AT&T DS1/DMi/ISDN-PRI ESF Framing, Data Link Signal Frame Sync Pattern, Bits Robbed BIT Optional

1-12	INTRODUCTION
ESF Framing
Initially,	this format was called F , pronounced “F sub e,” for framing extended. It is now called
	e

extended superframe (ESF). The ESF framing format was developed after the D4 format. Not all equipment used with a DS1/DMI-BOS interface supports ESF. Specifically, most D4-channel banks (unless they are configured as LIU-3ESF or equivalent) and CDMs do not currently support ESF framing. (See figure 1-5, DS1 Extended Superframe Format.)

FRAME	FRAME BIT
NUMBER	DEFINITIONS

1DATA LINK F BIT (DL)

2CRC-6 F BIT

3DATA LINK SIGNAL

4FRAME SYNC PATTERN

5DATA LINK SIGNAL

6CRC-6 F BIT

7DATA LINK SIGNAL

8FRAME SYNC PATTERN

9DATA LINK SIGNAL

10CRC-6 F BIT

11DATA LINK SIGNAL

12FRAME SYNC PATTERN

13DATA LINK SIGNAL

14CRC-6 F BIT

15DATA LINK SIGNAL

16FRAME SYNC PATTERN

17DATA LINK SIGNAL

18CRC-6 F BIT

19DATA LINK SIGNAL

20FRAME SYNC PATTERN

21DATA LINK SIGNAL

22CRC-6 F BIT

23DATA LINK SIGNAL

24FRAME SYNC PATTERN

FRAME BIT
		CHANNEL 1		CHANNEL 2
		8-BITS
		8-BITS
		8-BITS
	0	8-BITS
		8-BITS
		7-BITS	A	ROBBED BIT (OPTIONAL)
		8-BITS
	0	8-BITS
		8-BITS
		8-BITS
		8-BITS
	1	7-BITS	B	ROBBED	BIT	(OPTIONAL)
		8-BITS
		8-BITS
		8-BITS
	0	8-BITS
		8-BITS
		7-BITS	C	ROBBED	BIT	(OPTIONAL)
		8-BITS
	1	8-BITS
		8-BITS
		8-BITS
		8-BITS
	1	7-BITS	D	ROBBED	BIT	(OPTIONAL)

Figure 1-5.DS1 Extended Superframe Format

The ESF format consists of a 24-bit framing pattern. Compared to the 12-bit fixed pattern for D4, only 6 of the 24 bits carry a fixed pattern. The other 18-bits consist of a 6-bit error detection code, called the cyclic redundancy check (CRC) sum, and a 12-bit facility data link signal. At the transmit