teas                                                            R. Rokui
Internet-Draft                                                     Nokia
Intended status: Informational                                  S. Homma
Expires: January 13, 2021                                            NTT
                                                            K. Makhijani
                                                           LM. Contreras
                                                             J. Tantsura
                                                            Apstra, Inc.
                                                           July 12, 2020

                   IETF Definition of Transport Slice


   This document describes the definition of a slice in the transport
   networks and its characteristics.  The purpose here is to bring
   clarity and a common understanding of the transport slice concept and
   describe related terms and their meaning.  It explains how transport
   slices can be used in combination with end to end network slices, or

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
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 13, 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Rationale . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terms and Abbreviations . . . . . . . . . . . . . . . . . . .   3
   3.  Definition and Scope of Transport Slice . . . . . . . . . . .   4
   4.  Transport Slice System Characteristics  . . . . . . . . . . .   5
     4.1.  Service Level Objectives for Transport Slices . . . . . .   5
       4.1.1.  Minimal Set of SLOs . . . . . . . . . . . . . . . . .   5
       4.1.2.  Other Objectives  . . . . . . . . . . . . . . . . . .   7
     4.2.  Transport Slice Endpoints . . . . . . . . . . . . . . . .   8
       4.2.1.  Transport Slice Connectivity Types  . . . . . . . . .   9
     4.3.  Vertical Composition of Transport Slice . . . . . . . . .   9
     4.4.  Horizontal Composition of Transport Slice . . . . . . . .  11
   5.  Transport Slice Structure . . . . . . . . . . . . . . . . . .  11
     5.1.  Stakeholders  . . . . . . . . . . . . . . . . . . . . . .  13
     5.2.  Transport Slice Controller Interfaces . . . . . . . . . .  14
     5.3.  Transport slice Realization . . . . . . . . . . . . . . .  15
   6.  Relationship with End-to-End Network Slicing  . . . . . . . .  15
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
   9.  Acknowledgment  . . . . . . . . . . . . . . . . . . . . . . .  17
   10. Informative References  . . . . . . . . . . . . . . . . . . .  17
   Appendix A.  Discussions  . . . . . . . . . . . . . . . . . . . .  19
     A.1.  On Isolation Requirements In a Transport Slice  . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

1.  Introduction

   A number of use cases benefit from establishing network connectivity
   providing transport and assurance of a specific set of network
   resources.  In this document, as detailed in the subsequent sections,
   we refer to this connectivity and resource commitment as the
   transport slice.  Services that might benefit from the transport
   slices include but not limited to:

   o  5G services (e.g. eMBB, URLLC, mMTC)(See [TS.23.501-3GPP])

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   o  Network wholesale services

   o  Network infrastructure sharing among operators

   o  NFV connectivity and Data Center Interconnect

   This document defines the concept of transport slices that provide
   connectivity with a specific commitment of network resources between
   a number of end points over a shared network infrastructure.

1.1.  Rationale

   Transport slices are created and managed within the scope of one or
   more underlying network technologies (e.g., IP, MPLS, optical).
   Transport slices are expected to enable a diverse set of applications
   that have different requirements to coexist on the same network

   Transport slice is described as a construct that specifies
   connectivity requirements, emphasizing on assurance of those
   requirements.  Transport slice is unaware of the underlying
   infrastructure connectivity (hence, the term "transport").  The types
   of underlying networking technologies can be based on any combination
   of IP, Ethernet, MPLS, and optical technologies.  Transport slices
   also include specification of resources related to network functions
   required by customer applications.

   Traditionally, VPNs have focussed on segmentation, i.e., creation and
   management of the private networks.  They are bound to a specific
   traffic type and are technology specific.  In contrast, transport
   slices concern with the assurance of resources required from the
   network and provide a common user interface for describing those
   resources.  A service provider can use many aspects of the VPNs to
   build the transport slices.

   Transport slices relate to a more general topic of network slicing.
   It is not the goal of this document to define this broader concept,
   but in general, it is to identify the methodology to describe the
   logical (or abstract) partitioning of network resources associated
   with a service or an application.

2.  Terms and Abbreviations

   The terms and abbreviations used in this document are listed below.

   o  E2E NS: End to End Network Slice

   o  TS: Transport Slice

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   o  TSC: Transport Slice Controller

   o  EP: Endpoint

   o  EU: End User

   o  NBI: NorthBound Interface

   o  SBI: SouthBound Interface

   o  SLI: Service Level Indicator A well defined quantitative measure
      of some aspect of the level of service that is provided.

   o  SLO: Service Level Objective A target value or range of values for
      a service level that is measured by an SLI.  A natural structure
      for SLOs is thus SLI <= target, or lower bound <= SLI <= upper

   o  SLA: Service Level Agreement An explicit or implicit contract with
      the end users that includes consequences of meeting (or missing)
      the SLOs they contain.

   The above terminology is described in greater detail in the remainder
   of this document.

3.  Definition and Scope of Transport Slice

   The definition of a transport slice is as follows:

   "A transport slice is a logical network topology connecting a number
   of endpoints with a set of shared or dedicated network resources,
   that are used to satisfy specific Service Level Objectives (SLOs)".

   The text below describes transport slices in more details.

   Transport slice specification is technology-agnostic, and the means
   for transport slice realization can be chosen depending on several
   factors such as: service requirements, specifications or capabilities
   of underlying infrastructure.  The structure and different
   characteristics of transport slices are described in the following

   The term "transport" in transport slice is derived from the
   definition of Transport Network in the section 1.3.1 of [RFC5921] : A
   Transport Network provides transparent transmission of user traffic
   between attached client devices by establishing and maintaining
   point-to-point or point-to-multipoint connections between such
   devices.  "Slice" refers to a set of characteristics that separate

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   one type of user-traffic from other types.  Transport slice assumes
   that an underlying transport network is capable of changing the
   configurations of the network devices on demand, through in-band
   signaling or via controller(s) and to provide transport transmissions
   with fulfilling all or some of SLOs to all of the traffic in the
   slice or to specific flows.

4.  Transport Slice System Characteristics

   The following subsections describe the characteristics needed for
   support of transport slices.

4.1.  Service Level Objectives for Transport Slices

   A transport slice is defined in terms of several quantifiable
   characteristics or service level objectives (SLOs).  These objectives
   define a set of network resource parameters or values necessary to
   provide a service as requested for a given transport slice.  SLOs do
   not describe 'how' the transport slices will be implemented or
   realized in the underlying network layers.  Instead, they are defined
   in terms of dimensions of operations (time, capacity, etc.),
   availability and other attributes.  A transport slice can have one or
   more SLOs associated with it, all SLO's combined to form an SLA.  The
   SLO values are defined unidirectionally and for specific subsets of
   two or more endpoints (i.e. for a subset of connections in transport

   The SLOs and values associated with them that are exposed to the end
   user, are in the form of Service Level Indicators (SLIs).  If for
   example the range of latencies a network can provide is 50ms-100ms,
   then this would be the range of values the end user should be able to
   request, it would be as low as 50ms or as high as 100ms or anything
   in between.  The values of requested SLOs should always be in the
   range of values supported.  The underlying networks must provide
   means to monitor and measure the performance of transport slices
   against the SLOs requested and verify that they are being met.  Some
   SLOs can be measured directly through a collection of metrics and
   statistics from the network (commonly known as 'telemetry'), while
   others are deduced from measurable objectives and may require
   additional tools or mechanisms to measure their target values.

4.1.1.  Minimal Set of SLOs

   This document defines a minimal set of SLOs and later systems or
   standards could extend this set and define more SLOs.  For example,
   we included Guaranteed bandwidth which is the minimum requested
   bandwidth for the transport slice.  The later standard might define
   other SLOs related to bandwidth if needed.

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   Accordingly, SLOs can be categorized in to 'Directly Measurable
   Objectives' or 'Indirectly Measurable Objectives' as follows:

   Some of the 'Directly Measurable Objectives' are:

   o  Guaranteed Minimum Bandwidth

   o  Guaranteed Maximum Latency

   o  Maximum permissible delay variation

   o  Maximum permissible packet loss rate

   o  Availability

   o  Other objectives could be specified

   Some of the 'Indirectly Measurable Objectives' are:

   o  Security

   o  others objectives such as geographical restrictions, maximum
      occupancy level, etc. could be specified

   The definition of these objectives are as follows:

   o  Guaranteed Minimum Bandwidth: Minimum guaranteed bandwidth between
      two endpoints at any time.  The bandwidth is measured in data rate
      units of bits per second and is measured unidirectionally.

   o  Guaranteed Maximum Latency: Upper bound of network latency when
      transmitting between two endpoints.  The latency is measured in
      terms of network characteristics (excluding application-level
      latency).  [RFC2681] and [RFC7679] discuss round trip times and
      one-way metrics, respectively.

   o  Maximum permissible delay variation: Packet delay variation (PDV)
      as defined by [RFC3393], is measured by the difference in the one-
      way delay between sequential packets in a flow.  Minimizing
      variations in the delay is important for real-time applications.

   o  Maximum permissible packet loss rate: is defined by the ratio of
      packets dropped to packets transmitted between two endpoints.  See

   o  Availability: is defined as the ratio of uptime to
      total_time(uptime+downtime), where uptime is the time the

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      transport slice is available in accordance with the SLOs
      associated with it.

   o  Security: This objective may request for encryption [RFC4303]
      between two end-points explicitly to meet architecture
      recommendations as in [TS33.210] or for compliance with [HIPAA]
      [PCI].  Other security requests may be made as specified in

      *  Note: Security violations are not directly observable and
         cannot be measured as quantifiable metrics.  Still, the user of
         the transport slice should be able to request certain criteria
         for compliance and identify exceptions and unexpected traffic.
         For this purpose [i2nsf-nsf-monitoring-data-model] can be

4.1.2.  Other Objectives

   Additional objectives, such as certain geographical restrictions or
   well defined domains that a slice may transit may be necessary.

   Optionally, when the customer is traffic aware, other traffic
   specific characteristics may be provided.  These include for example,
   MTU, traffic-type (e.g., IPv4, IPv6, Ethernet or unstructured), or a
   higher-level behavior to process traffic according to user-
   application (which may be realized using network functions).

   Maximal occupancy for a transport slice should be provided.  Since it
   carries traffic for multiple flows between the two endpoints, the
   objectives should also say if they are for the entire connection,
   group of flows or on per flow basis.  Maximal occupancy should
   specify the scale of the flows (i.e. maximum number of accommodatable
   flows) and optionally a maximum number of countable resource units,
   e.g IP or MAC addresses a slice might consume.

   With these objectives incorporated, a customer sees transport slice
   as a dedicated network for its exclusive use.  Achieving this may
   require different types of isolation techniques in provider networks
   as described in Appendix A.1.

   Additional description of slice attributes is covered in a broader
   context of 'Generic Network Slice Template' in

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4.2.  Transport Slice Endpoints

   The transport slice endpoints are the conceptual entities that
   perform any required conversion, or adaptation, and forwarding of the
   user traffic.  The characteristics of the transport slice endpoints
   (TSE) are:

   o  They are conceptual points of connection of a network function,
      device or application to the transport slice

   o  They are identified in a request provided by the customer of
      transport slice (i.e.  higher level operation systems) during the
      creation of the transport slice

   o  They are associated with a device, application and/or network
      function nodes.  A non-exhaustive list of such nodes are routers,
      switches, firewalls, WAN, 4G/5G RAN nodes, 4G/5G Core nodes,
      application acceleration, Deep Packet Inspection (DPI), server
      load balancers, NAT44 [RFC3022], NAT64 [RFC6146], HTTP header
      enrichment functions, and TCP optimizers

   o  A TSE is identified by its associated node (its IP address, name ,
      ID, etc.), a unique identifier and/or a unique name and other
      data.  A non-exhaustive list of other data includes IP address (v4
      or v6), VLAN, port, connectivity type (P2P, P2MP, MP2MP).  TBD for

   Note that the TSE is different from access points (AP) defined in
   [RFC8453] as an AP is a logical identifier to identify the shared
   link between the customer and the operator where as TSE is an
   identifier of an endpoint.  Also TSE is different from TE Link
   Termination Point (LTP) defined in [I-D.ietf-teas-yang-te-topo] as it
   is a conceptual point of connection of a TE node to one of the TE
   links on a TE node.

   The TSE is similar to the Termination Point (TP) defined in [RFC8345]
   and can contain more attributes.  TSE could be modeled by augmenting
   the TP model.

   There is another type of the endpoints called "Transport Slice
   Realization endpoints (TSREs)".  These endpoints are allocated and
   assigned by the network controller during the realization of a
   transport slice and are technology-specific, i.e. they depend on the
   network technology used during the transport slice realization.  They
   are identified by a node and some associated data.  A non-exhaustive
   list of nodes containing TSREs are routers, switches, PON nodes,
   Wireless nodes and Optical devices.

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   Note that there will be a mapping between TSE and TSRE on Transport
   Slice Controller (TSC).  When TSC receives a request via its NBI to
   create a transport slice between multiple TSEs, it will send the
   request via its SBI to realize the transport slice.  The TSRE will be
   notified by network controller during TS realization to enable
   mapping between TSREs and the TSEs.

   Figure 1 shows an example of a transport slice and its realization
   between multiple TSEs and TSREs.

                          (  Transport Network  )
        DAN1             (                       )                DAN2
     --------  TSRE1 --------                  -------- TSRE2   --------
     |    o |-------o|  A   |                  |  B   |o--------| o    |
     |  TSE1|        --------                  --------         | TSE2 |
     --------        |   (                        )    |        --------
          |          |    (                      )     |          |
          |          |     (-------------------)       |          |
          |          |                                 |          |
          |          | <=============================> |          |
          |               Transport slice realization             |
          |                 between TSRE1 and TSRE2               |
          |                                                       |
          | <===================================================> |
                Transport slice between TSE1 and TSE2 with SLO1

      DAN: Device, application and/or network function

   Figure 1: A transport slice between TSEs and its realization between

4.2.1.  Transport Slice Connectivity Types

   The transport slices connection types can be point to point (P2P),
   point to multipoint (P2MP), multi-point to point (MP2P), or multi-
   point to multi-point (MP2MP).  The transport slice connection type
   will requested by the higher level operation system.

4.3.  Vertical Composition of Transport Slice

   Transport slice may follow a hierarchical relationship to provide a
   vertical structure to it.  This is used for composing multi-layer
   slices in which each layer provides an abstraction, as well as an
   independent monitoring, performance, control and management of the

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   resources.  The vertical transport slice characteristic could be used
   in 2 forms:

   o  The Transport slice itself where it represents a hierarchy of
      abstracted transport slices.  In this case, the realization will
      be done just once with a particular technology.  Thus, the lowest
      transport slice in the hierarchy that can not be decomposed
      further will be one to one mapping to its instance of the realized
      transport slice.

   o  Each layer (physical, datalink, or IP) has its own set of
      resources that can be provided to the upper layer as a transport
      slice.  Thus, transport slice at one layer is used by the layer
      above.  This type of multi-layer vertical transport slice
      associates resources at different layers.  For example, an IP
      transport slice would utilize one or more optical transport slice.
      In this case, the realization will be done for a particular
      technology at that particular layer.  Thus, the lowest transport
      slice in this type of hierarchy that can not be decomposed further
      will be an instance of realized physical layer transport slice.

           <======================== TS1 ========================>
           <=====TS11=======>  <==============TS12===============>
                               <====TS121====>  <=====TS122======>
               .--.             .--.                .--.
              (    )--.        (    )--.           (    )--.
              .'         '     .'         '        .'        '
    [EU-x]   (  Network-1  )  (  Network-2  ) ... (  Network-3 )  [EU-y]
              `-----------'    `-----------'       `----------'
           |                |                                   |
           |   Operator-y   |           Operator-z              |

      TSnnn: Level 3 vertical transport slice nnn
      TSnn:  Level 2 vertical transport slice nn
      TSn:   Level 1 transport Slice n

       Figure 2: Transport Slice Vertical and Horizontal Composition

   Figure 2 shows the transport slice hierarchy.  Slices TS11 and TS12
   are composed together to form TS1 that is the top level transport
   slice definition, TS121 and TS122 collectively define TS12.  The SLO
   for bandwidth guarantee will be shared and latency guarantee will be
   split into latency in networks 2 and 3.  To emphasize the
   hierarchical structure, consider Network-2 and Network-3 are in the
   same administrative domain but use different transport technologies
   respectively.  Then instead of presenting 2 transport slices,

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   Operator-z can expose only one transport slice TS12 abstracting the
   underlying transport technology details.

      Note: The specification to connect TS121 and TS122 are similar to
      those connecting TS12 and TS11.

4.4.  Horizontal Composition of Transport Slice

   In contrast, horizontal transport slices enable the composition of
   multiple realized transport slices.  Since transport slices are not
   necessarily a single encapsulation tunnel and may traverse through
   different data planes, each realized transport slice will require a
   stitching, interworking or mapping function.  These stitching
   functions can be viewed as a type of intermediate network function
   endpoints.  For instance in Figure 2, TS11 and TS12 are horizontal
   transport slices.  If we assume that TS11 is an L2 tunnel and TS12 is
   an SRV6 based path, then a 'Service type EP' (not shown in the
   figure) is needed for translation.

   Author's notes: This service type EP is a new type of transport slice
   specific service function.  We may call it transport slice gateway.

5.  Transport Slice Structure

   A transport slice is a set of connections among various endpoints to
   form a logical network that meets the SLOs agreed upon.

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           [EP11]------/                           /--[EP21]
                      /                           /
           [EP12]----/     Transport Slice       /----[EP22]
             :      /        (SLOs e.g.         /
             :     / B/W > x bps, Delay < y ms)/

           == == == == == == == == == == == == == == == == == ==

                      .--.               .--.
           [EP11]    (    )- .          (    )- .     [EP21]
                    .'         '  SLO  .'         '
           [EP12]  (  Network-1 ) ... (  Network-p )  [EP22]
            :       `-----------'      `-----------'     :
           [EP1m]                                     [EP2n]

             SLOs in terms of attributes, e.g. BW, delay.
             EP: Endpoint
             B/W: Bandwidth

                         Figure 3: Transport slice

   Figure 3 illustrates a case where a transport slice provides
   connectivity between a set of endpoints pairs with specific
   characteristics for each SLO (e.g. guaranteed minimum bandwidth of x
   bps and guaranteed delay of less than y ms).  The endpoints may be
   distributed in the underlay networks, and a transport slice can be
   deployed across multiple network domains.  Also, the endpoints on the
   same transport slice may belong to the same address space.

   Transport slices involve both customer's and provider's views.  A
   customer 'describes' its requirements in terms of connectivity with
   specific SLOs.  Provider networks address those requirements through
   'transport slice realization' (its implementation) using provider
   network specific technologies.

   A transport slice is requested from an entity (such as an
   orchestrator or a system-wide controller) performing broader service
   or application specific functions.  The interface from such an entity
   should express the needed connectivity in a technology-agnostic way
   and donot need to recognize configurations based on the technologies
   (e.g. being more declarative than imperative).  The request to
   instantiate a transport slice is only represented with some
   indicators such as SLOs based on which the underlying technologies
   are selected and managed.

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   Often, in other SDOs the term sub-slice or slice-subnet comes up.
   Some of those are mapped to transport network requirements in the
   form of a transport slice.  With in the scope of transport slices
   (w.r.t. the IP/MPLS based transport networks) there are no
   definitions for 'sub-slice' or 'slice subnets'.  'Transport slice'
   term universally represents SLO and connectivity requirements from
   the transport networks.

   Furthermore, the structure of transport slices may be layered
   vertically or composed horizontally, i.e. operationally, a transport
   slice maybe decomposed in two or more transport slices which are then
   independently realized and managed.  This is further described in
   Section 4.3.

5.1.  Stakeholders

   A transport slice and its realization involves the following
   stakeholders and it is relevant to define them for consistent

   Customer or User:  A customer is a user of a transport slice.
      Customers may request monitoring of associated resources or
      specific changes.  A user may either directly manage its service
      by interfacing with the transport slice controller or indirectly
      through an orchestrator.

   Orchestrator:  An orchestrator is an entity that composes different
      services, resource and network requirements.  It interfaces with
      the transport slice controllers.

   Transport Slice Controller (TSC):  It realizes a transport slice in
      the network, maintains and monitors the run-time state of
      resources and topologies associated with it.  A well-defined
      interface is needed between different types of transport slice
      controllers and different types of orchestrators.  A transport
      slice operator (or slice operator for short) manages one or more
      transport slices using the Transport Slice Controller(s).

   Transport Network Controller:  is a form of network infrastructure
      controller that offers network resources to TSC to realize a
      particular transport slice.  These may be existing network
      controllers associated with one or more specific technologies that
      may be adapted to the function of realizing transport slices in a

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5.2.  Transport Slice Controller Interfaces

   The interworking and interoperability among the different
   stakeholders to provide common means of provisioning, operating and
   monitoring the transport slices is a mandatory requirement.  The
   following communication interfaces are identified (see Figure 4).

   TSC Northbound Interface (NBI):  The TSC Northbound Interface is an
      interface between a higher level operation system, e.g.  'E2E
      network slice orchestrator' and the 'Transport slice controller'.
      It is a technology agnostic interface.  Over this NBI, slice
      characteristics and other requirements can be communicated to TSC
      and the operational state of a transport slice may be requested.

   TSC Southbound Interface (SBI):  The TSC Southbound Interface is an
      interface between 'Transport slice controller (TSC)' and network
      controller(s).  These interfaces are technology-specific and
      utilize many of the network models.

                   |                Customer                  |
                   |     A higher level operation system      |
                   |   (e.g e2e network slice orchestrator)   |
                                        | TSC NBI
                   |         Transport Slice Controller       |
                                        | TSC SBI
                   |           Network Controller(s)          |

             Figure 4: Interface of Transport Slice Controller

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5.3.  Transport slice Realization

   Realization of a Transport Slice is a mapping of underlying
   infrastructure with its definition.  It is a technology specific
   entity that is created and maintained over its southbound interfaces.
   The Network controller(s) export the connectivity and resource
   mappings to the TSC.  The network controller abstracts the details of
   underlying resources from the TSC.

   The realization can be achieved in the form of either physical or
   logical connectivity through VPNs, a variety of tunneling
   technologies such as Segment Routing, SFC, etc.  Accordingly,
   endpoints may be realized as physical or logical service or network

6.  Relationship with End-to-End Network Slicing

   An end-to-end (E2E) network slice is a complete logical network that
   provides a service in its entirety with a specific assurance to the
   customer.  A transport slice concerns with those assurance aspects
   only within the transport networks.  Consider Figure 5, where a
   network operator has an E2E network slice that traverses multiple
   technology-specific networks.  Each of these networks might use any
   number of technologies, including but not limited to IP, MPLS, Fiber-
   Optics (e.g.  WDM, DWDM), Passive Optical Networking (PON),
   Microwave, etc.

   Each of these networks includes multiple (physical or virtual) nodes
   and may also provide network functions beyond simply carrying of
   technology-specific protocol data units.  The types of nodes used in
   any of these networks may include:

   o  Packet/frame processing nodes (e.g., Routers, Switches)

   o  Application servers

   o  Service Functions(e.g., Firewall, Loadbalancer)

   o  Radio Access Network (RAN) components

   o  Mobile Core components

   o  Microwave transceivers

   o  Optical repeaters

   o  etc.

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   Each network may support different technologies and an E2E network
   slice is a combination of these networks.  As an example:

   o  Network 1 might contain multiple 5G RAN nodes connected to a few
      Cell Site Gateways (CSG) routers.

   o  Network 2 might have one or more layer-3 routers and layer-2
      switches which may run on top of an optical network.

   o  Network 3 might have a number of 5G RAN nodes connected to Passive
      Optical Network (PON) switches.

           <======================= E2E NS ======================>
           <-OS1-> <-TS1-> <-TS2-> <-OS2->   ...   <-TSn-> <-OSm->
          |    .--.             .--.                .--.         |
          |   (    )--.        (    )--.           (    )--.     |
          |   .'         '     .'         '        .'        '   |
   [EU-x] |  (  Network-1  )  (  Network-2  ) ... (  Network-p ) |[EU-y]
          |   `-----------'    `-----------'       `----------'  |
          |                                                      |
          |                      Operator-z                      |
     E2E NS: End-to-end network slice
     TSn: Transport Slice n
     OSm: Other Slice m
     EU-x: End User-x
     EU-y: End User-y

                        Figure 5: E2E network slice

   When operator-z creates a specific E2E network slice, it may create
   one or more of transport slices and other slices (application logic
   or other system functions).

   An independent E2E logical network (called E2E network slice) is
   created for a service (e.g.  CCTV, autonomous driving, HD map, etc.)
   with a specific network SLOs, e.g. a secure connection with an E2E
   latency less than 5ms, from End User-x (EU-x) to End User-y (EU-y).
   EU-x maybe a 5G user equipment such as an infotainment unit in a car,
   CCTV, or a car for autonomous driving, etc. and EU-y in 5G is 5G
   application server, IMS, etc.

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   In Figure 5, "E2E NS" is that logical network with requested SLO
   between EU-x to EU-y and is associated with a customer and a specific
   service type.

7.  Security Considerations

   Not applicable in this memo.

8.  IANA Considerations

   This memo includes no request to IANA.

9.  Acknowledgment

   The entire TEAS NS design team and everyone participating in those
   discussion has contributed to this draft.  Particularly, Eric Gray,
   Xufeng Liu, Jie Dong, and Jari Arkko for a thorough review among
   other contributions.

10.  Informative References

   [HIPAA]    HHS, "Health Insurance Portability and Accountability Act
              - The Security Rule", February 2003,

              Contreras, L., Homma, S., and J. Ordonez-Lucena,
              "Considerations for defining a Transport Slice NBI",
              draft-contreras-teas-slice-nbi-01 (work in progress),
              March 2020.

              Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
              Framework for Enhanced Virtual Private Networks (VPN+)
              Services", draft-ietf-teas-enhanced-vpn-05 (work in
              progress), February 2020.

              Bryskin, I., Liu, X., Lee, Y., Guichard, J., Contreras,
              L., Ceccarelli, D., and J. Tantsura, "SF Aware TE Topology
              YANG Model", draft-ietf-teas-sf-aware-topo-model-05 (work
              in progress), March 2020.

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

              Gray, E. and J. Drake, "Framework for Transport Network
              Slices", draft-nsdt-teas-ns-framework-02 (work in
              progress), March 2020.

   [NFVGST]   ETSI, "NFVI Compute and Network Metrics Specification",
              February 2018, <https://www.etsi.org/deliver/etsi_gs/NFV-

   [PCI]      PCI Security Standards Council, "PCI DSS", May 2018,

   [RFC2681]  Almes, G., Kalidindi, S., and M. Zekauskas, "A Round-trip
              Delay Metric for IPPM", RFC 2681, DOI 10.17487/RFC2681,
              September 1999, <https://www.rfc-editor.org/info/rfc2681>.

   [RFC3022]  Srisuresh, P. and K. Egevang, "Traditional IP Network
              Address Translator (Traditional NAT)", RFC 3022,
              DOI 10.17487/RFC3022, January 2001,

   [RFC3393]  Demichelis, C. and P. Chimento, "IP Packet Delay Variation
              Metric for IP Performance Metrics (IPPM)", RFC 3393,
              DOI 10.17487/RFC3393, November 2002,

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, DOI 10.17487/RFC4303, December 2005,

   [RFC5921]  Bocci, M., Ed., Bryant, S., Ed., Frost, D., Ed., Levrau,
              L., and L. Berger, "A Framework for MPLS in Transport
              Networks", RFC 5921, DOI 10.17487/RFC5921, July 2010,

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
              April 2011, <https://www.rfc-editor.org/info/rfc6146>.

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   [RFC7679]  Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
              Ed., "A One-Way Delay Metric for IP Performance Metrics
              (IPPM)", STD 81, RFC 7679, DOI 10.17487/RFC7679, January
              2016, <https://www.rfc-editor.org/info/rfc7679>.

   [RFC7680]  Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
              Ed., "A One-Way Loss Metric for IP Performance Metrics
              (IPPM)", STD 82, RFC 7680, DOI 10.17487/RFC7680, January
              2016, <https://www.rfc-editor.org/info/rfc7680>.

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

   [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 TS 23.501
              (V16.2.0): System Architecture for the 5G System (5GS);
              Stage 2 (Release 16)", September 2019,

              3GPP, "3G security; Network Domain Security (NDS); IP
              network layer security (Release 14).", December 2016,

Appendix A.  Discussions

A.1.  On Isolation Requirements In a Transport Slice

   Transport slices are perceived as if slice was provisioned for the
   customer as a dedicated network with specific SLOs.  These committed
   SLOs for a given customer should be maintained during the lifetime of
   the slice, even in the face of potential disruptions.  Such
   disruptions include sudden traffic volume changes either from the
   customer itself or others, equipment failures in the service provider
   network, and various misbehaviors or attacks.

   The service provider needs to ensure that its network can provide the
   requested slices with the availability agreed with its customers.
   Some of the main technical approaches to ensuring guarantees are

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   about network planning, managing capacity, prioritizing, policing or
   shaping customer traffic, selecting dedicated resources, and so on.

   One term that has commonly been used in this context is "isolation"
   and is also discussed in the [I-D.ietf-teas-enhanced-vpn].

   A transport slice customer may ask for traffic separation, selection
   of dedicated resources, or interference avoidance from other traffic.
   The term "isolation" can refer to any or all of them.  For instance,
   dedicated resources can help assure that traffic in other slices does
   not affect a given slice.  Similarly, VPN technologies can provide
   traffic separation, and interference avoidance may be provided by
   mechanisms such as technical approaches mentioned in the previous
   paragraph (network planning, capacity management, etc).  Moreover,
   these are some of the examples of a particular realization of the
   requirement for guarantees; other mechanisms may also be used.

Authors' Addresses

   Reza Rokui

   Email: reza.rokui@nokia.com

   Shunsuke Homma

   Email: shunsuke.homma.ietf@gmail.com

   Kiran Makhijani

   Email: kiranm@futurewei.com

   Luis M. Contreras

   Email: luismiguel.contrerasmurillo@telefonica.com

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   Jeff Tantsura
   Apstra, Inc.

   Email: jefftant.ietf@gmail.com

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