DataOne - Significance of SNR and Attenuation

AtoZ on DataOne


While going through some of the posts and queries I've got in my mail, I came to the conclusio that most of the common people who are using DataOne or any other ADSL broadband like VSL, doesn't the know the terms like SNR or Attenuation and their significance in the overall quality of the broadband service.

Both SNR and Attenuation has a significant part to play with the QOS( Quality of Service ), for common man the outcome will be the browsing speed and overall performance.


First I'd like to explain the term SNR. The full form of SNR is Signal to Noise Ratio. Technically saying, it is nothing but the ratio of usable data signals in the line. 'SIGNAL' can be explained as the data which is transmotted from the exchange. 'NOISE' can be termed as any unwanted disturbance that may interfere the signal in its path.

eg : If the usable data signal in your line is say 40, and the noise is 2 then your SNR ratio will be 40/2 = 20. And 'dB' or decibell is the unit for SNR, like kilogram is for weight. SNR will have a significant role to play, if you have a high bandwidtth line say 8 Mbps.

According to DataOne guidelines, for satisfactory performance your SNR ratio must be above 12dB. At worst conditions, depending on the signal extracting capability of the modem, a minimum of 7-8dB is required for a stable connection. A good SNR value can be told like, one above 25dB.

Factors affecting SNR ratio may be a lot. For your information, users has nothing to do with the Signal part in SNR ratio. The only thing that can be controlled from user side is the NOISE part. The thing is purely mathematical. In the above example if your noise is decreased to 1dB from the said 2dB, your SNR ratio will go up to 40dB which will give you a big quality in service and maximum speed attainable.

To decrease noise in the telephone line, first look for any joints in the line. There may be aconsiderable noise generation in the joints of the line. Another considerable thing is the quality of the pair cable used for transmission. If youhave a completely underground cable, the line will be less vulnerable to noise generation. Another important player in noise generation will be your electrical equipments, such as a cordless phone or even fluorescent lamps with electrnic chokes.

If you have a bad SNR ratio say something like 5 dB, just try checking the SNR ratio after switching off the main supply line in your house. Am not saying that you must browse on UPS always, but to just check the figure.

Attenuation :

Attenuation is nothing but the loss in signal while traversing from the exchange to your house. A low attenuation figure will be the base for a good bandwidth line. As the distance from exchange to your house increase, the attenuation will also increase at a common rate of around 13-14dB per km. This is the technical reason behind BSNL insisting the connection to be given within around 4kms of the exchange. Beyond that there will be a considerable loss in signal that, the bandwidth available will be tooo less,(speed).

In a nutshell, for good browsing experience in any ADSL connection with 2Mbps bandwidth, I am giving you a rough figure.

SNR ( both upstream and downstream ) - Above 16dB

Attenation - Less than 50dB.

If any of these parameters are less in your connection, contact your exchange JTO for help.

Guide to minimise noise in the line :

Revert back for any queries.


Comments 10 comments

Rajesh 8 years ago

Really useful stuff, thanks buddy.

Abhishek 6 years ago

Thanks !! Was very helpful :-)

chandru 5 years ago


chandru 5 years ago

what is the highest SNR value..?

chandru 5 years ago

morning 8:00 to evening 5:30 the connection did't disconnect...after 5:30 connection frequently disconnects...what is the reason...?

NOOR 5 years ago


Prachar 5 years ago

Do you really say these guys help you, have most knowledgeable staff around here, who just switch off their mobiles even.

suni 5 years ago

cool buddy...i just read u r article...

dk 4 years ago

use shannon capacity formula to find out speed

rony 2 years ago

My DSL lamp is not at all glowing. I have checked all the joints which is there in my building but could not help. My exchange office is located less than 1km from my house, so no attenuation issues. The line man tells that its a problem with my dataone telephone device, but my tel is working prefectly without any whitenoise or crosstalks. Plz help!!

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