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Preliminary Data Sheet, Rev. 1
October 2000
TMXF28155 Super Mapper
155/51 Mbits/s SONET/SDH x28/x21 DS1/E1
345
Lucent Technologies Inc.
M13/M23 Mux/Demux Block Functional Description
(continued)
M13/M23 Demultiplexer
(continued)
M12 Demultiplexers
Each M12 demultiplexer outputs either 4 DS1 signals from the DS2 frame as specified in GR-499-CORE (when
M13_DS1_E1Ny = 1 (Table 264)), or 3 E1 signals from the DS2 format specified in ITU-T Recommendation G.747
(when M13_DS1_E1Ny = 0). In the DS1 mode, the demultiplexed second and fourth channels are inverted before
being sent to the output selectors when M13_DEMUXCH2_4_INVy
= 1 (Table 273).
Each M12 Demux can be programmed independently to receive DS2 signal either from M23 demux (when
M13_M12DMX_MODEy[1:0] = 00 (Table 273)) or direct DS2 input
XC_DS2DMXDATAy
(when
M13_M12DMX_MODEy[1:0] = 01). In the latter case, an input DS2 clock
XC_DS2DMXCLKy
is also required.
When M13_M12DMX_MODEy[1:0] = 10/11, the M12 demultiplexer is idle and the outputs are held low.
The DS2 signal is monitored for AIS, which is declared (M13_DS2_AIS_DETy = 1 (Table 243)) if the demultiplexer
input is 0 for fewer than 5 clock cycles in each of two consecutive 840 clock periods and cleared if there are more
than 4 zeros in each of two consecutive 840-bit periods (G.775).
DS1 Mode
Framer.
The M12 demultiplexers determine if the input signal contains valid DS2 framing. This is done in two
stages by first finding a bit position that matches the M-subframe alignment pattern (F bits), and then locating the
M-frame alignment signal (M bits). After a matching F-bit sequence is found, in-frame is declared
(M13_DS2_OOFy = 0 (Table 241)) when correct M bits are received for three consecutive M-frames. The maxi-
mum average reframe time is 2.5 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_DS2_OOFy = 1) if too many errors are received in either the F bits (2 errors in 4 bits when M13_DS2_MODE
= 0 (Table 275), or at least 1 F-bit error in 4 consecutive M-subframe pairs when M13_DS2_MODE = 1) or the M
bits (at least 1 error in 3 consecutive M-frames). For testing purposes, the user may also force the framer out-of-
frame by setting M13_DS2_FORCE_OOFy (Table 258) to 1.
The traditional algorithm for declaring out-of-frame (2 errors in 4 F-bits) results in false out-of-frame approximately
every 5 seconds when the bit error rate is 10
-3
. By waiting for 4 consecutive errored M-subframe pairs (containing 4
F bits) before declaring out-of-frame (M13_DS2_MODE = 1), the M13 normally stays in frame for over 4 days when
the bit error rate is 10
-3
.
Overhead Processing.
The C bits for each DS1 channel are checked for loopback requests. If the third C bit dif-
fers from the first and second C bits in the zth M-subframe for 5 successive DS2 frames, M13_DS1_LB_DETx
(Table 250) is set to 1, where x = (4y – 4 + z). M13_DS1_LB_DETx is cleared when the third C bit does not differ
from the first two C bits in the zth M-subframe for 5 successive DS2 frames.
If the X bit in 4 consecutive frames is received as 0, the M13 sets M13_DS2_RAI_DETy (Table 244) to 1. Once
M13_DS2_RAI_DETy is set, it is not cleared until the X bit is received as 1 in 4 consecutive frames.