A Case for a Sensor Network Architecture

ion that permits a wide variety of uses above and a range of implementations below. At what level should it occur and what should it express? By requiring all network technologies to support IP, and all applications to run on top of IP, the Internet could accommodate, even encourage, a vast degree of heterogeneity and diversity in both applications and underlying technologies.1 We have an analogous goal for sensornets; in both the application and device arenas we are in the midst of extremely rapid developments. Sensornets will only flourish if we can identify a narrow waist in the architecture that will allow device and protocol developments to proceed apace, while permitting significant optimization. We claim that such a narrow waist can exist, let’s call it Sensor-net Protocol (SP), and that it should be a best-effort single-hop broadcast with a rich enough interface to allow multiple network layer components above to optimize for a range of potential link layers below in a hardware-independent fashion.2 It is not only the resource limitations of sensornet that cause the SP to be closer in nature to the data link layer than the network layer at which IP resides. Applications differ dramatically in their communication patterns and are intimately tied to the associated network protocols. They generally do not require and often do not benefit from a common, universally routable addressing scheme. Instead, a single, simple interface needs to be provided to efficiently implement a range of routing protocols, independent of the underlying link layer, that facilitate in-network processing and collective communication, in addition to point-to-point transport. Moving the point of universal abstraction downward presents new issues that we do not typically concern ourselves about in the Internet architecture. It also requires a careful design of the layers above SP to provide a reasonably genIndeed, it is straightforward to incorporate sensornets as edge networks of the Internet with gateway nodes providing a bridge, and IPv6 addressing makes this considerably easier. In the vast majority of cases, the gateway will also serve as a proxy, so TCP connections would rarely terminate at the actual sensor node. In the proxy case, it is also natural for collections of nodes to appear as a virtual Internet host. The most challenging question is the architecture within the sensornet. This is more than just another subnet, because distributed applications are spread over the many nodes in a manner dependent on its physical embeddment. While IEEE 802.2 provides a link interface to a variety of links, higher layers must know what physical layer is below and access the specific physical layer through a standardized set of calls.