NDIS Interface

The NBF transport driver processes the TDI requests as frames to be sent out on the network by the logical link control (LLC) layer. The LLC layer is the NBF layer that receives and sends frames from and to a remote computer on the network.

NBF conforms to the IEEE 802.2 LLC protocol standard and performs the following functions:

• Link establishment for connection-oriented communications

• Maintenance and termination of connections

• Frame sequencing and acknowledgment

• Frame flow control

• Connection-oriented and connectionless communications

At the LLC layer, NBF binds, receives, and sends packets to the underlying network adapter drivers by using the NDIS interface.

Communication within the LLC layer is based on service access points, links, and link stations. A link station is a logical point within a service access point that enables an adapter to establish connection-oriented communication with another adapter. Each LLC client program identifies itself by registering a unique service access point. A service access point is a mechanism by which the layer above can programmatically access a particular service implemented by the layer below. There are well-known service access points, similar to the well-known ports of TCP/IP. Because NBF is a NetBIOS implementation, it uses the well-known NetBIOS service access point (0xF0).

Figure 16.3 shows the NetBIOS service access point, other access points, and their relationships to the LLC layer.

Figure 16.3 NBF LLC Layer and NDIS Interface to the Service Access Points

When a network client program uses LLC to send a frame on to the network, LLC specifies the client or source service access point (SSAP), as well as the destination service access point (DSAP) in the header of the LLC frame.