## 1 Introduction
Driven by the momentum of photonic integration to meet the needs of classical photonic systems, emphasis has been placed on the integration of innovative QKD building blocks (sources, detectors) on well-established integration platforms [19], targeting compact, low-power and cheap quantum blocks. In the era of QKD demonstrations, the integration of QKD signals into existing backbone fiber networks has been extensively studied showing the potential of co-propagation of quantum links with Tbps data channels [20]. The practicality of the quantum solutions has also been confirmed through the deployment-oriented integration of commercially available Discrete Variable-QKD (DV-QKD) with Wavelength Division Multiplexing (WDM)-enabled optical transport layer [21]. Moving towards optical edge layer, the integration of quantum channels has also been demonstrated through experiments in Passive Optical Network (PON)-segments [22]. Multiplexing of both quantum and classical streams into existing edge infrastructure remains a challenge since the presence of classical data signals in a live fibre makes the retrieval of quantum information more difficult due to excess noise generated by inelastic Raman scattering [23]. Besides the physical connectivity-oriented experiments, the QKD-enabledreal-time encryption layer-1 in the field has been demonstrated using an AES-256 engine [24]. University of Bristol recently demonstrated the first end-to-end quantum secured inter-domain service orchestration by interconnecting 5G autonomous islands through quantum-enabled multiplexing nodes [25]. Very recently, a quantum-secured 5G-oriented fronthaul architecture over Multicore Fiber (MCF) was presented by assigning the quantum and fronthaul signals at different cores to prevent the contamination [26]. The potential of this MCF-based concept to meet the traffic demands of the 5G fronthaul was also verified for short fiber segments by demonstrating record coexistence transmission of DV-QKD with 11.2 Tbps classical channel traffic [27]. Welcoming the integration of quantum layer across the 5G and B5G cryptographic infrastructure, end-to-end studies targeting beyond the optimized classical/QKD coexistence scheme are still missing. More specifically, further studies are required to explore the capability of a QKD-enabled security framework to meet the strict requirements of 5G-oriented optical edge segments, such as the latency and the availability of quantum keys for AES-based encryption engines. An impressive study recently conducted emphasizing on the latency budget as well the security levels of an optical fronthaul segment operated by the evolved Common Public Radio Interface (eCPRI) [28]. Inspired by the above research, we take a step forward by presenting, for the first time to the best of our knowledge, a research study focusing on the QKD-enabled solutions assisting in the PLS of an Ethernet-based optical 5G fronthaul segment. Working towards the synergy between QKD/PQC presented above, the secure shared key resources which are available from QKD links should be also addressed in the context of the existing security infrastructure. Our research fills this gap by contributing to the definition of security parameters (quantum keys for AES encryption engines, key rotation times, attack success probabilities) of an eCPRI transport layer supported by QKD implementation. Considering the strict latency requirements imposed for 5G packetized fronthaul, performance evaluation is thoroughly discussed for Point-to-Point (P2P) topology as well as in a Point-to-MultiPoint (P2 MP) scenario with a centralized Alice station supporting up to \(N=64\) Bob stations located at 5G terminal nodes. Emphasis has been placed on a resilient classical/QKD coexistence scheme by relying either on appropriate wavelength assignments or on the use of advanced photon detection units at the Bob stations.