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Network lifetime is the time interval in which the nodes are operational. Considering that machine-to-machine (M2M) devices have limited energy resources, an important challenge in M2M communications is to prolong the network lifetime. The constrained application protocol (CoAP) supports multi-target monitoring applications in M2M communications, allowing the creation and maintenance of groups, as well as their periodic communication. It is essential to aggregate the CoAP group-communication over the paths to increase the network lifetime of low-power M2M devices, since data aggregation reduces the use of energy-consuming hardware (e.g., central processing unit and wireless interface). However, the current data aggregation solutions do not specify how to support data aggregation with multiple CoAP-based groups in multi-target monitoring applications. In this paper, the proposed approach, called two-tier aggregation for multi-target applications (TTAMAs), aggregates the data originated from nodes belonging to either the same or different CoAP groups. Furthermore, TTAMA is an adaptive solution because it performs the data aggregation in accordance with the CoAP configurations, such as communication periodicity and data aggregation functions. We compare TTAMA with current data aggregation approaches that use minimum spanning tree and shortest path tree. The results show that TTAMA outperforms the related works in terms of network lifetime and energy consumption.

Open authorization (OAuth) is an open protocol, which allows secure authorization in a simple and standardized way from third-party applications accessing online services, based on the representational state transfer (REST) web architecture. OAuth has been designed to provide an authorization layer, typically on top of a secure transport layer such as HTTPS. The Internet of Things (IoTs) refers to the interconnection of billions of resource-constrained devices, denoted as smart objects, in an Internet-like structure. Smart objects have limited processing/memory capabilities and operate in challenging environments, such as low-power and lossy networks. IP has been foreseen as the standard communication protocol for smart object interoperability. The Internet engineering task force constrained RESTful environments working group has defined the constrained application protocol (CoAP) as a generic web protocol for RESTful-constrained environments, targeting machine-to-machine applications, which maps to HTTP for integration with the existing web. In this paper, we propose an architecture targeting HTTP/CoAP services to provide an authorization framework, which can be integrated by invoking an external oauth-based authorization service (OAS). The overall architecture is denoted as IoT-OAS. We also present an overview of significant IoT application scenarios. The IoT-OAS architecture is meant to be flexible, highly configurable, and easy to integrate with existing services. Among the advantages achieved by delegating the authorization functionality, IoT scenarios benefit by: 1) lower processing load with respect to solutions, where access control is implemented on the smart object; 2) fine-grained (remote) customization of access policies; and 3) scalability, without the need to operate directly on the device.

The Internet of Things (IoT) enables a wide range of application scenarios with potentially critical actuating and sensing tasks, e.g., in the e-health domain. For communication at the application layer, resource-constrained devices are expected to employ the constrained application protocol (CoAP) that is currently being standardized at the Internet Engineering Task Force. To protect the transmission of sensitive information, secure CoAP mandates the use of datagram transport layer security (DTLS) as the underlying security protocol for authenticated and confidential communication. DTLS, however, was originally designed for comparably powerful devices that are interconnected via reliable, high-bandwidth links. In this paper, we present Lithe-an integration of DTLS and CoAP for the IoT. With Lithe, we additionally propose a novel DTLS header compression scheme that aims to significantly reduce the energy consumption by leveraging the 6LoWPAN standard. Most importantly, our proposed DTLS header compression scheme does not compromise the end-to-end security properties provided by DTLS. Simultaneously, it considerably reduces the number of transmitted bytes while maintaining DTLS standard compliance. We evaluate our approach based on a DTLS implementation for the Contiki operating system. Our evaluation results show significant gains in terms of packet size, energy consumption, processing time, and network-wide response times when compressed DTLS is enabled.