Data Sheet
June 2002
TMXF28155 Supermapper
155/51 Mbits/s SONET/SDH x28/x21 DS1/E1
477
Agere Systems Inc.
20 M13/M23 MUX/DeMUX Block Functional Description
(continued)
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 (three errors in 16 bits when
M13_DS3_MODE = 0 (
Table 299 on page 227
), or at least 1 F-bit error in each of four consecutive M-subframes
when M13_DS3_MODE = 1) or the M bits (at least 1 error in each of three consecutive M frames) (T1.231). For
testing purposes, the user may also force the framer out of frame by setting M13_DS3_FORCE_OOF (
Table 270
on page 218
) to 1.
The traditional algorithm for declaring out of frame (three errors in 16 F bits) results in false out of frame approxi-
mately every 30 s when the received bit error rate is 10
–3
. By waiting for four 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 236 on page 208
) bit is set if bit M13_DS3_OOF is high continuously for 28 frame peri-
ods (approximately 3 ms). Once set, M13_DS3_LOF is not cleared until M13_DS3_OOF is continuously low for 28
frame periods.
The user can provision the M13 to automatically output AIS if either bit M13_DS3_OOF
= 1 (by setting
M13_AUTO_AIS_OOF (
Table 271 on page 218
) 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 237
). 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.
AIS, Idle, and RAI Detection.
In
each M frame, the 4704 information bits are checked for the presence of the AIS
(1010) or idle (1100) pattern. In order to detect these patterns in the presence of a high error rate, AIS
(M13_DS3_AISPAT_DET = 1 (
Table 236 on page 208
)) or idle (M13_DS3_IDLEPAT_DET = 1 (
Table 236
)) pat-
tern detection is declared if fewer than five pattern errors are received in each of two consecutive frames. Once
AIS or idle is declared, these bits are not cleared until at least 16 pattern errors are received in each of 2 consecu-
tive frames (T1.231).
In addition to the fixed information bit patterns, AIS and idle signals are transmitted with all C bits set to 0 and both
X bits set to 1. These conditions are monitored by the M13 and reported in bits M13_DS3_CBZ_DET (
Table 236
)
and M13_DS3_RAI_DET (
Table 236
).
If every C bit in three consecutive DS3 frames is 0, the M13 sets M13_DS3_CBZ_DET to 1. If the three C bits in a
single M-subframe are all 1, M13_DS3_CBZ_DET is cleared. If both X bits in two consecutive frames are received
as 0, the device sets M13_DS3_RAI_DET to 1. Once M13_DS3_RAI_DET is set, it is not cleared until both X bits
in two consecutive frames are received as 1.
The user may wish to declare AIS or idle based on a combination of some or all of the following bits:
M13_DS3_CBZ_DET, M13_DS3_RAI_DET, and M13_DS3_AISPAT_DET or M13_DS3_IDLEPAT_DET.
C-Bit Processing.
The M13 can be provisioned to operate in either the M23 mode (M13_M23_CBP = 1
(
Table 272 on page 219
)) or the C-bit parity mode (M13_M23_CBP = 0). In the M23 mode, the C bits in each M-
subframe are interpreted as stuff indicator bits, and they are checked for loopback requests. If the third C bit differs
from the first and second C bits in the y
th
M-subframe for five successive DS3 frames, M13_DS2_LB_DETy is set
to 1; see
Table 256 on page 214
. The M13_DS2_LB_DETy bit is cleared when the third C bit does not differ from
the first two C bits in subframe y for five successive DS3 frames.
The first C bit of each frame, C1, provides C-bit parity identification. If for eight consecutive frames it is received as
a 1, the M13 sets M13_DS3_C1_DET to 1; see
Table 236 on page 208
. Once M13_DS3_C1_DET bit is set, three
consecutive frames with C1 = 0 must be received before it is cleared.
The RCBDATA (pin E15) output provides access to the received C2, C4, C5, C6, and C16 through C21 C bits. The
received data link bits, C13 through C15, are output as a serial stream on RDLDATA pin (H22).