This is a Windows system installed file with Windows File Protection (WFP) enabled.
ssdpsrv.dll has 43 known versions, the most recent one is 6.3.9600.16384 (winblue_rtm.130821-1623). The average file size is about 111.37 KB. This is a .NET Common Language Runtime (CLR) assembly.
The Simple Service Discovery Protocol (SSDP) is a network protocol based on the Internet Protocol Suite for advertisement and discovery of network services and presence information. SSDP is the basis of the discovery protocol of Universal Plug and Play.
(Note, the behaviors below are for all versions of ssdpsrv.dll, select a unique version for details.)
United States installs about 38.04% of SSDP Service DLL.