Examples of WANs are the Internet or Compuserve. This network could be on private circuits or on lines leased from common carriers. There are typically two types of networks used for teleprocessing they are voice network and data network. A voice network is the more common of the two. Most people are probably more familiar with a voice network.
Most personal computers connect to a network with the use of a voice system.
A voice system works as follows. The RS232C interface converts the digital signal into an analogue signal. Second, these signals could be amplitude modulation, frequency modulation or phase modulation. This process is called modulating. For incoming signals the RS232C interface must convert the analogue signal into a digital signal.