A router connects different networks together, minimum two. In small networks these are usualy refered to as WAN(Wide Area Network) and LAN (Local Area Network). The router connects the computers and devices in your local network to the internet.

1. A router holds the "driving directions" of packets to know where to send or "route" them. If they are destined for the local subnet network, or to the internet, or to another private network, they will go through the router.
2. In Large and Complex Networks, Routing can get complicated and tedious to program. Therefore there are many routing protocols that can be used such as OSPF, RIP, RIPv2, EIGRP, etc.
3. All-in-one routers usually include a firewall although it is better practice and more secure to have a dedicated firewall device.
4. The myth that routers needs to be restarted frequently when they are not working correctly is not true. If restarting a router solves the problem, it is likely that it is not configured correctly or it is not a good router.

A network Switch connects multiple networking devices together (eg computers, printers, IP Cameras, IP Phones, Servers, NAS's, and other IoT devices). Either by wire or by wireless WiFi Protocol.

Most IoT devices require power. And they require Network. So PoE or Power over Ethernet, is a method used to send both network/ethernet and power to a device via the same cable and the same interface. This greatly simplifies and reduces provisioning and installation costs, while also saving on Power Supplies.

The network topology design should be done and finalized long before construction starts. Reason being many conduits and pipes need to be placed into the concrete, therefore this needs to be done at a very early stage.