Echo TestNumberSet echo test number. If IAX2 server supports echo test,and echo test number is non- numeric, system could setan echo test number to replace the echo test text. So usercan dial the numeric number to test echo voice test. Thisfunction is provided with server to make endpoint to testwhether endpoint could talk through server normally.Echo Test Text Specify echo test text’s name.Refresh Time Set expire time of IAX2 server register, you can set itbetween 60 and 3600 seconds.EnableRegistrationStart to register the IAX2 server or not by selecting it ornot.Enable G.729AB Enable or disable code G.729 by selecting it or not.8.3.3.3 STUNIn this web page, you can config SIP STUN.STUN: By STUN server, the phone in private network could know the type ofNAT and the NAT mapping IP and port of SIP. The phone might register itselfto SIP server with global IP and port to realize the device both calling andbeing called in private network.