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nt-part2_23 Analysis of the Security of  Windows NT 1 March 1999 23 NWLink is Microsoft's implementation of the IPX/SPX protocol. It was the default protocol until NT version 3.5 [44]. To fully utilize this protocol, a NetWare redirector is needed, which will give the opportunity to access files and printers on a NetWare server. TCP/IP is an acronym for Transmission Control Protocol/Internet Protocol. It is a whole suite of protocols, including TCP, UDP, IP and ICMP. TCP/IP is, since version 3.5, the default transport protocol in NT. Yet another supported and included protocol is the Data Link Control (DLC) protocol, which provides an interface to the data-link layer (level 2 in the OSI model). In fact, it is not a true transport protocol. There are two reasons for using the DLC protocol [42]: (1) accessing IBM mainframes, and (2) printing to HP printers connected directly to the network. 4.1.4  STREAMS STREAMS is a driver environment that has been implemented to simplify porting of transport protocols from one operating system to another. UNIX System V is another operating system supporting this environment [3]. STREAMS maps to TDI at its upper boundary, and to NDIS at its lower boundary. Thus, Figure 5 is somewhat misleading. In NT version 3.1, both TCP/IP and NWLink were implemented as STREAM-based drivers. Due to the extra overhead involved with such implementation, these two proto- cols nowadays do not use STREAMS. 4.1.5  Transport Driver Interface (TDI) TDI was created to provide a uniform interface to the various transport protocols. The selected name is somewhat misleading. Essentially, it is not a driver, it is simply a stan- dard for message passing between the session layer and the transport layer. 4.1.6  Network APIs NT provides a rich set of network APIs. Each API finds its own way to the network through the set of protocols in the network architecture. In section 3.7, we described named pipes and mailslots. In the introduction to section 4, the redirector and the net- work server were presented. However, we have not yet mentioned the WinSock API, the NetBIOS API and RPC facility. The WinSock API is derived from the very popular standard UNIX networking inter- face. The interface was originally developed at the University of California at Berke- ley,  in  the  early  1980s.  TCP/IP  and  NWLink  can  both  be  accessed  through  the WinSock API. The NetBIOS API is a standard network programming interface for PCs, and has been used since the early 1980s. In NT, the NetBIOS interface is implemented as a driver, sometimes referred to as an emulator, and can be used over NetBEUI, NWLink and TCP/IP.