I want to make a call across firewall device.
I am using nf_conntrack_sip and nf_nat_sip(2.6.32) kernel modules as sip proxy.
Connection got established from private network to public network but no voice exchange is happening.
We can see RTP ports related UDP entry in conntrack -L.
How can I fix this problem?

Test Scenario:
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Device LAN IP -- 10.0.0.1
Device WAN IP -- 192.168.1.1

LAN side of device
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Analog phone with ATA(10.0.0.3)
Trixbox(Asterisk) - 10.0.0.2

WAN side of device
------------------
PC with SJphone - 192.168.1.2

I am trying to establish the connection from Analog phone to SJphone.

In the device iptable rule added in FORWARD chain to allow SIP packet(5060 port).
In NAT table under POSTROUTING chain MASQUERADE rule to allow packets to traverse from LAN side to WAN side.