I understand this lecture sir. 

★ Automatic switching system can be divided into two parts. They are :

1.Electromechanical and 

2.Electronic.

★ Electromechanical switching system can be divided into two parts:

1.Steb - by - step  and 

2.Crossbar. 

★In electronic switching system, we use control function and logic.That's why information are stored. Then that stored information are provided & information can be send.It's called Stored Program Control(SPC).

★ Stored program can be in two ways.One is space Division switching system and another one is time Division switching system. 

★In space Division switching system, dedicated and exclusive switching path should be established. 

★ In time Division switching system, we Don't need any dedicated  path.Here the same switching path may be shared by more than one subscriber pair.By using any node we can send data.