Jitter representation and statistics

Discussion in 'VOIP' started by Rocco, Feb 17, 2006.

  1. Rocco

    Rocco Guest

    Hi all.
    I need to graphically represent jitter effects over a voip RTP stream
    (ethereal dump)
    So I thought of histogram of the interarrival times.
    Shall I calculate these interarrival times considering consecutive
    "received" packets or the arrival times of consecutive "sent" packets (by
    considering sequence numbers, so negative values of the interarrival delay
    are possible in the case of out of order received packets).
    All the interarrival histograms I see on the net starts from 0 so I have two
    possibilities:
    -I must ignore sequence number (but this way the calculations are somehow
    wrong in case of out of orders)
    -I must calculate interarrival times of consecutive sent packets but then
    discarding negative values.
    As you can see, I'm not considering the RTP/RTCP moving average formula of
    jitter.
    That interarrival histogram (almost normal or bi-exponential, centered on
    the sending timing, but with lots of elements near the origin due to back to
    back received packets and a long tail of very late packets) approximates a
    probability density function (it should be normalized). What can I say about
    % of packet discards, given a fixed playout delay (a fixed jitter buffer).
    If I had the graph of one way delay I could say that the area to the right
    of a certain value is the probability that a packet arrives too late (so i
    get the % of discards) but I have only this interarrival distribution. What
    simplifications/approximations can led us to some conclusion?

    I hope someone can help

    Thanks in advance

    Rocco
     
    Rocco, Feb 17, 2006
    #1
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