One of the major uses of the DLC protocol is connecting personal computers to Systems Network Architecture (SNA) hosts¾that is, IBM mainframe or midrange computers such as the AS/400.
SNA provides equivalent functionality to the OSI Network, Transport, Session, and Presentation levels (although functionality might differ at each level). Because the DLC layer and the OSI Data Link layer are almost identical in functionality, a programming interface was developed for the DLC layer and passed on to programmers wanting to use this level of interface. The interface is described in the IEEE 802.2 standard.
Note
DLC is not robust enough to handle multi-threaded programming.
Figure 14.1 compares the SNA and OSI models.
Figure 14.1 Comparison of SNA and OSI Models
With the Token Ring Interface Connection (TIC), any SNA host can communicate with a token ring network. With the LAN Interface Connection (LIC), an AS/400 computer can communicate with an Ethernet network.
Figure 14.2 illustrates a mainframe connectivity path using token ring.
Figure 14.2 Mainframe Connectivity Path Using Token Ring
The Microsoft SNA Server uses the DLC protocol device driver when communicating to mainframes by using the token ring interface. Detailed configuration and installation information is provided in the Microsoft SNA Server Installation Guide and the Microsoft SNA Server Administration Guide.