Stop thinking of a "network" as a big thing.
They can be small too, the same software works, but the priorities are different.
@davew In fact “the Internet” is a collection of interconnected Autonomous System networks (there are about 80,000 ASNs registered), some huge, some small, connected to the “backbone network.” The size distribution follows a power law (large number of small networks, small number of huge ones). Your provider’s network may be an AS or a subnetwork of one. Your home network is a subnetwork of theirs.
This is all to a first approximation.
