Data transmission:
There are two main ways that data can be transmitted. The manner in which the data is transmitted tells us whether the phone is an analog phone or a digital phone.
Analog Phone:
An analog phone interprets sound as an electronic pulse. Hence, the sound is converted into electronic signals. The electronic pulse is analogous to the sound being interpreted. The term, analog is derived from this. The signal is then transferred over copper wires in the form of waves. Another way of saying this is in terms of small fluctuations in the signal which are meaningful.
Figure: Analog Telephone
Digital Phone:
In digital phone, first it converts data into a binary code, i.e. 1s and 0s. This is the same way in which computers store information. The data in the form of 1s and 0s is then transmitted where it is restructed into a representation of the sound, on the other end. VOIP (voice over internet protocol) is a type of digital signal.
Figure: Digital Phone