Researches On Transport Control Mechanisms In Ad Hoc Networks

With the rapid and extensive development of wireless communication and Internet, it hasbeen substantially essential to acquire information and communicate with other people atanytime, anywhere and for anybody. The ability to be set up quickly and operate withoutwired infrastructure makes Ad Hoc network a promising candidate for next generationwireless networks. Research on Ad Hoc from various aspects is now a hot spot in literature.In this thesis we will mainly study the architecture of Ad Hoc network and routing protocolfor Ad Hoc.Different from fixed wired network and conventional cellular network, it is difficulty toprovide reliable transport in Ad Hoc networks which have characteristics like dynamicalchanges of network topology, limited wireless bandwidth, power limitation etc. Because ofleaving out of consideration of the characteristics above, the traditional and guaranteemechanisms in Internet cannot be apply to Ad Hoc networks directly. As a result, it isrequired to design and study the novel traffic control mechanisms that enable to adapt thenetwork dynamic changes.In chapter one, a general introduction to Ad Hoc network is provided and the limitationof the traditional traffic control mechanisms is studied with respect to Ad Hoc network. Afteranalyzing the issues essentially, we propose the existing problems in Ad Hoc network.Researchers have proposed various traffic control algorithms to eliminate the drawbacksof Reno in Ad Hoc network. In Chapter two, recently proposed solutions are surveyed alongwith their main advantages and disadvantages. After an exhaustive analysis of the keyproblems within the traffic control mechanisms, we raise the corresponding solutions in thisfield. Finally, some constructive solutions are given for further research.Based on the problem of the performance degradation of traffic control mechanisms inAd Hoc networks, we propose a novel cross-layer scheme in Chapter three. It is implementedin the cooperation of multiple network protocol layers and makes full use of the advantagesof them. At first, it estimated the available bandwidth of neighboring area through to measurethe idle time of node in MAC layer. Secondly, the route protocol takes the availablebandwidth to choice a best path. Finally, transport protocol compute sender rate with thisinformation. The results of simulation show that the scheme has better advantages inweightily loaded scenario and does well in solving the problems raised from congestion.In order to improve the fairness and validity of traffic scheme in Ad Hoc network, we putforward a rate-based Ad Hoc traffic control (RATC) mechanisms in chapter four based on thecross-layer scheme. RATC computes the sender rate use available bandwidth, and adopt aspecial MAX-MIN fairness as our baseline fairness criterion. One of the key cornerstones ofRATC design is the use of lower layer information and explicit rate feedback from othernetwork nodes to assist in the transport layer mechanisms, therefore the sender could senddata steadily.We also present a number of simulations to demonstrate and evaluate the efficiency andperformance of RATC in Chapter five. The simulation results show that the throughputperformance of RATC is always better than that of default TCP and TCP-ELFN. Owing to itsquick-start mechanism of aggressively catching up to the available bandwidth, even when itexperiences a route failure and is forced to decrease its rate, it is able to catch up to theavailable bandwidth on the recomputed route in a shorter time duration. Besides, it also hasgood protocol friendliness.In a word, this paper does some research in the field of traffic control over Ad Hocnetworks. We hope it could promote the development of cross-layer scheme and rate basedtransmission strategies in Ad Hoc network.