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Preliminary Data Sheet, Rev. 1
October 2000
TMXF28155 Super Mapper
155/51 Mbits/s SONET/SDH x28/x21 DS1/E1
341
Lucent Technologies Inc.
M13/M23 Mux/Demux Block Functional Description
(continued)
M13/M23 Demultiplexer
(continued)
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 (Table 278) = 1.
The serial data interface, when enabled (M13_NSMI_MODE = 1), generates a clock
M13_DNSMI_CLK
and an
enable
M13_DNSMI_EN
for outputing 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 263).
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 1s. If the input data is 0 for fewer than 9 out of 8192 clock periods, bit M13_RDS3_ALL1_DET (Table 226) 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 225))
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
.
Once the demux is in-frame, the received frame bits are monitored for out-of-frame. Out-of-frame is declared
(M13_DS3_OOF = 1) when too many errors are received in either the F bits (3 errors in 16 bits when
M13_DS3_MODE = 0 (Table 288), or at least 1 F-bit error in each of 4 consecutive M-subframes when
M13_DS3_MODE = 1) or the M bits (at least 1 error in each of 3 consecutive M-frames) (T1.231). For testing pur-
poses, the user may also force the framer out-of-frame by setting M13_DS3_FORCE_OOF (Table 259) to 1.
The traditional algorithm for declaring out-of-frame (3 errors in 16 F bits) results in false out-of-frame approximately
every 30 seconds when the received bit error rate is 10
-3
. By waiting for 4 consecutive M-subframes with F bit
errors before declaring out-of-frame (M13_DS3_MODE = 1), the M13 normally stays in frame for over an hour
when the bit error rate is 10
-3
.
The M13_DS3_LOF (Table 225) bit is set if bit M13_DS3_OOF is high continuously for 28 frame periods (approxi-
mately 3 ms). Once set, M13_DS3_LOF is not cleared until M13_DS3_OOF is continuously low for 28 frame peri-
ods.
The user can provision the M13 to automatically output AIS if either bit M13_DS3_OOF
= 1 (by setting
M13_AUTO_AIS_OOF (Table 260) to 1), or M13_DS3_LOF
= 1 (by setting M13_AUTO_AIS_LOF
to 1).
The received DS3 frames are also checked for severely errored frames (SEF). An SEF defect is the occurrence of
three or more F-bit errors in 16 consecutive F bits and is reported through bit M13_RDS3_SEF (Table 226). An
SEF defect is terminated when the signal is in-frame and there are less than three F-bit errors in 16 consecutive
F bits.