[David Grau Serra <dgs@xxxxxxxxxx>]

Hi,

> > The softphone is X-Lite.
And now I show you one capture:

Real-time Transport Control Protocol (Sender Report)
   Stream setup by SDP (frame 32)
       Setup frame: 32
       Setup Method: SDP
   10.. .... = Version: RFC 1889 Version (2)
   ..0. .... = Padding: False
   ...0 0001 = Reception report count: 1
   Packet type: Sender Report (200)
   Length: 12
   Sender SSRC: 2307084394
   Timestamp, MSW: 3351350040
   Timestamp, LSW: 2280627634
   MSW and LSW as NTP timestamp: Feb 24, 2036 17:42:56,0000 UTC
   RTP timestamp: 1509280
   Sender's packet count: 5291
   Sender's octet count: 846560
   Source 1
       Identifier: 2307084394
       SSRC contents
           Fraction lost: 0 / 256
           Cumulative number of packets lost: 0
       Extended highest sequence number received: 346756267
           Sequence number cycles count: 5291
           Highest sequence number received: 5291
       Interarrival jitter: 0
       Last SR timestamp: 2333640687
       Delay since last SR timestamp: 1
Real-time Transport Control Protocol (Receiver Report)
   Stream setup by SDP (frame 32)
       Setup frame: 32
       Setup Method: SDP
   10.. .... = Version: RFC 1889 Version (2)
   ..0. .... = Padding: False
   ...0 0001 = Reception report count: 1
   Packet type: Receiver Report (201)
   Length: 7
   Sender SSRC: 2307084394
   Source 1
       Identifier: 428529494
       SSRC contents
           Fraction lost: 0 / 256
           Cumulative number of packets lost: 50
       Extended highest sequence number received: 65535
           Sequence number cycles count: 0
           Highest sequence number received: 65535
       Interarrival jitter: 7787
       Last SR timestamp: 2333640687
       Delay since last SR timestamp: 1


> > I know how can I calculate jitter and the packet loss rate.
> >
> > My problem now is how can I calculate delay (round trip delay).
> > I don't understand why the "Delay since last SR timestamp" is always 1.
> > I don't know how it works the "MSW" and "LSW" (Timestamp).
> These fields and the way the calculation should be done, is described 
> in RFC 3550, section 6.4.1.

I have read but I am still confuse, I will read again.
> Ethereal already does this calculation for you (if the preference is 
> turned on).  There have been fixes made to this calculation, the last 
> of which I believe was made after the last (0.10.14) release.

I am using 0.10.14, but I use tethreal command line.

> DLSR is defined as:
>
>      "The delay, expressed in units of 1/65536 seconds, between
>      receiving the last SR packet from source SSRC_n and sending this
>      reception report block.  If no SR packet has been received yet
>      from SSRC_n, the DLSR field is set to zero."
>
>
>
> If the DLSR is always 1, that indicates that either:
> - the RTCP stack isn't filling the value in properly, OR
> - it really is replying almost instantly after receiving a report from 
> the other side.  This could be because:
>    - both clients are sending reports at the same rate and they are 
> almost exactly in sync
>    - they are sending reports in response to an incoming SR rather 
> than on a timer (or some other trigger)

I was thinking as well if it could be the softphone X-Lite....

> Note that the Last SR timestamp is formed by taking the middle 32 bits 
> from the MSW and LSW fields.  Taken together they are the Most 
> Significant Word and Least Significant Word or an NTP timestamp.

I would like to know how can I translate the NTP timestamp a human and 
readable time?

Many thanks,

David