Copyright Goodheart-Willcox Co., Inc. Chapter 13 Internet and the World Wide Web 511 Internet The Internet is a worldwide communication network that connects individual computer networks. Messages are exchanged between these networks, and then the destination network must deliver the message to the correct computer in its network. It sounds complicated, but the process is very simple to understand. The routing mechanism is based on small fi le fragments called packets. The transmission control protocol (TCP) identifi es a fi le to be sent and breaks it into packets, each of which is given a header. The packet header contains the: • fi le’s source computer’s Internet protocol (IP) address • destination computer’s IP address • packet number and • total number of packets in the entire fi le. These packets are sent though the network of networked computers, possibly not on the same path, as shown in Figure 13-1. If a server along the way is too busy or not working, a packet sent to that server is rerouted to another network. When the packets arrive at the destination network, they are reassembled into the original fi le. If any packets are missing or corrupted in the transmission, messages are sent to the source computer and the lost packets are resent. The process of creating packets and transmitting them over a network is called packet-switching. It happens at the speed of light. Electricity and light travel a little less than one foot in one nanosecond, or about one billion feet in one second. That is why transmissions are so quick on the Internet. A public switched network makes use of packet switching to transfer information and is available to the general public. Examples are the Internet and the telephone network. A private switched network is protected from the general public by security measures. An Living Online 1.1.1.1 Living Online 1.1.1, 1.1.2, 1.1.3 Living Online 2.2.1 Goodheart-Willcox Publisher Macrovector/Shutterstock.com Figure 13-1. The TCP breaks a file into packets, which are then sent through the network. Computer A Packet Switch Packet Switch Packet Switch Computer B Computer C Computer D Packet Switch Packet Switch Packet Switch Packet Switch To C T o C To C To C T o D To D To D T o D T o D To D To C GS5 GS4 GS4