Research On Routing Mechanism And Buffer Management Strategy In Opportunity Network

Opportunistic networks (OPPNETS) is a kind of ad hoc network, which does notalways exist a connected path between the source node and destination node, andaccording to the random movement of nodes realize communication, and it is used inwildlife tracking and habitat monitoring sensor networks, inter-planetary networks,military networks and secluded region network,etc.OPPNETS is an intermittent network,the connected path is often broken because of the movement of some nodes，and theexisting routing and buffer managemeng strategy is not suitable for OPPNETS.Therefore, the research of the routing and buffer management problems is the keytechnology. Although many researchers have presented many effective routing andbuffer management strategies in recent years, the key problems have not been solved yet.So the presentation of routing and buffer management that are efficient and suitable forOPPNETS is still a challenging work at present. Based on some studies and discussionon the routing and buffer management, according to the problems of OPPNETS, somenew ideas and methods for routing and buffer management have been put forward inthis paper. The main contributions of the thesis are as follows.①According to statistical analysis and numerical methods, the link statisticalcharacteristics in the real opportunities network is analyzed from the contact times ofthe nodes. The distribution function and the rules with changes of the contact durationof the nodes are gotten through the curve fitting, and the simulation results show thatthe probability distribution of the contact duration of wireless link is as the law ofexponential distribution.②On the base of analyzing the shortcoming of the existing PROPHET, andestimating the contact probability through the contact frequency and contact duration,anenhanced PROPHET protocol is proposed，which forward the messages according to theorder from large to small of the probability. The results of simulation indicate that thisprotocol obviously makes the consumption of system lower and improves delivery raterelative to the PROPHET and Epidemic.③The traditional shortest path algorithm is not suitable for the routing choice incommunity model of OPPNETS.According to the routing features in OPPNETS，animproved Floyd shortest path algorithm is proposed,which is based on the hop and thecost varied with the time. The design of the routing algorithm not only considers thespace factor between the nodes, but also takes into account the time factor of the wireless links in OPPNETS.The simulation results, compared with the existing routingalgorithm such as First Contact (FC), Minimum Expected Delay (MED), indicate thatthe algorithm proposed by this paper is more effective to get the shortest path.④In OPPNETS, the connected path may be broken usually, and nodes may bepartitioned into several disconnected subsets because of the movement of some nodes.In order to overcome this phenomenon, it makes use of a special node message ferry(MF) which is a typical mobility-assisted communication node, and moves in a specifictrace and forwards data to provide communication opportunities in social transportationmodel. In this paper, we first consider the characteristics of nodes in thehighly-partitioned wireless ad-hoc networks in order to find an efficient path for theferry to deliver data. Then we propose an Improved Path Management Policy (IPMP)for the ferry to investigate the problem of controlling the ferry to visit nodes by differentstrategies.⑤On the basis of introducing and analyzing the buffer management strategies inOPPNETS, an enhanced buffer managemen strategy is proposed under conventionalepidemic routing, which is called buffer management based on copy Number (BMSCN).When the congestion of node happening, the copy rates of packets stored in buffer andjust arrived at this node are calculated according to the copy numbers and lapse time,and the packet which has the highest copy rate will be deleted, and then the congestioncan be relieved. And then, we employ optimal theory to propose a novel buffermanagement strategy named Optimal Buffer Scheduling Policy (OBSP) based onnumber of message copies to optimize the sequence of message forwarding andmessage discarding in this paper. In OBSP strategy, global optimization consideringdelivery ratio, delay, and overhead is adopt to improve the overall performance ofOPPNETS.Some theories about routing and buffer management of OPPNETS have beenexplored in this paper. According to the shortcomings of existing algorithms, a fewalgorithms based on some theoretical bases mentioned above have been presentedwhich are more suitable for selecting the paths and dropping the packets when thecongestion of node happening.Through the simulation results, we obviously see that theproposed methods improve the performance, such as packet delivery ratio, time delay,and overhead. Then, these proposed methods above will promote and boost the study inthis area.