Architecture of NBF

NBF is a transport driver that is composed of the following layers:

LLC802.2 Protocol

Corresponds to the Open Systems Interconnect (OSI) Logical Link Control (LLC) layer. It performs code, address, and control frame flow, and provides connectionless data transfer.

NetBIOS Frame Protocol (NBFP)

Corresponds to the OSI Transport and Session layers. It performs session establishment, multiplexing, and termination. It also performs message segmentation, delimiting, assembly, and acknowledgment.

Figure 13.1 shows the components of NBF and their relation to the OSI model.

Figure 13.1 The OSI Model and the Architecture of NBF

Notice that the upper edge of NBF, the NBFP component, connects to the bottom edge of the Windows NT-based Transport Driver interface (TDI). The lower edge of NBF, the LLC component, connects to the Network Driver Interface (NDIS).

Note

In the preceding illustration, the Network layer between NBFP and LLC is intentionally empty. In the OSI model, the Network layer lies between the Transport and LLC layers. However, NetBEUI uses IBM Token Ring source routing to perform network layer functions. Token Ring source routing conforms to a different standard, the IEEE 802.5 standard, and logically corresponds to the OSI Physical layer, not the OSI Network layer.

The following sections describe the NBF functions at its upper and lower edges:

• "NBF's Interface to the Upper OSI Layers—The TDI Interface"
• "NBF's Interface to the Lower OSI Layers—The NDIS Interface"