## 1 Introduction
### Routing in WMSNs  
Routing in Wireless Multimedia Sensor Networks (WMSNs) is very challenging due to several characteristics and constraints that distinguish them from contemporary communication and traditional wireless sensor networks [1; 2]. _For example_, classical IP-based routing protocols cannot be applied to WMSNs to build a global addressing scheme for a network of large number of sensor nodes. _Also_, sensor nodes are tightly constrained in terms of available energy, processing power, available bandwidth and storage capacity and thus require careful resource management. _Moreover_, the multimedia nature of the collected information in WMSN (video streaming, audio, and still images) adds more constraints on the design of the routing protocols in order to meet the application-specific QoS requirements and network conditions, and in consequence makes the proposed routing protocols for WSNs not directly applicable for WMSNs. _In addition_, the use of densely deployed sensor nodes provides significant redundancy in the collected sensor data, e.g., overlapping of FoVs (Field of Views) of two camera sensors located in the same cluster. In that case, the two cameras may collectively fuse their information to obtain a lower bandwidth aggregated result, which is then routed (and possibly fused with other sensor node readings along the way or within the cluster) to a cluster head or the sink. Therefore, such redundancy needs to be exploited by the routing protocols to improve energy and bandwidth utilization and for more accurate and robust observation results through effective data fusion and aggregation. Handling multimedia content in WMSNs produces many traffic classes and they can be categorized into three main classes or services depending on their QoS requirements: (1) Event-driven service which is delay intolerant and error intolerant but it requires less bandwidth, so a path with a little traffic and high signal to noise ratio is attractive for this kind of service. (2) Data query service is error intolerant but query-specific delay tolerant applications, so a path with significant congestion and a high signal to noise ratio may be used for this service. (3) Stream query service which is delay intolerant but query-specific error tolerant application (in a sense packet losses can be tolerated to a certain extent), so a path with less traffic and relatively lower signal to noise ratio is better for this type of service. Due to the above mentioned challenges and differences, new routing protocols have been proposed for WMSNs [1] that try to handle these new characteristics of WMSN and its design challenges by either modifying the previous work done in WSNs (e.g., using multiple performance metrics to meet the additional QoS requirements), or proposing new solutions based on new methodologies (e.g., usingmulti radio or MIMO systems, switching between multiple channels, selecting multi routing paths, or mixing among these methods). For WMSNs, cluster-based network architecture deployed with heterogeneous sensor nodes has more advantages than a flat network of homogeneous nodes. A single-tier flat architecture can cause the sink to overload with the increase in sensors density, which can affect the performance of the network and cause latency in communication and tracking events. Also, in the homogeneous flat network, all the nodes should have the same hardware capabilities and functionalities for multimedia processing and transmission, and this leads to increase the energy consumption and the cost of the deployed network. Therefore in this paper, cluster-based with multi-path routing protocol has been pursued in our proposal to allow the network to cover a large area of interest and cope with additional load without degrading the quality of service.