If Your asterisk server is behind NAT then to access asterisk from outside world you need to use the port forwarding features of iptables in Linux.

Steps for asterisk Port forwarding

1] Check rtp.conf file in asterisk

root@indiangnu.org:/etc/asterisk# cat rtp.conf
;
; RTP Configuration
;
[general]
;
; RTP start and RTP end configure start and end addresses
;

rtpstart=10000
rtpend=20000

root@indiangnu.org:/etc/asterisk#

* In rtp.conf file rtpstart and rtpend variables defines which range of port is your asterisk server using for data transfer at real time it is 10000 to 20000 range.

*supose IP address of Asterisk server is 192.168.1.150

2] Apply iptables rules for port forwarding

#Port forwarding for Asterisk
itables -I FORWARD -s 192.168.1.150 -p tcp –dport 5060 -j ACCEPT

#port forwarding for TCP
itables -A PREROUTING -t nat -i eth3 -p tcp -m tcp –dport 5060 -j DNAT –to-destination 192.168.1.150

#port forwarding for UDP

iptables -A PREROUTING -t nat -i eth3 -p udp -m udp –dport 5060 -j DNAT –to-destination 192.168.1.150

#port forwarding for RTP traffic
iptables -I FORWARD -s 192.168.1.150 -p udp –dport 10000:20000 -j ACCEPT

iptables -A PREROUTING -t nat -i eth3 -p udp –dport 10000:20000 -j DNAT –to-destination 192.168.1.150

Thank you,

Arun Bagul