IETF Network Slice Use Cases and Attributes for Northbound Interface of IETF Network Slice Controllers
draft-contreras-teas-slice-nbi-04

TEAS Working Group                                         LM. Contreras
Internet-Draft                                                Telefonica
Intended status: Informational                                  S. Homma
Expires: August 26, 2021                                             NTT
                                                       J. Ordonez-Lucena
                                                              Telefonica
                                                       February 22, 2021

IETF Network Slice Use Cases and Attributes for Northbound Interface of
                     IETF Network Slice Controllers
                   draft-contreras-teas-slice-nbi-04

Abstract

   This document analyses the needs of potential customers of network
   slices realized with IETF techniques in several use cases, identifies
   the functionalities for the North Bound Interface (NBI) of an IETF
   Network Slice Controller to satisfy such requests.

Status of This Memo

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document and terminology . . . . . .   3
   3.  Northbound Interface for IETF Network Slices  . . . . . . . .   3
   4.  IETF Network Slice Use Cases  . . . . . . . . . . . . . . . .   4
     4.1.  5G Services . . . . . . . . . . . . . . . . . . . . . . .   4
       4.1.1.  Generic network Slice Template  . . . . . . . . . . .   5
       4.1.2.  Categorization of GST attributes  . . . . . . . . . .   6
         4.1.2.1.  Attributes with direct impact on the IETF network
                   slice definition  . . . . . . . . . . . . . . . .   7
         4.1.2.2.  Attributes with indirect impact on the IETF
                   network slice definition  . . . . . . . . . . . .   7
         4.1.2.3.  Attributes with no impact on the IETF network
                   slice definition  . . . . . . . . . . . . . . . .   8
       4.1.3.  Provisioning procedures . . . . . . . . . . . . . . .   9
     4.2.  NFV-based services  . . . . . . . . . . . . . . . . . . .   9
       4.2.1.  Connectivity attributes . . . . . . . . . . . . . . .  10
       4.2.2.  Provisioning procedures . . . . . . . . . . . . . . .  10
     4.3.  Network sharing . . . . . . . . . . . . . . . . . . . . .  11
       4.3.1.  Connectivity attributes . . . . . . . . . . . . . . .  12
       4.3.2.  Provisioning procedures . . . . . . . . . . . . . . .  12
     4.4.  Additional use cases  . . . . . . . . . . . . . . . . . .  12
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   A number of new technologies, such as 5G, NFV and SDN are not only
   evolving the network from a pure technological perspective but also
   are changing the concept in which new services are offered to the
   customers [I-D.homma-slice-provision-models] by introducing the
   concept of network slicing.

   The transport network is an essential component in the end-to-end
   delivery of services and, consequently, it is necessary to understand
   what could be the way in which the transport network is consumed as a
   slice.  For a definition of IETF network slice refer to
   [I-D.ietf-teas-ietf-network-slice-definition].

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   In this document it is assumed that there exists a (logically)
   centralized component in the transport network, namely IETF Network
   Slice Controller (NSC) with the responsibilities on the control and
   management of the IETF network slices invoked for a given service, as
   requested by IETF network slice customers.

   This document analyses different use cases deriving the needs of
   potential IETF network slice customers in order to identify the
   functionality required on the North Bound Interface (NBI) of the NSC
   to be exposed towards such IETF network slice customers.  Solutions
   to construct the requested IETF network slices are out of scope of
   this document.

   This document addresses some of the discussions of the TEAS Slice
   Design Team.  However, it is not at this stage an official outcome of
   the Design Team.

2.  Conventions used in this document and terminology

   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 RFC2119 [RFC2119].

   The terminology in this draft will be aligned in forthcoming versions
   with the final terminology selected for describing the notion of IETF
   network slice when applied to IETF technologies, which is currently
   under discussion.  By now same terminology as used in
   [I-D.ietf-teas-ietf-network-slice-definition] and
   [I-D.nsdt-teas-ns-framework] is primarily used here.

   The term "transport network" in the context of this draft refers in
   broad sense to WAN, MBH, IP backbone and other network segments
   implemented by IETF technologies.

3.  Northbound Interface for IETF Network Slices

   In a general manner, the transport network supports different kinds
   of services.  These services consume capabilities provided by the
   transport network for deploying end-to-end services, interconnecting
   network functions or applications spread across the network and
   providing connectivity toward the final users of these services.

   Under the slicing approach, a IETF network slice customer requests to
   a IETF network slice controller a slice with certain characteristics
   and parametrization.  Such request it is assumed here to be done
   through a NBI exposed by the NSC to the customer, as reflected in
   Fig. 1.

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                            +--------------------+
                            |                    |
                            |    IETF Network    |
                            |   Slice Customer   |
                            |                    |
                            +--------------------+
                                       A
                                       |
                                       | IETF Network
                                       | Slice Controller
                                       | NBI
                                       |
                                       V
                            +--------------------+
                            |                    |
                            |    IETF Network    |
                            |  Slice Controller  |
                            |                    |
                            +--------------------+

                 Figure 1: IETF network slice NBI concept

   The functionality supported by the NBI depends on the requirements
   that the slice customer has to satisfy.  It is then important to
   understand the needs of the slice customers as well as the way of
   expressing them.

4.  IETF Network Slice Use Cases

   Different use cases for slice customers can be identified, as
   described in the following sections.

4.1.  5G Services

   5G services natively rely on the concept of network slicing. 5G is
   expected to allow vertical customers to request slices in such a
   manner that the allocated resources and capabilities in the network
   appear as dedicated for them.

   In network slicing scenarios, a vertical customer requests a network
   operator to allocate a network slice instance (NSI) satisfying a
   particular set of service requirements.  The content/format of these
   requirements are highly dependent on the networking expertise and use
   cases of the customer under consideration.  To deal with this
   heterogeneity, it is fundamental for the network operator to define a
   a unified ability to interpret service requirements from different
   vertical customers, and to represent them in a common language, with

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   the purposes of facilitating their translation/mapping into specific
   slicing-aware network configuration actions.  In this regard, model-
   based network slice descriptors built on the principles of
   reproducibility, reusability and customizability can be defined for
   this end.

   As a starting point for such a definition, GSMA developed the idea of
   having a universal blueprint that, being offered by network
   operators, can be used by any vertical customer to order the
   deployment of an NSI based on a specific set of service requirements.
   The result of this work has been the definition of a baseline network
   slice descriptor called Generic network Slice Template (GST).  The
   GST contains multiple attributes that can be used to characterize a
   network slice.  A Network Slice Type (NEST) describes the
   characteristics of a network slice by means of filling GST attributes
   with values based on specific service requirements.  Basically, a
   NEST is a filled-in version of a GST.  Different NESTs allow
   describing different types of network slices.  For slices based on
   standardized service types, e.g. eMBB, uRLLC and mIoT, the network
   operator may have a set of readymade, standardized NESTs (S-NESTs).
   For slices based on specific industry use cases, the network operator
   can define additional NESTs.

   Service requirements from a given vertical customer are mapped to a
   NEST, which provides a self-contained description of the network
   slice to be provisioned for that vertical customer.  According to
   this reasoning, the NEST can be used by the network operator as input
   to the NSI preparation phase, which is defined in [TS28.530]. 3GPP is
   working on the translation of the GST/NEST attributes into NSI
   related requirements, which are defined in the "ServiceProfile" data
   type from the Network Slice Information Object Class (IOC) in
   [TS28.541].  These requirements are used by the 3GPP Management
   System to allocate the NSI across all network domains, including
   transport network.  The IETF network slice defines the part of that
   NSI that is deployed across the transport network.

   Despite the translation is an on-going work in 3GPP it seems
   convenient to start looking at the GST attributes to understand what
   kind of parameters could be required for the IETF network slice NBI.

4.1.1.  Generic network Slice Template

   The structure of the GST is defined in [GSMA].  The template defines
   a total of 35 attributes.  For each of them, the following
   information is provided:

   o  Attribute definition, which provides a formal definition of what
      the attribute represents.

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   o  Attribute parameters, including:

      *  Value, e.g. integer, float.

      *  Measurement unit, e.g. milliseconds, Gbps

      *  Example, which provides examples of values the parameter can
         take in different use cases.

      *  Tag, which allow describing the type of parameter, according to
         its semantics.  An attribute can be tagged as a
         characterization attribute or a scalability attribute.  If it
         is characterization attribute, it can be further tagged as a
         performance-related attribute, a functionality-related
         attribute or an operation-related attribute.

      *  Exposure, which allow describing how this attribute interact
         with the slice customer, either as an API or a KPI.

   o  Attribute presence, either mandatory, conditional or optional.

   Attributes from GST can be used by the network operator (slice
   controller) and a vertical customer (slice customer) to agree SLA.

   GST attributes are generic in the sense that they can be used to
   characterize different types of network slices.  Once those
   attributes become filled with specific values, it becomes a NEST
   which can be ordered by slice customers.

4.1.2.  Categorization of GST attributes

   Not all the GST attributes as defined in [GSMA] have impact in the
   transport network since some of them are specific to either the radio
   or the mobile core part.

   In the analysis performed in this document, the attributes have been
   categorized as:

   o  Directly impactive attributes, which are those that have direct
      impact on the definition of the IETF network slice, i.e.,
      attributes that can be directly translated into requirements
      required to be satisfied by a IETF network slice.

   o  Indirectly impactive attributes, which are those that impact in an
      indirect manner on the definition of the IETF network slice, i.e.,
      attributes that indirectly impose some requirements to a IETF
      network slice.

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   o  Non-impactive attributes, that are those which do not have impact
      on the IETF network slice at all.

   The following sections describe the attributes falling into the three
   categories.

4.1.2.1.  Attributes with direct impact on the IETF network slice
          definition

   The following attributes impose requirements in the IETF network
   slice

   o  Availability

   o  Deterministic communication

   o  Downlink throughput per network slice

   o  Energy efficiency

   o  Group communication support

   o  Isolation level

   o  Maximum supported packet size

   o  Mission critical support

   o  Performance monitoring

   o  Slice quality of service parameters

   o  Support for non-IP traffic

   o  Uplink throughput per network slice

   o  User data access (i.e., tunneling mechanisms)

4.1.2.2.  Attributes with indirect impact on the IETF network slice
          definition

   The following attributes indirectly impose requirements in the IETF
   network slice to support the end-to-end service.

   o  Area of service (i.e., the area where terminals can access a
      particular network slice)

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   o  Delay tolerance (i.e., if the service can be delivered when the
      system has sufficient resources)

   o  Downlink (maximum) throughput per UE

   o  Network functions owned by Network Slice Customer

   o  Maximum number of (concurrent) PDU sessions

   o  Performance prediction (i.e., capability to predict the network
      and service status)

   o  Root cause investigation

   o  Session and Service Continuity support

   o  Simultaneous use of the network slice

   o  Supported device velocity

   o  UE density

   o  Uplink (maximum) throughput per UE

   o  User management openness (i.e., capability to manage users'
      network services and corresponding requirements)

   o  Latency from (last) UPF to Application Server

4.1.2.3.  Attributes with no impact on the IETF network slice definition

   The following attributes do not impact the IETF network slice.

   o  Location based message delivery (not related to the geographical
      spread of the network slice itself but with the localized
      distribution of information)

   o  MMTel support, i.e. support of and Multimedia Telephony Service
      (MMTel)as well as IP Multimedia Subsystem (IMS) support.

   o  NB-IoT Support, i.e., support of NB-IoT in the RAN in the network
      slice.

   o  Maximum number of (simultaneous) UEs

   o  Positioning support

   o  Radio spectrum

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   o  Synchronicity (among devices)

   o  V2X communication mode

   o  Network Slice Specific Authentication and Authorization (NSSAA)

4.1.3.  Provisioning procedures

   3GPP identifies in [TS28.541] a number of procedures for the
   provisioning of a network slice in general.  It can be assumed that
   similar procedures may also apply to a transport slice, facilitating
   a consistent management and control of end-to-end slices.

   The envisioned procedures are the following:

   o  Slice instance allocation: this procedure permits to create a new
      slice instance (or reuse an existing one).

   o  Slice instance de-allocation: this procedure decommissions a
      previously instantiated slice.

   o  Slice instance modification: this procedure permits the change in
      the characteristics of an existing slice instance.

   o  Get slice instance status: this procedure helps to retrieve run-
      time information on the status of a deployed slice instance.

   o  Retrieval of slice capabilities: this procedure assists on getting
      information about the capabilities (e.g. maximum latency
      supported).

   All these procedures fit in the operation of transport network
   slices.

4.2.  NFV-based services

   NFV technology allows the flexible and dynamic instantiation of
   virtualized network functions (and their composition into network
   services) on top of a distributed, cloud-enabled compute
   infrastructure.  This infrastructure can span across different points
   of presence in a carrier network.  By leveraging on transport network
   slicing, connectivity services established across geographically
   remote points of presence can be enriched by providing additional QoS
   guarantees with respect present state-of-the-art mechanisms, as
   conventional L2/L3 VPNs.

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4.2.1.  Connectivity attributes

   The connectivity services are expressed through a number of
   attributes as listed:

   o  Incoming and outgoing bandwidth: bandwidth required for the
      connectivity services (in Mbps).

   o  Qos metrics: set of metrics (e.g., cost, latency and delay
      variation) applicable to a specific connectivity service

   o  Directionality: indication if the traffic is unidirectional or
      bidirectional.

   o  MTU: value of the largest PDU to be transmitted in the
      connectivity service.

   o  Protection scheme: indication of the kind of protection to be
      performed (e.g., 1;1, 1+1, etc.)

   o  Connectivity mode: indication of the service is point-to-point of
      point-to-multipoint

   All those attributes will assist on the characterization of the
   connectivity slice to be deployed, and thus, are relevant for the
   definition of a IETF network slice supporting such connectivity.

4.2.2.  Provisioning procedures

   ETSI NFV defines the role of WAN Infrastructure Manager (WIM) as the
   component in charge of managing and controlling the connectivity
   external to the PoPs.  In [IFA032] a number of interfaces are
   identified to be exposed by the WIM for supporting the multi-site
   connectivity, thus representing the capabilities expected for a
   transport network slice, as well, in case of satisfying such
   connectivity needs by means of the slice concept.

   The interfaces considered are the following:

   o  Multi-Site Connectivity Service (MSCS) Management: this interface
      permits the creation, termination, update and query of MSCSs,
      including reservation.  It also enables subscription for
      notifications and information retrieval associated to the
      connectivity service.

   o  Capacity Management: this interface allows querying about the
      capacity (e.g. bandwidth), topology, and network edge points of

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      the connectivity service, as well as about information of consumed
      and available capacity on the underlying network resources.

   o  Fault Management: this interface serves for the provision of
      alarms related to the MSCSs.

   o  Performance Management: this interface assists on the retrieval of
      performance information (measurement results collection and
      notifications) related to MSCSs.

4.3.  Network sharing

   Network sharing is one of the means network operators exploit for
   increasing efficiencies.  There are different scenarios of network
   sharing, being especially popular in the deployment of mobile
   networks, typically referred to as Radio Access Network (RAN)
   sharing.  From an operational perspective, in RAN sharing we have two
   roles: master operator, being the actor (e.g. infrastructure
   provider, network operator) to which the deployment and daily
   operation of shared RAN elements are entrusted to; and the
   participant operators, who are the mobile operators who share the RAN
   facilities provided by the master operator.  Note that in this
   context the master and participant operator can be seen as provider
   and customer, respectively.

   While there exist different modes of RAN sharing [TS23.251],
   including passive RAN sharing (infrastructure site sharing) and
   active RAN sharing (e.g.  Multi-Operator Core Networks or MOCN), most
   of the cases require the establishment of separated connections in
   order to separate the traffic per participant operator.  Such
   connections typically extend from the cell site to some pre-defined
   and agreed interconnection points, from which the traffic is routed
   and delivered to individual participant operators.

   The above-referred connections can have specific attributes.  Aspects
   like guaranteed bandwidth (in line with the expected load from the
   aggregated cells), redundancy, bounded latency (per kind of traffic),
   or secure delivery of the information should be considered.

   The master operator is the one in charge of provisioning the
   connections and collecting management data (e.g. performance
   measurements, telemetry, fault alarms, trace data) for individual
   participant operators.  The use of network slicing could make the
   network sharing approach more flexible by allowing the other
   operators control and manage the established connections [MEF].

   The implications of the RAN sharing scenario here described can be
   extended to either fixed networks or even to mobile networks

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   leveraging on radio functional split (i.e., including fronthaul and
   midhaul network segments).

4.3.1.  Connectivity attributes

   The connections for RAN sharing typically consider attributes like:

   o  Maximum and Guaranteed Bit Rate (MBR and GBR respectively).

   o  Bounded latency (e.g., for user plane, control plane, etc)

   o  Packet loss rate.

   o  IP addressing (consistent among the operators sharing the
      infrastructure).

   o  L2/L3 reachability.

   o  Recovery time (on the event of failures).

   o  Secure connection (e.g., encryption support).

4.3.2.  Provisioning procedures

   The expected provisioning procedures are:

   o  Connection provisioning between site and interconnection point.
      Those connections could evolve in time in terms of capacity
      depending on the capacity growth of each particular site.

   o  Collection of management data, including performance measurements,
      fault alarms and trace data.

4.4.  Additional use cases

   This is a placeholder for describing additional use cases (e.g., data
   center interconnection, etc).  To be completed.

5.  Security Considerations

   This draft does not include any security considerations.

6.  IANA Considerations

   This draft does not include any IANA considerations

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7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

7.2.  Informative References

   [GSMA]     "Generic Network Slice Template, version 3.0", NG.116 ,
              May 2020.

   [I-D.homma-slice-provision-models]
              Homma, S., Nishihara, H., Miyasaka, T., Galis, A., OV, V.,
              Lopez, D., Contreras, L., Ordonez-Lucena, J., Martinez-
              Julia, P., Qiang, L., Rokui, R., Ciavaglia, L., and X.
              Foy, "Network Slice Provision Models", draft-homma-slice-
              provision-models-02 (work in progress), November 2019.

   [I-D.ietf-teas-ietf-network-slice-definition]
              Rokui, R., Homma, S., Makhijani, K., Contreras, L., and J.
              Tantsura, "Definition of IETF Network Slices", draft-ietf-
              teas-ietf-network-slice-definition-00 (work in progress),
              January 2021.

   [I-D.nsdt-teas-ns-framework]
              Gray, E. and J. Drake, "Framework for Transport Network
              Slices", draft-nsdt-teas-ns-framework-04 (work in
              progress), July 2020.

   [IFA032]   "IFA032 Interface and Information Model Specification for
              Multi-Site Connectivity Services V3.2.1.", ETSI GS NFV-IFA
              032 V3.2.1 , April 2019.

   [MEF]      "Slicing for Shared 5G Fronthaul and Backhaul", MEF White
              paper , April 2020.

   [TS23.251]
              "TS 23.251 Network Sharing; Architecture and functional
              description (Release 16) V16.0.0.", 3GPP TS 23.251
              V16.0.0 , July 2020.

   [TS28.530]
              "TS 28.530 Management and orchestration; Concepts, use
              cases and requirements (Release 16) V16.0.0.", 3GPP TS
              28.530 V16.0.0 , September 2019.

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   [TS28.541]
              "TS 28.541 Management and orchestration; 5G Network
              Resource Model (NRM); Stage 2 and stage 3 (Release 16)
              V16.2.0.", 3GPP TS 28.541 V16.2.0 , September 2019.

Authors' Addresses

   Luis M. Contreras
   Telefonica
   Ronda de la Comunicacion, s/n
   Sur-3 building, 3rd floor
   Madrid  28050
   Spain

   Email: luismiguel.contrerasmurillo@telefonica.com
   URI:   http://lmcontreras.com/

   Shunsuke Homma
   NTT
   Japan

   Email: shunsuke.homma.ietf@gmail.com

   Jose A. Ordonez-Lucena
   Telefonica
   Ronda de la Comunicacion, s/n
   Sur-3 building, 3rd floor
   Madrid  28050
   Spain

   Email: joseantonio.ordonezlucena@telefonica.com

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