Survey of QoS routing protocols in Wireless Multimedia Sensor Networks <s> Cross-Layer Functionality. <s> The recent technological advances in micro electro-mechanical systems have promoted the development of a powerful class of sensor-based distributed intelligent systems capable of ubiquitously retrieving multimedia information, namely Wireless Multimedia Sensor Networks (WMSNs). WMSNs are gaining more popularity day by day as they are envisioned to support a large number of both non-real time and real-time multimedia applications. However, satisfying the stringent quality of service (QoS) requirements of multimedia transmission in a resource-constrained sensor network environment places new challenges to routing. As an outcome, optimal energy and application-specific QoS aware routing for WMSNs has gained considerable research attention recently. In this paper, current state-of-the-art in energy-efficient routing techniques for WMSNs is surveyed together with the highlights of the performance issues of each strategy. We outline the design challenges of routing protocols for WMSNs followed by the limitations of current techniques designed for non-multimedia data transmission. Further, a classification of recent routing protocols for WMSNs and a discussion of possible future research trends are presented. <s> BIB001 </s> Survey of QoS routing protocols in Wireless Multimedia Sensor Networks <s> Cross-Layer Functionality. <s> Wireless Sensor Networks (WSNs) have enjoyed dramatic developments over the last decade. The availability of CMOS cameras and microphones enlarged the scope of WSNs paving the way to the development of Wireless Multimedia Sensor Networks (WMSN). Among the envisaged WMSN applications, Real-time Multimedia Monitoring constitutes one of the most promising. However, the resource requirements of these applications place difficult challenges in terms of network lifetime and scalability. This paper starts by identifying the main characteristics and requirements of Real-time Multimedia Monitoring applications and then highlights key research directions that may help to overcome those challenges. <s> BIB002 </s> Survey of QoS routing protocols in Wireless Multimedia Sensor Networks <s> Cross-Layer Functionality. <s> The emergence of wireless multimedia sensor networks (WMSN) has given birth to several civilian as well as defense applications. Some of the interesting applications employing low cost sensor nodes to manipulate rich multimedia content include traffic monitoring, border surveillance, smart homes, environment and habitat monitoring. Unlike the traditional sensor networks which are aimed at maximizing network lifetime by decreasing energy utilization, the main objective of WMSNs is optimized delivery of multimedia content along with energy efficiency. Multimedia communications in WMSNs, has stringent delay and high bandwidth requirement as compared to scalar data transfer in WSNs. Fulfilling these constraints in resource and energy constrained WMSNs is a huge challenge. In WMSNs, each layer of the protocol stack is responsible and fully involved in providing QoS guarantees. There is a need for new schemes at each layer of the protocol stack- from advanced coding techniques that reduce encoder complexity and achieve maximum compression to dynamic routing and MAC protocols that provide service differentiation and reduce end-to-end latency. In wireless sensor networks, where all layers have dependency on each other, QoS guarantees are possible through the cross layer interaction of different layers. This paper gives an overview of the different existing layered schemes in WMSNs, followed by a discussion on the significance and efficiency gains that can be achieved from cross layer interactions in WMSNs along with the review of the existing cross layer approaches. Finally, we identify the open research issues which have not been adequately addressed so far. <s> BIB003 </s> Survey of QoS routing protocols in Wireless Multimedia Sensor Networks <s> Cross-Layer Functionality. <s> Multimedia applications are gradually becoming an essential--and flourishing--part of our daily lives. The area of wireless sensor networks is not an exception to this trend, as multimedia data have attracted the attention of researchers. Their importance is due to the shift of focus from traditional scalar sensors to sensors equipped with multimedia devices, as well as to the next-generation wireless multimedia sensor networks (WMSNs). The highly sensitive nature of multimedia traffic makes data routing with security even more important in WMSNs. This paper discusses the challenges of secure routing in WMSNs, where most of the proposed works in the literature deal with routing and security as individual issues. A critical and comprehensive review of state-of-the-art routing and security approaches for WMSNs is presented, followed by the discussion of their limitations and features. It is hoped that this extensive review and discussion ultimately identifies the future research directions and the open challenges of secure routing approaches in WMSNs. <s> BIB004
In traditional layered approach functionalities and services are divided among layers. Each layer allows interaction or procedure calls between adjacent layers, but it does not allow interaction between nonadjacent layers. As shown in Figure 4 (a), each layer works independently, with no sharing of QoS requirements with nonadjacent layers. However, error-prone nature of wireless channel and other factors make the layered approach unsuitable for optimizing overall WMSNs performance. The crosslayer approach shown in Figure 4 (b) allows the exchange of information across multiple layers to support optimal performance. It appears to be the most practical approach for guaranteeing QoS in WMSNs. Although little work is performed, the cross-layer approach provides a potential direction for research in WMSNs BIB001 BIB004 BIB003 BIB002 . To guarantee QoS new protocols can be designed to integrate a minimum of two layers, for example, a combination of the network layer and the transport layer, a combination of the network layer and the data link layer, and a combination of the data link layer and the physical layer as shown in Figure 4 (c). Furthermore, one can even explore possibility of integrating three or more layers. In addition, a cross-layer framework for WMSNs can be developed by considering service differentiation, admission control awareness, and rate adaption along with QoS routing BIB003 .