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Cisco ONS 15501 User Guide
78-14134-02, Release 2.0
Chapter1 Product Overview
Key Features
Some attributes (optical input, optical output, temperature and gain) allow alarm trigger points to be set
on them. The alarms are triggered, or asserted when the measured value crosses the value of Mean

±

Trigger. Once triggered the alarm is cleared only when the measured value is at Mean

±

90% of Trigger.
This approach builds a hysteresis window of 1 0% of trigger value. I f chattering is noted f or one of the
alarms, increase the trigger value (so that the hysteresis is bi gger) to kill the alarm chatter.
Key Features
The Cisco ONS 15501 has the following key fe atures:
•Constant flat gain of 17dB over the 1530 to 1563 nm band
•Optimized automatic gain con trol for the MAN
•Variable gain for flexibility in network design
•Typical transient suppression within 50 microseconds
•Low noise figure of < 6.0 dB
•Input power range of -29 to 0 dBm
•Network management

Constant Gain Flatness

The CiscoONS 15501 is a constant gain amplifier. It does not deliver a constant output, but rather
ensures that the output energy spectrum is gain -flattened irrespective of input power (up to the maximum
allowed). If a channe l is removed, the outpu t level will drop at the wavelength that is remo ved, but the
remaining energy spe ctrum will remain ne arly flat over its wavele ngth band. The gain fl atness is also
only minimally affected if the input signal i s not flat by several deci bels.

Optimized Automatic Gain Control

The CiscoONS 15501 has a wide input power range of 0 to -29 dBm, over which it maintains gain
flatness as well as a low noise figu re across the entire C band. Th e Cisco ONS 15501 maintains a high
level of precision, as well as speed, which allows it to be u sed as a booster, inline or pr eamplifier, thus
reducing sparing expenses. The constant gain and noise figure capabilities of the CiscoONS 15501
make network designs simpler and more predictable.
The lower gain available in the Ci sco ONS 15501, combined w ith its ability to handle in put signal
powers of up to 0 dBm, also enables the network designer to achieve much higher OSNR (optical
signal-to-noise ratio) after cascading several EDFAs. In addition, it allows the network to expand beyond
32 wavelengths to a maxi mum of 128 wavelengths if necessary. The OSNR i mprovements of 6 dB i s
equivalent to a four-fold increase in the number of EDFAs that can be cascaded. Al ternatively, the unit
can accommodate signals with four times the data rate (for instance, OC-192 as opposed to OC-48).
Thus, the limitations of higher gain EDFAs that have input powers limited to -6 dBm can b e easily
overcome by using the CiscoONS 15501. Some representative figures are included in Table 1- 3,
assuming a flat input to the first Cisco ONS 155 01.