dslreports logo
site
 
    All Forums Hot Topics Gallery
spc

spacer




how-to block ads


Search Topic:
uniqs
107127
share rss forum feed


SNR vs ATTN

@routermonkey.net

SNR Margin vs Line Attenuation


Shot
What do you think of these numbers?

Should I worry about a bad Upstream SNR Margin?
Is the very good Line Attn is compensating?

My connection seems stable but I'd like to know your opinions.

Thanks


HiVolt
Premium
join:2000-12-28
Toronto, ON
kudos:21
There's nothing wrong with those stats... Remember, its ADSL G.DMT, the maximum upstream is 1mbps, but bell doesn't even have profiles for that... so 800k upstream is close enough to max to be relatively low SNR.
--
GO LEAFS GO!

TheMG
Premium
join:2007-09-04
Canada
kudos:3
reply to SNR vs ATTN
That's not that bad, I've got between 6-7dB upstream SNR. Upstream profile is 975k and is actually quite stable.


Oinktastic
Let them use fibre

join:2005-08-24
Scarborough
kudos:2
reply to SNR vs ATTN
You're less than a kilometer away from the central office/remote. Chances are, the transmit power has been turned down because it isn't needed, resulting in a low, but stable upstream SNRM.

Those are pretty good stats...


vk2

@10/24.bsnl.in
reply to SNR vs ATTN
SNR
SNR means Signal to Noise Ratio. Simply put divide the Signal value by Noise Value and you get SNR. You need high SNR for a stable connection. In general, a higher signal to noise ratio will result in less errors.

* 6bB. or below = Bad and will experience no line synchronisation and frequent disconnections
* 7dB-10dB. = Fair but does not leave much room for variances in conditions.
* 11dB-20dB. = Good with little or no disconnection problems
* 20dB-28dB. = Excellent
* 29dB. or above = Outstanding

Note that most modems display value as SNR Margin and not pure SNR.

SNR Margin
You can think of SNR margin as the measure of quality of the service; it defines the ability of the service to work error free during noise bursts.

This is a measure of the difference between your current SNR and the SNR that is required to keep a reliable service at your connection speed. If your SNR is very close to the minimum required SNR, you are more likely to suffer intermittent connection faults, or slowdowns. You need a high margin to ensure that bursts of interference don't cause constant disconnections.

With traditional broadband, the higher the SNR Margin, the better. With MaxDSL the faster speeds are only available as a trade-off with what your line can reliably support. The Target SNR Margin is about 6dB. If your broadband is provided through an LLU (Local Loop Unbundled) network, this target SNR Margin may be as high as 12dB.

Line Attenuation
In gerneral, attenuation is the loss of signal over distance. Unfortunately, dB loss is not just dependent on distance. It also depends on cable type and gauge (which can differ over the length of the cable), the number and location other connection points on the cable.

* 20bB. and below = Outstanding
* 20dB-30dB. = Excellent
* 30dB-40dB. = Very Good
* 40dB-50dB. = Good
* 50dB-60dB. = Poor and may experience connectivity issues
* 60dB. and above = Bad and will experience connectivity issues

Line attenuation also affects your speed.

* 75 dB+: Out of range for broadband
* 60-75 dB: max speed up to 512kbps
* 43-60dB: max speed up to 1Mbps
* 0-42dB: speed up to 2Mbps+


Oinktastic
Let them use fibre

join:2005-08-24
Scarborough
kudos:2
Reviews:
·localphone.com
said by vk2 :

Line attenuation also affects your speed.

* 75 dB+: Out of range for broadband
* 60-75 dB: max speed up to 512kbps
* 43-60dB: max speed up to 1Mbps
* 0-42dB: speed up to 2Mbps+
I'm not so sure I quite agree with those numbers. I think they're a bit pessimistic in terms of speed for the given attenuation.

If the line is clear of noise, you can still do 5Mbit with 40dB+ of signal attenuation.


Bicephale

join:2005-09-24
kudos:3
That's a plain obsolete scale!... One can dream of this under ideal conditions:

»/r0/download/1···!%20.GIF

Sunfox

join:2003-12-14
Markham, ON

1 edit
I'm 47db and the modem claims 6.7mbit possible on fast path.


Bicephale

join:2005-09-24
kudos:3
So, would you say the wiring which goes to your home seems "ideal"?


Sunfox

join:2003-12-14
Markham, ON
No, I wouldn't. The trunk line on the street is 50+ years old and paper wrapped, with dozens of known bad pairs (I've been through numerous ones myself). It travels far AWAY from the CO to join up with another old below-ground line that has several splices in it due to road construction accidents and somehow seems to get flooded with water occasionally.

I would say my actual line quality is remarkably good considering everything. I have the best possible pairs going from the street back to the CO, and the line from the street to my house has also been made as perfect as possible. Overall I'm satisfied, however given ideal circumstances I think 47db could do even better.

So those ancient charts claiming "up to 1mbps" are utter crap, and I'm even thinking the so-called ideal charts posted may be a bit conservative.


Bicephale

join:2005-09-24
kudos:3