VA-TCP

We describe TCP performance under a token bucket policer and also show the performance problems, especially for the short round trip time (RTT) area. We also present a new algorithm to improve TCP throughput for short RTT flows using shorter-sized packets than its maximum transfer unit (MTU). Through simulations, we show the TCP throughput with packet size determined by our algorithm and compare it with the MTU-sized packets.

To coordinate the various access technologies in the 4G-communication system, intelligent vertical handoff algorithms are required. This paper mainly deals with a novel vertical handoff decision algorithm based on fuzzy logic with the aid of grey theory and dynamic weights adaptation. The grey prediction algorithm (GPA) takes 4 sampled received signal strengths as input parameters, and calculates the predictive received signal strength in order to reduce the call dropping probability. The fuzzy logic theory based Quantitative Decision Algorithm takes 3 QoS metrics, received signal strength (RSS), available bandwidth (BW), and monetary cost(C) of candidate networks as input parameters. And the weight of each QoS metrics is adjusted along with the networks changing to trace the network condition. The final optimized vertical handoff decision is made by comparing the quantitative decision values of the candidate networks. Simulation results demonstrate that the proposed algorithm provides high performance in heterogeneous as well as homogeneous network environment.

This paper provides a preliminary investigation into the impact a link with changing propagation delay has on the performance of TCP file transfers. We investigate over a dozen different variable delay patterns, based on spacecraft movement. We highlight the performance impact of such variability, paying close attention to TCP's retransmission timer, which is based on the observed round-trip time of the network path. In addition, we explore one scenario in which the round-trip time across a network path suddenly changes due to a large change in the path between the two end-points. We conclude that the variable delay network paths studied in this paper do not drastically impact TCP performance.

In this paper, we propose a user cooperative mobility to improve Transmission Control Protocol-Bottleneck Bandwidth and Round-trip propagation time (TCP-BBR) throughput. In a single-flow ad-hoc network with TCP-BBR traffic, the TCP-BBR does not work well due to the variation of Round-Trip Time (RTT). By considering the fact that TCP-BBR does not work well, the proposed Data suppression Acknowledge character (ACK) retention method stabilizes the RTT and improves the Wireless Local Area Network (WLAN) bandwidth at the same time. After giving an overview of the proposed method, we show the results of evaluating the throughput characteristics by NS3 simulation. The results show that the proposed method successfully improves the throughput by up to 232% compared to the throughput before moving, which is better than the conventional method, demonstrating the effectiveness of the proposed method.

With the integration of heterogeneous wireless technologies and the popularization of all-IP networks,network-layer soft handoff approaches have gradually evolved to improve the performance of vertical handoffs(VHOs).Unfortunately,the existing soft handoff approaches lead to plenty of out-of-order packets during downward VHOs.In this paper,the authors present a new network-layer soft vertical handoff scheme,called SHORDER.In the scheme,the mobile node(MN)starts or stops buffering packets from its new network based on a few interactive messages with its home agent(HA).With the buffering technique,the scheme can prevent mobile terminals from receiving reordered packets caused by downward VHOs,and is compatible with various transport-layer protocols and their variants due to its independence.Then,the authors theoretically analyze the influence of the proposed scheme on the handoff latency,the goodput and the congestion window of the TCP in comparison with a typical existing network-layer soft VHO method.Additionally,the authors also derive the applicable condition of the SHORDER scheme.Experiments show that the deployment of the proposed scheme is easy and the scheme has better performance under its applicable condition,further,experimental and analytical results are consistent with each other.Finally,based on the applicable condition of the SHORDER scheme,the scheme further is improved.

We propose the first practical solution to the longstanding problem of secure wireless routing in the presence of colluding attackers. Our secure routing protocol, Sprout, continuously tries new routes to the destination. Routes are probabilistically generated, with complete disregard for performance metrics. This makes Sprout uniquely resilient to attack: it cannot be tempted by shortcuts. In order to avoid compromised routes, and to ensure good overall performance, the quality of each active route is monitored by means of signed end-to-end acknowledgments. The amount of traffic sent on each route is adjusted accordingly. Sprout effectively mitigates the vast majority of known routing layer attacks, even when under assault from a large number of colluding attackers. Experiments on our 31-node testbed demonstrates the real-world performance of Sprout in terms of packet delivery ratio, round-trip times and TCP throughput. Our security analysis and simulation results show that Sprout is able to quickly find working paths in networks of hundreds of nodes and dozens or more attackers. For example, in a network of 200 nodes and an astounding 64 attackers, Sprout, on average, found a successful route within less than 10 attempts. Yet, in benign settings, Sprout provides TCP throughput within 15% of the shortest path throughput Overall, Sprout consistently delivers high, reliable performance in benign as well as hostile environments.

Next generation wireless networks environment (4G) could provide the users with free moving experience and desirable quality of services among heterogeneous networks. Thus vertical handoff is one of the most important issues. The existing vertical handoff decision algorithms are usually designed for low speed cases, which are not suitable when terminals move fast across several networks covering scales. To resolve this problem, we propose a novel speed sensitive vertical handoff algorithm based on fuzzy control. Based on collected information on RSS, load conditions of candidate networks, velocity of mobile terminals and user preference, the vertical handover decision is made by fuzzy logic process. It improves the handoff efficiency when users are moving at a high speed. Simulation results show that the proposed algorithm can reduce unnecessary vertical handoffs caused by high speed.

The wireless network environment in the future is going to include various heterogeneous wireless networks. In a heterogeneous wireless network environment, vertical handoff processes caused by the movement of users are inevitable. However, the research related to how to achieve seamless vertical handoff and improve QoS guarantees in today's heterogeneous wireless networks is still something to work on. Therefore, this paper proposed the Advanced Vertical Handoff Translation Center (Advanced VHTC) architecture for Wi-Fi/WiMAX heterogeneous wireless networks, aiming to improve the quality of services in heterogeneous wireless networks by means of packet formats translation between heterogeneous wireless networks and the MIH-based seamless vertical handoff mechanism, which cut down the time for vertical handoff and obtain high quality and persistent connection service. Lastly, with the brilliant results of a complete simulation, this paper will show the performance in terms of delay, jitter, packets loss and throughput to prove that the Advanced VHTC for next generation heterogeneous wireless networks can provide good QoS guarantees and obtain persistent transmission with high performance while performing seamless vertical handoff.

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.

Recently, Mobile Ad-hoc Networks (MANET) are continuing to attract the attention for their potential use in several fields. Most of the work has been done in simulation, because a simulator can give a quick and inexpensive understanding of protocols and algorithms. However, experimentation in the real world are very important to verify the simulation results and to revise the models implemented in the simulator. In this paper, we present the implementation and analysis of our testbed considering the Link Quality Window Size (LQWS) parameter for Optimized Link State Routing (OLSR) protocol. We investigate the effect of mobility in the throughput of a MANET. The mobile nodes move toward the destination at a regular speed. When the mobile nodes arrive at the corner, they stop for about three seconds. In our experiments, we consider two cases: only one node is moving (mobile node)and two nodes (intermediate nodes) are moving at the same time. We assess the performance of our testbed in terms of throughput, round trip time, jitter and packet loss. From our experiments, we found that throughput of TCP was improved by reducing LQWS.

In this paper, we present the implementation and analysis of our testbed considering the Link Quality Window Size (LQWS) parameter of Optimized Link State Routing (OLSR) and Better Approach To Mobile Ad-hoc Networking (B.A.T.M.A.N.) protocols. We investigate the effect of mobility in the throughput of a Mobile Ad-hoc Network (MANET). The mobile nodes move toward the destination at a regular speed. When the mobile nodes arrive at the corner, they stop for about three seconds. In our experiments, we consider two cases: only one node is moving (mobile node)and two nodes (intermediate nodes) are moving at the same time. We assess the performance of our testbed in terms of throughput, round trip time, jitter and packet loss. From our experiments, we found that throughput of TCP was improved by reducing LQWS.

TCP transmission is mostly governed by Re–Transmission Timeout (RTO) values of each segment sent across the network. It is found that the fairness in the RTO is more need on effective management of the TCP. Most of the model calculates the RTO based on the Round Trip Time (RTT), which is the critical parameter in determining the behaviors of TCP. The RTO lacks in reflecting network foot prints. This paper presents algorithm which improves RTO, considering the network foot print for each segment sent across the network. Algorithm uses 3–way connection establishments RTT of TCP as the primary value to fine-tune the RTO. Using this RTT as base value and Advertise Window value of the receiver it calculates the rate of change of throughput as function of time to fix the RTO. The experiment has being simulated through OPNET.

High-speed networks with large delays present a unique environment where TCP may have a problem utilizing the full bandwidth. Several congestion control proposals have been suggested to remedy this problem. The existing protocols consider mainly two properties: TCP friendliness and bandwidth scalability. That is, a protocol should not take away too much bandwidth from standard TCP flows while utilizing the full bandwidth of high-speed networks. This work presents another important constraint, namely, RTT (round trip time) unfairness where competing flows with different RTTs may consume vastly unfair bandwidth shares. Existing schemes have a severe RTT unfairness problem because the congestion window increase rate gets larger as the window grows ironically the very reason that makes them more scalable. RTT unfairness for high-speed networks occurs distinctly with drop tail routers for flows with large congestion windows where packet loss can be highly synchronized. After identifying the RTT unfairness problem of existing protocols, This work presents a new congestion control scheme that alleviates RTT unfairness while supporting TCP friendliness and bandwidth scalability. The proposed congestion control algorithm uses two window size control policies called additive increase and binary search increase. When the congestion window is large, additive increase with a large increment ensures square RTT unfairness as well as good scalability. Under small congestion windows, binary search increase supports TCP friendliness. The simulation results confirm these properties of the protocol.

Distributed Denial of Service (DoS) attacks is one of the major threats and among the hardest security problems in the Internet world. In this paper, we study the impact of a UDP flood attack on TCP throughputs, round-trip time, and CPU utilization on the latest version of Windows and Linux platforms, namely, Windows Server 2012 and Linux Ubuntu 13. This paper also evaluates several defense mechanisms including Access Control Lists (ACLs), Threshold Limit, Reverse Path Forwarding (IP Verify), and Network Load Balancing. Threshold Limit defense gave better results than the other solutions.

Denial of Service (DoS) attacks is one of the major threats and among the hardest security problems in the Internet world. Of particular concern are Distributed Denial of Service (DDoS) attacks, whose impact can be proportionally severe. With little or no advance warning, an attacker can easily exhaust the computing resources of its victim within a short period of time. In this paper, we study the impact of a UDP flood attack on TCP throughput, round-trip time, and CPU utilization for a Web Server with the new generation of Linux platform, Linux Ubuntu 13. This paper also evaluates the impact of various defense mechanisms, including Access Control Lists (ACLs), Threshold Limit, Reverse Path Forwarding (IP Verify), and Network Load Balancing. Threshold Limit is found to be the most effective defense