## 7 Testbeds and Experimental Resources  
In the paradigm of wireless sensor networks, testbeds and experimentation, play a significant role in the successful deployment of the sensing network. Furthermore, testbeds allow testing of all the sensing and communicating aspects of the sensor networks in a realistic setup [141, 142]. Testbeds are crucial for debugging and evaluating middleware for wireless sensor networks. Testbeds play vital role in testing the behavior of embedded systems e.g., effect of temperature on sensor nodes is tested in [143]. There are number of tools that support testbed composition [142], like hardware devices provide the real evaluation of the system. However, the hardware costs and heterogeneity of testbeds formed are usually limited and provide less flexibility due to static configurations and small size. Moreover, for the IoE to be a reality we require large scale federated networks to be formed and tested. The hardware approach is usually limited to a single network and don't allow large federated networks to be tested and evaluated. The research community is working on the testbeds that allow large federated heterogeneous networks to be evaluated and tested. The easiest technique for evaluation of middleware for sensor network is a simulation; it speeds up the development process. Simulation provides flexibility in terms of radios, sensor nodes, heterogeneity, scalability, mobility, debugging facility, OS. Furthermore, it supports large scale federated networks to be easily tested. However, it lacks the conviction due to its inaccuracy and unrealistic approach. Therefore, this technique is limitedly used for planning and deployment middleware for WSNs and systems. There are two extremes in testing so WISEBED [141] came up with the concept of combining both the testing techniques: simulation and the hardware testbeds by virtualization of the testbeds. Furthermore, this concept provides flexibility and accuracy at the same time. Testbed virtualization can provide high efficiency in testing without hampering the realism of experiments. There are a number of testbeds for WSN that include SensLAB, moteLab, CitySense, Sensei and Wisebed having different approaches [144]. Few of the testbeds that allow evaluation of middleware based on virtualization are discussed as under. **WISEBED**[141] uses the concept of virtual testbed (VTB) that combines the physical and simulated sensor testbeds using overlay network technology that could be used to support different physical and simulated testbeds. VTB allows large federated networks to be tested with a fair amount of accuracy. VTB provides flexibility in connectivity between any physical, simulated or emulated sensor nodes through virtual links and virtual radios, it also supports virtual mobility [145]. WISEBED has come up with the middleware based on the web service called iWSN. Middleware supports multiple OS, simulators and provides a high level API for the application development. Furthermore, it also provides the software development kit (SDK) for the researchers around the globe to design, implement, develop and synthesize the algorithms on top of the VTB. Moreover, it supports multiple OS like TinyOS [146], iSense and Lorien [147]. VTB is specified through WiseML based on XML and WiseLib algorithm library for networked embedded devices. WISEBED contain a number of heterogeneous nodes that includes Pacemate, iSense, TelosB, Tmote, MicaZ, SunSPOT, TNode, Tmote Sk, MSB-A2 distributed around the globe [144,148]. There are a total of 9 geographical sites with 550 nodes [149]. **FlockLab**[150] testbed based on the physical sensor nodes, it overcomes this limitation of the previous test beds by allowing several services to run simultaneously on all nodes. Furthermore, FlockLab provides timing information in the low microsecond range that enables events to be correlated with power samples. FlockLab also achieves a better synchronization, allowing for a better alignment of power traces recorded at nodes.