Networking APIs provide a protocol-independent way for applications to communicate across a network. Networking APIs can be implemented in user mode or in both user mode and kernel mode, and in some cases are wrappers around another networking API that implements a specific programming model or provides additional services.

Transport Driver Interface (TDI) clients are kernel-mode device drivers that usually implement the kernel-mode portion of a networking API's implementation. TDI clients get their name from the fact that the I/O request packets (IRPs) they send to protocol drivers are formatted according to the Windows 2000 Transport Driver Interface standard . This standard specifies a common programming interface for kernel-mode device drivers.

TDI transports, also known as transports, Network Driver Interface Specification (NDIS) protocol drivers, and protocol drivers, are kernel-mode protocol drivers. They accept IRPs from TDI clients and process the requests these IRPs represent. This processing might require network communications with a peer, prompting the TDI transport to add protocol-specific headers (such as TCP, UDP, IPX) to data passed in the IRP and to communicate with adapter drivers using NDIS functions . TDI transports generally facilitate application network communications by transparently performing message operations such as segmentation and reassembly, sequencing, acknowledgment, and retransmission.

The NDIS library (Ndis.sys) provides encapsulation for adapter drivers, hiding from them specifics of the Windows 2000 kernel-mode environment. The NDIS library exports functions for use by TDI transports as well as support functions for adapter drivers.

NDIS miniport drivers are kernel-mode drivers that are responsible for interfacing TDI transports to particular network adapters. NDIS miniport drivers are written so that they are wrapped by the Windows 2000 NDIS library. The encapsulation provides cross-platform compatibility with Consumer Windows. NDIS miniport drivers don't process IRPs; rather, they register a call-table interface to the NDIS library that contains pointers to functions corresponding to ones that the NDIS library exports to TDI transports. NDIS miniport drivers communicate with network adapters by using NDIS library functions that resolve to hardware abstraction layer (HAL) functions.