Research On Congestion Control Mechanism For DTN And Its Application

Delay tolerant network is a new type of network architecture to solve the packetloss and retransmission problem. This problem is caused by frequent networkdisconnection. The Bundle protocol, which is one of the most important proto cols inDTN, supports the hop-by-hop custody transfer service. Every network node storesthe received packet before transfers it to the next-hop node. It effectively avoids thepacket loss and retransmission. DTN is widely used, such as deep-spacecommunication networks, vehicular ad-hoc networks, opportunistic networks,underwater wireless networks, pocket switched networks and so on. DTN node’smovement often makes the communication disconnection between the nodes and thenode buffer space is limited. So it is easy to cause congestion, resulting in thedecrease of network distribution rate. Therefore, it is of important significance toresearch the efficient congestion control according to the movement characteristicsand communication characteristics of the different nodes. In this paper, we focus onstudying efficient congestion control mechanism in different DTN environment. Theprincipal works are as following:1) For congestion in deep-space delay tolerant network is mainly caused by thelimited node memory space, an improved strategy for multi-attribute decision makingto select the next hop node is proposed. The basic idea of the improved strategy wasto divide the node status into normal, semi-congestion and congestion statesaccording to the node storage occupancy, combined with the packet received historyand then used multi-attribute decision theory to select the best next hop node, so as toachieve the purpose of prevention of congestion. Simulation results show that theimproved strategy is more effective than the original one in the single node’s queuelength, average queue length, packet acceptance rate and the average packetdistributed time. It alleviates the congestion effectively.2) In pocket switched networks the node’s movement often leads tocommunication disconnection between nodes. For a higher packet delivery ratio, thenodes keep the messages and then adopt the Epidemic routing protocol which is basedon multicopies to forward the packets. However, the limited buffer size tends to causetraffic congestion. This paper proposes a buffer management scheme based onworking day movement model to ease the congestion. The scheme first adopts the N-Hop strategy to control the number of packet copies by limiting the hop count.Then according to the characteristics of node’s movement, the NRM and LFMalgorithms are designed and implemented to select a packet to drop. Theoreticalanalysis and experimental results show that the proposed scheme offers a high packetdelivery ratio, low average delay and overhead for the pocket switched networksunder the working day movement model.