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Preliminary Data Sheet, Rev. 1
October 2000
TMXF28155 Super Mapper
155/51 Mbits/s SONET/SDH x28/x21 DS1/E1
335
Lucent Technologies Inc.
M13/M23 Mux/Demux Block Functional Description
(continued)
M23 Multiplexer
(continued)
Overhead Bit Generation (GR-499)
For testing purposes the F bits, M bits, and P bits can be generated with errors. The frame alignment signal (F-bit
pattern that is normally 1001) is generated with the last bit inverted (1000) if M13_DS3_FINV (Table 277) is set.
The multiframe alignment signal (M-bit pattern that is normally 010) is generated as (011) if M13_DS3_MINV
(Table 277) is set. The parity bits (P bits) are generated as odd rather than the normal even parity if
M13_DS3_PINV (Table 277) is set. Both P bits within the first DS3 frame after a 0 to 1 transition of
SMPR_BER_INSRT (Table 13) are also inverted if M13_DS3_P_BERy (Table 278) is set to 1.
The X bits are set to the inverse of the remote alarm indication (RAI) bit (GR-499) M13_DS3_RAI_SEND
(Table 278).
C-bit transmission is a function of whether the M13 mux/demux is in the M23 mode or the C-bit parity mode.
M23 Mode
(M13_M23_CBP = 1 (Table 261))
The information bits in the DS3 frame are drawn from the 7 DS2 select blocks. If M13_M23CLK_MODE = 0
(Table 277) and a select block is in the loopback or direct DS2 input state, the selected DS2 must be synchronized
to the DS3 frame generation clock. To do this, the M13 contains 7 DS2 FIFOs each with a depth of 8. The fill level
of each FIFO determines the need for bit stuffing its DS2 input.
When M13_M23CLK_MODE = 0 and DS2 select blocks are not in the loopback or direct DS2 input state, the
selected DS2s are generated using the DS3 frame generation clock. In this case, a fixed stuffing ratio is used for
the DS2s in order to produce a nominal 6.312 MHz DS2 clock rate.
When M13_M23CLK_MODE = 1, the FIFOs are not used and DS2 stuff request inputs
(XC_DS2STFREQ[7—1])
will determine when stuff bits are needed.
The three C bits in each M-subframe of the DS3 frame are stuff indication bits. If the stuff opportunity bit in an M
subframe is filled by a DS2 bit, the first and second C bits in that M-subframe are transmitted as 0s. If the stuff
opportunity bit in an M-subframe is filled with a stuff bit, the first and second C bits in that M-subframe are transmit-
ted as 1s.
The third C bit in each M-subframe is normally transmitted with the same value as the first and second C bits. How-
ever, if M13_DS2_LB_REQy = 1 (Table 282), the third C bit is transmitted as the inverse of the first two C bits
(which indicates a loopback request for DS2 channel y).
C-Bit Parity Mode
(M13_M23_CBP = 0 (Table 261))
The M23 mux can operate in the C-bit parity mode under the following two circumstances:
I
When M13_M23CLK_MODE = 0 and 28 DS1 or 21 E1 signals are being muxed into the DS3.
I
When M13_M23CLK_MODE = 1 and 7 DS2 signals are being muxed into the DS3.
In the C-bit parity mode, every DS2 stuffing opportunity is filled with a stuff bit. Because stuffing is not used for syn-
chronization, the selected DS2s cannot come directly from the M13 inputs, and the selected DS2s cannot be
looped back from the M23 demultiplexer. The 21 C bits in each DS3 frame are not required as stuffing indicators.
Their use is described in Table 212 on page 336.