TCP／IP协议问题透析

针对TCP／IP在无线和安全领域的应用展开论述,详细分析了TCP／IP在几个关键的地方存在的问题,并分别就慢速启动算法、初始窗口大小、初始窗口增加策略、RTO估计器、延迟响应、内核实现的不足和安全漏洞进行了研究,给出了一些建设性的解决办法,为今后的进一步研究奠定了基础。     

VANET中基于捎带确认机制的自适应数据传播策略

车载自组网（VANET）通过自组织分散环境传播交通数据,交通数据的特点使得VANET数据传播方法更适合依赖广播。然而,当在高密度场景下广播数据时,可扩展问题和数据传播冗余问题变得尤为突出,可能导致广播风暴的发生。针对数据传播冗余和广播开销等问题,以最远转发策略和捎带确认机制为基础,提出一种捎带确认的自适应最远转发策略（AckAMFR）,根据存储转发的概念进行信息的传输和存储,降低了数据冗余,具有较强的可靠性和较小的广播开销。仿真结果表明,该转发策略具有低广播开销和高数据传输率的特性。     

An AM-RLC scheme with adaptive acknowledgement interval

The acknowledged mode radio link control (AM-RLC) protocol is one of the most important radio protocols in wideband code division multiple access (WCDMA) and time division-synchronization code division multiple access (TD-SCDMA) mobile communication systems. A modified AM-RLC scheme with adaptive acknowledgement interval is proposed. At the receiver, the acknowledgement interval is dynamically changed according to the channel status. The simulation results show that the proposed AM-RLC scheme outperforms the fixed acknowledgement interval AM-RLC scheme in terms of frame delivery delay and protocol overhead. __________ Translated from Journal on Communications, 2008, 29(3): 119–122 [译自: 通信学报]     

面向卫星网络的TCP代理

当传统TCP协议用于卫星网络时面临各种问题,原因包括:卫星信道的高传输延迟、较大的误码率、带宽不对称、信号衰减等.为了提高卫星网络环境下TCP的性能,在不破坏TCP端到端特性的前提下,提出了一种新的主动代理方案.拥塞控制算法通过具有不同优先级的双报文对实施主动监测,能够根据网络带宽的变化自适应地调整TCP窗口.并且,对代理控制系统进行了稳定性分析.针对卫星网络下的TCP丢包恢复,提出了一种不依赖时钟同步的选择性否定应答算法.模拟实验表明,提出的TCP代理能够充分利用卫星网络的带宽,从而达到获得最佳有效吞吐率的目的.     

Design and realization of ad-hoc VoIP with embedded p-SIP server

In this paper we design and implement the pseudo session initiation protocol (p-SIP) server embedded in each mobile node to provide the ad-hoc voice over Internet protocol (VoIP) services. The implemented p-SIP server, being compatible with common VoIP user agents, integrates the standard SIP protocol with SIP presence to handle SIP signaling and discovery mechanism in the ad-hoc VoIP networks. The ad-hoc VoIP signaling and voice traffic performances are analyzed using E-model R rating value for up to six hops in the implemented test-bed. We also conduct the interference experiments to imitate the practical ad-hoc VoIP environment. The analyzed results demonstrate the realization of ad-hoc VoIP services by using p-SIP server.     

RabbitMQ小消息确认机制优化

RabbitMQ的消息确认机制包括生产者确认（confirm）与消费者确认（ack）.若消息不需要进行持久化,生产者收到确认,消息仍有可能丢失,且生产者不知道消息已丢失,消费者可能无法收到该消息.若消息需要进行持久化,生产者收到确认时,消费者可能还没有收到消息.本文对RabbitMQ的消息确认机制进行优化,在收到消费者确认后向生产者发送确认消息,消息丢失时由生产者重发消息,减少消息确认过程记录的信息.生产者收到确认即可保证消息被消费者成功接收,提高了非持久化小消息投递的可靠性.实验结果表明,在客户端数量较少时,该方法能够明显提高持久化小消息的发送速率.     

基于IEEE802.11n的长距离无线链路性能分析

IEEE802.11n-2009在传统802.11协议上添加了帧聚合和块回复功能,实现了MAC层增强,显著提高了网络吞吐量,使其更加适用于长距离无线网络。通过长距离(45km)无线链路信道利用率的理论计算和网络仿真,论证了节点采用帧聚合与块回复功能时的信道利用率明显优于不采用的情况。仿真结果进一步表明,速率越高、聚合帧越大在长距离传输时的吞吐量越高,且距离越远时帧聚合的优势越明显。     

基于UDP的数据可靠传输技术研究与应用

针对使用UDP协议实现网络实时音视频数据传输时的丢包问题,在对基于UDP的数据可靠传输协议——UDT的原理进行深入分析的基础上,提出了基于时间和数据包数目相结合的确认机制和改进的AIMD（加性增加乘性减少）拥塞控制算法,由此实现网络音视频数据的高质量实时传输。实验证明,使用改进的UDT协议,可以有效提高数据传输的可靠性和效率。     

TCP traffic performance improving in LTE-A networks

This paper presents a novel way to improve Transmission Control Protocol (TCP) performance of the users at the edge areas of the macro cells in Long Term Evolution Advanced (LTE-A) systems. Previous works on improving wireless TCP performance are reviewed and current considerations on TCP in LTE-A are explained. However, those solutions are neither too complex nor limited to some presuppositions which are too restricting for the deployment of LTE-A networks. In this paper a substituted TCP acknowledgement transmission scheme based on Automatic Repeat reQuest (ARQ) information in layer 2 is proposed. The simulation result shows that the proposed method can reduce the delay and improve the throughput of the edging users of the cell, as well as reducing radio resources in LTE-A macro cells.     

《抵达之谜》：混杂身份的解构与重构

从后殖民身份认同的角度切入,来研究英国作家奈保尔在《抵达之谜》中对自身迷失在多元文化时代的混杂身份所进行的解构与重构。奈保尔不断地寻求自我文化身份和文学创作定位,经历了一系列的痛苦裂变,最终将身份定位在某种特定的混杂文化之中,这种定位既有妥协的成分同时又是后殖民作家们摆脱危机、寻求认同的唯一出路。