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Sensor networks exhibit a unique funneling effect which is a product of the distinctive many-to-one, hop-by-hop traffic pattern found in sensor networks, and results in a significant increase in transit traffic intensity, collision, congestion, packet loss, and energy drain as events move closer toward the sink. While network (e.g., congestion control) and application techniques (e.g., aggregation) can help counter this problem they cannot fully alleviate it. We take a different but complementary approach to solving this problem than found in the literature and present the design, implementation, and evaluation of a localized, sink-oriented, funneling-MAC capable of mitigating the funneling effect and boosting application fidelity in sensor networks. The funneling-MAC is based on a CSMA/CA being implemented network-wide, with a localized TDMA algorithm overlaid in the funneling region (i.e., within a small number of hops from the sink). In this sense, the funneling-MAC represents a hybrid MAC approach but does not have the scalability problems associated with the network-wide deployment of TDMA. The funneling-MAC is 'sink-oriented' because the burden of managing the TDMA scheduling of sensor events in the funneling region falls on the sink node, and not on resource limited sensor nodes; and it is 'localized' because TDMA only operates locally in the funneling region close to the sink and not across the complete sensor field. We show through experimental results from a 45 mica-2 testbed that the funneling-MAC mitigates the funneling effect, improves throughput, loss, and energy efficiency, and importantly, significantly outperforms other representative protocols such as B-MAC, and more recent hybrid TDMA/CSMA MAC protocols such as Z-MAC.

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We present a signaling architecture for network traffic authorization, Permission-Based Sending (PBS). This architecture aims to prevent Denial-of-Service (DoS) attacks and other forms of unauthorized traffic. Towards this goal, PBS takes a hybrid approach: a proactive approach of explicit permissions and a reactive approach of monitoring and countering attacks. On-path signaling is used to configure the permission state stored in routers for a data flow. The signaling approach enables easy installation and management of the permission state, and its use of soft-state improves robustness of the system. For secure permission state setup, PBS provides security for signaling in two ways: signaling messages are encrypted end-to-end using public key encryption and TLS provides hop-by-hop encryption of signaling paths. In addition, PBS uses IPsec for data packet authentication. Our analysis and performance evaluation show that PBS is an effective and scalable solution for preventing various kinds of attack scenarios, including Byzantine attacks.