Paul Baran’s three topologies of networks: centralized, decentralized, distributed.
Simplified model of the internet. It’s made of routers. Home devices are connected to your router, which is connected to your internet network provider. Business and academic networks are similarly made up of individual computers connected to local routers, which are, in turn, connected to those institutions’ network providers. Mobile devices are connected to mobile network providers, and those providers in turn connect to other network providers to make sure your texts get to your friends phones and computers.