Skip to main content

Instantiation of IETF Network Slices in Service Providers Networks
draft-barguil-teas-network-slices-instantation-04

Document Type Active Internet-Draft (individual)
Authors Samier Barguil , Luis M. Contreras , Victor Lopez , Reza Rokui , Oscar Gonzalez de Dios
Last updated 2022-07-11
Stream (None)
Intended RFC status (None)
Formats
Stream Stream state (No stream defined)
Consensus boilerplate Unknown
RFC Editor Note (None)
IESG IESG state I-D Exists
Telechat date (None)
Responsible AD (None)
Send notices to (None)
draft-barguil-teas-network-slices-instantation-04
Network Working Group                                         S. Barguil
Internet-Draft                                            L.M. Contreras
Intended status: Informational                                Telefonica
Expires: 12 January 2023                                        V. Lopez
                                                                   Nokia
                                                                R. Rokui
                                                                   Ciena
                                                     O. Gonzalez de Dios
                                                              Telefonica
                                                            11 July 2022

   Instantiation of IETF Network Slices in Service Providers Networks
           draft-barguil-teas-network-slices-instantation-04

Abstract

   Network Slicing (NS) is an integral part of Service Provider
   networks.  The IETF has produced several YANG data models to support
   the Software-Defined Networking and network slice architecture and
   YANG-based service models for network slice (NS) instantiation.

   This document describes the relationship between IETF Network Slice
   models for requesting the IETF Network Slices and (e.g., Layer-3
   Service Model, Layer-2 Service Model) and Network Models (e.g.,
   Layer-3 Network Model, Layer-2 Network Model) used during their
   realizations.  In addition, this document describes the communication
   between the IETF Network Slice Controller and the network controllers
   for the realization of IETF network slices.

   The IETF Network Slice YANG model provides the customer-oriented view
   of the network slice.  Thus, once the IETF Network Slice controller
   (NSC) receives a request, it needs to map it to accomplish the
   specific parameters expected by the network controllers.  The network
   models are analyzed to satisfy the IETF Network Slice requirements,
   and the gaps in existing models are reported.

   The document also provides operational and security considerations
   when deploying network slices in Service Provider networks.

Status of This Memo

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

Barguil, et al.          Expires 12 January 2023                [Page 1]
Internet-Draft   Network models for IETF Network Slices        July 2022

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 12 January 2023.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Reference Architecture and Components . . . . . . . . . . . .   4
     2.1.  Possible architectural options for IETF Network Slice
           Controller  . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Possible relationship of IETF Network Slice service model
           with other models . . . . . . . . . . . . . . . . . . . .   7
   3.  IETF Network Slice Requirements and Data Models . . . . . . .   8
   4.  IETF Network Slice Procedure  . . . . . . . . . . . . . . . .   9
   5.  Network Controller Operation  . . . . . . . . . . . . . . . .  10
     5.1.  LxVPN Service Models  . . . . . . . . . . . . . . . . . .  10
     5.2.  LxVPN Network Models  . . . . . . . . . . . . . . . . . .  11
     5.3.  Traffic Engineering Models  . . . . . . . . . . . . . . .  11
     5.4.  Traffic Engineering Service Mapping . . . . . . . . . . .  11
   6.  Operational Considerations  . . . . . . . . . . . . . . . . .  11
     6.1.  Availability  . . . . . . . . . . . . . . . . . . . . . .  12
     6.2.  Downlink throughput / Uplink throughput.  . . . . . . . .  12
     6.3.  Protection scheme . . . . . . . . . . . . . . . . . . . .  12
     6.4.  Delay . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     6.5.  Packet loss rate  . . . . . . . . . . . . . . . . . . . .  13

Barguil, et al.          Expires 12 January 2023                [Page 2]
Internet-Draft   Network models for IETF Network Slices        July 2022

   7.  Relationship between IETF NBI model parameters and L3SM and
           L2SM model parameters . . . . . . . . . . . . . . . . . .  13
   8.  Network Slice Procedure . . . . . . . . . . . . . . . . . . .  17
     8.1.  IETF Network Slice requested to Hierarchical Network
           Controller  . . . . . . . . . . . . . . . . . . . . . . .  18
     8.2.  IETF Network Slice requested to Network Slice
           Controller  . . . . . . . . . . . . . . . . . . . . . . .  19
     8.3.  Network Slice Controller as part of the domain
           controller  . . . . . . . . . . . . . . . . . . . . . . .  20
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  22
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  23
   11. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . .  23
   12. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  23
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  23
   14. Normative References  . . . . . . . . . . . . . . . . . . . .  24
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

1.  Introduction

   The IETF has produced several YANG data models to support the
   Software-Defined Networking and network slice architecture.

   The IETF Network Slice YANG service model provides the customer-
   oriented view of the network slice.  Once the IETF Network Slice
   controller (NSC)receives a request, it needs to map it to accomplish
   the specific parameters expected by the network controller.

   Several Service Models and Network Models, including Layer-3 Service
   Model (L3SM), Layer-2 Service Model (L2SM) and Network Models which
   may be utilized for IETF Network Slicing, are analyzed can satisfy
   the IETF Network Slice requirements.  In addition, identified gaps on
   existing models are reported.

   This document describes the architecture and communication process
   between the Network Slice Controller and a network controller for
   IETF network slice creation.

   Editor's Note: the terminology in this draft will be aligned with the
   final terminology selected for describing the notion of IETF Network
   Slice when applied to IETF technologies, as being defined in
   [I-D.ietf-teas-ietf-network-slices].

1.1.  Terminology

   The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
   document, are to be interpreted as described in [RFC2119].

Barguil, et al.          Expires 12 January 2023                [Page 3]
Internet-Draft   Network models for IETF Network Slices        July 2022

2.  Reference Architecture and Components

   As described in [I-D.ietf-teas-ietf-network-slices], the IETF Network
   Slice Controller (NSC) is a functional entity for control and
   management of IETF network slices.  As shown in Figure A, NSC from
   its Northbound Interface (NBI exposes set of APIs that allow a higher
   level system to request an IETF network slice.  The NSC NBI supports
   the request for enabling of an IETF Network Slice (i.e., creation,
   modification or deletion).  Upon receiving a request from its NBI,
   NSC finds the resources needed for realization of the IETF Network
   Slice and in turn interfaces from its Southbound Interface (SBI) with
   one or more Network Controllers for the realization of the requested
   IETF Network Slice.

   This document focuses on how IETF Network Slice Controller (NSC) can
   be implemented in the operator's network.

                +------------------------------------------+
                |         A higher level system            |
                |   (e.g E2E network slice orchestrator)   |
                +------------------------------------------+
                                     A
                                     | NSC NBI
                                     V
                +------------------------------------------+
                |   IETF Network Slice Controller (NSC)    |
                +------------------------------------------+
                                     A
                                     | NSC SBI
                                     V
                +------------------------------------------+
                |           Network Controller(s)          |
                +------------------------------------------+

   Figure 1 Network Slice Controller as a module of the Hierarchical SDN
   controller.

2.1.  Possible architectural options for IETF Network Slice Controller

   Several architectural definitions have arisen on the IETF to support
   SDN and network slicing deployments.  The architectural proposal
   defined in [I-D.ietf-teas-ietf-network-slices] includes a three-level
   hierarchy and expresses how each level relates with the ACTN
   architecture framework.

   Figure 2 defines depicts a possible architecture using those
   concepts.  It starts from a top consumer or high-level operational
   systems.  Next, the IETF Network Slice Controller function might be

Barguil, et al.          Expires 12 January 2023                [Page 4]
Internet-Draft   Network models for IETF Network Slices        July 2022

   part of the Hierarchical network controller (e.g., as the MDSC in the
   ACTN context [RFC8453]) as a modular function.  At the bottom, two
   network controllers, each one can handle multiple or single underlay
   technologies.

                  +------------------------------+
                  | High-level operation system. |
                  +--------------+---------------+
                                 |IETF Network Slice Request
                                 |
             +-------------------v------------------+
             |                                      |
             |    Hierarchical Network              |
             |    Controller/Orchestrator           |
             |                                      |
             |   +-------------------------------+  |
             |   | IETF Network Slice Controller |  |
             |   +-------------------------------+  |
             |                                      |
             +-------------------+------------------+
                                 |
                                 |
                  +--------------+---------------+
                  |                              |
                  v                              v
    +-------------+----------+     +-------------+----------+
    |   Network Controller   |     |   Network Controller   |
    +-------------+----------+     +-------------+----------+
                  |                              |
                  |                              |
                  v                              v
           Network Elements                Network Elements

   Figure 2 IETF Network Slice Controller as a module of the
   Hierarchical SDN controller.

   In other implementations, the IETF Network Slice Controller can be a
   stand-alone element and directly interact with the network
   controller, as depicted in Figure 2.  In this scenario, the services
   request follows a data-enrichment path, where each entity adds more
   information to the service request.  This document describes how the
   available service models and network models interact to deliver the
   network slices in a service provider environment.

Barguil, et al.          Expires 12 January 2023                [Page 5]
Internet-Draft   Network models for IETF Network Slices        July 2022

                 +-------------------------------+
                 |  High-level operation system  |
                 +-------------+-----------------+
                               |IETF Network Slice Request
                               |
                 +-------------v-----------------+
                 | IETF Network Slice Controller |
                 +-------------+-----------------+
                               |
                               |
                 +-------------v-----------------+
                 |       Network Controller      |
                 +-------------+-----------------+
                               |
                               |
                               v
                       Network Elements

   Figure 3 The IETF Network Slice Controller as a stand-alone entity.

   As another implementation possibility, the IETF Network Slice
   Controller can be integrated with the Network controller and directly
   realize the network slice using device data models to configure the
   network devices.  The sample architecture is depicted in Figure 4.

                 +-------------------------------+
                 |  High-level operation system  |
                 +-------------+-----------------+
                               |IETF Network Slice Request
                               |
                 +-------------v----------------+
                 |      Network Controller      |
                 |                              |
                 |+----------------------------+|
                 ||   Network Slice Controller ||
                 |+----------------------------+|
                 |                              |
                 +-------------+----------------+
                               |
                               |
                               v
                       Network Elements

   Figure 4 IETF Network Slice Controller as a module of the Network
   controller.

Barguil, et al.          Expires 12 January 2023                [Page 6]
Internet-Draft   Network models for IETF Network Slices        July 2022

2.2.  Possible relationship of IETF Network Slice service model with
      other models

   IETF Network Slice service is expected to serve as input from where
   deriving some other models in the network.  According to the
   architectural options before, different relationships could be
   considered.  Figure 5 reflects a couple of options.

       Operations Support and Business Support YANG Modules

       +-----------------------+       +-----------------------+
       |                       |       |                       |
       |    Customer Service   |       |         Other         |
       |      YANG Modules     |       |  Operations Support   |
       |                       |       |          and          |
       |  +-----------------+  |       |    Business Support   |
       |  |  IETF Network   |  |       |      YANG Modules     |
       |  |  Slice service  |  |       |                       |
       |  |      model      |  |       |                       |
       |  +------------+----+  |       |                       |
       |           |   |       |       |                       |
       |           |   +------------+  |                       |
       | __________V_________  |    |  |                       |
       |/ +------+   +------+\ |    |  |                       |
       |  |      |   |      |  |    |  |                       |
       |  | L2SM |   | L3SM |  |    |  |                       |
       |  |      |   |      |  |    |  |                       |
       |  +------+   +------+  |    |  |                       |
       |\____________________/ |    |  |                       |
       +-----------|-----------+    |  +-----------------------+
                   |                |
       - - - - - - | - - - - - - - -| - - - - - - - - - - - - - - - -
                   |                |      Network Service YANG Modules
      _____________V________________V__________________________________
     /                                                                 \
    / +------------+  +-------------+  +-------------+  +-------------+ \
      |            |  |             |  |             |  |             |
      |  - L2VPN   |  |   - L2VPN   |  |    EVPN     |  |    L3VPN    |
      |  - VPWS    |  |   - VPLS    |  |             |  |             |
      |            |  |             |  |             |  |             |
      +------------+  +-------------+  +-------------+  +-------------+

   Figure 5 Possible relationships between models.

   Thus, the IETF Network Slice model (e.g., as defined in
   [I-D.ietf-teas-ietf-network-slice-nbi-yang] could feed existing
   service models, such as L2SM or L3SM, or could feed existing network

Barguil, et al.          Expires 12 January 2023                [Page 7]
Internet-Draft   Network models for IETF Network Slices        July 2022

   models (e.g., EVPN, L3VPN, etc).  Existing models both for service or
   network level could require some extensions themselves, or their
   application in conjunction with some other complementary models
   (e.g., TE model) to accomplish the service objectives and
   expectations as declared in the IETF Network Slice model.

3.  IETF Network Slice Requirements and Data Models

   The main set of requirements for the IETF Slice, based on the high-
   level slice requirements from multiple organizations and use cases,
   are compiled in [I-D.contreras-teas-slice-nbi] and reproduced bellow
   the slice use cases reported:

             +-----------------------------------------------+
             |  Network Slice Requirements for 5G service    |
             +-----------------------------------------------+
             | Availability                                  |
             | Deterministic communication                   |
             | Downlink throughput per network slice         |
             | Energy efficiency                             |
             | Group communication support                   |
             | Isolation level                               |
             | Maximum supported packet size                 |
             | Mission critical support                      |
             | Performance monitoring                        |
             | Slice quality of service parameters           |
             | Support for non-IP traffic                    |
             | Uplink throughput per network slice           |
             | User data access                              |
             | Delay tolerance                               |
             +-----------------------------------------------+

             +-----------------------------------------------+
             |  NFV-based services                           |
             +-----------------------------------------------+
             | Incoming and outgoing bandwidth               |
             | Qos metrics                                   |
             | Directionality                                |
             | MTU                                           |
             | Protection scheme                             |
             | Connectivity mode                             |
             +-----------------------------------------------+

Barguil, et al.          Expires 12 January 2023                [Page 8]
Internet-Draft   Network models for IETF Network Slices        July 2022

             +-----------------------------------------------+
             |  Network sharing                              |
             +-----------------------------------------------+
             | Maximum and Guaranteed Bit Rate               |
             | Bounded latency                               |
             | Packet loss rate                              |
             | IP addressing                                 |
             | L2/L3 reachability                            |
             | Recovery time                                 |
             | Secure connection                             |
             +-----------------------------------------------+

   To accomplish those requirements, a set of YANG data models have been
   proposed.  Those Yang models could be used by an IETF Network Slice
   Controller to manage CRUD operations on the IETF Network Slice.  That
   is, these models aim capturing the requirements from the consumer of
   the slice point of view and avoid entering into the detail of how the
   slice is actually created.

   *  [I-D.ietf-teas-ietf-network-slice-nbi-yang]: A Yang Data Model for
      IETF Network Slice NBI.

   *  [I-D.liu-teas-transport-network-slice-yang]: Transport Network
      Slice YANG Data Model.

4.  IETF Network Slice Procedure

   An IETF Network Slice may use several underlying technologies.  The
   creation of a new IETF Network Slice will be initiated with following
   three steps:

   1.  A higher level system requests connections with specific
       characteristics via the NBI.

   2.  This request will be processed by an IETF NSC which specifies a
       mapping between northbound request to any IETF Services, Tunnels,
       and paths models.

   3.  A series of requests for creation of services, tunnels and paths
       will be sent to the network to realize the transport slice.

Barguil, et al.          Expires 12 January 2023                [Page 9]
Internet-Draft   Network models for IETF Network Slices        July 2022

5.  Network Controller Operation

   As a functional entity responsible for managing a network domain, the
   network controller, can expose its northbound interface based on YANG
   models.  The IETF Network Slice Controller can use the network
   controller's NBI during the realization of IETF Network Slice.  The
   following network models can be used for realization of IETF Network
   slices:

   *  LxVPN Network models:

      -  These models describe a VPN service from the network point of
         view.  It supports the creation of Layer 3 and Layer 2 services
         using several control planes.

   *  Traffic Engineering models:

      -  These models allow to manipulate Traffic Engineering tunnels
         within the network segment.  Technology-specific extensions
         allow to work with a desired technology (e.g.  MPLS RSVP-TE
         tunnels, Segment Routing paths, OTN tunnels, etc.)

   *  TE Service Mapping extensions:

      -  These extensions allow to specify for LxVPN the details of an
         underlay based on TE.

   *  ACLs and routing policies models:

      -  Even though ACLs and routing policies are device models, it's
         exposure in the NBI of a domain controller allows to provide an
         additional granularity that the network domain controller is
         not able to infer on its own.

5.1.  LxVPN Service Models

   The framework defined in [RFC8969] compiles a set of YANG data models
   for automating network services.  The data models can be used during
   the service and network management life cycle (e.g., service
   instantiation, service provisioning, service optimization, service
   monitoring, service diagnosing, and service assurance).  The Service
   models could be a realization of IETF Network slice requests.

   The following models are examples of Network models that describe
   services.

   *  [RFC8049]: YANG Data Model for L3VPN Service Delivery

Barguil, et al.          Expires 12 January 2023               [Page 10]
Internet-Draft   Network models for IETF Network Slices        July 2022

   *  [RFC8466]: A YANG Data Model for Layer 2 Virtual Private Network
      (L2VPN) Service Delivery

5.2.  LxVPN Network Models

   Similar to the Service Models, the framework defined in [RFC8969]
   compiles a set of YANG data models for automating network services.
   The Network models could be reused for the realization of Network
   slice requests.

   The following models are examples of Network models that describe
   services.

   *  [RFC9182]: A Layer 3 VPN Network YANG Model

   *  [I-D.ietf-opsawg-l2nm]: A Layer 2 VPN Network YANG Model

5.3.  Traffic Engineering Models

   TEAS has defined a collection of models to allow the management of
   Traffic Engineering tunnels.

   *  [I-D.ietf-teas-yang-te]: A YANG Data Model for Traffic Engineering
      Tunnels, Label Switched Paths and Interfaces.  The model allows to
      instantiate paths in a TE enabled network.  Note that technology
      augmented models are require to particular per-technology
      instantiations.

5.4.  Traffic Engineering Service Mapping

   The IETF has defined a YANG model to set up the procedure to map VPN
   service/network models to the TE models.  This model, known as
   service mapping, allows the network controller to assign/retrieve
   transport resources allocated to specific services.  At the moment
   there is just one service mapping model
   [I-D.ietf-teas-te-service-mapping-yang].  The "Traffic Engineering
   (TE) and Service Mapping Yang Model" augments the VPN service and
   network models.

6.  Operational Considerations

   This section outlines the compliance and operational aspects of
   Network Controller models with IETF Network slice requirements.
   Section presented the requirements of the IETF Network slice.  In
   this subsection it is analyzed how available YANG models that can be
   used by a Network Controller can satisfy those requirements and
   identify gaps.

Barguil, et al.          Expires 12 January 2023               [Page 11]
Internet-Draft   Network models for IETF Network Slices        July 2022

6.1.  Availability

   As per [draft-ietf-teas-te-service-mapping-yang], Availability is a
   probabilistic measure of the length of time that a VPN/VN instance
   functions without a network failure.  As per RFC 8330, The parameter
   "availability", as described in [G.827], [F.1703], and [P.530], is
   often used to describe the link capacity.  The availability is a time
   scale, representing a proportion of the operating time that the
   requested bandwidth is ensured".

   The calculation of the availability is not trivial and would need to
   be clearly scoped to avoid misunderstandings.

   The set of Yang models proposed today allow to request tunnels/paths
   with different resiliency requirements in terms of protection and
   restoration.  However, none of them include the possibility of
   requesting a specific availability (e.g. 99.9999%).

6.2.  Downlink throughput / Uplink throughput.

   The LxVPN Models ([RFC9182] and [I-D.ietf-opsawg-l2nm]) allow to
   specify the bandwdidth at the interface level between the slice and
   the customer.  In addition, the Service Mapping model [draft-ietf-
   teas-te-service-mapping-yang] allows to bind a VPN to a given LSP,
   which have its bandwidth requirements.  Additionally, TE models can
   force a give bandwidth in the connection between Provider Edges.

   Previous comment applies to the incoming and outgoing bandwidth
   parameters required for the NFV-based services use case in
   [I-D.contreras-teas-slice-nbi].  The Network sharing use case has
   Maximum and Guaranteed Bit Rate parameters.  These parameters can be
   mapped to the TE tunnel models when setting up LSPs [draft-ietf-teas-
   yang-te].

6.3.  Protection scheme

   Protection schemes are mechanisms to define how to setup resources
   for a given connection.  TE tunnel models [draft-ietf-teas-yang-te]
   includes protection and restoration as two main attributes.  The
   parameters included in the containers for protection and restoration
   cover the requirements of the IETF NS related with protection
   schemes.  Similarly, TE models cover the parameter 'recovery time'
   for the network sharing use case.

Barguil, et al.          Expires 12 January 2023               [Page 12]
Internet-Draft   Network models for IETF Network Slices        July 2022

6.4.  Delay

   Delay is a critical parameter for several IETF NS types.  Every use-
   case defined in [I-D.contreras-teas-slice-nbi] contains delay
   constraints. 5G use cases require 'delay tolerance', NFV-based
   services have the delay information within 'QoS metrics' and 'Bounded
   latency' in the network sharing use case.

   During the realization of the IETF Network Slice, these parameters
   are part of the requirements of a TE tunnel configuration [draft-
   ietf-teas-yang-te].  They can be included within the 'path-metric-
   bounds' parameter, so the created LSP fulfils the given metrics
   bounds like 'path-metric-delay-average' or 'path-metric-delay-
   minimum'.

6.5.  Packet loss rate

   The packet loss rate indicates the maximum rate for lost packets that
   the service tolerates in the link.  During the realization of the
   IETF Network Slice, this attribute will influence the tunnel
   selection and the value is included in the [draft-ietf-teas-yang-te]
   document as the 'path-metric-loss".  The 'path-metric-loss' is a
   metric type, which measures the percentage of packet loss of all
   links traversed by a P2P path.  This parameter is required for 5G
   services and network sharing use-case, while it is part of the 'QoS
   metrics' for the NFV-based services.

7.  Relationship between IETF NBI model parameters and L3SM and L2SM
    model parameters

   This section presents an initial analysis of the relationship between
   IETF NBI model parameters and L3SM and L2SM service model parameters.

   The L3SM service parameters are defined in section 6.2 of RFC 8299.
   The following parameters are considered, so far:

   *  Bandwidth.  This parameter indicates the bandwidth requirement
      between each CE and PE participating in the service, then
      referrign essentially to the required WAN link bandwidth.  It is
      expressed in terms of bits per second and individually specified
      for both input and output.  Despite it is not stated in RFC 8299,
      this parameter can be interpreted as the CIR/PIR expected for the
      CE - PE connection.

   *  MTU.  This parameter indicates the maximum PDU size expected for
      the layer-3 service.  It is relevant since packets could be
      discarded in case the customer sends packets with longer MTU than
      the one expressed by this parameter.

Barguil, et al.          Expires 12 January 2023               [Page 13]
Internet-Draft   Network models for IETF Network Slices        July 2022

   *  QoS.  Regardign QoS, two different kind of parameters are
      detailed.

      -  QoS classification policy.  This policy is used to classify the
         traffic received from the customer, and it is expressed as a
         set of ordered rules.  It is used for marking the input traffic
         (from CE to PE) when the customer flows match any of the rules
         in the list, setting the appropriate target class of service
         (target-class-id).

      -  QoS profile.  This profile defines the traffic-scheduling to be
         applied to the flows for either Site-to-WAN, WAN-to-Site, or
         both directions.  It contains the following information per
         class of service: rate-limit, latency, jitter and guaranteed
         bandwidth.

   *  Multicast.  This parameter identifies if the service is multicast,
      and if so, what is the role of the site in the customer multicast
      service topology (i.e., source, receiver, or both).  It also
      defines the kind of multicast relationship with the customer
      (i.e., as a router requiring PIM, host requiring either IGMP or
      MLD, or both), as well as the support of IPv4, IPv6 or both.

   Similarly L2SM model parameters are described in section 5.9 and 5.10
   of RFC 8466.

   *  Bandwidth.  This parameter is related to the bandwidth between
      both CE and PE and can be expressed as CIR/EIR/PIR, in the ingress
      or egress direction, taking the CE as the point of reference.

   *  MTU.  This parameter refers to the maximum layer-2 PDU frame size.

   *  QoS.  The specification of the QoS follows a similar structure to
      the one described in the case of L3SM.  Some differences apply,
      for instance, at the time of QoS classification, which is
      performed on top of layer-2 parameters (e.g., MAC addresses).

   *  BUM traffic.  This parameter allows to determine if a site acts as
      source, receiver, or both.

   *  Availability.  This parameter in the L2SM model relates to the
      capability of supporting multi-homing.

Barguil, et al.          Expires 12 January 2023               [Page 14]
Internet-Draft   Network models for IETF Network Slices        July 2022

   On the other hand, the IETF NS NBI YANG model supports a number of
   SLOs and SLEs in the form of network slice service policy attributes.
   Such policy can apply to per-network slice, per-connection group or
   per-connection indivudually (over-writting of attributes is allowed
   as more granular information is provided).  The following SLO
   attributes are detailed:

   *  One-way / Two-way bandwidth, indicating the guaranteed minimum
      bandwidth between any two NSEs (unidirectional / bidirectional).

   *  One-way / Two-way latency, indicating the guaranteed minimum
      latency between any two NSEs (unidirectional / bidirectional).

   *  One-way / Two-way delay variation, indicating the maximum
      permissible delay variation of the slice (unidirectional /
      bidirectional).

   *  One-way / Two-way packet loss, indicating the maximum permissible
      packet loss rate between endpoints (unidirectional /
      bidirectional).

   Additionally, the following SLEs are defined:

   *  MTU, referring to the the maximum PDU size that the customer may
      use.

   *  Security, indicating if encryption or other security measures are
      required between two endpoints.

   *  Isolation, as a way of indicating the isolation level expected by
      the customer in the allocation of network resources.

   *  Maximum occupancy level, to express the amount of flows to be
      admitted (and optionally a maximum number of countable resource
      units such as IP or MAC addresses).

   Thus, an initial mapping between L3SM, L2SM and IETF NS NBI model can
   be performed as indicated in the follwoing table.

Barguil, et al.          Expires 12 January 2023               [Page 15]
Internet-Draft   Network models for IETF Network Slices        July 2022

+-------------------------+-------------------------+---------------------------------+
| L3SM (RFC 8299)         | L2SM (RFC 8466)         | IETF NSC NBI YANG model         |
+-------------------------+-------------------------+---------------------------------+
| Bandwidth               | Bandwidth (CIR, PIR)    | Sum of bandwidth SLO per NSE    |
|                         |                         | counting all connections        |
+-------------------------+-------------------------+---------------------------------+
| MTU (later 3 service)   | MTU (later 2 service)   | MTU attribute in SLE            |
+-------------------------+-------------------------+---------------------------------+
| QoS                     | QoS                     | QoS                             |
| ........................| ........................|................................ |
|  - QoS classification   |  - QoS classification   | Defined in the model as         |
|    policy               |    policy               | network-access-qos-policy-name  |
|                         |                         | to be applied per access-point  |
| ........................| ........................|................................ |
|  - QoS profile          |  - QoS profile          |                                 |
|      - rate-limit       |      - rate-limit       | Defined in the model as         |
|                         |                         | incoming/outgong rate-limits    |
|                         |                         | per end-point (or access-point) |
|      - latency          |      - latency          | One-way / Two-way latency SLO   |
|      - jitter           |      - jitter           | One-way / Two-way delay         |
|                         |                         | variation SLO                   |
|      - bandwidth        |      - bandwidth        | One-way / Two-way bandwidth SLO |
+-------------------------+-------------------------+---------------------------------+
| Multicast               | Broadcast, Unknown,     | The need of replication can be  |
|                         | Unicast and Multicast   | inferred from                   |
|                         | (BUM)                   | ns-connectivity-type. Further   |
|                         |                         | details are not available (e.g. |
|                         |                         | source or receiver role)        |
+-------------------------+-------------------------+---------------------------------+
|                         | Availability as dual    | Availability as the ratio of    |
|                         | homing                  | up-time to                      |
|                         |                         | total_time(up-time+down-time)   |
+-------------------------+-------------------------+---------------------------------+

   Table 1 Mapping of IETF NS NBI and LxSM service attributes.

   The following consideration can be made.

   *  While the QoS profile in L3SM and L2SM applies per service class,
      the parameters in IETF NS NBI apply per connection.  So if per-
      class granularity is required in an IETF network slice, then
      different connections have to be defined between the same end-
      points, one per service class.

Barguil, et al.          Expires 12 January 2023               [Page 16]
Internet-Draft   Network models for IETF Network Slices        July 2022

   *  A number of attributes are not defined in L3SM nor L2SM such as
      packet loss, isolation or security.  Then L3SM and L2SM could not
      be sufficient to realize IETF network slices with such specific
      needs, unless those other objectives and expectations are provided
      by other means (e.g., realizing the L3SM thorugh technologies
      guaranteing dedicated resource allocation such as OTN).

8.  Network Slice Procedure

   Draft [draft-contreras-teas-slice-controller-models] shows the
   internal structure of an IETF Network Slice Controller which can be
   divided into two components:

   *  IETF Network Slice Mapper: this high-level component processes the
      customer request, putting it into the context of the overall IETF
      Network Slices in the network.

   *  IETF Network Slice Realizer: this high-level component processes
      the complete view of transport slices including the one requested
      by the customer, decides the proper technologies for realizing the
      IETF Network Slice and triggers its realization.

                             Higher Level System
                                      |
                                      | NSC NBI
                         +-------------------------+
                         | NSC        |            |
                         |            v            |
                         |   +-----------------+   |
                         |   |                 |   |
                         |   |    NS Mapper    |   |
                         |   |                 |   |
                         |   +-----------------+   |
                         |            |            |
                         |            v            |
                         |   +-----------------+   |
                         |   |                 |   |
                         |   |    NS Realizer  |   |
                         |   |                 |   |
                         |   +-----------------+   |
                         |            |            |
                         +-------------------------+
                                      | NSC SBI
                                      v
                             Network Controllers

   Figure 8: IETF Network Slice Controller Structure

Barguil, et al.          Expires 12 January 2023               [Page 17]
Internet-Draft   Network models for IETF Network Slices        July 2022

   The details of IETF network slice mapper and realize are provided
   below for various implementation of NCS.

8.1.  IETF Network Slice requested to Hierarchical Network Controller

   Referring to Figure 1 in an integrated architecture, the IETF Network
   Slice Controller (NCS) is part of a Hierarchical SDN controller
   module, the NSC's and the Hierarchical Network Controller should
   share the same internal data and the same NBI.  Thus, the H-SDN
   module must be able to:

   *  Map: The customer request received using the [draft-wd-teas-ietf-
      network-slice-nbi-yang] must be processed by the NCS.  The mapping
      process takes the network-slice SLAs selected by the customer to
      available Routing Policies and Forwarding policies.

   *  Realize: Create necessary network requests.  The slice's
      realization can be translated into one or several LXNM Network
      requests, depending on the number of underlay controllers.  Thus,
      the NCS must have a complete view of the network to map the orders
      and distribute them across domains.  The realization should
      include the expansion/selection of Forwarding Policies, Routing
      Policies, VPN policies, and Underlay transport preference.

   To maintain the data coherence between the control layers, the IETF
   Network Slice ID ns-id used of the [draft-wd-teas-ietf-network-slice-
   nbi-yang] must be directly mapped to the transport-instance-id at the
   VPN-Node level.

Barguil, et al.          Expires 12 January 2023               [Page 18]
Internet-Draft   Network models for IETF Network Slices        July 2022

                                 +
                                 |
                                 | IETF Network Slice Request:
                     draft-wd-teas-ietf-network-slice-nbi-yang
                                 | * network-slice-id
                                 |
             +-------------------v------------------+
             |                                      |
             |    Hierarchical Network              |
             |    Controller/Orchestrator           |
             |                                      |
             |   +-------------------------------+  |
             |   | IETF Network Slice Controller |  |
             |   +-------------------------------+  |
             |                                      |
             +-------------------+------------------+
         IETF Network Slice Realizer: LXNM
           VPN-id                |
        * transport-instance-id  |
                                 |
                  +--------------+---------------+
                  |                              |
                  v                              v
    +-------------+----------+     +-------------+----------+
    |   Network Controller   |     |   Network Controller   |
    +-------------+----------+     +-------------+----------+
                  |                              |
                  |                              |
                  v                              v
           Network Elements                Network Elements

   Figure 9 Workflow for the slice request in an integrated
   architecture.

8.2.  IETF Network Slice requested to Network Slice Controller

   Referring to Figure 2 when the Network Slice Controller is a stand-
   alone controller module, the NSC's should perform the same two tasks
   described in section 6.1:

   *  Map: Process the customer request.  The customer request can be
      sent using the [draft-liu-teas-transport-network-slice-yang].
      This draft allows the topology mapping of the Slice request.

Barguil, et al.          Expires 12 January 2023               [Page 19]
Internet-Draft   Network models for IETF Network Slices        July 2022

   *  Realize: Create necessary network requests.  The slice's
      realization will be translated into one LXNM Network request.  As
      the NCS has a topological view of the network, the realization can
      include the customer's traffic engineering transport preferences
      and policies.

                               +
                               |IETF Network Slice Request
                draft-liu-teas-transport-network-slice-yang
                network-id
                               |
                 +-------------v-----------------+
                 | IETF Network Slice Controller |
                 +-------------+-----------------+
                               |
                    IETF Network Slice Realizer: LXNM
                      VPN-id   |
                      * Underlay-transport
                      * transport-instance-id
                               |
                 +-------------v----------------+
                 |       Network Controller     |
                 +-------------+----------------+
                               |
                               |
                               v
                       Network Elements

   Figure 10 Workflow for the slice request in an stand-alone
   architecture.

8.3.  Network Slice Controller as part of the domain controller

   The Network Slice Controller can be a module of the Network
   controller.  In that case, two options are available.  One is to
   share the same device data model in the NBI and SBI of the SDN
   controller.  The direct translation would reduce the service logic
   implemented at the SDN controller level, grouping the mapping and
   translation into a single task:

   *  Realize: As the device models are part of the network controller's
      NBI thus, the realization can be done by the network controller
      applying a simple service logic to send the Network elements.

Barguil, et al.          Expires 12 January 2023               [Page 20]
Internet-Draft   Network models for IETF Network Slices        July 2022

                                   +
                                   | Slice Request based on
                                   |   Device Models
                                   |
                                   |
                +------------------v------------------+
                |                                     |
                |    Network                          |
                |    Controller                       |
                |                                     |
                |   +------------------------------+  |
                |   |   Network Slice Controller   |  |
                |   +------------------------------+  |
                |                                     |
                +------------------+------------------+
                                   | Device Models
                                   |
                                   v
                           Network Elements

   Figure 11 Workflow for the slice request in an stand-alone
   architecture.

   A second option introduces a more complex logic in the network
   controller and creates an abstraction layer to process the transport
   slices.  In that case, the controller should receive network slices
   creation requests and maintain the whole set of implemented slices:

   *  Map & Realize: The mapping and realization can be done by the
      Domain controller applying the service logic to create policies
      directly on the Network elements.

Barguil, et al.          Expires 12 January 2023               [Page 21]
Internet-Draft   Network models for IETF Network Slices        July 2022

                               +
                               |Slice Request
                draft-liu-teas-transport-network-slice-yang-01
                network-id
                               |
                               |
            +------------------v------------------+
            |                                     |
            |    Network                          |
            |    Controller                       |
            |                                     |
            |   +------------------------------+  |
            |   |   Network Slice Controller   |  |
            |   +------------------------------+  |
            |                                     |
            +------------------+------------------+
                               |
                               |
                               v
                       Network Elements

   Figure 12 Workflow for the slice request in an stand-alone
   architecture.

9.  Security Considerations

   There are two main aspects to consider.  On the one hand, the IETF
   Network Slice has a set of security related requirements, such as
   hard isolation of the slice, or encryption of the communications
   through the slice.  All those requirements need to be analyzed in
   detailed and clearly mapped to the Network Controller and device
   interfaces.

   On the other hand, the communication between the IETF network slicer
   and the network controller (or controllers or hierarchy of
   controllers) need to follow the same security considerations as with
   the network models.

   The network YANG modules defines schemas for data that is designed to
   be accessed via network management protocols such as NETCONF
   [RFC6241] or RESTCONF [RFC8040].

   The lowest NETCONF layer is the secure transport layer, and the
   mandatory-to-implement secure transport is Secure Shell (SSH)
   [RFC6242].

   The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement
   secure transport is TLS [RFC8466].

Barguil, et al.          Expires 12 January 2023               [Page 22]
Internet-Draft   Network models for IETF Network Slices        July 2022

   The Network Configuration Access Control Model (NACM) [RFC8341]
   provides the means to restrict access for particular NETCONF or
   RESTCONF users to a preconfigured subset of all available NETCONF or
   RESTCONF protocol operations and content.

   The following summarizes the foreseen risks of using the Network
   Models to instantiate IETF network Slices:

   *  Malicious clients attempting to delete or modify VPN services that
      implements an IETF network slice.  The malicious client could
      manipulate security related aspects of the network configuration
      that impact the requirements of the slice, failing to satisfy the
      customer requirement.

   *  Unauthorized clients attempting to create/modify/delete a VPN hat
      implements an IETF network slice service.

   *  Unauthorized clients attempting to read VPN services related
      information hat implements an IETF network slice

   *  Malicious clients attempting to leak traffic of the slice.

10.  IANA Considerations

   This document is informational and does not require IANA allocations.

11.  Conclusions

   A wide variety of yang models are currently under definition in IETF
   that can be used by Network Controllers to instantiate IETF network
   slices.  Some of the IETF slice requirements can be satisfied by
   multiple means, as there are multiple choices available.  However,
   other requirements are still not covered by the existing models.  A
   more detailed definition of those uncovered requirements would be
   needed.  Finally, a consensus on the set of models to be exposed by
   Network Controllers would facilitate the deployment of IETF network
   slices.

12.  Contributors

   Daniel King, daniel@olddog.co.uk

13.  Acknowledgements

   This work is partially supported by the European Commission under
   Horizon 2020 grant agreement number 101015857 Secured autonomic
   traffic management for a Tera of SDN flows (Teraflow).

Barguil, et al.          Expires 12 January 2023               [Page 23]
Internet-Draft   Network models for IETF Network Slices        July 2022

14.  Normative References

   [I-D.contreras-teas-slice-nbi]
              Contreras, L. M., Homma, S., Ordonez-Lucena, J. 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-contreras-teas-slice-nbi-06, 7 March 2022,
              <https://datatracker.ietf.org/doc/html/draft-contreras-
              teas-slice-nbi-06>.

   [I-D.ietf-opsawg-l2nm]
              Boucadair, M., Dios, O. G. D., Barguil, S., and L. A.
              Munoz, "A YANG Network Data Model for Layer 2 VPNs", Work
              in Progress, Internet-Draft, draft-ietf-opsawg-l2nm-19, 2
              June 2022, <https://datatracker.ietf.org/doc/html/draft-
              ietf-opsawg-l2nm-19>.

   [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-12, 30 June 2022,
              <https://datatracker.ietf.org/doc/html/draft-ietf-teas-
              ietf-network-slices-12>.

   [I-D.ietf-teas-te-service-mapping-yang]
              Lee, Y., Dhody, D., Fioccola, G., Wu, Q., Ceccarelli, D.,
              and J. Tantsura, "Traffic Engineering (TE) and Service
              Mapping YANG Data Model", Work in Progress, Internet-
              Draft, draft-ietf-teas-te-service-mapping-yang-11, 11 July
              2022, <https://datatracker.ietf.org/doc/html/draft-ietf-
              teas-te-service-mapping-yang-11>.

   [I-D.ietf-teas-yang-te]
              Saad, T., Gandhi, R., Liu, X., Beeram, V. P., Bryskin, I.,
              and O. G. D. Dios, "A YANG Data Model for Traffic
              Engineering Tunnels, Label Switched Paths and Interfaces",
              Work in Progress, Internet-Draft, draft-ietf-teas-yang-te-
              29, 7 February 2022,
              <https://datatracker.ietf.org/doc/html/draft-ietf-teas-
              yang-te-29>.

Barguil, et al.          Expires 12 January 2023               [Page 24]
Internet-Draft   Network models for IETF Network Slices        July 2022

   [I-D.ietf-teas-ietf-network-slice-nbi-yang]
              Wu, B., Dhody, D., Rokui, R., Saad, T., and L. Han, "IETF
              Network Slice Service YANG Model", Work in Progress,
              Internet-Draft, draft-ietf-teas-ietf-network-slice-nbi-
              yang-02, 11 July 2022,
              <https://datatracker.ietf.org/doc/html/draft-ietf-teas-
              ietf-network-slice-nbi-yang-02>.

   [I-D.liu-teas-transport-network-slice-yang]
              Liu, X., Tantsura, J., Bryskin, I., Contreras, L. M., Wu,
              Q., Belotti, S., and R. Rokui, "IETF Network Slice YANG
              Data Model", Work in Progress, Internet-Draft, draft-liu-
              teas-transport-network-slice-yang-05, 6 March 2022,
              <https://datatracker.ietf.org/doc/html/draft-liu-teas-
              transport-network-slice-yang-05>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <https://www.rfc-editor.org/info/rfc6242>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,
              <https://www.rfc-editor.org/info/rfc8341>.

   [RFC8453]  Ceccarelli, D., Ed. and Y. Lee, Ed., "Framework for
              Abstraction and Control of TE Networks (ACTN)", RFC 8453,
              DOI 10.17487/RFC8453, August 2018,
              <https://www.rfc-editor.org/info/rfc8453>.

   [RFC8466]  Wen, B., Fioccola, G., Ed., Xie, C., and L. Jalil, "A YANG
              Data Model for Layer 2 Virtual Private Network (L2VPN)
              Service Delivery", RFC 8466, DOI 10.17487/RFC8466, October
              2018, <https://www.rfc-editor.org/info/rfc8466>.

Barguil, et al.          Expires 12 January 2023               [Page 25]
Internet-Draft   Network models for IETF Network Slices        July 2022

   [RFC8969]  Wu, Q., Ed., Boucadair, M., Ed., Lopez, D., Xie, C., and
              L. Geng, "A Framework for Automating Service and Network
              Management with YANG", RFC 8969, DOI 10.17487/RFC8969,
              January 2021, <https://www.rfc-editor.org/info/rfc8969>.

   [RFC9182]  Barguil, S., Gonzalez de Dios, O., Ed., Boucadair, M.,
              Ed., Munoz, L., and A. Aguado, "A YANG Network Data Model
              for Layer 3 VPNs", RFC 9182, DOI 10.17487/RFC9182,
              February 2022, <https://www.rfc-editor.org/info/rfc9182>.

Authors' Addresses

   Samier Barguil
   Telefonica
   Distrito T
   28050 Madrid
   Spain
   Email: samier.barguilgiraldo.ext@telefonica.com

   Luis M. Contreras
   Telefonica
   Distrito T
   28050 Madrid
   Spain
   Email: luismiguel.contrerasmurillo@telefonica.com

   Victor Lopez
   Nokia
   Calle de MarĂ­a Tubau, 9
   28050 Madrid
   Spain
   Email: victor.lopez@nokia.com

   Reza Rokui
   Ciena
   Canada
   Email: rrokui@ciena.com

   Oscar Gonzalez de Dios
   Telefonica
   Distrito T
   28050 Madrid
   Spain
   Email: oscar.gonzalezdedios@telefonica.com

Barguil, et al.          Expires 12 January 2023               [Page 26]