Supports Class C or Class D traffic, which is non realtime variable bit rate (nrt-VBR) data traffic with no timing relationship between the source and the sink. Class C traffic, such as X.25 and frame relay, is connection-oriented VBR traffic with no timing relationship between source and sink. Class D traffic, such as LAN and SMDS, is connectionless VBR traffic that is sensitive to loss, but not highly sensitive to delay. Message mode service is used for framed data in which only one interface data unit (IDU) is passed. Streaming mode service is used for framed data in which multiple IDUs are passed in a stream. See also ATM, Class C ATM traffic, Class D, connectionless, connectionoriented, frame relay, IDU, message mode service, nrt-VBR, streaming mode service, and X.25.