Topology Awareness Research Articles

Topological awareness towards collision-free multi-axis curved layer additive manufacturing

We present a topology-aware computational framework that enables global collision-free and support-structure-free material extrusion for curved layer multi-axis printing of a range of high-genus and simply connected models. The nature of multi-axis additive manufacturing facilitates continuous variation of build direction, which paves the way for numerous approaches of geometry-based curved layer design. However, due to unawareness of global topological features, prevention of collision between the printer nozzle and the workpiece can either remain uncertain or demand for exhaustive algorithmic approaches, depending on the topological and geometrical complexity of a given mesh model. In this paper, we present a topological analysis framework that draws inspiration from the concepts of Reeb graph and Morse theory, to distinguish between collision-prone and collision-free regions of mesh models. We provide an exact definition for global collision-inducing features in regions of risk and optimise the nozzle orientation vector field to avoid global collisions whilst adhering to the overhang angle constraints. A new shape analysis method is then proposed to find the model orientation which maximises the manufacturability of bifurcating simply connected models. To validate our algorithmic framework, several high-genus and bifurcating simply connected models are printed using a robotic multi-axis printer. The experimental results demonstrate the feasibility and effectiveness of our framework for minimising global collisions in multi-axis curved layer additive manufacturing for a range of mesh models.

BigSMARTS: A Topologically Aware Query Language and Substructure Search Algorithm for Polymer Chemical Structures.

Molecular search is important in chemistry, biology, and informatics for identifying molecular structures within large data sets, improving knowledge discovery and innovation, and making chemical data FAIR (findable, accessible, interoperable, reusable). Search algorithms for polymers are significantly less developed than those for small molecules because polymer search relies on searching by polymer name, which can be challenging because polymer naming is overly broad (i.e., polyethylene), complicated for complex chemical structures, and often does not correspond to official IUPAC conventions. Chemical structure search in polymers is limited to substructures, such as monomers, without awareness of connectivity or topology. This work introduces a novel query language and graph traversal search algorithm for polymers that provides the first search method able to fully capture all of the chemical structures present in polymers. The BigSMARTS query language, an extension of the small-molecule SMARTS language, allows users to write queries that localize monomer and functional group searches to different parts of the polymer, like the middle block of a triblock, the side chain of a graft, and the backbone of a repeat unit. The substructure search algorithm is based on the traversal of graph representations of the generating functions for the stochastic graphs of polymers. Operationally, the algorithm first identifies cycles representing the monomers and then the end groups and finally performs a depth-first search to match entire subgraphs. To validate the algorithm, hundreds of queries were searched against hundreds of target chemistries and topologies from the literature, with approximately 440,000 query-target pairs. This tool provides a detailed algorithm that can be implemented in search engines to provide search results with full matching of the monomer connectivity and polymer topology.

Node Essentiality Assessment and Distributed Collaborative Virtual Network Embedding in Datacenters

Network virtualization (NV) has extensive and significant applications in cloud computing and parallel and distributed systems. Virtual network embedding (VNE) is a key issue in NV, which is an effective means to advance systems' performance. While existing VNE research lacks resource allocation coordination between mappings of different virtual network requests, resulting in insufficient resource utilization and high overhead. In this paper, we propose a novel node essentiality evaluation model for data center networks (DCNs), and design an efficient distributed collaborative virtual network embedding. Firstly, we propose a node essentiality evaluation scheme based on dynamic model, which combines the characteristics of network topology and nodes to make the evaluation results more comprehensive. Secondly, we establish the two-stage node importance evaluation criteria for the deviation mean of the data center dynamic model and the variance based on the deviation mean. Furthermore, we investigate a nodal importance assessment method based on the data center dynamic model for perturbation testing. Finally, we design a distributed coordinated VNE algorithm ( <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CNI-VNE</b> ) which calculates the importance index of physical nodes through topology awareness. The proposed algorithm can increase the coordination between different request mappings, thereby reducing the mapping cost of physical node resources and minimizing the cost of VNE. We use the real Fat-tree DCN of 128 servers and 80 switches as testbed, and evaluate them from indicators such as average reliability, average bandwidth consumption, average energy consumption, and average mapping time. Massive simulation results in different scenarios show that our algorithm achieves the best performance on most indicators compared with the existing state-of-the-art proposals, mapping acceptance and average revenue increased by 19.4% and 21.3%, respectively, and DCN reduced bandwidth consumption by about 30%.

Integration- and separation-aware adversarial model for cerebrovascular segmentation from TOF-MRA

PurposeCerebrovascular segmentation from time-of-flight magnetic resonance angiography (TOF-MRA) is important but challenging for the simulation and measurement of cerebrovascular diseases. Recently, deep learning has promoted the rapid development of cerebrovascular segmentation. However, model optimization relies on voxel or regional punishment and lacks global awareness and interpretation from the texture and edge. To overcome the limitations of the existing methods, we propose a new cerebrovascular segmentation method to obtain more refined structures. MethodsIn this paper, we propose a new adversarial model that achieves segmentation using segmentation model and filters the results using discriminator. Considering the sample imbalance in cerebrovascular imaging, we separated the TOF-MRA images and utilized high- and low-frequency images to enhance the texture and edge representation. The encoder weight sharing from the segmentation model not only saves the model parameters, but also strengthens the integration and separation correlation. Diversified discrimination enhances the robustness and regularization of the model. ResultsThe adversarial model was tested using two cerebrovascular datasets. It scored 82.26% and 73.38%, respectively, ranking first on both datasets. The results show that our method not only outperforms the recent cerebrovascular segmentation model, but also surpasses the common adversarial models. ConclusionOur adversarial model focuses on improving the extraction ability of the model on texture and edge, thereby achieving awareness of the global cerebrovascular topology. Therefore, we obtained an accurate and robust cerebrovascular segmentation. This framework has potential applications in many imaging fields, particularly in the application of sample imbalance. Our code is available at the website https://github.com/MontaEllis/ISA-model.

A resilient network recovery framework against cascading failures with deep graph learning

Because of the increasing importance and dependencies of infrastructure networks and the potential for massive cascading failures in real-world network systems, maintenance optimization to effectively reduce system performance loss caused by diverse disruptions is of significant interest among researchers and practitioners. In this work, a new recovery framework was developed to rapidly identify important system components for maintenance to improve network resilience against cascading failures. This work provides distinct advantages to determine an optimal maintenance priority by combining real-time network structure importance with other maintenance prioritization based on customer preference. This approach adopts structural graph embedding and deep reinforcement learning to extract real-time network topology information (such as minimum vertex cover) to update the maintenance priority during the recovery process. Based on the case studies on synthetic networks and a US airport network, the proposed recovery framework with real-time network topology awareness shows better performance than other maintenance prioritization strategies regarding resilience enhancement. This work improves the understanding of how the changing network structure influences maintenance effects. It also provides insights of the practical usefulness of advanced deep learning on helping optimal maintenance prioritization to effectively reduce the intensity and extent of cascading failures.

Towards general-purpose representation learning of polygonal geometries

Neural network representation learning for spatial data (e.g., points, polylines, polygons, and networks) is a common need for geographic artificial intelligence (GeoAI) problems. In recent years, many advancements have been made in representation learning for points, polylines, and networks, whereas little progress has been made for polygons, especially complex polygonal geometries. In this work, we focus on developing a general-purpose polygon encoding model, which can encode a polygonal geometry (with or without holes, single or multipolygons) into an embedding space. The result embeddings can be leveraged directly (or finetuned) for downstream tasks such as shape classification, spatial relation prediction, building pattern classification, cartographic building generalization, and so on. To achieve model generalizability guarantees, we identify a few desirable properties that the encoder should satisfy: loop origin invariance, trivial vertex invariance, part permutation invariance, and topology awareness. We explore two different designs for the encoder: one derives all representations in the spatial domain and can naturally capture local structures of polygons; the other leverages spectral domain representations and can easily capture global structures of polygons. For the spatial domain approach we propose ResNet1D, a 1D CNN-based polygon encoder, which uses circular padding to achieve loop origin invariance on simple polygons. For the spectral domain approach we develop NUFTspec based on Non-Uniform Fourier Transformation (NUFT), which naturally satisfies all the desired properties. We conduct experiments on two different tasks: 1) polygon shape classification based on the commonly used MNIST dataset; 2) polygon-based spatial relation prediction based on two new datasets (DBSR-46K and DBSR-cplx46K) constructed from OpenStreetMap and DBpedia. Our results show that NUFTspec and ResNet1D outperform multiple existing baselines with significant margins. While ResNet1D suffers from model performance degradation after shape-invariance geometry modifications, NUFTspec is very robust to these modifications due to the nature of the NUFT representation. NUFTspec is able to jointly consider all parts of a multipolygon and their spatial relations during prediction while ResNet1D can recognize the shape details which are sometimes important for classification. This result points to a promising research direction of combining spatial and spectral representations.

Traffic ahead: Navigating the road to carbon neutrality

The journey to carbon neutrality will require trillions of dollars of capital investment over many years. Analytical models based on foresight offer guidance, but an overreliance on them can lead to a myopic focus on a single pathway. Some argue that the solution is to develop higher-resolution models, fed with increasingly granular data. Here, we note that real-time feedback is an important and underappreciated complement to this approach.We discuss how nations and corporations are currently embarking on the energy transition with the equivalent of a high-level map. The ambition is clear, but there is a lack of confidence in the best route. Routing options and conditions are changing rapidly. We outline the features of a navigation app for the energy transition that offers real-time, actionable guidance for the energy transition would be hugely beneficial. The essential function of such an app would be to collect, secure, process, and present data in a way that can support decisions by relevant actors. Such a capability would require three essential elements: route topology awareness with high-resolution details of the benefits and costs of different decarbonization options; data platforms that provide insight into the real-time situation; and trade-off tools that readily convey accurate, up-to-date, and easily-interpretable estimates of switching costs. These elements exist at varying levels of maturity, and improvement and integration is needed to deliver the utility and convenience of a road travel app.This Perspective draws on our collective experience mapping paths to carbon neutrality for the Princeton Net-Zero America study and one of China's largest energy companies (China Energy) to develop the idea of navigation apps for the energy transition. Starting with a resolved accounting of CO2 emissions, we illustrate the importance of accounting for differing motivations and leverage among actors. We discuss the essential features of a navigation app and show how progress in these areas can help address bottlenecks in large-scale clean energy deployment. We conclude with a call for increased collaboration with tech companies to accelerate development of these capabilities.

Joint topology control and routing in a UAV swarm for crowd surveillance

Aerial surveillance using unmanned aerial vehicles (UAVs) provides an on-demand and cost-effective solution to smart-city monitoring needs, owing to their three-dimensional positioning adjustment and autonomy. The optimal deployment of a UAV swarm, also known as a flying ad hoc network (FANET), to achieve on-demand coverage of mobile ground targets (MGTs) is challenging in terms of controlling UAV mobility to maximize coverage while maintaining quality of service. Data routing from UAVs to a base station (BS) without awareness of the updated topology causes link breakages, excessive retransmissions, high congestion, and energy holes. Therefore, we propose a joint topology control and routing (JTCR) protocol comprising three modules to perform crowd surveillance. The first JTCR module provides virtual force-based mobility control (VFMC), which controls the mobility of UAVs to track MGTs, ensuring stable bi-connectivity. The second module provides energy-efficient mobility-aware fuzzy clustering that clusters the FANET to aggregate the sensed data to each cluster head (CH) by utilizing the UAV mobility provided by the VFMC. The third module provides topology-aware Q-routing, which routes the aggregated data from CH UAVs to the BS by selecting an optimal path in terms of delay, path stability, and energy consumption. According to our performance study, the proposed JTCR outperforms existing routing protocols in terms of tracking-coverage rate, connectivity rate, the number of retransmissions, packet delivery ratio, end-to-end delay, and energy consumption. This is mainly enabled by the realistic mobility control of the UAV swarm at the reasonable cost of control overhead.

Balanced Scheduling Method for Big Data of Network Traffic Based on Set-pair Analysis Strategy

The continuous surge in the total amount of big data of network traffic leads to excessive data transmission load on the network channel. To effectively alleviate this problem, a scheduling method for regulating big data load is designed and proposed. The link discovery is applied to perform set-pair analysis of network topology awareness; the cloud computing algorithm is used to perform calculations for data transmission; based on the measurement results, traffic routing is controlled and measured to achieve link analysis and reorganization, as well as completing balanced scheduling of traffic big data, which proves that the method can effectively alleviate the big data scheduling load problem and has an important role for research in network optimization fields.

A Fast Hierarchical Physical Topology Update Scheme for Edge-Cloud Collaborative IoT Systems

The awareness of physical network topology in a large-scale Internet of Things (IoT) system is critical to enable location-based service provisioning and performance optimization. However, due to the dynamics and complexity of IoT networks, it is usually very difficult to discover and update the physical topology of the large-scale IoT systems in real-time. Considering the stringent latency requirements in IoT systems, while the initial processing time for topology discovery can be tolerated, latency due to real-time topology update constitutes an even higher level of challenge. In this paper, a novel fast hierarchical topology update scheme is proposed for the large-scale IoT systems enabled by using the edge-cloud collaborative architecture. Specifically, an event-driven neighbor update algorithm, termed as TriggerOn, is firstly developed to update the local neighbor table of the end devices when device association or disassociation occurs. Based on the updated neighbor tables, the physical topology update of the subnet is conducted at the coordinated edge device, where a hybrid multidimensional scaling (MDS) based 3D localization algorithm is developed to locate the newly associated devices. Simulation results have indicated that as compared to the benchmark methods, the neighbor discovery latency has been reduced dramatically, and the 3D localization accuracy has been improved. Furthermore, the overall latency incurred by the proposed hierarchical physical topology update scheme is significantly lower than the distributed consensus-based update scheme, especially for the large-scale IoT subnets.

Dynamic Topology Awareness in Active Distribution Networks Under DG Uncertainties Using GMM-PSEs and KL Divergence

The frequent switching operations and triggering events of automation devices are poorly documented in distribution management systems, leading to challenging work regarding the timely detection of system state changes. Additionally, the limited measurements in distribution networks and the randomness of plug-and-play devices make obtaining real-time observations of system states difficult. Furthermore, distributed generation (DG) output uncertainties exacerbate the situation. Thus, we propose a dynamic topology awareness (DTA) approach to make judgments regarding operational states and identify all possible topology changes (including normal operations, islanding and outages) in the absence of real-time DG measurements. The method consists of two steps. The first step applies parallel Gaussian mixture model-based probabilistic state estimators (GMM-PSEs) of subareas and extended subareas to calculate the probability distributions of border bus voltages with full consideration of DG uncertainties. The second step utilizes the Kullback-Leibler (KL) divergence measure to evaluate the difference between the two probability distributions estimated by subareas and extended subareas, thereby obtaining an indicator (average KL divergence) for identifying possible topologies. The effectiveness of the proposed method is examined on the IEEE 33-bus and IEEE 123-bus test cases. It is computationally efficient and accurate when identifying all possible topologies under limited measurements and DG uncertainties.

Dynamic Topology Awareness in Active Distribution Networks Using Blockchain-Based State Estimations

With growing complexity and uncertainty from distributed generations and active customers, distribution networks are facing more unexpected events and topology changes; while very limited measurements may degrade the observability of distribution system states and endanger the security of the system. Meanwhile, massive data from various types of users (if they can be used), can be valuable for power utilities. This makes privacy and data security a more critical issue, while being endowed with operation and market flexibilities. Thus, we propose a blockchain-based privacy-protecting approach for Dynamic Topology Awareness (DTA) to distinguish topology changes from cyber anomalies, including physical, cyber and business layers. At the bottom layer (physical layer), the distribution network is partitioned into subareas and tie-line areas, coping with local data from measurement devices or users. Estimated border values from parallel local estimations would be examined through data consistency checking. And DTA consensus algorithm might be triggered, querying historical status stored as blockchain contracts for anomalies detections and new block formations. Voting mechanism is then adopted to verify new blocks from data tampering. The performance of the proposed DTA approach is validated through simulations to identify topology changes and cyber anomalies, with additional discussions on the trade-off between DTA sensitivity and estimation accuracy.

Communication Optimization Technology Based on Network Dynamic Performance Model

This work analyses different communication modes in applications of supercomputing, proposes a communication dynamic performance model based on topology awareness, and realizes the prototype system of all-to-all communication and stencil communication optimization based on this model. Basic tests on the optimization of all-to-all communication and stencil communication were carried out on the Sunway TaihuLight System, and this achieved obvious optimization results. Several applications, including molecular dynamics simulation and turbulence simulation, have been optimized and tested. The average performance has been improved obviously. It can be expected that, for other large-scale applications, this optimization method can also be used to obtain significant improvement in communication performance.

Dynamic Topology Awareness and Localization for Power Distribution Networks Considering Non-Gaussian Noise

Increasing operational flexibilities of power system devices and generation/load components have intensified the dynamic changing of power network topologies. Dynamic Topology Awareness (DTA) with limited measurements are vital for subsequent analyses and operations of power distribution networks. Considering the economical limitation of extensive installations of PMUs, thus, we proposed in this paper a DTA method through capturing perturbations in voltage amplitude covariance matrix with statistical inference model that considering non-Gaussian noise and requiring only synchronous measurements of voltage amplitudes. The method was developed and proved to be robust without preconditions of Gaussian noises which is more accordant with practical circumstances. Simulations are performed based on IEEE 123 system, and three types of DTA scenarios can be effectively detected and located with high accuracy.

Advanced spatial network metrics for cognitive management of 5G networks

The emerging fifth-generation (5G) mobile networks are empowered by softwarization and programmability, leading to the huge potentials of unprecedented flexibility and capability in cognitive network management such as self-reconfiguration and self-optimization. To help unlock such potentials, this paper proposes a novel framework that is able to monitor and calculate 5G network topological information in terms of advanced spatial metrics. These metrics, together with enabling and optimization algorithms, are purposely designed to address the complexity of 5G network topologies introduced by network virtualization and infrastructure sharing among operators (multi-tenancy). Consequently, this new framework, centred on a topology monitoring agent (TMA), enables on-demand 5G networks’ spatial knowledge and topological awareness required by 5G cognitive network management in making smart decisions in various autonomous network management tasks including but not limited to virtual network function placement strategies. The paper describes several technical use cases enabled by the proposed framework, including proactive cache allocation, computation offloading, node overloading alerting, and load balancing. Finally, a realistic 5G testbed is deployed with the central component TMA, together with the new spatial metrics and associated algorithms, implemented. Experimental results empirically validate the proposed approach and demonstrate the scalability and performance of the TMA component.

Power Distribution Network Dynamic Topology Awareness and Localization Based on Subspace Perturbation Model

Identifying network dynamic topology changes with limited measurement data is a primary challenge for power distribution system analysis. Existing methods require the measurement of the nodal voltage (both amplitudes and phase angles) of a majority of nodes, which means that large-scale installation of advanced monitors is necessary. In this paper, a distribution network dynamic topology awareness method that only requires a synchronized voltage amplitude measurement of a limited number of nodes is proposed. The key idea of the design is to relate network topology changes (including line topology changes, node topology changes and switch actions) to the resultant perturbations in the voltage amplitude covariance matrix. Because perturbations can be identified with incomplete observations, the corresponding topology changes can be identified with limited measurements of voltage amplitude data. With no need for phase-angle measurement, only ordinary root mean square (RMS) based monitors are needed, which can be made available with a relatively minor investment. Simulation tests are performed with the IEEE 123-node system and 8500-node system. Remarkably, 80% of the topology changes can be detected with only 10% of the nodes equipped with monitors, and a 100% correct localization rate can be achieved with 50% of the nodes equipped with monitors.

A Scheme for Delay-Sensitive Spatiotemporal Routing in SDN-Enabled Underwater Acoustic Sensor Networks

In underwater acoustic sensor networks (UASNs), the sensors are deployed at different areas of the ocean, which perform information collection and delay-sensitive routing to the data center for further processing or industrial computing. However, in UASNs, the network states have spatiotemporal characteristics due to tides or autonomous underwater vehicles. To steadily route the traffic especially when the spatiotemporal characteristics of the UASNs are considered, a network architecture with intelligent traffic engineering or routing policies is indispensable. In this paper, we employ software-defined networking (SDN) technology and propose an SDN-enabled distributed architecture for UASNs. Based on the proposed architecture, we propose a scheme DSR-SDN for delay-sensitive spatiotemporal routing in SDN-enabled UASNs. The DSR-SDN includes three phases: First, topology awareness; second, spatiotemporal characteristics estimation; and third, routing computation. Particularly, with SDN features, DSR-SDN provides topology awareness based on a proposed software-defined beaconing scheme. Based on the detected topology, the spatiotemporal characteristics of the network states are estimated based on a proposed SDN-based hierarchical node localizing approach SDN-HL. Lead by the SDN controllers, SDN-HL makes use of the proposed “minimum weighted gap” formulation and Adam algorithm to optimize the localization and builds the indirect links to increase the localization rate. To route the traffic through the network with spatiotemporal characteristics, we adopt the time-expanded network approach, based on which a spatiotemporal route decision can be made before the routing starts. The simulation results demonstrate that the proposed scheme, i.e., DSR-SDN, can conduct accurate spatiotemporal characteristic estimation for the network states and provide delay-sensitive spatiotemporal routing for the sensed data.

A Multi-Dimension Spatial Method for Topology Awareness and Multipath Generating

Multipath diversity significantly impacts multipath transmission quality. Enough multipath diversity would minimize the negative influence brought by an individual path, thus improving tolerance capability of network congestion and failure. However, multipath diversity is hard to guarantee on overlay networks because of inaccurate awareness of underlay network and multipath generating methods considering little about underlay diversity. In this paper, we design a multi-dimension spatial method for topology awareness and multipath generating. Analyzing that the complicated underlay networks with multiple autonomous systems reduce the accuracy of network positioning for topology awareness, we decompose the underlay networks into multiple dimensions, namely intra and inter autonomous system dimensions. We generate independent views for each autonomous system and merge views by embedding exchange points. Then, we design some spatial mechanisms to evaluate link diversity and to constrain multipath generating. Based on the multi-dimensional view, multipath generating is conducted in inter and intra autonomous system phases. Experiments demonstrate that the proposed method improves topology awareness accuracy and guarantees multipath diversity better and the transmission quality is improved.

Cognitive Virtual Network Embedding Algorithm Based on Weighted Relative Entropy

Current Internet is designed by lots of service providers with different objects and policies which make the direct deployment of radically new architecture and protocols on Internet nearly impossible without reaching a consensus among almost all of them. Network virtualization is proposed to fend off this ossification of Internet architecture and add diversity to the future Internet. As an important part of network virtualization, virtual network embedding (VNE) problem has received more and more attention. In order to solve the problems of large embedding cost, low acceptance ratio (AR) and environmental adaptability in VNE algorithms, cognitive method is introduced to improve the adaptability to the changing environment and a cognitive virtual network embedding algorithmbased on weighted relative entropy (WRE-CVNE) is proposed in this paper. At first, the weighted relative entropy (WRE) method is proposed to select the suitable substrate nodes and paths in VNE. In WRE method, the ranking indicators and their weighting coefficients are selected to calculate the node importance and path importance. It is the basic of the WRE-CVNE. In virtual node embedding stage, the WRE method and breadth first search (BFS) algorithm are both used, and the node proximity is introduced into substrate node ranking to achieve the joint topology awareness. Finally, in virtual link embedding stage, the CPU resource balance degree, bandwidth resource balance degree and path hop counts are taken into account. The path importance is calculated based on the WRE method and the suitable substrate path is selected to reduce the resource fragmentation. Simulation results show that the proposed algorithm can significantly improve AR and the long-term average revenue to cost ratio (LTAR/CR) by adjusting the weighting coefficients in VNE stage according to the network environment. We also analyze the impact of weighting coefficient on the performance of the WRE-CVNE. In addition, the adaptability of the WRE-CVNE is researched in three different scenarios and the effectiveness and efficiency of the WRE-CVNE are demonstrated.

Topology-aware multi-objective virtual machine dynamic consolidation for cloud datacenter

With help of virtualization technology, cloud datacenters provide affordable computation power to numerous enterprises and business users. Virtual machine dynamic consolidation (VMDC) plays an important role in the energy consumption management of datacenters. Previous solutions on VMDC either fail to consider impact resulting from the interaction between datacenter network topology and communication topology, or handle this issue in coarse granular level. In this paper, we propose a new approach to coordinate datacenter network topology and communication topology. The proposed VMDC approach adopts a multi-objective genetic algorithm to simultaneously minimize energy consumption and communication traffic causing performance bottlenecks, while meeting SLA constraint on migration time. In this approach, both SLA constraint and objective function on communication traffic are formulated with topology awareness in switch link level. A comprehensive simulation study shows that the proposed approach can significantly save energy consumption of datacenters and provide SLA assurance for different types of datacenter topologies. Simulation results demonstrate that the proposed approach outperforms prior approaches in terms of reducing energy consumption, bottleneck ratio and SLA violation ratio.