Individual                                                      S. Homma
Internet-Draft                                              H. Nishihara
Intended status: Informational                                       NTT
Expires: May 6, 2020                                         T. Miyasaka
                                                           KDDI Research
                                                                A. Galis
                                               University College London
                                                               V. Ram OV
                                   Independent Research Consultant India
                                                                D. Lopez
                                                           LM. Contreras
                                                       J. Ordonez-Lucena
                                                          Telefonica I+D
                                                       P. Martinez-Julia
                                                                L. Qiang
                                                     Huawei Technologies
                                                                R. Rokui
                                                            L. Ciavaglia
                                                               X. de Foy
                                                       InterDigital Inc.
                                                        November 3, 2019

                     Network Slice Provision Models


   Network slicing is an approach to provide separate virtual network
   based on service requirements, and it's a key feature of the 5G.
   3GPP has standardized the specifications for network slicing in the
   5GS, but there are still some problems for realization of end-to-end
   network slices.  For complementing the lacks or expanding the
   usability, several organizations are proceeding standardization.
   However, the definitions and scopes of network slicing vary to some
   degree from one organization to another.  This document provides
   classification of provisioning models of network slice for clarifying
   the differences on the definitions and scopes.

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

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   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   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 May 6, 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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   ( in effect on the date of
   publication of this document.  Please review these documents
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction and Motivation . . . . . . . . . . . . . . . . .   3
     1.1.  Roles in Network Slice Provisioning . . . . . . . . . . .   3
       1.1.1.  Definitions in 3GPP on NS Provision Roles . . . . . .   4
     1.2.  High-level Problem Statement  . . . . . . . . . . . . . .   5
   2.  Definition of Terms . . . . . . . . . . . . . . . . . . . . .   5
   3.  General Requirements for Network Slicing  . . . . . . . . . .   8
   4.  Network Slice Structure . . . . . . . . . . . . . . . . . . .   8
     4.1.  Resources for Structuring Network Slices  . . . . . . . .   9
     4.2.  Basic Network Slice Structure . . . . . . . . . . . . . .  12
     4.3.  Stakeholders in the Structuring Network Slices  . . . . .  15
   5.  Variations of Network Slice Creation  . . . . . . . . . . . .  15
     5.1.  Ready-made Network Slice  . . . . . . . . . . . . . . . .  16
     5.2.  Custom-made Network Slice . . . . . . . . . . . . . . . .  16
     5.3.  semi-Custom-made Network Slice  . . . . . . . . . . . . .  16
   6.  Network Slice Provision Models  . . . . . . . . . . . . . . .  16
     6.1.  Categorization of NS Provision Models . . . . . . . . . .  16
       6.1.1.  SaaS-like Model . . . . . . . . . . . . . . . . . . .  17
       6.1.2.  PaaS-like Model . . . . . . . . . . . . . . . . . . .  17
       6.1.3.  IaaS-like Model . . . . . . . . . . . . . . . . . . .  17
     6.2.  Mapping of NS Provision Models and Infrastructure
           Layering  . . . . . . . . . . . . . . . . . . . . . . . .  18

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     6.3.  Configurable Parameters/Attributes for NS . . . . . . . .  20
     6.4.  Capability of NS Tenant on each Provision Model . . . . .  20
       6.4.1.  Capability in SaaS-like Model . . . . . . . . . . . .  21
       6.4.2.  Capability in PaaS-like Model . . . . . . . . . . . .  21
       6.4.3.  Capability in IaaS-like Model . . . . . . . . . . . .  21
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
   9.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .  22
   10. Informative References  . . . . . . . . . . . . . . . . . . .  22
   Appendix A.  NS Structure in the 3GPP 5GS . . . . . . . . . . . .  23
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24

1.  Introduction and Motivation

   Network slicing is an approach to provide separate virtual networks
   depending on requirements of each service.  Network slicing receives
   attention due to factors such as diversity of services and devices,
   and it is also a fundamental concept of the 5G for applying networks
   to such various types of requirements.

   In addition, network slicing is expected to enable a business model
   to provide dedicated logical networks to 3rd parties or vertical
   customers on-demand, called NSaaS (Network Slice as a Service).  For
   such usage, in network slicing, provision of networks able to
   guarantee communication characteristics end to end would be required.
   However, the definitions are not harmonized over several SDOs
   (Standards Developing Organizations).

   This document clarifies provision patterns of network slice, and
   provides the definitions and scope of network slicing which are
   available over several organizations.  Furthermore, the deliverables
   would be help for evaluating applicability of existing technologies/
   solutions to network slicing.

1.1.  Roles in Network Slice Provisioning

   The widespread of system and network virtualization technologies has
   conducted to new business opportunities, enlarging the offer of IT
   resources in the form of Network Slices (NS).  As a consequence,
   there is a clear differentiation between the owner of physical
   resources, the infrastructure operator, and the intermediary that
   conforms and delivers network services to the final customers, the
   Virtual Network Operator (VNO).

   VNOs aim to exploit the virtualized infrastructures to deliver new
   and improved services to their customers.  However, current NS
   techniques offer poor support for VNOs to control their resources.
   It has been considered that the infrastructure operator is

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   responsible of the reliability of the NS elements but several
   situations advocate the VNO to gain a finer control on its resources.
   For instance, dynamic events, such as the identification of new
   requirements or the detection of incidents within the virtual system,
   might urge a VNO to quickly reform its virtual infrastructure and
   resource allocation.  However, the interfaces offered by current
   virtualization platforms do not offer the necessary functions for
   VNOs to perform the elastic adaptations they require to tackle with
   their dynamic operation environments.

1.1.1.  Definitions in 3GPP on NS Provision Roles

   3GPP has defined multiple roles related to 5G networks and network
   slicing management in [TS.28.540-3GPP] and they include:

   o  Communication Service Customer (CSC): Uses communication services,
      e.g. end user, tenant, vertical

   o  Communication Service Provider (CSP): Provides communication
      services.  Designs, builds and operates its communication
      services.  The CSP provided communication service can be built
      with or without network slice.

   o  Network Operator (NOP): Provides network services.  Designs,
      builds and operates its networks to offer such services.

   o  Network Equipment Provider (NEP): Supplies network equipment to
      network.  For sake of simplicity, VNF Supplier is considered here
      as a type of Network Equipment Provider.  This can be provided
      also in the f orm of one or more appropriate VNF(s).

   o  Virtualization Infrastructure Service Provider (VISP): Provides
      virtualized infrastructure services.  Designs, builds and operates
      its virtualization infrastructure(s).  Virtualization
      Infrastructure Service Providers may also offer their virtualized
      infrastructure services to other types of customers including to
      Communication Service Providers directly, i.e. without going
      through the Network Operator.

   o  Data Centre Service Provider (DCSP): Provides data centre
      services.  Designs, builds and operates its data centres.

   o  NFVI Supplier: Supplies network function virtualization
      infrastructure to its customers.

   o  Hardware Supplier: Supplies hardware.

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   In case of Network Slice as a Service (NSaaS), the Communication
   Service Provider (CSP) role can be refined into Network Slice
   Provider (NSP).  The Communication Service Customer (CSC) role can be
   refined into Network Slice Customer (NSC).  A NSC can, in turn, offer
   its own communication services to its own customers, being thus CSP
   at the same time.

1.2.  High-level Problem Statement

   Beyond their heterogeneity, which can be resolved by software
   adapters, NS platforms do not offer common methods and functions, so
   it is difficult for the virtual network controllers used by the VNOs
   to actually manage and control virtual resources instantiated on
   different platforms, not even considering different infrastructure
   operators.  Therefore, it is necessary to reach a common definition
   of the functions that should be offered by underlying platforms to
   enable such overlay controllers with the possibility of allocate and
   deallocate resources dynamically and get monitoring data about them.

   Such common methods should be offered by all underlying controllers,
   regardless of being network-oriented (e.g., ODL, ONOS, Ryu) or
   computing-oriented (e.g., OpenStack, OpenNebula, Eucalyptus).
   Furthermore, it is also important for those platforms to offer some
   "PUSH" function to report resource state, avoiding the need for the
   VNO's controller to "POLL" for such data.  A starting point to get
   proper notifications within current REST APIs could be to consider
   the protocol proposed by the [WEBPUSH-WG].

   Finally, in order to establish a proper order and allow the
   coexistence and collaboration of different systems, a common ontology
   regarding network and system virtualization should be defined and
   agreed, so different and heterogeneous systems can understand each
   other without requiring to rely on specific adaptation mechanisms
   that might break with any update on any side of the relation.

2.  Definition of Terms

   This section lists definitions and terms related to network slicing.
   This document refers terms and view points on network slicing in some
   SDOs, such as 3GPP([TS.23.501-3GPP], [TS.28.530-3GPP],
   [TS.28.540-3GPP], [TR.28.801-3GPP]and [TR.28.804-3GPP]), and NGMN
   ([NGMN-5G-White-Paper]).  However the scope of this document is not
   network slicing which is mobile specific but one for general
   networks, and thus some of definitions in this document may be
   different from ones of those documents.

   Network Slicing:  Network slicing indicates a technology, an
      approach, or a concept to create logical separate networks in

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      support of services, depending on several requirements, on the
      same physical resources.  This is possible by combinations of
      several network technologies.

   Network Slice (NS):  An NS is a logical separate network that
      provides specific network capabilities and characteristics.  In
      3GPP definitions, an NS potentially includes both data plane and
      control plane resources/functions.  An NS can have multiple
      network slice subnets (Radio Access Network/RAN, Transport
      Network/TN, Core Network/CN, etc.).

   Network Slice Instance (NSI):  An NSI is a logical network instance
      composed with required infrastructure resources, including
      networking (WAN), computing (NFVI) resources, and some include
      additional network service functions such as firewall or load-
      balancer.  It is composed of one or more Network Slice Subnet

   Network Slice Subnet:  A Network Slice Subnet is a representation of
      a set of required resources.  It is composed and managed as a
      group of network elements.

   Network Slice Subnet Instance (NSSI):  An NSSI is a partial logical
      network instance represented as a network slicce instance.  It is
      a minimul unit managed or provided as a network slice.  One or
      more NSSI structure an NSI or an E2E-NSI.

   End-to-End Network Slice Instance (E2E-NSI):  An E2E-NSI is a virtual
      network connecting among end points.  It is composed of one or
      multiple NSSIs.  This term is original of this document and is
      used when it should be emphasized that the target NSI provides
      connectivity from end to end.  As an example, for providing an
      E2E-NSI on the 3GPP 5G network, combining three types of NSIs:
      RAN-, TRN-, and CN-NSIs would be required.

   Transport Network(TN)-NSSI:  A set of connections between various
      network functions (VNF or PNF) with deterministic SLAs.  They can
      be implemented (aka realized) with various technologies (e.g.  IP,
      Optics, FN, Microwave) and various transport (e.g.  RSVP, Segment
      routing, ODU, OCH etc).  The overview of NSI composed with TRN-
      NSSI is shown in Appendix A.

   Radio Access Network(RAN)-NSSI:  Regardless of RAN deployment (e.g.
      distributed-RAN, Centralized-RAN or Cloud-RAN, a RAN-NSSI creates
      a dedicate and logical resource on RAN for each NSI which are
      completely.  The overview of NSI composed with RAN-NSSI is shown
      in Appendix A.

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   Core Network(CN)-NSSI:  Regardless of Core deployment, a CN-NSI
      creates a dedicate and logical resource on Core network for each
      NSI which are completely.  The overview of NSI composed with CN-
      NSSI is shown in Appendix A.

   Network Slice as a Service (NSaaS):  An NSaaS is a service delivery
      model in which a third-party provider or a vertical customer hosts
      NSIs and makes them available to customers.  In this model, there
      mainly two roles: NS provider and NS tenant.

   Network Slice Provider (NS Provider):  An NS provider is a person or
      group that designs and instantiates one or more NSIs/NSSIs, and
      provides them to NS tenants.  In some cases, an NS provider is an
      infrastructure operator simultaneously.  This includes NSI, NSSI,
      and E2E-NSI providers.

   Network Slice Tenant (NS Tenant):  An NS tenant is a person or group
      that rents and occupies NSIs from NS providers.

   Network Slice Stakeholder (NS Stakeholder):  An NS stakeholder is an
      actor in network slicing, and has roles of either NS provider or

   Infrastructure Operator:  An infrastructure operator is an
      organization who manages infrastructure networks or data centers
      for running NSIs.  In the most of cases, infrastructure operators
      are initial NS providers on NSaaS.  Also, some of them may be NS
      tenants simultaneously.

   Vertical Customer:  A vertical customer is a organization who
      provides some communicating services with using NSIs on NSaaS
      model.  In many cases, a vertical customer become the final NS
      tenant on NSaaS.  For example, video gaming companies or vehicle
      vendors will possibly be vertical customers.

   Virtual Network Operator (VNO):  A VNO is a person or group that
      operates virtual networks composed with resources or NSSIs rent
      from infrastructure operators and provides such virtual networks
      as NSIs to vertical customers who are final NS tenants.  In some
      cases, infrastructure operators have this role in addition to
      operating their own infrastructure simultaneously.

   Domain:  A domain is a group of a network and devices administrated
      under a policy-based common set of rules and procedures.

   Resource:  A resource is an element used to create virtual networks.
      There are several types of resources, i.e., connectivity,
      computing and storage.  The details are described Section 4.1

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   Virtual Network:  A virtual network is a network running a number of
      virtual network functions.

   Virtual Network Function (VNF):  A virtual network function (VNF) is
      a network function whose functional software is decoupled from
      hardware.  One or more VNFs run as different software and
      processes on top of industry-standard high-volume servers,
      switches and storage, or cloud computing infrastructure.  They are
      capable of implementing network functions traditionally
      implemented via custom hardware appliances and middleboxes (e.g.,
      router, NAT, firewall, load balancer, etc.).

   Network Operation System:  A network operation system is an entity or
      a group of entities for operating network nodes and functions as
      compositions of infrastructure network.  For example, OSS/BSS,
      orchestrator, and EMS are considered to be network operation

3.  General Requirements for Network Slicing

   On network slice operations, capabilities for dynamic instantiation,
   change, and deletion should be required because an NSI is established
   based on received orders from tenants in NSaaS.  From this aspect,
   some mechanisms to design a network based on service requirements and
   to convert those to concrete configurations based on the design would
   be required.

   In addition, each NS has to maintain concrete communication
   characteristics end to end, and resource reservations on data plane
   and isolation among NSIs would be required.  Isolation is a concept
   to prevent the reduction of communication quality caused by
   disturbance from other NSs, and it may have some levels of
   enforcement, such as hard or soft isolations.  In some cases, for
   providing appropriate communication between client and server, it
   would be allowed for NS tenants to put their applications as contents
   server on NSIs by using computing resources.

   The required agility of slice operation and granularity of end to end
   communication quality requested can vary depending on provision

4.  Network Slice Structure

   This section describes resources used for structuring NSs and the
   basic structure of E2E-NS.

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4.1.  Resources for Structuring Network Slices

   A network slice is structured as combinations of the resources it
   uses.  Such resources are mainly categorized into three classes:
   network/WAN, computing/NFVI, and functionality resources.  Variations
   of each resources are described below.  (Note that the lists are not

   Network(WAN) Resources:

      *  Connectivity:

         +  (v)Link

            -  Bandwidth per link/session

            -  Connected area/end points

            -  Forwarding route/path (e.g., for traffic engineering,

            -  Communication Priority (e.g., QoS class)

            -  Range of jitter amount

         +  Interface of vNode

            -  QoS setting (e.g., Queue size, DSCP remarking, PIR/CIR)

            -  Filter setting

         +  vRouter/vSwitch (# Treated as a set of (v)links and
            interfaces of vNodes.)

      *  Multicast support

      *  Encryption support

      *  Authentication support

      *  Metadata conveyance (e.g., subscriber ID)

      *  Protocols for slice data plane:

         +  VLAN

         +  IPoE (IPv4 or IPv6)

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         +  MAP-E

         +  DS-Lite

         +  PPPoE

         +  L2TP

         +  GRE

         +  MPLS

         +  VxLAN

         +  Geneve

         +  GTP-U

         +  Segment Routing MPLS

         +  Segment Routing IPv6

         +  NSH

         +  FlexE

         +  Other

   Computing(NFVI) Resources:

      *  (v)CPU core

      *  Storage

      *  Memory

      *  Disk

      *  vNIC

      *  Connectivity to VNF instances

      *  Virtual Deployment Unit:

         +  Virtual Machine (VM)

         +  container

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         +  micro kernel

      *  Resource Deployment Location (i.e., edge DC, central DC, public
         cloud, ..., etc.)

   Functionality Resources:

      *  Image:

         +  Data Plane(DP) NF:

            -  GateWay(GW) function:

               o  Access Point Type (e.g., for radio, Wi-Fi, and fixed

               o  Slice Selection Setting

               o  Terminate protocol

               o  Authentication

            -  Security Appliance:

               o  IPS (Intrusion Prevention System)

               o  IDS (Intrusion Detection System)

               o  WAF (Web Application Firewall)

            -  DPI

            -  Load Balancer

            -  TCP Accelerator

            -  Video Optimizer

            -  Parental Control

            -  Mobile DP functions (Ref. 3GPP 5GS)



                  Uplink Classifier

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         +  Control Plane(CP) NF:

            -  DHCP

               o  Fixed IP address allocation

               o  Dynamic IP address allocation

               o  The number of registered devices

            -  DNS

            -  VoIP (SBC, SIP server)

            -  Mobile CP function (Ref. 3GPP 5GS)

               o  AMF (Access and Mobility management Function)

               o  SMF (Session Management Function)

               o  PCF (Policy Control Function)

               o  UDM (Unified Data Management)

               o  NEF (Network Exposure Function)

      *  Provided VNF Type (e.g., open source, product of vender#A, ...,

      *  Function location (e.g., edge DC, central DC, Public cloud,

   In terms of security or usability for NS tenants, some abstraction on
   resource information would be required, however both setting
   parameters of underlay infrastructure and abstracted information may
   coexist in these lists.

   For abstraction of parameters of underlay networks, some additional
   protocols or functions (like [RFC8453] ) would be required.
   Moreover, for providing strict communication qualities, combinations
   of some technologies may be useful (ref.

4.2.  Basic Network Slice Structure

   An E2E-NSI is constructed by stitching NSSIs instantiated on each
   participating domain.  This includes the simplest case of a single

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   NSSI as an E2E NS.  Domain types where some NSSIs are established are
   described below:

   o  Fixed access network

   o  Mobile access network

   o  Transport network

   o  Fixed core network

   o  Mobile core network

   o  Data center (DC)

      *  Edge DC

      *  Central DC

   o  Private network

      *  Enterprise

      *  Factory

      *  Utilities

      *  Farming

      *  Home/SOHO

      *  Other

   Figure 1 describes the overview of this structure.  Resources in each
   domain (e.g., access, core networks, and DC) are handled by
   management entities and constitute an NSSI.  An E2E-NSI is
   established by stitching these NSSIs.  Ways to stitch NS-subnets are
   described in [I-D.defoy-coms-subnet-interconnection] and

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              /                                          /
                  A              A              A
                  |              |              |
               ____________   ___________   ______________
              /           /  /          /  /             /
             /___________/  /__________/  /_____________/
                NSSI#1         NSSI#2         NSSI#3
                  A              A              A
                  |              |              |

              o---o         [PNF]              /----[VM]
                 / `--.     /  `----.         /----[VM]

             NW Rsrc#1     NW Rsrc+PNF      NW+CMP Rsrcs
                 A               A              A
                 |               |              |

             ,-------.      ,-------.      ,----------.
            / Access  \    / Core    \    /            \
            | Network |-TN-| Network |-TN-| DC Domain  |
            \ Domain  /    \ Domain  /    \            /
             `-------'     `--------'      `----------'

             NW Rsrc : Network Resource
             CMP Rsrc: Computing Resource
              o   : virtual/physical node structuring NSI
              --  : virtual/physical link structuring NSI
             -TN-: Transport Network
             [PNF]: Physical Network Function Appliance on NSI
             [VM] : Virtual Machine Instance on NSI

                    Figure 1: Overview of NS Structure

   Although it is shown that an NSSI belongs to just only one E2E-NSI in
   Figure 1, it may be allowed that multiple E2E-NSIs share an NSSI.
   Some resources may belong to multiple NSSI as well.

   In addition, structure on composition of NSI may be recursive.  In
   other words, even though Figure 1 shows a case where NSSIs compose
   directly an E2E-NSI, in some cases, NSSIs compose an NSI which is a
   part of an E2E-NSI.  The overview is shown in Figure 2.  In this

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   figure, NSI#4 is composed of NSSI#1 and NSSI#2, and it structures
   E2E-NSI#5 with NSSI#3.

                /                                          /
                             A                    A
                             |                    |
                 ___________________________      |
                /                          /      |
               /__________________________/       |
                 NSI#4 (= NSSI#1 + NSSI#2)        |
                    A              A              |
                    |              |              |
                 ____________   ___________   _____________
                /           /  /          /  /            /
               /___________/  /__________/  /____________/
                  NSSI#1         NSSI#2         NSSI#3

               Figure 2: Overview of NS recursive structure

4.3.  Stakeholders in the Structuring Network Slices

   Potential stakeholders in network slicing are described below:

   o NSSI provider:  infrastructure operator

   o Intermediate-NSI provider:  infrastructure operator, VNO

   o E2E-NSI provider:  infrastructure operator, VNO, service provider

   o NS tenant:  infrastructure operator, VNO, service provider,
      enterprise, mass user

   o End customer:  enterprise, mass user, etc.

5.  Variations of Network Slice Creation

   NSs can be classified according to their creation pattern into two
   types: ready-made(RM) NS, custom-made(CM), and semi-custom-made(sCM)
   NS.  This section describes the features of these types.

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5.1.  Ready-made Network Slice

   RM-NS is an NS creation pattern in which an infrastructure operator
   decides service requirements by itself, and established based on the
   requirements in advance.  NS tenants select one of RM-NSs whose
   features are closer to their requirements.

   This model doesn't need immediacy on designing of NSI and enables to
   mitigate the difficulty of implementation compared with other models.

5.2.  Custom-made Network Slice

   CM-NS is an NS creation pattern in which an NS is established based
   on an order from a tenant and is provided to it.  As examples of
   usage of CM-NS, an enterprise builds and operates a virtual private
   network for connecting several bases, or OTT (Over The Top) or other
   industrial service providers create NSs based on their own
   requirements and use them as a part of their own services (e.g.,
   connected vehicles/drones, online video games, or remote surgery).

   In this model, network operation system would be required to have
   incorporate intelligence for designing appropriate NSs on-demand.

5.3.  semi-Custom-made Network Slice

   sCM-NS is a derivation of a CM-NS.  In sCM-NS, an NS provider designs
   the outline of NSs in advance, and a tenant tunes an NS with deciding
   some parameters or applications run on resources.  For example, an
   infrastructure operator designs a logical network presenting
   connectivity, and tenants install their own applications on servers
   running on the logical network.

6.  Network Slice Provision Models

   This document classifis NS provision models into three categories
   defined in the following section.  The capabilities which NS tenants
   can have on management of NSs would vary depending on the selected
   provision model.

6.1.  Categorization of NS Provision Models

   The provision models are categorized into three models: SaaS
   (Software as a Service) -like Model, PaaS (Platform as a Service)
   -like Model, and IaaS (Infrastructure as a Service) -like Model.

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6.1.1.  SaaS-like Model

   In SaaS-like Model, underlay infrastructure is hidden from tenants,
   and tenants can receive desired communication environment without
   deep knowledge about network and servers.  An NS tenant decides
   attribute values of its NS, such as bandwidth or latency, based on
   their requirements, and NS providers design and create NSIs which
   fulfill the values.

   NS tenants need not to grasp detailed configurations in underlay
   networks in this model.  However, it may not be possible to provide
   strictly desired NS to tenants because of abstruction of configurable
   parameters.  Moreover, it may cause complexity on designing NS
   catalog due to quantities of selected attributes.

6.1.2.  PaaS-like Model

   In PaaS-like Model, an NS is represented with several components such
   as nodes and connectivities among them.  An NS tenant can design and
   customize its desired NS with combining such components.  NS
   providers breakdown the NS designed by the NS tenant to concrete
   configurations of their infrastructure, and create/change NSSIs by
   inputting the configurations.  An NS tenant is also able to
   incorporate its own functions or applications into its NSI by using
   computing resources provided from NS providers.

   This model potentially has high customizability of NS rather than
   SaaS-like model, but needs NS tenants to have some knowledge about
   network management.  In terms of designing NS, the tenants provide
   outline of their NSs, and thus it would make creation of concrete
   configurations be easier.

6.1.3.  IaaS-like Model

   In IaaS-like model, an NS is represented with concrete configurations
   of underlay infrastructure.  NS tenants are able to structure or
   change their desired NS by controlling infrastructure resources

   This model potentially has high customizability of NS rather than
   other models, but needs NS tenants to have deep knowledge about
   network and server operation.  Also, NS providers need not to
   recognize NSs on their infrastructure because NS tenants directly
   manage their NS.  Meanwhile, in terms of security and prevention of
   disturbances among NSs, some limitations on expositions of resources
   to tenants would be needed.

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6.2.  Mapping of NS Provision Models and Infrastructure Layering

   An example of mapping of each NS provision model is shown in
   Figure 3.

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                           [NS Tenant] ---------------------------+
       . . . . . . . . . . . . . . . . . . . . . . . .            |
       *Service Layer                                             |
                                            .--.                  |
        .------.                           (    )-.               |
       | Area#A |<==== Connectivity ====> .' [APL] '     SaaS-like|
        `------' [BW:100Mbps, Delay<10ms](           )  <---------+
        .------.                          (  [APL] -'             |
       | Area#B |<==== Connectivity ====>  '-(     )              |
        `------' [BW:100Mbps, Delay<10ms]     '---'               |
                                        Virtual Private           |
                                             Cloud                |
       . . . . . . . . . . . . . . . . . . . . . . . .            |
       *NS Layer                                                  |
                  __________________________________              |
                 /                                 /              |
                / [AP]----o                       /      PaaS-like|
               /         / `--.     /---[VM]     /      <---------+
              /  [AP]---o-----o--[FW]--[VM]     /                 |
             /_________________________________/                  |
                              NSI                                 |
       . . . . . . . . . . . . . . . . . . . . . . . .            |
       *Infra Layer                                               |
                  [AP]----o          /---[SV]                     |
                         / `--.     /---[SV]             IaaS-like|
                 [AP]---o-----o--[FW]--[SV]             <---------+
                         .---'    /---[SV]

         o  : virtual/physical node
         -- : virtual/physical link
         [AP] : Access point
         [APL]: Application owned by NS Tenant
         [FW] : Firewall Function
         [VM] : Virtual Machine Instance on Sever
         [SV] : Server as Infrastructure

                 Figure 3: Mapping of NS provision models

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   In some cases, NSIs provided based on IaaS- or PaaS-like models are
   coordinated to a form of SaaS-like model by an NS broker , and the NS
   broker or by the tenant, becoming a NS provider in a recursive
   manner.  For example, a vertical customer sends its high-level
   requirements to an NS broker create an appropriate NSI with resources
   provided by infrastructure operators.

6.3.  Configurable Parameters/Attributes for NS

   In the NS creating procedure, configuration parameters are decided
   based on requirements which the intended service has.  Such service
   requirements are expressible in the following attribute values.

   o  Attributes for Network Resource

      *  bandwidth

      *  latency

      *  jitter

      *  packet loss rate

      *  reliability (e.g., MTBF, MTTF)

   o  Attributes for Functionalities Resources

      *  function type (e.g., security, parental control)

      *  throughput

      *  packet error rate

      *  availability

   Configurable parameters of components in underlay infrastructure will
   vary depending on the implementation and structure.  Controlled
   resource types are described in Section 4.1.

6.4.  Capability of NS Tenant on each Provision Model

   Capability of NS tenants on NS management would vary depending on the
   NS provision model.  This section describes clarification about such
   capability in each model.

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6.4.1.  Capability in SaaS-like Model

   In SaaS-like Model, an NS is represented for a tenant with attributes
   values listed in Section 6.3.  In other words, an NS tenant never
   know the concrete configurations of components in underlay

   An NS tenant chooses a value from the range presented by the NS
   provider in each attribute.  The NS provider creates or changes a NS
   by configuraing components in underlay infrastructures based on the
   decided attribute values.

   In terms of telemetry for assurance of service qualities on a NS, a
   tenant can obtain telemetry information with unit of NSI, and never
   know ones of underlay components structuring the NS.

6.4.2.  Capability in PaaS-like Model

   In PaaS-like model, an NS is represented with NF nodes and their
   connectivities.  An NS tenant can indicate functionalities of NF
   nodes and thier locations.  Also, the tenant decides attribute values
   of connectivities.  An NS provider creates or changes an NSI by
   configuring underlay nodes and links depending on the indication of
   the tenant.  An NS tenant is also able to deploy its own NF as
   software with provided computing resources.

   In terms of telemetry, an NS tenant can obtain telemetry information
   of NF nodes and connectivities structuring an NS, in addition to
   whole of NSI.

6.4.3.  Capability in IaaS-like Model

   In IaaS-like Model, an NS is represented with configurations of
   (virtual) nodes and (virtual) links connecting the nodes.  An NS
   tenant is able to configure nodes and links in underlay
   infrastructure.  In short, an NS tenant directly design detailed NS
   and manages it.  In addition, an NS tenant inserts its own functions
   or applications in the NS with using computing resources.

   In terms of telemetry, an NS tenant can obtain telemetry information
   of nodes and links in addition of whole of NSI.

7.  Security Considerations

   In NSaaS, parts of controls of infrastructures are opened to
   externals, and thus some mechanisms, such as authentication for APIs,
   to prevent illegal access would be required.

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   Other considerations are TBD

8.  IANA Considerations

   This memo includes no request to IANA.

9.  Acknowledgement

   The author would like to thank Toru Okugawa for his kind review and
   valuable feedback.

10.  Informative References

              Foy, X., Rahman, A., Galis, A.,
    , k., and L. Qiang,
              "Interconnecting (or Stitching) Network Slice Subnets",
              draft-defoy-coms-subnet-interconnection-01 (work in
              progress), October 2017.

              Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
              Framework for Enhanced Virtual Private Networks (VPN+)
              Service", draft-dong-teas-enhanced-vpn-03 (work in
              progress), November 2018.

              Homma, S., Foy, X., and A. Galis, "Gateway Function for
              Network Slicing", draft-homma-nfvrg-slice-gateway-00 (work
              in progress), July 2018.

              NGMN, "NGMN 5G White Paper", February 2015,

   [RFC8453]  Ceccarelli, D., Ed. and Y. Lee, Ed., "Framework for
              Abstraction and Control of TE Networks (ACTN)", RFC 8453,
              DOI 10.17487/RFC8453, August 2018,

              3rd Generation Partnership Project (3GPP), "3GPP TR 28.801
              (V15.1.0): Study on Management and Orchestration of
              Network Slicing for next generation network (Release 15)",
              June 2018, <

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              3rd Generation Partnership Project (3GPP), "3GPP TR 28.804
              (V16.1.0): Study on tenancy concept in 5G networks and
              network slicing management (Release 16)", October 2019,

              3rd Generation Partnership Project (3GPP), "3GPP TS 23.501
              (V16.0.0): System Architecture for 5G System; Stage 2",
              September 2018, <

              3rd Generation Partnership Project (3GPP), "3GPP TS 28.530
              (V1.0.0): Management and orchestration of networks and
              network slicing; Concepts, use cases and requirements
              (work in progress)", June 2018,

              3rd Generation Partnership Project (3GPP), "3GPP TS 28.540
              (V16.0.0): 5G Netowkr Resource Model (NRM); Stage
              1(Release 16)", June 2019,

              3rd Generation Partnership Project (3GPP), "3GPP TS 28.541
              (V15.1.0): 5G Netowkr Resource Model (NRM); Stage 2 and
              stage 3 (Release 15)", June 2018,

              IETF, "Web-Based Push Notifications(webpush)",

Appendix A.  NS Structure in the 3GPP 5GS

   The overview of structure of NS in the 3GPP 5GS is shown in Figure 4.
   The terms are described in the 3GPP documents (e.g., [TS.23.501-3GPP]
   and [TS.28.530-3GPP]).

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

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

   RW         RAN                MBH               CN               DN

  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

             Figure 4: Overview of Structure of NS in 3GPP 5GS

Authors' Addresses

   Shunsuke Homma


   Hidetaka Nishihara


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   Takuya Miyasaka
   KDDI Research


   Alex Galis
   University College London


   Vishnu Ram OV
   Independent Research Consultant India


   Diego R. Lopez
   Telefonica I+D


   Luis M. Contreras
   Telefonica I+D


   Jose A. Ordonez-Lucena
   Telefonica I+D


   Pedro Martinez-Julia


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   Li Qiang
   Huawei Technologies


   Reza Rokui


   Laurent Ciavaglia


   Xavier de Foy
   InterDigital Inc.


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