## 4 Discussion and Conclusions  
We presented and assessed a novel flat OW-DCN architecture based on SOA-based SWS, FPGA-based switch schedulers, N \(\times\) N-port AWGRs, and SDN-enabled reconfiguration. The introduced optical wireless technology avoids cable complexity and produces a flexible and low-power-consuming DCN while enabling fast and reconfigurable all-optical packet switching.  
Table 4 compares the proposed architecture with the existing research on OW-DCNs. Different switching technologies have been applied to provide wireless interconnections. However, most of them, i.e., MEMS, have been demonstrated with a millisecond switching timescale and complexity control methodology, making the network results limited in throughput and scalability. Furthermore, only theoretical model simulations or simple-link experimental demonstrations are reported in these studies. Moreover, no OW-DCN has been proposed with both a complete network switching system and a full architecture design.  
For the proposed architecture, a nanosecond fast optical switch with complete architectural design interconnection and switching system was proposed. A fully functional control plane based on label processing, contention solving, retransmission, fast reconfiguration for supporting dynamic traffic patterns and facilitating network provision was experimentally verified. The transmission performance with the functional block of SWS was evaluated with a 4 \(\times\) 4-rack OW-DCN based on a 4 \(\times\) 4-port AWGR. It was shown that a 50-gigabyte-per-second error-free (BER \(<\) 10\({}^{-9}\)) transmission for all the validated links between the  
Figure 10: BER curves for the 50 Gb/s packet switch transmission.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Input**} & \multicolumn{2}{c}{**Output**} \\ \cline{2-3}  & **ToR3** & **ToR4** \\ \hline ToR1 & 1560.70 nm & 1559.08 nm \\ ToR2 & 1562.26 nm & 1560.64 nm \\ \hline \hline \end{tabular}
\end{table}
Table 3: Wavelength routing mapping of AWGR.  
ToRs was achieved. The results of the fast (50 Gb/s) optical packet switching showed a good performance, with a power penalty of around 0.6 dB with respect to the back-to-back packetized traffic. This confirms the ability of the proposed OW-DCN switching system to support fast and accurate packet-level switching.  
It should be noted that the scalability of our architecture only relies on the AWGR and the SWS system. Therefore, we believe that exploiting an AWGR with more ports [25] and introducing photonic integration technology to integrate the SWS, a scalable OW-DCN with high throughput, small footprint, low cost, and low power consumption, is achievable. In addition, benefiting from the format-transparent all-optical switching technology and the periodical FSR of AWGR, the throughput of this OW-DCN can be further increased by employing a multi-level modulation format and wavelength multiplexing without changing the infrastructure.  
Conceptualization, S.Z.; validation, S.Z. and X.X.; writing, S.Z.; supervision, E.T. and N.C. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The authors declare no conflict of interest.