Wireless ad hoc networks are different from wired networks by the multitude of data packet loss situations they are subjected to. This is due to the characteristics of wireless channel that might obstruct the proper reception of data packet at the destination end. In some case, these vulnerabilities of wireless channel can result in a complete link failure. Although link failure is of low probability in wired networks, it is rather common in wireless networks. The volatility of communication channel is a typical problem with wireless links, which is not the case with wired cables. TCP is a transport protocol that aims at ensuring high reliability and guarantying reception of data packets. However, TCP was designed for wired networks to address congestion, which is the main cause for data packet loss in wired networks. Therefore, other types of data packet loss encountered in wireless networks are prone to misinterpretation by TCP, which will lead to TCP performance degradation within the network. To overcome the performance limitation of TCP when used within ad hoc networks, the aim of this thesis is twofold. First, a complete performance study of TCP over ad hoc networks is achieved. This evaluation concerns two performance metrics: the achievable throughput and the energy consumption of TCP within ad hoc networks. This study allows identifying the potential room of improvement to enhance TCP efficiency in ad hoc networks. Second, we propose a new TCP variant, TCP-WELCOME that optimizes the performance of TCP in ad hoc networks through its ability to distinguish among, and efficiently deal with, different data packet loss situations, within ad hoc networks.
High speed data wireless networks in multipath environments suffer channel impairment from many sources such as thermal noise, path loss, shadowing, and fading. In particular, short-term fading caused by mobility imposes irreducible error floor bounds on system performance. We study the effect of fading on the performance of the widely used TCP/UDP protocol, and investigate how to improve TCP performance over fading channels. Our solutions target upcoming mobile wireless systems such as IEEE 802.16e wireless MANs "Metropolitan Area Networks" where adaptive modulation is enabled and the underlying medium access scheme is On-Demand Time Division Multiple Access "On-Demand TDMA". Adaptive modulation is used in the new generation of wireless systems to increase the system throughput and significantly improve spectral effciency by matching parameters of the physical layer to the time-varying fading channels. Most high-rate applications for such wireless systems rely on the reliable service provided by TCP protocol. The effect of adaptive modulation on TCP throughput is investigated. A semi-Markov chain model for TCP congestion/flow control behavior and a multi-state Markov chain model for Rayleigh fading channels are used together to derive the steady state throughput of TCP Tahoe and Reno. The theoretical prediction based on our analysis is consistent with simulation results using the network simulator NS2. The analytical and simulation results triggered the idea of cross-layer TCP protocol design for single-user scenarios. The fading parameters of wireless channels detected in the physical layer can be used to dynamically tune the parameters "such as packet length and advertised receiver window size" of the TCP protocol in the transport layer so that TCP throughput is improved. For multi-user scenarios, we study how multi-user diversity can be used to improve th.
TCP is the widely used transport protocol across the internet but it was originally designed for wired networks. In wireless networks, TCP encounters serious problems due to the physical properties of the wireless medium. The proposed model has implemented by TCP-LPA (Loss Piece ACK) for wireless network and its performance has compared with that of TCP-DBA (Demand Base ACK). In this thesis, it may be concentrated on two main strategies for enabling the TCP congestion control mechanism to determine the cause for a packet loss. The main objective of our proposed proxy based mechanisms is to explicitly inform the TCP source of any effects caused by wireless links while maintaining the end-to-end design philosophy. However, the implementation technique is network dependent. Finally, it may be developed an analytical TCP throughput model with enhanced TCP-DBA fast retransmit algorithm to avoid timeouts. The model captures the TCP fast retransmit mechanism and expresses the steady state congestion window and throughput as a function of network utilization factor, RTT and loss rate.
This dissertation, "TCP Adaptation Schemes in Heterogeneous and Ad Hoc Wireless Networks" by Zhi, Li, 李志, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled TCP Adaptation Schemes in Heterogeneous and Ad Hoc Wireless Networks submitted by Zhi LI for the degree of Doctor of Philosophy at The University of Hong Kong August 31 2005 TCP (Transmission Control Protocol) has extended its reach to the wireless realm, and is widely used in all sorts of wireless environments. However, severe performance degradation results when TCP is used over a wireless link. The main reason is the assumption in TCP, i.e., congestion is the primary reason for packet losses. Although a large number of wireless TCP adaptation schemes have been proposed in the literature, improving TCP performance is still very much unexplored in wireless environments. Traditionally, various enhancements to the TCP have been evaluated based on an unrealistic channel model-two-state (good or bad) link. We incorporate into our NS-2 based simulation platform a realistic channel model with an adaptive physical layer that exploits the continuously time-varying channel quality (instead of just two states) to compare several well-known TCP al- gorithms in a homogeneous/heterogeneous wireless network. Our results indicate that even re- portedly inferior wireless TCP approaches can utilize the varying channel conditions to generate better performance. Furthermore, we propose a new explicit congestion control strategy called differentiated marking (DM). DM works by using a two-way approach to further reduce the time required for the sender and the receiver to note the congestion problem, possibly induced by too heavy traffic or burst errors caused by the time-varying channel quality. Mobility is an important characteristic of the mobile nodes in multihop ad hoc wireless net- works. Much research has been done on designing ad hoc routing protocols, principally in order to solve the problem of route failure for mobility. However, the modification of TCP is needed at least for the communication end points. In view of this drawback, we propose a routing protocol called local route recovery (LR) to solve this problem. In our proposed algorithm, since route breakage is found locally, the remedial work should be done locally. Thus, the route error is shielded from the TCP sender and, as such, no TCP modification is needed. Extensive simulations using the NS-2 platform have demonstrated that LR outperforms several well-known algorithms, such as DSR, AODV and ELFN. A number of effective security mechanisms have been used in the Internet. However, these methods are not fully applicable in mobile ad hoc wireless networks due to the features of in- frastructureless, dynamic topology and self-organization. We propose a data multipath routing algorithm called Multipath TCP Security (MTS) to enhance data security. In MTS, the source node adaptively chooses the available routes rather than exhaustively testing the "stored routes"one by one. Simulation results show that MTS provides a reasonably good level of security and performance. (Total words: 421) DOI: 10.5353/th_b3203732 Subjects: TCP/IP (Computer network protocol) Wireless communication systems
Since the early 1990s, the wireless communications field has witnessed explosive growth. The wide range of applications and existing new technologies nowadays stimulated this enormous growth and encouraged wireless applications. The new wireless networks will support heterogeneous traffic, consisting of voice, video, and data (multimedia). This necessitated looking at new wireless generation technologies and enhance its capabilities. This includes new standards, new levels of Quality of Service (QoS), new sets of protocols and architectures, noise reduction, power control, performance enhancement, link and mobility management, nomadic and wireless networks security, and ad-hoc architectures. Many of these topics are covered in this textbook. The aim of this book is research and development in the area of broadband wireless communications and sensor networks. It is intended for researchers that need to learn more and do research on these topics. But, it is assumed that the reader has some background about wireless communications and networking. In addition to background in each of the chapters, an in-depth analysis is presented to help our readers gain more R&D insights in any of these areas. The book is comprised of 22 chapters, written by a group of well-known experts in their respective fields. Many of them have great industrial experience mixed with proper academic background.
Ad-hoc Wireless Local Area Networks (WLANs) are becoming very attractive and useful in many kinds of communication and networking applications. This is due to their efficiency, simplicity (in installation and use), relatively low cost, and availability. Unfortunately, Internet application performance over wireless links is disappointing due to wireless impairments that adversely affect higher layers, specifically TCP and UDP which are the de facto standards for connection oriented and connectionless transport layer protocol, respectively. This work analyzes how TCP and UDP (individually and together) perform in an IEEE 802.11 WLAN consisting of several non-mobile nodes. The focus is on performance evaluation in terms of throughput, delay, jitter, and packet loss ratio at the transport layer. Based on the obtained results, suggestions and recommendations are made which can help improve the performance in such scenarios. These include packet size optimization, effect of RTS/CTS scheme, TCP versions, effect of loading the network with UDP traffic, and MAC buffer size optimization, among other things. File transfer and Constant Bit Rate (CBR) applications are simulated, and the simulations are done using the Network Simulator Version 2 software.
The evolution of the mobile communication market is causing a major increase in data traffic demands. This could lead to disrupted mobility and intermittent degraded channel conditions that contribute to poor transmission control protocol (TCP) performance. TCP Performance over UMTS-HSDPA Systems presents a comprehensive study of the effect of TCP on achieved application bit rate performance and system capacity, and shows how to reduce the interaction of wireless networks on TCP with minimal cost. With self-contained chapters, the book consists of two main sections. The first several chapters provide background and describe the state of the art for wireless networks, emphasizing one of the third-generation (3G) wireless technologies: the universal mobile telecommunications system (UMTS). These chapters also include an analysis of the overall cell capacity for UMTS Release 99 and high-speed downlink packet access (HSDPA) systems. The second section focuses on the interaction of TCP with wireless systems, presenting an exhaustive list of TCP versions and link layer solutions that adapt TCP (often modifying the original TCP) to a wireless network. This section also displays mathematical modeling of the interaction of hybrid automatic repeat request (HARQ) and TCP in UMTS networks. While offering information for advanced undergraduate students who are unfamiliar with code division multiple access (CDMA) wireless systems as well as UMTS and HSDPA cellular systems, the book also provides extensive coverage of "TCP over wireless systems" problems and solutions for researchers, developers, and graduate students.
