Introduction

Thanks to the resurgence in the space industry [41, 46, 48], big competitors such as SpaceX and Amazon are actively planning and deploying hundreds or even thousands of broad-band satellites in low earth orbits (LEO). Such emerging mega-constellations (e.g., Starlink [34], Kuiper [9]) can be integrated into existing terrestrial Internet, i.e., constructing an integrated space and terrestrial network (ISTN) to:

(1) provide pervasive last-mile network access;

(2) enable low-latency and high-bandwidth Internet transit [40, 52, 56];

and (3) facilitate efficient acquisition and delivery for big data from space (e.g., earth observation images) [44, 74, 77, 78].

得益于航天产业的复兴 [41, 46, 48]，像SpaceX和Amazon这样的主要竞争者正积极规划并部署数百甚至数千颗低地轨道（LEO）宽带卫星。这些新兴的巨型星座（例如Starlink [34]、Kuiper [9]）可以与现有的地面互联网网络集成，即构建一个综合的空间与地面网络（ISTN），以实现：（1）提供普及的最后一公里网络接入；（2）实现低延迟和高带宽的互联网传输 [40, 52, 56]；（3）促进大数据从太空的高效获取与传输（例如地球观测图像） [44, 74, 77, 78]。

While holding great promise, several unique characteristics of LEO satellites (e.g., high LEO dynamics) impose new challenges at various layers of the ISTN networking stack, and open a door to many new research problems, such as: (1) how should LEO satellites and ground facilities be interconnected to provide low-latency and continuous network services? (2) how should satellite routers be integrated into existing terrestrial Internet routing? and (3) are current constellation and protocol designs resilient enough to satellite failures in complex and harsh space environments? With many unexplored problems facing the “NewSpace” industry, it is thus foreseen that in the near future, there will be a surge of new ideas on the system and networking research relevant to ISTNs. But, how can researchers build an experimental network environment (ENE) to test, evaluate and understand their new thoughts?

尽管低地轨道（LEO）卫星具有巨大的潜力，但其独特的特性（例如高动态的LEO轨道）在ISTN网络栈的各个层面上带来了新的挑战，并为许多新的研究问题开辟了空间，例如：

（1）LEO卫星与地面设施应如何互联，以提供低延迟和持续的网络服务？

（2）卫星路由器应如何与现有的地面互联网路由系统进行集成？

（3）当前的星座和协议设计是否足够稳健，能够应对复杂和恶劣太空环境下的卫星故障？

随着“新航天”（NewSpace）产业面临诸多尚未解决的问题，预计在不久的将来，将会涌现出大量关于ISTN相关系统和网络研究的新思路。那么，研究人员如何构建一个实验性网络环境（ENE）来测试、评估并理解他们的新想法呢？

Typically, existing approaches for creating an ENE can be classified into three categories:

(1) live networks or platforms [7, 20, 34, 75, 81], which allow experiments in real deployments;

(2) network simulation [60,61,76], which uses discrete events to model and replicate the behavior of a real network;

and (3) network emulation [6, 55, 68, 69], which can test real applications/protocols in a virtual network.

However, as will be illustrated in §3, all existing approaches have their limitations in creating a desired ENE for ISTNs:

(1) the feasibility and flexibility of live satellite networks are technically and economically limited for normal researchers;

(2) the abstraction level of simulation might be too high to capture low-level system effects, hiding practical issues such as the resource competition under heavy workload, energy drain or software errors;

(3) existing emulators fail to characterize the high dynamicity of LEO satellites and thus are insufficient to build an experimental environment with acceptable fidelity.

现有的创建实验性网络环境（ENE）的方法通常可以分为三类：

（1）实时网络或平台 [7, 20, 34, 75, 81]，允许在实际部署中进行实验；

（2）网络仿真 [60, 61, 76]，通过离散事件来模拟和复制实际网络的行为；

（3）网络仿真器 [6, 55, 68, 69]，能够在虚拟网络中测试真实的应用程序和协议。

然而，正如§3中所述，所有现有方法在为ISTN创建所需的实验性网络环境方面都有其局限性：

（1）实时卫星网络的可行性和灵活性在技术和经济上对普通研究人员具有一定限制；

（2）仿真方法的抽象层次可能过高，无法捕捉低层次系统效应，隐藏了诸如重负载下的资源竞争、能量消耗或软件错误等实际问题；

（3）现有的仿真器无法表征LEO卫星的高动态性，因此不足以构建具有足够保真度的实验环境。

The key challenge of building an expected ENE for ISTN research is: it is difficult to simultaneously achieve realism and flexibility in the experimental environment. First, terrestrial devices inherently lack the ability to reasonably mimic the high dynamics, system and network behaviors of realistic satellites. Second, mega-constellations typically consist of thousands of satellites. Thus the network scale required by an ENE for mega-constellations might be far more than the extent supported by existing ENE methods (e.g., [54,55,69]). Third, as a large number of satellites simultaneously move at a high velocity, continuously mimicking such frequent variations at scale could involve significant system overhead on the ENE.

构建一个期望的ISTN研究实验性网络环境（ENE）的关键挑战在于：很难在实验环境中同时实现真实感和灵活性。

首先，地面设备本身缺乏合理模拟现实卫星的高动态性、系统和网络行为的能力。

其次，巨型星座通常由数千颗卫星组成。因此，针对巨型星座所需的网络规模，可能远远超过现有ENE方法所能支持的范围（例如 [54, 55, 69]）。

第三，由于大量卫星同时以高速度移动，持续在大规模上模拟这种频繁变化可能会给ENE带来显著的系统开销。

This paper presents STARRY NET, an integrated experimentation framework that empowers researchers to conveniently build ENEs with acceptable realism, flexibility and cost (e.g., requiring only a few number of local/cloud machines) to satisfy various experimental requirements of ISTNs. The design of STARRY NET is inspired by a key insight obtained from the satellite Internet ecosystem: many organizations or communities in this ecosystem have released and shared their constellation-relevant data, including regulatory information [2,73], satellite trajectories [16,38], ground station distribution [26,39] and measurements from user terminals [32,33], etc. Therefore, the key idea behind STARRY NET is to build an experimental digital twin, i.e., a virtual presentation of a physical ISTN, in terrestrial environments by:

(1) leveraging terrestrial machines to virtualize a large number of lightweight virtual nodes to emulate satellites in mega-constellations; and

(2) exploiting a crowdsourcing approach to collect, combine and use realistic constellation information to drive the emulation of spatial and temporal characteristics of ISTNs.

本文提出了STARRY NET，一个集成的实验框架，旨在帮助研究人员便捷地构建具有可接受真实感、灵活性和成本效益（例如，仅需少量本地/云端机器）的实验性网络环境（ENE），以满足ISTN的各种实验需求。

STARRY NET的设计灵感来源于从卫星互联网生态系统中获得的一个关键洞见：该生态系统中的许多组织或社区已经发布并共享了与星座相关的数据，包括监管信息 [2,73]、卫星轨迹 [16,38]、地面站分布 [26,39] 和用户终端的测量数据 [32,33] 等。

因此，STARRY NET的核心思想是通过以下方式， 在地面环境中构建一个实验性的数字孪生，即物理ISTN的虚拟呈现 ：

（1）利用地面机器虚拟化大量轻量级虚拟节点，以模拟巨型星座中的卫星；

（2）利用众包方法收集、整合并使用现实的星座信息，驱动ISTN空间和时间特性仿真。

Note

说白了，就是把当前卫星的情况“高保真”地映射到地面系统

在地面系统使用虚拟节点等方式构建模拟器，同时利用各种开源社区平台提供的实时数据进行仿真

To achieve acceptable realism, STARRY NET employs a constellation synchronizer based on realistic constellation-relevant information to make the virtual ENE as consistent as possible to a real ISTN, such as:

(1) constellation consistency: the ENE is built with the same scale of a physical mega-constellation, where each node emulates a satellite, a ground station or a terrestrial host. The spatial and temporal characteristics, such as time-varying satellite locations and inter-visibility, are also configured and updated in each node based on our data-driven model-based analysis;

(2) system and networking stack consistency: the ENE can support the run of unmodified applications as in real deployments;

and (3) capability consistency: network and computation capabilities in the ENE are configured based on real hardware specifications.

Further, to flexibly support various ISTN experiments and mimic large-scale and highly-dynamic mega-constellations, STARRY NET adopts a constellation orchestrator that judiciously schedules and manages system resources on multiple machines to collaboratively construct ENE on demand.

为了实现可接受的真实感，STARRY NET采用了基于真实星座相关信息的星座同步器（constellation synchronizer），以使虚拟的实验性网络环境（ENE）尽可能与真实的ISTN保持一致，具体包括：

(1) 星座一致性（constellation consistency）：ENE按物理巨型星座的规模构建，每个节点分别模拟卫星、地面站或地面主机。空间和时间特性（例如随时间变化的卫星位置和可视性）均基于数据驱动的模型分析，在各节点中进行配置和更新；

(2) 系统和网络栈一致性（system and networking stack consistency）：ENE能够支持未经修改的应用程序运行，如同在真实部署环境中一样；

(3) 能力一致性（capability consistency）：ENE中的网络和计算能力依据真实硬件规格进行配置。

此外，为了灵活支持多种ISTN实验，并模拟大规模、高动态的巨型星座，STARRY NET采用星座编排器（constellation orchestrator），通过智能调度和管理多台机器上的系统资源，按需协同构建ENE。

Note

想起上面提到的“高保真”，这该如何实现呢？

我们采用:

1. 星座同步器 (constellation sync): 使虚拟的实验性网络环境（ENE）尽可能与真实的ISTN保持一致
2. 星座编排器 (constellation orch): 智能调度和管理多台机器上的系统资源，协同构建ENE

We evaluate the ability of STARRY NET based on real constellation information in two steps. First, we show the acceptable fidelity of STARRY NET by comparing the experiment results obtained by STARRY NET with live satellite networks and other state-of-the-art ISTN simulators. Second, facing futuristic ISTN scenarios, we demonstrate STARRY NET’s flexibility by conducting three case studies to:

(1) explore the tradespace of various space-ground inter-networking mechanisms;

(2) evaluate the resilience of routing protocols in various constellation designs; and (3) perform hardware-in-the-loop tests to measure system effects under various workloads.

我们通过两步评估STARRY NET基于真实星座信息的能力。首先，通过将STARRY NET获得的实验结果与实时卫星网络及其他最先进的ISTN仿真器的结果进行对比，展示STARRY NET的可接受的保真度。其次，面向未来的ISTN场景，我们通过进行三个案例研究来展示STARRY NET的灵活性，具体包括：

（1）探索不同的空间与地面互联机制的权衡空间；

（2）评估不同星座设计下路由协议的韧性；以及

（3）进行硬件在环测试，以测量不同负载下的系统效应。

Summarily, this paper makes the following key contributions: (1) we design STARRY NET, a data-driven, emulationaided ISTN experimentation framework (§4); (2) we implement STARRY NET with a collection of open APIs for creating and manipulating user-defined ENEs (§5); (3) we evaluate and analyze STARRY NET’s experimentation overhead and fidelity (§6), and show STARRY NET’s flexibility (§7) by conducting various case studies driven by realistic constellation information. STARRY NET is now available at: https://github.com/SpaceNetLab/StarryNet.

总之，本文做出了以下关键贡献：

（1）我们设计了STARRY NET，一个数据驱动、仿真辅助的ISTN实验框架（§4）；

（2）我们实现了STARRY NET，并提供了一组开放的API，用于创建和操作用户定义的实验性网络环境（ENE）（§5）；

（3）我们评估并分析了STARRY NET的实验开销和保真度（§6），

并通过进行多个基于真实星座信息驱动的案例研究，展示了STARRY NET的灵活性（§7）。

STARRY NET现已开放，地址为：https://github.com/SpaceNetLab/StarryNet