Multipath routing in elastic optical networks with distance-adaptive modulation formats

Elastic optical path networks have been proposed as a promising approach to flexibly use the optical spectrum (hence the name flexi-grid) thus overcoming the rigidness of traditional WDM networks where optical channel spacing is equidistant irrespectively of the type of signal transmitted. Past research effort in spectrum allocation focused on single transmission paths with a uniform modulation format in the network. However, by using optical OFDM technologies, the flexi-grid networks can benefit from multipath routing with parallel transmission that uses flexible modulation format assignment. In this paper, we propose novel multipath routing and spectrum assignment (RSA) algorithms with distance-adaptive modulation format assignment and analyze the effectiveness in dynamic traffic scenarios. We show that a combined usage of multipath routing and flexible distance-adaptive modulation format assignment can reduce blocking ratio while consuming portions of spectrum comparable to single path routing. Our results also show that a careful dimensioning of guard-band size is a critical factor, and that the full benefits of parallel transmission can be better achieved in networks requiring a small guard-band size.