User guide

VOIP INFORMATION 127
the Internet Engineering Task Force (IETF), the body responsible for
administering and developing the mechanisms that comprise the Internet.
The IETF’s philosophy is simplicity: specify only what you need to specify.
SIP just initiates, terminates and modifies sessions.
TalkSwitch phone systems use the Appello® SIP Stack for VoIP communications.
The Appello® SIP Stack was developed by TalkSwitch — a division of
Centrepoint Technologies Inc.
What is a VPN? Can a VPN help me to carry data securely
over the Internet?
VPN stands for Virtual Private Network. It is a means of having the
advantages of a private network on a shared public infrastructure like the
Internet. A VPN provides security by using encryption/decryption. Using a
process called ‘tunneling’, private data is encrypted and then encapsulated
before being sent across the network. These packets of information are sent
to their destination. Only those with the correct protocol information are
able to enter a company’s network.
A VPN is very useful for providing employees with remote access to the
company network without compromising security. Encryption can have a
negative impact on the call quality, as the overhead on the network
connection is increased. For example, IPSec adds approximately 10 per cent
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. Also known as your “real” or “external”
address.
Private IP Addresses are typically assigned to devices on a LAN (Local Area
Network) and are not routable 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 1 IP address but you have more than 1 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).