This section shows the relationship of Windows NT RAS and how drivers for wide area network cards such as ISDN, X.25, and Switched 56 adapters use the services of NDIS and NDISWAN to communicate in a WAN environment.
The following describes the NDISWAN intermediate NDIS driver and the NDISTAPI driver and provide a more detailed view of the entire RAS system.
The components of RAS that are shown in this picture are described next.
This set of functions allows user-mode applications to make RAS connections. After a RAS connection is established, applications can connect to network services using standard network interfaces such as Windows Sockets, NetBIOS, Named Pipes, or RPC.
PPP Authentication (PAP, CHAP) and network configuration protocols (IPCP, IPXCP, NBFCP, LCP, and so forth) are provided by the RAS system component. A WAN NIC driver implements only PPP media-specific framing. However, if a WAN NIC driver manages a NIC that implements these capabilities in hardware, it replaces this NDISWAN capability. The miniport informs NDISWAN during driver initialization when it responds to the OID_WAN_GET_INFO query.
This component presents an SPI interface to user-mode applications and converts user-mode requests to corresponding TAPI OIDs.
This component implements TAPI with a kernel-mode portion of the TAPI interface. The ndistapi.sys component communicates with WAN drivers by routing TAPI-related OID requests with the NdisRequest function to the appropriate WAN driver.
The NDISWAN intermediate NDIS driver supports PPP protocol/link framing, compression, and encryption. NDISWAN converts an NDIS_PACKET from an upper layer transport driver to an NDIS_WAN_PACKET and passes the reformatted packet to an underlying WAN NIC miniport driver. The ndiswan.sys driver communicates with WAN NIC drivers through two interfaces:
This component is a standard Windows NT device driver for internal serial ports or multiport serial cards. The built-in asynchronous WAN miniport NIC driver for Windows NT uses the internal serial driver for modem communications. Any driver that exports the same functions as the Windows NT serial driver will work with the built-in async WAN NIC driver.
X.25 vendors can choose to implement serial driver emulators for the X.25 card. In this case, each virtual circuit on the X.25 card appears as a serial port (with an X.25 PAD attached to it). The connection interface must correctly emulate serial signals such as DTR, DCD, CTS, RTS, and DSR.
X.25 vendors who choose to implement a serial driver emulator for their X.25 card must also make an entry for their PAD in the pad.inf file. This file contains the command/response script needed to make a connection through the X.25 PAD. See the Remote Access Service Administrator’s Guide for details on the pad.inf file.
ISDN, Switched 56, and X.25 vendors should write a WAN NIC driver for their adapters.