arXiv subjects

Konstantinos Christodoulopoulos

Publications and source records attributed to Konstantinos Christodoulopoulos.

5 recordsLinked to original sources

arXiv2026

Optimal Entanglement Routing in Quantum Repeater Chains: Beyond Fixed Operation Order and Purification Schedule

Entanglement routing establishes entangled pairs between distant nodes of a quantum network by purifying and swapping pairs generated on elementary links. Existing methods typically restrict the decision space along two axes: the operation order, often fixed to purify-then-swap (PtS), and the purification schedule of each link, often restricted to pumping. Focusing on linear repeater chains with finite link capacities, we relax both restrictions and study the maximization of the expected end-to-end throughput subject to a fidelity threshold under two quantum-noise models. We develop a unified capacity-aware optimization framework comprising an exact mixed-integer linear program (MILP) under PtS, instantiated with either pumping or general tree purification schedules, and an exact dynamic program (DP) over arbitrary operation orders. Under symmetric Pauli noise, we prove that pumping converges to a fidelity strictly below unity, imposing a capacity-independent feasibility bound and a maximum chain length on every pumping-based PtS method, whereas general tree schedules yield a capacity-dependent bound. We further prove that post-swap purification never increases the throughput, so a free operation order can only increase feasibility. Numerical evaluations confirm the bounds: tree schedules serve over 90\% of the requests that pumping cannot at moderate fidelity thresholds; within the pumping class, a free operation order recovers much of this advantage; but once links use tree schedules, the tree-based MILP and the order-exact DP serve identical request sets throughout. Operation order and purification schedule are thus substitutes, with the purification schedule the dominant factor governing feasibility under symmetric Pauli noise.

quant-ph↗

arXiv2026

Automated Synthesis of Deterministic Cross-Domain Interfaces

Deterministic networking spans heterogeneous domains. At each boundary, two domains must agree on an assume--guarantee contract: what traffic the client may inject, and the QoS the carrier will hold for it. Composing such contracts into an end-to-end guarantee is standardized, but deriving each domain's contract is not. Today they are hand-crafted, static, and over-provisioned. The difficulty rises when traffic changes and the contract must become dynamic. We present a framework that automatically synthesizes the per-domain contract for both static and dynamic classes, along with the registration the dynamic one rests on. Two reasoning modules implemented with large language models (LLMs) drive it: an agent takes the client's traffic declaration and searches the carrier's configuration mechanisms, and a handler builds the network model from a typed disclosure of the substrate. The handler calls a network-calculus kernel for the model's hard terms, and an independent oracle---a faithful simulator, testbed, or live network---which verifies each candidate and discovers what lacks an a-priori algebraic form: when a reconfiguration is safe, and the instant to apply it. We synthesized a dynamic contract for uplink 5G fronthaul over a TDM-PON, grounded against a packet-level simulator. Across six draws from two LLM families, every synthesis produced a feasible, verified contract tight to ${\sim}1.2\,μ$s, holding a $100$-$μ$s deadline that reactive scheduling cannot meet, at up to $3.5$ times the bandwidth efficiency of static over-provisioning. Tasked instead with computing the worst-case delay directly, the LLMs were unsound in five of six attempts---evidence for the division of labor: LLMs construct the model, formal tools hold numeric authority. The same framework, unchanged, synthesized a static 5G--TSN bridge contract on a second substrate.

cs.NI↗

arXiv2026

Evaluating Relayed and Switched Quantum Key Distribution (QKD) Network Architectures

We evaluate the performance of two architectures for network-wide quantum key distribution (QKD): Relayed QKD, which relays keys over multi-link QKD paths for non-adjacent nodes, and Switched QKD, which uses optical switches to dynamically connect arbitrary QKD modules to form direct QKD links between them. An advantage of Switched QKD is that it distributes quantum keys end-to-end, whereas Relayed relies on trusted nodes. However, Switched depends on arbitrary matching of QKD modules. We first experimentally evaluate the performance of commercial DV-QKD modules; for each of three vendors we benchmark the performance in standard/matched module pairs and in unmatched pairs to emulate configurations in the Switched QKD network architecture. The analysis reveals that in some cases a notable variation in the generated secret key rate (SKR) between the matched and unmatched pairs is observed. Driven by these experimental findings, we conduct a comprehensive theoretical analysis that evaluates the network-wide performance of the two architectures. Our analysis is based on uniform ring networks, where we derive optimal key management configurations and analytical formulas for the achievable consumed SKR. We compare network performance under varying ring sizes, QKD link losses, QKD receivers' sensitivity and performance penalties of unmatched modules. Our findings indicate that Switched QKD performs better in dense rings (short distances, large node counts), while Relayed QKD is more effective in longer distances and large node counts. Moreover, we confirm that unmatched QKD modules penalties significantly impact the efficiency of Switched QKD architecture.

cs.CR↗

arXiv2023

Feedback-Based Channel Frequency Optimization in Superchannels

Superchannels leverage the flexibility of elastic optical networks and pave the way to higher capacity channels in space division multiplexing (SDM) networks. A superchannel consists of subchannels to which continuous spectral grid slots are assigned. To guarantee superchannel operation, we need to account for soft failures, e.g., laser drifts causing interference between subchannels, wavelength-dependent performance variations, and filter misalignments affecting the edge subchannels. This is achieved by reserving spectral guardband between subchannels or by employing a lower modulation format. We propose a process that dynamically retunes the subchannel transmitter (TX) lasers to compensate for soft failures during operation and optimizes the total capacity or the minimum subchannel quality of transmission (QoT) performance. We use an iterative stochastic subgradient method that at each iteration probes the network and leverages monitoring information, particularly subchannels signal-to-noise ratio (SNR) values, to optimize the TX frequencies. Our results indicate that our proposed method always approaches the optima found with an exhaustive search technique, unsuitable for operating networks, irrespective of the subchannel number, modulation format, roll-off factor, filters bandwidth, and starting frequencies. Considering a four-subchannel superchannel, the proposed method achieves 2.47 dB and 3.73 dB improvements for a typical soft failure of +/- 2 GHz subchannel frequency drifts around the optimum, for the two examined objectives.

cs.NI↗

arXiv2021

A Scalable Factory Backbone for Multiple Independent Time-Sensitive Networks

Convergence of time-sensitive machine control networks as part of the operational technology (OT) with the ubiquitous information technology (IT) networks is an essential requirement for the ongoing digitalization of production. In this paper, we review the fundamental differences between both technologies, the challenges to be solved, existing and upcoming solutions like TSN and their limitations. Furthermore, we introduce an Ethernet extension for a backbone network at factory scale and line rates of 10 - 100Gbit/s. The backbone is intended to carry massive amounts of IT traffic together with the traffic of multiple independent OT networks at the precision of leading-edge field bus technologies in the sub-microsecond range. The backbone remains transparent and does not require changes to the attached OT sub-networks. We prove our claims by prototype measurements, interoperability tests and field trials.

cs.NI↗