The Windows Sockets 2 specification defines an extension mechanism that exposes advanced transport functionality to application programs. For more information, see Function Extension Mechanism.
The following Microsoft-specific extensions were added to Windows Sockets 1.1. They are also available in Windows Sockets 2.
These functions are not exported from the WS2_32.DLL; they are exported from MSWSOCK.DLL.
An application written to use the Microsoft-specific extensions to Windows Sockets will not run correctly over a Windows Sockets service provider that does not support those extensions.