What Is Difference Between IP Telephony, Digital and Analog Telephones Circuits?

Long answer (kinda) short: analog telephony is plain old telephone lines like we all (used to) have at home. They use analog technology, the same way an LP record player or cassette deck used analog signals: the signal that goes in at the receiver is analogous to the signal that comes out at the speaker at the other end. The signal can become degraded over distance and quality of the line, however.

Digital telephony is the technology your CD player uses. The sound is converted into digits at one end (“1”s and “0”s), and then decoded as sound at the other end. That means what is encoded at one end is EXACTLY the same as what is decoded at the far end. Many businesses use digital telephony, commonly called ISDN, but few consumers do.

IP Telephony is a type of digital telephony that uses the IP protocol we use on the Internet. This means that telephone calls can be sent over private networks and the internet, instead of the traditional public switched telephone network that has been used for voice calls for 150 years.