Re: Issue with RTT values in Wireshark

[Martin Mathieson <martin.r.mathieson () googlemail com>]

Hi Nitin,

Is this the RTCP network roundtrip propagation delay?

If it is, then the calculated time is between the point of capture and one
of the endpoints. You must be capturing fairly close to one of the
endpoints?
If you look at the generated fields attached to the frame with the report,
it has a detailed explanation of where the inputs came from and how the
calculation was done (also see RFC 3550).

When I first added this calculation, lots of RTCP stacks weren't filling
the relevant fields in correctly, but your numbers sound very plausible.
 If you want to send a small capture I can explain how the calculation was
done.

I was interested to see recently that for Voice over LTE (VoLTE)
implementers and being told not to fill the relevant fields in that would
allow this calculation, but instead to fill them in with zeros....

Martin

On Fri, Apr 6, 2012 at 6:09 AM, NITIN GOYAL <nitinkumgoyal () gmail com> wrote:

> Hi All
>
> Can anybody help me out in the below query related to RTT calculation??
>
> Thanks
> Nitin
>
>
> On Wed, Apr 4, 2012 at 1:16 PM, NITIN GOYAL <nitinkumgoyal () gmail com>wrote:
>
> > Hi All
> >
> > I have an issue with the Wireshark for calcuating the RTT values. For few
> > pcaps, I have a higher value of RTT on one side or direction but the lower
> > value of RTT on other side.
> >  I have taken the trace in the middle of the connections and in one
> > direction the RTT calculated by Wireshark is around 40 ms but on what other
> > direction its 1.5 ms.
> >
> > But i think ideally both the sides should have the same values as its
> > round trip time(like a loop).
> >
> > The trace is RTP over UDP over a VoIP tool.
> >
> > Now, when i use some other licensed tool based on libpacp used by
> > Wireshark as well, the values for both the sides is almost same with the
> > same pcap file.
> >
> > So, i am not sure if Wireshark is calculating the wrong RTT values or the
> > interpreation is differnet by other tools as how to calcuate the RTT
> > vlaues??
> >
> > Any idea about this??
> >
> > Regards
> > Nitin
>
>
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