10-28
Cisco ONS 15454 DWDM Reference Manual, R8.5
78-18343-02
Chapter 10 Network Reference
10.8 Network-Level Gain—Tilt Management of Optical Amplifiers
Two photodiodes at Node B monitor the received signal strength for the optical payload. When the fiber
is cut, an LOS is detected on the channel photodiode while the other one never gets a signal because the
OSC is not present. The AND function then indicates an overall LOS condition, which causes the
OPT-BST amplifier transmitter to shut down. This in turn leads to a LOS for the optical payload at Node
A, which causes Node A to turn off the OPT-BST amplifier lasers.
The sequence of events after a fiber cut is as follows (refer to the numbered circles in Figure 10-18):
1. Fiber is cut.
2. The Node B power monitoring photodiode detects an LOS-P on the OPT-BST card. Refer to the
Cisco ONS 15454 DWDM Troubleshooting Guide for LOS-P troubleshooting procedures.
3. On the OPT-BST card, the LOS-P detection triggers a command to shut down the amplifier. CTC
reports an LOS alarm (loss of continuity), while LOS-P is demoted. Refer to the Cisco ONS 15454
DWDM Troubleshooting Guide for alarm troubleshooting procedures.
4. The OPT-BST card amplifier is shut down within one second.
5. The Node A power monitoring photodiode detects a LOS-P on the OPT-BST card. Refer to the Cisco
ONS 15454 DWDM Troubleshooting Guide for alarm troubleshooting procedures.
6. On the OPT-BST, the LOS-P detection triggers a command to shut down the amplifier. CTC reports
an LOS alarm (loss of continuity), while LOS-P is demoted. Refer to the Cisco ONS 15454 DWDM
Troubleshooting Guide.
7. The OPT-BST card amplifier is shut down within one second.
When the fiber is repaired, a manual restart with 90 sec restart pulse time (MANUAL RESTART FOR
TEST) is required at the Node A OPT-BST transmitter and at the Node B OPT-BST transmitter. A system
that has been shut down is reactivated through the use of a 90 sec restart pulse. The pulse indicates that
the optical path is restored and transmission can begin.
For example, when the far end, Node B, receives a pulse, it signals to the Node B OPT-BST transmitter
to begin transmitting an optical signal. The OPT-BST receiver at Node A receives that signal and signals
the Node A OPT-BST transmitter to resume transmitting.
Note During a laser restart pulse, APR ensures that the laser power does not exceed Class 1 limits. See the
“10.7.2 Automatic Power Reduction” section on page 10-19 for more information about APR.
10.8 Network-Level Gain—Tilt Management of Optical
Amplifiers
The ability to control and adjust per-channel optical power equalization is a principal feature of
ONS 15454 DWDM metro core network applications. A critical parameter to assure optical spectrum
equalization throughout the DWDM system is the gain flatness of erbium-doped fiber amplifiers
(EDFAs).
Two items, gain tilt and gain ripple, are factors in the power equalization of optical amplifier cards such
as the OPT-BST and OPT-PRE. Figure 10-19 shows a graph of the amplifier output power spectrum and
how it is affected by gain tilt and gain ripple.
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