Delayed Internet routing convergence

This paper examines the latency in Internet path failure, failover, and repair due to the convergence properties of interdomain routing. Unlike circuit-switched paths which exhibit failover on the order of milliseconds, our experimental measurements show that interdomain routers in the packet-switched Internet may take tens of minutes to reach a consistent view of the network topology after a fault. These delays stem from temporary routing table fluctuations formed during the operation of the border gateway protocol (BGP) path selection process on the Internet backbone routers. During these periods of delayed convergence, we show that end-to-end Internet paths will experience intermittent loss of connectivity, as well as increased packet loss and latency. We present a two-year study of Internet routing convergence through the experimental instrumentation of key portions of the Internet infrastructure, including both passive data collection and fault-injection machines at major Internet exchange points. Based on data from the injection and measurement of several hundred thousand interdomain routing faults, we describe several unexpected properties of convergence and show that the measured upper bound on Internet interdomain routing convergence delay is an order of magnitude slower than previously thought. Our analysis also shows that the upper theoretic computational bound on the number of router states and control messages exchanged during the process of BGP convergence is factorial with respect to the number of autonomous systems in the Internet. Finally, we demonstrate that much of the observed convergence delay stems from specific router vendor implementation decisions and ambiguity in the BGP specification     

Iterative approach to multivariable control

An iterative technique is proposed for the design of control inputs for linear multivariable systems. Using aggregation to reduce the problem size at each step, compensation can be accomplished in as few as N steps, where N is the controllability index of the system. For controllable systems, arbitrary pole placement is possible subject only to mild restrictions. Applications to deadbeat control and minimal-order observers are illustrated.     

A new approach to kinescope beam convergence

Misconvergence of the beams in color kinescopes because of deflection has been corrected in the past by the use of dynamic convergence devices. Six independent fields are required to deflect three beams without misconvergence. Conventional deflection yokes supply two of these fields; the remaining four are supplied by convergence magnets. This paper describes a more general system that uses six coexistent deflection fields. Such a system is capable of producing deflection without misconvergence, and in contrast to conventional systems produces no loss in color purity tolerance. A particular embodiment of this system is discussed in detail. It employs a six-coil "converger" used in combination with a conventional deflection yoke. The results of an experimental investigation of this embodiment are given.     

A localized adaptive proportioning approach to QoS routing

In QoS routing, paths for flows are selected based on knowledge of resource availability at network nodes and the QoS requirements of flows. Several QoS routing schemes have been proposed that differ in the way they gather information about the network state and select paths based on this information. We broadly categorize these schemes into best path routing and proportional routing. The best path routing schemes gather global network state information and always select the best path for an incoming I-low,based on this global view. It has been shown that best path routing schemes require frequent exchange of network state, imposing both communication overhead on the network and processing overheads on the core routers. On the other hand, proportional routing schemes proportion incoming flows among a set of candidate paths. We have shown that it is possible to compute near-optimal proportions using only locally collected information. Furthermore, a few good candidate paths can be selected using infrequently exchanged global information and thus with minimal communication overhead. We describe these schemes in detail and demonstrate that proportional routing schemes can achieve higher throughput with lower overhead than best path routing schemes     

Adaptive proportional routing: a localized QoS routing approach

Most of the QoS routing schemes proposed so far require periodic exchange of QoS state information among routers, imposing both communication overhead on the network and processing overhead on core routers. Furthermore, stale QoS state information causes the performance of these QoS routing schemes to degrade drastically. In order to circumvent these problems, we focus on localized QoS routing schemes where the edge routers make routing decisions using only local information and thus reducing the overhead at core routers. We first describe virtual capacity based routing (vcr), a theoretical scheme based on the notion of virtual capacity of a route. We then propose proportional sticky routing, an easily realizable approximation of vcr and analyze its performance. We demonstrate through extensive simulations that adaptive proportional routing is indeed a viable alternative to the global QoS routing approach.     

A novel two-step approach to restorable dynamic QoS routing

Aiming at minimizing the combined bandwidth cost of a pair of disjoint active and backup paths, a popular approach to designing restorable dynamic quality of service (QoS) routing schemes is based on the integer linear programming (ILP) formulation. Owing to the very different natures of active and backup paths, we found this approach problematic. In this paper, we propose an alternative approach, called two-step restorable QoS routing. In the first step, an active path is found using the widest shortest path (WSP) routing. In the second step, the corresponding backup path is determined using one of the three variants of shortest widest path (SWP) routing: basic SWP, approximate SWP or composite SWP. Combining the two steps, three novel two-step routing algorithms, denoted by SBW, SAW, and SCW, are obtained. Comparing with the best known algorithms, we show that our two-step routing approach yields noticeably lower call blocking probability, shorter active-path length, and additional flexibility of adjusting backup-path length (depending on the SWP variant adopted). Besides, our two-step routing approach gives a much shorter running time than the ILP approach, which makes it more suitable for dynamic routing.     

一种基于TMN的集中式信令路由管理新方法

本文提出了一种基于ＴＭＮ的集中式路由管理新方法Ｃ－ＭＲＶＴ,并运用排队理论对Ｃ－ＭＲＶＴ和传统ＭＲＶＴ方法进行了性能分析比较,最后给出了该方法的实现方案和模拟结果。理论分析和模拟结果表明,Ｃ－ＭＲＶＴ是一种有前景的、技术可靠的信令网络由管理方法。     

Iterative methods for solving the Gabor expansion: considerationsof convergence

J.G. Daugman's (1988) neural network solution to the Gabor expansion of an image is reformulated as a steepest descent implementation. Nonlinear optimization theory is then applied to select an appropriate convergence factor. Two quasi-Newton-based nonlinear optimization techniques are applied to improve the convergence for certain types of lattice.     

A new approach to optimizing the base profile for high-speedbipolar transistors

It is shown using first-order analytical analysis and extensive device simulations that, for a given base resistance and peak base doping, a uniform base profile gives a higher cutoff frequency than a graded profile. This result is explained by the narrower base width that can be achieved with a uniform profile, which more than compensates for the lack of the aiding electric field present in graded-base transistors     

Age-based anonymity: a randomized routing approach to communication unobservability

Providing anonymous communication on networks of interconnected computers is an active area of research which aims to enhance the privacy of the users of such networks. Communication unobservability, stronger property compared to anonymity, attempts to guarantee that legitimate messages are not discernible from dummy traffic. A network with an active global adversary is one which it is assumed that all nodes in the network are potentially being monitored at all times, and also that at any time any node could be an adversary. This paper introduces a set of anonymous system design requirements for providing enhanced communication unobservability. A new anonymous networking system was designed based on these requirements to provide both sender and receiver anonymity. The proposed system has a structured peer-to-peer network architecture and a randomized routing algorithm to obfuscate the detection of communication paths and the message routing patterns. An age-based method is proposed to prevent even the first node after the sender from identifying the original sender. A simulation program was designed and implemented to test the proposed system. The effect of different parameters on the proposed algorithm is demonstrated using a simulation program.     

Rendezvous point based approach to the multi-constrained multicast routing problem

The Quality of Service (QoS) routing requires a special approach to graph algorithms modeling. One of the mathematical concepts that reflects this class of problems is the multi-constrained minimum Steiner tree problem (MCMST). In this article, the RDP (named after the concept of the RenDezvouz Point), a novel algorithm for solving the MCMST problem is presented.     

Improved NSGA-II optimizing coding-link cost trade-offs for multicast routing in WDM networks

The present study proposed a high-data-rate underwater optical wireless communication (UOWC) system to propagate the laser blue–green waves through water. The presented study not only focuses on analysis of challenges in UOWC link including attenuation, absorption, scattering and turbulence model, but also investigates the performance of the proposed system using two different methods of balanced modulation schemes. Spectrum efficiency of the system can be improved by using appropriate modulation formats. Return-to-zero differential phase shift keying (RZ-DPSK) and non-return-to-zero differential phase shift keying (NRZ-DPSK) schemes are two modulation formats that we investigate them to improve the characteristics of the proposed UOWC system. The paper explains a real model and exhaustive analysis for advanced UOWC works by using channel model and modulation formats for presented underwater link. Performance of the proposed system under different modulation schemes and physical aspects of UOWC is studied with several parameters like max quality factor, min bit error rate (BER) and eye diagram. For clear ocean, the performance of the proposed system is good and min BER less than 10^?90 for two modulation formats. Generally, results at different condition show that the operation of NRZ-DPSK modulation has better performance than RZ-DPSK scheme.     

QL-STCT：一种SDN链路故障智能路由收敛方法

针对软件定义网络（SDN）链路故障发生时的路由收敛问题,提出了Q-Learning子拓扑收敛技术（QL-STCT）实现软件定义网络链路故障时的路由智能收敛。首先,选取网络中的部分节点作为枢纽节点,依据枢纽节点进行枢纽域的划分。然后,以枢纽域为单位构建区域特征,利用特征提出强化学习智能体探索策略来加快强化学习收敛。最后,通过强化学习构建子拓扑网络用于规划备用路径,并保证在周期窗口内备用路径的性能。实验仿真结果表明,所提方法能够有效提高链路故障网络的收敛速度与性能。     

A novel approach to source routing for multi-hop ad hoc networks

The popularity of wireless ad hoc networks has significantly increased over the past years. As a result, a great scientific effort has been made to develop and implement efficient routing protocols, able to cope with the stochastically varying topology of such networks. We present an efficient routing protocol that combines source routing, caching of routes, and the use of sequence numbers to alleviate the routing load and at the same time increase the successful delivery of data packets.     

A neural network approach to routing without interference inmultihop radio networks

The issues of routing and scheduling the activation of links in packet radio networks are highly interdependent. The authors consider a form of the problem of routing for the minimization of congestion as a step toward the study of the joint routing-scheduling problem. They formulate this as a combinatorial-optimization problem, and they use Hopfield neural networks (NN) for its solution. The determination of the coefficients in the connection weights is the most critical issue in the design and simulation of Hopfield NN models. They use the method of Lagrange multipliers, which permits these coefficients to vary dynamically along with the evolution of the system state. Extensive software simulation results demonstrate the capability of their approach to determine good sets of routes in large heavily congested networks     

A framework for self-healing and optimizing routing techniques for mobile ad hoc networks

On demand routing protocols provide scalable and cost-effective solutions for packet routing in mobile wireless ad hoc networks. The paths generated by these protocols may deviate far from the optimal because of the lack of knowledge about the global topology and the mobility of nodes. Routing optimality affects network performance and energy consumption, especially when the load is high. In this paper, we define routing optimality using different metrics such as path length, energy consumption along the path, and energy aware load balancing among the nodes. We then propose a framework of Self-Healing and Optimizing Routing Techniques (SHORT) for mobile ad hoc networks. While using SHORT, all the neighboring nodes monitor the route and try to optimize it if and when a better local subpath is available. Thus SHORT enhances performance in terms of bandwidth and latency without incurring any significant additional cost. In addition, SHORT can be also used to determine paths that result in low energy consumption or to optimize the residual battery power. Thus, we have detailed two broad classes of SHORT algorithms: Path-Aware SHORT and Energy-Aware SHORT. Finally, we evaluate SHORT using the ns-2 simulator. The results demonstrate that the performance of existing routing schemes can be significantly improved using the proposed SHORT algorithms. This research was supported in part by the National Science Foundation under the grants CCR-0296070 and ANI-0296034, and a generous gift from the Hewlett Packard Corporation. A preliminary version of this paper appeared in the proceedings of the ACM MobiHoc 2003. Chao Gui is a Technical Research Staff at Kiyon Inc (www.kiyon.com). His research interests include wireless networking and mobile computing. His current efforts are on industrial implementation of wireless mesh networks and embedded systems. Dr. Gui has received Ph.D. in Computer Science from University of California at Davis in 2005. Dr. Prasant Mohapatra is currently a Professor in the Department of Computer Science at the University of California, Davis. He has also held various positions at Iowa State University, Michigan State University, Intel Corporation, Panasonic Technologies, Institute of Infocomm Research, Singapore, and the National ICT, Australia. Dr. Mohapatra received his Ph.D. in Computer Engineering from the Pennsylvania State University in 1993. He was/is on the editorial boards of the IEEE Transactions on computers, ACM/Springer WINET, and Ad hoc Networks Journal. He has served on numerous technical program committees for international conferences, and served on several panels. He was the Program Vice-Chair of INFOCOM 2004, and the Program Co-Chair of the First IEEE International Conference on Sensor and Ad Hoc Communications and Networks, (SECON-2004). Dr. Mohapatra’s research interests are in the areas of wireless networks, sensor networks, Internet protocols and QoS.     

光组播路由代价与波长使用量的联合优化方法

为解决光组播路由中组播中路由代价和波长资源消耗单一化造成的组播路树路由的代价过高问题,在分光节点约束条件下,提出了光组播路由代价与波长使用量联合优化的长路优先(LPF)方法和短路优先(SPF)方法。算法通过检查最小光组播树是否存在节点分光约束的问题,根据设置的波长使用代价控制因子,使LPF或SPF的路由代价和波长使用量最小。LPF方法首先选择组播树最长路径或新波长通道重路由受分光约束的目的节点,SPF方法先选择组播树中最短路径或新波长通道重路由受分光约束的目的节点,仿真结果表明,本文提出的两种联合优化方法都能实现路由代价较低和波长需求较少的目的。     

A genetic algorithm-based methodology for optimizing multiservice convergence in a metro WDM network

We consider the multi-objective optimization of a multi-service arrayed-waveguide grating-based single-hop metro WDM network with the two conflicting objectives of maximizing throughput while minimizing delay. We develop and evaluate a genetic algorithm based methodology for finding the optimal throughput-delay tradeoff curve, the so-called Pareto-optimal frontier. Our methodology provides the network architecture (hardware) and the medium access control (MAC) protocol parameters that achieve the Pareto-optima in a computationally efficient manner. The numerical results obtained with our methodology provide the Pareto-optimal network planning and operation solutions for a wide range of traffic scenarios. The presented methodology is applicable to other networks with a similar throughput-delay tradeoff.     

Swarm intelligence routing approach in networked robots

Robot swarm combined with wireless communication has been a key driving force in recent few years and has currently expanded to wireless multihop networks, which include ad hoc radio networks, sensor networks, wireless mesh networks, etc. The aim of this paper is to propose an approach which introduces a polynomial time approximation path navigation algorithm and constructs dynamic state-dependent navigation policies. The proposed algorithm uses an inductive approach based on trial/error paradigm combined with swarm adaptive approaches to optimize simultaneously two criteria: cumulative cost path and end-to-end delay path. The approach samples, estimates, and builds the model of pertinent aspects of the environment. It uses a model that combines both a stochastic planned prenavigation for the exploration phase and a deterministic approach for the backward phase. To show the robustness and performances of the proposed approach, simulation scenario is built through the specification of the interested network topology and involved network traffic between robots. For this, this approach has been compared to traditional optimal path routing policy.     

Volterra series approach for optimizing fiber-optic communicationssystem designs

A new methodology for designing long-haul fiber-optic communication systems is presented. We derive the overall Volterra series transfer function of the system including linear dispersion, fiber nonlinearities, amplified spontaneous emission (ASE) noise from the fiber amplifiers, and the square-law nature of the direct detection (DD) system. Since analytical expressions for the probability of error are difficult to derive for the complex systems being used, we derive analytical expressions for an upper bound on probability of error for integrate-and-threshold detection at the receiver. Using this bound as a performance criterion, we determine the optimal dispersion parameters of each fiber segment required to minimize the effects of linear dispersion, fiber nonlinearities and ASE noise from the amplifiers. We study the dependence of optimal dispersion parameters on the average power levels in the fiber by varying the peak input power levels and the amplifier gains. Analytical expressions give us the freedom to choose system parameters in a practical manner, while providing optimum system performance. Using a simple system as an example, we demonstrate the power of the Volterra series approach to design optimal optical communication systems. The analysis and the design procedure presented in this work can be extended to the design of more complex wavelength division multiplexed (WDM) systems