Re: why circuit switching is not used in internet connection
Circuit switching is used in telephone networks,, when the internet was first designed (ARPANET) they tried to find a more flexible way of connecting the devices.
In circuit switching each time two devices want to communicate they'll have to use signaling in what is called a call setup phase to establish a connection and then a circuit is reserved along the way between them, and it will be reserved all the time whether they are actually transfering data or not. The problem in circuit switching is that resources are not effectively utilized and other aspects as fault tolerance and scalability are very hard to achieve.
So they chose to use packet switching, in which no resources are reserved in advance, and the data is chopped into packets that have addressing information that may traverse different links to the destination. This allows better utilization of the resources along the way, but packets may face varying delays and may be lost.
However there are a lot of discussions on the use of circuit switching in the internet.