In asynchronous transfer mode (ATM), a class of traffic that is bursty, with periods of intense activity and periods of low or no activity, and of a non real-time nature that is not dependent on loss or delay because there is time to recover through retransmission.Traffic parameters include peak cell rate (PCR), cell delay variation tolerance (CDVT), sustainable cell rate (SCR), maximum burst size (MBS), and burst tolerance (BT). The quality of service (QoS) parameter is cell loss ratio (CLR). ATM also defines available bit rate (ABR), constant bit rate (CBR), real-time Variable Bit Rate (rt-VBR), unspecified bit rate (UBR), and variable bit rate (VBR) traffic classes. Examples of nrt-VBR traffic include data traffic such as X.25, frame relay, transaction processing, LAN-to-LAN, and non real-time buffered voice and video traffic. See also ABR, ATM, BT, CBR, CDVT, CLR, compression, frame relay, LAN, MBS, PCR, QoS, realtime, rt-VBR, SCR, time slot, UBR, and VBR, and X.25.