[Users] Ack is not received the openser, when the phone lefted up.

Hi Users,

I installed Openser server and Using the Nathelper with RtpProxy .

The openser server and RtpProxy are located in the Same system with ip add (192.168.2.2) ,

And Public IP address is xx.xxx.xxx.xxx., openSER sip_doamin name is xx.xxx.xxx.xxx

Ours Network connect for openser System is given below

modem------xx.xxx.xxx.xxx.-------------> router(firewall) ---------------------------------> server 1

|________________ > server 2

|

|_________________> server 3 ( openser and rtp )

For Testing i'm X-lite softphones with different network og openser system

When made the call from one softphone to other softphones.. When caller calls to callee , after the phone rings ,