On-board regenerative repeaters applied to digital satellite communications

In pulse-code modulation/time-division multiple access (PCM/TDMA) satellite communications, though the number of repeating stage is usually only one, the regenerative repeater will be worthwhile enough to be introduced on board the satellite. This is because the improvement of the communication quality by the increase of the transmission power is difficult in the satellite link and the regenerative repeater is very effective for removing cochannel interferences which will become predominant factor of signal degradation in the future and it will also provide great facility for various kinds of on-board processings. This paper first presents basic configurations of the on-board regenerative repeater, and discusses about simplification of the repeater. Next various kinds of on board processings ate discussed in connection with the regenerative repeating. Then a concrete regenerative repeater applied to satellite switched/TDMA (SS/TDMA) satellite system which augments the communication capacity by frequency reuse is presented and compared with the conventional frequency translating type in terms of link budget, power dissipation, and weight. Lastly the result of the development of an experimental regenerative repeater is described.     

Performance evaluation of a TCP proxy in WCDMA networks

The article addresses the end-to-end performance of TCP in a scenario where WCDMA is used as the access link. In particular, the performance gain that can be achieved by placing a TCP split connection proxy in the WCDMA core network is examined. It is well known that performance enhancing proxies are able to improve the performance of TCP over wireless links that suffer from impairments. However, while previous work on TCP proxies for wireless systems either focused on other wireless systems, like wireless LAN or satellites, or provided a more generic framework, we address in detail the characteristics of a WCDMA access scenario supported by a TCP proxy. The characteristics of WCDMA as perceived by TCP are discussed thoroughly. We argue that the motivation for introducing a proxy is only to overcome problems stemming from a large bandwidth delay product and not to assist local transport layer error recovery at the wireless link. Based on simulations that consider both link layer protocols and TCP, the end-to-end performance for file downloads is investigated. Simulation results show that a proxy can significantly improve performance in the case of high data rates like 384 kb/s. For lower data rates, like 64 and 128 kb/s, it is sufficient to use a well configured TCP implementation.     

Site-based mapping for parallel proxy servers with fewer TCP connections

Many mapping schemes for parallel proxy servers have been proposed in previous research. The operations of these schemes are mainly URL-based, and therefore cannot fully benefit from the new persistent connection feature of HTTP/1.1. In this article we propose a site-based mapping scheme that forwards all requests targeting the same Web site to the same proxy server. This allows a proxy to leave the TCP connections open between consecutive operations so as to avoid the costs of multiple open and close connections to the remote servers. Simulation results show that the proposed site-based scheme reduces 40-70 percent of connection setups and teardowns compared to conventional URL-based mapping schemes.     

TCP/IP enhancements for satellite networks

With the emerging market for high-mobility remote access broadband services, satellite networks are becoming increasingly popular. Although the ubiquitous TCP/IP protocol is widely used to provide reliable data delivery in terrestrial networks, it faces many challenges in satellite environments. These stem from the inherent features of satellite channels, such as large delays, increased error rates, and bandwidth asymmetry. To address these concerns, a variety of solutions have been proposed. These include direct TCP enhancements to better tune the TCP/IP stack and additional selective acknowledgment mechanisms. Other proposals use advanced interworking to reduce sensitivity to various channel features. Examples include multiple TCP sessions, link-layer interworking, and ACK control schemes. Improving onboard satellite features (buffer management, flow control) can also provide benefits for TCP/IP transport. The objective of this article is to present the various solutions and discuss their possible trade-offs. Overall, there exists a rich set of alternatives to meet the challenges in this important arena     

TCP/IP performance over satellite links

Achieving high data rates using TCP/IP over satellite networks can be difficult. This article explains some of the reasons TCP/IP has difficulty with satellite links. We present solutions to some problems, and describe the state of the research on some the unsolved problems     

基于TCP代理的数据传输系统的安全性优化

随着网络技术的发展和普及,企业异地分支局域网之间的网络通信越来越频繁,用户对于安全性和数据传输的可靠性也更加重视。针对以上需求,本文对现有的基于TCP代理的数据压缩传输系统进行了分析,并进行安全性优化,提高了系统对于攻击的防御能力和数据传输的安全性。     

卫星网中的TCP慢启动机制的研究

摘要：TCP连接中的慢启动在卫星网的环境下对TCP性能有着非常重要的影响，讨论了动的相关的因素以及针对卫星网的特点做出的改进。在文章的最后，分析了一个实际操作系统中TCP／IP协议的滑动窗口实现。     

TCP over satellite links: Problems and solutions

Satellite communications are destined to play an important role in future telecommunications infrastructure. There is in particular an increasing interest in transporting Internet traffic over satellite links. Many studies have shown that TCP has a poor performance in the context of satellite communications. This is due to many factors inherent to satellite communications and for which TCP – originally designed for terrestrial networks – is inadequate. Our study is an overview of the many factors limiting TCP performance over a satellite link and the different solutions proposed to address the problem. This revised version was published online in June 2006 with corrections to the Cover Date.     

Considering spurious timeout in proxy for improving TCP performance in wireless networks

In this letter, we introduce a new proxy that effectively prevents unnecessary retransmissions from flowing over a wireless link on a path with sudden delay. The proposed Spurious Timeout (STD) algorithm detects spurious timeout based on the data and acknowledge sequence number. It responses to spurious timeout by filtering duplicate acknowledgements that can cause spurious fast retransmission. Simulation results show that the proposed STD algorithm performs better than, or as well as, other end-to-end mechanisms.     

一种基于卫星信道的TCP数据加速方法

TCP/IP发展迅猛,卫星信道承载TCP/IP业务势在必行。卫星信道具有长时延特性,而TCP是一种基于连接的互联网协议,分组传输需要确认,从而给卫星信道传输TCP业务带来效率低下的问题。卫星信道传输TCP分组的速度受限于延时,而不是取决于信道速率。采用TCP协议欺骗的方法可以有效提高卫星信道传输速率,进而提高卫星信道利用效率,最终达到有效解决延时限制信道的问题。     

BIPR: a new TCP variant over satellite networks

Standard TCP perform poorly in satellite networks since the long delay, high bit error ratio and other characters. A new TCP variant, called BIPR for satellite networks is presented in this paper. Using the binary increase of window growth function, long bandwidth-delay product can be overcome, while probe method is also adopted in BIPR for conquer the high bit error rates in satellite links. Simulation results show that good performances in terms of throughput, link utilization and RTT fairness can be achieved in satellite networks using our method.     

Effects on TCP of routing strategies in satellite constellations

A broadband satellite network uses a constellation of a number of similar satellites to provide wireless networking services to the Earth. A number of these constellation networks are under development. This article introduces the types of satellite constellation networks, and examines how overall performance of TCP communications carried across such a network can be affected by the choice of routing strategies used within the network. Constellations utilizing direct intersatellite links are capable of using multiple paths between satellites simultaneously as a strategy to spread network load. This allows more general routing strategies than shortest-path routing, but we show these strategies to be detrimental to the performance of individual TCP connections     

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     

卫星网络中的TCP跨层技术研究

CCSDS链路层协议TC的重传功能可以减少误码丢包而导致TCP窗口缩减、吞吐量降低的情况,但是链路层对丢失的数据反复重传易引起数据包端到端传输时延的剧烈变化,可能导致TCP数据包失序和重传定时器发生超时,引起传输层和链路层重复重传的情况.该文通过链路层与传输层的差错控制信息交互,传输层将TCP数据的序列号通告链路层,链...     

TCP协议在宽带多媒体卫星通信系统中的性能分析与增强（上）

作为承载多媒体业务的一种重要协议,TCP协议在宽带多媒体卫星通信（BSM,Broadband Satellite Multimedia）系统中的地位十分重要,然而TCP的内在机制（滑动窗口、慢启动、拥塞避免等）差,即而出现了许多针对卫星应用环境的TCP增强策略。由于篇幅关系,本文分为两个篇次：（上）主要分析TCP协议在卫星应用环境中的局限性并介绍目前常见的TCP性能增强方法,（下）主要关注TCP性能增强方法中最常用的性能增强代理（PEP,Performance Enhancement Proxy）的原理和性能,最后对目前TCPPEP中的行业标准“基于SCPS—TP协议的PEP”进行介绍.     

TCP协议在宽带多媒体卫星通信系统中的性能分析与增强（下）

由于目前大部分用户终端系统仍采用标准TCP协议,用户无法对TCP协议相关参数进行设置和调整,短期内新的改进协议也很难大规模应用于终端系统,因此针对TCP传输性能的优化只能在卫星段进行,最常见的是性能增强代理（PEP,Performance Enhancement Proxy）法,即通过增加硬件设备,将TCP端到端语义连接断开实现协议性能的增强。PEP的实现方案有很多,根据层次不同可分为基于链路层PEP、基于运输层PEP、基于应用层PEP。其中基于运输层PEP应用最为广泛,主要通过TCP进程之间的交互实现对TCP性能的增强;根据实现方式不同还可以分为TCP欺骗（TCP spoofing）和TCP分段（TCP splitting）两种。PEP的优势在于,终端系统感觉不到PEP的存在,也无需针对PEP做任何改动。     

Analytical expression and performance evaluation of TCP packet loss probability over geostationary satellite

The letter contains the formulation of an analytical expression of the Transmission Control Protocol (TCP) packet loss probability over geostationary satellite channels on the basis of the state-of-the-art in the field. The expression obtained is function of the bandwidth available and is suited to be used in control mechanisms. It is compared with the results obtained through a satellite network emulator already validated in the literature.     

Providing differentiated service to TCP flows over bandwidth on demand geostationary satellite networks

The elasticity of transmission control protocol (TCP) traffic complicates attempts to provide performance guarantees to TCP flows. The existence of different types of networks and environments on the connections' paths only aggravates this problem. In this paper, simulation is the primary means for investigating the specific problem in the context of bandwidth on demand (BoD) geostationary satellite networks. Proposed transport-layer options and mechanisms for TCP performance enhancement, studied in the single connection case or without taking into account the media access control (MAC)-shared nature of the satellite link, are evaluated within a BoD-aware satellite simulation environment. Available capabilities at MAC layer, enabling the provision of differentiated service to TCP flows, are demonstrated and the conditions under which they perform efficiently are investigated. The BoD scheduling algorithm and the policy regarding spare capacity distribution are two MAC-layer mechanisms that appear to be complementary in this context; the former is effective at high levels of traffic load, whereas the latter drives the differentiation at low traffic load. When coupled with transport layer mechanisms they can form distinct bearer services over the satellite network that increase the differentiation robustness against the TCP bias against connections with long round-trip times. We also explore the use of analytical, fixed-point methods to predict the performance at transport level and link level. The applicability of the approach is mainly limited by the lack of analytical models accounting for prioritization mechanisms at the MAC layer and the nonuniform distribution of traffic load among satellite terminals.