Tree Reconfiguration Research Articles

Characterizing wind-induced reconfiguration of coaxial branched tree

Tree dynamics have been extensively studied because of their reconfiguration ability under oncoming wind flow. However, there is still a gap in the effect of crown configuration on the tree reconfiguration. The present study examined the wind-induced reconfiguration performance of 9 coaxial branched trees with three different pruning techniques by wind tunnel tests, to comprehensively and thoroughly reveal the effects of crown configurations on tree reconfiguration. Results showed that normalized crown mass is the best parameter for correlating with the maximum normalized drag force acting on the tree. Meanwhile, it was found that area reduction effect decreases with an increase in LAI1 (the ratio of leave area and ground area) and LAI2 (the ratio of leave area and frontal area). Streamlining effect is gradually enhanced with an increase in λct (the ratio of crown height and trunk height), but shows a trend of first increasing and then decreasing with the increase of LAI1 and LAI2. Finally, a reconfiguration model was proposed to show the dynamic behavior of the coaxial branched tree under different dimensionless tree parameters. The revealed tree reconfiguration mechanism and the reconfiguration model can guide tree managers and researchers for understanding the tree behavior and tree dynamics.

QoS-Aware Management Reconfiguration of vNF Service Trees With Heterogeneous NFV Platforms

The rapid development of in-network computing motivates people to consider deploying virtual network functions (vNFs) on heterogeneous platforms that include both software systems like virtual machines and docker containers and hardware systems like programmable data plane switches. Meanwhile, with the emergence of multi-client network services, service providers need to build vNF service trees (vNF-STs) in their substrate networks (SNTs). In this work, we study how to optimize the management reconfiguration of vNF-STs in an SNT equipped with heterogeneous platforms. An integer linear programming (ILP) model is first formulated to consider three common reasons for vNF-ST reconfiguration and reduce both the total resource usage after reconfiguration and the overall vNF migration cost during reconfiguration. Then, we design a two-step algorithm to reduce the time complexity of problem-solving. Specifically, the algorithm first checks all the active vNF-STs to select the vNF-STs that should be reconfigured, and then leverages an approach based on layered auxiliary graphs (LAGs) to reconfigure the selected vNF-STs. Extensive simulations verify the effectiveness of our algorithms on optimizing the management reconfiguration, and demonstrate that they can outperform existing benchmarks.

Link Expiration Time and Minimum Distance Spanning Trees based Distributed Data Gathering Algorithms for Wireless Mobile Sensor Networks

The high-level contributions of this paper are the design and development of two distributed spanning tree-based data gathering algorithms for wireless mobile sensor networks and their exhaustive simulation study to investigate a complex stability vs. node-network lifetime tradeoff that has been hitherto not explored in the literature. The topology of the mobile sensor networks changes dynamically with time due to random movement of the sensor nodes. Our first data gathering algorithm is stability-oriented and it is based on the idea of finding a maximum spanning tree on a network graph whose edge weights are predicted link expiration times (LET). Referred to as the LET-DG tree, the data gathering tree has been observed to be more stable in the presence of node mobility. However, stability-based data gathering coupled with more leaf nodes has been observed to result in unfair use of certain nodes (the intermediate nodes spend more energy compared to leaf nodes), triggering pre-mature node failures eventually leading to network failure (disconnection of the network of live nodes). As an alternative, we propose an algorithm to determine a minimum-distance spanning tree (MST) based data gathering tree that is more energy-efficient and prolongs the node and network lifetimes, at the cost frequent tree reconfigurations.

DTMR: An adaptive Distributed Tree-based Multicast Routing protocol for vehicular networks

The modern driver-assistance and autonomous technologies in vehicles increase the ease of driving vehicles. The increased vehicle usage increases the requirement of efficient group communication between the vehicles to support the safety as well as the non-safety applications in Vehicular Ad-hoc NETworks (VANET). In VANET, multicast communication is mostly preferred for the effective utilization of computational resources and the attainment of the Quality of Service (QoS). To implement an efficient multicast communication, we need to build and retain a multicast tree. Due to the high mobility and rapid topology changes, the formation and maintenance of a multicast tree are challenging in VANET. Existing multicast communication techniques are either centralized or location-based flooding and suffer from tree reconfiguration overhead. In this paper, a novel Distributed Tree-based Multicast Routing (DTMR) algorithm is proposed. During the link failure, the connection is switched to a predetermined and highly stable guardian node. Further, the tree fragmentation and the rejoining delay is reduced in VANET using the proposed algorithm, DTMR. From the simulation results, it is evident that the DTMR achieves a significant performance improvement against the existing multicast techniques such as Distributed Time-limited Reliable Broadcast Incremental Power Strategy (DTRBIP) and Energy Efficient Multicast routing protocol based on Software Defined Networks and Fog computing for Vehicular networks (EEMSFV) in terms of delay, packet loss ratio, scalability, and reliability. In terms of end-to-end delay, packet loss rate, and reliability, the DTMR outperforms the existing DTRBIP and EEMSFV protocols. DTMR achieves 94--96% reliability in highway scenarios and 96--99% reliability in urban environments. Further, as a proof of concept, the proposed, DTMR is implemented and analyzed in real-time. It is found that the real-time experimental results are on par with the simulation results. Hence, the proposed DTMR achieves network stability and reliability in real-time.

The Complexity of Induced Tree Reconfiguration Problems

A reconfiguration problem asks when we are given two feasible solutions A and B, whether there exists a reconfiguration sequence \((A_0 = A, A_1, \dots , A_\ell = B)\) such that (i) \(A_0, \dots , A_\ell \) are feasible solutions and (ii) we can obtain \(A_i\) from \(A_{i-1}\) under the prescribed rule (the reconfiguration rule) for each \(i = 1, \dots , \ell \). In this paper, we address the reconfiguration problem for induced trees, where an induced tree is a connected and acyclic induced graph of an input graph. This paper treats the following two rules as the prescribed rules: Token Jumping; removing u from an induced tree and adding v to the tree, and Token Sliding; removing u from an induced tree and adding v adjacent to u to the tree, where u and v are vertices in an input graph. As the main results, we show (I) the reconfiguration problem is PSPACE-complete, (II) the reconfiguration problem is W[1]-hard when parameterized by both the size of induced trees and the length of the reconfiguration sequence, and (III) there exists an FPT algorithm when parameterized by both the size of induced trees and the maximum degree of an input graph, under each of Token Jumping and Token Sliding.

How stand tree motion impacts wind dynamics during windstorms

Understanding how wind and trees interact during wind storms is crucial for better predicting forest wind damage. The complexity of this interaction is enhanced by the fragmented environment of forests. Here, we present an unprecedented field experiment (TWIST) where both the wind dynamics and the tree motion in the edge region of a maritime pine forest have been recorded simultaneously during four non-destructive wind storms. For three of them, the instrumented trees were under stand flow while for one of them they were under an edge flow. Our measurements demonstrate that the well-known characteristics of stand-flow dynamics remain valid under high wind conditions. Only the sub-canopy flow appeared more intermittent as canopy-top turbulent structures penetrate easier within the canopy due to the tree foliage reconfiguration. Under similar storm intensity, the tree motions were lower under edge flow than under stand flow due to the lower turbulence of the former flow while the mean wind speed was higher. This result demonstrates the importance of considering both the turbulence and the mean wind speed in wind risk models. No impact of tree motion other than tree reconfiguration were observed on the stand flow dynamics. On the other hand, for the edge flow, our measurements reveal a peak in frequency on the wind velocity fluctuations related to the fundamental tree vibration mode. This peak was especially visible at canopy top and in the upper trunk space under high wind conditions. Compared to the stand flow, we suspect that the velocity fluctuations induced by the tree motion emerge in the edge flow due to the lower background turbulence. Our edge storm was nonetheless not strong enough for tree motion to enhance flow turbulence and for trees to enter into resonance. These findings may suggest a higher susceptibility of near-edge trees to reach resonance than stand trees due to the motion of upwind trees in a lower background turbulence.

Bounded latency spanning tree reconfiguration

One of the main obstacles to the adoption of Ethernet technology in carrier-grade metropolitan and wide-area networks is the large recovery latency, in case of failure, due to spanning tree reconfiguration. In this paper we present a technique called Bounded Latency Spanning Tree Reconfiguration (BLSTR), which guarantees worst case recovery latency in the case of single faults by adopting a time-bounded bridge port reconfiguration mechanism and by eliminating the bandwidth-consuming station discovery phase that follows reconfiguration. BLSTR does not replace the Rapid and Multiple Spanning Tree reconfiguration protocols, which remain in control of network reconfiguration, whereas it operates in parallel with them.

Stability-based and energy-efficient distributed data gathering algorithms for wireless mobile sensor networks

The high-level contributions of this paper are the design and development of two distributed spanning tree-based data gathering algorithms for wireless mobile sensor networks and their exhaustive simulation study to investigate a complex stability-delay-throughput vs. node-network lifetime-coverage loss tradeoff that has been hitherto not explored in the literature. The topology of the mobile sensor networks changes dynamically with time due to random movement of the sensor nodes. Our first data gathering algorithm is stability-oriented and it is based on the idea of finding a maximum spanning tree on a network graph whose edge weights are predicted link expiration times (LETs). Referred to as the LET-DG tree, the data gathering tree has been observed to be more stable in the presence of node mobility, as well as incur a significantly lower delay per round of data gathering (due to the shorter height of the tree with more leaf nodes) and larger throughput per tree. However, stability-based data gathering coupled with more leaf nodes has been observed to result in unfair use of certain nodes (the intermediate nodes spend more energy compared to leaf nodes), triggering premature node failures eventually leading to network failure (disconnection of the network of live nodes). As an alternative, we propose an algorithm to determine a minimum-distance spanning tree (MST) based data gathering tree that is more energy-efficient and prolongs the node and network lifetimes as well as inflicts a lower coverage loss on the underlying network at any time instant, all of these at the cost frequent tree reconfigurations. The MST-DG trees also incur a significantly longer delay per round, due to their larger height and fewer leaf nodes.

A drag force model to incorporate the reconfiguration of full-scale riparian trees under hydrodynamic loading

This paper investigates the response of full-scale submerged riparian vegetation to hydrodynamic loading, using data from towing tank experiments of high resolution and accuracy. Drag force and physical property data are presented for 21 foliated and defoliated trees, including specimens of Alnus glutinosa, Populus nigra and Salix alba. The force–velocity data and contribution of foliage to the total drag are first discussed, highlighting the non-classical drag force behaviour of flexible vegetation. A theoretical model, based on the vegetative Cauchy number, is proposed from dimensional consideration to account for the bending and reconfiguration of the trees under flow action. The model links measurable vegetation properties, such as volume, height and flexural rigidity, to the force–velocity response. This allows the otherwise complex drag force of flexible vegetation to be predicted with greater accuracy than compared with a rigid cylinder approximation.

Tree reconfiguration without lightpath interruption in WDM optical networks

Efficient reconfiguration of optical multicast trees in wavelength division multiplexing (WDM) networks is required. Multimedia applications which consume a huge bandwidth, require multicasting. So, multicast concept is extended to optical networks to improve performance. Today, networks are facing many phenomena such as changes in the traffic model, failures, additions or deletions of some network resources due to a maintenance operation. To cope with these phenomena, network operators compute new topology according to the applications requirements. Some real-time multicast applications are not indulgent with lightpath interruptions. So the configuration of the network must be done as quickly as possible to be spontaneously deal with the problem before other events appear and without connection interruption. To the best of our knowledge, there is no work in the literature that considers the reconfiguration of an optical multicast tree to another one without connection interruption. We prove that it is impossible to reconfigure any initial tree into any final tree using only one wavelength and without connection interruption. We propose in this paper BpBAR_2 method, using several wavelengths to reconfigure optical WDM network. This algorithm does tree reconfiguration without lightpath interruption, reduce the reconfiguration setup time and the cost of wavelengths used.

Cross-layer failure restoration of IP multicast with applications to IPTV

Recent applications such as broadcast TV distribution over an IP network require that stringent QoS constraints, such as low latency and loss be met. Streaming content in IPTV is typically delivered to distribution points on an IP backbone using IP multicast, in particular Protocol Independent Multicast (PIM). Local restoration from link failures using MPLS or layer-2 Fast Reroute (FRR) is a proven technique to achieve rapid failure restoration. Link-based FRR creates a pseudo-wire or tunnel in parallel to the IP adjacencies; thus, single link failures are transparent to the Interior Gateway Protocol (IGP) such as OSPF. Although one may choose the back-up path’s IGP link weights appropriately to avoid traffic overlap during any single physical link failure, multiple failures may still cause packet loss because of (a) congestion resulting from overlap of an active FRR path with the multicast tree, (b) congestion resulting from overlap of two active FRR paths, or (c) a hit resulting from an OSPF reconvergence after the failure of a link in an active FRR path. We present a cross-layer restoration approach that combines both FRR-based restoration for single link failures and “hitless” (i.e., without loss) PIM tree reconfiguration algorithms to prevent traffic overlap when multiple failures occur. We demonstrate the efficacy of our schemes through simulations. The average recovery time on double failures can be reduced from more than 10s to only approximately 100 ms with our enhancements.

Distributed dynamic mobile multicast

Traditional mobile multicast schemes have either high multicast tree reconfiguration cost or high packet delivery cost. The former affects service disruption time while the latter affects packet delivery delay. Although existing region-based mobile multicast schemes offer a trade-off between two costs to some extent, most of them do not determine the size of the service range, which is critical to network performance. In this paper, we propose a novel approach, called Distributed Dynamic Mobile Multicast ( D 2 M 2 ), to dynamically determine the optimal service range according to the mobility and service characteristics of a user. We derive an analytical model to formulate the costs of multicast tree reconfiguration and multicast packet delivery. The model is based on a Markov chain that analyzes a mobile node’s movement in a 2D mesh network. As the complexity of computing steady probability is high, we aggregate the Markov states by leveraging mobility symmetry. Simulation shows that the network performance is enhanced through D 2 M 2 .

Dynamic region‐based mobile multicast

AbstractTraditional mobile multicast schemes have higher multicast tree reconfiguration cost or multicast packet delivery cost. Two costs are very critical because the former affects the service disruption time during handoff while the latter affects the packet delivery delay. Although the range‐based mobile multicast (RBMoM) scheme and its similar schemes offer the trade‐off between two costs to some extent, most of them do not determine the size of service region, which is critical to the network performance. Hence, we propose a dynamic region‐based mobile multicast (DRBMoM) to dynamically determine the optimal service region for reducing the multicast tree reconfiguration and multicast packet delivery costs. DRBMoM provides two versions: (i) the per‐user version, named DRBMoM‐U, and (ii) the aggregate‐users version, named DRBMoM‐A. Two versions have different applicability, which are the complementary technologies for pursuing efficient mobile multicast. Though having different data information and operations, two versions have the same method for finding the optimal service region. To that aim, DRBMoM models the users' mobility with arbitrary movement directional probabilities in 2‐D mesh network using Markov Chain, and predicts the behaviors of foreign agents' (FAs') joining in a multicast group. DRBMoM derives a cost function to formulate the average multicast tree reconfiguration cost and the average multicast packet delivery cost, which is a function of service region. DRBMoM finds the optimal service region that can minimize the cost function. The simulation tests some key parameters of DRBMoM. In addition, the simulation and numerical analyses show the cost in DRBMoM is about 22∼50% of that in RBMoM. At last, the applicability and computational complexity of DRBMoM and its similar scheme are analyzed. Copyright © 2010 John Wiley & Sons, Ltd.

Resource optimisation in a wireless sensor network with guaranteed estimator performance[Note 1

New control paradigms are needed for large networks of wireless sensors and actuators in order to efficiently utilise system resources. In this study, the authors consider the problem of discrete-time state estimation over a wireless sensor network. Given a tree that represents the sensor communications with the fusion centre, the authors derive the optimal estimation algorithm at the fusion centre, and provide a closed-form expression for the steady-state error covariance matrix. They then present a tree reconfiguration algorithm that produces a sensor tree that has low overall energy consumption and guarantees a desired level of estimation quality at the fusion centre. The authors further propose a sensor tree construction and scheduling algorithm that leads to a longer network lifetime than the tree reconfiguration algorithm. Examples are provided throughout the paper to demonstrate the algorithms and theory developed.

Dynamic Multiresolution Data Dissemination in Wireless Sensor Networks

Recent years have seen the deployments of wireless sensor networks (WSNs) in a variety of applications to gather the information about physical environments. A key requirement of many data-gathering WSNs is to deliver the information about dynamic physical phenomena to users at multiple temporal resolutions. In this paper, we propose a novel solution called the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Minimum</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Incremental</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Dissemination</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Tree</i> (MIDT) for dynamic multiresolution data dissemination in WSNs. MIDT includes an online tree construction algorithm with an analytical performance bound and two lightweight tree adaptation heuristics for handling data requests with dynamic temporal resolutions. Our simulations based on realistic settings of Mica2 motes show that MIDT outperforms several typical data dissemination schemes. The two tree adaptation heuristics can effectively maintain desirable energy efficiency of the dissemination tree while reducing the overhead of tree reconfigurations under representative traffic patterns in WSNs.

New multicast scheme based on dynamic mobility prediction in mobile IPv6 environment

A new mobile multicast scheme called mobility prediction based mobile multicast(MPBMM) was proposed. In MPBMM, when a mobile node (MN) roams among subnets during a multicast session, MN predicts the next subnet, to which MN will attach, by the information of its position and mobility speed, consequently speeds up the handoff procedure. Simulation results show that the proposed scheme can minimize the loss of multicast packets, reduce the delay of subnet handoff, decrease the frequency of multicast tree reconfiguration, and optimize the delivery path of multicast packets. When MN moves among subnets at different speeds (from 5 to 25 m/s), the maximum loss ratio of multicast packets is less than0.2%, the maximum inter-arrival time of multicast packets is 117 ms, so the proposed scheme can meet the QoS requirements of real-time services. In addition, MPBMM can support the mobility of multicast source.

Iterative Reconfigurable Tree Search Detection of MIMO Systems

This paper is concerned with reduced-complexity detection, referred to as iterative reconfigurable tree search (IRTS) detection, with application in iterative receivers for multiple-input multiple-output (MIMO) systems. Instead of the optimum maximum a posteriori probability detector, which performs brute force search over all possible transmitted symbol vectors, the new scheme evaluates only the symbol vectors that contribute significantly to the soft output of the detector. The IRTS algorithm is facilitated by carrying out the search on a reconfigurable tree, constructed by computing the reliabilities of symbols based on minimum mean-square error (MMSE) criterion and reordering the symbols according to their reliabilities. Results from computer simulations are presented, which proves the good performance of IRTS algorithm over a quasistatic Rayleigh channel even for relatively small list sizes.

Localized Communication and Topology Protocols for Ad Hoc Networks-Part II: A Preface to the Special Section

1 THE SCOPE WE are very proud and honored to have been entrusted to guest edit this special section. The main goal was to put together a strong issue emphasizing quality and relevance to current interests in this important field. Papers were sought to cover comprehensively the algorithmic issues in the “hot” area of ad hoc and sensor networking. The concentration was on the network layer problems which can be divided into two groups: data communication and topology control problems. In data communication problems, such as routing, quality-of-service routing, geocasting, multicasting, and broadcasting, the primary goal is to fulfill a given communication task successfully between nodes in an ad hoc network. The secondary task is to minimize the communication overhead and power consumption given that in the vast majority of applications nodes run on batteries. Topology control problems are further subdivided into neighbor discovery and network organization problems. In the neighbor discovery problem, the problem is to detect neighboring nodes located within transmission range. In the network organization problem, each node should decide what communication links to establish with neighboring nodes (an example is the Bluetooth scatternet formation problem), and what power management schemes to adopt (examples are “sleep” period operations and adjusting transmission ranges). Due to their theoretical challenges and myriads of practical applications, wireless sensor networks are emerging as one of the priority research and development areas. The applications of sensor networks are envisioned primarily for monitoring the environment (e.g., motion detection, chemicals, temperature) or as key components in embedded systems (e.g., biomedical sensor engineering). This special section also sought submissions on this “hot” topic, including problems such as: physical properties, sensor training, security through intelligent node cooperation, medium access, sensor area coverage with random and deterministic placement, object location, sensor position determination, energy efficient broadcasting and activity scheduling, routing, connectivity, data dissemination and gathering, sensor centric quality of routing, path exposure, tree reconfiguration, topology construction, and transport layer. The main paradigm shift is to apply localized schemes as opposed to existing protocols requiring global information. Localized algorithms are distributed algorithms where simple local node behavior achieves a desired global objective. Localized protocols provide scalable solutions, that is, solutions for wireless networks with an arbitrary number of nodes, which is the main goal of this plan. Sensor and rooftop/mesh networks, for instance, have hundreds or thousands of nodes.

PPMA, a probabilistic predictive multicast algorithm for ad hoc networks

Ad hoc networks are collections of mobile nodes communicating using wireless media without any fixed infrastructure. Existing multicast protocols fall short in a harsh ad hoc mobile environment, since node mobility causes conventional multicast trees to rapidly become outdated. The amount of bandwidth resource required for building up a multicast tree is less than that required for other delivery structures, since a tree avoids unnecessary duplication of data. However, a tree structure is more subject to disruption due to link/node failure and node mobility than more meshed structures. This paper explores these contrasting issues and proposes PPMA, a Probabilistic Predictive Multicast Algorithm for ad hoc networks, that leverages the tree delivery structure for multicasting, solving its drawbacks in terms of lack of robustness and reliability in highly mobile environments. PPMA overcomes the existing trade-off between the bandwidth efficiency to set up a multicast tree, and the tree robustness to node energy consumption and mobility, by decoupling tree efficiency from mobility robustness. By exploiting the non-deterministic nature of ad hoc networks, the proposed algorithm takes into account the estimated network state evolution in terms of node residual energy, link availability and node mobility forecast, in order to maximize the multicast tree lifetime, and consequently reduce the number of costly tree reconfigurations. The algorithm statistically tracks the relative movements among nodes to capture the dynamics in the ad hoc network. This way, PPMA estimates the node future relative positions in order to calculate a long-lasting multicast tree. To do so, it exploits the most stable links in the network, while minimizing the total network energy consumption. We propose PPMA in both its centralized and distributed version, providing performance evaluation through extensive simulation experiments.

TDBMA--A Novel Multicast Algorithm for IPv6-Based Mobile Networks

IP multicasting has naturally been considered the ideal technique to be used with multimedia communications but is difficult to mobile hosts due to the addition of mobility in the host group. In this paper, we propose a novel multicast algorithm, namely time and distance-based multicast algorithm (TDBMA), for IPv6-based mobile networks. TDBMA intends to trade off between the shortest delivery path and the frequency of the multicast tree reconfiguration. When a mobile host (MH) moves into a new foreign network which is managed by a foreign network router and re-subscribes to an existing multicast tree, the foreign network router uses the TDBMA to determine whether the MH joins the multicast tree directly or receives the tunneled multicast packets from its home agent (HA). The TDBMA is subject to two key factors, called time and distance. The visited foreign network router can join the multicast tree directly only when the value of both time and distance is true. The simulation results have shown that TDBMA has better performance than other algorithms, especially in the case where the number of MHs is large.