# Analysis of the Most Relevant Factors for Routing in Internet of Space Things Networks
## 3 Methodology
### Factors Considered in the Analysis of Routing Strategies for Ad Hoc IoT Networks  
The efficiency of routing algorithms for ad hoc networks can be assessed by measuring their performance related to their efficiency in establishing and maintaining routes. There are different factors that can affect routing protocol performance, such as active or reactive routing approach, node density, node behavior, etc. Specifically, the factors considered for our analysis of the routing task in ad hoc IoT networking are described next:  
1. _Routing scheme_: Selecting the routing approach is not trivial, as the participant nodes' characteristics and network topology changes must be considered [67; 68]. The two main approaches are reactive and proactive, with AODV and OLSR being the most representative protocols, respectively.
2. _Density_: A low number of participating nodes (low density) in the network reduces contention. However, this also reduces the route establishment options. Therefore, the number of nodes in the network (density) is a relevant factor in the proposed analysis. As previously explained, densities of 20 and 240 nodes were considered for our analysis.
3. _Node behavior_: In ad hoc IoT networks, satellites could eventually avoid participation because of events such as low energy or primary mission priorities. Therefore, it is essential to research the impact of node availability to partake in routine tasks. In particular, we studied the impact of having 20% of satellites in a group unable to participate in networking tasks.
4. _Hello message period (HMP)_: Hello messages are broadcast packets used by routing protocols to periodically share control information with other nodes, such as geographic location, number of neighbors, and battery level. The nodes use this information to update neighbors and routing tables and perform actions related to the particular routing strategy implemented. Neighborhood information reliability is directly related to HMP [69]. However, there is a trade-off between node information reliability and the overhead caused by the periodic messages. Considering the relevance of Hello messages, this work included HMP as a relevant factor in the 2k factorial analysis.
5. _Neighbor's refresh time (NRT)_: Each node maintains a neighbors table to store the routes previously found and their on-hop neighbors. Note that the age of the information in the neighbors table represents the freshness of the routing information. This work defines the NRT as the time a node is stored in the neighbors table after the last update. A short NRT allows the routing protocol to achieve early detection of broken links. However, packet loss because of interference or propagation issues could occur. Thus, a short NRT could unnecessarily trigger repair mechanisms with the consequent waste of resources. Therefore, it was relevant to analyze the impact of varying the NRT on routing performance.
6. _Number of retransmissions_: Packet retransmission is a simple and efficient strategy to cope with errors at the MAC and PHY layers. However, this mechanism can lead to increased network overhead. As retransmissions could delay the route discovery process when the network topology changes, this was a factor considered in the analysis.  
Considering the number of parameters for 2k factorial analysis, the number of satellite groups generated, the number of trial repetitions per parameter and group combinations, and the different routing approaches studied, the total number of simulations performed for the analysis presented in this work is given by (1)  
\[\text{Total\_number\_of\_Simulations}=2^{5}\times 30\times 10\times 2=19,200 \tag{1}\]