Internet DRAFT - draft-contreras-tvr-alto-exposure
draft-contreras-tvr-alto-exposure
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
draft-contreras-tvr-alto-exposure-00
Abstract
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.
Status of This Memo
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This Internet-Draft will expire on 3 September 2023.
Copyright Notice
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
Controller.
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
[I-D.ietf-alto-performance-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
[RFC8896]:
* "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
advertisements
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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[I-D.birrane-tvr-use-cases]
Birrane, E. J., "TVR (Time-Variant Routing) Use Cases",
Work in Progress, Internet-Draft, draft-birrane-tvr-use-
cases-00, 24 October 2022,
<https://datatracker.ietf.org/doc/html/draft-birrane-tvr-
use-cases-00>.
[I-D.contreras-alto-ietf-nef]
Contreras, L. M., "Considering ALTO as IETF Network
Exposure Function", Work in Progress, Internet-Draft,
draft-contreras-alto-ietf-nef-01, 11 July 2022,
<https://datatracker.ietf.org/doc/html/draft-contreras-
alto-ietf-nef-01>.
[I-D.ietf-alto-performance-metrics]
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,
<https://datatracker.ietf.org/doc/html/draft-ietf-alto-
performance-metrics-28>.
[I-D.irtf-nmrg-network-digital-twin-arch]
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,
<https://datatracker.ietf.org/doc/html/draft-irtf-nmrg-
network-digital-twin-arch-02>.
[I-D.taylor-tvr-prb-stmt]
Taylor, R., "Time Variant Routing Problem Statement", Work
in Progress, Internet-Draft, draft-taylor-tvr-prb-stmt-00,
24 October 2022, <https://datatracker.ietf.org/doc/html/
draft-taylor-tvr-prb-stmt-00>.
[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,
<https://www.rfc-editor.org/info/rfc7285>.
[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,
<https://www.rfc-editor.org/info/rfc7971>.
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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, <https://www.rfc-editor.org/info/rfc8896>.
Acknowledgements
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
Telefonica
Ronda de la Comunicacion, s/n
28050 Madrid
Spain
Email: luismiguel.contrerasmurillo@telefonica.com
URI: http://lmcontreras.com
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