Basic description of a telephone system

[nvd]

I want to find about the different voltage levels of the phone line when the phone system is in different modes i,e ringing, dialing, communicating.

How duplex coil is used?

Can anyone provide me with the brief explanation or any free book which give me the full explanation of the phone system?

 

[hsodan]

Telephone System

https://www.jkaudio.com/article_03.htm
(differes for varius countries, but is a good start)