ABR

from The Free On-line Dictionary of Computing (8 July 2008)

automatic baud rate detection
ABR
autobaud

   <communications> (ABR, autobaud) A process by which a
   receiving device determines the speed, {code level}, and {stop
   bits} of incoming data by examining the first character,
   usually a preselected sign-on character.  ABR allows the
   receiving device to accept data from a variety of transmitting
   devices operating at different speeds without needing to
   establish data rates in advance.

   (1996-06-18)

from V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006)

ABR
       Available Bit Rate (ATM, CBR, VBR, UBR, QOS, BIT)