TVR                                                      L. M. Contreras
Internet-Draft                                                Telefonica
Intended status: Informational                              2 March 2023
Expires: 3 September 2023

        Using ALTO for exposing Time-Variant Routing information


   Network operations can require time-based, scheduled changes in
   nodes, links, adjacencies, etc.  All those changes can alter the
   connectivity in the network in a predictable manner, which is known
   as Time-Variant Routing (TVR).  Existing IETF solutions like ALTO can
   assist on the exposure of such predicted changes to both internal and
   external applications then anticipating the occurence of routing
   changes.  This document describes how ALTO helps in that purpose.

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   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Capabilities of ALTO for exposing information . . . . . . . .   3
     2.1.  ALTO exposed information  . . . . . . . . . . . . . . . .   4
     2.2.  Mechanism for anticipating routing changes in ALTO  . . .   4
   3.  Interaction with routing protocols augmented to support TVR
           advertisements  . . . . . . . . . . . . . . . . . . . . .   5
   4.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security and operational considerations . . . . . . . . . . .   5
   6.  Informative References  . . . . . . . . . . . . . . . . . . .   5
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   There can be operational situations where changes in the network,
   such as modifications in either nodes, links or adjacencies, can
   introduce variations on the routing of that network.  Use cases
   representative of such operational situations are documented in
   [I-D.birrane-tvr-use-cases].  Those predictable changes can be
   scheduled from a higher-level system (e.g., OSS) or from a Network

   Since the expected changes can be predicted beforehand, then it is
   possible to anticipate the impacts of that changes in the routing of
   the network, for instance by means of algorithms embedded in the
   Network Controller allowing to recalculate the resulting routing
   metrics, or through experimental observations e.g. in network digital
   twins [I-D.irtf-nmrg-network-digital-twin-arch].

   Being feasible then to automatize the changes and to pre-calculate
   the impacts that those changes can introduce into the routing of the
   network, it is possible to expose such changes in advance in a way
   that applications (both internal and external) can become aware of
   those routing variations along time.

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   Current IETF solutions like ALTO [RFC7285] have been conceived for
   exposing topological information with associated metrics.  In
   consequence, ALTO can be perceived as a suitable piece for allowing
   to expose the impacts due to changes in the routing of a network.
   Figure 1 sketches a potential architecture facilitating the exposure
   of changes introduced by TVR operation.  There can be multiple
   variants of such architecture.

        Network             (programming       (impact
        Operator ---------+ of scheduled      estimation
                          | TVR changes)     of scheduled
                          V                  TVR changes)
                   +-------------+       +--------------+
                   |   Network   |       |   Network    |
                   |  Controller |<----->| Digital Twin |
                   +-------------+       +--------------+
                       A     |
   (feeding impacts    |     |        (activation
   of scheduled +------+     +------+ of scheduled
   TVR changes) |                   | TVR changes)
                |                   |
                V                   V
           +--------+            ,------._
           |  ALTO  |         ,-'         `-.
           | Server |        /               \
           +--------+       (     Network     )
                A            \               /
                |             `-.         ,-'
     (exposure  |                `+------'
   of scheduled |                     ^
   TVR changes) |                     :
                |  (awareness         :
                | of scheduled        v
                | TVR changes) +-------------+
                +------------->| Application |

   Figure 1.  Potential architecture using ALTO for TVR

2.  Capabilities of ALTO for exposing information

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2.1.  ALTO exposed information

   ALTO [RFC7285] provides topological-related information in the form
   of both network and cost maps.  The network map basically summarizes
   the IP address ranges aggregated in each Provider-defined Identifier
   (PID).  Such IP addresses define either customers or service
   functions attached to each network node.  The cost map details the
   topological relationship among PIDs in terms of a certain metric.
   The basic metric provided is the routing cost among PIDs, but other
   metrics can be also provided such as performance-related metrics

   Because of the possibility of incorporating additional metrics and a
   variety of topological information, ALTO can be considered as a
   generic IETF network exposure function [I-D.contreras-alto-ietf-nef].

2.2.  Mechanism for anticipating routing changes in ALTO

   For the purpose of exposing future changes on the reachability
   between PIDs in the network, ALTO defines in [RFC8896] a calendared
   cost map (named ALTO cost calendar) which allows to signal future
   changes on the cost metric.  Thus, for a metric related to routing,
   the cost calendar can expose scheduled modifications in the
   connectivity between PIDs in a natural manner.

   The ALTO cost calendar presents the information (i.e., metrics
   between PIDs) in the form of JSON arrays, where each listed value
   corresponds to a certain time interval.  The ALTO cost calendar also
   includes attributes to describe the time scope of the calendar.  The
   calendar provided by ALTO has the following attributes defined in

   *  "Calendar-start-time", which indicates the date at which the first
      value of the calendar applies.

   *  "Time-interval-size", that defines the duration of an ALTO
      Calendar time interval in a unit of seconds.

   *  "Number-of-intervals", that indicates the number of values of the
      cost calendar array.

   *  "Repeated", which is an optional attribute that indicates how many
      iterations of the calendar value array have the same values.

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3.  Interaction with routing protocols augmented to support TVR

   The architecture in Figure 1 assumes the intervention of a Network
   Controller in order to schedule and activate the changes in the
   network in a predictable manner.  However, it could be the case that
   existing routing protocols become augmented in order to natively
   support the advertisement of network changes along the time, as
   suggested in [I-D.taylor-tvr-prb-stmt].  If that is the case, ALTO
   can participate of the network routing information by listening to
   IGPs and/or peering with BGP speakers, as described in [RFC7971].

4.  Discussion

   Several topics require further discussion with regards the usage of
   ALTO for TVR.

   *  ALTO enables a way of exposing Time-Variant Routing information to
      applications.  It is necessary to assess if the exposed
      information reflects the set of actions that can be scheduled in
      TVR according to [I-D.taylor-tvr-prb-stmt].

   *  ALTO cost calendar defines a number of time-related attributes.
      It is necessary to analyze if such attributes are sufficient for
      expressing the time variance nature of the routing changes in TVR.

   *  The expectation in [I-D.taylor-tvr-prb-stmt] is to extend existing
      routing protocols to convey TVR information.  It is necessary to
      define how ALTO can participate of the routing information
      processing and analyzing the new TVR-related information included
      in the routing protocols.

   *  The data model (or models) that could be defined in TVR could be
      leveraged by ALTO, so that can be aligned in terms of the time-
      variant routing information to be exposed to applications.  It is
      needed an analysis of potential improvements to calendared
      routing-related information in ALTO cost calendar.

   These topics can motivate further work in TVR and/or ALTO WGs.

5.  Security and operational considerations

   Same security and operational considerations as described in
   [RFC8896] apply also in this document.

6.  Informative References

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              Birrane, E. J., "TVR (Time-Variant Routing) Use Cases",
              Work in Progress, Internet-Draft, draft-birrane-tvr-use-
              cases-00, 24 October 2022,

              Contreras, L. M., "Considering ALTO as IETF Network
              Exposure Function", Work in Progress, Internet-Draft,
              draft-contreras-alto-ietf-nef-01, 11 July 2022,

              Wu, Q., Yang, Y. R., Lee, Y., Dhody, D., Randriamasy, S.,
              and L. M. Contreras, "ALTO Performance Cost Metrics", Work
              in Progress, Internet-Draft, draft-ietf-alto-performance-
              metrics-28, 21 March 2022,

              Zhou, C., Yang, H., Duan, X., Lopez, D., Pastor, A., Wu,
              Q., Boucadair, M., and C. Jacquenet, "Digital Twin
              Network: Concepts and Reference Architecture", Work in
              Progress, Internet-Draft, draft-irtf-nmrg-network-digital-
              twin-arch-02, 24 October 2022,

              Taylor, R., "Time Variant Routing Problem Statement", Work
              in Progress, Internet-Draft, draft-taylor-tvr-prb-stmt-00,
              24 October 2022, <

   [RFC7285]  Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S.,
              Previdi, S., Roome, W., Shalunov, S., and R. Woundy,
              "Application-Layer Traffic Optimization (ALTO) Protocol",
              RFC 7285, DOI 10.17487/RFC7285, September 2014,

   [RFC7971]  Stiemerling, M., Kiesel, S., Scharf, M., Seidel, H., and
              S. Previdi, "Application-Layer Traffic Optimization (ALTO)
              Deployment Considerations", RFC 7971,
              DOI 10.17487/RFC7971, October 2016,

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   [RFC8896]  Randriamasy, S., Yang, R., Wu, Q., Deng, L., and N.
              Schwan, "Application-Layer Traffic Optimization (ALTO)
              Cost Calendar", RFC 8896, DOI 10.17487/RFC8896, November
              2020, <>.


   This work has been partially funded by the Spanish Ministry of
   Economic Affairs and Digital Transformation and the European Union -
   NextGenerationEU under projects OPTIMAIX_OaaS (Ref.  TSI-
   063000-2021-34) and OPTIMAIX_NDT (Ref.  TSI-063000-2021-35).

Author's Address

   Luis M. Contreras
   Ronda de la Comunicacion, s/n
   28050 Madrid

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