Cisco 521SG Administration Guide - Page 294

Cisco SPA IP Phone Field Reference Ext Tab A NAT Settings Parameter NAT Mapping Enable NAT Keep Alive Enable NAT Keep Alive Msg NAT Keep Alive Dest Description To use externally mapped IP addresses and SIP/ RTP ports in SIP messages, select yes. Otherwise, select no. Defaults to no. To send the configured NAT keep alive message periodically, select yes. Otherwise, select no. Defaults to no. Enter the keep alive message that should be sent periodically to maintain the current NAT mapping. If the value is $NOTIFY, a NOTIFY message is sent. If the value is $REGISTER, a REGISTER message without contact is sent. Defaults to $NOTIFY. Destination that should receive NAT keep alive messages. If the value is $PROXY, the messages are sent to the current or outbound proxy. Defaults to $PROXY. Cisco Small Business SPA300 Series, SPA500 Series, and WIP310 IP Phone Administration Guide 293