Few questions about SNR margin

Discussion in 'Broadband' started by kimiraikkonen, Jun 18, 2007.

  1. Hi there,
    Sometimes router is opened or re-booted it begins with 30.3db SNR
    margin which is great. But somedays it's opened it begins with 10.5db
    SNR margin. And with the router stays opened after few days passes,
    SNR decreases about low to 10db from 30.3db.

    I want to ask:
    1-Why does SNR margin value reduce/decrease after a few days with
    router stays open steady without ANY reboot or turn off?
    2-Is low SNR effect performance? (downloading speed)

    Thanks in advance.
    kimiraikkonen, Jun 18, 2007
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  2. kimiraikkonen

    James Egan Guest

    The SNR margin will go up and down at different times of day depending
    on line noise. Usually there is more line noise in the evening so the
    margin will be lower then.

    The initial download speed negotiated will be based on whatever the
    SNR is at the time, Thereafter that connection will be sustained at
    that speed until line noise causes the SNR margin to drop below an
    acceptable threshold (usually about 4) at which time the connection
    will drop and have to be re-negotiated.

    James Egan, Jun 18, 2007
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  3. Is it normal decreasing SNR margin value day to day with no router
    turn off?
    kimiraikkonen, Jun 18, 2007
  4. kimiraikkonen

    Graham Guest

    That's the idea, the speed will increase and the SNR margin will decrease to
    a point where communications reliability begins to fall, and there it will
    stop. I my experience this usually happens at an SNR mrgin of about 7dB.
    If your line is intermittently noisy the speed will stay low and the SNR
    margin remain rather higher, as being the best compromise.

    -- Graham J
    Graham, Jun 18, 2007
  5. kimiraikkonen

    James Egan Guest

    In a normal situation it fluctuates up and down. It shouldn't just
    keep going down.

    You shouldn't look at the SNR margin in isolation. Does it keep going
    down while the download speed stays the same?

    James Egan, Jun 18, 2007
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