TMXF28155 Supermapper
155/51 Mbits/s SONET/SDH x28/x21 DS1/E1
Data Sheet
June 2002
468
Agere Systems Inc.
20 M13/M23 MUX/DeMUX Block Functional Description
(continued)
20.5.3 Loopback Select
DS1/E1 loopback selectors allow DS1 or E1 received within the DS2 or DS3 inputs from the deMUX path to be
looped back. This loopback can be performed automatically if M13_AUTO_FLB (
Table 271 on page 218
) or
M13_AUTO_LB (
Table 271
) bits are set. Regardless of the state of
M13_AUTO_FLB and M13_AUTO_LB, the
user can force a DS1 or E1 loopback by setting M13_SEL_DS1_LBx (
Table 276 on page 220
) to 1.
When M13_AUTO_LB
= 1, loopback of channel x is activated if M13_DS1_LB_DETx = 1 (
Table 261 on page 215
)
(see
Section 20.11.4 on page 479
). In the C-bit parity mode, automatic loopback can also be activated as a result
of receiving a loopback request through the far-end alarm and control (FEAC) channel. Such a request is indicated
by status bit M13_DS1_FEAC_LB_DETx (
Table 263 on page 216
) (see
Section 20.7.6 on page 472
). If status bit
M13_DS1_FEAC_LB_DETx = 1 and M13_AUTO_FLB = 1, loopback of channel x is activated.
20.5.4 DS1/E1 FIFOs
When M13_M12_MODEy[1] = 0 (
Table 275 on page 220
), the 4 selected DS1 or 3 selected E1 signals for each
M12 MUX are fed into single bit 16-word-deep FIFOs that are used to synchronize the selected signals to the DS2
frame generation clock. The DS2/DS3 transmit clock (XC_DS2M12CLKy) is used to derive the clock source for
DS2 frame generation blocks. In the C-bit parity mode, all DS2 stuff opportunities are used, which produces a nom-
inal 6.306 MHz DS2 clock. In the M23 mode, the DS2 stuffing ratio is fixed so that the DS2 clock is nominally 6.312
MHz.
The fill level of each FIFO determines the need for bit stuffing its DS1/E1 input. This block allows the M13 to accept
DS1/E1 signals with nominal frequency offsets of ±130 ppm and up to 5 unit intervals peak jitter.
When operating in M13_M12_MODEy[1:0] = 10 mode, the FIFOs are not used.
20.6 DS2 Frame Generation
Each M12 MUX generates a DS2 frame either from 4 DS1 signals multiplexed as specified in T1.107 and GR-499-
CORE when M13_DS1_E1Ny = 1 (
Table 275 on page 220
), or from 3 E1 signals multiplexed using the format
specified in ITU-T recommendation G.747 when M13_DS1_E1Ny = 0.
When M13_M12_MODEy[1:0] = 01/10 (
Table 275
), each M12 MUX is operating independently. In this case, the
output DS2 signals are retimed by the associated clocks. The edge of the clocks that is used to retime the data is
user provisionable to either the rising edge (M13_DS2M12_EDGEy = 1; see
Table 287 on page 223
) or falling
edge (M13_DS2M12_EDGEy = 0). The AIS signal can be inserted into any DS2 output by setting
M13_DS2_FORCE_AISy to 1; see
Table 283
.
20.6.1 DS1 Mode
In the DS1 mode, the 4 signals interleaved to generate the y
th
DS2 signal are the outputs from DS1/E1 loopback
selectors 4y – 3, 4y – 2, 4y – 1, and 4y. Bits multiplexed into the second and fourth channels (from selectors 4y – 2
and 4y) are inverted before being interleaved (T1.107) when bit M13_MUXCH2_4_INVy = 1 (
Table 275 on
page 220
).
Loopback requests for a DS1 channel are indicated by inverting the third C bit for that channel (T1.107). This is
done when bit M13_DS1_LB_REQx is set to 1 (
Table 275
). The 4 M13_DS1_LB_REQx bits that affect the y
th
DS2
are 4y – 3, 4y – 2, 4y – 1, and 4y.
The X bit is set to the inverse of the remote alarm indication (RAI) bit (T1.107) M13_DS2_RAI_SENDy (
Table 277
on page 220
).
For testing purposes, the M-frame alignment signal (normally 011) is generated with the last bit inverted (010) if
M13_DS2_MPINVy is set (
Table 279 on page 221
), and the M-subframe alignment signal (01) is generated as (00)
if M13_DS2_FINVy is set (
Table 280 on page 221
).