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DS3171/DS3172/DS3173/DS3174
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P-bit parity errors are determined by calculating the parity of the current DS3 frame (payload bits only), and
comparing the calculated parity to the P-bits (P
1
and P
2
) in the next DS3 frame. If the calculated parity does not
match P
1
or P
2
, a single P-bit parity error is declared.
C-bit parity errors (C-bit format only) are determined by calculating the parity of the current DS3 frame (payload bits
only), and comparing the calculated parity to the C-bits in subframe three (C
31
, C
32
, and C
33
) in the next DS3 frame.
If the calculated parity does not match C
31
, C
32
, or C
33
, a single C-bit parity error is declared.
FEBE errors (C-bit format only) are determined by the C-bits in subframe four (C
41
, C
42
, and C
43
). A value of 111
indicates no error and any other value indicates an error.
The receive alarm indication (RAI) bit will be set high in the transmitter when one or more of the indicated alarm
conditions is present, and low when all of the indicated alarm conditions are absent. Setting the receive alarm
indication on LOS, SEF, LOF, or AIS is individually programmable (on or off).
The Application Identification Channel (AIC) is stored in a register bit. It is determined from the C
11
bit. The AIC is
set to one (C-bit format) if the C
11
bit is set to one in thirty-one consecutive multiframes. The AIC is set to zero (M23
format) if the C
11
bit is set to zero in four of the last thirty-one consecutive multiframes. Note: The stored AIC bit
must not change when an LOS, OOF, or AIS condition is present.
A FEBE is transmitted by default upon reception of a DS3 frame in which a C-bit parity error or a framing error is
detected and counted.
10.6.5 C-Bit DS3 Framer/Formatter
10.6.5.1 Transmit C-bit DS3 Frame Processor
The C-bit DS3 frame format is shown in
shows the function of each overhead bit in the
DS3 Frame.
Table 10-27. C-Bit DS3 Frame Overhead Bit Definitions
Bit Definition
X
1
, X
2
Remote Defect Indication
(RDI)
P
1
, P
2
Parity Bits
M
1
, M
2
, and M
3
Multiframe Alignment Bits
F
XY
Subframe Alignment Bits
C
11
Application Identification
Channel (AIC)
C
12
Reserved
C
13
Far-End Alarm and Control
(FEAC) signal
C
21
, C
22
, and C
23
Unused
C
31
, C
32
, and C
33
C-bit parity bits
C
41
, C
42
, and C
43
Far-End Block Error (FEBE)
bits
C
51
, C
52
, and C
53
Path Maintenance Data Link
(or HDLC) bits
C
61
, C
62
, and C
63
Unused
C
71
, C
72
, and C
73
Unused