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Advance Data Sheet
T7633 Dual T1/E1 3.3 V Short-Haul Terminator
May 1998
62
Lucent Technologies Inc.
Frame Formats
(continued)
T1 Framing Structures
(continued)
Cyclic redundancy checking is performed over the entire ESF data payload (4,608 data bits, with all 24 framing bits
(F
E
, D
L
, CRC-6) set to 1 during calculations). The CRC-6 bits transmitted in ESF will be determined as follows:
I
The check bits, c1 through c6, contained in ESF(n + 1) will always be those associated with the contents of
ESF(n), the immediately preceding ESF. When there is no ESF immediately preceding, the check bits may be
assigned any value.
I
For the purpose of CRC-6 calculation only, every F bit in ESF(n) is set to 1. ESF(n) is altered in no other way.
I
The resulting 4632 bits of ESF(n) are used, in order of occurrence, to construct a polynomial in x such that the
first bit of ESF(n) is the coefficient of the term x
4631
and the last bit of ESF(n) is the coefficient of the term x
0
.
I
The polynomial is multiplied by the factor x
6
, and the result is divided, modulo 2, by the generator polynomial x
6
+
x + 1. The coefficients of the remainder polynomial are used, in order of occurrence, as the ordered set of check
bits, c1 through c6, that are transmitted in ESF(n + 1). The ordering is such that the coefficient of the term x
5
in
the remainder polynomial is check bit c1 and the coefficient of the term x
0
in the remainder polynomial is check
bit c6.
The ESF remote frame alarm consists of a repeated eight 1s followed by eight 0s transmitted in the data link posi-
tion of the framing bits.
T1 Loss of Frame Alignment (LFA)
Loss of frame alignment condition for the superframe or the extended superframe formats is caused by the inability
of the receive framer to maintain the proper sequence of frame bits. The number of errored framing bits required to
detect a loss of frame alignment is given is Table 25.
The receive framer indicates the loss of frame and superframe conditions by setting the LFA and LSFA bits
(FRM_SR1 bit 0 and bit 1), respectively, in the status registers for the duration of the conditions. The local system
may give indication of its LFA state to the remote end by transmitting a remote frame alarm (RFA). In addition, in
the LFA state, the system may transmit an alarm indication signal (AIS) to the system interface.
Table 25. T1 Loss of Frame Alignment Criteria
Format
Number of Errored Framing Bits That Will Cause a Loss of Frame Alignment Condition
D4
2 errored frame bits (F
T
or F
S
) out of 4 consecutive frame bits if FRM_PR10 bit 2 = 1.
2 errored F
T
bits out of 4 consecutive F
T
bits if PRM_PR10 bit 2 = 0.
2 errored frame bits (F
T
or F
S
) out of 4 consecutive frame bits if FRM_PR10 bit 2 = 1.
2 errored F
T
bits out of 4 consecutive F
T
bits if FRM_PR10 bit 2 = 0.
3 errored frame bits (F
T
or F
S
) or channel 24 FAS pattern out of 12 consecutive frame bits.
2 errored F
E
bits out of 4 consecutive F
E
bits or optionally 320 or more CRC-6 errored
checksums within a one second interval if loss of frame alignment due to excessive CRC-6
errors is enabled in FRM_PR9.
SLC-96
DDS: Frame
ESF