| Summary: | With the widespread use of networked embedded systems operating over wireless sensor networks, a standardized architecture is required to enable the rapid development of applications. An embedded operating system serves as an important building block of the standardized architecture. The support of the most commonly used services and protocols should be made available in it as a system service to improve the development speed. Real-time services are commonly required by many time-sensitive applications, such as automation control, real-time monitoring. Events need a global time notion or must happen within a deadline. Collected data should arrive at the destination before it becomes old and loses its meaning. But there is no common notion of time in a wireless sensor network in which all the nodes are physically separated and no global clock or common memory exists. Moreover, there is no guarantee that the sensed data will get to the destination before the deadline. To address these real-time issues, we develop real-time services including time synchronization and low-latency data collection to provide therapid development of time-critical applications. Meanwhile, security becomes an important issue to wireless sensor network due to the vulnerability of the wireless channel. The adversaries can simply capture and change the data and then resend it. The real-time services utilizing the wireless communication are vulnerable to the attacks and might be the weakest link for the whole system if it is not designed with security in mind. As the building block of real-time services, time synchronization comes into the first place to provide a global time scale for a distributed networking system. We study current time synchronization protocols for wireless sensor networks, propose our protocol design and implement it in the experimental platform, Contiki OS on the hardware platform Tmote Sky. To show the feasibility and performance of our protocol, we perform extensive experimental evaluation. Low-latency data collection services will also play a significant role for the time-critical applications. It aims to provide the guarantee of a time limit for the data collection. Based on the synchronized notion of time over the network, we implement a protocol for data collection aiming at low end-to-end latency for the same platform. To show the performance of data collection using this protocol, we test end-to-end latency in a multi-hop network and evaluate it based on the hop count and the estimation of the point-to-point delay in a single-hop communication. Security issues pose a great challenge to the applications as well as the underlying services due to vulnerability of the wireless channel, hostile environment as well as the severe resource constraint. To make the real-time services resilient to security attacks, we analyse the security attacks that might interrupt the services and present countermeasures to resist these security breaches. The hardware platform in use provides a crypto accelerator in the radio chip and frees the microcontroller from the long computation time for the security operations. We implement the security protocol utilizing hardware-assisted security operation to provide the link-layer security services. In addition, we provide data freshness service using authenticated MAC timestamping for each packet. Then we show how to secure the real-time services using these security services and integrate them into the protocol implementation.
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