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Networking Working Group                                           Q. Wu
Internet-Draft                                                    Huawei
Intended status: Informational                              M. Boucadair
Expires: January 4, 2020                                    C. Jacquenet
                                                                  Orange
                                             L. Miguel Contreras Murillo
                                                              Telifonica
                                                                D. Lopez
                                                          Telefonica I+D
                                                                  C. Xie
                                                           China Telecom
                                                                W. Cheng
                                                            China Mobile
                                                                  Y. Lee
                                                               Futurewei
                                                            July 3, 2019


  A Framework for Automating Service and Network Management with YANG
           draft-wu-model-driven-management-virtualization-05

Abstract

   Data models for service and network management provides a
   programmatic approach for representing (virtual) services or networks
   and deriving configuration information that will be forwarded to
   network and service components that are used to build and deliver the
   service.  Data Models can be used during various phases of the
   service and network management life cycle, such as service
   instantiation, service provisioning, optimization, monitoring, and
   diagnostic.  Also, data models are are instrumental in the automation
   of network management.  They also provide closed-loop control for the
   sake of adaptive and deterministic service creation, delivery, and
   maintenance.

   This document provides a framework that describes and discusses an
   architecture for service and network management automation that takes
   advantage of YANG modeling technologies.  This framework is drawn
   from a network provider perspective irrespective of the origin of a
   data module andcan accommodate even modules that are developed
   outside the IETF.

   The document aims to exemplify an approach that specifies the journey
   from technology-agnostic services to technology-specific actions.







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Status of This Memo

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   This Internet-Draft will expire on January 4, 2020.

Copyright Notice

   Copyright (c) 2019 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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   5
   2.  Layered YANG Modules: An Overview . . . . . . . . . . . . . .   6
     2.1.  Network Service and Resource Models . . . . . . . . . . .   6
       2.1.1.  Network Service Models: Definition and Samples  . . .   7
       2.1.2.  Network Resource Models: Definitions and Samples  . .   7
     2.2.  Network Element Models: Definitions and Samples . . . . .  10
       2.2.1.  Model Composition . . . . . . . . . . . . . . . . . .  11
       2.2.2.  Protocol/Function Configuration Models: Definitions
               and Samples . . . . . . . . . . . . . . . . . . . . .  12
   3.  Architectural Concepts  . . . . . . . . . . . . . . . . . . .  15
     3.1.  Data Models: Layering and Representation  . . . . . . . .  15
     3.2.  Automation of service delivery procedures . . . . . . . .  15
     3.3.  Service Fullfillment Automation . . . . . . . . . . . . .  16



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     3.4.  Module Decomposition and Composition  . . . . . . . . . .  16
   4.  Architecture Overview . . . . . . . . . . . . . . . . . . . .  17
     4.1.  End-to-End Service Delivery and Service Assurance
           Procedure . . . . . . . . . . . . . . . . . . . . . . . .  18
       4.1.1.  Resource Collection and Abstraction (a) . . . . . . .  18
       4.1.2.  Service Exposure & Abstraction (b)  . . . . . . . . .  18
       4.1.3.  IP Service Mapping (c)  . . . . . . . . . . . . . . .  19
       4.1.4.  IP Service Composition (d)  . . . . . . . . . . . . .  19
       4.1.5.  IP Service Provision (e)  . . . . . . . . . . . . . .  20
       4.1.6.  Performance Measurement and Alarm Telemetry (g) . . .  20
       4.1.7.  IP Service to TE Mapping (f)  . . . . . . . . . . . .  20
       4.1.8.  Path Management (h) . . . . . . . . . . . . . . . . .  21
       4.1.9.  TE Resource Exposure (i)  . . . . . . . . . . . . . .  21
   5.  Sample Service Coordination via YANG Moodules . . . . . . . .  22
     5.1.  L3VPN Service Delivery via Coordinated YANG Modules . . .  22
     5.2.  5G Transport Service Delivery via Coordinated YANG
           Modules . . . . . . . . . . . . . . . . . . . . . . . . .  22
   6.  Modules Usage in Automated Virtualized Network Environment:
       Sample Examples . . . . . . . . . . . . . . . . . . . . . . .  24
     6.1.  Network-initiated Resource Creation . . . . . . . . . . .  24
     6.2.  Customer-initiated Dynamic Resource Creation  . . . . . .  25
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  27
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  27
   9.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  28
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  28
   11. Informative References  . . . . . . . . . . . . . . . . . . .  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  36

1.  Introduction

   The service management system usually comprises service activation/
   provision and service operation.  Current service delivery
   procedures, from the processing of customer's requirements and order
   to service delivery and operation, typically assume the manipulation
   of data sequentially into multiple OSS/BSS applications that may be
   managed by different departments within the service provider's
   organization (e.g., billing factory, design factory, network
   operation center, etc.).  In addition, many of these applications
   have been developed in-house over the years and operating in a silo
   mode.  The lack of standard data input/output (i.e., data model) also
   raises many challenges in system integration and often results in
   manual configuration tasks.  Secondly, many current service
   fulfillment might not support real time streaming telemetry
   capability in high frequency and in high throughput on the current
   state of networking and therefore have slow response to the network
   changes.  Software Defined Networking (SDN) becomes crucial to
   address these challenges.




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   Software-Defined Networking techniques [RFC7149] are meant to
   automate the overall service delivery procedures and typically rely
   upon (standard) data models that are used to not only reflect service
   providers'savoir-faire but also to dynamically instantiate and
   enforce a set of (service-inferred) policies that best accommodate
   what has been (contractually) defined (and possibly negotiated) with
   the customer.  [RFC7149] provides a first tentative to rationalize
   that service provider's view on the SDN space by identifying concrete
   technical domains that need to be considered and for which solutions
   can be provided:

   o  Techniques for the dynamic discovery of topology, devices, and
      capabilities, along with relevant information and data models that
      are meant to precisely document such topology, devices, and their
      capabilities.

   o  Techniques for exposing network services [RFC8309] and their
      characteristics.

   o  Techniques used by service-requirement-derived dynamic resource
      allocation and policy enforcement schemes, so that networks can be
      programmed accordingly.

   o  Dynamic feedback mechanisms that are meant to assess how
      efficiently a given policy (or a set thereof) is enforced from a
      service fulfillment and assurance perspective.

   Models are key for each of these technical items.  Service and
   network management automation is an important step to improve the
   agility of network operations and infrastructures.

   YANG module developers have taken both top-down and bottom-up
   approaches to develop modules [RFC8199] and to establish a mapping
   between network technology and customer requirements on the top or
   abstracting common construct from various network technologies on the
   bottom.  At the time of writing this document (2019), there are many
   data models including configuration and service models that have been
   specified or are being specified by the IETF.  They cover many of the
   networking protocols and techniques.  However, how these models work
   together to configure a device, manage a set of devices involved in a
   service, or even provide a service is something that is not currently
   documented either within the IETF or other SDOs (e.g., MEF).

   This document provides a framework that describes and discusses an
   architecture for service and network management automation that takes
   advantage of YANG modeling technologies and investigates how
   different layer YANG data models interact with each other (e.g.,
   service mapping, model composing) in the context of service delivery



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   and fulfillment.  This framework is drawn from a network provider
   perspective irrespective of the origin of a data module andcan
   accommodate even modules that are developed outside the IETF.

   The document also identifies a list of modules and use cases to
   exemplify the proposed approach, but it does not claim to be
   exhaustive.

   It is not the intent of this document to provide an inventory of
   tools and mechanisms used in specific network and service management
   domains; such inventory can be found in documents such as [RFC7276].

1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   The following terms are defined in [RFC8309][RFC8199] and are not
   redefined here:

   o  Network Operator

   o  Customer

   o  Service

   o  Data Model

   o  Service Model

   o  Customer Service Model

   o  Service Delivery Model

   o  Network Service Module

   o  Network Element Module

   The following terms are defined in this document as follows:

   Network Resource Module:  The Network Resource Module is used by a
      network operator to allocate the resource(e.g., tunnel resource,
      topology resource) for the service or schedule the resource to
      meet the service requirements define in the Service Model.




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2.  Layered YANG Modules: An Overview

   Figure 1 provides an overview of various macro-functional blocks at
   different levels that articulate the various YANG data modules.  In
   this figure, we use IETF defined YANG data model as an example
   Models.

   <<Network Service Models>>
+-------------------------------------------------------------------------+
| << Network Service Models>>                                             |
| +----------------+ +----------------+                                   |
| |      L3SM      | |     L2SM       |                                   |
| |  Service Model | |  Service Model |          .............            |
| +----------------+ +----------------+                                   |
+------------------------------------------------------------------------ +
  <<Network Resource Models>>
+------------------------------------------------------------------------ +
| << Network Resource Models >>                                           |
|      +------------+  +-------+  +----------------+   +------------+     |
|      |Network Topo|  | Tunnel|  |Path Computation|   |FM/PM/Alarm |     |
|      |   Models   |  | Models|  | API Models     |   | OAM  Models|...  |
|      +------------+  +-------+  +----------------+   +------------+     |
+-------------------------------------------------------------------------+
 --------------------------------------------------------------------------
 <Network Element Models>>
+-------------------------------------------------------------------------+
|  <<Composition Models>>                                                 |
|      +-------------+ +---------------+ +----------------+               |
|      |Device Model | |Logical Network| |Network Instance|               |
|      |             | |Element Model  | |   Model        |    ...        |
|      +-------------+ +---------------+ +----------------+               |
|-------------------------------------------------------------------------|
| << Function Models>>                                                   |
|+---------++---------++---------++----------++---------++---------+      |
||         ||         ||         ||Common    ||         || OAM:    |      |
|| Routing ||Transport|| Policy  ||(interface||Multicast||         |      |
||(e.g.,BGP||(e.g.,   ||(e.g, ACL||multicast || (IGMP   ||FM,PM,   |      |
|| OSPF)   || MPLS)   ||  QoS)   || IP, ... )|| MLD,...)||Alarm    | ...  |
|+---------++---------++---------++----------++---------++---------+      |
+-------------------------------------------------------------------------+

               Figure 1: An overview of Layered YANG Modules

2.1.  Network Service and Resource Models







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2.1.1.  Network Service Models: Definition and Samples

   As described in [RFC8309], the service is "some form of connectivity
   between customer sites and the Internet and/or between customer sites
   across the network operator's network and across the Internet".  More
   concretely, an IP connectivity service can be defined as the IP
   transfer capability characterized by a (Source Nets, Destination
   Nets, Guarantees, Scope) tuple where "Source Nets" is a group of
   unicast IP addresses, "Destination Nets" is a group of IP unicast
   and/or multicast addresses, and "Guarantees" reflects the guarantees
   (expressed in terms of Quality Of Service (QoS), performance, and
   availability, for example) to properly forward traffic to the said
   "Destination" [RFC7297].

   For example:

   o  L3SM model [RFC8299] defines the L3VPN service ordered by a
      customer from a network operator.

   o  L2SM model [RFC8466] defines the L2VPN service ordered by a
      customer from a network operator.

   o  VN model [I-D.ietf-teas-actn-vn-yang]provides a YANG data model
      generally applicable to any mode of Virtual Network (VN)
      operation.

2.1.2.  Network Resource Models: Definitions and Samples

   Figure 2 depicts a set of Network resource YANG modules such as
   topology models or tunnel models:





















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                       |                             |
     Topo YANG modules |   Tunnel YANG modules       |Resource NM Tool
     ------------------------------------------------|-- ------------
  +------------+       |                             |
  |Network Top |       | +------+  +-----------+     |       +-------+
  |   Model    |       | |Other |  | TE Tunnel |     |       | LIME  |
  +----+-------+       | |Tunnel|  +------+----+     |       | Model |
       |   +--------+  | +------+         |          |       |/PM/FM |
       |---+Svc Topo|  |         +--------+-+--------+       |Model  |
       |   +--------+  |    +----+---+  +---+----+ +-+-----+ +-------+
       |   +--------+  |    |MPLS-TE |  |RSVP-TE | |SR TE  | +--------+
       |---+L2 Topo |  |    | Tunnel |  | Tunnel | |Tunnel | |  Alarm |
       |   +--------+  |    +--------+  +--------+ +-------+ |  Model |
       |   +--------+  |                                     +--------+
       |---+TE Topo |  |                                   +-----------+
       |   +--------+  |                                   |Path       |
       |   +--------+  |                                   |Computation|
       +---+L3 Topo |  |                                   |API Model  |
           +--------+  |                                   +-----------+

              Figure 2: Sample Resource Facing Network Models

   Topology YANG module Examples:

   o  Network Topology Models: [RFC8345] defines a base model for
      network topology and inventories.  Network topology data include
      link resource, node resource, and terminate-point resources.

   o  TE Topology Models: [I.D-ietf-teas-yang-te-topo] defines a data
      model for representing and manipulating TE topologies.

      This module is extended from network topology model defined in
      [RFC8345] with TE topologies specifics.  This model contains
      technology-agnostic TE Topology building blocks that can be
      augmented and used by other technology-specific TE Topology
      models.

   o  L3 Topology Models

      [RFC8346] defines a data model for representing and manipulating
      L3 Topologies.  This model is extended from the network topology
      model defined in [RFC8345] with L3 topologies specifics.

   o  L2 Topology Models

      [I.D-ietf-i2rs-yang-l2-topology] defines a data model for
      representing and manipulating L2 Topologies.  This model is




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      extended from the network topology model defined in [RFC8345] with
      L2 topologies specifics.

   Tunnel YANG module Examples:

   o  Tunnel identities [I-D.ietf-softwire-iftunnel] to ease
      manipulating extensions to specific tunnels.

   o  TE Tunnel Model

      [I.D-ietf-teas-yang-te] defines a YANG module for the
      configuration and management of TE interfaces, tunnels and LSPs.

   o  SR TE Tunnel Model

      [I.D-ietf-teas-yang-te] augments the TE generic and MPLS-TE
      model(s) and defines a YANG module for Segment Routing (SR) TE
      specific data.

   o  MPLS TE Model

      [I.D-ietf-teas-yang-te] augments the TE generic and MPLS-TE
      model(s) and defines a YANG module for MPLS TE configurations,
      state, RPC and notifications.

   o  RSVP-TE MPLS Model

      [I.D-ietf-teas-yang-rsvp-te] augments the RSVP-TE generic module
      with parameters to configure and manage signaling of MPLS RSVP-TE
      LSPs.

   Resource NM Tool Models:

   o  Path Computation API Model

      [I.D-ietf-teas-path-computation] YANG module for a stateless RPC
      which complements the stateful solution defined in [I.D-ietf-teas-
      yang-te].

   o  OAM Models (including Fault Management (FM) and Performance
      Monitoring)

      [RFC8532] defines a base YANG module for the management of OAM
      protocols that use Connectionless Communications.  [RFC8533]
      defines a retrieval method YANG module for connectionless OAM
      protocols.  [RFC8531] defines a base YANG module for connection
      oriented OAM protocols.  These three models are intended to




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      provide consistent reporting, configuration and representation for
      connection-less OAM and Connection oriented OAM separately.

      Alarm monitoring is a fundamental part of monitoring the network.
      Raw alarms from devices do not always tell the status of the
      network services or necessarily point to the root cause.  [I.D-
      ietf-ccamp-alarm-module]defines a YANG module for alarm
      management.

   o  Generic Policy Model

      The Simplified Use of Policy Abstractions (SUPA) policy-based
      management framework [RFC8328] defines base YANG modules
      [I-D.ietf-supa-generic-policy-data-model]to encode policy.  These
      models point to device-, technology-, and service-specific YANG
      modules developed elsewhere.  Policy rules within an operator's
      environment can be used to express high-level, possibly network-
      wide, policies to a network management function (within a
      controller, an orchestrator, or a network element).  The network
      management function can then control the configuration and/or
      monitoring of network elements and services.  This document
      describes the SUPA basic framework, its elements, and interfaces.

2.2.  Network Element Models: Definitions and Samples

   Network Element models (Figure 3) are used to describe how a service
   can be implemented by activating and tweaking a set of functions
   (enabled in one or multiple devices, or hosted in cloud
   infrastructures) that are involved in the service delivery.  The
   following figure uses IETF defined models as an example.





















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                                          +----------------+
                                        --|Device Model    |
                                        | +----------------+
                                        | +------------------+
                     +---------------+  | |Logical Network   |
                     |               |  --|  Element Mode    |
                     | Architecture  |  | +------------------+
                     |               |  | +----------------------+
                     +-------+-------+  --|Network Instance Mode |
                             |          | +----------------------+
                             |          | +-------------------+
                             |          --|Routing Type Model |
                             |            +-------------------+
     +-------+----------+----+------+------------+-----------+-------+
     |       |          |           |            |           |       |
   +-+-+ +---+---+   +--+------+  +-+-+    +-----+---+   +---+-+     |
   |ACL| |Routing|   |Transport|  |OAM|    |Multicast|   |  PM |  Others
   +---+ |-------+   +---------+  +---+    +---------+   +-----+
         | +-------+  +----------+ +-------+   +-----+    +-----+
         --|Core   |  |MPLS Basic| |BFD    |   |IGMP |    |TWAMP|
         | |Routing|  +----------+ +-------+   |/MLD |    +-----+
         | +-------+  |MPLS LDP  | |LSP Ping   +-----+    |OWAMP|
         --|BGP    |  +----------+ +-------+   |PIM  |    +-----+
         | +-------+  |MPLS Static |MPLS-TP|   +-----+    |LMAP |
         --|ISIS   |  +----------+ +-------+   |MVPN |    +-----+
         | +-------+                           +-----+
         --|OSPF   |
         | +-------+
         --|RIP    |
         | +-------+
         --|VRRP   |
         | +-------+
         --|SR/SRv6|
         | +-------+
         --|ISIS-SR|
         | +-------+
         --|OSPF-SR|
           +-------+

                Figure 3: Network Element Modules Overview

2.2.1.  Model Composition

   o  Device Model

      [I.D-ietf-rtgwg-device-model] presents an approach for organizing
      YANG modules in a comprehensive logical structure that may be used
      to configure and operate network devices.  The structure is itself



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      represented as an example YANG module, with all of the related
      component models logically organized in a way that is
      operationally intuitive, but this model is not expected to be
      implemented.

   o  Logical Network Element Model

      [RFC8530] defines a logical network element module which can be
      used to manage the logical resource partitioning that may be
      present on a network device.  Examples of common industry terms
      for logical resource partitioning are Logical Systems or Logical
      Routers.

   o  Network Instance Model

      [RFC8529] defines a network instance module.  This module can be
      used to manage the virtual resource partitioning that may be
      present on a network device.  Examples of common industry terms
      for virtual resource partitioning are Virtual Routing and
      Forwarding (VRF) instances and Virtual Switch Instances (VSIs).

2.2.1.1.  Schema Mount

   Modularity and extensibility were among the leading design principles
   of the YANG data modeling language.  As a result, the same YANG
   module can be combined with various sets of other modules and thus
   form a data model that is tailored to meet the requirements of a
   specific use case.  [RFC8528] defines a mechanism, denoted schema
   mount, that allows for mounting one data model consisting of any
   number of YANG modules at a specified location of another (parent)
   schema.

   That capability does not cover design time.

2.2.2.  Protocol/Function Configuration Models: Definitions and Samples

   BGP:       [I-D.ietf-idr-bgp-yang-model] defines a YANG module for
              configuring and managing BGP, including protocol, policy,
              and operational aspects based on data center, carrier and
              content provider operational requirements.

   MPLS:      [I-D.ietf-mpls-base-yang] defines a base model for MPLS
              which serves as a base framework for configuring and
              managing an MPLS switching subsystem.  It is expected that
              other MPLS technology YANG modules (e.g.  MPLS LSP Static,
              LDP or RSVP-TE models) will augment the MPLS base YANG
              module.




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   QoS:       [I-D.asechoud-netmod-diffserv-model] describes a YANG
              module of Differentiated Services for configuration and
              operations.

   ACL:       Access Control List (ACL) is one of the basic elements
              used to configure device forwarding behavior.  It is used
              in many networking technologies such as Policy Based
              Routing, Firewalls, etc.  [RFC8519] describes a data model
              of Access Control List (ACL) basic building blocks.

   NAT:       For the sake of network automation and the need for
              programming Network Address Translation (NAT) function in
              particular, a data model for configuring and managing the
              NAT is essential.  [RFC8512] defines a YANG module for the
              NAT function covering a variety of NAT flavors such as
              Network Address Translation from IPv4 to IPv4 (NAT44),
              Network Address and Protocol Translation from IPv6 Clients
              to IPv4 Servers (NAT64), customer-side translator (CLAT),
              Stateless IP/ICMP Translation (SIIT), Explicit Address
              Mappings (EAM) for SIIT, IPv6-to-IPv6 Network Prefix
              Translation (NPTv6), and Destination NAT.  [RFC8513]
              specifies a YANG module for the DS-Lite AFTR.

   Stateless Address Sharing:  [I-D.ietf-softwire-yang] specifies a YANG
              module for A+P address sharing, including Lightweight
              4over6, Mapping of Address and Port with Encapsulation
              (MAP-E), and Mapping of Address and Port using Translation
              (MAP-T) softwire mechanisms.

   Multicast: [I-D.ietf-pim-yang] defines a YANG module that can be used
              to configure and manage Protocol Independent Multicast
              (PIM) devices.  [I-D.ietf-pim-igmp-mld-yang] defines a
              YANG module that can be used to configure and manage
              Internet Group Management Protocol (IGMP) and Multicast
              Listener Discovery (MLD) devices.  [I-D.ietf-pim-igmp-mld-
              snooping-yang] defines a YANG module that can be used to
              configure and manage Internet Group Management Protocol
              (IGMP) and Multicast Listener Discovery (MLD) Snooping
              devices.

   EVPN:      [I-D.ietf-bess-evpn-yang] defines a YANG module for
              Ethernet VPN services.  The model is agnostic of the
              underlay.  It apply to MPLS as well as to VxLAN
              encapsulation.  The model is also agnostic of the services
              including E-LAN, E-LINE and E-TREE services.  This
              document mainly focuses on EVPN and Ethernet-Segment
              instance framework.




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   L3VPN:     [I-D.ietf-bess-l3vpn-yang] defines a YANG module that can
              be used to configure and manage BGP L3VPNs [RFC4364].  It
              contains VRF specific parameters as well as BGP specific
              parameters applicable for L3VPNs.

   L2VPN:     [I-D.ietf-bess-l2vpn-yang] defines a YANG module for MPLS
              based Layer 2 VPN services (L2VPN) [RFC4664] and includes
              switching between the local attachment circuits.  The
              L2VPN model covers point-to-point VPWS and Multipoint VPLS
              services.  These services use signaling of Pseudowires
              across MPLS networks using LDP [RFC8077][RFC4762] or BGP
              [RFC4761].

   Routing Policy:  [I-D.ietf-rtgwg-policy-model] defines a YANG module
              for configuring and managing routing policies in a vendor-
              neutral way and based on actual operational practice.  The
              model provides a generic policy framework which can be
              augmented with protocol-specific policy configuration.

   BFD:       [I-D.ietf-bfd-yang]defines a YANG module that can be used
              to configure and manage Bidirectional Forwarding Detection
              (BFD) [RFC5880].  BFD is a network protocol which is used
              for liveness detection of arbitrary paths between systems.

   SR/SRv6:   [I-D.ietf-spring-sr-yang] a YANG module for segment
              routing configuration and operation.  [I-D.raza-spring-
              srv6-yang] defines a YANG module for Segment Routing IPv6
              (SRv6) base.  The model serves as a base framework for
              configuring and managing an SRv6 subsystem and expected to
              be augmented by other SRv6 technology models accordingly.

   Core Routing:  [RFC8349] defines the core routing data model, which
              is intended as a basis for future data model development
              covering more-sophisticated routing systems.  It is
              expected that other Routing technology YANG modules (e.g.,
              VRRP, RIP, ISIS, OSPF models) will augment the Core
              Routing base YANG module.

   PM:

              [I.D-ietf-ippm-twamp-yang] defines a data model for client
              and server implementations of the Two-Way Active
              Measurement Protocol (TWAMP).

              [I.D-ietf-ippm-stamp-yang] defines the data model for
              implementations of Session-Sender and Session-Reflector
              for Simple Two-way Active Measurement Protocol (STAMP)
              mode using YANG.



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              [RFC8194] defines a data model for Large-Scale Measurement
              Platforms (LMAPs).

3.  Architectural Concepts

3.1.  Data Models: Layering and Representation

   As described in [RFC8199], layering of modules allows for better
   reusability of lower-layer modules by higher-level modules while
   limiting duplication of features across layers.

   The data modules developed by IETF can be classified into service
   level, network level and device level modules.  Different service
   level modules may rely on the same set of network level or device
   level modules.  Service level modules usually follow top down
   approach and are mostly customer-facing modules providing a common
   model construct for higher level network services, which can be
   further mapped to network technology-specific modules at lower layer.

   Network level modules mostly follow a bottom-up approach and are
   mainly network resource-facing modules and describe various aspects
   of a network infrastructure, including devices and their subsystems,
   and relevant protocols operating at the link and network layers
   across multiple devices (e.g., Network topology and TE Tunnel
   modules).

   Device level modules usually follow a bottom-up approach and are
   mostly technology-specific modules used to realize a service.

3.2.  Automation of service delivery procedures

   To dynamically provide service offerings, Service level modules can
   be used by an operator.  One or more monolithic Service modules can
   be used in the context of a composite service activation request
   (e.g., delivery of a caching infrastructure over a VPN).  Such
   modules are used to feed a decision-making intelligence to adequately
   accommodate customer's needs.

   Also, such modules may be used jointly with services that require
   dynamic invocation.  An example is provided by the service modules
   defined by the DOTS WG to dynamically trigger requests to handle DDoS
   attacks [I-D.ietf-dots-signal-channel][I-D.ietf-dots-data-channel].

   Network level modules can be derived from service level modules and
   used to provision, monitor, instantiate the service and provide
   lifecycle management of network resources, e.g., expose network
   resources to customers or operators to provide service fulfillment
   and assurance and allow customers or operators to dynamically adjust



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   the network resources based on service requirements as described in
   service level modules and the current network performance information
   described in the Northbound telemetry modules.

3.3.  Service Fullfillment Automation

   To operate the service, Device level modules derived from Service
   level modules or Network level modules can be used to provision each
   involved network function/device with the proper configuration
   information, and operate the network based on service requirements as
   described in the Service level module(s).

   In addition, the operational state including configuration that is in
   effect together with statistics should be exposed to upper layers to
   provide better network visibility (and assess to what extent the
   derived low level modules are consistent with the upper level
   inputs).  Note that it is important to relate telemetry data with
   configuration data to used closed loops at the different stages of
   service delivery, from resource allocation to service operation, in
   particular.

3.4.  Module Decomposition and Composition

   To support top-down service delivery, the service parameters captured
   in service level module(s) need to be decomposed into a set of
   configuration parameters that may be specific to one or more
   technologies; these technology-specific parameters will be grouped
   together per technique to define technology-specific device level
   modules or network level modules.

   In addition, these technology-specific device level models can be
   further assembled together to provision each involved network
   function/device or each involved administrative domain to improve
   provision efficiency.

   For example, IETF rtgwg and netmod working groups have already been
   tasked to define a model composition mechanism (i.e., Schema Mount
   mechanism) and relevant grouping base models such as network instance
   model, logical network element model . The model composition
   mechanism can be used to assembler different model together while
   grouping based models can be used to setup and administrate both
   virtualized system and physical systems .

   IETF also developed a YANG catalog tool to manage metadata around
   IETF- defined modules; it allows both YANG developers and operators
   to discover appropriate YANG modules that may be used to automate
   services operations.  This YANG tool catalog tools can be used to




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   select appropriate models for grouping purposes or even to identify
   gaps.

4.  Architecture Overview

   The architectural considerations described in the previous section
   lead to the architecture described in this section and illustrated in
   Figure 4.

   The interfaces and interactions shown in the figure and labeled (a)
   through (j) are further described in Section 4.1.

       +-----------------+                              ----------------
       |Service Requester|                              Service Level|
       +-----------------+                                           |
 +-------------|--------------------------------------------------+  |
 |             |                       +----------------------+   |  |
 |             |                       |                      |   |  |
 |    +--------V---------+             |  +------------+  +---+--+|  |
 |    | Service Exposure |-------------V--- IP Service |  |Alarm/||  |
 |    +-------(b)--------+                |  Mapping   |  |  PM  ||  |
 |             |                          +--(c)-|-----+  +-(g) -+|  |
 |             |                                 |            |      |
 | +---------->|<----------------+               +------------+      |
 | |           |                 |               |      -------------+--
 | |           |                 |               |      Network Level|
 | |  +--------V---------+       |               |                |  |
 | |  | IP Service to TE         |      +------->|<-----------+   |  |
 | |  |    Mapping       |       |      |        |            |   |  |
 | |  +-------(f)--------+       |      | +------|-----+      |   |  |
 | |           |           +-----|-----+| | IP Service |  +---+--+|  |
 | |  +--------V---------+ |TE Resource|| | Composition|  |Alarm/||  |
 | |  |     TE Path      | | Exposure  || +--(d)-|-----+  |  PM  ||  |
 | |  |   Management       +----(h)----+|        |        +-(g) -+|  |
 | |  +-------(e)--------+       |      | +------|------+         |  |
 | |           |                 |      | | IP Service  |     |   |  |
 | |           +-----------------+      | | Provision   +-----|   |  |
 | |                                    | +-(e)--|------+         |  |
 | |                        +-----------++                        |  |
 | |                        | Resource   |                        |  |
 | |                        | Collection |                        |  |
 | |------------------------+&Abstraction|                        |  |
 |                          +----(a)-----+             ----------------
 +----------------------------------------------------------------+

       Figure 4: Service and Network Management Automation with YANG





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4.1.  End-to-End Service Delivery and Service Assurance Procedure

4.1.1.  Resource Collection and Abstraction (a)

   Network Resources such as links, nodes, or terminate-point resources
   can be collected from the network and aggregated or abstracted to the
   management system.  Periodic fetching of data is not an adequate
   solution for applications requiring frequent or prompt updates of
   network resources.  Applying polling-based solutions to retrieve
   network resource information impacts networks, devices, and
   applications' loads.  These limitations can be addressed by including
   generic object subscription mechanisms within network elements.

   These resources can be modelled using network topology models, L3
   topology model, L2 topology model, TE topology model, L3 TE topology
   model, SR TE topology models at different layers.

   In some cases, there may be multiple overlay topologies built on top
   of the same underlay topology, and the underlay topology can also be
   built from one or more lower layer underlay topologies.  The network
   resources and management objects in these multi-layer topologies are
   not recommended to be exposed to customers, but rather exposed to the
   management system for IP service mapping and Path Management.

4.1.2.  Service Exposure & Abstraction (b)

   Service exposure & abstraction is used to capture services offered to
   customers.

   Service abstraction can be used by a customer to request a service
   (ordering and order handling).  One typical example is that a
   customer can use a L3SM service model to request L3VPN service by
   providing the abstract technical characterization of the intended
   service.

   Service catalogs can be created to expose the various services and
   the information needed to invoke/order a given service.

   YANG modules can be grouped into various service bundles; each
   service bundle corresponds to a set of YANG modules that have been
   released or published.  Then, a mapping can be established between
   service abstraction at higher layer and service bundle or a set of
   YANG modules at lower layer.








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4.1.3.  IP Service Mapping (c)

   Service abstraction starts with high-level abstractions exposing the
   business capabilities or capturing customer requirements.  Then, it
   needs to map them to resource abstraction and specific network
   technologies.

   Therefore, the interaction between service abstraction in the overlay
   and network resource abstraction in the underlay is required.  For
   example, in the L3SM service model, a VPN service topology is
   described as e.g., hub and spoke and any-to-any, single-homed, dual-
   homed, multi-homed relation between PEs and CEs, but we don't know
   how this service topology can be mapped into the underlying network
   topology Section 4.1.8

   In addition, there is a need to decide on a mapping between service
   abstraction and the underlying specific network technologies.  Take
   L3SM service model as an example, to deliver a L3VPN service, we need
   to map L3SM service view defined in Service model into detailed
   configuration view defined by specific configuration models for
   network elements, configuartion information includes:

   o  VRF definition, including VPN Policy expression

   o  Physical Interface

   o  IP layer (IPv4, IPv6).

   o  QoS features such as classification, profiles, etc.

   o  Routing protocols: support of configuration of all protocols
      listed in the document, as well as routing policies associated
      with those protocols.

   o  Multicast Support

   o  NAT or address sharing

   o  Security functions

4.1.4.  IP Service Composition (d)

   These configuration models are further grouped together into service
   bundles, as described in Figure 3using, e.g., device models, logical
   network element models or network instance models defined in [I.D-
   ietf-rtgwg-device-model] [RFC8530] [RFC8529] and provide the
   association between an interface and its associated LNE and NI and
   populate them into appropriate devices(e.g., PE and CE).



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4.1.5.  IP Service Provision (e)

   IP Service Provision is used to provide IP network devices with a set
   of configuration information, e.g., network element models such as
   BGP, ACL, QoS, Interface model, Network instance models to configure
   PE and CE devices within the site, etc.  A BGP policy model is used
   to establish VPN membership between sites and VPN Service Topology.
   Experience shows that "pushing" configuration information to each
   device one after the other is not efficient.

   To automate the configuration of service elements, we first assemble
   all the related network elements models into logical network element
   model as defined in [RFC8530] and then establish an association with
   an interface and a set of network element configurations.

   In addition, not all the parameters of the service level model or
   network level model(e.g., mapped from service level model) needs to
   be specified, in many cases, some default values, or even some values
   depending of some contextual information (e.g., the particular
   service / network element / location / etc) should be taken to
   automate the configuration process.

   Seconldy, IP Service Provision can be used to setup tunnels between
   sites and setup tunnels between PEs and CEs based upon tunnel-related
   configuration information that can be derived from service
   abstraction.  However, when tunnel-related configuration parameters
   cannot be generated from service abstraction, other service Mapping
   procedure is required,e.g.,IP Service to TE mapping procdure
   described in Section 4.1.7.

4.1.6.  Performance Measurement and Alarm Telemetry (g)

   Once the tunnel or VPN is setup, PM and Alarm information per tunnel
   or per link based on network topology can be collected and report to
   the management system.  This information can be further aggregated
   and abstracted from layered network topology to monitor and manage
   network Performance on the topology at different layer or the overlay
   topology between VPN sites.  These network performance information or
   VPN performance information (e.g., latency or bandwidth utilization
   between two VPN sites) can be put into NBI telemetry model or NBI
   performance monitoring model at either service level or network level
   to further optimize the network or provide troubleshooting support.

4.1.7.  IP Service to TE Mapping (f)

   Take L3VPN service model as an example, the management system will
   use L3SM service model to determine where to connect each site-
   network-access of a particular site to the provider network (e.g.,



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   PE, aggregation switch).  The L3SM Service model includes parameters
   that can help design the VPN, according to customer's requirements,
   for example.

   Nodes used to connect a site may be captured in relevant clauses of a
   service exposure model (e.g., Customer Nodes Map [RFC7297]).

   When Site location is determined, PE and CE device location will be
   selected.  Then we can replace parameters and constraints that can
   influence the meshing of the site-network-access with specified PE
   and CE device information associated with site-network-access and
   generate resource facing VN Overlay Resource model.  One example of
   resource facing VN Overlay Resource model is TEAS VN Service Model
   [I-D.ietf-teas-actn-vn-yang].

   This VN model can be used to calculate node and link resource to meet
   service requirements based on Network Topology models collected at
   step (a).

4.1.8.  Path Management (h)

   Path Management includes Path computation and Path setup.  For
   example, we can derive an instantiated L3SM service model into a
   resource facing VN Model, with selected PE and CE in each site, we
   can calculate point- to-point or multipoint end-to-end paths between
   sites based on the VPN Overlay Resource Model.

   After identifying node and link resources required to meet service
   requirements, the mapping between overlay topology and underlay
   topology can be established, e.g., establish an association between
   VPN service topology defined in customer-facing model and underlying
   network topology defined in the TE topology model (e.g., one overlay
   node is supported by multiple underlay nodes, one overlay link is
   supported by multiple underlay nodes) and generate end-to-end VPN
   topology.

4.1.9.  TE Resource Exposure (i)

   When tunnel-related configuration parameters cannot be derived from
   service abstraction, IP Service-to-TE Mapping procedure can be used
   to generate TE Resource Exposure view, this TE resource Exposure view
   can be modeled as a resource-facing VPN model which is translated and
   instantiated from a L3SM model and manage TE resources based on path
   management information and PM and alarm telemetry information.

   Operators may use this dedicated TE resource Exposure view to
   dynamically capture the overall network status and topology to:




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   o  Perform all the requested recovery operations upon detecting
      network failures affecting the network service.

   o  Adjust resource distribution and update to end to end Service
      topology models

   o  Provide resource scheduling to better guarantee services for
      customers and to improve the efficiency of network resource usage.

5.  Sample Service Coordination via YANG Moodules

5.1.  L3VPN Service Delivery via Coordinated YANG Modules

   Take L3VPN service as an example, IETF has already developed L3VPN
   service model [RFC8299] which can be used to describe L3VPN service.
   To enforce L3VPN service and program the network, a set of network
   element models are needed, e.g., BGP model, Network Instance model,
   ACL model, Multicast Model, QoS model, or NAT model.

   These network element models can be grouped into different release
   bundles or feature bundles using Schema Mount technology to meet
   different tailored requirements and deliver the L3VPN service.

   To support the creation of logical network elements on a network
   device and deliver a virtualized network, Logical Network Element
   (LNE) models can be used to manage its own set of modules such as
   ACL, QoS, or Network Instance modules.

5.2.  5G Transport Service Delivery via Coordinated YANG Modules

   The overview of network slice structure as defined in the 3GPP 5GS is
   shown in Figure 5.  The terms are described in specific 3GPP
   documents (e.g., [TS.23.501-3GPP] and [TS.28.530-3GPP]).


















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   <==================          E2E-NSI         =======================>
                :                 :                  :           :  :
                :                 :                  :           :  :
   <======  RAN-NSSI  ======><=TRN-NSSI=><====== CN-NSSI  ======>VL[APL]
       :        :        :        :         :       :        :   :  :
       :        :        :        :         :       :        :   :  :
   RW[NFs ]<=TRN-NSSI=>[NFs ]<=TRN-NSSI=>[NFs ]<=TRN-NSSI=>[NFs ]VL[APL]

    . . . . . . . . . . . . ..          . . . . . . . . . . . . ..
    .,----.   ,----.   ,----..  ,----.  .,----.   ,----.   ,----..
 UE--|RAN |---| TN |---|RAN |---| TN |---|CN  |---| TN |---|CN  |--[APL]
    .|NFs |   `----'   |NFs |.  `----'  .|NFs |   `----'   |NFs |.
    .`----'            `----'.          .`----'            `----'.
    . . . . . . . . . . . . ..          . . . . . . . . . . . . ..

   RW         RAN                MBH               CN               DN

 *Legends
  UE: User Equipment
  RAN: Radio Access Network
  CN: Core Network
  DN: Data Network
  TN: Transport Network
  MBH: Mobile Backhaul
  RW: Radio Wave
  NF: Network Function
  APL: Application Server
  NSI: Network Slice Instance
  NSSI: Network Slice Subnet Instance

             Figure 5: Overview of Structure of NS in 3GPP 5GS

   To support 5G service (e.g., 5G MBB service), L3VPN service model
   [RFC8299] and TEAS VN model [I-D. ietf-teas-actn-vn-yang] can be both
   provided to describe 5G MBB Transport Service or connectivity
   service.  L3VPN service model is used to describe end-to-end
   connectivity service while TEAS VN model is used to describe TE
   connectivity service between VPN sites or between RAN NFs and Core
   network NFs.

   VN in TEAS VN model and support point-to-point or multipoint-to-
   multipoint connectivity service and can be seen as one example of
   network slice.

   TE Service mapping model can be used to map L3VPN service requests
   onto underlying network resource and TE models to get TE network
   setup.




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   For IP VPN service provision, L3VPN service model is used to derive a
   set of configuration parameterswhich will be bound to different
   network element models and group them together to form feature or
   service bundles to deliver the VPN service.

6.  Modules Usage in Automated Virtualized Network Environment: Sample
    Examples

6.1.  Network-initiated Resource Creation

                                     |(2)
                                     |
                                     V
                         +-------------------+
                         | Management System | (3)(4)(5)
                         +-------------------+

           +--------------------------------------------------------+
          /     _[CE2]                      _[CE3]                 /
         /    _/  :   \_                  _/  :   \_              /
        /   _/     :    \_              _/     :    \_           /
       /  _/        :     \_          _/        :     \_        /
      /  /           :      \        /           :      \      /
     /[CE1]_________________[PE1] [PE2]_________________[CE4] /
    +---------:--------------:------------:--------------:---+
                                                             "Service"
   --------------------------------------------------------------------
           +---------------------+    +---------------------+"Resource"
          /   [Y5]...           /    / [Z5]______[Z3]      /
         /    /  \  :          /    /  : \_       / :     /
        /    /    \  :        /    /   :   \_    /  :    /
       /    /      \  :      /    /   :      \  /   :   /
      /   [Y4]____[Y1] :    /    /   :       [Z2]   :  /
     +------:-------:---:--+    +---:---------:-----:-+       ^
     vNet1  :        :   :         :          :     :  vNet2  |
            :         :   :       :           :     :         |(1)
            :  +-------:---:-----:------------:-----:-----+   |
            : /       [X1]__:___:___________[X2]   :     /    |
            :/         / \_  : :       _____/ /   :     /     |
            :         /    \_ :  _____/      /   :     /
           /:        /       \: /           /   :     /
          / :       /        [X5]          /   :     /
         /   :     /       __/ \__        /   :     /
        /     :   /    ___/       \__    /   :     /
       /       : / ___/              \  /   :     /
      /        [X4]__________________[X3]..:     /
     +------------------------------------------+
                          L3 Topology



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   The following steps are performed to deliver the service within the
   network management automation architecture proposed in this document:

   1.  Pre-provision multiple virtualized networks on top of the same
       basic network infrastructure based on pre-configured service
       requirements and establish resource pool for each virtualized
       network and expose to the customer with several service templates
       through web portal.

   2.  Selects and uses one which best accommodates its requirement
       among the service templates.

   3.  Calculate the node resource, link resource corresponding to
       connectivity between sites and create resource facing VN Network
       based on selected service template, and

   4.  Setup tunnels between sites and map them into the selected
       virtualized network topology and establish resource facing VN
       topology based on TEAS VN model [I-D.ietf-teas-actn-vn-yang] and
       TE tunnel based on TE Tunnel model.

       The resource-facing VN model and corresponding TE Tunnel model
       can be further used to notify all the parameter changes and event
       related to VN topology or Tunnel.  This information can be
       further used to adjust network resource distributed in the
       network.

   The network initiated resource creation is similar to ready-made
   Network Slice creation pattern discussed in Section 5.1 of [I-
   D.homma-slice-provision-models].

6.2.  Customer-initiated Dynamic Resource Creation



















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                                  |(2)
                                  |
                                  V
                      +-------------------+
                      | Management System | (3)(4)(5)
                      +-------------------+

        +--------------------------------------------------------+
       /     _[CE2]                      _[CE3]                 /
      /    _/  :   \_                  _/  :   \_              /
     /   _/     :    \_              _/     :    \_           /
    /  _/        :     \_          _/        :     \_        /
   /  /           :      \        /           :      \      /
  /[CE1]_________________[PE1] [PE2]_________________[CE4] /
 +---------:--------------:------------:--------------:---+
                                                          "Service"
--------------------------------------------------------------------
                                                        "Resource"                             ^
         :                                                 |
         :         :   :                                   |(1)
         :  +-------:---:-----:------------:-----:-----+   |
         : /       [X1]__:___  __________[X2]         /    |
         :/         / \_  :         _____/ /         /     |
         :         /    \_ :  _____/      /         /
        /:        /       \: /           /         /
       / :       /        [X5]          /         /
      /   :     /       __/ \__        /         /
     /     :   /    ___/       \__    /         /
    /       : / ___/              \  /         /
   /        [X4]__________________[X3].       /
  +------------------------------------------+
                       L3 Topology

   The following steps are performed to deliver the service within the
   network management automation architecture proposed in this document:

   1.  Establish resource pool for the basic common network
       infrastructure.

   2.  Request to create two sites based on L3SM Service model with each
       having one network access connectivity:

          Site A: Network-Access A, Bandwidth=20M, for class "foo",
          guaranteed-bw-percent = 10, One-Way-Delay=70 msec

          Site B: Network-Access B, Bandwidth=30M, for class "foo1",
          guaranteed-bw-percent = 15, One-Way-Delay=60 msec




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   3.  Create a new service topology based on Service Type and service
       requirements (e.g., Service Type, Site location, Number of
       Slices, QoS requirements corresponding to network connectivity
       within a L3VPN) defined in L3SM service model.

   4.  Translate L3SM service model into resource facing TEAS VN Model
       [I-D.ietf-teas-actn-vn-yang] and a set of Network element models
       to enable the protocols on the network device and get the network
       setup, and the generated resource facing TEAS VN model can be
       further used to calculate the node resource, link resource
       corresponding to connectivity between sites.

   5.  Setup tunnels between sites and map them with the network
       infrastructure and establish resource facing VN topology based on
       TEAS VN model and TE tunnel based on TE Tunnel model.  The
       resource facing TEAS VN model and corresponding TE Tunnel model
       can be used to notify all the parameter changes and event related
       to VN topology or Tunnel.  These information can be further used
       to adjust network resource distributed within the network.

   The customer-initiated resource creation is similar to customer made
   Network Slice creation pattern discussed in Section 5.2 of [I-
   D.homma-slice-provision-models].

7.  Security Considerations

   Security considerations specific to each of the technologies and
   protocols listed in the document are discussed in the specification
   documents of each of these techniques.

   (Potential) security considerations specific to this document are
   listed below:

   o  Create forwarding loops by mis-configuring the underlying network.

   o  Leak sensitive information: special care should be considered when
      translating between the various layers introduced in the document.

   o  ...tbc

8.  IANA Considerations

   There are no IANA requests or assignments included in this document.








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9.  Contributors

      Shunsuke Homma
      Japan

      Email: s.homma0718+ietf@gmail.com

10.  Acknowledgements

   Thanks to Joe Clark and Greg Mirsky for the review.

11.  Informative References

   [I-D.arkko-arch-virtualization]
              Arkko, J., Tantsura, J., Halpern, J., and B. Varga,
              "Considerations on Network Virtualization and Slicing",
              draft-arkko-arch-virtualization-01 (work in progress),
              March 2018.

   [I-D.asechoud-netmod-diffserv-model]
              Choudhary, A., Shah, S., Jethanandani, M., Liu, B., and N.
              Strahle, "YANG Model for Diffserv", draft-asechoud-netmod-
              diffserv-model-03 (work in progress), June 2015.

   [I-D.clacla-netmod-model-catalog]
              Clarke, J. and B. Claise, "YANG module for
              yangcatalog.org", draft-clacla-netmod-model-catalog-03
              (work in progress), April 2018.

   [I-D.homma-slice-provision-models]
              Homma, S., Nishihara, H., Miyasaka, T., Galis, A., OV, V.,
              Lopez, D., Contreras, L., Ordonez-Lucena, J., Martinez-
              Julia, P., Qiang, L., Rokui, R., Ciavaglia, L., and X.
              Foy, "Network Slice Provision Models", draft-homma-slice-
              provision-models-00 (work in progress), February 2019.

   [I-D.ietf-bess-evpn-yang]
              Brissette, P., Shah, H., Hussain, I., Tiruveedhula, K.,
              and J. Rabadan, "Yang Data Model for EVPN", draft-ietf-
              bess-evpn-yang-07 (work in progress), March 2019.

   [I-D.ietf-bess-l2vpn-yang]
              Shah, H., Brissette, P., Chen, I., Hussain, I., Wen, B.,
              and K. Tiruveedhula, "YANG Data Model for MPLS-based
              L2VPN", draft-ietf-bess-l2vpn-yang-10 (work in progress),
              July 2019.





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   [I-D.ietf-bess-l3vpn-yang]
              Jain, D., Patel, K., Brissette, P., Li, Z., Zhuang, S.,
              Liu, X., Haas, J., Esale, S., and B. Wen, "Yang Data Model
              for BGP/MPLS L3 VPNs", draft-ietf-bess-l3vpn-yang-04 (work
              in progress), October 2018.

   [I-D.ietf-bfd-yang]
              Rahman, R., Zheng, L., Jethanandani, M., Networks, J., and
              G. Mirsky, "YANG Data Model for Bidirectional Forwarding
              Detection (BFD)", draft-ietf-bfd-yang-17 (work in
              progress), August 2018.

   [I-D.ietf-ccamp-alarm-module]
              Vallin, S. and M. Bjorklund, "YANG Alarm Module", draft-
              ietf-ccamp-alarm-module-09 (work in progress), April 2019.

   [I-D.ietf-ccamp-flexigrid-media-channel-yang]
              Madrid, U., Perdices, D., Lopezalvarez, V., Dios, O.,
              King, D., Lee, Y., and G. Galimberti, "YANG data model for
              Flexi-Grid media-channels", draft-ietf-ccamp-flexigrid-
              media-channel-yang-02 (work in progress), March 2019.

   [I-D.ietf-ccamp-flexigrid-yang]
              Madrid, U., Perdices, D., Lopezalvarez, V., Dios, O.,
              King, D., Lee, Y., and G. Galimberti, "YANG data model for
              Flexi-Grid Optical Networks", draft-ietf-ccamp-flexigrid-
              yang-03 (work in progress), March 2019.

   [I-D.ietf-ccamp-l1csm-yang]
              Fioccola, G., Lee, K., Lee, Y., Dhody, D., and D.
              Ceccarelli, "A YANG Data Model for L1 Connectivity Service
              Model (L1CSM)", draft-ietf-ccamp-l1csm-yang-09 (work in
              progress), March 2019.

   [I-D.ietf-ccamp-mw-yang]
              Ahlberg, J., Ye, M., Li, X., Spreafico, D., and M.
              Vaupotic, "A YANG Data Model for Microwave Radio Link",
              draft-ietf-ccamp-mw-yang-13 (work in progress), November
              2018.

   [I-D.ietf-ccamp-otn-topo-yang]
              Zheng, H., Guo, A., Busi, I., Sharma, A., Liu, X.,
              Belotti, S., Xu, Y., Wang, L., and O. Dios, "A YANG Data
              Model for Optical Transport Network Topology", draft-ietf-
              ccamp-otn-topo-yang-06 (work in progress), February 2019.






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   [I-D.ietf-ccamp-otn-tunnel-model]
              Zheng, H., Guo, A., Busi, I., Sharma, A., Rao, R.,
              Belotti, S., Lopezalvarez, V., Li, Y., and Y. Xu, "OTN
              Tunnel YANG Model", draft-ietf-ccamp-otn-tunnel-model-06
              (work in progress), February 2019.

   [I-D.ietf-ccamp-wson-tunnel-model]
              Lee, Y., Dhody, D., Guo, A., Lopezalvarez, V., King, D.,
              Yoon, B., and R. Vilata, "A Yang Data Model for WSON
              Tunnel", draft-ietf-ccamp-wson-tunnel-model-03 (work in
              progress), March 2019.

   [I-D.ietf-dots-data-channel]
              Boucadair, M. and R. K, "Distributed Denial-of-Service
              Open Threat Signaling (DOTS) Data Channel Specification",
              draft-ietf-dots-data-channel-29 (work in progress), May
              2019.

   [I-D.ietf-dots-signal-channel]
              K, R., Boucadair, M., Patil, P., Mortensen, A., and N.
              Teague, "Distributed Denial-of-Service Open Threat
              Signaling (DOTS) Signal Channel Specification", draft-
              ietf-dots-signal-channel-34 (work in progress), May 2019.

   [I-D.ietf-idr-bgp-model]
              Jethanandani, M., Patel, K., and S. Hares, "BGP YANG Model
              for Service Provider Networks", draft-ietf-idr-bgp-
              model-06 (work in progress), June 2019.

   [I-D.ietf-ippm-stamp-yang]
              Mirsky, G., Xiao, M., and W. Luo, "Simple Two-way Active
              Measurement Protocol (STAMP) Data Model", draft-ietf-ippm-
              stamp-yang-03 (work in progress), March 2019.

   [I-D.ietf-ippm-twamp-yang]
              Civil, R., Morton, A., Rahman, R., Jethanandani, M., and
              K. Pentikousis, "Two-Way Active Measurement Protocol
              (TWAMP) Data Model", draft-ietf-ippm-twamp-yang-13 (work
              in progress), July 2018.

   [I-D.ietf-mpls-base-yang]
              Saad, T., Raza, K., Gandhi, R., Liu, X., and V. Beeram, "A
              YANG Data Model for MPLS Base", draft-ietf-mpls-base-
              yang-10 (work in progress), February 2019.







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   [I-D.ietf-pim-igmp-mld-snooping-yang]
              Zhao, H., Liu, X., Liu, Y., Sivakumar, M., and A. Peter,
              "A Yang Data Model for IGMP and MLD Snooping", draft-ietf-
              pim-igmp-mld-snooping-yang-08 (work in progress), June
              2019.

   [I-D.ietf-pim-igmp-mld-yang]
              Liu, X., Guo, F., Sivakumar, M., McAllister, P., and A.
              Peter, "A YANG Data Model for Internet Group Management
              Protocol (IGMP) and Multicast Listener Discovery (MLD)",
              draft-ietf-pim-igmp-mld-yang-15 (work in progress), June
              2019.

   [I-D.ietf-pim-yang]
              Liu, X., McAllister, P., Peter, A., Sivakumar, M., Liu,
              Y., and f. hu, "A YANG Data Model for Protocol Independent
              Multicast (PIM)", draft-ietf-pim-yang-17 (work in
              progress), May 2018.

   [I-D.ietf-rtgwg-device-model]
              Lindem, A., Berger, L., Bogdanovic, D., and C. Hopps,
              "Network Device YANG Logical Organization", draft-ietf-
              rtgwg-device-model-02 (work in progress), March 2017.

   [I-D.ietf-rtgwg-policy-model]
              Qu, Y., Tantsura, J., Lindem, A., and X. Liu, "A YANG Data
              Model for Routing Policy Management", draft-ietf-rtgwg-
              policy-model-06 (work in progress), March 2019.

   [I-D.ietf-softwire-iftunnel]
              Boucadair, M., Farrer, I., and R. Asati, "Tunnel Interface
              Types YANG Module", draft-ietf-softwire-iftunnel-07 (work
              in progress), June 2019.

   [I-D.ietf-softwire-yang]
              Farrer, I. and M. Boucadair, "YANG Modules for IPv4-in-
              IPv6 Address plus Port (A+P) Softwires", draft-ietf-
              softwire-yang-16 (work in progress), January 2019.

   [I-D.ietf-spring-sr-yang]
              Litkowski, S., Qu, Y., Lindem, A., Sarkar, P., and J.
              Tantsura, "YANG Data Model for Segment Routing", draft-
              ietf-spring-sr-yang-12 (work in progress), February 2019.








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   [I-D.ietf-supa-generic-policy-data-model]
              Halpern, J. and J. Strassner, "Generic Policy Data Model
              for Simplified Use of Policy Abstractions (SUPA)", draft-
              ietf-supa-generic-policy-data-model-04 (work in progress),
              June 2017.

   [I-D.ietf-teas-actn-vn-yang]
              Lee, Y., Dhody, D., Ceccarelli, D., Bryskin, I., and B.
              Yoon, "A Yang Data Model for VN Operation", draft-ietf-
              teas-actn-vn-yang-05 (work in progress), June 2019.

   [I-D.ietf-teas-sf-aware-topo-model]
              Bryskin, I., Liu, X., Lee, Y., Guichard, J., Contreras,
              L., Ceccarelli, D., and J. Tantsura, "SF Aware TE Topology
              YANG Model", draft-ietf-teas-sf-aware-topo-model-03 (work
              in progress), March 2019.

   [I-D.ietf-teas-te-service-mapping-yang]
              Lee, Y., Dhody, D., Ceccarelli, D., Tantsura, J.,
              Fioccola, G., and Q. Wu, "Traffic Engineering and Service
              Mapping Yang Model", draft-ietf-teas-te-service-mapping-
              yang-01 (work in progress), March 2019.

   [I-D.ietf-teas-yang-l3-te-topo]
              Liu, X., Bryskin, I., Beeram, V., Saad, T., Shah, H., and
              O. Dios, "YANG Data Model for Layer 3 TE Topologies",
              draft-ietf-teas-yang-l3-te-topo-04 (work in progress),
              March 2019.

   [I-D.ietf-teas-yang-path-computation]
              Busi, I., Belotti, S., Lopezalvarez, V., Dios, O., Sharma,
              A., Shi, Y., Vilata, R., Sethuraman, K., Scharf, M., and
              D. Ceccarelli, "Yang model for requesting Path
              Computation", draft-ietf-teas-yang-path-computation-05
              (work in progress), March 2019.

   [I-D.ietf-teas-yang-rsvp-te]
              Beeram, V., Saad, T., Gandhi, R., Liu, X., Bryskin, I.,
              and H. Shah, "A YANG Data Model for RSVP-TE Protocol",
              draft-ietf-teas-yang-rsvp-te-06 (work in progress), April
              2019.

   [I-D.ietf-teas-yang-sr-te-topo]
              Liu, X., Bryskin, I., Beeram, V., Saad, T., Shah, H., and
              S. Litkowski, "YANG Data Model for SR and SR TE
              Topologies", draft-ietf-teas-yang-sr-te-topo-04 (work in
              progress), March 2019.




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   [I-D.ietf-teas-yang-te]
              Saad, T., Gandhi, R., Liu, X., Beeram, V., and I. Bryskin,
              "A YANG Data Model for Traffic Engineering Tunnels and
              Interfaces", draft-ietf-teas-yang-te-21 (work in
              progress), April 2019.

   [I-D.ietf-teas-yang-te-topo]
              Liu, X., Bryskin, I., Beeram, V., Saad, T., Shah, H., and
              O. Dios, "YANG Data Model for Traffic Engineering (TE)
              Topologies", draft-ietf-teas-yang-te-topo-22 (work in
              progress), June 2019.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

   [RFC4664]  Andersson, L., Ed. and E. Rosen, Ed., "Framework for Layer
              2 Virtual Private Networks (L2VPNs)", RFC 4664,
              DOI 10.17487/RFC4664, September 2006,
              <https://www.rfc-editor.org/info/rfc4664>.

   [RFC4761]  Kompella, K., Ed. and Y. Rekhter, Ed., "Virtual Private
              LAN Service (VPLS) Using BGP for Auto-Discovery and
              Signaling", RFC 4761, DOI 10.17487/RFC4761, January 2007,
              <https://www.rfc-editor.org/info/rfc4761>.

   [RFC4762]  Lasserre, M., Ed. and V. Kompella, Ed., "Virtual Private
              LAN Service (VPLS) Using Label Distribution Protocol (LDP)
              Signaling", RFC 4762, DOI 10.17487/RFC4762, January 2007,
              <https://www.rfc-editor.org/info/rfc4762>.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
              <https://www.rfc-editor.org/info/rfc5880>.

   [RFC7149]  Boucadair, M. and C. Jacquenet, "Software-Defined
              Networking: A Perspective from within a Service Provider
              Environment", RFC 7149, DOI 10.17487/RFC7149, March 2014,
              <https://www.rfc-editor.org/info/rfc7149>.

   [RFC7276]  Mizrahi, T., Sprecher, N., Bellagamba, E., and Y.
              Weingarten, "An Overview of Operations, Administration,
              and Maintenance (OAM) Tools", RFC 7276,
              DOI 10.17487/RFC7276, June 2014,
              <https://www.rfc-editor.org/info/rfc7276>.






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   [RFC7297]  Boucadair, M., Jacquenet, C., and N. Wang, "IP
              Connectivity Provisioning Profile (CPP)", RFC 7297,
              DOI 10.17487/RFC7297, July 2014,
              <https://www.rfc-editor.org/info/rfc7297>.

   [RFC8077]  Martini, L., Ed. and G. Heron, Ed., "Pseudowire Setup and
              Maintenance Using the Label Distribution Protocol (LDP)",
              STD 84, RFC 8077, DOI 10.17487/RFC8077, February 2017,
              <https://www.rfc-editor.org/info/rfc8077>.

   [RFC8194]  Schoenwaelder, J. and V. Bajpai, "A YANG Data Model for
              LMAP Measurement Agents", RFC 8194, DOI 10.17487/RFC8194,
              August 2017, <https://www.rfc-editor.org/info/rfc8194>.

   [RFC8199]  Bogdanovic, D., Claise, B., and C. Moberg, "YANG Module
              Classification", RFC 8199, DOI 10.17487/RFC8199, July
              2017, <https://www.rfc-editor.org/info/rfc8199>.

   [RFC8299]  Wu, Q., Ed., Litkowski, S., Tomotaki, L., and K. Ogaki,
              "YANG Data Model for L3VPN Service Delivery", RFC 8299,
              DOI 10.17487/RFC8299, January 2018,
              <https://www.rfc-editor.org/info/rfc8299>.

   [RFC8309]  Wu, Q., Liu, W., and A. Farrel, "Service Models
              Explained", RFC 8309, DOI 10.17487/RFC8309, January 2018,
              <https://www.rfc-editor.org/info/rfc8309>.

   [RFC8328]  Liu, W., Xie, C., Strassner, J., Karagiannis, G., Klyus,
              M., Bi, J., Cheng, Y., and D. Zhang, "Policy-Based
              Management Framework for the Simplified Use of Policy
              Abstractions (SUPA)", RFC 8328, DOI 10.17487/RFC8328,
              March 2018, <https://www.rfc-editor.org/info/rfc8328>.

   [RFC8345]  Clemm, A., Medved, J., Varga, R., Bahadur, N.,
              Ananthakrishnan, H., and X. Liu, "A YANG Data Model for
              Network Topologies", RFC 8345, DOI 10.17487/RFC8345, March
              2018, <https://www.rfc-editor.org/info/rfc8345>.

   [RFC8346]  Clemm, A., Medved, J., Varga, R., Liu, X.,
              Ananthakrishnan, H., and N. Bahadur, "A YANG Data Model
              for Layer 3 Topologies", RFC 8346, DOI 10.17487/RFC8346,
              March 2018, <https://www.rfc-editor.org/info/rfc8346>.

   [RFC8349]  Lhotka, L., Lindem, A., and Y. Qu, "A YANG Data Model for
              Routing Management (NMDA Version)", RFC 8349,
              DOI 10.17487/RFC8349, March 2018,
              <https://www.rfc-editor.org/info/rfc8349>.




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   [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>.

   [RFC8512]  Boucadair, M., Ed., Sivakumar, S., Jacquenet, C.,
              Vinapamula, S., and Q. Wu, "A YANG Module for Network
              Address Translation (NAT) and Network Prefix Translation
              (NPT)", RFC 8512, DOI 10.17487/RFC8512, January 2019,
              <https://www.rfc-editor.org/info/rfc8512>.

   [RFC8513]  Boucadair, M., Jacquenet, C., and S. Sivakumar, "A YANG
              Data Model for Dual-Stack Lite (DS-Lite)", RFC 8513,
              DOI 10.17487/RFC8513, January 2019,
              <https://www.rfc-editor.org/info/rfc8513>.

   [RFC8519]  Jethanandani, M., Agarwal, S., Huang, L., and D. Blair,
              "YANG Data Model for Network Access Control Lists (ACLs)",
              RFC 8519, DOI 10.17487/RFC8519, March 2019,
              <https://www.rfc-editor.org/info/rfc8519>.

   [RFC8528]  Bjorklund, M. and L. Lhotka, "YANG Schema Mount",
              RFC 8528, DOI 10.17487/RFC8528, March 2019,
              <https://www.rfc-editor.org/info/rfc8528>.

   [RFC8529]  Berger, L., Hopps, C., Lindem, A., Bogdanovic, D., and X.
              Liu, "YANG Data Model for Network Instances", RFC 8529,
              DOI 10.17487/RFC8529, March 2019,
              <https://www.rfc-editor.org/info/rfc8529>.

   [RFC8530]  Berger, L., Hopps, C., Lindem, A., Bogdanovic, D., and X.
              Liu, "YANG Model for Logical Network Elements", RFC 8530,
              DOI 10.17487/RFC8530, March 2019,
              <https://www.rfc-editor.org/info/rfc8530>.

   [RFC8531]  Kumar, D., Wu, Q., and Z. Wang, "Generic YANG Data Model
              for Connection-Oriented Operations, Administration, and
              Maintenance (OAM) Protocols", RFC 8531,
              DOI 10.17487/RFC8531, April 2019,
              <https://www.rfc-editor.org/info/rfc8531>.

   [RFC8532]  Kumar, D., Wang, Z., Wu, Q., Ed., Rahman, R., and S.
              Raghavan, "Generic YANG Data Model for the Management of
              Operations, Administration, and Maintenance (OAM)
              Protocols That Use Connectionless Communications",
              RFC 8532, DOI 10.17487/RFC8532, April 2019,
              <https://www.rfc-editor.org/info/rfc8532>.




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   [RFC8533]  Kumar, D., Wang, M., Wu, Q., Ed., Rahman, R., and S.
              Raghavan, "A YANG Data Model for Retrieval Methods for the
              Management of Operations, Administration, and Maintenance
              (OAM) Protocols That Use Connectionless Communications",
              RFC 8533, DOI 10.17487/RFC8533, April 2019,
              <https://www.rfc-editor.org/info/rfc8533>.

Authors' Addresses

   Qin Wu
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

   Email: bill.wu@huawei.com


   Mohamed Boucadair
   Orange
   Rennes 35000
   France

   Email: mohamed.boucadair@orange.com


   Christian
   Orange
   Rennes 35000
   France

   Email: christian.jacquenet@orange.com


   Luis Miguel Contreras Murillo
   Telifonica

   Email: luismiguel.contrerasmurillo@telefonica.com


   Diego R. Lopez
   Telefonica I+D
   Spain

   Email: diego.r.lopez@telefonica.com






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   Chongfeng Xie
   China Telecom
   Beijing
   China

   Email: xiechf.bri@chinatelecom.cn


   Weiqiang Cheng
   China Mobile

   Email: chengweiqiang@chinamobile.com


   Young Lee
   Futurewei

   Email: younglee.tx@gmail.com

































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