What is VoIP?
VoIP stands for 'V'oice 'o'ver 'I'nternet 'P'rotocol. As the term says VoIP tries to let go voice (mainly human) through IP packets and, in definitive through Internet. VoIP can use accelerating hardware to achieve this purpose and can also be used in a PC environment.
How does it work?
sending a signal to a remote destination could have be done also in a digital fashion: before sending it we have to digitalize it with an ADC (analog to digital converter), transmit it, and at the end transform it again in analog format with DAC (digital to analog converter) to use it.
VoIP works like that, digitalizing voice in data packets, sending them and reconverting them in voice at destination.
Digital format can be better controlled: we can compress it, route it, convert it to a new better format, and so on; also we saw that digital signal is more noise tolerant than the analog one
TCP/IP networks are made of IP packets containing a header (to control communication) and a payload to transport data: VoIP use it to go across the network and come to destination.
Voice (source) - - ADC - - - - Internet - - - DAC - - Voice (dest)
What is the advantages using VoIP rather PSTN?
When we are using PSTN line, we typically pay for time used to a PSTN line manager company: more time we stay at phone and more you'll pay. In addition we couldn't talk with other that one person at a time.
In opposite with VoIP mechanism we can talk all the time with every person we want (the needed is that other person is also connected to Internet at the same time), as far as we want (money independent) and, in addition, we can talk with many people at the same time.
we can consider that, at the same time, we can exchange data with people are we talking with, sending images, graphs and videos.
Then, why everybody doesn't use it yet?
Unfortunately we have to report some problem with the integration between VoIP architecture and Internet. As you can easy imagine, voice data communication must be a real time stream (we couldn't speak, wait for many seconds, then hear other side
answering): this is in contrast with the Internet heterogeneous architecture that can be made of many routers (machines that route packets), about 20-30 or more and can have a very high round trip time (RTT), so we need to modify something to get it properly working.
we will show how to solve this great problem. In general we know that is very difficult to guarantee a bandwidth in Internet for VoIP application