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ADSL error rates and SNR margin

decomplexity
Rising Star
Posts: 493
Thanks: 26
Registered: 30-07-2007

ADSL error rates and SNR margin

Despite very low attenuation (2.5dB downstream) – the exchange is three doors away – my ADSL MAX synch speed stays stuck at 7615 kbps (which leaves the bRAS profile at 6500 kbps). My downstream SNR margin is around 11.5 and varies little, but the exchange’s DLM appears to be making no effort to reduce it and thus ramp up the synch speed.
I can only assume this is due to the line error rate (on a physically new line – to the pole at least, with an ADSLNation NTE5 faceplate and no extension wiring). But what error rates rank as low / medium / high?
At the ADSL level, my % of words with correctable RS errors is around 0.0007% and the % of words with uncorrectable RS errors is around 0.004%.
At the block level, superframe errors are around 0.024%.
At the ADSL/ATM boundary, header error checksum (HEC) errors are around 1 per 300,000 RS words, and in the AAL5 (cell assembly/disassembly) level there were 70 errors in a run of 900 million downstream octets but no other ATM errors per se. There were no cell delineation (LCD or OCD) errors.
So does anyone know how error-free my line has to be to notch up my synch speed to 7968 kbps (which should reprofile the link to 7Mbps) or even the Grail of 8128kbps, and is the DLM influenced by ATM and AAL5 errors or just RS (i.e. ADSL parity) errors? 
Zen from May 17. PN Business account from 2004 - 2017
2 REPLIES
Superuser
Superuser
Posts: 9,771
Thanks: 1,151
Fixes: 63
Registered: 06-04-2007

Re: ADSL error rates and SNR margin

Do you have interleaving turned on?  It's my impression - I don't know of any hard evidence - that some router/DSLAM combinations lead to a maximum achievable sync of 7616kbps when interleaving is on.
With the DSLAM I connect to (with interleaving on) with both a Voyager 210 and a Belkin F5D9830-4 router the maximum seems to be 8096kbps but with a Solwise 600E I achieved 8128kbps.
Your error percentages seem low to me but - but I'm not an expert -  my RS correctable errors count is slightly larger than the number of RS words, RS uncorrectable errors is 0.1%.  So I reckon interleaving is good value for me.
If you have interleaving on I suggest raising a ticket to ask for it to be turned off (I have an icon in Connection Settings to action this, though I believe not everyone does).
David
James
Grafter
Posts: 21,036
Registered: 04-04-2007

Re: ADSL error rates and SNR margin

Yeah, Dave told me the other day that interleaving can/does result in lower sync rates, which was news to me!
I've put a ticket on your account, decomplexity, do you want me to remove interleaving for you?