A Routing Architecture for Satellite Networks
draft-li-arch-sat-00

Network Working Group                                              T. Li
Internet-Draft                                          Juniper Networks
Intended status: Informational                           5 December 2023
Expires: 7 June 2024

             A Routing Architecture for Satellite Networks
                          draft-li-arch-sat-00

Abstract

   Satellite networks present some interesting challenges for packet
   networking.  The entire topology is continually in motion, with links
   that are far less reliable than what is common in terrestrial
   networks.  Some changes to link connectivity can be anticipated due
   to orbital mechanics.

   This document proposes a routing architecture for satellite networks
   based on existing routing protocols and mechanisms, enhanced with
   scheduled link connectivity change information.  This document
   proposes no protocol changes.

Status of This Memo

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   Please review these documents carefully, as they describe your rights

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   and restrictions with respect to this document.  Code Components
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terms and Abbreviations . . . . . . . . . . . . . . . . .   2
     1.2.  Topological Considerations  . . . . . . . . . . . . . . .   4
     1.3.  Link Changes  . . . . . . . . . . . . . . . . . . . . . .   4
     1.4.  Scalability . . . . . . . . . . . . . . . . . . . . . . .   5
     1.5.  Assumptions . . . . . . . . . . . . . . . . . . . . . . .   5
       1.5.1.  Traffic Patterns  . . . . . . . . . . . . . . . . . .   5
       1.5.2.  Stochastic Connectivity . . . . . . . . . . . . . . .   6
     1.6.  Problem Statement . . . . . . . . . . . . . . . . . . . .   6
   2.  Forwarding Plane  . . . . . . . . . . . . . . . . . . . . . .   7
   3.  IGP Selection . . . . . . . . . . . . . . . . . . . . . . . .   8
   4.  Stripes and Areas . . . . . . . . . . . . . . . . . . . . . .   9
   5.  Traffic Engineering . . . . . . . . . . . . . . . . . . . . .   9
   6.  Scheduling  . . . . . . . . . . . . . . . . . . . . . . . . .  11
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     10.2.  Informative References . . . . . . . . . . . . . . . . .  14
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   Satellite networks present some interesting challenges for packet
   networking.  The entire topology is continually in motion, with links
   that are far less reliable than what is common in terrestrial
   networks.  Some changes to link connectivity can be anticipated due
   to orbital mechanics.

   This document proposes a routing architecture for satellite networks
   based on existing routing protocols and mechanisms, enhanced with
   scheduled link connectivity change information.  This document
   proposes no protocol changes.

1.1.  Terms and Abbreviations

   *  Downlink: The half of a ground link leading from a satellite to a
      ground station.

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   *  Gateway: A ground station that participates as part of the network
      and acts as the interconnect between satellite constellations and
      the planetary network.  Gateways have a much higher bandwidth than
      user stations, have ample computing capabilities, and perform
      traffic engineering duties.  Multiple gateways are assumed to
      exist, with each serving a portion of the network.

   *  GEO: Geostationary Earth Orbit.  A satellite in GEO has an orbit
      that is synchronized to planetary rotation, so it effectively sits
      over one spot on the planet.

   *  Ground link: A link between a satellite and a ground station.

   *  IGP: Interior Gateway Protocol.  A routing protocol that is used
      within a single administrative domain.  Note that 'gateway' in
      this context is semantically equivalent to 'router' and has no
      relationship to the 'gateway' used in the rest of this document.

   *  IS-IS: Intermediate System to Intermediate System routing
      protocol.  An IGP that is commonly used by service providers.

   *  ISL: Inter-satellite link.  Frequently a free space laser.

   *  L1: IS-IS Level 1

   *  L1L2: IS-IS Level 1 and Level 2

   *  L2: IS-IS Level 2

   *  LEO: Low Earth Orbit.

   *  Local gateway: Each user station is associated with a single
      gateway in its region.

   *  LSP: IS-IS Link State Protocol Data Unit.  An LSP is a set of
      packets that describe a node's connectivity to other nodes.

   *  MEO: Medium Earth Orbit.

   *  SID: Segment Identifier [RFC8402]

   *  Stripe: A set of satellites in a few adjacent orbits.  These form
      an IS-IS L1 area.

   *  SR: Segment Routing [RFC8402]

   *  Uplink: The half of a ground link leading from a ground station to
      a satellite.

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   *  User station: A ground station interconnected with a small end
      user network.

1.2.  Topological Considerations

   Satellites travel in specific orbits around their parent planet.
   Some of them have their orbital periods synchronized to the rotation
   of the planet, so they are effectively stationary over a single
   point.  Other satellites have orbits that cause them to travel across
   regions of the planet gradually or quite rapidly.  Respectively,
   these are typically known as Geostationary Earth Orbits (GEO), Medium
   Earth Orbit (MEO), or Low Earth Orbit (LEO), depending on altitude.
   For this discussion, nothing is Earth-specific and generalizes to any
   celestial body, so we use these common terms with the understanding
   that they could be equally applicable to Mars, Venus, lunar, or even
   solar orbits.

   Satellites may have data interconnections with one another through
   Inter-Satellite Links (ISLs).  Due to differences in orbits, ISLs may
   be connected temporarily, with periods of potential connectivity
   computed through orbital mechanics.  Multiple satellites may be in
   the same orbit but separated in time and space, with a roughly
   constant separation.  Satellites in the same orbit may have ISLs that
   have a higher duty cycle than cross-orbit ISLs but are still not
   guaranteed to always be connected.

   Ground stations can communicate with one or more satellites that are
   in their region.  Some ground stations have a limited capacity and
   communicate with only a single satellite at a time.  These are known
   as user stations.  Other ground stations that may have richer
   connectivity and higher bandwidth are commonly called gateways and
   provide connectivity between the satellite network and conventional
   wired networks.  Gateways serve ground stations that are in their
   geographic region and are replicated as necessary to meet the needs
   of the service.  Traffic from one ground station to another may need
   to traverse a path across multiple satellites via ISLs.

1.3.  Link Changes

   Like conventional network links, ISLs and ground links can fail at
   any time.  However, unlike conventional links, there are predictable
   times when ISLs and ground links can potentially connect and
   disconnect.  These predictions can be computed and cataloged in a
   schedule that can be distributed to relevant network elements.
   Predictions of a link connecting are not a guarantee: a link may not
   connect for a variety of reasons.  Predictions of a link
   disconnecting due to orbital mechanics are effectively guaranteed, as
   the underlying physics is extremely unlikely to improve unexpectedly.

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1.4.  Scalability

   Some proposed satellite networks are fairly large, with tens of
   thousands of proposed satellites.  A key concern is the ability to
   reach this scale and larger.

   As we know, the key to scalability is the ability to create
   hierarchical abstractions, so a key question of any routing
   architecture will be about the abstractions that can be created to
   contain topological information.

   Normal routing protocols are architected to operate with a static but
   somewhat unreliable topology.  Satellite networks lack the static
   organization of terrestrial networks, so normal architectural
   practices may not apply and alternative approaches may need
   consideration.

1.5.  Assumptions

   In this section, we discuss some of the assumptions that are the
   basis for this architectural proposal.

   The data payload is IP packets.

1.5.1.  Traffic Patterns

   We assume that the primary use of the satellite network is to provide
   access from a wide range of geographic locations.  We assume that
   providing high bandwidth bulk transit between peer networks is not a
   goal.  It has been noted that satellite networks can provide lower
   latencies than terrestrial fiber networks [Handley].  This proposal
   does not preclude such applications but also does not articulate the
   mechanisms necessary for user stations to perform the necessary
   traffic engineering computations.  Low-latency applications are not
   discussed further.

   As with most access networks, we assume that there will be
   bidirectional traffic between the user station and the gateway, but
   that the bulk of the traffic will be from the gateway to the user
   station.  We expect that the uplink from the gateway to the satellite
   network to be the bandwidth bottleneck, and that gateways will need
   to be replicated to scale the uplink bandwidth.

   We assume that it is not essential to provide optimal routing for
   traffic from user station to user station.  If this traffic is sent
   first to a gateway and then back into the satellite network, this
   would be acceptable.  This type of route is commonly called a
   'hairpin' and is not discussed further.

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   We assume that traffic for a user station should enter the network
   through a gateway that is in some close topological proximity to the
   user station.  This is to maximize the practical capacity of the
   satellite network.  Similarly, we assume that user station traffic
   should exit the network through the gateway that is in the closest
   topological proximity.

   This architecture does not preclude gateway-to-gateway traffic, but
   it does not seek to optimize it.

   We assume that a user station registers with one satellite at a time,
   forming a temporary association that is relayed to the local gateway.
   The mechanism for this registration is outside of the scope of this
   document.

1.5.2.  Stochastic Connectivity

   We assume that links in general will be available when scheduled.  As
   with any network, there will be failures, and the schedule is not a
   guarantee, but we also expect that the schedule is mostly accurate.
   We assume that at any given instant, there is enough connectivity to
   run the network and support the traffic demand.  If this assumption
   does not hold, then no routing architecture can magically make the
   network more capable.

   We assume that, in general, intra-orbit ISLs have higher reliability
   and persistence than inter-orbit ISLs.

   We assume that the network is connected at all times, even if some
   links are down.  This implies that there is always some path to the
   destination.  In the extreme case where there is no such path, we
   assume that it is acceptable to drop the payload packets.  We do not
   require buffering of traffic when a link is down.  Instead, traffic
   should be rerouted.

1.6.  Problem Statement

   The goal of the routing architecture is to provide an organizational
   structure to protocols running on the satellite network such that
   topology information is conveyed through relevant portions of the
   network, that paths are computed across the network, and that data
   can be delivered along those paths, and the structure can scale to a
   very large network without undue changes to the organizational
   structure.

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2.  Forwarding Plane

   The end goal of a network is to deliver traffic.  In a satellite
   network where the topology is in a continual state of flux and the
   user stations are frequently changing their association with the
   satellites, having a highly flexible and adaptive forwarding plane is
   essential.  Toward this end, we propose to use MPLS as the
   fundamental forwarding plane architecture [RFC3031].  Specifically,
   we propose to use a Segment Routing (SR) [RFC8402] based approach
   with an MPLS data plane [RFC8660], where each satellite is assigned a
   node Segment Identifier (SID).  A path through the network can be
   then expressed as a label stack of node SIDs.  IP forwarding is not
   used within the internals of the satellite network, although each
   satellite may be assigned an IP address for management purposes.
   Existing SR label stack compression algorithms may be used, so that
   the label stack need only contain the significant waypoints along the
   path.  This implies that the label stack operates as a form of loose
   source routing through the network.  If there is an unexpected
   topology change in the network, then the IGP will compute a new path
   to the next waypoint, allowing packet delivery despite ISL failures.

   We assume that there is a link-layer mechanism for a user station to
   associate with a satellite.  User stations will have an IP address
   that is assigned from a prefix managed by its local gateway.  The
   mechanisms for this assignment and its communication to the end
   station are not discussed herein but might be similar to DHCP
   [RFC2131].  User station IP addresses change infrequently and do not
   reflect their association with their first-hop satellite.  Gateways
   advertise a prefix into the global Internet for all of its local user
   stations.

   User stations may be assigned a node SID, in which case MPLS
   forwarding can be used for all hops to the user station.
   Alternatively, if the user station does not have a node SID, then the
   last hop from the satellite to the end station can be performed based
   on the destination IP address of the packet.  This does not require a
   full longest prefix match lookup as the IP address is merely a unique
   identifier at this point.

   Similarly, gateways may be assigned a node SID.  A possible
   optimization is that a single SID value be assigned as a global
   constant to always direct traffic to the topologically closest
   gateway.  If traffic engineering is required for traffic that is
   flowing to a gateway, a specific path may be encoded in a label stack
   that is attached to the packet by the user station or by the first-
   hop satellite.

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   Gateways can also perform traffic engineering by using different
   paths and label stacks for different traffic flows.  Routing a single
   traffic flow across multiple paths has proven to cause performance
   issues with transport protocols, so that approach is not recommended.

3.  IGP Selection

   The IETF currently actively supports two Interior Gateway Protocols
   (IGPs): OSPF [RFC2328][RFC5340] and IS-IS [ISO10589] [RFC1195].

   OSPF requires that the network operate around a backbone area, with
   subsidiary areas hanging off of the backbone.  While this works well
   for traditional terrestrial networks, this does not seem appropriate
   for satellite networks, where there is no centralized portion of the
   topology.

   IS-IS has a different hierarchical structure, where Level 1 (L1)
   areas are connected sets of nodes, and then Level 2 (L2) is a
   connected subset of the topology that intersects all of the L1 areas.
   Individual nodes can be L1, L2, or both (L1L2).  In particular, we
   propose that all nodes in the network be L1L2 so that local routing
   is done based on L1 information and then global routing is done based
   on L2 information.

   IS-IS also has the interesting property that it does not require
   interface addresses.  This feature is commonly known as 'unnumbered
   interfaces'.  This is particularly helpful in satellite topologies
   because it implies that ISLs may be used flexibly.  Sometimes an
   interface might be used as an L1 link to another satellite and a few
   orbits later it might be used as an L1L2 link to a completely
   different satellite without any reconfiguration or renumbering.

   Scalability for IS-IS can be achieved through the use of a proposal
   known as Area Proxy [I-D.ietf-lsr-isis-area-proxy].  With this
   proposal, all of the nodes in an L1 area combine their information
   into a single L2 Link State Protocol Data Unit (LSP).  This implies
   that the size of the L1 Link State Database (LSDB) scales as the
   number of nodes in the L1 area and the size of the L2 LSDB scales
   with the number of L1 areas.

   The Area Proxy proposal also includes the concept of an Area SID.
   This is useful because it allows traffic engineering to construct a
   path that traverses areas with a minimal number of label stack
   entries.

   Suppose, for example, that a network has 1,000 L1 areas, each with
   1,000 satellites.  This would then mean that the network supports
   1,000,000 satellites, but only requires 1,000 entries in its L1 LSDB

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   and 1,000 entries in its L2 LSDB; numbers that are easily achievable
   today.  The resulting MPLS label table would contain 1,000 node SIDs
   from the L1 (and L2) LSDB and 1,000 area SIDs from the L2 LSDB.  If
   each satellite advertises an IP address for management purposes, then
   the IP routing table would have 1,000 entries for the L1 management
   addresses and 1,000 area proxy addresses from L2.

   In this proposal, IS-IS does not carry any IP routes other than those
   that are in the satellite topology.  In particular, there are no IP
   routes for user stations or the remainder of the Internet.

4.  Stripes and Areas

   A significant problem with any link state routing protocol is that of
   area partition.  While there have been many proposals for automatic
   partition repair, none has seen significant production deployment.
   It seems best to simply avoid this issue altogether and ensure that
   areas have an extremely low probability of partitioning.

   As discussed above, intra-orbit ISLs are assumed to have higher
   reliability and persistence than inter-orbit ISLs.  However, even
   intra-orbit ISLs are not sufficiently reliable to avoid partition
   issues.  Therefore, we propose to group a small number of adjacent
   orbits as an IS-IS L1 area, called a stripe.  We assume that for any
   given reliability requirement, there is a small number of orbits that
   can be used to form a stripe that satisfies the reliability
   requirement.

   Stripes are connected to other adjacent stripes using the same ISL
   mechanism, forming the L2 topology of the network.  Each stripe
   should have multiple L2 connections and should never become
   partitioned from the remainder of the network.

   MEO and GEO constellations that have intra-constellation ISLs can
   also form an IS-IS L1L2 area.  Satellites that lack intra-
   constellation ISLs are better as independent L2 nodes.

5.  Traffic Engineering

   Forwarding in this architecture is straightforward.  A path from a
   gateway to a user station on the same orbit only requires a single
   node SID for the satellite that provides the downlink to the user
   station.

   Similarly, a user station returning a packet to a gateway need only
   provide a gateway node SID.

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   For off-orbit forwarding, the situation is a bit more complex.  A
   gateway would need to provide the area SID of the destination area
   plus the node SID of the downlink satellite.  For return traffic,
   user stations or first-hop satellites would want to provide the area
   SID for the gateway as well as the gateway SID.

   As an example, consider a packet from an Internet destination S to a
   user station D.  A local gateway L has injected a prefix covering D
   into BGP and advertised it globally.  The packet is forwarded to L
   using legacy IP forwarding.  When L receives the packet, it performs
   a lookup in a pre-computed forwarding table.  This contains a SID
   list for the user station that has already been converted into a
   label stack.  Suppose that the user station is currently associated
   with a different orbit so that the label stack will contain an area
   label A and a label for the satellite associated with the user
   station U, resulting in a label stack (A, U).

   The local gateway forwards this into the satellite network.  The
   first hop satellite now forwards based on the area label A at the top
   of the stack.  All area labels are propagated as part of the L2
   topology.  This forwarding continues until the packet reaches a
   satellite that is adjacent to the destination area.  That satellite
   performs a penultimate hop pop on label A, removing that label and
   forwarding the packet into the destination area.

   The packet is now forwarded based on the remaining label U, which was
   propagated as part of the L1 topology.  The last satellite forwards
   the packet based on the destination address D and forwards the packet
   to the user station.

   The return case is similar.  The label stack, in this case, consists
   of a label for the local gateway's area, A', and the label for the
   local gateway, L, resulting in the stack (A', L).  The forwarding
   mechanisms are similar to the previous case.

   Very frequently, access networks congest due to oversubscription and
   the economics of access.  Network operators can use traffic
   engineering to ensure that they are getting higher efficiency out of
   their networks by utilizing all available paths and capacity near any
   congestion points.  In this particular case, the gateway will have
   information about all of the traffic that it is generating and can
   use all of the possible paths through the network in its topological
   neighborhood.  Since we're already using SR, this is easily done just
   by adding more explicit SIDs to the label stack.  These can be
   additional area SIDs, node SIDs, or adjacency SIDs.  Path computation
   can be performed by traditional Path Computation Elements (PCE).

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   Each gateway or its PCE will need topological information from all of
   the areas that it will route through.  It can do this by being a
   participant in the IGP, either directly, via a tunnel, or another
   delivery mechanism such as BGP-LS [RFC7752].  User stations do not
   participate in the IGP.

   Traffic engineering for traffic into a gateway can also be provided
   by an explicit SR path on the traffic.  This can help ensure that
   ISLs near the gateway do not congest with traffic for the gateway.
   These paths can be computed by the gateway or PCE and then
   distributed to the first-hop satellite or user station, which would
   then apply them to traffic.  The delivery mechanism is outside of the
   scope of this document.

6.  Scheduling

   The most significant difference between terrestrial and satellite
   networks from a routing perspective is that some of the topological
   changes that will happen to the network can be anticipated and
   computed.  Both link and node changes will affect the topology and
   the network should react smoothly and predictably.

   The management plane is responsible for providing information about
   scheduled topological changes.  The exact details of how the
   information is disseminated are outside of the scope of this document
   but could be done through a YANG model
   [I-D.united-tvr-schedule-yang].  Scheduling information needs to be
   accessible to all of the nodes that will make routing decisions based
   on the topological changes in the schedule, so information about an
   L1 topological change will need to be circulated to all nodes in the
   L1 area and information about L2 changes will need to propagate to
   all L2 nodes, plus the gateways and PCEs that carry the related
   topological information.

   There is very little reaction that the network should do in response
   to a topological addition.  A link coming up or a node joining the
   topology should not have any functional change until the change is
   proven to be fully operational based on the usual liveness mechanisms
   found within IS-IS.  Nodes may pre-compute their routing table
   changes but should not install them before all of the relevant
   adjacencies are flooded.  The benefits of this pre-computation appear
   to be very small.  Gateways and PCEs may also choose to pre-compute
   paths based on these changes, but should be careful to not install
   paths using the new parts of the topology until they are confirmed to
   be operational.  If some path pre-installation is performed, gateways
   and PCEs must be prepared for the situation where the topology does
   not become operational and may need to take alternate steps instead,
   such as reverting any related pre-installed paths.

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   The network may choose to not do any pre-installation or pre-
   computation in reaction to topological additions, at a small cost of
   some operational efficiency.

   Topological deletions are an entirely different matter.  If a link or
   node is to be removed from the topology, then the network should act
   before the anticipated change to route traffic around the expected
   topological loss.  Specifically, at some point before the topology
   change, the affected links should be set to a high metric to direct
   traffic to alternate paths.  This is a common operational procedure
   in existing networks when links are taken out of service, such as
   when proactive maintenance needs to be performed.  This type of
   change does require some time to propagate through the network, so
   the metric change should be initiated far enough in advance that the
   network converges before the actual topological change.  Gateways and
   PCEs should also update paths around the topology change and install
   these changes before the topology change takes place.  The time
   necessary for both IGP and path changes will vary depending on the
   exact network and configuration.

7.  Security Considerations

   This document discusses one possible routing architecture for
   satellite networks.  It proposes no new protocols or mechanisms and
   thus has no new security impact.  Security for IS-IS is provided by
   [RFC5304].

8.  Acknowledgements

   We would like to thank Dino Farinacci, Olivier De jonckere, and Dean
   Bogdanovic for their comments.

9.  IANA Considerations

   This document makes no requests for IANA.

10.  References

10.1.  Normative References

   [ISO10589] International Organization for Standardization,
              "Intermediate System to Intermediate System Intra-Domain
              Routing Exchange Protocol for use in Conjunction with the
              Protocol for Providing the Connectionless-mode Network
              Service (ISO 8473)", ISO/IEC 10589:2002 , November 2002,
              <https://standards.iso.org/ittf/
              PubliclyAvailableStandards/
              c030932_ISO_IEC_10589_2002(E).zip>.

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   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031,
              DOI 10.17487/RFC3031, January 2001,
              <https://www.rfc-editor.org/info/rfc3031>.

   [RFC8660]  Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing with the MPLS Data Plane", RFC 8660,
              DOI 10.17487/RFC8660, December 2019,
              <https://www.rfc-editor.org/info/rfc8660>.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, DOI 10.17487/RFC2131, March 1997,
              <https://www.rfc-editor.org/info/rfc2131>.

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

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <https://www.rfc-editor.org/info/rfc5340>.

   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, DOI 10.17487/RFC1195,
              December 1990, <https://www.rfc-editor.org/info/rfc1195>.

   [I-D.ietf-lsr-isis-area-proxy]
              Li, T., Chen, S., Ilangovan, V., and G. S. Mishra, "Area
              Proxy for IS-IS", Work in Progress, Internet-Draft, draft-
              ietf-lsr-isis-area-proxy-09, 12 March 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-lsr-
              isis-area-proxy-09>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,
              <https://www.rfc-editor.org/info/rfc7752>.

   [I-D.united-tvr-schedule-yang]
              Qu, Y., Lindem, A., Kinzie, E., Fedyk, D., and M.
              Blanchet, "YANG Data Model for Scheduled Attributes", Work

Li                         Expires 7 June 2024                 [Page 13]
Internet-Draft           Routing for Satellites            December 2023

              in Progress, Internet-Draft, draft-united-tvr-schedule-
              yang-00, 11 October 2023,
              <https://datatracker.ietf.org/doc/html/draft-united-tvr-
              schedule-yang-00>.

   [RFC5304]  Li, T. and R. Atkinson, "IS-IS Cryptographic
              Authentication", RFC 5304, DOI 10.17487/RFC5304, October
              2008, <https://www.rfc-editor.org/info/rfc5304>.

10.2.  Informative References

   [Handley]  Handley, M., "Delay is Not an Option: Low Latency Routing
              in Space", ACM Proceedings of the 17th ACM Workshop on Hot
              Topics in Networks, DOI 10.1145/3286062.3286075, November
              2018, <https://doi.org/10.1145/3286062.3286075>.

Author's Address

   Tony Li
   Juniper Networks
   Email: tony.li@tony.li

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