| The Ad Hoc network is also called MANET. Because of the flexible networking, low cost, and some other unique advantages of Ad Hoc, it has been widely used in military, disaster relief and e-commerce, etc. Nowadays, more and more multimedia services data , such as VoIP, video conference and so on, which are based on UDP protocol , are transmitted by Ad Hoc networks. First of all, the multimedia data are often large flow in long duration, which increase the network burden and the rate of congestion. Secondly, UDP has no back off algorithm when it meets congestion during the transmission, so UDP based data consumes more bandwidth than TCP based data.In recent years, in order to provide QoS support for Ad Hoc, scholars have proposed many improvements to traditional Ad Hoc routing protocols. Prof. Jitendranath proposed to expend two 16 bits fields(Cost and Delay) and building up a QoS sign bit in RREP (route reply) and RREQ (route request) respectively. Intermediate nodes update the Cost and Delay (if delay sensitive) before forward the RREQ, then the source node chose the route which has smallest cost to achieve load balance. Yuan uses a threshold to illustrate loading state and filter paths based on these informations to achieve QoS support. But the existing routing protocols with QoS guarantees often are limited in routing layer and make use of the informations related to end-to-end delay , node loads or node power. None of them put forward exploring the node data access categories information.The 802.11e work group of IEEE defined 4 data access categories (ACs) for transmitting frame with priority. First of all, each ACi assigned different arbitration inter-frame space (AIFS) to obtain corresponding channel access opportunity. If the value of AIFSN is smaller, the ACi with high priority will start to reduce its back off counter earlier than the ACi with low priority. Moreover, In EDCA mechanism, each ACi has different minimum and maximum contention window size during the back off period. The access categories which have high priorities are assigned small value of CWmin and CWmax. Then the back off interval time is chosen in the range [0, CWi] randomly, where CWi=2ik-1CWmin and k illustrate the back off stage.We propose QCAODV routing protocol which is simple yet effective to gain QoS support for Ad Hoc. Contrast to those existing routing protocols using end-to-end delay, node load or node power information, our protocol make the use of cross layer QoS structure system idea, consider the effect of data access categories to network state, implement QoS guarantees and congestion avoidance in both MAC layer and routing layer.First of all, QCAODV is a cross layer routing solution which works in the conjunction between MAC layer and routing layer. Therefore, MAC layer is responsible for updating node data category changing information to IP layer. During the route discovery process, we detect the priority information contained in the frame head and mark the nodes on the path. Then we utilize the new routing metric considering the effect of access categories to choose the optimal path. Then route request nodes will choose the path with smallest metric as route when they receive multiple RREPs.Secondly, in AODV, intermediate nodes will send RREP if they have the path to destination when they receive RREQ. Intermediate nodes reply could reduce RREQ flood but it is also generate overlap routes, thus lead to congestion. In QCAODV,we prescribe that intermediate nodes are prohibited to reply even they have the routes to the destination. In this way, the latest node data access category information could be used for route judgments and decrease the possibility of network congestion due to contention of transmission opportunity between different ACs.In this paper, considering the effect of node load data access categories on network state, we proposed QCAODV routing protocol based on original AODV. During the route discovery process, mobile nodes monitor the data type buffered in its queue and utilize this information to choose optimal route. Our protocol decreases the probability of different ACs use the same node to transport data, thereby improves the performance parameters of Ad Hoc network. Through the simulation experiments, QCAODV provides better QoS guarantees. |
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