Network Switching: Definition & Types :circuit-switched networks VS packet-switched networks ...

Switching :

What is Switching ?
An internet is a switched network in which a switch connects at least two links together.
A switch needs to forward data from a network to another network when required.

Network Switching: Definition & Types :
The two most common types of switched networks are :
1__circuit-switched networks :
What is circuit-switched networks?
What is the difference between a circuit-switched and a packet-switched networks ?

In a circuit-switched network, 

• a dedicated connection, called a circuit, is always available between the two end systems.
• the switch can only make it active or inactive.
• circuit switching was very common in telephone networks in the past, although part of
• the telephone network today is a packet-switched network.

Example_1_circuit-switched network :
A circuit-switched network

OR

Example_2_circuit-switched network :

• the four telephones at each side are connected to a switch. 
• The switch connects a telephone set at one side to a telephone set at the other side.
• The thick line connecting two switches is a high capacity communication line that can handle
• four voice communications at the same time.
• the capacity can be shared between all pairs of telephone sets.
• The switches used in this example have forwarding tasks but no storing capability.
• Let us look at two cases.

In the first case :

• all telephone sets are busy.
• four people at one site are talking with four people at the other site .
• the capacity of the thick line is fully used.

In the second case :

• only one telephone set at one side is connected to a telephone set at the other side;
• only one-fourth of the capacity of the thick line is used.
• This means that a circuit-switched network is efficient only when it is working at its full capacity; most of the time, it is inefficient because it is working at partial capacity.

NOTE:

The reason that we need to make the capacity of the thick line four times the capacity of each voice line is that we do not want communication to fail when all telephone sets at one side want to be connected with all telephone sets at the other side. 

2__packet-switched networks:
What is packet-switched networks?
In a computer network, the communication between the two ends is done in blocks of data called packets. 
In other words, instead of the continuous communication we see between two telephone sets when they are being used, we see the exchange of individual data packets between the two computers. 

This allows us to make the switches function for both storing and forwarding because a packet is an independent entity that can be stored and sent later.

Example_1_packet-switched networks :
A packet-switched network

OR

Example_2_packet-switched network :

• small packet-switched network that connects four computers at one site to four computers at the other site.
• A router in a packet-switched network has a queue that can store and forward the packet.
• Now assume that the capacity of the thick line is only twice the capacity of the data line connecting the computers to the routers.
• If only two computers (one at each site) need to communicate with each other, there is no waiting for the packets.
• However, if packets arrive at one router when the thick line is already working at its full capacity,
• the packets should be stored and forwarded in the order they arrived.
• The two simple examples show that a packet-switched network is more efficient than a circuit switched network, but the packets may encounter some delays.