# A Stable Backup Routing Protocol for Wireless Ad Hoc Networks
## 3 Simulation and Analysis  
In this section, we perform a simulation experiment to compare the performance of the proposed SBR scheme with the previous work, AODV-SLR [30], using NS2-2.34. Through the analysis of Part I of the paper, the SBR algorithm proposed in this paper uses a similar way to AODV-SLR [30] to build backup routes. Meanwhile, algorithms that improve stability of the MANET involved in the literature [4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16] mainly focus on the routing protocol itself rather than backup routes. Therefore, we chose AODV-SLR algorithm as the comparison object of computer simulation. The AODV-SLR algorithm has the best comparability with the SBR presented in this paper. We integrate our SBR into AODV and DYMO, respectively, named as AODV-SBR and DYMO-SBR. In AODV-SBR, the main route discovery phase is fulfilled by AODV, whereas SBR takes responsibility for backup route construction and local link repairing. Similarly in DYMO-SBR, DYMO completes the main route building process using its path accumulation function. Actually, SBR can also cooperate with other QoS-guaranteed Ad hoc routing protocols, such as algorithms presented in [4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16], to further improve the network performance. The simulation parameters are shown in Table 1. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Value** & **Parameter** & **Value** \\ \hline Simulation time & 300 s & Simulation terrain & 1500 m \(\times\) 300 m \\ Number of nodes & 50 & Mobility model & Random waypoint \\ Speed & 0–20 m/s & Path loss model & Two-ray \\ Radio frequency & 2.4 GHz & Bandwidth & 2 MHz \\ MAC protocol & 802.11 & Transmission range & 250 m \\ Entry lifetime & 10 s & \(\mathrm{T_{th}}\) & 50 ms \\ Pause time & 0–300 s & CBR data rate & 2–10 packets/s \\ CBR data sessions & 0–20 & Packet size & 512 bytes \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Simulation parameters in the experiments. In our topology, each node randomly selects a position and moves toward that location with a random speed. Once it reaches that position, it becomes stationary for a predefined pause time. After that pause time, it selects another position and repeats the process. For each simulation, ten runs are carried out to obtain the average values of experiment results. The lifetime of all entries in the MAC cache and the accessing period \(\mathrm{P_{a}}\) are both set as 10 s. The duration \(\mathrm{T_{th}}\) that is used to wait for BRREPs is 50 ms. In the simulation, route performances are compared based on two scenarios: varying pause time from 0 to 300 s with CBR (Constant Bit Rate) = 4 packets/s and varying CBR data rate from 2 packets/s to 10 packets/s with pause time = 50 s. In practice, through the parameters set in Table 1 as well as the received/noise power from physical layer, the values of the BER and successful rates can be then calculated by (1) and (2). We use three metrics to evaluate the algorithm performance, i.e., packet delivery ratio, average delay and control overhead. Specifically, packet delivery ratio is defined as the ratio of the number of delivered data packets to the total number of data packets generated by sources. Average delay is the sum of time taken by successful transmissions from sources to destinations divided by the total number of data packets delivered. Control overhead is defined as the number of all control packets required divided by the number of data packets successfully received. Firstly, packet delivery ratio is compared by varying pause time and packet generation rate, respectively. From Figure 6a, it can be seen that AODV-SBR and DYMO-SBR outperform AODV-SLR especially when the topology changes frequently. If the topology is relatively stable, the frequency of link breaking is low and the performances of the three protocols are quite close. However, as pause time decreases, network topology changes more frequently, AODV-SLR does not guarantee packet delivery ratio any more.