Architectural considerations in the design of WDM-based optical access networks

We describe a WDM-based optical access network architecture for providing broadband Internet services. The architecture uses a passive collection and distribution network and a configurable Feeder network. Unlike earlier papers that concentrate on the physical layer design of the network, we focus on higher layer architectural considerations. In particular we discuss the joint design of the electronic and optical layers including: WDM Medium Access Control protocols; the choice of electronic multiplexing and switching between the IP and WDM layers; joint optical and electronic protection mechanisms; network reconfiguration algorithms that alter the logical topology of the network in response to changes in traffic; and traffic grooming algorithms to minimize the cost of electronic multiplexing. Finally we also discuss the impact of the optical topology on higher layer protocols such as IP routing, TCP flow control and multi-layer switching.     

Performance analysis of sleep mode mechanisms in the presence of bidirectional traffic

Short battery life being a major impediment to a more widespread use of wireless devices, industry standards like WiMAX and 3GPP Long Term Evolution (LTE) embed power saving mechanisms in their protocol stack. Trading in network delay performance for extended battery life, these mechanisms require a careful balance to optimize overall network performance. Therefore, this paper assesses the impact of these mechanisms on network delay performance and battery life, thereby refining existing performance studies of the power saving mechanisms. In particular, this paper explicitly takes into account presence of both downlink and uplink traffic and their influence on the power saving mechanism. This contrasts with previous studies, where the analyses only accounted for downlink traffic. We obtain numerically efficient procedures to compute packet delay as well as energy efficiency characteristics under Markovian traffic. Then, performance of power saving is investigated by some numerical examples. Our results clearly indicate that uplink traffic heavily impacts the energy efficiency of the power saving mechanism.     

LTRES: A loss-tolerant reliable event sensing protocol for wireless sensor networks

Many Wireless Sensor Network (WSN) transport protocols proposed in recent studies focus on providing end-to-end reliability as in TCP. However, traditional end-to-end reliability enforcement is energy and time consuming for common loss-tolerant applications in WSNs. In this paper, a Loss-Tolerant Reliable Event Sensing protocol (LTRES) is proposed based on the particular reliability requirements for dynamic event observation in WSNs. According to the application-specific requirements, a reliable event sensing threshold at the transport layer is determined by the sink. A distributed source rate adaptation mechanism is designed, incorporating a loss rate based lightweight congestion control mechanism, to regulate the data traffic injected into the network so that the reliability requirements can be satisfied. An equation based fair rate control algorithm is designed to improve the fairness among the traffic flows sharing the congestion path. The performance evaluations show that LTRES can provide event-based loss-tolerant reliable data transport service for multiple events with short convergence time, low loss rate and high overall bandwidth utilization.     

Energy efficiency of femtocell deployment in combined wireless/optical access networks

Optical/wireless convergence has become of particular interest recently because a combined radio wireless and optical wired network has the potential to provide both mobility and high bandwidth in an efficient way. Recent developments of new radio access technologies such as the Long Term Evolution (LTE) and introduction of femtocell base stations open new perspectives in providing broadband services and applications to everyone and everywhere, but the instantaneous quality of radio channel varies in time, space and frequency and radio communication is inherently energy inefficient and susceptible to reflections and interference. On the other hand, optical fiber-based networks do not provide mobility, but they are robust, energy efficient, and able to provide both an almost unlimited bandwidth and high availability.In this paper, we analyze the energy efficiency of combined wireless/optical access networks, in which LTE technology provides ubiquitous broadband Internet access, while optical fiber-based technologies serve as wireless backhaul and offer high-bandwidth wired Internet access to business and residential customers. In this contest, we pay a particular attention to femtocell deployment for increasing both access data rates and area coverage. The paper presents a novel model for evaluating the energy efficiency of combined optical/wireless networks that takes into account the main architectural and implementational aspects of both RF wireless and optical parts of the access network. Several hypothetical network deployment scenarios are defined and used to study effects of femtocell deployment and power saving techniques on network’s energy efficiency in urban, suburban and rural areas and for different traffic conditions.     

A power consumption sensitivity analysis of circuit-switched versus packet-switched backbone networks

While telecommunication networks have historically been dominated by a circuit-switched paradigm, the last decades have seen a clear trend towards packet-switched networks. In this paper we evaluate how both paradigms (which have also been referred to as optical bypass and non-bypass, respectively) perform in optical backbone networks from a power consumption point of view, and whether the general agreement of circuit switching being more power-efficient holds. We consider artificially generated topologies of various sizes, mesh degrees and – not yet previously explored in this context – transport linerates. We cross-validate our findings with a number of realistic topologies.Our results show that circuit switching is preferable when the average node-to-node demands are higher than half the transport linerates. However, packet switching can become preferable when the traffic demands are lower than half the transport linerate. We find that an increase in the network node count does not consistently increase the energy savings of circuit switching over packet switching, but the savings are heavily influenced by the mesh degree and (to a minor extent) by the average link length. Our results are consistent for uniform traffic demands and realistic traffic demands.A key take-away message for other research on power saving solutions in backbone networks is that the ratio between the average demand and the demand bitrate has considerable effect on the overall efficiency, and should be taken into account.     

Energy efficiency analysis for flexible-grid OFDM-based optical networks

As the Internet traffic grows, the energy efficiency gains more attention as a design factor for the planning and operation of telecommunication networks. This paper is devoted to the study of energy efficiency in optical transport networks, comparing the performance of an innovative flexible-grid network based on Orthogonal Frequency Division Multiplexing (OFDM) with that of conventional fixed-grid Wavelength Division Multiplexing (WDM) networks with a Single Line Rate (SLR) and with a Mixed Line Rate (MLR) operation. The power consumption values of the network elements are introduced. Energy-aware heuristic algorithms are proposed for the resource allocation both in static (offline) and dynamic (online) scenarios with time-varying demands for the Elastic-bandwidth OFDM-based network and the WDM networks (with SLR and MLR). The energy efficiency performance of the two network technologies under different traffic load conditions have been demonstrated for different network sizes through simulations based on the proposed algorithms. The results in energy efficiency and network blocking highlight the benefits of the bandwidth elasticity and the flexibility of selecting different modulation formats offered by OFDM networks.     

A virtual service placement approach based on improved quantum genetic algorithm

Despite the critical role that middleboxes play in introducing new network functionality, management and innovation of them are still severe challenges for network operators, since traditional middleboxes based on hardware lack service flexibility and scalability. Recently, though new networking technologies, such as network function virtualization (NFV) and software-defined networking (SDN), are considered as very promising drivers to design cost-efficient middlebox service architectures, how to guarantee transmission efficiency has drawn little attention under the condition of adding virtual service process for traffic. Therefore, we focus on the service deployment problem to reduce the transport delay in the network with a combination of NFV and SDN. First, a framework is designed for service placement decision, and an integer linear programming model is proposed to resolve the service placement and minimize the network transport delay. Then a heuristic solution is designed based on the improved quantum genetic algorithm. Experimental results show that our proposed method can calculate automatically the optimal placement schemes. Our scheme can achieve lower overall transport delay for a network compared with other schemes and reduce 30% of the average traffic transport delay compared with the random placement scheme.     

Intelligent shared-segment protection

Progress in network technologies and protocols is paving the road towards flexible optical transport networks, in which dynamic leasable circuits could be set up and released on a short-term basis according to customers’ requirements.Recently, new solutions for automatized network management promise to allow customers to specify the terms of the service level agreement (SLA) to be guaranteed (with different price range) by the service provider. In this paper we consider that these service level specifications (SLS), since they are now made available on-demand during the connection request, could be exploited to retrieve useful information able to improve the routing efficiency.In particular, we propose to exploit the knowledge of connection holding time, among the other SLS, to develop a novel intelligent approach for shared-segment protection (SSP).We will exploit the knowledge of the holding-time of connection requests to minimize resource overbuild due to backup capacity and hence to achieve resource-usage efficiency. For a typical US nationwide network, we compare our two proposed holding-time aware approaches to the respective two holding-time-unaware approaches: both of them, even in their holding-time unaware version, have been shown to be very efficient solutions for shared-segment protection. Nonetheless, we have obtained additional savings on resource overbuild of up to 11% for practical scenarios exploiting holding-time knowledge.     

Dynamic power management in energy-aware computer networks and data intensive computing systems

Energy awareness is an important aspect of modern network and computing system design and management, especially in the case of internet-scale networks and data intensive large scale distributed computing systems. The main challenge is to design and develop novel technologies, architectures and methods that allow us to reduce energy consumption in such infrastructures, which is also the main reason for reducing the total cost of running a network. Energy-aware network components as well as new control and optimization strategies may save the energy utilized by the whole system through adaptation of network capacity and resources to the actual traffic load and demands, while ensuring end-to-end quality of service. In this paper, we have designed and developed a two-level control framework for reducing power consumption in computer networks. The implementation of this framework provides the local control mechanisms that are implemented at the network device level and network-wide control strategies implemented at the central control level. We also developed network-wide optimization algorithms for calculating the power setting of energy consuming network components and energy-aware routing for the recommended network configuration. The utility and efficiency of our framework have been verified by simulation and by laboratory tests. The test cases were carried out on a number of synthetic as well as on real network topologies, giving encouraging results. Thus, we come up with well justified recommendations for energy-aware computer network design, to conclude the paper.     

An energy-efficient,transport-controlled MAC protocol for wireless sensor networks

In wireless sensor networks (WSNs), one major cause of wasted energy is that the wireless network interface is always on to accept possible traffic. Many medium access control (MAC) protocols therefore adopted a periodic listen-and-sleep scheme to save energy, at sacrifice of end-to-end latency and throughput. Another cause is packet dropping due to network congestion, necessitating a lightweight transport protocol for WSNs. In this paper, we suggest a transport-controlled MAC protocol (TC-MAC) that combines the transport protocol into the MAC protocol with the aims of achieving high performance as well as energy efficiency in multi-hop forwarding. Although TC-MAC also works through a periodic listen-and-sleep scheme, it lowers end-to-end latency by reserving data forwarding schedules across multi-hop nodes during the listen period and by forwarding data during the sleep period, all while increasing throughput by piggybacking the subsequent data forwarding schedule on current data transmissions and forwarding data consecutively. In addition, TC-MAC gives a fairness-aware lightweight transport control mechanism based on benefits of using the MAC-layer information. The results show that TC-MAC performs as well as an 802.11-like MAC in end-to-end latency and throughput, and is more efficient than S-MAC in energy consumption, with the additional advantage of supporting fairness-aware congestion control.     

Performance analysis and improvement of PR-SCTP for small messages

PR-SCTP, a partially reliable extension of SCTP, provides a flexible QoS trade-off between timeliness and reliability for application traffic. However, the performance of PR-SCTP can be affected by certain traffic characteristics and network scenarios. We previously proposed an NR-SACK based optimization for PR-SCTP. In this work, we extensively evaluate and analyze the performance of PR-SCTP with NR-SACKs using different network scenarios. Moreover, we compare the performance of our NR-SACK based PR-SCTP with existing transport protocols for syslog traffic. In the evaluation, we use real syslog traces from an operational syslog system. The results indicate that NR-SACK based PR-SCTP significantly improves the overall message transfer delay as compared to SCTP and TCP.     

一种光传送网分层结构及其业务量疏导优化模型

提出一种包括IP、SDH和WDM三种网络层次的光传送网分层结构及其业务量疏导优化模型。IP和SDH层的逻辑拓扑由优化模型根据这两层的业务请求矩阵生成，IP和SDH层以多种带宽颗粒度串路承栽具有不同请求带宽的业务流，模型以最大化网络流量为目标，定义了三种网络层次上不同颗粒度串路之间和串路与业务流之间的相关性约束。在不同网络资源配置下，利用Lingo优化软件对模型的求解结果验证了模型的有效性。     

无线数据中心网络：进展、挑战和展望

随着动态数据流量的迅速增长,庞杂的有线数据中心网络架构给网络扩张、能耗管理和运营维护等方面均带来了巨大的挑战。高速无线技术具有高带宽、动态连接且灵活可控的特征优势,成为一种潜在的数据中心组网解决方案,可以缓解数据中心长期存在的流量拥塞热点问题,减少部署和维护光缆所花费的时间、精力和成本。首先介绍了当前数据中心网络架构的发展趋势,分析比较了毫米波、太赫兹和自由空间光作为无线数据中心网络候选高速无线技术的优缺点。然后深入讨论了当前典型的无线数据中心网络架构,阐述了无线数据中心网络设计和部署面临的挑战,并对其未来发展方向进行了展望。     

Reduced Carbon and Energy Footprint in Highway Operations: The Highway Energy Assessment (HERA) Methodology

Global demand for mobility is increasing and the environmental impact of transport has become an important issue in transportation network planning and decision-making, as well as in the operational management phase. Suitable methods are required to assess emissions and fuel consumption reduction strategies that seek to improve energy efficiency and furthering decarbonization. This study describes the development and application of an improved modeling framework – the HERA (Highway EneRgy Assessment) methodology – that enables to assess the energy and carbon footprint of different highways and traffic flow scenarios and their comparison. HERA incorporates an average speed consumption model adjusted with a correction factor which takes into account the road gradient. It provides a more comprehensive method for estimating the footprint of particular highway segments under specific traffic conditions. It includes the application of the methodology to the Spanish highway network to validate it. Finally, a case study shows the benefits from using this methodology and how to integrate the objective of carbon footprint reductions into highway design, operation and scenario comparison.     

RETRACTED ARTICLE: Hierarchical evaluation algorithm of logistics carrying capacity based on transfer learning in multimedia environment

In order to measure and enhance the carrying capacity of regional logistics system scientifically and give full play to the efficiency of regional logistics system, based on the perspective of sustainable development, this paper analyzes the network topology structure of regional logistics system. Combining the component elements and operation flow of regional logistics system, we take link line, operation capacity and energy environment as constraint conditions, and construct the measurement model of regional logistics system carrying capacity. The integrated management of logistics requires systematic integration of various modes of transportation, such as highway transportation, water transportation, rail transportation and air transportation, as well as the network of key nodes and their network. Therefore, we need to solve the different transportation models and the nodal carrying capacity calculation methods that constitute the logistics system. Therefore, this paper analyzes the connotation, various transportation mode and port capacity related to the concept of research ideas, research tools and methods, the related calculation formula, traffic flow as the main line to construct different modes of transport carrying capacity between the inner link, and the bearing capacity formula of each transport mode into a unified unit, the transportation mode of coordinated development that is the basis of the overall optimization and decision of logistics system.

     

Energy-efficient routing over coordinated sleep scheduling in wireless ad hoc networks

In this paper, we study how energy-efficient routing at the network layer can be coordinated with sleep scheduling at the link layer to increase network-wide energy efficiency in wireless ad hoc networks. We identify a trade-off between the reduced transmit power at senders with multi-receiver diversity and the increased receive power at forwarders with coordinated sleep scheduling. Moreover, we provide a comprehensive study of how coordinated sleep scheduling affects the energy-efficient routing performance based on a 2-D gird topology and time division multiple access (TDMA) medium access control (MAC). Simulation results demonstrate the effectiveness of the integrated routing and sleep scheduling, significant impact of coordinated sleep scheduling on the energy-efficient routing performance, and relationship between networking conditions (in terms of the traffic load and node density) and overall system performance achieved by different energy-efficient routing protocols.     

Comparison of capacity efficiency of DCS network restoration routing techniques

A crucial issue in the management of telecommunications networks is restoration after a network failure. We compare the capacity efficiency (the amount of traffic restored over fixed capacity) of several types of restoration methods for Digital Crossconnect Systems (DCSs) under both node or link failures in metropolitan networks. These restoration methods can be broadly categorized based on the type of control of the restoration process and the type of procedure for rerouting traffic around the failure. It is easily shown that point-to-point methods (where traffic is rerouted end-to-end) restore a higher percent of traffic than patch methods (where traffic is rerouted only around the failed segment). However, quantification of the difference in efficiency among the methods is important to fully evaluate other trade-offs, such as cost and speed of restoration. To evaluate the efficiency difference, we generated random network traffic distributions by simulation and then failed links and nodes for each simulation sample. Statistics were generated on the expected amount of restored traffic for each restoration method. In particular, we found that the efficiency advantage of point-to-point methods over patch methods is greater for link failure than for node failure. Also, the difference was not statistically significant in low levels of network congestion (i.e., networks with large amounts of excess capacity) and became more significant as network congestion increased.     

基于B/S模式和JSP技术的网络流量动态监控系统

网络流量监控是进行网络管理的一种手段,可以通过监控对网络资源的运行效率和配置的合理性进行全面了解。论文基于B/S模式和JSP技术,论述了一个网络流量动态监控系统的设计与实现技术。该系统具有交互性和实时性好、数据库自动维护、不影响网络运行等特点。     

Medium-access control protocols for WDM-based optical access networks with passive-star clusters interconnected by a backbone ring

This paper investigates the performance of medium access control (MAC) protocols in a wavelength-division multiplexing (WDM) based optical access network consisting of a backbone ring interconnecting several passive-star-based clusters of optical networking units (ONUs) at customer premises. Each cluster is connected to the backbone through an access node (AN). A scheduler located in each AN, executes two MAC protocols, one for the intracluster traffic and the other for the intercluster traffic. In order to maintain the quality of service, the scheduler in the AN employs, priority-based queuing for the intercluster traffic on pre-assigned wavelengths. For controlling the intracluster traffic, the scheduler employs pre-transmission coordination with ranging and look-ahead functionalities in the MAC protocol. The performance of MAC protocol for intracluster traffic is evaluated through event-driven simulation, while for intercluster traffic the MAC performance is evaluated through analytical modeling of the queuing system employing two dynamic bandwidth management schemes. Performance of the intracluster MAC protocol is shown to be improved by novel use of subcarrier multiplexing on the wavelength used for the control packet transmission. A comparative study of the two intercluster schemes in terms of end-to-end delay is carried out, to understand the effect of priority queuing on the real-time and non-real-time service packets.