The Free On-line Dictionary of Computing (30 December 2018):

Basic Rate Interface
2B1D
2B+D
BRI

    (BRI, 2B+D, 2B1D) An Integrated Services
   Digital Network channel consisting of two 64 kbps "bearer"
   (B) channels and one 16 kbps "delta" (D) channel, giving a
   total data rate of 144 kbps.  The B channels are used for
   voice or user data, and the D channel is used for control and
   signalling and/or X.25 packet networking.  BRI is the kind
   of ISDN interface most likely to be found in residential
   service.

   (2002-01-13)