Satellite Semantic Addressing for Satellite Constellation
draft-lhan-satellite-semantic-addressing-00

Document Type Active Internet-Draft (individual)
Authors Lin Han  , Richard Li 
Last updated 2021-10-19
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Network Working Group                                        L. Han, Ed.
Internet-Draft                                                     R. Li
Intended status: Informational              Futurewei Technologies, Inc.
Expires: 22 April 2022                                   19 October 2021

       Satellite Semantic Addressing for Satellite Constellation
              draft-lhan-satellite-semantic-addressing-00

Abstract

   This document presents a semantic addressing method for satellites in
   satellite constellation connecting with Internet.  The satellite
   semantic address can indicate the relative position of satellites in
   a constellation.  The address can be used with traditional IP address
   or MAC address or used independently for IP routing and switching.

Status of This Memo

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   This Internet-Draft will expire on 22 April 2022.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Basics of Satellite Constellation and Satellite Orbit . . . .   5
     4.1.  Satellite Orbit . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  Satellite Constellation Compositions  . . . . . . . . . .   6
     4.3.  Communication between Satellites by ISL . . . . . . . . .   6
   5.  Addressing of Satellite . . . . . . . . . . . . . . . . . . .   9
     5.1.  Indexes of Satellite  . . . . . . . . . . . . . . . . . .   9
     5.2.  The Range of Satellite Indexes  . . . . . . . . . . . . .  11
     5.3.  Other Info for satellite addressing . . . . . . . . . . .  12
     5.4.  Encoding of Satellite Semantic Address  . . . . . . . . .  13
     5.5.  Link Identification by Satellite Semantic Address . . . .  15
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  17
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  17
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  17
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  18
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   Satellite constellation technologies for Internet are emerging and
   expected to provide Internet service like the traditional wired
   network on the ground.  A typical satellite constellation will have
   couple of thousands or over ten thousands of LEO and/or VLEO.
   Satellites in a constellation will be connected to adjacent
   satellites by Inter-Satellite-Links (ISL), and/or connected to ground
   station by microwave or laser links.  ISL is still in research stage
   and will be deployed soon.  This memo is for the satellite networking
   with the use of ISL.

   The memo proposes to use some indexes to represent a satellite's
   orbit information.  The indexes can form satellite semantic address,
   the address can then be embedded into IPv6 address or MAC address for
   IP routing and switching.  The address can also be used independently
   if the shorter than 128-bit length of IP address is accepted.  As an
   internal address for satellite network, it only applies to satellites
   that will form a constellation to transport Internet traffic between
   ground stations, and will not be populated to Internet by BGP.

2.  Terminology

   LEO               Low Earth Orbit with the altitude from 180 km to

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                     2000 km.

   VLEO              Very Low Earth Orbit with the altitude below 450 km

   GEO               Geosynchronous orbit with the altitude 35786 km

   ISL               Inter Satellite Link

   ISLL              Inter Satellite Laser Link

   3D                Three Dimensional

   GS                Ground Station, a device on ground connecting the
                     satellite.  In the document, GS will hypothetically
                     provide L2 and/or L3 functionality in addition to
                     process/send/receive radio wave.  It might be
                     different as the reality that the device to
                     process/send/receive radio wave and the device to
                     provide L2 and/or L3 functionality could be
                     separated.

   SGS               Source ground station.  For a specified flow, a
                     ground station that will send data to a satellite
                     through its uplink.

   DGS               Destination ground station.  For a specified flow,
                     a ground station that is connected to a local
                     network or Internet, it will receive data from a
                     satellite through its downlink and then forward to
                     a local network or Internet.

   L1                Layer 1, or Physical Layer in OSI model [OSI-Model]

   L2                Layer 2, or Data Link Layer in OSI model
                     [OSI-Model]

   L3                Layer 3, or Network Layer in OSI model [OSI-Model],
                     it is also called IP layer in TCP/IP model

   BGP               Border Gateway Protocol [RFC4271]

   IGP               Interior gateway protocol, examples of IGPs include
                     Open Shortest Path First (OSPF [RFC2328]), Routing
                     Information Protocol (RIP [RFC2453]), Intermediate
                     System to Intermediate System (IS-IS [RFC7142]) and
                     Enhanced Interior Gateway Routing Protocol (EIGRP
                     [RFC7868]).

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3.  Overview

   For IP based satellite networking, the topology is very dynamic and
   the traditional IGP and BGP based routing technologies will face
   challenges according to the analysis in
   [I-D.lhan-problems-requirements-satellite-net].  From the paper, we
   can easily categorize satellite links as two types, steady and un-
   steady.  For un-steady links, the link status will be flipping every
   couple of minutes.

   Section 5.5 has more details about how to identify different links.

   Some researches have been done to handle such fast changed
   topologies. one method to overcome the difficulties for routing with
   un-steady links is to only use the steady links, and get rid of un-
   steady links unless it is necessary.  For example, for real
   deployment, only links between satellite and ground stations are
   mandatory to use, other un-steady links can be avoided in routing and
   switching algorithms.  [Routing-for-LEO] proposed to calculate the
   shortest path by avoiding un-steady links in polar area and links
   crossing Seam line since satellites will move in the opposite
   direction crossing the Seam line.

   Traditionally, to establish a IP network for satellites, each
   satellite and its interface between satellites and to ground stations
   have to be assigned IP addresses (IPv4 or IPv6).  The IP address can
   be either private or public.  IP address itself does not mean
   anything except routing prefix and interface identifier [RFC8200].

   To utilize the satellite relative position for routing, it is desired
   that there is a easy way to identify the relative positions of
   different satellites and identify un-steady links quickly.  The
   traditional IP address cannot provide such functionality unless we
   have the real-time processing for 3D coordinates of satellites to
   figure out the relative positions of each satellite, and some math
   calculation and dynamic database are also needed in routing algorithm
   to check if a link is steady or not.  This will introduce extra data
   exchanged for routing protocols and burden for the computation in
   every satellite.  Considering the ISL link speed (up to 10G for
   2000km) and hardware cost (Radiation-hardened semiconductor
   components are needed) in satellite are more constraint than for
   network device on ground, it is expected to simplify the routing
   algorithm, reduce the requirement of ISL, onboard CPU and memory.

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   The document proposes to form a semantic address by satellite orbit
   information, and then embedded it into a proper IP address.  The IP
   address of IGP neighbors can directly tell the relative position of
   different satellites and if links between two satellites are stead or
   not.

   The document does not describe the details how the semantic address
   is used to improve routing and switching or new routing protocols,
   those will be addressed in different documents.

4.  Basics of Satellite Constellation and Satellite Orbit

   This section will introduce some basics for satellite such as orbit
   parameters.

4.1.  Satellite Orbit

   The orbit of a satellite can be either circular or ecliptic, it can
   be described by following Keplerian elements [KeplerianElement]:

   1.  Inclination (i)

   2.  Longitude of the ascending node (Omega)

   3.  Eccentricity (e)

   4.  Semimajor axis (a)

   5.  Argument of periapsis (omega)

   6.  True anomaly (nu)

   The circular orbit is widely used by proposals of satellite
   constellation from different companies and countries.

   For a circular orbit, we will have:

   *  Eccentricity e = 0

   *  Semimajor axis a = Altitude of satellite

   *  Argument of periapsis omega = 90 degree

   So, three parameters, Altitude, Inclination and Longitude of the
   ascending node, will be enough to describe the orbit.  The satellite
   will move in a constant speed and True anomaly (nu) can be easily
   calculated after the epoch time is defined.

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4.2.  Satellite Constellation Compositions

   One satellite constellation may be composed of many satellites (LEO
   and VLEO), but normally all satellites are grouped in a certain order
   that is never changed during the life of satellite constellation.
   Each satellite constellation's orbits parameters described in
   Section 4.1 must be approved by regulator and cannot be changed
   either.  Follows are characters of one satellite constellation:

   1.  One Satellite Constellation is composed of couple of shell groups
       of satellites.

   2.  Same shell group of satellite will have the same altitude and
       inclination.

   3.  The total N orbit planes in the same shell group of satellites
       will be evenly distributed by the same interval of Longitude of
       the ascending node (Omega).  The interval equals to (360 degree/
       N).  As a result, all orbit planes in the same shell group will
       effectively form a shell to cover earth (there will be a coverage
       hole for the shell if the inclination angle is less than 90
       degree).

   4.  Each orbit plane in the same shell group will have the same
       number of satellites, all satellites in the same orbit plane will
       be evenly distributed angularly in the orbit plane.

   5.  All satellites in the same shell group are moving in the same
       circular direction within the same orbit plane.  As a result, at
       any location on earth, we can see there will have two group of
       satellites moving on the opposite direction.  One group moves
       from south to north, and another group moves from north to south.
       Section 5.5 has more details.

4.3.  Communication between Satellites by ISL

   When ISL is used for the communication between satellites, each
   satellite will have a fixed number of links to connect to its
   neighbor.  Due to the cost of ISL and the constraints of power supply
   on satellite, the number of ISL is normally limited to connect to its
   closest neighbors.  In 3D space, each satellite may have six types of
   adjacent satellites, each type represents one direction.  The number
   of adjacent neighbors in one direction is dependent on the number of
   deployment of ISL device on satellites, for example, the laser
   transmitter and receiver for ISLL.  Figure 1 illustrates satellite S0
   and its adjacent neighbors.

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                 /           /           /
                /           /           /
               /           /           /
              S7          S8          S9
             /           /           /
            /           /           /
           /           /           /
                 /           S1          /
                S5          /           S3
               /           /           /
              /           S0          /
             /           /           /
            S6          /           S4
           /           S2          /
                 /           /           /
                /           /           /
               /           /           /
              S10         S11         S12
             /           /           /         ^ Moving direction
            /           /           /         /
           /           /           /         /
          orbit      orbit       orbit

             Figure 1: Satellite S0 and its adjacent neighbors

   All adjacent satellites of S0 in Figure 1 are listed below:

   1.  The front adjacent satellite S1 that is on the same orbit plane
       as S0.

   2.  The back adjacent satellite S2 that is on the same orbit plane as
       S0

   3.  The right adjacent satellites S3 and S4 that are on the right
       orbit plane of S0

   4.  The left adjacent satellites S5 and S6 that are on the left orbit
       plane of S0

   5.  The above adjacent satellites S7 to S9 that are on the above
       orbit plane of S0

   6.  The below adjacent satellite S10 to S12 that are on the below
       orbit of plane S0

   The relative position of adjacent satellites will directly determine
   the quality of ISL and communication.  From the analysis in
   [I-D.lhan-problems-requirements-satellite-net], The speed of

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   satellite is only related to the altitude of the satellite (on
   circular orbit), all satellites with a same altitude will move with
   the same speed.  So, in above adjacent satellites, some adjacent
   satellite's relative positions are steady and the ISL can be alive
   without interruption caused by movement.  Some adjacent satellites
   relative positions are changing quickly, the ISL may be down since
   the distance may become out of reach for the laser of ISL, or the
   quick changed positions of two satellite make the tracking of laser
   too hard.  Below are details:

   *  The relative position of satellites in the same orbit plane will
      be the steadiest.

   *  The relative position of satellites in the direct neighbor orbit
      planes in the same shell group and moving in the same direction
      will be steady at equator area, but will be changing when two
      orbits meet on the polar area.  Whether the link status will be
      flipping depends on the tracking technology and the range of laser
      pointing angle of ISL.  See Figure 2.

   *  The relative position of satellites in the neighbor orbit planes
      in the same shell group but moving in the different direction will
      not be steady at all times.  More details are explained in
      Figure 7

   *  The relative position of satellites in the neighbor orbit planes
      in the different shell group will be dependent on the difference
      of altitude and inclination.  This has been analyzed in
      [I-D.lhan-problems-requirements-satellite-net].

                  \      /
                   P3   P4
                    \  /
                     \/
                     /\
                    /  \
                   P1   P2
                  /      \

     * Two satellites S1 and S2 are at position P1 and P2 at time T1
     * S1's right facing ISL connected to S2's left facing ISL
     * S1 and S2 move to the position P4 and P3 at time T2
     * S1's left facing ISL connected to S2's right facing ISL
     * So, if the range of laser pointing angle is 360 degree and
       tracking technology supports, the ISL will not be flipping
       after passing polar area; Otherwise, the link will be flipping

        Figure 2: Satellite's Position and ISL Change at Polar Area

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5.  Addressing of Satellite

   When ISL is deployed in satellite constellation, all satellites in
   the constellation can form a network like the wired network on
   ground.  Due to the big number of satellites in a constellation, the
   network could be either L2 or L3.  The document proposes to use L3
   network for better scalability.

   When satellites form a L3 network, it is expected that IP address is
   needed for each satellite and its ISLs.

   While the traditional IP address can still be used for satellite
   network, the document proposes an alternative new method for
   satellite's addressing system.  The new addressing system can
   indicate a satellite's orbit info such as shell group index, orbit
   plane index and satellite index.  This will make the adjacent
   satellite identification for link status easier and benefit the
   routing algorithms.

5.1.  Indexes of Satellite

   As described in Section 4.2, one satellite has three important orbit
   related information as described below.

   1.  Index for the shell group of satellites in a satellite
       constellation

   2.  Index for the orbit plane in a shell group of satellites

   3.  Index for the satellite in a orbit plane

   It should be noted that for all type of indexes, it is up to the
   owner to assign the index number.  There is no rule for which one
   should be assigned with which number.  The only important rule is
   that all index number should be in sequential to reflect its relative
   order and position with others.  Below are an example of assignment
   rules:

   1.  The 1st satellite launched in a orbit plane can be assigned for
       the 1st satellite index (0), the incremental direction of the
       satellite index in the same orbit plane is the incremental
       direction of "Argument of periapsis (omega)"

   2.  The 1st orbit plane established can be assigned for the 1st orbit
       plane index (0), the incremental direction of the orbit plane
       index is the incremental direction of "Longitude of the ascending
       node (Omega)".

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   3.  The shell group of satellites with the lowest altitude can be
       assigned for the 1st shell group index (0), the incremental
       direction of shell group index is the incremental direction of
       altitude.

   Figure 3 and Figure 4 illustrate three types of indexes for
   satellite.

             /           /           /   \
            /           /           /    |
           /           /           /     |
          S           S           S      > shell group3
         /           /           /       |
        /           /           /        |
       /           /           /         /
             /           S           /   \
            S           /           S    |
           /           /           /     |
          /           S           /       > shell group2
         /           /           /       |
        S           /           S        |
       /           S           /         /
             /           /           /   \
            /           /           /    |
           /           /           /     |
          S           S           S       > shell group1
         /           /           /       |
        /           /           /        |
       /           /           /         /
      orbit     orbit      orbit           ----> Earth self-rotation
      plane1    plane2     plane3

        Figure 3: Shell Group and Orbit Plane Indexes for Satellites

   Shell Group and Orbit Plane Indexes for Satellites

                   , - ~ S1 ~ - ,
               S2 '              ' S8
             ,                       ,
            ,                         ,
           ,                           ,      Indexed
           S3                          S7 <-- satellite
           ,                           ,      in one orbit plane
            ,                         ,
             ,                       ,      ^  move direction
               S4                 , S6     /
                 ' - , _ S5_ ,  '         /

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                                  Figure 4

   Three type of Index for satellites

5.2.  The Range of Satellite Indexes

   The ranges of different satellite indexes will determine the range
   the dedicated field for semantic address.  The maximum indexes depend
   on the number of shell group, orbit plane and satellite per orbit
   plane.  The number of orbit plane and satellite per orbit plane have
   relationship with the coverage of a satellite constellation.  There
   is minimum numbers required to cover earth.
   [I-D.lhan-problems-requirements-satellite-net] has given the detailed
   math to estimate the minimal number required to cover the earth.
   There are two key parameters that determine the minimal number of
   satellite required.  One is the elevation angle, another is the
   altitude.  SpaceLink has proposed two elevation angles, 25 and 35
   degrees [SpaceX-Non-GEO].  The lowest LEO altitude can be 160km
   according to [Lowest-LEO-ESA].  The Table 1 and Table 2 illustrate
   the estimation for different altitude (As), the coverage radius (Rc),
   the minimal required number of orbit planes (No) and satellite per
   orbit plane (Ns).  The elevation angle is 25 degree and 35 degree
   respectively.

     +============+=======+=======+======+======+======+======+======+
     | Parameters | VLEO1 | VLEO2 | LEO1 | LEO2 | LEO3 | LEO4 | LEO5 |
     +============+=======+=======+======+======+======+======+======+
     |   As(km)   |  160  |  300  | 600  | 900  | 1200 | 1500 | 2000 |
     +------------+-------+-------+------+------+------+------+------+
     |   Rc(km)   |  318  |  562  | 1009 | 1382 | 1702 | 1981 | 2379 |
     +------------+-------+-------+------+------+------+------+------+
     |     Ns     |   73  |   42  |  23  |  17  |  14  |  12  |  10  |
     +------------+-------+-------+------+------+------+------+------+
     |     No     |   85  |   48  |  27  |  20  |  16  |  14  |  12  |
     +------------+-------+-------+------+------+------+------+------+

         Table 1: Satellite coverage (Rc), minimal number of orbit
        plane (No) and satellite (Ns) per orbit plane for different
                   LEO/VLEOs, Elevation angle = 25 degree

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     +============+=======+=======+======+======+======+======+======+
     | Parameters | VLEO1 | VLEO2 | LEO1 | LEO2 | LEO3 | LEO4 | LEO5 |
     +============+=======+=======+======+======+======+======+======+
     |   As(km)   |  160  |  300  | 600  | 900  | 1200 | 1500 | 2000 |
     +------------+-------+-------+------+------+------+------+------+
     |   Rc(km)   |  218  |  392  | 726  | 1015 | 1271 | 1498 | 1828 |
     +------------+-------+-------+------+------+------+------+------+
     |     Ns     |  107  |   59  |  32  |  23  |  19  |  16  |  13  |
     +------------+-------+-------+------+------+------+------+------+
     |     No     |  123  |   69  |  37  |  27  |  22  |  18  |  15  |
     +------------+-------+-------+------+------+------+------+------+

         Table 2: Satellite coverage (Rc), minimal number of orbit
         plane (No) and satellite (Ns) per orbit for different LEO/
                     VLEOs, Elevation angle = 35 degree

   The real deployment may be different as above analysis.  Normally,
   more satellites and orbit planes are used to provide better coverage.
   So far, there are only two proposals available, one is StarLink,
   another is from China Constellation.  For proposals of [StarLink],
   there are 7 shell groups, the number of orbit plane and satellites
   per orbit plane in all shell groups are 72 and 58; For proposals of
   [China-constellation], there are 7 shell groups, the number of orbit
   plane and satellites per orbit plane in all shell groups are 60 and
   60;

   It should be noted that some technical parameters, such as the
   inclination and altitude of orbit planes, in above proposals may be
   changed during the long-time deployment period, but the total numbers
   for indexes normally do not change.

   From the above analysis, to be conservative, it is safe to conclude
   that the range of all three satellite indexes are less than 256, or
   8-bit number.

5.3.  Other Info for satellite addressing

   In addition to three satellite indexes described in Section 5.1,
   other information is also important and can also be embedded into
   satellite address:

   1.  The company or country code, or the owner code.  In the future,
       there may have multiple satellite constellations on the sky from
       different organizations, and the inter-constellation
       communication may become as normal that is similar to the network
       on the ground.  This code will be useful to distinguish different
       satellite constellation and make the inter-constellation
       communication possible.  One satellite constellation will have

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       one code assigned by international regulator (IANA or ITU).
       Considering the limit of LEO orbits and the cost of satellite
       constellations, the total number of satellite constellation is
       very limited.  So, the size of code is limited.

   2.  The Interface Index.  This index is to identify the ISL or ISLL
       for a satellite.  As described in Section 4.3, the total number
       of ISL is limited.  So, the size of interface index is also
       limited.

5.4.  Encoding of Satellite Semantic Address

   The encoding for satellite semantic address is dependent on what
   routing and switching (L2 or L3 solution) technologies are used for
   satellite networking, and finally dependent on the decision of IETF
   community.

   Follows are some initial proposals:

   1.  When satellite network is using L3 solution, the satellite
       semantic address is encoded as the interface identifier (i.e.,
       the rightmost 64 bits) of the IPv6 address for IPv6.  Figure 5
       shows the format of IPv6 Satellite Address.

   2.  When satellite network is using L2 solution, the satellite
       semantic address can be embedded into the field of "Network
       Interface Controller (NIC) Specific" in MAC address
       [IEEE-MAC-Address].  But due to shorter space for NIC, the "Index
       for the shell group" and "Index for Interface" will only have
       4-bit.  This is illustrated in Figure 6.  This encoded MAC
       address can also be used for L3 solution where the interface MAC
       may be also needed to be configured for each ISL.

   3.  Recently, some works suggested to use Length Variable IP address
       for routing and switching [Length-Variable-IP] or use flexible IP
       address [I-D.jia-flex-ip-address-structure] or shorter IP address
       [I-D.li-native-short-addresses] to solve some specific problems
       that regular IPv6 is not very suitable.  Satellite network also
       belongs to such specific network.  Due to the resource and cost
       constraints and requirement for radiation hardened electronic
       components, the ISL speed, on-board processor and memory are
       limited in performance, power consumption and capacity compared
       with network devices on ground.  So, using IPv6 directly in
       satellite network is not an optimal solution because IPv6 header
       size is too long for such small network.  From above analysis,
       32-bit to 64-bit length of IP address is enough for satellite
       networking.  Using 128-bit IPv6 will consume more resource
       especially the ISL bandwidth, processing power and memory, etc.

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       If shorter than 128-bit IP address is accepted as IETF work, the
       satellite semantic address can be categorized as a similar use
       case.  The detailed coding for the shorter IP address can be
       addressed later on in different document.

     0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                     Subnet Prefix (64 bits)                   ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Owner Code  |  Shell_Index  |  Orbit_Index  |   Sat_Index   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Intf_Index  |                    Reserved                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Owner Code: Identifier for the owner of the constellation
   Shell_Index: Index for the shell group of satellte in a satellite
                constellation
   Orbit_Index: Index for the orbit plane in a shell group of satellite
   Sat_Index: Index for the satellite in a orbit plane
   Intf_Index: Index for interface on a satellite
   Reserved: 24-bits reserved

                    Figure 5: The IPv6 Satellite Address

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              3 Octets             3 Octets
        /---------^--------\ /--------^--------\
        +-------------------+-------------------+
        |        OUI        |     Sat Address   |
        +-------------------+-------------------+
                                     |
                                     |
     +-------------------------------+
     |
     |
     v

      0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Shell |  Orbit_Index  |   Sat_Index   |Intf_Id|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    OUI: Organizationally Unique Identifier assigned by IEEE
    Shell: 4-bit Index for the shell group of satellite in a satellite
           constellation
    Orbit_Index: Index for the orbit plane in the group of satellite
    Sat_Index: Index for the satellite in the orbit plane
    Intf_Id: 4-bit Index for interface on a satellite

                    Figure 6: The MAC Satellite Address

5.5.  Link Identification by Satellite Semantic Address

   Using above satellite semantic addressing scheme, to identify steady
   and un-steady links is as simple as below:

   Assuming:

   1.  The total number of satellites per orbit plane is M

   2.  The total number of orbit planes per shell group is N.

   3.  Two satellites have:

       *  Satellite Indexes as: Sat1_Index, Sat2_Index

       *  Orbit plane Indexes as: Orbit1_Index, Orbit2_Index

       *  Shell group Indexes as: Shell1_Index, Shell2_Index

   Steady links:

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   1.  The links between adjacent satellites on the same orbit plane,
       or, the satellite indexes satisfy:

       *  Sat2_Index = Sat1_Index + 1, when Sat1_Index < M-1; Sat2_Index
          = 0, when Sat1_Index = M-1; and

       *  Orbit1_Index = Orbit2_Index, Shell1_Index = Shell2_Index.

   2.  The links between satellites on adjacent orbit planes on the same
       altitude.  and two satellites are moving to the same direction,
       or, the satellite indexes satisfy:

       *  Orbit2_Index = Orbit1_Index + 1, when Orbit1_Index < N-1;
          Orbit2_Index = 0, when Orbit1_Index = N-1; and

       *  Shell1_Index = Shell2_Index.

       *  Sat1_Index and Sat2_Index may be equal or have difference,
          depend on how the link is established.

   Un-Steady links:

   1.  The links between satellite and ground stations.

   2.  The links between satellites on adjacent orbit planes on the same
       altitude.  Two satellites are moving to the different direction.
       Or, the satellite indexes do not satisfy conditions described in
       above #2 for Steady links.

   3.  The links between satellites on adjacent orbit planes on
       different altitude.  Or, the satellite indexes satisfy:

       *  Shell1_Index != Shell2_Index.

   Figure 7 illustrates the links for adjacent orbit planes (#2 for
   Steady Link and Un-steady Link above).  From the figure, it can be
   noticed that some links may have shorter distance than steady link,
   but they are unsteady.  For example, the links between S1 and S4; S4
   and S2; S2 and S5, etc.

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                   i+N/2         i+1+N/2       i+2+N/2
                 / \           / \           / \
                /   \         /   \         /   \
               S1............S2............S3    \
              /       S4 ..........S5............S6
             /         \   /         \   /         \
            /           \ /           \ /           \
            i-1           i             i+1

       * The total number of orbit planes are N
       * The number (i-1, i, i+1,...) represents the Orbit index
       * The bottom numbers (i-1, i, i+1) are for orbit planes on
         which satellites (S1, S2, S3) are moving from bottom to up.
       * The top numbers (i+N/2, i+1+N/2, i+2+N/2) are for orbit
         planes on which satellites (S4, S5, S6) are moving from up
         to bottom.
       * Dot lines are the steady links

      Figure 7: The links between satellites on adjacent orbit planes

6.  IANA Considerations

   This memo may include request to IANA for owner code, see
   Section 5.4.

7.  Contributors

8.  Acknowledgements

9.  References

9.1.  Normative References

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

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

   [RFC7142]  Shand, M. and L. Ginsberg, "Reclassification of RFC 1142
              to Historic", RFC 7142, DOI 10.17487/RFC7142, February
              2014, <https://www.rfc-editor.org/info/rfc7142>.

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   [RFC2453]  Malkin, G., "RIP Version 2", STD 56, RFC 2453,
              DOI 10.17487/RFC2453, November 1998,
              <https://www.rfc-editor.org/info/rfc2453>.

   [RFC7868]  Savage, D., Ng, J., Moore, S., Slice, D., Paluch, P., and
              R. White, "Cisco's Enhanced Interior Gateway Routing
              Protocol (EIGRP)", RFC 7868, DOI 10.17487/RFC7868, May
              2016, <https://www.rfc-editor.org/info/rfc7868>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

9.2.  Informative References

   [I-D.lhan-problems-requirements-satellite-net]
              Han, L. and R. Li, "Problems and Requirements of Satellite
              Constellation for Internet", Work in Progress, Internet-
              Draft, draft-lhan-problems-requirements-satellite-net-01,
              19 October 2021, <https://datatracker.ietf.org/doc/html/
              draft-lhan-problems-requirements-satellite-net-01>.

   [I-D.jia-flex-ip-address-structure]
              Jia, Y., Chen, Z., and S. Jiang, "Flexible IP: An
              Adaptable IP Address Structure", Work in Progress,
              Internet-Draft, draft-jia-flex-ip-address-structure-00, 31
              October 2020, <https://datatracker.ietf.org/doc/html/
              draft-jia-flex-ip-address-structure-00>.

   [I-D.li-native-short-addresses]
              Li, G., Jiang, S., and D. E. 3rd, "Native Short Addresses
              for the Internet Edge", Work in Progress, Internet-Draft,
              draft-li-native-short-addresses-01, 25 May 2021,
              <https://datatracker.ietf.org/doc/html/draft-li-native-
              short-addresses-01>.

   [Routing-for-LEO]
              E. Ekici, I. F. Akyildiz and M. D. Bender, ""Datagram
              routing algorithm for LEO satellite networks," Proceedings
              IEEE INFOCOM 2000. Conference on Computer Communications.
              Nineteenth Annual Joint Conference of the IEEE Computer
              and Communications Societies (Cat. No.00CH37064), 2000,
              pp. 500-508 vol.2, doi: 10.1109/INFCOM.2000.832223.",
              <https://ieeexplore.ieee.org/document/832223>.

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   [Length-Variable-IP]
              Shoushou Ren, Delei Yu, Guangpeng Li, Shihui Hu, Ye Tian,
              Xiangyang Gong, Robert Moskowitz, ""Routing and Addressing
              with Length Variable IP Address," NEAT'19: Proceedings of
              the ACM SIGCOMM 2019 Workshop on Networking for Emerging
              Applications and Technologies, August 2019",
              <https://doi.org/10.1145/3341558.3342204>.

   [IEEE-MAC-Address]
              "IEEE Std 802-2001 (PDF). The Institute of Electrical and
              Electronics Engineers, Inc. (IEEE). 2002-02-07. p. 19.
              ISBN 978-0-7381-2941-9. Retrieved 2011-09-08.",
              <https://standards.ieee.org/getieee802/
              download/802-2001.pdf>.

   [Lowest-LEO-ESA]
              "Lowest LEO by ESA",
              <https://www.esa.int/ESA_Multimedia/Images/2020/03/Low_Ear
              th_orbit#:~:text=A%20low%20Earth%20orbit%20(LEO,very%20far
              %20above%20Earth's%20surface.>.

   [KeplerianElement]
              "Keplerian elements",
              <https://en.wikipedia.org/wiki/Orbital_elements>.

   [OSI-Model]
              "OSI Model", <https://en.wikipedia.org/wiki/OSI_model>.

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

   [China-constellation]
              "China Constellation", <https://www.itu.int/ITU-
              R/space/asreceived/Publication/DisplayPublication/23706>.

   [SpaceX-Non-GEO]
              "FCC report: SPACEX V-BAND NON-GEOSTATIONARY SATELLITE
              SYSTEM", <https://fcc.report/IBFS/SAT-LOA-
              20170301-00027/1190019.pdf>.

Appendix A.  Change Log

   *  Initial version, 10/19/2021

Authors' Addresses

   Lin Han (editor)
   Futurewei Technologies, Inc.
   2330 Central Expy

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   Santa Clara, CA 95050,
   United States of America

   Email: lhan@futurewei.com

   Richard Li
   Futurewei Technologies, Inc.
   2330 Central Expy
   Santa Clara, CA 95050,
   United States of America

   Email: rli@futurewei.com

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