
DS3171/DS3172/DS3173/DS3174
85
A FEBE error is generated by forcing the C
41
, C
42
, and C
43
bits in a single multiframe to zero. FEBE error(s) can be
inserted one error at a time, or continuously. The FEBE error insertion rate (single or continuous) is programmable.
Each error type (framing, P-bit parity, C-bit parity, or FEBE) has a separate enable. Continuous error insertion
mode inserts errors at every opportunity. Single error insertion mode inserts an error at the next opportunity when
requested. the framing multi-error modes (SEF or OOMF) insert the indicated number of error(s) at the next
opportunities when requested; i.e., a single request will cause multiple errors to be inserted. The requests can be
initiated by a register bit(TSEI) or by the manual error insertion input (TMEI). The error insertion initiation type
(register or input) is programmable. The insertion of each particular error type is individually enabled. Once all error
insertion has been performed, the data stream is passed on to overhead insertion.
10.6.5.4 Transmit C-Bit DS3 Overhead Insertion
Overhead insertion can insert any (or all) of the DS3 overhead bits into the DS3 frame. The DS3 overhead bits X
1
,
X
2
, P
1
, P
2
, M
X
, F
XY
, and C
XY
can be sourced from the transmit overhead interface (TOHCLK, TOH, TOHEN, and
TOHSOF). The P-bits (P
1
and P
2
) and C
31
, C
32
, and C
33
bits are received as an error mask (modulo 2 addition of
the input bit and the internally generated bit). The DS3 overhead insertion is fully controlled by the transmit
overhead interface. If the transmit overhead data enable signal (TOHEN) is driven high, then the bit on the transmit
overhead signal (TOH) is inserted into the output data stream. Insertion of bits using the TOH signal overwrites
internal overhead insertion.
10.6.5.5 Transmit C-Bit DS3 AIS/Idle Generation
C-bit DS3 AIS/Idle generation overwrites the data stream with AIS or an Idle signal. If transmit Idle is enabled, the
data stream payload is forced to a 1100 pattern with two ones immediately following each DS3 overhead bit. M
1
,
M
2
, and M
3
bits are overwritten with the values zero, one, and zero (010) respectively. F
X1
, F
X2
, F
X3
, and F
X4
bits are
overwritten with the values one, zero, zero, and one (1001) respectively. X
1
and X
2
are overwritten with 11. And,
P
1
, P
2,
C
31
, C
32
, and C
33
are overwritten with the calculated payload parity from the previous output DS3 frame.
If transmit AIS is enabled, the data stream payload is forced to a 1010 pattern with a one immediately following
each DS3 overhead bit. M
1
, M
2
, and M
3
bits are overwritten with the values zero, one, and zero (010) respectively.
F
X1
, F
X2
, F
X3
, and F
X4
bits are overwritten with the values one, zero, zero, and one (1001) respectively. X
1
and X
2
are overwritten with 11. P
1
, P
2,
C
31
, C
32
, and C
33
are overwritten with the calculated payload parity from the previous
output DS3 frame. And, C
X1
, C
X2
, and C
X3
(X
≠
3) are overwritten with 000. AIS will overwrite a transmit Idle signal.
10.6.5.5.1 Receive C-Bit DS3 Frame Format
The DS3 frame format is shown in
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 that define the multiframe boundary. F
XY
are the subframe alignment bits that
define the subframe boundary. Note: Both the M-bits and F-bits define the DS3 frame boundary. C
11
is the
Application Identification Channel (AIC). C
12
is reserved for future network use, and has a value of one. C
13
is the
Far-End Alarm and Control (FEAC) signal. C
21
, C
22
, and C
23
are unused, and have a value of one. C
31
, C
32
, and C
33
are the C-bit parity bits used for path error monitoring. C
41
, C
42
, and C
43
are the Far-End Block Error (FEBE) bits
used for remote path error monitoring. C
51
, C
52
, and C
53
are the path maintenance data link (or HDLC) bits. C
61
,
C
62
, and C
63
are unused, and have a value of one. C
71
, C
72
, and C
73
are unused, and have a value of one.
10.6.5.5.2 Receive C-Bit DS3 Overhead Extraction
Overhead extraction extracts all of the DS3 overhead bits from the C-bit DS3 frame. All of the DS3 overhead bits
X
1
, X
2
, P
1
, P
2
, M
X
, F
XY
, and C
XY
are output on the receive overhead interface (ROH, ROHSOF, and ROHCLK). The
P
1
, P
2
, C
31
, C
32
, and C
33
bits are output as an error indication (modulo 2 addition of the calculated parity and the
bit). The C
13
bit is sent over to the receive FEAC controller. The C
51
, C
52
, and C
53
bits are sent to the receive HDLC
overhead controller.