Editing Superframe (section)

==Extended superframe==
In [[telecommunication]]s, '''extended superframe''' ('''ESF''') is a [[T-carrier|T1]] [[Frame synchronization|framing]] standard. ESF is 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&nbsp;bit/s [[channel capacity]] for a [[data link]] [[Communication channel|channel]] (used to pass [[out-of-band data]] between equipment.)  It requires less frequent [[synchronization]] than the earlier superframe format, and provides on-line, real-time [[wikt:Monitoring|monitoring]] of [[Telecommunication circuit|circuit]] capability and operating condition.

===Structure===
An extended superframe is 24 [[Data frame|frames]] long, and the framing [[bit]] of each frame is used in the following manner:
* All odd-numbered frames (1, 3, ..., 23) are used for the [[data link]] (totalling 4000 bits per second),
* Frames 2, 6, 10, 14, 18, and 22 are used to pass the [[Cyclic redundancy check|CRC]] total of the previous extended superframe (all 4632 bits, framing and data), and
* Frames 4, 8, 12, 16, 20, and 24 are used to send the fixed framing pattern, 001011.

The CRC is computed using the polynomial {{math|''x''<sup>6</sup>+''x''+1}} over all 24×193 = 4632 bits (framing and data) of the previous superframe, but with its framing bits forced to 1 for the purpose of CRC computation.<ref>{{Cite thesis |last=Yoon |first=Hee Byung |title=The Error Performance Analysis Over Cyclic Redundancy Check Codes |date=June 1991 |degree=M.Sc. |publisher=Naval Postgraduate School |pages=8–10 |url=http://apps.dtic.mil/dtic/tr/fulltext/u2/a246020.pdf|archive-url=https://web.archive.org/web/20151210214431/http://www.dtic.mil/dtic/tr/fulltext/u2/a246020.pdf|url-status=live|archive-date=December 10, 2015}}</ref>  The purpose of this small CRC is not to take any immediate action, but to keep statistics on the performance of the link.

Like the predecessor superframe, every sixth frame's least-significant data bit can be used for [[robbed-bit signaling]] of call supervision state.  However, there are four such bits (ABCD) per channel per extended superframe, rather than the two bits (AB) provided per superframe.  
(Specifically, the robbed bits follow framing bits 6, 12, 18 and 24.)

Unlike the superframe, it is possible to avoid robbed-bit signalling and send call supervision over the data link instead.