UPnP is a very common protocol. It is used by almost all network-enabled consumer electronics products used in your home or office, and as such, it is a vital part of Digital Living Network Alliance (DLNA). The standard body for UPnP is the UPnP Forum (upnp.org). UPnP is largely based on an HTTP application where both clients and servers are participants. This HTTP is, however, extended so that it can be used over TCP as well as UDP, where both use unicast addressing (HTTPU) and multicast addressing (HTTPMU).

Discovery of devices in the network is performed using Simple Service Discovery Protocol (SSDP), which is based on HTTP over UDP, and event subscriptions and notifications are based on General Event Notification Architecture (GENA). Both SSDP and GENA introduce new HTTP methods to search, notify and subscribe to and unsubscribe from an event. Devices find each other by notifying the network of their existence using multicast addressing and the available services....