Optical packet and burst switched networks: a review

Over the past several years, a significant amount of research has been conducted in the areas of optical packet switching (OPS) and optical burst switching (OBS). This research has been motivated by the need for techniques that are capable of supporting the demanding requirements of emerging dynamic high-bandwidth network applications in a flexible and efficient manner. Although optical packet and burst switching have yet to be widely deployed in commercial settings, recent research progress indicates that such deployments are not infeasible in the near future. The authors review the literature on OPS and OBS. Basic concepts are discussed and an overview of current and emerging research issues and challenges for optical packet and burst switched networks is presented. The authors attempt to cover issues that are essential for the practical deployment of such networks and highlight promising research directions that are likely to facilitate such deployments.     

A pinwheel packet scheduling scheme for broadband wireless networks

Abstract

A frame‐based packet scheduling scheme, the pinwheel scheduling (PWS) scheme, is proposed and investigated at the medium access control (MAC) layer in broadband wireless networks. The objective of the proposed scheduling scheme is to provide low delay and low jitter for real‐time traffic. We have demonstrated in this paper that the proposed PWS scheme not only satisfies the packet‐level QoS requirements but also has low implementation cost. The PWS scheme gives the highest priority to CBR connections in a service cycle to minimize their delay and jitter. For ABR traffic, a number of slots are allocated to fit their MCR. The remaining time slots are then allocated to VBR traffic according to their PCR. Thus, the VBR traffic may suffer large delay and jitter when the number of CBR connections increases. The PWS with modular strategy (PWS/MS) is proposed to improve the performance of the VBR traffic. We also introduce three different slot‐reuse strategies named real‐time traffic first (RTF), non‐real‐time traffic first (NRTF) and longest queue first (LQF), respectively, to improve resource utilization. In order to demonstrate the performance of the PWS and PWS/MS schemes, comparisons are made with existing schemes such as the round‐robin (RR) and weighted‐round‐robin (WRR) by using OPNET software. Simulation results show that the proposed schemes are capable of maintaining the lowest delay and jitter for VBR and CBR traffic while not sacrificing the available bit rate (ABR) traffic.     

Analysis, simulation and measurement in large-scale packet networks

The authors review analysis, simulation and measurement techniques, the three fundamental methods for performance evaluation in packet networks, looking at what's known, what's new and some outstanding issues. In trying to avoid re-reviewing material which has already been well summarised elsewhere, the authors concentrate on areas that are relatively new or possibly less generally well appreciated. So, under analysis, the focus is on models for network topologies and connectivity, and on wireless access. In the simulation section the focus is on techniques for scalable simulation for large-scale packet networks. Compared to the other two areas measurement is relatively new anyway, and more time is spent on motivation, techniques and some recently discovered limitations.     

Cooperative wireless networks for better green services

During the last two decades, mobile communication systems (such as GSM, GPRS and 3G networks), wireless broadcasting networks, wireless local area networks (WLAN or WiFi), and wireless sensor networks have been successfully developed and widely deployed through different technological routes for providing a variety of communication services in different application scenarios. While making tremendous contributions to social progress and economic growth, these heterogeneous wireless networks consume a lot of energy in achieving overlapped service coverage, and at the same time, generate strong electromagnetic interference (EMI) and radiation pollution, especially in big cities with high building density and user population. In order to guarantee the overall return on investment (ROI), improve user experience and quality of service (QoS), save energy, reduce EMI and radiation pollution, and enable the sustainable deployment of new profitable applications and services, this paper proposes a cross-network cooperation mechanism to effectively share network resources and infrastructures, and then adaptively control and match multi-network energy distribution characteristics according to actual user/service requirements in different geographic areas. Some idle or lightly-loaded Base Stations (BS or BSs) will be temporally turned off for saving energy and reducing EMI. Initial simulation results show the proposed approach can significantly improve the overall energy efficiency and QoS performance across multiple cooperative wireless networks.     

基于T-MPLS网络的多等级分组业务传送特性研究

基于国际电信联盟制定的传送多协议标记交换(T-MPLS)标准,在T-MPLS网络中电路业务和分组业务并存的情况下,对业务开关时间和数据包长服从帕雷托、对数正态、威布尔和指数分布的多等级分组业务传送质量进行了研究。理论分析表明,电路业务在边缘节点适配时被切割成的数据包的长度以及以业务源开关时间及分组数据包长分布为代表的流量特性,会对高等级分组业务的时延及其方差、路由器出端口处的队列长度和丢包率造成不同程度的影响。通过基于OPNET软件搭建的软件平台进行仿真,验证了理论分析的结论。     

Load-balanced wavelength assignment strategies for optical burst/packet switching networks

Loss-free schemes are defined to ensure successful packet/burst transmissions in optical packet/burst switching networks. To this end, they rely on a collision-free routing and wavelength assignment (CF-RWA) scheme combined with simple contention resolution mechanisms that guarantee the absence of losses in intermediate links. Here, the CF-RWA problem is studied. In particular, by using graph theory, the problem of finding CF-RWA schemes that minimise the number of wavelengths to serve a given traffic matrix is set. The problem is simplified when it is formulated by using pre-defined sets of non-colliding paths. Within this framework, the problem is shown to be equivalent to finding a given vertex-set colouring of the so-called restriction digraph. Here, two heuristic algorithms are proposed to obtain such vertex-set colourings. One of them provides a suitable CF-RWA without having to solve the minimisation problem. By way of example, the proposed method is applied to the NSFNet and the EON network providing quasi-optimal results.     

Dynamic non-collision packet reservation MAP for time division duplex-based wireless networks

The non-collision packet reservation multiple access (NC-PRMA) protocol was proposed by Wen and Wang to eliminate the unstable phenomenon in the PRMA protocol under heavy load conditions by allocating dedicated control mini-slots to mobile terminals (MTs). However, this does not utilise the channel resource efficiently. A dynamic non-collision PRMA (DNC-PRMA) protocol has been proposed to dynamically allocate control mini-slots to MTs such that the channel resource can be utilised efficiently. Using simulation, the proposed DNC-PRMA protocol is shown to yield significantly higher channel utilisation, lower packet dropping probability and lower channel access delay than a protocol that allocates a dedicated mini-slot to each MT.     

Combined methodology for measurement of available bandwidth and link capacity in wired packet networks

Accurate measurement of network parameters such as available bandwidth (ABW), link capacity, delay, packet loss and jitter are used to support and monitor several network functions, for example traffic engineering, quality-of-service (QoS) routing, end-to-end transport performance optimisation and link capacity planning. However, proactive network measurement schemes can impact both the data traffic and the measurement process itself, affecting the accuracy of the estimation if a significant amount of probe traffic is injected into the network. In this work, the authors propose two measurement schemes, one for measuring ABW and the other for measuring link capacity, both of them use a combination of data probe packets and Internet control messaging protocol (ICMP) packets. Our schemes perform ABW and link-capacity measurements in a short time and with a small amount of probe traffic. The authors show a performance study of our measurement schemes and compare their accuracy to those of other existing measurement schemes and also show that the proposed schemes achieve shorter convergence time than other existing schemes and high accuracy.     

Operation strategies for scheduling problems in project management

Abstract

This article analyzes different operation strategies in project management from an economic viewpoint and proposes a general procedure to schedule a project when inflation is either considered, with linear or ladder type, or not considered.     

Providing differentiated services in CDMA wireless networks

With much more advanced techniques employed, various applications can be supported by 3G CDMA-based wireless networks. Providing differentiated service over wireless networks has become a very important issue in the design of wireless networks. A new media access control protocol with a hierarchical scheduling algorithm to provide differentiated service for CDMA-based wireless networks is proposed. This protocol evolves from the distributed queuing random access protocol for CDMA wireless network. The proposed protocol has been designed to have an ability to accommodate integrated traffic in the networks with effective scheduling schemes. A series of simulation experiments have been carried out to evaluate the performance of the proposed protocol with the hierarchical scheduling algorithm. The results reveal that the proposed solution performs effectively in the integrated traffic composed of messages with or without time constraints and achieves proportional fairness among different types of traffic.     

航天工程精细化质量管理

中国航天工程质量管理以钱学森系统工程理论为指导,以“坚持、完善、发展”为原则,以完成重大工程任务为牵引,不断进行理论和管理创新。“十一五”以来,航天科技集团实施了航天型号精细化质量管理,保证了载人航天、嫦娥工程等一系列重大航天任务的圆满成功。精细化质量管理强调持续提升总体设计、整体优化、有效地识别与控制技术风险及快速聚焦、放大和量化控制关键细节的能力,强调单位质量管理体系和项目产品保证体系的有机结合和有效运行,强调实用的管理工具的开发和应用,强调技术、产品、队伍和管理成熟度的同步提升。笔者简要回顾了航天质量管理的发展历程,提出了航天工程精细化质量管理的概念和内涵,论述了精细化质量管理的理论、方法和体系及管理实践的主要做法。     

Energy management in sensor networks

This paper presents a holistic view of energy management in sensor networks. We first discuss hardware designs that support the life cycle of energy, namely: (i) energy harvesting, (ii) energy storage and (iii) energy consumption and control. Then, we discuss individual software designs that manage energy consumption in sensor networks. These energy-aware designs include media access control, routing, localization and time-synchronization. At the end of this paper, we present a case study of the VigilNet system to explain how to integrate various types of energy management techniques to achieve collaborative energy savings in a large-scale deployed military surveillance system.     

基于动态虚拟权重的自动交换光网络(ASON)域间路由优化

在研究利用域到域路由协议(DDRP)实现自动交换光网络(ASON)域间路由的基础上,针对实现过程中星型拓扑汇聚策略带来的等代价路由问题提出了基于动态虚拟权重的域间路由优化方法,并在利用OPNET Modeler网络仿真软件搭建的ASON域间路由仿真平台上,对传统随机边界节点选择方式和基于动态虚拟权重选择方式进行了仿真对比,验证了所提出的域间路由优化方法具有减小路由代价、降低业务阻塞率和提高网络资源利用率等性能优势.     

Energy-efficient cluster-based scheme for failure management in sensor networks

Wireless sensor networks are characterised by dense deployment of energy constrained nodes. Owing to the deployment of large number of sensor nodes in uncontrolled hostile environments and unmonitored operation, it is common for the nodes to exhaust its energy and become inactive. The failing nodes create holes in the network topology causing connectivity loss, which may lead to critical information loss. To avoid degradation of performance, it is necessary that the failures are detected well in advance and appropriate measures are taken to sustain the network operation. An energy-efficient cluster-based technique is proposed to detect failures and recover the cluster structure. The proposed technique relies on the cluster members to detect the failures in the cluster and recover the connectivity. The proposed failure detection and recovery technique recovers the cluster structure in less than one-fourth of the time taken by the Gupta algorithm and is also proven to be 70% more energy-efficient than the same. The proposed cluster-based failure detection and recovery scheme proves to be an efficient and quick solution to robust and scalable sensor network for long and sustained operation.     

Layered connection management for dynamic all-optical networks

Traditionally, optical channels are manually provisioned and exist for months or years. New automated means of managing network resources, together with demands for greater flexibility from the customers, have led to the concept of dynamic optical connections. However, over time, the establishment and removal of these connections in the presence of changing traffic demands can lead to inefficient exploitation of the underlying resources. The authors propose a novel dual-layered connection management system. Distributed, fast and simplified control plane functionalities are used at the lower layer to provide efficient real-time per-connection resource management. The time-consuming optimisation functions are located in a centralised upper layer where they are able to achieve more efficient solutions that can improve the overall network utilisation. The control of the lower layer by the upper level is carried out via two means, namely: influence-based path calculation for short-lived connections and intrusive redeployment for long-lived connections. Simulation results, under a variety of conditions, show an improvement in performance of over 10% in each of the metrics considered for both long-lived and short-lived connections for two commonly cited test networks. We therefore conclude that the proposed system can offer worthwhile improvements in network performance.     

All-optical router with pulse-position modulation header processing in high-speed photonic packet switching networks

In future high-speed photonic packet switching networks, it is highly desirable to carry out robust alloptical header recognition to provide high-throughput routing. The authors present a pulse-position modulation header processing (PPM-HP) scheme, offering significantly reduced routing table size and employing a single bitwise AND operation to carry out correlation of the packet header with the entire routing table entries. The downsized routing table also offers multiple transmission modes (unicast, multicast and broadcast) in the optical layer and improves core network scalability where the number of core/edge nodes could be altered without the need for changing the number of routing table entries. The authors present modelling and simulation of the packet switching router based on PPM-HP. Noise propagation and crosstalk incurred in a multiple-hop routing scenario are investigated. The simulation results are presented and compared with the theoretical calculations.     

区分服务的无线传感器网络路由协议

在优先级多路径路由协议PRIMAR（PRIoritize MultipAth Routing）的基础上,提出了NRE-PRI—MAR协议：以邻居节点剩余能量（NRE）作为衡量路径优先级大小的依据,通过建立节点的二级路由表来决定下一跳转发节点．仿真实验表明,该协议有效地提高了网络的生存期,实现了区分服务．     

基于服务曲线的TDMA无线网络上行信道时隙调度算法

研究了采用TDMA接入方式的无线分组网络上行信道时隙分配策略,基于移动台的QoS要求,提出了一种自适应时隙分配算法。利用服务曲线对移动台的QoS要求进行了建模。算法的目标是在尽量满足所有移动台Qos要求的基础上提高系统的上行吞吐量。在无法满足所有移动台QoS要求的情况下,使得移动台实际发送的数据与满足服务曲线要求之间的偏差最小。仿真结果表明：该算法能够在系统吞吐量和系统偏差之间进行折衷,从而有效地平衡上述两个目标。     

一种多源协作网络中轮询节点选择算法

针对放大转发(AF)的多源多中继两跳协作通信网络模型,提出了一种基于轮询分组调度算法的节点选择与用户调度策略.与之前所提出的中继选择选择算法相比,所提出的中继节点轮询分组调度算法,不需要额外的信令开销,复杂度低,并保证中继间的负载均衡.此外,为保证用户传输的公平性,提出一种结合多用户分集的轮询分组调度算法.最后在已选择的中继节点和所调度的源节点用户中引入分布式空时编码.仿真结果表明,该节点选择和用户调度算法能保证所有节点使用的公平性,并且结合分布式空时编码之后,可以提高频谱利用率,从而提高了系统性能.