Risk assessment methodology for network integrity

Modern, high functionality networks support an ever-increasing range of sophisticated services; but this strength is also a weakness due to the fragility of the complex distributed-processing capability. Unexpected perturbations can cause widespread network outages, i.e. brownout. The risks to network integrity are exacerbated by regulatory policies that demand open network interconnection between competing network operators and service providers; and the increasing complexity where single experts cannot comprehend the whole problem space. This paper proposes a design methodology for a formal and systematic framework to assess the risk to network integrity and hence minimise network and service failure probability.     

Service-level availability estimation of GPRS

The General Packet Radio Service (GPRS) extends the Global System Mobile Communication (GSM) by introducing a packet-switched transmission service. This paper analyzes the GPRS behavior under critical conditions. In particular, we focus on outages, which significantly impact the GPRS dependability. In fact, during outage periods, the cumulative number of users trying to access the service grows proportionally over time. When the system resumes its operations, the overload caused by accumulated users determines a higher probability of collisions on resources assignment and, therefore, a degradation of the overall QoS. This paper adopts a stochastic activity network modeling approach for evaluating the dependability of a GPRS network under outage conditions. The major contribution of this study lies in the novel perspective the dependability study is framed in. Starting from a quite classical availability analysis, the network dependability figures are incorporated into a very detailed service model that is used to analyze the overload effect GPRS has to face after outages, gaining deep insights on its impact on user's perceived QoS. The result of this modeling is an enhanced availability analysis, which takes into account not only the bare estimation of unavailability periods, but also the important congestion phenomenon following outages that contribute to service degradation for a certain period of time after operations resume.     

Incorporating reliability specifications in the design oftelecommunication networks

The current state of reliability specification and design methods is described. These methods aim to keep the expected value of the effect of network failures on the users under a certain level by assuming that the effect is approximately proportional to the outage time. The evaluation of long outages is discussed. Future reliability specification and design methods are also discussed     

Meeting the challenge of assuring dependable telecommunicationservices in the '90s

Assuring the dependability of telecommunication services in the face of increasing customer expectations, revolutionary changes being made or proposed in networks, and recent disruptive disasters are discussed. Work focused on reducing vulnerability to network element outages is described and examined for three new technologies: fiber network architectures, common channel signaling, and intelligent network architectures. A comprehensive service dependability management process to be established by service providers is recommended     

The story of Bonneville Power: 1937-1968-1987 ... Thermal generation, EHV transmission, telecommunications, automation, and service reliability

The present thrust of BPA, as it reaches toward the goals of the future, is along the parallel lines of simultaneous planning, design, and development of 1. Long-distance EHV transmission lines to expanding and emerging industrial load centers in the Pacific Northwest and Southwest. 2. Digital controls, on a comprehensive systemic basis, to replace certain analog and manual controls. 3. An expansion of the telecommunications network for the instantaneous transmission and reception of data. 4. A long-range philosophy for service reliability that will minimize outages and service interruptions. These objectives will be closely coordinated with the plans of the Bureau of Reclamation, Corps of Engineers, and other public and private agencies for the construction of new power dams, the installation of additional generating units at existing facilities, and the building of thermal generating plants to meet the power demands of the next two decades.     

传感器网络多路径区分服务的Qos路由协议

针对传感器网络多类型业务混合传输时服务质量难以保证的问题,提出一种多路径区分服务的QoS路由协议DSMQR(Differentiated Services Multipath QoS Routing Protocol)。该协议利用跨层协作的思想设计了传感器网络节点的通信模型,通过网络层与MAC层协作处理建立区分服务框架,采用以数据为中心的多优先级队列调度分发模式,利用综合代价函数实现了多业务流的路由路径选取。仿真实验表明,DSMQR能够满足传感器网络时延敏感分组与可靠性敏感分组的QoS需求,有效地优化利用了系统资源。      

A review of fault management in WDM mesh networks: basic concepts and research challenges

The article first presents a broad overview of the fault management mechanisms involved in deploying a survivable optical mesh network which employs optical crossconnects. We review various protection and restoration schemes, primary and back-up route computation methods, shareability optimization, and dynamic restoration. We then describe different parameters that can measure the quality of service provided by a WDM mesh network to upper protocol layers (e.g., IP network backbones, ATM network backbones, leased lines, virtual private networks), such as service availability, service reliability, restoration time, and service restorability. We review these concepts, the factors that affect them, and how to improve them. In particular, we present a framework for cost-effective availability-aware connection provisioning to provide differentiated services in WDM mesh networks. Through the framework, the more realistic scenario of multiple near-simultaneous failures can be handled. In addition, the emerging problem of protecting low-speed connections of different bandwidth granularities is also reviewed.     

The weak link

Public network reliability has become a mandatory issue. In the second quarter of 1991 alone, there were 331 switch-related outages, which affected more than 3.5 million phone lines and lasted an average of 45 minutes each. The carriers are trying but they still represent the ‘Weak Link’ in data and voice communications. There will be improvements but will they be enough?     

The reliability of LEC telephone networks

The reliability of local exchange carrier (LEC) networks is described using data obtained from diverse sources. These sources are Bellcore's Outage Performance Monitoring (OPM) process, which is designed to collect information on switch outages lasting two minutes or longer, the Automated Report Management Information System (ARMIS), which supplies reports to the US Federal Communications Commission (FCC) to show industry trends in network reliability, and the US General Accounting Office (GAO), which has recently collected information on each outage lasting at least 15 min and affecting at least 10000 lines during 1990 and 1991. The data show that the availability of network switches is at least 99.9981%, meaning that 99.9981% of the time a customer wants to make an intraoffice call, the switch will be up. The chance that the path between two switches is available is 99.9986%. For interoffice calls involving two switches, the availability of the interoffice network is estimated to be 99.9948%     

A census of Tandem system availability between 1985 and 1990

A census of customer outages reported to Tandem showing a clear improvement in the reliability of hardware and maintenance has been taken. It indicates that software is now the major source of reported outages (62%), followed by system operations (15%). This is a dramatic shift from the statistics for 1985. Even after discounting systematic underreporting of operations and environmental outages, the conclusion is clear: hardware faults and hardware maintenance are no longer a major source of outages. As the other components of the system become increasingly reliable, software necessarily becomes the dominant cause of outages. Achieving higher availability requires improvement in software quality and software fault tolerance, simpler operations, and tolerance of operational faults     

Power and energy

Major power outages in various parts of the world have cast doubt on the electric power industry's claimed readiness for deregulation. Here, the author argues that, in the next few years, as service areas expand and bulk transfers of power grow ever greater, the electric utility industry's main technological challenge will be to maintain the reliability that customers now take almost for granted     

ATM network resilience

With the prospect of widespread deployment of ATM by public network operators, it is crucial to ensure resilience to network outages caused by cable breaks and node failures. The general aim of resilience is to make network failures transparent to users. If a failure happens to affect a circuit, it would be very desirable to reconfigure that circuit as quickly as possible with no information loss. However, if this functionality incurs a significant cost overhead, it may be necessary to charge customers according to the resilience they receive. Since user requirements vary from service to service, it is highly likely that different customers will demand variable levels of resilience. For example, mission-critical business-oriented data services will rely on virtually fault-transparent service, whereas residential customers may tolerate breaks in service as long as they do not occur frequently or last a long time. Fortunately, different ATM restoration mechanisms are possible which suit varied customer requirements. This article summarizes a range of research papers describing ATM restoration techniques. The viable options to provide ATM network resilience are discussed, along with the customer requirements which they satisfy and aspects of ATM resilience being assessed by standards bodies. Taking all such matters into consideration, conclusions are drawn on the current and future scope for ATM resilience     

Common-Cause Outages In Multiple Circuit Transmission Lines

Reliability evaluation of a power system involving both generation and transmission elements is extremely complex. Outages of these elements are usually considered to be s-independent events. Recent investigations, however, have indicated that common-cause outages of multicircuit transmission configurations can appreciably affect the predicted reliability. Closed form expressions for steady state probabilities in 2- and 3-line cases (including certain common-cause failures) are developed. These expressions provide transmission-line state probabilities for composite generation and transmission system reliability studies. The procedure can also be used to develop state probabilities for other line models and for systems with four or more lines on the same right-of-way. The examples show the influence of the common-cause outage rate on the state probabilities. There is a definite need to include commoncause outages in reliability evaluation of transmission systems. This will require a more comprehensive approach to collecting transmission line outage data than has previously been used by most utilities.     

基于节点动静态指标的电网节点重要度的评估研究

随着智能电网技术的不断发展,对高可靠性的智能电网的精确评估提出了更高的要求。智能电网中重要节点的故障将会导致大规模停电,因此对智能电网中重要节点的评估是评估智能电网可靠性程度的重要体现。文中针对节点所处的局部环境、全局属性、网络拓扑结构以及节点所承载负荷等级等多个不同的动静态综合指标进行研究,以这些综合指标模型来评估节点在智能电网中的重要度,最后使用TOPSIS方法将动静态指标糅合,共同对智能电网节点重要度进行评估,并对IEEE-30节点进行了仿真验证。结果显示节点6的重要度较高,应对其重点保护。     

一种移动互联网技术框架的探讨

移动互联网业务是高速发展的互联网、移动通信两大电信业务相结合产生的融合业务,本文根据互联网和移动网的特点及差异性,对移动互联网的业务模式需求进行了分析,提出了一种满足移动互联网业务发展模式的技术框架,并针对技术框架提出了具体实现方案.     

Jitter‐minimized reliability‐maximized management of networks

We propose a joint optimization network management framework for quality‐of‐service (QoS) routing with resource allocation. Our joint optimization framework provides a convenient way of maximizing the reliability or minimizing the jitter delay of paths. Data traffic is sensitive to droppage at buffers, while it can tolerate jitter delay. On the other hand, multimedia traffic can tolerate loss but it is very sensitive to jitter delay. Depending on the type of data, our scheme provides a convenient way of selecting the parameters which result in either reliability maximization or jitter minimization. We solve the optimization problem for a GPS network and provide the optimal solutions. We find the values of control parameters which control the type of optimization performed. We use our analytical results in a multi‐objective QoS routing algorithm. Finally, we provide insights into our optimization framework using simulations. Copyright © 2011 John Wiley & Sons, Ltd.     

移动互联网业务能力开放研究

移动互联网业务是通信领域最具发展潜力的业务,通过构建移动互联网业务能力开放环境,将移动网络特有元素通过API形式开放,可促进移动、互联网元素的融合,构建具有差异化的移动互联网业务。本文对移动业务能力开放关键特征和要素进行了分析,提出基于Mashup技术实现移动、互联网元素融合的业务能力开放平台,并结合能力开放平台通过移动互联网差异化应用案例进行验证分析。     

Remote Control of Standby Engine Generator Sets Over a Microwave System

Experience in actual operation of microwave relay systems throughout the country has shown that involuntary outages have been caused principally by failure of the input power to the microwave equipment. Where substantially continuous service is required of the microwave system the common practice is to have emergency standby power available. This emergency power is supplied by an emergency generator set at the microwave station site. Failure of the normal input power supply initiates starting the engine generator set to supply a particular microwave station with power. This paper describes the units used to improve reliability of engine generators in microwave applications.     

A resource‐tuned QoS multicast routing protocol

This paper presents a novel framework for quality‐of‐service (QoS) multicast routing with resource allocation that represents QoS parameters, jitter delay, and reliability, as functions of adjustable network resources, bandwidth, and buffer, rather than static metrics. The particular functional form of QoS parameters depends on rate‐based service disciplines used in the routers. This allows intelligent tuning of QoS parameters as functions of allocated resources during the multicast tree search process, rather than decoupling the tree search from resource allocation. The proposed framework minimizes the network resource utilization while keeping jitter delay, reliability, and bandwidth bounded. This definition makes the proposed QoS multicast routing with resource allocation problem more general than the classical minimum Steiner tree problem. As an application of our general framework, we formulate the QoS multicast routing with resource allocation problem for a network consisting of generalized processor sharing nodes as a mixed‐integer quadratic program and find the optimal multicast tree with allocated resources to satisfy the QoS constraints. We then present a polynomial‐time greedy heuristic for the QoS multicast routing with resource allocation problem and compare its performance with the optimal solution of the mixed‐integer quadratic program. The simulation results reveal that the proposed heuristic finds near‐optimal QoS multicast trees along with important insights into the interdependency of QoS parameters and resources.