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VoIP and the Windows XP Firewall and Address Translation using NAT
Transversing the firewall was once an issue for Internet telephony. Now, as you will see from the setup menu of an Xten SIP phone, your phone will navigate the firewall easily in most cases.
The purpose of a firewall is to stop attacks from the Internet. Depending upon the strength of the firewall it may stop certain applications form working, such as those that send information out to the Internet and expect to receive information back from the Internet. For home software applications, developers should not expect users to understand how a firewall works. If their software does not work the developer gets the blame and the average user will remove the program.
The Xten phone starts by discovering the type of firewall used. For those that share one cable or DSL connection with multiple computers, the router has a NAT firewall built in.
When the telephone connects to the server (established by your service provider such as Addaline, Free World Dialup, Inphonex, etc.) it opens a port from your computer to the service. The purpose of the firewall is to protect your computer and network. The purpose of NAT is to translate your private address to a publically readable address (routing) and to control address translation (NAT).
NAT basically tells the firewall that, for instance, if a specific phone behind the firewall goes out into the world on port 15543 any replies to that port belong to, and should be routed back to the computer that sent it in the first place. Kinda like dancing with the one who brought you to the dance.
Your Windows XP firewall should simply ask if you want to unblock your new outgoing SIP phone. Tell it yes and well behaved software should funtion normally without further intervention unless you have a unique network configuration.
