## 11 Hardware and Testbeds
### Testbeds  
To evaluate different protocols and algorithms pertaining for different networking layers (transport, network, MAC, or physical layer) of wireless multimedia sensor network or test various applications over the WMSN, researchers may perform analytical analysis, conduct experiments, or use simulations. Sometimes, analytical analysis neither gives an accurate model for such complicated wireless system nor truly depicts the behavior of real-time wireless networks. Also, in many cases, tests and experiments in wireless sensor network in general and in wireless multimedia sensor network in particular are somehow complex and time-consuming, and hard to be re-conducted by other researchers. For these reasons, simulation has been the preferred methodology for many researchers in the wireless multimedia sensor network domain. However, the existing simulators have many defects and are unable to model many critical characteristics of real-time wireless systems. Also, because of not following the scientific research standards in conducting of such simulation studies, simulation results are sometimes doubtful and have less credibility [111]. For these reasons and in order to minimize the differences in results between theoretical and practical approaches, which will significantly affect the behavior of real-time systems, testbeds have been increasingly used by the researchers and developers to evaluate their proposed algorithms and applications. WMSN testbeds are used for better understanding and satisfying the practical and technical challenges of networks deployed in real-time systems. While testbeds have become the preferred method for testing and evaluating with wireless multimedia sensor network applications, they also provide means for integrating several individual sensors on a common wireless platform in a controlled and instrumented environment. Thus, research on experimental testbeds with current hardware and software platforms, allows users not only to demonstrate applicability and evaluate application-level and network-level performance metrics (e.g., detection probability, end-to-end delay, jitter, quality of received multimedia streams, _etc._) in real environments, but also to validate research prototypes. Compared with conducting real-time experiments and field deployments, testbeds give considerable efficiency in testing potentially long-time experiments, which is important in debugging, validation, and integration phases of reliable wireless multimedia sensor networks. WMSN testbeds can be classified into two categories, _Software Testbeds_ and _Hardware Testbeds_. Table 6 illustrates the existing software and hardware testbeds found in the literature and summarizes their specifications and important features. To facilitate advanced research in wireless multimedia sensor network technology, software driver interfaces and libraries are designed to help researchers in testing and evaluating various algorithms and applications through using easy-to-use Application Program Interfaces (APIs) and functions. These APIs and functions provide testing environment through abstraction layers that hide the low-level details of the underlying hardware in order to enable easy and fast development of multimedia sensor network applications. WiSNAP [112] is a Matlab-based software testbed designed for wireless multimedia sensor networks, where the developers can test and evaluate algorithms and applications using its standardized and easy-to-use Application Program Interfaces (APIs). WiSNAP provides a Matlab framework as a high-level and powerful programming environment for implementing interfaces to the existing wireless motes and image sensors though simple easy-to-use functions and libraries. These functions and libraries hide the internal details of dealing with more or sensor specific interfaces from the end-users and provide the users with many powerful and rich image processing tools.