A cognitive model‐based approach for autonomic fault management in OpenFlow networks

Autonomic network management is an approach to the management of complex networks and services that incorporates the detection, diagnosis and reconfiguration, as well as optimization, of their performance. A control loop is fundamental as it facilitates the capture of the current state of the networks and the reconfiguration of network elements without human intervention. For new networking architectures such as software‐defined networking and OpenFlow networks, in which the control plane is moved onto a centralized controller, an efficient control loop and decision making are more crucial. In this paper, we propose a cognitive control loop based on a cognitive model for efficient problem resolving and accurate decision making. In contrast to existing control loops, the proposed control loop provides reactive, deliberative and reflective loops for managing systems based on analysis of current status. In order to validate the proposed control loop, we applied it to fault management in OpenFlow networks and found that the protection mechanism provides fast recovery from single failures in OpenFlow networks, but it cannot cover multiple‐failure cases. We therefore also propose a fast flow setup (FFS) algorithm for our control loop to manage multiple‐failure scenarios. The proposed control loop adaptively uses protection and FFS based on analysis of failure situations. We evaluate the proposed control loop and the FFS algorithm by conducting failure recovery experiments and comparing its recovery time to those of existing methods. Copyright © 2013 John Wiley & Sons, Ltd.     

A simple void node and loop‐free three‐dimensional routing protocol for multi‐hop wireless networks

Wireless networks are now very essential part for modern ubiquitous communication systems. The design of efficient routing and scheduling techniques for such networks have gained importance to ensure reliable communication. Most of the currently proposed geographic routing protocols are designed for 2D spatial distribution of user nodes, although in many practical scenarios user nodes may be deployed in 3D space also. In this paper, we propose 3D routing protocols for multihop wireless networks that may be implemented in two different ways depending on how the routing paths are computed. When the routing paths to different user nodes from the base station in the wireless network are computed by the base station, we call it centralized protocol (3DMA‐CS). A distributed routing (3DMA‐DS) protocol is implemented when respective routing path of each user node to the base station is computed by the user node. In both of these protocols, the user (base station) selects the relay node to forward packets in the direction of destination, from the set of its neighbours, which makes minimum angle with the reference line drawn from user (base station) to the base station (user), within its transmission range. The proposed protocols are free from looping problem and can solve the void node problem (VNP) of multihop wireless networks. Performance analysis of the proposed protocol is shown by calculating end‐to‐end throughput, average path length, end‐to‐end delay, and energy consumption of each routing path through extensive simulation under different network densities and transmission ranges.     

Achieving energy‐neutral data transmission by adjusting transmission power for energy‐harvesting wireless sensor networks

Recently, benefiting from rapid development of energy harvesting technologies, the research trend of wireless sensor networks has shifted from the battery‐powered network to the one that can harvest energy from ambient environments. In such networks, a proper use of harvested energy poses plenty of challenges caused by numerous influence factors and complex application environments. Although numerous works have been based on the energy status of sensor nodes, no work refers to the issue of minimizing the overall data transmission cost by adjusting transmission power of nodes in energy‐harvesting wireless sensor networks. In this paper, we consider the optimization problem of deriving the energy‐neutral minimum cost paths between the source nodes and the sink node. By introducing the concept of energy‐neutral operation, we first propose a polynomial‐time optimal algorithm for finding the optimal path from a single source to the sink by adjusting the transmission powers. Based on the work earlier, another polynomial‐time algorithm is further proposed for finding the approximated optimal paths from multiple sources to the sink node. Also, we analyze the network capacity and present a near‐optimal algorithm based on the Ford–Fulkerson algorithm for approaching the maximum flow in the given network. We have validated our algorithms by various numerical results in terms of path capacity, least energy of nodes, energy ratio, and path cost. Simulation results show that the proposed algorithms achieve significant performance enhancements over existing schemes. Copyright © 2016 John Wiley & Sons, Ltd.     

Outage Analysis of OFDM‐Based Cognitive AF Relay Network in the Presence of Narrowband Interference

Orthogonal frequency‐division multiplexing (OFDM) is one of the most widely used technologies in current wireless communication systems and standards. Cognitive radio (CR) provides a robust solution to the problem of spectrum congestion as it offers opportunistic usage of frequency bands that are not occupied by primary users. Due to the underlying sensing, spectrum shaping, scaling, and interoperable capabilities of OFDM, it has been adapted as a best transmission technology for CR wireless systems. However, the performance of an OFDM‐based CR wireless system is affected by the existence of narrowband interference (NBI) from other users. Further, due to carrier frequency offset in NBI sources, NBI energy may spread over all subcarriers of an OFDM signal. In this paper, a fixed Amplify‐and‐Forward (AF) relay that operates at a frequency band that is different from that of direct mode is introduced to suppress the effect of NBI. Analytical expressions are derived for outage probability in direct, AF‐relay, and incremental relaying modes. The outage performance of the proposed AF relay–based CR network is proven to be better than that of direct mode.     

Closed‐form expression for the BER of m‐QAM‐OFDM systems over time‐ and frequency‐selective wireless channels

The broadcast DVB‐T system is an m‐QAM‐OFDM communication system that includes pilot‐symbol‐assisted modulation (PSAM) in order to enhance channel estimation at the receiver. This characteristic makes DVB‐T suitable for a mobile reception, over time‐ and frequency‐selective wireless channels. In this work, a closed‐form expression for the BER as a function of the transmission system, channel model and the channel estimation strategy employed at the receiver is derived. In addition, adjacent channel interference due to Doppler effects is also considered. The results are focused on the DVB‐T system under different scenarios. The channel estimation at the receiver has been shown to be very critical, and the impact of channel estimation errors on the BER is analysed in detail. Copyright © 2005 John Wiley & Sons, Ltd.     

Progressive image transmission over differentially space‐time coded OFDM systems

In this paper, we consider progressive image transmission over differentially space‐time coded orthogonal frequency‐division multiplexing (OFDM) systems and treat the problem as one of optimal joint source‐channel coding (JSCC) in the form of unequal error protection (UEP), as necessitated by embedded source coding (e.g., SPIHT and JPEG 2000). We adopt a product channel code structure that is proven to provide powerful error protection and employ low‐complexity decision‐feedback decoding for differentially space‐time coded OFDM without assuming channel state information. For a given SNR, the BER performance of the differentially space‐time coded OFDM system is treated as the channel condition in the JSCC/UEP design via a fast product code optimization algorithm so that the end‐to‐end quality of reconstructed images is optimized in the average minimum MSE sense. Extensive image transmission experiments show that SNR/BER improvements can be translated into quality gains in reconstructed images. Moreover, compared to another non‐coherent detection algorithm, i.e., the iterative receiver based on expectation‐maximization algorithm for the space‐time coded OFDM systems, differentially space‐time coded OFDM systems suffer some quality loss in reconstructed images. With the efficiency and simplicity of decision‐feedback differential decoding, differentially space‐time coded OFDM is thus a feasible modulation scheme for applications such as wireless image over mobile devices (e.g., cell phones). Copyright © 2006 John Wiley & Sons, Ltd.     

Performance analysis of WPM‐based transmission with equalization‐aware bit loading

Wavelet packet modulation (WPM) is a multicarrier modulation (MCM) technique that has emerged as a potential alternative to the widely used orthogonal frequency‐division multiplexing (OFDM) method. Because WPM has overlapped symbols, equalization cannot rely on the use of the cyclic prefix (CP), which is used in OFDM. This study applies linear minimum mean‐square error (MMSE) equalization in the time domain instead of in the frequency domain to achieve low computational complexity. With a modest equalizer filter length, the imperfection of MMSE equalization results in subcarrier attenuation and noise amplification, which are considered in the development of a bit‐loading algorithm. Analytical expressions for the bit error rate (BER) performance are derived and validated using simulation results. A performance evaluation is carried out in different test scenarios as per Recommendation ITU‐R M.1225. Numerical results show that WPM with equalization‐aware bit loading outperforms OFDM with bit loading. Because previous comparisons between WPM and OFDM did not include bit loading, the results obtained provide additional evidence of the benefits of WPM over OFDM.     

Second generation wireless information networks

To enhance the capacity and capabilities of wireless information networks, five standardized second-generation networks will be deployed in Europe, North America, and Japan. All are based on digital voice transmission and improved network control relative to the first generation. The author describes the motivation behind the standards and presents details of transmission technologies and logical control channels. Specifically, a system operation is discussed in the context of the first two layers of the open systems interconnection model. The physical layer, the multiple-access technique, the modulation format, and the method of speech coding are discussed. Regarding the data link layer, the information formats of the logical channels that convey control information to and from wireless terminals are presented     

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.     

Bandwidth estimation in high mobility scenarios of IEEE 802.11 infrastructure‐less mobile ad hoc networks

Bandwidth estimation in mobile ad hoc networks (MANET), where each node can move randomly and is capable of frequently changing its link with other nodes, is a challenging task. Motivation of this work is in contrast with TCP new‐reno which decreases the congestion window both in the event of link failure and congestion, which in the case of packet loss due to link failure should be close to available channel bandwidth. The proposed novel approach capture the node's mobility behavior in broadcast and unicast scenarios of IEEE 802.11 standard to efficiently estimate the sender's window size. This proposal introduces a data structure and source‐to‐destination path stability metric to imitate the mobility behavior of network and presents the analytic characterization of steady‐state throughput as a function of packet loss, round trip time, and path stability over IEEE 802.11 infrastructure‐less MANET. The performance is evaluated over random‐walk, random‐waypoint, and Gauss‐Markov mobility models in 2D and 3D environments using QualNet 7.4 network simulator. The proposed analytical model is also evaluated through two‐tailed statistical test. Analytical, statistical, and simulation‐based comparisons demonstrate the effectiveness of proposed method in high‐mobility scenarios.     

可变带宽光网络：提出、优势和关键技术

新型互联网业务迅速发展。使网络流量急剧增长,推动了对光通信容量的需求。同时,新型的互联网应用对带宽的需求具有不可预测性。这两方面因素驱动光网络朝着灵活、动态、高效的方向发展。可变带宽光网络可以在收发端根据传输距离、链路质量、业务需求动态调整传输速率、调制格式以匹配网络实际需求,提高了网络灵活性和网络生存性。可变带宽光网络关键技术包括可变带宽可重构光分插复用器、可变带宽收发机技术、可变带宽的电层技术和可变带宽管控层技术。     

ESIM‐OFDM‐based transceiver design of a visible light communication system

Visible light communication (VLC) system has been becoming a potential technology for short‐range data communication over wireless optical channel. In this paper, a real‐time state‐of‐the‐art VLC system prototype is implemented mainly based on enhanced subcarrier index modulation orthogonal frequency division multiplexing (ESIM‐OFDM) modulation scheme. The prototype has been designed using NI cDAQ hardware equipment programmed in matlab /labview . In other words, the developed VLC transceiver labview model is loaded into cDAQ to perform real‐time transmission of text data. The design mainly comprises VLC transmitter, VLC receiver, interfacing NI cDAQ with labview , and implementation of ESIM‐OFDM. It should be noted that the direct output of ESIM‐OFDM is not suitable to drive VLC transmitter circuit; therefore, the key contribution lies in making use of sigma–delta modulator to modify ESIM‐OFDM output to produce constant current signal which in turn could drive VLC transmitter. The second main contribution of the work targets the luminous properties of the designed transmitter that have experimentally been characterized using a LUX meter. Finally, the last contribution of the work is the simulation carried out to analyze the performance of the proposed system with other existing VLC modulation schemes. Copyright © 2016 John Wiley & Sons, Ltd.     

Adaptive multilevel modulation for grooming in elastic cloud optical networks

In order to mitigate the mismatch of granularities between fixed grid and client traffic, the elastic optical network (EON) was proposed by using orthogonal frequency division multiplexing. In EONs, the bandwidth variable transponder adjusts the number of bits per symbol, so that an optical signal generates by using just enough sub-carriers each with appropriate modulation level. Owing to the advantage of line-rate adaption above, the application of cloud computing has witnessed rapid growth in EONs. However, bandwidth variable transponders consume more power compared with ordinary ones, which will lead to a power-thirsty EON if no effective measure is taken. As a result, the green grooming was proposed for EONs. Unfortunately, the adaptive multilevel modulation was neglected in the current works focusing on green grooming. Thus, in this paper, we design a novel modulation adaptive grooming with guaranteeing transmission performances in green EONs. The distance-adaptive spectrum resource allocation is applied to the green grooming algorithm previously designed by us for EONs. The simulation results show that the adaptive multilevel modulation plays an important role on saving spectrum and power consumption for the green grooming in EONs, because the spectral bandwidth can be saved by increasing the number of bits per symbol to transmit the same data rate.     

Availability-aware service provisioning in SD-EON-based inter-datacenter networks

The tremendous transmission capacity and flexible spectrum allocation scheme make elastic optical networks (EONs) one of the most promising infrastructures for constructing the interconnection in datacenter (DC) networks. Meanwhile, as DC traffics exhibit highly dynamic and heterogeneous features, differentiated service provisioning schemes are desired. In this paper, we take the advantage of centralized network control and management provided by the software-defined elastic optical networks (SD-EONs) and investigate availability-aware service provisioning in SD-EON-based inter-datacenter (inter-DC) networks. We first describe the problem of availability-aware service provisioning in SD-EON-based inter-DC networks and present the theoretical analysis for service availability. Then, we propose an availability-aware service provisioning algorithm (ASP) that leverages different path protection schemes to satisfy different service availability requirements. A service downgrading (SD) strategy is also designed as a supplement of ASP to further improve its performance. Simulation results show that the proposed ASP-SD algorithm can effectively improve the spectrum efficiency without sacrificing availability.     

Adaptive BU association and resource allocation in integrated PON‐WiMAX networks

This paper addresses the issues of Base station—User Association and Resources Allocation (BUA‐RA) in OFDM‐TDMA based broadband wireless access (BWA) networks under passive optical networks (PON)‐WiMAX integration. With the powerful coordination capability at the optical line terminal (OLT), a key technology of inter‐cell cooperative transmission (CT) is incorporated in the integrated network architecture, which is called cooperative PON‐WiMAX network (CPWN). To achieve an efficient integration and inter‐cell cooperative transmission in the CPWNs, the BUA‐RA scheme is critical to the Quality of Service (QoS) provisioning for each user. In order to minimize the network resource usage, we provide three new BUA‐RA schemes which first time employ the cooperative transmission in a multi‐cell BWA network. The three schemes are designed for three kinds of subscribers with different moving types, and can be adaptively applied based on the network load. Simulations are conducted to verify the proposed BUA‐RA schemes by comparing with those without cooperative transmission technology. Our results demonstrate the efficiency of our proposed schemes, which are based on mathematical formulations and linearization. Copyright © 2010 John Wiley & Sons, Ltd.     

Optical transport networks

The key technologies required for the development of optical transport networks, namely, optical fiber transmission and digital transport, which includes transmission signal multiplexing, transport nodes, and network operation functions, are highlighted. The trends in transport technology, the impact of synchronous digital hierarchy (SDH) and asynchronous transfer mode (ATM), the role of telecommunications management networks, and network integrity enhancement techniques are elucidated. It is demonstrated that these technologies have brought about a great change in transport network design and performance. Further innovations are required to fully realize a high-performance computer communication network, a cost-effective nationwide B-ISDN, and local networks for video distribution. These include the realization of an optical access transport network and the extension of trunk network capabilities which will be possible with optical path layer technologies     

Multi‐hour design of survivable classical IP networks

Most of Internet intra‐domain routing protocols (OSPF, RIP, and IS–IS) are based on shortest path routing. The path length is defined as the sum of metrics associated with the path links. These metrics are often managed by the network administrator. In this context, the design of an Internet backbone network consists in dimensioning the network (routers and transmission links) and establishing the metric. Many requirements have to be satisfied. First, Internet traffic is not static as significant variations can be observed during the day. Second, many failures can occur (cable cuts, hardware failures, software failures, etc.). In this paper, we present algorithms (meta‐heuristics and greedy heuristic) to design Internet backbone networks, taking into account the multi‐hour behaviour of traffic and some survivability requirements. Many multi‐hour and protection strategies are studied and numerically compared in this paper. Our algorithms can be extended to integrate other quality of service constraints. Copyright © 2002 John Wiley & Sons, Ltd.     

A next-generation optical regional access network

We describe an optical regional access network which combines electronic IP routing with intelligent networking functionality of the optical WDM layer. The optical WDM layer provides such networking functions as network logical topology reconfiguration, optical flow switching to offload traffic and bypass IP routers, wavelength routing of signals, protection switching and restoration in the optical domain, and flexible network service provisioning by reconfigurable wavelength connectivity. We discuss key enabling technologies for the WDM layer and describe their limitations. The symbiosis of electronic and optical WDM networking functions also allows support for heterogeneous format traffic and will enable efficient gigabit-per-second user access in next-generation Internet networks     

SDN‐based fault‐tolerant on‐demand and in‐advance bandwidth reservation in data center interconnects

Geographically distributed data centers are interconnected through provisioned dedicated WAN links, realized by circuit/wavelength–switching that support large‐scale data transfer between data centers. These dedicated WAN links are typically shared by multiple services through on‐demand and in‐advance resource reservations, resulting in varying bandwidth availability in future time periods. Such an inter‐data center network provides a dynamic and virtualized environment when augmented with cloud infrastructure supporting end‐host migration. In such an environment, dynamically provisioned network resources are recognized as extremely useful capabilities for many types of network services. However, the existing approaches to in‐advance reservation services provide limited reservation capabilities, eg, limited connections over links returned by the traceroute over traditional IP‐based networks. Moreover, most existing approaches do not address fault tolerance in the event of node or link failures and do not handle end‐host migrations; thus, they do not provide a reliability guarantee for in‐advance reservation frameworks. In this paper, we propose using multiple paths to increase bandwidth usage in the WAN links between data centers when a single path does not provide the requested bandwidth. Emulation‐based evaluations of the proposed path computation show a higher reservation acceptance rate compared to state‐of‐art reservation frameworks, and such computed paths can be configured with a limited number of static forwarding rules on switches. Our prototype provides the RESTful Web service interface for link‐fail and end‐host migration event management and reroutes paths for all the affected reservations.     

Survivability using traffic balancing and backup resource reservation in multi‐domain optical networks

Survivability in the geographically distributed backbone multi‐domain optical networks (MDONs) is critical because of issues related to its size, usage of resources, and domain management policies of the comprising domains. In MDONs, the emerging scheduled traffic is increasingly multivendor, multimedia, and periodic. It is high during the office (working) hours and low during the non‐office (non‐working) hours in a day. A connection failure during the office hours may result in huge amount of information being lost. Towards providing an acceptable level of service even when a connection fails, we first provide traffic balancing (TB) based solutions where the intra/inter‐domain traffic is slided (S1‐TB), shifted (S2‐TB), or slided as well as shifted (S3‐TB) based on the service level agreement between the client and domain service provider. Of the above solutions, the solution based on sliding as well as shifting (S3‐TB) performs best, and hence for further improvement in S3‐TB, we incorporate backup multiplexing with advance backup resource reservation (BRR) and evaluate the performance of the strategy and report results. The performance evaluation of the above strategies is compared with the existing extended path shared protection (EPSP) by a simulator developed in MATLAB and tested on three‐domain and five‐domain standard network topologies, on the metrics of blocking probability, network resource utilization ratio, network capacity utilized by backup route, wavelength link used per backup lightpath, and a newly introduced metric, network resource utilization index. As compared with the existing strategy EPSP, the S3‐TB and S3‐TB with BRR showed improved performance on all the metrics.