Contents 1. Introduction
The next-generation data centers (DCs) are expected to evolve towards new switching technologies and architectures to upturn the performance in terms of throughput, latency and scalability. Several DC networks (DCNs) switching the traffic in the optical domain have been proposed providing high capacity and low latency interconnections benefitting from the data rate and format transparency [1], [2]. However, the optical bandwidth of these optical DCNs between top of racks (ToRs) is determined by the deployed transceivers at the ToRs and cannot be reallocated on-demand to serve the dynamic DC traffic once the network is deployed. For most practical scenarios, the static bandwidth allocation is not optimal for handling the dynamic traffic patterns generated by the heterogeneous applications. Only a few ToRs are operated at high capacity at a certain time in the practical DCNs while bandwidth and capacity of other ToRs are underutilized. Moreover, the bandwidth requirements for each ToR dynamically varies as the applications run. Therefore, even for optical DCNs with high capacity, the rigid bandwidth appears to be either overkill or insufficient for the running applications. In this work, we propose and experimentally assess an SDN controlled flexible optical DCN architecture based on SOA-based optical switches and a novel reconfigurable optical ToR (OToR) employing a 40-λ 1×2 photonic integrated wavelength selective switch (PIC- WSS). The deployed PIC-WSS provides high flexibility and excellent cost efficiency. By automatically and elastically controlling the deployed TRXs and the PIC-WSS, the total capacity of the fixed TRXs at each OToR can be dynamically reallocated. This enables a flexible optical bandwidth allocation between OToRs links to be adapted to the dynamic traffic matrix generated by the heterogeneous applications. Experimental results show that the PIC- WSS introduces <0.5 dB penalty at bit error rate (BER) of 1E-9 and the SOA based optical switch fully compensates the WSS loss avoiding costly and power consuming EDFAs. The network performance assessments confirm that 1.75 μs end-to-end latency and 0.015 packet loss at load of 0.6. Numerical investigation of the DCN scalability based on experimental parameters indicates the proposed optical DCN can be scaled out to 40960 servers with 0.043 packet loss and 6.4 μs latency at the load of 0.5.
