The Internet: Computer Network Hierarchy
Every device that is connected to the internet is part of a network, even the one in your home. F or example, your computer may use a cable or fiber modem to connect to an internet service provider (ISP). At work, your device may be part of a local area network (LAN), but your internet connection is provided by your employer's ISP. Once you connect your computer it becomes part of your employer's network. The ISP may then connect to a larger network. The internet is simply a network of networks.
Large communications companies have their own dedicated backbones, always-on connections to the internet that have enough bandwidth to allow many people to use the connection at the same time. In each region, a company has a local office that connects local homes and businesses to its main network. The amazing thing here is that there is no centralized network. Traffic travels from point to point, and if one computer drops out of the network, the packets that make up a digital file are routed to another computer. Files arrive as expected, and you'd never notice the change in the traffic pattern.