The NBF protocol, like NetBEUI, provides for both connectionless or connection-oriented traffic. Connectionless communications can be either unreliable or reliable. NBF and NetBEUI provide only unreliable connectionless, not reliable connectionless communications.
Unreliable communication is similar to sending a letter in the mail. No response is generated by the receiver of the letter to ensure the sender that the letter made it to its destination. In comparison, reliable connectionless communications is like a registered letter whose sender is notified that the letter arrived.
Connection-oriented communications provide reliable communications between two computers in a way that is analogous to a phone call, where two callers connect, a conversation occurs, and then the connection is dropped when the conversation ends. A reliable connection requires more overhead than connectionless communications do.
NBF communicates via the NDIS interface at the Logical Link Control (LLC) sublayer. A connection at the LLC sublayer is called a link, which is uniquely defined by the adapter's address and the destination service access point (DSAP). A service access point (SAP) can be thought of as the address of a port to a layer as defined by the OSI model. Because NBF is a NetBIOS implementation, it uses the NetBIOS SAP (0xF0). While the 802.2 protocol governs the overall flow of data, the primitives are responsible for passing the data from one layer to the next. The primitives are passed through the SAPs between layers.
Figure 6.1 NBF Communicates via the NDIS Interface at the LLC Sublayer