## 5 Conclusions  
WMSNs are the driving force behind many multimedia applications in the age of Internet of things (IoT) thanks to their ability to produce multimedia surveillance data including image, video, and streaming media. Over the years, the research community has made much progress toward the proliferation of WMSNs. Nonetheless, challenges still exist due to the resource constraints and the unique characteristics of WMSNs. In this paper, we not only outline the characteristics of WMSNs, but at the same time we identify the respectively enforced requirements and for each specific requirement we sum up the existing solution approaches. In doing so, we also formally introduce many definitions of the requirements and solution approaches, e.g., intrinsic camera calibration and extrinsic camera calibration. Our work is also the first to provide an all-including big picture of WMSNs by presenting it as an inter-connected unibody. We believe such an illustration will act as the bond among policy makers, network planners, and researchers and therefore foster interdisciplinary cooperations and accelerate the advance of WMSNs. Moreover, we survey MAC protocols and routing protocols which are two major classes of communication protocols for data communication and QoS provision. Specifically, energy efficient MAC protocols with prioritization and service differentiation properties are our focus. We find that hybrid protocols of CSMA/CA and TDMA might hold the key for MAC in WMSNs, since they enable switching in between CSMA/CA for lower data rate communication to avoid channel under utilization and TDMA for high data rate communication to reduce collision and improve throughput. In terms of routing, we center around disjoint multipath routing protocols. To disseminate large amount of multimedia data across the network, we believe disjoint and interference aware multipath routing protocol is necessary as it is able to realize higher aggregated bandwidth with multiple concurrent paths. Although the existing multipath routing protocols mainly focus on load balancing and energy efficiency while most lack when it comes to QoS provisions. In the meantime, it is worth pointing out that under current literature, both MAC protocols and multipath routing protocols largely fail to consider the existence of camera sensors and the nature of multimedia data, which we argue should be the future focus of designing communication protocols for WMSNs.  
**Author Contributions:** Conceptualization, S.L. and J.G.K.; Methodology, S.L. and J.G.K.; Software, S.L.; Validation, S.L. and J.G.K.; Investigation, S.L. and J.G.K.; Resources, D.H.H. and K.S.L.; Writing-Original Draft Preparation, S.L.; Writing-Review & Editing, S.L. and J.G.K.; Visualization, S.L.; Supervision, J.G.K.; Project Administration, K.S.L.; Funding Acquisition, D.H.H. and K.S.L.  
**Funding:** This research was supported by the IITP (Institute for Information & communications Technology Promotion) grant funded by the Korea government MSIT (Ministry of Science and ICT) support programme No.2017-0-00824 (Development of Intelligent and Hybrid OCC-LiFi Systems for Next Generation Optical Wireless Communications). This research was also supported by the MSIP (Ministry of Science, ICT and Future Planning), Korea, under the ITRC (Information Technology Research Center) support programme (IITP-2018-2016-0-00291 supervised by the IITP (Institute for Information & communications Technology Promotion).  
**Conflicts of Interest:** The authors declare no conflict of interest.