A heuristic algorithm for lightpath scheduling in next-generation WDM optical networks

We study the routing and wavelength assignment (RWA) problem of scheduled lightpath demands (SLDs) in all-optical wavelength division multiplexing networks with no wavelength conversion capability. We consider the deterministic lightpath scheduling problem in which the whole set of lightpath demands is completely known in advance. The objective is to maximize the number of established lightpaths for a given number of wavelengths. Since this problem has been shown to be NP complete, various heuristic algorithms have been developed to solve it suboptimally. In this paper, we propose a novel heuristic RWA algorithm for SLDs based on the bee colony optimization (BCO) metaheuristic. BCO is a newborn swarm intelligence metaheuristic approach recently proposed to solve complex combinatorial optimization problems. We compare the efficiency of the proposed algorithm with three simple greedy algorithms for the same problem. Numerical results obtained by numerous simulations performed on the widely used realistic European Optical Network topology indicate that the proposed algorithm produces better-quality solutions compared to those obtained by greedy algorithms. In addition, we compare the results of the BCO–RWA–SLD algorithm with four other heuristic/metaheuristic algorithms proposed in literature to solve the RWA problem in the case of permanent (static) traffic demands.     

An Algorithm for Traffic Grooming in WDM Optical Mesh Networks with Multiple Objectives

This paper studies a traffic grooming in wavelength-division multiplexing (WDM) mesh networks for the SONET/SDH streams requested between node pairs. The traffic could be groomed at the access node before converting to an optical signal carried in the all-optical network. We design a virtual topology with a given physical topology to satisfy multiple objectives and constraints. The grooming problem of a static demand is considered as an optimization problem. The traditional algorithms found in the literatures mostly focus on a single objective either to maximize the performance or to minimize the cost. We propose a multi-objective evolutionary algorithm to solve a grooming problem that optimizes multiple objectives all together at the same time. In this paper we consider the optimization of three objectives: maximize the traffic throughput, minimize the number of transceivers, and minimize the average propagation delay or average hop counts. The simulation results show that our approach is superior to an existing heuristic approaches in an acceptable running time.     

An algorithm for optimal assignment of a wavelength in a tree topology and its application in WDM networks

In this paper, we present a polynomial time algorithm that gives an optimal solution to the routing and wavelength assignment (RWA) problem in a tree topology. One of the major design issues in wavelength-division multiplexed networks is the assignment of the limited number of wavelengths among network stations so that greater capacity can be achieved. The problem of RWA is known to be NP-hard problem. Many researchers have tackled the problem of RWA with a number of efficient heuristic algorithms. This paper presents an algorithm that optimally assigns a single wavelength to maximize one-hop traffic in a tree topology. The algorithm uses dynamic programming and is shown to be optimal with a time complexity of O(N/sup 4/). We also propose a heuristic scheme to use our optimal algorithm for wavelength assignment in a general graph. The heuristic works on the tree subgraphs of a given graph and the remaining spare wavelengths can be assigned with an existing RWA policy.     

Design Method of Logical Topologies with Quality of Reliability in WDM Networks

As the bandwidth capacity of WDM networks continues to grow rapidly,traffic loss caused by a failure of network components is becoming unacceptable. To prevent such traffic loss and thus enhance network reliability, a protection method that prepares backup lightpaths for each working path is now being developed. In this paper, we first introduce the concept of QoR (quality of reliability), which is a realization of QoS with respect to the reliability needed in a WDM network. We define QoR in terms of the recovery time from when a failure occurs to when traffic on the affected primary lightpath is switched to the backup lightpath. After that, we propose a heuristic algorithm that can be used to design a logical topology that satisfies the QoR requirement for every node pair. The objective is to minimize the number of wavelengths needed for a fiber in the logical topology to carry the traffic with the required QoR. We compare this algorithm with two existing algorithms and show that it enables more effective use of wavelength resources; with the proposed algorithm, up to 25% fewer wavelengths are needed than with the other algorithms.     

Algorithms for the global design of WDM networks including the traffic grooming

In this paper, we propose a model and algorithms for the global design problem of wavelength division multiplexing (WDM) networks including the traffic grooming. This problem consists in finding the number of fibres between each pair of nodes (i.e. the physical topology), finding the number of transponders at each node, choosing the set of lightpaths (i.e. the virtual topology), routing these lightpaths over the physical topology and, finally, grooming and routing the traffic over the lightpaths. Since this problem is NP-hard, we propose two heuristic algorithms and a tabu search metaheuristic algorithm to find solutions for real-size instances within a reasonable amount of computational time.     

Constrained light-tree design for WDM mesh networks with multicast traffic grooming

Multicast applications such as IPTV, video conferencing, telemedicine and online multiplayer gaming are expected to be major drivers of Internet traffic growth. The disparity between the bandwidth offered by a wavelength and the bandwidth requirement of a multicast connection can be tackled by grooming multiple low bandwidth multicast connections into a high bandwidth wavelength channel or light-tree. Light-trees are known to be especially suited for networks that carry ample multicast traffic. In this paper, we propose new algorithms to address the problem of multicast traffic grooming. In particular, an Integer Linear Programming (ILP) formulation is proposed for optimal assignments of hop constrained light-trees for multicast connections so that network throughput can be maximized. Hop constrained light-trees improve the scalability of the approach by reducing the search space of the ILP formulation. Since solving the ILP problem is very time consuming for realistically large networks, we are motivated to propose a heuristic algorithm with a polynomial complexity, called Dividable Light-Tree Grooming (DLTG) algorithm. This algorithm is based on grooming traffic to constrained light-trees and also divides a light-tree to smaller constrained light-trees on which traffic is groomed for better resource utilization. Simulations show that the proposed DLTG heuristic performs better than other algorithms. It achieves network throughputs which are very close to the ILP formulation results, but with far lower running times.     

IPoverWDM光网络中基于滑动调度业务模型的节能业务量疏导算法研究(英文)

In this paper,we investigate on the problem of energy-efficient traffic grooming under sliding scheduled traffic model for IP over WDM optical networks,so as to minimize the total energy consumption of the core network.We present a two-layer auxiliary graph model and propose a new energyefficient traffic grooming heuristic named Two-Dimension Green Traffic Grooming(TDGTG) algorithm,which takes both space and time factors into consideration for network energy efficiency.We compare our proposed TDGTG algorithm with the previous traffic grooming algorithms for scheduled traffic model in terms of total energy consumption and blocking probability.The simulation results in three typical carrier topologies show the efficiency of our proposed TDGTD algorithm.     

Minimizing the Number of Switchings in an SS/TDMA System

In this paper, we investigate the problem of constructing a TDMA frame for a multibeam satellite system. Our objective is to permit the transmission of a given pattern of traffic, while ensuring that the number of times that the on-board switch needs to be reconfigured is minimized. We find that the underlying optimization problem is computationally intractable, but go on to suggest an efficient heuristic algorithm which we validate through experiments on randomly generated traffic patterns.     

Optimization for Fault Localization in All-Optical Networks

Fault localization is a critical issue in all-optical networks. The limited-perimeter vector matching (LVM) protocol is a novel fault-localization protocol proposed for localizing single-link failures in all-optical networks. In this paper, we study the optimization problems in applying the LVM protocol in static all- optical networks. We consider two optimization problems: one is to optimize the traffic distribution so that the fault-localization probability in terms of the number of localized links is maximized, and the other is to optimize the traffic distribution so that the time for localizing a failed link is minimized. We formulate the two problems into an integer linear programming problem, respectively, and use the CPLEX optimization tool to solve the formulated problems. We show that by optimizing the traffic distribution the fault-localization probability can be maximized and the fault-localization time can be minimized. Moreover, a heuristic algorithm is proposed to evaluate the optimization results through simulation experiments.     

Hop count based optimization of Bluetooth scatternets

In the past five years Bluetooth scatternets were one of the most promising wireless networking technologies for ad hoc networking. In such networks, mobility together with the fact that wireless network nodes may change their communication peers in time, generate permanently changing traffic flows. Thus, forming an optimal scatternet for a given traffic pattern may be not enough, rather a scatternet that best supports traffic flows as they vary in time is required.In this paper we study the optimization of scatternets through the reduction of communication path lengths. After demonstrating analytically that there is a strong relationship between the communication path length on one hand and throughput and power consumption on the other hand, we propose a novel heuristic algorithm suite capable of dynamically adapting the network topology to the existing traffic connections between the scatternet nodes. The periodic adaptation of the scatternet topology to the traffic connections enables the routing algorithms to identify shorter paths between communicating network nodes, thus allowing for more efficient communications. We evaluate our approach through simulations, in the presence of dynamic traffic flows and mobility.     

Adaptive load-balancing in WDM mesh networks with performance guarantees

In nowadays, wavelength-division multiplexing (WDM) networks, on the one hand, increasingly more users expect the network to provide high-priority QoS services demanding no congestion and low latency. On the other hand, it is significantly more difficult for network operators to forecast future traffic demands, as the packet traffic running over WDM networks fluctuates over time for a variety of reasons. Confronted with a rough understanding of traffic patterns as well as the increasing number of time-sensitive applications, most networks today are grossly over-provisioned. Thus, designing cost-effective WDM networks in an uncertain traffic environment, which includes network planning and robust routing, is both an important and a challenging task. In this paper, we explore adaptive load-balancing to investigate the problems of network planning and robust routing for WDM mesh networks under varying traffic matrices. We first propose an efficient heuristic algorithm called Maximizing Network Capability (MNC) to provision congestion-free and cost-effective WDM networks based on load-balancing to deal with traffic uncertainty. Then, a novel traffic grooming algorithm called Adding Direct Traffic (ADT) is proposed to implement robust routing with partial traffic information. Finally, we demonstrate by simulation that MNC consumes less resources than previous methods and performs quite close to the optimal solution, while ADT achieves the desirable performance in delay, jitter (delay variation), and throughput compared with existing robust routing and traffic grooming algorithms.     

Optimal Allocation of Limited Optical-Layer Resources in WDM Networks Under Static Traffic Demand*

In this paper, four heuristic algorithms for the optimal allocation of limited optical-layer resources in WDM networks (virtual-topology optimization by routing and wavelength assignment) under static traffic demand are compared. While some previous papers assumed that all connection requests must be necessarily satisfied, in this work algorithms are studied aiming at comparing their ability in minimizing both the usage of optical-layer resources and the number of connection requests that cannot be allocated. This paper reports the results obtained on a 13-nodes simplified topology of the pan-European optical transport network designed in the COST239 Project. The results of a few hundreds simulations with different traffic matrices have been gathered, by considering separately the cost of resources allocated and the percentage of rejected connections. One algorithm resulted best performing, because in most tests it allocated the lowest cost of optical-layer resources. On the other hand, the four algorithms exhibited comparable performance with respect to the percentage of rejected connections.     

一种新的ISAR距离对齐算法

距离对齐是逆合成孔径雷达(ISAR)成像处理中的或对齐精度不够高,或运算效率过低,无法满足ISAR实时成像的要求.由于距离对齐算法本质上是一种优化方法,基于优化原理,将启发式方法与搜索法相结合,提出了一种新的距离对齐算法.该算法结合使用频域法和累积互相关法,具体分两步实现:首先利用频域法进行粗对齐,然后将第一步得到的结果作为启发式信息进行累积互相关,大大减小了其搜索范围,得到了精确的距离对齐效果.通过将新算法与其他算法的运算量进行分析比较,结果表明该算法运算效率较高.而对实测数据的成像处理结果证明该算法具有良好的对齐精度.这说明新算法在效率和性能上达到了良好的平衡,适合于ISAR实时成像.     

New vehicle sequencing algorithms with vehicular infrastructure integration for an isolated intersection

Traffic congestion at intersections is one of the main issues to be addressed by today??s traffic management schemes. Countless efforts have been made directed toward efficiently improving the traffic situation at intersections. In this paper, we present a new traffic control strategy for an isolated intersection, in which there are no more traffic lights. Instead, vehicles embedded with In-Vehicle Information Systems communicate with the center Infrastructure to obtain their access time to the intersection. We mainly focus on the vehicle sequencing algorithms with the analysis of received information. A Branch and Bound algorithm and a heuristic are proposed to evacuate the approaching vehicles as soon as possible. Structural properties of the problem are carefully investigated to simplify the search procedure of an optimal passing sequence. Computational experiments and simulations in evacuation time, average waiting time and average queue size demonstrate the performance gain obtained when using the proposed schemes.     

Panda－Map：真值表结构FPGA的性能驱动的逻辑映射优化算法

基于真值表ＴＬＵ（ＴａｂｌｅｏｆＬｏｏｋ－Ｕｐ）结构的ＦＰＧＡ（ＦｉｅｌｄＰｒｏｇｒａｍｍａｂｌｅＧａｔｅＡｒｒａｙ）在各种ＦＰＧＡ结构中占有越来越重要的地位。但迄今为止各种针对ＴＬＵＦＰＧＡ的逻辑映射算法都无法实现对面积和延迟的折衷考虑：不是只考虑面积优化，就是只考虑延迟优化，本文提出并实现了进行面积和延迟折衷的性能驱动的逻辑映射优化算法：Ｐａｎｄａ－Ｍａｐ，它是对面积驱动的Ｃｈｏｒｔｌｅ－ｃｒｆ［７］及延迟驱动的Ｃｈｏｒｔｌｅ－ｄ［６］的较大改进，并且Ｐａｎｄａ－Ｍａｐ采用了一种新的启发性算法将组合网络分割成若干个单输出子网络。     

Dynamic traffic grooming algorithms for reconfigurable SONET over WDM networks

The emergence of wavelength-division multiplexing (WDM) technology provides the capability for increasing the bandwidth of synchronous optical network (SONET) rings by grooming low-speed traffic streams onto different high-speed wavelength channels. Since the cost of SONET add-drop multiplexers (SADM) at each node dominates the total cost of these networks, how to assign the wavelength, groom the traffic, and bypass the traffic through the intermediate nodes has received a lot of attention from researchers recently. Moreover, the traffic pattern of the optical network changes from time to time. How to develop dynamic reconfiguration algorithms for traffic grooming is an important issue. In this paper, two cases (best fit and full fit) for handling reconfigurable SONET over WDM networks are proposed. For each approach, an integer linear programming model and heuristic algorithms (TS-1 and TS-2, based on the tabu search method) are given. The results demonstrate that the TS-1 algorithm can yield better solutions but has a greater running time than the greedy algorithm for the best fit case. For the full fit case, the tabu search heuristic yields competitive results compared with an earlier simulated annealing based method and it is more stable for the dynamic case.     

Energy-Aware Broadcast Trees in Wireless Networks

In this paper we address the problem of broadcasting in wireless networks, so that the power consumed by any node is as small as possible. This approach is motivated by the fact that nodes in such networks often use batteries and, hence, it is important to conserve energy individually, so that they remain operational for a long time. We formulate the problem as a lexicographic node power optimization one. The problem is in general NP-complete. We provide an optimal algorithm which runs in polynomial time in certain cases. We also provide a heuristic algorithm whose performance relative to the optimal one is fairly satisfactory. We next show that these algorithms can also be used to solve the problem of broadcasting so that the residual energy of any node after the broadcast process is as large as possible. Finally, we discuss the issues of implementing the above algorithms distributively, as well as their multicast extensions.     

Traffic grooming algorithms for reducing electronic multiplexingcosts in WDM ring networks

We develop traffic grooming algorithms for unidirectional SONET/WDM ring networks. The objective is to assign calls to wavelengths in a way that minimizes the total cost of electronic equipment [e.g., the number of SONET add/drop multiplexers (ADM's)]. We show that the general traffic grooming problem is NP-complete. However, for some special cases we obtain algorithms that result in a significant reduction in the number of ADM's. When the traffic from all nodes is destined to a single node, and all traffic rates are the same, we obtain a solution that minimizes the number of ADM's. In the more general case of all-to-all uniform frame we obtain a lower bound on the number of ADM's required, and provide a heuristic algorithm that performs closely to that bound. To account for more realistic traffic scenarios, we also consider distance dependent traffic, where the traffic load between two nodes is inversely proportional to the distance between them, and again provide a nearly optimal heuristic algorithm that results in substantial ADM savings. Finally, we consider the use of a hub node, where traffic can be switched between different wavelength, and obtain an optimal algorithm which minimizes the number of ADM's by efficiently multiplexing and switching the traffic at the hub. Moreover, we show that any solution not using a hub can be transformed into a solution with a hub using fewer or the same number of ADM's     

Evaluation of algorithms for efficient partitioning and scheduling of data bursts in satellite communications

We evaluate four scheduling algorithms for satellite communications that use the Time Division Multiple Access methodology. All the algorithms considered are based on the open‐shop model. The open‐shop model is suitably represented or modified to exploit some existing algorithms to solve the satellite communication problem. In the first two algorithms, namely pre‐emptive scheduling with no intersatellite links and greedy heuristics with two intersatellite links, a (traffic) matrix representation of the open‐shop model is used to get a near optimal schedule. In the next two algorithms, generalized heuristic algorithm and the branch and bound algorithm, the open‐shop model is modified to accommodate the inter‐satellite link and this modified open‐shop model is used to solve for a near optimal schedule. The basic methodology of all the algorithms are briefly described and their performance was evaluated through extensive simulations. The performance criteria to evaluate the algorithms are—run time of the algorithms, schedule lengths, and optimality of the algorithm against theoretical bounds. Three of the above‐mentioned algorithms are evaluated by comparing the performance criteria under similar conditions. Optimal branch and bound algorithm is not evaluated due to its high complexity. The general heuristic algorithm is found to give a good trade off between computation time and optimality. The computation time is comparable with the pre‐emptive scheduling algorithm and greedy heuristic algorithm and the schedule length achieved is near to the lower bound value. Copyright © 2005 John Wiley & Sons, Ltd.     

Waveband Switching for Dynamic Traffic Demands in Multigranular Optical Networks

Waveband switching (WBS) in conjunction with multigranular optical cross-connect (MG-OXC) architectures can reduce the cost and complexity of OXCs. In this paper, we study the performance of different MG-OXC architectures under dynamic traffic. In the case with online incremental traffic, we compare two MG-OXC architectures in terms of the blocking probability of new lightpath requests and study the impact of port counts and traffic loads. We develop an online integer linear programming model (On-ILP), which minimizes the number of used ports and the request blocking probability, given a fixed number of wavelengths and MG-OXC architecture. The On-ILP optimizes the routing of new lightpaths so as to maximize lightpath grouping and reduce the port count given that existing traffic cannot be rearranged. We also propose a new efficient heuristic algorithm, called maximum overlap ratio (MOR) to satisfy incremental traffic and compare it with the On-ILP, first-fit, and random-fit algorithms. Our results and analysis indicate that using WBS with MG-OXCs can reduce the size (and, hence, the cost) of switching fabrics compared to using ordinary OXCs. Based on the results and observations in the incremental traffic case, we further study the performance of a particular MG-OXC architecture under fully dynamic or fluctuating traffic. Our simulations show that the proposed heuristic algorithm waveband assignment with path graph, which groups wavelengths to bands and uses wavelength converters efficiently under fluctuating traffic, significantly outperforms other heuristic algorithms.