V O I P I N F O R M A T I O N
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Can a VPN help to carry data securely over the Internet?
A VPN provides security by using encryption/decryption. Using a process called tunneling,
private data is encrypted and encapsulated before being sent across the network. The packets of
information are sent to their destination. Only the ones with the correct protocol information
can enter a company’s network.
A VPN is most useful for providing employees with remote access to the company network
without compromising security. Encryption can have a negative impact on the call quality
because of the increased overhead on the network connection. IPSec adds approximately 10%
overhead to VPN traffic.
What’s the difference between a public IP address and a private IP address?
A public IP address is a globally unique number that identifies a device on the Internet. If you
want someone on the Internet to connect to you, they must know your public address. This is
also known as your real or external address.
A private IP address is typically assigned to a device on a Local Area Network (LAN) and cannot
be routed outside the LAN. Private IP addresses are usually in the range 192.168.x.x, 172.16.x.x
or 10.x.x.x. These IP addresses are used where you have multiple computers all sharing the same
Internet connection.
To access the Internet, a computer or VoIP device must have an IP address. So what do you do if
your ISP (Internet Service Provider) has provided you with only one IP address but you have
more than one device that requires Internet access? The solution is to give each of the devices
on the LAN a private IP address. A router makes them work by performing Network Address
Translation (NAT — See the next topic for details).
Addresses of the form 192.168.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 router that performs NAT, the private IP address assigned to
the VoIP device 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 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.
