How can we connect a normal SIP trunk from the cisco router to the IP PBX?
We just need to have an incoming call from outside to the IP PBX. Here the IP PBX we are using are elastix and trixbox. Thank you
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Easiest way is to just get a static IP for the PBX, do a static NAT on the Cisco router and allow the ports. You would need to open port 5060 for the SIP messaging and you need to allow ports 1024-65535 for UDP as RTP can come from any of those ports as it is dynamic. You will have to tweak your access lists to make this secure. Most SIP providers I have dealt with want the PBX on a public IP. Otherwise you would have to have your router setup for voice and you will have to make dial peers to send calls to the PBX which is rather complicated and unnecessary in this instance. I would recommend a static IP. Last thing is make sure your PBX has the NAT pass through setup if it has the option (most do).