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Have BT changed SNR margins?

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Have BT changed SNR margins?

hi,

My SNR has jumped up to 9db (losing almost 1mb) which i put down to a fault that appeared on my line for a few hours causing re-sync every 10 secs. Raised a ticket and was told that BT Max runs at a target of 9db which is news to me. How come i have been on 6 since the day i startedHuh

Cheers
Nicky
16 REPLIES
Community Veteran
Posts: 2,322
Registered: 01-08-2007

Have BT changed SNR margins?

I really hope this is not the case, as my router performs quite happily at 5/6db or even below.

I thought it worked out the sustainable rate by trying ever higher speeds each time it connected until the connection kept dropping, then turned it back a notch.
Community Veteran
Posts: 1,139
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Registered: 20-07-2007

Have BT changed SNR margins?

The same thing has also happened to me - my target SNR has increased from around 10dB to around 13/14 dB. I started a thread about this here http://portal.plus.net/central/forums/viewtopic.php?t=51002.

Bob
Plusnet Staff
Plusnet Staff
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Registered: 04-04-2007

Have BT changed SNR margins?

Hi,

The default target SNR on a Max line is 6dB, however if problems are seen with the line such as a number of disconnections in a short period of time, then they will increase the target SNR automatically to 9, 12 or 15dB.

It looks like that's what's happened here, the automated systems at BT saw the re-syncs and upped the target SNR to try and compensate.
Community Veteran
Posts: 2,322
Registered: 01-08-2007

Have BT changed SNR margins?

If this happens - i.e. through multiple restarts of a router due to maintenance or installing/deinstalling of telephones in the house etc.

Is it possible to ask BT to put it back to 6 again?
kitz
Rising Star
Posts: 817
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Registered: 08-06-2007

Have BT changed SNR margins?

You can try to get PN to get BT to reduce the target SNR.. but in all fairness BTw like to play ticket tennis with PN.

If you can leave things alone for 14 full days and if youre router doesnt need a resync and your line is stable for that period.. then the DLM may well automatically reduce your target SNR back down again.
Community Veteran
Posts: 1,139
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Registered: 20-07-2007

Have BT changed SNR margins?

Quote
Hi,

The default target SNR on a Max line is 6dB, however if problems are seen with the line such as a number of disconnections in a short period of time, then they will increase the target SNR automatically to 9, 12 or 15dB.

It looks like that's what's happened here, the automated systems at BT saw the re-syncs and upped the target SNR to try and compensate.

That's interesting I wasn't aware of the 6dB target. It doesn't explain why my SNR is so high though as I've never suffered from disconnections. The only disconnections problem I've had was when there was a global problem a few weeks ago (11 November).

Bob
Community Veteran
Posts: 1,139
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Registered: 20-07-2007

Have BT changed SNR margins?

I've just had a thought about this :idea:

My PC has a built-in broadband modem which disconnects every time the PC is switched off and re-syncs every time it is switched back on. Lately I've been switching the PC on and off two or three (and sometimes more) times a day. Could it be that this is being interpreted as dropped connections and that this is forcing my SNR up?

Bob
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Registered: 10-04-2007

Have BT changed SNR margins?

Yep - get a router!
jelv (a.k.a Spoon Whittler)
   Why I have left Plusnet (warning: long post!)   
Broadband: Andrews & Arnold Home::1 (FTTC 80/20)
Line rental: Pulse 8 Home Line Rental (£13/month)
Mobile: iD mobile (£4/month)
N/A

Have BT changed SNR margins?

Quote
Yep - get a router!


I just replaced my PlusNet Binatone ADSL modem with a router.

My SNR was 15 before, so I'll have to see if it comes down. I know my Stable Rate has changed from flicking up and down from 500-2000 to 2000 for a few days and now up again to 3000 (haven't seen that for months).

HOWEVER, what I have also picked up in the last two weeks is about 3-4 gigs worth of peak usage which I can only guess is attempted P2P traffic from other people whilst my PC is off.
Community Veteran
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Registered: 10-04-2007

Have BT changed SNR margins?

3-4 gigs sounds an awful lot for that.
jelv (a.k.a Spoon Whittler)
   Why I have left Plusnet (warning: long post!)   
Broadband: Andrews & Arnold Home::1 (FTTC 80/20)
Line rental: Pulse 8 Home Line Rental (£13/month)
Mobile: iD mobile (£4/month)
Plusnet Staff
Plusnet Staff
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Registered: 04-04-2007

Have BT changed SNR margins?

Quote
Lately I've been switching the PC on and off two or three (and sometimes more) times a day. Could it be that this is being interpreted as dropped connections and that this is forcing my SNR up?


Three or four times per day I would say unlikely, there's no real concrete solid, this many times in this amount of time but we're talking more like 5-10 times in half an hour or so rather than a few times spread out over the day.

There are different types of "normal" usage, some people have a router and leave it connected all the time, some turn the equipment off overnight or when they aren't in and some only connect a few times a day or once a day when they use it or when they turn the PC on. The systems will generally not adjust the target SNR if it's "normal" it's where the connection is dropping an "abnormal" amount of times.
Community Veteran
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Registered: 20-07-2007

Have BT changed SNR margins?

Dave, so on that basis my usage would be considered normal. Any idea then why my SNR is so high and my line rate below 7,616 (I'm assuming this is the maximum with interleaving switched on)?

Bob
Plusnet Staff
Plusnet Staff
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Registered: 04-04-2007

Have BT changed SNR margins?

Can you post the full line stats please? It may just be that there was a period of instability for a short period which you didn't notice or it could be down to something else.
Community Veteran
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Registered: 20-07-2007

Have BT changed SNR margins?

I'm not at home at the moment but stats are generally of the order:

Line rate varies between around 6,500 and 7,400
SNR varies between 12dB and 15dB
Attenuation (upstream and downstream) always around 17dB
Errors are very low.

Do you need anything else (I'm not sure that my modem gives any further information).

Bob

Edit, I've just logged-on and current stats are as follows:

Upstream Rate:448 kbps
Downstream Rate: 7,392 kbps

Bytes Received: 1,506,406
Bytes Sent: 347,076
ADSL CRC: 1
Local RS Corrected: 6
AAL5 CRC: 0

SNR Margin: 13dB
Attenuation Remote: 17dB
Attenuation Local: 17dB

VPI Number: 0
VCI Number: 38
Line Standard: G.DMT
Modulation: Interleaved