Author: Javier Lucio
The virtualization of sensor networks concept was explained in an older post .
In that post, the concept under the title of the virtualization of sensor networks and the EU fp7 project VITRO, were introduced and described.
Now, a set of practical scenarios (6) covering the virtualization concept are described here for a better understanding and an open door for conceptualizing new services, functionalities and business models in the development, deploying and use of sensor networks.
Each of the selected scenarios is intended to demonstrate relevant VITRO functionalities. Namely, we concentrate on service virtualization, resource virtualization, service composition, service provisioning and security among additional functionalities.
Scenario 1: Service virtualization
A virtual service is obtained by extending, merging and reconfiguring the behaviour of existing services and by composing involved resources in a transparent way with respect to the underlying technology.
A number of different sensor islands are connected. These heterogeneous islands are administrated by different administrative domains and provide access to existing services and resources e.g. Energy Efficient Smart Schools and Buildings in general. The end-user would be able to monitor observations and measurements on room temperature, humidity and lighting for multiple buildings at disparate locations.
Each Wireless Sensor Island (WSI) is deployed in order to form a unique Virtual Sensor Network (VSN). Each WSI is equipped with different types of sensors, therefore information about one metric of observation may come from one out of the different WSIs.
Scenario 2: Service virtualization II
This scenario consists on the formation of 2 Virtual Sensor Networks (VSN) using the same sensor network infrastructure. Two VSN instantiations are formed within the same Wireless Sensor Island (WSI). A sensor participating in the first VSN e.g. providing one of its sensing capabilities can be part of the second VSN providing a supporting service such as routing for data packets of the second VSN.
Service Virtualization scenario can be distinguished in two different cases: 1) two users requesting data from the same node and 2) users request data from different nodes but one or more of the traversed nodes serve as routers, supporting both network instances.
This scenario could be applicable for use cases as controlling the traffic lights and managing the traffic in a city.
Scenario 3: Resource virtualization
The third scenario demonstrates the concept of node resources virtualization in order to provide relaying capabilities and form a Virtual Sensor Network (VSN) able to recover from network disconnections.
A Delay Tolerant Networking (DTN) scheme is used when a formerly connected Wireless Sensor Island (WSI) becomes disconnected for a long period of time, and therefore partitioned in a number of smaller WSI. DTN basically relies on some nodes’ mobility in order to deliver data among these WSIs and establish end‐to‐end communication.
This scenario could be applicable for the management of disasters or security in public spaces where the recovery of the network connection is an issue. For that, the scenario uses the employment of DTN mechanisms supporting the delivery of data when end-to-end connectivity within a VSN is intermitted or unavailable.
Scenario 4: Security related virtualization
This scenario is based on trust-aware routing protocols, and could be applicable to services as monitoring the production in sales chains or security in public spaces.
The scenario deals with the case when a Wireless Sensor Island (WSI) has some malicious nodes. The routing metrics that are utilized by the routing protocol for establishing the routes to forward the data packets, will be shown to efficiently detect any malicious nodes (e.g. grey or black nodes that drop part of or all of their incoming traffic) and re-route the data traffic around them. Also, this scenario demonstrates the effectiveness of excluding a node that does not support encryption capabilities, providing robustness and attack resistance to the WSI.
Scenario 5: Service composition
This scenario consists on the composition of a new high-level service from a set of available primary services. For example:
- Composition of a new service called “fire detection” from two primary services: C02 measurements and temperature/light intensity measurements.
- Composition of a “public security” service from a composed motion-detection and light intensity observation services.
In both cases, a wireless sensor network (WSN) is formed by a set of nodes (CO2 and light sensors or motion-detection and light sensors), which are deployed in order to monitor a given area. The sensors run the CoAP protocol, so they are able both to periodically send data to a specific CoAP client, who is querying the information and to answer to specific interrogation.
The nodes are connected to a Gateway which acts as a bridge between the sensor and the service provider in charge of processing the data received from the WSN, combining the observations carried out by the WSN and, eventually, raising an alarm if a target event is detected. In the scenario of “fire detection”, the SP will aggregate the data received from the light intensity and the fire temperature. When both these values are too elevated, exceeding a given threshold, an alarm is raised. In the scenario of “public security”, the behaviour of the SP is similar: the sensor publishes the measurements collected by the sensor and the SP processes received data, notifying the end-user in case of event detection.
Scenario 6: Service provisioning
This last scenario is devoted to demonstrating the continuation of service provisioning under adverse circumstances. Let’s use as the example service a composite service providing average temperature measurements from a set of temperature sensors in a room or another predefined area. The scenario demonstrates the robust and continued provision of this service in the event that one of the sensors participating in the corresponding Virtual Sensor Network (VSN) goes “down” (for example, due to energy depletion or malfunction). The system shall be able to select another sensor (in the vicinity) or group of sensors that provides an equivalent operational service and integrate it to the VSN, thus allowing the continuation of service provisioning, in a transparent way to the final user.
An end-user requests from a Service Provider an average temperature monitoring service for one or more locations, additionally specifying the number of sensors that will be providing the measurements per location. For example, the user can define that it is required that the average temperature result is reliable only when it is calculated based on 5 measurements from different sensors in a location.
After the service is initiated and the end-user receives the first results for the average temperature at each location, some sensors involved in the formed VSN will become unavailable (e.g. when they have exhausted their power resources and shut down). In this case, the gateway should be able to detect that the required number of sensors supporting the VSN is not met, based on a “disappearing node” event and inquire the “Resource and Services Controller” for other nodes within its Wireless Sensor Island (WSI) that can also provide temperature measurements. Finally, the required number of these equivalent temperature sensing nodes will be tasked to join the VSN, so that the service will continue to be provided to the end-user uninterrupted.