In ITU-T standards for asynchronous transfer mode (ATM), a class of traffic supported by ATM Adaptation Layer 3/4 (AAL3/4). Such traffic is connectionless variable bit rate (VBR) traffic that is sensitive to loss, but not highly sensitive to delay. Examples of Class D traffic include LAN and SMDS.With the demise of SMDS, Class D has all but disappeared in favor of AAL5 and Class C. See also AAL, AAL3/4, AAL5, ATM, Class C, connectionless, ITU-T, LAN, sink, SMDS, source, and VBR.