SNR Margin and Line Attenuation - What do they mean?

[Chinmay]

There have been many posts regarding SNR and Line Attenuation.

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
[/list]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
[/list]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+
[/list]Please comment on this article.
(and if you give me reputation on this, I shall return the favour)
Information contributed by my friend Mr. Prasanna

 

[Chinmay]

Any replies or questions on SNR MARGIN & LINE ATTENUATION ?
I hope above post will solve all misconceptions of ADSL users.
To check ADSL status please enter 192.168.1.1 on your Internet Explorer/firefox/opera/chrome address bar.

For any further clarifications regarding how to increase SNR margin & Line Att, please PM me.
I m at ur service, and if you give me reputation on this, I shall return the favour!🙂

 

[warthog]

thanks for this explanation.susbsh plz sticky this.This is a very important article.again kudos to you:cool2:here is mine dl ulRate (Kbps) 2557 1022 SNR Margin (dB) 21.4 16.0 Attenuation (dB) 15.5 8.0 Output Power (dBm) -12.8 12.4 how can i optimize this?

 

[Chinmay]

Do u suffer from any kind of disconnections?If not then its not needed to do any kind of improvements, Ur line has SNR of 20 which is quite good, also line attenuations r low that means u r very close to exchange, what concerns me is ur output power is in neagtive, can anyone tell me is this happens with all airtel subscribers? I'll post status of mine-ADSL Firmware Version: E.37.5.3Line State: Showtime/DataModulation: ADSL2+Local/Remote Tx Power: 0.63 dB / 2.5 dB Downstream UpstreamSNR Margin 19.5db 10.5dbLine Attenuation 25.5db 21.0dbLoss of Signal 00CRC Errors 00Data Rate 6143 Kbps 519 Kbps kbpsLatency Fast Fast Now u decide, who's lucky?You r d one!:thumbsup:

 

[ganesh177]

Firstly, thanks for the info sharing.

I am using D-Link GLB 502T, and i am unable to find SNR values. This is what my modem status is. Can you help me finding my snr values?

http://img519.imageshack.us/img519/6558/statustv2.jpg

 

[Lokesh]

SNR Margin 11 17 dB Line Attenuation 35 13 dB Data Rate 2048 512 kbps I am using DSL-502T. When mtnl synched my upload speed to 512 kbps, from that time onwards, net has been unstable and SNR margin is very low! earlier it used to be from 20 to 30 dB. please Help me guys. 😢

 

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[Chinmay]

Dear Ganesh,
Here's ur SNR margin status
http://img295.imageshack.us/img295/1976/statustv2dr3.jpg

Dear Tehelka,
How many telephone instruments do u use at ur house?
Remove parallel wiring if any.

 

[ganesh177]

So ,US Margin -14DS Margin - 8 How does it sound ?:huh:

 

[Chinmay]

very poor!BTW ganesh whats ur speedtest results? R u on plans higher than 2mbps or have IPTV at home??

 

[ganesh177]

I am on upto 2 mbps plan. And dont have iptv.

This is the speedtest i just did ...

 

[Chinmay]

U r getting more speeds than what u r supposed to get.U r a lucky guy:thumbsup: Do u suffer from any disconnections/low speeds?

 

[ganesh177]

I used to have disconnection problem, but that was related to my modulation type and now its solved. Slow speed ? I dont think so, i browse normally, and on healthy torrents i allways get the average of 240 KBps and max i have seen is 335 KBps.I hope you are not confusing with the whole concept.😗 😕:redface:

 

[rajusaha]

Thanks for such a nice post and discussion. My stats are as followsUS Margin 6 DS Margin 7 Modulation GDMT LOS Errors 1 DS Line Attenuation 32 US Line Attenuation 16Is my connection okay? Please let know me.Thank you once again.

 

[Chinmay]

Dear rajusaha, as per d info I've provided minimum SNR margin of 10 is needed for a stable connection, or else router reboots very often with ADSL light blinking continuosly.

So try to remove any parallel connections before ur splitter, try to use a single uncut wire from gangbox of ur building/ common gangbox in ur area to ur splitter. If still problem persists, register a complaint. If all d above tricks wont solve ur problem, then 'DSLAM' needs to be checked which can be done by BSNL/MTNL staff.

All d best for ur movement in order to improve SNR!:thumb:

I used to have disconnection problem, but that was related to my modulation type and now its solved. Slow speed ? I dont think so, i browse normally, and on healthy torrents i allways get the average of 240 KBps and max i have seen is 335 KBps.
I hope you are not confusing with the whole concept.😗

😕:redface:
dude SNR margin affects speeds, as in my case I m supposed to get Upload speed of 512 kbps but I m getting half of that.
Many users r concerned with DL speed, no one is interested in good UL speed:evil:

 

[rajusaha]

Dear Chinmay,Thanks for your reply. I have been using an uncut cable from the gearbox of our building to the splitter and there's no parallel connection before the splitter. Will I be able to lodge a complaint on the basis of the SNR Margin? I am facing disconnection problem when I pick up the receiver of the phone to make or receive a phone call. I have made several complaints for that problem, but the BSNL staffs do not pay any attention.Besides, I would like to know the meaning of "DSLAM". How is it checked?