Cross-layer routing in clustered optical networks

Physical layer impairment aware routing algorithms have been proposed for optical transparent networks in order to calculate the feasibility of dynamically establishing an optical path when no regeneration is used. The benefit of node clustering in optical networks, regarding routing with physical layer impairment awareness, is investigated under the CANON network architecture where regenerators are conveniently placed and routing is confined among a small subset of nodes. The CANON architecture exhibits enhanced blocking performance, high resource utilisation and adequate physical performance; hence, it can serve Quality of Service.     

A novel method to evaluate clustering algorithms for hierarchical optical networks

The routing issues in multi-layer and multi-domain optical networks have drawn much attention in current research. With the introduction of the path computation element, routes can be calculated more efficiently in multi-domain optical networks. However, the optimal degree of routing approach in multi-layer and multi-domain optical networks is also determined by the clustering algorithms deployed for construction of hierarchical networks. Therefore, it is important to investigate the way to evaluate the impact of the clustering algorithm on the routing approach (e.g., blocking probability) in optical networks with dynamic traffic, which has not been studied sufficiently. In this paper, a novel method to describe and evaluate the clustered structures generated by different clustering algorithms for hierarchical optical networks is proposed. This method deploys a novel evaluation metric that represents blocking probability of clustered optical networks, so it can be used as guidelines for designing clustered structures. Besides theoretical analysis, simulations are carried out on different network topologies and clustered types to validate the effectiveness of the method presented.     

Performance Evaluation of an All-Optical ShuffleNet using Optical Buffering and Deflection Routing

All-optical multihop networks, where the data portion of a packet is maintained in an optically encoded format from the source to the destination, can be achieved by augmenting optical switching nodes with optical buffering. Topologically, the ShuffleNet network is a strong contender for implementing such networks ranging from cluster networks to metropolitan area networks. The performance of a regular multihop network whose nodes are augmented with optical buffering and use deflection routing is evaluated. Using the ShuffleNet network as an example, we show that performance, in terms of throughput, average delay, and loss probability, can be improved as multiple fiber delay loops are added for a large range of network parameters. We then compare the performance of ShuffleNet with the Manhattan Street networks with similar features.     

K-means clustering-based data detection and symbol-timing recovery for burst-mode optical receiver

Burst-mode receivers are key components of optical transmission systems, including passive optical networks, and have received much attention in recent years. We present new, efficient methods for burst optical signal detection in burst-mode data transmission using a modified K-means clustering technique. We also develop a data-aided feedforward symbol-timing recovery method based on a polynomial interpolation and maximum-likelihood estimation theory. A performance criterion considering the error caused by the interpolation approximation is derived for this method. The proposed detection and timing recovery approaches can be implemented effectively and rapidly; therefore, they are very suitable for burst-mode receivers. We also provide some numerical examples to demonstrate the performance of the proposed methods.     

A Framework for Evaluating the Performance of Cluster Algorithms for Hierarchical Networks

Table-driven routing algorithms in flat networks have the scalability problem due to the need for global topology updates. To reduce update cost, networks are hierarchically organized. Clustering algorithms organize flat networks into hierarchical networks. One important problem, which has not been adequately addressed so far, is to evaluate how good a clustering algorithm is. In other words, it is useful to know what the desired properties of hierarchical networks are. In this paper, we address this issue by considering the routing update cost, which can be measured by the total routing table size and the variance of cluster size distribution. We provide a set of desired properties of clustering algorithms. Applying these properties to the cluster structure generated by an algorithm, we can determine how good a clustering algorithm is. Specifically, we discuss how to choose appropriate number of hierarchy levels, number of clusters, and cluster size distribution, such that the topology update cost is minimized. The desired properties obtained from the analysis can be used as guidelines in the design of clustering algorithms for table-driven hierarchical networks. We apply the idea developed in this paper to evaluate three routing algorithms, namely the lowest ID algorithm, the maximum degree algorithm, and the variable degree clustering algorithm. We show how the variable degree clustering algorithm, which takes into account these desired properties, improves routing performance.     

Optimal search performance in unstructured peer-to-peer networks with clustered demands

This paper derives the optimal search time and the optimal search cost that can be achieved in unstructured peer-to-peer networks when the demand pattern exhibits clustering (i.e. file popularities vary across the set of nodes in the network). Clustering in file popularity patterns is evident from measurements on deployed peer-to-peer file sharing networks. In this paper, we provide mechanisms for modeling clustering in file popularity distributions and the consequent non-uniform distribution of file replicas. We derive relations that show the effect of the number of replicas of a file on the search time and on the search cost for a search for that file for the clustered demands case in such networks for both random walk and flooding search mechanisms. The derived relations are used to obtain the optimal search performance for the case of flooding search mechanisms. The potential performance benefit that clustering in demand patterns affords is captured by our results. Interestingly, the performance gains are shown to be independent of whether the search network topology reflects the clustering in file popularity (the optimal file replica distribution to obtain these performance gains, however, does depend on the search network topology)     

Analytical study of crosstalk propagation in all-optical networks using perturbation theory

The performance of current optical networks is inherently limited by the speed of electronic components and, in particular, by electronic switches. A new generation of optical networks, referred to as all-optical networks, overcomes this limitation by switching data entirely optically using all-optical crossconnects (OXCs). However, all-optical networks are prone to phenomena that are unknown to current optical networks with electrical regeneration: OXCs are subject to optical leaks, called crosstalk, resulting in unwanted components being added to transmitted signals, and this crosstalk is transmitted over very long paths without any signal regeneration. In this paper, we consider the interplay between fiber nonlinearity and crosstalk signals over long distances as the source of performance degradation, measured in terms of Q factor. We present an analytical crosstalk model for all-optical networks and give expressions for the performance degradation resulting from the joint propagation of a signal [using a continuous-wave (CW) assumption and perturbation theory] and crosstalk in large networks. Analytical calculations required by this model are shown to be much less computationally intensive than simulations. Simulations are carried out to validate our analytical model and good agreement is found between the analytical model and simulations for wide ranges of parameters.     

多域光网络生存性的关键技术研究

多域光网络的生存性作为衡量网络性能优劣的关键指标,与实际网络应用的关系最为密切,是当前迫切需要解决的关键问题;聚焦高速化、多业务化驱动的多域光网络环境下的生存性技术.基于光网络的多业务、分布式控制的特性,分析了多域光网络生存性机制的研究现状及面临的挑战;给出了一种针对多域光网络生存性问题的分类方法;结合多域光网络对生存性的需求,对相关关键技术进行了归类和研究,并指明了进一步研究的方向和重点.     

FULL-RCMA: a high utilization EPON

This paper proposes an alternate solution for Ethernet passive optical networks. Our solution uses a novel protocol named full utilization local loop request contention multiple-access protocol to efficiently provide communications in passive optical networks. We study the physical layer implementation, as well as medium access control (MAC) layer protocol performance to illustrate the feasibility and benefit of our solution. The performance studies show that the MAC protocol is capable of offering 95% channel utilization under heavy load conditions. The performance results also indicate that delivery of multimedia traffic with a high quality-of-service can be achieved with our solution.     

Transmission Range-Aware Clustering for Green Cognitive Radio Ad Hoc Networks

The absence of network infrastructure and opportunistic spectrum access in cognitive radio ad hoc networks (CRAHNs) results in connectivity and stability problems. Clustering is known as an effective technique to overcome this problem. Clustering improves network performance by implementing a logical network backbone. Therefore, how to efficiently construct this backbone among CRAHNs is of interest. In this paper, we propose a new clustering algorithm for CRAHNs. Moreover, we model a novel cluster head selection function based on the channel heterogeneity in term of transmission ranges. To the best of our knowledge, this is the first attempt to model the channel heterogeneity into the clustering formation in cognitive radio networks. Simulation results show that the performance of clustering is significantly improved by the channel heterogeneity considerations.     

Traffic grooming in mesh WDM optical networks - performance analysis

Traffic grooming is an important task in interworking between the wavelength-division multiplexing (WDM) optical network that supplies "pipes" at the wavelength granularity, and the attached client networks that usually require connections of subwavelength granularity. The focus of this paper is to conduct performance analysis of grooming dynamic client traffic in WDM optical networks with a mesh topology. This paper first briefly introduces the traffic grooming problem in WDM optical networks and the issues related to performance analysis. It then develops two link blocking models, an exact model based on the stochastic knapsack problem and an approximation model based on an approximate continuous time Markov chain (CTMC). The end-to-end performance analysis is conducted using the reduced load approximation. The result obtained from analysis is shown to be accurate compared with the numerical result obtained from simulation.     

无标度网络的局部搜索策略

基于最小聚类系数搜索和贪婪算法在搜索中的优点,根据BA无标度网络的结构特性,以最小聚类系数和度量距离两个影响搜索性能的参数,设计出最小聚类系数最小距离搜索策略。并通过仿真实验对最小聚类系数最小距离搜索策略、最小聚类系数搜索策略、贪婪算法和随机游走搜索策略的性能进行对比。理论分析与仿真结果均表明,最小聚类系数最小距离搜索策略在BA无标度网络模型上能取得较好地搜索效果。     

Architectures and performance of optical packet switching nodes for IP networks

As new bandwidth-hungry Internet protocol (IP) services are demanding more and more capacity, transport networks are evolving to provide a reconfigurable optical layer in order to allow fast dynamic allocation of wavelength-division-multiplexing (WDM) channels. To achieve this goal, optical packet-switched systems seem to be strong candidates as they allow a high degree of statistical resource sharing, which leads to an efficient bandwidth utilization. In this paper, we propose an architecture for optical packet-switched transport networks, together with an innovative switching node structure based on the concept of per-packet wavelength routing. The traffic performance of such node when loaded by a typical IP traffic is evaluated through computer simulation; packet loss probability and average delay performance are shown for various load conditions.     

Effects of Optical Buffering on the Performance of Manhattan Street Networks

Multihop networks are strong candidates for the implementation of high-speed networks, ranging from back-plane networks for cluster computing to metropolitan-area networks. Besides using deflection routing for contention resolution, optical buffering may be used to enhance the performance of optical multihop networks and to reduce or even eliminate the need for optical-electrical conversions. The enhancements obtained by augmenting traditional MSN (Manhattan Street Networks) with optical buffering are evaluated. The MSN considered here is based on a novel 6 × 6 optical switching node with up to two fiber delay loops. Impact of the parameters associated with optical buttering, such as the number of delay loops and the loop length, are discussed in detail.     

一种传感器网络跨层能量优先成簇算法

文中提出CLEEC跨层能量优先成簇算法,基于节点剩余能量来选举簇头节点,使网络能量均匀消耗,延长网络的生存时间.模拟实验结果显示,与现有的典型成簇方案相比,新的成簇算法在传感器网络下提供了更长的网络生存时间和更大的网络吞吐量.     

Hybrid hierarchical optical networks

Hybrid hierarchical optical cross-connects enhance the performance/cost ratio of optical networks by providing transparent (optical) switching of sets of wavelengths (wavebands) in addition to opaque (electrical) switching of individual wavelengths. As network bandwidth gets cheaper, and the performance bottleneck moves to switching nodes, these systems provide an attractive scalable solution for next-generation optical networks. We describe key technological components (including flexible nonuniform wavebands) of hybrid hierarchical optical cross-connects and discuss their performance/cost implications.     

Absolute QoS differentiation in optical burst-switched networks

A number of schemes have been proposed for providing quality-of-service (QoS) differentiation in optical burst-switched (OBS) networks. Most existing schemes are based on a relative QoS model in which the service requirements for a given class of traffic are defined relative to the service requirements of another class of traffic. In this paper, we propose an absolute QoS model in OBS networks which ensures that the loss probability of the guaranteed traffic does not exceed a certain value. We describe two mechanisms for providing loss guarantees at OBS core nodes: an early dropping mechanism, which probabilistically drops the nonguaranteed traffic, and a wavelength grouping mechanism, which provisions necessary wavelengths for the guaranteed traffic. It is shown that integrating these two mechanisms outperforms the stand-alone schemes in providing loss guarantees, as well as reducing the loss experienced by the nonguaranteed traffic. We also discuss admission control and resource provisioning for OBS networks, and propose a path clustering technique to further improve the network-wide loss performance. We develop analytical loss models for the proposed schemes and verify the results by simulation.     

光层性能监测

光层监测是下一代光网络自动控制的关键方法,除实时反应和对邻近信道的保护外,在维持有效的高服务质量(QoS)时,光性能监测也确保了构建和控制复杂拓扑网络的能力.文章分析了在光层里光参数变化对光信号性能的影响以及光信号性能监测选项的评估,并对光信道性能监测设备(OCPM)进行了简要描述.     

A game theoretical approach to clustering of ad-hoc and sensor networks

Game theory has been used for decades in fields of science such as economics and biology, but recently it was used to model routing and packet forwarding in wireless ad-hoc and sensor networks. However, the clustering problem, related to self-organization of nodes into large groups, has not been studied under this framework. In this work our objective is to provide a game theoretical modeling of clustering for ad-hoc and sensor networks. The analysis is based on a non-cooperative game approach where each sensor behaves selfishly in order to conserve its energy and thus maximize its lifespan. We prove the Nash Equilibria of the game for pure and mixed strategies, the expected payoffs and the price of anarchy corresponding to these equilibria. Then, we use this analysis to formulate a clustering mechanism (which we called Clustered Routing for Selfish Sensors??CROSS), that can be applied to sensor networks in practice. Comparing this mechanism to a popular clustering technique, we show via simulations that CROSS achieves a performance similar to that of a very popular clustering algorithm.