There was a time – perhaps a decade ago, perhaps more – when the network was simply the network. It was routers and switches and cables and power. It was responsible for carrying data to and fro, and for acting as a hard wall gatekeeper that would prevent data from getting from one place to another.
As time went on, the network added more functions. It connected the network to the Internet, it measured traffic, it acted as a firewall, blocking traffic based on any number of criteria. It dabbled in security, as well.