The IP in VoIP is “internet protocol,” but what, exactly, is internet protocol? A protocol, in computing terms, is the language computers use while talking to each other. The protocol contains rules for such important things as where the data goes, how it gets there, and what to do if part of the data gets lost.
Internet Protocol works by what’s called “packet switching.” A packet contains three parts: a header the payload, and the trailer. The payload would be like a letter inside an envelope-it contains the information; the header would be like the address and the envelope—it has the IP address of the sender and receiver, as well as data about the size of the packet, and how to reassemble the payload. The trailer, also called the footer, contains data to indicate the end of the packet and also contain information for error correction. This way, the information does not even have to be received in the order it is sent. It is “switched” because it is sent through switches, which are the devices that connect different parts of a network.
The Public Switched Telephone Network is also a network that is connected by switches, but unlike the internet, the PSTN is switched by a circuit, and the circuits must be connected. In Internet Protocol, once the data is broken down into packets, the individual packets are sent to their destination. If part of the network is too congested, then the packets simply take another path. The packets, remember, do not have to stay together, because they all contain information about their destination. When the packets reach their destination, they are reassembled. Internet Protocol automatically balances network traffic by taking whatever path is fastest.
There are a number of different ways that internet protocol can deal with packets that get corrupted or otherwise lost: The data itself can be redundant, meaning that part of the payload is repeated in the next payload. If data is lost, the terminating device can ask for another copy of the data packet. Internet protocol has algorithms to reconstruct missing data. Remember, all of this is taking place in microseconds.
One of the major hurdles for Voice over Internet Protocol was to be able to send enough sound information without the voice sounding choppy. You may not have known this, but the early development of sound in movies had to deal with the same problem. “Talkies” were developed to have 24 frames every second because our ears are less tolerant of changes in frequency than our eyes. Early audio codecs had about half the sample rate of telephones. Today, because of higher internet speeds and better compression algorithms, VoIP has up to twice the sound quality of a traditional phone.