## 2 The Ubiquitous Sensor Network Platform
### Technological Context and NGNs  
The increasing diversity of communication technologies, either IP-based (such as 6 LoWPAN or CoAP) or non ip-based technologies which are often proprietary (e.g., ZigBee or KNX), has motivated the research of new solutions to bridge the gap between Sensor Networks and the Sensor Web. For instance, the SensorBus [4] has been proposed (as a part of the open source implementation of OGC SWE by the North 52 \({}^{\circ}\) (52 north.org/) community) as an intermediary layer between geosensor networks and the Sensor Web. A particular SensorBus implementation based on Twitter has been proposed in [5] that allows reusing useful Twitter functionalities such as authentication and scalability management. Another extension of SensorBus, called SensorAdapter, has been presented in [6] as a real-time communication adapter designed to allow simultaneous communication between different sensors protocols and the data service layer in the Sensor Web. Also recently [7], a web service proxy has been proposed to link the low level sensor networks to the high level SWE. In a similar direction, relevant European projects have addressed this challenge of bridging the gap between sensor networks and the Sensor Web, for example, the SANY project [16] has proposed the SensorSA Data AcquisitionSystem (SensorSA DAS) designed as a network capable appliance which allows seamless integration of various sensors using communications based on OGC SWE interfaces. Current services and technologies to access real-world information are typically vertical, application-specific solutions. However, cross-domain IoT platforms foster the increasingly efficient creation of new services by enabling the re-use of deployed infrastructures, in a competitive scenario where multiple applications can choose dynamically among different infrastructures based on their availability, security, quality of service, _etc_. The main contribution of our USN-Platform is to integrate Sensor Networks and Sensor Web around the Next Generation Network (NGN) [17], which is a packet-based network capable of making use of multiple broadband, QoS-enabled transport technologies, and in which service-related functions are independent from underlying transport-related technologies. NGNs embody a good set of principles that can help the development of IoT applications at two levels: the integration of heterogeneous IoT devices and the facilities offered to develop services. Sensor and Actuator Networks (SANs) will be used in a broad set of heterogeneous application scenarios leading to a big variety of deployments with completely different communication infrastructures, protocols, speeds, latencies, _etc_. For example, in some cases SANs could be available through a broadband Internet connection, while in others they could be accessible through GRPS connectivity. One of the most crucial aspects of NGNs is the homogeneous support of multiple mobile and fixed access networks such as hybrid fiber-coaxial (HFC), power line communications (PLC), satellite, GPRS, CDMA, GSM, HSDPA or xDSL. This characteristic makes it key for supporting highly diverse deployment scenarios, e.g., a Sensor Network connected to an xDSL line or a sensor attached to a mobile phone. Moreover, since these networks are spread almost everywhere, they offer a huge range of geographic coverage for potential deployments. But even more importantly, NGNs provide a set of core functions needed for developing final customer services like identification, authorization, authentication, privacy, security or quality of service (QoS), accounting, billing, service discovery and mobility. These functions are critical for the deployment of IoT services. This notion of interconnecting sensor networks over Telco infrastructures has been proposed before. The EU project e-SENSE [18] can be identified as one of the first references proposing the integration of sensor networks into IP based telecommunication networks, but does not account for Sensor Web infrastructures.