HFC网络中的PHS技术

接入网是目前网络接入技术的一个热点。介绍HFC接入网的发展现状，讨论如何充分利用接入网的带宽资源，重点对HFC网络中采用的净负荷标头抑制(PHS)技术作探讨，给出PHS技术的原理、实现方法并举例说明。     

适于异步光分组交换的反射式光分组头提取方案

基于半导体光放大器(SOA),提出了一种适于异步光分组交换的反射式全光分组头提取方案,它具有比特率透明、开关比(CR)大等特点,适于变长、全光分组交换。仿真了不同速率光分组头的提取效果,分析了系统参数对CR的影响。结果表明,当分组头脉冲速率分别为622Mb/s、2.5Gb/s及10Gb/s时,CR分别为25.46、25及21.7dB。CR随输入脉冲能量、小信号增益及SOA饱和能量的增大而增大,通过适当选取这些参数,可进一步提高系统性能。     

Design and Realization of a Novel Header Compression Scheme for Ad Hoc Networks

IP header compression schemes offer a valuable measure for bandwidth preservation. Such schemes have been practically implemented in infrastructure‐based IP networks for point‐to‐point links. However, minimal research and practical implementation efforts have been conducted in the direction of an IP header compression strategy that can meet the peculiar requirements of multi‐hop ad hoc wireless networks. In this paper, we present a practically implemented multi‐hop IP header compression scheme using the Robust Header Compression (ROHC) protocol suite. The scheme runs on a novel identifier (ID) based networking architecture, known as an ID‐based ad hoc network (IDHOCNET). IDHOCNET additionally solves a number of bottlenecks of pure IP‐based ad hoc networks that have emerged owing to IP address auto‐configuration service, distributed naming and name resolution, and the role of an IP address as an identifier at the application layer. The proposed scheme was tested on a multi‐hop test bed. The results show that the implemented scheme has better gain and requires only O (1) ROHC contexts.     

一个无线传感器网络中的ipv6协议栈头部压缩方案

提出了一个无线传感器网络中的IPv6协议栈的头部压缩方案,包括IPv6头部、扩展头部和UDP头部的压缩.该方案易于实现,能够较大程度的减少无线传感器网络中报文的传输时间,从而降低能量消耗,延长节点寿命.     

All-Optical Label/Payload Separation at 40 Gb/s

We demonstrate an all-optical label/payload separation circuit implemented with hybridly integrated semiconductor-optical-amplifier-based Mach–Zehnder switches. It is shown to operate error-free with 40-Gb/s variable length data packets containing$2 ^7-1$pseudorandom bit sequence and short guardbands between them. The circuit requires only the data packets as input and its complexity does not increase with label length.     

A Flexible Analytical Markov Model for the IEEE 802.15.4 Unslotted Mechanism in Single-Hop Hierarchical Wireless Networks with Hidden Nodes

In this paper, an analytical Markov model (AMM) for the IEEE 802.15.4 unslotted CSMA/CA mechanism in single-hop hierarchical wireless networks (HWN) with hidden nodes is presented. The proposed AMM is flexible enough to operate both in saturation and non-saturation regions. Its prediction accuracy was compared with that of two well known models in the literature as well as with simulation results obtained by using the network simulator (NS)-2. The comparison has indicated that when $r$ , which denotes the maximum frame retransmission attempts, is set to zero and one-tier single-hop HWN with no hidden nodes is considered, the proposed AMM predicts the simulation results with a very small mean absolute percentage error (MAPE). Similarly, when a single-hop HWN with two tiers and hidden nodes is considered, then only one of the two well known models is applicable and the proposed AMM predictions present the smallest MAPE over the simulation results. Lastly, in the case of four-tier single-hop HWN with hidden nodes, only the proposed AMM is applicable and it predicts the simulation results at a respectable level of accuracy. When $r>0$ and the unslotted mechanism continues by incrementing the number of retransmission attempt by one upon channel access failure events, only the proposed AMM can imitate the behavior of the NS-2 IEEE 802.15.4 module.     

空间有效载荷电磁兼容设计

结合实际案例中的电磁兼容问题,有针对性地采取了软启动设计、DC/DC及滤波设计、PCB设计与屏蔽设计等措施。结果表明：浪涌电流减少至原来的1/20,输出纹波减少至原来的1/3,通过对载荷的输出电源线传导发射测试和二次电源机箱的辐射发射测试,其测量值均满足相关标准的要求。     

Performance Analysis of Header Compression Schemes in Heterogeneous Wireless Multi–Hop Networks

Wireless multi–hop networks are becoming more popular and the demand for multimedia services in these networks rises with the number of their implementations. Header compression schemes that compress the IP/UDP/RTP headers to save bandwidth for multimedia streams were typically evaluated only for individual links, not taking into account the savings that can be achieved using header compression over a complete path. In this paper, we evaluate the performance of three categories of header compression schemes: (i) delta coding, (ii) framed delta coding, and (iii) framed referential coding. We evaluate the performance for these schemes on reliable and unreliable links. We then extend our evaluations to several links constituting a path. As nodes in multi–hop ad-hoc and mesh networks may differ with respect to their capabilities, we assume in our evaluation that (forwarding) nodes may not be able or choose not to perform header compression. We find that the framed referential header compression scheme is the most suitable scheme in case that no or long-delay feedback channels exist. We additionally compare the packet drop savings due to header compression and the combined savings of compression and drops. We again find that the framed referential coding scheme exhibits good performance that can lead to significant header compression and packet drop savings for reasonable bit error rates. Patrick Seeling is a Faculty Research Associate in the Department of Electrical Engineering at Arizona State University (ASU), Tempe. He received the Dipl.-Ing. degree in Industrial Engineering and Management (specializing in electrical engineering) from the Technical University of Berlin (TUB), Germany, in 2002. He received his Ph.D. in electrical engineering from Arizona State University, Arizona, in 2005. His research interests are in the area of multimedia communications in wired and wireless networks and engineering education. He is a member of the IEEE and the ACM. Martin Reisslein is an Associate Professor in the Department of Electrical Engineering at Arizona State University (ASU), Tempe. He received the Dipl.-Ing. (FH) degree from the Fachhochschule Dieburg, Germany, in 1994, and the M.S.E. degree from the University of Pennsylvania, Philadelphia, in 1996. Both in electrical engineering. He received his Ph.D. in systems engineering from the University of Pennsylvania in 1998. During the academic year 1994–1995 he visited the University of Pennsylvania as a Fulbright scholar. From July 1998 through October 2000 he was a scientist with the German National Research Center for Information Technology (GMD FOKUS), Berlin and lecturer at the Technical University Berlin. From October 2000 through August 2005 he was an Assistant Professor at ASU. He is editor-in-chief of the IEEE Communications Surveys and Tutorials and has served on the Technical Program Committees of IEEE Infocom, IEEE Globecom, and the IEEE International Symposium on Computer and Communications. He has organized sessions at the IEEE Computer Communications Workshop (CCW). He maintains an extensive library of video traces for network performance evaluation, including frame size traces of MPEG-4 and H.263 encoded video, at http://trace.eas.asu.edu. He is co-recipient of the Best Paper Award of the SPIE Photonics East 2000 – Terabit Optical Networking conference. His research interests are in the areas of Internet Quality of Service, video traffic characterization, wireless networking, optical networking, and engineering education. Tatiana K. Madsen has received her M.Sc. and Ph.D. degrees in Mathematics from Moscow State University, Russia in 1997 and 2000, respectively. In 2001 she joined Dept. of Communication Technology, Aalborg University, Denmark where she is currently an Assistant Professor. Her research interests lie within the areas of wireless networking with the focus on IP header compression techniques and mathematical modeling of wireless protocols behavior. Frank Fitzek is an Associate Professor in the Department of Communication Technology, Unversity of Aalborg, Denmark heading the Future Vision gorup. He received his diploma (Dipl.-Ing.) degree in electrical engineering from the University of Technology – Rheinish-Westflische Technische Hochschule (RWTH) – Aachen, Germany, in 1997 and his Ph.D. (Dr.-Ing.) in Electrical Engineering from the Technical Univeristy Berlin, Germany in 2002 for quality of service support in wireless CDMA networks. As a visiting student at the Arizona State University he conducted research in the field of video services over wireless networks. He co-founded the start-up company acticom GmbH in Berlin in 1999. In 2002 he was Adjunct Professor at the University of Ferrara, Italy giving lectures on wireless communications and conducting research on multi-hop networks. In 2005 he won the YRP award for the work on MIMO MDC. His current research interests are in the areas of 4G wireless communication networks and cooperative networking. Dr. Fitzek serves on the Editorial Board of the IEEE Communications Surveys and Tutorials.     

一种基于改进TOAD结构的全光分组信头提取方案

文中提出了一种基于改进的太赫非对称光解复用器（TOAD：Terahertz Optical Asymmetric Demultiplexer）结构和差分调制的方案,用以完成光分组交换网络中的全光分组级信头提取。分组包中信头与净荷的速率分别为2．5Gbit／s和40Gbit／s。经数值仿真得到系统对信头和净荷的开关比可达15dB以上。此外,还具体讨论了SOA-TOAD的系统参数对性能的影响,从而得到使其性能优化的系统参数。     

Unslotted CSMA-CD protocol with combined retransmission strategy for fibre optic bus and ring networks

An efficient unslotted 1-persistent CSMA-CD protocol for fibre optic bus and ring networks is presented. It provides stability and good delay performance.<>     

Throughput Analysis of DS CDMA/Unslotted ALOHA Wireless Networks with Fixed Packet Length in Rayleigh Fading Finite-State Markov Channel Model

We propose the finite-state Markov channel (FSMC) model to the throughput analysis of DS CDMA/unslotted ALOHA wireless networks in the mobile environment. The FSMC model can characterize the correlation structure of Rayleigh fading process, and the degree of correlation depends on the Doppler frequency shift. The FSMC model is suited to the throughput analysis by queueing theory due to its Markov chain nature. The previous papers in DS CDMA/unslotted ALOHA wireless networks in Rayleigh fading consider a whole packet. They ignore that the channel gain or multiple access interference can change symbol-to-symbol. In our proposed analysis, both the channel gain and multiple access interference can change from symbol to symbol. It is not just a packet-level analysis in the previous papers, and is a more general symbol-level analysis. Our generalized scheme should be more suited to realistic Rayleigh fading in the mobile environment. We consider two cases: (1) the system without carrier load sensing protocol (CLSP) and (2) systems with CLSP. For both cases, we analyze the theoretical throughput by queueing theory for various averaged signal-to-noise ratios and Doppler frequency shifts, and the computer simulated throughput matches the theoretical throughput.     

RObust Header Compression (ROHC) Performance for Multimedia Transmission over 3G/4G Wireless Networks

RObust Header Compression (ROHC) has recently been proposed to reduce the large protocol header overhead when transmitting voice and other continuous media over IP based protocol stacks in wireless networks. In this paper we evaluate the real-time transmission of GSM encoded voice and H.26L encoded video with ROHC over a wireless link. For the voice transmission we examine the impact of ROHC on the consumed bandwidth, the voice quality, and the delay jitter in the voice signal. We find that for a wide range of error probabilities on the wireless link, ROHC roughly cuts the bandwidth required for the transmission of GSM encoded voice in half. In addition, ROHC improves the voice quality compared to transmissions without ROHC, especially for large bit error probabilities on the wireless link. The improvement reaches 0.26 on the 5-point Mean Opinion Score for a bit error probability of 10^–3. For the video transmission we examine the impact of ROHC on the consumed bandwidth. We find that the bandwidth savings with ROHC depend on the quantization scale used for the video encoding and the video content and ranges between 5–40% for typical scenarios.Frank H.P. Fitzek is an Associate Professor in the Department of Communication Technology, University of Aalborg, Denmark heading the Future Vision group. He received his diploma (Dipl.-Ing.) degree in electrical engineering from the University of Technology – Rheinisch-Westflische Technische Hochschule (RWTH) – Aachen, Germany, in 1997 and his Ph.D. (Dr.-Ing.) in Electrical Engineering from the Technical University Berlin, Germany in 2002. As a visiting student at the Arizona State University he conducted research in the field of video services over wireless networks. He co-founded the start-up company acticom GmbH in Berlin in 1999. In 2002 he was Adjunct Professor at the University of Ferrara, Italy giving lectures on wireless communications and conducting research on multi-hop networks. His current research interests are in the areas of 4G wireless communication, QoS support for multimedia services, access techniques, security for wireless communication, and the integration of multi hop networks in cellular systems. Dr. Fitzek serves on the Editorial Board of the IEEE Communications Surveys and Tutorials. He is the program chair for the International Conference on Advances in Computer Entertainment Technology (ACE2004) and serves in the program committee for VTC2003, VTC2004, ACE2004, and IEEE MWN2004.Stephan Rein studied Electrical Engineering at the Technical University of Aachen, Germany, and the Technical University of Berlin (TUB), Germany. He received the Dipl.-Ing. degree in electrical engineering from the TUB in 2003. From March 2003 to October 2003 he visited the multimedia networking group in the Department of Electrical Engineering at Arizona State University, Tempe. He is currently pursuing the Ph.D. degree at the Institute for Energy and Automation Technology, Technical University of Berlin. His current research interests include data compression and digital signal processing with emphasis on wavelet theory.Patrick Seeling received the Dipl.-Ing. degree in industrial engineering and management (specializing in electrical engineering) from the Technical University of Berlin (TUB), Germany, in 2002. Since 2003 he has been a Ph.D. student in the Department of Electrical Engineering at Arizona State University. His research interests are in the area of video communications in wired and wireless networks. He is a student member of the IEEE and the ACM.Martin Reisslein is an Assistant Professor in the Department of Electrical Engineering at Arizona State University, Tempe. He received the Dipl.-Ing. (FH) degree from the Fachhochschule Dieburg, Germany, in 1994, and the M.S.E. degree from the University of Pennsylvania, Philadelphia, in 1996. Both in electrical engineering. He received his Ph.D. in systems engineering from the University of Pennsylvania in 1998. During the academic year 1994–1995 he visited the University of Pennsylvania as a Fulbright scholar. From July 1998 through October 2000 he was a scientist with the German National Research Center for Information Technology (GMD FOKUS), Berlin. While in Berlin he was teaching courses on performance evaluation and computer networking at the Technical University Berlin. He is editor-in-chief of the IEEE Communications Surveys and Tutorials and has served on the Technical Program Committees of IEEE Infocom, IEEE Globecom, and the IEEE International Symposium on Computer and Communications. He has organized sessions at the IEEE Computer Communications Workshop (CCW). He maintains an extensive library of video traces for network performance evaluation, including frame size traces of MPEG-4 and H.263 encoded video, at . He is co-recipient of the Best Paper Award of the SPIE Photonics East 2000 – Terabit Optical Networking conference. His research interests are in the areas of Internet Quality of Service, video traffic characterization, wireless networking, and optical networking.     

物理隔离技术及其在政府网络中的应用

在当今网络信息安全的重要性日益凸现的现实环境下,政府等重要部门如何做好网络信息安全工作已成为一个重要的研究课题,物理隔离技术应运而生。物理隔离目前常见的实现方式以隔离卡和隔离集线器为主,实现多个网络的真正物理隔离。物理隔离作为一种更彻底、更安全的网络安全技术,在保密性要求较高的政府网络中得到了较广泛的应用。在实际应用中,为了弥补物理隔离技术的不足,还须将物理隔离和常规的网络安全技术结合起来,使网络信息安全得到最大的保障。     

Scaling Laws for Dense Gaussian Sensor Networks and the Order Optimality of Separation

We investigate the optimal performance of dense sensor networks by studying the joint source-channel coding problem. There are N uniformly spaced sensor nodes sampling noiselessly a one-dimensional spatial random process over an interval [0, U₀]. The overall goal of the sensor network is for the sensor nodes to code and transmit the measurement samples to a collector node over a cooperative multiple-access channel with noisy feedback, and for the collector node to reconstruct the entire random process with minimum expected distortion. We provide separation-based lower and upper bounds for the minimum achievable expected distortion when the underlying random process is Gaussian. When the Gaussian random process satisfies some general conditions, such as the eigenvalues of its Karhunen-Loeve expansion decrease roughly inverse polynomially in order x, i.e., the kth eigenvalue is roughly k^-x, we evaluate the lower and upper bounds explicitly, and show that they are of the same order for a wide range of power constraints. Thus, for these random processes, under these power constraints, we show that the minimum achievable expected distortion decreases as (log NP(N)^1-x, where P(N) is the sum power constraint on the sensor nodes. Further, we show that the achievability scheme that achieves the lower bound on the distortion is a separation-based scheme that is composed of multiterminal rate-distortion coding and amplify-and-forward channel coding. Therefore, we conclude that separation is order-optimal for the dense Gaussian sensor network scenario under consideration, when the underlying random process satisfies some general conditions.     

Unslotted deflection routing: a practical and efficient protocolfor multihop optical networks

This paper is concerned with all-optical networks using deflection routing and time division multiplexing. Slotted networks make use of the synchronous arrival of the packets to the routers to minimize locally the number of deflections. We show that the difference in performance between slotted and unslotted networks is mainly due to the fact that unslotted networks cannot easily perform such local optimization. We also show that minimizing locally the number of deflections in unslotted networks gives rise to an NP-complete problem. To overcome this problem, we have designed a heuristic whose aim is to limit locally the number of deflections. We experimentally demonstrate that this heuristic enhances unslotted routing almost at the same performance level as slotted routing. As a consequence, we have shown that unslotted deflection routing can be implemented is a way which makes it a competitive alternative to slotted deflection routing for optical time division multiplexing deflection networks     

Header signature maintenance for Internet traffic identification

Various traffic identification methods have been proposed with the focus on application‐level traffic analysis. Header signature–based identification using the 3‐tuple (Internet Protocol address, port number, and L4 protocol) within a packet header has garnered a lot of attention because it overcomes the limitations faced by the payload‐based method, such as encryption, privacy concerns, and computational overhead. However, header signature–based identification does have a significant flaw in that the volume of header signatures increases rapidly over time as a number of applications emerge, evolve, and vanish. In this article, we propose an efficient method for header signature maintenance. Our approach automatically constructs header signatures for traffic identification and only retains the most significant signatures in the signature repository to save memory space and to improve matching speed. For the signature maintenance, we define a new metric, the so‐called signature weight, that reflects its potential ability to identify traffic. Signature weight is periodically calculated and updated to adapt to the changes of network environment. We prove the feasibility of the proposed method by developing a prototype system and deploying it in a real operational network. Finally, we prove the superiority of our signature maintenance method through comparison analysis against other existing methods on the basis of various evaluation metrics.     

无人机技侦载荷技术

本文在对无人技术侦察飞机的独特优点、国外无人机侦察系统发展现状作了简要阐述后,着重对无人机侦察系统的主要技术进行了分析。     

Simpler Throughput Analysis of CDMA/Unslotted ALOHA Radio Networks with Variable Message Length Based on M/M/inf Queueing Model

We propose a new and exact method to analyze the throughput of the DS CDMA unslotted ALOHA system with variable number of fixed-length packets. The proposed scheme requires two-dimensional summation while the previous requires four. Thus the proposed analysis scheme is of less computational complexity. The proposed analysis result is also slightly closer to the simulation result than the previous analysis result is, especially in heavier offered load.     

An Approximate Analysis of Delay for Fixed and Variable Length Packets in an Unslotted ALOHA Channel

In this paper we compute the mean delay for an unslotted ALOHA random access channel for both fixed and variable length packets. The analysis is based on the concept of a user cycle and obtains steady state results. When the channel is "stable", the results seem quite accurate. The input parameters to the model are the number of users, the mean think time, and mean retransmission time. The model yields total traffic, throughput and delay but only the latter is emphasized here. Because of the steady state nature of the analysis, no information is obtained on stability. The results are verified by simulation.