Unspecified Bit Rate: UBR is an ATM service category which does not specify traffic related service guarantees. Specifically, UBR does not include the notion of a per-connection negotiated bandwidth. No numerical commitments are made with respect to the cell loss ratio experienced by a UBR connection, or as to the cell transfer delay experienced by cells on the connection.
UBR
Meaning of UBR in English
ATM Forum English vocabulary. Английский словарь организации Форум ATM. 2012