Detecting network power connection status using AC signals

A local area network (LAN), comprising:

• a plurality of LAN nodes;
• a LAN switch;
• communication cabling comprising multiple twisted wire pairs connecting the plurality of nodes to the switch for providing data communication among the nodes;
• and
• a power supply subsystem, which is operative to supply DC power to at least one of the nodes via the communication cabling over at least one of the wire pairs, substantially without interfering with the data communication, while coupling a periodic time-varying signal into the at least one of the wire pairs, and which is further operative to sense a time-varying voltage on the at least one of the wire pairs due to the time-varying signal and, responsive to the sensed time-varying voltage, to control the DC power supplied to the at least one of the nodes.

A method for supplying power over a local area network (LAN), in which a plurality of LAN nodes are coupled to a LAN switch by communication cabling, the cabling including multiple twisted wire pairs connecting the plurality of nodes to the switch for providing data communication among the nodes, the method comprising:

• supplying DC power to at least one of the nodes via the communication cabling over at least one of the wire pairs substantially without interfering with the data communication;
• coupling a time-varying signal into the at least one of the wire pairs;
• sensing a time-varying voltage on the at least one of the wire pairs due to the time-varying signal generated by the signal generator;
• and
• responsive to the sensed time-varying voltage, controlling the DC power supplied to the at least one of the nodes.