TEAS Working Group                                               J. Dong
Internet-Draft                                                     Z. Li
Intended status: Informational                       Huawei Technologies
Expires: 8 September 2022                                   7 March 2022


         Considerations about Hierarchical IETF Network Slices
           draft-dong-teas-hierarchical-ietf-network-slice-01

Abstract

   Network slicing is targeted at existing or emerging customers or
   services which may request for network connectivity services with a
   specific set of Service Level Objectives (SLOs) and Service Level
   Expectations (SLEs).  In some network scenarios, there can be
   requirements for the deployment of hierarchical network slices.The
   general framework of IETF network slice supports hierarchical network
   slicing, while the technologies for realizing hierarchical IETF
   network slice need to be considered.

   This document describes the typical scenarios of hierarchical IETF
   network slices, and provides the considerations and requirements on
   the technologies in different network planes to realize hierarchical
   IETF network slices.

Status of This Memo

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   This Internet-Draft will expire on 8 September 2022.

Copyright Notice

   Copyright (c) 2022 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
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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Scenarios of Hierarchical IETF Network Slices . . . . . . . .   3
     2.1.  Per-Customer Network Slices in an Industrial Network
           Slice . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Per-application Network Slices in a Customer Network
           Slice . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Network Slice Services in a Wholesale Network Slice . . .   5
   3.  Considerations about Hierarchical Network Slice
           Realization . . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Forwarding Plane Network Resource Partitioning  . . . . .   6
     3.2.  Data Plane Identifiers  . . . . . . . . . . . . . . . . .   8
     3.3.  Control Plane . . . . . . . . . . . . . . . . . . . . . .   9
     3.4.  Management Plane  . . . . . . . . . . . . . . . . . . . .  10
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   6.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  10
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  10
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Network slicing is targeted at existing or emerging customers or
   services which may request for network connectivity services with a
   specific set of Service Level Objectives (SLOs) and Service Level
   Expectations (SLEs).  The concept and general framework of IETF
   network slice are described in [I-D.ietf-teas-ietf-network-slices].
   [I-D.ietf-teas-enhanced-vpn] describes the framework and technologies
   which can be used for IETF network slice realization by utilizing
   Virtual Private Network (VPN) and Traffic Engineering (TE) mechanisms
   with enhancements that specific services require over traditional
   VPNs.






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   [I-D.ietf-teas-ietf-network-slices] mentions that IETF Network Slices
   may be combined hierarchically, which means that a network slice may
   itself be further sliced.  The technologies for realizing
   hierarchical IETF network slice need to be considered.

   This document describes the typical scenarios in which the deployment
   of hierarchical IETF network slices may be needed.  This document
   also provides the considerations and requirements on the technologies
   in different network planes to realize hierarchical IETF network
   slices.

2.  Scenarios of Hierarchical IETF Network Slices

   In this section, several possible network scenarios of hierarchical
   IETF network slicing are introduced.

2.1.  Per-Customer Network Slices in an Industrial Network Slice

   One of the typical network slice deployment is in the multi-
   industrial network case, in which a physical network is used to
   deliver services of multiple vertical industries.  Separate IETF
   network slices are provided for different industries, such as health-
   care, education, manufacturing, governmental affairs, etc.  Then
   within the network slice of a specific industry, there may be need to
   create separate network slices for some or all of the customers
   within this industry.

   For example, within the education network slice, some of the
   universities may require for a separate network slice to connect with
   a set of the branch campuses.  Another examples is within the health-
   care network slice, some of the hospitals may require for a separate
   network slice for the connectivity and services between a set of the
   branch hospitals.


















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                          ---------------------------------/
                         /        Industry Slice 1        /
                        /     -----------------------    /
                       /     /   Customer Slice 1   /   /
                      /     -----------------------/   /
                     /     -----------------------    /
                    /     /    Customer Slice 2  /   /
                   /     -----------------------/   /
                  /                ...             /
                 ---------------------------------/
                                  ...
                        ---------------------------------/
                       /        Industry Slice 2        /
                      /     -----------------------    /
                     /     /   Customer Slice 1   /   /
                    /     -----------------------/   /
                   /     -----------------------    /
                  /     /    Customer Slice 2  /   /
                 /     -----------------------/   /
                /                ...             /
               ---------------------------------/
             Figure 1. Hierarchical Network Slices: Scenario 1

2.2.  Per-application Network Slices in a Customer Network Slice

   Another network slice deployment case is to provide dedicated IETF
   network slices for some important customers as the first-level
   network slices.  While the customers may require to further split
   their network slices into different sub-network slices for different
   applications.

   For example, a network slice for a hospital may be further divided to
   carry different type of medical services, such as remote patient
   monitoring, remote ultrasound diagnose, medical image transmission
   etc.
















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                          ---------------------------------/
                         /        Customer Slice 1        /
                        /     -----------------------    /
                       /     /      APP Slice 1     /   /
                      /     -----------------------/   /
                     /     -----------------------    /
                    /     /      APP Slice 2     /   /
                   /     -----------------------/   /
                  /                ...             /
                 ---------------------------------/
                                  ...
                        ---------------------------------/
                       /        Customer Slice 2        /
                      /     -----------------------    /
                     /     /      APP Slice 1     /   /
                    /     -----------------------/   /
                   /     -----------------------    /
                  /     /       APP Slice 2    /   /
                 /     -----------------------/   /
                /                ...             /
               ---------------------------------/
             Figure 2. Hierarchical Network Slices: Scenario 2

2.3.  Network Slice Services in a Wholesale Network Slice

   IETF network slice can also be delivered as a wholesale service to
   other network operators.  In this case a network operator can be the
   customer of a network slice, and it may also need to deliver IETF
   network slice services to its customers.  This is similar to the
   Carrier's Carrier VPN service mode, while some additional
   requirements on the SLOs and SLEs may be required by the second-level
   network slice customer.



















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                          ---------------------------------/
                         /        Wholesale Slice 1       /
                        /     -----------------------    /
                       /     /    Customer Slice 1  /   /
                      /     -----------------------/   /
                     /     -----------------------    /
                    /     /   Customer Slice 2   /   /
                   /     -----------------------/   /
                  /                ...             /
                 ---------------------------------/
                                  ...
                        ---------------------------------/
                       /        Wholesale Slice 2       /
                      /     -----------------------    /
                     /     /   Customer Slice 1   /   /
                    /     -----------------------/   /
                   /     -----------------------    /
                  /     /   Customer Slice 2   /   /
                 /     -----------------------/   /
                /                ...             /
               ---------------------------------/
             Figure 3. Hierarchical Network Slices: Scenario 3

3.  Considerations about Hierarchical Network Slice Realization

   To support the realization of hierarchical network slices, there will
   be specific requirements on the technologies used in each network
   plane.  In this section, the requirements of hierarchical network
   slicing on the forwarding plane network resource partitioning, the
   data plane encapsulations, the control plane protocols and the
   management plane are analyzed.

3.1.  Forwarding Plane Network Resource Partitioning

   For the realization of IETF network slices, the network resources in
   the underlying forwarding plane needs to be partitioned into
   different network resource partitions (NRPs), each NRP is used as the
   underlay network construct to support one or a group of IETF network
   slice services.  In order to support hierarchical network slices, the
   forwarding plane network resources needs to be able to be partitioned
   in a hierarchical manner.  Taking a two-level hierarchical network
   slice as an example, the bandwidth resource of a physical interface
   needs to be partitioned in two levels.  There can be different
   options in modeling the interface resources of network resource
   partition.






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   The first option is to treat the network resources in the first-level
   NRPs as a set of layer-3 sub-interfaces, each with dedicated link
   bandwidth, and the second-level NRPs are represented as virtual data
   channels under the layer-3 sub-interfaces, as shown in the figure
   below:

  +----------------------+
  |  +----------------+  |
  |  | +------------+ |  |
  |  | |Data Channel| |  |
  |  | +------------+ |  |
  |  |       ...      |  |
  |  | +------------+ |  |
  |  | |Data Channel| |  |
  |  | +------------+ |  |
  |  +----------------+  |
  | layer-3 subinterface |
  |                      |
  |        . . .         |
  |  +----------------+  |
  |  | +------------+ |  |
  |  | |Data Channel| |  |
  |  | +------------+ |  |
  |  |       ...      |  |
  |  | +------------+ |  |
  |  | |Data Channel| |  |
  |  | +------------+ |  |
  |  +----------------+  |
  | layer-3 subinterface |
  +----------------------+
     Physical Interface

 Figure 4. Modeling of Network Resource Partition on Interface: Option 1

   The second option is to treat the first-level NRPs as layer-2 sub-
   interface of the layer-3 interface, and the second-level NRPs are
   represented as virtual data channels under the layer-2 sub-interface,
   as shown in the figure below:













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  +----------------------+
  |  +----------------+  |
  |  | +------------+ |  |
  |  | |Data Channel| |  |
  |  | +------------+ |  |
  |  |        ...     |  |
  |  | +------------+ |  |
  |  | |Data Channel| |  |
  |  | +------------+ |  |
  |  +----------------+  |
  | layer-2 subinterface |
  |                      |
  |        . . .         |
  |  +----------------+  |
  |  | +------------+ |  |
  |  | |Data Channel| |  |
  |  | +------------+ |  |
  |  |        ...     |  |
  |  | +------------+ |  |
  |  | |Data Channel| |  |
  |  | +------------+ |  |
  |  +----------------+  |
  | layer-2 subinterface |
  +----------------------+
  Layer-3 Physical Interface

 Figure 5. Modeling of Network Resource Partition on Interface, Option 2

   The options of the network resource partition modeling may have
   different impact to the control plane in terms of the number of
   control protocol sessions to be maintained, and the amount and types
   of information to be distributed in the control plane.  Depends on
   the network deployment requirements, different resource partition
   modeling options may be used.

3.2.  Data Plane Identifiers

   Traffic of IETF network slices can be steered into the corresponding
   underlay network construct based on one or multiple fields in the
   data packet, so that the corresponding NRPs are used for processing
   and forwarding the packet.  On the edge nodes of an IETF network
   slice, traffic flows can be classified and mapped to IETF network
   slices using flexible matching rules based on operators' local
   policy.  While on the intermediate network nodes, a dedicated data
   plane NRP Identifier [I-D.dong-teas-nrp-scalability] can facilitate
   the identification of the NRP and the set of network resources
   allocated on the network nodes for packet processing.




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   For hierarchical IETF network slices, such data plane identifiers may
   need to be able to identify both the first-level NRP and the second-
   level NRP.  There are several options in the design of the data plane
   NRP identifier for hierarchical network slices.

   The first option is to use a unified data plane identifier for both
   the first-level NRP and the second-level NRP.  In this case, the
   first-level NRPs and the second-level NRPs are identified using
   distinct identifier values.

                +-----------------------------------------+
                |   Unified NRP ID for different levels   |
                +-----------------------------------------+

               Figure 6. Unified NRP ID

   The second option is to use a hierarchical identifiers for the first-
   level NRP and the second-level NRP.  In this case, the first part of
   the identifier is used to identify the first-level NRP, and the
   second part of the identifier is used to identify the second-level
   NRP.  Depends on the data plane technologies used, the hierarchical
   NRP may be encapsulated in a continuous field in the packet, or may
   be positioned in separate fields.

                +--------------------+--------------------+
                |   Level-1 NRP ID   |   Level-2 NRP ID   |
                +--------------------+--------------------+

               Figure 7. Hierarchical NRP IDs


3.3.  Control Plane

   The control plane may be used for the distribution of the attributes
   and states of the hierarchical NRPs and the associated data plane
   identifiers among network nodes in the NRP and also to the network
   controller.  With different NRP modeling, the information may be
   advertised as either layer-3 or layer-2 network information, which
   may have different scalability implications to the control plane.
   And as the number of hierarchical network slices increases, some
   control plane optimization mechanisms may be needed to adopt to the
   amount of information advertised.









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3.4.  Management Plane

   For the management hierarchical network slices, the management system
   of network operator needs to provide life-cycle management to both
   the first-level network slices and the second-level network slices.
   It should allow to manage the first-level and second-level network
   slices separately, while the relationship between the first-level and
   second-level network slices also need to be maintained in the
   management system.  The management system may need to support
   additional functions and procedures for the management of
   hierarchical network slices.  Further analysis about the requirement
   on the management plane is for further study.

4.  Security Considerations

   TBD

5.  IANA Considerations

   This document makes no request of IANA.

6.  Contributors

   Zhibo Hu
   Email: huzhibo@huawei.com

7.  Acknowledgments

   The authors would like to thank Yawei Zhang for the review and
   discussion of this document.

8.  References

8.1.  Normative References

   [I-D.ietf-teas-ietf-network-slices]
              Farrel, A., Drake, J., Rokui, R., Homma, S., Makhijani,
              K., Contreras, L. M., and J. Tantsura, "Framework for IETF
              Network Slices", Work in Progress, Internet-Draft, draft-
              ietf-teas-ietf-network-slices-08, 6 March 2022,
              <https://www.ietf.org/archive/id/draft-ietf-teas-ietf-
              network-slices-08.txt>.

8.2.  Informative References

   [I-D.dong-teas-nrp-scalability]
              Dong, J., Li, Z., Gong, L., Yang, G., Guichard, J. N.,
              Mishra, G., Qin, F., Saad, T., and V. P. Beeram,



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              "Scalability Considerations for Network Resource
              Partition", Work in Progress, Internet-Draft, draft-dong-
              teas-nrp-scalability-01, 7 February 2022,
              <https://www.ietf.org/archive/id/draft-dong-teas-nrp-
              scalability-01.txt>.

   [I-D.ietf-teas-enhanced-vpn]
              Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
              Framework for Enhanced Virtual Private Network (VPN+)
              Services", Work in Progress, Internet-Draft, draft-ietf-
              teas-enhanced-vpn-09, 25 October 2021,
              <https://www.ietf.org/archive/id/draft-ietf-teas-enhanced-
              vpn-09.txt>.

Authors' Addresses

   Jie Dong
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Road
   Beijing
   100095
   China
   Email: jie.dong@huawei.com


   Zhenbin Li
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Road
   Beijing
   100095
   China
   Email: lizhenbin@huawei.com



















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