Windows NT supports three types of network drivers:
·Network Interface Card or NIC drivers
·Intermediate protocol drivers
·Upper level protocol drivers
Network drivers under Windows NT support peer-to-peer and client-server communication between a local node and a remote node on a LAN or WAN. Windows NT uses drivers at one or more network layers to pass data packets and make the protocol translations necessary for error-free communication between nodes.
In some special cases, a single monolithic driver can include the functions of all driver types.
This document describes the design of the Windows NT network drivers. It also describes the NDIS services available to such drivers and how they use these services.
The following figure illustrates Windows NT network driver components.
The types of drivers described include:
1.NIC drivers — NIC drivers directly manage network interface cards, referred to as NICs. The NIC drivers interface directly to the hardware at their lower edge and at their upper edge present an interface to allow upper layers to send packets on the network, to handle interrupts, to reset the NIC, to halt the NIC and to query and set the operational characteristics of the driver. NIC drivers can be either miniports or legacy full NIC drivers. The WAN miniport is a special type of miniport. A WAN miniport has a few additional and different requirements and gives upper-layer applications remote access to a wide area network using connection-oriented services supplied by WAN NDIS services.
2.Intermediate protocol drivers — Intermediate protocol drivers interface between an upper-level driver such as a legacy transport driver and a miniport. To the upper-level driver, an intermediate driver looks like a miniport. To a miniport, the intermediate driver looks like a protocol driver. An intermediate protocol driver can layer on top of another intermediate driver although such layering could have a negative effect on system performance. A typical reason for developing an intermediate protocol driver is to perform media translation between an existing legacy transport driver and a miniport that manages a NIC for a new media type unknown to the transport driver. For instance, an intermediate driver could translate from LAN protocol to ATM protocol.
3.Upper level protocol driver — An upper level protocol driver implements a TDI interface, or possibly another application-specific interface at its upper-edge to provide services to users of the network. Such a driver allocates packets, copies data from the sending application into the packet, and sends these packets to the lower level driver by calling NDIS. At its lower edge, this type of driver provides a protocol interface to receive incoming packets from the next lower level driver. This highest-level driver transfers received data to the destination application.
A WAN miniport can operate in one of two modes. A miniport that operates in pass-through mode implements PPP framing, encryption, and compression at the miniport level rather than in NDIS. A WAN miniport only operates in this mode if its NIC performs the compression, encryption, and PPP framing in its hardware, otherwise these operations are best done by NDIS.
While an intermediate protocol driver presents a miniport driver interface at it upper edge, the list of functions it must provide is different from that of a lowest level miniport. For instance, an intermediate protocol driver does not need to have an ISR routine or a DPC routine. However, it can be thought of as two drivers in one with a private interface between its protocol piece and its miniport piece.