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Versions: 00 01

none                                                       L. Qiang, Ed.
Internet-Draft                                                    Huawei
Intended status: Informational                         P. Martinez-Julia
Expires: January 4, 2018                                            NICT
                                                                 L. Geng
                                                            China Mobile
                                                                 J. Dong
                                                            K. Makhijani
                                                                  Huawei
                                                                A. Galis
                                               University College London
                                                                S. Hares
                                                 Hickory Hill Consulting
                                                            S. Kuklinski
                                                                  Orange
                                                            July 3, 2017


               Gap Analysis for Transport Network Slicing
                 draft-qiang-netslices-gap-analysis-01

Abstract

   This document presents network slicing differentiation from the non-
   partition network or from simply partition of connectivity resources.
   It lists 7 standardization gaps related to 4 key requirements for
   network slicing in transport network.  It also presents an analysis
   of existing related work and other potential solutions on network
   slicing.

   This gap analysis document aims to provide a basis for future works
   in transport network slicing.

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 http://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."




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   This Internet-Draft will expire on January 4, 2018.

Copyright Notice

   Copyright (c) 2017 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology and Abbreviation  . . . . . . . . . . . . . . . .   4
   3.  Overall Requirements in Network Slicing . . . . . . . . . . .   4
   4.  Network Slicing Specification . . . . . . . . . . . . . . . .   7
     4.1.  Description . . . . . . . . . . . . . . . . . . . . . . .   7
     4.2.  Related Work in IETF  . . . . . . . . . . . . . . . . . .   8
       4.2.1.  YANG Data Models  . . . . . . . . . . . . . . . . . .   8
       4.2.2.  Building NSS from Protocol Independent Traffic
               Engineering Models  . . . . . . . . . . . . . . . . .   9
   5.  Network Slicing Cross-Domain Coordination . . . . . . . . . .  10
     5.1.  Description . . . . . . . . . . . . . . . . . . . . . . .  10
     5.2.  Related Work in IETF  . . . . . . . . . . . . . . . . . .  11
       5.2.1.  Autonomic Networking Integrated Model and Approach
               (ANIMA) . . . . . . . . . . . . . . . . . . . . . . .  11
       5.2.2.  Connectivity Provisioning Negotiation Protocol (CPNP)  12
       5.2.3.  Abstraction and Control of Traffic Engineered
               Networks (ACTN) . . . . . . . . . . . . . . . . . . .  13
     5.3.  Other Potential Solutions . . . . . . . . . . . . . . . .  14
   6.  Network Slicing Performance Guarantee and Isolation . . . . .  14
     6.1.  Description . . . . . . . . . . . . . . . . . . . . . . .  14
     6.2.  Related Work in IETF  . . . . . . . . . . . . . . . . . .  15
       6.2.1.  Virtual Private Networks  . . . . . . . . . . . . . .  15
       6.2.2.  NVO3  . . . . . . . . . . . . . . . . . . . . . . . .  15
       6.2.3.  RSVP-TE . . . . . . . . . . . . . . . . . . . . . . .  15
       6.2.4.  Segment Routing . . . . . . . . . . . . . . . . . . .  16
       6.2.5.  Deterministic Networking  . . . . . . . . . . . . . .  16
       6.2.6.  Flexible Ethernet . . . . . . . . . . . . . . . . . .  17
   7.  Network Slicing OAM with Customized Granularity . . . . . . .  17
     7.1.  Description . . . . . . . . . . . . . . . . . . . . . . .  17



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     7.2.  Related Work in IETF  . . . . . . . . . . . . . . . . . .  18
       7.2.1.  Overview of OAM tools . . . . . . . . . . . . . . . .  18
       7.2.2.  Overlay OAM . . . . . . . . . . . . . . . . . . . . .  19
       7.2.3.  Service Function Chaining . . . . . . . . . . . . . .  19
       7.2.4.  Slice Identification  . . . . . . . . . . . . . . . .  19
   8.  Summary . . . . . . . . . . . . . . . . . . . . . . . . . . .  20
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  22
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  22
     12.2.  Informative References . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

1.  Introduction

   Network slicing is an approach to enable flexible isolation of
   network resources and functions for dedicated services, providing a
   certain level of customization and quality guarantee.  It establishes
   customized dedicated network upon a common infrastructure for
   vertical industries with flexible design of functions, different
   performance requirements, system isolation and OAM tools.

   Several SDOs have investigated network slicing.  To list a few: NGMN
   initiated a study of network slicing in the context of 5G from the
   mobile network point of view [NGMN-2016].  Around the same time ITU-T
   IMT 2020 and ITU-T SG13 studied network softwarization that also
   included network slicing concept.  ITU-T has issued a number of
   recommendations, such as: Gap Analysis [IMT2020-2015], Network
   Softwarization [IMT2020-2016], Terms & Definitions [IMT2020-2016bis].
   Open Network Foundation (ONF) has developed a recommendation on
   applying SDN architecture to Network Slicing [ONF-2016].  Finally,
   3GPP standards development for 5G includes network slicing in radio
   access and core networks. 3GPP issued TS 23.501 [TS23-501] about the
   system architecture for 5G in 2017.  BBF started the project SD-406
   focusing on the end-to-end architecture enhancement and requirements
   gathering for transport networks.  Although these SDOs have done a
   lot of work, potential requirements especially in the transport
   network and end-to-end enabling need to be investigated in order to
   elicit and identify the technical gaps in IETF for transport network
   slicing.

   In order to establish a network slice that meets various customer's
   demands, an infrastructure owner needs to understand how these
   demands map with the available network resources and accessible
   capabilities.  This also requires end-to-end coverage and inter-
   domain coordination.  Meanwhile, the slice provider provides
   customized OAM to the tenants under provisioning.  Slicing OAM



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   approach is a fundamental capability to guarantee stable, effective
   and reliable services for the vertical industries.  It is also
   expected to be capable of operations with customized granularity
   levels that provides robust management flexibilities.

   This document presents the identified key requirements and
   investigates potential technical gaps accordingly.  To assist
   understanding of this document, Section 2 outlines the terminology.
   Section 3 introduces overall requirements of network slicing.
   Sections 4~7 illustrates resource specification, end-to-end
   consideration, performance guarantee and OAM concerns respectively.
   Section 8 summarizes the identified gaps.

2.  Terminology and Abbreviation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119.

   All of the network slicing related words used in this document are to
   interpreted as described in [NS-Framework]

3.  Overall Requirements in Network Slicing

   This section introduces 4 key requirements of network slicing derived
   from [NS-UseCase] as shown in Table 1.  These 4 requirements are
   organized according to a general network slice working process as
   shown in Figure 1:

   1:  describe network slicing resource/functions and capture
       requirements (Req. 1)

   2:  network slicing cross-domain coordination (Req. 2)

   3:  construct a performance guaranteed and isolated end-to-end
       network slice (Req. 3)

   4:  provide necessary Operation & Maintenance & Administration (OAM)
       (Req. 4)












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   +----------------------------------------------------------+
   |      network slice management and orchestration          <-----+
   +----------------------^-------^---------------------------+     |
                          |       |                     resource/functions
                          |  OAM  |                          specification
                          |       |                                 |
 +------------------------v-------+------------------------------+  |
 |            abstracted network slice instance 1                |  |
 +--------------------------------+------------------------------+  |
                                  |                                 |
 +--------------------------------v------------------------------+  |
 |            abstracted network slice instance 2                |  |
 +---------------------------------------------------------------+  |
                                                                    |
                                                                    |
  +---------+              +---------+              +---------+     |
  |NS-Domain| cross-domain |NS-Domain| cross-domain |NS-Domain<-----+
  | Manager <--------------> Manager <--------------> Manager |
  +---------+ coordination +---------+ coordination +---------+

  +---------+              +---------+              +---------+
  |         |              |         |              |         |
+-+---------+--------------+---------+--------------+---------+-+
|                  network slice instance 1                     <---+
+-+---------+--------------+---------+--------------+---------+-+   |
  | Domain 1|              | Domain 2|              | Domain 3|  isolation
+-+---------+--------------+---------+--------------+---------+-+   |
|                  network slice instance 2                     <---+
+-+---------+--------------+---------+--------------+---------+-+
  |         |              |         |              |         |
  +---------+              +---------+              +---------+


                Figure 1: Illustration of Key Requirements

   Table 1: Requirement Association















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+-----------------------------------------+------------------------------+
| Requirements Illustrated in NS UseCase  |  Extracted KEY Requirements  |
+-----------------------------------------+------------------------------+
|1) Resource Reservation                  |                              |
|2) Abstraction                           | Req 1. Network Slicing       |
|3) Multi-Access Knowledge                |                              |
|4) Multi-Dimensional Service Vertical    |        Specification         |
|5) Agile Resource Adjustment             |                              |
+-----------------------------------------+------------------------------+
|6) Multi-Domain Coordination             | Req 2. Network Slicing       |
|                                         |        Cross-Domain          |
|7) Resource Assurance                    |        Coordination          |
+-----------------------------------------+------------------------------+
|                                         | Req 3. Network Slicing       |
|8) Performance/Operation Isolation       |        Performance Guarantee |
|                                         |        and Isolation         |
+-----------------------------------------+------------------------------+
|9) Independent Slice Management Plane    | Req 4. Network Slicing OAM   |
|   Reliability                           |                              |
+-----------------------------------------+------------------------------+

   Table 1: Requirements Association

   o  Req 1.  Network Slicing Specification (NSS) - The management
      systems of both network slice providers and operators need to know
      what and how much resources/network functions they have, so that
      they can accurately and abstractedly describe the available
      resources/network functions to tenants or peers.  The objective of
      NSS is to deliver the network slicing requests without incurring
      any over-utilization of resources.  In order to cooperate and
      provide consistent network slicing service, the way that
      resources/network functions are described should be homogeneous
      and compatible among all of the involved technology-specific
      domains, provides, and slicing platforms.

   o  Req 2.  Network Slicing Cross-Domain Coordination (NS-CDC) - From
      terminal to server (or other terminal), an end-to-end network
      slice will involve different infrastructural domains (e.g., AN,
      TN, CN, etc. ) that may be owned by different providers/operators.
      Each infrastructural domain may be further divided into different
      administrative domains.  That is an end-to-end slice is a logical
      entity composed by multiple separated components, and the cross-
      domain coordination is a way to integrate these components
      together.

   o  Req 3.  Network Slicing Performance Guarantee and Isolation (NS-
      PGI) - In order to enable the safe, secure, privacy-preservation
      service for multi-tenancy on a common physical network, the



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      isolation among network slices in each of the
      Data/Control/Management/Service planes are needed.  Furthermore,
      network slices that provide differentiated services usually
      require different resources.  The resources allocated to a network
      slice must be able to guarantee the service performance
      requirement.

   o  Req 4.  Network Slicing OAM (NS-OAM) - On one end of the spectrum
      we have those operators that will require a finalized service that
      they will simply commercialize.  On the other end we have those
      operators that may want to fine-tune all the low-level aspects of
      the network resources that form their system or service.
      Moreover, in the middle there is plenty of room for variations.
      Therefore, the underlying network layers must offer different
      levels of granularity for the management of their resources, that
      the upper layer operators can choose according to their needs and
      objectives.

4.  Network Slicing Specification

4.1.  Description

   Network Slicing Specification (NSS) is meant to describe the network
   slicing resources and capture requirements from tenants or peer
   networks to characterize the service expected to be delivered by a
   network.  These requirements include (non-exhaustive): reachability
   scope (e.g., limited scope, Internet-wide), direction, bandwidth
   requirements, performance metrics (e.g., one-way delay [RFC2679],
   loss [RFC2680], or one-way delay variation [RFC3393]), protection and
   high-availability guidelines (e.g., uRLLC service restoration in less
   than 50 ms, 100 ms, or 1 second), traffic isolation constraints, and
   flow identification.  NSS is used by a network provider to decide
   whether existing network slice instances can be reused or (some of
   them) even combined, or if another network slice instance is needed
   for a given service.

   Technology-specific actions are then derived from the technology-
   agnostic requirements depicted in an NSS.  Such actions include
   configuration tasks and operational procedures.  A standard
   definition of NSS is needed to facilitate the dynamic/ automated
   negotiation procedure of NSS parameters, but also to homogenize the
   processing of service requirements.

   To explain by an example, a network slice may cross multiple domains:

   o  A cloud deployed, NFV enabled, chain of network functions in a
      virtualized 5G core.




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   o  A segment routing [I-D.ietf-spring-segment-routing] based IGP
      network transport/aggregation or slice-specific application
      functions.

   o  A PCE [RFC4655] monitored TE-tunnel with ingress and egress
      points.

   o  Optical, carrier Ethernet or cellular networks.

   The network slice is a combination of the above technologies.  It
   creates a compelling need for a common resource specification
   interface across these domains.

4.2.  Related Work in IETF

4.2.1.  YANG Data Models

   As rightfully discussed in [I-D.wu-opsawg-service-model-explained],
   the IETF has already published several YANG data models that are used
   to model monolithic functions as well as very few services (e.g.,
   L2SM, L3SM, EVPN).  These models may be used in the context of
   network slicing if corresponding technologies are required for a
   given network slice, but none of them can be used to model an NSRD.

   [RFC7297] describes the Connectivity Provisioning Profile (CPP) and
   proposes a CPP template to capture connectivity requirements to be
   met within a service delivery context.  Such a generic CPP template
   is meant to

   o  facilitate the automation of the service negotiation and
      activation procedures, thus accelerating service provisioning;

   o  set (traffic) objectives of Traffic Engineering (TE) functions and
      service management functions;

   o  improve service and network management systems with 'decision-
      making' capabilities based upon negotiated/offered CPPs.

   [RFC7297] may be considered as a candidate specification for NSRD.
   Releasing a RFC7297-bis to take into account specific requirements
   from network slicing is needed.  Since [RFC7297] may not be
   implemented by all providers, the [SLA-Exchange] may be adopted to
   implement indirect SLA negotiation and SLA events report.
   [SLA-Exchange] provides an in-band method to exchange the SLA
   parameters, and then by the receiving devices to translate SLA in
   technical specific provisioning languages.  However, there still does
   not exist any standard protocol to translate SLA agreements into
   technical clauses and configurations.



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4.2.2.  Building NSS from Protocol Independent Traffic Engineering
        Models

   The NSS requirement for reachability, direction, bandwidth
   requirements, performance metrics, traffic isolation constraints, and
   flow identification can be built utilizing protocol which can perform
   operations (read, write, notification, actions (aka rpcs)) on a yang
   service layer that supports these traffic engineer and resource
   definition at the service layers.  The network slicing service data
   model can extend existing work in the TEAS and I2RS working group for
   protocol-independent topology models.  These models support
   configuration or the dynamic datastores defined in [NMDA] which will
   be abbreviated as NMDA in this section.  This section provides the
   detail on how the NSS can be built from these models and the RESTCONF
   protocol.

4.2.2.1.  Basic Topology Model

   The basic topology model is defined in [I2RS-Yang] to include a
   service layer.  This topology model is protocol independent and can
   be utilized as a configuration data model or a dynamic datastores
   model.  The configuration data model must abide by the configuration
   persistence and referential requirements.  The dynamic datastores do
   not need to abide by the same requirements as the configuration
   datastore.  I2RS is defining a dynamic datastores reference model for
   a data store which ephemeral.  The network slices may want to use
   configuration, ephemeral datastores, or define a third type of
   dynamic datastores.  The I2RS WG provides a place to collaborate this
   work on the dynamic datastores.

4.2.2.2.  TEAS Model Utilization of Basic Topology Model

   The TEAS topology model [TE-Yang] provides a general description of a
   Traffic engineering model that provides:

   o  abstract topologies with TE constraints (bandwidth, delay metrics,
      links to lower layers, some traffic isolation constraints, and
      some link identifiers);

   o  templates for links or resources;

   o  functionality to read, write, notification, and rpcs.

   Options that need to be consider are:

      Augmenting TEAS - The TEAS models provide substantial traffic
      engineering.  It was envisioned in the early topology model that a
      service resource model would be part of the service layer.  This



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      work was delayed until the maturation of the service requirements
      from L2VPN, L3VPN, and EVPN plus the maturation of resource
      requirements from 5G.  Network slicing provides a good application
      use case for this work.

      Why not Augment TEAS - The TEAS models are TE specific, lack of
      the abstraction for Layer 3+ resources.

      Dynamic models to combine TEAS models for network-slicing - The
      network slicing controller operating across domains may wish to
      create a multiple-domain data model based on the service layer
      data models exposed by different providers.  These service models
      would not need to be configured, but only learned as providers
      exchange data with one another.  The rules for combining these
      models could be defined as part of the dynamic datastore for
      network-slicing.

      Protocol within a domain - The RESTCONF and NETCONF protocol can
      support read, write, notification and actions (rpcs) within a
      domain.

      Protocol across domains: The RESTCONF protocol currently supports
      Configuration protocols and 90% of the dynamic datastores.  The
      RESTCONF protocol is being enhanced to support the push of
      telemetry messages.  The RESTCONF protocol could be used to
      exchange a specific Yang network-slicing service-layer topology
      (TE and Resources) and for the I2NSF security capabilities between
      domains.

      If a multicast of telemetry data is required between domains, then
      the push model for telemetry information or the IPFIX protocol may
      be utilized.

5.  Network Slicing Cross-Domain Coordination

5.1.  Description

   The network slicing cross-domain coordination (NS-CDC) requirement
   includes the following aspects:

   o  Network slice resource/functions coordination: for example, a
      tenant requests for a network slice with at most 10 ms latency
      from terminal to server.  Different infrastructure/administrative
      domains should coordinate and negotiate to reach an agreement such
      as RAN provides at most 2 ms service, TN domain I provides at most
      4ms service, TN domain II provides at most 2 ms service and CN
      provides at most 2 ms service;




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   o  Configuration information coordination: for example, for a given
      TN domain, the configuration information such as VLAN ID, remote
      IP address, physical port ID, etc. need to be coordinated with
      other TN domains;

   o  Other coordination: for example, RAN (or other access network)
      needs to notify TN about the information of new attachment point
      when user moves.

   From terminal to server, an end-to-end network slice will involve
   different infrastructure domains (e.g., RAN, TN and CN).  An
   infrastructure domain may be further divided into multiple domains
   due to geographic isolation, administrative isolation and other
   reasons.  There are two ways to enable an end-to-end network slice:
   based on a common platform or based on cross-domain coordination.

   If all of the involved domains belong to the same operator or the
   same operator union, the common platform solution may be work.  In
   this case, all of the domain controllers only need to communicate
   with the common platform, and follow the coordination management of
   this common platform.  Whilst the most common case is that the
   domains belong to different owners/operators/administrators, making
   it difficult to realize such a common platform.  Consequently, the
   cross-domain coordination will be essential throughout the whole
   lifecycle of an end-to-end network slice.

5.2.  Related Work in IETF

   There are some related works studies the inter-operation/coordination
   between different entities.  Coordination of different components of
   a slice requires automation.  It can be achieved either by

   1.  Coordination protocols such as ANIMA, CPNP

   2.  Or through abstraction and corresponding interfaces as in ACTN.

   This subsection will briefly review these related work to provide a
   basis for the gap analysis.

5.2.1.  Autonomic Networking Integrated Model and Approach (ANIMA)

   Autonomic Networking Integrated Model and Approach (ANIMA) WG
   provides a series of tools for distributed and automatic management,
   which includes: Generic Autonomic Signaling Protocol (GRASP),
   Autonomic Networking Infrastructure (ANI), etc.

   GRASP [ANIMA-GRASP] is a protocol for the negotiation between ASAs
   (Autonomic Service Agent).  In GRASP, ASAs could be considered as



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   "APPs" installed on a device.  Different ASAs fulfill different
   management tasks such as parameter configuration, service delivery,
   etc.  Based on GRASP, the same purpose ASAs that installed on
   different devices are able to inter-operate and negotiate with each
   other.  Network slicing could make use of GRASP for the coordination
   among devices in the underlying infrastructure layer, as well as the
   negotiation among different domain managers.  However, the security
   issue incurred by cross-domain usage should be fixed in GRASP.

   ANI [ANI] is a technical packet consisting of BootStrap (for
   authentication, domain certification distribution, etc.), ACP (a
   separate control plane), and GRASP (for control message
   coordination).  ANI could be used to construct the management tunnel
   among devices in underlying infrastructure layer within a single
   domain.  While the network slicing and cross-domain oriented
   extensions are necessary.

5.2.2.  Connectivity Provisioning Negotiation Protocol (CPNP)

   [I-D.boucadair-connectivity-provisioning-protocol] defines the
   Connectivity Provisioning Negotiation Protocol (CPNP) that is meant
   to dynamically exchange and negotiate connectivity provisioning
   parameters, and other service-specific parameters, between a Customer
   and a Provider.  CPNP is a tool that introduces automation in service
   negotiation and activation procedures, thus fostering the overall
   service provisioning process.

   CPNP runs between a Customer and a Provider carrying service orders
   from the Customer and respective responses from the Provider to the
   end of reaching a connectivity service provisioning agreement.  As
   the services offered by the Provider are well-described, by means of
   the CPP template, the negotiation process is essentially a value-
   settlement process, where an agreement is pursued on the values of
   the commonly understood information items (service parameters)
   included in the service description template.

   The protocol is transparent to the content that it carries and to the
   negotiation logic, at Customer and Provider sides, that manipulates
   the content.

   The protocol aims at facilitating the execution of the negotiation
   logic by providing the required generic communication primitives.

   CPNP can be used in the context of network slicing to request for
   network resources together with a set of requirements that need to be
   satisfied by the Provider.  Such requirements are not restricted to
   basic IP forwarding capabilities, but may also include a
   characterization of a set of service functions that may be invoked.



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5.2.3.  Abstraction and Control of Traffic Engineered Networks (ACTN)

   ACTN [TEAS-ACTN] is an information model proposed by TEAS WG, which
   enables the multi-domain coordination in Traffic Engineering (TE)
   network.  In order to enable network slicing in transport networks,
   portion of transport domain will need to be engineered.  In
   particular, building a TE entity and stitching service for this
   entity is within the scope of ACTN.  As an end-to-end network slicing
   solution, ACTN is able to provide cross-domain coordination.  In
   ACTN, each physical transport network domain is under the control of
   a Physical Network Controller (PNC) as shown in Figure 2.  A Multi-
   Domain Service Coordinator (MDSC) controls multiple PNCs.  Although
   the MDSCs may form a hierarchical structure, a hierarchical MDSC can
   still be regarded as a logical common platform.  As Section 5.1
   discussed, such a common platform solution has a strict presumption
   that all domains are assumed to follow a common coordination
   management.

   While ACTN does carry out network slicing-related work, some proposed
   concepts are similar the concepts of today's network slicing: in
   particular, the virtual network (VN) is similar to a slice instance.
   ACTN enables VN based on LSP technique, different LSP tunnels
   correspond to different VNs.  However, ACTN focuses on resource
   abstraction and management on Layer 2 and Layer 1.  For transport
   network slicing, resources abstraction and management on Layer 3+
   (e.g., IP routing table, etc.) may also be necessary but have not
   been addressed by ACTN.

                  +-------+     +-------+       +-------+
                  | CNC-A |     | CNC-B |       | CNC-C |
                  +---+---+     +---+---+       +---+---+
                      |             |               |
                      +-------\     |CMI     /------+
                               \    |       /
                          +---------+----------+
                          | (Hierarchical)MDSC |
                          +---------+----------+
                              /     |      \
                     +-------+      |MPI    +---------+
                     |              |                 |
                 +---+---+      +-------+        +----+--+
                 |  PNC  |      |  PNC  |        |  PNC  |
                 +-------+      +-------+        +-------+

               Figure 2: A Three-tier ACTN Control Hierarchy






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5.3.  Other Potential Solutions

   5G Exchange (5GEx) [FGEx] is a 5G-PPP project which aims to enable
   cross-domain orchestration of services over multiple administrations
   or over multi-domain single administration networks.  The main
   infrastructure considered in 5GEx is the NFV/SDN compatible software
   defined infrastructure, which limits the scope of network slicing to
   SDN based architecture.

6.  Network Slicing Performance Guarantee and Isolation

6.1.  Description

   Network slicing is expected to enable the deployment of various
   services with diverse requirements, independently on a common
   physical network.  Each network slice is characterized by particular
   service requirements, which usually are expressed using in the form
   of several key performance indicators (KPIs) such as bandwidth,
   latency, jitter, packet loss, etc., and different degrees of
   isolation.  Isolation requirements include performance isolation,
   which means performance guarantee are maintained regardless of
   activity in other slices, as well as secure isolation (e.g.,
   including privacy), and management (or OAM) isolation.  Additionally,
   performance isolation in network slicing has to maintain while
   scaling up or down computing capabilities of a slice (i.e., for
   elastic scaling).  Moreover, since IoT is also a use case for NS, and
   since some IoT applications are sensitive to data plane or bits on
   wire overheads, data path encapsulation in the form of labels, VLANs,
   VxLANs should be optional, or minimized for those cases.

   As we will discuss in the detailed sections below, each of these
   technologies can address some but not all performance and isolation
   requirements:

   o  RSVP-TE, Segment Routing (SR), DETNET, FlexE are mostly related to
      performance guarantee and performance isolation requirements

   o  Virtual Private Networks (VPN), NVO3 are mostly related to
      security and management isolation requirements

   A Network Slicing solution, to support performance guarantee and
   isolation requirements, will therefore need to merge in some way
   characteristics from these two families of technologies, through the
   combination of (possibly enhanced) existing technologies and/or
   specifically developed ones.  We can also consider the possibility
   that multiple such technology stacks may be deployed in different
   domains, and rely on cross-domain coordination, as described
   inSection 5, to form a single abstracted network slice.



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6.2.  Related Work in IETF

6.2.1.  Virtual Private Networks

   VPN technologies such as L3VPN [RFC4364], L2VPN [RFC4664], EVPN
   [RFC7432], etc. have been widely deployed to provide different
   virtual networks on common service provider networks.  Although VPNs
   can provide logically separated routing/bridging domains between
   different VPN customers, essentially it is an overlay network
   technology with little control of the network resources, so it is
   challenging for VPN to meet the performance and isolation requirement
   of some emerging application scenarios such as industrial verticals.
   VPNs essentially are private networks of enterprises by connecting
   remote sites.  The following two issues illustrate limitations of
   VPNs for network slicing:

   o  An end-to-end VPN tunnel competes with other traffic in the
      network and end-to-end network resource policies cannot be
      guaranteed.

   o  The reachability and resource reservation protocols are not
      tightly integrated and often solutions require centralized PCE-P
      like methods.

6.2.2.  NVO3

   [NVO3-WG] defines several network encapsulations which support the
   network virtualization and multi-tenancy in the data center networks.
   Similar to the VPN technologies of service provider networks, NVO3 is
   also an overlay network technology, which relies on the performance
   characteristics provided by the IP-based underlay networks.  Thus
   NVO3 may not meet by itself the performance and isolation
   requirements of network slicing.

6.2.3.  RSVP-TE

   RSVP-TE [RFC3209] is the signaling protocol to establish end-to-end
   traffic-engineered Label Switched Paths (LSPs).  It can reserve the
   required link bandwidth along an end-to-end path for specific network
   flows, which is suitable for services with particular requirement on
   traffic bandwidth.  RSVP-TE LSPs can be used as the underlay tunnels
   of the VPN service connections.  However, the requirement of some
   emerging services is not only about traffic bandwidth, but also has
   quite strict requirement on latency, jitter, etc.  Such requirements
   can hardly be met with existing RSVP-TE.






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6.2.4.  Segment Routing

   [I-D.ietf-spring-segment-routing] provides the ability to specify a
   traffic-engineered path by the source node of data packets.  It can
   provide traffic-engineering features comparable to RSVP-TE with
   better scalability, by eliminating the per-path state in the transit
   network nodes.  It is therefore a candidate method of creating an
   NSI, mapping a packet into an NSI and specifying the passage of the
   packet through the resources dedicated to the NSI.  Further study
   will be required to determine if/how SR as designed today can be used
   as a core technology for building an NSI.  With respect to
   performance guarantee and isolation, some further investigation may
   be needed to understand whether SR can provide the same or better
   performance characteristics as RSVP-TE.  In addition, it is not clear
   whether SR-based LSPs can provide the guaranteed latency and jitter
   performance required by network slicing.

6.2.5.  Deterministic Networking

   [DETNET-WG] is working on the deterministic data paths over layer 2
   and layer 3 network segments.  Such deterministic paths can provide
   identified flows with extremely low packet loss rates, low packet
   delay variation (jitter) and assured maximum end-to-end delivery
   latency.  This is accomplished by dedicating network resources such
   as link bandwidth and buffer space to DetNet flows and/or classes of
   DetNet flows.  DetNet also aims to provide high reliability by
   replicating packets along multiple paths.  It is a characteristic of
   DetNet that it is concerned solely with worst-case values for the
   end-to-end latency.

   The primary target of DetNet is real-time systems and as such
   average, mean, or typical latency values are not protected, because
   they do not affect the ability of a real-time system to perform their
   tasks.  This contrasts with a normal priority-based queuing scheme
   which will give better average latency to a data flow than DetNet,
   but, on the other side, the worst-case latency can be essentially
   unbounded.  As such DetNet seems to be a useful technique that may be
   applied to either a complete NSI, or to part of the traffic within an
   NSI to address the emerging low latency requirement for real time
   application.

   DetNet can therefore address some of the requirements of NS.  It was
   however not designed with network slicing in mind, which means a
   mapping between an NSI and a DetNet service may need to be defined.







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6.2.6.  Flexible Ethernet

   [FLEXE-1.0] was initially defined by Optical Internetworking Forum
   (OIF) as an interface technology which allows the complete decoupling
   of the Media Access Control layer (MAC) data rates and the standard-
   based Ethernet Physical layer (PHY) rates.  The channelization
   capability of FlexE can be used to partition a FlexE interface into
   several independent sub-interfaces, which can be considered as a
   useful component for the slicing of network interfaces.  Currently
   there is ongoing work in IETF to define the control plane framework
   for FlexE [FlexE-FWK], which aims to identify the routing and
   signaling extensions needed for establishing FlexE-based end-to-end
   LSPs in IP/MPLS networks.

7.  Network Slicing OAM with Customized Granularity

7.1.  Description

   In accordance with [RFC6291], OAM is used to denote the following:

   o  Operations: refer to activities that are undertaken to keep the
      network and the services it deliver up and running.  It includes
      monitoring the underlying resources and identifying problems.

   o  Administration: refer to activities to keep track of resources
      within the network and how they are used.

   o  Maintenance: refer to activities to facilitate repairs and
      upgrades.  Maintenance also involves corrective and preventive
      measures to make the managed network run more effectively, e.g.,
      adjusting configuration and parameters.

   As per [RFC6291], network slicing provisioning operations are not
   considered as part of OAM.  Provisioning operations are discussed in
   other sections.

   Maintaining automatically-provisioned slices within a network raises
   the following requirements:

   o  Ability to run OAM activities on a provider's customized
      granularity level.  In other words, ability to run OAM activities
      at any level of granularity that a service provider see fit.  In
      particular:

      *  Per slice OAM: An operator must be able to execute OAM tasks on
         a per slice basis.





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      *  Per domain OAM: These tasks can cover the "whole" slice within
         a domain or a portion of that slice (for troubleshooting
         purposes, for example).

      *  Per service OAM: When a given slice is shared among multiple
         services/customers, an operator must be able to execute (per-
         slice) OAM tasks for a particular service or customer.

      *  For example, OAM tasks can consist in tracing resources that
         are bound to a given slice, tracing resources that are invoked
         when forwarding a given flow bound to a given network slice,
         assessing whether flow isolation characteristics are in
         conformance with the NS Resource Specification, or assessing
         the compliance of the allocated slice resource against flow/
         customer requirements.

      *  An operator must be able to enable differentiated failure
         detect and repair features for a specific/subset of network
         slices.  For example, a given slice may require fast detect and
         repair mechanisms (e.g., as a function of the nature of the
         traffic (pattern) forwarded through the NS), while others may
         not be engineered with such means.

   o  Ability to automatically discover the underlying service functions
      and the slices they are involved in or they belong to.

   o  Ability to dynamically discover the set of network slicing that
      are enabled within a network.  Such dynamic discovery capability
      facilitates the detection of any mismatch between the view
      maintained by the control plane and the actual network
      configuration.  When mismatches are detected, corrective actions
      must be undertaken accordingly.

   o  Ability to efficiently OAM on shared resources.  If multiple
      network slices share some resources, the same kind of OAM
      operations from different network slices should be performed only
      once for efficiency.  For example, several network slices share a
      link.  We only need to execute once status query, and directly
      return the queried result to other status query requests.

7.2.  Related Work in IETF

7.2.1.  Overview of OAM tools

   The reader may refer to [RFC7276] for an overview about available OAM
   tools.  These technology-specific tools can be reused in the context
   of network slicing.  Providers that deploy network slicing
   capabilities should be able to select whatever OAM technology-



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   specific feature that would be address their needs.  No gap that
   would legitimate specific requirements has been identified so far.

7.2.2.  Overlay OAM

   [I-D.ooamdt-rtgwg-ooam-header] specifies a generic OAM header that
   can be used if overlay technologies are enabled.  Obviously, this
   effort can be reused in the context of network slicing when overlay
   techniques are in use.  Nevertheless, For slice designs that do not
   assume an overlay technology, OAM packets must be able to fly over
   the appropriate slice and for a given service/customer.  This is
   possible by reusing some existing tools if and only if no specific
   fields are required (e.g., carry a slice identifier as Req. 5
   stated).

7.2.3.  Service Function Chaining

   SFC WG [SFCWG] is chartered to describe data plane service
   encapsulation, control and manageability aspects of service
   functions.  Extensions that will be specified by the SFC WG will be
   reused in the context of network slicing.  Nevertheless, The current
   charter of the WG does not imply work on the automated discovery of
   SF instances and their capabilities, nor the automatic discovery of
   control elements.  An additional specification effort is therefore
   required in this area.

7.2.4.  Slice Identification

   A network slice data plane, may or may not follow traditional data
   plane tagging/labeling.  However, each network element (router/
   switch) still has to classify an incoming packet and associated with
   the slice instance for proper treatment.  Network slice instance
   identification is essential for network element to make local
   decisions on forwarding policies, QoS mechanism and etc.  The
   performance requirements of a network slice instance can therefore
   been met by making the correct decision.  Meanwhile, it is also
   important for OAM so that configuration and provisioning can be
   delicately performed to particular network slice instances by their
   identifications.

   For flow identification, many existing technologies provide mature
   solutions.  These approaches might be able to be re-used in network
   slicing by adding an additional layer of mapping to a network slice
   instance ID.  The network slice instance ID further maps to a group
   of performance requirements and OAM profiles, based on which the
   network elements within the slice can make local decisions.  However,
   per flow level identification could have adverse impact on the scale
   of the forwarding entries in the routers.



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   With traditional IP/MPLS VPNs, the set of Route Targets configured
   for the VPN can be used as some sort of identifier of the VPN in the
   control plane, and in the data plane, the VPN service labels can be
   used to identify the data packets belonging to a particular VPN.
   NVO3 uses the Virtual Network Identifiers (VNIs) in the header of
   data packets to identify different overlay network tenants.  However,
   It is not clear if the existing identifiers can meet the requirements
   of network slicing in terms of making local decisions on forwarding
   policy, QoS and OAM mechanisms, etc.

8.  Summary

   The following table is a summary of the identified gaps based on
   previous analysis in this document.





































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+--------------------------------+---------------------------------------+
|         Requirements           |                  Gaps                 |
+--------------------------------+---------------------------------------+
|                                |                                       |
|Req 1. Network Slicing          |  1) A detailed specification of NSS   |
|       Specification            |                                       |
|       (NSS)                    |  2) A companion YANG data model for   |
|                                |     NSS                               |
+--------------------------------+---------------------------------------+
|                                |                                       |
|Req 2. Network Slicing Cross-   |                                       |
|       Domain Coordination      |  3) A companion data model for        |
|       (NS-CDC)                 |     NS-CDC                            |
|                                |                                       |
+--------------------------------+---------------------------------------+
|                                |                                       |
|Req 3. Network Slicing          |  4) Slicing specific extension on     |
|       Performance Guarantee and|     existing technologies             |
|       Isolation (NS-PGI)       |                                       |
|                                |                                       |
+--------------------------------+---------------------------------------+
|                                |                                       |
|                                |  5) Mechanisms for dynamic discovery  |
|                                |     of service function instances and |
|                                |     their capabilities. Mechanisms for|
|Req 4. Network Slicing OAM      |     dynamic discovery of instantiated |
|       (NS-OAM)                 |     network slices                    |
|                                |                                       |
|                                |  6) non-overlay OAM solution          |
|                                |                                       |
|                                |  7) Mechanisms for customized         |
|                                |     granularity OAM                   |
|                                |                                       |
+--------------------------------+---------------------------------------+

   Table 2: Summary of Gaps

9.  Security Considerations

   This document analyzes the standardization work on network slicing in
   different WGs.  As no solution proposed in this document, no security
   concern raised.

10.  IANA Considerations

   There is no IANA action required by this document.





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11.  Acknowledgements

   The authors wish to thank Hannu Flinck, Akbar Rahman, Ravi Ravindran,
   Xavier de Foy, Young Lee and Igor Bryskin for their detailed and
   constructive reviews.  Many thanks to Mohamed Boucadair, Christian
   Jacquenet and Stewart Bryant for their valuable contributions and
   comments.

12.  References

12.1.  Normative References

   [NS-Framework]
              "NS Framework", <https://datatracker.ietf.org/doc/draft-
              geng-netslices-architecture/>.

   [NS-UseCase]
              "NS Use Case", <https://datatracker.ietf.org/doc/draft-
              netslices-usecases/>.

12.2.  Informative References

   [ANI]      "A Reference Model for Autonomic Networking",
              <https://datatracker.ietf.org/doc/draft-ietf-anima-
              reference-model/?include_text=1>.

   [ANIMA-GRASP]
              "A Generic Autonomic Signaling Protocol (GRASP)",
              <https://datatracker.ietf.org/doc/draft-ietf-anima-
              grasp/>.

   [DETNET-WG]
              "Deterministic Networking",
              <https://datatracker.ietf.org/wg/detnet/about/ >.

   [FGEx]     "5G Exchange (5GEx) - Multi-domain Orchestration for
              Software Defined Infrastructures",
              <https://www.researchgate.net/
              publication/296486303_5G_Exchange_5GEx_-_Multi-domain_Orch
              estration_for_Software_Defined_Infrastructures>.

   [FLEXE-1.0]
              "Flexible Ethernet 1.0", <http://www.oiforum.com/wp-
              content/uploads/OIF-FLEXE-01.0.pdf>.

   [FlexE-FWK]
              "FlexE-FWK", <https://datatracker.ietf.org/doc/draft-izh-
              ccamp-flexe-fwk/>.



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   [I-D.boucadair-connectivity-provisioning-protocol]
              Boucadair, M., Jacquenet, C., Zhang, D., and P.
              Georgatsos, "Connectivity Provisioning Negotiation
              Protocol (CPNP)", draft-boucadair-connectivity-
              provisioning-protocol-14 (work in progress), May 2017.

   [I-D.ietf-spring-segment-routing]
              Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
              and R. Shakir, "Segment Routing Architecture", draft-ietf-
              spring-segment-routing-12 (work in progress), June 2017.

   [I-D.ooamdt-rtgwg-ooam-header]
              Mirsky, G., Kumar, N., Kumar, D., Chen, M., Yizhou, L.,
              and D. Dolson, "OAM Header for use in Overlay Networks",
              draft-ooamdt-rtgwg-ooam-header-03 (work in progress),
              March 2017.

   [I-D.wu-opsawg-service-model-explained]
              Wu, Q., LIU, W., and A. Farrel, "Service Models
              Explained", draft-wu-opsawg-service-model-explained-06
              (work in progress), May 2017.

   [I2RS-Yang]
              "A Data Model for Network Topologies",
              <https://datatracker.ietf.org/doc/draft-ietf-i2rs-yang-
              network-topo/ >.

   [IMT2020-2015]
              "Report on Gap Analysis", <http://www.itu.int/en/ITU-
              T/focusgroups/imt-2020/Pages/default.aspx >.

   [IMT2020-2016]
              "Draft Technical Report Application of network
              softwarization to IMT-2020 (O-041)",
              <http://www.itu.int/en/ITU-T/focusgroups/imt-2020/Pages/
              default.aspx >.

   [IMT2020-2016bis]
              "Draft Terms and definitions for IMT-2020 in ITU-T
              (O-040)", <http://www.itu.int/en/ITU-T/focusgroups/imt-
              2020/Pages/default.aspx >.

   [NGMN-2016]
              "Description of Network Slicing Concept",
              <https://www.ngmn.org/uploads/
              media/160113_Network_Slicing_v1_0.pdf>.





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   [NMDA]     "Network Management Datastore Architecture",
              <https://datatracker.ietf.org/doc/draft-ietf-netmod-
              revised-datastores/>.

   [NVO3-WG]  "Network Virtualization Overlays".

   [ONF-2016]
              TS, "Applying SDN Architecture to 5G Slicing",
              <https://www.opennetworking.org/images/stories/downloads/
              sdn-resources/technical-reports/
              Applying_SDN_Architecture_to_5G_Slicing_TR-526.pdf >.

   [RFC2679]  Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
              Delay Metric for IPPM", RFC 2679, DOI 10.17487/RFC2679,
              September 1999, <http://www.rfc-editor.org/info/rfc2679>.

   [RFC2680]  Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
              Packet Loss Metric for IPPM", RFC 2680,
              DOI 10.17487/RFC2680, September 1999,
              <http://www.rfc-editor.org/info/rfc2680>.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <http://www.rfc-editor.org/info/rfc3209>.

   [RFC3393]  Demichelis, C. and P. Chimento, "IP Packet Delay Variation
              Metric for IP Performance Metrics (IPPM)", RFC 3393,
              DOI 10.17487/RFC3393, November 2002,
              <http://www.rfc-editor.org/info/rfc3393>.

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

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <http://www.rfc-editor.org/info/rfc4655>.

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







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   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <http://www.rfc-editor.org/info/rfc5440>.

   [RFC6291]  Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
              D., and S. Mansfield, "Guidelines for the Use of the "OAM"
              Acronym in the IETF", BCP 161, RFC 6291,
              DOI 10.17487/RFC6291, June 2011,
              <http://www.rfc-editor.org/info/rfc6291>.

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

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

   [RFC7432]  Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
              Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
              Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
              2015, <http://www.rfc-editor.org/info/rfc7432>.

   [SFCWG]    "\Service Function Chaining (sfc)",
              <https://datatracker.ietf.org/wg/sfc/about/>.

   [SLA-Exchange]
              "Inter-domain SLA Exchange Attribute",
              <https://datatracker.ietf.org/doc/draft-ietf-idr-sla-
              exchange/>.

   [TE-Yang]  "YANG Data Model for TE Topologies",
              <https://datatracker.ietf.org/doc/draft-ietf-teas-yang-te-
              topo/>.

   [TEAS-ACTN]
              "Information Model for Abstraction and Control of TE
              Networks (ACTN)", <https://datatracker.ietf.org/doc/html/
              draft-ietf-teas-actn-info-model>.

   [TS23-501]
              "System Architecture for the 5G System",
              <https://portal.3gpp.org/desktopmodules/Specifications/
              SpecificationDetails.aspx?specificationId=3144>.



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Authors' Addresses

   Li Qiang (editor)
   Huawei

   Email: qiangli3@huawei.com


   Pedro Martinez-Julia
   NICT

   Email: pedro@nict.go.jp


   Liang Geng
   China Mobile

   Email: gengliang@chinamobile.com


   Jie Dong
   Huawei

   Email: jie.dong@huawei.com


   Kiran Makhijani
   Huawei

   Email: Kiran.Makhijani@huawei.com


   Alex Galis
   University College London

   Email: a.galis@ucl.ac.uk


   Susan Hares
   Hickory Hill Consulting

   Email: shares@ndzh.com


   Slawomir
   Orange

   Email: slawomir.kuklinski@orange.com



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