QoS-aware MAC protocols for wireless sensor networks: A survey <s> Qos requirements <s> In future smart environments, wireless sensor networks will play a key role in sensing, collecting, and disseminating information about environmental phenomena. Sensing applications represent a new paradigm for network operation, one that has different goals from more traditional wireless networks. This paper examines this emerging field to classify wireless micro-sensor networks according to different communication functions, data delivery models, and network dynamics. This taxonomy will aid in defining appropriate communication infrastructures for different sensor network application sub-spaces, allowing network designers to choose the protocol architecture that best matches the goals of their application. In addition, this taxonomy will enable new sensor network models to be defined for use in further research in this area. <s> BIB001 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Qos requirements <s> In this paper, we assess the state of the art of Quality of Services (QoS) support in wireless sensor networks (WSNs). Unlike traditional end-to-end multimedia applications, many non-end-to-end mission-critical applications envisioned for WSNs have brought forward new QoS requirements on the network. Further, unique characteristics of WSNs, such as extremely resource-constrained sensors, large-scale random deployment, and novel data-centric communication protocols, pose unprecedented challenges in the area of QoS support in WSNs. Thus, we first review the techniques for QoS support in traditional networks, analyze new QoS requirements in WSNs from a wide variety of applications classified by data delivery models, and propose some non-end-to-end collective QoS parameters. Next, the challenges of QoS support in this new paradigm are presented. Finally, we comment on current research efforts and identify many exciting open issues in order to stimulate more research interest in this largely unexplored area. Keywords— Wireless networks, wireless sensor networks, QoS, collective QoS <s> BIB002
Although our focus is on network-specific QoS in WSNs, as we mentioned in Section 2.2, QoS requirements of different applications differ from each other. For instance, traditional low-rate data collection applications may tolerate delay and jitter but packet losses may be important for the application whereas high rate, real time applications, such as target tracking, require a bound on the maximum acceptable delay. Therefore, application requirements are also important for network-specific QoS. Rather than investigating the QoS requirements of every application in WSNs, it is a better approach to focus on the data delivery models that are used in different applications and map the requirements of these data collection models to a set of QoS metrics. This approach was also followed in BIB002 . Depending on the application requirements, there are three basic data delivery models: continuous, querydriven, and event-driven model BIB001 . In the following part, we discuss these models and their associated QoS requirements: 1. Event-driven: In this model, sensor nodes report data only if an event of interest occurs. Usually, the events are rare. Yet, when an event occurs, a burst of packets are often generated that need to be transported reliably, and usually in real-time, to a base station. The success of the network depends on the efficient detection and notification of the event that is of interest to the user. This is bound to quality and accuracy of the observation related to the observed phenomena with reliable and fast delivery of the information about the detected event. Since more than one sensor nodes will detect the event and generate related data, this type of applications are not end-to-end. Also creation of highly redundant and bursty traffic by sensors affected by the same event is very likely to be observed in eventdriven applications. Surveillance and target tracking can be an example for this class. 2. Query-driven: Query-driven data delivery model is very similar to the event-driven model with an exception: Data is pushed to the sink without any demand by the sensor nodes in event-driven model while data is requested by the sink and pushed by the sensor nodes in the query-driven model. Hence, contrary to the one-way traffic of event-driven model, two-way traffic comes into scene which consists of requests of the sink and replies of the sensor nodes. Both requests and replies must be delivered quickly and reliably for achieving higher performance in query-driven applications. Environmental control or habitat monitoring can be an example for this class. 3. Continuous: In this model, sensor nodes transmit the collected data at periodic intervals and can be considered as the basic model for traditional monitoring applications based on data collection. The data rates can be usually low and to save energy the radios can be turned on only during data transmissions if scalar data is collected. However, real-time data such as voice or image are delay-intolerant and requires a certain level of bandwidth. Also packet losses are tolerated in a limited threshold. For periodically collected non real-time data, latency and packet losses are tolerable. Surveillance or reconnaissance can be an example of this class. 4. Hybrid: If the mentioned data delivery models coexist in the same network, carried traffic must be classified and requirements of these traffic classes must be satisfied. A surveillance application that sends both periodic temperature and event-triggered video data is an example of the hybrid model.