Towards a Computing Platform for the LEO Edge Tobias Pfandzelter Jonathan Hasenburg David Bermbach TU Berlin & ECDF TU Berlin & ECDF TU Berlin & ECDF Mobile Cloud Computing Mobile Cloud Computing Mobile Cloud Computing Berlin, Germany Berlin, Germany Berlin, Germany [email protected] [email protected] [email protected] ABSTRACT satellite access networks can be a viable option for connecting all The new space race is heating up as private companies such as kinds of edge devices, even if terrestrial access is readily available. SpaceX and Amazon are building large satellite constellations in High-bandwidth, low-latency connections to client ground stations low-earth orbit (LEO) to provide global broadband internet access. and via inter-satellite links (ISL) enable direct low-latency routing As the number of subscribers connected to this access network between any two ground stations; thus, many argue that satellite grows, it becomes necessary to investigate if and how edge com- Internet will see broad adoption in the future [5, 7, 12]. puting concepts can be applied to LEO satellite networks. Still, sending data from all end devices to a centralized location In this paper, we discuss the unique characteristics of the LEO for processing can put a substantial strain on the satellite network. edge and analyze the suitability of three organization paradigms for Especially for applications that transfer large amounts of data or applications considering developer requirements. We conclude that require low latency event processing, this can quickly become a the serverless approach is the most promising solution, opening up problem [25]. The same issue applies to terrestrial networks for the field for future research. which edge computing, a computing paradigm that uses compute resources at the edge of the network in direct proximity to end CCS CONCEPTS users and devices, has been proposed as a promising solution [3, 9]. Applications can use these resources through edge platforms that • Computer systems organization ! Heterogeneous (hybrid) abstract from the geo-distributed server deployment and resource systems; Distributed architectures; • Networks ! Cloud comput- heterogeneity. These platforms are based on different organiza- ing. tion paradigms for applications (OPA), e.g., VMs, containers, or KEYWORDS serverless functions. Only recently, it has been proposed to also use computing re- satellite internet, LEO constellations, edge computing sources at the LEO edge to facilitate novel applications serving a ACM Reference Format: global user base [6]. To realize this vision, however, edge platforms Tobias Pfandzelter, Jonathan Hasenburg, and David Bermbach. 2021. To- must consider the unique characteristics of the LEO edge while still wards a Computing Platform for the LEO Edge. In 4th International Work- satisfying general requirements of application developers. As a first shop on Edge Systems, Analytics and Networking (EdgeSys ’21), April 26, step towards this goal, we must consider the core of such a platform, 2021, Online, United Kingdom. ACM, New York, NY, USA, 6 pages. https: the OPA, and analyze different options in light of the challenges at //doi.org/10.1145/3434770.3459736 the LEO edge. We therefore make the following contributions: 1 INTRODUCTION (1) We discuss the unique characteristics of the LEO edge (Sec- tion 3). Private Internet and aerospace companies are currently building (2) We derive requirements for building LEO edge applications the largest satellite constellations in existence: SpaceX, Amazon, from a developer perspective (Section 4). and Telesat – the so-called “New Space” companies – are deploy- (3) We analyze the suitability of three OPAs with regards to how ing or planning to launch tens of thousands of satellites into low they might satisfy developer requirements considering LEO Earth orbit (LEO) to provide global high-speed Internet access from arXiv:2104.02396v1 [cs.DC] 6 Apr 2021 edge characteristics (Section 5). space [28]. SpaceX’s Starlink constellation has already entered a public beta phase for subscribers in North America and the United 2 BACKGROUND & RELATED WORK Kingdom with more than 1,500 satellites in use [32]. Beyond enabling Internet access for underserved regions such In this section, we briefly introduce and describe the state of the art as rural areas, planes, or cargo and passenger ships, these new for large LEO satellite communication networks, edge computing, and OPAs. Furthermore, we also provide an overview of existing Permission to make digital or hard copies of all or part of this work for personal or LEO edge computing research. classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than the 2.1 LEO Communication Networks author(s) must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission Satellite-backed Internet access has been available for decades with and/or a fee. Request permissions from [email protected]. geostationary satellites at altitudes of 35,000km. The high altitude EdgeSys ’21, April 26, 2021, Online, United Kingdom combined with the requirement to orbit above the equator, however, © 2021 Copyright held by the owner/author(s). Publication rights licensed to ACM. ACM ISBN 978-1-4503-8291-5/21/04...$15.00 result in high access latency for consumers which renders satellite https://doi.org/10.1145/3434770.3459736 Internet inviable for many use cases [10, 17]. EdgeSys ’21, April 26, 2021, Online, United Kingdom Tobias Pfandzelter, Jonathan Hasenburg, and David Bermbach app app app app app app app runtime runtime runtime runtime runtime runtime OS OS OS OS OS VM VM H/W H/W H/W H/W (1) no sharing (2) virtual machines (3) containers (4) serverless Figure 2: OPAs by levels of abstraction [16]: while less ab- straction offers more freedom and flexibility, more abstrac- tion simplifies writing applications and shifts execution control to the platform which often increases efficiency. between ground stations and satellites. These factors mean that any change to the constellations requires a substantial lead time [5, 31]. Figure 1: Overview of a LEO satellite constellation compris- ing different shells. Shown here is the proposed first phase 2.2 Edge Computing of the Starlink deployment with five shells of 1,584 satellites The demand for processing data close to its origin led to an in- at 550km, 1,600 at 1110km, 400 at 1130km, 375 at 1275km, creased popularity of the edge computing paradigm in research and 450 at 1325km altitude [20]. and industry [3, 9]. The main idea behind edge computing is to embed computing resources into the edge of the network, i.e., close to clients. Compared to cloud computing, resources are thus avail- Now, a new generation of Internet satellites is being developed able with low latency and bandwidth costs. Preventing data from by companies such as SpaceX, Amazon, and Telesat. Thousands of being transmitted to the cloud can also reduce privacy and security these satellites are being deployed in large constellations at altitudes risks [24]. of below 600km, i.e., in the LEO. Thus, satellites continuously orbit Typically, edge computing infrastructures comprise a multitude the globe and cover large ground distances in short periods of time. of geo-distributed nodes with different compute, storage, and net- Each satellite is equipped with radio transmitters and receivers to work capabilities. Using such a heterogeneous infrastructure is connect to ground stations. As ground station equipment is small significantly more difficult than the ease-of-adoption developers enough for use in family homes or airplanes, each satellite serves are used to from the cloud: Applications need to consider geo- many user terminals concurrently [5, 7, 12, 13]. distribution, horizontal scalability, and network availability for fully A complete LEO satellite constellation comprises different shells leveraging edge resources. To remedy this, a number of edge com- of satellites. Each shell is a collection of orbital planes with the puting platforms have been proposed to abstract from the underly- same orbital parameters equally distributed across the earth, with ing infrastructure. To this end, they employ service offloading tech- each plane comprising a number of equally spaced satellites. We niques, data geo-replication, or resource sharing [3, 14, 15, 27, 29]. show such a constellation in Figure 1. Edge computing platforms are usually developed around a spe- Given the low altitude, a single satellite has a relatively small cific OPA. In Figure 2, we show that the three main paradigms cone of coverage yet it must be connected to some form of uplink that have initially evolved in the context of cloud computing offer to provide Internet access. If no ground station uplink is available, different levels of abstractions. e.g., because a satellite currently crosses an ocean, satellites may Virtual Machines. Virtual machines (VM) are virtualized servers connect to adjacent satellites via ISLs. This way, satellites can ac- that run operating systems which have often been slightly modified quire Internet access even if no ground station is within their field for VM usage to increase performance. Multiple virtual machines of view. Satellites also use ISLs for providing low latency broadband can share a common physical machine, hence a single server can access since light propagates faster in a vacuum than in fiber. This be made to look like many smaller machines. VMs can be used just makes satellite based Internet an attractive alternative for many like regular servers and host long-running applications, often with Internet subscribers [5, 11, 21]. multiple connected services sharing a virtual host [9]. A main driver of the “new space race” are decreasing satellite launch cost due to the development of reusable rockets such as Containers.