Research On Some Key Issues Of Service Composition In Mobile Ad Hoc NETworks

Mobile Ad hoc NETworks (MANET) is composed of a number of mobile nodes in self-organized style, which communicate with each other in multi-hops way. MANET is a temporary network system with no network infrastructure requirements, easy and flexible for networking, and so MANET is widely used in digitized battlefield, disaster relief site, traffic information sharing scene, personal communications, scientific explorement and so on. However, since the node in network is limited in resoures and processing power, nodes need to collaborate with each other to provide users their required services. As a mean of realization of Service oriented computing (SOC), Web services technology can package the hardware capabilities, software applications, data and resources in networks into a single Web Service (WS), and composite these Web services, which provides an effective solution for what we issued.Now the researches on Web service composition focuse on wired network environment and infrastructure-based wireless network environment, which provide a reference for service composition in MANET. However, due to volatile network topology, limited bandwidth, unstable transmission medium and the node resource constraints and other characteristics, service composition in MANET faces numerous challenges. Currently, the researches in MANET are still in its infancy, and there are some key issues need to be solved which are given as follows.1) The existing service discovery approaches are either not suitable for MANET, or less efficient. There are already lots of service discovery methods now, and most of them require a stable infrastructure support, which is not suitable for infrastructureless and dynamic topology MANET. On the other hand, the service discovery designed for MANET only can be mainly divided into two categories:structured-based service discovery and distributed service discovery. The former methods need to maintain a virtual network structure, which requires a lot of packages for highly dynamic MANET, while the later would lead to discovery delay, broadcast storms and low efficiency when the network size increases. 2) As an important attribute in QoS, service availability is also important for MANET, but the current methods of quantitative assessment for it can not be implemented. That is because the current quantitative assessment methods is based on statistical or mathematical model by a trusted central node, which have characteristics that the longer the statistical time is, and the values are more precise. However, MANET is a temporary formed network, so these methods can not be implemented in it.3) The performance of current QoS-aware service selection approaches declines rapidly when the scale of the problem increases. QoS-aware service selection problem is a proved NP complete problem. The performance of current QoS-aware service selection approaches declines rapidly, and the quality of solutions is not so good when the scale of the problem increases.In order to solve these above problems, some deep researches are done for the three above-mentioned key issues, and make five aspects attributions which are generalized as follows.1) Present a service discovery protocol IS-SDP, short for Information Sharing based Service Discovery Protocol, which is based on an improved biased random walk model. In IS-SDP, the service request packet forwarding probability function is improved firstly, and then services request packet structure and a service information sharing mechanism are designed. Simulation results show that the IS-SDP is efficient for MANET.2) Present an Environment-aware Quantitative Assessment Model for Service Availability (EQAM-SA), which is based on AHP principles. After analyzing the running environment of services and the environmental factors that impact the service availability, the factors are divided into fundamental resource environment and network resource environment in order to build the quantitative assessment indicators system for service availability. Then the indicators'calculation methods are given. Finally, the availability value is computed by a weighted-based comprehensive approach. The feasibility and effectivenss are demonstrated through the simulation experiments and model analysis.3) A service selection approach for high-availability composite services is proposed as well. The approach is based on EQEM-SA, and a service field concept is presented as well as the availability attenuation equation, where the availability value is considered as the field strength. EQEM-SA also adopts "Selection-Execution-Selection" Mechanism. Through simulations, the effectivenss of EQEM-SA is validated too, and the approach would inspire deeper researches for high-availability composite services.4) Present a QoS-aware service selection approach based on an improved Particle Swarm Optimization Algorithm (iPSOA). QoS-aware service selection problem is a NP-complete issue. Firstly we redefine the parameters in decimal format, such as position, velocity and updating operations, and then in order to improve the quality of QoS of composite services, a non-uniform mutation (NUM) strategy is proposed. Also, Adaptive Weight Adjustment (AWA) and Local Best First (LBF) strategies are given to improve the convergence speed in global and local level respectively. Simulation results show our approach is quicker as well as high quality by comparison with other algorithms.5) Based on iPSOA, ISPCA is proposed. Service pool is used to save more composite service schemes with" better" QoS performance in the service selection process. Although the schemes in the service pool have some difference in QoS performance, more candidate schemes would be saved for services execution, which can reduce the reselection times. Simulations take some researches on the time and efficiency of ISPCA.