  Wireless sensor networks (WSNs) have become pervasive and are used in many
applications and services. Usually the deployments of WSNs are task oriented
and domain specific; thereby precluding re-use when other applications and
services are contemplated. This inevitably leads to the proliferation of
redundant WSN deployments. Virtualization is a technology that can aid in
tackling this issue, as it enables the sharing of resources/infrastructure by
multiple independent entities. In this paper we critically review the state of
the art and propose a novel architecture for WSN virtualization. The proposed
architecture has four layers (physical layer, virtual sensor layer, virtual
sensor access layer and overlay layer) and relies on the constrained
application protocol (CoAP). We illustrate its potential by using it in a
scenario where a single WSN is shared by multiple applications; one of which is
a fire monitoring application. We present the proof-of-concept prototype we
have built along with the performance measurements, and discuss future research
directions.
