Asymmetric Topology Research Articles

Towards fine-grained load balancing with dynamical flowlet timeout in datacenter networks

In modern datacenter networks (DCNs), load balancing mechanisms are widely deployed to enhance link utilization and alleviate congestion. Recently, a large number of load balancing algorithms have been proposed to spread traffic among the multiple parallel paths. The existing solutions make rerouting decisions for all flows once they experience congestion on a path. They are unable to distinguish between the flows that really need to be rerouted and the flows that potentially have negative effects due to rerouting, resulting in frequently ineffective rerouting. Fine-grained rerouting will also cause severe packet reordering, especially in asymmetric topology scenarios. To address the above issues, we present a fine-grained traffic-differentiated load balancing (TDLB) mechanism, which aims to distinguish flows that are necessarily to be rerouted and reroute traffic in fine-grained without packet reodering. Specifically, TDLB distinguishes the traffic that must be rerouted through the host pair information in the packet header, and selects an optimal path for rerouting. To prevent severe packet reodering caused by excessive path delay differences, TDLB dynamically adjusts the flowlet timeout to segment the traffic and select the optimal path for rerouting. The NS-2 simulation results show that TDLB effectively reduces tail latency and average flow completion time (FCT) for short flows by up to 49% and 46%, respectively, compared to the state-of-the-art load balancing schemes.

Distributed secondary frequency control scheme with A-symmetric time varying communication delays and switching topology

A distributed control of a Microgrid (MG) depends on the communication network for the exchange of information among the Distributed Generators (DGs). Most of the control schemes consider ideal communication among the DGs; however, in practical systems, delays are inherited in a system that can affect the dynamic performance and even destabilize an MG. Therefore, in this research work, delay independent distributed secondary frequency control for MGs is presented. Sufficient delay independent conditions for robust stability of the buffer-free Distributed Averaging Integral (DAI) control scheme is proposed while considering A-symmetric time varying communication delays and switching network topology. Moreover, in this work, slow as well as fast varying delays are analyzed using Lyapunov Krasovskii and Lyapunov Razumikhin's approach. Furthermore, a Lyapunov function based adaptive control approach is employed that updates the constant gain parameters to compensate for the uncertain or varying parameters. Finally, the efficacy of the controller is demonstrated through simulation studies that validate its performance in different scenarios.

Effects of Reynolds Number on the Wake Characteristics of a Notchback Ahmed Body

Abstract This paper investigates the effects of Reynolds number on the wake characteristics of a notchback Ahmed body with effective backlight angle, βe=17.8 deg. The Reynolds number based on the body height was varied from 5×103 to 5×104. Prior to the Reynolds number investigation, a Reynolds-averaged Navier–Stokes (RANS) model assessment was performed using nine turbulence models consisting of one- and two-equation eddy-viscosity models and second moment closure models. The standard Spalart–Allmaras model was the only model that accurately predicted the asymmetric time-averaged wake topology, as reported in previous studies, for the βe=17.8 deg notchback Ahmed body at Re=5×104. The drag coefficient decreased with increasing Reynolds number, while the lift coefficient remained constant for Re≥1×104. The wake structure exhibited three regimes: symmetric (Re≤1×104), transitionally asymmetric (1×104<Re≤3.5×104), and fully asymmetric (Re>3.5×104) states. The wake asymmetry was attributed to an imbalance in entrainment from the sides and asymmetric separation from the roof and the C-pillars of the body. The tilting and stretching terms in the vorticity transport equation were used to provide insight into the source of asymmetry in the vorticity field around the body.

A new single modulating and single carrier signal based control technique for symmetrical and asymmetrical multilevel inverter topology

Abstract In literature, to generate gate pulses for any inverter topology, most of the authors are using a single modulating signal with (level-1) or (level-1)/2 carrier-based pulse width modulation (PWM) techniques and single carrier (SC) signal with (level-1)/2 modulating signal based PWM techniques. Then, while going to higher-level inverter topologies, the complexity of the PWM control approach in both cases can increase. To reduce the control complexity, few authors have reported a single modulating signal with single carrier-based PWM techniques. However, these techniques need more mathematical equations and if-else loops. This article proposes a new single-modulating and single-carrier signal-based generalized PWM control approach using floor function (FF). This technique has been verified by considering one of the single-phase conventional symmetrical and asymmetrical multilevel inverter (MLI) topologies. Generally, FF rounds the value to the nearest integer towards the negative infinity. The proposed PWM control implementation process is very simple and suitable for both high switching frequency (HSF) and low switching frequency (LSF) operations. The proposed control technique (PCT) has been experimentally verified with different steady-state and transient-state studies of results under standalone operation.

Design considerations for efficient spanwise-inclined air-jet vortex generators for separation control in supersonic and hypersonic flows

Shock-wave/boundary-layer interactions and associated flow separation are frequently occurring phenomena in many high-speed flow applications. Injection of spanwise-inclined air-jets is an efficient means to control shock-induced flow separation in supersonic and transonic flows. Separation-control studies in hypersonic flow are scarce and so far mostly restricted to microramp control. The objectives of the current work are to broaden the scope into hypersonic regime, investigate the influence of crossflow Mach and Reynolds number on the jet-injection flow field, and to find a suitable control parameter that is valid across a wide range of flow conditions. For this purpose, we study injection of a single spanwise-inclined jet in supersonic and hypersonic crossflows using large-eddy simulations. We analyzed the flow topology, induced vortical structures and boundary-layer statistics. The general characteristics of the jet/crossflow interactions are similar in the supersonic and hyperonic regimes: the injection of a spanwise-inclined jet induces an asymmetric flow topology with a complex system of shocks and vortical structures. We identified the ratio of injection-pressure-to-freestream-pressure as a suitable parameter to characterize and compare jet/crossflow interactions in different flow regimes. In addition, we recommend larger boundary-layer-to-jet-diameter ratio for control applications, because it delays the lift-off of major vortices. The present results suggest that rows of spanwise-inclined jets can be efficiently used to control separation also in hypersonic flow. Moreover, low momentum-flux jet injection can be potentially also used for cooling purposes.

A new reduced switch count symmetrical and asymmetrical modular topology for multilevel inverters

A new reduced switch count symmetrical and asymmetrical modular topology for multilevel inverters

A New Reduced Switch Count Symmetrical and Asymmetrical Modular Topology for Multilevel Inverters

A New Reduced Switch Count Symmetrical and Asymmetrical Modular Topology for Multilevel Inverters

PDLB: Path Diversity-aware Load Balancing with adaptive granularity in data center networks

Modern data center topologies often take the form of a multi-rooted tree with rich parallel paths to provide high bandwidth. However, various path diversities caused by traffic dynamics, link failures and heterogeneous switching equipment widely exist in the production datacenter network. Therefore, the multi-path load balancer in data center should be robust to these diversities. Although prior fine-grained schemes such as RPS and Presto make the best use of available paths, However, they are prone to experiencing packet reordering problem under the asymmetric topology. The coarse-grained solutions such as ECMP and LetFlow effectively avoid packet reordering, but easily lead to under-utilization of multiple paths. To cope with these inefficiencies, we propose a load balancing mechanism called PDLB, which adaptively adjusts flowcell granularity according to path diversity. PDLB increases flowcell granularity to alleviate packet reordering under large degrees of topology asymmetry, while reducing flowcell granularity to obtain high link utilization under small degrees of topology asymmetry. PDLB is only deployed on the sender without any modification on switch. We evaluate PDLB through large-scale NS2 simulations. The experimental results show that PDLB reduces the average flow completion time by up to ∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim$$\\end{document}8-53% over the state-of-the-art load balancing schemes.

Various matching keys for asymmetric topology encryption

With the fast development of quantum computer technology, one has to focus on the security of information running in real networks. Topological coding is a technology of basic topological structure, number theory and algebra has potential application value in asymmetric encryption system. The public key and private key of topological graph encryption system designed by topological coding may be able to resist attacks equipped with artificial intelligence technology and quantum computer. In order to further investigate topology encoding, we propose new techniques for designing public and private keys using graph coloring and labeling.

Distributed web hacking by adaptive consensus-based reinforcement learning

In this paper, we propose a novel adaptive consensus-based learning algorithm for automated and distributed web hacking. We aim to assist ethical hackers in conducting legitimate penetration testing and improving web security by identifying system vulnerabilities at an early stage. Ethical hacking is modeled as a capture-the-flag style task addressed within a distributed reinforcement learning framework. To achieve our goal, we employ interconnected intelligent agents that interact with their copies of the environment simultaneously to reach the target. They perform local information processing to optimize their policies and exchange information with neighboring agents. We propose a novel adaptive consensus scheme for inter-agent communications, which enables the agents to efficiently share network-wide information in a decentralized manner. The scheme dynamically adjusts its weights based on heuristics, involving both recency and frequency metrics of actions selected at a given state by an individual agent, similar to eligibility traces. We extensively analyze the convergence properties of our algorithm and introduce a new communication scheme design. We demonstrate that this design ensures the fastest convergence to the desired asymptotic values under the general setting of asymmetric communication topologies. Additionally, we provide a comprehensive review of the current state of the field and propose a web agent model with improved scalability compared to existing solutions. Numerical simulations are conducted to illustrate the key characteristics of our algorithm. The results demonstrate that it outperforms both non-cooperative and average consensus schemes. Moreover, our algorithm significantly reduces hacking times when compared to baseline algorithms that rely on more complex models. These findings offer valuable insights to system security administrators, enabling them to address identified shortcomings and vulnerabilities effectively.

Mean-square asymptotic synchronization of complex dynamical networks subject to communication delay and switching topology

Abstract This paper addresses the issue of mean-square asymptotic synchronization (MSAS) of complex dynamical networks with communication delay and switching topology. The communication delay is assumed to be time-variant and bounded, and the switching topology is governed by a semi-Markovian process and allowed to be asymmetric. A distributed control law based on state feedback is presented. Two criteria for the MSAS are derived using a mode-dependent Lyapunov-Krasovskii functional, the Bessel-Legendre integral inequality, and a parameter-dependent convex combination inequality, for the asymmetric and symmetric topology cases, respectively. The scenario of fixed topology is also considered, for which two asymptotic synchronization criteria are proposed. Two simulation examples are provided to illustrate the effectiveness and reduced conservatism of the proposed theoretical results.

FAMG: A flow-aware and mixed granularity method for load-balancing in data center networks

In current Data center Networks (DCNs), Equal-Cost Multipath (ECMP) is a default load-balancing scheme. However, using ECMP may result in the rapid growth of Flow Completion Time (FCT) due to its well-known drawbacks. In order to solve the problems of ECMP, load balancing schemes with per-packet granularity (such as RPS) and per-flowlet granularity (such as LetFlow) are proposed. These two different granularities have their features, but there is no existing load-balancing scheme considering both their advantages. Moreover, these schemes ignore the traffic characteristics in DCNs. In this paper, we mix per-flowlet and per-packet granularity in scheduling decisions and consider traffic characteristics. Based on this idea, we propose a flow-aware and mixed granularity method for load-balancing, referred to as FAMG. The key idea of FAMG is to distinguish elephant and mouse flows and schedule them with different granularities. We evaluate FAMG in simulations with NS-3. Experimental results show that FAMG slightly sacrifices elephant flows FCT but it is worth it since our results demonstrate that FAMG is a good trade-off that outperforms RPS, LetFlow, and TLB in terms of mouse flows FCT in both symmetric and asymmetric network topology.

A polarimetrically oriented X-ray stare at the accreting pulsar EXO 2030+375

Accreting X-ray pulsars (XRPs) are presumed to be ideal targets for polarization measurements, as their high magnetic field strength is expected to polarize the emission up to a polarization degree of ∼80%. However, such expectations are being challenged by recent observations of XRPs with the Imaging X-ray Polarimeter Explorer (IXPE). Here, we report on the results of yet another XRP, namely, EXO 2030+375, observed with IXPE and contemporarily monitored with Insight-HXMT and SRG/ART-XC. In line with recent results obtained with IXPE for similar sources, an analysis of the EXO 2030+375 data returns a low polarization degree of 0%–3% in the phase-averaged study and a variation in the range of 2%–7% in the phase-resolved study. Using the rotating vector model, we constrained the geometry of the system and obtained a value of ∼60° for the magnetic obliquity. When considering the estimated pulsar inclination of ∼130°, this also indicates that the magnetic axis swings close to the observer’s line of sight. Our joint polarimetric, spectral, and timing analyses hint toward a complex accreting geometry, whereby magnetic multipoles with an asymmetric topology and gravitational light bending significantly affect the behavior of the observed source.

Asymmetry-Aware Load Balancing With Adaptive Switching Granularity in Data Center

Datacenter networks provide large bisection bandwidth by load balancing traffic over rich parallel paths in multi-rooted tree topologies. Nevertheless, production datacenters operate under various path diversities caused by traffic dynamics, hardware failures and heterogeneous switching equipment. Therefore, the load balancing schemes in data center should be resilient to network asymmetry. Prior fine-grained schemes such as RPS and Presto are prone to experience packet reordering problem under asymmetric topology since they split flows into small units which are spread across all parallel paths. The coarse-grained solutions such as ECMP and LetFlow effectively avoid packet reordering, but easily leading to under-utilization of multiple paths. To solve these problems, we propose a load balancing mechanism called AG, which adaptively adjusts switching granularity according to the asymmetric degree of multiple paths. AG increases switching granularity to alleviate packet reordering under large degrees of topology asymmetry, while reducing switching granularity to obtain high link utilization under small degrees of topology asymmetry. Moreover, we design a switch-based scheme which measures the difference of one-way delay of multiple paths to obtain accurate state of topology asymmetry with low overhead. AG is a practical switch-based solution without modification at end hosts. The experimental results of NS2 simulations and real implementation show that AG reduces the average and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$99^{th}$</tex-math> </inline-formula> flow completion time by up to 54% and 65% compared with the state-of-the-art load balancing schemes, respectively.

A reliable alternating multi‐path transmission control protocol scheduling for bandwidth aggregation performance

SummaryThe Multi‐Path Transmission Control Protocol is a new generation protocol for the transport layer which allows multihomed devices to exploit simultaneously their own interfaces. This feature would normally lead to some high‐performance achievement in regard to regular TCP. However, the heterogeneous paths might cause the occurrence of the 'out‐of‐order' problem which requires the intervention of a more efficient scheduler to reach a high level of global bandwidth utilization. Since scheduling plays a key role in performance improvements, several studies have been implemented exploiting this idea, namely those that adopt the reactive approach and those others adopting the proactive one. In this paper, our goal is to improve the multipath throughput. The testbed experimentation consists primarily in the evaluation and analysis of the behaviour of different recent scheduling approaches with an asymmetric paths topology. Then, we propose an alternating scheduling approach which shed the light on bandwidth utilization. The results show that this approach is a more efficient solution than taking the reactive and proactive ones separately as it is based on a preliminary study that we conducted on the main performance and reliability parameters and has been implemented in the asymmetric multipath networks. This technique has led to a smart scheduling that provides a high level of throughput aggregation.

Revisiting frequency coupling effects in grid-tied converter: A phase shifting transformer based circuit modeling framework

Due to asymmetric control algorithms and topology, the frequency coupling effect (FCE) extensively exists in the grid-tied converter (GTC), increasing the order of traditional impedance models and sacrificing their inherent physical insight. The two problems can be solved using the recently reported order reduction techniques. However, FCE is roughly regarded as a coupling phenomenon in the existing studies, which is not rigorous because a GTC system will present various degrees of FCE in different situations. Therefore, this paper revisits the FCE from the viewpoint of the complex circuit and categorizes the GTC systems into three types for analysis, i.e., strongly, weakly coupled, and decoupled systems. Firstly, the plausibility of using the complex-valued vectors to depict FCE is illustrated, and thus FCE is clarified as resulting from the rotation of complex-valued vectors and the admittance mismatching. Based on this new clarification, the phase-shifting transformer-based circuit modeling framework is proposed. Then GTC system can be intuitively presented by the proposed circuit model, whose mathematical model is still order-reduced. More importantly, coupling paths of strongly, weakly coupled, and decoupled systems can be flexibly modeled by adjusting the ratio of the phase-shifting transformer. Finally, simulations and experiments prove the analysis and proposed modeling framework.

Graphic Groups, Graph Homomorphisms, and Graphic Group Lattices in Asymmetric Topology Cryptography.

Using asymmetric topology cryptography to encrypt networks on the basis of topology coding is a new topic of cryptography, which consists of two major elements, i.e., topological structures and mathematical constraints. The topological signature of asymmetric topology cryptography is stored in the computer by matrices that can produce number-based strings for application. By means of algebra, we introduce every-zero mixed graphic groups, graphic lattices, and various graph-type homomorphisms and graphic lattices based on mixed graphic groups into cloud computing technology. The whole network encryption will be realized by various graphic groups.

Design and Optimization of an Asymmetric Rotor IPM Motor with High Demagnetization Prevention Capability and Robust Torque Performance

In this paper, an asymmetric rotor interior permanent magnet (ARIPM) motor with high demagnetization prevention capability and robust torque performance is proposed. The key contribution of this paper lies in two aspects. On the one hand, a novel asymmetric rotor with a shifted magnet axis is proposed to improve the demagnetization prevention capability and torque density. In order to obtain a proper asymmetric rotor topology of the ARIPM motor, the multi-physical performances, especially the PM demagnetization characteristics of five types of PM arrangements, are analyzed. Furthermore, an asymmetric rotor with V- and VV-type PM arrangement is preliminarily designed, considering the multi-physical performance balance and the potentially high anti-demagnetization ability. On the other hand, it is found that the asymmetric rotor structure can not only improve the nominal value of motor performance but also can enhance the resistance to the influence of manufacturing uncertainties. Therefore, multi-objective optimization of the ARIPM motor with rotor notch design is carried out to obtain an optimal motor structure with both high nominal value and robustness of motor performances. By comparing the simulation results with those of a benchmark motor, the superiority and validity of the proposed ARIPM motor are confirmed. Experimental tests will be carried out in the future to further verify the effectiveness of the proposed motor.

Asymmetric Topology Design and Quasi-Zero-Loss Switching Composite Modulation for IGCT-Based High-Capacity DC Transformer

Asymmetric Topology Design and Quasi-Zero-Loss Switching Composite Modulation for IGCT-Based High-Capacity DC Transformer

Inductive Wireless Power Transfer Systems for Low-Voltage and High-Current Electric Mobility Applications: Review and Design Example

Along with the technology boom regarding electric vehicles such as lithium-ion batteries, electric motors, and plug-in charging systems, inductive power transfer (IPT) systems have gained more attention from academia and industry in recent years. This article presents a review of the state-of-the-art development of IPT systems, with a focus on low-voltage and high-current electric mobility applications. The fundamental theory, compensation topologies, magnetic coupling structures, power electronic architectures, and control methods are discussed and further considered in terms of several aspects, including efficiency, coil misalignments, and output regulation capability. A 3D finite element software (Ansys Maxwell) is used to validate the magnetic coupler performance. In addition, a 2.5 kW 400/48 V IPT system is proposed to address the challenges of low-voltage and high-current wireless charging systems. In this design, an asymmetrical double-sided LCC compensation topology and a passive current balancing method are proposed to provide excellent current sharing capability in the dual-receiver structures under both resonant component mismatch and misalignment conditions. Finally, the performance of the proposed method is verified by MATLAB/PSIM simulation results.