Modern protocols for wireless sensor networks efficiently support multi-hop upward traffic from many sensors to a collection point, a key functionality enabling monitoring applications. However, the ever-evolving scenarios involving low-power wireless devices increasingly require support also for downward traffic, e.g., enabling a controller to issue actuation commands based on the monitored data. The IETF Routing Protocol for Low-power and Lossy Networks (RPL) is among the few tackling both traffic patterns. Unfortunately, its support for downward traffic is significantly unreliable and inefficient compared to its upward counterpart. We tackle this problem by extending RPL with mechanisms inspired by opposed, yet complementary, principles. At one extreme, we retain the route-based operation of RPL and devise techniques allowed by the standard but commonly neglected by popular implementations. At the other extreme, we rely on flooding as the main networking primitive. Inspired by these principles, we define three base mechanisms, integrate them in a popular RPL implementation, analyze their individual and combined performance, and elicit the resulting tradeoffs in scalability, reliability, and energy consumption. The evaluation relies on simulation, using both real-world topologies from a smart city scenario and synthetic grid ones, as well as on testbed experiments validating our findings from simulation. Results show that the combination of all three mechanisms into a novel protocol, T-RPL (i) yields high reliability, close to the one of flooding, (ii) with a low energy consumption, similar to route-based approaches, and (iii) improves remarkably the scalability of RPL with respect to downward traffic.

中文翻译：

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路线还是洪水？可靠高效地支持 RPL 中的下行流量

无线传感器网络的现代协议有效地支持多跳向上从许多传感器到收集点的流量，这是启用监控应用程序的关键功能。然而，涉及低功耗无线设备的不断发展的场景也越来越需要支持向下流量，例如，使控制器能够基于监控的数据发出致动命令。IETF 低功耗和有损网络路由协议 (RPL) 是少数同时处理这两种流量模式的协议之一。不幸的是，与上行流量相比，它对下行流量的支持明显不可靠且效率低下。我们通过使用受对立但互补原则启发的机制扩展 RPL 来解决这个问题。在一个极端，我们保留了 RPL 的基于路由的操作，并设计了标准允许但通常被流行实现忽略的技术。在另一个极端，我们依赖泛洪作为主要的网络原语。受这些原则的启发，我们定义了三种基本机制，将它们集成到流行的 RPL 实现中，分析它们的单独和组合性能，并在可扩展性、可靠性和能耗方面进行权衡。评估依赖于模拟，使用来自智能城市场景和合成网格的现实世界拓扑，以及验证我们从模拟中发现的测试台实验。结果表明，结合全部将三种机制整合到一个新颖的协议中，T-RPL (i) 产生高可靠性，接近泛洪的可靠性，(ii) 具有低能耗，类似于基于路由的方法，以及 (iii) 显着提高了 RPL 的可扩展性关于下行流量。