unspecified bit rate (ATM) (UBR)

Unspecified Bit Rate (UBR) is one of five service classes defined by the ATM Forum.

The UBR service class supports data traffic with variable bit rates up to a maximum transmission rate at which a tolerable delay can occur. A UBR connection has no cell loss ratio( CLR) or cell transfer delay( CTD) commitment.

In terms of transmission capabilities, UBR is only suitable for burst traffic, i.e. for data transmission and LAN data traffic.