  In this paper we study different options for the survivability implementation
in MPLS over Optical Transport Networks (OTN) in terms of network resource
usage and configuration cost. We investigate two approaches to the
survivability deployment: single layer and multilayer survivability and present
various methods for spare capacity allocation (SCA) to reroute disrupted
traffic. The comparative analysis shows the influence of the offered traffic
granularity and the physical network structure on the survivability cost: for
high bandwidth LSPs, close to the optical channel capacity, the multilayer
survivability outperforms the single layer one, whereas for low bandwidth LSPs
the single layer survivability is more cost-efficient. On the other hand,
sparse networks of low connectivity parameter use more wavelengths for optical
path routing and increase the configuration cost, as compared with dense
networks. We demonstrate that by mapping efficiently the spare capacity of the
MPLS layer onto the resources of the optical layer one can achieve up to 22%
savings in the total configuration cost and up to 37% in the optical layer
cost. Further savings (up to 9 %) in the wavelength use can be obtained with
the integrated approach to network configuration over the sequential one,
however, at the increase in the optimization problem complexity. These results
are based on a cost model with different cost variations, and were obtained for
networks targeted to a nationwide coverage.
