Talkswitch 24-CA User Manual page 136

Note that addresses of the form192.168.x.x, 172.16.x.x or 10.x.x.x are not
recognized on the Internet and can only be used for private networks. For
example, if you tell someone on the Internet to connect to you using a
192.168.x.x address, it will not work. Instead, you must provide your real/
Public IP Address.
What is NAT and how does it affect VoIP?
Network Address Translation (NAT) allows multiple devices to share the same
external IP address to access resources on the Internet. NAT is typically used
to allow all the devices in a subscriber's local area network to access the
Internet through a router with a single public IP address assigned by the
Internet Service Provider.
If a VoIP device is sitting behind a NAT, the private IP address assigned to it is
not usable for communications with the entities outside the private network.
The VoIP device must substitute the private IP address information with the
proper external IP address/port in the mapping chosen by the underlying
NAT to communicate with a particular public peer address/port. TalkSwitch
can automatically check for the current public IP address and substitute the
private IP address with the public address so that VoIP traffic is properly
routed through the NAT.
What's the difference between a Static IP Address and a Dynamic
IP Address and what effect does this have on VoIP?
A Static IP Address is an address that is permanently assigned to a device.
Typically, a Static IP Address has to be assigned by the network administrator
or Internet Service Provider (ISP).
A Dynamic IP Address is an address that is temporarily assigned to devices by
a DHCP or PPP server that maintains and assigns a pool of IP addresses.
When deploying VoIP devices, it's best to have a Static Public IP Address as
this prevents destinations from becoming unreachable for periods of time
when the IP address changes. But since this can be an expensive option,
TalkSwitch 48-CVA supports the ability to handle Dynamic Public IP addresses
for the Internet connection. TalkSwitch can automatically check for the
current public IP address and substitute the private IP address with the
public address so that VoIP traffic is properly routed through the NAT.
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