We focus on quality of transmission (QoT) guaranteed routing, modulation, and spectrum allocation (RMSA) in shared backup path protection (SBPP) based elastic optical networks (EONs) in the presence of nonlinear impairments. Allocating a suitable modulation format (MF) to ensure end-to-end QoT (E2E QoT) in a survivable EON offers critical challenges because each single link failure results in the failure of different network connections. As a consequence, different working and backup path allocations exist in the network for different failures, which lead to different nonlinear interference (NLI) power on any frequency slots (FSs). This demands a robust RMSA design to decide the suitable MF for each FS to ensure the E2E QoT under two scenarios: any single link failure and no failure. For this purpose, we propose a robust SBPP-NLI aware (SBPP-NLIA) algorithm to ensure E2E QoT with a multi-objective function that enables the joint sharing of backup FSs as well as transceivers and minimizes the overall network fragmentation. In the process, we introduce robust bitloading in our SBPP-NLIA to allocate different MFs for different FSs where we also perform optimal MF allocation for each FS of every connection. Next, we ensure the QoT of existing connections while establishing each new connection without reserving any margin. To achieve this with less complexity, we propose a recursive method to calculate the NLI for existing connections. Simulation results demonstrate that our proposed SBPP-NLIA performs 10.01% and 14.19% better in terms of, respectively, the bandwidth blocking probability and fragmentation compared to a full-load assumption scheme with an 85 Tb/s traffic load.

Survivability is mission-critical for elastic optical networks (EONs) as they are expected to carry an enormous amount of data. In this paper, we consider the problem of designing shared backup path protection (SBPP) based EON that facilitates the minimum quality-of-transmission (QoT) assured allocation against physical layer impairments (PLIs) under any single link/shared risk link group (SRLG) failure for static and dynamic traffic scenarios. In general, the effect of PLIs on lightpath varies based on the location of failure of a link as it introduces different active working and backup paths. To address these issues in the design of SBPP EON, we formulate a mixed integer linear programming (MILP) based robust optimization framework for static traffic with the objective of minimizing overall fragmentation. In this process, we use the efficient robust bitloading technique for spectrum allocation where each frequency slot of a request is assigned with different modulation format. In addition, we propose novel SBPP-impairment aware (SBPP-IA) algorithm considering the limitations of MILP for larger networks. For this purpose, we introduce a novel sorting technique named most congested working-least congested backup first (MCW-LCBF) to sort the given set of requests. Next, we employ our SBPP-IA algorithm for dynamic traffic scenario and compare it with existing algorithms in terms of different QoT parameters. Further, we guarantee the QoT of existing requests while allocating each new request without reserving any margin. We demonstrated through simulations that our study provides 33.94-41.02% more QoT guaranteed requests compared to existing ones at 70 Tbps traffic load.INDEX TERMS Elastic optical networks, fragmentation, mixed integer linear programming, physical layer impairments, quality of transmission, shared backup path protection.