Transition-Aware Routing in Hybrid Hollow-Core/Single-Mode Fiber Networks: A Cost–Throughput Investigation

A comparative simulation study of six protected routing schemes reveals the tradeoff between minimizing HCF-SMF transitions and preserving carried traffic in incrementally deployed hybrid optical networks.

Md Ghulam Saber; Zhiping Jiang· 2026· DOI 10.48550/arXiv.2607.14324

The core problem

The incremental deployment of hollow-core fiber (HCF) into existing single-mode-fiber (SMF) networks creates a fundamental routing tension. HCF offers superior physical-layer characteristics, but each HCF-SMF transition introduces a signal-to-noise ratio (GSNR) penalty and an elevated splice-failure risk. Routing algorithms that aggressively avoid transitions can reduce these penalties, yet they may force traffic onto excessively long detours, degrading carried traffic. Conversely, fiber-blind or purely GSNR-aware schemes may route through many transitions, undermining the very benefits HCF promises. This paper investigates that tradeoff systematically. The authors pose a central question: how do different protected routing schemes balance transition count against carried traffic in hybrid HCF/SMF topologies? To answer it, they develop a common event-driven simulator that models a per-transition GSNR penalty and an exploratory splice-failure availability term. Six protected routing schemes are compared, spanning three design philosophies: fiber-blind, generalized signal-to-noise ratio (GSNR)-aware, and explicitly transition-aware. The evaluation covers six reference topologies, fi

Innovation

The simulation results reveal a clear cost–throughput tradeoff. Across all topologies and deployment fractions, the strongest transition minimizers—TPAR and GFJ—halve the mean transition count relative to DA-RSA, but at a substantial 20–25% carried-traffic penalty. This confirms that overly transition-averse routing forces harmful path detours.Among intermediate designs, GMR-T cuts transitions by approximately 22% relative to DA-RSA at only a 3% throughput cost. BD-TPAR achieves an approximately 11% transition reduction at a mere 1% throughput cost, making it the most efficient tradeoff observed.Deployment pattern emerges as a critical factor. Contiguous HCF rollout lowers transitions by approximately 40% on average while simultaneously improving carried traffic. This reduces the marginal benefit of aggressive transition-aware routing: when HCF is deployed in large contiguous blocks, even simpler schemes achieve low transition counts without throughput loss.A Mermaid diagram summarizes the decision flow for selecting a routing scheme based on deployment fragmentation and external transition cost:

The incremental deployment of hollow-core fiber (HCF) into existing single-mode-fiber (SMF) networks creates a fundamental routing tension. HCF offers superior physical-layer characteristics, but each HCF-SMF transition introduces a signal-to-noise ratio (GSNR) penalty and an elevated splice-failure risk. Routing algorithms that aggressively avoid transitions can reduce these penalties, yet they may force traffic onto excessively long detours, degrading carried traffic. Conversely, fiber-blind or purely GSNR-aware schemes may route through many transitions, undermining the very benefits HCF promises.

This paper investigates that tradeoff systematically. The authors pose a central question: how do different protected routing schemes balance transition count against carried traffic in hybrid HCF/SMF topologies? To answer it, they develop a common event-driven simulator that models a per-transition GSNR penalty and an exploratory splice-failure availability term. Six protected routing schemes are compared, spanning three design philosophies: fiber-blind, generalized signal-to-noise ratio (GSNR)-aware, and explicitly transition-aware. The evaluation covers six reference topologies, five HCF deployment fractions, and dynamic loads at 300 Erlang. The goal is to identify practical routing defaults for network operators navigating the gradual, often fragmented, rollout of HCF technology.

Why it matters

The findings support a nuanced, context-dependent approach to routing in hybrid HCF/SMF networks. BD-TPAR emerges as a practical default under fragmented deployment: it captures most of the transition-reduction benefit (11%) at negligible throughput cost (1%). GMR-T offers a lower-complexity alternative with a 22% transition reduction at 3% throughput cost, suitable when operators prefer simpler implementation or when transition penalties are moderate. TPAR and GFJ should be reserved for scenarios where the external cost of transitions is high—for example, where splice-failure availability is critical or where each transition incurs significant operational expense. Their 20-25% throughput penalty is justified only when transition avoidance is paramount. The study also highlights the importance of deployment strategy. Contiguous HCF rollout reduces transitions by ~40% on average and improves carried traffic, effectively lowering the need for sophisticated transition-aware routing. This suggests that network planners should prioritize contiguous HCF deployment where feasible, as it yields both physical-layer and routing benefits. Limitations include the exploratory nature of the splice-failure availability term and the use of a common simulator that may abstract some real-world hardware effects. Future work could validate these findings with field trials and extend the model to consider multi-period deployment planning. Overall, the paper provides a clear framework for selecting routing schemes based on deployment fragmentation and the external cost of transitions, offering actionable guidance for network operators navigating the HCF transition.

Who should read this

CS practitioners and researchers

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