5.2  Implementing WAN Miniports

In order to support such media as ISDN, Frame Relay, Switch 56, and so forth with NT RAS, vendors must supply a WAN miniport NIC driver. The driver should be written to the current version of NDIS, which is 4.0, however, existing drivers written to NDIS 3.0 will continue to run. WAN NIC drivers call the WAN-specific variations of a few NDIS functions. While a WAN miniport calls many of the same NDIS functions as a LAN NIC driver, equivalent WAN-specific NDIS calls replace certain LAN NIC driver NDIS calls. In addition, a WAN miniport driver provides a WAN-specific send function whose definition differs from the definition of the MiniportSend function implemented by LAN miniport NIC drivers. These WAN-specific calls are described here.

WAN miniport drivers communicate with the NDISWAN intermediate NDIS driver through the NDIS library. NDISWAN can provide common services such as data compression, encryption, loopback, simple PPP framing, and so forth, so that the WAN NIC drivers need only features specific to the medium (for example, Q931 signalling required for ISDN). If a WAN miniport manages a NIC with compression, PPP, and encryption capabilities, it can specify to NDISWAN that the driver will offload these operations. When the miniport responds to the OID_WAN_GET_INFO query during initialization, it indicates that it will perform one or more of these functions.

A WAN NIC driver is an NDIS miniport NIC driver that:

·Performs connection-management operations passed from the NDISWAN intermediate NDIS driver to the WAN NIC driver.

·Accepts send requests and indicates received data to the NDISWAN driver.

The following sections define the interface between the NDISWAN driver and a WAN NIC driver. Note that in addition to the information in this chapter, developers of WAN NIC drivers also should refer to the previous chapters on LAN miniport NIC drivers and to the Network Driver Reference for details on the many NDIS functions, for instance, NdisMSetTimer, NdisOpenConfiguration, and so forth, that are provided for all miniport NIC drivers.