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Re: [Linphone-developers] help in unit of RTT in RTCP parse

From: julien thai
Subject: Re: [Linphone-developers] help in unit of RTT in RTCP parse
Date: Thu, 30 Jun 2005 11:11:46 +0200

Hi Nicola,

Thank for your explanation.
Actually, i also think that the unit of RTT is in seconds from
your algorithm.
But when i made a test between two softphone via Proxy.
I heard very well the voice, but RTT was about > 3000 ( if it's in
seconds, i can't imagine) so i asked a question.
For RFC 1889 and RFC 3550, for RFC 3550, page 33, it recommend that
unit of DLSR is in 1/ 65536 s. But it don't recommend the unit of LSR, can
you show me where they indicate in RFC? Thank you so much.

2005/6/28, Nicola Baldo <address@hidden>:
julien thai wrote:
> I read rtcpparse, in function report_block_parse,
> you found that you calcule RTT ( actually, i spent one day to understand
> your algorithm, it's great )

The algorithm is actually defined within RFC 1889, it's a part of the
RTP standard. If you look on the above mentioned RFC, on page 28,
there's a pretty straightforward explanation on how it works.

> I think unit of RTT you calculed is microsecond.
> Can you confirme it?

Well, referring to the file rtcpparse.c, the 'delay_snc_last_sr' and
'lsr' values are in units of 1/65536 seconds (that's the specification
in the RFC for the LSR and DLSR fields), the 'rcv_time' variable is also
calculated in the same units. So the value of the 'rtt' variable, after
the division by 65536, is in seconds.



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