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I n t r o d u c t i o n t o V o I P
5
When you initiate a VoIP call, your device (TalkSwitch 48-CVA, gateway or phone) will
contact the TalkSwitch 48-CVA that is configured as the SIP Server to obtain the
contact information for the destination you are trying to reach. Once the information
is received, the call is established directly between your location and the destination.
The SIP Server is no longer involved in the call.
If the location of the SIP Proxy and Registrar has a Dynamic IP Address, then you will
have to use Dynamic DNS since the SIP Server location will be unreachable as soon as
the IP address changes.
What is Dynamic DNS?
Dynamic DNS is a Domain Name Service that is used with Dynamic IP addresses. DNS is
used to allow devices to find other devices on the Internet by name rather than by IP
address. Dynamic DNS allows you to use a domain name - FQDN (which does not
change) to locate a device with a Dynamic IP address.
There are companies on the Internet which can provide you with a DNS Address, even
if your IP address changes. For example www.dyndns.org or hn.org or www.no-ip.com.
You should consult with them about how to use their service. But the basic idea is that
you will receive an address something like myname.homeip.net which points to your IP
address (something like 209.210.230.140). This is important for locations where the
SIP Server resides and where the public IP address is dynamic. All other locations will
point to this SIP Server’s domain instead of an IP address.
What is the drawback of using Dynamic DNS?
When DNS records are updated, they have to be sent all over the world so that
everyone will be aware of the changes. Basically, one DNS server connects to another
and swaps information. In many cases, the DNS servers are updated very quickly.
Updates should take no longer than 15 minutes to propagate throughout the DNS
system. It is possible that propagation could take longer under extenuating
circumstances, but propagation shouldn’t take much more than an hour at the very
most.
How often will my Public IP address change?
This depends on the policies of your Internet Service Provider (ISP, the company that
provides your Internet access). It can be a matter of days, weeks or even months
before your IP address changes. A power loss or reboot to your cable or DSL modem
usually results in the assignment of a new IP address.
TalkSwitch has technology that helps keep this information up to date so that the
system can function properly after an IP address change has been detected and
updated.