high?

I have also noticed i get lots of RS correctable errors and quite a few uncorrectable errors? what do these mean?