# Performance and Challenges of Service-Oriented Architecture for Wireless Sensor Networks
## 1 Introduction  
Increased use of Wireless Sensor Networks (WSNs) in numerous surveillance, healthcare, and industrial applications calls for more reliability in the transmitted data [1]. Sensor nodes associated with WSNs communicate with each other wirelessly by using different protocols and algorithms. Reliable and efficient communication between sensor nodes transmitting important data remains a major challenge in next generation WSNs [2]. Sensor nodes have several limitations such as security, data aggregation, high-level programming, localization, middleware requirements, Quality of Service (QoS), heterogeneity of the sensors' networks, and power consumption. There is a tremendous need to integrate an innovative middleware design based on Service-Oriented Architecture (SOA) with WSNs to address the challenges associated with their reliability and efficiency. Middleware is implemented as a web service or an interface that connects with client applications. The purpose of middleware is to control sensor data, deal with a sensor node request, and provide temporary data storage for the current sensor data [3]. Middleware controls and monitors sensor data by using intelligent mechanisms to determine when and how to query and access data that comes from sensor nodes. In some cases, the communication method between the sensor nodes needs to update and obtain a new measurement of data. The intelligent technique in middleware provides an efficient process to transmit sensor data with minimum power usage. The middleware provides a model referred to as a virtual machine with two different layers called the cluster layer and theresources management layer [4]. The cluster layer forms the cluster of sensor nodes located close to the target events. It is the responsibility of the management layer to adapt and distribute the resources required by particular applications such as security, QoS, and reliability [4]. SOA is a software design that allows communication between the hardware and applications through a secure protocol independent of the product and technologies. The communications that occur over a SOA are loosely coupled and allow for functional modifications and upgrades depending on the business needs [5]. SOA is used in a variety of industrial, military, and smart home applications. Most applications require real-time monitoring with high accuracy and reliability as applied in the European Research(EU) project called Service-Oriented Cross-layer infrastructure for Distributed smart Embedded devices (SOCRADES) for WSN systems on factory automations in industrial applications [6]. The most common applications used in smart homes are based on the concept of home energy management systems. These systems are based on one universal internet that results in a reduction of development time and cost. An example of this can be seen in the development of a peer energy cloud for monitor energy consumption through unique platforms. This platform has the capability to hide itself from the applications and allow sensors to individually measure the energy consumption for all devices [7]. Another study attempts to reduce energy in smart homes do so by using energy distributed system [8]. Similar system applied in smart homes and industrial facilities is a Distributed Operating System based on SOA (DOS-SOA) [9] and optimal control of a legacy power grid by using WSNs [10]. The SOA-DOS manages all embedded devices at a high-level of interoperability in the network [9]. The SOA is also applied in military and civil domains due to its flexibility and the interoperability of services. However, in a tactical domain like military networks, the services are mostly constrained with limited bandwidth and unreliable radio networks. This challenge is addressed by Wireless Broadband Mobile Networks (WBMNs) [11]. Moreover, SOA is integrated with WSNs for Intelligent Transportation Systems (ITS), obtaining the best results for safety and security in ITS applications. This system has modules for monitoring, management, and the user (client).