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Windows Sockets transport and namespace–service providers are DLLs with a single exported procedure entry point for the service provider initialization function WSPStartup or NSPStartup, respectively. All other service provider functions are made accessible to the Ws2_32.dll through the service provider's dispatch table. Service provider DLL's are loaded into memory by the Ws2_32.dll only when needed, and are unloaded when their services are no longer required.
The SPI also defines several circumstances in which a transport service provider calls up into the Ws2_32.dll (upcalls) to obtain DLL support services. The transport service provider DLL is given the Ws2_32.dll's upcall dispatch table through the UpcallTable parameter to WSPStartup.
Service providers should have their file name extension changed from "DLL" to ".WSP" or ".NSP". This requirement is not strict. A service provider will still operate with the Ws2_32.dll with any file name extension.
The Winsock SPI uses the following function prefix naming convention:
| Prefix | Meaning | Description |
|---|---|---|
| WSP | Windows Sockets Service Provider | Transport service provider entry points |
| WPU | Windows Sockets Provider Upcall | Ws2_32.dll entry points for service providers |
| WSC | Windows Sockets Configuration | WS2_32.dll entry points for installation applets |
| NSP | Namespace Provider | Namespace provider entry points |
As described above, these entry points are not exported (with the exception of WSPStartup and NSPStartup), but are accessed through an exchange of dispatch tables.