Talkswitch 24-CA - Manual (Page 189)

V O I P I N F O R M A T I O N 1 7 7
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.
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 automatically checks for
the current public IP address and substitutes the private IP address with the
public address, so that VoIP traffic is properly routed through the NAT.
What is a IP Proxy and Registrar?
The basic IP architecture is client/server in nature. The main entities in the
IP server are the proxy, redirect server and the registrar.
TalkSwitch 48-CVA has the IP server fully integrated for easy deployment
and maintenance of your VoIP network. If you are deploying a multi-site
configuration which can comprise of TalkSwitch 48-CVA units, certified
third-party gateways and certified third-party IP phones, one TalkSwitch
48-CVA can act as the IP proxy and registrar. The other IP end-points will
register with this TalkSwitch 48-CVA and all calls will be negotiated through
this TalkSwitch48-CVA.