DS3181/DS3182/DS3183/DS3184
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10.10.6.5 Transmit M23 DS3 AIS/Idle Generation
M23 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 an 1100 pattern with two ones immediately following each DS3 overhead bit. M1,
M2, and M3 bits are overwritten with the values zero, one, and zero (010) respectively. FX1, FX2, FX3, and FX4 bits are
overwritten with the values one, zero, zero, and one (1001) respectively. X1 and X2 are overwritten with 11.. P1 and
P2 are overwritten with the calculated payload parity from the previous output DS3 frame. And, C31, C32, and C33
are overwritten with 000.
If transmit AIS is enabled, the data stream payload is forced to a 1010 pattern with a one immediately following
each DS3 overhead bit. M1, M2, and M3 bits are overwritten with the values zero, one, and zero (010) respectively.
FX1, FX2, FX3, and FX4 bits are overwritten with the values one, zero, zero, and one (1001) respectively. X1 and X2
are overwritten with 11. P1 and P2 are overwritten with the calculated payload parity from the previous DS3 frame.
And, CX1, CX2, and CX3 are overwritten with 000. AIS will overwrite a transmit Idle signal.
10.10.6.5.1Receive M23 DS3 Frame Format
The DS3 frame format is shown in Figure 10-40. The 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). CX1, CX2, and CX3 are the stuff control bits for tributary #X.
10.10.6.5.2Receive M23 DS3 Overhead Extraction
Overhead extraction extracts all of the DS3 overhead bits from the M23 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 and P2 bits are output as an error indication (modulo 2 addition of the calculated parity and the bit). In addition,
the Application Identification Channel (AIC) is extracted from the C11 bit and stored in a register. 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.
10.10.6.5.3Receive DS3 Downstream AIS Generation
Downstream DS3 AIS (all ‘1’s) can be automatically generated on an OOF, LOS, or AIS condition or manually
inserted. If automatic downstream AIS is enabled, downstream AIS is inserted when an LOS or AIS condition is
declared, or no earlier than 2.25 ms and no later than 2.75 ms after an OOF condition is declared. Automatic
downstream AIS is programmable (on or off). If manual downstream AIS insertion is enabled, downstream AIS is
inserted. Manual downstream AIS insertion is programmable (on or off). Downstream AIS is removed when all
OOF, LOS, and AIS conditions are terminated and manual downstream AIS insertion is disabled.