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Networking Working Group                                           Q. Wu
Internet-Draft                                                    Huawei
Intended status: Standards Track                            M. Boucadair
Expires: September 4, 2018                                        Orange
                                                           March 3, 2018


 An Architecture for Data Model Driven Network Management: the Network
                          Virtualization Case
           draft-wu-model-driven-management-virtualization-00

Abstract

   Data Model driven network management can be used at various phases of
   service and network management life cycle such as service
   instantiation, service provision, optimization, monitoring, and
   diagnostic.  Also, it can be designed to provide closed-loop control
   for the sake of agile service creation, delivery and maintenance.

   This document describes an architecture for data model driven network
   management with a sample applicability case: network virtualization
   environments.

Status of This Memo

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

   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 September 4, 2018.

Copyright Notice

   Copyright (c) 2018 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



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   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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Architectural Concepts  . . . . . . . . . . . . . . . . . . .   4
     2.1.  Data Models: Layering and Representation  . . . . . . . .   4
     2.2.  Service and Network Resources Exposure: Service Level
           Model Decomposition . . . . . . . . . . . . . . . . . . .   4
     2.3.  Service Element Configuration Model Composition . . . . .   4
     2.4.  A Catalog for YANG Modules  . . . . . . . . . . . . . . .   5
   3.  IETF YANG Modules: An Overview  . . . . . . . . . . . . . . .   5
     3.1.  Network Service and Resource Models . . . . . . . . . . .   6
       3.1.1.  Customer facing Service Models: Definition and
               Samples . . . . . . . . . . . . . . . . . . . . . . .   6
       3.1.2.  Resource Facing Network Models  . . . . . . . . . . .   7
     3.2.  Network Element Models  . . . . . . . . . . . . . . . . .   9
       3.2.1.  Model Composition . . . . . . . . . . . . . . . . . .  10
       3.2.2.  Protocol/Function Configuration Models  . . . . . . .  11
   4.  Architecture Overview . . . . . . . . . . . . . . . . . . . .  12
     4.1.  End-to-End Service Delivery Procedure . . . . . . . . . .  13
       4.1.1.  Resource Collection and Abstraction (a) . . . . . . .  13
       4.1.2.  Service Exposure & Abstraction (b)  . . . . . . . . .  14
       4.1.3.  Model Decomposition/Composition (c) . . . . . . . . .  14
       4.1.4.  Model Configuration (d) . . . . . . . . . . . . . . .  15
       4.1.5.  Model Translation (e) . . . . . . . . . . . . . . . .  16
       4.1.6.  Path Management (f) . . . . . . . . . . . . . . . . .  16
       4.1.7.  Overlay and Underlay Interaction (g)  . . . . . . . .  16
       4.1.8.  Performance Measurement and Alarm Reporting (h) . . .  17
       4.1.9.  (Continuous) Network Optimization (i) . . . . . . . .  17
     4.2.  Overlay and Underlay Interaction Usage: Sample Examples .  17
       4.2.1.  Network Topology Resource Pre-Provision . . . . . . .  17
       4.2.2.  On Demand Network Topology Resource Creation  . . . .  19
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
   7.  Informative References  . . . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

1.  Introduction

   As observed in [I-D.arkko-arch-virtualization], many IETF discussions
   earlier in the summer of 2017 started from a top-down view of new
   virtualization technologies, but were often unable to explain the



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   necessary delta to the wealth of existing IETF technologies in this
   space.  Therefore, [I-D.arkko-arch-virtualization] considered a
   bottom-up approach to provide an overview of existing technologies
   which is aiming at identifying areas for further development.

   For years, the IETF was driving the industry transition from an
   overloaded Software Defined Networking (SDN) buzzword to focus on
   specific areas such as data modeling-driven management.  [RFC7149]
   provided a first tentative to rationalize that space by identifying
   concrete technical domains that need to be considered:

   o  Techniques for the dynamic discovery of network 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 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.

   Later, as described in [RFC8199], YANG module developers have taken
   both top-down and bottom-up approaches to develop modules and
   establish mapping between network technology and customer
   requirements on the top or abstracting common construct from various
   network technologies.  At the time of writing this document (2018),
   we see the large number of data models including configuration models
   and service models developed or under development in IETF covering
   much of networking protocols and techniques.  In addition, how these
   models work together to fully configure a device, or manage a set of
   devices involved in a service aren't developed yet in IETF.

   This document takes both bottom up approach and top down approach to
   provide a framework that discusses the architecture for data model
   driven network management, with a focus on network virtualization
   environment.

   This document also describes specific YANG modules needed to realize
   connectivity services and investigate how top down built model (e.g.,
   customer-facing data models) interact with bottom up built model



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   (resource-facing data models) in the context of service delivery and
   assurance.

2.  Architectural Concepts

2.1.  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 IETF has developed large number of network level and device level
   modules, and few service ones.  Service level modules follow top down
   approach and are mostly customer-facing models providing a common
   model construct for higher level network services, which can be
   further mapped to network technology-specific models at lower layer.

   Network level modules mostly follow bottom up approach and are mostly
   resource-facing model 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 follow bottom up approach and are mostly
   technology-specific modules used to realize a service.

2.2.  Service and Network Resources Exposure: Service Level Model
      Decomposition

   Service level model defines a service ordered by a customer from an
   operator.  The service can be built from a combination of network
   elements and protocols configuration which also include various
   aspects of the underlying network infrastructure, including
   fucntions/devices and their subsystems, and relevant protocols
   operating at the link and network layers across multiple device.

2.3.  Service Element Configuration Model Composition

   To provide service agility (including network management automation),
   lower level technology-specific models need to be assembled together
   to provision each involved network function/device and operate the
   network based on service requirements described in the service level
   model.

   IETF RTGWG working group has already been tasked to define service
   elements configuration model composition mechanism and develop
   several composition model such as network instance model, logical
   network element model and device model.



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   These models can be used to setup and administrate both virtualized
   system and physical system.

2.4.  A Catalog for YANG Modules

   The idea of a catalog is similar to service catalogs in traditional
   IT environments.  Service catalogs serve as a software-based
   registries of available services with information needed to discover
   and invoke available services.

   The IETF has already tasked to develop a YANG catalog which can be
   used to manage not only IETF defined modules, but also non-IETF
   defined ones [I-D.clacla-netmod-model-catalog].

   The YANG catalog allows to align IETF work with other SDOs work and
   prevent duplicated building blocks being developed.  It also
   encourages reusability of common building blocks.

   The YANG catalog allows both YANG developers and operators to
   discover the more mature YANG modules that may be used to automate
   services operations .

3.  IETF YANG Modules: An Overview




























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  << Customer facing Service Models>>
                                        +-------------+  +-------------+
  +----------------+ +----------------+ |DOTS Data    |  |   I2NSF     |
  |      L3SM      | |     L2SM       | |and Signaling|  |   Customer  |
  |  Service Model | |  Service Model | |  Models     |  | Facing Model|
  +----------------+ +----------------+ +-------------+  +-------------+
 -------------------------------------------------------------------
  << Resource Facing Models>>
       +------------+  +-------+  +----------------+   +------------+
       |Network Topo|  | Tunnel|  |Path Computation|   |OAM,PM,Alarm|
       |   Models   |  | Models|  | API Models     |   |   Models   |
       +------------+  +-------+  +----------------+   +------------+
<<Network Service and Resource Models>>
 --------------------------------------------------------------------
<<Network Element Models>>
   <<Composition Models>>
       +-------------+ +---------------+ +----------------+
       |Device Model | |Logical Network| |Network Instance|
       |             | |Element Model  | |   Model        |
       +-------------+ +---------------+ +----------------+
 ----------------------------------------------------------------------

  << Component Models>>
                                           +------------+
     +-----+   +------+ +---++----+ +----+ |OAM,PM,Alarm|
     | BGP |   | MPLS | |ACL||QoS | |NAT | |   Models   |  .....
     +-----+   +------+ +---++----+ +----+ +------------+

3.1.  Network Service and Resource Models

   Service and Network Resource Exposure modules define what the
   "service"/"resource" is.  These modules can be classified into two
   categories:

   o  Customer-facing Models

   o  Resource-facing Models

3.1.1.  Customer facing Service Models: Definition and Samples

   As described in [RFC8309], the service is some form of connectivity
   between customer sites and the Internet or between customer sites
   across the network operator's network and across the Internet.

   For example,

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



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

   The IETF is currently defining three other customer-facing modules:
   ietf-dots-signal-channel [I-D.ietf-dots-signal-channel] and ietf-
   dots-data-channel [I-D.ietf-dots-data-channel] and I2NSF Consumer-
   Facing Interface YANG module
   [I-D.jeong-i2nsf-consumer-facing-interface-dm].  The first two
   modules are meant to be used by clients to signal DDoS attacks or to
   request installing filters for the sake of DDoS mitigation.  Those
   modules do not intervene directly in the configuration of underlying
   network devices.  The third module is required for enabling different
   users of a given I2NSF system to define, manage, and monitor security
   policies for specific flows within an administrative domain.

3.1.2.  Resource Facing Network Models

   Figure 1 shows a set of resource-facing network YANG modules:

                       |                             |
      Topo YANG Models |    Tunnel Service Models    |Resource NM Tool
     ------------------------------------------------|-- ------------
  +------------+       |                             |
  |Network Top |       |           +-----------+     |       +-------+
  |   Model    |       |           | TE Tunnel |     |       | LIME  |
  +----+-------+       |           +------+----+     |       | Model |
       |   +--------+  |                  |          |       |/PM/OAM|
       |---+TE Topo |  |         +--------+-+--------+       |  Model|
       |   +--------+  |    +----+---+  +---+----+ +-+-----+ +-------+
       |   +--------+  |    |MPLS-TE |  |RSVP-TE | |SR TE  | +--------+
       +---+L3 Topo |       | Tunnel |  | Tunnel | |Tunnel | |  Alarm |
           +----|---+       +--------+  +--------+ +-------+ |  Model |
      +---------+---------+                                  +--------+
      |         |         |                                +-----------+
  +---|---+  +--|---+ +---|-+                              |Path       |
  |SR Topo|  |SR TE | |L3 TE|                              |Computation|
  | Model |  | Topo | |Topo |                              |API Model  |
  +-------+  +------+ +-----+                              +-----------+

              Figure 1: Sample Resource Facing Network Models

   o  Network Topology Models: [I.D-ietf-i2rs-yang-network-topo] defines
      base model for network topology and inventories.  Network topology
      data include link resource, node resource and terminate-point
      resource.

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



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      This module is extended from network topology model defined in
      [I.D-ietf-i2rs-yang-network-topo] 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

      [I.D-ietf-i2rs-yang-l3-topology] defines a data model for
      representing and manipulating L3 Topologies.  This model is
      extended from the network topology model defined in [I.D-ietf-
      i2rs-yang-network-topo] 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
      extended from the network topology model defined in [I.D-ietf-
      i2rs-yang-network-topo] with L2 topologies specifics.

   o  L3 TE Topology Models

      When traffic engineering is enabled on a layer 3 network topology,
      there will be a corresponding TE topology.  [I.D-liu-teas-yang-l3-
      te-topo] defines data models for layer 3 traffic engineering
      topologies.  Two data models are defined, one is layer 3 TE
      topology model, the other is packet switching TE topology model.
      Layer 3 TE topology model is extended from Layer 3 topology model.
      Packet switching TE topology model is extended from TE topology
      model.

   o  SR TE Topology Models

      [I-D.liu-teas-yang-sr-te-topo] defines a YANG module for Segment
      Routing (SR) topology and Segment Routing (SR) traffic engineering
      (TE) topology.  Two models are defined, one is SR topology model,
      the other is SR TE topology model, SR topology model is extended
      from L3 Topology model.  SR TE topology model is extended from
      both SR Topology model and L3 TE topology model.

   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





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      [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.

   o  Path Computation API Model

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

   o  OAM Models

      [I.D-ietf-lime-yang-connectionless-oam] defines a base YANG module
      for the management of OAM protocols that use Connectionless
      Communications.  [I.D-ietf-lime-yang-connectionless-oam-methods]
      defines a retrieval method YANG module for connectionless OAM
      protocols.  [I.D-ietf-lime-yang-connection-oriented-oam-model]
      defines a base YANG module for connection oriented OAM protocols.
      These three models can be used to provide consistent reporting,
      configuration and representation.

   o  PM Models

   o  Alarm Models

      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.

3.2.  Network Element Models

   Network Element models are used to describe how a service can be
   implemented by activating and tweaking a set of functions (enabled in
   one or multiple devices) that are involved in the service delivery.



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                                          +----------------+
                                        --|Device Model    |
                                        | +----------------+
                                        | +------------------+
                     +---------------+  | |Logical Network   |
                     |               |  --|  Element Mode    |
                     | Architecture  |  | +------------------+
                     |               |  | +----------------------+
                     +-------+-------+  --|Network Instance Mode |
                             |          | +----------------------+
                             |          | +-------------------+
                             |          --|Routing Type Model |
                             |            +-------------------+
     +-------+----------+----+------+------------+-----------+-------+
     |       |          |           |            |           |       |
   +-+-+ +---+---+   +--+-+       +-+-+    +-----+---+   +---+-+     |
   |ACL| |Routing|   |MPLS|       |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   |
         | +-------+
         --|ISIS-SR|
         | +-------+
         --|OSPF-SR|
         | +-------+

3.2.1.  Model Composition

   o  Device Model

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



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   o  Logical Network Element Model

      [I.D-ietf-rtgwg-lne-model] 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

      [I.D-ietf-rtgwg-ni-model] 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).

3.2.1.1.  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.  [I-D.ietf-netmod-schema-mount] 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.

3.2.2.  Protocol/Function Configuration Models

   BGP:       [I.D-mks-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 models (e.g.  MPLS LSP Static,
              LDP or RSVP-TE models) will augment the MPLS base YANG
              model.

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




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   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.  [I.D-ietf-netmod-acl-model]
              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.  [I.D-ietf-opsawg-nat-yang] defines a
              YANG module for the NAT function.

   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.

4.  Architecture Overview

   The architectural considerations and conclusions described in the
   previous section lead to the architecture described in this section
   and illustrated in Figure 2.

   The interfaces and interactions shown in the figure and labeled (a)
   through (j) are further described in Section 5.1.























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         +-----------------+
         |Service Requester|
         +-^--|------------+
   +-------|--|------------------------------------------------------+
   |       | (b)+---(h)------ feedback                               |
   |       |  V |                                                    |
   |    +--|----V+ +-------------+                                   |
   |    |Service&| |   Model     |-----(c)-----------------+         |
   | +-->Resource|->Decomposition|                         |         |
   | |  |Exposure| |/Composition |                         |         |
   | |  +--------+ +-------------+                         |         |
   | |        |                                            |         |
   | | +------V-----+          +-----------+        +------V------+  |
   | | |   Model    |   (e)    |  Path     |  (f)   |    Model    |  |
   | | | Translation|--------->|Computation|------->|Configuration|  |
   | | +------------+          +-^---------+        +-----(d)-----+  |
   | (a)Exposure&Abstraction     |   |                     |         |
   | |       --------------------+   |(f)                  V         |
   | |       |                       |                               |
   | |  +----|------+         +------V----+                          |
   | |  |Basic Topo |         |    Path   |                          |
   | +--|Collection |     +---|   Setup   |                          |
   |    +----^--|---+     |   +-----------+                          |
   |         |  |         |                   (h)                    |
   |        (a) |  +------V----+Service  +-----------+     (i)       |
   |         |  |  |   Topo    | Topo    |  PM/Alarm | Network Opt   |
   |         |  +--> Mapping   ------->  | Collection------>         |
   |         |     +-----------+         +-----------+               |
   +--------------------(g)------------------------------------------+

                  Figure 2: Data Model Driven Management

4.1.  End-to-End Service Delivery Procedure

4.1.1.  Resource Collection and Abstraction (a)

   Network Resource such as links, nodes, or terminate-point resources
   can be collected from the network and aggregated or abstracted to the
   management system.

   These resources can be modelled using network topology model, 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 have multiple overlay topologies built on
   top of the same underlay topology, and the underlay topology can be
   also built from one or more lower layer underlay topology.




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   The network resources and management objects are exposed in a more
   abstract way to the management system or customers who (will) order
   the service from the management system.

   The abstract view is likely to be technology-agnostic.

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 L3SM service model to request L3VPN service by
   providing the abstract technical characterization of the intended
   service.  Such L3VPN service describes various aspects of network
   infrastructure, including devices and their subsystems, and relevant
   protocols operating at the link and network layers across multiple
   device.  The L3SM service model can be used to interact with the
   network infrastructure, e.g., configure sites, decide QoS parameters
   to be applied to each network access within a site, select PEs, CEs,
   etc.

   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 is corresponding to a set of YANG modules that have
   been released or published.  Then, a mapping can be established
   between service abstraction and service bundles at higher layer and
   between service bundle and a set of YANG modules at lower layer.

4.1.3.  Model Decomposition/Composition (c)

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

   Therefore, the interaction between service abstraction and resource
   abstraction or between overlay and underlay is required.  For
   example, in the L3SM service model, we describe VPN service topology
   including sites relationship, 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
   underlying network topology.  For detailed interaction, please refer
   to . (Section 4.1.7)




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   In addition, there is a need to decide on a mapping between service
   abstraction and underlying specific network technologies.  Take L3SM
   service model as an example, to realize 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, these configuration models include:

   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

   These detailed configuration models are further assembled together
   into service bundle using, e.g., device model, logical network
   element model or network instance model defined in [I.D-ietf-rtgwg-
   device-model] [I.D-ietf-rtgwg-lne-model] [I.D-ietf-rtgwg-ni-model]
   provide the association between an interface and its associated LNE
   and NI and populate into appropriate devices(e.g., PE and CE).

4.1.4.  Model Configuration (d)

   Model Configuration is used to provision service or network
   infrastructure using various configuration models, e.g., use service
   element models such as BGP, ACL, QoS, Interface model, Network
   instance models to configure PE and CE device within the site.  BGP
   Policy model is used to establish VPN membership between sites and
   VPN Service Topology.  Traditionally, "push" service element
   configuration model one by one to the network device and provide
   association between an interface and each service element
   configuration model is not efficient.

   To automate configuration of the service elements, we first assemble
   all related service elements models into logical network element
   model defined in [I.D-ietf-rtgwg-lne-model] and then establish
   association with an interface and a set of service elements.





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   In addition, Model configuration can be used to setup tunnels between
   sites and setup tunnels between PE and CE within the site when
   tunnels related configuration parameters can be generated from
   service abstraction.

4.1.5.  Model Translation (e)

   In L3SM Service Model, the management system will have to determine
   where to connect each site-network-access of a particular site to the
   provider network (e.g., PE, aggregation switch).  L3SM Service model
   proposes parameters and constraints that can influence the meshing of
   the site-network-access.

   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.

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

4.1.6.  Path Management (f)

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

4.1.7.  Overlay and Underlay Interaction (g)

   After identifying node and link resources required to meet service
   requirements, the mapping between overlay topology and underlay
   topology can be set, e.g., establish an association between VPN
   service topology defined in customer facing model and underlying
   network topology defined in I2RS network 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
   VN topology model.







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4.1.8.  Performance Measurement and Alarm Reporting (h)

   Once the mapping between overlay and underlay has been setup, PM and
   Warning information per link based on end to end VN topology can be
   collected and report to the management system.

   Performance metrics can be collected before instantiating a service,
   too.

4.1.9.  (Continuous) Network Optimization (i)

   Operators may use dedicated features to dynamically capture the
   overall network status and topology to:

   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.

4.2.  Overlay and Underlay Interaction Usage: Sample Examples

4.2.1.  Network Topology Resource Pre-Provision

























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                                     |(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

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

   o  Pre-provision multiple (virtualized) overlay networks on top of
      the same basic network infrastructure and establish resource pool
      for each overlay network.

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



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         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

   o  Select appropriate virtualized overlay networks topology based on
      Service Type and service requirements defined in L3SM service
      model.

   o  Translate L3SM service model into resource facing VN Network
      Model, based on selected virtualized overlay network topology and
      PE and CE info in the generated resource facing VN network model,
      calculate node resource, link resource corresponding to
      connectivity between sites or connectivity between PE and CE
      within a Site.

   o  Setup tunnels between sites and tunnels between PE and CE within a
      Site and map them into the selected (virtualized) overlay topology
      and establish resource facing VN topology model.

      The source facing VN topology model and corresponding 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 distributing in the network.

4.2.2.  On Demand Network Topology 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 model
   driven management architecture proposed in this document:

   o  Establish resources pool for basic network infrastructure.

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

   o  Translate L3SM service model into resource facing VN Network
      Model, based on generated resource facing VN network model,
      calculate node resource, link resource corresponding to
      connectivity between sites or connectivity between PE and CE
      within Site in the service topology.

   o  Setup tunnels between sites and tunnel between PE and CE within
      Site and map them into basic network infrastructure and establish
      resource facing VN topology model.  The source facing VN topology
      model and corresponding 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
      distribution within the network.

5.  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

6.  IANA Considerations

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

7.  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-00 (work in progress),
              November 2017.





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   [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-02
              (work in progress), October 2017.

   [I-D.ietf-ccamp-alarm-module]
              Vallin, S. and M. Bjorklund, "YANG Alarm Module", draft-
              ietf-ccamp-alarm-module-01 (work in progress), February
              2018.

   [I-D.ietf-dots-data-channel]
              Reddy, T., Boucadair, M., Nishizuka, K., Xia, L., Patil,
              P., Mortensen, A., and N. Teague, "Distributed Denial-of-
              Service Open Threat Signaling (DOTS) Data Channel
              Specification", draft-ietf-dots-data-channel-13 (work in
              progress), January 2018.

   [I-D.ietf-dots-signal-channel]
              Reddy, T., 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-17 (work in progress), January
              2018.

   [I-D.ietf-i2rs-yang-l3-topology]
              Clemm, A., Medved, J., Varga, R., Liu, X.,
              Ananthakrishnan, H., and N. Bahadur, "A YANG Data Model
              for Layer 3 Topologies", draft-ietf-i2rs-yang-
              l3-topology-16 (work in progress), December 2017.

   [I-D.ietf-i2rs-yang-network-topo]
              Clemm, A., Medved, J., Varga, R., Bahadur, N.,
              Ananthakrishnan, H., and X. Liu, "A Data Model for Network
              Topologies", draft-ietf-i2rs-yang-network-topo-20 (work in
              progress), December 2017.

   [I-D.ietf-l2sm-l2vpn-service-model]
              Wen, B., Fioccola, G., Xie, C., and L. Jalil, "A YANG Data
              Model for L2VPN Service Delivery", draft-ietf-l2sm-l2vpn-
              service-model-08 (work in progress), February 2018.






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   [I-D.ietf-lime-yang-connection-oriented-oam-model]
              Kumar, D., Wu, Q., and Z. Wang, "Generic YANG Data Model
              for Connection Oriented Operations, Administration, and
              Maintenance(OAM) protocols", draft-ietf-lime-yang-
              connection-oriented-oam-model-07 (work in progress),
              February 2018.

   [I-D.ietf-lime-yang-connectionless-oam]
              Kumar, D., Wang, Z., Wu, Q., Rahman, R., and S. Raghavan,
              "Generic YANG Data Model for the Management of Operations,
              Administration, and Maintenance (OAM) Protocols that use
              Connectionless Communications", draft-ietf-lime-yang-
              connectionless-oam-18 (work in progress), November 2017.

   [I-D.ietf-lime-yang-connectionless-oam-methods]
              Kumar, D., Wang, Z., Wu, Q., Rahman, R., and S. Raghavan,
              "Retrieval Methods YANG Data Model for the Management of
              Operations, Administration, and Maintenance (OAM)
              Protocols that use Connectionless Communications", draft-
              ietf-lime-yang-connectionless-oam-methods-13 (work in
              progress), November 2017.

   [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-06 (work in progress), February 2018.

   [I-D.ietf-netmod-acl-model]
              Jethanandani, M., Huang, L., Agarwal, S., and D. Blair,
              "Network Access Control List (ACL) YANG Data Model",
              draft-ietf-netmod-acl-model-16 (work in progress),
              February 2018.

   [I-D.ietf-netmod-schema-mount]
              Bjorklund, M. and L. Lhotka, "YANG Schema Mount", draft-
              ietf-netmod-schema-mount-08 (work in progress), October
              2017.

   [I-D.ietf-opsawg-nat-yang]
              Boucadair, M., Sivakumar, S., Jacquenet, C., Vinapamula,
              S., and Q. Wu, "A YANG Module for Network Address
              Translation (NAT) and Network Prefix Translation (NPT)",
              draft-ietf-opsawg-nat-yang-13 (work in progress), February
              2018.







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   [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-06 (work in progress),
              October 2017.

   [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-15 (work in
              progress), February 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-lne-model]
              Berger, L., Hopps, C., Lindem, A., Bogdanovic, D., and X.
              Liu, "YANG Model for Logical Network Elements", draft-
              ietf-rtgwg-lne-model-09 (work in progress), March 2018.

   [I-D.ietf-rtgwg-ni-model]
              Berger, L., Hopps, C., Lindem, A., Bogdanovic, D., and X.
              Liu, "YANG Model for Network Instances", draft-ietf-rtgwg-
              ni-model-11 (work in progress), March 2018.

   [I-D.ietf-teas-yang-path-computation]
              Busi, I., Belotti, S., Lopezalvarez, V., Dios, O.,
              ansharma@infinera.com, a., Shi, Y., Vilata, R.,
              Sethuraman, K., Scharf, M., and D. Ceccarelli, "Yang model
              for requesting Path Computation", draft-ietf-teas-yang-
              path-computation-00 (work in progress), November 2017.

   [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", draft-ietf-
              teas-yang-rsvp-te-03 (work in progress), February 2018.

   [I-D.ietf-teas-yang-te]
              Saad, T., Gandhi, R., Liu, X., Beeram, V., Shah, H., and
              I. Bryskin, "A YANG Data Model for Traffic Engineering
              Tunnels and Interfaces", draft-ietf-teas-yang-te-12 (work
              in progress), February 2018.






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   [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-15 (work in
              progress), February 2018.

   [I-D.jeong-i2nsf-consumer-facing-interface-dm]
              Jeong, J., Kim, E., Ahn, T., Kumar, R., and S. Hares,
              "I2NSF Consumer-Facing Interface YANG Data Model", draft-
              jeong-i2nsf-consumer-facing-interface-dm-05 (work in
              progress), November 2017.

   [I-D.liu-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-liu-teas-yang-l3-te-topo-05 (work in progress),
              October 2017.

   [I-D.liu-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-liu-teas-yang-sr-te-topo-04 (work in
              progress), October 2017.

   [I-D.mks-idr-bgp-yang-model]
              Patel, K., Jethanandani, M., and S. Hares, "BGP YANG
              Model", draft-mks-idr-bgp-yang-model-01 (work in
              progress), November 2017.

   [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>.

   [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>.

   [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>.




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   [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>.

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






























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