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SummaryElastic optical networks (EONs) based on orthogonal frequency division multiplexing (OFDM) technologies are seen as a promising solution for next-generation optical transport networks to support the rapidly growing and heterogeneous traffic. In EONs, the elastic bandwidth allocation and modulation format agilities combined with reconfiguration capabilities pave the new way for leveraging the network efficiency. In this paper, we recast the network-side path protection in EONs considering the opportunities and challenges enabled by the flexible operation of OFDM technologies. For the first time, we propose to take advantages of the reconfiguration capabilities of OFDM transponders for adapting to transmission condition variations when switching from the working to protection path in network-side protection. The idea is inspired by the observation that in reach-diverse networks, the transmission margin between the working path and protection path of a connection might be large enough, and thus, the most spectrum-efficient modulation format for each path could be separately tailored, rather than imposed by a common one based on the worse condition as with current fixed transmission technologies. We formulate survivable transparent network designs for both dedicated and shared path protection in the form of integer linear programming model taking into account our proposal for enabling different transmission operations between working and protection mode. Numerical results based on extensive simulations on a realistic network topology, COST239, are presented to highlight the benefits of our proposal compared to conventional approaches in terms of spectrum efficiency for un-capacitated scenarios and improvements in blocking ratio for capacitated scenarios. KEYWORDSelastic optical networks, mixed integer linear programming, OFDM transponders, optical protection, routing and spectrum assignment

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