认知无线电环境下TCP性能分析

首先讨论分析了认知无线电环境下影响TCP性能的关键因素,并通过NS2仿真软件搭建认知网络环境,仿真分析了不同TCP版本协议在认知网络环境下的性能状况,包括reno,newreno,westwood,vegas和sack。仿真结果表明,在认知网络环境下,westwood性能最好而vegas最差。     

基于OPNET的IPSec VPN的性能分析

采用OPNET仿真软件对网络性能进行仿真与分析,既可以减少统在网络设计、性能研究及开发的费用,提高网络设计的效率,又使得数据统计与分析变得非常容易。文章主要论述了网络仿真的流程、建模的方法,并通过实验利用OPNET软件对IPv6环境下IPSecVPN的性能作出详细的分析。     

软件定义机动通信网云仿真技术研究

针对软件定义网络(Software Defined Network,SDN)技术在机动通信网络中的应用问题,给出软件定义机动通信网体系架构;结合OpenStack云管理系统,设计了基于云环境下的多模式联合仿真平台,采用虚拟化仿真建模技术模拟机动通信网络的体系结构和系统组成,数字仿真实现对无线环境的模拟并将无线传输效果叠加到网络仿真系统中,弥补虚拟化仿真在无线环境模拟方面的不足;通过搭建仿真演示环境,对比分析了软件定义机动通信网基于带内和带外传输的控制开销,推动了软件定义机动通信网的研究。     

MANET仿真软件的分析与研究

网络仿真软件是网络性能理论分析、评估网络设计方案以及网络故障诊断的有力工具由于MANET自身环境的复杂性．对其的设计．仿真以及优化显得更加的困难本文介绍了3种主流网络仿真软件：商业软件OP-NET Modeler和免费软件NS-2及GloMoSim,分析了其各自的特点及适用范围。接下来详细介绍了目前在研究领域广泛使用的NS仿真软件的原理,并给出了使用NS仿真软件进行网络仿真和MANET仿真的一般步骤．最后对全文作出总结。     

基于OPNET的MPLS实用仿真分析

基于OPNET网络仿真环境对单播的数据传输模式进行了仿真,研究TMPLS技术在网络中的应用情况,通过对比分析仿真结果,表明将MPLS技术应用于传统IP网络可以有效地提高网络负载均衡、时延以及网络整体带宽的使用率等性能,尤其是对于复杂的网络更能使QoS得到优化。     

基于半实物接口的网络攻防仿真

随着网络仿真应用领域不断拓展,促使网络仿真技术快速发展,利用半实物仿真技术来评估网络系统的安全是对网络安全的理论和实践研究一种行之有效的方法。针对军事网络安全的需求,阐述了在网络攻防环境下进行安全评估分析的意义,分析了网络攻防仿真的现状,提出了基于半实物接口技术来实现网络攻防的仿真,然后论述了半实物仿真的原理和半实物接口的设计,最后结合实例进行了网络攻防效果的评估。     

基于OPNET的网络模型仿真

网络仿真是一种全新的网络规划、设计和分析技术,它能够验证实际方案的有效性和比较多个不同的设计方案,为网络的规划设计提供可靠的定量依据。介绍OPNET的特点、建模机制及仿真方法,并利用OPNET对一个局域网进行仿真,结合实例给出在OPNET环境下进行网络仿真的步骤,针对不同设置,仿真实验将获得各种情况下的网络性能参数指标,有效指导网络设计和优化。     

基于NS2的无线传感器网络仿真平台设计

在研究无线传感器网络特点和协议栈的基础上,利用网络仿真软件NS2对无线传感器网络环境的仿真进行了研究与二次开发,构建了一个基于多种无线传感器网络关键性能的可视可控的仿真界面.用户可以通过仿真界面来自主配置网络元素,搭建网络,利用具体的动画演示过程和性能分析图表来了解整个网络运行过程与性能.简化了仿真的复杂过程,有助于加快研究者的研究开发进程.     

多径下Turbo码IDMA网络编码中继合作系统性能分析

基于交织多址网络编码中继合作系统,分析了其采用Turbo编码后在多径信道环境下的系统性能。研究了该系统中利用不同交织器来实现多用户的多址接入方式以及网络编码的中继合作机制。将多径信道以及Turbo编码融入该系统中,搭建计算机仿真环境,通过仿真数据分析系统性能。仿真结果表明,在多径信道环境下,采用Turbo编码的交织多址网络编码中继合作系统的系统误码率有明显改善。     

光突发交换汇聚算法的仿真及算法性能分析

对光突发交换网络的汇聚算法进行了研究,使用OPNET仿真软件搭建了统一网络环境的仿真平台,基于自相似业务源对三种典型的汇聚算法进行了仿真,并根据仿真结果分析了这些算法对网络性能的影响.     

How network asymmetry affects TCP

Several emerging wireline and wireless access network technologies exhibit asymmetry in their network characteristics. For instance, cable modem networks exhibit significant bandwidth asymmetry, while packet radio networks exhibit media access asymmetry. A high degree of asymmetry can have an adverse effect on the performance of feedback-based transport protocols. We study the effects of bandwidth and media access asymmetry on the performance of the TCP protocol. We identify the fundamental reasons for the mismatch between TCP and asymmetric networks, and then present several techniques to address this problem     

The Behavior of TCP Over DOCSIS-Based CATV Networks

This paper studies the impact of the data-over-cable service interface specification (DOCSIS) media-access control (MAC) protocol on the performance of the transmission control protocol (TCP) in hybrid fiber coax (HFC) broadband access networks. We find that the asymmetry ratio expressed in existing work cannot adequately explain the behavior of TCP in DOCSIS-based networks. To better capture the effect of DOCSIS on TCP, we express the asymmetry ratio (denoted by$eta$) in another way (denoted by$k$), considering the time-division multiple-access-like MAC layer operation of DOCSIS. When$eta≫1$, TCP behaves as in a symmetric network, and when$etaleqq 1$, the system acts as in an asymmetric network, and the performance of TCP degrades. We find that the number of simultaneous TCP transfers significantly affects the asymmetry ratio. When the number of active transfers is below two times the maximum number of pending requests in a transmission period, the value of$eta$is larger than one, regardless of the value of$k$. However, when the number of active transfers becomes very large, the effect of DOCSIS on TCP becomes negligible, and the asymmetry ratio is determined by the bandwidth ratio of the channels times the length ratio of data and acknowledgement packets. Based on$eta$, we develop the round-trip delay of sending a data packet for both one-way and two-way transfers, and discuss the buffer requirement at the head end. The accuracy of the analytical model is validated by ns-2 simulations. The analytical result can provide useful guidelines in the design of slot allocation or scheduling mechanisms for any DOCSIS-based broadband access networks, including the emerging IEEE 802.16 WiMAX networks.     

On TCP performance in a heterogeneous network: a survey

Transmission media carrying Internet traffic present a wide range of characteristics, some of which, such as transmission errors, long end-to-end delay, and bandwidth asymmetry, may cause a degradation of the TCP performance. Many works have studied the performance of TCP over these media, most of which focus on a particular network type. In this work we study TCP performance independent of the type of network by considering the different possible characteristics of the connection path. We present the problems and the different proposed solutions. This study permits us to understand the limitations of the actual solutions and the required modifications to let TCP cope with a heterogeneous Internet on an end-to-end basis     

TCP-BIAD for Enhancing TCP Performance in Broadband Wireless Access Networks

In this paper a new TCP variant, named TCP-Binary Increase, Adaptive Decrease is presented. The suggested congestion control algorithm is a joint approach of Westwood and an enhanced version of BIC, for improving TCP performance in broadband wireless access networks. BIAD has been evaluated with respect to other TCP variants such as Reno, Westwood, BIC, CUBIC, HSTCP and STCP with the use of network simulator 2. The results indicate that the proposed solution achieves high network utilization levels in a wide range of network settings, including wireless channel errors, link asymmetry and congestion. We also evaluated TCP-BIAD when multiple flows share a bottlenecked access link and we show that it demonstrates the fairness features required for network deployment.     

TCP/IP performance with random loss and bidirectional congestion

With the growth in Internet access services over networks with asymmetric links such as asymmetric digital subscriber line (ADSL) and cable-based access networks, it becomes crucial to evaluate the performance of TCP/IP over systems in which the bottleneck link speed on the reverse path is considerably slower than that on the forward path. In this paper, we provide guidelines for designing network control mechanisms for supporting TCP/IP. We determine the throughput as a function of buffering, round-trip times, and normalized asymmetry (defined as the ratio of the transmission time of acknowledgment (ACK) in the reverse path to that of data packets in the forward path). We identify three modes of operation which are dependent on the forward buffer size and the normalized asymmetry, and determine the conditions under which the forward link is fully utilized. We also show that drop-from-front discarding of ACKs on the reverse link provides performance advantages over other drop mechanisms in use. Asymmetry increases the TCP already high sensitivity to random packet losses that occur on a time scale faster than the connection round-trip time. We generalize the by-now well-known relation relating the square root of the random loss probability to obtained TCP throughput, originally derived considering only data path congestion. Specifically, random loss leads to significant throughput deterioration when the product of the loss probability, the normalized asymmetry and the square of the bandwidth delay product is large. Congestion in the reverse path adds considerably to TCP unfairness when multiple connections share the reverse bottleneck link. We show how such problems can be alleviated by per-connection buffer and bandwidth allocation on the reverse path     

Transport protocols for Internet-compatible satellite networks

We address the question of how well end-to-end transport connections perform in a satellite environment composed of one or more satellites in geostationary orbit (GEO) or low-altitude Earth orbit (LEO), in which the connection may traverse a portion of the wired Internet. We first summarize the various ways in which latency and asymmetry can impair the performance of the Internet's transmission control protocol (TCP), and discuss extensions to standard TCP that alleviate some of these performance problems. Through analysis, simulation, and experiments, we quantify the performance of state-of-the-art TCP implementations in a satellite environment. A key part of the experimental method is the use of traffic models empirically derived from Internet traffic traces. We identify those TCP implementations that can be expected to perform reasonably well, and those that can suffer serious performance degradation. An important result is that, even with the best satellite-optimized TCP implementations, moderate levels of congestion in the wide-area Internet can seriously degrade performance for satellite connections. For scenarios in which TCP performance is poor, we investigate the potential improvement of using a satellite gateway, proxy, or Web cache to “split” transport connections in a manner transparent to end users. Finally, we describe a new transport protocol for use internally within a satellite network or as part of a split connection. This protocol, which we call the satellite transport protocol (STP), is optimized for challenging network impairments such as high latency, asymmetry, and high error rates. Among its chief benefits are up to an order of magnitude reduction in the bandwidth used in the reverse path, as compared to standard TCP, when conducting large file transfers. This is a particularly important attribute for the kind of asymmetric connectivity likely to dominate satellite-based Internet access     

TCP/IP协议在卫星链路上的应用研究

因特网的发展对带宽的要求越来越高,现有的地面网络远远不能满足用户的需求,因而卫星网与IP网结合成了目前研究的热点。简要介绍了TCP/IP的协议结构和工作原理。针对卫星网的信道差错率高、传播延迟长和信道不对称性对TCP传播性能有恶化影响,按照从链路层到应用层的分类方法,分别提出了改善措施,包括:传输控制协议层的窗口控制、快速重传、快速重发、ACK控制等改进方案以及基于TCP欺骗技术和TCP分段技术的联接分段代理方案。     

A Cross-Layer Approach for Per-Station Fairness in TCP over WLANs

In this paper, we investigate the issue of per-station fairness in TCP over IEEE 802.11-compliant wireless local area networks (WLANs), especially in Wi-Fi hot spot. It is asserted that the hot spot suffers from the unfairness among stations in exploiting the wireless medium. The source of this unfairness is analyzed from two aspects, TCP-induced asymmetry and MAC-induced asymmetry; the former causes TCP congestion control with a cumulative acknowledgment mechanism to prefer the sending stations to receiving stations, while the later exacerbates the unfairness problem in the hot spots. We investigate the interaction between TCP congestion control and MAC contention control, and propose a cross-layer feedback approach to assure per-station fairness and to ensure high channel utilization. In this approach, we introduce the notion of channel access cost to quantify the system-wide traffic load and per-station channel usage. The access cost is estimated at the MAC in an access point and conveyed to the TCP sender. Then, the TCP sender adjusts its sending rate based on the access cost, so as to assure per-station fairness. The simulation results indicate that the proposed approach can provide both per-station fairness and high channel utilization, irrespective of network configurations.     

基于TCP/IP的卫星通信传输链路的改进

卫星网络固有的一些特性影响了TCP／IP的性能。针对延迟、拥塞率、比特差错率、网络不对称性等问题,提出了支持较大的流量控制窗口及改进拥塞控制算法的方法,对现有的TCP／IP进行了改进。     

基于卫星移动通信的网络移动研究

文中研究了利用卫星移动通信支持网络移动的必要性,提出了利用卫星移动通信网扩展地面IP网覆盖范围的设想和实现方案,分析了该方案的特点及需要解决的关键技术问题,重点分析了卫星移动信道对TCP/IP协议的影响及网络移动过程中的连接和路由选择问题,卫星移动信道误码率、往返时延、变化率、信道不对称性及信道频繁通断对TCP/IP协议工作效率的影响,以及提供网络移动应解决的双重隧道问题。