NMRG LM. Contreras
Internet-Draft Telefonica
Intended status: Informational P. Demestichas
Expires: 27 April 2023 WINGS
J. Tantsura
Microsoft
October 2022
IETF Network Slice Intent
draft-contreras-nmrg-transport-slice-intent-06
Abstract
Slicing at the transport network is expected to be offered as part of
end-to-end network slices, fostered by the introduction of new
services such as 5G. This document explores the usage of intent
technologies for requesting IETF network slices.
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Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. IETF network slice intent . . . . . . . . . . . . . . . . . . 3
3. Foundation of IETF network slice intents . . . . . . . . . . 4
3.1. Slice templates . . . . . . . . . . . . . . . . . . . . . 4
3.2. Additional information needed for a network slice at the
IETF domain . . . . . . . . . . . . . . . . . . . . . . . 4
3.3. Slice intent lifecycle . . . . . . . . . . . . . . . . . 5
4. Mechanisms for translating IETF network slice intents . . . . 7
4.1. Translation approaches and interaction with the upper
systems . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.2. Intent-based system suite . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 9
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
Network slicing is emerging as the future model for service offering
in telecom operator networks. Conceptually, network slicing provides
a customer with an apparent dedicated network built on top of logical
(i.e. virtual) and/or physical functions and resources supported by a
shared infrastructure, provided by one or more telecom operators.
The concept of network slicing has been largely fostered by the
advent of 5G services that are expected to be deployed on top of
different kind of slices, each built to support specific
characteristics (extreme low latency, high bandwidth, etc).
As part of an end-to-end network slice it is expected to have a
number of network slices at transport level (referred as IETF network
slices) providing the necessary connectivity to the rest of
components of the end-to-end slice, e.g., mobile packet core slice.
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For a definition of an IETF network slice refer to
[I-D.ietf-teas-ietf-network-slices]. The following paragraph is
directly taken from it: "An IETF Network Slice Service enables
connectivity between a set of CEs with specific Service Level
Objectives (SLOs) and Service Level Expectations (SLEs) over a common
underlay network."
Intent is a high-level, declarative goal that operates at the level
of a network and services it provides, not individual devices. It is
used to define outcomes and high-level operational goals.
In consequence, it seems very convenient to apply the intent-based
mechanisms for the provision of IETF network slices, providing the
adequate level of abstraction towards the transport network control
and management planes.
This document leverages current industry trends in the definition of
end-to-end network slices. The final objective is to describe
intents that can be used to flexibly declare the operational aspects
and goals of an IETF network slice, meaning that the customer could
declare what kind of IETF network slice is needed (the outcome) and
not how to achieve the goals of the IETF network slice.
2. IETF network slice intent
As stated in [RFC9315], "Intent is a declaration of operational goals
that a network is supposed to meet and outcomes that the network is
supposed to deliver, without specifying how to achieve or how to
implement them. Those goals and outcomes are defined in a manner
that is purely declarative - they specify what to accomplish, not how
to achieve it."
When applied to transport networks, this implies that an intent for
IETF network slices should provide the necessary abstraction with
respect to implementation details, including the final devices (or
resources) involved, and be focused on the characteristics and
performance expectations related to it.
With that aim it can be expected that the intent based system can
fulfill and assure the requested IETF network slice, triggering
initial configurations at the time of initial provisioning and
corrective actions during the IETF network slice lifetime.
Regarding the corrective actions it is possible to differentiate two
levels. First, corrective actions that could be performed by the
management and control capabilities of the network (i.e., by the IETF
Network Slice Controller) to maintain the Service level Objectives
(SLOs) as originally declared in the slice intent, so being these
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internal actions to the management and control elements of the
network. Second, corrective actions that could be necessary to
perform due to incongruences between the SLOs expressed in the intent
and the observed monitoring information, then requiring some
adaptation to the intent itself in order to perform the corrective
action.
3. Foundation of IETF network slice intents
3.1. Slice templates
The industrial interest around 5G is accelerating network deployments
and operational changes.
With this respect, the GSMA has been developing a universal blueprint
that can be used by any vertical customer to request the deployment
of a network slice instance (NSI) based on a specific set of service
requirements. Such a blueprint is a network slice descriptor called
Generic Slice Template (GST) [GSMA]. The GST contains multiple
attributes that can be used to characterize a network slice. A
particular template filled with values generates a specific Network
Slice Type(NEST).
Such templates refer to the end-to-end network slice, including the
transport part. Despite the fact that some of the values would not
have applicability for the transport network, others do. An analysis
of the relevant attributes is performed in
[I-D.ietf-teas-ietf-network-slice-use-cases].
According to 3GPP propositions [TS28.541], an upper 3GPP Management
System interacts with the transport network for establishing the
necessary slices at the transport level. Such interaction can be
expected to happen using the IETF network slice intent, described to
an intent-based system (IBS) in the transport network part.
3.2. Additional information needed for a network slice at the IETF
domain
The previous slice templates provide a number of parameters that
functionally characterizes the behavior of the network slice as
expected by the slice customer. However, apart from the slice
characteristics, further information is needed in order to request
the realization of a slice towards the IETF Network Slice controller,
as follows:
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* Identification of the slice endpoints to be connected where a
given slice template applies. It is necessary to clearly identify
which are the origins and destinations of the traffic flows in
each IETF Network Slice.
* Information that could assist the slice provider in order to
identify the endpoint counterpart at the provider side. This
information could come in terms of some identifier meaningful for
both customer and provider which can help to retrieve the
necessary information to clearly identify the entry point of the
traffic flow at the provider side. Such an identifier could have
been negotiated beforehand between customer and provider (e.g.,
allocation of an administrative identifier corresponding to the
attachment circuit connecting customer and provider premises).
* For advanced slices where the customer could have some control
over the allocated network slice resources, the customer could
provide information about the virtual network topology expected to
form the requested IETF Network Slice. This relates e.g. to the
concept of virtual network topology types in [RFC8454].
* Additional information that could assist on the further
realization of the IETF network slice (e.g., protocols or
mechanisms to used).
The customer needs then to combine the information coming from the
slice templates with this additional information to form the IETF
network slice template for further processing.
3.3. Slice intent lifecycle
According to the intent lifecycle in [RFC9315], the IBS, after
recognizing the intent, will proceed to translate it in order to
interact with a IETF network slice controller by using a NBI as
proposed in [I-D.ietf-teas-ietf-network-slice-use-cases].
Figure 1 captures the intent procedure for the fulfillment phase.
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User Space : Translation / IBS : Network Ops
: Space : Space
: :
+----------+ : +----------+ +-----------+ : +-----------+
Fulfill |recognize/|---> |translate/|-->| learn/ |-->| configure/|
|generate | | | | plan/ | | provision |
|intent |<--- | refine | | render | : | |
+----------+ : +----------+ +-----------+ : +-----------+
: :
.........................................................................
Slice Customer : Slice Provider
-------------- : --------------
:
- Customized Slice : - Identification of IETF : - Slice request
Templates : network slice endpoints : to IETF NSC by
- Service SLOs as : and connectivity pattern : using slice
understood by : - Derivation of network SLOs : NBI YANG model
slice customer : and SLEs from high-level :
: Customer Service SLOs :
: :
Figure 1: Fulfillment phase of the IETF Network Slice service Intent
Similarly, Figure 2 sketches the intent procedure for the assurance
phase.
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: +--------+ :
: |validate| : +----------+
: +----^---+ <----| monitor/ |
Assure +-------+ : +---------+ +-----+---+ : | observe/ |
|report | <---- |abstract |<---| analyze | <----| |
+-------+ : +---------+ |aggregate| : +----------+
: +---------+ :
.....................................................................
Slice Customer : Slice Provider
-------------- : --------------
:
- Analysis of the : - Checking of monitored data : - Collection of
reported metrics : for internal closed loops : monitoring info
against the slice : to ensure commited SLOs and : related to the
request : SLEs (inner closed loop) : slice (i.e.,
- Trigger of actions : - Aggregation of data : SLOs and SLEs of
if needed, e.g., : producing an abstracted view: connectivity
slice modification : fitted to the slice request : constructs, sdp,
(outer closed loop): : etc.)
Figure 2: Assurance phase of the IETF Network Slice service Intent
Both Fulfillment and Assurance phases are integral part of the IETF
Network Slice service intent.
4. Mechanisms for translating IETF network slice intents
This section describes approaches for implementing mechanisms to
translate IETF network slice intents. As part of such translation it
could be necessary to translate the slice needs expressed by the
customer in terms of service-specific SLOs (e.g., high-resolution
real-time video quality) to network- or connectivity-specific SLOs
(e.g., a correspondent throughput and/or latency) which are the SLOs
an IETF Network Slice Controller understands. More on this can be
found in [TMV].
4.1. Translation approaches and interaction with the upper systems
A suite of mechanisms will be required to allow instantiation of the
user's intent into a IETF network slice. In order to be able to
deliver an end2end Intent driven slice - a well defined set of
context aware attributes that allow unambiguous instantiation of the
intent should be agreed upon. A combination of a structured set of
attributes communicated between an IBN and an upper layer system with
user input would allow an IBN to have intent modeled and reason about
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its completeness/validity. Translation approaches and interaction
with the upper systems might benefit from Natural Language Processing
(NLP) technics that are needed for enabling high level expression of
requirements found missing. The goal would be to identify and
classify the answers for as many fields as possible from the Generic
Slice Template (GST), based on the free text / speech provided by the
user. As it is highly unlikely that the minimum set of fields to
properly define an IETF network slice (geo-temporal characteristics,
performance characteristics, SLO and SLA properties) will be
fulfilled in this first step, a follow up two-step approach might
need to be implemented.
* The minimum missing fields from the GST have to be identified and
appropriate questions have to be generated (e.g. based on a pool
of available questions correlated with each field, or based on AI
approaches).
* An iterative interrogation phase will be initiated towards the
user using the previously generated questions, until the user
provides all the missing information, so the intent can be modeled
accordingly.
Interaction with the user and higher-up systems can potentially be
further improved by utilizing Machine Learning techniques.
4.2. Intent-based system suite
In order to consolidate on the set of devices, technologies and
resources to be used, a combination of deterministic or stochastic
computation approaches will be needed. Deterministic approaches will
rely on mathematical models and respective algorithms. Stochastic
approaches will rely on technologies like machine learning. Their
goal will be to learn from experience, so as to optimize future
decisions from the viewpoint of speed and reliability. The target of
learning will be related to the service behavior and to the
anticipated network status in the area and time period of the service
provision.
5. Security Considerations
To be done.
6. IANA Considerations
This draft does not include any IANA considerations
7. References
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[GSMA] "Generic Network Slice Template, version 7.0", NG.116 ,
June 2022.
[I-D.ietf-teas-ietf-network-slice-use-cases]
Luis Contreras, M., Homma, S., Jose Ordonez-Lucena, A.,
Tantsura, J., and H. Nishihara, "IETF Network Slice Use
Cases and Attributes for Northbound Interface of IETF
Network Slice Controllers", Work in Progress, Internet-
Draft, draft-ietf-teas-ietf-network-slice-use-cases-00, 24
July 2022, <https://www.ietf.org/archive/id/draft-ietf-
teas-ietf-network-slice-use-cases-00.txt>.
[I-D.ietf-teas-ietf-network-slices]
Farrel, A., Drake, J., Rokui, R., Homma, S., Makhijani,
K., Contreras, L. M., and J. Tantsura, "Framework for IETF
Network Slices", Work in Progress, Internet-Draft, draft-
ietf-teas-ietf-network-slices-14, 3 August 2022,
<https://www.ietf.org/archive/id/draft-ietf-teas-ietf-
network-slices-14.txt>.
[RFC8454] Lee, Y., Belotti, S., Dhody, D., Ceccarelli, D., and B.
Yoon, "Information Model for Abstraction and Control of TE
Networks (ACTN)", RFC 8454, DOI 10.17487/RFC8454,
September 2018, <https://www.rfc-editor.org/info/rfc8454>.
[RFC9315] Clemm, A., Ciavaglia, L., Granville, L. Z., and J.
Tantsura, "Intent-Based Networking - Concepts and
Definitions", RFC 9315, DOI 10.17487/RFC9315, October
2022, <https://www.rfc-editor.org/info/rfc9315>.
[TMV] "Service performance measurement methods over 5G
experimental networks", 5G-PPP TMV , May 2021.
[TS28.541] "TS 28.541 Management and orchestration; 5G Network
Resource Model (NRM); Stage 2 and stage 3 (Release 16)
V16.2.0.", 3GPP TS 28.541 V16.2.0 , September 2019.
Acknowledgments
This work has been partly funded by the European Commission through
the H2020 project 5G-EVE (Grant Agreement no. 815074).
Contributors
Kostas Tsagkaris, Kostas Trichias, Vassilis Foteinos, and Thanasis
Gkiolias (all from WINGS ICT Solutions) have also contributed to this
work.
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Authors' Addresses
Luis M. Contreras
Telefonica
Ronda de la Comunicacion, s/n
Sur-3 building, 1st floor
28050 Madrid
Spain
Email: luismiguel.contrerasmurillo@telefonica.com
URI: http://lmcontreras.com/
Panagiotis Demestichas
WINGS ICT Solutions
Greece
Email: pdemest@wings-ict-solutions.eu
Jeff Tantsura
Microsoft
Email: jefftant.ietf@gmail.com
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