Throughout the standard for Internet Protocol you will see the description of packet switching, "fragment and reassemble internet datagrams when necessary for transmission through small packet networks." A message is divided into smaller parts know as packets before they are sent. Each packet is transmitted individually and can even follow different routes to its destination. Once all the packets forming a message arrive at the destination, they are recompiled into the original message.
Internet data, whether in the form of a Web page, a downloaded file or an e-mail message, travels over a system known as a packet-switching network. Each of these packages gets a wrapper that includes information on the sender's address, the receiver's address, the package's place in the entire message, and how the receiving computer can be sure that the package arrived intact.
There are two huge advantages to the packet switching. The network can balance the load across various pieces of equipment on a millisecond-by-millisecond basis. If there is a problem with one piece of equipment in the network while a message is being transferred, packets can be routed around the problem, ensuring the delivery of the entire message.
Packet switching explained in simple terms
In teaching the concept of packet switching in the classroom, I would take a piece of paper with a message written on it, and from the front of the classroom, ask the person in the front seat simply to turn around and pass the paper to the person behind him, and in turn continue the process until the paper made it to the person in the back row.
In the next phase of the illustration, I would take the same piece of paper that had the message written on it, and tear it into four pieces. On each individual piece of paper I would address it as if sending a letter through the postal service, by writing my name as the sender, and also the name of the person in the back of the room as the recipient. I would also label each individual piece of paper as one of four, two of four, three of four, and four of four.
This time I would take the four individual pieces of paper and walk across the front row, and as I handed one piece of paper to four different students, I would explain to them who was to receive the paper, and asked them to pass it to the person marked as the recipient by using the people behind them. When all four pieces of paper arrived at the destination, I would ask the recipient to read the label I had put on each piece of paper, and confirm they had received the entire message.
My original passing of the paper represented Circuit switching, the telecommunications technology which used circuits to create the virtual path, a dedicated channel between two points, and then delivered the entire message.
My second passing of the "packets" or scraps of paper illustrated packet switching, and each individual in the room acted as a router. The key difference between the two methods was the additional routes that the pieces of the message took. A very primitive, but effective demonstration of packet switching and the way in which a message would be transmitted across the internet.
Once the concept of packet switching was developed the next stage in the evolution was to create a language that would be understood by all computer systems. This new standard set of rules would enable different types of computers, with different hardware and software platforms, to communicate in spite of their differences.