The main function of this middleware is to integrate wireless sensor networks into the enterprise networks. It connects the "sensor world" with the backend computing environment of the enterprise, thus making the field data collected by the sensors available to all applications in the same way as any other enterprise information. This can be achieved by using the sensor/telemetry integration capability of IBM WebSphere MQ Integrator (see Fig. 1), which is based on a publish/subscribe messaging model for distributing information to interested applications.

The publish/subscribe messaging model consists of a number of publishers and subscribers connected to a broker. Publishers send (publish) messages to the broker on a specific "topic" (similar to the subject of an e-mail). Subscribers register (subscribe) their interest in certain topics with the broker. The broker manages the connections to the publishers and subscribers and distributes the messages it receives from the publishers to the subscribers according to their subscribed topics. The broker can also perform certain message processing tasks. For example it can transform raw sensor data into an XML-formatted message, which is more useful to most enterprise applications. The Networking between publishers and subscribers is anonymous — they do not need to be known to each other. This decoupling makes the system future-proof, since the binding between information producers and information consumers is performed via the topics, and new applications with new combinations of topics can be added and deployed at any time.

Resource-constrained sensor gateways can use the WebSphere MQ Telemetry Transport (MQtt) protocol to communicate with the WebSphere MQ brokers. It is an open and lightweight publish/subscribe protocol designed specifically for remote telemetry applications and optimized for Networkings over low-bandwidth, high-cost networks. A Java implementation of the client side of the MQtt protocol can be downloaded from this location.

Another function of the middleware is to provide a platform for the deployment and maintenance of services and applications on networked devices. It supports the remote installation and update of software packages without interrupting the operation of the devices. Such a platform is specified by the OSGi Alliance, an independent worldwide organization founded in March of 1999 by IBM, Sun, Ericsson and Oracle. The OSGi architecture (see Fig. 2) is based on Java to ensure its independence from operating systems and processor architecture. It allows applications to share a single Java Virtual Machine (JVM), and can install, start, stop, update and uninstall applications on the fly without affecting the operation of other applications.

The Service Management Framework (SMF) is IBM’s implementation of the OSGi specification. It is optimized for embedded use to enable the deployment on resource-constrained sensor gateways.

At the IBM Zurich Research Laboratory, we have built a sensor network testbed to verify the integration capability of the IBM WebSphere MQ concept (see also the Advanced messaging technologies project). We connect a sensor gateway to a WebSphere broker using the MQtt protocol mentioned above to distribute sensor data to multiple applications. We also use the IBM SMF to remotely install and manage applications running on the gateway. The main aim is to evaluate the performance and scalability of the software components. Equally important is the use of the testbed as a reference design and demo platform for various customer engagements.