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Versions: 00                                                            
Benchmarking Methodology Working Group                            Z. Lai
Internet-Draft                                                     H. Li
Intended status: Informational                                   Y. Deng
Expires: 28 April 2022                                             Q. Wu
                                                                  J. Liu
                                                     Tsinghua University
                                                         25 October 2021


Problems and Requirements of Evaluation Methodology for Integrated Space
                        and Terrestrial Networks
                   draft-lai-bmwg-istn-methodology-00

Abstract

   With the rapid evolution of the aerospace industry, many "NewSpace"
   upstarts are actively deploying their mega-constellations in low
   Earth orbits (LEO) and building integrated space and terrestrial
   networks (ISTN), promising to provide pervasive, low-latency, and
   high-throughput Internet service globally.  Due to the high
   manufacturing, launching, and updating cost of LEO mega-
   constellations, it is expected that ISTNs can be well designed and
   evaluated before the launch of satellites.  However, the progress of
   designing, assessing, and understanding new network functionalities
   and protocols for futuristic ISTNs faces a substantial obstacle: lack
   of standardized evaluation methodology with acceptable realism,
   flexibility, and cost that can involve the unique dynamic behaviors
   of ISTNs.  This memo first reviews the unique characteristics of LEO
   mega-constellations.  Further, it analyzes the limitation of existing
   network evaluation and analysis methodologies under ISTN
   environments.  Finally, it outlines the key requirements of future
   evaluation methodology tailored for ISTNs.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."




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   This Internet-Draft will expire on 28 April 2022.

Copyright Notice

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Notation and Terminology  . . . . . . . . . . . . . . . . . .   4
   3.  Quick Primer for Integrated Space and Terrestrial Networks  .   5
     3.1.  Mega-constellation  . . . . . . . . . . . . . . . . . . .   5
     3.2.  Topological Dynamics  . . . . . . . . . . . . . . . . . .   6
     3.3.  Long Manufacturing and Deployment Duration  . . . . . . .   7
   4.  Problem Statement: We Need the Right Evaluation
           Methodology . . . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Live networks and platforms . . . . . . . . . . . . . . .   8
     4.2.  Network Simulators  . . . . . . . . . . . . . . . . . . .   9
     4.3.  Network Emulators . . . . . . . . . . . . . . . . . . . .  10
     4.4.  Summary . . . . . . . . . . . . . . . . . . . . . . . . .  11
   5.  Requirements: New Evaluation Methodology Tailored for
           ISTNs . . . . . . . . . . . . . . . . . . . . . . . . . .  12
     5.1.  Realism . . . . . . . . . . . . . . . . . . . . . . . . .  12
     5.2.  Flexibility . . . . . . . . . . . . . . . . . . . . . . .  13
     5.3.  Low-cost and Easy-to-use  . . . . . . . . . . . . . . . .  13
     5.4.  Cross-domain Dataset Support  . . . . . . . . . . . . . .  13
   6.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . .  14
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  14
     10.2.  Informative References . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16







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1.  Introduction

   Integrated Space and Terrestrial Networks (ISTN), combining diverse
   spacecraft and ground infrastructures, are extending the frontier of
   today's terrestrial network, promising to provide low-latency, high-
   bandwidth Internet access with broader coverage globally.

   Low Earth Orbit (LEO) satellites are the key building block for
   constructing ISTN.  Recently, we have witnessed a renaissance in the
   space industry, stimulating an exponential increase in constructing
   mega-constellations.  As compared to their predecessor, cutting-edge
   satellites can be equipped with high-resolution sensors, space-grade
   multi-core processors, high-data-rate communication links, and
   multifunctional space software.

   While ISTNs hold great promise, to completely unleash the network
   potential of emerging ISTN, it still needs to address a series of new
   research issues.  The unique characteristics of LEO satellites (e.g.,
   high-dynamics), not only impose new challenges at various layers of
   the ISTN networking stack but also open the door to many new research
   problems.  With many unexplored problems facing the "NewSpace"
   industry, it is thus foreseen that in the near future, there will be
   a surge of new research (e.g. topology, addressing, routing,
   transport, etc.) to rethink and reshape network functionalities and
   protocols in ISTNs.  In addition, the cost/ timeline of
   manufacturing, launching, operating, and updating satellite
   constellations is typically much higher/longer than that in
   traditional terrestrial networks.  Therefore, it is expected that new
   network functionalities and protocols can be well evaluated before
   they are launched and deployed in realistic satellite constellations.

   However, the network community lacks the proper analysis tools and
   evaluation methodologies that can mimic the unique dynamic behavior
   to analyze many of the ISTN challenges that have been highlighted by
   prior studies.  At high level, existing evaluation methodologies in
   the network community can typically be grouped into three major
   categories: live networks or platforms, simulation, and emulation.
   However, the feasibility and flexibility of live satellite networks
   are technically and economically limited.  The abstraction level of
   network simulation might be too high to capture low-level system
   effects.  Existing network emulators fail to characterize the high
   dynamicity of LEO satellites and thus cannot accomplish an
   environment with acceptable fidelity.  The community hence needs a
   reasonable and standardized evaluation methodology to build proper
   experimental environments which can mimic the behavior of ISTNs,
   supporting the community to deeply understand the problems, and to
   evaluate new functionalities and protocols (e.g. for topology,
   addressing, routing, transport, etc.) for ISTNs, before the mega-



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   constellation is completely deployed.  In this memo, we first review
   the unique characteristics of emerging LEO mega-constellations and
   the key challenges of integrating satellites and terrestrial
   Internet.  Further, we analyze the limitation of existing network
   analysis tools and evaluation methodologies in ISTNs.  Finally, we
   outline key requirements of evaluation methodologies tailored for
   ISTNs.

2.  Notation and Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   This document uses the following acronyms and terminologies:

   Mega-constellation: A group of satellites working as a system.

   LEO: Low Earth Orbit with an altitude no more than 2000 km.

   MEO: Medium Earth Orbit with an altitude from 2000 km to 35786 km.

   GEO: Geostationary Earth Orbit with an altitude of 35786 km.

   NGSO: Non-Geostationary Orbit

   LSN: LEO Satellite Networks

   ISTN: Integrated Satellite and Terrestrial Network

   ISL: Inter-satellite Links

   EO: Earth Observation

   GS: Ground Station

   AS: Autonomous System

   EOS: Earth Observation Satellite

   BGP: Border Gateway Protocol [RFC4271]

   OSPF: Open Shortest Path First [RFC2328]

   VM: Virtual Machine






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3.  Quick Primer for Integrated Space and Terrestrial Networks

   Emerging mega-constellations with inter-satellite links (ISLs) can
   build a satellite network in outer space, and further be integrated
   with terrestrial ground infrastructures to construct an integrated
   space and terrestrial network (ISTN).

3.1.  Mega-constellation

   A constellation is a group of satellites working as a system to give
   a coverage of the Earth surface, among which satellites are
   positioned in fixed orbital planes with regular trajectories.  LEO
   and MEO satellites often belong to a constellation, because a single
   satellite only covers a small area with high angular velocity.  Thus,
   continuous coverage over an area could be maintained by the relay
   within a constellation, as compared with GEO satellites that only
   provides a permanent coverage over a target area.  Walker Delta
   constellation is the most common formation for constellations.  It is
   defined as a bunch of circular orbits with a fixed inclination,
   satellite number, number of equally spaced planes and the relative
   spacing between satellites in adjacent planes.  The famous Ballard
   rosette constellation is another name of Walker Delta constellation,
   where it uses a different notation.  Near-polar Walker Star is one of
   this kind, initially used by Iridium [Iridium].  Constellations with
   a higher inclination give the polar regions more chances to get
   accessed.  The well-known emerging commercial constellations are
   Starlink [Starlink-Fcc], Kuiper [Kuiper-Fcc] and Telesat
   [Telesat-Fcc], as shown in Table 1 below.  And all of them contain
   more than one shell.






















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     +==========+==========+=============+========+=================+
     | Name and | Altitude | Inclination |  # of  | # of satellites |
     |  Shell   |   (km)   |   (degree)  | orbits |    per orbit    |
     +==========+==========+=============+========+=================+
     | Starlink |   550    |      53     |   72   |        22       |
     |    S1    |          |             |        |                 |
     +----------+----------+-------------+--------+-----------------+
     | Starlink |   1110   |     53.8    |   32   |        50       |
     |    S2    |          |             |        |                 |
     +----------+----------+-------------+--------+-----------------+
     | Starlink |   1130   |      74     |   8    |        50       |
     |    S3    |          |             |        |                 |
     +----------+----------+-------------+--------+-----------------+
     | Starlink |   1275   |      81     |   5    |        75       |
     |    S4    |          |             |        |                 |
     +----------+----------+-------------+--------+-----------------+
     | Starlink |   1325   |      70     |   6    |        75       |
     |    S5    |          |             |        |                 |
     +----------+----------+-------------+--------+-----------------+
     |  Kuiper  |   630    |     51.9    |   34   |        34       |
     |    K1    |          |             |        |                 |
     +----------+----------+-------------+--------+-----------------+
     |  Kuiper  |   610    |      42     |   36   |        36       |
     |    K2    |          |             |        |                 |
     +----------+----------+-------------+--------+-----------------+
     |  Kuiper  |   590    |      33     |   28   |        28       |
     |    K3    |          |             |        |                 |
     +----------+----------+-------------+--------+-----------------+
     | Telesat  |   1015   |    98.98    |   27   |        13       |
     |    T1    |          |             |        |                 |
     +----------+----------+-------------+--------+-----------------+
     | Telesat  |   1325   |    50.88    |   40   |        33       |
     |    T2    |          |             |        |                 |
     +----------+----------+-------------+--------+-----------------+

                 Table 1: Mega-constellation information.

3.2.  Topological Dynamics

   Unlike geostationary satellite networks or terrestrial core
   infrastructure that keep a stable topology, LEO satellite networks
   suffer from high topological dynamics, since LEO satellites move
   fast, causing short-lived coverage for fixed terrestrial users.  For
   example, considering the first shell of Starlink Phase-I, a fixed
   user sees each satellite for only up to 3 minutes in one pass, after
   which the satellite moves away from the user's perspective.  Table 2
   shows the medium space-ground link churn intervals
   [link-churn-interval] between existing GS and constellations.  If



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   each GS only uses one antenna to connect the satellite with the
   shortest distance, the medium interval is no more than one minute.
   This kind of high dynamic motion incurs frequent link changes between
   LEO satellites and GS or users, thus causing frequent topology
   changes.  Moreover, inter-satellites visibility may also change if
   LEO satellites move in different directions or in different shells,
   resulting in connectivity change of ISLs.

   Such high LEO dynamics can impose significant challenges in the
   networking stack of ISTNs.  The high dynamics make the logical
   network and mega-constellations and physical ISTN inconsistent.  One
   big challenge is how to overcome the routing oscillation properly in
   the high dynamic ISTN environment.  Frequent satellite-GS link
   changes make the inter-connectivity of space and ground segments in
   ISTNs unstable.  Thus, the routing have to be re-calculated every
   time the link changes.  In addition, the topological dynamics also
   result in RTT fluctuations in end-to-end paths, involving new
   challenges for congestion control in ISTNs, as a RTT variation
   observed by end-host might not indicate congestions.

                        +==========+==============+
                        |   Name   | Interval (s) |
                        +==========+==============+
                        | Starlink |    3.0901    |
                        +----------+--------------+
                        |  Kuiper  |    5.0562    |
                        +----------+--------------+
                        |  OneWeb  |   10.6824    |
                        +----------+--------------+
                        | Telesat  |   45.5696    |
                        +----------+--------------+

                           Table 2: Space-ground
                            link churn interval.

3.3.  Long Manufacturing and Deployment Duration

   Different from terrestrial network infrastructures, the timeline of
   manufacturing and deploying satellite networks could be much longer
   due to the high cost and complex process during the development and
   launch period.  Satellites, as well as the orbit and spectrum they
   used, have to be regulated, and launches have to be carefully
   scheduled (e.g. to avoid the impact of poor weather conditions).  In
   addition, the maintenance and update cost of a satellite network is
   also typically much higher than that of a terrestrial network.






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   For example, a review of 24 Air Force and Navy space vehicle (SV)
   development programs found that on average it took about 7.5 years
   from contract start to launch a government satellite.
   [Development-Timeline] Commercial satellite programs typically take 2
   to 3 years from contract start to launch.  [Production-Cycles]
   SpaceX's Starlink constellation plan to launch about 42,000
   satellites to construct a mega-constellation in outer space.  On 15
   October 2019, the United States Federal Communications Commission
   (FCC) submitted filings to the International Telecommunication Union
   (ITU) on SpaceX's behalf to arrange spectrum for 30,000 additional
   Starlink satellites to supplement the 12,000 Starlink satellites
   already approved by the FCC.  As of the date of September 2021, two
   years after the first launch in May 2019, SpaceX has launched about
   1791 Starlink satellites, which is about 4% of the ultimate
   constellation plan consisting of 42,000 satellites.  Foreseeably, it
   may take many years to complete the entire constellation deployment.
   Even the first phase of Starlink which consists of about 4400
   satellites is not expected to be completed until 2024.

4.  Problem Statement: We Need the Right Evaluation Methodology

   The unique characteristics of LEO mega-constellations involve new
   challenges on various layers of the networking stack of ISTNs.  On
   one hand, it is foreseen that in the near future, there will be a
   surge of new network functionalities and protocols designed or
   optimized for ISTNs.  On the other hand, because the cost/timeline of
   manufacturing, launching, operating, and updating satellite
   constellations is typically much higher/longer than that in
   traditional terrestrial networks, it is expected that those new
   network functionalities and protocols tailored for ISTNs should be
   well evaluated before they are launched and deployed in realistic
   satellite constellations.

   Existing methodologies for testing, assessing, and understanding a
   network functionality or protocol can typically be classified into
   three categories: (1) live networks; (2) network simulators; and (3)
   network emulators.  The subsections discuss these three categories of
   network evaluation methodologies, along with their using deficiencies
   and possible remedies respectively.

4.1.  Live networks and platforms

   Representative platforms such as Emulab [Emulab] and Sparta [Sparta]
   are successful pioneers that build a large-scale experimental network
   environment.  These test environments are originally designed to
   provide special and exclusive test services for affiliated
   universities, scientific research institutions or Internet business
   companies.  And for the resource competition, each independent



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   experiment needs to completely monopolize a part of the test bed, so
   the researcher cannot deploy the experiment until being allocated
   with enough nodes.  PlanetLab [PlanetLab] is truly global ground
   testbed prototype.  Started from 2003, it consists of 1353 nodes at
   717 sites spanning 48 countries.  Together the nodes form a global
   network system to support new design of network services.

   The live platforms described above were initially proposed for
   terrestrial networks and they are developed and repaired at the same
   time.  The key limitation of them in ISTN environment is that they
   are designed for terrestrial network experiments, and do not
   incorporate the realistic characteristic of LEO mega-constellations
   to support experiments and evaluations in ISTNs.

   We may search for help from live satellites, but still there is only
   limited help.  It seems that with the help of live ISTN, researchers
   are capable to assess, verify and evaluate their ideas and thoughts.
   Live ISTN can give a real constellation-consistency and stack-
   consistency testing environment.  However, current satellites only
   provide users a bent-pipe service, which is purely relaying the
   transmission messages, such as the current deployment of Starlink
   [Starlink].  The construction is far from a comprehensive ISTN, so
   the research scope is limited.  Even if there is a live ISTN, it
   lacks flexibility, owning to the inconvenient control over
   satellites.  Besides, the access to satellites is also limited.

   Therefore, live networks or platforms for terrestrial networks can
   give us a large-scale experimental environment but they lack the
   support for ISTN characteristics.  On the other hand, live ISTN is
   able to guarantee a real space environment, but it is not that
   affordable and flexible.

4.2.  Network Simulators

   Simulators are testing methodology tools that enable researchers to
   reproduce their testing experiments by simulating a real-world
   process or system over time.  Simulators work by using discrete event
   simulation to calculate the interactive states among all the network
   entities, ranging from switches, routers, nodes, access points, links
   and so on.  While working fast and efficiently, the fidelity is only
   brought by the state variable changes at discrete points.

   Such tools like Systems Tool Kit (STK) [Systems-Tool-Kit] and General
   Mission Analysis Tool (GMAT) [General-Mission-Analysis-Tool] are good
   for orbit analysis.  STK is a powerful tool to help researchers to
   model the behavior of mission entities in aerospace,
   telecommunications and so forth.  It also provides visualization and
   analysis functions.  GMAT is a similar tool for space trajectory



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   optimization and mission modeling.  Nevertheless, both tools do not
   support networking simulations such as topology and protocol
   simulations. ns-3 [ns-3] goes a step further with support for
   Internet simulation, but on the contrary, it was not designed for
   ISTN and lacks the support for high-dynamics of ISTN.  StarPerf
   [StarPerf] is a simulator that helps researchers to study network
   performance under a range of constellation conditions.  But still, it
   lacks the ability to support interactive network traffic simulation
   and system codes in the systems.

   Overall, while flexible and low-cost, the realism of simulators is
   not content enough, because they are too abstract to realize the low-
   level characteristics.  In other words, simulators are being too
   object-oriented to involve additional overhead in the actual
   execution of programs.  Besides, when accessing the network
   performance, a number of recent emerging algorithms for congestion
   control, reliable transmission or even protocols are not supported,
   for example ns-3 [ns-3] only supports basic congestion control like
   Reno [RFC6582] and so forth, so the need to work with some new
   algorithms cannot be satisfied and the research to discover new
   mechanisms, such as new routing algorithms and re-transmission
   schemes, is extensively prohibited.  Another problem of simulators,
   such as ns-3 [ns-3], is that it difficult to trace or understand the
   previous codes, without appropriate documentations.  Simulators
   usually face the additional compatibility problem, which means they
   is not portable with other systems, or they do not support kernel
   codes.  Since there are multiple simulators developed by different
   group of users, sometimes users are required to be familiar with the
   writing language, scripting style and modelling technique.  So, the
   Tool Command Language might be difficult to understand and write.

4.3.  Network Emulators

   Emulators are another kind of paradigm for testing methodology tool
   over a virtual network.  The difference between a simulator and an
   emulator is that emulators leverage VM or containers to keep the
   realism which is close to actual performances.  Therefore, in
   emulators, virtual nodes. virtual network links, virtual models of
   traffic, and protocols are all applied.  Emulators are capable to run
   real kernel and application code.  Thus, emulators not only support
   diverse topology design, but also protocol emulation in a synthetic
   network environment.  They emulate the network behavior in a more
   real way.  Mininet [Mininet] is commonly regarded as the most
   illustrious emulator for networking with its strong ability to
   support experiments with Software-Defined Networking (SDN)
   [Software-defined-networking] systems.  EstiNet [EstiNet] is another
   emulator that supports evaluating and testing the performances of
   software-defined networks.  Based on containers, they can emulate



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   real TCP/IP protocol stack in the Linux kernel.  However, existing
   emulation tools lack the ability to construct the dynamic links and
   orbits in ISTN like simulators.  Thus, more problems could happen in
   higher-level protocols such as routing protocols (e.g.  OSPF and
   BGP).  Besides, since emulators run containers or virtual machines
   which occupy more software overhead, compared with simulators, it
   will be hard to emulate the large-scale mega-constellations.
   Existing work has shown the capability of 25 physical machines
   working together as a system to emulate 250 network nodes, but still,
   it is far less for ISTN scalability.

   To conclude, emulators are relatively good methodologies for network
   experiments, but emulators still have limitations when using them for
   ISTN research.  While keeping a moderate realism by using VM or
   containers for entity emulation and flexibility, emulators still lack
   the supports for ISTN characteristics, such as frequent link changes,
   satellite network topology uncertainty, and so on.  More
   specifically, current emulators only support fixed network topology
   emulation.  It is not flexible to emulate the time-varying link
   packet loss, bandwidth, and other traits.  A possible way is to
   frequently replace the link with a new one from time to time
   sequentially for the entire ISTN.  However, it is far from the real
   situation.  Besides, VM or containers are able to deploy a range of
   network nodes in a physical server, but the actual CPU, memory and
   other resources should not be shared in reality for each satellite.
   In addition, it is still difficult to emulate thousands or ten
   thousand of satellites for ISTN even with VM or containers, subject
   to hardware limitations.  For flexibility, some emulators do not
   support a good network animator tool.  Especially in ISTN emulation,
   GUI is important for users to observe and analyze orbit trajectories
   and real time satellite positions.

4.4.  Summary

   In this section, we explain the necessity of an evaluation
   methodology specifically for ISTN.  Then we demonstrate the problems
   with existing methodologies related to ISTN.  The performance
   comparison result is shown in Table 3.  Above all, ISTN should be
   designed first and then launched.  Live satellites enable good
   realism but they lack flexibility and require very high cost as well
   as a very long deployment period.  Other testing tools such as
   simulators and emulators are either functional for merely aerospace
   analysis or simply terrestrial networks.  None of the existing
   methodologies guarantees a practical and user-friendly methodology
   while keeping the evaluation environment realism with low costs.






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    +================+=========+=============+======+=================+
    | Platform/Tool  | Realism | Flexibility | Cost |   Cross-domain  |
    |                |         |             |      | Dataset Support |
    +================+=========+=============+======+=================+
    | Live satellite |    Y    |      N      | High |        Y        |
    |    network     |         |             |      |                 |
    +----------------+---------+-------------+------+-----------------+
    |  ns-3 [ns-3]   |    N    |      Y      | Low  |        N        |
    +----------------+---------+-------------+------+-----------------+
    |    Hypatia     |    N    |      Y      | Low  |        N        |
    |   [Hypatia]    |         |             |      |                 |
    +----------------+---------+-------------+------+-----------------+
    |    StarPerf    |    N    |      Y      | Low  |        N        |
    |   [StarPerf]   |         |             |      |                 |
    +----------------+---------+-------------+------+-----------------+
    |    Mininet     |    N    |      Y      | Low  |        N        |
    |   [Mininet]    |         |             |      |                 |
    +----------------+---------+-------------+------+-----------------+

         Table 3: Existing platforms/tools for network analysis and
                     evaluation.  (Y for yes/N for no)

5.  Requirements: New Evaluation Methodology Tailored for ISTNs

   A proper evaluation methodology tailored for ISTNs is expected to
   help developers, researchers, engineers to explore various design-
   space of the networking stack of ISTNs in a technically and
   economically feasible manner.  Based on the comparative analysis
   results in the prior section, we sum up the following requirements
   for the new evaluation methodology in ISTNs.

5.1.  Realism

   The first requirement is realism.  Realism represents the testing
   authenticity and fidelity, compared with real ISTN.  It could be
   further divided into constellation-consistency and networking stack
   realism.  Constellation-consistency requires the testing to keep the
   actual characteristics of mega-constellations both spatially and
   temporally.  In other words, the orbit-level information including
   the latitude, longitude, and height of each satellite in any given
   time and the same information for GS and elevation angles of antennas
   of each GS spatially.  Note that the spatial information also
   determines the visibility, links and even topology of ISTN.  Since
   the mega-constellations are unstable, how the temporal satellite
   locations, visibility, link propagation delays and so on should also
   be considered carefully.  Similarly, the networking stack realism
   requires the network nodes to communicate and negotiate their
   messages following the actual protocol process.  For example, when



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   doing a test for OSPF in an ISTN, we would like the nodes to send
   Hello packets, Link-State-Request (LSR) packets, Link-State-Update
   (LSU) packets and so on.  A real network stack is preferred to
   provide researchers an opportunity to see the performance of
   different protocols in ISTN.

5.2.  Flexibility

   Another requirement is flexibility and feasibility.  The testing
   methodology should be technically easy to use and easy to learn.
   Without extra modifications or process, the methodology should help
   researchers learn and use it without much effort and can evaluate
   their ideas as they wish, which means it should support multiple
   environments for researchers.

5.3.  Low-cost and Easy-to-use

   Meanwhile, the evaluation methodology is expected to be low-cost.  A
   well-acceptable methodology should be economically feasible for users
   to create an experimental network environment.  Researchers do not
   want to conduct their tests all in live ISTN, which is over-
   cumbersome and unaffordable, let alone launching their own
   spacecraft.  Even if there are a number of orbiting satellites,
   whether users can easily gain access to satellites is also a problem.

5.4.  Cross-domain Dataset Support

   The evaluation methodology is expected to be driven by realistic
   datasets from multi-dimensions to support its realism.  Multi-
   dimension refers to multi-disciplinary research on ISTN.  Since a
   standard ISTN evaluation methodology not only contains high-level
   benchmarks from topology, routing to transmission, but also considers
   the low-level traits such as wireless link conditions, weather
   conditions and Earth rotations.  To be more concrete, the former one
   requires knowledge in networks while the latter one relies more on
   aerospace.  Hence, to build a high-fidelity methodology, we need
   community efforts both from networks and aerospace.  On the other
   hand, an authentic dataset is an indispensable element for data
   driven testing methodology.  Actual data is the first step to obtain
   a realistic emulation. with characteristics of a real ISTN.  Thus,
   the dataset is a collection of messages for testing, in which
   geographical mega-constellation information (orbit number, satellite
   number, height), orbital information (orbit inclination angle and
   link strategies), weather information as well as ground station
   information (positions, antenna angle and so forth) are involved.






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6.  Conclusion

   To conclude, the emergence of mega-constellations brings us new
   opportunities for the development of ISTN that extends the Internet
   to the space era.  Combined with terrestrial networks, ISTN is
   expected to supply pervasive, low-latency and high-speed services to
   users globally, which greatly enhances the current Internet.  At the
   same time, the unique characteristics (e.g. high-dynamics) of ISTN
   impose challenges in topology, routing, transportation, application,
   and security.  However, we simply believe addressing the challenges
   also gives us open opportunities for future research by our
   community-driven effort.  To accelerate the research speed and to
   help make testing more feasible, new methodologies that satisfy user
   requirements should be proposed.  To this extent, this draft reviews
   the limitation of existing network analysis tools in ISTNs,
   considering the unique characteristics of emerging LSNs and the key
   challenges.  This draft further analyzes the limitation of existing
   evaluation methodologies in ISTN environments.  Finally, this draft
   outlines key requirements of evaluation methodologies tailored for
   future ISTNs.

7.  Acknowledgements

8.  IANA Considerations

   This memo includes no request to IANA.

9.  Security Considerations

   This entire draft discusses security considerations from different
   perspectives of ISTN in Section 3.

10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <https://www.rfc-editor.org/info/rfc2328>.

   [RFC4271]  Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
              Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271,
              January 2006, <https://www.rfc-editor.org/info/rfc4271>.



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   [RFC6582]  Henderson, T., Floyd, S., Gurtov, A., and Y. Nishida, "The
              NewReno Modification to TCP's Fast Recovery Algorithm",
              RFC 6582, DOI 10.17487/RFC6582, April 2012,
              <https://www.rfc-editor.org/info/rfc6582>.

10.2.  Informative References

   [Development-Timeline]
              "Development-Timeline", <http://www.iceaaonline.com/ready/
              wp-content/uploads/2014/03/Davis-Satellite-ICEAASoCal-
              090915.pdf>.

   [Emulab]   "Emulab", <https://www.emulab.net/portal/frontpage.php>.

   [EstiNet]  "EstiNet", <http://www.estinet.com/
              fckimages/14117014621397232509.pdf>.

   [General-Mission-Analysis-Tool]
              "General-Mission-Analysis-Tool",
              <https://en.wikipedia.org/wiki/
              General_Mission_Analysis_Tool>.

   [Hypatia]  "Hypatia", <http://people.inf.ethz.ch/asingla/papers/
              imc2020-hypatia.pdf>.

   [Iridium]  "Iridium", <https://en.wikipedia.org/wiki/Iridium>.

   [Kuiper-Fcc]
              "Kuiper-Fcc", <https://www.itu.int/ITU-
              R/space/asreceived/Publication/DisplayPublication/8716>.

   [link-churn-interval]
              "link-churn-interval",
              <https://conferences.sigcomm.org/hotnets/2021/
              accepted.html>.

   [Mininet]  "Mininet", <http://mininet.org/>.

   [ns-3]     "ns-3", <https://www.nsnam.org/>.

   [PlanetLab]
              "PlanetLab", <https://citeseerx.ist.psu.edu/viewdoc/
              download?doi=10.1.1.99.7006&rep=rep1&type=pdf>.








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   [Production-Cycles]
              "Production-Cycles",
              <http://www.futron.com/upload/wysiwyg/Resources/
              Whitepapers/Satellite_Manufacturing_Productio
              n_Cycles_0504.pdf>.

   [Software-defined-networking]
              "Software-defined-networking",
              <https://en.wikipedia.org/wiki/Software-
              defined_networking>.

   [Sparta]   "Sparta", <https://s3-us-west-
              2.amazonaws.com/ieeeshutpages/xplore/xplore-shut-
              page.html>.

   [Starlink] "Starlink", <https://en.wikipedia.org/wiki/Starlink>.

   [Starlink-Fcc]
              "Starlink-Fcc",
              <https://fcc.report/IBFS/SAT-LOA-20161115-00118/1158350>.

   [StarPerf] "StarPerf", <https://www.semanticscholar.org/paper/
              StarPerf%3A-Characterizing-Network-Performance-for-Lai-
              Li/18aa32309eb857afdace1ad02d1091ae64dcd330>.

   [Systems-Tool-Kit]
              "Systems-Tool-Kit", <https://www.agi.com/products/gmat>.

   [Telesat-Fcc]
              "Telesat-Fcc", <https://fcc.report/IBFS/SAT-MPL-
              20200526-00053/2378318.pdf>.

Authors' Addresses

   Zeqi Lai
   Tsinghua University
   30 ShuangQing Ave
   Beijing
   100089
   China

   Email: zeqilai@tsinghua.edu.cn


   Hewu Li
   Tsinghua University
   30 ShuangQing Ave
   Beijing



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   100089
   China

   Email: lihewu@cernet.edu.cn


   Yangtao Deng
   Tsinghua University
   30 ShuangQing Ave
   Beijing
   100089
   China

   Email: dengyt21@mails.tsinghua.edu.cn


   Qian Wu
   Tsinghua University
   30 ShuangQing Ave
   Beijing
   100089
   China

   Email: wuqian@cernet.edu.cn


   Jun Liu
   Tsinghua University
   30 ShuangQing Ave
   Beijing
   100089
   China

   Email: juneliu@mail.tsinghua.edu.cn

















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