Performance analysis of TCP with delayed acknowledgments in multi-hop ad-hoc networks.

The acknowledgment strategy has great potential to increase TCP throughput when it runs over 802.11 MAC protocol. In particular, TCP acknowledgments (ACK) carry out an extensive number of medium accesses as they compete in the same route as data packets for media. In this paper, we first propose a dynamic TCP-MAC interaction strategy which tries to reduce the number of induced ACKs by monitoring the channel condition. To this end, the total collision probability collected along the path from sender to receiver in MAC layer has been used to properly set the number of delayed ACKs (DA) in TCP. Based on the estimated collision probability, TCP sender dynamically adjusts itself to the channel condition by delaying less ACKs in high traffic conditions and more ACKs in low traffic conditions. The simulation results show a throughput improvement up to 15% over the existing method called Dynamic Adaptive Acknowledgment (TCP-DAA) and much more over the regular TCP in different scenarios dealing with a dynamic loss rate. In addition, we show that our proposed strategy does not always benefit from a fixed delay policy along with a fixed congestion window size. In fact, the optimal number of delayed ACKs is based on the path length of a TCP connection and a large delay window may solely improve TCP throughput in short ranges with less number of flows. However, in a longer path congestion window limit provides more throughput gain

Node Feedback TCP Based Mechanism for Mobile Ad-hoc Network

A mobile ad-hoc network is an autonomous system of mobile nodes establishing a network in the absence of any fixed infrastructure. Mobile ad-hoc network due to potentially high mobility have provided new challenges by introducing special consideration differentiating from the unique characteristics of the wireless medium and the dynamic nature of the network topology. Due to unique network formation, routing in mobile ad-hoc network is a challenging issue. Effort has been undergoing to transform TCP so that it could support routing function in an ad-hoc network. This research has discovered that most of the TCP based variant routing solutions of mobile ad-hoc network has not been successful in addressing problem at full. Taking TCP based routing solution as a main problem, this research has proposed a novel routing solution called Node feedback TCP based mechanism as a routing scheme for mobile ad-hoc network.Node feedback TCP based mechanism introduces a new flavor of TCP for mobile ad-hoc network. It follows an intermediate approach in between some of the existing mechanisms of TCP based schemes for mobile ad-hoc network. We have addressed TCP slow start mechanism in the context of mobile ad-hoc network and introduce measures through whom TCP can differentiate between real congestion and congestion assumed by TCP due to packet lost or route failure in mobile ad-hoc network. In addition our proposed mechanisms also deal with out-of-order delivery problem of TCP in mobile ad-hoc network. It is important to mention that NFBTCP not only address TCP related issues but also provides a number of different operations to assists in the smooth running of an ad-hoc network.The scheme has been developed in Java and Evaluated in SWANS. In the light of the simulation experiments, it could be seen that NFBTCP performed well in all simulation environment. It can be confirmed that NFBTCP has proven itself as a fully functional and operationalable for mobile ad-hoc network, thus should be seen or taken as a new novel TCP based solution for mobile ad-hoc network. A higher number of route requests and route replies representing networking activities were observed with the increase of mobile nodes. In addition to the messages activities, good numbers of routes were added at the end of each simulation cycle. It is quite understandable that the more routes available for data transfer in mobile ad-hoc network, the better. Moreover, such additions to the available routes could directly impact overall throughout. Lastly, nodes in mobile ad-hoc network suffer with limited resources. That makes conservation of all such resources an important issue in the context of mobile ad-hoc network. The results of simulation experiments validate the main concepts of the scheme especially congestion avoidance and out-of-order packet delivery. The scheme generates a higher number of routes suggesting that the implemented congestion avoidance and out-of-order packet delivery mechanisms of NFBTCP are successful in reducing the impact of link breakage since subsequently it was not possible for more routes to be added. The addition of more routes demonstrates that more packets are broadcast and suggests smooth flow of data and control packets. We believe NFBTCP offers a complete and an effective TCP based routing solution for mobile ad-hoc network

Mobile Ad-Hoc Networks

Being infrastructure-less and without central administration control, wireless ad-hoc networking is playing a more and more important role in extending the coverage of traditional wireless infrastructure (cellular networks, wireless LAN, etc). This book includes state-of the-art techniques and solutions for wireless ad-hoc networks. It focuses on the following topics in ad-hoc networks: vehicular ad-hoc networks, security and caching, TCP in ad-hoc networks and emerging applications. It is targeted to provide network engineers and researchers with design guidelines for large scale wireless ad hoc networks