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Data center performance is affected by three main factors; bandwidth, latency, and reliability of intra-data center interconnection network. Bandwidth and latency are definitely improved by adopting optical technology for intra-data center communication, but fault tolerance of the corresponding optical networks has been raised less. Recently, we introduced two Torus-based, all-optical, and non-blocking networks, i.e. O-TF and O-FTF, addressing reliability of optical networks, and now, in this paper, to address the scalability problem, we propose a novel Optical Clos-based architecture which reduces minimum number of required wavelength channels, as well as, the switch size in each node. Moreover, we examine three different types of redundancies; including (a) wavelength (adopted in O-TF network), (b) hardware (adopted in O-FTF network), and (c) path (adopted Optical Clos)) redundancies, in terms of throughput drop under failures, implementation cost, optical power loss, electrical power, latency, topology, and wiring complexity. In addition to simulating networks utilizing generated traffic based on Microsoft data, realistic traffic has also been considered. Our simulation results confirm that in addition to improving power consumption and latency, O-TF, O-FTF, and O-Clos architectures lead to throughput increment up to 80%, 90%, and 70%, respectively, comparing to WaveCube at the presence of network failure, as result of adopting our proposed fault-tolerant method, named as RAOP. [ABSTRACT FROM AUTHOR]

• An optical band-pass filter-assisted offset DSB direct-detection receiver is proposed for low-cost data center interconnect applications. • The proposed scheme uses an OBPF to filter out the optical carrier as the local oscillator for the receiver. As such, signal-signal beat interference can be eliminated. • Compared with the previous offset DSB CADD scheme, the optimal CSPR of the proposed scheme can be reduced to less than 0 dB, and the OSNR sensitivity can be significantly improved. • The effectiveness of the proposed offset DSB self-coherent detection is fully verified by simulation. The numerical results show the potential of proposed scheme. The offset double-sideband (DSB) scheme has attracted attention because it can achieve field recovery at low carrier-to-signal power ratio (CSPR) and improve the spectral efficiency (SE) of self-coherent detection. In this paper, an offset DSB filter-assisted direct detection (FADD) scheme is proposed and studied for the first time, which uses an optical bandpass filter (OBPF) to filter out the optical carrier as the local oscillator for the receiver. As such, signal-signal beat interference (SSBI) can be eliminated. Since the offset DSB signal has a large frequency gap, the requirement for the bandwidth of the OBPF is not high. The performance of the proposed offset DSB FADD scheme is evaluated for 16-QAM signals. It is comprehensively compared with offset DSB carrier-assisted differential detection (CADD) scheme in terms of OSNR sensitivity, optimal CSPR, and receiver power sensitivity. In addition, the effect of frequency gap compression is significant as SSBI is completely eliminated from the system, thereby utilizing as many low-frequency resources as possible and improving SE. Finally, the proposed offset DSB FADD scheme is resilient to the wavelength offset up to several GHz between the transmitter laser and the center wavelength of the OBPF. [ABSTRACT FROM AUTHOR]

• A low-power solution for short-distance high-speed data center interconnects. • Self-homodyne (SH) systems provide a line-width tolerant and LO-less receiver. • Applicability of a proposed cascaded equalizer is verified by analysis and results. • A self-homodyne QPSK system with cascaded equalizer is experimentally demonstrated. • Analog implementation of such equalizer results in a low-power lowcost receiver. Self-homodyne fiber optic links appear to be ideal for high-capacity low-power data center interconnects. In this work, a polarization multiplexed carrier based Self-Homodyne Quadrature Phase Shift Keying (SH-QPSK) system has been experimentally demonstrated with a cascaded equalizer structure. The proposed cascade combination of a Constant Modulus Algorithm (CMA) based equalizer with a Decision Feedback Equalizer (DFE) improves the performance by virtue of the difference of the Mean Squared Error (MSE) of the two equalizers. The reduction in the MSE for a CMA equalizer, when an additional DFE stage is used, is confirmed by theoretical framework and simulation results. Simulation results also validate that the difference in the performance measurement for the standalone CMA and the cascaded equalizer is more in the case of such SH system as compared to the conventional coherent system. The 25 Gbaud SH-QPSK system results in a Bit Error Rate (BER) of 4.14 × 10 - 6 for 80 km Standard Single Mode Fiber (SSMF) with the CMA-DFE equalizer. The CMA-DFE equalizer exhibits one to two orders of magnitude improvement in the BER for various lengths of SSMF channel, as compared to the BER obtained from a commonly used standalone CMA equalizer. [ABSTRACT FROM AUTHOR]

• Orchestrated deployment of slices over a data centre with optical DCN is presented. • The optical data plane allows for high bandwidth and low latency communications. • The resource orchestration approach increases the number of accepted slices. The emergence of new paradigms and services is pushing the limits of nowadays cloud infrastructures. It is a fact that current solutions lack in the flexibility and configurability to adapt to heterogeneous requirements coming from the applications/services to be supported over them. This results most of the time in severe underutilization of the underlying physical substrate. In light of this, newer approaches on resource provisioning and infrastructure management are needed. The Infrastructure as a Service (IaaS) paradigm is proposed as a solution to overcome these limitations. Thanks to IaaS, the physical infrastructure is partitioned onto virtual slices, encompassing heterogeneous resources (e.g. network, computing). Such a concept is expected to be harnessed by future data center (DC) infrastructures in order to cope efficiently with multi-tenancy as well as heterogeneous application requirements. However, current DC networks (DCNs) impose sever limitations onto traffic handling to fully exploit this vision. In light of this, optical technologies are seen as prime candidates for realizing the high performance network fabrics that future DC architectures will need. Under such an umbrella, it becomes primordial to develop specific provisioning solutions that account for the particularities of the optical medium, while providing the means to efficiently slice the DC infrastructure. With all of these in mind, in this article we present a solution for orchestrating and controlling virtual slices in a DC scenario with optical intra-DCN, with the scope of optimizing the underlying physical infrastructure utilization. The benefits of the presented solution are demonstrated against legacy architectures through exhaustive experiments and simulations. [ABSTRACT FROM AUTHOR]

Increased traffic demands within and between data centers now necessitate low-cost and low-power systems with per-wavelength bit rates beyond what can be easily achieved using conventional on/off keying. We review spectrally efficient links based on direct detection, Stokes vector detection, coherent detection and differentially coherent detection for data center applications. We show that limited spectral efficiency and power margin will inhibit scaling of direct detection-compatible formats beyond 100 Gbit/s. Stokes vector receivers can provide higher spectral efficiency without requiring a local oscillator laser, but require power-hungry analog-to-digital converters (ADCs) and digital signal processing (DSP). Similarly, existing DSP-based coherent systems designed for long-haul transmission may be excessively complex and power-hungry for short-reach data center links. We present low-power DSP-free coherent and differentially coherent alternatives that avoid high-speed ADCs and DSP and achieve similar performance to their DSP-based counterparts in intra-data center links and dispersion-compensated inter-data center links. [ABSTRACT FROM AUTHOR]

Increased demands for web and cloud-based services have been driving exponential growth of datacenter bandwidth. This paper discusses, from Google’s perspective, emerging challenges and possible technical solutions for scaling intra-datacenter and intra-campus interconnection network bandwidth. [ABSTRACT FROM AUTHOR]

On the basis of profound understanding of data center (DC) traffic demands and optical switching technologies, we present a hybrid optical network design for future data center network (DCN). Such design integrates optical circuit switching (OCS) and optical packet switching (OPS) schemes via hybrid Top-of-the-Rack (ToR) switches which provide flexible function-switchover between different traffic patterns in the DCN. Simulations of network behaviors under such DC traffic loads indicate that the proposed OPS/OCS DCN can effectively improve the network performance. Moreover, via a preliminary analysis of OCS and OPS network configurations, the construction of hybrid DCN is also proved as the most cost- and energy-efficient way for DCN upgrading while offering a promised quality of service. An experimental demonstration shows a complete implementation of data center virtualization in the proposed hybrid data center network. [ABSTRACT FROM AUTHOR]

Universal fiber is a multimode fiber that has an LP 01 mode field diameter approximately matched to that of standard single-mode fiber. It can transmit both multimode and single-mode signals using transceivers designed for either multimode fiber or single-mode fiber. By using universal fibers, one can bridge the needs for both single-mode and multimode transmission through a uniform and simplified cable infrastructure to accommodate the full distance range needed, while having upgradability from 10G to 40G to 100G and to even higher data rates. We build on our previous work that analyzed the dependence of LP 01 mode-field diameter on fiber parameters, and the coupling loss for both single-mode and multi-mode transmission, with a further study of mode coupling and multiple path interference associated with single-mode operation. We demonstrate system performance in both single-mode and VCSEL-based multimode transmissions for a number of 100G transceiver types using a QSFP form factor − the preferred choice in data centers. [ABSTRACT FROM AUTHOR]

• A network architecture supporting ONUs' discretionary peer-to-peer communication is created, and a skillful wavelength allocation strategy is proposed. • The proposed architecture improves the flexibility and efficiency of direct communication, and reduces the cost of manufacturing and maintenance of network. • The proposed strategy improves the utilization of wavelength resources, and weakens the Rayleigh backscattering in signal transmission. This paper proposes a low-cost access network architecture supporting flexible point-to-point communication between any optical network units (ONUs). By sharing transceivers between upstream/downstream communication and ONU communication, the number of transceivers required in ONU can be decreased. Coupled with using passive components instead of active transmitters and adopting modular design of nodes for integration, the cost of manufacturing and maintenance of network equipment can be significantly reduced. In addition, by skillfully allocating wavelengths, not only wavelength multiplexing can be realized and thereby improving the utilization of network wavelength resources, but also the Rayleigh backscattering (RB) in signal transmission can be effectively weakened. Finally, by the simulation experiment, the effectiveness of the proposed architecture is demonstrated. [ABSTRACT FROM AUTHOR]

We report on achieving 28 Gbaud 4-PAM transmission with post-equalization over a 240 km SSMF link without re-engineering the transmission link design. The results demonstrate the prospect of re-using conventional links for inter data center connections. [ABSTRACT FROM AUTHOR]

With the rapid growth of data center services, the elastic optical network is a very promising networking architecture to interconnect data centers because it can elastically allocate spectrum tailored for various bandwidth requirements. In case of a link failure, to ensure a high-level quality of service (QoS) for user request after the failure becomes a research focus. In light of it, in this paper, we propose and experimentally demonstrate multipath protection for data center services in OpenFlow-based software defined elastic optical network testbed aiming at improving network reliability. We first propose an OpenFlow-based software defined elastic optical network architecture for data center service protection. Then, based on the proposed architecture, multipath protection scheme is figured based on the importance level of the service. To implement the proposed scheme in the architecture, OpenFlow protocol is extended to support multipath protection in elastic optical network. The performance of our proposed multipath protection scheme is evaluated by means of experiment on our OpenFlow-based testbed. The feasibility of our proposed scheme is also demonstrated in software defined elastic optical networks. [ABSTRACT FROM AUTHOR]

Due to the performance guarantee of low delay, huge bandwidth and high reliability at a low cost, IP over Flexi-Grid optical network is a very promising networking architecture applied to the interconnection of geographically distributed data centers. It can enable efficient resource utilization and support heterogeneous bandwidth demands in cost-effective, highly-available and energy-effective manner. In case of edge Flexi-Grid optical network node failure, to ensure a high-level quality of service (QoS) for user request after the failure becomes a research focus. In this paper, we propose a novel service-aware resources integrated resilience (SA-RIR) scheme for data center services in software defined data center networking architecture based on IP over Flexi-Grid optical networks. Different from previous works which restore the services just exploiting the optical stratum, the proposed scheme provides the resilience using the multiple stratums resources in case of the edge optical node failure. We quantitatively evaluate the feasibility and performances through the simulation under heavy traffic load scenario in terms of path blocking probability, path resilience latency and resource occupation rate with different failure rates. Simulation results show that, the SA-RIR scheme can enable joint optimization of IP network, Flexi-Grid optical network and data center application stratum resources, and enhance the data center service resilience responsiveness to the dynamic end-to-end demands. [ABSTRACT FROM AUTHOR]

• The minimum MCMSA problem is proposed and investigated in EODCNs. • Various proportions of secure services are considered in the proposed problem. • An ILP and a heuristic algorithm are developed for the DST-MCMSA scheme. • We compare the performance of the proposed methods with other existing methods. Multicast provisioning is important for supporting applications such as data backup and cloud computing in elastic optical data center networks (EODCNs). As the traffic demand from these applications is quickly increasing, it is important to reduce the resource usage and implement cost-effective multicasting. By mapping multiple traffic flows into a single light-tree, the light-tree-based multicast service aggregation can reduce the number of required transceivers while accommodating many multicast requests. However, it may increase the spectrum usage, and it is not always feasible because some subscription-based or secure multicast services in the network should be sent only to authorized users. In this paper, we focus on the problem of routing, modulation level selection, spectrum, and transceiver assignment for multicast services with different security levels. We study potential performance gains resulting from applying a distributed sub-tree scheme to multi-class multicast service aggregation, realizing reduced overall cost. By formulating the mathematical models using an integer linear program (ILP), we obtain results for a small-scale network. We also propose a heuristic algorithm for large-scale networks, and results show that our proposed algorithm can be beneficial in terms of both spectrum and transceiver utilization in EODCNs. [ABSTRACT FROM AUTHOR]

• We propose a transmitter based on DS-EML to realize quasi-linear complex modulation. • We use the DS-EML to realize 112 Gb/s CD pre-compensation PAM4 signal transmission over 320 km. • We compare the proposed transmitter with IQ modulator and DDMZM. The growing traffic demand in data center interconnections (DCIs) requires high-speed and low-cost transceivers that can flexibly adapt to different transmission distances up to 80 km or further. In this paper, based on the double-side electro-absorption modulated laser (DS-EML), we propose a transmitter with a fixed 90-degree phase rotation on one side of the DS-EML that can realize quasi-linear complex modulation. We verify the application of the quasi-linear DS-EML for a 112 Gb/s CD pre-compensation 4-level pulse amplitude modulation (PAM4) signal transmission over 320 km by simulation. Compared with the LiNbO 3 in-phase quadrature (IQ) modulator and the dual-drive Mach-Zehnder modulator (DDMZM), our proposed transmitter has several obvious advantages, such as low cost, small footprint, ease of integration and reduced power consumption. [ABSTRACT FROM AUTHOR]

In recent years, the technology to narrow the gap between the achievable information rate and the Shannon capacity limits attracts increasing attention. In this paper, a probabilistic shaping coding method based on multi-repeat mapping is proposed. By applying block coding to the information sequences with our method, we transform the modulated constellation points from a uniform distribution to the desired distribution. Rate adaption and controllable distribution are achieved by adjusting the block length and the size of different mapping sets. The proposed algorithm has better coding efficiency, low storage and computational complexity, so is more suitable for data center optical networks. An experiment that demonstrates probabilistically shaped data transmission is successfully conducted over 10 km standard single-mode fiber (SSMF) with 16 quadrature amplitude modulation – discrete multi-tone (16-QAM-DMT). We evaluate our method for a set of code rates, i.e., 16 QAM with code rate 6/8, 7/8 and 9/12. The experimental results show that the improved signal to noise ratios (SNR) can be up to 1.1 dB at a bit error rate (BER) of 10-3 after using the proposed method for probabilistic shaping. [ABSTRACT FROM AUTHOR]

• Deadline-driven manycast requests' scheduling in survivable inter-datacenter EON. • Manycast survivable RMLSA based on deadline-driven queuing with capacity weighting. • Reduction of blocking probability and spectrum resources occupying. In inter-datacenter elastic optical networks (IDC-EONs), many demands, such as data backup, focus on being served before a specific moment rather than immediately. In addition, as a point to multi-point transmission framework, manycast is particularly applicable for these services because it could select destinations from a set of candidate nodes flexibly. As one of key measures to improve the network survivability and spectrum utilization, survivable routing, modulation level and spectrum assignment (SRMLSA) has attracted much attention. The traditional SRMLSA scheme could not optimize the spectrum assignment in time domain. In this paper, SRMLSA problem has been addressed for deadline-driven manycast requests against single-link failure in IDC-EONs. A manycast survivable routing, modulation level and spectrum assignment based on deadline-driven queuing with capacity weighting (MA-SRMLSA-DQCW) scheme is proposed, which could achieve joint optimization in both frequency and time domains while providing 100% protection. Numerical results demonstrate that MA-SRMLSA-DQCW scheme offers a substantial reduction of blocking probability and occupies less spectrum resources compared to reference algorithms. [ABSTRACT FROM AUTHOR]