The Research Of QoS Technology In Wireless Mesh Network

Wireless mesh network is an emerging wireless network technology, it produces in Ad hoc networks, Ad hoc networking is to meet the needs of war, and enhance the robustness of wireless sensor networks , with the end of the war, Ad hoc networks are applied widely in civil and commercial fields, so the development of Ad hoc networks have two trends, one is to continue along the traditional service in the military's direction, the other turned to the service in civil and commercial direction, is now the wireless mesh network. Compared with traditional wireless network technologies, Information in wireless mesh network is not limited to "one-hop" can be subjected to "multi-hop", that is, can get to the destination node after the relay of multiple nodes , the fundamentally different, making the Wireless mesh networks have unique advantages, self-group, robustness, self-healing, so it can be used in areas wired networks hard to reach , or post-disaster communications applications.With the increase in wireless mesh network applications, some applications such as voice, image transmission is sensitive to the delay, bandwidth and other QoS(Quality of Service) parameters, while the traditional routing protocols are based on hop count metric, in the pathes from sending node to destination node , the path with the least number of hops, link state (latency, bandwidth, etc.) are not necessarily good, therefore, need to study or develop new routing protocols or improve the exist protocols so that it can get QoS parameters, and can find the route which meet the QoS parameters in the route discovery .This article introduces the the generation, characteristics, structure, of wireless mesh networks. It has three structures: the mesh structure of infrastructure, the mesh structure of client , hybrid mesh structure, the hybrid mesh structure is the way most value .This article studies deeply working mechanism of the typical routing protocols such as DSDV, AODV, DSR and structure three simulation experiments, the first experiment and second experiment are to construct a wireless network enviroment of 200 nodes. In the first experiment nodes is still, and In the scond experiment ,the nodes stay 50 seconds after reaching a location. Other conditions are the same, simulation time 100s, using cbr flow, the maximum number of 20 online, sending 15 packets per second, the range of 300×300. Not only variety of performances are compared, but also test the influence to the effect of protocol with the moving of nodes. The third experiment constructs a 100 node wireless network environment, change number of packets a node sents per second, from 20 packets to 200 packets per second, the average end-to-end delay, packet reception success rate were compared.Routing metric is criterion of selecting path. This paper study the following metrics such as hops, one hop round trip time, per-hop packet pair delay, expected transmission frequency, transmission time. The result of a single routing metric is not ideal, should seek a comprehensive metric.This article studies the necessary tools and doucmentations of structuring simulation environment, the working mechanism and commands of NS2 simulation tool, awk language, trace file format, gnuplot drawing tools, the script of measuring wireless network performance.Study deeply the concept of QoS and three typical QoS guarantee model, illustrates the steps to add a new routing protocol, analyzes the source code of the protocol AODV , based on the work, the AODV protocol has been improved:(1) congestion avoidanceAODV routing protocol is based on hop count metric, there is no congestion control, therefore, it may appear, sometimes the network traffic is not great, but too much traffic through certain nodes, leading to packet delay at the node increases, if packets flow further increases, there will have a loss. To solve this problem, it need to make a few improvements to the AODV protocol. First, define a concept node load , which is defined as the length of the queue packet accounted for the proportion of the total length of the queue. Test the node load periodically, if the node load is more than 80%, this value can be adjusted according to actual network traffic, then the route discovery should be "detour" to avoid passing the node of large load.This way can distribute traffic evenly. Perhaps the path the packet go through,may be not optimal from the hop count, but to avoid congestion, reduce delays, and costs are not great.(2) delay controlSome applications such as voice services are sensitive to delay ,so,it should be meet the need of the service such as voice or image transmission through selecting the routh which can meet the need of the QoS parameters. The source node sending the route request add the delay request to the rreq packet, the network node received this route request need to calculate the total delay experienced from the source node, find a better routh, namely less delay, if it can not meet the request , discarded the packet..(3) bandwidth controlIn the AODV protocol, it only to select the route whose hop count is minmum, but this path does not guarantee the bandwidth requirements that packet need, so when the node receives a packet for bandwidth sensitive, it should be adopt a mechanism to calculate bandwidth to its every neighbour, then select the path that meets the bandwidth request.By the improvement, formed a QoS routing protocol with congestion control, delay control , bandwidth control. The formats of hello packets, rreq packets, rrep packet are expanded and the processing of rreq packets and rrep packets are given.