## 4 Research Problem and Hypotheses Definition  
This work is devoted to the performance characterization of various DTN CLA selections in a controlled simulation manner in typical primary and secondary cislunar relay communications architectures. We intend to find an answer to the following problem: Which configuration of DTN CLAs and cislunar relay path has the highest goodput in cislunar communications? To find an answer, we select protocol comparison pairs based on discussions with DTN protocol developers and run simulations for file transfer over both primary and secondary cislunar relay architectures. We then compare their performance. In comparison to TCP and UDP, which are mainly designed to operate over short-delay and less lossy links, the newly developed LTP targets long-haul links. Therefore, for all the protocol configurations in this work, BP/LTPCL is configured to run over UDP/IP/PPP (i.e., BP/LTPCL/UDP/IP/PPP) for file transfer over the long-delay cislunar links either from the Moon orbiter to the Earth ground station or from the Moon surface to the Earth orbiting satellite. In contrast, either BP/TCPCL/TCP/IP/PPP or BP/UDPCL/UDP/IP/PPP is adopted for the proximity links from the Moon surface to the Moon orbiter or from the Earth orbiter to the Earth ground station. Specifically, as illustrated in Figure 3, the file transfer simulations are run with four hybrids of DTN protocol configurations over two cislunar relay architectures (i.e., the primary (PRIM) and secondary (SEC) relay paths shown in Figure 1). Each of four configurations in Figure 3 is clarified below:  
* LTP LTP PRIM (or simply L_L_P) in Figure 3a--For this configuration, we conduct a DTN test over the PRIM relay path in Figure 1, with BP/LTPCL/UDP/IP/PPP running over both link segments from TX to MX (i.e., from Moon to its orbiter) and from MX to RX (i.e., from a Moon orbiter to Earth ground station), i.e., a single protocol stack, BP/LTPCL/UDP/IP/PPP, runs over both links of a typical primary relay path. * UDP LTP PRIM (or simply U_L_P) in Figure 3b--For this configuration, we conduct a DTN test over the PRIM relay path in Figure 1, with BP/UDPCL/UDP/IP/PPP running from TX to MX (i.e., from Moon to its orbiter) and BP/LTPCL/UDP/IP/PPP running from MX to RX (i.e., from a Moon orbiter to Earth ground station). * LTP UDP SEC (or simply L_U_S) in Figure 3c--For this configuration, we conduct a DTN test over the SEC relay path in Figure 1, with BP/LTPCL/UDP/IP/PPP running from TX to MX (i.e., from Moon to an Earth orbiter) and BP/UDPCL/UDP/IP/PPP running from MX to RX (i.e., from an Earth orbiter to Earth ground station). * LTP TCP SEC (or simply L_T_S) in Figure 3d--For this configuration, we conduct a DTN test over the SEC relay path in Figure 1, with BP/LTPCL/UDP/IP/PPP running from TX to MX (i.e., from Moon to an Earth orbiter) and BP/TCPCL/TCP/IP/PPP running from MX to RX (i.e., from an Earth orbiter to Earth ground station). A null hypotheses, \(H_{0}\), and an alternative hypotheses, \(H_{1}\), are created for each comparison pair for each channel condition of the BERs and link delays. The null hypothesis is that two configurations, when compared, do not have a significant goodput performance difference, while the alternative null hypothesis is that two configurations, when compared, have a significant goodput performance difference. Based on the protocol choices and communication relay architectures, the following comparison pairs and corresponding null hypotheses and alternative hypotheses are created:  
1. Comparison between LTP LTP PRIM and UDP LTP PRIM. \[H_{0}:\mu_{L\_P}=\mu_{L\_P}\quad\text{ versus }\quad H_{1}:\mu_{L\_L\_P}\
eq\mu_{U\_L\_P}\]
2. Comparison between LTP LTP PRIM and LTP TCP SEC. \[H_{0}:\mu_{L\_L\_P}=\mu_{L\_T\_S}\quad\text{ versus }\quad H_{1}:\mu_{L\_L\_P}\
eq\mu_{L\_T\_S}\]  
Figure 3: Comparison of simulated cisunar communication relay architecture and DTN protocol configurations. (**a**) LTP LTP PRIM. (**b**) UDP LTP PRIM. (**c**) LTP UDP SEC. (**d**) LTP TCP SEC.