An analytical model for adaptive routing networks

Real-time network routing (RTNR) is a new adaptive routing method. With RTNR, switches have a simple way of exchanging link status bit map information, thereby determining the availability and load conditions of the direct and all two-link paths to the destination. Link busy-idle status is exchanged between the network nodes using a bit map data exchange through the common channel signaling (CCS) network, and calls are set up where there is the most available capacity in the network. To date the analysis of RTNR networks has been limited to simulation models. The present authors develop an analytical model for the AT&T network under RTNR, which is shown to provide good agreement with simulation models. The analytical model for RTNR networks uses an Erlang fixed point method to solve the nonlinear equations describing dynamical network behavior. The equations include the link state probability, network flows, link arrival rates, adaptive trunk reservation level, and adaptive path selection depth. The link state model provides the aggregate link state probabilities through solution of the birth-death equations, and models the adaptive nature of trunk reservation. The network flow model provides a method to calculate the traffic flow using the least busy concept employed in RTNR, and also models the adaptive nature of the path selection depth. The analytical model addresses asymmetrical networks, and computational examples show the differences from the simulation model to be small. The authors also use the analytical model to examine key RTNR parameters over a range of values     

An efficient way to compare ABCs

The authors present a performance comparison of absorbing-boundary conditions (ABCs), including the introduced perfectly matched layer (PML), for finite-difference time-domain (FDTD) simulations. This innovative PML for truncating FDTD domains was introduced by J. Berenger (see J. Comp. Phys. vol.114, p.195-200, 1994), and has since been the subject of intensive study. The key feature of the PML is its extremely low reflectivity over a broad range of (real) incidence angles, and its broadband characteristics. The authors provide color-coded graphs, which can be easily used to measure the PML's performance as a function of frequency and incidence angle. An important component of these graphs is that they also display the performance of the PML for evanescent waves. For comparison, similar graphs are given for the second order Mur and Lindman (see J. Comp. Phys., vol.18, p.66-78) ABCs. The superior performance of the PML (for propagating) waves is clearly seen, but for evanescent waves, the Lindman ABC gives better performance     

Congestion-based routing strategies in multihop TDD-CDMA networks

In this paper, a network topology is investigated that allows both peer-to-peer and nonlocal traffic in a cellular-based time-division duplex code-division multiple-access (TDD-CDMA) system known as opportunity driven multiple access (ODMA). The key to offering appropriate performance of peer-to-peer communication in such a system relies on the use of a routing algorithm which minimizes interference. This paper presents a study of the constraints and limitations on the capacity of such a system using a variety of routing techniques. A congestion-based routing algorithm is presented that attempts to minimize the overall power of the system as well as providing a measure of feasibility. This technique provides the lowest required transmit power in all circumstances, and the highest capacity in nearly all cases studied. All of the routing algorithms studied here allocate TDD time slots on a first come first served basis according to a set of predefined rules. This fact is utilized to enable the development of a combined routing and resource allocation algorithm for TDD-CDMA relaying. A novel method of time slot allocation according to relaying requirements is then developed. Two measures of assessing congestion are presented based on matrix norms. One is suitable for current interior point solution, the other is more elegant but is not currently suitable for efficient minimization and, thus, practical implementation.     

基于社会环境的一种优化Prophet延迟容忍网络路由算法

在移动智能终端普及的今天,延迟容忍网络作为数据的补充传输方案具有重要的意义。在社会环境中,节点移动规律具有明显周期性,Prophet路由算法在该类场景中效果较好。因此文章提出了一种基于加强传统概率的路由算法,其在工作日模型下对E Prophet算法进行了仿真实验。实验结果表明,所提出的E Prophet算法在该场景下优于传统的Prophet算法。     

Electronic protection and routing optimization of MANETs operating in an electronic warfare environment

Domination of the electromagnetic spectrum is a crucial component of the 21st century warfare. In the harsh electromagnetic environment of the modern battlefield, it is of the utmost importance to deny the opposing force the opportunity to attack or exploit the detection/interception of friendly communications assets through the deployment of electronic protection (EP) measures in order to attain low probability of detection (LPD), low probability of interception (LPI) and anti-jam (A/J). Given that directional antennas are a suitable means to achieve both extended range and LPD/LPI, this paper proposes mechanisms to optimize the trade-off between these capabilities, minimizing the number of hops and end-to-end delay when routing packets in a multi-hop ad-hoc network, while taking into account stealth requirements. The novel scheme is based on a variant of Fisheye State Routing, coupled with a power control algorithm to guarantee a LPD/LPI beyond the zone covered by the omni-directional radiation footprint of the network. The performance of the proposed scheme is evaluated through computer simulation.     

面向城市环境的角度矢量分簇选择协议

在车载自组织网VANETs(vehicular ad hoc networks)中,高动态的拓扑结构和频繁断裂的链路给车间通信提出挑战。为此,针对VANETs城市场景,提出基于方向矢量角簇群和桥节点的车间通信VAC-BNR(Vector-angle-cluster and bridge nodes-based routing)协议。VAC-BNR协议将城市道路划分为十字路口区域和十字路口间的直线路段区域。在十字路口区域内,选择合适的车辆作为桥节点,并由桥节点连通断裂的链路。而在直线路段区域,利用矢量角将车辆划分不同的簇群,然后计算每个簇群内节点的效用值,并选择效用值最高的车辆传输数据。仿真结果表明,提出的VAC-BNR协议能够有效地降低端到端传输时延、提高数据包传递率。与AMD相比,VAC-BNR协议的平均端到端传输时延下降了约30%,当车流密度大于80辆/km~2时,数据包传递率提高了约50%。     

浅水环境中基于熵的能量均衡路由优化算法

浅水环境具有覆盖面积小、水位低、水底环境较为复杂的特点,当在水下部署传感器节点时,其传输路径容易受到水底障碍物、水中杂物、水浪等影响,给水下传感器的路由选择带来困扰。针对浅水中传感器节点路由选择困难、能量消耗不均、生命周期短的问题,提出一种基于熵的能量均衡路由算法。该算法综合多种节点部署形式,在节点均匀分布和非均匀分布两种条件下分别计算传感器网络通信的能量损耗,权衡考虑节点的剩余能量和位置信息来选择下一跳节点,从而均衡网络能耗。利用NS-2仿真工具对该算法的性能进行仿真分析。结果表明该算法能够实现浅水中的节点通信,有效延长网络生命周期。     

An analytical framework for neighbor discovery strategies in ad hoc networks with sectorized antennas

This letter analyzes a class of neighbor discovery algorithms in ad hoc networks using directional antennas for both reception and transmission. We consider synchronized and random sector - timeslot assignment strategies and compare their behaviors. Analytic results validated by simulation clearly show the latency benefits of the synchronized sector assignment over the random assignment.     

Exploring the routing strategies in next-generation satellite networks

Employing an efficient routing algorithm in satellite networks is a critical issue, because satellite network resources are costly and must be managed in an optimal and effective manner. Because of the particular features of satellite networks, such as dynamic topology, non-homogeneous traffic distribution, limited power and processing capabilities, and high propagation delays, new routing approaches should be developed. In this article, we first examine these properties with particular emphasis on their effect on the routing objectives. Subsequently, we provide a survey of various routing protocols that aims to address the crucial issues stemming from these properties of satellite systems. We classify these protocols according to their objectives, and discuss their advantages and disadvantages. We also elaborate on relevant technical aspects.     

Effects on TCP of routing strategies in satellite constellations

A broadband satellite network uses a constellation of a number of similar satellites to provide wireless networking services to the Earth. A number of these constellation networks are under development. This article introduces the types of satellite constellation networks, and examines how overall performance of TCP communications carried across such a network can be affected by the choice of routing strategies used within the network. Constellations utilizing direct intersatellite links are capable of using multiple paths between satellites simultaneously as a strategy to spread network load. This allows more general routing strategies than shortest-path routing, but we show these strategies to be detrimental to the performance of individual TCP connections     

下一代光网络选路策略研究

简述了下一代光网络选路的基本问题;综述了有关方面近年来的研究状况,包括支持优先级的选路及波长分配(RWA)算法、IP业务在光网络中的选路策略及业务量疏导问题.根据各种方法的性能和实际网络建设优化的需要,指出了下一代光网络选路策略领域还需进一步研究的问题.     

An analytical approach to dynamic crosstalk in coupled interconnects

This paper deals with waveform analysis, crosstalk peak and delay estimation of CMOS gate driven capacitively and inductively coupled interconnects. Simultaneously switching inputs for the coupled interconnects are considered. A transmission line-based coupled model of interconnect is used for analysis. Alpha-power Law model of MOS transistor is used to represent the transistors in CMOS driver. Peaks and delays at far-end of victim line are estimated for conditions when the inputs to the two coupled interconnects are switching in-phase and out-of-phase. The comparison of analytically obtained results with SPICE simulations show that the proposed model captures noise peak and their timing; 90% propagation delay; transition time delay and waveform shape with good accuracy, such as not more than 5% error in crosstalk peak estimation.     

Design of efficient lightweight strategies to combat DoS attack in delay tolerant network routing

Delay tolerant networks (DTNs) are characterized by delay and intermittent connectivity. Satisfactory network functioning in a DTN relies heavily on co-ordination among participating nodes. However, in practice, such co-ordination cannot be taken for granted due to possible misbehaviour by relay nodes. Routing in a DTN is, therefore, vulnerable to various attacks, which adversely affect network performance. Several strategies have been proposed in the literature to alleviate such vulnerabilities—they vary widely in terms of throughput, detection time, overhead etc. One key challenge is to arrive at a tradeoff between detection time and overhead. We observe that the existing table-based reactive strategies to combat Denial-of-service (DoS) attacks in DTN suffer from two major drawbacks: high overhead and slow detection. In this paper, we propose three secure, light-weight and time-efficient routing algorithms for detecting DoS attacks (Blackhole and Grey-hole attacks) in the Spray & Focus routing protocol. The proposed algorithms are based on use of a small fraction of privileged (trusted) nodes. The first strategy, called TN, outperforms the existing table-based strategy with 20–30 % lesser detection time, 20–25 % higher malicious node detection and negligible overhead. The other two strategies, CTN_MI and CTN_RF explore the novel idea that trusted nodes are able to utilize each others’ information/experience using their long range connectivity as and when available. Simulations performed using an enhanced ONE simulator reveals that investing in enabling connectivity among trusted nodes (as in CTN_RF) can have significant performance benefits.     

An analytical solution to the microstrip line problem

An analytical method for determining the line capacitance of a microstrip line is presented. The solution is exact, but it is expressed by means of the solution of an infinite system of linear equations whose coefficients are the result of certain numerical quadratures. The analysis is carried out for the case of two dielectric substrates. Changes to include additional stratified layers are readily available using the transfer matrix method described by P.M. van Berg et al. (1985). Comparison of the results obtained using the proposed formula with those obtained using exact formulas (available in particular cases) shows that, in cases of practical interest, it is sufficient to consider only the first two equations in the above-mentioned infinite set of linear equations     

An adaptive routing algorithm considering position and social similarities in an opportunistic network

An opportunistic network (OPPNET) is a wireless networks without an infrastructure. In OPPNET, communication intermittently occurs when one node meets with another node. Thus, a connected path between the source and destination nodes rarely exists. For this reason, nodes need not only to forward messages but are also to store and carry messages as relay nodes. In OPPNET, several routing algorithms that rely on relay nodes with appropriate behavior have been proposed. Some of these are referred to as context-ignorant routing algorithms, which manipulate flooding, and others are referred to as context-aware routing algorithms, which utilize the contextual information. We propose a routing algorithm that employs a novel similarity based on both position and social information. We combine the position similarity with the social similarity using the fuzzy inference method to obtain the enhanced performance. Through this method, the proposed algorithm utilizes more proper relay nodes in forwarding adaptively and achieves significant improvement on the performance especially under memory constrained environment. We analyze the proposed algorithm on the NS-2 network simulator with the home-cell community-based mobility model. Experimental results show that the proposed algorithm outperforms typical routing algorithms in terms of the network traffic and delivery delay.     

An analytical approach to the partial scan problem

The scan design is the most widely used technique used to ensure the testability of sequential circuits. In this article it is shown that testability is still guaranteed, even if only a small part of the flipflops is integrated into a scan path. An algorithm is presented for selecting a minimal number of flipflops, which must be directly accessible. The direct accessibility ensures that, for each fault, the necessary test sequence is bounded linearly in the circuit size. Since the underlying problem is NP-complete, efficient heuristics are implemented to compute suboptimal solutions. Moreover, a new algorithm is presented to map a sequential circuit into a minimal combinational one, such that test pattern generation for both circuit representations is equivalent and the fast combinational ATPG methods can be applied. For all benchmark circuits investigated, this approach results in a significant reduction of the hardware overhead, and additionally a complete fault coverage is still obtained. Amazingly the overall test application time decreases in comparison with a complete scan path, since the width of the shifted patterns is shorter, and the number of patterns increase only to a small extent.     

An analytical approach to the dynamic topology problem

Currently, it is possible to modify (say, hourly) the topology of a data communications network by adding or deleting network links and/or by increasing or decreasing bandwidth on existing links in response to changing traffic loads and/or projected network conditions. The intent of this paper is to study a Markov decision process (MDP) model of the dynamic topology problem (DTP), the problem of activating and/or deleting links, as a function of the current traffic in the network and of the most recent network topology design. We present a decomposition of this model and structural results for the decomposition. The decomposition and structural results enhance the tractability of procedures for determining optimal link control policies. A numerical example is used to illustrate these results.Research supported by ARO Contract No. DAAG-29-85-K0089, NSF Grant No. ECS-8708183, and DCA Contract No. DCA 100-89-C-0031.     

An analytical solution to the problem of formation of an intense axially symmetrical cylindrical beam

The problem of calculation of electrodes that form an axially symmetrical cylindrical beam in the r regime (where the current is limited by the spatial charge) is considered. A new technique based on the variable separation method is proposed. It is shown that the technique can also be applied to solve the interior Dirichlet problem.     

一种针对RF-LDMOST结构改进的解析模型

本文提出一种基于2D泊松方程,针对RF-LDMOST结构改进的解析模型。借助此模型研究了RF-LDMOST电场分布与高掺杂的浅漂移区和低浓度p型外延层之间的关系,能清楚地从解析角度阐明p外延层厚度对电场分布的影响。ISE TCAD仿真和实验结果与解析结果吻合较好。此模型对于RF-LDMOST的理解和设计有一定价值。     

An improved analytical model for the electric field distribution in an RF-LDMOST structure

This paper presents an improved analytical model for an RF-LDMOST structure based on the 2D Poisson equation.The derived model indicates the influence of high doped shallow drift and low doping concentration p epitaxial layer on the electric field distribution.In particular,the importance of the thickness of the p epitaxial layer for electric field distributions in RF-LDMOST are shown through MATLAB analytical results based on the model.Then ISE TCAD simulations and experiments are processed and their re...