MOS Scores

Discussion in 'VOIP' started by Mitch, Dec 3, 2004.

  1. Mitch

    Mitch Guest

    I have a need to calculate MOS Scores for my VoIP traffic. We are
    using Cisco CallManager. I know the codec, jitter, latency, and
    packet loss on each call. Is there any way to take this information
    and calculate a MOS Score?
    Mitch, Dec 3, 2004
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  2. Mitch

    BobS Guest

    I have no idea but your question piqued my interest, so I looked up MOS:

    (Mean Opinion Score) The quality of a digitized voice line. It is a
    subjective measurement that is derived entirely by people listening to the
    calls and scoring the results from 1 to 5, with a 5 meaning that speech
    quality is perfect. The MOS is an average of the numbers for a particular
    codec. Because MOS testing requires carefully prepared and controlled test
    conditions, the best way to get an MOS test done is to have it outsourced.
    BobS, Dec 3, 2004
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  3. Hi Mitch,

    as BobS also found MOS you cannot calculate MOS values. You could
    try to locate a table that has some MOS values in with the matching
    numbers for jitter,loss and delay. I have build an aaplication like
    this some time ago and cam pretty close to actually predicting a sort
    of guestimated MOS value.

    Since than PESQ has been introduced. Read about it at:

    PESQ can be used to measure voice quality by using programs rather
    than test panels.

    Arnold Ligtvoet, Dec 3, 2004
  4. Mitch

    stephen Guest

    Or you could ask your supplier, or search on the cisco web site - they must
    have been asked for this a lot, since it is part of the evaluation often
    used for commercial bids.
    stephen, Dec 4, 2004
  5. This is the trouble with MOS. You cannot state any MOS values untill
    that specific network with all it's users, applications and so on is in
    place. Only after this it is possible to bring in a test team and start
    making calls.

    Of course if you ask any vendor they will happily claim a MOS better or
    around 4 should be possible.

    Arnold Ligtvoet, Dec 4, 2004
  6. Mitch

    Hank Karl Guest

    You can calculate a MOS score based on codec, jitter, latency and
    packet loss, but you need to know the "bursty-ness" of the jitter and
    packet loss.

    For example, if you use G.711 with PLC, and have a 3% loss rate, the
    distribution of errors makes a big difference. One packet lost
    exactly every 33 packets will not noticeably affect the quality of the
    call. But if all the errors are grouped together you will notice a
    significant voice quality degradation (e.g. you may have part of the
    call with no loss, and part of the call has a 20% packet loss rate.)

    Jitter may or may not count, what matters is how it affects the jitter
    buffer. A small amount of jitter may not affect the buffer at all, a
    little more jitter may just cause the jitter buffer to adapt by
    growing larger (increasing the end-to-end delay) while a larger amount
    of jitter may cause the jitter buffer to be flushed (resulting in a
    noticeable impairment). has more
    detailed information. Even more detailed information can be found at
    Hank Karl, Dec 6, 2004
  7. Mitch

    Hank Karl Guest

    Even then, network traffic will change over time, bursts of network
    activity will occur (people watching CNN on the web or downloading big
    files like "Mars Rover" pictures), routing protocols like BGP will
    change the path your call takes in the network (sometimes during a
    call), etc. And if you use a VoIP service provider, or go over the
    Internet, you have to consider all the delays, jitter, loss, and other
    impairments that will cause.

    So you can measure the MOS and say what it was, and monitor the
    network so you can take action when the MOS drops too low. And you
    can predict that the MOS should be about xx with a "normally
    operating" network.
    Hank Karl, Dec 6, 2004
  8. Mitch

    Isaac Guest

    Edgewater networks makes a great device
    that can do MOS scoring and log it to a SYSLOG server if you want.

    Isaac, Dec 17, 2004
  9. Mitch

    Jacques911 Guest


    does the jitter value measured takes into account the jitter buffe
    mechanism that can be very fancy, I am a bit confused, does the valu
    measure typically with a tool comes from info provided in RTP frames
    do the values obtained accurate ? If I use Ethereal for instance !
    Jacques911, Jan 5, 2005
  10. Mitch


    Sep 29, 2008
    Likes Received:
    You need a dedicated tool to analyze the VoIP packets in order to calculate the MOS. One of these tools is the PBXMate from SoliCall. In addition to reporting the MOS it also improves the quality of the call. Another tool is the VQManage which report the MOS on your VoIP network.
    valer77, Sep 29, 2008
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