Available Bit Rate (ABR) refers to an ATM transfer capability where the limiting ATM layer transfer characteristics provided by the network may change subsequent to connection establishment. It is expected that a user which adapts its traffic to the changing ATM layer transfer characteristics will experience a low cell loss ratio.
Recommendation Q.2961 covers the support of additional traffic parameters for the B-ISDN at the TB reference point or coincident SB and TB reference point as defined in Recommendation I.413 by means of the DSS 2. This Recommendation defines the DSS 2 protocol procedures, formats and functions needed to support the ABR ATM transfer capability as defined in Recommendation I.371. This Recommendation includes the use of the DSS 2 signalling procedures for the negotiation of Minimum Cell Rate (MCR) during call establishment. ABR precludes use of DSS 2 signalling procedures for the modification of traffic parameters during the active phase of the call.