Novel Slow Start Algorithm

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.

TCP performs slow start phase based on an exponential increase of the congestion window to predict the current network. Current TCP slow start does not work well under large bandwidth networks. The exponential growth of slow start phase cause burst packet loss if there are many traffic in the network. In this paper, we use a statistical slow start method to solve heavy packet loss from collision between flows in the network and to improve TCP performance.

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 Satellite network has many disadvantages such as long round-trip-time (RTT), high bit error rate. The issues above pose challenge to existing Slow start algorithm. Slow start algorithm is a key component which directly affects startup performance of TCP. This paper mainly improves startup performance of TCP and proposes a slow start algorithm that adopts logarithmic function to overcome multiple congestion packet loss caused by inaccurate ssthresh (slow start threshold) estimation and improves throughput performance.

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.

The performance of transmission control protocol (TCP) over ad hoc wireless networks (or simply ad hoc networks) has been extensively studied through simulations by the research community. Although many theoretical models, such as [1], have been proposed for estimating the performance of TCP over wired networks, researchers have faced many difficulties in modeling TCP over ad hoc networks. These difficulties are mainly due to the behavior of the underlying physical and MAC layers. Recently, [2] attempted to solve this problem by simplifying the behavior of TCP, besides assuming that no packet losses occur. In this work, we attempt to provide a theoretical model for TCP by considering the main phases of TCP, namely the slow start phase and the congestion avoidance phase, thus providing a more accurate model that captures all of its main features. To the best of our knowledge, ours is the first model that considers the slow start phase while analyzing TCP's performance in ad hoc networks. We make use of multi-dimensional Markovian chains to model each of these phases. We then use the resulting steady state probabilities to estimate the goodput. Furthermore, the analysis is validated by comparing the theoretical and simulation results using various error models.

TCP Vegas is regarded as balanced congestion control strategy, however, shortcomings such as low bandwidth utilization and not gain fairness when sharing link with TCP Reno. We reinvestigate these issues and propose a modification strategy called Dynamic Vegas, which changes initial TCP Vegas’ in slow start and congestion avoidance phase. It dynamically chooses slow start algorithm and adjust decrease/increase rate in congestion avoidance phase according to specific network environment. Experiments show that within a single link network, it performs as well as TCP Vegas. Additionally, in Multi-link environment, it achieves strong competitiveness against TCP Reno and gains fairness in throughput of all senders in the end of transmission.KeywordsSlow startCongestion avoidanceCompetitivenessFairness

Analytical modeling of TCP flow in wireless LANs

One-way delay estimation and its application

We show that different flavors of TCP may be viewed as implementations of age-based scheduling disciplines. By parameterizing the scheduling disciplines of interest we are able to position variants of TCP in a wide spectrum having FCFS (first-come first-served) and LAS (least attained service first) as extremal policies, and including PS (processor sharing) as an intermediate case. We argue that for highly loaded systems, providing a fair bandwidth allocation among all users is secondary to ensuring network stability. So as to isolate protocol fairness from congestion effects, we therefore focus on scenarios with infinite buffers. This way, asymmetries in capacity shares are the consequences of the protocol only, and not affected by the packet loss process. The model, however, is flexible enough to include finite buffers with random packet loss as a special case (for example to capture Active Queue Management). The results are helpful in studying fairness and performance concerned with transmission protocols in communication networks. For persistent HTTP connections we study the distributions of the transmission rates and the relative fairness index under various assumptions on the file size distributions and scheduling disciplines. For infinite file sizes, we show that protocols that increase priority more than linearly with the attained service asymptotically behave similar to FCFS. In contrast, protocols with at most linearly increasing (or even decreasing) priority, with TCP's Congestion Avoidance mechanism as the most prominent example, converge to PS scheduling (even in absence of losses). When the priority is exactly linear in the attained service, such as for scalable TCP and TCP's slow start phase, the shares remain constant in between file initiations and completions.

Reducing startup delay of video streaming is important for attracting more users. In LTE networks, even though available bandwidth has increased, behavior of TCP, which has a slow start phase and estimates available capacity based on packet loss event, increases the startup delay of video streaming. To solve this issue, we design a proxy-based TCP rate control (PTRC) scheme for achieving low startup delay of mobile video streaming by using the explicit radio related information from a base station (BS). We introduce a target queue length (Qtarget) as feedback information to a proxy, which represents a desired value at the BS. Here, the Qtarget is dynamically calculated by referring to average data rate of a radio link and backhaul delay. Then the proxy is informed of this Qtarget by an in-band signaling message from the BS, and controls its sending rate accordingly. Hence, the proposed PTRC scheme can boost up its transmission rates in the initial phase, and keep instant queue length at the BS close to the Qtarget. We verify that the proposed PTRC scheme achieves about 71.2% reduction of startup delay for mobile video streaming in LTE environment, compared to conventional schemes.

In wired networks, congestion is the main reason for most of the packet losses and the original TCP is the best option to implement. However, in wireless networks, these losses will arise for reasons other than congestion. TCPW has been proved to work better in performance and bandwidth utilization than Reno and New Reno in wireless networks. Our research mainly focuses on the slow-start phase of TCPW and develops an algorithm to divide the phase into two parts. In this paper, we propose a simple refinement of slow-start algorithm of TCP Westwood (TCPW), which is a TCP variant focused on to achieve higher performance in wireless and wired networks. We show by results that the new theme could reduce possibility of packet loss in wireless networks. In the first half of slow-start, we use the exponential increase just like the original slow-start. Moreover, we grow the congestion window gradually to decrease packet burstiness in the second half of slow-start.

General Additive Increase and Multiplicative Decrease (General AIMD or GAIMD) congestion control generalizes the standard TCP congestion control mechanism. In this paper, we present GAIMD-SS, an enhanced model for predicting the long-term steady-state mean throughput of the GAIMD congestion control, towards more accurate results than previous GAIMD model. We develop a three-state Markov chain for analyzing the behaviors of the GAIMD, and enhance previous works by taking into account the slow start phase and receiver's maximum window limitation. Our experiment and simulation results show that the GAIMD-SS model predicts the sending rate of GAIMD congestion control more accurately than the previous works in a wider range of packet loss rate.

An Application of the Modification of Slow Start Algorithm in Campus Network

This paper has clarified the simulation study of optical time division multiplexing/wavelength division multiplexing system based static/dynamic optical transparent networks demonstration through all-optical fiber amplifiers. Received signal power per channel is measured against network reach for both static and dynamic networks in the presence of all-optical Raman/erbium doped fiber amplifier/semiconductor optical amplifier amplifiers. Data rate transmission per channel is demonstrated against repeater spacing for all proposed optical fiber amplifiers based on various near infrared operating wavelengths for both static and dynamic optical transparent networks. In addition, the overall signal per noise ratio is clarified in relation to network throughput and various near infrared operating wavelengths for the static and dynamic transparent optical network based on all proposed amplification techniques. Moreover, the overall system bit error rate is studied and tested against network throughput and various near infrared operating wavelengths for both static and dynamic transparent optical networks based on all proposed amplification techniques.