Modeling TCP over Ad hoc Wireless Networks using Multi-dimensional Markov Chains

TCP (transmission control protocol) is the prevalent reliable transport protocol used for many of the Internet's most popular services like Web browsing and e-mail. Since these services are the dominant applications on the Internet, TCP can be said to control the large majority of today's Internet traffic and we can say the enhancement of TCP performance means the improvement of the most Internet performance. In this paper, we compare various ACK generation TCP strategies that play very important roles in TCP operation and propose advanced delayed ACK algorithms to mitigate the negative effect of delayed ACK algorithm. Even if delayed ACK has a bright side to save network resources and power consumption that are the very important factors especially for mobile and wireless environments, it has also a dark side not to take full advantage of network bandwidth in the slow start phase. It is reported that delayed ACK timeout of the first and last segment causes a severe degradation problem in TCP throughput performance. We suggest new algorithms to solve delayed ACK penalty and to guarantee fairness with other traffic in slow start. In wired-cum-wireless network environments, BADA (base station aided delayed ACK) with SNDA (sender notification delayed ACK), the combination of our proposed algorithm shows the best performance in terms of throughput as well as in terms of network resource sharing. Our simulation shows significantly improved performance in TCP throughput.

In this paper, we study the performance of the transmission control protocol (TCP) over mobile ad‐hoc networks. We present a comprehensive set of simulation results and identify the key factors that impact TCP's performance over ad‐hoc networks. We use a variety of parameters including link failure detection latency, route computation latency, packet level route unavailability index, and flow level route unavailability index to capture the impact of mobility. We relate the impact of mobility on the different parameters to TCP's performance by studying the throughput, loss‐rate and retransmission timeout values at the TCP layer. We conclude from our results that existing approaches to improve TCP performance over mobile ad‐hoc networks have identified and hence focused only on a subset of the affecting factors. In the process, we identify a comprehensive set of factors influencing TCP performance. Finally, using the insights gained through the performance evaluations, we propose a framework calledAtraconsisting of three simple and easily implementable mechanisms at the MAC and routing layers to improve TCP's performance over ad‐hoc networks. We demonstrate thatAtraimproves on the throughput performance of a default protocol stack by 50%–100%. Copyright © 2004 John Wiley & Sons, Ltd.

Long distance high bandwidth networks are spanning several continents and many remote Healthcare centers are centralizing their data centers for economic reasons. For the best performance of their data centers, TCP (Transmission Control Protocol) performance and data security are the main critical issues in these network scenarios. TCP performance is directly related to its congestion control mechanism which is responsible for detecting and reacting to the overload traffic on the network. Data security is related to the security mechanism being used by sender and receiver nodes during communication. Linux users, which have rapidly increased in the last five years and most of the Healthcare data centers are being deployed on the Linux operating system, focus the researchers to work on Linux to enhance its performance and security accordingly. The Linux operating system uses TCP CUBIC as a congestion control mechanism with TCP during communication. TCP CUBIC became the default congestion control mechanism of Linux in 2006 after kernel 2.6.18. TCP CUBIC is fundamentally a loss based TCP congestion control mechanism and at each packet loss detection, it reduces its Congestion Window ( $cwnd$ c w n d ) size 20 percent instead of 50 percent as in trademark congestion control mechanism Standard TCP. The aim of this paper is to design a new security mechanism that will work with TCP CUBIC to achieve the maximum possible performance and security over the network link. In this paper, Network Simulator 2 (NS-2) is used to compare the performance of TCP CUBIC with state-of-the-art mechanisms in long and short Round Trip Time (RTT), high bandwidth network scenarios. Results show that when new security mechanism is used with TCP CUBIC, overall better performance in the form of protocol fairness, TCP friendliness, goodput, and convergence time is achieved over the network link.

Many smart healthcare centers are deploying long distance, high bandwidth networks in their computer network infrastructure and operation. Transmission control protocol (TCP) is responsible for reliable and secure communication of data in these medial infrastructure networks. TCP is reliable and secure due to its congestion control mechanism, which is responsible for detecting and reacting to the congestion in the network. Many TCP congestion control mechanisms have been developed previously for different operating systems. TCP CUBIC, TCP Compound, and TCP Fusion are the default congestion control mechanism in Linux, Microsoft Windows, and Sun Solaris operating systems, respectively. The earliest congestion control mechanism Standard TCP acts as the trademark congestion control mechanism. The exponential growth of congestion window ( $cwnd$ ) in slow start phase of the TCP CUBIC causes burst losses of packets, and TCP flows did not share available link bandwidth fairly. The prime aim of this paper is to enhance the performance of TCP CUBIC for long distance, high bandwidth secured networks to achieve better performance in medical infrastructure, concerning packet loss rate, protocol fairness, and convergence time. In this paper, congestion control module for slow start is proposed, which reduces the effect of the exponential growth of $cwnd$ by designing the new limits of $cwnd$ size in slow start phase, which in turn decreases the packet loss rate in healthcare networks. NS-2 is used to simulate the experiments of enhanced TCP CUBIC and state-of-the-art congestion control mechanisms. Results show that the performance of enhanced TCP CUBIC outperforms by 18% as compared with the state-of-the-art congestion control mechanisms.

This paper analyzes performance of Transmission Control Protocol (TCP) in multi-hop cellular networks. Multi-hop transmission shortens communication distance and can make channel quality at each hop better. However it needs channel resources at every hop for packet transmission, and thus effective throughput on end-to-end links can be decreased. Related researches have shown that multi-hop transmission may reduce TCP performance in the systems. However, it may be because improvement of channel quality derived by multi-hop transmission has not been considered fairly. We analyze TCP performance with considering channel quality improvement on a multi-hop system. By simulation, we derived the throughput gain by multi-hop transmission for various values of the number of hops. We also have analyzed the gain according to position of active users in a cell. From the results, we show that multi-hop transmission can improve TCP performance, especially for the users near the cell edge. We also show a proper number of hops that gives maximum TCP performance.

Analytical modeling of TCP flow in wireless LANs

We propose a packet-level model to investigate the impact of channel error on the transmission control protocol (TCP) performance over IEEE-802.11-based multihop wireless networks. A Markov renewal approach is used to analyze the behavior of TCP Reno and TCP Impatient NewReno. Compared to previous work, our main contributions are listed as follows: 1) modeling multiple lossy links, 2) investigating the interactions among TCP, Internet Protocol (IP), and media access control (MAC) protocol layers, specifically the impact of 802.11 MAC protocol and dynamic source routing (DSR) protocol on TCP throughput performance, 3) considering the spatial reuse property of the wireless channel, the model takes into account the different proportions between the interference range and transmission range, and 4) adopting more accurate and realistic analysis to the fast recovery process and showing the dependency of throughput and the risk of experiencing successive fast retransmits and timeouts on the packet error probability. The analytical results are validated against simulation results by using GloMoSim. The results show that the impact of the channel error is reduced significantly due to the packet retransmissions on a per-hop basis and a small bandwidth delay product of ad hoc networks. The TCP throughput always deteriorates less than ~ 10 percent, with a packet error rate ranging from 0 to 0.1. Our model also provides a theoretical basis for designing an optimum long retry limit for IEEE 802.11 in ad hoc networks.

Recent years internet blended multi-hop wireless networking technology experience growth in diverse sectors ranging from health care to the defense industry. An immense internet data traffic quantity depends on the transmission control protocol (TCP) due to its reliable data carrying ability between end process. TCP's congestion control algorithm performance under multi-hop wireless networks (MWN) is heavily influenced by retransmission timer (RT timer). The retransmission timeout (RTO) algorithm governs RT timer's clock duration. In MWN environment, Jacobson RTO prediction fails to endure sudden traffic delay spike that occurs due to inadequate recovery time during a link failure. In this paper, an analysis carried out to study the RTO's negative impact on TCP's performance under the multi-hop wireless scenario.

Minimum TCP throughput guarantee on minimum rate guaranteed networks

Due to the development and evolution in Cognitive Radio Networks (CRNs), the performance of Transmission Control Protocol (TCP) over CRN has become a crucial factor. TCP ensures the reliable end-to-end delivery of data, which is very important for the quality of service (QoS) requirements. TCP performance is severely affected by channel switching and channel availability in CRNs. The frequent occurrence of such events is due to CRNs nature which unnecessarily reduces the transmission rate which results in degrading the overall performance. In this paper, the authors investigate the limitations of using TCP NewReno (i.e., standard TCP) over CRNs, and further propose a cross-layer-design protocol based on an interaction between transport layer and lower layers to improve TCP performance over CRNs. The design is called Cross-Layer Design for TCP (TCP-CLD). It primarily aims at improving the TCP performance over CRNs via controlling and adapting a few selected TCP parameters. Specifically, the authors propose freezing the data transmission and re-transmission timeout (RTO) of TCP during the time of channel switching and channel unavailability. In addition, the authors update the size of congestion window (cwnd) of TCP based on the bandwidth and buffer size of relay nodes. Moreover, in the case of channel switching, the authors update the Round Trip Time (RTT) of TCP based on the new route delay. Simulation experiments have been conducted using ns-2 network simulator tool whereas results show that the proposed design achieves a significant performance improvement compared with the standard TCP NewReno protocol and the other known protocol, namely, TCP-CRAHN.

Most of the traffic in today's Internet is controlled by the Transmission Control Protocol (TCP). Hence, the performance of TCP has a significant impact on the performance of the overall Internet. TCP is a complex protocol with many user-configurable parameters and a range of different implementations. In addition, research continues to produce new developments in congestion control mechanisms and TCP options, and it is useful to trace the deployment of these new mechanisms in the Internet. As a final concern, the stability and fairness of the current Internet relies on the voluntary use of congestion control mechanisms by end hosts. Therefore it is important to test TCP implementations for conformant end-to-end congestion control. Since web traffic forms the majority of the TCP traffic, TCP implementations in today's web servers are of particular interest. We have developed a tool called TCP Behavior Inference Tool (TBIT) to characterize the TCP behavior of a remote web server. In this paper, we describe TBIT, and present results about the TCP behaviors of major web servers, obtained using this tool. We also describe the use of TBIT to detect bugs and non-compliance in TCP implementations deployed in public web servers.

Transmission control protocol (TCP) performance over multi-hop networks is currently attracting considerable interest from the research community. The characteristics of multi-hop networks, such as mobility, link layer contention, high bit error rate, asymmetric path, network partition, hidden exposed nodes and dynamic routing, do not fit the requirements of for a good reliable data delivery. Here we want to provide an overview of the research progress in applying algorithms to the problem of multi-hop conditions and characteristics. The scope of this review will encompass core methods and protocols of over multi-hop networks, including cross-layer, network layer protocols and medium access control (MAC) layer protocols. The research contributions in each field are systematically summarized and compared, allowing us to clearly define existing research challenges, and to highlight promising new research directions. The findings of this review should provide useful insight into current multi-hop networks literature and be a good source for anyone who is interested in TCP in wireless approaches or related fields.

The transmission control protocol (TCP) is one of the most important Internet protocols. It provides reliable transport services between two end-hosts. Since TCP performance affects overall network performance, many studies have been done to model TCP performance in the steady state. However, recent researches have shown that most TCP flows are short-lived. Therefore, it is more meaningful to model TCP performance in relation to the initial stage of short-lived flows. In addition, the next-generation Internet will be an unified all-IP network that includes both wireless and wired networks integrated together. In short, modelling short-lived TCP flows in wireless networks constitutes an important axis of research. In this paper, we propose simple wireless TCP models for short-lived flows that extend the existing analytical model proposed in [IEEE Commun. Lett. 2002; 6(2):85–88]. In terms of wireless TCP, we categorized wireless TCP schemes into three types: end-to-end scheme, split connection scheme, and local retransmission scheme, which is similar to the classification proposed in [IEEE/ACM Trans. Networking 1997; 756–769]. To validate the proposed models, we performed ns-2 simulations. The average differences between the session completion time calculated using the proposed model and the simulation result for three schemes are less than 9, 16, and 7 ms, respectively. Consequently, the proposed model provides a satisfactory means of modelling the TCP performance of short-lived wireless TCP flows. Copyright © 2005 John Wiley & Sons, Ltd.

Behaviors of various TCPs have been analyzed over wired and wireless links, how they initialize their congestion window during slow start and congestion avoidance phase and what is the effect in the performance in wired and wireless networks. Here the study of TCP version called TCP Westwood which adjusts the congestion window is included. It controls the congestion window by using end-to-end bandwidth estimation. TCP Westwood continuously estimates the end to end available bandwidth on the basis of ACK arrival rate that is used to reset the window to match the availability of bandwidth. This makes TCP Westwood highly robust to the sporadic losses because of wireless channel problems. In this research paper performance of TCP Westwood has been evaluated in the presence of older versions of TCP over wired and wireless networks using a network simulator tool, NS-2.35. Some of the issues with TCP Westwood are addressed in this paper they are, firstly TCP Westwood is unable to distinguish the losses when timeout occurs in wireless links. It is unable to distinguish them due to congestion or link failure. Secondly in slow start phase, TCP Westwood increases congestion window exponentially according to the predefine value of ssthresh. Then switches to the congestion avoidance phase when cwnd value becomes greater than or equal to slow start threshold. Due to this Westwood cannot increase cwnd efficiently during the availability of suddenly increased bandwidth because of network conditions. More elaborately, though available bandwidth is more utilized in slow start phase it cannot enhance the slow start phase and as a result it cannot efficiently access the available bandwidth.

Wireless internet has become popular in recent years due to the tremendous growth in the number of mobile computing devices and high demand for continuous network connectivity regardless of physical locations. In this paper, we investigate the effects of routing protocols on the performance of Transmission Control Protocol (TCP) variants in multi-hop wireless networks. Through simulations we study the effects of Destination Sequenced Distance Vector (DSDV), Optimized Link State Routing (OLSR), Ad hoc On demand Distance Vector (AODV) and Dynamic Source Routing (DSR) routing protocols on TCP Tahoe, TCP Reno, TCP Newreno, TCP with Selective Acknowledgment (SACK) option and TCP Vegas. The simulations are carried out for static as well as mobile nodes. The performance metric used is throughput. Another metric, expected throughput is used for the comparison of throughput when nodes are mobile.