The original intent was to construct a network that would continue to function even if a large portion of it were destroyed, in the event of nuclear war, for example. The Internet is now a public, self-sustaining facility accessible to millions of people worldwide. Physically, the Internet uses a portion of the total resources of all the currently existing public telecommunication networks.
Electronic mail is the most widely used application on the Net.
To use e-mail, you need an Internet address. Typing and reading messages in real time is more personal than e-mail, but it is less personal than talking on the telephone. However, Internet telephony hardware and software is available that allows real-time voice conversations on the Net. These programs work best when the Net is not being heavily used. When there are many people using the Net, Internet telephony becomes somewhat less reliable and the audio quality is compromised.