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.
Today’s wireless network complexity and the new applications from various user devices call for an in-depth understanding of the mutual performance impact of networks and applications. It includes understanding of the application traffic and network layer protocols to enable end-to-end application performance enhancements over wireless networks. Although Transport Control Protocol (TCP) behavior over wireless networks is well known, it remains as one of the main drivers which may significantly impact the user experience through application performance as well as the network resource utilization, since more than 90% of the internet traffic uses TCP in both wireless and wire-line networks. In this dissertation, we employ application traffic measurement and packet analysis over a commercial Long Term Evolution (LTE) network combined with an in-depth LTE protocol simulation to identify three critical problems that may negatively affect the application performance and wireless network resource utilization: (i) impact of the wireless MAC protocol on the TCP throughput performance, (ii) impact of applications on network resource utilization, and (iii) impact of TCP on throughput performance over wireless networks. We further propose four novel mechanisms to improve the end-to-end application and wireless system performance: (i) an enhanced LTE uplink resource allocation mechanism to reduce network delay and help prevent a TCP timeout, (ii) a new TCP snooping mechanism, which according to our experiments, can save about 20% of system resources by preventing unnecessary video packet transmission through the air interface, and (iii) two Split-TCP protocols: an Enhanced Split-TCP (ES-TCP) and an Advanced Split-TCP (AS-TCP), which significantly improve the application throughput without breaking the end-to-end TCP semantics. Experimental results show that the proposed ES-TCP and AS-TCP protocols can boost the TCP throughput by more than 60% in average, when exercised over a 4G LTE network. Furthermore, the TCP throughput performance improvement may be even superior to 200%, depending on network and usage conditions. We expect that these proposed Split-TCP protocol enhancements, together with the new uplink resource allocation enhancement and the new TCP snooping mechanism may provide even greater performance gains when more advanced radio technologies, such as 5G, are deployed. Thanks to their superior resource utilization efficiency, such advanced radio technologies will put to greater use the techniques and protocol enhancements disclosed through this dissertation.
Transmission Control Protocol (TCP) was designed and optimized to work well over wired networks. It suffers significant performance degradation in wireless networks due to their different characteristics, such as high Bit-Error Rate (BER), large and variable delay and bursty traffic. In this thesis, I propose packet control algorithms to be deployed in intermediate network routers. They improve TCP performance in wireless networks with packet delay variations and long sudden packet delays. The ns-2 simulation results show that the proposed algorithms reduce the adverse effect of spurious fast retransmits and timeouts and greatly improve the goodput compared to the performance of TCP Reno. The TCP goodput was improved by 3̃0% in wireless networks with 1% packet loss. TCP performance was also improved in cases of long sudden delays. These improvements highly depend on the wireless link characteristics.
Transmission Control Protocol (TCP) designed to deliver seamless and reliable end-to-end data transfer across unreliable networks works impeccably well in wired environment. In fact, TCP carries the around 90% of Internet traffic, so performance of Internet is largely based on the performance of TCP. However, end-to-end throughput in TCP degrades notably when operated in wireless networks. In wireless networks, due to high bit error rate and changing level of congestion, retransmission timeouts for packets lost in transmission is unavoidable. TCP misinterprets these random packet losses, due to the unpredictable nature of wireless environment, and the subsequent packet reordering as congestion and invokes congestion control by triggering fast retransmission and fast recovery, leading to underutilization of the network resources and affecting TCP performance critically. This thesis reviews existing approaches, details two proposed systems for better handling in networks with random loss and delay. Evaluation of the proposed systems is conducted using OPNET simulator by comparing against standard TCP variants and with varying number of hops.
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.
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
