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 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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 22 April 2022. Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Han & Li Expires 22 April 2022 [Page 1] Internet-Draft Satellite Semantic Addressing October 2021 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 Han & Li Expires 22 April 2022 [Page 2] Internet-Draft Satellite Semantic Addressing October 2021 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]). Han & Li Expires 22 April 2022 [Page 3] Internet-Draft Satellite Semantic Addressing October 2021 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. Han & Li Expires 22 April 2022 [Page 4] Internet-Draft Satellite Semantic Addressing October 2021 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. Han & Li Expires 22 April 2022 [Page 5] Internet-Draft Satellite Semantic Addressing October 2021 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. Han & Li Expires 22 April 2022 [Page 6] Internet-Draft Satellite Semantic Addressing October 2021 / / / / / / / / / 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 Han & Li Expires 22 April 2022 [Page 7] Internet-Draft Satellite Semantic Addressing October 2021 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 Han & Li Expires 22 April 2022 [Page 8] Internet-Draft Satellite Semantic Addressing October 2021 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)". Han & Li Expires 22 April 2022 [Page 9] Internet-Draft Satellite Semantic Addressing October 2021 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_ , ' / Han & Li Expires 22 April 2022 [Page 10] Internet-Draft Satellite Semantic Addressing October 2021 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 Han & Li Expires 22 April 2022 [Page 11] Internet-Draft Satellite Semantic Addressing October 2021 +============+=======+=======+======+======+======+======+======+ | 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 Han & Li Expires 22 April 2022 [Page 12] Internet-Draft Satellite Semantic Addressing October 2021 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. Han & Li Expires 22 April 2022 [Page 13] Internet-Draft Satellite Semantic Addressing October 2021 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 Han & Li Expires 22 April 2022 [Page 14] Internet-Draft Satellite Semantic Addressing October 2021 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: Han & Li Expires 22 April 2022 [Page 15] Internet-Draft Satellite Semantic Addressing October 2021 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. Han & Li Expires 22 April 2022 [Page 16] Internet-Draft Satellite Semantic Addressing October 2021 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, . [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, DOI 10.17487/RFC2328, April 1998, . [RFC7142] Shand, M. and L. Ginsberg, "Reclassification of RFC 1142 to Historic", RFC 7142, DOI 10.17487/RFC7142, February 2014, . Han & Li Expires 22 April 2022 [Page 17] Internet-Draft Satellite Semantic Addressing October 2021 [RFC2453] Malkin, G., "RIP Version 2", STD 56, RFC 2453, DOI 10.17487/RFC2453, November 1998, . [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, . [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200, July 2017, . 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, . [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, . [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, . [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.", . Han & Li Expires 22 April 2022 [Page 18] Internet-Draft Satellite Semantic Addressing October 2021 [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", . [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.", . [Lowest-LEO-ESA] "Lowest LEO by ESA", . [KeplerianElement] "Keplerian elements", . [OSI-Model] "OSI Model", . [StarLink] "Star Link", . [China-constellation] "China Constellation", . [SpaceX-Non-GEO] "FCC report: SPACEX V-BAND NON-GEOSTATIONARY SATELLITE SYSTEM", . Appendix A. Change Log * Initial version, 10/19/2021 Authors' Addresses Lin Han (editor) Futurewei Technologies, Inc. 2330 Central Expy Han & Li Expires 22 April 2022 [Page 19] Internet-Draft Satellite Semantic Addressing October 2021 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 Han & Li Expires 22 April 2022 [Page 20]