# Time Slotted Channel Hopping and ContikiMAC for IPv6 Multicast-Enabled Wireless Sensor Networks
## 2 Related Work  
Multicast is an advantageous communication means in WSANs. An important number of papers describe the implementation of new multicast protocols. At least three other recent papers have analyzed BMRF, the network layer protocol we used in this research. In [3], the authors proposed a new RPL-based protocol with a new objective function for unicast forwarding and an enhanced BMRF (EBMRF) version for LL broadcast forwarding. This new version added redundant paths for multicast packet delivery while reducing the occurrence of duplicates by introducing a unique identifier (ID) in each multicast packet. They used LL unicast forwarding only when the packet received by a node does not come from the preferred parent. They compared EBMRF with Stateless Multicast RPL Forwarding (SMRF) and BMRF only considering BMRF's broadcast mode. Neither BMRF's unicast and mixed mode nor the influence of the MAC layer were part of their study. In [4], the authors proposed a new multicast protocol, the Reliable and secure Multicast routing protocol for Internet of Things networks (REMI). This protocol's functioning was based on clusters built on top of the destination-oriented directed acyclic graph (DODAG) formed by RPL. The cluster heads were chosen from the set of children of the DODAG root and behaved similarly to a root node. LL broadcast was used for both upward and downward communication. REMI organized duplicate avoidance for unicast messages and multi-directional forwarding. The protocol's performance was compared against SMRF and BMRF. The clustering mechanism improved robustness. The disadvantages of this new protocol were related to energy and memory consumption. The Robust multicast communication protocol for low power and lossy networks (RECOUP) [5] is another protocol based on BMRF that addressed some of its disadvantages using a similar clustering mechanism to that REMI. The cost for improving end-to-end delay and robustness was reflected in energy and memory consumption. In both papers, the authors analyzed ContikiMAC-based networks, but they did not refer to the particularities of this RDC protocol. None of the above-mentioned protocols used the threshold in BMRF that allowed for the nodes to switch from the LL unicast mode to the LL broadcast mode, depending on the node's number of interested children and the network's requirements. None of these papers discussed the interaction between BMRF and the MAC layer. The authors of [6] proposed a Bidirectional Multicast Forwarding Algorithm (BMFA) for RPL-based IPv6 low-power wireless personal area networks (6 LoWPANs). The authors stressed the importance and advantages of multicast transmissions in networks where P2 MP communication is widely used. Multicast can reduce bandwidth utilization, improve energy consumption, and improve scalability. BMFA improves the SMRF protocol and allows for both upward and downward traffic. To support bi-directional traffic, BMFA uses RPL's group membership scheme and 20 flow label bits of the IPv6 header. BMFA was implemented in Contiki, and it was compared with Trickle Multicast (TM), the default multicast algorithm in Contiki. Network delay and energy consumption were used to compare these two algorithms. After conducting several simulations, the authors concluded that their new algorithm, BMFA, outperformed TM in terms of end-to-end delay, design complexity, and energy consumption, with reduced reliability as a drawback. A new RPL-based multicast routing mechanism for wireless sensor networks was proposed in [7]. The authors developed the proactive multicast forwarding with RPL (PMFR) protocol, which includes the wireless shortest path heuristic (W-SPH), specifically designed to build a multicast tree and increase the reliability of multicast packet transmission. To achieve this, they modified the destination advertisement object (DAO) control message by adding the DAO metric container option, which carries information about the cost to the root. As routing metric, they chose the expected transmission count (ETX).