Performance analysis of multi-fiber WDM network with limited-range wavelength conversion

Wavelength routed optical networks have emerged as a technology that can effectively utilize the enormous bandwidth of the optical fiber. Wavelength conversion technology and wavelength converters play an important role in enhancing fiber utilization and in reducing the overall call blocking probability of the network. In this paper, we develop a new analytical model to calculate the average blocking probability in multi-fiber link networks using limited-range wavelength conversion. Based on the results obtained, we conclude that the proposed analytical model is simple and yet can effectively analyze the impact of wavelength conversion ranges and number of fibers on network performance. Also a new heuristic approach for placement of wavelength converters to reduce blocking probabilities is explored. Finally, we analyze network performance with the proposed scheme. It can be observed from numerical simulations that limited-range converters placed at a few nodes can provide almost the same blocking probability as full range wavelength converters placed at all the nodes. We also show that being equipped with a multi-fiber per-link has the same effect as being equipped with the capability of limited-range wavelength conversion. So a multi-fiber per-link network using limited-range wavelength conversion has similar blocking performance as a full wavelength convertible network. Since a multi-fiber network using limited-range wavelength conversion could use fewer converters than a single-fiber network using limited range wavelength conversion and because wavelength converters are today more expensive than fiber equipment, a multi-fiber network in condition with limited-range wavelength conversion is less costly than a single-fiber network using only limited-range wavelength conversion. Thus, multi-fiber per-link network using limited-range wavelength conversion is currently a more practical method for all optical WDM networks. Simulation studies carried out on a 14-node NSFNET, a 10-node CERNET (China Education and Research Network), and a 9-node regular mesh network validate the analysis.     

Adaptive alternate routing in WDM networks and its performance tradeoffs in the presence of wavelength converters

Routing in wavelength-routed all-optical WDM networks has received much attention in the past decade, for which fixed and dynamic routing methods have been proposed. Taking into account the observation that wavelength-routed all-optical WDM networks are similar to circuit-switched voice networks, except with regard to wavelength conversion, we propose an adaptive alternate routing (AAR) scheme for wavelength-routed all-optical WDM networks. A major benefit of AAR is that it can operate and adapt without requiring an exchange of network status, i.e., it is an information-less adaptive routing scheme. The scope of this work is to understand this scheme in its own right since no other dynamic routing schemes are known to have the information-less property. In this paper, we conduct a systematic study of AAR with regard to factors such as the number of converters, load conditions, traffic patterns, network topologies, and the number of alternate paths considered. We observe that the routing scheme with multiple alternate routes provides more gain at a lower load instead of requiring any nodes to be equipped with wavelength converters. On the other hand, the availability of wavelength converters at some nodes, along with adaptive routing, is beneficial at a moderate to high load without requiring all nodes to be equipped with wavelength converters. We also observed that a small number of alternate routes considered in a network without wavelength converters gives a much better performance than a network with full wavelength converters and fewer alternate routes. Throughout this study, we observed that the proposed adaptive alternate routing scheme adapts well to the network traffic condition.     

IP over WDM网中的策略路由算法

业务量工程允许管理者通过赋予业务主干不同的业务量工程属性来体现一定的管理策略,在为业务主干建立标记交换路径(LSP)时也应该考虑这些策略的影响,该文讨论了业务主干具有不同优先权属性时的 LSP建立问题,针对中断 LSP个数最少和中断业务量最小两种指标,分别提出不同的解决策略:最小连接数中断法(MCNIM)和最小连接带宽中断法(MCBIM),并在不同负载的动态业务下对所提算法进行了仿真研究,给出了仿真结果。     

Blocking performance of time switching in TDM wavelength routing networks

Advances in optical WDM technology have paved the way for high-capacity wavelength channels capable of carrying information at Gb/s rates. However, with current traffic streams requiring only a fraction of a wavelength’s bandwidth, it becomes necessary to groom these independent low rate traffic streams on to higher capacity wavelength channels. An all-optical approach to grooming is to allow many connections to time-share a wavelength. Accordingly, in a TDM wavelength routing network, the establishment of a connection requires the assignment of time slots in addition to routing and wavelength assignment. One of the primary challenges in such networks is the need for quick reconfiguration at the routing nodes. In this paper, we investigate the effects of switch reconfigurability, wavelength conversion and time slot interchangers (TSIs) on the blocking performance of connections with multiple rates. Heuristics for time slot assignment that consider constraints imposed by six different node architectures are proposed, and the blocking performance of the TDM wavelength routing network is evaluated through simulations. Results indicate that limited reconfigurability at the nodes is sufficient to attain the performance obtained with full reconfigurability, especially when connections occupy only a small fraction of the wavelength capacity. Furthermore, the blocking performance is not seen to benefit significantly with the introduction of wavelength converters and TSIs, thus signifying that the improvement in blocking is largely dependent on the switch reconfigurability at the nodes.     

WDM网络中确定波长变换器位置与数目的启发式算法

该文首次研究了波分复用(Wavelength Division Multiplex,WDM)网络中如何在最佳节点中确定波长变换器数目的算法,设计了3种启发式算法,通过在NSFNET(the U.S.NationalScience Foundation backbone NETwork,美国科学基金会骨干网络),ARPANBT(the AdvancedResearch Projects Agency NETwork,美国高级研究规划局网络),CERNET(China Educationand Research NETwork,中国教育科研网络)上的仿真,比较了3种算法的性能差异,得出算法1的性能最优,且复杂度最低。另外,通过比较在部分节点以及全部节点中运用算法1确定波长变换器的数目,得出:在WDM网络中,在部分节点中装配有限的波长变换器也可以达到全部节点中装备波长变换器的性能,并且还可以降低光交叉连接设备(Optical Cross-Connects,OXC)的成本,减少复杂的控制。     

Wavelength assignment with sparse wavelength conversion for optical multicast in WDM networks

This paper addresses the problem of multicast wavelength assignment for sparse wavelength conversion (MWA-SWC) in wavelength-routed wavelength-division-multiplexing (WDM) networks. It aims to optimally allocate the available wavelength for each link of the multicast tree, given a sparse wavelength conversion network and a multicast request. To our knowledge, little research work has been done to address this problem in literature.In this paper, we propose a new technique called MWA-SWC algorithm to solve the problem. The algorithm first maps the multicast tree from the sparse conversion case to the full conversion case by making use of a novel virtual link method to carry out the tree mapping. The method provides a forward mapping to generate an auxiliary tree as well as a reverse mapping to recover the original tree. Applying the auxiliary tree, we propose a dynamic programing algorithm for the wavelength assignment (WA) aiming to minimize the number of wavelength converters (NWC) required. Simulation results show that our new algorithm outperforms both random and greedy algorithms with regard to minimizing the NWC. Testing on various scenarios by varying the number of wavelength conversion nodes in the tree has confirmed the consistency of the performance. The primary use of the MWA-SWC algorithm is for static traffic. However, it can also serve as a baseline for dynamic heuristic algorithms. Typically, the MWA-SWC algorithm will provide great benefit when the number of available wavelengths on each link of the multicast tree is relatively large and the performance advantage is significant.     

A novel dynamic survivable routing in WDM optical networks with/without sparse wavelength conversion

In this paper, we study the dynamic survivable routing problem, both in optical networks without wavelength conversion and in optical networks with sparse wavelength conversion, and propose a novel hybrid algorithm for it based on the combination of mobile agents technique and genetic algorithms (GA). By keeping a suitable number of mobile agents in the network to cooperatively explore the network states and continuously report cycles (that are formed by two disjoint-link routes) into the routing tables, our new hybrid algorithm can promptly determine the first population of cycles for a new request based on the routing table of its source node, without the time consuming process associated with current GA-based lightpath protection schemes. We further improve the performance of our algorithm by introducing a more advanced fitness function that is suitable for both the above networks. Extensive simulation studies on the ns-2 network simulator show that our hybrid algorithm achieves a significantly lower blocking probability than the conventional survivable routing algorithms for all the cases we studied.     

IP/MPLS over WDM网中的动态选路和波长分配算法

该文研究了IP/MPLS over WDM网中,利用综合路由法为到达的业务流建立标签交换路径(LSP)时,如何选择是在WDM层为它新建一条光路,还是利用现有的逻辑IP链路来满足其要求,提出一种带宽碎片消除的策略,该策略在决定是否利用逻辑IP链路来建立LSP时,总是尽量减少造成带宽碎片,从而可以有效提高全网的资源利用率,仿真结果表明带宽碎片消除策略可以进一步改善综合路由算法的性能。     

Study of multicast wavelength arrangement for maximizing network capacity in WDM networks with sparse wavelength converters

The issue of wavelength assignment is one of the most important factors that affect the capacity for the deployment of optical networks. This issue becomes more critical for multicast connections, especially when the network nodes have no wavelength conversion capability. Although the wavelength assignment can be more flexible if each node can perform wavelength conversion, the deployment cost increases accordingly. A compromise is to support a limited portion of conversion nodes in the WDM network. We propose a systematic approach for the wavelength assignment of multicast connections in WDM networks with sparse wavelength conversion nodes. The efficiency of the arrangement of wavelength is measured by its influences on the available capacity of the network and the consumption of wavelengths. By using the proposed approach, the Static Cost Greedy (SCG) algorithm [8] can be easily extended to be applicable in a Sparse Wavelength Conversion Network (SWCN). In addition, instead of SCG, the Minimum-Effect-First (MEF) algorithm is proposed to maximize the network capacity during wavelength assignment. We compare the performance of the proposed MEF methods with the extended SCG scheme through exhaustive simulations. The experimental results indicate that the proposed MEF schemes demonstrate much better performance than the SCG scheme. We also found that the performance is not always improved proportionally to the increment of the wavelength conversion nodes. The improvement reaches saturation when the number of conversion nodes is above 35% of the total number of nodes.

A protocol for piggy-backing on Markov based wavelength reservation in WDM optical networks

During lightpath establishment in WDM optical networks, two important steps, other than routing, are: wavelength selection and wavelength reservation. If two or more lightpaths select the same wavelength, wavelength collision occurs. The basic reason for collision is the non-availability of the updated wavelength usage information. Markov based wavelength selection guesses a unique wavelength in advance, where each node periodically broadcasts its adjoining link usage information at a regular interval T. But, at any intermediate time t (0<t<T), all nodes use the old update which is already outdated by time t. If T is large, the problem becomes severe. To get around this problem without introducing any extra overhead, we propose a novel technique where the normal control packets, passing through the relevant nodes during [0,T], can be leveraged to carry the desired link state information. This may allow us even to increase the value of T (thereby reducing broadcast overhead), when control packets are frequent in the network. We apply the proposed modification to our previous work on Markov selection Split Reservation Protocol (MSRP) and call the modified protocol Fast updated MSRP (FMSRP). In fast update, we “piggy-back” normal control packets with link usage information, in addition to the usual periodic broadcasting of the same at every T. It obviously increases the chance for the nodes to get the latest information of link usage. We have simulated FMSRP and compared it with MSRP and also with another current best protocol (i.e., Markov based Backward Reservation Protocol) to show that the blocking probability for FMSRP improves considerably over them in some regions of offered load.     

WDM网络中支持QoS的路由与波长分配算法

针对波分复用(wDM)网络中的路由与波长分配问题。提出了一种支持服务质量(QoS)的约束搜索算法。基于多目标规划模型,这种搜索算法可为网络各节点创建路由表,根据路由表信息求出非支配路径集合,从而一次性完成寻找路由和分配波长两项任务。仿真实例证明了该算法的有效性。     

Design of grooming architectures for optical WDM mesh networks: limited grooming with electronic wavelength conversion

In this article, we consider the problem of traffic grooming in optical wavelength division multiplexed (WDM) mesh networks under static traffic conditions. The objective of this work is to minimize the network cost and in particular, the electronic port costs incurred for meeting a given performance objective. In earlier work, we have shown the benefits of limited grooming switch architectures, where only a subset of wavelengths in a network are equipped with expensive SONET Add Drop Multiplexers (SADM) that provide the grooming functionality. In this work, we also consider the wavelength conversion capability of such groomers. This can be achieved using a digital cross-connect (DCS) in the grooming switch to switch low-speed connections between the SADMs (and hence, between wavelengths). The grooming switch thus avoids the need for expensive optical wavelength converters. Based on these observations, we propose a limited conversion-based grooming architecture for optical WDM mesh networks. The local ports at every node in this architecture can be one of three types: an add-drop port, a grooming port that allows wavelength conversion or a grooming port that does not allow wavelength conversion. The problem studied is: given a static traffic model, where should the different ports be placed in a network? We formulate this as an optimization problem using an Integer Linear Programing (ILP) and present numerical results for the same. We also present a heuristic-based approach to solve the problem for larger networks.     

多光纤WDM网中的QoS路由算法

利用区分光业务(DOS)模型可以将WDM光传送网中客户层(如IP)具有不同QoS要求的业务汇聚力较粗粒度的流,直接映射到光信道上,从而使客户层业务的不同QoS要求可以体现在DOS域的边缘光节点处的光路建立请求的不同优先级上。该文首先探讨了如何将多光纤WDM网转化为波长图,从而一次性解决选路和分配波长(RWA)问题,在此基础上,提出两种用于多光纤WDM网的QoS路由算法,对二者进行了比较,并进行了计算机仿真。     

Buffer analysis with finite number of tunable receivers in WDM passive star networks

This study develops a performance model as an expansion of the receiver collision analysis presented in [I.E. Pountourakis, Performance evaluation with receiver collisions analysis in very high-speed optical fiber local area networks using passive star topology, J. Lightwave Technol. 16 (12) (1998) 2303–2310] for WDM networks. By theoretical analysis we estimate the receiver collision phenomenon and evaluate the performance measures and the rejection probability at destination for finite number of tunable receivers. Receiver collision analysis makes the performance behavior more realistic and expands the original analysis.     

Minimum connection count wavelength assignment strategy for WDM optical networks

In this paper, we have proposed one wavelength assignment strategy for optical networks which assigns the wavelength according to minimum connection count. The performance of proposed strategy is compared with the most commonly used strategy among the existing strategies in terms of number of searches to find the wavelength for connection establishment. The searching takes the time and directly affects the connection establishment time. The simulation is done using different network models. The results show that the proposed strategy is much better than existing strategy in terms of number of searches required to find a wavelength for establishing the connection and hence connection establishment time reduces.     

多光纤波分复用网的一种新的备用路由算法

基于经典的LLR算法,研究了波分复用光网络的路由问题,提出了一种用于多光纤网的新算法—LLHR,该算法综合考虑了链路负载和路由跳数两个因素。文章深入研究了网络光纤数、备用路由数和网络负载对算法性能的影响。计算机仿真结果表明,与LLR算法相比,该算法能有效降低网络的阻塞率,提高网络的性能。     

IP over WDM网络中业务持续时间感知的绿色路由算法

研究了IP over WDM网络的低碳路由问题,综合 考虑业务持续时间和利用可再生能源和传统能源供能两个 因素,基于分层图模型,提出一种带有业务持续时间感知的绿色路由(HTAGR)算法。HTAGR 依据节点处太阳能 供能情况以及节点和链路的能耗情况动态调整链路权值,并鼓励选择业务持续时间内需要额 外消耗传统能源最少的 路径建立连接。仿真结果表明,与传统节能路由算法相比,HTAGR 有利于消耗更少的传统能 源和使用更多的可再 生能源,在保持较低阻塞率的同时,进一步降低了业务平均传统能耗和CO₂排放量。     

A token-based routing mechanism for GMPLS-controlled WDM networks

This paper analyzes destination initiated reservation for Generalized Multi-Protocol Label Switching (GMPLS) based wavelength division multiplexing (WDM) networks and determines, via simulation, probabilities of both forward blocking and backward blocking. During light traffic load, any degradation in performance is due to backward blocking, whereas during heavy traffic load forward blocking dominates. In order to minimize performance degradation due to blocking, this paper proposes a token based routing scheme that is capable of searching for the availability of more than one route from source to destination, meeting the desired quality of service (QoS). Extensive simulation results show that the proposed technique significantly improves the blocking performance and setup delay.     

稀疏波长变换网络性能分析与研究

文章对动态业务模型下的稀疏波长变换网络性能进行了分析与研究，对波分复用（WDM）网络中引入波长变换器后的网络性能进行了系统的仿真，分析了波长变换器数量、波长变换器位置、波长变换范围以及路由波长算法等因素对网络性能的影响。     

Dynamic routing and wavelength assignment in multi-granularity WDM networks

For the purpose of reducing the complexity and cost of optical large-scale cross-connect, wavelengths are grouped into wavebands or fiber to be switched as a single entity, which is called multi- granularity switching. However, it introduces more complexity into the routing and wavelength assignment problem. In this paper, we propose a novel graph model for describing the states of the multi-granularity switching WDM networks. Based on the model, the dynamic routing and wavelength assignment problems for multi-granularity traffic can be solved jointly, and different on-line wavelength grooming policies can be achieved simultaneously. By simulation, we compared the performance of our algorithms under different policy and different percent of fibers for fiber switching. The result proved that our algorithms yield better performance than those deal with the routing and wavelength assignment separately. This work was supported in part by NSFC Project No. 90104003, 60272023, 60372025 and National 863 project No. 2005AA122310.