Opportunistic networks aim to deal with the unpredictable environment for data communication. Messages in opportunistic networks need to be stored with the node in the absence of any suitable forwarder. With such a store-carry-forward paradigm, it aims to eliminate challenges of no pre-determined/fixed connectivity, absence of direct/in-direct routes from source to destination, and high error rate and delay in the network. Node carrying message roams in the network to find a suitable forwarding node. In this study, the survey for various routing protocols and mobility models for opportunistic networks is discussed along with tools available for simulations of opportunistic networks. Further, various challenges in opportunistic networks such as storage management, congestion management, and energy constraints are discussed. Many applications for the opportunistic network, along with real-time case study, are presented in the paper. The objective of the study is to provide future direction to the researchers, along with the systematic review. Hence, future objectives are discussed to mitigate the challenges faced in the current scenario. Also, based upon the study, it is observed that most researchers have taken epidemic, ProPHET, and spray and wait routing protocols as their base of study. Performance analysis for these protocols is done using opportunistic network environment (ONE) simulator.

中文翻译：

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机会主义网络回顾：评估过去、现在和未来

机会主义网络旨在处理不可预测的数据通信环境。在没有任何合适的转发器的情况下，机会网络中的消息需要与节点一起存储。通过这种存储-结转范式，它旨在消除无预定/固定连接、缺少从源到目的地的直接/间接路由以及网络中的高错误率和延迟等挑战。携带消息的节点在网络中漫游以寻找合适的转发节点。在这项研究中，讨论了机会网络的各种路由协议和移动模型的调查以及可用于模拟机会网络的工具。此外，还讨论了机会网络中的各种挑战，例如存储管理、拥塞管理和能源限制。论文中介绍了机会网络的许多应用以及实时案例研究。该研究的目的是为研究人员提供未来的方向以及系统评价。因此，讨论了未来的目标，以减轻当前情景中面临的挑战。此外，根据该研究，观察到大多数研究人员已将流行病、ProPHET 和喷雾等待路由协议作为他们的研究基础。这些协议的性能分析是使用机会网络环境 (ONE) 模拟器完成的。讨论了未来的目标，以减轻当前情景中面临的挑战。此外，根据该研究，观察到大多数研究人员已将流行病、ProPHET 和喷雾等待路由协议作为他们的研究基础。这些协议的性能分析是使用机会网络环境 (ONE) 模拟器完成的。讨论了未来的目标，以减轻当前情景中面临的挑战。此外，根据该研究，观察到大多数研究人员已将流行病、ProPHET 和喷雾等待路由协议作为他们的研究基础。这些协议的性能分析是使用机会网络环境 (ONE) 模拟器完成的。