abstract:In telecommunications, an extended superframe (ESF) is a T1 framing standard, sometimes called D5 framing because it was first used in the D5 channel bank, invented in the 1980s. It is preferred to its predecessor, superframe, because it includes a cyclic redundancy check (CRC) and 4000 bit/s channel capacity for a data link channel (used to pass out-of-band data between equipment.