# A Realistic, Flexible and Extendible Network Emulation Platform for Space Networks
## 2 Related Work
### Space Network Experimental Validation Approaches  
Typical network experimental validation approaches include simulation, a live testbed, and emulation. Discrete-event network simulation has enough flexibility, e.g., ns-2 [15] and OPNET [16]. However, the network simulation has no real network traffic and is hard to realize the real description of complex SN equipment and its environment through the abstraction of various environmental parameters. An actual hardware-based testbed has the highest emulation authenticity, e.g., ORBIT [17], UMassieselNet [18]. However, for the high cost and poor extendibility of SN nodes, it is difficult for the testbed to support the requirements of changeable SN emulation scenarios.  
Compared with network simulation and the live testbed, network emulation is a hybrid approach which balances authenticity and flexibility. Typical emulators are Mininet [19], vEmulab [20], and NEAaS [21]. However, these emulation options only support the emulation of static terrestrial networks rather than dynamic SN. Ref. [22] proposes TUNIE which is capable of simulating reliable DTN environments and obtaining an accurate system performance evaluation. Ref. [23] presents a state-of-the-art DTN testbed for satellite and space communications. The core of the testbed relies on the Bundle Protocol and its architecture have been designed to support multiple DTN implementations and a variety of underlying and overlying protocols. Based on OpenStack, Ref. [2] proposes a large-scale, real-time and distributed emulation platform for DTN, namely EmuStack. These platforms are designed for some types of network architecture, such as DTN, and lack support for others. Ref. [1] designs a network protocol validation testbed for integrated space-terrestrial network. However, large-scale scenarios emulated on the testbed is realized by the expansion of routing table, which lacks enough authenticity. As shown in Table 1, comparisons among different SN emulation systems are listed. Overall, in consideration of authenticity, flexibility and extendibility, all the emulators above focus on limited aspects.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Literature** & \begin{tabular}{c} **Dynamic** \\ **Topology** \\ **Connection** \\ \end{tabular} & \begin{tabular}{c} **Dynamic Link** \\ **Characteristics** \\ \end{tabular} & \begin{tabular}{c} **Protocol** \\ **Architecture** \\ \end{tabular} & \begin{tabular}{c} **Supported** \\ **Various** \\ **Scenarios** \\ \end{tabular} & \begin{tabular}{c} **Supported** \\ **Scalability** \\ \end{tabular} & \begin{tabular}{c} **Construction** \\ **Cost** \\ \end{tabular} \\ \hline NPVT & yes & yes & TCP/IP, CCSDS & yes & yes & low \\ \hline EmuStack & yes & no & DTN & yes & yes & low \\ \hline VITT & - & - & \begin{tabular}{c} different TCP \\ variants \\ \end{tabular} & - & yes & low \\ \hline SCNT & no & no & BP, TCP/IP & no & \begin{tabular}{c} Limited \\ scalability \\ \end{tabular} & low \\ \hline TUNIE [22] & yes & yes & \begin{tabular}{c} DTN, other new \\ routing \\ protocols and \\ applications \\ \end{tabular} & yes & yes & low \\ \hline SPICE [23] & no & - & CCSDS, DTN & yes & yes & high \\ \hline SCT [24] & yes & yes & \begin{tabular}{c} CCSDS, \\ TCP/IP \\ \end{tabular} & yes & - & high \\ \hline TATPA [25] & - & - & \
\begin{tabular}{c} different TCP \\ variants \\ \end{tabular} & - & yes & low \\ \hline MACHETE [26] & - & - &
\begin{tabular}{c} CCSDS, DTN, \\ TCP/IP \\ \end{tabular} & yes & - & low \\ \hline DEN & - & yes & BSP, BP, LTP & no & yes & low \\ \hline \hline \end{tabular}
\end{table}
Table 1: Comparisons among existing space network emulation systems.