QD-MLL-Based Single-Sideband Superchannel Generation Scheme With Kramers–Kronig Direct Detection Receivers

This work is licensed under a Creative Commons Attribution 4.0 International License.For their capability of electronic dispersion compensation, transmission systems based on direct detection of single-sideband (SSB) signals are attractive candidates as energy-efficient and cost-effective alternative solutions to intradyne digital coherent systems for interdata center and metro applications. The Kramers-Kronig (KK) receiver scheme has been shown to provide superior performance compared to other schemes in signal-to-signal beat interference (SSBI) cancellation in these direct-detection systems. In this paper, we propose a low-complexity and cost-effective scheme of generating an optical superchannel comprising multiple SSB channels, based on a single quantum-dot mode-locked laser source. The proposed system does not require additional photonic or RF components at the transmitter to generate the required SSB signal with a continuous wave (CW) carrier. It also preserves the full digital-to-analog converters' bit resolution for data modulation, in contrast to other methods based on digital generation of the CW component. Simulations of system performance with KK receiver, based on measured laser output field, show that the proposed system can achieve bit-error ratio below the hard-decision forward error correction threshold for 16-QAM Nyquist SSB signals after transmission through three amplified spans of single-mode fiber in a 240-km link. Using 8 KK channels at 23 GBaud each, the proposed scheme will be able to achieve a transmission rate of 736 Gb/s with noncoded spectral efficiency of 2.45 b/s/Hz. The impacts of carrier-to-signal power ratio, per channel launch power into the fiber, and component frequency drifting on transmission system performance are also discussed

Network traffic characteristics of hyperscale data centers in the era of cloud applications

We present the network architecture of Alibaba Cloud DCs and investigate their traffic characteristics based on statistical data and captured traces. The statistical coarse-grained data are in the granularity of one minute, while the captured traces are fine-grained data that are in the granularity of one packet. We study the traffic features from the perspective of a macroscopic view, network performance, and microscopic view. The results report that the average utilization ratio of spine switches is stable when the observation time period reaches one day and the intra-ToR traffic ratio is in the range of 2%-10%. By mapping the folded-Clos topology to a tree topology and considering logical switching planes, we obtain the traffic matrix among pods from the average port utilization ratio. As we further investigate the perspective of network performance and the microscopic view, we find that there is no cell loss happening as the normalized queue speed Q_s is lower than 0.4. The normalized queue speed Q_s is defined as the total bytes of a queue sent in 1 s divided by 100 Gb, which reflects the packet sending speed of the queue. The observed maximum buffer size for one port conforms with the calculated maximum buffer occupation of 2.8 MB. By analyzing the captured traces, we find that the packet length is subject to a trimodal distribution. Under a time granularity of 10 ms, the instant bandwidth of one ToR port could reach 96 Gb/s at an average load of around 0.2 under a maximum link bandwidth of 100 Gb/s.</p

Traffic Rate Matrix Decomposition Based Conflict Free Scheduling for a Fast Optical Switching Network

We propose a traffic rate matrix decomposition (TRMD) based conflict free scheduling for a fast optical switching network and show that TRMD outperforms a flow control protocol with &lt;10s latency and &gt;92% throughput at load of 1.</p

Dynamic Buffer Status Based Conflict Free Scheduling for a Fast Optical Switching Network

We propose a dynamic buffer status matrix decomposition (BSMD) based conflict free scheduling for a fast optical switching network. The performance of BSMD outperforms both static and retransmission scheduling mechanisms, and BSMD achieves 10.1 µs latency and 98.8% throughput at load of 0.8.</p

Traffic Rate Matrix Decomposition Based Conflict Free Scheduling for a Fast Optical Switching Network

We propose a traffic rate matrix decomposition (TRMD) based conflict free scheduling for a fast optical switching network and show that TRMD outperforms a flow control protocol with &lt;10s latency and &gt;92% throughput at load of 1.</p

Supporting Bandwidth Guarantee for a Fast Optical Switching Network with Micro Buffer Switching Fabric

We propose a micro buffer fast optical switch (MFOS) fabric for a data center network. MFOS highly improves the network performance, and achieves 6.7 μs latency and 99.9% throughput at a load of 0.8.</p