Routing And Reliability In Delay Tolerant Networks

In the recent years, as a new class of network architecture, delay tolerant net-works(DTN) have received extensive research and application. The path of end toend from the source to destination node may not exist, since the network environ-ments of DTN are extremely particular. The absence of connectivity among nodesresult in the crash of the networks. Many challenges are brought for the routingprotocols of DTN. The traditional routing protocols have not suitable for DTN, anda lot of routing of DTN are proposed. Message delivery is mainly relied on mobil-ity and contact process of nodes. It is important problem to design DTN routingthat messages are successfully delivered and the consumption of network resourcesis reduced to a minimum. The main contributions of this thesis are as follows:1. Two routing schemes are proposed according to the problem of messageredundancy in DTN. One is a scheme to control message redundancy e?cientlyin DTN. By using counter method, every node adds an encounter counter basedon epidemic routing scheme, and the counter records the number which the nodeencounters other nodes with the same copy for a message. Theoretical analysisgives a lower bound of threshold in wireless mobile networks. According to thelower bound of threshold, proper threshold is installed in real environment. Thesuccessful delivery e?ciency is still the same and the redundant copies are controllede?ciently. Another is a routing scheme about message redundancy control based onbirth and death model in delay tolerant networks. We construct a special Markovchain birth and death model on the number of message copies, then calculate andobtain a stationary distribution of the birth and death process. The message copiesare controlled e?ciently.2. A new graph-based single-copy routing based on DTN is proposed. DTNconnectivity graph is constituted with mobility of nodes and communication, and thecorresponding greedy tree is obtained using greedy algorithm in DTN connectivitygraph. While there are some bad nodes such as disabled nodes or selfish nodes indelay tolerant networks, the nodes can choose the next proper intermediate node totransmit the message by comparing the location of neighboring nodes in the greedytree. The single-copy routing method is very appropriate for energy-constrained,storage-constrained and bandwidth-constrained DTN networks. The delivery ratiois increased significantly by using the graph-based single-copy routing when the badnodes exist. 3. Two-tiered mobile wireless sensor network is constructed without infrastruc-ture including the mobile sink tier and the fixed sensor tier. The sensor nodes onlycommunicate with the mobile sinks. The data that the mobile sinks receive fromthe sensors is fused to form the messages. The message is copied and stored andcarried by other mobile sinks relay and then it is transferred to the access point. Weuse multiple copies method of epidemic routing and present a redundant removingmethod for message copies based on the threshold of nodes encountering each other.The method guarantees the message transferred successfully and decreases copiese?ectively in the network to reduce the consumption of resource, bu?er, bandwidthand energy arisen by many copies. The delivery e?ciency stays the same and thedelay and the hop count do not increase with the appropriate threshold.4. With the increase of number and complexity of space mission, the inter-networking of space communications gradually substitutes traditional telecommuni-cation protocols. The DTN architecture more facilitate the growing complexity ofspace communication. A transport model based on random hypergraph for spacedelay tolerant networks is proposed, which shows the message transport processfrom the satellite to the ground stations. The data is transmitted between a smallsatellite near earth and the ground stations. For transmitting reliably, the datais divided into many fragments, and these fragments are encapsulated as multiplebundles with the bundle protocol of DTN. Some bundles which may be error arerequested to retransmit in next communication link. An r-uniform random hyper-graph model is introduced and the relation is analyzed between the error probabilityof bundle and the structure of hypergraph.5. A trustworthy routing protocol based on social network for DTN is proposed,which ensure the messages to be sent to the destination node e?ciently and reliablyagainst more selfness nodes in DTN. With the method of relation evaluation amongnodes in social networks, we figure out the relation intensity matrix between thegroups. The source node chooses the proper member nodes as next intermediatenodes to forward the messages according to the relation intensity matrix, whichavoid the messages to be sent to the selfness nodes and reduce the probability ofdropping the messages. At the same time, due to intermittent connectivity of DTN,a method of identity-based cryptography is introduced during messages forwarding,it ensures the security of messages forwarding. Our method can ensure the securityand e?ciency of messages to the destination.