## 5 Insights and Future Directions
### Guidelines for Energy, QoS, Security and Related Areas of Routing in WSNs
* Employing security along with routing requires additional energy, storage and processing capability. Security mechanisms may induce processing delays and bandwidth loss in WSNs which may seriously impact QoS-routing in WSNs. Therefore it is desirable to write such routing surveys that may highlight the issues, applications and comparisons of security and QoS [130] oriented routing in WSNs. Such surveys may discuss state-of-the-art secure-QoS routing approaches and highlight future research directions in this regards. * Secure routing improves reliability of both static and dynamic WSNs. Since traditional cryptography and network security techniques are infeasible for secure routing in WSNs, therefore there is a need to analyze and survey novel featherweight multi-factor authentication and authorization approaches and security mechanism in WSNs. * Although it is more energy efficient to-process than to-transmit the same amount of data [155], however it is also a fact that data fusion complicates secure-routing design [35], introduces delay [49] and compromises reliability [49]. Therefore, there is a need to extensive survey the issues, challenges and comparisons of data fusion and secure-QoS oriented routing in WSNs. * Since, single-sink oriented routing techniques under-perform than multi-sink based routing approaches [84], therefore there is a need to in-depth survey those routing techniques that implement multi-sink approach in WSNs. The advantages of multi-sink oriented routing may be further highlighted under energy, security, QoS and scalability constraints for achieving high performance in WSNs. * The computational intelligence based routing approaches such as biologically inspired (e.g., ant based, bee based, particle swarm, termite colony and spider monkey based optimization), machine learning, genetic algorithm, fuzzy logic, evolutionary computing, reinforcement learning and artificial neural networks should be reviewed in more depth. From the recent past, the researchers have started applying these techniques for routing in WSNs and they have exhibited promising results. However, there is a need to survey various aspects of these techniques more deeply for achieving further technological advancements in WSNs. * The multichannel routing approach may allow sensor nodes to use a variety of orthogonal channels for sending data to destination. It may ensure parallel communications [156], decreases delay [156; 157] and increases throughput [156; 157] in WSNs. However, it requires additional resources in the form channel scanning, channel decision and channel switching, etc. which may require additional energy for providing the desired QoS in WSNs. Only one multichannel routing survey [114] is published so far for WSNs that may put forth a novel taxonomy for classifying and analyzing the single/multi-path and single/multi-radio multichannel routing protocols in WSNs into JOINT and DISJOINT categories. Although the survey brings forth the applications, prevailing issues and future research challenges of multichannel routing in WSNs in a detailed manner, however still there many dimensions in which novel multichannel routing surveys can be written e.g., one of such dimension is the mobile multi-radio multichannel routing in WSNs where to the best of our knowledge no multichannel survey is written so far. Additionally, the pros and cons of multichannel routing protocols may be critically surveyed in-terms of energy-efficiency and QoS using various analytical and simulating mechanisms for unveiling further hidden aspects of this area of research.