# Research on Communication Stability of Inter-Cannonball Network Based on OPNET
## 3 Routing Protocol Modelling Analysis
### Routing Protocol Comparison  
DSR is a network routing protocol based on the notion of source routing that is self-organizing. As a sort of on-demand routing, the DSR protocol does not need individual nodes to constantly maintain the whole network structure. When a source node delivers data, the message header will contain the source node's entire routing information to the destination node, and the data will be forwarded depending on this routing information. Two parts comprise the whole of the DSR networking procedure: route discovery and route maintenance [29].  
If the source node does not have a path to the destination node during the route discovery phase, the DSR protocol will enable a flooding mechanism to broadcast route request information (RREQ) to neighbouring nodes. Neighbouring nodes that receive the request will then broadcast it again, and so on, until a path to the destination node is discovered. When a destination node or an intermediary node having a path to the destination node is discovered, the node passes the route reply message (RREP) in the same manner in the opposite direction and returns the path information to the source node. The source node now has the entire route to the destination. If a link is broken during route maintenance, the intermediate node will send the source node a route error message (RER). The source node will examine its cache and use the remaining cached pathways or re-enable route discovery [30].  
DSR employs the notion of source routing to decrease the overhead associated with route finding and prevent routing loops. However, since each piece of data must contain the whole route information, this produces an increase in message overhead during transmission. AODV, on the other hand, communicates by constructing a dynamic routing table, which is maintained by each node [31]. Therefore, AODV is more efficient than DSR when the number of nodes is high and the network topology changes often. In Section 3.2, the AODV communication protocol will be detailed.  
Due to the large range of node movement and the high rate of node destruction in the inter-cannonball self-organizing network, the network topology is unstable; therefore, the effect of node failure rate communication stability must be studied. We build a communication network with 50 fixed nodes (speed is 0) and configure routing protocols as DSR and AODV, respectively. Four nodes are set to be damaged at 10 min and 20 min each, and four nodes to be restored at 30 min, for a total simulation time of 40 min.  
The simulation results for the average routing hops under the above conditions is shown in Figure 4. AODV has a lower number of routing hops compared to DSR, because it is more targeted to the destination node and only performs route search activities when data transmission is taking place. Therefore, the effectiveness of the search is increased.  
A comparison on the wireless LAN delay of AODV and DSR is shown in Figure 5. AODV completes information transfer through route request, route answer, and route delivery between nodes. Each node maintains its own routing information. The DSR protocol uses source routing and stores a large amount of routing information in the packet header, which causes a difference in their wireless LAN delay.  
Figure 4: Comparison of average routing hops for AODV and DSR routing protocol.  
The AODV routing protocol is more suitable for the inter-cannonball ad hoc network. It is scalable, does not require real-time maintenance, and can effectively avoid routing loops, which meets the needs of inter-cannonball ad hoc networks.