A generalized framework for analyzing time-space switched opticalnetworks

The advances in photonic switching have paved the way for realizing all-optical time switched networks. The current technology of wavelength division multiplexing (WDM) offers bandwidth granularity that matches peak electronic transmission speed by dividing the fiber bandwidth into multiple wavelengths. However, the bandwidth of a single wavelength is too large for certain traffic. Time division multiplexing (TDM) allows multiple traffic streams to share the bandwidth of a wavelength efficiently. While introducing wavelength converters and time slot interchangers to improve network blocking performance, it is often of interest to know the incremental benefits offered by every additional stage of switching. As all-optical networks in the future are expected to employ heterogeneous switching architectures, it is necessary to have a generalized network model that allows the study of such networks under a unified framework. A network model, called the trunk switched network (TSN), is proposed to facilitate the modeling and analysis of such networks. An analytical model for evaluating the blocking performance of a class of TSNs is also developed. With the proposed framework, it is shown that a significant performance improvement can be obtained with a time-space switch with no wavelength conversion in multiwavelength TDM switched networks. The framework is also extended to analyze the blocking performance of multicast tree establishment in optical networks. To the best of our knowledge, this is the first work that provides an analytical model for evaluating the blocking performance for tree establishment in an optical network. The analytical model allows a comparison between the performance of various multicast tree construction algorithms and the effects of different switch architectures     

Optimal nonuniform wavebanding in WDM mesh networks

Grouping together a set of consecutive wavelengths in a WDM network and switching them together as a single waveband could achieve savings in switching costs of an optical cross-connect. This technique is known as waveband switching. While previous work has focused on either uniform band sizes or nonuniform band sizes considering a single node or ring networks, in this paper we focus on optimizing the number of wavebands and their sizes for mesh topologies. We formulate a problem of optimizing the number of wavebands in a mesh network for a given set of lightpaths. The objective of the band minimization problem is to minimize the number of nonuniform wavebands in the network while satisfying the traffic requests. We formulate an integer linear program and propose efficient heuristics. Simulation results are presented to demonstrate the effectiveness of the proposed approaches under static traffic case. Our results show that the number of switching elements can be reduced by a large amount using waveband switching compared to wavelength switching. We also apply the proposed waveband strategy to the dynamic stochastic traffic case and evaluate the network performance in terms of blocking probability through numerical simulations.     

An efficient dynamic multicast traffic-grooming algorithm for WDM networks

With the growth of multi-granularity multicast applications, there comes into being a huge gap between the bandwidth of a wavelength provided and a multicast traffic required in the wavelength division multiplexing (WDM) networks. The dynamic multicast traffic-grooming is an effective way for WDM networks to improve the wavelength utilization and decrease the traffic blocking probability. A novel switching node architecture with the multicast switching matrix and traffic-grooming fabric is studied in the paper. Then, an efficient dynamic multicast traffic-grooming algorithm is proposed for the architecture. According to the ratio of network available grooming port number to network transceiver number, the proposed algorithm estimates whether the traffic-grooming port is a scarce resource for input traffic and chooses the appropriate grooming strategy. If the traffic-grooming port is scarce, the minimized use grooming port strategy is designed for the coming traffic. On the contrary, the minimized use node transceiver strategy is applied for the coming traffic. Simulation results show that the proposed algorithm can groom traffic efficiently with low blocking probability and high network throughput constraint by limiting number of node transceivers and grooming ports.     

A Node-Level Blocking Probability Analysis for WRONs

This work presents the blocking performance of a single node with (full or limited) wavelength conversion in wavelength routed optical networks (WRON) based on the theory of probability. A blocking probability model is proposed. Particularly, we pay more attention to investigate wavelength routing node performance improvement by using the more feasible case of limited wavelength conversion. Based on our analytical model, we calculate the blocking probability for a single wavelength routing node and then make a simulation to validate it. It is shown that a node with low conversion degrees having a small number of fiber link ports and a large number of wavelengths per link is a more realistic choice.     

光开关大小对光网络阻塞概率的影响

引入一种基于电路交换WDM光网络的业务模型,推导出波长连续光网络和波长可转换光网络中阻塞概率关于光开关大小的公式。通过波长转换器的增益定性分析了光开关大小对这两种网络阻塞概率的影响,并用Matlab仿真验证。结果表明:光开关大小对网络(尤其是波长连续网络)有着很大的影响,但比起通道长度来其影响相对较小,网络的拓扑设计中需同时考虑这两者。     

波分复用波长路由节点的阻塞特性分析

利用概率统计理论的方法，从节点层次上定量分析了节点规模、复用波长数目以及波长转换对波分复用(WDM)波长路由网络中波长路由节点的影响。提出了基于概率统计的节点阻塞模型。数值结果突出表明波长转换能力越强的全光节点，其性能越优。为了提高网络资源的使用效率并增强全光网络的灵活性，必须实现全光网络中的虚波长路由波长转换器。通过数值计算找到了阻塞性能和代价的折中，研究中发现配置较低波长转换能力波长转换器的波长路由节点将会具备更强的性价比优势，当前在构建光通信系统时使用弱波长转换能力的光节点更可行。     

An analysis of limited wavelength translation in regularall-optical WDM networks

We analyze limited-wavelength translation in regular all-optical, wavelength division multiplexed (WDM) networks, where up to W wavelengths, each of which ran carry one circuit, are multiplexed onto a network link. All-optical wavelength translators with a limited translation range permit an incoming wavelength to be switched only to a small subset of the outgoing wavelengths. We focus on the wraparound mesh and hypercube WDM networks, and analyze the case where an incoming wavelength can he switched to one of k (k=2, 3) outgoing wavelengths (called the feasible wavelength set). Our analysis captures the state of a feasible wavelength set at a network node, which allows us to obtain the probability that a session arriving at a node at a random time successfully establishes a connection from its source node to its destination node in each of these topologies. Based on this probability, we quantify the throughput and blocking performance of limited wavelength translation, and compare it to that of no wavelength translation and full wavelength translation. We demonstrate that in regular networks it can obtain most of the performance advantages of full translation at a fraction of the cost, and we present a simple, economical switch architecture to effect limited wavelength translation at a cost that is effectively independent of the number of wavelengths W in the system     

一种低成本智能全光波长交叉交换连接器的设计和实现

报道了一种采用多个4×4,一个8×8光开关以及固定波长转换器组成的大容量全光波长交叉交换连接器(OWXC)的新颖结构,可以实现低串扰、低延迟的无阻塞光信号交换和转换,降低成本30%左右。同时,提出了应用于该结构的智能控制信号传输帧结构以及通过设置可用波长被锁定的时间门限来实现三种具有服务等级的智能光链路建立方式。实验结果显示,一条光链路从被断开到自动重新建立的时间是22 ms,可以实现人工、自动和半自动三种链路建立方式以及三根光纤,24个波长的全无阻塞交换,交换容量达到960 Gb/s。对组建大容量的光交叉连接(OXC)具有参考意义。     

动态业务条件下多粒度全光网性能分析与研究

多粒度交换技术利用波带级路由以及光纤级路由,可有效降低光交叉连接器的复杂度。但多粒度交换增加了光网络的逻辑层次结构,使得网络中的路由与资源分配问题更为复杂,多粒度全光网中的多层联合路由机制是影响网络性能的关键。本文对动态业务下多粒度全光网中的资源分配策略进行了深入研究,比较了采用不同节点交换比例时网络的阻塞性能,分析了不同业务量时多粒度交叉连接节点的最佳波带粒度,并结合经济性对多粒度全光网的性能进行了综合分析。     

Blocking performance analysis on adaptive routing over WDM networks with finite wavelength conversion capability

Analytical blocking probability analysis is important for network design. In this paper, we present an analytical model for the blocking probability analysis on adaptive routing over the WDM networks with finite wavelength conversion capability. Modeling the finite nature of wavelength conversion has been a difficult task. We make use of the idea of segmented route to handle the finite wavelength conversion property. In this approach, a route is divided into a number of segments separated by wavelength converting nodes. We then combine the single-link model and the overflow model to derive the network-wide blocking probability. There are two distinct features in our technique. First, a concept of segmented route is used. Second, link state is considered when calculating the traffic flow. The latter ensures that the analytical results match closely to practical network status. Extensive simulations show that the analytical technique is effective in modeling the blocking probability performance for sparse networks.     

Mini-slot TDM WDM optical networks

In recent years, optical transport networks have evolved from interconnected SONET/WDM ring networks to mesh-based optical WDM networks. Time-slot wavelength switching is to aggregate the lower rate traffic at the time-slot level into a wavelength in order to improve bandwidth utilization. With the advancement of fiber-optics technologies, continual increase of fiber bandwidth and number of wavelengths in each fiber, it is possible to divide a wavelength in a fiber into time-slots, and further divide a time-slot into mini-slots so that the fiber bandwidth can be more efficiently utilized. This article proposes a router architecture with an electronic system controller to support optical data transfer at the mini-slot(s) of a time-slot in a wavelength for each hop of a route. The proposed router architecture performs optical circuit switching and does not use any wavelength converter. Each node in the mini-slot TDM WDM optical network consists of the proposed router architecture. Three different network topologies are used to demonstrate the effectiveness and behavior of this type of network in terms of blocking probability and throughput.     

Performance modeling of bufferless WDM packet switching networks with limited-range wavelength conversion

All optical communication is attracting more and more attention because of the huge bandwidth of optics. In this paper, we study the performance of bufferless optical wavelength-division multiplexing (WDM) packet switching networks with limited-range wavelength conversion capabilities. We first introduce an optimal scheduling algorithm that maximizes the throughput of the switch. We then derive an analytical model to evaluate the performance of the switch in terms of packet-loss probability. Our model is the first accurate analytical model for a bufferless WDM packet switch with variable conversion distances, and can be used to quantitatively determine the maximum load for a given conversion distance or the minimum conversion distance for a given traffic load. We also conducted simulations to validate the analytical model. Both the analytical and simulation results reveal that limited-range wavelength conversion can achieve almost the same performance as full-range wavelength conversion.     

Computing blocking probabilities in survivable WDM optical networks

One of the most important performance measurements in wavelength-division multiplexing (WDM) networks is the call blocking probability. In this paper, we present an approximate analytical method to evaluate the blocking probabilities in survivable WDM networks with dynamically arriving connection requests. Our approach utilizes the wavelength independence whereby WDM network can be regarded as an aggregation of disjoint single wavelength sub-networks with a common physical topology. In each single wavelength sub-network, we derive the calculation of the blocking probability from an exact analysis. We assume dedicated protection with fixed routing and either first-fit or random wavelength assignment. Simulation results demonstrate the accuracy of the proposed method.     

Analysis of blocking probability in optical burst switched networks

In this article, we study the blocking probability in a wavelength division multiplexing (WDM) based asynchronous bufferless optical burst switched (OBS) network, equipped with a bank of wavelength converters. Our analysis encloses two wavelength reservation schemes JIT (just-in-time) and JET (just-enough-time), and two-class data rate. The contribution of our work includes: (i) derivation of an accurate model for blocking probability of lower priority bursts in case of a non-preempted model; (ii) provision of the analytical model for blocking probability calculation in the OBS network, which includes these variables: two signaling schemes, partial wavelength conversion, two-class data, traffic intensity, cross-connect speed, number of wavelengths in WDM fiber, number of fibers in the node, number of wavelength converters, and number of nodes in the path; (iii) simulation results, which show that partial wavelength conversion provide quite satisfactory quality of service. We compare performance in a single OBS node, under various sets of parameter values. The OBS network shows great flexibility in terms of used multiclass data, and there is no dependence on the used higher layer protocol.     

Wavelength-exchanging cross connects (WEX)-a new class of photonic cross-connect architectures

All-optical wavelength division multiplexing (WDM) networks are expected to realize the potential of optical technologies to implement different networking functionalities in the optical domain. A key component in WDM networks is the optical switch that provides the basic functionality of connecting input ports to output ports. Existing WDM switches make use of space switches and wavelength converters (WCs) to realize switching. However, this not only increases the size and the complexity of the switch but also bears heavily on the cost. In this paper, the authors propose a new class of photonic switch architectures called wavelength-exchanging cross connect (WEX) that provides several advantages over existing switches by enabling a single-step space switching and wavelength conversion and thus eliminating the need for a separate conversion stage. This greatly enhances the switch architecture by reducing its size and complexity. The new class of cross-connect architectures is based on the proposed concept of a wavelength-exchange optical crossbar (WOC). The WOC concept is realized using the simultaneous exchange between two optical signals. The proposed WEX architecture is highly scalable. To establish scalability, the authors present a systematic method of developing instances of the switch architectures of an arbitrary large size.     

WDM网状网络中一种动态多播自适应业务疏导算法

光多播业务需要消耗大量的WDM光网络带宽资源,业务疏导是光多播网络降低业务请求阻塞率和提高带宽资源利用率的有效方法。提出了一种新型光多播疏导节点结构,研究了疏导端口优先的多播业务疏导算法(TGPFA)和新建光树优先的多播业务疏导算法(TCLFA),进而提出了一种能够适应网络资源变化的动态多播业务疏导算法(ADMGA)。结果表明,在网络资源有限的情况下,ADMGA算法能取得较低的请求阻塞率和带宽阻塞率,获得较好的网络性能。     

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.     

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.     

Routing Mechanisms Employing Adaptive Weight Functions for Shortest Path Routing in Optical WDM Networks

Optical dense wavelength division multiplexed (DWDM) networks are an attractive candidate for the next generation Internet and beyond. In this paper, we consider routing and wavelength assignment in a wide area wavelength routed backbone network that employs circuit-switching. When a session request is received by the network, the routing and wavelength assignment (RWA) task is to establish a lightpath between the source and destination. That is, determine a suitable path and assign a set of wavelengths for the links on this path. We consider a link state protocol approach and use Dijkstras shortest path algorithm, suitably modified for DWDM networks, for computing the shortest paths. In [1] we proposed WDM aware weight functions that included factors such as available wavelengths per link, total wavelengths per link. In this paper, we present new weight functions that exploit the strong correlation between blocking probability and number of hops involved in connection setup to increase the performance of the network. We also consider alternate path routing that computes the alternate paths based on WDM aware weight functions. The impact of the weight functions on the blocking probability and delay is studied through discrete event simulation. The system parameters varied include number of network nodes, wavelengths, degree of wavelength conversion, and load. The results show that the weight function that incorporates both hop count and available wavelength provides the best performance in terms of blocking probability.     

一种全光波长路由器的设计及性能分析研究

该文基于一种简单低成本的、波长转换节点共享型全光波长路由器结构,设计了以排队理论为基础的M/M/T/T模型,研究了波长路由器在波分复用波长路由网络中的阻塞特性。数值结果表明,全光网波长路由器的阻塞特性与复用波长数目,链路波长利用率,节点接入光纤端口数,有无波长转换器密切相关。尤其在受限波长转换条件下的配置优化分析,可看出波长路由器无需可调谐器件,也能获得灵活的波长转换能力,不但可避免波长路由器因为精确调谐所开销的时间,而且所有的控制均为简单的开关控制,可降低工程实现的复杂度。