TMXF28155 Supermapper
155/51 Mbits/s SONET/SDH x28/x21 DS1/E1
Data Sheet
June 2002
476
Agere Systems Inc.
20 M13/M23 MUX/DeMUX Block Functional Description
(continued)
When M13_BIPOLAR = 0, the received DS3 data and clock are passed directly to the M23 demultiplexer. When
M13_BIPOLAR = 0 and M13_BPV_IN = 1, the received DS3 data and clock are passed to the M23 demultiplexer
while the bipolar violation indication is forwarded to the internal BPV counter for performance monitoring (B3ZS
decoder is not used). When M13_BIPOLAR = 1 and M13_BPV_IN = 0, the received SMPR_RDS3POS_DATA and
SMPR_RDS3NEG_BPV data inputs are first B3ZS decoded.
The B3ZS decoder block performs decoding as follows. For each clock period that both SMPR_RDS3POS_DATA
and SMPR_RDS3NEG_BPV are 0 (no pulse), the decoder outputs a 0. For each clock period that either
SMPR_RDS3POS_DATA or SMPR_RDS3NEG_BPV is 1 (pulse), the decoder determines whether or not the
pulse is part of a zero substitution (ZS) sequence. A ZS sequence is [00V] or [B0V], where B is a pulse on either
the positive or negative input that is opposite in polarity to the last nonzero input, and V is a pulse that is the same
polarity as the last nonzero input.
If the received pulse is not part of a ZS sequence, the decoder outputs a 1. Otherwise, the decoder outputs three
consecutive zeros in place of the received ZS sequence.
The B3ZS decoder also checks for bipolar coding violations. Bipolar coding violations are defined as received
V-pulses that are not opposite in polarity to the last V-pulse or are not immediately preceded by a 0, or received
zeros that are immediately preceded by two other zeros.
The M13 contains a counter that increments on each occurrence of a received bipolar coding violation (BPV). It
also monitors the occurrence of excessive zeros (EXZ), which is defined as any zero string length equal to or
greater than 3 (T1.231). These are part of the performance monitoring counters that can be sampled and simulta-
neously reset (see DS3 Performance Monitors Section on
page 479
). Their last sampled values are available in
registers M13_BPV_CNT_R[1—3] (
Table 307 on page 229
) and M13_EXZ_CNT_R[1—3] (
Table 308 on
page 230
).
20.11.2 DS3 T-to-R Loopback
The M13 can be configured to loopback the internal transmit DS3 from the output of the M23 MUX
(M13_LOOP_T_TO_R = 1 (
Table 271 on page 218
)), or accept the received DS3 signal after B3ZS decoding
(M13_LOOP_T_TO_R = 0) and send it into the M23 deMUX block.
20.11.3 M23 Demultiplexer
The M23 demultiplexer will take the received DS3 signal and either deMUX it into 7 DS2 data streams or strip off the
overhead bits and send payload out through the NSMI serial interface when M13_NSMI_MODE = 1; see
Table 289
on page 224
.
The serial data interface, when enabled (M13_NSMI_MODE = 1), generates a clock M13_DNSMI_CLK and an
enable M13_DNSMI_EN for outputting DS3 payload data M13_DNSMI_DATA. A sync pulse M13_DNSMI_SYNC,
in reference to and ahead of the first M bit within a DS3 frame, is also generated. The offset from the sync pulse to
the first M bit is programmable through bits M13_D_SP_OFFSET[7:0] (
Table 274 on page 219
).
In the case of the received DS3 signal being deMUXed into 7 DS2s, those DS2s can be sent out of the device, or
looped back to the transmit side, or passed to M12 demultiplexers for further breakdown into DS1s/E1s.
DS3 Framer.
After being B3ZS decoded, the incoming DS3 data stream is checked for the presence of unframed
all ones. If the input data is 0 for fewer than 9 out of 8192 clock periods, bit M13_RDS3_ALL1_DET (
page 209
) will be set.
The M23 demultiplexer determines if the input signal contains valid DS3 framing. This is done in two stages by first
finding a bit position that matches the frame alignment pattern (F bits), and then locating the multiframe alignment
signal (M bits). After a matching F-bit sequence is found, in-frame is declared (M13_DS3_OOF = 0 (
Table 236 on
page 208
)) when correct M bits are received for three consecutive M frames (T1.231). The maximum average
reframe time is 0.5 ms in the presence of a bit error rate of 10
–3
.