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SNR going up, sync-rate going down

pacem
Grafter
Posts: 175
Registered: 07-09-2007

SNR going up, sync-rate going down

I've been on ADSLMax for 2 months or more now and other than the initial switch over it has been rock solid (though I will admit to having noisy line problems in the past).

I complained and had problems at the switch over time. For a week or so I had a stable sync of 2700Kbs ish with a SNR ot 6dB.

Because I messed with the BT socket (and possible because I complained) interleaving was added:

New SNR of 9dB and a sync of 2500Kbs ish.

This remained until 2 days ago:
SNR is now 11dB and sync has dropped to 2144Kbs.

(Now, I did upgrade the firmware on my Solwise SARBig something [which is really a reboxed Billion 7400] a week ago, but the latest SNR/sync change has only just happend.)

My Line has never dropped without my intervention (other than initial training), so why is my SNR rising and my sync rate falling?

This latest sync-rate of 2144Kbs means that my stable rate has now dropped to 1500Kbs. That coupled with the higher pings of interleaving means that webpages (particularly ones requiring multiple GET operations) load noticably slower than my old 1Mb connection.

Is there anything I can do get the sync back up and if necessary the SNR down?

(I already have a good router, BT master filer [which isolates the ring wire anyway but yes I've tried that too], I've not had a thunder storm recently... all the screws in my house have their slots alligned virtically when its a full moon...)

And if there's nothing I can do, is there anything PN can do?

Paul.<><
PS current stats: down/up
sync: 2144/448
SNR: 11dB/21dB
ATT: 60db/30dB
CRC errors: 441/22 (in last 40hours)
3 REPLIES
geoffers
Grafter
Posts: 47
Registered: 30-07-2007

SNR Values

The excellent Kitz site ( http://www.kitz.co.uk/adsl/linestats.htm ) says a bigger SNR is better (whilst a bigger attenuation is worse - further from the exchange)

Quote
An upgrade in speed often causes the SNR to decrease by up to 5 dB.
The higher your SNR figure then the better your line quality and therefore a higher chance of getting faster speeds.
It is very important to note that SNR plays much more importance in maxdsl than it did on the traditional adsl product.
shellsong
Grafter
Posts: 2,191
Registered: 03-08-2007

SNR going up, sync-rate going down

Synch rate is related to SNR in such a way that a doubling of the synch rate results in a reduction of SNR of approximately 6dB. Normally when rate adaptive ADSL such as MaxDSL is functioning correctly the equipment at the exchange will attempt to adjust the synch rate to allow a minimum SNR of about 6dB which should allow your modem sufficient discrimination of the signals used for ADSL above the noise level of the connection between you and the exchange for reliable, "clean" communication.
pacem
Grafter
Posts: 175
Registered: 07-09-2007

SNR going up, sync-rate going down

Thanks guys, although you haven't told me anything I didn't already know (or answered the question). I guess I'll have to guess and put it down to my target SNR margin having been set to a higer value than 9dB when interleaving was originally added and some sort of compromise in the router firmware settling on 9dB which has now changed to 11dB since I've upgraded the firmware.

I'm getting more and more tempted to risk having interleaving removed as I didn't have any problems before it was added, but I'm mindful of my occasional noisy line problems in the past.

Paul.<><