[asterisk-users] RTP timestamps

[Liivo Vöörmann]

Hi All,

Could somebody explain me how the timestamps are computed in asterisk 
while bridging two sip channels ?
I've got situation with my provider, who changed some things in config 
and added some codecs (that much i know) and after that we got one way 
audio issues. It seems that the problem is with RTP timestamps. Within 
one outgoing stream the RTP timestamps are growing, as it should be, but 
sometimes while the asterisk plays MOH (or somebody transfers call to 
another extension) the timestamps on RTP packets will fall to past. 
Providers media gateway dosn't like that. The marker bit is correctly 
set but it seems like that dosn't change anything. Sequences and SSRC-s 
are Ok, no packet loss. Has anyone seen something like this before and 
knows what is the cause and how to fix this?
I've tried many changes in config and upgraded to 1.6.1 but it didnt 
change anything, currently running asterisk 1.4.26.1 on 64 bit intel 
platform with opensuse.
Here is the tcpdump view from wireshark, xxx is providers ip and yyy is 
asterisk:

6218    207.717454    xxx.xxx.xxx.xxx    yyy.yyy.yyy.yyy    RTP    
PT=ITU-T G.711 PCMA, SSRC=0x85048346, Seq=54364, Time=1987711680
6219    207.717481    yyy.yyy.yyy.yyy    xxx.xxx.xxx.xxx    RTP    
PT=ITU-T G.711 PCMA, SSRC=0x35276954, Seq=22826, Time=2202453496
6220    207.737442    xxx.xxx.xxx.xxx    yyy.yyy.yyy.yyy    RTP    
PT=ITU-T G.711 PCMA, SSRC=0x85048346, Seq=54365, Time=1987711840
6221    207.757430    xxx.xxx.xxx.xxx    yyy.yyy.yyy.yyy    RTP    
PT=ITU-T G.711 PCMA, SSRC=0x85048346, Seq=54366, Time=1987712000
6222    207.759283    yyy.yyy.yyy.yyy    xxx.xxx.xxx.xxx    RTP    
PT=ITU-T G.711 PCMA, SSRC=0x35276954, Seq=22827, Time=736089280, Mark
6223    207.765349    yyy.yyy.yyy.yyy    xxx.xxx.xxx.xxx    RTP    
PT=ITU-T G.711 PCMA, SSRC=0x35276954, Seq=22828, Time=736089440

Help!

Greetings,
Liivo