I  understand  this lecture. 

★ Strowger was invented automatic switching system. In automatic switching system, human operator doesn’t exist actually. 

★There are many advantages of automatic switching system:

1. In a manual exchange, subscriber needs to communicate with the operator and a common language becomes an important factor.

2.Establishment and release of calls are faster in automatic switching system. 

★ Two methods used for rotary dial telephone purpose are :

1.Pulse dialling  and 

2.Multifrequency dialling. 

★ A rotary dial telephone uses the following for implementing pulse dialling :

# Finger plate and spring. 

# Shaft, gear and pinion wheel.

# pawl and ratchet mechanism. 

# Impulsing contact.

# Transmitter,receiver and bell by - pass circuits.

★ A rotary dial telephone is classified either as camp type or trigger type, depending on whether a cam mechanism or a trigger mechanism is used for operating the impulsing contact.