Survivable Elastic Optical Network: A survey of failure scenarios and solutions

Survivable Elastic Optical Networks (SEON) are at the forefront of high-speed, flexible, and bandwidth-efficient optical communication. Modern flex-grid Elastic Optical Networks (EON) allocate variable-width frequency slots to match heterogeneous traffic demands and modulation formats; the survivability mechanisms discussed here operate at the spectrum slot layer and are agnostic to the underlying transponder waveform. Despite these advantages, ensuring survivability against diverse failures, including single-link, multi-link, node and hardware outages, remains a major challenge. This paper presents a comprehensive survey of SEON survivability, with a particular emphasis on classifying solutions according to different failure scenarios. State-of-the-art strategies such as Dedicated Path Protection, Shared Backup Path Protection, segmented and span restoration, and p-cycle protection are systematically analyzed and compared. Unlike previous surveys, this work integrates a classification framework with performance insights, highlighting how existing mechanisms fare under different types of failures. To bridge existing gaps, we also discuss open research challenges, including centralized control, spectrum management, AI-driven resilience, physical layer impairments and disaster recovery. Furthermore, we outline the potential of a hybrid protection paradigm combining state-aware traffic splitting, dynamic allocation, and vulnerability scoring to improve spectrum utilization and reduce blocking probability. By linking failure scenarios with recovery strategies and future research needs, this survey provides a unique perspective to guide the design of scalable, adaptive and intelligent SEON architectures.