NetMod: a design tool for large-scale heterogeneous campus networks

A network modeling tool, called NetMod, which uses simple analytical models to provide the designers of large interconnected local area networks with an in-depth analysis of the potential performance of these systems is presented. This tool can be used in either a university, industrial, or governmental campus networking environment consisting of thousands of computer sites. NetMod is implemented with a combination of the easy-to-use Macintosh software packages, HyperCard, and Excel. The objectives of NetMod, the analytical models, and the user interface are described in detail, along with its application to an actual campus-wide network     

Achieving Network Availability in a Multilayered Protocol Environment

The software/hardware is available now to quickly construct very large networks. These networks contain various layers of connectivity with the possibility of different vendors providing each layer. Each layer may have its own means of operator management and control. The growth of these networks is starting to outstrip the ability of network operators to effectively recognize and attack problems. Future networking with independent microcomputers provide even fewer tools for network support personnel. What should network management software provide the operator in a multilayered multivendor environment, and what role do network protocols play in solving the problems they created? The author will he expressing his own opinion based on his experience with a large IBM SNA network (28 hosts) connected through a privately owned X.25 network.     

Throughput-Delay Performance of Interconnected CSMA Local Area Networks

The interconnection of two local area networks, each of which connects a large population of users via a carrier-sense multipleaccess (CSMA) channel is considered. In each network, a bridge node receives internetwork packets from the local users and forwards them to the bridge node of the other network via a point-to-point link; the bridge node of the destination network queues these internetwork packets for subsequent broadcasting to the local users. For the multiplexing of the user transmissions and the bridge node transmissions on the available broadcast channel in each network, frequency division, and contention are considered. The throughput-delay characteristics of the interconnected system operating under the above multiplexing techniques are found and comparisons are made. It is shown that contention multiplexing can yield system performance comparable to that of frequency division multiplexing, while requiring no hardware or software modification of either network in the interconnected system.     

NetScope: traffic engineering for IP networks

Managing large IP networks requires an understanding of the current traffic flows, routing policies, and network configuration. However, the state of the art for managing IP networks involves manual configuration of each IP router, and traffic engineering based on limited measurements. The networking industry is sorely lacking in software systems that a large Internet service provider can use to support traffic measurement and network modeling, the underpinnings of effective traffic engineering. This article describes the AT&T Labs NetScope, a unified set of software tools for managing the performance of IP backbone networks. The key idea behind NetScope is to generate global views of the network on the basis of configuration and usage data associated with the individual network elements. Having created an appropriate global view, we are able to infer and visualize the networkwide implications of local changes in traffic, configuration, and control. Using NetScope, a network provider can experiment with changes in network configuration in a simulated environment rather than the operational network. In addition, the tool provides a sound framework for additional modules for network optimization and performance debugging. We demonstrate the capabilities of the tool through an example traffic engineering exercise of locating a heavily loaded link, identifying which traffic demands flow on the link, and changing the configuration of intradomain routing to reduce the congestion     

An overlay approach to data security in ad-hoc networks

While it has been argued that application-layer overlay protocols can enhance services in mobile ad-hoc networks, hardly any empirical data is available on the throughput and delay performance achievable in this fashion. This paper presents performance measurements of an application-layer overlay approach that ensures integrity and confidentiality of application data in an ad-hoc environment. A key management and encryption scheme, called neighborhood key method, is presented where each node shares secrets only with authenticated neighbors in the ad-hoc network, thus avoiding global re-keying operations. All proposed solutions have been implemented and empirically evaluated in an existing software system for application-layer overlay networking. Results from indoor and outdoor measurement experiments with mobile handheld devices provide insight into the performance and overhead of overlay networking and application-layer security services in ad-hoc networks.     

An SDN approach to route massive data flows of sensor networks

With the advent of the Internet of Things (IoT), more and more devices can establish a connection with local area networks and use routing protocols to forward all information to the sink. But these devices may not have enough resources to execute a complex routing protocol or to memorize all information about the network. With proactive routing protocols, each node calculates the best path, and it needs enough resources to memorize the network topology. With reactive routing protocols, each node has to broadcast the message to learn the right path that the packets must follow. In all cases, in large networks such as IoT, this is not an appropriate mechanism. This paper presents a new software‐defined network (SDN)–based network architecture to optimize the resource consumption of each IoT object while securing the exchange of messages between the embedded devices. In this architecture, the controller is in charge of all decisions, and objects only exchange messages and forward packets among themselves. In the case of large networks, the network is organized into clusters. Our proposed network architectures are tested with 1000 things grouped in five clusters and managed by one SDN controller. The tests using OpenDayLight and IoT embedded applications have been implemented on several scenarios providing the ability and the scalability from dynamic reorganization of the end‐devices. This approach explores the network performance issues using a virtualized SDN‐clustered environment which contributes to a new model for future network architectures.     

Internet 0 — Inter-Device Internetworking

The assumptions behind Internet architectures do not scale to small devices — they have a baseline cost that is still too high for small, few-dollar, embedded objects. This barrier either leaves many devices network disenfranchised or encourages the creation of segmented networks. Internet 0 attempts to enable pervasive computing and networking on the embedded level by providing the Internet protocol as a communications substrate, and, through the use of an end-to-end modulation scheme, to speak to devices. I0 is a framework to bridge together heterogeneous devices via IP in a manner that is still compatible with designing globally large computer networks.     

Scalable proxy caching of video under storage constraints

Proxy caching has been used to speed up Web browsing and reduce networking costs. In this paper, we study the extension of proxy caching techniques to streaming video applications. A trivial extension consists of storing complete video sequences in the cache. However, this may not be applicable in situations where the video objects are very large and proxy cache space is limited. We show that the approaches proposed in this paper (referred to as selective caching), where only a few frames are cached, can also contribute to significant improvements in the overall performance. In particular, we discuss two network environments for streaming video, namely, quality-of-service (QoS) networks and best-effort networks (Internet). For QoS networks, the video caching goal is to reduce the network bandwidth costs; for best-effort networks, the goal is to increase the robustness of continuous playback against poor network conditions (such as congestion, delay, and loss). Two different selective caching algorithms (SCQ and SCB) are proposed, one for each network scenario, to increase the relevant overall performance metric in each case, while requiring only a fraction of the video stream to be cached. The main contribution of our work is to provide algorithms that are efficient even when the buffer memory available at the client is limited. These algorithms are also scalable so that when changes in the environment occur it is possible, with low complexity, to modify the allocation of cache space to different video sequences.     

How different messaging semantics can affect SCA applications performances: a benchmark comparison

Software Communications Architecture (SCA) compliant radios typically contain a large number of software components. Some software components provide access to hardware devices while others perform signal processing. By interacting with each other, the software components implement a radio communications standard. To interact, the software components use a middleware called Common Object Request Broker Architecture (CORBA). Using CORBA, each interaction is carried out as an exchange of messages between two components. CORBA supports two main types of messaging: one-way and two-way. This article explores the differences between the two types of messaging and provides performance metrics. The article also describes design approaches that can be used to avoid common pitfalls associated with the use of both types of messaging.     

Toward management systems for emerging hybrid fiber-coax accessnetworks

Advances in networking and hardware are motivating the development of high bandwidth local access networks that connect subscriber communities to the Information Superhighway. Hybrid fiber-coaxial (HFC) technology is emerging as one of the few economical viable technologies for designing new local access networks. These HFC local access networks are expected to support a variety of services in different spheres in an integrated manner, by drawing upon diverse technologies from the cable, computer, and telecommunications industries: the tree-and-branch network topology is typical of the cable network; intelligence in the end devices is a characteristic of the computer industry; and addressability, global interconnectivity, and quality of service (QoS) are characteristic of the telecommunications industry. It is this combination of diverse services and technologies that poses fundamental challenges in architecting a management system for HFC networks. The design of a management framework for HFC access networks is discussed     

机载计算机RS422A通讯的软硬件设计与实现

RS422A、RS485等异步串行通讯技术广泛应用于机载计算机实时控制系统,提高了飞机的可维护性和可扩展性。为使其稳定工作,不仅需要可靠硬件平台,还需严密的软件算法。文中描述了某机载计算机为实现与多个设备进行实时异步串行通讯,设计了统一的硬件平台,并根据每个设备不同的通讯协议,给出了不同的软件算法,重点阐述了软件设计及原理。根据该原理研制的产品已经过试验、联试和用户使用,证明其工作可靠、性能良好。     

Home networking and the CableHome project at CableLabs

Home networking technologies and capabilities are receiving increased attention from consumers, software developers, hardware manufacturers, and service providers. Rapid innovation in home networking technology-advances in silicon, digital signal processing, and protocols-are improving the performance and lowering the cost of home network solutions. Cable system operators will depend on home networks for deployment of advanced services. The goal of the CableHome architecture is to establish a hone network environment within which the delivery of quality cable-based services can be ensured     

Hardware implementation of fair queuing algorithms for asynchronoustransfer mode networks

Providing quality-of-service guarantees in both cell- and packet-based networks requires the use of a scheduling algorithm in the switches and network interfaces. These algorithms need to be implemented in hardware in a high-speed switch. The authors present a number of approaches to implement scheduling algorithms in hardware. They begin by presenting a general methodology for the design of timestamp-based fair queuing algorithms that provide the same bounds on end-to-end delay and fairness as those of weighted fair queuing, yet have efficient hardware implementations. Based on this general methodology, the authors describe two specific algorithms, frame-based fair queuing and starting potential-based fair queuing, and discuss illustrative implementations in hardware. These algorithms may be used in both cell switches and packet switches with variable-size packets. A methodology for combining a traffic shaper with this class of fair queuing schedulers is also presented for use in network interface devices, such as an ATM segmentation and reassembly device     

Application of IEEE 802.16 Mesh Networks as the Backhaul of Multihop Cellular Networks

Cellular networks have been widely used to support many new audio-and video-based multimedia applications. The demand for higher data rate and diverse services has driven the research on multihop cellular networks (MCNs). With its ad hoc network features, an MCN can offer many additional advantages, such as increased network throughput, scalability and coverage. However, providing ad hoc capability to MCNs is challenging as it may require proper wireless interfaces. In this article, the architecture of IEEE 802.16 network interface to provide ad hoc capability for MCNs is investigated, with its focus on the IEEE 802.16 mesh networking and scheduling. Several distributed routing algorithms based on network entry mechanism are studied and compared with a centralized routing algorithm. It is observed from the simulation results that 802.16 mesh networks have limitations on providing sufficient bandwidth for the traffic from the cellular base stations when a cellular network size is relatively large.     

A software defined radio modeling framework for enabling cognitive applications

The rapid advances in software defined radio (SDR) technologies over the past decade encouraged their transition from the lab to field deployment, and shifted the usage from disparate communication devices to the creation of large resilient wireless networks capable of adapting to highly variable environment conditions in a cognitive manner. Simulation models capable of accurately representing the behavior and properties of SDR devices operating in a networked environment thus become a prerequisite for both the evaluation of such networks as well as for providing a development platform for creating new cognitive capabilities. This paper describes our work in creating a network simulation model framework for software defined radios that takes into account some of the unique behaviors and requirements of SDRs not previously seen in purely hardware devices. Factors such as large and variable communication delays between software modules, contention to shared resources, such as CPU or memory, as well as continuous tuning and environment awareness functionality essential to SDR demand a different modeling approach as well as novel techniques that enable accurate scale testing.     

基于CPLD的功率输出自测试及保护技术研究

机载供电系统中存在大量的功率接触器和继电器,在驱动这些装置时,如果电路中的瞬态电流过大,将损坏机载计算机本身及后级控制电路.本文设计并实现了一种基于CPLD的功率输出自测试及短路保护技术,由硬件分立元器件和可编程逻辑器件代替DSP处理器,无需软件参与,完全由硬件实现功率驱动和过流保护,使其具有非常高的可靠性和安全性,性能大大优于传统控制开关.     

A fieldbus prototype for educational purposes

One of the problems with instrumentation systems is the interconnection between the multiple devices with different communication protocols. Exacerbating this problem are two typical requirements of interconnection: minimize cabling cost and avoid degradation of the signal during transmission. Cabling cost can be reduced through several multidrop communication systems: industrial local area networks or wireless communication. Reduction of signal to noise can restrict system performance and the quality of manufactured products, even if high-accuracy devices are used. Another problem in the field of manufacturing instrumentation networks is that industry uses multiple solutions to interconnect instrumentation with different communication protocols. This article presents the development of a prototype for an instrumentation network with the goal to study and analyze the characteristics of the different communication solutions. The overall system contains a large number of instrumentation devices, which is a great advantage for educational purposes and laboratory experiments. The students can configure, calibrate, and operate a large number of instruments connected to different segments of the DCS. We also connected some current-loop devices to the FF system to evaluate their performance when connected to a fully digital network. Results from the prototype DCS show that networking between different instrumentation devices and protocols can be successful and that a hybrid solution using conventional 4-20 mA current loop and fully digital instrumentation can work to leverage existing analogue systems. Future work will include the development of a fieldbus network analyzer to trace messages in the network and study the quality of FF service parameters, such as packet loss and delay measurement, as a function of network load.     

面向大规模网络的快速重叠社团挖掘算法

重叠社团在社交网络大数据中普遍存在.针对现有重叠社团挖掘算法易将重叠区域错误地划分为独立的社团且计算复杂的问题,提出了一种基于局部信息度量的快速重叠社团挖掘算法（Local information based Fast Overlapped Communities Detection,Li-FOCD）.首先,为节点定义局部信息度量指标——社团连接度和邻居连接度,建模节点与社团的关系,缩小了计算范围;然后,每次并行地迭代执行缩减、扩展、去重等操作,并更新局部度量指标,通过松弛每次迭代的终止条件,发现近似最优社团集合而不是最优社团,最终算法复杂度为O（m+n）.基于真实的大规模社交网络数据的试验分析表明：与当前流行的重叠社团挖掘算法相比,Li-FOCD在不损失检测质量的前提下,大幅提升了计算效率.