DS3181/DS3182/DS3183/DS3184
171
are overwritten with 11. P1, P2, C31, C32, and C33 are overwritten with the calculated payload parity from the previous
output DS3 frame. And, CX1, CX2, and CX3 (X ≠ 3) are overwritten with 000. AIS will overwrite a transmit Idle signal.
10.10.5.5.1Receive C-bit DS3 Frame Format
The DS3 frame format is shown in Figure 10-40. 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 that define the multiframe boundary. FXY are the sub-frame alignment bits that
define the sub-frame boundary. Note: Both the M-bits and F-bits define the DS3 frame boundary. 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.
10.10.5.5.2Receive 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
X1, X2, P1, P2, MX, FXY, and CXY are output on the receive overhead interface (ROH, ROHSOF, and ROHCLK). The
P1, P2, C31, C32, and C33 bits are output as an error indication (modulo 2 addition of the calculated parity and the
bit). In addition, the Application Identification Channel (AIC), which is stored in a register bit, is determined from the
C11 bit. The AIC is set to one (C-bit format) if the C11 bit is set to one in 31 consecutive multiframes. The AIC is set
to zero (M23 format) if the C11 bit is set to zero in four of the last 31 consecutive multiframes. Note: The stored AIC
bit must not change when a LOS, OOF, or AIS condition is present. The C13 bit is sent over to the receive FEAC
controller. The C51, C52, and C53 bits are sent to the receive HDLC overhead controller.
10.10.6 M23 DS3 Framer/Formatter
10.10.6.1 Transmit M23 DS3 Frame Processor
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 sub-frame
alignment bits. C11 is the Application Identification Channel (AIC). CX1, CX2, and CX3 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 other bit positions in the
DS3 frame are payload bits.
Table 10-35. M23 DS3 Frame Overhead Bit Definitions
BIT
DEFINITION
X1, X2
Remote Defect Indication
(RDI)
P1, P2
Parity Bits
M1, M2, and M3
Multiframe Alignment Bits
FXY
Sub-frame Alignment Bits
C11
Application Identification
Channel (AIC)
CX1, CX2, and CX3
Stuff Control Bits for Tributary
#X