PoE injectors are part of larger PoE systems that include network devices such as routers and switches.
Using an uninterruptible power supply (UPS), power is injected at the network's head end.
If necessary, midpoint spans powered by additional UPS systems can supply more power.
According to the IEEE 802.3af specification, power must be injected every 328 ft.,
which is the maximum distance for an Ethernet connection.