asterisk users - Jan 2007 - one way audio when forwarding from ser to asterisk

Hi all,

i have ser and asterisk on the same box with a public
ip address. When an UA behind NAT registred on SER try
to call the Voicemail or another UA registred on
Asterisk i have one way audio (caller cannot hear the
callee).

[UA/SER]--[router/nat]----------[SER/Asterisk]


UA has private IP(192.168.204.19) and public IP is
89.106.xxx.yyy
SER/ASterisk has public ip (89.106.yyy.zzz).

In the sip trace one can see that signaling is ok but
Asterisk sends RTP from 89.106.xxx.zzz to
192.168.204.19 not to 89.106.xxx.yyy

ps: when UA registred on SER try to call UA2 registred
on SER every thing works fine.

how can i fix this issue.
thx                   


 
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