Pervasive networks formed by users' mobile devices have the potential to exploit a rich set of distributed service components that can be composed to provide each user with a multitude of application level services. However, in many challenging scenarios, opportunistic networking techniques are required to enable communication as devices suffer from intermittent connectivity, disconnections and partitions. This poses novel challenges to service composition techniques. While several works have discussed middleware and architectures for service composition in well-connected wired networks and in stable MANET environments, the underlying mechanism for selecting and forwarding service requests in the significantly challenging networking environment of opportunistic networks has not been entirely addressed. The problem comprises three stages: i) selecting an appropriate service sequence set out of available services to obtain the required application level service; ii) routing results of a previous stage in the composition to the next one through a multi-hop opportunistic path; and iii) routing final service outcomes back to the requester. The proposed algorithm derives efficiency and effectiveness by taking into account the estimated load at service providers and expected time to opportunistically route information between devices. Based on this information the algorithm estimates the best composition to obtain a required service. It is shown that using only local knowledge collected in a distributed manner, performance close to a real-time centralized system can be achieved. Applicability and performance guarantee of the service composition algorithm in a range of mobility characteristics are established through extensive simulations on real/synthetic traces.
翻译:用户移动装置所形成的渗透式网络有可能利用由用户移动装置组成的大量分布式服务组件,向每个用户提供多种应用级服务,但在许多具有挑战性的情景中,需要机会性网络技术才能使通信因装置断断续续连接、断开和隔断而受到影响。这对服务构成技术提出了新的挑战。虽然一些工作讨论了在连接良好的有线网络和稳定的MANOET环境中服务构成的中间软件和结构,但在机会网络极具挑战性的网络环境中,选择和转发服务请求的基本机制尚未完全解决。问题包括三个阶段:一)从现有服务中选择一个适当的服务序列,以获得所需的应用级服务;二)通过多机会途径,将先前阶段与下一个阶段的构成的路线排列结果纳入到下一个阶段;三)将最终服务结果追溯到提出请求者。提议的算法通过考虑到服务提供者的估计工作量和在机会式网络之间传输信息的预期时间,提高了效率和效力。根据这一信息,算法估计获得所需服务的最佳构成,以获得所需的应用级服务;二)通过多种机会途径将当地业绩的准确性分析,只能通过一种收集到的业绩,通过一种最接近的递增的系统,显示一种最接近性的业绩。