In ITU-T standards for asynchronous transfer mode (ATM), a class of traffic supported by ATM Adaptation Layer 5 (AAL5). Class X traffic is variable bit rate (VBR) and specifically either unspecified bit rate (UBR) or available bit rate (ABR) in nature. Class X traffic can be characterized as either connection-oriented or connectionless traffic with no timing relationship between the source and the sink. Class X traffic examples include LAN Emulation (LANE) and Internet Protocol (IP). See also AAL, AAL5, ABR, ATM, connectionless, connection-oriented, IP, ITU-T, LANE, sink, source, UBR, and VBR.