[Ethereal-users] RE: rtp statistics--how is delay calculated?

[Miha Jemec <m.jemec@xxxxxxxxxxx>]

Hi!

Answering the above question (I forgot there is also ethereal-users not
only ethereal-dev, that is why it took so long):

about delay and jitter calculation in rtp_analysis.c (or before in
tap_rtp.c).

delay - this is delay between two consecutive packets (this is the only
information you have from a captured stream of RTP packets because in
RTP header you don't get any absolute time information). Note that there
in no average delay calculation in current version, only max delay is
stored and displayed at the bottom (where delay between frames with
silence detecion enabled (MARKER bit set) is ignored in this
calculation).

jitter- is calculated as for RCTP - RFC 1889
J = J + ( | D(i-1, i) | - J) / 16
where J is jitter and D is delay between two frames

Regards, Miha

>I found a post on this in the archives, but no one answered.  So …

>The new RTP statistics tool (tools > statistics > rtp analysis) is
>great, and I especially like the ability to save the data in csv
>format.  I can then compute average delay, plot histograms of jitter,
>lost packet data, etc.

>However, I’m trying to document the quality of our h.323 traffic across
>the WAN and I’m getting strange results.  The average delay for a
>connection between 2 units on the same switch is about 59 msec.  When I
>do the same measurement and computation for 2 units connected across
>the WAN, the average delay is still 59 msec.  This can’t be correct. 
>Can anyone tell me how delay and jitter are calculated in Ethereal?

>Thanks

>John