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SETTINGS THROUGH THE WEB INTERFACE
3.1.5 Transport
Transport: The type of transport used for data transmission (by default is UDP).
3.1.6 NAT
NAT: Enables / disables the usage of the STUN server.
STUN server address: The address of the STUN server.
Port: The port of the STUN server.
3.2. Advanced
Select "Advanced" to access advanced settings of the SIP account: