(Simple Service Discovery Protocol) A standard for advertising services on a TCP/IP network and discovering them. The Universal Plug and Play (UPnP) protocol uses SSDP to announce and find devices in order, for example, to stream video from a source to a playback system. The description of services returned from an SSDP request may include a URL that provides additional information. SSDP queries and responses are transferred in UDP packets rather than the more reliable TCP. See UPnP, SLP, UDP and FDSSDP.