Aps (Automatic Protection Switching) - NEC UPD98413 User Manual

3.4.4 APS (Automatic Protection Switching)

(1) Transmit APS signal
The µ PD98413 can transmit APS signal by using K12T register. The mPD98413 always transmit the K1 and K2
byte by setting the K12T register. If occur the transmission Line AIS or Line RDI, those alarm transmission is
take precedence the setting K12T register.
(2) Receive APS signal
The µ PD98413 has a function for monitoring the K1 and K2 bytes and reporting the arrival of the APS signal
when frame synchronization is established. Each time a frame has been received, the APS signal are recorded
and compared with the next APS signal. If an APS signal different from that received previously is detected, and
if that APS signal is the same in three frames in a row, the APS bit of the DSLER register is set to report the CPU.
The APS bit is not set as long as the same APS signals are received. When the CPU detects that the APS bit
has been set, it reads the K12R register of the OH drop register to obtain the APS signal. The K12R register is
updated only if the same value has been received in three frames in succession. It is not updated if random
values are received in three frames in a row, or if frame synchronization is not established.
(3) Protection Switching Byte Failure (PSBF)
The µ PD98413 checks the K1 byte to monitor whether a stable K1 byte has been received. If a frame having the
same K1 byte is missing three times in a row in 12 continuous frames, the µ PD98413 indicates this status as the
PSBF. The PSBF status is terminated if a frame having the same K1 byte has been received three times in a
row.
If µ PD98413 detecting Line AIS, status of PSBF is not change.
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CHAPTER 3 FUNCTIONAL OUTLINE
PRELIMINARY
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