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Versions: 00                                                            
Path Aware Networking Research Group                            S. Zheng
Internet-Draft                                                    P. Liu
Intended status: Informational                                   Z. Chen
Expires: August 26, 2021                                    China Mobile
                                                       February 22, 2021

     Required path properties for applying path aware networking in
                 integrated space-terrestrial networks


   Integrated space-terrestrial networks are heterogeneous networks with
   various path characteristic, and usually belong to different
   administrative domains.  Therefore integrated space-terrestrial
   networks can be seen as a use case of path-aware networking.  This
   memo introduces requirements on path properties when applying path-
   aware-network in integrated space-terrestrial networks.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on August 26, 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology and Abbreviation  . . . . . . . . . . . . . . . .   3
   3.  Path properties . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Fine granular properties  . . . . . . . . . . . . . . . . . .   3
     4.1.  node properties . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Link properties . . . . . . . . . . . . . . . . . . . . .   4
   5.  Summary . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   In the integrated space-terrestrial networks, endpoint is capable to
   access space networks, mobile networks, and fixed networks.  These
   heterogeneous networks have essential difference on characteristics
   and come from different service providers, which makes it difficult
   to carry out unified management and control.  Furthermore, different
   with ground networks, the quality of links in space is fluctuating,
   the network topology changes dynamically, and the resources of space
   node is limited.  It is necessary to come out a system to release the
   burden of networks(especially space nodes with limited resource) and
   leaving the complex function to endpoint.  In other words, the path-
   aware network may help to cope with the dynamics of this kind of

   According to the definition of [RFC5136], a path is a series of links
   that connect a series of nodes from the source node to destination.
   The properties of path can be seen from the overall point of view, or
   decomposed into node properties and link properties.  Corresponding
   granular path awareness can be performed in the basis of the
   capability of the endpoint and/or the required quality of service.
   This memo will describe the required path properties from different
   granularity in integrated space-terrestrial networks.

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2.  Terminology and Abbreviation

   Integrated space-terrestrial Networks(ISTN): A network system that
   comprehensively utilizes a variety of communication network
   technologies including space networks and terrestrial networks to
   achieve global coverage.  The integrated system includes ground
   segment and space segment.  The ground segment includes terrestrial
   network nodes such as ground stations, terminals, servers controllers
   and terrestrial links such as cable, fiber.  Space segment includes
   space node such as satellites and space links such as laser and

3.  Path properties

   The path properties describe the overall properties of the whole path
   from an end-to-end perspective.

   Space and ground networks share some common properties, but due to
   the essential differences between the space network and the
   terrestrial network on characteristics such as mobility, link
   stability, resources etc., some additional properties are required to
   support path selection at the endpoint.

   Common path properties

   1.  Properties in path
   properties[I-D.irtf-panrg-path-properties],such as one way delay and
   one way packet loss.

   Additional path properties in space

   1.Available time: path available time; due to the topological
   dynamics of the space link, the path in the world-ground integrated
   network is not always available.  Therefore, it is necessary to set
   an available time for each path;

4.  Fine granular properties

   In addition to the fluctuating latency, and bandwidth, the complex
   space environment will lead to unpredictable wireless link
   disconnection.The mobility of space nodes will lead to periodic
   dynamic topology change.  Therefore, the performance of the path
   changes more frequently, and the fine granular properties can help
   the integrated space-terrestrial networks to quickly locate
   unpredictable faults and find the optimal alternative link instead of
   discarding the entire path.  For example, path properties can be
   decomposed into node properties and link properties.

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4.1.  node properties

   Common properties of nodes

   1.Node computing resources: computing resources available on ground
   nodes/space nodes.  When the available computing resource is less, it
   indicates that the node is heavy-loaded, and the path that contains
   the node should be avoided when selecting a path.

   2.Node storage resources: available storage resources of ground
   nodes/space nodes.

   Additional node properties in space

   1.Node power: This is actually the most important property of space,
   because the energy of satellite in space comes from solar panels,
   which make the node energy fluctuating with time.  If the power of
   the satellite node is not sufficient to support additional computing/
   communication functions, the satellite node is not available; it can
   be simply set to 0/1 to indicate whether the node supports additional
   computing/communication functions.

   2.Available interfaces of the node.  The interface that can be used
   to establish a link, it may contain a set of information indicating
   the direction of interface and available next hop.  This property can
   be use to derive the topology information.  The specific link status
   is excluded and needs to query the link properties described below.

   3.The future available interfaces of the node.  The movement of
   satellite nodes is periodic.  Periodicity can be used to predict the
   topology in the future to help make routing decisions.  This property
   can be sent in different manners, depending on the mechanism the
   system used to deal with the network mobility.  This property can be
   sent in each time slot if the system use snapshot.  Or to reduce the
   interaction cost, event triggered property notification can be used,
   that is the notification only executes when the available interfaces
   changes due to unexpected event.

4.2.  Link properties

   Common link properties

   1.Propagation delay:When a data packet propagates from the source
   node to the destination node, the time required for the transmission
   from the beginning to the end of the link is the propagation delay.
   Data packets are propagated at the propagation rate of the link, and
   its rate depends on the physical medium of the link.  The propagation
   delay is equal to the ratio of the distance between the nodes and the

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   propagation rate.  As the distance between the nodes changes as space
   node moves, the delay changes as well.

   2.Link media: the link media can be laser/cable/radio etc., and the
   different media can have different priority and cost, which should be
   used to do the path selection decision.

   3.Quality of link: This property can be indicated by bit error rate
   or packet loss rate, depending on the network system.

   Additional link properties in space

   1.  Available time: When the nodes at both ends of a link are
   constantly moving relative to each other, the link may be unavailable
   because the nodes move out of mutual visible area.  Therefore, it is
   necessary to know the available time of the link.

   2.  Link status: different from bit error rate, this property
   indicates the state of link, for example, when the link is
   temporarily unavailable due to space environment, it can be set in
   leave and; when the link is unavailable due to mobility, it can be
   set to down . The link state information may not come from space node
   itself but from ground measurement and control station.

5.  Summary

   Integrated space-terrestrial Networks can take advantage of the PAN
   and can be seen as a typical use cases.  When PAN is introduced into
   ISTN, it will have some different requirements on the path
   properties, and this memo study the first question in
   [I-D.irtf-panrg-questions] by list and explain some potential path

6.  Security Considerations

   It should be noticed that under the Integrated space-terrestrial
   Networks background, the topology information comes from different
   operators, they may not willing to expose their network information
   to other operators or other 3rd parties, so it is crucial to find a
   way to supply the information to end user while not expose to others.

7.  IANA Considerations

   This document has no requests to IANA.

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8.  Normative References

              Enghardt, T. and C. Krahenbuhl, "A Vocabulary of Path
              Properties", draft-irtf-panrg-path-properties-01 (work in
              progress), September 2020.

              Trammell, B., "Current Open Questions in Path Aware
              Networking", draft-irtf-panrg-questions-08 (work in
              progress), December 2020.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC5136]  Chimento, P. and J. Ishac, "Defining Network Capacity",
              RFC 5136, DOI 10.17487/RFC5136, February 2008,

Authors' Addresses

   Shaowen Zheng
   China Mobile
   Beijing  100053

   Email: zhengshaowen@chinamobile.com

   Peng Liu
   China Mobile
   Beijing  100053

   Email: liupengyjy@chinamobile.com

   Danyang Chen
   China Mobile
   Beijing  100053

   Email: chendanyang@chinamobile.com

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