# A Realistic, Flexible and Extendible Network Emulation Platform for Space Networks
## 1 Introduction  
With the proliferation of low cost spatial information systems, powerful on-board processing capacity, and mature inter-satellite link techniques, space networks (SN) are emerging as an important part of the national infrastructure and research frontier. However, due to some unique characteristics of SN, e.g., long propagation delay, frequent link disruption, etc., mature terrestrial networking technologies cannot be applied to SN directly. To tackle this problem, network researchers propose various new network protocols and technologies. Meanwhile, the process of designing and developing network protocols and technologies is complex, in which the experiment phase plays an important role to decipher the performance and make helpful suggestions for improvement. So it is urgent to set up a testbed to carry out the research on basic theory and key technologies for SN. Network emulation provides manageable and reproducible environments for deploying real applications and communicating practical data flow. However, owing to the particularity of the SN communication environment, existing emulation methods find it difficult to balance the authenticity, flexibility and extendibility of the emulation, some lack enough authenticity, such as NPVT [1], some lack flexibility and are only designed for a specific protocol system, such as EmuStack [2], VITT [3], or only support some specific network topologies, such as DEN [4], and some do not have extendibility and can only emulate small-scale scenes, such as SCNT [5]. Therefore, the challenge in the research on SN emulation methods is to realize the reliable emulation of dynamic network topology, time-varying link characteristics, multiple protocol architectures and large-scale network scenarios with the goal of authenticity, flexibility and extendibility. This paper aims to present an SN emulation platform. When we design this platform, following goals are taken in mind:  
* Authenticity. (a) Network nodes in the platform have the same functionality as real hardware and execute exactly the same code. (b) The network of the platform can change automatically as does the real space communication environment. * Extendibility. (a) The platform should have an extensible structure used to support computing resource expansion. (b) The platform should provide access interfaces for external physical devices to fulfil the special needs of researchers. * Flexibility. (a) The platform should be agile enough to create any target networks, and deploy various network protocols and upper application software conveniently. (b) Experiments conducted on the platform could follow a workflow. For the same experiment, any researcher can obtain identical results in the same manner. To meet our goals, an SN emulation architecture, which consists of a logical plane, control plane, data plane, and a measurement plane, is proposed. On the basis of the emulation architecture, the SN emulation platform is constructed in a hierarchical star structure to support hardware resource expansion and access external physical devices. Integrating with software-defined networking (SDN) and a traffic control mechanism, the platform supports the emulation of dynamic SN. Combining with container technology, various SN protocols and communication technologies could be implemented on the platform flexibly as real deployments. Considering changeable simulation scenarios and different network concerns, the flexible configuration of network measurement on demand is realized. Furthermore, the verification and analysis workflow of SN technologies based on the platform are given. The structure of the paper is presented as follows. Section 2 provides an overview of related work. Section 3 describes the architecture of the emulation platform and the physical implementation model. According to different emulation elements, the design of this architecture is presented in Section 4. Section 5 includes the proposed experiments, experimental results and discussion.