"Discovery" describes how Windows determines that a device is present. For physically connected devices, discovery occurs through PCI, USB, and other physical bus enumerators. For network-connected devices, Windows uses network communication protocols to discover the presence of a device.
Under Windows Vista and Windows 7, Plug and Play Extensions (PnP-X) allows network-connected devices to be discovered and installed on a PC client as if they were connected physically.
To take advantage of PnP-X, the device manufacturer must support either Devices Profile for Web Services or UPnP 1.0. Specifically, PnP-X relies on the discovery of network-connected devices by using SSDP and WS-Discovery.