UPnP Discovery
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4/8/2010
The UPnP discovery protocol allows a device to announce to control points that it has become available on the network. It also allows control points to find devices that support services it wants to control.
When a device becomes available on a network, it advertises its embedded devices and services to control points on the network by multicasting Simple Service Discovery Protocol (SSDP) NOTIFY messages.
When a control point becomes available on the network, it searches for available devices and services by multicasting an SSDP M_SEARCH message using an HTTP multicast over UDP (HTTPMU) request. The search message contains a list of qualifications that specify the type of device or service for which the control point is searching.
If a device on the network contains embedded devices or services that match the search criteria, it responds to the control point with a UDP response that contains SSDP headers. Each response contains a URL from which the control point can retrieve device description information for that device.