Data Centric Storage (DCS) is a well-known data storage and query processing mechanism for Wireless Sensor Networks (WSNs), storing sensed data or their metadata at pre-specified locations. Queries issued by mobile users are sent to, and processed at, such storage nodes. However, securing DCS is very difficult because WSNs usually operate in an unattended environment and hence are subject to node-capture attacks. Even after capturing a single node, an attacker may be able to subvert the entire system by using the keying material extracted from the captured node.

Location services are essential to many applications running on a hybrid of wirelessly-networked mobile actors and static sensors, such as surveillance systems and the pursuer and evader game (PEG). To our best knowledge, there has been no previous location service protocol for wireless sensor networks. A number of location service protocols have been proposed for mobile ad hoc networks, but they are not applicable to sensor networks due to the usually large per-hop latency between sensors. This paper presents a distributed location service protocol (DLSP) for wireless sensor networks. Using a rigorous analysis of DLSP, we derive the condition for achieving a high packet-delivery ratio, and show how to configure the protocol parameters to ensure the scalability of DLSP. We find that DLSP is scalable if the mobile's speed is below a certain fraction of the packet-transmission speed, which depends on a movement threshold. For example, if the movement threshold for the location servers at the lowest level equals the radio range, the speed limit is one-tenth of the packet-transmission speed. The mobile's theoretical speed limit is one-fifth of the packet-transmission speed, beyond which DLSP cannot scale regardless of the movement threshold. Because of the high location-update overhead of DLSP, we propose an optimization, DLSP-SN, which can reduce the overhead by over 70%, while achieving high packet-delivery ratios. However, due to the griding effect, the packet's path length of DLSP-SN may be longer than that of DLSP, incurring higher data-delivery cost

Due to the low price and robustness resulting from its wide acceptance and deployment, Ethernet has become an attractive candidate for real-time control networks. However, it is difficult to build a real-time control network using the standard Ethernet because the Ethernet MAC protocol-1-persistent CSMA/CD protocol-may cause unpredictable access delay. When both real-time and nonreal-time packets are concurrently transported over an ordinary Ethernet, real-time (RT) packets from a node may experience a large delay due to 1) contention with nonRT packets in the local node where they originate and 2) collision with RT and nonRT packets from the other nodes. To resolve this problem, we design, implement, and evaluate an adaptive traffic smoother. Specifically, we design two adaptive traffic smoothers, one at the kernel level and the other at the user level. The kernel-level traffic smoother is installed between the IP layer and the Ethernet MAC layer for better performance, and the user-level traffic smoother is installed on top of the transport layer for better portability. The kernel-level traffic smoother first gives RT packets priority over nonRT packets in order to eliminate contention within the local node. Second, it smoothes nonRT traffic so as to reduce collision with RT packets from the other nodes. This traffic smoothing can dramatically decrease the packet-collision probability on the network. The traffic smoother, installed at each node, regulates the node's outgoing nonRT traffic to maintain a certain rate. In order to provide a reasonable nonRT throughput while providing probabilistic delay guarantees for RT traffic, the nonRT traffic-generation rate is allowed to adapt itself to the underlying network load condition. Our implementation of the traffic smoother requires only a minimal change in the OS kernel without any modification to the current standard of Ethernet MAC protocol or the TCP or UDP/IP stack. The traffic smoother has been implemented on the Linux OS and is shown to reduce the RT message deadline-miss ratio up to two orders of magnitude under a heavily loaded condition, while the nonRT throughput drops only by half. For better portability, we also implemented and evaluated a user-level traffic smoother on top of the transport layer. Moreover, we emulate a switch using a kernel-level traffic smoother to evaluate the performance of traffic smoother in a switched Ethernet environment that can scale to a large control network.