10-11
Cisco ONS 15454 DWDM Reference Manual, R8.5
78-18343-02
Chapter 10 Network Reference
10.4.1 APC at the Amplifier Card Level
10.4.1 APC at the Amplifier Card Level
In constant gain mode, the amplifier power out control loop performs the following input and output
power calculations, where G represents the gain and t represents time.
Pout (t) = G * Pin (t) (mW)
Pout (t) = G + Pin (t) (dB)
In a power-equalized optical system, the total input power is proportional to the number of channels. The
amplifier software compensates for any variation of the input power due to changes in the number of
channels carried by the incoming signal.
Amplifier software identifies changes in the read input power in two different instances, t1 and t2, as a
change in the traffic being carried. The letters m and n in the following formula represent two different
channel numbers. Pin/ch represents the input power per channel.
Pin (t1)= nPin/ch
Pin (t2) = mPin/ch
Amplifier software applies the variation in the input power to the output power with a reaction time that
is a fraction of a millisecond. This keeps the power constant on each channel at the output amplifier, even
during a channel upgrade or a fiber cut.
The per-channel power and working mode (gain or power) are set by automatic node setup (ANS). The
provisioning is conducted on a per-side basis. A preamplifier or a booster amplifier facing Side i is
provisioned using the Side i parameters present in the node database, where i - A, B, C, D, E, F, G, or H.
Starting from the expected per-channel power, the amplifiers automatically calculate the gain setpoint
after the first channel is provisioned. An amplifier gain setpoint is calculated in order to make it equal
to the loss of the span preceding the amplifier itself. After the gain is calculated, the setpoint is no longer
changed by the amplifier. Amplifier gain is recalculated every time the number of provisioned channels
returns to zero. If you need to force a recalculation of the gain, move the number of channels back to
zero.
10.4.2 APC at the Shelf Controller Layer
Amplifiers are managed through software to control changes in the input power caused by changes in
the number of channels. The software adjusts the output total power to maintain a constant per-channel
power value when the number of input channel changes.
Changes in the network characteristics have an impact on the amplifier input power. Changes in the input
power are compensated for only by modifying the original calculated gain, because input power changes
imply changes in the span loss. As a consequence, the gain to span loss established at amplifier start-up
is no longer satisfied, as shown in Figure 10-10.
Figure 10-10 Using Amplifier Gain Adjustment to Compensate for System Degradation
159501
Node 1
G1
Node 2
G2
PP
L
out1
P
out2in2
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