Survivable Monitoring in Dynamic Networks

We present a monitoring system for a dynamic network in which a set of domain nodes shares the responsibility for producing and storing monitoring information about a set of visitors. This information is stored persistently when the set of domain nodes grows and shrinks. Such a system can be used to store traffic or other logs for auditing or can be used as a subroutine for many applications to allow significant increases in functionality and reliability. The features of our system include authenticating visitors, monitoring their traffic through the domain, and storing this information in a persistent, efficient, and searchable manner. The storage process is O(log n){hbox{-}}{rm competitive} in the number of network messages with respect to an optimal offline algorithm; we show that this is as good as any online algorithm can achieve and significantly better than many commonly used strategies for distributed load balancing.     

Dynamic Grooming Algorithms for Survivable WDM Mesh Networks

Within a WDM grooming mesh network and under the constraints of the number of transceivers per node and wavelength continuity, we propose a novel dynamic grooming graph which models the number of transceivers per node in addition to the usage of wavelength and bandwidth resources. Based on the grooming graph, we first propose a dynamic traffic-grooming algorithm called integrated grooming algorithm (IGA). And we also propose two dynamic survivable traffic-grooming algorithms, which are called protection per lightpath traffic-grooming algorithm (PPL) and protection per connection traffic-grooming algorithm (PPC). These algorithms are evaluated via simulations.     

Priority-based Dynamic Lightpath Allocation for Survivable WDM Networks

In recent years, there has been considerable research interest in the design of survivable wavelength division multiplexing (WDM) networks. Many papers have proposed mixed-integer linear program (MILP) formulations as well as heuristics to optimally allocate lightpaths, using protection based schemes. Such schemes provide quick and guaranteed recovery, but do not use resources efficiently. About 50% of allocated resources remain idle, under fault-free conditions. If these “idle” resources were used for low-priority connections (which could be pre-empted if necessary), the resource utilization would improve significantly. This paper introduces two MILP formulations for priority-based dynamic lightpath allocation in survivable WDM networks. We define three different levels of service and allocate resources based on the requested service level. An important advantage of our approach is that while we can handle multiple levels of service, the traditional (single level) shared and dedicated path protection schemes can be treated simply as a special case of the proposed formulations. The first formulation solves the problem optimally, but is quite time consuming. The second formulation makes some simplifications, and is more efficient. The results demonstrate that our approach can significantly improve resource utilization and is feasible for practical sized networks, particularly under low- to medium-traffic load. For large networks and high traffic conditions, simpler heurtistic algorithms are more appropriate. In such cases, the proposed MILP formulation can be a useful tool to validate the performance of the heuristics.     

信息网络模型结构化研究方法综述

从统计性能层次，逻辑层次和时间层次对现代信息网络建模仿真及性能评价各种研究方法的发展历程，应用现状及研究方向进行综述，提出了为适应信息网络日益增长的系统复杂性，结构非线性的要求，结构化模型方法体系有待扩充和探索的有关问题。     

Capacity Requirements for Node and Arc Survivable Networks

We consider a route in a rectilinear grid communications network and compute the ratio of the additional capacity per tandem node required to make the route immune to a single tandem node failure (which causes all arcs incident to the node to fail), divided by the additional capacity per arc required to make the route immune to a single arc failure. For any route satisfying a mild assumption, we prove the ratio is between 1 and 4/3. For random routes, we show that the expected value of the ratio is 10/9 for routes using 2 arcs, 202/189 for routes using 3 arcs, and has the limit (as the number of arcs increases to infinity) of 7/6. The theoretical results are in close agreement with empirical results, using a network design algorithm, for large data communications networks.     

Integrated VP-Based Control Strategies for ATM Survivable Networks

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Generalized Sharing in Survivable Optical Networks

Shared path protection has been demonstrated to be a very efficient survivability scheme for optical networking. In this scheme, multiple backup paths can share a given optical channel if their corresponding primary routes are not expected to fail simultaneously. The focus in this area has been the optimization of the total channels (i.e., bandwidth) provisioned in the network through the intelligent routing of primary and backup routes. In this work, we extend the current path protection sharing scheme and introduce the Generalized Sharing Concept. In this concept, we allow for additional sharing of important node devices. These node devices (e.g., optical-electronic-optical regenerators (OEOs), pure all-optical converters, etc.) constitute the dominant cost factor in an optical backbone network and the reduction of their number is of paramount importance. For demonstration purposes, we extend the concept of 1:N shared path protection to allow for the sharing of electronic regenerators needed for coping with optical transmission impairments. Both design and control plane issues are discussed through numerical examples. Considerable cost reductions in electronic budget are demonstrated     

Current Reconstruction Techniques for Survivable Three-Phase PWM Converters

In high-performance three-phase pulsewidth-modulated (PWM) converter systems used in generator and motor drives, failure of current sensors will directly interrupt the system performance, and will even cause disastrous consequences. Redundancy in design is one of the popular choices to overcome this issue. However, this usually leads to an undesirable increase in size and cost. This letter presents two novel model-independent current reconstruction methods for three-phase PWM converter systems based on space vector modulation. Using the proposed sensor placement and software algorithm, phase currents within a three-phase converter can be reconstructed to an acceptable level of accuracy under single-survived-sensor ($S^3$) scenario. A hardware prototype is built and fault tolerant algorithm is implemented using a DSP (TMS320F2812). Experiments are conducted under worst-case scenario to verify the flexibility of sensor placement/converter layout and software algorithm.      

A Framework for Differentiated Survivable Optical Virtual Private Networks

Wavelength division multiplexed (WDM) networks are matured to provide, scalable data centric infrastructure, capable of delivering flexible, value added, high speed and high bandwidth services directly from the optical domain. Optical virtual private networks (OVPNs) make use of the concept of highly reconfigurable nature of lightpaths offered by WDM, to create secure tunnels of high bandwidth across the intelligent WDM optical transport network. An OVPN is a private connection between two or more edge devices (access nodes), that allows a group of clients to fully exploit the flexibility of the switched intelligent optical network. However, OVPNs will not be a viable alternative unless they can guarantee a predictable bandwidth, availability, response time, and fault-tolerance to users. In this paper, we study the problem of dynamically establishing lightpaths for OVPNs over intelligent optical transport networks to provide varying classes of service based on the type of primary and backup lightpaths and the number of backup lightpaths, when each OVPN is specified by the desired logical connectivity and Class of Service. The type of primary and backup lightpaths determines the QoS parameters such as response time and bandwidth. Whereas, the number of backup lightpaths determines the level of fault-tolerance and availability of OVPN. Based on the service classes, any OVPN in the network falls into one of the six classes viz. single dedicated primary and single dedicated backup (SDPSDB), single dedicated primary and multiple dedicated backups (SDPMDB), single dedicated primary and single shared backup (SDPSSB), single shared primary and single shared backup (SSPSSB), single shared primary and multiple shared backups (SSPMSB), and best-effort (BE). In BE, we consider two variations—(1) OVPN as dedicated logical ring topology (DLRT) and (2) OVPN as shared logical ring topology (SLRT). We conduct extensive simulation experiments to compare and evaluate the effectiveness of different classes of OVPNs for varying network configurations–varying number of fibers, wavelengths on physical links, and number of nodes in OVPN.     

电信网络成本研究

电信网络成本是电信管制经济学的基础。目前中国尚无系统的电信网络成本工程学测算模型，以工程学分析模型为主结合计量经济学方法来研究电信网络成本是电信网络成本工程学研究的主要问题。使用网络成本工程学方法对电信网络成本进行研究，可以在电信管制经济学基础研究方面有所突破。文章介绍了电信网络成本的研究现状、研究内容、研究目标和关键问题，以及采用工程学模型方法测算电信网络成本的主要特色与创新之处。     

Design of Survivable Networks with Connectivity Requirements

In this paper we study the problem of survivable network design (SND). The problem can be stated as follows: Given a set of nodes, possible edges and costs for each edge and the number of permitted node or edge failures between each pair of nodes, we want to design a cost effective communications network which has the property that there is at least one communication route present between all the communicating node pairs, even in the case of node or link failure. We present the formulation of the problem and present a solution technique based on a constraint addition approach. We decompose the problem into smaller problems that are computationally not difficult to solve. We use the solutions of these smaller problems to generate new constraints that are added to the overall design problem. This iterative procedure is able to solve the survivable network design problem very efficiently. Extensive computational results show the effectiveness of our solution procedure.     

Advanced Cordless Telecommunications Service

Present analog cordless telephones suffer from lack of privacy, limited facilities and can support only a relatively low density of users. This restricts their benefits and market opportunities. Hence the need for an advanced cordless telecommunications service (ACTS). Consideration is given here to the needs of this service in terms of requirements, demand, system aspects, spectrum needs, propagation, and performance. This leads to a proposed system design for the service which is already under consideration within Europe. It uses 32 kbit/s speech encoding and time-division duplex operation to achieve both-way speech communication on a single 100 KHz-wide radio channel. A pool of radio channels are available to choose from at both base and handset in order to minimize overall interference and maximize system capacity. The addition of another aerial at only the base unit can provide the full spatial diversity improvement to both directions of transmission. The service is due for introduction in the United Kingdom in 1987.     

WDM网状网中基于共享风险链路组限制的业务量疏导算法

该文研究了业务量疏导WDM网状网中如何建立可靠的业务连接问题,提出一种新的基于共享风险链路组(SRLG)限制的共享通路保护算法。该算法既可以保证用户业务不同的可靠性要求,同时又能够有效提高全网的资源利用率,从而大大降低全网的业务阻塞率。该文还对所提算法进行了仿真研究,并给出了仿真结果。     

Enterprise Modelling the Telecommunications Industry

The telecommunications industry is becoming both more co-operative and more competitive and this has dramatic consequences on the character of operational support. Operational activities make up the majority of telecommunications companies, and investment in these activities is huge. Dynamic markets and emerging new roles and supply chains stress the design of such operational systems and processes, some of which can trace their origins back to the monopolistic days of the past. This paper presents preparatory work in the search for new architectural tools to prepare operational support for the next millennium. The paper provides a definition for a value-adding enterprise and shows how conversation theory can help analyse the interaction of roles within an enterprise model. Such models can describe the interaction between responsibilities within enterprises and, in future, the required operational support systems, activities, data and processes.     

Survivable Passive Optical Networks Based on Arrayed-Waveguide-Grating Architectures

By arranging a small number of arrayed-waveguide gratings in survivable topologies with specific interconnection patterns, we can construct passive optical networks with a high degree of protection. A variety of designs are presented that differ in the level of survivability, the protection mechanism, and the amount of required end-user equipment.     

Advanced Call Scheduling for Testing a Telecommunications Network

This paper describes an advanced scheduling system and method for generating large volumes of calls to be used for testing a telecommunications network. The system is capable of preparing large-scale and complex network tests by viewing the task as a scheduling problem. The various requirements of the scheduling problem are analysed and represented as constraints or optimisation criteria. A fast heuristic method is proposed for solving the problem. The approach is based on a greedy algorithm for constructing solutions and it incorporates limited backtracking and dynamic value-ordering heuristics. The algorithm and system are currently being used for call charge verification in BT's PSTN and CSP networks.