UPnP Discovery
The UPnP discovery protocol allows a device to announce to the control points that it has become available on the network. On joining the network, the device multicasts SSDP NOTIFY messages to advertise its embedded devices and services to all the control points on the network. When a new control point becomes available on the network, it multicasts a SSDP M_SEARCH discovery message through an HTTPMU request to search for available devices and services. The search message can contain qualifications on the type of device or service that the control point is searching for. All devices on the network must respond to the control point if their devices or services match the search criteria in the discovery message. The response that is transmitted to the control point by one or more matching devices contains a URL to the device description. The response message is sent to the control point using the User Datagram Protocol (UDP) with Simple Service Discovery Protocol (SSDP) headers.
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