  Network monitoring is essential to collect compre-hensive data on signal
quality in optical networks. As deploying large amounts of monitoring equipment
results in elevated cost and power consumption, novel low-cost monitoring
methods are continuously being investigated. A new technique called Power
Profile Monitoring (PPM) has recently gained traction thanks to its ability to
monitor an entire lightpath using a single post-processing unit at the
lightpath receiver. PPM does not require to deploy an individual monitor for
each span, as in the traditional monitoring technique using Optical Time-Domain
Reflectometer (OTDR). PPM and OTDR have different monitoring applications,
which will be elaborated in our discussion, hence they can be considered either
alternative or complementary techniques according to the targeted monitoring
capabilities to be implemented in the network. In this work, we aim to quantify
the cost and power consumption of PPM (using OTDR as a baseline reference), as
this analysis can provide guidelines for the implementation and deployment of
PPM. First, we discuss how PPM and OTDR monitors are deployed, and we formally
state a new Optimized Monitoring Placement (OMP) problem for PPM. Solving the
OMP problem allows to identify the minimum number of PPM monitors that
guarantees that all links in the networks are monitored by at least n PPM
monitors (note that using n > 1 allows for increased monitoring accuracy). We
prove the NP-hardness of the OMP problem and formulate it using an Integer
Linear Programming (ILP) model. Finally, we also devise a heuristic algorithm
for the OMP problem to scale to larger topologies. Our numerical results,
obtained on realistic topologies, suggest that the cost (power) of one PPM
module should be lower than 2.6 times and 10.2 times that of one OTDR for
nation-wide and continental-wide topology, respectively.
