# Fast Reroute Mechanism for Satellite Networks Based on Segment Routing and Dual Timers Switching
###### Abstract  
Low-Earth-Orbit (LEO) satellite networks have the advantage of global internet coverage and low latency, and they have enjoyed great success in the past few years. In LEO satellite networks, laser-based inter-satellite links (ISLs) are widely employed to achieve on-board data relay, and further to provide high-capacity backhaul worldwide. However, ISLs are prone to break due to the outage of the ISL capturing, tracking, and aiming systems. Meanwhile, breaks caused by different reasons can last from milliseconds to hours. The hybrid ISL fault leads to the on-board routing protocol to flap frequently, thus causing high routing overheads, low convergence speed, and degraded service consistency. In this work, we propose a hybrid fault detection mechanism to identify transient and long-term ISL outage. Further, for transient link outage, the segment routing-based loop-free backup path is adopted to provide real-time transmission recovery, and precise global route convergence is adopted to restore the long-term routing failure. For the inconsistent routing table switch between the phase from transient to long-term fault, we propose a dual timer mechanism to make sure the path can be smoothly switched without micro-loops. Simulation results validate the feasibility and efficiency of the proposed scheme. s 2025 20  
When addressing satellite network ISL failures, common emergency measures involve swiftly adjusting the physical state of devices to restore the underlying transport network [3]. Nevertheless, solely relying on such physical adjustments is often insufficient to ensure reliability, as network layer rerouting [4; 5] is typically required to address failure scenarios. Upon detecting ISL failures through fault detection mechanisms, satellite network routing protocols leverage fast reroute mechanisms to redirect traffic to alternative paths that bypass the affected regions. The impact of these two defects is manifested when the link failure detection mechanism is solely used to perceive stable failures. If the failure detection time threshold is set too long, the stability of traffic forwarding in the satellite network under transient failures will decrease. Conversely, if the failure detection time threshold is set too short, the entire underlay routing table will frequently re-converge, causing the primary and backup paths to switch irrationally and frequently, leading to unnecessary overhead. Existing FRR schemes for satellite networks fail to differentiate between stable second-level link failures and transient faults that last only milliseconds [6]. This leads to the insufficient detection of transient faults and instability in traffic forwarding. Furthermore, current FRR schemes have shortcomings in the design of both primary and backup paths, overlooking the importance of a rational switch between them [7]. To address these issues, this paper proposes an innovative fast rerouting scheme for satellite networks, based on segment routing and dual-timer control, designed to overcome these limitations. By employing effective fault detection mechanisms and optimized path switching strategies, the proposed approach aims to improve satellite network performance in complex fault scenarios. The main contributions of this work are outlined as follows. Joint Failure Sensing Method. To address the insufficient detection of transient failures in existing approaches, this paper proposes a joint failure sensing method that integrates hardware-based detection for transient faults and link failure detection for stable failures. Dual-Timer Controlled Path Switching. To counteract irrational switching between primary and backup paths in existing schemes, a dual-timer controlled path switching mechanism is proposed. Optimized Backup Path Design Using Segmented Routing. An optimized backup path design is proposed, leveraging segmented routing and virtual port mechanisms to enhance traffic redirection.