Windows Sockets network services follow the WOSA model, meaining his means that there exists a Windows Sockets Application Programming Interface (API), which is the application programmer's access to network services, Windows Sockets Service Provider Interfaces (SPIs) which are implemented by transport service provider and name resolution service provider vendors, and WS2_32.DLL. Windows Sockets 2's WOSA compliant architecture is illustrated below.
Windows Sockets 2 Architecture
The SPI is intended to be used within all 32-bit implementations and versions of Microsoft Windows including Windows NT and Windows 95.