It is possible to use monitoring measurements collected from a
subset of all the network lightpaths (LP1, LP2, LP3, LP4) to estimate
accurately the corresponding end-to-end metric (e.g., OSNR) of a
lightpath that is not monitored (LP5) using the "network kriging"
estimation framework. Placing monitoring devices at the
termination points of LP1, LP2, LP3, and LP4 would allow the
operator to also estimate the QoT of LP5 using only partial network
information. See Angelou et al., pp. 15-24