Also known as ESF, Extended Super Frame is an enhanced version of D4 frame formatting. It is used most often in conjunction with B8ZS line coding in building point-to-point clear-channel T1 data lines. ESF has 24 frames of 192 bits each and provides 16 signaling states in the 193rd bit to ensure sychronization, supervisory control, and maintenance capabilities.


Thanks to Dwight Baker for this information

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.

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