DS3171/DS3172/DS3173/DS3174
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X1 and X2 are the Remote Defect Indication (RDI) bits (also referred to as the far-end SEF/AIS bits). P1 and P2 are
the parity bits used for line error monitoring. M1, M2, and M3 are the multiframe alignment bits. FXY are the subframe
alignment bits. C11 is the Application Identification Channel (AIC). C12 is reserved for future network use, and has a
value of one. C13 is the Far-End Alarm and Control (FEAC) signal. C21, C22, and C23 are unused, and have a value
of one. C31, C32, and C33 are the C-bit parity bits used for path error monitoring. C41, C42, and C43 are the Far-End
Block Error (FEBE) bits used for remote path error monitoring. C51, C52, and C53 are the path maintenance data link
(or HDLC) bits. C61, C62, and C63 are unused, and have a value of one. C71, C72, and C73 are unused, and have a
value of one. The X-bit, P-bit, M-bit, C-bit, and F-bit positions are overhead bits, and the other bit positions in the
T3 frame are payload bits regardless of how they are marked by TDEN.
10.6.5.2 Transmit C-Bit DS3 Frame Generation
C-bit DS3 frame generation receives the incoming payload data stream, and overwrites all of the overhead bit
locations.
The multiframe alignment bits (M1, M2, and M3) are overwritten with the values zero, one, and zero (010)
respectively.
The subframe alignment bits (FX1, FX2, FX3, and FX4) are overwritten with the values one, zero, zero, and one (1001)
respectively.
The X-bits (X1 and X2) 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 (P1 and P2) 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.
The bits C11, C12, C21, C22, C23, C61, C62, C63, C71, C72, and C73 are all overwritten with a one.
The bit C13 is overwritten with the Far-End Alarm and Control (FEAC) data input from the transmit FEAC controller.
The bits C31, C32, and C33 are all overwritten with the calculated payload parity from the previous DS3 frame.
The bits C41, C42, and C43 are all overwritten with the Far-End Block Error (FEBE) bit. The FEBE bit can be
generated automatically or inserted from a register bit. The FEBE bit source is programmable (automatic or
register). If the FEBE bit is generated automatically, it is zero when at least one C-bit parity error has been detected
during the previous frame.
The bits C51, C52, and C53 are overwritten with the path maintenance data link input from the HDLC controller.
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 to error insertion. Frame generation is programmable
(on or off). Note: P-bit generation may still be performed even if frame generation is disabled.
10.6.5.3 Transmit C-bit DS3 Error Insertion
Error insertion inserts various types of errors into the different DS3 overhead bits. The types of errors that can be
inserted are framing errors, P-bit parity errors, C-bit parity errors, and Far-End Block Error (FEBE) errors.
The framing error insertion mode is programmable (F-bit, M-bit, SEF, or OOMF). An F-bit error is a single subframe
alignment bit (FXY) error. An M-bit error is a single multiframe alignment bit (M1, M2, or M3) error. An SEF error is an
error in all the subframe alignment bits in a subframe (FX1, FX2, FX3, and FX4). An OOMF error is a single multiframe
alignment bit (M1, M2, or M3) error in two consecutive DS3 frames.
A P-bit parity error is generated by is inverting the value of the P-bits (P1 and P2) in a single DS3 frame. P-bit parity
error(s) can be inserted one error at a time, or continuously. The P-bit parity error insertion mode (single or
continuous) is programmable.
A C-bit parity error is generated by is inverting the value of the C31, C32, and C33 bits in a single DS3 frame. C-bit
parity error(s) can be inserted one error at a time, or continuously. The C-bit parity error insertion mode (single or
continuous) is programmable.