C837 High value 'BER valid sec' (2nd post)

Discussion in 'Cisco' started by Tom Lauwereins, Apr 28, 2005.

  1. On one of our 837's we have a very high value for "BER Valid Sec"
    What does this mean?
    Any ideas?

    rt-*****-a036#sh dsl int atm 0
    ATU-R (DS) ATU-C (US)
    Modem Status: Showtime (DMTDSL_SHOWTIME)
    DSL Mode: ANSI T1.413
    ANSI Issue/rev: 2/1 2/1
    Vendor ID: 0x0022 0x0022
    Capacity Used: 23% 47%
    Noise Margin: 23.5 dB 23.0 dB
    Output Power: 20.0 dBm 12.0 dBm
    Attenuation: 32.5 dB 14.0 dB
    Defect Status: None None
    Last Fail Code: None
    Selftest Result: 0x49
    Subfunction: 0x15
    Interrupts: 666 (1 spurious)
    Activations: 1
    Init FW: embedded
    Operartion FW: embedded
    SW Version: 3.8129
    FW Version: 0x1A04

    Interleave Fast Interleave Fast
    Speed (kbps): 0 1120 0 384
    Reed-Solomon EC: 0 0 0 0
    CRC Errors: 0 0 0 0
    Header Errors: 0 0 0 0
    Bit Errors: 0 0
    BER Valid sec: 0 *13537*
    BER Invalid sec: 0 0
    Tom Lauwereins, Apr 28, 2005
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  2. This is - in my experience - normal beheavior.

    I have never seen a formal cisco explanation of sh dsl int atm0 output,
    but my interpretation is is that the bit error rate measurements were
    valid for that amount of time.

    However, managing a lot of these c8xx routers, i also have lots of these
    were this timer stays at 0...

    What is more important are the dB values and the "percentage used",
    together with the error counters. These give much better insights on
    the adsl line quality and stability.
    Joop van der Velden, Apr 28, 2005
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  3. Thanks for your answer,

    I have about 150 827 and 837 routers and most of them have a value 0 for
    the "BER valid sec".

    But it looks like on those where the value is high we got sometimes
    problems with the connection, the ATM line is dropped without any reason.

    Very strange.

    Did you find other sites with some explanation on the sh dsl int atm 0

    Kind Regards
    Tom Lauwereins, Apr 29, 2005
  4. Tom Lauwereins

    RobO Guest

    RobO, Apr 29, 2005
  5. A noise margin can never be too high, only too low.

    This is the way i interpret these numbers:

    Capacity used: lower = better (for the same speed)
    Noise margin: higher = better
    Attentuation: Lower = better
    Joop van der Velden, Apr 29, 2005
  6. Tom Lauwereins

    Peter Guest

    Hi Joop,
    Are you sure about it never being too high?

    When my ADSL was first installed about 3 years ago, my Noise Margin
    reading would bounce between 2db and 5db. Whenever it dropped below
    about 4db, I suffered from frequent retrains of the ATM connection (10
    - 20+ per day!!!). I contacted my ISP and they agreed, the reading was
    a bit low, so they "tweaked" the DSLAM end and it eventually rose to
    between 7 - 11db and has hovered around those values ever since. As
    long as it was within those values the ATM link has been VERY stable
    for me, for months at a time...

    About 9 months after the level change, I suffered some retrains again
    (about 3-4 per day), and when I checked I found that the Noise Margin
    was reading 14-15db. Anything over about 13db would eventually result
    in ATM retrains, anything less was stable for me. However this
    situation only lasted for a few days and then it returned to "normal"
    (about 8db).

    A tech I know subsequently explained this to me that raising my Noise
    Margin meant my transmit level at the DSLAM was higher, which can
    adversely affected other ADSL services into the same DSLAM via Near
    End Cross-talk, due to the density of copper cable into the DSLAM
    premises. The reason for my issue when the reading was higher was
    because an adjacent user had had their line level increased too much,
    and that it was adversely affecting my line, so there seems to be some
    fine tuning required to establish "normal" use patterns for this
    reading. As explained to me, they only like increasing the users Noise
    Margin to just enough to provide stable service, without affecting
    adjacent users on the same DSLAM.

    Peter, Apr 30, 2005
  7. Well, we are both correct here ;-)

    As seen from the end user, the noise margin can never be too high. The
    higher it is, the better the signal-to-noise distance is and the smaller
    the chance is on errors and unstable beheavior, e.g. depending on
    external factors.

    As seen from the adsl provider, there is an optimal signal level with a
    good compromise between crosstalk and error rate. He has to cope with
    the effects of more dsl signals in the wire bundles. So he does not
    like unnessecary high signal levels and he tweaks the signal levels so
    that they are 'just good enough'.
    Joop van der Velden, Apr 30, 2005
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