非对称无线网络中增强TCP性能的方法

针对非对称无线网络中,源节点和目的节点之间可能存在多条通信路径,通过计算反向路径带宽和平均吞吐量的关系,提出了将TCP数据报文段和确认报文段（ACK）的传输路径分离的方法。把路径的带宽作为判断标准,选择带宽大的那条路径返回ACK信号。仿真证明了提出的方法可以更加有效地提高TCP吞吐量,增强TCP的性能。     

TCP Veno: TCP enhancement for transmission over wireless access networks

Wireless access networks in the form of wireless local area networks, home networks, and cellular networks are becoming an integral part of the Internet. Unlike wired networks, random packet loss due to bit errors is not negligible in wireless networks, and this causes significant performance degradation of transmission control protocol (TCP). We propose and study a novel end-to-end congestion control mechanism called TCP Veno that is simple and effective for dealing with random packet loss. A key ingredient of Veno is that it monitors the network congestion level and uses that information to decide whether packet losses are likely to be due to congestion or random bit errors. Specifically: (1) it refines the multiplicative decrease algorithm of TCP Reno-the most widely deployed TCP version in practice-by adjusting the slow-start threshold according to the perceived network congestion level rather than a fixed drop factor and (2) it refines the linear increase algorithm so that the connection can stay longer in an operating region in which the network bandwidth is fully utilized. Based on extensive network testbed experiments and live Internet measurements, we show that Veno can achieve significant throughput improvements without adversely affecting other concurrent TCP connections, including other concurrent Reno connections. In typical wireless access networks with 1% random packet loss rate, throughput improvement of up to 80% can be demonstrated. A salient feature of Veno is that it modifies only the sender-side protocol of Reno without changing the receiver-side protocol stack.     

Packet concatenation at the IP level for performance enhancement in wireless local area networks

Wireless local area networks experience performance degradation in presence of small packets. The main reason for that is the large overhead added at the physical and link layers. This paper proposes a concatenation algorithm which groups IP layer packets prior to transmission, called PAC-IP. As a result, the overhead added at the physical and the link layers is shared among the grouped packets. Along with performance improvement, PAC-IP enables packet-based fairness in medium access as well as includes QoS support module handling delay-sensitive traffic demands. The performance of the proposed algorithm is evaluated through both simulations and an experimental WLAN testbed environment covering the single-hop and the widespread infrastructure network scenarios. Obtained results underline significant performance enhancement in different operating scenarios and channel conditions. Dzmitry Kliazovich received his Masters degree in Telecommunication science from Belarusian State University of Informatics and Radioelectronics in 2002. He is currently working towards the Ph.D. degree in University of Trento, Italy. From September 2005 to February 2006 he was a visiting researcher at the Computer Science Department of the University of California at Los Angeles. He is an author of more than 20 research papers published in international books, journals and conference proceedings. His main research interest lies in field of wireless networking with a focus on performance optimization and cross-layer design. Fabrizio Granelli was born in Genoa in 1972. He received the “Laurea” (M.Sc.) degree in Electronic Engineering from the University of Genoa, Italy, in 1997, with a thesis on video coding, awarded with the TELECOM Italy prize, and the Ph.D. in Telecommunications from the same university, in 2001. Since 2000 he is carrying on his teaching activity as Assistant Professor in Telecommunications at the Dept. of Information and Communication Technology—University of Trento (Italy). In August 2004, he was visiting professor at the State University of Campinas (Brasil). He is author or co-author of more than 60 papers published in international journals, books and conferences, and he is member of the Technical Committee of the International Conference on Communications (from 2003 to 2007) and Global Telecommunications Conference (GLOBECOM2003 and GLOBECOM2004). Dr. Granelli is guest-editor of ACM Journal on Mobile Networks and Applications, special issues on “WLAN Optimization at the MAC and Network Levels” and “Ultra-Wide Band for Sensor Networks”, and Co-Chair of 10th IEEE Workshop on Computer-Aided Modeling, Analysis, and Design of Communication Links and Networks (CAMAD’04). Dr. Granelli is General Vice-Chair of the First International Conference on Wireless Internet (WICON’05) and General Chair of the 11th IEEE Workshop on Computer-Aided Modeling, Analysis, and Design of Communication Links and Networks (CAMAD’06). His main research activities are in the field of networking and signal processing, with particular reference to network performance modeling, medium access control, wireless networks, cognitive radio systems, and video transmission over packet networks. He is Senior Member of IEEE and Associate Editor of IEEE Communications Letters.     

A new ATM adaptation layer for TCP/IP over wireless ATM networks

This paper describes the design and performance of a new ATM adaptation layer protocol (AAL‐T) for improving TCP performance over wireless ATM networks. The wireless links are characterized by higher error rates and burstier error patterns in comparison with the fiber links for which ATM was introduced in the beginning. Since the low performance of TCP over wireless ATM networks is mainly due to the fact that TCP always responds to all packet losses by congestion control, the key idea in the design is to push the error control portion of TCP to the AAL layer so that TCP is only responsible for congestion control. The AAL‐T is based on a novel and reliable ARQ mechanism to support quality‐critical TCP traffic over wireless ATM networks. The proposed AAL protocol has been validated using the OPNET tool with the simulated wireless ATM network. The simulation results show that the AAL‐T provides higher throughput for TCP over wireless ATM networks compared to the existing approach of TCP with AAL 5. This revised version was published online in July 2006 with corrections to the Cover Date.     

Low‐loss TCP/IP header compression for wireless networks

Wireless is becoming a popular way to connect mobile computers to the Internet and other networks. The bandwidth of wireless links will probably always be limited due to properties of the physical medium and regulatory limits on the use of frequencies for radio communication. Therefore, it is necessary for network protocols to utilize the available bandwidth efficiently. Headers of IP packets are growing and the bandwidth required for transmitting headers is increasing. With the coming of IPv6 the address size increases from 4 to 16 bytes and the basic IP header increases from 20 to 40 bytes. Moreover, most mobility schemes tunnel packets addressed to mobile hosts by adding an extra IP header or extra routing information, typically increasing the size of TCP/IPv4 headers to 60 bytes and TCP/IPv6 headers to 100 bytes. In this paper, we provide new header compression schemes for UDP/IP and TCP/IP protocols. We show how to reduce the size of UDP/IP headers by an order of magnitude, down to four to five bytes. Our method works over simplex links, lossy links, multi‐access links, and supports multicast communication. We also show how to generalize the most commonly used method for header compression for TCP/IPv4, developed by Jacobson, to IPv6 and multiple IP headers. The resulting scheme unfortunately reduces TCP throughput over lossy links due to unfavorable interaction with TCP's congestion control mechanisms. However, by adding two simple mechanisms the potential gain from header compression can be realized over lossy wireless networks as well as point‐to‐point modem links. This revised version was published online in June 2006 with corrections to the Cover Date.     

一种高效的具有用户匿名性的无线认证协议

提出了一种高效的具有用户匿名性的无线认证协议。利用Hash函数和Smart卡实现了协议的用户匿名性。协议充分考虑了无线网络自身的限制和移动设备存储资源及计算资源的局限性，在认证过程中移动用户只需要进行一次对称加密和解密运算，用户与访问网络、本地网络与访问网络都只进行一次信息交换，而且所有对称加密都使用一次性密钥。本协议具有实用、安全、高效的特点。     

Improving TCP performance for vertical handover in heterogeneous wireless networks

The incorporation of wireless local area networks (WLANs) into existing cellular networks as supplementary access technologies has become an issue of great interest. However, vertical handover (VHO), which allows users to roam between a WLAN and a cellular network, causes an abrupt change in certain link characteristics such as the round trip time and data rate. Owing to such changes, reordering problem and premature timeout occur and trigger unnecessarily fast retransmission during VHO, causing throughput degradation. Thus, we propose a new transmission control protocol (TCP) mechanism, which resolves the reordering problem by suppressing unnecessary retransmission caused by spurious duplicate acknowledgments (dupacks) incurred because of the reordering problem, and prevents premature timeout by employing an adaptive retransmission timer. We analytically investigate the throughput of our proposed TCP scheme. The numerical and simulation results show that our proposed TCP performs better in terms of throughput than other schemes appearing in the literature. Copyright © 2009 John Wiley & Sons, Ltd.     

An enhancement of TCP Veno over light-load wireless networks

This letter observes that TCP Veno behaves conservatively over light-load wireless networks. A new variable, congestion loss rate, is introduced into Veno's algorithm. It helps Veno deal with random loss more intelligently, by keeping its congestion window increasing if the link load is in light state. The simulation results demonstrate that, such enhancement can improve Veno's throughput up to 60% without any fairness or friendliness sacrificed.     

TCP CERL: congestion control enhancement over wireless networks

In this paper, we propose and verify a modified version of TCP Reno that we call TCP Congestion Control Enhancement for Random Loss (CERL). We compare the performance of TCP CERL, using simulations conducted in ns-2, to the following other TCP variants: TCP Reno, TCP NewReno, TCP Vegas, TCP WestwoodNR and TCP Veno. TCP CERL is a sender-side modification of TCP Reno. It improves the performance of TCP in wireless networks subject to random losses. It utilizes the RTT measurements made throughout the duration of the connection to estimate the queue length of the link, and then estimates the congestion status. By distinguishing random losses from congestion losses based on a dynamically set threshold value, TCP CERL successfully attacks the well-known performance degradation issue of TCP over channels subject to random losses. Unlike other TCP variants, TCP CERL doesn’t reduce the congestion window and slow start threshold when random loss is detected. It is very simple to implement, yet provides a significant throughput gain over the other TCP variants mentioned above. In single connection tests, TCP CERL achieved an 175, 153, 85, 64 and 88% throughput gain over TCP Reno, TCP NewReno, TCP Vegas, TCP WestwoodNR and TCP Veno, respectively. In tests with multiple coexisting connections, TCP CERL achieved an 211, 226, 123, 70 and 199% throughput improvement over TCP Reno, TCP NewReno, TCP Vegas, TCP WestwoodNR and TCP Veno, respectively.     

An enhanced TCP mechanism – Fast‐TCP in IP networks with wireless links

This paper presents the results of the first study on performance of Fast‐TCP over wireless links with transmission errors. We have studied a case in which a TCP source is connected with a TCP receiver over two routers. The link between the routers is wireless and has bit errors. We compare the performance of Fast‐TCP with plain TCP in the wireless environment. We evaluate Fast‐TCP using the OPNET Radio Modeler^TM discrete event simulation tool. Simulation results show that even without any adaptations of other wireless protocols Fast‐TCP still has more advantages over plain TCP. This revised version was published online in July 2006 with corrections to the Cover Date.     

Improving performance of TCP over mobile wireless networks

Mobile IP is a network layer protocol for handling mobility of hosts in the Internet. However, mobile IP handoff causes degradation of TCP performance. Hence, there is a need for improving performance of TCP over mobile IP in wireless mobile networks. We propose an approach which handles losses due to both wireless link errors and host mobility. To handle losses due to host mobility, a method for seamless handoff is proposed. Empirical results show that the scheme provides substantial improvement of performance.

A multilayer fault localization framework for IP over all-optical multilayer networks

IP over all-optical multilayer networks is a promising solution to combine highspeed transmission using end-to-end lightpaths with the flexibility required to handle traffic increases and fluctuations at layer-2 (e.g., Ethernet) and/or layer-3 (e.g., IP). Fault management is a key issue for the successful deployment of these networks due to their high bit-rate and service-quality demands. To decrease complexity, the problems of locating the roots of multiple failures and initiating recovery actions in a network traditionally were approached from a single-layer perspective. This article analyzes the major challenges for fault detection, fault localization, and survivability in wavelength-routed, IP over all-optical multilayer networks and then, proposes a framework for efficient fault localization in this kind of network.     

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.     

对Windows TCP/IP协议栈的一种简化设计

为了让Windows下的网络数据快速发送与接收,提高实时性能,采用对Windows TCP/IP协议栈进行一种简化设计,通过利用Windows提供的用户与设备对象的交互,减少Windows从用户态到内核态的分层,对Socket层进行简单的封装,并且利用零拷贝技术减少数据的拷贝次数以及设置多级优先级队列使数据按照优先级发送,从而使数据达到快速发送和接收的目的。实验结果验证了这种方法能达到预期效果。     

区分服务网络中的TCP友好公平体系

区分服务(Differentiated Services)是IETF为实现IP服务质量(QoS)而定义的一个体系结构。研究表明,在该体系中存在不公平问题,该文将TCP友好(TCP Friendly)的概念引入到DS网络中,并定义了DS网络中的TCP友好的公平性,仿真验证了目前IETF定义的流量调节(TrafficConditioning)以及丢包策略等机制不能很好地实现TCP友好公平性,因而提出了直接拥塞控制机制来实现这一公平性。     

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     

Internet protocol performance over networks with wireless links

This article discusses the problems that arise when standard Internet protocols such as TCP are used over wireless links. We review wireless link characteristics with case studies drawn from commercial wireless LANs and cellular telephony systems. We discuss problems with Internet protocols when employed over these systems, such as degraded TCP performance when wireless errors are interpreted as congestion losses. We survey various proposed approaches to mitigating such problems and examine their applicability. Finally, we look at the future of wireless systems and the new challenges that they will create for Internet protocols, and state some goals for further protocol enhancement and evolution, pointing out the need for better protocol integration across layers     

Improving TCP performance over wireless networks at the link layer

We present the transport unaware link improvement protocol (TULIP), which dramatically improves the performance of TCP over lossy wireless links, without competing with or modifying the transport- or network-layer protocols. TULIP is tailored for the half-duplex radio links available with today's commercial radios and provides a MAC acceleration feature applicable to collision-avoidance MAC protocols (e.g., IEEE 802.11) to improve throughput. TULIP's timers rely on a maximum propagation delay over the link, rather than performing a round-trip time estimate of the channel delay. The protocol does not require a base station and keeps no TCP state. TULIP is exceptionally robust when bit error rates are high; it maintains high goodput, i.e., only those packets which are in fact dropped on the wireless link are retransmitted and then only when necessary. The performance of TULIP is compared against the performance of the Snoop protocol (a TCP-aware approach) and TCP without link-level retransmission support. The results of simulation experiments using the actual code of the Snoop protocol show that TULIP achieves higher throughput, lower packet delay, and smaller delay variance. This revised version was published online in June 2006 with corrections to the Cover Date.     

Improving TCP performance over wireless networks at the link layer

We present the transport unaware link improvement protocol (TULIP), which dramatically improves the performance of TCP over lossy wireless links, without competing with or modifying the transport- or network-layer protocols. TULIP is tailored for the half-duplex radio links available with today's commercial radios and provides a MAC acceleration feature applicable to collision-avoidance MAC protocols (e.g., IEEE 802.11) to improve throughput. TULIP's timers rely on a maximum propagation delay over the link, rather than performing a round-trip time estimate of the channel delay. The protocol does not require a base station and keeps no TCP state. TULIP is exceptionally robust when bit error rates are high; it maintains high goodput, i.e., only those packets which are in fact dropped on the wireless link are retransmitted and then only when necessary. The performance of TULIP is compared against the performance of the Snoop protocol (a TCP-aware approach) and TCP without link-level retransmission support. The results of simulation experiments using the actual code of the Snoop protocol show that TULIP achieves higher throughput, lower packet delay, and smaller delay variance. This revised version was published online in June 2006 with corrections to the Cover Date.     

Throughput stability and flow fairness enhancement of TCP traffic in multi-hop wireless networks

Wireless Networks - In the multi-hop wireless network, transmission control protocol (TCP) throughput stability and flow fairness performances are worsened due to slower flow convergence in the...