SNR Margin and Line Attenuation - What do they mean?

Discussion in 'Broadband How to' started by just4kix, Sep 8, 2008.

  1. just4kix

    just4kix Guardian Angel Staff Member

    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

    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+

    Please comment on this article.

    (and if you give me reputation on this, I shall return the favour)
    Parminder and Ishita_Arora like this.
  2. gurusam

    gurusam New Member

    Thanks just4kix it was good to about it...can u also state the difference b/w adsl+ and g.dmt
  3. Chinmay

    Chinmay New Member

    Lessons from corporates! Given by management guru just4kix!:D
    ^^Thanks for d info! I've added to ur reputation, now its ur turn!
  4. just4kix

    just4kix Guardian Angel Staff Member

    Basically it is the technology difference.

    G.DMT is ADSL1 whereas ADSL2+ is, well, ADSL2+.

    Refer these articles: G.DMT and ADSL2+
  5. SmoothVibes

    SmoothVibes Super Moderator Staff Member

    added repo

    and thanks for such a nice and informative post

    you are rocking just4kix :rockon:
  6. gurusam

    gurusam New Member

    I too added repo for just4kix for this post but the repo power of just4kix has not increased??
  7. just4kix

    just4kix Guardian Angel Staff Member

    Each repo gives a point. I have 36 points so far. I do not know how Rep Power is calculated.

    Post something informative and I promise that I will return your favours. :)
  8. parshanth

    parshanth New Member

    just4kix u r kix smart buddy i think u r the favourite here .................. Cheers buddy..........................
  9. Spectre

    Spectre New Member

    If you get problems regarding those shits then how do we fix it?

    Nice article ,by the way.

    best regards,
    Spectre
  10. DZire

    DZire New Member

    J4X you are tempting me to one more Modem / Router crash !!!
    I'll surely be up on something Tonight !!!
  11. just4kix

    just4kix Guardian Angel Staff Member

  12. itsmemad

    itsmemad Alligator

    How could I miss this article(and your offer:D) for so many days... I played with my router settings to increase SNR... but once achieving that, never cared to research about it... Thanx for the compiled information... U r wonderful...

    Reps for u...:)

    lol... system is asking me to spread some reps 1st... so its due...
    Last edited: Sep 22, 2008
  13. DZire

    DZire New Member

    You are really generous on Reps Mad.... we must admit !! (Rep from my side to you. Like the Way !!)

    What exactly you played with your router to increase SNR ?
  14. just4kix

    just4kix Guardian Angel Staff Member

    Assuming that your SNR is low, you can do the following to increase your SNR are the following:

    a) Identify where the telephone wire runs into your home
    b) Trace it all the way back to the junction box
    c) Check whether the cable is in good shape - not too much weathered, etc.
    d) At the junction box, check the connection. Is it corroded, oxidised? If yes, note it down.

    Make a written complaint in duplicate to the exchange about frequent disconnections (even if you are not suffering that). Tell them the wire/connection is weathered/corroded/oxidised.

    A promise of Rs.100 baksheesh to the linesman will work wonders.

    p/s. I have assumed that the splitter is correctly splitting the voice and data circuits at the point of entry.
  15. DZire

    DZire New Member

    Thx J4X...
    I'll check. I am sure there is corrosion in line but not much exposure to weather..
    The J.Box has a chaos like condition .... Rs. 200/- chai paani has already worked wonders !!
  16. Rameshjeee

    Rameshjeee Good to be Back

    From the junction box,the telephone wire directly runs to my house. Its a new wire,I got it changed recently.
    I dont have any paralled connection.
    But still the SNR value is around 7~8.
    Attn Value is around 40~45.
    I do experience frequent disconnection for 10 sec...
    When the connection is there...I get the expected speed & I dont face any issues.
  17. just4kix

    just4kix Guardian Angel Staff Member

    Then there is a problem with the port at the exchange. Make a written complaint in duplicate. Get the duplicate signed by the DE of the circle.
  18. Rameshjeee

    Rameshjeee Good to be Back

    Ok..THanks....will do that....
  19. DZire

    DZire New Member

    Hey you found what port your BSNL guy was talking about ??? Is this the same you had problem with ??
  20. just4kix

    just4kix Guardian Angel Staff Member

    I have no idea about what port? After repeated queries they would not clarify. They said that the BB connection runs to the exchange and to the port of the DSLAM. Probably something similar like an ethernet port.

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