NEC UNIVERGE SV9100 Manual page 27

show the tunnels that have been created through the internet. Each network can connect to the
others as though they are connected with private connections (kilostream, etc.), without the issues
relating to NAT.
Conclusion
When IP address translation is applied to a VoIP packet, the application fails and the communication
path is broken. VoIP packets contain the IP address information and the ports used as part of its
payload. When NAT
(Network Address Translation) is applied, only the header parameter is changed, not the payload
data that affects the process of data packets within the VoIP switch and terminal. In order to support
the addressing and port fluctuation that occurs when system IP Phones are deployed in remote
facilities, VPN services are required.
Three most common scenarios for remote IP deployment are as follows;
1) Implementation of a system IP Phone behind a NAT talking to an SV9100 that has a public IP
address. This would be a scenario where a telecommuter or a branch office talking to the SV9100
at the central site.
2) Implementation of a system IP Phone with a public IP address talking with an SV9100 behind
NAT. An example would be a telecommuter.
3) Implementation of a system IP Phone behind a NAT, which connects to the internet, terminating
into an SV9100 behind a different NAT.
When selecting VPN equipment it is important to consider Quality of Service. Generally VPN
hardware is connected to internet connections which are unreliable and out of the control of the
customer. (See: Internet Based Connections). However, it is possible to set prioritisation on some
VPN units for voice traffic. This does not solve the unreliability of the internet, but helps to ensure
that the data traffic to and from your LAN do not impair the quality of the voice traffic. (QoS is
discussed in the Quality of Service section above).
Part 1: VoIP Reference Manual 27