What is a Circuit Switched Telephone call ?
circuit switched – During the set up portion of a telephone call, a circuit is created, which is then torn down when the call is completed.
Originally, the entire telephone network was analog, but it is now mostly digital. The digital parts include the switches and backbone lines between them (called trunk lines).The connection between the customer premises equipment and the first telephone switch, called the local loop, is still analog.
Telecom R & D 
precise and crisp , needs more detailing though .
Hello alicia , thank you for commenting again . Of course you have a good point . I shall sincerely try to improve . thanks again .
The legacy networks are still very prevalent and require integration with the latest rather bleeding technologies such as VOIP , IMS , NGN .. even WebRTC , which is a funny requirement in itself .