Simply speaking, there are three different kinds of VoIP. The simplest are VoIP telephone handsets that look and work much like traditional telephones, except that instead of being wired to a telephone line, they're either directly connected to your computer (by something like a USB cable) or indirectly connected to it by a wireless (Wi-Fi) router. You'll find a slightly different kind of VoIP on cellphones (mobile phones).
You make and receive mobile VoIP calls much the same as normal cellphone calls but, instead of calls being sent and received on a permanently open line, like a traditional cellphone call, they're broken into packets and sent back and forth—rather like a web page that you're browsing with something like a smart phone.
In other words, they're using packet switching over the cellphone network. A third kind of VoIP is entirely computer based. When you call someone, the VoIP software running on your computer (known as a client) sets up a more or less direct connection (known as a peer-to-peer or P2P) connection with someone else's computer, across the Internet. You send and receive text messages, voice data, or webcam chat over this direct link. Apart from the initial logging on process, there is no intermediate computer managing the communication between the sender and receiver, which makes this relatively secure compared to other forms of telephone communication. Skype worked this way until a few years ago but now uses a much more centralized cloud-computing system.
All the information that travels over the Net—from the latest music videos on YouTube to the confirmation email from Amazon that your book is on its way—is sent by a method called packet switching. Something like an email, which might be pages and pages of characters, isn't actually sent as one big chunk: when it leaves your computer, it's broken down into many small pieces called packets, each of which travels independently across the Internet (theoretically by a completely different route from other packets) before being reassembled into a copy of the original email when it arrives at its destination.
how does voip work
It's a bit like sending a book through the post not as a big fat parcel but by putting every single page into a separate envelope, individually addressed and dispatched. It might sound odd to send things this way, but packet switching is actually an extremely quick and efficient way of handling the billions of emails, web pages, and everything else that has to zip back and forth across the Net every single day. (You can read more about how it works in our main article on how the Internet works.) All the computers connected to the Internet understand how to send and receive packets like this; thankfully, they all agree to work in exactly the same way using exactly the same system, which is known as the Internet Protocol or IP. (One of the key parts of the IP that you may be familiar with is that every computer can be "addressed" by quoting a unique number, known as its IP address, which is a bit like the computer equivalent of a telephone number or building address.
How, then, do you send a telephone call over the Internet? There are really three separate problems to solve before you can do it: alerting someone that you want to call them, turning your voice into digital sound and sending it over the Net (and receiving replies in the opposite direction), and "interfacing with" (linking in to) the ordinary telephone network, if your call is going to a traditional landline telephone or cellphone (mobile phone). Let's look at each of these in turn
