Preliminaries

Integrated space and terrestrial networks (ISTN). Recent satellite operators/organizations are actively developing their mega-constellations [4,8,9,25,34,36], with hundreds to thousands of low earth orbit (LEO) satellites working together as a system. These satellites can be equipped with high-speed inter-satellite links (ISLs), and construct an LEO satellite network (LSN). An LSN can further be integrated into existing terrestrial Internet via globally distributed ground stations [3,26,39] and very-small-aperture terminals (VSAT) [31], constructing an integrated space and terrestrial network (ISTN) that promises to provide pervasive, low-latency, broadband Internet services [40,52,56,57] for terrestrial users globally.

集成空间与地面网络（ISTN）

近年来，主要卫星运营商及组织正积极推进由数百至数千颗低地球轨道（LEO）卫星构成的巨型星座系统建设[4,8,9,25,34,36]。这些卫星可搭载高速星间链路（ISL），构建低轨卫星网络（LSN）。通过全球部署的地面站[3,26,39]与甚小孔径终端（VSAT），LSN可进一步融入现有地面互联网，形成天地一体化网络（ISTN），旨在为全球地面用户提供泛在、低时延、宽带的互联网服务[40,52,56,57]。

Unique characteristics of ISTNs, as well as the new challenges. Two critical characteristics differentiate LSNs from existing terrestrial networks, and involve new challenges on the integration of satellites and terrestrial Internet. First, LEO satellites are moving at a high-speed with the respect to the earth surface. An LEO satellite might be visible for a certain ground vantage point only within a few minutes in one pass. Such high dynamics could inevitably result in technical challenges (e.g., frequent connectivity disruptions and routing re-convergence) at the networking stack of ISTNs. Second, while evolved, resources (e.g., bandwidth, CPU, energy) are still limited and costly in space, as compared with terrestrial network systems. Resource-intensive technologies might not be doable for resource-constrained satellites to sustain good network performance (e.g., applying sophisticated network coding techniques for packet recovery in remote space).

ISTN的独特性与新型挑战

LEO卫星网络相较地面网络具有两大显著特征，并衍生出天地融合的新挑战：

第一是动态性：LEO卫星相对于地表高速运动，单颗卫星对地面观测点的可见时间窗口通常仅有数分钟。这种高动态特性将引发网络协议栈的系列技术难题，例如频繁的连通性中断与路由重构问题。

第二是资源受限性：尽管技术持续演进，但相较于地面网络系统，卫星在带宽、计算、能源等资源方面仍显稀缺且成本高昂。资源密集型技术（如复杂网络编码技术在深空包恢复中的应用）可能因卫星资源限制而难以维持良好网络性能。

Note

LEO卫星网络相较地面网络具有两大显著特征:

1. 动态性: LEO卫星相对于地表高速运动
2. 资源受限性: 很多技术由于卫星资源限制而难以维持良好网络性能

Call for new research for futuristic ISTNs. The above characteristics and challenges accordingly raise a series of unexplored research problems in ISTNs, such as: (1) topology: how should LEO satellites and ground facilities be interconnected under the high space-ground dynamicity? (2) routing: how should we integrate hundreds or thousands of LEO satellites into Internet routing and tackle the potential performance degradation due to intermittent connectivity? (3) system effect: how much energy would a new functionality consume in space under various workloads? It is foreseeable that in the near future, in parallel with the evolution of real mega-constellations, there would be a surge of new research focusing on emerging satellite network systems. But, how should researchers test, assess and understand their new thoughts? The community requires a technically and economically feasible approach to construct Experimental Network Environments (ENE) and advance futuristic ISTN research.

面向未来ISTN的研究呼吁

上述特征与挑战催生了天地一体化网络中一系列亟待探索的研究方向，例如：

1. 拓扑架构：如何在天地高动态环境下实现LEO卫星与地面设施的互联配置？
2. 路由机制：如何将数千LEO卫星融入互联网路由体系，并缓解间歇性连通导致的性能劣化？
3. 系统效应：新型功能在多样化工作负载下将消耗多少星载能源？

随着现实巨型星座系统的演进，未来针对新兴卫星网络系统的研究必将蓬勃兴起。但研究者应如何验证、评估与理解创新方案？学界亟需构建技术可行、经济可负担的实验性网络环境（ENE），以此推进未来ISTN的前沿探索。