Impact of transmission impairments on the teletraffic performanceof wavelength-routed optical networks

In a wavelength-routed optical network, a transmitted signal remains in the optical domain over the entire route (lightpath) assigned to it between its source and destination nodes. The optical signal may have to traverse a number of crossconnect switches (XCSs), fiber segments, and optical amplifiers, e.g., erbium-doped fiber amplifiers (EDFAs). Thus, while propagating through the network, the signal may degrade in quality as it encounters crosstalk at the XCSs and also picks up amplified spontaneous emission (ASE) noise at the EDFAs. Since these impairments continue to degrade the signal quality as it progresses toward its destination, the received bit error rate (BER) at the destination node might become unacceptably high. Previous work on the lightpath routing and wavelength assignment (RWA) problem assumed an ideal physical layer and ignored these transmission impairments. The main contribution of our work is to incorporate the role of the physical layer in setting up lightpaths by employing appropriate models of multiwavelength optical devices (XCSs and EDFAs) such that the BER of a candidate lightpath can be computed, in advance, to determine if this lightpath should be used for the call. Features from existing RWA algorithms are integrated with our on-line BER calculation mechanism. Our simulation studies indicate that employing BER-based call-admission algorithms has a significant impact on the performance of realistic networks     

Bit-parallel message exchange and data recovery in optical packet switched interconnection networks

Multiwavelength optical messages encoded in a bit-parallel fashion are successfully routed through five switching nodes of a 12-port optical packet switching interconnection network. The data payloads are entirely recovered and processed at the destination node using an embedded clock signal with a measured clock-to-data skew tolerance window of 150 ps.     

一种基于光纤传输的监测信号处理系统

为了解决高压监测系统中的实时监测问题,设计了一种光纤传输的监测信号处理系统,监测信号通过高速模数转换变成数字信号后,通过光发射模块变成光数字信号,用光纤作为传输通道,传到目的地后再由光接收模拟把数字光信号变换成数字电信号,经过数模转换后恢复成模拟的监测信号。经过模拟验证后发现这个系统具有实时性强、失真小、系统体积小、抗干扰能力强等优点。     

Optimal virtual topologies for one-to-many communication in WDM paths and rings

In this paper we examine the problem of constructing optimal virtual topologies for one-to-many communication in optical networks employing wavelength-division multiplexing. A virtual topology is a collection of optical lightpaths embedded in a physical topology. A packet sent from the source node travels over one or more lightpaths en route to its destination. Within a lightpath, transmission is entirely optical. At the terminus of a lightpath the data is converted into the electronic domain where it may be retransmitted on another lightpath toward its destination. Since the conversion of the packet from the optical to the electronic domain introduces delays and uses limited physical resources, one important objective is to find virtual topologies which minimize either the maximum or average number of lightpaths used from the source to all destination nodes. Although this problem is NP-complete in general, we show that minimizing the maximum or average number of lightpaths in path and ring topologies can be solved optimally by efficient algorithms.     

Impairment-aware ordered scheduling in dual-header optical burst switched networks

Optical burst switching (OBS) is a promising technology for bridging the gap between optical wavelength switching and optical packet switching. Optical signal transmission quality is subject to various types of physical impairment introduced by optical fibers, switching elements, or other network components. The signal degradation due to physical impairment may be significant enough such that the bit-error rate of received signals is unacceptably high at the destination, rendering the signal to not usable. In this article, based on earlier study, we study the burst-scheduling problem in OBS networks using two control packets for each data burst, taking into account physical impairment effects. We propose a burst-scheduling algorithm that accommodates incoming bursts by primary path routing, deflection routing, and burst scheduling. We design an admission control mechanism to use network resources efficiently. At an OBS node, the proposed algorithm schedules bursts for transmission by searching for available resources as well as verifying signal quality. Our simulation results demonstrate that the proposed algorithm is effective in terms of reducing the burst-blocking probability.     

All-optical remote switching for multiplexed optical fiber sensorsand communications systems

All-optical self-routing switches are described which automatically route optical data signals. These switches require no separate source of power, and have been demonstrated to operate from a single input laser beam of 300 μW. The input laser beam contains the data, destination address, and optical power. These optical switches can be used for all-optical communication systems, and are used as an example in this paper to demonstrate remote switching via an optical fiber to a sensor. The sensor modulates the optical carrier which returns the modulated carrier to the source end of the fiber. The switch demonstrates auto-aligning properties which ensure correct rerouting of the modulated signal back to the source. Operation has been demonstrated for all the visible lines of an argon ion laser     

WDM光网络的光路传输质量估计算法

在波长路由WDM光网中,信号在路由与波长分配算法(RWA)选定的光路上传输．传输过程中引入的各种串扰和噪声使信号的传输质量受到损伤,信号质量不断下降,目的结点无法正确有效地接收光信号。通过定义合理的结点和传输链路模型．提出了一种考虑线性传输损伤的比特错误率估算方法．在光路建立之前预先估计WDM网络中将要建立光路的传输质量,以此作为网络优化设计过程中RWA算法选路的依据。通过网络仿真和实验验证了算法的正确性。     

FWM aware evolutionary programming algorithm for transparent optical networks

This paper proposes and evaluates a four-wave mixing (FWM) aware evolutionary programming algorithm for dynamically setting up lightpaths in an optical wavelength division multiplexed network (WDM network). The proposed algorithm also considers the effect of amplified spontaneous emission noise (ASE noise) on a lightpath during propagation of the optical signal from any source to the intended destination. As crosstalk due to FWM and ASE noise are two transmission impairments that degrade the quality of optical signal even at low to medium data rates, it is mandatory for an algorithm for dynamic routing and wavelength assignment in a WDM network to consider the effect of these two impairments on the lightpath to be established. The distinguishing feature of the proposed algorithm is that it is based on an initial population of a single individual and uses a fitness function that is expressed in terms of the number of hops, path cost, variance contributions due to FWM crosstalk, amplifier noise, and different beat noises at the receiver. The performance of a newly introduced FWM aware priority-based wavelength assignment technique is compared with few of the existing wavelength assignment techniques in the present work.     

Modeling human mobility in obstacle-constrained ad hoc networks

In this paper we present a mobility model for ad hoc networks consisting of human-operated nodes that are deployed in obstacle-constrained environments. According to this model, the network nodes move around the obstacles in a way that resembles how humans bypass physical obstructions. A recursive procedure is executed by each node at its current position to determine the next intermediate destination point until the final destination point is reached. The proposed mobility model is validated using real-life trace data and studied using both mathematical analysis and simulations. Furthermore, the model is extended to incorporate several operational aspects of ad hoc networks in mission critical scenarios, where it is best applicable. These extensions include hierarchical node organization, distinct modes of node activity, event-based destination selection and impact of the physical obstacles on signal propagation. The model is implemented as an add-on module in Network Simulator (ns-2).     

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.     

Deflection routing in IP optical networks

This paper deals with optical packet switching in a full-IP transport network scenario. Given the technological limits of accomplishing packet buffering in the optical domain, deflection routing is here explored as an alternative technique for resolving packet contentions without buffering packets. Two different network topologies have been considered here, that is a regular six-node network with different connectivity factors and the classical NSF network. A limited amount of optical buffering is considered in the switching nodes that performs both input queuing and shared queuing of packets to be switched. The performance improvements that can be obtained by deflection routing have been evaluated considering different methods for choosing the alternative paths where to deflect packets that cannot be transmitted onto the shortest path to the addressed destination.     

基于光森林的弹性光网络能效组播路由频谱分配策略

在弹性光网络中,光树传输组播可以节省链路代价,但较长的光树需要选择更低的调制等级,消耗更多的频谱资源和发射机功耗.提出一种基于遗传算法的光森林组播和光树重配置(GAMF-TR)优化组播的能效路由、调制格式和频谱分配(RMSA)策略.GAMF-TR策略设计染色体编码表示光森林的组播目的节点划分和光路径组合,通过染色体的基因位概率交叉和变异得到更多的光森林RMSA策略,设计了一个频谱分配效率和发射机功耗折中的适应度函数选择能效最高的光森林RMSA策略,并设计在网络资源充足时将组播从光森林重配置到光树传输,进一步减少发射机功耗的消耗.仿真结果表明:提出的GAMF-TR策略获得了组播的最低带宽阻塞率和最高能效性能.     

Survivable traffic grooming with non‐service‐interruptive wavelength retuning in a WDM mesh network

This paper proposes a new survivable traffic grooming wavelength retuning (STGWR) scheme in an all‐optical wavelength division multiplexing (WDM) network. In a dynamic WDM network, a connection may require a bandwidth less than a wavelength capacity. In addition, a connection should be protected against any network failures. Survivable traffic grooming (STG) can protect connections at subwavelength granularities. Wavelength retuning is a promising approach in an all‐optical WDM network, where a signal must remain on the same wavelength from its source to the destination, to alleviate the wavelength continuity constraint and reduce the connection blocking probability. Although both STG and wavelength retuning have attracted extensive research attentions nowadays, no effort has been made to combine these two promising approaches in one network. In this paper, we propose a wavelength retuning scheme with no service interruption in an all‐optical network with STG capability. The scheme allocates two routes, one for the active path and other for the backup path, in a shared mesh restoration manner to each incoming connection request and conducts wavelength retuning only on the backup path. Both wavelength retuning and mesh protection are done at the connection level instead of at the lightpath level. The simulation results of the proposed schemes are also presented. Copyright © 2008 John Wiley & Sons, Ltd.     

Performance Analysis of Full-Duplex Relaying with Parial Relay Selection

This paper addresses full-duplex relaying with partial relay selection, where the relay with the best instantaneous signal-to-noise ratio across the source-relay link is selected to amplify the signal received from the source and forward it to the destination. Some expressions for outage probability and symbol error rate are derived to provide the performance analysis in an independent and identically distributed Rayleigh fading environment. Monte-Carlo simulations are also performed to demonstrate the validity of the analytical results.     

The Wiretap Channel With Feedback: Encryption Over the Channel

In this work, the critical role of noisy feedback in enhancing the secrecy capacity of the wiretap channel is established. Unlike previous works, where a noiseless public discussion channel is used for feedback, the feed-forward and feedback signals share the same noisy channel in the present model. Quite interestingly, this noisy feedback model is shown to be more advantageous in the current setting. More specifically, the discrete memoryless modulo-additive channel with a full-duplex destination node is considered first, and it is shown that the judicious use of feedback increases the secrecy capacity to the capacity of the source–destination channel in the absence of the wiretapper. In the achievability scheme, the feedback signal corresponds to a private key, known only to the destination. In the half-duplex scheme, a novel feedback technique that always achieves a positive perfect secrecy rate (even when the source–wiretapper channel is less noisy than the source–destination channel) is proposed. These results hinge on the modulo-additive property of the channel, which is exploited by the destination to perform encryption over the channel without revealing its key to the source. Finally, this scheme is extended to the continuous real valued modulo-$Lambda $ channel where it is shown that the secrecy capacity with feedback is also equal to the capacity in the absence of the wiretapper.      

On dimensioning optical grids and the impact of scheduling

When deploying Grid infrastructure, the problem of dimensioning arises: how many servers to provide, where to place them, and which network to install for interconnecting server sites and users generating Grid jobs? In contrast to classical optical network design problems, it is typical of optical Grids that the destination of traffic (jobs) is not known beforehand. This leads to so-called anycast routing of jobs. For network dimensioning, this implies the absence of a clearly defined (source, destination)-based traffic matrix, since only the origin of Grid jobs (and their data) is known, but not their destination. The latter depends not only on the state of Grid resources, including network, storage, and computational resources, but also the Grid scheduling algorithm used. We present a phased solution approach to dimension all these resources, and use it to evaluate various scheduling algorithms in two European network case studies. Results show that the Grid scheduling algorithm has a substantial impact on the required network capacity. This capacity can be minimized by appropriately choosing a (reasonably small) number of server site locations: an optimal balance can be found, in between the single server site case requiring a lot of network traffic to this single location, and an overly fragmented distribution of server capacity over too many sites without much statistical multiplexing opportunities, and hence a relatively large probability of not finding free servers at nearby sites.     

An all-optical amplifier for terahertz AM signals: A proposal

We propose an all-optical amplifier for AM signals which, in principle, is an integrated Mach-Zehnder interferometer where both arms are pumped with light from the incoming signal, amplified in a semiconductor laser amplifier. Thus the pump is the time integrated phase and amplitude average of the signal. In one of the arms a part of the nonamplified signal is injected, which modulates the optical path length in that arm with the optical Kerr effect. After the final junction between the arms, the outgoing light is proved to carry a part of the amplitude of the pump and the modulation of the signal.     

Analytical investigation to achieve the highest phase difference between two orthogonal components of light in lithium niobate based electro-optic system

Electro-optic Pockels cell are important opto-electronic devices for conduction of optical switching, optical modulation, where an electrical biasing signal acts on a polarized light passing through the system. Since last few decades lots of works are reported in this area. Again, it is observed that a good switching or modulation becomes realized if the depth of modulation is increased by increasing more phase difference between two orthogonal polarized components of light passing through the material against a biasing signal. Here in this paper the authors propose a new scheme, where multi-passing technique is used to create a high degree of phase difference between those two orthogonal polarized components of light against the biasing signal. The multi-passing of light through the material enables more and more optical path length for the light. So, more and more phase difference between the components of light beams, one passing outside the material and other passing through the material multiple times is created. This method ultimately generates a high degree of depth of modulation in optical switching.     

基于高非线性光纤中四波混频效应的全光取样系统

为了克服高比特率光信号实时取样时所面临的高速模数转换(ADC)限制,构建了一套基于高非线性光纤(HNLF)中四波混频效应的全光等效取样系统。全光取样系统主要包括取样脉冲信号产生、全光取样门和信号处理3部分,其中全光取样门为本系统的核心部分。取样脉冲和信号共同注入到HNLF中,基于四波混频效应实现全光取样。实验中,分别以10Gb/s、40Gb/s非归零OOK信号进行了取样实验验证。实验结果表明该取样系统可以实现高速光信号的取样过程。本文取样系统结构简单,且不受光信号速率的限制,可应用于更高速率的信号测量。     

BIDIRECTIONAL TRANSMISSION OF ADDRESSED AUDIO SIGNAL THROUGH GI MULTIMODE OPTICAL FIBRES

This paper describes two types of bidirectional addressed audio signal transmission systems where the square-wave frequency modulation (SWFM) and intensity modulation (IM) are used to obtain the optical SWFM signals generated from LEDs at 850 nm. The first one is an addressed audio signal transmission network of tree structure. The sender and auxiliary receiver in the centre are connected to four terminals, each consisting of a receiver and an auxiliary sender, through pairs of optical fibres and an optical splitter used as an optical signal distributor. The second one is a new type of full-duplex one-to-one communication system. The sender and auxiliary receiver in one terminal are connected to the receiver and auxiliary sender in the other terminal through an optical fibre and a pair of directional couplers. Although LEDs in the second system deliver optical SWFM signals at the same wavelength of 850 nm at the same time, the communications are satisfactory because there is no interference from one LED to the other. In both the first and second experimental systems, the audio signal, address, and SWFM carrier occupy 10 Hz to 20 kHz, 65 kHz to 710 kHz, and 6 MHz, respectively. The SNR and distortion were 62 dB and 0.4 per cent, respectively.