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Thread: What should my "Noise Margin" and "Line Attenuation" be?

  1. #1

    Default What should my "Noise Margin" and "Line Attenuation" be?

    Recently I've been having plenty of issues with my ADSL line (dropping multiple times per day, often taking between 20 minutes and 3 hours before it will reconnect). Had the Telkom technicians out 7 times and they seem incapable of fixing it.

    Now, the Line Attenuation Downstream is 57.0db and upstream 31.5db and the Noise Margin Downstream 10.4db and upstream 6.0db.

    What are acceptable boundaries for these parameters?


  2. #2


    Line Attenuation.

    Line attention is in relation to the "loop loss" on your line.
    The further you are away from the exchange the higher your attenuation figure will be as the signal loss increases.
    The lower your attenuation figure the more chance you have of getting the faster speeds.

    SNR (Signal to Noise Ratio).

    The SNR margin can only be measured from your own property and therefore to be measured correctly may need an engineer visit to check this figure from the BT test socket behind your master phone socket.Your SNR figure can fluctuate on a day to day basis and may vary depending upon local equipment, conditions and interference.
    An upgrade in speed often causes the SNR to decrease by up to 5 dB.The higher your SNR figure then the better your line quality and therefore a higher chance of getting faster speeds.

    Line Length.

    Ideally your line length should be below 3.5km from the exchange to get a 2Mb connection.
    At the present time the general public has no way of checking themselves this figure.
    However, you may be able to get an indication by using Sams checker.

    Downstream Attenuation

    0-43 dB - 2Mbps
    43-60 dB - 1Mbps
    > 60 dB - 512kbps

    Downstream SNR

    Should be at least 10 dB to get adsl - ideally above 12dB.
    Anything less than this will see frequent disconnections and other problems.

  3. #3
    Join Date
    Apr 2005
    a paper bag in a septic tank


    Here is some info I got from some other forum a little while back. I can't remember where I cut it from but it gives a little more info about SNR than tibby.dude's response.

    Noise Margin (AKA Signal to Noise Margin or Signal to Noise Ratio)
    Relative strength of the DSL signal to Noise ratio. The higher the number the better for this measurement. In some instances interleaving can help raise the noise margin to an acceptable level.

    6dB or below is bad and will experience no synch or intermittent synch problems
    7dB-10dB is fair but does not leave much room for variances in conditions
    11dB-20dB is good with little or no synch problems* (but see note below)
    20dB-28dB is excellent
    29dB or above is outstanding

    * Note that there may be short term bursts of noise that may drop the margin, but due to the sampling time of the management utility in your modem, will not show up in the figures.

    Line Attenuation
    Measure of how much the signal has degraded between the DSLAM and the modem. This is largely a function of the distance from the exchange. The lower the dB the better for this measurement.

    20dB and below is outstanding
    20dB-30dB is excellent
    30dB-40dB is very good
    40dB-50dB is good
    50dB-60dB is poor and may experience connectivity issues
    60dB or above is bad and will experience connectivity issues

    DSL Rate ***/tx/rx/Rate
    The actual service data rate that your ISP has provisioned.

    Attainable Line Rate
    This is the maximum rate at which your modem can connect to the DSLAM if there was no service provisioning limiting the bandwidth. The higher the number the better.

    Occupancy is the percentage of line capacity used. Each DSL line is capable of a certain maximum speed or "capacity" dependant on line distance and other varying factors. The occupancy is an expression of your current sync rate setting over your maximum capacity. There are occupancy rates for both upload and download. The lower the figure, the better. Because of error correction and other factors in the DSL protocols, a margin is required so that a connection can be maintained under varying line conditions. If the occupancy approaches 100%, any interference can cause the ADSL sync to be lost. A useful measurement to monitor when sync problems occur. [AFAIK the billion SNMP utility does not give a direct measurement of occupancy :-( ]

  4. #4


    Where can I check these dB values?

  5. #5



    You can normally find it on your routers config (GUI) page or telnet sessions.
    What kind of router do you have?

  6. #6


    I've got a Billion BiPAC 7202GR2A.. Can't seem to find it on my GUI config page.. Maybe i'm looking in the wrong place?

  7. #7

    Default Telnet for the 7202GR2

    If you open up a telnet(in command prompt) session on the router and type in the following command: ( wan adsl linedatan ) This should bring up the line attenuation and SNR margin.

  8. #8
    Senior Member
    Join Date
    Apr 2004
    Pretoria, South Africa.


    On the Billion BiPAC 7202GR2 you can find these line parameters by going to "Configuration | WAN | ADSL".

  9. #9
    Super Grandmaster Gnome's Avatar
    Join Date
    Sep 2005
    Cape Town


    I had 1 question regarding the Noise Margin and Line Attenuation:

    My Noise Margin: 40.4dB
    Attenuation: 20.3dB

    Yet I still get errors on both Downstream & Upstream! I have a Telkom modem (Whoopi) but it reports Loss of Signal(usually 3 errors) as well as Errored Seconds(3 or so also). The Downstream is usually low 2 or 3 errors for 1 day of uptime but the Upstream is usually some figure like 117 Errored Seconds and 3 Loss of signal.
    EDIT: Oh yeah I also have about 90 CRC errors on Upstream

    What the hell is up with that? When I moved in the guy said the port was damaged(Telkom Tech, nice guy really) and they had to repair it, could the modem be reporting wrong information or is the port/DSLAM the problem? Btw. it's a marconi Mini-DSLAM...

  10. #10


    DSL 384

    Elaspsed Time: 11 days 6 hours 15 minutes 8 seconds

    Downstream Upstream

    SNR Margin 26.5 16.0 dB
    Line Attenuation 45.4 27.0 dB
    Errored Seconds 40 2
    Loss of Signal 0 0
    Loss of Frame 0 0
    CRC Errors 70 2
    Data Rate 512 256 kbps
    Latency FAST FAST

  11. #11


    Quote Originally Posted by JAS
    On the Billion BiPAC 7202GR2 you can find these line parameters by going to "Configuration | WAN | ADSL".
    ADSL Mode Annex A
    Modulator ADSL Multimode
    DSP FirmwareVersion DMT FwVer:, HwVer:T14F7_0.0
    DMT Status Up
    Operational Mode ADSL G.Dmt
    Upstream 384 kbps
    Downstream 640 kbps

    That's all I have. It's been like that for the past 2 firmware upgrade's aswell.

  12. #12


    Quote Originally Posted by Snormossel
    If you open up a telnet(in command prompt) session on the router and type in the following command: ( wan adsl linedatan ) This should bring up the line attenuation and SNR margin.
    Uh, how do i open up a telnet 'on the router' ??

  13. #13


    a little bit of "intellectual" masturbation (from my readings, studying applied physics):

    "attenuation" can be compared to absorbtion, or filtering out of an incoming signal.

    The higher the SNR or signal to noise ratio is, the better the end-product, be it an image on a television, information, or sound, as "noise", or useless data is never desirable. It's a ratio or value used extensively in medical imaging. I suppose in telecommunications it might be affected by things like line length, age, distance from exchange, though I could be talking ****.

    none of which probably helps you.

  14. #14

    Default Telnet for the 7202GR2

    Go to the dos prompt and type " telnet " or whatever your routers IP is. Next you will be asked for your username and password.
    Type in the following command " wan adsl linedatan " and this will give you ur SNR margin and attenuation......

  15. #15


    down up
    Connection Speed 512 kbps 256 kbps
    Line Attenuation 40 db 12.5 db
    Noise Margin 16 db 13 db

    not a single problem (using Netgear DG834).
    change is inevitable...

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