Data Sheet
June 2002
TMXF28155 Supermapper
155/51 Mbits/s SONET/SDH x28/x21 DS1/E1
471
Agere Systems Inc.
20 M13/M23 MUX/DeMUX Block Functional Description
(continued)
20.7.3 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 288 on
page 223
) is set. The multiframe alignment signal (M-bit pattern that is normally 010) is generated as (011) if
M13_DS3_MINV (
Table 288
) is set.
The parity bits (P bits) are generated as odd rather than the normal even parity if M13_DS3_PINV (
Table 288
) is
set. Both P bits within the first DS3 frame after a 0 to 1 transition of SMPR_BER_INSRT (
Table 75 on page 68
) are
also inverted if M13_DS3_P_BERy (
Table 289 on page 224
) 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 289
).
C-bit transmission is a function of whether the M13 MUX/deMUX is in the M23 mode or the C-bit parity mode.
20.7.4 M23 Mode
Please refer to M13_M23_CBP = 1 in
Table 272 on page 219
.
The information bits in the DS3 frame are drawn
from the 7 DS2 select blocks. If M13_M23CLK_MODE = 0 (
Table 288 on page 223
) 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 seven 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 zeros. 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 ones.
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 293 on page 225
), the third C bit is transmitted as the inverse of the first
two C bits (which indicates a loopback request for DS2 channel y).
20.7.5 C-Bit Parity Mode
Please refer to M13_M23_CBP = 0 in
Table 272 on page 219
.
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 587 on page 472
.