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DS3171/DS3172/DS3173/DS3174
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10.6.6 M23 DS3 Framer/Formatter
10.6.6.1 Transmit M23 DS3 Frame Processor
The M23 DS3 frame format is shown in
defines the framing bits for M23 DS3. X
1
and X
2
are the Remote Defect Indication (RDI) bits (also referred to as the far-end SEF/AIS bits). P
1
and P
2
are the parity
bits used for line error monitoring. M
1
, M
2
, and M
3
are the multiframe alignment bits. F
XY
are the subframe
alignment bits. C
11
is the Application Identification Channel (AIC). C
X1
, C
X2
, and C
X3
are the stuff control bits for
tributary #X. The X-bit, P-bit, M-bit, C-bit, and F-bit positions are overhead bits, and the remainder of the bit
positions in the T3 frame are payload bits regardless of how they are marked by TDEN.
Table 10-28. M23 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
X1
, C
X2
, and C
X3
Stuff Control Bits for Tributary
#X
10.6.6.2 Transmit M23 DS3 Frame Generation
M23 DS3 frame generation receives the incoming payload data stream, and overwrites all of the DS3 overhead bit
locations.
The multiframe alignment bits (M
1
, M
2
, and M
3
) are overwritten with the values zero, one, and zero (010)
respectively.
The subframe alignment bits (F
X1
, F
X2
, F
X3
, and F
X4
) are overwritten with the values one, zero, zero, and one (1001)
respectively.
The X-bits (X
1
and X
2
) are both overwritten with the Remote Defect Indicator (RDI). The RDI source is
programmable (automatic, 1, or 0). If the RDI is generated automatically, the X-bits are set to zero when one or
more of the indicated alarm conditions is present, and set to one when all of the indicated alarm conditions are
absent. Automatically setting RDI on LOS, SEF, LOF, or AIS is individually programmable (on or off).
The P-bits (P
1
and P
2
) are both overwritten with the calculated payload parity from the previous DS3 frame. The
payload parity is calculated by performing modulo 2 addition of all of the payload bits after all frame processing has
been completed. P-bit generation is programmable (on or off). The P-bits will be generated if either P-bit generation
is enabled or frame generation is enabled.
If C-bit generation is enabled, the bit C
11
is overwritten with an alternating one zero pattern, and all of the other C-
bits (C
XY
) are overwritten with zeros. If C-bit generation is disabled, then all of the C-bit timeslots (C
XY
) will be
treated as payload data, and passed through. C-bit generation is programmable (on or off). Note: Overhead
insertion may still overwrite the C-bit time slots even if C-bit generation is disabled.
Once all of the DS3 overhead bits have been overwritten, the data stream is passed on to error insertion. If frame
generation is disabled, the incoming DS3 signal is passed on directly to error insertion. Frame generation is
programmable (on or off). Note: P-bit generation may still be performed even if frame generation is disabled.