Circuit Switching vs. Packet Switching

Switching and routing

Switching and routing are technically two different things, but for the sake of simplicity, let us take switches and routers (which are devices that make switching and routing respectively) as devices doing one job: make a link in the connection and forward data from the source to the destination.

Paths or circuits

The important thing to look for in transmitting information over such a complex network is the path or circuit. The devices making up the path are called nodes. For instance, switches, routers and some other network devices, are nodes.

In circuit-switching, this path is decided upon before the data transmission starts. The system decides on which route to follow, based on a resource-optimizing algorithm, and transmission goes according to the path. For the whole length of the communication session between the two communicating bodies, the route is dedicated and exclusive, and released only when the session terminates. 

Packets

To be able to understand packet-switching, you need to know what a packet is. The Internet Protocol(IP), just like many other protocols, breaks data into chunks and wraps the chunks into structures called packets. Each packet contains, along with the data load, information about the IP address of the source and the destination nodes, sequence numbers and some other control information. A packet can also be called a segment or datagram. Once they reach their destination, the packets are reassembled to make up the original data again. It is therefore obvious that, to transmit data in packets, it has to be digital data.

In packet-switching, the packets are sent towards the destination irrespective of each other. Each packet has to find its own route to the destination. There is no predetermined path; the decision as to which node to hop to in the next step is taken only when a node is reached. Each packet finds its way using the information it carries, such as the source and destination IP addresses.