cancel
Showing results for 
Search instead for 
Did you mean: 

Stuck SNRM?

198kHz
All Star
Posts: 3,394
Thanks: 371
Fixes: 10
Registered: 30-07-2008

Stuck SNRM?

Mornin' All,
Until recently I had a fixed 1Mbps ADSL service, with the 1-port Linksys ADSL2MUE router plugged into one of  three extension phone sockets (‘star’ wired from a junction box adjacent to the master socket) via the usual flat cable. No stats available with that model, apart from sync rate, but it worked well and the connection never dropped. Hindsight of course is 20/20, and I should have modified this arrangement before applying to Plusnet. However…
On migrating to BBYW Option 2, initial sync was 3968, which gradually decreased over the next 18 days to 2496, though the connection remained solid. At this point I acquired a 2Wire 2700HG-B router, which indicated excessive impulse noise, thousands of CRC errors in a few hours, and an SNR Margin of 12dB.
After seeing a vast improvement when using the test socket, I fitted a master filtered faceplate, moved things around, and now the router is connected to the faceplate, via a twisted pair cable, since 3 August.
Would it be reasonable to expect the SNR Margin to at least come down to 9dB? Stats attached.
Remember you are unique - just like everyone else
8 REPLIES
Community Veteran
Posts: 6,735
Thanks: 12
Registered: 02-02-2008

Re: Stuck SNRM?

With that attenuation (line length) your "predicted" speed would only be about 4mbps anyway and you're within 10% of that.
So frankly I wouldn't worry, it may well be a genuine figure due to "conditions" and small adjustments happen quite slowly with BT's new logic (if that applies).
Most of the references to stuck SNRM I've seen have been at the 15dB level anyway.
Community Veteran
Posts: 3,789
Registered: 08-06-2007

Re: Stuck SNRM?

Whilst the theoretical speed for your attenuation line is around 4Mbps, having an SNRM at 12dB does indicate you could push your particular line further as long as it's stable.
Raise a *fault* ticket, asking for your SNRM to be reduced to 6dB, (or hopefully one of the helpful Comms bods will see this thread) and indicate this thread in the ticket, which explains why you believe you have a high SNRM and what you've done to rectify it.
A very loose rule of thumb is every 3dB increment of SNRM equates to approximately 800Kbps sync speed so you could be seeing a fair improvement.
B.
Community Veteran
Posts: 38,460
Thanks: 1,027
Fixes: 62
Registered: 15-06-2007

Re: Stuck SNRM?

I would normally agree with Barry about reducing margin increasing synch speed by about 800kbps  (that used to be about right for me).
However I just had a fault resolved and an odd side effect is that reducing the noise margin from 15dB to 12dB gave a speed increase of about 700kbps to 3480kbps but a subsequent reduction to 10dB (best I could do with DMT) only gave an extra 200kbps.
This is with an attenuation of 51dB.
Looking at the noise margin per tone the problem for me is that the reduction in default noise margin doesn't allow me to use the higher frequency tones (too much attenuation per tone at these frequencies) so I suspect that there is a law of diminishing returns limiting a long line.
198kHz
All Star
Posts: 3,394
Thanks: 371
Fixes: 10
Registered: 30-07-2008

Re: Stuck SNRM?

It's certainly very stable now, so I'll give it a go and raise a ticket. Just another 224kbps would add 500 to the IP Profile, which would be a 17% increase - worth having if the line will support it.  Smiley
Thanks to all for the input.
Remember you are unique - just like everyone else
Community Veteran
Posts: 38,460
Thanks: 1,027
Fixes: 62
Registered: 15-06-2007

Re: Stuck SNRM?

Update on my previous post - using DMT to reduce my default noise margin from 15dB to 12 dB and BT in their wisdom reduced my default noise margin to 12dB (I think the automatic systems must like the fact that I have over-ridden them) which dropped my tweaked default noise margin from 12dB to 9dB but the speed only increased from 3550kbps to 3950kbps which left the IP rate at 3000kbps. The noise margin then dropped to 5dB in the evening which is a bit low for my line si I have untweaked the noise margin - for the moment  Grin
MickKi
Grafter
Posts: 543
Registered: 30-09-2007

Re: Stuck SNRM?

So if you had resynce'd when the SNRM was at 6dB you would probably get the maximum speed that your line could hold!  I have found that resync'ing when the SNRM is below 6dB invariably lands you with a lower sync speed.
198kHz
All Star
Posts: 3,394
Thanks: 371
Fixes: 10
Registered: 30-07-2008

Re: Stuck SNRM?

Raised by PN CSC with BTw last night - fingers crossed...    Smiley
Remember you are unique - just like everyone else
198kHz
All Star
Posts: 3,394
Thanks: 371
Fixes: 10
Registered: 30-07-2008

Re: Stuck SNRM?

Yay - success!
DSL Connection Details
DSL Line (Wire Pair): Line 1 (inner pair)
Protocol: G.DMT Annex A
Downstream Rate: 4352 kbps 
Upstream Rate: 448 kbps 
Channel: Interleaved
Current Noise Margin: 9.0 dB (Downstream), 22.0 dB (Upstream)
Current Attenuation: 52.9 dB (Downstream), 31.5 dB (Upstream)
Current Output Power: 19.6 dBm (Downstream), 12.3 dBm (Upstream)
DSLAM Vendor Information: Country: {0xB5} Vendor: {TSTC} Specific: {0x04}
PVC Info: 0/38
First 24 hrs SNRM attached.
All straightforward and hassle-free via the PN ticket system - thanks guys!   Smiley  And on a Bank Holiday too!
Remember you are unique - just like everyone else