| unspecified bit rate A QoS class defined by the ATM Forum for Asynchronous Transfer Mode (ATM) networks. UBR allows any amount of data up to a specified maximum to be sent across the network, but there are no guarantees in terms of cell loss rate and delay. Compare with available bit rate (ABR), constant bit rate (CBR), and variable bit rate (VBR). Compare with ABR (available bit rate), CBR, and VBR. |