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Regular Contributor
Posts: 408

Re: ADSL SNR and Attenuation

The bogstandard Telkom DSL-2750U modem leaves off the decimal point in the reporting tables.


For instance your downstream SNR margin is 10.1dB and NOT 101 as it shows.


Your downstream attenuation is 32.5dB and NOT 325 as it shows.

Regular Contributor
Posts: 408

Re: ADSL SNR and Attenuation

A confusing term will be SNR margin. This is not SNR, but the headroom if you like, between what SNR you need for a specific speed and the SNR that you currently have.


For instance say your SNR is 45dB


For an 8Mbps speed you need minimum 35dB SNR.


Your SNR margin is therefore 10dB


6dB is the absolute minimum but >10dB is better :-)

Posts: 196

Re: ADSL SNR and Attenuation


@AW here is some interesting reading material. Signal-to-noise ratio (SNR) is another figure you can check in the ADSL stats of your home / corporate router (show dsl interface atm(something) for Cisco). This number is also expressed in dBs and describes the relation between your speaking strength (signal) and the street’s noise strength (noise). The higher this number is,  the better, as your speaking voice outperforms the noise.


10dB and below is bad

11db – 20dB is OK

20dB – 28dB is excellent

29dB  and above is outstanding


Some routers instead (or additionally) of the signal-to-noise ratio (SNR) figure are displaying thesignal-to-noise margin (SNR Margin) which is the difference between the actual SNR and theSNR required to sync at a specific “speed”:


actual SNR = 44dB

SNR to sync at 8Mb = 35dB

SNR MARGIN = 44-35 = 9dB


A higher number is better and the numbers bellow 6dB may cause problems. It is easier to understand if your line is in an acceptable SNR level, by using the margin figure, because you don’t need to know the SNR dB value you should have, for the line to perform at a specific speed.You just need to  know that above 6 dBs you are doing just fine.


You just need to know that above 6 dBs you are doing just fine.



As you are probably thinking, noise is a subject of change according to various sources. On-peak hours, the noise increases as your provider’s DSLAM becomes crowded (people talking in the street) and the SNR margin gets worse. Florescent light sources, telephone devices installed on your phone line, your mom’s cake-blender, all these may decrease the SNR margin. Luckily, there are some things you can do to improve the SNR margin:


Buy a router that is good enough to manage low SNR margin figuresInstall a good quality ADSL filter to your router and to each phone device installed on the same lineTry to change the ADSL provider, as some providers are less crowded than others. You can check out with your neighbors to see how they perform with their ISP.Change the faceplate of your line with a better one and check that the cable terminates properly to it.Change the in-building cabling. Poor, low quality telephone cabling can introduce noise to the line. You can check if you have a problem with the in-building cabling, just by placing the router (temporarily) directly to the intrusion point (probably at the basement) and by checking the router’s statistics.


The verdict


You need to consider both attenuation and SNR margin figures to determine the quality of your ADSL line. The SNR margin figure should be above 6dB and the attenuation figure  must meet some standards.


SpeedAttenuation2Mbbelow 69dB4Mbbelow 56dB8Mbbelow 41dB16Mbbelow 25dB21Mbbelow 20dB


Note, that the router will probably display statistics for the upstream and the downstream traffic. These statisctics will be different, as upstream/downstream speed is different. Also consider reducing the “purchased speed”, in a case where you have a SNR margin lower than 6dB which may cause frequent disconnections. That may improve the SNR margin thus line stability.


Finally, there are some error statistics that a router may display. The most important are LOSES,CRC and HEC errors. The CRC is an error correction code that is used to detect and retransmit corrupted packets. The HEC is a form of a CRC on the header of an ATM cell. If these errors are high, within a period of time, it will slow or even disconnect the line. The LOSES refer to a loss of signal which can indicate a problem with noise, in the case where the number is high.



Posts: 4

Re: ADSL SNR and Attenuation

Confussed, Attenuation should be like 2 digits. 

Not in the hundreds. Mine is 43 for example.

Says im  3.1 km away from exchange.

When i called to check though they tiold me i am 2.8 km away.

Anyways i really wish they can sort out my line because my SNR is only 6.1 and it drops to 4.3 odd at times.

the current data rate is 10nnnn and max detected is 11nnn .

I get equivalent to 4-5 meg speed BUT poor speed because i downloaded a test ISO of Ubuntu on a local site and it is downloading at 35kb/s which is pathetic. I tried multithreading downoad and it pushes it to 160kb/s  Still shocking.

I have tested different times and also 2 ISPS.

My speed test gets to 8.5 odd then it drops gradually to 4.8-5.2 so this is crap. It seems good as it is 4-6 megs... BUT it is not good because my downloads are useless. 13 hours to download a 1.3 GIG iso.

I am told 10 megs is supported to my home in my area. 

I know my previous location i got 6 megs synched and good speeds and i was more than 4 km from the exchange.

Here i am only 2.8 according to Telkom and my theoretical check says 3.1



Established Member
Posts: 6

Re: ADSL SNR and Attenuation



Seems that the new Telkom system us causing more fuss than its worth.

It regulates the sync speed on ADSL depending on the line errors / SNR and Attenuation.


My line was fixed 2 days ago... swopped ports. 


It is a 10mb port and only syncs at 6.4mb.

The line is running Attenuation 20+ and SNR 32.5.


I know once the sync increases to 10mb then it will surely reduce the Attenuation and SNR will decrease.


How do i get the guys to stop messing with the sync and leave it on 10mb and make me a very camper...

Moderator Moderator
Posts: 206

Re: ADSL SNR and Attenuation

Hi @Otternoster It might be best for you to contact @HelloTelkom on Twitter or @TelkomZA on Facebook for your request.

Established Member
Posts: 6

Re: ADSL SNR and Attenuation

Hi there. 


I had contacted the Call Centre and the consultant was helpful to resolve my issue.


The low sync speed (less than what i am paying for) 6mb was due to the automated system checking for

errors generated on the line. So if I am on 10mb i have more errors.


The consultant was able to get the Supervisor to set my sync to static 10mb.


Few more errors than usual, but much better latency and speed.


My issue is resolved! Many Thanks to the friendly consultant!

Posts: 8

Re: ADSL SNR and Attenuation

How do i use telnet to get those stats???

Frequent Contributor
Posts: 268

Re: ADSL SNR and Attenuation

hi @Liaquate not sure how to telnet for those stats but, if you login to your router interface and access the status scrren, you'll see the line states under the WAN connection.

Established Member
Posts: 7

Re: ADSL SNR and Attenuation

[ Edited ]

For ADSL distance matters.

How far are you away from the exchage?

What is the length of the copper wire?


Please click here ...



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