Trunk congestion control in heterogeneous circuit switched networks

A circuit-switched network with two types of traffic is modeled as a finite two-dimensional Markov chain. The problem of trunk congestion under different routing schemes is analyzed. It is shown that the trunk reservation technique can be used to alleviate trunk congestion in this heterogeneous traffic environment. It is also shown that two control schemes, namely, the restricted access and preemption, when properly applied, may minimize the blocking of one type of traffic while keeping that of the other at a certain level. Some numerical examples are presented     

Adaptive point-to-point communication approach for subscriber stations in broadband wireless networks

The point-to-multipoint (PMP) mode is considered the well-adopted transmission type that is supported by the IEEE 802.16 standard. The base station (BS) is served as the centralized coordinator to control and forward packets for the subscriber stations (SSs) within the network. In the case that two SSs intend to conduct packet transmission, it is required for the packets to be rerouted to the BS before arriving at the destination SS. The communication bandwidth is apparently wasted due to the rerouting processes. In this paper, an adaptive point-to-point communication (APC) approach is proposed to achieve direct communication between SSs within the PMP mode of the IEEE 802.16 standard. The BS is coordinating and arranging specific time intervals for the two SSs that are actively involved in packet transmission. Based on channel conditions among the BS and the SSs, the packet transmission operation is switched between direct communication and indirect communication in the APC approach. Both the architectural design and analytical modeling of the proposed scheme are conducted in this paper. The effectiveness of the proposed APC approach in terms of user throughput and its corresponding overhead can be observed via both the analytical and simulation results.     

A feedback-based congestion control mechanism for labeled optical burst switched networks

In this article we describe a feedback-based OBS network architecture in which core nodes send messages to source nodes requesting them to reduce their transmission rate on congested links. Within this framework, we introduce a new congestion control mechanism called congestion control with explicit reduction request (CCERQ). Through feedback signals, CCERQ proactively attempts to prevent the network from entering the congestion state. Basic building blocks and performance tradeoffs of CCERQ are the main focus of this article.

Optimal routing in circuit switched communication networks

Consideration is given to the optimal circuit routing problem in an existing circuit-switched network. The objective is to find circuit routing which accommodates a given circuit demand while maximizing the residual capacity of the network. In addition, the cost of accommodating the circuit demand should not exceed a given amount. Practical considerations require that a solution be robust to the variations in circuit demand and cost. The objective function for the optimal circuit routing problem is not a smooth one. In order to overcome the difficulties of nonsmooth optimization, the objective function is approximated by smooth concave functions. The optimization algorithm for the circuit routing problem is obtained as a limiting case of the sequence of optimal routing strategies for the corresponding smooth convex optimization problems, and the proof of its convergence to the optimal solution is given. An approach to calculating the optimal multicommodity flow is presented. The optimization algorithm efficiently handles networks with a large number of commodities, satisfies the robustness requirements, and can be used to solve circuit routing problems for large networks     

计算机通信网络中基于速率的端对端拥塞控制

运用现代控制理论和方法，在多个信源节点单个信终端节点的端对端模型基础上，考虑到信终端节点的缓冲占有量的动态稳定，设计了一类可以比较好地调节ABR信源节点发送速率的控制器，使得终端节点的缓冲占有量可以逐渐稳定。     

BLIP condition in point-to-point optical communication

Analysis of the signal-to-noise ratio of optical point detectors under conditions of large background radiation (BLIP detection) gives relations describing the background limit to the sensitivity of point-to-point optical communication systems. In narrowband applications, noise-equivalent-power (NEP) has a utility for study of the point BLIP detector which is equivalent to that of the detectivity D^*for large area BLIP detectors; for wide bandwidths, a more suitable parameter is the retrieval efficiency β of the receiver. Each of these is expressed in terms of DBLIP^*, a quantity graphed in references on infrared detectors. A numerical exmple shows that even on the surface of the earth, broadband point-to-point communications may well be receiver limited rather than background limited.     

Comparison of different congestion control strategies for low priority controllable traffic in packet switched backbone networks

It is expected that a significant part of the data flows of future multi‐service packet switched backbone networks will use low priority, non‐real‐time data transmission services of the networks. The common benefit for both user applications and network operators is that the data flows of the low priority services could use the free capacity of the networks, after the load of higher priority data flows. Congestion control methods are needed for these low priority data flows to reach an optimal utilisation level of the networks, high throughput and low packet loss ratios. This kind of low priority data transmission service which adjusts the data rates of the data flows according to the data rate changes of higher priority data flows, but does not guarantee any specific service for these data flows, is called a controlled load service. In this paper, we have compared the performance, efficiency and scalability of four different congestion control methods designed for the controlled load service. Two of these methods were based on very simple congestion control algorithms and the other two used relatively complex control algorithms based on control methods utilising computational intelligence. The principal aim of this study was to research how remarkable were the effects that the different complexities of the congestion control methods had on the achieved level of service. The simulation tests indicate that the complexity of the methods clearly affects the performance and efficiency of the methods. Copyright © 2001 John Wiley & Sons, Ltd.     

Timeliness of real-time IP communication in switched industrial Ethernet networks

Through several giant evolutionary steps, Ethernet has become an almost ubiquitous technology for communication. Being versatile enough to be employed in new and various fields of application, it is now making inroads in factories. However, automated systems are different from many other applications of Ethernet,first and foremost because they require the network technology to deliver real-time performance. In the present study, a number of critical aspects of Ethernet, usually referred to as an Industrial Ethernet, are examined. More specifically, there is a focus on the application-to-application delay and jitter characteristics of such networks, when using Internet protocols such as UDP and TCP. It is demonstrated how important it is to take control of the latency in the station nodes, since the main communication delays occur inside the nodes, and different solutions are presented for controlling these delays. In particular, a priority-based protocol stack is assessed. The results show that real-time, Ethernet-based IP communication is now adequate even for demanding automated applications. In this paper, substation automation (power distribution) is used as an example of a demanding automation system.     

战术通信网络的识别方法

战术通信对抗系统中识别通信目标及其所属的通信网络,可以实现网络目标的活动监控并有效利用干扰资源对其实施干扰。提出利用辐射源的方位信息和信号时间特征进行通信网络或专向识别,可以提高信号分析处理速度,增强设备的单站能力。     

一种挑战环境下中基于点到点的可靠传输确认机制

分析了TCP端到端传输确认机制在挑战环境下存在的一些问题,提出一种点到点的传输排队和确认机制,通过理论分析和实验证明,该机制能够明显降低端到端传输确认机制中存在的大量无法被捎带的ACK数据包,同时,对端到端的延时抖动有更强的容忍能力。     

An early congestion feedback and rate adjustment schemes for many-to-one communication in cloud-based data center networks

Cloud data centers are playing an important role for providing many online services such as web search, cloud computing and back-end computations such as MapReduce and BigTable. In data center network, there are three basic requirements for the data center transport protocol such as high throughput, low latency and high burst tolerance. Unfortunately, conventional TCP protocols are unable to meet the requirements of data center transport protocol. One of the main practical issues of great importance is TCP Incast to occur many-to-one communication sessions in data centers, in which TCP experiences sharp degradation of throughput and higher delay. This important issue in data center networks has already attracted the researchers because of the development of cloud computing. Recently, few solutions have been proposed for improving the performance of TCP in data center networks. Among that, DCTCP is the most popular protocol in academic as well as industry areas due to its better performance in terms of throughput and latency. Although DCTCP provides significant performance improvements, there are still some defects in maintaining the queue length and throughput when the number of servers is too large. To address this problem, we propose a simple and efficient TCP protocol, namely NewDCTCP as an improvement of DCTCP in data center networks. NewDCTCP modified the congestion feedback and window adjusting schemes of DCTCP to mitigate the TCP Incast problem. Through detailed QualNet experiments, we show that NewDCTCP significantly outperforms DCTCP and TCP in terms of goodput and latency. The experimental results also demonstrate that NewDCTCP flows provide better link efficiency and fairness with respect to DCTCP.     

Engineering ATM networks for congestion avoidance

With the combination of telecommunication, entertainment and computer industries, computer networking is adopting a new method called Asynchronous Transfer Mode (ATM) networking. Congestion control plays an important role in the effective and stable operation of ATM networks. Traffic management concerns with the design of a set of mechanisms which ensure that the network bandwidth, buffer and computational resources are efficiently utilized while meeting the various Quality of Service (QoS) guarantees given to sources as part of a traffic contract. In this paper, the most widely recognized congestion control schemes for ABR service are investigated. Some of these schemes show either lack of scalability or fairness while other well‐behaved schemes may require a highly complex switch algorithm that is unsuitable for implementation in cell‐switching high‐speed ATM networks. A new and improved congestion control scheme is proposed to support the best‐effort ABR traffic. This algorithm provides the congestion avoidance ability with high throughput and low delay, in addition to achieving the max–min fairness allocation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nondissipative switched networks for high-power applications

The letter seeks to extend the concepts of active-filter theory to high-power applications. Current-fed switched-capacitor networks and voltage-fed switched-inductor networks are efficient topologies suitable for high-power operation. Passive and active switched networks realised include the transformer, gyrator and a negative inductor using a generalised impedance convertor.     

Flowmeter for QoS provision in packet switched networks

A flowmeter is a set of traffic-related variables associated with a connection established in a network node as a result of the connection setup. Comprehensive quality-of-service provision to each packet flow is the purpose of flowmeter-based dynamic packet scheduling. The earliest deadline first (EDF) scheduling algorithm is adopted for rate allocation, delay control, and flow control. A gas pressure admission control algorithm is also presented to simplify EDF admission test. The delay performance of the scheduler is evaluated on a subnetwork of the Internet     

A congestion control framework for ATM networks

The authors propose a congestion control framework for ATM networks that requires simple protocols and that provides guaranteed grade of service The authors suggest that the network provides two different services: express service and first-class service. Express service is appropriate for real-time applications, whereas first-class service is appropriate for nonreal-time applications. To provide such services, the proposed congestion control scheme prevents congestion inside the network by controlling the congestion at two levels: VC (virtual circuit) level and cell level. The VC-level control takes place during the call setup in the form of (logical) bandwidth reservation for individual VCs. The cell-level control is exercised across the network interface in the form of the choking/relieving of only first-class VC traffic in case of congestion. The authors analyze the performance of the proposed scheme, and show how to engineer various parameters to satisfy cell-level performance requirements (e.g., cell delay and loss)     

一种点对点高速通信控制器的设计与实现

为了提高CPU模块之间的点对点通信速率,通过对以太网控制器MAC的研究,设计出一种点对点高速通信控制器。该控制器是基于媒体无关接口MII和以太网收发器的点对点高速通信控制器。利用VHDL语言编写该控制器的相关代码,使用MAXPLUSⅡ对该控制器的数据发送和数据接收进行仿真,并在实验室样机上进行实现。仿真结果和实验结果表明这种点对点高速通信控制器的设计方法是可行的。     

Adaptive congestion control for DSRC vehicle networks

Dedicated short range communications (DSRC) was proposed for collaborative safety applications (CSA) in vehicle communications. In this article we propose two adaptive congestion control schemes for DSRC-based CSA. A cross-layer design approach is used with congestion detection at the MAC layer and traffic rate control at the application layer. Simulation results show the effectiveness of the proposed rate control scheme for adapting to dynamic traffic loads.     

Heuristic optimization techniques for self-orientation of directional antennas in long-distance point-to-point broadband networks

A self-orientation system for a directional antenna is capable of determining the best orientation to receive the strongest wireless signal. In the event of two antennas being deployed randomly or deployed in a dense space where the effects of multipath and other wireless interference exist, efficient search algorithms are required to find the best orientation. Therefore, this paper presents four heuristic optimization techniques for the self-orientation of directional antennas in such events: Pattern Search method, Downhill Simplex method, DIRECT method, and Genetic Algorithm. The modification of each technique for this orientation problem is described, and the performance of each algorithm using different test cases with real world experiments is also described. From our study, we show that the Pattern Search method is the most suitable optimization technique for the self-orientation of directional antennas in long-distance point-to-point broadband networks.     

便携式点对点可见光通信终端的实验研究

利用开关键控-非归零码(OOK-NRZ)调制编码技术,设计并实现了一对基于ARM7处理器(LPC2148)的便携式点对点可见光通信(VLC)收/发终端。发送端由编码器、光源驱动器及单个白色发光二极管(WLED)构成,接收端由可见光探测器、信号处理电路及解码器构成。实验研究了WLED的发射谱和可见光探测器的响应谱,测试分析了VLC信道的时域和频域的电-光-电(EOE)响应。阐述了系统结构和原理,编写了通信软件并制定了相关协议,实现了系统的软、硬件集成。利用研制出的通信装置,建立了点对点通信链路,并开展了数据通信实验。结果表明,在发送端,为了最大化地降低误码率(BER),WLED的调制系数应设置为0.68~1.00,即在一定的交流调制信号幅度下,需要向WLED提供合适的直流偏置电压;在接收端,在一定的阈值判决门限电压下,VLC传输呈带通特性。在所优化选择的系统参数下,系统的通信距离为0.5m,可达到的最快信息传输速率约为4 Mbps,BER小于10-6。利用多个WLED构成阵列光源,系统可进一步满足更长距离的通信需求,从而在室内、外短途通信方面具有潜在的应用价值。     

Avoiding complex matrix manipulation for switched networks

A simple scheme is proposed for solving periodically time-varying networks using the advantages of matrix methods but overcoming their drawbacks. Initial diagonalisation of the A-matrix converts the problem into the formation of the sum of partial scalar solutions. The conditions necessary fo the adoption of this scheme, which can also yield an improved response, are given.