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More than the functionalities it provides the key issue of the USN-Enabler is the
way in which it has been designed, since it follows the OGC Sensor Web
Enablement Family of Standards and the OMA Presence Simple and XDM
Standardized homogeneous representation of sensor data and metadata : It provides
homogeneous representation of the sensors and actuators representations and mea-
surements following the OGC® SensorML and Observations & Measurements
(O&M) standards.
The more interesting issues brought by the platform, more than the functionalities
it provides, are the way in which these functionalities are provided, since this
approach, instead of redefining some existing functions, uses the existing standards.
Especially important is the use of SensorML as the language that unifies the het-
erogeneous sensors and actuator definition. Even considering that the USN Platform
presents an interesting approach to tackle the problem of integrating sensors and
actuators to services, mainly due to the extensive use of standards, it is still a first
step and much work still needs to be carried out for it to be considered as a solution
for the USN. Issues like billing, trust, accounting, and high-level interaction mecha-
nisms are not still attached. The architecture can be viewed as centralized, but with
catalog functionality in order to have some distribution of functionality. It is men-
tioned that some of the functionalities could be provided by elements like the
Gateway, but it is not yet defined.
The framework presented by the e-SENSE approach [ 17 ] aims at integrating sensor
networks into the IP multimedia subsystem (IMS) of future mobile and converged
networks. The framework allows applications in IMS-based service platforms to
access sensor and context information from a variety of sensor networks with het-
erogeneous capabilities. The framework introduces two architectural components,
a context service enabler and gateway extensions to sensor networks. The context
service enabler provides sensor-based context information as a dedicated service
via a unified interface using standardized IMS protocols (such as SIP). Thus, the
context service enabler can be used as a service building block for the realization
of various different context-aware applications hosted on application servers in the
IMS domain. Gateway extensions allow the integration of heterogeneous sensor
networks into the IMS domain by implementing sensor-network-specific mecha-
nisms on one side and provide service functions for interaction with the context
service enabler on the other. Each sensor network gateway is an IMS user identified
by a unique IP multimedia private identity, several public ones for each gateway.
Using the proposed gateway extensions, the sensor network systems register their
presence with the IMS core platform and available services with the context service
enabler. It is expected that applications and services will express their context
requirements on a semantically high level of abstraction and that the context service
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