Linksys WIP310 SPA500 Series and WIP310 IP Phone Administration Guide - Page 235

Cisco SPA 500 Series and Wireless IP Phone Field Reference SIP Tab B Parameter STUN Test Enable STUN Server EXT IP EXT RTP Port Min NAT Keep Alive Intvl Description If the STUN Enable feature is enabled and a valid STUN server is available, the IP phone can perform a NATtype discovery operation when it powers on. It contacts the configured STUN server, and the result of the discovery is reported in a Warning header in all subsequent REGISTER requests. If the IP phone detects symmetric NAT or a symmetric firewall, NAT mapping is disabled. Defaults to no. IP address or fully-qualified domain name of the STUN server to contact for NAT mapping discovery. You can use a public STUN server or set up your own STUN server. External IP address to substitute for the actual IP address of the IP phone in all outgoing SIP messages. If 0.0.0.0 is specified, no IP address substitution is performed. If this parameter is specified, the IP phone assumes this IP address when generating SIP messages and SDP (if NAT Mapping is enabled for that line). However, the results of STUN and VIA received parameter processing, if available, supersede this statically configured value. Defaults to blank. External port mapping number of the RTP Port Min. number. If this value is not zero, the RTP port number in all outgoing SIP messages is substituted for the corresponding port value in the external RTP port range. Defaults to blank. Interval between NAT-mapping keep alive messages. Defaults to 15. Cisco SPA 500 Series and WIP310 IP Phone Administration Guide 224