# Enhanced Multicast Repair Fast Reroute Mechanism for Smart Sensors IoT and Network Infrastructure
## 3 Related Works  
In the IoT area, several existing solutions dealing with rerouting have been proposed. In paper [36], a new approach of jamming attack tolerant routing using multiple paths based on zones is presented. The proposed scheme in that paper separates the system network into specific number of zones and directs the candidate forward nodes of neighbor zones. After detecting a specific attack, detour nodes in the network determine zones for rerouting and detour packets destined for victim nodes through forward nodes in the decided zones.  
In work [37], the authors present a detailed review of IoT sensing applications in WSN and the difficulties and challenges that need to be overcome. Some of these challenges are fault tolerance, the effectiveness of the energy harvesting, communication interference, cost feasibility, and an appropriate integration of these elements.  
At present, there are many unicast IPFRR mechanisms that differ in the way that alternative routes are calculated. Three of the most common and widely used IPFRR mechanisms are the Equal-Cost Multi-Path (ECMP) [30; 31], Loop Free Alternates (LFA) [24; 31; 38] and its extended version, Remote LFA (RLEA) [39; 30].  
The LFA mechanism calculates alternative routes based on conditions that consider metrics for each next-hop router. These conditions ensure that if a packet is redirected to this alternate next-hop router (that has met the conditions), the router delivers the packet to the destination over a longer path that is still loop-free and bypasses the network failure. The Remote LFA is an improved version of the original LFA. The idea of Remote LFA is to use a tunneling mechanism from the source router S to the remote LFA router. The tunnel is used to bypass the part of the network that, in the event of an error, would route packets (not tunneled) from the affected site back to the source router S or would forward them through a failed link or router. The RLFA router may be a few hops away from the source router S.  
Other mechanisms, although less common, are Multiple Routing Configurations (MRC) [11; 30; 40; 41; 42; 43; 44] and Not-Via Addresses [35; 45]. Furthermore, there are tunneling-based mechanisms, such as Maximally Redundant Trees (MRT) [46; 47], and, finally, IPFRR mechanisms based on alternative trees [22; 48; 49; 50]. IPFRR mechanisms such as Not-Via Addresses, Multiple Routing Configurations and Maximally Redundant Trees can provide protection that is close to 100% of repair coverage [26; 51]. The main challenge of these IPFRR mechanisms is the complexity of internal algorithms that calculate alternate paths.  
There is also another FRR group of mechanisms that focus on the protection of multicast communication [52; 53]. In general, these solutions utilize precomputed multicast disjoint trees. Examples of these mechanisms are Multicast Only Fast Re-Route (MoFRR) [54] and Bit Index Explicit Replication-Traffic Engineering (BIER-TE) [51; 55].  
We have been analyzing and researching FRR mechanisms for several years [56; 57; 21; 58; 59; 60; 61]. Based on the obtained results, we can summarize the most significant properties of the existing FRR mechanisms in Table 1.