卫星网络中基于UDP的可靠数据传输协议

在卫星网络中,标准的传输控制协议TCP不能充分发挥网络的性能。论文通过分析卫星网络的特点提出了一个基于UDP的应用层传输协议UDT-Sat。该协议使用基于带宽估计的拥塞控制和基于选择性负向确认的快速重传机制实现数据高效可靠的传输。实验表明,UDT-Sat在卫星网络中具有很高的带宽利用率,同时保持了良好的公平性和稳定性。     

TCP友好的速率控制

TCP友好的速率控制(TFRC)主要适用于实时数据传输的一种拥塞控制机制,具有突出的TCP友好性即在相同的环回时间(RTT)下可以和TCP流享有近乎相同的带宽,从而避免了由于UDP等传输层协议缺乏拥塞控制而带来的网络拥塞甚至崩溃.本文简要介绍了它的协议机制并通过一些仿真和试验的结果初步讨论了其性能.     

网络中的拥塞控制管理算法分析与比较

随着网络技术的发展,网络拥塞日益严重,如何解决拥塞,充分、高效地利用网络资源,成为当今急需解决的问题.由于Internet上大多数业务都采用TCP协议,因此TCP的拥塞控制机制对控制网络拥塞具有特别重要的意义.本文介绍了TCP基于窗口的拥塞控制策略和目前常用端到端拥塞控制算法,并对它们的性能进行比较.     

一种基于带宽估计的战术互联网TCP改进机制

无线的战术互联网通常面临复杂的电磁环境,高误码率、终端的频繁移动等恶劣的通信环境使得针对有线网络设计的TCP协议传榆性能急剧下降.针对战术互联网提出了一种基于带宽估计的TCP改进机制,该机制利用TCP确认帧携带的数据包到达时间来估算带宽,并用动态的低通滤波器来平滑带宽的估计值.在此基础上用带宽的估计值更新拥塞窗口,避免在发生链路错误时启动拥塞控制机制,由此提高TCP在战术互联网中的性能.实验结果表明,该算法能减少链路差错对TCP性能带来的影响,提高TCP在战术互联网上的传输性能.     

基于TCP的卫星链路性能分析与改进策略

针对低误码率有线网络所设计的TCP协议,具有使用广泛、算法成熟、可移植性好等优点,然而卫星链路自身的高误码率、长传播时延、高时延带宽积等因素导致了TCP性能的大幅下降.这使得传统TCP协议应用到卫星网络时性能不理想.本文在梳理TCP协议特点的基础上,对卫星链路影响TCP性能的原因进行了分析,并提出了几种基于卫星链路传输TCP协议的性能改进方法.     

改善卫星融合网络随机丢包和间歇性中断的方法研究*1

当移动自组织网用户通过网关经卫星网络发送数据时,存在卫星链路的长传播时延、随机丢包以及移动终端的移动性引起链接的间歇性中断,导致TCP触发拥塞控制机制而降低传输性能降低。针对以上卫星网络的特点,提出了TCP M-Veno方法。在发送端对TCP Veno进行优化改进使得它能够缓解卫星网络中长的传播时延和随机丢包的影响。在网关中结合M-TCP算法来解决卫星融合网络移动终端间歇性中断。仿真表明,所提出的TCP M-Veno比NewReno、Veno以及M-TCP有更好的传输性能。     

基于可靠UDP的卫星IP网关设计

TCP是面向连接的可靠点到点协议,但是由于卫星网络中典型的长延时、高误码率以及非对称带宽的特点,导致TCP通过宽带卫星网络时,信道利用率非常低。可靠UDP协议基于标准UDP协议并在应用中增加窗口、应答和重传算法来实现。网关采用该协议将TCP连接分段,在应用中明显地改善了TCP在宽带卫星信道上传输的性能,增加TCP的信道利用率。     

基于跳到跳信息的卫星网络传输控制协议研究

设计了一种适用于卫星网络的传输控制协议TPSN。该协议使用异步跳到跳确认,快速恢复成段丢失数据,并采用基于检测窗口的端到端选择性否定应答(SNACK)机制,减少协议控制信息,保证数据可靠传输。在跳到跳可靠性保证机制基础上传输网络负载,实现在避免网络拥塞条件下高效利用网络带宽资源,并保证具有不同端到端往返时延的异种数据流之间的公平性。仿真结果表明TPSN能够在长延迟、误码率高、链路频繁切换的卫星网络中保证高效的带宽利用、可靠的数据传输以及各数据流之间的公平。     

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。     

MPLS网络主动式流量和拥塞控制机制及性能分析

MPLS是具有大带宽一时延迟的网络,用传统的TCP解决MPLS拥塞问题显得十分困难,该文结合MPLS的网络特点,提出了一种适合MPLS网络的主动式流量和拥塞控制机制,在网络边缘节点引入拥塞反馈处理,对实验模型进行了性能仿真分析,实验证明,与传统的TCP协议相比,该机制将流量和拥塞控制从用户端点扩展到MPLS边缘路由器,能够更及时地检测和控制网络拥塞,缩短了控制时延,可以进行较精确的流量调节,实现了提高吞吐量和改善缓冲区利用率的目的。     

Traffic management for TCP/IP over satellite ATM networks

Several Ka-band satellite systems have been proposed that will use ATM technology to seamlessly transport Internet traffic. The ATM UBR, GFR, and ABR service categories have been designed for data. However, several studies have reported poor TCP performance over satellite ATM networks. We describe techniques to improve TCP performance over satellite ATM networks. We first discuss the various design options available for TCP end systems, IP-ATM edge devices, as well as ATM switches for long-latency connections. We discuss buffer management policies, guaranteed rate services, and the virtual source/virtual destination option in ATM. We present a comparison of ATM service categories for TCP transport over satellite links. The main goal of this article is to discuss design and performance issues for the transport of TCP over UBR, GFR, and ABR services for satellite ATM networks     

Basestation flow control for wired to wireless networks

With the exponential growth of the internet, wireless networks such as satellite networks are becoming increasingly popular. The characteristics of satellite networks such as long latency, large delay-bandwidth product, high bit error rate over satellite links and variable round trip time, severely degrade TCP/IP performance. At the conjunction of the satellite link and the fixed link, the basestation, the difference in capacity between the satellite link and the fixed link causes the basestation to experience congestion losses that adversely impact TCP performance. We propose a technique that substantially reduces the congestion at the base station and enforces fairness among the TCP connections that are sharing the satellite link. The technique does not require any change in the TCP sender or the receiver. The stability of our algorithm is analytically proven and its performance is evaluated using ns-2 simulations. Preliminary results yield almost a null congestion loss rate, a 60% decrease in average queue length, and more than 30% increase in the throughput. Fairness is well enforced.     

Performance evaluation of TCP extensions on ATM over high bandwidthdelay product networks

Practical experiments in a satellite network environment assist in the design and understanding of future global networks. This article describes the practical experiences gained from TCP/IP on ATM networks over a high-speed satellite link and presents performance comparison studies of such networks with the same host/traffic configurations over local area and wide area networks. These comparison studies on the LAN, WAN, and satellite environments increase our understanding of the behavior of high-bandwidth networks. NASA's Advanced Communications Technology Satellite (ACTS), with its special characteristics and high data rate satellite channels, and the ACTS ATM Internetwork (AAI) were used in these experiments to deliver broadband traffic. Network performance tests were carried out using application-level software (Netspec) on SONET OC-3 (155.52 Mb/s) satellite links. Finally, we experimentally study the performance, efficiency, fairness, and aggressiveness of TCP Reno, TCP New Reno, and TCP SACK end hosts on ATM networks over high BDP networks     

Evaluation of SCTP for space networks

The stream control transmission protocol has recently been standardized as a new transport layer protocol in the IP protocol suite. SCFP is based on the TCP protocol, but incorporates a number of advanced and unique features that are not available in TCP. Although the suitability of TCP over satellite networks has been widely studied, the suitability of SCTP over satellite networks remains to be evaluated. The objective of this article is to investigate the suitability of SCTP for data communications over satellite networks. We focus on the advanced features of SCTP that enhance its performance in satellite networks. Finally, we provide recommendations on the use of SCTP over satellite networks.     

长传播延时卫星环境中TCP性能分析

卫星通信系统中的长传播延时是影响TCP性能的主要特性之一,对长传播延时卫星环境中TCP在整个动态连接过程中的工作情况进行了分析,综合考虑了单连接情况中连接建立初期不稳定阶段的情况和连接达到稳态阶段时的情况,并给出了Goodput的理论分析和仿真结果,进一步证明了连接的Goodput性能随着卫星链路传播延时的增大而下降。     

卫星TCP加速技术研究

由于卫星链路长时延高误码的特点,传输控制协议(TCP)在卫星链路上效率很低。提出了一种卫星通信系统中TCP加速网关的设计实现方法,介绍了基于加速网关的卫星网络结构,描述了其关键技术实现,对提出的设计实现方法在OPNET中进行了仿真验证。仿真结果表明,该技术大大提高了TCP应用在卫星链路上的传输效率,而且在多连接共享带宽时保持了较好的公平性。     

A Simulation Study of Scalable TCP and HighSpeed TCP in Geostationary Satellite Networks

This paper investigates the performance of two TCP enhancements (i.e., Scalable TCP and HighSpeed TCP), recently proposed for high-speed backbone networks with a very large bandwidth-delay product, in a geostationary satellite environment. Both persistent and elastic traffic patterns are considered, performance being evaluated in terms of TCP throughput and mean session delay, respectively. The impact of channel characteristics (packet error rate, correlation between successive losses) is widely discussed. Fairness issues are also accounted for, together with the impact of some system parameters, such as the satellite link bandwidth. Extensive comparisons are carried out among Scalable TCP, HighSpeed TCP and other congestion control schemes. The obtained results show the soundness for the use of such protocols in geostationary satellite networks. Indeed, both protocols permit to improve the performance of TCP connections in a wide range of channel conditions, showing (especially Scalable TCP) to be able to cope well with rainy conditions and to exploit a future increase in the satellite link capacity. This work was carried out within the framework of the SatNex Network of Excellence, http://www.satnex.org     

Deploying Internet Protocol Security in satellite networks using Transmission Control Protocol Performance Enhancing Proxies

Applications that use the reliable Transmission Control Protocol (TCP) have a significant degradation over satellite links. This degradation is mainly a consequence of the congestion control algorithm used by standard TCP, which is not suitable for overcoming the impairments of satellite networks. To alleviate this problem, two TCP Performance Enhancing Proxies (PEPs) can be deployed at the edges of the satellite segment. Then these PEPs can use different mechanisms such as snooping, spoofing and splitting to achieve a better TCP performance. In general, these mechanisms require the manipulation of the Internet Protocol (IP) and TCP headers that generates a problem when deploying the standard IP security (IPsec) protocol. The security services that IPsec offers (encryption and/or authentication) are based on the cryptographic protection of IP datagrams, including the corresponding IP and TCP headers. As a consequence, these cryptographic protections of IPsec conflict with the mechanisms that PEPs use to enhance the TCP performance in the satellite link. In this article, we detail the reasons that cause this conflict, and we propose three different approaches to deploy IPsec in a scenario with TCP PEPs. Our proposals provide different trade‐offs between security and TCP performance in some typical scenarios that use satellite networks. Copyright © 2012 John Wiley & Sons, Ltd.     

适用于卫星网络的TCP跨层改进机制

该文提出基于跨层信息交互,将链路层ARQ重传状态信息通知TCP的机制,避免了链路层重传引起的时延变化对TCP的不利影响。该机制使用完全可靠选择性重传ARQ为TCP提供可靠的链路,避免卫星链路上发生丢包,并且不必要求链路层保证包按序递交,消除了重排序的等待时延,适合带宽时延积较大的卫星网络。仿真结果表明,能显著提高TCP在卫星网中的性能,特别是在误帧率较高条件下。