Wireshark · Ethereal-users: Re: [Ethereal-users] question regarding VoIP

[Scott Lowrey <slowrey@xxxxxxxxxxx>]

No, you're OK.  You can capture the packets.  If you want to measure the latency between two different machines, though, I doubt that you can get your clocks syncronized closely enough...?

What I do is send the media from one network interface to another on the same machine.  That allows me to use a single instance of Ethereal (or two separate instances, followed by a merge) so that clock sync isn't an issue.  (I don't typically use discrete endpoints while testing.)

You should be able to measure jitter without to much of a problem.  Obviously, you'll need to extract the inter-packet arrival deltas and apply some statistical calculations... it would be interesting to automate this.

Janice Lau wrote:

i just want to make sure i didn't misunderstood what you have written..


  

If you're sending actual RTP media streams, you can certainly capture
the packets as they come in.  Analysis of the interpacket timing and
point-to-point delay could probably be done with some (very) careful set up.

But Ethereal is not designed for this.  QoV involves some complex
measurements that go beyond delay and inter-arrival jitter.  Also, the
endpoints you're using probably incorporate jitter buffers that
compensate for some of the packet arrival variations (with latency being
the trade-off).  Ethereal will not be able to account for this.

    

Do you mean that Ethereal cannot be used to capture the RTP media
streams when the packets come in? Or it doen't help when i want to do
the analysis of the interpacket timing and point-to--point delay?

For the moment, my scope of QoV does not include the MOS
measurement...i just want to find out the delay and inter-arrival
jitter from sending end to the receiving end.

Is it Ethereal not able to capture the voice packets at the instant it
arrives the network card..before it goes through the playout buffer ?

thank you for your help.

Janice

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--
Scott Lowrey
Test Engineering Manager
NexTone Communications
Gaithersburg, Maryland USA

1.240.912.1369