# A New Bit Repair Fast Reroute Mechanism for Smart Sensors IoT Network Infrastructure
## 3 The Proposal of the B-REP FRR Mechanism  
In this section, we provide a more detailed description of the B-REP mechanism operation principles. As mentioned before, the B-REP belongs to FRR mechanisms. However, it is designed to protect specific unicast flows delivered from customer devices or IoT sensors over the transport network. This network comprising the devices responsible for data delivery (i.e., layer 3 routers) is typically organized into administrative or policy areas or domains. For the proper operation of the B-REP mechanism, two new parameters and one mandatory condition are introduced. The first necessary parameter is the device or router identifier (ID). We require that each router in such a common network domain must have a unique identifier. This means that if a given router is assigned a certain ID, no other router can use it within the domain. Therefore, we propose a new router ID, which we will call the B-REP router-ID (B-REP R-ID). The R-ID is similar to, for example, the BFR-ID in BIER enabled networks [50] and is crucial for the proper operation of the B-REP. The assignment process is not precisely specified. B-REP R-ID can be set manually (preferred option) by the administrator for example, or it can be created and derived from another unique identifier that is already assigned to the router. The second parameter is the bit-string (B-S) that is the special variable length array where the B-REP IDs of B-REP enabled routers are defined. Thereby de facto the whole alternative transport path can be defined. Being able to do this, we finally assume, as a prerequisite for the proper functioning of B-REP, that some type of link-state (LS) routing protocol is enabled and is running in the transport network. Link-state routing protocols provide all area routers with accurate topological information about all other LS routers in the area and therefore allow B-REP to specify precise bit string parameter as a definition of alternative paths applicable to different failure scenarios. B-REP requires access to the LSDB database of the given LS protocol. The obtained data are then processed by B-REP and the Dijkstra algorithm is used to calculate the alternative route. Dijkstra can run as a specific low-priority process when the router's central processing unit (CPU) is idle. Therefore, the B-REP mechanism also calculates an alternative path during the CPU idle time. The alternative B-REP route is then stored in the B-REP backup path (B-REP BP) table (Table 2). Let us show the use of these parameters on the example of a network running the OSPF routing protocol (Figure 6). OSPF is a LS routing protocol. In OSPF all active routers must be assigned unique router-IDs (R-ID). OSPF R-ID can be set manually or automatically. In the case of automatic assignment, the OSPF R-ID is assigned based on one of the local IP addresses of the router. Therefore, as one of the alternatives, it allows setting the B-REP R-ID according to the OSPF R-ID, which perfectly meets the condition of uniqueness. The mapping process is not specified however there can be applied some kind of algorithmic mapping. An example of R-ID and corresponding B-REP ID mapping is illustrated in Table 3. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Protected Interface** & **Destination B-REP R-ID (OSPF Router ID)** & **Bit-String Value** \\ \hline Interface R1-R3 & 3 (3.3.3.3) &... 01110 (LSB) \\ Interface R1-R3 & 4 (4.4.4.4) &... 01010 (LSB) \\... &... &... \\ \hline \hline \end{tabular}
\end{table} 
Table 2: B-REP BP table. OSPF as an LS routing protocol that allows a router to obtain and maintain precise topological information about all other routers, their interconnections, and network links of the area. This information is identical on all routers, which store it locally in a database called the link-state database (LSDB) database.