VoIP, or Voice over Internet Protocol, is the transmission of voice traffic over Internet protocol (IP)-based networks. VoIP systems use session control protocols, which control the set-up and overall tear-down of calls and audio codecs, guaranteeing the digital audio transmission of speech over an IP network.
How it works
The working of VoIP is very simple. The user establishes a hi-speed broadband connection over a router and a VoIP gateway. The VoIP gateway is a network device which helps to convert voice and fax calls between a Public Switched Telephone Network (PSTN) and an Internet Protocol (IP) network. This gateway is placed somewhere in direct proximity to the connected Internet service. It converts the analog signals into digital format, which are in turn bifurcated into smaller 'packets.' This process is similar to the data transmission that takes place in a computer. These packets, embedded with instructions, are then sent to their final destination. Once this process is over, these packets pass through (with instructions from the other side) another gateway where they are reconverted into the normal analog format by the Public Switched Telephone Network (PSTN).
You will require a broadband or a high speed Internet connection to use VoIP. It can be a local area network, a cable modem or high speed service such as DSL. You will also require a computer, a specialized phone or an adaptor. Some VoIP services allow you to use a traditional phone, which you can connect to a VoIP adapter, while others work only on your computer or require a special VoIP phone. These VoIP phones come with the advantage that you can use them simply by plugging them into the broadband connection; when using a computer, you will require the right software and a microphone. 
What are VoIP phones?
Voice over Internet Protocol phones are telephones that connect to VoIP networks instead of PSTN. They are also available in different forms depending on the types of connection. The basic types are:
- VoIP phones with Wi-Fi/ 802.11 connections
- Software VoIP phones
- Phones connected with dialup modem connections
- VoIP phones with Ethernet connections
Types of VoIP calls
You can use your standard Internet connection to make free phone calls. There are many free VoIP softwares that allow you to make free phone calls. There are different ways you can make calls using VoIP, including:
- ATA: The simplest way is by using Analog Telephone Adaptor (ATA). This adaptor allows you to connect your standard phone to the computer. The ATA is an analog to digital converter. It takes your analog telephone signal and converts it to digital format for transmission over the Internet. You can simply buy an ATA, plug it between your phone and computer and you are ready to make calls using VoIP.
- IP Phones: These phones are similar to normal phones. However, they have a RJ-45 Ethernet connector instead of RJ-11 connector found in a standard phone. These phones have the necessary hardware and software onboard to handle the IP call. They are connected directly to a router. Wi-Fi phones allow subscribers to make a VoIP call from any Wi-Fi spot.
- Computer to Computer: This is the easiest way to make calls using VoIP. You need a microphone, speakers, a sound card, software and a fast Internet connection such as DSL modem or cable Internet. You can find much low-cost or free VoIP software available on Internet. You normally do not have to pay any additional fee other than monthly ISP charges, if you are making calls using VoIP.