Nomadic service discovery in smart cities

Smart cities blend the boundaries between infrastructure and consumer devices, and rely on their cooperation for making new applications possible. This poses a challenge, as extremely resource-constrained devices such as ubiquitous sensors and actuators need to communicate with more powerful devices, such as smartphones and servers. Users move through this infrastructure, and their devices need to find and use services based on their current location. In this chapter, we focus on these interoperability issues on the service discovery (SD) layer. We examine requirements for a Smart City context and we analyze the standardized Multicast Domain Name System with DNS-Based SD (mDNS/DNS-SD) protocol as a potential SD protocol for Smart Cities. We show that mDNS/DNS-SD requires devices to be always online, which is inappropriate for battery-powered devices, and its discovery features are not discriminative enough to be used in large networks. As a solution, we propose a proxy scheme, where resource-constrained devices delegate their SD responsibilities to proxy servers. Then, we describe a new naming scheme, which enables devices to be looked up based on their physical properties, such as location, available sensors, and other criteria. Both extensions are backward-compatible with the mDNS/DNS-SD standard, making them favorable for use in smart cities.