IP Telephony is the way to may phone calls via IP (internet protocol). IP Telephony was first introduced in 1995 and since that time the number of users grow exponentially mostly due to the increased availability of broadband internet connection and the advantages of IP telephony.
There are several ways to transmit phone calls over internet offered by VoIP providers. The ways are classified according to what devices are placed at both communicating ends. The call can be initiated and received by either a computer of a PSTN (public switched telephone network) device.
Computer to Computer
This IP telephony scenario offers the greatest easiness that makes it the most popular way to use VoIP services. To make IP telephony possible you should have a sound card on both computers and microphones and earphones (or headsets). VoIP softphones (part of VoIP software) are to be installed at the both ends. IP telephony allows integrating of other services such as e-mail, IM (instant messages), etc.
PC to Telephone
IP telephony initiated by a PC can reach a user of a traditional PSTN (public switched telephone network). To make this set-up work a VoIP gateway is used to convert the digital data into the format supported by the PSTN and vice versa. Either mobile or residential phones may participate in this IP telephony scenario.
Telephone to telephone
IP telephony is cost-effective but not all the users can benefit from it as not each of them may have internet access or computers sufficient to use as part of IP telephony scheme. Special VoIP phones are available that allow making calls using VoIP. If you want to use a residential or mobile phone you should add a VoIP gateway to your phone line to convert the signals into voice and voice into signals. In this IP telephony set-up the data goes through two VoIP gateways: PSTN to internet and vice versa.
Telephone to Computer
IP telephony can be performed for calls initiated by a telephone to reach a PC. The computer should have VoIP software installed and be equipped with a microphone and a headset or earphones.
IP phone systems are often configured to use the benefits of IP telephony within a business company or any organization. A typical IP phone system includes:
-VoIP/SIP server (proxy) that manages all the phone calls
-VoIP phones (VoIP softphones, or ordinary telephones with a VoIP adapter)
-VoIP gateways (in case a traditional telephone is used)
