# Quantum-Secure Coherent Optical Networking for Advanced Infrastructures in Industry 4.0
## 7 Discussion  
### Research Result Contributions and Positioning  
The research presents multiple insight levels regarding the secure operation of coherent optical networks that connect current classical attacks to future potential quantum threats. The research investigates network vulnerabilities from architectural to protocol to physical levels while assessing modern optical encryption techniques to generate advanced knowledge regarding network defense in high-speed 400 Gbps+ systems without proper security measures. This Section presents results that both validate and diverge from and extend the current literature while sharing the benefits and constraints of integrating physical encryption with quantum key distribution systems. Our analysis confirmed the concerns raised by previous research [15; 16] that Media Access Control Security (MACsec) faces acute challenges in high-speed optical networks--particularly in coherent environments. While prior studies emphasize timing-based attacks and unauthorized access at the router-optical boundary, our work adds granularity by showing that buffer synchronization gaps at gearbox interfaces, though small (1-2 ns), can create covert channels even when MACsec is deployed. This finding contradicts the assumption that MACsec alone can reliably safeguard data at terabit speeds. Furthermore, our results reinforce the post-quantum concerns expressed by previous work [7; 33] that when MACsec depends on vulnerable key exchange methods, future quantum computers could eventually decrypt previously recorded traffic. We go beyond these studies by showing that bridging MACsec with OTU4 overhead fields, where overhead bytes like the Trail Trace Identifier (TTI) and Bit Interleaved Parity (BIP-8) are susceptible, widens the overall attack surface. The research in [3] indicates that lower-layer encryption becomes less important because TLS/IPSec provides strong upper-layer security. The research shows that as data transfer speeds grow alongside performance requirements, some organizations decide to use upper-layer security measures alone, which omits essential hardware-based exploit vulnerabilities in optical communication components. Comprehensive optical network security approaches predominantly study isolated components such as physical channels and overhead frames [4; 5]. The security evaluation we conducted shows that fragmentation still exists as an ongoing threat. Each technology group including MACsec operates uniquely from optical-layer encryption, which is separate from quantum key distribution systems that stand alone as individual systems. The research findings indicate that the dispersed implementation of optical encryption, MACsec, or QKD security elements does not achieve complete network protection. Our methodology departs somewhat from the previous research in [5] because it suggested that physical-layer protection and eavesdropping-aware routing are all that is required to stop sophisticated interception attacks. While such methods do enhance privacy, our evidence highlights that adversaries can still exploit overhead channels and management plane interfaces to bypass route-based defenses. This underscores the notion that successful security must address vulnerabilities across all layers, not solely the transport path. Our findings resonate with previous research [11; 18], which cautions that post-quantum cryptography demands more than simply deploying new mathematical algorithms. These works point out the realities of deploying QKD in existing networks, issues of scalability, distance limitations, and hardware compatibility. In line with these insights, we show how layering QKD onto a coherent system must be executed with clear isolation (e.g., dedicated wavelengths or time-division multiplexing) to prevent signal degradation. Where we expand upon these discussions is in demonstrating that the synergy of optical phase mask encoding, multi-homodyne coherent detection (MHCD), and QKD can protect network traffic comprehensively, whereas each alone remains vulnerable.