Physical Network Topology Research Articles

An Algorithm of Physical Network Topology Discovery in Multi-VLANs

The most recent physical topology discovery knowledge of the Ethernet network is the key to network management tasks. Virtual LANs (VLANs) allow network managers to completely break the correlation between the logical and physical network by grouping the interfaces of the same network elements into different subnets. An efficient and general algorithm for discovering physical network topology across multi-VLANs is very necessary. Our topology discovery algorithms are simple for VLANs if we know the VLANs interface groups. The algorithm based on MIB information of SNMP standard is widely supplied by modern IP network elements and does not need modify the operating system software running on hosts or elements. The experimental results prove the correctness of the algorithm and the sufficient and necessary conditions for the uniqueness of the restored topology.

Topology Discovery for Linear Wireless Networks With Application to Train Backbone Inauguration

A train backbone network consists of a sequence of nodes arranged in a linear topology. A key step that enables communication in such a network is that of topology discovery, or train inauguration, whereby nodes learn in a distributed fashion the physical topology of the backbone network. While the current standard for train inauguration assumes wired links between adjacent backbone nodes, this work investigates the more challenging scenario in which the nodes communicate wirelessly. The key motivations for this desired switch from wired topology discovery to wireless one are the flexibility and capability for expansion and upgrading of a wireless backbone. The implementation of topology discovery over wireless channels is made difficult by the broadcast nature of the wireless medium, and by fading and interference. A novel topology discovery protocol is proposed that overcomes these issues and requires relatively minor changes to the wired standard. The protocol is shown via analysis and numerical results to be robust to the impairments caused by the wireless channel including interference from other trains.

Transient Stability Analysis of Microgrids with Network-Preserving Structure

Abstract: The angle stability of a power system typically refers to its ability to remain in synchronism when severe failures or faults occur. This stability definition characterizes the capability of the post-fault power system returning to a system equilibrium after disrupting events. In fact, power system experiences a variety of disturbances and fluctuations in load and generation around the nominal operation conditions even in the absence of serve system faults. Taking these issues into account, this paper extends the definition of stability and considers the transient stability of microgrids equipped with inverter-based energy sources. The model of microgrids is presented in a network-preserving fashion without conducting network reduction and hence the irregularity of the physical power network topology is retained. The objective of the paper is to investigate the impact of the underlining network topology and system parameters on the stability of the power system. We propose a new analysis method that enables this exploration and derives a simple algebraic condition that relates the stability, system dynamics and network topology.

Virtual network function embedding in real cloud environments

Future network architectures will be completely reshaped by the emerging Network Function Virtualization (NFV) paradigm, and telco operators will likely deploy flexible infrastructures based on the cloud, offering programmable connectivity services and computing/storage facilities in the form of Virtual Data Centers (VDCs). This paper introduces and discusses some challenging technical issues associated with this promising approach, with a special focus on the exploitation of industry-relevant cloud platforms, such as OpenStack, and on network-aware optimal placement problem of entire VDCs, taking into account multiple virtual (Virtual Machines – VMs, virtual networks, …) and physical (host capacities, network topology and capacity, …) resources and constraints. The proposed placement, computed for real production OpenStack deployments, not only satisfies the predicted communication for all VDCs deployed atop the same physical data center, but also accounts for the (real) computing overhead due to intense communication load of VMs co-located on the same physical host, such as in the case of Virtual Network Functions (VNF) embedding, typically neglected by similar existing works.

GreeDi: An energy efficient routing algorithm for big data on cloud

The ever-increasing density in cloud computing parties, i.e. users, services, providers and data centres, has led to a significant exponential growth in: data produced and transferred among the cloud computing parties; network traffic; and the energy consumed by the cloud computing massive infrastructure, which is required to respond quickly and effectively to users requests. Transferring big data volume among the aforementioned parties requires a high bandwidth connection, which consumes larger amounts of energy than just processing and storing big data on cloud data centres, and hence producing high carbon dioxide emissions. This power consumption is highly significant when transferring big data into a data centre located relatively far from the users geographical location. Thus, it became high-necessity to locate the lowest energy consumption route between the user and the designated data centre, while making sure the users requirements, e.g. response time, are met.The main contribution of this paper is GreeDi, a network-based routing algorithm to find the most energy efficient path to the cloud data centre for processing and storing big data. The algorithm is, first, formalised by the situation calculus. The linear, goal and dynamic programming approaches are used to model the algorithm. The algorithm is then evaluated against the baseline shortest path algorithm with minimum number of nodes traversed, using a real Italian ISP physical network topology.

Cost of Loop-Free Alternates in IP-Over-WDM Networks

In Internet protocol (IP) networks, the failure recovery time of IP restoration, of several hundreds of milliseconds or up to seconds, is sufficient for most applications. But protection switching is needed for services that require very short recovery times of at most 50 ms. Loop-free alternates (LFAs) is a protection switching mechanism that is in the IP layer. We consider IP-over-WDM (wavelength division multiplexed) networks where IP routing eventually restores all traffic, while LFAs protect the fraction of the traffic that has high priority. Simulations show that if 50% of the traffic has high priority, then the additional cost to protect the high-priority traffic using LFAs is just a percent on average, under a particular cost model. Thus, with very little additional network cost, LFAs can guarantee that a large fraction of traffic will be protected between all source-destination pairs. In addition, a network design algorithm is presented that, given a traffic matrix and a physical network topology, will find a low-cost network design that includes determining the IP network topology, IP-link capacities, lightpath routing, and LFAs.

基于OPNET的动态路由协议仿真研究

合适的路由选择和设计不仅可以优化网络效能，还可以在一定程度上提高网络的安全性和可靠性。本文依据实体网络拓扑，利用OPNET搭建仿真环境，对动态路由协议中的RIP、OSPF和EIGRP三种协议的性能进行仿真对比分析。仿真结果表明，EIGRP在路由收敛时间以及网络队列时延上均具有较大性能优势，但由于EIGRP为思科设备私有协议，使得该协议的进一步推广受到考验；RIP受其算法限制，比较适合小型网络；OSPF协议由于其对各类规模网络均有不错的支持，所以其应用范围最广。网络路由协议的选择和设计要根据网络的实际情况具体问题具体分析，而在实际大型的网络中，静态和动态路由协议通常会被同时采用，以确保网络综合效能的最大化。 The appropriate route selection and design not only can optimize network performance, but also can improve the safety and reliability of the network to a certain extent. This paper, based on physical network topology, uses OPNET simulation environment to simulate and comparatively analyzes the performance of dynamic routing protocols RIP, OSPF and EIGRP. Simulation results show that, on the routing convergence time and network queue delay, EIGRP has bigger perfor-mance advantages, however, because EIGRP is Cisco’s proprietary protocol device, the further promotion of it is challenged; RIP algorithm, subject to restrictions, is more suitable for small networks; OSPF protocol has good support for networks of all sizes, and it has the most extensive range of applications. Selection and design of network routing protocol should be based on the actual situation, but in the actual large-scale networks, static and dynamic routing protocol will usually be adopted at the same time, to ensure the maximum effectiveness of the integrated net-work.

Towards centralized and semi‐automatic VLAN management

SUMMARYVirtual local area networks (VLANs) are widely used in many enterprises, campuses, and data‐centre networks. Although VLANs can restrict broadcast domains and contain hosts in one network or separate networks, the management of VLANs is an ad hoc and error‐prone work. In this paper, we design and implement a centralized and semi‐automatic system for VLAN management (CSS‐VM). Based on the physical network topology and user group (examples are engineering, student cluster, and faculty cluster) information, CSS‐VM can decide the number of VLANs that each user group would be partitioned into. In addition, CSS‐VM can not only monitor the status of devices and links but can also calculate an optimal spanning tree for each affected VLAN after a link or device failure is detected, so that it does not need to enable the Spanning Tree Protocol on devices but still has the ability of converging from device or link failures and avoiding bridging loops. We have evaluated CSS‐VM on the topology and VLAN partition data of an operational enterprise network. Our results show that CSS‐VM can obviously keep the broadcast traffic cost reasonable, efficiently partition and configure VLANs, quickly converge from link and device failures, and intelligently make a balanced use of links. Copyright © 2014 John Wiley & Sons, Ltd.

Application-driven bandwidth guarantees in datacenters

Providing bandwidth guarantees to specific applications is becoming increasingly important as applications compete for shared cloud network resources. We present CloudMirror, a solution that provides bandwidth guarantees to cloud applications based on a new network abstraction and workload placement algorithm. An effective network abstraction should enable applications to easily and accurately specify their requirements, while simultaneously enabling the infrastructure to provision resources efficiently for deployed applications. Prior research has approached the bandwidth guarantee specification by using abstractions that resemble physical network topologies. We present a contrasting approach of deriving a network abstraction based on application communication structure, called Tenant Application Graph or TAG. CloudMirror also incorporates a new workload placement algorithm that efficiently meets bandwidth requirements specified by TAGs while factoring in high availability considerations. Extensive simulations using real application traces and datacenter topologies show that CloudMirror can handle 40% more bandwidth demand than the state of the art (e.g., the Oktopus system), while improving high availability from 20% to 70%.

Survivable virtual topology mapping in IP-over-WDM networks using differential evolution optimization

In IP-over-WDM networks, a virtual topology is placed over a physical topology of the optical network. Since a simple link failure or a node failure on the physical topology can lead to a huge loss of information, an important challenge is to make the routing of the virtual topology on to the physical topology survivable. This problem is known as the Survivable Virtual Topology Mapping (SVTM), which is an NP-complete problem. So far, this problem has been analysed using heuristic strategies or by the application of optimization tools. In this paper we introduce the application of Differential Evolution (DE) to solve the SVTM problem. The method typically requires few control parameters. An illustrative example is presented showing the effectiveness and efficiency of the proposed algorithm. To the best of our knowledge, our work is the first application of a DE algorithm to the SVTM problem.

Geo-Chord: Geographical Location based Chord Protocol in Grid Computing

Grid computing is a service for sharing computer resources and data storage capacity over the internet. As resource requirements of recent applications increased greatly, grid systems have gained importance in the last decade. Resource discovery is the essential job in Grid computing which provides searching and identifying necessary resources for given processes. There are various Resource Discovery mechanisms in which Peer-to-Peer (P2P) technology witnessed a rapid development. Current Peer-to-Peer system is based on DHTs struggle with routing locality because of random node ID assignment. Locality awareness is one of the important properties of P2P Systems, which builds and operates their topology independently in the underlying network topology. Among structured P2P system Chord is well-known protocol due to its simplicity, dynamicity, scalability and flexibility in node join and departure. Due to the use of logical overlay network, Chord suffered from high routing latency and low efficiency in data lookup. In this paper, Geo-Chord is introduced, which is based on geographical location of nodes. Based on the Euclidian distance among nodes neighbors are identified and many Region-Rings are formed. Ring heads of Regions form the main Chord ring. Geo-Chord makes use of the physical network topology of the overlay network to demonstrate more efficient key lookup. Simulation results show that our proposed algorithm performs better in terms of average number of messages, hops and average communication time.

Network Topology Discovery Algorithm Based on MIB

Network topology is the core of configuration management and the infrastructure of resource management.And it is based on the detection of a network failure and the analysis of network performance.This requires the network topology complete, accurate and friendly interface with visualization.This article describes the classification of the physical network topology discovery.Based on Bridge-MIB and MIB-II of SNMP devices, designed topology discovery algorithm in data link layer and network layer.Test results show that the algorithm can accurately find the device and connection on the network layer and the data link layer.

A Novel Routing Algorithm for Power Line Communication over a Low-voltage Distribution Network in a Smart Grid

A novel artificial cobweb routing algorithm (ACRA) for routing the tree-type physical topology of a low-voltage distribution network in a smart grid is proposed and analyzed in this paper. The establishment, maintenance and reconstruction of the route are presented. The artificial cobweb routing algorithm is shown to have broad general applicability for power line communication. To provide a theoretical foundation for further research, the communication delay of the network is calculated accurately. Simulation analysis of the communication delay and throughputs, which were based on Opnet14.5, demonstrate the accuracy of the theoretical calculation. For the performance evaluation of ACRA, a test-bed that includes PLC nodes with the ACRA is set up in a noisy environment. Experimental results show the feasibility of the ACRA algorithm. These indicate that ACRA is effective for guaranteeing Quality of Service (QoS) and reliability in power line communication.

Analysis of Frequency Dynamics in Power Grid: A Bayesian Structure Learning Approach

The oscillation of frequency in power grid is studied in this paper. The possibility association of frequencies measured at different locations are modeled by a Bayesian network with the logical structure learned using Bayesian structure learning and real measurements in the U.S. power grid. Frequency data analysis and the detection of incorrect frequency measurements (caused by equipment error or malicious attack) are performed over the logical Bayesian network structure. Such application of Bayesian network is a powerful mathematical tool in computational intelligence. Without the physical power network topology information, a two-branch search-and-score structure learning algorithm with <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> -1 regulation is proposed to learn the logical structure, achieving around 97% correct prediction rate for future frequency and 92% detection rate for false frequency data with 2% false alarm rate. The tool of epidemic propagation over this logical network is also exploited to analyze the propagation of frequency changes. Using the Kolmogorov-Smirnov test, such logical structure is demonstrated to be well approximated by the Small World network model. And the propagation of frequency changes is demonstrated to be described by the Susceptible-Infectious-Susceptible (SIS) model quite well. The Bayesian structure obtained from the real measurement is statistically validated using a 5-fold training data and the Pearson system.

Heuristic Scheduling Algorithms for Allocation of Virtualized Network and Computing Resources

Cloud computing technology facilitates computing-intensive applications by providing virtualized resources which can be dynamically provisioned. However, user’s requests are varied according to different applications’ computation ability needs. These applications can be presented as meta-job of user’s demand. The total processing time of these jobs may need data transmission time over the Internet as well as the completed time of jobs to execute on the virtual machine must be taken into account. In this paper, we presented V-heuristics scheduling algorithm for allocation of virtualized network and computing resources under user’s constraint which applied into a service-oriented resource broker for jobs scheduling. This scheduling algorithm takes into account both data transmission time and computation time that related to virtualized network and virtual machine. The simulation results are compared with three different types of heuristic algorithms under conventional network or virtual network conditions such as MCT, Min-Min and Max-Min. e evaluate these algorithms within a simulated cloud environment via an abilenenetwork topology which is real physical core network topology. These experimental results show that V-heuristic scheduling algorithm achieved significant performance gain for a variety of applications in terms of load balance, Makespan, average resource utilization and total processing time.

Visualizing Network Traffic to Understand the Performance of Massively Parallel Simulations

The performance of massively parallel applications is often heavily impacted by the cost of communication among compute nodes. However, determining how to best use the network is a formidable task, made challenging by the ever increasing size and complexity of modern supercomputers. This paper applies visualization techniques to aid parallel application developers in understanding the network activity by enabling a detailed exploration of the flow of packets through the hardware interconnect. In order to visualize this large and complex data, we employ two linked views of the hardware network. The first is a 2D view, that represents the network structure as one of several simplified planar projections. This view is designed to allow a user to easily identify trends and patterns in the network traffic. The second is a 3D view that augments the 2D view by preserving the physical network topology and providing a context that is familiar to the application developers. Using the massively parallel multi-physics code pF3D as a case study, we demonstrate that our tool provides valuable insight that we use to explain and optimize pF3D's performance on an IBM Blue Gene/P system.

X-BOT: A Protocol for Resilient Optimization of Unstructured Overlay Networks

Gossip, or epidemic, protocols have emerged as a highly scalable and resilient approach to implement several application level services such as reliable multicast, data aggregation, publish-subscribe, among others. All these protocols organize nodes in an unstructured random overlay network. In many cases, it is interesting to bias the random overlay in order to optimize some efficiency criteria, for instance, to reduce the stretch of the overlay routing. In this paper, we propose X-BOT, a new protocol that allows to bias the topology of an unstructured gossip overlay network. X-BOT is completely decentralized and, unlike previous approaches, preserves several key properties of the original (nonbiased) overlay (most notably, the node degree and consequently, the overlay connectivity). Experimental results show that X-BOT can generate more efficient overlays than previous approaches independently of the underlying physical network topology.

Spiralchord: a space-filling curve based location awareness, cross-layering P2P file sharing system in WMNs

The common characteristics of peer-to-peer (P2P) overlay networks and wireless multi-hop network, such as self-organization, decentralization, hop-by-hop message transmission mode and high degree of dynamicity, lead to research of operating wired P2P applications on wireless multi-hop networks. Wireless mesh network (WMN) as a relative static multi-hop wireless network which is extended from Ad-Hoc networks, has become one of the key technologies for providing increased network coverage of Internet infrastructures. This paper investigates the problem of enabling P2P file sharing in WMNs. A special chord algorithm—spiralchord is proposed to address the major problem in wireless file sharing system—how to efficiently find resources currently available. Spiralchord put forward an identifier (ID) assignment technique based on spiral space-filling curve to integrate location-awareness with cross-layering. Location awareness aims at alleviating the mismatch of physical network topology and overlay network topology, and requires close-by IDs in logical ring of neighboring peers, while cross-layering aims at speeding up resource lookup operations, requires faraway IDs of neighboring peers. Spiralchord uses spiral curve to assign peers' IDs which meet the contradictory requirements of location-awareness and cross-layering. The simulation results show spiralchord is effective in reducing message overhead, and increasing lookup performance with respect to basic chord.

K-최단 분리 경로 배정을 적용한 장애 복구형 선박 백본 네트워크의 성능 평가

The concept of k-shortest disjoint paths is considered important because the establishment of primary and backup forwarding paths exploiting shorter distance and faster propagation time is a dominant consideration for the design of a survivable backbone network. Therefore, we need to evaluate how well the concept of k-shortest disjoint paths is exploited for the design of a survivable ship backbone network considering the international standard related to ship backbone networks, the IEC61162-410 standard specifying how to manage redundant message transmissions among ship devices. Performance evaluations are conducted in terms of following objective goals: link capacity, hop and distance of primary and backup paths, even distribution of traffic flows, restoration time of backup forwarding paths, and physical network topology connectivity.

AMPLE: an adaptive traffic engineering system based on virtual routing topologies

Handling traffic dynamics in order to avoid network congestion and subsequent service disruptions is one of the key tasks performed by contemporary network management systems. Given the simple but rigid routing and forwarding functionalities in IP base environments, efficient resource management and control solutions against dynamic traffic conditions is still yet to be obtained. In this article, we introduce AMPLE - an efficient traffic engineering and management system that performs adaptive traffic control by using multiple virtualized routing topologies. The proposed system consists of two complementary components: offline link weight optimization that takes as input the physical network topology and tries to produce maximum routing path diversity across multiple virtual routing topologies for long term operation through the optimized setting of link weights. Based on these diverse paths, adaptive traffic control performs intelligent traffic splitting across individual routing topologies in reaction to the monitored network dynamics at short timescale. According to our evaluation with real network topologies and traffic traces, the proposed system is able to cope almost optimally with unpredicted traffic dynamics and, as such, it constitutes a new proposal for achieving better quality of service and overall network performance in IP networks.