Extended Super Frame (ESF)
A group of twenty-four 193-bit T1 frames. ESF goes through a framing pattern of 001011, which appears in frames 4, 8, 12, 16, 20, and 24. Other occurrences of the framing bit are used to store a 6-bit cyclic redundancy check (CRC), which monitors the overall quality of the line. The remaining 12 occurrences of the framing bit are used to create a 4Kbps facility data link. Like D4 framing, ESF uses signaling bits from every sixth frame. However, ESF creates four signaling channels: A, B, C, and D.