Research On Connectivity Technology Of Mobile Ad Hoc Network Based On IPv6

With the development of information technology, the requirements of mobile communication become higher and higher. Mobile communication technology has been developed rapidly in recent years. With the development improved rapidly, Wireless networks productions become more maturely. Wireless network plays an important role in many fields such as various offices and net connection across domain. From the IP layer, the high-speed WLAN is a signal hop net. It can only cover little area and have poor mobility. To meet the requirements of network, it needs a kind of temporary, swift and automatic network. In many technologies of wireless network, Mobile Ad Hoc Network is believed to be one of the feasible.Mobile Ad Hoc Network (MANET) is a multi-hop self-organizing network composed of an amount of wireless receiving and sending equipments. It has own features of dynamic network structure and network nodes self-organizing. The nodes in the MANET can not only act as the mobile terminal but also have the ability of forwarding messages. In this kind of net structure, two nodes that can't communicate directly will transmit messages with the assistance of other nodes, thus this paper realizes the multi-hop communication. With the multi-hop thought in Ad Hoc network, we can extend the scope of wireless access network, especially in the places where network can't be built and signals can't be received. As long as one Ad Hoc mobile node is covered by the AP, other nodes which are not in the scope can multi-hop communicate with gateway with the help of middle nodes, and then they can connect with Internet successfully.How to extend the mobility of Ad Hoc network and combine with next generation mobile network is the main problem of MANET application. It is also an important method of wireless network to enlarge its scope.There are some differences between Ad Hoc network and traditional network both in the structure and method of building network. Firstly, it is the address structure, the IP address in Internet is hierarchical, including network address and host address. The hosts located in the same network have the same network address. This can simplify the disposal of routing. The routing information can be gathered and each item of routing lists can deal with all the hosts with the same network address. But the Ad Hoc network doesn't have these features. You can't estimate the nodes whether they are located in the same network or Ad Hoc network through the network address. That is to say, the address isn't hierarchical and routing default in the Ad Hoc network. Secondly, it is the influence of multi-hop. On the one hand, supposing that there is a hop between a mobile node and a mobile agent in the mobile IP, then there are many hops in the Ad Hoc network, so it needs corresponding routing protocols to forward and control message. Finally, it is the influence of routing protocol on demand. In order to decrease the cost, the Ad Hoc network often uses routing protocol on demand, but the mobile IP uses the proactive routing protocols.Based on the mobile IPv6 network MANET routing technologies, and researched on some theories summarized by scientists, this paper presents an multi-gateway interconnected scenario between Ad Hoc network and Internet based on IPv6, it also describes how to prevent congestion in the multi-gateway environment.Ad Hoc network and Internet will be interconnected by the edge nodes of Ad Hoc network, after the edge nodes reaching the IPv6 network, the special Ad Hoc network routing protocols will be used to interconnected Ad Hoc network and higher layer network smoothly. The main contributions of the paper are listed below:Firstly, gateway node send Gateway advertisements (GADV). The AODV routing protocol will be used as the basis protocol to access IPv6 network. This paper modifies RREP message format in the protocol by adding new flag G in reserved bit. When G is 1 indicates that the nodes can come to the higher layer network, that is, the gateway nodes. The nodes will advertise itself by broadcasting the GADV messages and the other nodes can get the information of the higher layer network from GADV message, realizing the interconnected between Ad Hoc network and higher layer network by creating multi-hop routing to reach the gateway. Because of no center and dynamic structure of Ad Hoc network, there exist many gateways at the same time, this also can bring some problems such as loading balance, switching and usability and so on. This paper researches on the load balance and also presents a method named Early prevention Congestion to prevent the occurrence of congestion.Secondly, Early prevention Congestion. To improve the disposal ability and forward speed of network, it needs to control the load of network. This paper uses a method of forecasting by gateway nodes in the early time. When the forwarding queue gets to 75 percent of max_queue_length for a long time ( T ) , the gateway nodes will give Early prevention Congestion. The method is to add a flag in the GADV message and set it 1. When other nodes which need access to a higher layer network receive this message, they will choose other non-congestion paths. If there is no non-congestion path, the access to network will be postponed.According to the application features of Ad Hoc network, in some emergent communication military cases, the data packets which are forwarded need to be grading. When some very emergent communications appear, other communications must be suspended to ensure the emergent communications go well.At last, the simulator of NS-2 test bed is used to the experiment on Linux Operating System. The AODV was upgraded to AODV6 in the Ns-2 environment. The experiment validates the cases of multi-gateway Ad Hoc network and congestion prevention in mobile IPv6 network. It also gives the performances of this method. The experiment data proved that the methods of this paper are feasible.This paper gives a method of how to interconnected MANET and Internet based on IPv6, and there are a lot of problems in popularization process of network based on IPv6, which is the next research for us to do.