336 ◾ IP Communications and Services for NGN
Testing
Testers found that turning on the router’s QoS feature improved voice quality dra-
matically, even over non-busy networks. However, the NAT (network address trans-
lation) feature that many companies use as a security feature on their routers breaks
VoIP entirely. In a recent article by Tim Green [1], volunteers set up five model
enterprise networks fitted with VoIP equipment, network firewalls, application fire-
walls, Wi-Fi access points, and VPNs; they ran VoIP calls through them, using a
variety of VoIP phones—softphones, hardphones, Wi-Fi handsets, and PDAs. e
tests involved equipment from two dozen vendors. e calls ran over a combination
of the public phone network and the Internet, u