The Data Link Control (DLC) protocol is a special purpose, non-routable protocol provided with Windows NT. Windows NT –based DLC provides applications only with direct access to the data link layer.
Windows NT–based DLC does not support the TDI interface as do other Windows NT–based transport protocols. Because DLC does not support the TDI, it cannot be used for communication with TDI client applications, such as the Windows NT redirector and server. Because the redirector cannot use DLC, this protocol is not used for normal session communication between Windows NT–based computers.
The DLC protocol driver provided with Windows NT enables the computer to communicate with other computers running the DLC protocol stack (for example, an IBM mainframe) and other network peripherals (for example, print devices such as a Hewlett-Packard HP 4Si that use a network adapter card (NIC) to connect directly to the network.)
The DLC protocol driver provides access to IEEE 802.2 class I and class II services. It also provides the direct interface to send and to receive raw 802.5, 802.3, and Ethernet type network frames. The interface consists of a dynamic-link library and a device driver.
Windows NT DLC contains an 802.2 Logical Link Control (LLC) Finite State Machine, which is used when transmitting and receiving type 2 connection-oriented frames. DLC can also transmit and receive type 1 connectionless frames, such as Unnumbered Information (UI) frames. Type 1 and 2 frames can be transmitted and received simultaneously.
Windows NT–based DLC works with either token ring or Ethernet Media Access Control (MAC) drivers and can transmit and receive Digital.Intel.Xerox (DIX) format frames when bound to an Ethernet MAC.
The DLC interface can be accessed from 32-bit Windows NT–based programs and from 16-bit MS-DOS-based and 16-bit Windows–based programs. The 32-bit interface conforms largely to the CCB2 interface, the segmented 16-bit pointers being replaced with flat 32-bit pointers. The 16-bit interface conforms to the CCB1 interface.
Note
For definitions of the CCB interfaces, see the IBM Local Area Network Technical Reference.