In asynchronous transfer mode (ATM), a class of traffic intended to support non real-time (nrt) applications that may require a minimum rate guarantee and can benefit from accessing additional bandwidth dynamically, as it becomes available. GFR does not require adherence to a flow control protocol. The GFR service guarantee is based on AAL5 protocol data units (PDUs), also known as frames. During periods of network congestion, GFR attempts to discard entire frames, rather than cells that are segments of frames. Traffic descriptors in both the forward and backward directions include maximum frame size (MFS), burst cell tolerance (BCT), minimum cell rate (MCR), and peak cell rate (PCR). Specific applications have yet to be identified. ATM also defines available bit rate (ABR), constant bit rate (CBR), non real-time Variable Bit Rate (nrt-VBR), real-time Variable Bit Rate (rt-VBR), unspecified bit rate (UBR), and variable bit rate (VBR) traffic classes. See also AAL5, ABR, ATM, BCT, CBR, cell, frame, MCR, MFS, nrt, nrt-VBR, PCR, PDU, QoS, real-time, rt-VBR, UBR, and VBR.