5. Data Features

The Dialogic drivers used with the BRI/2 enables the BRI/2 to function like an ISDN network interface card (NIC). The BRI/2 provides link layer access (across the B channel) that allows reliable transfer of data across an ISDN network. To enable Windows applications to communicate with the BRI/2, the Dialogic driver implement an NDIS driver.

5.1. NDIS Compatibility

NDIS (Network Device Interface Specification) is a Microsoft^® standard that allows for multiple network adapters and multiple protocols to coexist. NDIS permits the high-level protocol components to be independent of the BRI/2 by providing a standard interface. This means that the BRI/2 may be used by applications that use the standard networking APIs that are part of the Windows operating system, such as Sockets (WinSock), NetBIOS, and SPX/IPX. The NDIS Wrapper is made up of the NDIS WAN driver and the BRI/2 WAN Miniport driver. Both the LAN (transport) protocols and the TAPI protocols communicate with the NDIS WAN driver (refer to Figure 6).

The BRI/2 WAN Miniport driver (dlgcbri.sys) is installed when you install the BRI/2 ISDN Network Adapter driver.

Figure 6. NDIS Driver Model

The BRI/2 WAN Miniport driver is at the bottom of the network architecture. Because the Windows network architecture supports NDIS , it requires that network adapter card drivers be written to the NDIS 3.0 specification. The BRI/2 driver is written to the NDIS specification. In Windows NT, NDIS has been implemented in a module called ndis.sys, which is referred to as the NDIS interface.

NDIS enables the following:

• The Dialogic driver to receive a network packet from any one of several upper layer drivers for transmission on the network.
• The Dialogic driver to accept a network packet from the BRI/2 and pass it up to one or more upper layer drivers that may receive it.
• The Remote Access Service (RAS) to set specific configuration parameters for the BRI/2.
• Upper layer drivers to query the Dialogic driver for specific configuration and statistics from the BRI/2.
• The Dialogic driver to asynchronously inform an overlying driver of changes in network status or BRI/2 status.

User data transmitted over the B channels are sent in HDLC frames. These frames are 8-bits long and are sent in the appropriate B channel block in layer 1 (refer to Figure 7.) The BRI/2 extracts the HDLC data and sends a raw bit stream to the NDIS driver.

Figure 7. Data Transfer Model

When using the BRI/2 as an ISDN NIC to transfer files, the following procedures occur:

• A TAPI-aware application, such as RAS (Remote Access Service), sends a call connect request through the NDIS TAPI driver to the NDIS WAN driver. The BRI/2 Miniport Driver then translates the TAPI call control information into instructions used by the BRI/2 to place a call. TAPI is used to support essentially all dialing functions within the Windows operating system.
• After the telephone connection has been established, the RAS is used to connect remote computers for data transfer applications. Windows also supports the PPP (Point-to-Point Protocol) in RAS. The PPP is a set of framing and authentication protocols. It negotiates configuration parameters for multiple layers of the OSI model, thereby enabling any combination of IPX, TCP/IP, and NetBEUI.

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