# Enhanced Multicast Repair Fast Reroute Mechanism for Smart Sensors IoT and Network Infrastructure
## 7 Conclusions  
The paper presents the Enhanced Multicast Repair (EM-REP) FRR mechanism, which solves several limitations of the legacy M-REP FRR mechanism. This means mainly support for fast reroute in the event of continuous link and node failures throughout the whole network and that the destination host does not have to be directly connected to a network with a router that performs decapsulation, which also reduces a flooding process of M-REP packets in a network with multiple routing areas. Both mechanisms belong to the family of Fast Reroute solutions. The EM-REP mechanism presented in this paper, makes it possible to create an alternate backup path that allows packets to bypass the failures of one or more links or nodes at a given time. To achieve this goal, the EM-REP has been built on two cornerstones, the PIM-DM protocol and tunneling. The PIM-DM delivers multicast data thorough a distribution tree constructed by the flooding and reverse pruning. The EM-REP is based on this behavior, where in the event of a failure (or even multiple failures), for specific traffic flow an alternate path is built by PIM-DM flooding and pruning. In this case, the router begins encapsulating unicast packets of the protected flow into multicast packets flooded out and around the failure. To ensure correct operation of routers, we have not modified the PIM-DM process as such, i.e., for a common multicast traffic the PIM-DM process works as usual. However, for the correct construction of alternative FRR paths (distribution trees), we have modified the PIM-DM RPF process, where we use the rule of the first arrival. Alternative paths are created only for protected flows, so the router must identify correct packets in some way. In short, we expect that flow identifiers are predefined and preconfigured by the network administrator in advance. However, in future, some dynamic distribution mechanism may be used, inspired, for example, by those used for a dynamic distribution of Rendezvous Point (RP) addresses (Auto-RP, BSR Bootstrap Router mechanism), but here used for the distribution of protected flow identifiers. As has been already mentioned, most FRR mechanisms require the pre-calculation of alternative routes for different network failure scenarios. On the one hand, these preparatory calculations have undesirable effects on the router's limited resources, such as CPU load and memory. On the other hand, they may depend on a specific link-state routing protocol. The EM-REP mechanism does not require any preparatory calculations, which is effective for IoT devices such as sensors. Moreover, the EM-REP does not depend on any unicast routing protocol. In addition, although EM-REP can bring benefits resulting from the use of a specific routing protocol supporting the organization of unicast routing to areas, as is presented here for OSPF, it could work for IS-IS as well. Furthermore, the EM-REP FRR mechanism provides 100% repair coverage for single as well as multiple failures occurring at different times and places in the network. Finally, EM-REP eliminates the condition of directly connected destination to router D of legacy M-REP. The EM-REP mechanism uses the generic flooding process of the PIM-DM protocol to provide the protection for specific flows that expect special handling inside the network. The behavior and goal are generic enough with a wider application domain. In the area of WSN and the IoT, it can be used to distribute, for example, urgent messages across the WSN network or to assure the time-critical delivery of important information from sensors to gateways or behind to analytic servers. The EM-REP was fully implemented, and its correctness was tested using the OMNeT++ simulator. We have performed extensive tests of the implementation in different networking scenarios, which validated the functional correctness of all the mechanism functions.