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Extended Super Frame (ESF) refers to a T1 framing standard that includes 24 frames of 192 bits each. ESF helps to extend D4 super frame from 12 frames to 24 frames. Also, the 193rd bit location is redefined by ESF to add increased efficiency, such as timing and other similar functions. ESF is more useful when compared with its predecessor super frame, because ESF enables facility data link communications and cyclical redundancy check (CRC) error detection.
ESF significantly enhances customer service values by creating real-time metrics about efficiency, and network health and performance. ESF is sometimes referred to as D5 framing.
Techopedia Explains Extended Super Frame
As opposed to the earlier bit-robbing framing methods, ESF is able to maintain 64 Kbps channels and uses an overhead of only 8 Kbps out of each 1.544 Mbps of user data. Out of 8 Kbps overhead, 4 Kbps is used for facility data link, 2 Kbps for framing, and 2 Kbps for CRC.
In ESF, the 193-bit location is redefined to serve mainly three objectives:
- Maintenance communications
- Error detection
- Frame synchronization
Inside an ESF super frame, there are 24 bits available to carry out these functions. Out of these, synchronization is carried out by using six bits, error detection is performed by using another six bits, and the remaining 12 bits are used for maintenance communications.
In D4 framing, 12 bits are used for every super frame to carry out synchronization, whereas in ESF framing, only six bits are used for every super frame to carry out synchronization. D4 framing does not include any link-level error checking, whereas the ESF framing implements a six-bit cyclic redundancy check (CRC) pattern to make sure that the frame received has no bit errors.
In addition, the 12 bits assigned for maintenance communications provide the maintenance communications channel with a 4,000 bps capacity. This allows the network control center operators to examine remote devices for information regarding the link performance. ESF makes use of the "robbed bits" to execute in-band signaling. ESF uses four frames for each super frame to carry out this kind of signaling.
