abr - Computer Definition
Also known as best-effort ATM. In asynchronous transfer mode (ATM), a class of traffic in which the network attempts to pass the maximum number of cells, but with no absolute guarantees. Subsequent to the establishment of the connection, the network may change the transfer characteristics through a flow control mechanism that communicates to the originating end-user device.This flow control feedback mechanism is in the form of resource management cells (RM-Cells). During periods of congestion, the network can buffer cells and advise the sender to throttle back on the rate of transmission. ABR supports variable bit rate (VBR) traffic with flow control, a minimum transmission rate, and specified performance parameters.Traffic parameters include peak cell rate (PCR), cell delay variation tolerance (CDVT), and minimum cell rate (MCR). No quality of service (QoS) commitment is made. ABR traffic examples include bursty LAN traffic and e-mail, neither of which requires guarantees of network access, but rather can deal with time slot access on an as-available basis. ABR service is not intended to support real-time applications. ATM also defines 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 ATM, buffer, CDVT, cell, e-mail, flow control, LAN, MCR, nrt-VBR, PCR, QoS, RMCell, rt-VBR, time slot, UBR, and VBR.
(1) (AutoBaud Rate detect) The analysis of the first characters of a message to determine its transmission speed and number of start and stop bits.
(2) (Available Bit Rate) An asynchronous transfer mode (ATM) level of service that adjusts bandwidth according to the congestion levels in the network. ABR is not used for time-critical data such as real-time voice and video.