UDP Keep Alive message: If enabled, IP phone will send UDP
keep-alive message periodically to router to keep NAT port alive.
UDP Alive Msg Interval: Keep alive message interval.
Rport: Remote port, if enabled, it will add remote port into outgoing
SIP message for designated account.
Go to Account - Advanced to configure. One can customize user
agent field in the SIP message; if user agent is set to specific value,
users can see the information from PCAP. If user agent is not set
by default, users can see the company name, model number and
firmware version from PCAP.