Delay Tolerant Network Data Transmission In The Key Technology Research

The Delay Tolerant Network (DTN) is a special kind of Mobile Ad Hoc Network (MANET), which composes of people or vehicle carried mobile ter-minals equipped with short distance communication devices. Most of the time, a DTN usually has sparse node distribution and is partitioned into isolated con-nected subareas. Thus, a contemporaneous path between the source and the destination may not exist. The messages in DTN are carried and forwarded between mobile nodes, until the messages arrive at their destinations.Recently, the researches of DTN are concentrated on message routing, da-ta dissemination, key performance analysis, and hybrid network architectures. The research objective is improving the data delivery ratio, pulling down the delivery delay and reducing the overhead of the data delivery protocols.The mobile nodes are usually carried by people or vehicles, thus the mo-bility of the nodes has social properties. Data delivery in DTN is based on short distance communication technologies, and considering the social and lo-cation properties of the mobile nodes can improve the efficiency of the rout-ing algorithms; It is more likely to generate supernumerary content messages when disseminating messages by matching query messages and content mes-sages. Merging query messages can reduce the redundant transmission of con-tent messages; Network performance analysis is the prerequisite of designing optimal data delivery protocols, especially in vehicular delay tolerant networks. The message delivery delay may affect the road safety, thus analysis of the de-livery delay in vehicle delay tolerant networks is significant; In vehicular delay tolerant networks, deploying roadside units can improve the network perfor-mance. However, the relationship between roadside unit deployments and the network performance still need in-depth studies. Based on the above mentioned problems that still exist in the DTN research, this thesis studied message rout- ing, data dissemination, message delivery delay and RSU deployment in DTN, and the research results are shown as follow.1. A Venue Aware Routing (VAR) algorithm is proposed for DTN. Based on social properties of the mobile nodes, a discrete time Markov Chain mo-bility model is proposed which considers both the transfer time between venues and residence time in venues of the mobile nodes. When selecting a relay node, VAR considers not only the encounter probabilities among different nodes, but also the encounter time in future to reduce the mes-sage delivery latency. For each message with a TTL (Time to Live), the consideration of encounter time also improves the message delivery ratio. We designed two multi-copy message routing algorithms for DTNs. The first algorithm uses the proportional spray strategy and the other one uses the binary spray strategy.2. To achieve more efficient and robust message dissemination, a Content Encounter Probability based Message Dissemination (CEPMD) scheme for DTN is proposed. In CEPMD, we use request predicates to represent subscribers’interests and propagate request predicate messages over the network. A request predicate is tagged with an ep, representing the prob-ability that the predicate’s host node will encounter the destination node. Content messages are forwarded to the nodes that have a request predi-cate that matches the content message and have a greater ep value. The corresponding content messages can be forwarded to the subscriber along the probability gradient of predicates.3. Message delivery delay is mainly caused by mobility and sparse distri-bution of vehicles in Vehicular DTN. It directly impacts the application design and deployments for Vehicular DTN. We conduct an in-depth s-tudy on the insights of message delivery delay in Vehicular DTN towards the identified two major factors:1) message delivery distance,2) density of vehicles, based on a bidirectional vehicle traffic model. The bidirec-tional vehicle traffic was modeled as a combination of multiple Poisson point processes. Based on the sub-additive ergodic theory, theoretically, we found that the message delivery delay has a linear relationship with the message delivery distance. Furthermore, the upper bound of the co-efficient of the linear relationship has an exponential polynomial relation with the density of vehicles on the road and decreases with the increase of the velocity of the traffic.4. A roadside unit deployment algorithm for content downloading in vehic-ular DTN is proposed. The encounters between vehicles and RSUs are modeled as a time continuous homogeneous Markov chain. The optimal inter-meeting time between vehicles and RSUs is analyzed based on the encounter model. Then, the road network is modeled as a weighted undi-rected graph, and a RSU deployment algorithm is designed based on the depth-first traversal algorithm for edges of a graph.