# Performance and Challenges of Service-Oriented Architecture for Wireless Sensor Networks
## 6 Service-Oriented Middleware (SOM) Architectures Approaches for WSNs
### Other SOM Architectures for WSNs  
The implementation of SOM architecture is based on Devices Profile for Web Services (DPWS) architecture that contains new layers [14]. The SOM architecture provides a mechanism that mediates data exchange between a web service and the heterogeneous sensors [14]. The limitation of resource  
Figure 10: SOA-based Patient Monitoring System [41]. Figure 9: ESOA Architecture [54]. constraints in WSNs are addressed by using optimization mechanisms that can reduce the overhead required through using traditional WS. The energy-aware mechanism is important for extending the network lifetime. This architecture focuses on sensor nodes that impose restrictions on the resources and data aggregation. Also, SOA controls the energy consumption of each sensor by reducing transmission messages to the base station using multi-hop communication. DPWS used inside the middleware has various new components that include binary encoding, WS-eventing, and a roaming manager. The binary encoding mechanism is used instead of an XML message to reduce the overhead generated by XML. Before messages are transmitted between the layers, they should be encoded in a binary format. WS-eventing removes the requirement for necessary periodic call services and the user can subscribe to the interface of service eventing [14]. Also, WS-eventing has the ability to report to clients that a change in the data occurred. This method helps save the limited network bandwidth [14]. This approach lacks the mechanisms that can handle interaction with different components. Another SOM architecture approach to consider is called the Service-Oriented Wireless Platform for Acquisition and Control (SOWPAC) [55]. SOWPAC is introduced in [55] as a design with an open interface to have an efficient and cost-effective deployment. Most of the platform studies focus on the industrial acquisition and control of using WSNs, which are considered only at the network, node, or data abstraction level. This consideration lacks a holistic point of view, which can limit the use of these approaches [55]. The middleware API is used to manage data, facilitate communications, and define the processes of data exchanged between functional blocks. The SOWPAC consists of a basic element called Remote Terminal Units (RTU), which is responsible for remote sensing and actuation. The WSN-gateway is used as an intermediate element to send data from the RTU to the Central Control Point (CCP) through the WSN. The internal database in an RTU [55] can store sensing data and has the capability to recover from any failure of communication and reset the entire network. The Central Control Point (CCP) provides a user interface and application programming to manage platforms, data, and services. It also offers a Service-Oriented Protocol based on SensorML that provides an easy way to integrate a web service with high-level applications. The WSN-gateway is responsible for translating data and meta-data [55]. In addition to an Open Framework Middleware (OFM), [56] introduced a comprehensive framework designed a middleware architecture for WSNs. OFM architecture consists of a protocol stack which has some limitations, such as overhead and load on execution. The Hybrid Native Architecture (HNA) [56] addresses the drawbacks of the OFM by removing the stack-based protocol layers. It runs the Service-Oriented OFM Micro-Middleware through the device abstraction level [56]. The solution of HNA lies within system distribution services and the management of node operations which can interact with low level resources. In order to solve the above-mentioned issues, HNA should collaborate with OFM functionality to improve WSNs. Therefore, OFM-HNA enables access to available resources in the nodes through implementing a standard abstraction system that does not require access to the device. The OFM-HNA approach provides flexibility, adaptability, and reliability with control of the WSN by using models.