# A Realistic, Flexible and Extendible Network Emulation Platform for Space Networks
## 5 Experiments and Discussion
### Ip Satellite Network Scenario  
#### 5.4.1 Experimental Scenario  
An IP satellite network scenario was designed and experiments were conducted to evaluate the performance of different network protocols. The experimental scenario, described in Figure 14, included a Ground Station (GS), 12 LEOs, and 6 GEOs. Satellite orbit parameters are listed in Tables 6 and 7 separately. Different right ascension of ascending nodes represented different satellite orbits, while distinct true anomalies refer to different initial positions of satellites in the same orbit. GEOs were evenly distributed in the geosynchronous orbit above the equator which constructed a backbone link for data transmission. LEOs served as remote sensing satellites [34] and were directly linked to GEOs. The GS located at 116.40 deg longitude and 39.90 deg latitude only communicated with GEO3. Figure 12: Experimental scenario. Figure 13: Bundle transfer from lander to MCC (Markers: from [33], star: emulation platform). \begin{table}
\begin{tabular}{c c} \hline \hline
**Orbit Parameter** & **Value** \\ \hline Period (s) & 5400 \\ Eccentricity & 0.0 \\ Orbital Inclination (deg) & 28.5 \\ Argument of Perigee (deg) & 0.0 \\ Right Ascension of the Ascending Node & 107.419/137.419/167.419/192.419/287.419/17.419 \\ True Anomaly (deg) & 0/60 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: LEO satellite orbit parameters and corresponding values. Figure 14: Topology of the IP satellite scenario. \begin{table}
\begin{tabular}{c c} \hline \hline
**Orbit Parameter** & **Value** \\ \hline Period (s) & 86,400 \\ Eccentricity & 0.0 \\ Orbital Inclination (deg) & 0.113287 \\ Argument of Perigee (deg) & 0.0 \\ Right Ascension of the Ascending Node (deg) & 90 \\ True Anomaly (deg) & 0/60/120/180/240/300 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: GEO satellite orbit parameters and corresponding values. and LEO2 or GS, the concrete topology is shown in Figure 15. LEO1 and LEO2 are initially connected to GEO1 and GEO2 separately, and access to each GEO is in a clockwise direction. Corresponding measurement results from 0 to 30 min are show in Figure 16.  
Figure 16a presents the bidirectional end-to-end delay between LEO1 and GS with or without deploying MIP. Because LEO1 moves from GEO1 to GEO3 during this period, the routing hops between LEO1 and GS are reduced. So the delay from LEO1 to GS is also reduced. However, owing to the home agent mechanism in MIP where all packets sent to LEO1 need to be forwarded by GEO1, the delay from GS to LEO1 is not changed. Referring to the scheme without deploying MIP, the communication between nodes is interrupted immediately when the access point is changed. Figure 16b describes the bidirectional end-to-end delay between LEO1 and LEO2 with or without deploying MIP. Even though LEO1 and LEO2 move in the same direction simultaneously, the delay between them is increased for the home agent mechanism. (2) Backup Routing and OSPF  
The routing convergence process, caused by links variation, makes OSPF routing unstable. In SN, the node mobility and the instability of channel quality cause the uncertain communication connections between nodes which further aggravate OSPF's shortcoming. Our lab proposes a OSPF-based backup routing. Compared with OSPF, except for the optimal path, backup routing saves a sub-optimal path. When links change and the optimal path cannot work, the sub-optimal path takes effect immediately. After the links are restored, backup routing switches to the optimal path again. This process omits the convergence process in OSPF and improves the stability of routing. To verify the performance of this routing strategy, OSPF and backup routing are deployed on GEOs respectively. The experimental scenario is presented in Figure 17. We choose the time period from 0 to 500 s. LEO1 is connected to GEO1, and GS is connected to GEO3 at the start. A 60 s interrupt is inserted between GEO2 and GEO3 every 60s, and repeats four times. Figure 16: Delay variation. Figure 15: Topology of the mobile IP scenario.