The software that implements the various network protocols needed in TCP/IP environments is usually referred as a TCP/IP stack. On most systems including all versions of Windows NT, the TCP/IP stack is implemented in kernel mode. In the case of Windows NT, the tcpip.sys driver implements the TCP/IP stack.
All Windows NT versions up to Windows XP and Windows Server 2003 shipped with the first generation of Windows TCP/IP stack. Windows Vista and Windows Server "Longhorn" include the second generation of Windows TCP/IP stack.