  In facing with the explosive Internet traffic growth, optical transport
networks based on WDM technologies forming the core part of Internet
infrastructure carrying multi-Tb/s has to be re-considered from both designing,
planning, operation and management perspectives to attain greater efficiency.
Thanks to the convergence of significant advances in optical transmission
technologies, and photonic switching, transparent (all-optical) architecture
has come into practice, paving the way for eliminating the over-utilization of
costly optical-electrical-optical (O-E-O) interfaces and hence, yielding
remarkable savings of cost and energy consumption compared to opaque
architecture. Traditional designs for transparent optical networks based on
single-objective optimization model aiming at optimizing solely a single
performance metric appears to be insufficient to capture the nuances of
practical designs while conventional multi-objective approach tends to reach
(non-) optimal solutions. Different from existing works, we present a new
framework for multi-objective WDM network designs capturing several goals on
one hand and on the other hand, achieving optimal solutions. Moreover, our
proposal exploits the characteristics of each constituent objectives to lay the
foundation for setting up weight coefficient so that the order of optimization
is guaranteed. Equally important, our proposal is pragmatic in the sense that
the complexity of the optimization model remains the same as the
single-objective model while the quality of solution has been greatly improved.
We have extensively tested realistic optical core networks topologies, that is,
COST239 and NSFNET, with various network traffic conditions and it turns out
that our design brings about a saving of wavelength link usage up to roughly
$28\%$ in the most favorable cases while $14\%$ is expected for the least
favorable cases.
