Industry 4.0 promises to unlock the new capabilities for Industrial Internet of Things (IIoT) by transforming a rigid hierarchical automation pyramid into a flatter networked system. IEEE Time-Sensitive Networking, chosen as one of the Industry 4.0 pillars on the network level, offers mechanisms for deterministic data exchange and high reliability for such systems. Yet, to ensure a flexible and reliable service, a flat networked system requires a more sophisticated orchestration. Consecutively, such orchestration requires certain memory and CPU capacity from the IIoT devices, and the state of the art discusses the three candidate protocols, namely: 1) NETCONF; 2) RESTCONF; and 3) CORECONF. This article analyzes these protocols with a focus on resource-constrained IIoT devices. To compare the parameters a prototype implementation of CORECONF is developed, and extensively benchmarked against other protocols. Results suggest that CORECONF could be an ideal candidate in terms of time, power, and memory characteristics for resource-constrained devices.

Content objects are confined data elements that carry meaningful information. Massive amounts of content objects are published and exchanged every day on the Internet. The emerging Internet of Things (IoT) augments the network edge with reading sensors and controlling actuators that comprise machine-to-machine communication using small data objects. IoT content objects are often messages that fit into single IPv6 datagram. These IoT messages frequently traverse protocol translators at gateways, which break end-to-end transport and security of Internet protocols. To preserve content security from end to end via gateways and proxies, the IETF recently developed Object Security for Constrained RESTful Environments (OSCORE), which extends the Constrained Application Protocol (CoAP) with content object security features commonly known from Information Centric Networking (ICN). This paper revisits the current IoT protocol architectures and presents a comparative analysis of protocol stacks that protect request-response transactions. We discuss features and limitations of the different protocols and analyze emerging functional extensions. We measure the protocol performances of CoAP over Datagram Transport Layer Security (DTLS), OSCORE, and the information-centric Named Data Networking (NDN) protocol on a large-scale IoT testbed in single- and multi-hop scenarios. Our findings indicate that (a) OSCORE improves on CoAP over DTLS in error-prone wireless regimes due to omitting the overhead of maintaining security sessions at endpoints, (b) NDN attains superior robustness and reliability due to its intrinsic network caches and hop-wise retransmissions, and (c) OSCORE/CoAP offers room for improvement and optimization in multiple directions.

Content replication to many destinations is common in the IoT. IP multicast has proven inefficient due to a missing layer-2 support by IoT radios and its synchronous end-to-end transmission, which is susceptible to interference. Information-centric networking (ICN) introduced hop-wise multiparty dissemination of cacheable content, which proves valuable for lossy networks. Even Named-Data Networking (NDN), a prominent ICN, suffers from a lack of deployment.We explore a multiparty content distribution in an information-centric Web of Things built on CoAP. We augment CoAP proxies by request aggregation and response replication, which together with caches enable asynchronous group communication. Further, we integrate object security with OSCORE into the CoAP multicast proxy system for ubiquitous caching of certified content. We compare NDN, CoAP, and our data-centric approach in testbed experiments. Our findings indicate that multiparty content distribution with CoAP proxies performs equally well as NDN, while remaining compatible with the protocol world of CoAP.

Common use cases in the Industrial Internet of Things (IIoT) deploy massive amounts of sensors and actuators that communicate with each other or to a remote cloud. While they form too large and too volatile networks to run on ultra-reliable, time-synchronized low-latency channels, participants still require reliability and latency guaranties. We elaborate this for safety-critical use cases. This paper focuses on the effects of networking protocols for industrial communication services. It analyzes and compares the traditional Message Queuing Telemetry Transport for Sensor Networks (MQTT-SN) with the Constrained Application Protocol (CoAP) as a current IETF recommendation, and also with emerging Information-centric Networking (ICN) approaches, which are ready for deployment. Our findings indicate a rather diverse picture with a large dependence on deployment: Publish-subscribe protocols are more versatile, whereas ICN protocols are more robust in multi-hop environments. MQTT-SN competitively claims resources on congested links, while CoAP politely coexists on the price of its performance.

Information Centric Networking is considered a promising communication technology for the constrained IoT, but NDN was designed only for standard network infrastructure. In this paper, we design and evaluate an NDN convergence layer for low power lossy links that (1) augments the NDN stateful forwarding with a highly efficient name eliding, (2) devises stateless compression schemes for standard NDN use cases, (3) adapts NDN packets to the small MTU size of IEEE 802.15.4, and (4) generates compatibility with 6LoWPAN so that IPv6 and NDN can coexist on the same LoWPAN links. Our findings indicate that stateful compression can reduce the size of NDN data packets by more than 70 % in realistic examples. Our experiments show that for common use cases ICNLoWPAN saves 33 % of transmission resources over NDN, and about 20 % over 6LoWPAN.

This paper revisits NDN deployment in the IoT with a special focus on the interaction of sensors and actuators. Such scenarios require high responsiveness and limited control state at the constrained nodes. We argue that the NDN request-response pattern which prevents data push is vital for IoT networks. We contribute HoP-and-Pull (HoPP), a robust publish-subscribe scheme for typical IoT scenarios that targets IoT networks consisting of hundreds of resource constrained devices at intermittent connectivity. Our approach limits the FIB tables to a minimum and naturally supports mobility, temporary network partitioning, data aggregation and near real-time reactivity. We experimentally evaluate the protocol in a real-world deployment using the IoT-Lab testbed with varying numbers of constrained devices, each interconnected via IEEE 802.15.4 wireless LoWPANs. Implementations are built on CCN-lite with RIOT and support experiments using various single-and multi-hop scenarios.

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As the Internet of Things (IoT) emerges, compact operating systems (OSs) are required on low-end devices to ease development and portability of IoT applications. RIOT is a prominent free and open source OS in this space. In this paper, we provide the first comprehensive overview of RIOT. We cover the key components of interest to potential developers and users: the kernel, hardware abstraction, and software modularity, both conceptually and in practice for various example configurations. We explain operational aspects like system boot-up, timers, power management, and the use of networking. Finally, the relevant APIs as exposed by the OS are discussed along with the larger ecosystem around RIOT, including development and open source community aspects.