Research On Publish-Subscribe Key Technologies In Mobile Environment

With the rapid development of Internet, Internet of Things, cloud computing, mobile networks and so on, the size and structure of the distributed systems have been greatly changed by the relevant platforms and key technologies. Modern distributed computing requires the scalability and high-efficiency, as well as an unprecedented high degree of adaptability in dynamic scenario. This demands one kind of flexible communication interaction mechanism with the characteristics of dynamic and loose coupling between the various participants in the distributed systems, in order to meet the requirements of the large-scale distributed control and dynamic change. The Publish/Subscribe system, which has the properties of dynamic plug and play, many-to-many, asynchronous and decoupled communication, is suitable for highly dynamic information-centric network environment and has been widely applied in large-scale distributed systems. This dissertation mainly focuses on the Publish/Subscribe systems with distributed-broker architecture in the mobile environment, especially the publish/subscribe client-mobility management strategy and publish/subscribe routing algorithms in MANET environment. The main innovations are listed as follows:(1) To guarantee the scalability and reliability of publish/subscribe system in mobile environment, a new client-mobility management strategy CMMAPS is proposed for the acyclic publish/subscribe broker network. This strategy adopts a transfer link mechanism and restricts the information transmission and filter table alteration caused by client-mobility to limited brokers on the transfer link, which helps to reduce the influence on the network caused by subscription tables update, as well as the overhead and event transfer delay. On the other hand, it ensures that the roaming client could receive complete and orderly events matching the subscriptions during the period of disconnection when it reconnects to a broker. In addition, the subscription filter table is divided into two parts, i.e. MFT and LFT, which effectively ensures that the event transmission and subscription table update process do not affect other unrelated brokers to receive events, and do not conflict between the concurrent transfer processes. The simulation results show that CMMAPS can effectively reduce the network overhead and average delay of the information transfer and subscription table update processes, and improve event transfer ratio.(2) A broker-broadcasting publish/subscribe routing strategy called BBPSR is proposed, which efficiently solve the contradiction between efficiency and scalability of the information distribution services in MANET. We dynamically select a series of broker nodes in MANET by using broker selection algorithm to receive the publications and subscriptions from non-broker nodes, but it doesn’t mean that the whole network will be divided into several clusters where the brokers are the cluster headers. The brokers periodically flood their location information, while the non-broker nodes send messages to the selected brokers through the reverse routes formed by prior flooding messages only in the case of sending publications or subscriptions. In this way, it’s able to reduce the overhead caused by dynamic topology while maintaining an efficient forwarding route. The brokers complete matching operations between the publications and subscriptions, and transfer the matching events in the way of broker-based or rendezvous-based to reduce load of brokers. The simulation results show that this method can provide relatively precise event forwarding path, obtain lower computational overhead of most nodes as well as lower control overhead and failed transmission ratio of network links at the cost of increasing a small amount of transmission delay and computing load of the brokers.(3) This paper proposes a clustering publish/subscribe routing protocol based on hierarchical network structure, termed CPSR, in order to implement efficiency publish/subscribe in large-scale MANET. The protocol divides the network into finite clusters, and constructs limited size of rooted publish/subscribe tree intra-cluster by Parent-Selection-Metric which uses content-based routing to forward events. Through the method above, it can effectively avoid high maintenance overhead and make full use of the efficient forwarding performance of content-based publish/subscribe tree structure. A (?)igh-layer of virtual backbone is formed between the cluster heads, and uses destination-based routing to forward events inter-cluster, which can effectively avoid the redundant communications among the cluster heads. The simulation results show that this hierarchical network structure can effectively limit the information exchange within a certain range in the cluster, and reduce the overhead and influence scope of routing maintenance by dynamic topology change, thus effectively improve the performance and scalability of network.