# Time Slotted Channel Hopping and ContikiMAC for IPv6 Multicast-Enabled Wireless Sensor Networks
## 7 Conclusions  
In this paper, the influence of the MAC/RDC protocol on the performance of IPv6 multicast-enabled WSNs was studied. We analyzed the default RDC of Contiki3.x (Contiki-MAC) and the default RDC of Contiki-NG (TSCH), as well as how the link layer broadcast and unicast forwarding of the IPv6 multicast packets behaved in terms of PDR, delay, and energy consumption.  
In terms of PDR, for ContikiMAC and TSCH, LL unicast outperformed LL broadcast. This was mainly due to the LL unicast retransmission mechanism. We demonstrated that setting the number of retransmissions to zero notably decreased the PDR for the LL unicast. We also showed that on topologies with an increased level of interference, TSCH outperformed ContikiMAC regarding PDR.  
In terms of delay, for topologies with low interference, BMRF in the unicast mode with ContikiMAC outperformed BMRF in the unicast mode with TSCH since the time between two wakeups in ContikiMAC was lower than the time between available slots in TSCH. However, after increasing the interference between nodes, TSCH with our custom settings became the better protocol because most transmissions were done on different channels and, therefore, the level of interference in the network had no effect on the delay. In terms  
Figure 17: Energy comparison between LL unicast and LL broadcast and between ContikiMAC and TSCH on topologies with a random placement of nodes. (**a**) Results for LL unicast in BMRF over TSCH. (**b**) Results for LL broadcast in BMRF over TSCH. (**c**) Results for LL unicast in BMRF over ContikiMAC. (**d**) Results for LL broadcast in BMRF over ContikiMAC.  
of delay, BMRF in the broadcast mode on top of TSCH as found to be the preferred solution for topologies with the random placement of nodes and a lot of interference.  
The energy needed to operate TSCH without sending packets was higher than the energy needed for ContikiMAC, since a slot in TSCH resulted in a much longer wake-up time than a clear channel assessment (CCA) from ContikiMAC. However, as found to be the preferred protocol when there is a lot of traffic, mainly because of the scheduling mechanism. This mechanism reduces interference, which saves energy.  
Future work on BMRF and how it operates on top of TSCH should consider the implementation of an entirely new scheduler. The scheduler should be efficient for both LL unicast and LL broadcast transmission. Moreover, it should adapt to highly dynamic and scalable networks. Clear guidelines and mathematical models should help determine the value for the threshold that enables the switch between LL unicast and LL broadcast in the case of the BMRF mixed mode.  
In general, we conclude that TSCH and multicast forwarding have a lot of potential but might need some more improvements to become the best solution available for all situations.  
Conceptualization, E.T.; software, S.T., D.D., and M.C.; validation, K.S. and A.B.; formal analysis, E.T.; investigation, E.T., D.D., and M.C.; resources, E.T.; data curation, E.T., D.D. and S.T.; writing--original draft preparation, D.D.; writing--review and editing, K.S., A.B., and V.D.; revision, D.D.; supervision, K.S. and V.D.; project administration, K.S and A.B.; funding acquisition, A.B. and K.S., E.T. and D.D. contributed equally to this work as first authors. All authors have read and agreed to the published version of the manuscript.  
This research was partially funded by Vlaio (Flanders Innovation and Entrepreneurship) OpenCloudEdge project, HBC.2019.2017.  
Not applicable.  
The data that support the findings of this study are available from the corresponding author, D.D., upon reasonable request.  
This research has been supported by the Agency for Innovation by Science and Technology in Flanders (IWT).  
The authors declare no conflict of interest.