Extended Super Frame or ESF is a T1 framing standard. Sometimes called D5 framing. Preferred over its predecessor, Super Frame, because it includes a CRC and bandwidth for a data link channel (used to pass out-of-band data between equipment).
In ESF, a superframe is 24 frames long, and the 193rd bit of each frame is used in the following manner:
- Frames 4, 8, 12, 16, 20, and 24 are used to send the framing pattern, 001011.
- Frames 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21 and 23 are used for the data link. (Totalling half of all framing bits, or 4000 bits per second.)
- Frames 2, 6, 10, 14, 18, and 22 are used to pass the CRC total for each superframe.