We present empirical measurements of the packet delivery performance of the latest sensor platforms: Micaz and Telos motes. In this paper, we present observations that have implications to a set of common assumptions protocol designers make while designing sensornet protocolsspecifically -the MAC and network layer protocols. We first distill these common assumptions in to a conceptual model and show how our observations support or dispute these assumptions. We also present case studies of protocols that do not make these assumptions. Understanding the implications of these observations to the conceptual model can improve future protocol designs.

Sensor networks are notoriously difficult to program, given that they encompass the complexities of both distributed and embedded systems. To address this problem, we present the design and implementation of a declarative sensor network platform, DSN: a declarative language, compiler and runtime suitable for programming a broad range of sensornet applications. We demonstrate that our approach is a natural fit for sensor networks by specifying several very different classes of traditional sensor network protocols, services and applications entirely declaratively -these include tree and geographic routing, link estimation, data collection, event tracking, version coherency, and localization. To our knowledge, this is the first time these disparate sensornet tasks have been addressed by a single high-level programming environment. Moreover, the declarative approach accommodates the desire for architectural flexibility and simple management of limited resources. Our results suggest that the declarative approach is well-suited to sensor networks, and that it can produce concise and flexible code by focusing on what the code is doing, and not on how it is doing it.

We present empirical measurements of the packet delivery performance of the Telos and MicaZ sensor platforms. At a high level, their behavior is similar to that of earlier platforms. They exhibit link asymmetry, a reception "grey region," and temporal variations in packet loss. Looking more deeply, however, there are subtle differences, and looking deeper still, the patterns behind these complexities become clear. Packet losses are highly correlated over short time periods, but are independent over longer periods. Environmental noise (802.11b) has high spatial correlation. Packet loss occurs when a receiver operating near its noise floor experiences a small decrease in received signal strength, rather than an increase in environmental noise. These variations cause the reception "grey region." While short-term link asymmetries are not uncommon, long-term asymmetries are rare. Based on these findings, we suggest several ways in which current practices could be easily changed that would greatly improve the efficiency, performance, and lifetime of sensor networks.

Today's data centers deploy a variety of middleboxes (e.g., firewalls, load balancers and SSL offloaders) to protect, manage and improve the performance of the applications and services they run. Unfortunately, existing networks provide limited support for middleboxes. Administrators typically overload layer-2 path selection mechanisms to make sure that traffic traverses the desired sequence of middleboxes. These ad-hoc practices result in a data center network that is hard to configure, upgrade and maintain, wastes middlebox resources on unwanted traffic, and cannot guarantee middlebox traversal under network churn.To address these issues, we propose the policy-aware switching layer, or PLayer. The PLayer separates policies from reachability by allowing administrators to explicitly specify sequences of middleboxes. Middleboxes are connected to policy-aware switches, or pswitches, whose forwarding state is configured by a centralized controller according to the policy requirements. This way, the PLayer addresses the limitations of current middlebox deployments without modifying existing middleboxes or servers. To demonstrate the feasibility of our approach we implemented a prototype of the PLayer using the Click modular software router. Preliminary experimental results suggest that the PLayer is flexible, uses middleboxes efficiently, and ensures the correctness of middlebox traversal under churn.