Experimental Demonstration of Adaptive Combinational QoT Failure Restoration in Flexible Bandwidth Networks Xinran Cai, Ke Wen, Roberto Proietti, Yawei Yin, Ryan Scott, Chuan Qin, S. J. B. Yoo Department of Electrical and Computer Engineering, University of California, Davis, One Shields Ave., Davis, CA 95616, USA sbyoo@ucdavis.edu Abstract: We propose and demonstrate an adaptive quality of transmission restoration scheme combining methods of lightpath rerouting and modulation format switching to combat real-time impairments in flexible bandwidth networks. Testbed demonstration achieved error-free performance. OCIS codes: 060.4261 Networks, protection and restoration; 060.2330 Fiber optics communications 1. Introduction Flexible bandwidth elastic optical networking [1, 2] offers spectrally efficient and adaptive methods to allocate spectral resources to varying traffic demands with differing Quality of Transmission (QoT) requirements. Specifically, it enables simultaneous transmission of multiple connections of different data rates on variable bandwidth channels (flexpaths) with variable modulation formats [1, 2]. Each flexpath can utilize high spectral efficiency if the QoT for the required end-to-end transmission is satisfactory even with the increased sensitivity to physical layer impairments (PLIs). Failure to meet the required QoT would trigger protection or restoration. Traditional WDM networks perform restoration via the typical method of lightpath rerouting (LR) when the QoT of a particular connection degrades below an acceptable threshold. Due to the ITU-T grid spacing, this process can be spectrally inefficient. Further, rerouting many simultaneously-affected connections on an impaired span can result in a surge of high blocking probability and of load leap on the restoration links. Flexible bandwidth networking can achieve real-time impairment-aware networking by performance monitoring and modulation format switching (MFS) [2, 3]. In this paper, we propose and experimentally demonstrate an adaptive combinational QoT restoration scheme (ACQoTRe), which jointly uses both LR and MFS methods to combat impairments and coordinate the restoration of simultaneously-impaired connections within the common risk group on the same physical link. Simulation results show significant decrease in blocking probability (by more than 2x) and reduces the load leap in the bypass path down to 25% compared to rerouting only. The flexible bandwidth network testbed with an adaptive control plane successfully demonstrates the ACQoTRe algorithm. 2. Networking Scenario and Hybrid Objective Algorithm The objective of the ACQoTRe is to a) re-establish QoT-degraded flexpaths (e.g. FP A and FP B in Fig. 2) by jointly exploiting MFS and rerouting while b) using the least amount of spectral consumption, i.e., bypass load leap in this case. Here we perform the “hybrid-objective heuristic” which can adaptively use the better objective to guide the selection of restoration paths when the network is in different condition. The hybrid penalty to be minimized consists of two parts: a) the spectral consumption (SC) penalty, which is the additional SC of this solution compared with the least-SC one for the same demand and b) the interference penalty, which represents how this solution would interfere other demands and is used to avoid creating paths which would render many other restoration paths infeasible. A simple but effective way for defining the interference function is shown as below: The auto-tuning feedback for adaptive control is made possible by the denominator, which increases the weight of interference penalty in the gross penalty as network utilization (NU) grows high. Preliminary evaluation of ACQoTRe in comparison with the conventional rerouting based restoration scheme using the COST266 Pan- European network topology indicates that ACQoTRe (with µ=4) significantly reduces BP (by more than 2x) compared with rerouting. Also, it greatly reduces the bypass load leap of restoration (as low as 25% of that of rerouting), since the spectrum of the impaired span is efficiently utilized rather than abandoned, which in return helps reduce the BP. Fig.1 (a) and (c) show the four-node topology of the flexible bandwidth network used for the experimental demonstration. The upper part of Fig. 1(b) and (d) show the original bandwidth utilization on link b, c, d, and e. The OSNR on link b suffers from OSNR degradation over time. Each node includes a performance monitoring module OFC/NFOEC Postdeadline Papers © 2012 OSA ©Optical Society of America PDP5D.l PDP5D.1