Rainbow Electronics DS3170 - Manual (Page 87)

DS3170 DS3/E3 Single-Chip Transceiver
87 of 233
9.6.5.5.1 Receive C-bit DS3 Frame Format
The DS3 frame format is shown in Figure 9-13 . 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 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.
9.6.5.5.2 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.
9.6.6 M23 DS3 Framer/Formatter
9.6.6.1 Transmit M23 DS3 Frame Processor
The M23 DS3 frame format is shown in Figure 9-13 . Table 9-28 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 9-28. 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
9.6.6.2 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