超宽带IP网络环境下的视频分组丢失修复技术研究

基于IP超宽带网络传送视频节目已经成为三网融合背景下的发展趋势。相对于传统广电运营商的同轴广播网,IP网络更加复杂,出现分组丢失的可能性更大,可能会影响用户的观赏体验。目前的视频编码技术本身的冗余机制大多适用于同轴网络,因此有必要对IP网络中的视频分组丢失修复机制进行研究。本文分析了分组丢失对视频质量的影响,并对目前主流的分组丢失修复技术进行了针对性分析和比较,结合测试结果,给出了可行的分组丢失修复技术应用建议。     

WCDMA空中接口RLC层的AM传输方式关键技术的研究

以WCDMA标准为依据，简要介绍了该标准空中接口方案的无线链路控制子层（RLC层）,并对RLC层确认数据传输方式中发送／接收缓冲区的设置以及状态报告的形成进行了深入探讨。     

新的TCP拥塞控制机制

拥塞控制已成为确保Internet稳定性、鲁棒性的关键因素.针对目前TCP拥塞控制机制中存在的实际问题,提出了一种新的拥塞控制机制,包括COS-Slow-Start和A-AIMD两种改进策略.NS2仿真实验结果表明,该机制能有效地减少分组的丢失、平缓突发流量的冲击,并可增加带宽的有效利用率.     

基于TCP层拥塞避免算法的研究与实现

阐述了TCP利用滑动窗口技术进行数据包传输的机制,在拥塞控制方面详细讨论了拥塞避免的相关算法.指出在网络拥塞的情况下,由于超时引起的数据包重传机制对于提高网络的服务质量重要性,通过研究分析传统的快速重传机制和算法,提出了新的解决方案.结果表明,改进后的拥塞避免算法比传统上的算法不仅能够更好的解决拥塞问题,提高网络的传输质量,而且还能够更好的利用网络资源,提高网络的整体性能.     

基于分组重传时延的操作系统探测新技术

指出现有操作系统远程探测技术中的不足之处,结合TCP协议原理,介绍了一种新型的基于报文重传时延的探测技术,同时在分析具体实例的基础上,给出了系统探测的特定算法.     

TCP SACK突发分组丢失吞吐量模型

利用Gilbert分组丢失模型描述端对端突发分组丢失特性,提出了基于RFC6675的快重传和快恢复模型,推导并基于该模型建立TCP SACK吞吐量模型。数值实验和仿真实验表明,快重传和快恢复模型能准确描述基于RFC6675的快重传和快恢复过程;TCP SACK流吞吐量模型估计的准确性得到提升。     

Rate control for streaming media transmission over WLAN

In order to solve the problems of link layer retransmission and packet fragment strategies for IEEE 802.11, this paper proposes a variable packet TCPfriendly rate control (VPTFRC) scheme for streaming media transmission over wireless local area network (WLAN) by researching on the policy of packet size adjustment in transport layer based on the minimum retransmit-delay constraint. Unlike other proposals, this process considers the impact of wireless packet error ratio (PER) on the packet size adjustment and the performance of rate control. Simulation results demonstrate that our proposed process can simultaneously achieve higher throughput, better fairness, shorter transmission delay and less jitter than TFRC. Among them, the ratio of delay, jitter and packet loss rate can reach a maximum improvement ratio of 58%, 42% and 85% respectively. __________ Translated from Journal of Huazhong University of Science and Technology (Nature Science Edition), 2007, 35(1): 1–3 [译自: 华中科技大学学报(自然科学版)]     

Optimization of total traffic in a slotted ALOHA based access network considering the capture and retransmission effects

The combined effect of capture ratio and number of transmission on the performance of a slotted ALOHA based wireless access network is analyzed. The network quality parameters are evaluated to investigate the effect of lowering the capture ratio and increasing the number of transmission. It is found that the slotted ALOHA based access network shows its stable operation in low capture environment even if the retransmission cut‐off is increased. As a result the success rate of accessing the core network is improved. Copyright © 2005 John Wiley & Sons, Ltd.     

A fast self-similarity matrix-based method for shrew DDoS attack detection

ABSTRACT

Shrew DDoS attack mainly targets the TCP’s retransmission timeout (RTO) mechanism that handles severe cases of congestion and packet losses. This attack is very hard to detect due to its stealthy nature and low-rate in volume which if remained undetected can affect the legitimate TCP flows. In this paper, we propose a fast shrew DDoS attack detection method based on self-similarity matrix (SSM) that measures the self-similarity of network traffic across multiple time scales over a subset of relevant features. The method can detect any presence of shrew attack in-line with the incoming traffic samples and thus identify the attack flows. We experimented our method over real-life low-rate datasets for multiple scenarios and the results demonstrate its efficiency both in terms of detection accuracy and speed.     

Random network coding‐based optimal scheme for perfect wireless packet retransmission problems

Solving wireless packet retransmission problems (WPRTPs) using network coding (NC) approach is increasingly attracting research efforts. However, existing researches are almost all focused on solutions in Galois field GF(2), and consequently, the solutions found by these schemes are usually less optimal. In this paper, we focus on optimal NC‐based scheme for perfect WPRTPs (P‐WPRTPs) where, with respect to each receiver, a packet is either requested by or already known to it. The number of retransmitted packets in optimal NC‐based solutions to P‐WPRTPs is firstly analyzed and proved. Then, random network coding‐based optimal scheme (RNCOPT) is proposed for P‐WRPTPs. RNCOPT is optimal in the sense that it guarantees to obtain a valid solution with minimum number of packet retransmissions. Furthermore, in RNCOPT, each coding vector is generated using a publicly known pseudorandom function with a randomly selected seed. The seed, instead of the coding vector, is used as decoding information to be retransmitted together with the coded packet. Thus, packet overhead of RNCOPT is reduced further. Extensive simulations show that RNCOPT distinctively outperforms some previous typical schemes for P‐WPRTPs in saving the number of retransmitted packets. Copyright © 2011 John Wiley & Sons, Ltd.