
PRELIMINARY
XRT86SH221
66
REV. P1.0.5
SDH-TO-PDH FRAMER/MAPPER WITH INTEGRATED 21-CHANNEL E1 SH LIU
AIS-L CONTROL
The txstoh_cont provides AIS-L insertion capabilities according to the SDH standard:
I
STE shall generate AIS-L downstream within 125
μ
s of detecting an LOS or LOF defect on the incoming
signal or the failure of LTE supporting provisioned line origination functions. The AIS-L shall be
generated as an STM-N electrical signal that contains valid section overhead and a scrambled all-ones
pattern for the remainder of the signal.
The txstoh_cont allows software to insert an AIS-L condition on the transmitted data by writing to an
appropriate bit in the register file. The AIS-L condition is set/unset on frame boundaries. AIS-L insertion
overrides all other frame data insertion schemes with the exception of LOS insertion.
LOS INSERTION
The txstoh_cont block allows software to specify an LOS condition on the transmitted data which sets all data
bytes to zero after scrambling. LOS insertion is enabled by writing a "1" to the appropriate register file bit. LOS
insertion, if specified, overrides all other transmit frame data insertion schemes.
TXSTOH_PROC BLOCK
The txstoh_proc has one 8 bit internal data bus interface. The txstoh_proc multiplexes transport overhead data
from the txstoh_cont block and SPE data from the txspoh_proc block and inserts them into the data stream.
The txstoh_proc block generates timing and location signals for the other transmitter blocks and performs
primitive SDH tasks such as scrambling, B1/B2 calculation and insertion, and start of frame (A1/A2) insertion
using control signals from the txstoh_cont block.
LOCATION STROBE GENERATION
The txstoh_proc block maintains the location of the current byte (byte lanes) being transmitted and outputs
time-advanced row, column, and time slot numbers of the data on the byte lane(s) for the other SDH
transmitter blocks. The time-advanced location signals allow for pipeline delays necessary to move the data
from the other transmit blocks to the txstoh_proc block.
A1/A2 INSERTION
During normal operation, the txstoh_proc block inserts the SDH framing pattern F628 (hex) for the A1 and A2
bytes respectively. This can be overridden by non-zero values from the tx_toh_data input from the txstoh_cont
block at the time of insertion.
B1 CALCULATION AND INSERTION
The txstoh_proc block calculates the BIP-8 B1 error code on the scrambled data of the current frame and
inserts it into the B1 byte of the next frame before scrambling. Errors can be inserted for diagnostic purposes
from the tx_toh_data input from the txstoh_proc block.
B2 CALCULATION AND INSERTION
The txstoh_proc block calculates the BIP-8 B2 error code on the unscrambled data of the current frame except
for the section overhead bytes and inserts it into the B2 bytes of the next frame before scrambling. Errors can
be inserted for diagnostic purposes from the tx_toh_data input from the txstoh_proc block.
Two memories are used in the B2 error code calculations for the txstoh_proc block. One memory is used to
store the running value of the B2 error calculations. This memory is a 12x8 dual port RAM with one port for
reads and one port for writes. This is necessary because as the hardware is calculating the B2 code for each
STS, it needs to store the new value into the memory and at the same time fetch the current code for the next
STS from memory. The second memory is a single port 12x8 RAM used to store the final B2 codes for all the
STS's. This memory is read at the B2 byte locations for comparisons and written into in the A1 byte locations to
store the final B2 codes for the previous frame. For the 8 bit version of the rxstoh_proc block, the B2 RAM
widths are 8 bits.