Logical topology design for linear and ring optical networks

The design of logical topologies in wavelength-routing multihop optical networks is a well-studied problem. We consider logical topology (LT) design over the popular ring and linear topologies. Our objective is the minimization of the electronic processing delay for the worst case traffic flow. For uniform traffic between nodes, this delay minimization corresponds to minimizing the number of hops on a shortest path between the farthest two nodes in the logical topology (the diameter of the logical topology). The simple structure of the physical topologies enables us to present a rigorous analysis of the problem. We present lower bounds for the achievable diameter wherever possible and propose practical logical topology design algorithms and corresponding upper bounds. We also present an application of the LT designs in the linear topology to the survivability of ring networks     

Efficient algorithm for virtual topology design in multihoplightwave networks

One of the major challenges in the virtual topology design of a WDM star based system, is to incorporate in the optimization process both realistic objective functions and real system behavior. The authors present an efficient discrete optimization algorithm that meets these goals while incorporating the prevailing traffic conditions. They simulate the real system and then approximate the objective function by a short term simulation. The optimization process is based on an ordinal optimization approach, i.e., is insensitive to the approximation of the objective function obtained by short term simulation. Another crucial issue in virtual topology design is how to evaluate the quality of the solution obtained by the algorithm. They propose a new metric to evaluate the solution quality, the so called suboptimal quality, obtained by deriving the solution's relative position in the state space according to the performance order. The experiments presented in the paper attest to the quality (efficiency and robustness) of the optimization algorithm and its suitability to solve the wavelength assignment problem     

Efficient heuristics for data broadcasting on multiple channels

The problem of data broadcasting over multiple channels consists in partitioning data among channels, depending on data popularities, and then cyclically transmitting them over each channel so that the average waiting time of the clients is minimized. Such a problem is known to be polynomially time solvable for uniform length data items, while it is computationally intractable for non-uniform length data items. In this paper, two new heuristics are proposed which exploit a novel characterization of optimal solutions for the special case of two channels and data items of uniform lengths. Sub-optimal solutions for the most general case of an arbitrary number of channels and data items of non-uniform lengths are provided. The first heuristic, called Greedy+, combines the novel characterization with the known greedy approach, while the second heuristic, called Dlinear, combines the same characterization with the dynamic programming technique. Such heuristics have been tested on benchmarks whose popularities are characterized by Zipf distributions, as well as on a wider set of benchmarks. The experimental tests reveal that Dlinear finds optimal solutions almost always, requiring good running times. However, Greedy+ is faster and scales well when changes occur on the input parameters, but provides solutions which are close to the optimum. This work has been supported by ISTI-CNR under the BREW research grant. Stefano Anticaglia received the bachelor’s degree in Computer Science from the University of Perugia (Italy) in 2005. At present, he is a student in the master’s of Computer Science of the University of Perugia. Ferruccio Barsi received the doctor engineering degree from the University of Pisa, Italy, in 1969. From 1969 to 1992 he has been with he National Council of Research at the Istituto di Elaborazione dell’Informazione, Pisa. Since 1992, he is a Full Professor of Computer Science in the Mathematics and Computer Science Department of the University of Perugia, Italy. His main contributions are in the areas of computer architecture, error-control coding, systems diagnosis, VLSI design, digital signal processing, and computer graphics. He is currently involved in researches concerning network security and wireless communications. Alan Bertossi was born in London (England) in 1956. He got the Laurea Degree summa cum laude in Computer Science from the University of Pisa (Italy) in 1979. Afterwards, he worked as a System Programmer and Designer. From 1983 to 1994 he was with the University of Pisa as a Research Associate first, and later as an Associate Professor. From 1995 to 2002 he was with the University of Trento (Italy), as a Full Professor. Since 2002, he has been with the Department of Computer Science of the University of Bologna (Italy), as a Professor of Computer Science. His main research interests are the computational aspects of high-performance, parallel, VLSI, distributed, fault-tolerant, and real-time systems. He has published about 40 refereed papers on international journals, as well as several papers in international conferences, workshops, and encyclopedias. He has authored a book (on design and analysis of algorithms, in Italian) and he served as a guest coeditor for special issues of Algorithmica, Discrete Applied Mathematics, and Mobile Networks and Applications. He is a member of the editorial board of Information Processing Letters. His biography is included in the 1999 edition of Who’s Who in the World and in the 2000 edition of Who’s Who in Science and Engineering. Since 1999, he has been a scientific collaborator at the Institute of Information Sciences and Technologies of the Italian National Research Council (ISTI-CNR, Pisa, Italy). During 2001–2003, he was the national coordinator of an Italian research project on algorithms for wireless networks. Lucio Iamele received the bachelor’s degree in Computer Science from the University of Perugia (Italy) in 2004. At present, he is working at Noranet (Italy) as a system programmer and designer. M. Cristina Pinotti received the Dr. degree cum laude in Computer Science from the University of Pisa, Italy, in 1986. During 1987–1999 she was a Researcher with the National Council of Research at the Istituto di Elaborazione dell’Informazione, Pisa. From 2000–2003 she was an Associate Professor at the University of Trento. From 2004, she is a Full Professor at the University of Perugia. In 1994 and 1995 she was a Research Associate at the Department of Computers Sciences, University of North Texas, Denton, TX. In 1997 she visited the Department of Computer Science, Old Dominion University, Norfolk, VA (USA). Her research interests are in wireless networks, sensor networks, design and analysis of algorithms, data broadcasting, channel assignment problems, graph coloring, multiprocessor interconnection networks, design and analysis of parallel algorithms, parallel data structures, distributed computer arithmetic, residue number systems, VLSI special purpose architectures. She has published about 50 refereed papers on international journals, in international conferences and workshops. She has been a guest co-editor for special issues of Mobile Networks and Applications, Wireless Networks and Journal of Parallel and Distributed Computing. She is a member of the editorial board of International Journal of Parallel, Emergent and Distributed Systems.     

Efficient routing and wavelength assignment for reconfigurable WDM ring networks with wavelength converters

We consider the problem of wavelength assignment in reconfigurable WDM networks with wavelength converters. We show that for N-node P-port bidirectional rings, a minimum number of /spl lceil/PN/4/spl rceil/ wavelengths are required to support all possible connected virtual topologies in a rearrangeably nonblocking fashion, and provide an algorithm that meets this bound using no more than /spl lceil/PN/2/spl rceil/ wavelength converters. This improves over the tight lower bound of /spl lceil/PN/3/spl rceil/ wavelengths required for such rings given in if no wavelength conversion is available. We extend this to the general P-port case where each node i may have a different number of ports P/sub i/, and show that no more than /spl lceil//spl sigma//sub i/P/sub i//4/spl rceil/+1 wavelengths are required. We then provide a second algorithm that uses more wavelengths yet requires significantly fewer converters. We also develop a method that allows the wavelength converters to be arbitrarily located at any node in the ring. This gives significant flexibility in the design of the networks. For example, all /spl lceil/PN/2/spl rceil/ converters can be collocated at a single hub node, or distributed evenly among the N nodes with min{/spl lceil/P/2/spl rceil/+1,P} converters at each node.     

Architecture and design of optical channel protected ring networks

In this paper, different optical ring architectures are considered and the optical add/drop multiplexer (OADM) functional architecture is described. In addition, different aspects of ring network design and their impact on the network architecture are discussed     

On the design of node architectures and MAC protocols for optical burst-switched ring networks

Efficient multiple-token-based MAC protocols have been proposed for optical burst-switched (OBS) unidirectional ring networks using a TT-TR-based node architecture in our previous research. However, the unidirectional OBS ring network is difficult to scale to larger networks. As wavelengths accessibilities are dominated by tokens, network performance is restricted by the frequency of capturing a token. If the network is too large, it takes a long time for tokens to rotate. Thus, a destination queue may wait for a long time to be served, which results in large queuing delays and inefficiency of network resource utilization. In order to improve network efficiency and scalability for OBS ring networks using multiple tokens, this work is extended to a bidirectional ring system that uses the tunable transmitter and tunable receiver (TT-TR)-based node architecture with two pairs of transceivers, so that each queue can be served by tokens from both directions. Furthermore, two kinds of node architectures differing in sharing the two pairs of transceivers, either shared or not, are proposed. Then, two MAC protocols considering different queue scheduling algorithms are proposed for the ring network using the proposed node architectures, in order to use the network resources more efficiently. They are improved from general round-robin (GRR) and termed as half-ring round-robin (HfRR) and co-work round-robin (CoRR), respectively. The network performance of the two proposed node architectures and the two proposed MAC protocols for the networks using them as well as the network scalability are evaluated with the OPNET simulator.     

Improved heuristics for multicast routing in wireless mesh networks

Multicast is a communication technique that allows a source to transmit data to a set of recipients in an efficient manner. Therefore, the primary objective of a multicast routing protocol would be to minimize number of transmissions to conserve bandwidth. The problem of computing multicast trees with minimal bandwidth consumption is similar to Steiner tree problem and has shown to be NP-complete. So, heuristic based algorithms are suitable to approximate such bandwidth optimal trees. This paper proposes a multicast routing protocol based on minimum number of transmission trees using an heuristic approach. The simulation results show that the proposed algorithm offers better performance over existing protocols, even in the worst-case scenario when the set of multicast receivers are sparsely distributed across the network.     

DESIGN OF MULTI—SERVICE SDH NETWORKS：FORMULATION AND HEURISTICS

Multi-service SDH networks support both packet-and circuit-switched traffic.Optimal design of such a network means to guarantee the circuit connections and configure a logical packet-switched topology with lowest congestion.This letter first formulates the problem as a mixed integer linear programming,which achieves optimal solution but has high computation.Then a heuristic algorithm is proposed to yield near-optimal soultion effciently.Performance of the algorithm is verified by an example.     

Efficient complementary caching for ISP-aware networks

Internet service providers(ISPs) have taken some measures to reduce intolerable inter-ISP peer-to-peer(P2P) traffic costs,therefore user experiences of various P2P applications have been affected.The recently emerging offline downloading service seeks to improve user experience by using dedicate servers to cache requested files and provide high-speed uploading.However,with rapid increase in user population,the server-side bandwidth resource of offline downloading system is expected to be insufficient in the near future.We propose a novel complementary caching scheme with the goal of mitigating inter-ISP traffic,alleviating the load on servers of Internet applications and enhancing user experience.Both architecture and caching algorithm are presented in this paper.On the one hand,with full knowledge of P2P file sharing system and offline downloading service,the infrastructure of complementary caching is designed to conveniently be deployed and work together with existing platforms.The co-operational mechanisms among different major components are also included.On the other hand,with in-depth understanding of traffic characteristics that are relevant to caching,we develop complementary caching algorithm with respect to the density of requests,the redundancy of file and file size.Since such relevant information can be real-time captured in our design,the proposed policy can be implemented to guide the storage and replacement of caching unities.Based on real-world traces over 3 months,we demonstrate that the complementary caching scheme is capable to achieve the ’three-win’ objective.That is,for P2P downloading,over 50% of traffic is redirected to cache;for offline downloading,the average server-dependence of tasks drops from 0.71 to 0.32;for user experience,the average P2P transfer rate is increased by more than 50 KB/s.     

Ethernet ring protection for carrier ethernet networks

Ethernet technologies are rapidly gaining importance as a prevailing solution for carrier networks. Ethernet ring protection switching, defined in ITU-T Recommendation G.8032, provides a means of achieving carrier network requirements for ring network topologies. This article outlines the novel concepts in this Ethernet ring protection switching mechanism and discusses the fundamental operating principles by which the automatic protection switching (APS) protocol works. In addition, several feature enhancements in protection behavior and solutions being considered for the next phase of standardization are discussed.     

基于最小化平均分组跳的波长路由环网逻辑拓扑设计

本文提出了用混合整数线性规则（ＭＩＬＰ）进行波长路由环网的逻辑拓扑设计。对于给定的通信流量矩阵,其目标函数是最小经平均分组跳。以双向环网为例,对于不同网络结构参数的情况,进行了计算分析并给出了数值结果。对双向环网和单向环网的网络性能进行了比较分析。     

GPON-based transmission hierarchy for metro ring networks

Nowadays, almost all of metro network operators face the challenge that how to give a uniform support to multiple client networks, and meanwhile increase traffic's transmission efficiency. In an attempt to address this problem, here we first propose a gigabit passive optical network (GPON) based transmission hierarchy (GTH) for metro networks, by modifying the frame structures and application scenarios of traditional GPON technology. Then we study the GTH technology by analyzing the network operating principles and dynamic bandwidth allocation mechanisms. In order to evaluate GTH's performance, we build a simulation testbed for metro ring networks, and compare GTH with multi-service transport platform (MSTP) and technologies of packet transport network (PTN). Simulation results show that for transmission efficiency, GTH outperforms MSTP and is comparable to PTN. Furthermore, each time point of network expansion in GTH networks is further than it is in MSTP and PTN networks.     

应用于无线传感器网络的门限环签名方案

针对节点的能量损耗、通信带宽、存储空间等有严格限制的无线传感器网络环境,基于双线性配对,本文提出门限签名方案。在假设计算Diffie-Hellman问题困难的前提下,利用规约到矛盾的方法给出在随机预言机模型下的严格安全性证明。此外所提的方案具备群合作条件下应有的顽健性,可以进行多签,满足分布式并行计算等特点,非常适应于无线传感器网络。     

Efficient mobility prediction scheme for pervasive networks

This paper aims towards probabilistic reasoning and Bayesian‐based recommendations to predict the next movement of a person. The proposed model in this work observes the behavior and movement patterns of humans for a day both at home and at their office to predict their future activities. To achieve this, an efficient model has been designed that provides the probable context‐based location of a person and predicts his next movement based on his behavior on some particular day at a particular time. The proposed model allows ubiquitous services to adapt to uncertain situations in today's world using different mechanisms such as monitoring the human behavior patterns and evaluating the user preferences and profiles. A case study of the office activity chart has been provided, and based on the experimentation performed on the related events, the probability in evaluating some “N”chained events of a person in a consecutive order using the proposed model has been found to be 0.002, which infers that there are fewer chances that the person will perform the same particular sequence of events.     

Efficient link-heterogeneous multicast for wireless mesh networks

A wireless mesh network (WMN) is a type of communication network made up of wireless devices and organized in a mesh topology. Multicast is a fundamental service in WMNs because it efficiently distributes data among a group of nodes. Multicast algorithms in WMNs are designed to maximize system throughput and minimize delay in order to satisfy the end users?? requirement. Previous work has unrealistically assumed that the underlying WMN is link-homogeneous. We consider one important form of link heterogeneity: different link loss ratios, or equivalently different ETX. Different from other work addressing multicast in wireless networks, we point out that the local broadcast quality relies on the worst involved link. We model different link loss ratios by defining a new graph theory problem, Heterogeneous Weighted Steiner Connected Dominating Set (HW-SCDS), on an edge-weighted directed graph, where the edge weights model ETX, the reciprocal of link loss ratios. We minimize the number of transmissions in a multicast by computing a minimum HW-SCDS in the edge-weighted graph. We prove that HW-SCDS is NP-hard and devise a greedy algorithm for it. To improve the effectiveness of our algorithm, we design a dedicated channel assignment algorithm. Simulations show that our algorithm significantly outperforms the current best WMN multicast algorithm by both increasing throughput and reducing delay.     

Efficient fair queueing algorithms for packet-switched networks

Although weighted fair queueing (WFQ) has been regarded as an ideal scheduling algorithm in terms of its combined delay bound and proportional fairness properties, its asymptotic time complexity increases linearly with the number of sessions serviced by the scheduler, thus limiting its use in high-speed networks. An algorithm that combines the delay and fairness bounds of WFQ with O(1) timestamp computations had remained elusive so far. In this paper we present two novel scheduling algorithms that have O(1) complexity for timestamp computations and provide the same bounds on end-to-end delay and buffer requirements as those of WFQ. The first algorithm, frame-based fair queueing (FFQ), uses a framing mechanism to periodically recalibrate a global variable tracking the progress of work in the system, limiting any short-term unfairness to within a frame period. The second algorithm, starting potential based fair queueing (SPFQ), performs the recalibration at packet boundaries, resulting in improved fairness while still maintaining the O(1) timestamp computations. Both algorithms are based on the general framework of rate-proportional servers (RPSs) introduced by Stiliadis and Varma (see ibid., vol.6, no.2, p.164-74, 1998). The algorithms may be used in both general packet networks with variable packet sizes and in asynchronous transfer mode (ATM) networks     

Amplifier placement methods for metropolitan WDM ring networks

This paper presents two new amplifier placement methods to minimize the number of amplifiers in metropolitan wavelength-division-multiplexing (WDM) rings based on integer programming techniques. The first method describes the amplifier placement problem exactly and uses a nonlinear programming solver to obtain a solution. The second method approximates some requirements in the problem and employs a linear programming solver to derive the amplifier placement solution. A new amplifier placement method for self-healing WDM rings is also reported in this paper. The new method is based on iteratively solving an amplifier placement problem for a ring network under different link failure scenarios. The solution provides a minimum number of amplifiers required to operate the self-healing ring under a normal or any single-link or single-node failure conditions.     

Optical cross-connect structures for interleaved multiwavelengthbidirectional ring networks

Novel bidirectional optical cross-connect structures using a single arrayed waveguide grating router and tunable fibre Bragg gratings have been proposed for interleaved multiwavelength ring networks. In the proposed structures, each wavelength channel is independently switched by tuning the centre wavelength of the gratings. The feasibility of the cross-connectors has been experimentally demonstrated. A homodyne crosstalk less than -26 dB and a backscattering suppression ratio of -35 dB have been obtained     

SONET ring applications for survivable fiber loop networks

Synchronous optical network (SONET) self-healing rings (SHR) are studied in the loop environment. SONET SHR architectures for loop feeder networks are discussed, focusing on three possible dual central office (CO) architectures for fiber loop networks, using SONET SHRs to reduce network costs and provide network service survivability. These architectures reflect an integrated planning concept for SONET networks that eliminates the boundary between the access network and the inter-office network. It is shown that the use of SONET SHRs makes it easy to evolve to a protected dual CO access architecture. Economic and survivability studies are discussed. The economic studies show that using the ring approach yields significant advantages over the traditional diverse protection approach in terms of cost and survivability, especially for the dual CO architectures     

WDM光环网的几种保护倒换方案

WDM光网络技术的应用正迅速地提升传输速率与带宽,不断地促进着电信业的发展。WDM光网络的可靠性与生存性变得日益重要。目前的研究热点是在网络的生存性和可重构性方面开发类似于SONET/SDH环网保护的WDM光环网结构,使之具备在经受各种网络故障后能够维持可接受的业务质量的能力。与SDH光环网相比,WDM光环网具有自身的特点：光层的保护与恢复时间比SDH电层快,光层恢复可靠性高,光层恢复成本低,光层保护支持多协议、多业务恢复等等。WDM光网络在传统的传送网络的电通道层和物理层之间引入光层。光层由光通道层、光复用段层…