[Freeswitch-users] RTP Timing

David Ponzone david.ponzone at gmail.com
Wed Jul 21 07:51:57 PDT 2010 

Neil,

as far as I know, by default, FS is transparent for timestamps.
It writes in outbound RTP the exact timestamp that it received in  
inbound RTP.
So you should perhaps have a look at the sending endpoint ?

David Ponzone  Direction Technique
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Le 21/07/2010 à 16:36, Neil Burgess a écrit :

> Hi,
>
> We are capturing packets for call quality monitoring purposes, and  
> as part of the capture, we are grabbing the outbound packets from  
> FreeSwitch. We are noticing what appears to be an odd behaviour in  
> the RTP sequence timing where suddenly the timing will jump from the  
> regular 160 increments to a number in the 10’s of millions! See  
> packet 38 below. Now I have no idea as to whether such a timing  
> change is OK in RTP, and although the actual RTP stream does not  
> appear to be affected, I do see that Wireshark believes there is a  
> massive amount of jitter on the line when it analyses the packets,  
> and any RTCP Sender Reports from the target device (and indeed  
> several different target types have been tried) also report very  
> large inter arrival jitter numbers at this point! It’s the RTCP  
> side of things that are more of interest here, as trying to get  
> accurate results of our downstream jitter by capturing the returned  
> RTCP packets. I believe that all the times we see this, there is  
> however a Marker bit present!
>
> So I guess the question is whether this is expected behaviour, and  
> if not any ideas?
>
> No.     Time        Source                Destination            
> Protocol Info
>       1 0.000000    gmtpbx02.redmatter.com sil1.magrathea.net    SIP/ 
> SDP  Request: INVITEsip:441277849884 at sipipgw.magrathea.net, with  
> session description
>       2 0.001595    sil1.magrathea.net    gmtpbx02.redmatter.com  
> SIP      Status: 100 Giving a try
>       3 1.103160    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=0, Time=0
>       4 1.124816    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=1, Time=160
>       5 1.142758    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=2, Time=320
>       6 1.163702    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=3, Time=480
>       7 1.184239    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=4, Time=640
>       8 1.203259    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=5, Time=800
>       9 1.223456    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=6, Time=960
>      10 1.243953    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=7, Time=1120
>      11 1.264504    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=8, Time=1280
>      12 1.284839    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=9, Time=1440
>      13 1.304590    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=10, Time=1600
>      14 1.323589    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=11, Time=1760
>      15 1.344672    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=12, Time=1920
>      16 1.359227    sil1.magrathea.net    gmtpbx02.redmatter.com SIP/ 
> SDP  Status: 183 Session Progress, with session description
>      17 1.364522    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=13, Time=2080
>      18 1.377484    gmtpbx02.redmatter.com lon-avon- 
> four.magrathea.net RTP      PT=ITU-T G.711 PCMU, SSRC=0x1855F3A7,  
> Seq=53974, Time=160, Mark
>      19 1.383466    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=14, Time=2240
>      20 1.397476    gmtpbx02.redmatter.com lon-avon- 
> four.magrathea.net RTP      PT=ITU-T G.711 PCMU, SSRC=0x1855F3A7,  
> Seq=53975, Time=320
>      21 1.403953    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=15, Time=2400
>      22 1.417484    gmtpbx02.redmatter.com lon-avon- 
> four.magrathea.net RTP      PT=ITU-T G.711 PCMU, SSRC=0x1855F3A7,  
> Seq=53976, Time=480
>      23 1.423616    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=16, Time=2560
>      24 1.437474    gmtpbx02.redmatter.com lon-avon- 
> four.magrathea.net RTP      PT=ITU-T G.711 PCMU, SSRC=0x1855F3A7,  
> Seq=53977, Time=640
>      25 1.444930    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=17, Time=2720
>      26 1.457475    gmtpbx02.redmatter.com lon-avon- 
> four.magrathea.net RTP      PT=ITU-T G.711 PCMU, SSRC=0x1855F3A7,  
> Seq=53978, Time=800
>      27 1.463341    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=18, Time=2880
>      28 1.477473    gmtpbx02.redmatter.com lon-avon- 
> four.magrathea.net RTP      PT=ITU-T G.711 PCMU, SSRC=0x1855F3A7,  
> Seq=53979, Time=960
>      29 1.484235    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=19, Time=3040
>      30 1.497483    gmtpbx02.redmatter.com lon-avon- 
> four.magrathea.net RTP      PT=ITU-T G.711 PCMU, SSRC=0x1855F3A7,  
> Seq=53980, Time=1120
>      31 1.503415    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=20, Time=3200
>      32 1.517474    gmtpbx02.redmatter.com lon-avon- 
> four.magrathea.net RTP      PT=ITU-T G.711 PCMU, SSRC=0x1855F3A7,  
> Seq=53981, Time=1280
>      33 1.523541    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=21, Time=3360
>      34 1.537472    gmtpbx02.redmatter.com lon-avon- 
> four.magrathea.net RTP      PT=ITU-T G.711 PCMU, SSRC=0x1855F3A7,  
> Seq=53982, Time=1440
>      35 1.543428    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=22, Time=3520
>      36 1.557567    gmtpbx02.redmatter.com lon-avon- 
> four.magrathea.net RTP      PT=ITU-T G.711 PCMU, SSRC=0x1855F3A7,  
> Seq=53983, Time=1600
>      37 1.563656    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=23, Time=3680
>      38 1.577496    gmtpbx02.redmatter.com lon-avon- 
> four.magrathea.net RTP      PT=ITU-T G.711 PCMU, SSRC=0x1855F3A7,  
> Seq=53984, Time=130238272, Mark
>      39 1.584747    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=24, Time=3840
>      40 1.597474    gmtpbx02.redmatter.com lon-avon- 
> four.magrathea.net RTP      PT=ITU-T G.711 PCMU, SSRC=0x1855F3A7,  
> Seq=53985, Time=130238432
>      41 1.603871    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=25, Time=4000
>      42 1.617465    gmtpbx02.redmatter.com lon-avon- 
> four.magrathea.net RTP      PT=ITU-T G.711 PCMU, SSRC=0x1855F3A7,  
> Seq=53986, Time=130238432
>      43 1.624224    lon-avon-four.magrathea.net  
> gmtpbx02.redmatter.com RTP      PT=ITU-T G.711 PCMU,  
> SSRC=0x216DE2D9, Seq=26, Time=4160
>      44 1.637466    gmtpbx02.redmatter.com lon-avon- 
> four.magrathea.net RTP      PT=ITU-T G.711 PCMU, SSRC=0x1855F3A7,  
> Seq=53987, Time=130238592
>
> Many thanks,
> Neil
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