Why is it that the SIP voice does not pass through the SIP server?

Zyxel_Charlie

Question

I have a SIP server at the LAN site with three SIP phones, Phone#A and Phone#B in the LAN site, and Phone#C at the external site.

The connection between Phone#A and Phone#B works fine.

The connection between the internal Phone and Phone#C fails.

What is the cuase of this problem? 

Answer
This is because; currently, the SIP ALG function only supports the SIP server at the external site, but not the SIP server at the LAN site.