Specifications

5-4
Cisco ONS 15530 Planning Guide
OL-7708-01
Chapter 5 Amplified Network Planning
VOA Modules
Figure 5-3 Dual Band PB-OE Module and Single WB-VOA Module Example
The PB-OE modules can also be use to provide an optical seam that terminates unused bands in a meshed
ring topology. Unlike a hubbed ring network, the unused and dark channels in a meshed ring topology
are not terminated by any OADM module anywhere in the network. If optical amplifiers are used in a
meshed ring network, the EDFA-generated noise corresponding to the unused channels or bands is
circulated in the ring and amplified by the EDFAs. If the loss around the ring is less than the gain around
the ring, then power oscillations can occur, leading to network instability. An optical seam terminates all
unused and dark channels and eliminates potential network instability due to power oscillations.
Figure 5-4 shows an example of an optical seam at network site with two pass through bands, band B
and band C. The optical seam consists of a band B PB-OE module cascaded with a band C PB-OE
module (to allow bands B and C to pass through) and with the attenuation set to a minimum level. The
upgrade ports of the band C PB-OE module are unconnected to terminate the unused bands.
Single WB-VOA module
In Out
= Power monitor
OutIn
Upgrade out Upgrade in
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