Arguments for cross-layer optimizations in Bluetooth scatternets

Bluetooth, an innovation in short-range radio technology, has gone through the first stage of standardization, and commercial products based on ν1.0 specifications will be appearing. While much work has gone into developing the radio technology and hardware for this system, little effort has been focused on additional infrastructure that is necessary for applications in this environment. We examine the issue of supporting ubiquitous computing applications (Weiser, 1991) in a Bluetooth network. The Bluetooth standard defines a multi-hop routing structure, called a scatternet, to address the limitations caused by short-range and small fanout of the underlying link technology. We identify several characteristics, the combination of which makes scatternets different from previously considered networks. Importantly, Bluetooth links are connection-oriented with low-power link modes. We show that the unique aspects of the technology require a redesign of the protocol structure for link formation, IP routing and service discovery. When existing approaches to these protocols are applied to scatternets, the multiple protocol layers would operate without knowledge of each other, resulting in inefficient use of power in many cases. We suggest an alternative approach where there is a single protocol layer providing a level of indirection within the scope of a scatternet. That is, we argue for extensive cross-layer optimizations