1. Automatic switching system there is no 3rd person interrupt. In this calling system it call established time every short and faster.

2. Manual switching system it at fast we need to build up a communication with operator . Then it established the call . And it is vary lengthy process.

3. Rotary dial telephone has two parts. 

# pulse dialing 

# Multifrequency dialing

4. In this Rotary dial telephone system the pulse established base on digit.

5. In Rotary dial when we press 3 and after 2 . Between this 3 and 2 it creat a gap it's call interdigit gap.