Regeneration savings in flexible optical networks with a new load-aware reach maximization

This paper addresses the physical layer design of flexible optical networks [1–8] and its interplay with the routing layer. In such circuit-switched dispersion uncompensated (DU) fiber-optic networks, wavelength division multiplexed (WDM) dual polarization (DP) optical digital signals are transmitted and coherently detected. Each fiber carries at most W wavelengths with possibly mixed modulation formats. From the source, the destination may be transparently reached via a single lightpath at a specific wavelength without opto-electronic regeneration (OER), or through a concatenation of lightpaths on possibly different wavelengths, with OER from one lightpath to the next one. To minimize the number of costly OERs, the qualityof-transmission (QoT) aware routing and wavelength assignment (RWA) unit first tries to set-up a circuit along a single lightpath. A connection may be unfeasible for two reasons: i) unavailability of the same wavelength across successive fibers along the lightpath, leading to wavelength blocking (WB); ii) the received signal to noise ratio (SNR) for the considered modulation format is below a required minimum S0, leading to SNR blocking (SB). In this paper, which is an extension of [9], we concentrate on the SB due to accumulation of linear and nonlinear optical impairments [1, 3, 6–8]. The standard approach is to set-up only lightpaths whose physical length is below the full-load (FL) reach, i.e., the maximum length guaranteeing a received SNR above S0 when all W wavelengths on all fibers are occupied. The FL reach is used as a lightpath-length threshold above which intermediate regenerations are introduced, regardless of the actual wavelength load, i.e., the fraction of wavelengths actually utilized along the current lightpath. Using the FL reach is clearly conservative, since wavelengths saturation at the network core prevents the wavelength load to reach unity. In this paper, we propose a new power selection and OER regeneration strategy where the reach is maximized at the actual wavelength load, and quantify the potential OER savings with respect to using the FL reach and the power