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none                                                           X. de Foy
Internet-Draft                                                 A. Rahman
Intended status: Informational                         InterDigital Inc.
Expires: May 3, 2018                                            A. Galis
                                               University College London
                                                            K. Makhijani
                                                                L. Qiang
                                                     Huawei Technologies
                                                        October 30, 2017


          Interconnecting (or Stitching) Network Slice Subnets
               draft-defoy-coms-subnet-interconnection-01

Abstract

   This document aims to define a network slice subnet as a general
   concept, and to augment a baseline network slice model with
   attributes that describe interconnections between network slice
   subnets.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 3, 2018.

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   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   (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



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   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.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Interconnection Concepts  . . . . . . . . . . . . . . . . . .   3
   3.  Information Model . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Representing Interconnections . . . . . . . . . . . . . .   5
     3.2.  Relation to NS Information Model  . . . . . . . . . . . .   5
   4.  Operations  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  Next Steps  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   8.  Informative References  . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Network Slicing enables deployment and management of services with
   diverse requirements on end-to-end partitioned virtual networks,
   including compute and storage resources, over the same
   infrastructure.  [I-D.geng-coms-problem-statement] describes a
   problem statement for supervised heterogeneous network slicing,
   enabling users to deploy network slices including connectivity,
   computing and storage components.

   Nevertheless, defining and managing a network slice (NS) end-to-end
   does not always have to be done directly: it may be convenient to
   define and manage subsets of NS components.  The concept of network
   slice subnet is defined originally in [NGMN_Network_Slicing], though
   we only need to retain its definition in the most universal form:
   network slice subnet instances are similar to slice instances in most
   ways but cannot be operated in isolation as a complete network slice.
   They can be interconnected with other NS subnets to form a complete,
   end-to-end network slice (i.e. interconnection and/or stitching of NS
   subnets).  To summarize: a NS subnet can be seen as a network slice
   with unconnected links.  The term "network slice segment" has also
   occasionally been used to designate a NS subnet.  Use cases for using
   NS subnets include managing multi-domain network slices, or even
   within one domain, isolate management and maintenance of different
   portions of a network slice.  It includes also mapping services to an
   ordered chain of network slice subnets instances.





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   A model for network slicing is currently being defined in
   [I-D.qiang-coms-netslicing-information-model].  One question we would
   like to address is how to augment this base model to describe
   interconnections between NS subnets.  The base model is not
   technology specific, and therefore the description of
   interconnections should not be either.  Moreover, such an
   augmentation should both enable describing the intent for
   interconnection, as well as describing actual interconnections once
   NS subnets have been stitched together.

1.1.  Terminology

   Network slicing related terminology used in this document should be
   interpreted as described in [I-D.geng-coms-problem-statement].

   "Network slice subnet" is a term defined in this draft.  It is
   comprised of groups of connectivity, compute and storage resources,
   possibly together with network functions and network management
   entities, forming a complete instantiated logical/physical network in
   support of certain network and service characteristics but cannot be
   activated in isolation as an overall network slice.

2.  Interconnection Concepts

   The general goal of an interconnection between 2 NS subnets is to
   have links established between nodes from both subnets.  A secondary
   goal is to keep NS subnet descriptions isolated from each other.
   This relative isolation will contribute to simplify and decentralize
   management, as well as enabling operations such as substituting a
   subnet with another, composing slice subnets of different domains,
   etc.

   As described in Figure 1, we can represent a network slice subnet as
   a network slice that also has one or more logical nodes, which
   terminate (at logical termination points) links that need to be
   interconnected with external nodes (cross-subnet links).

   During a stitching operation, logical termination points from both NS
   subnets can be paired together into an interconnection point.  When
   implemented at the infrastructure layer, this interconnection point
   may be either implemented as a gateway, or abstracted away, in which
   case nodes from both NS subnets end up being directly interconnected
   between each other.  In any cases, interconnected links will need to
   have compatible QoS attributes.







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                               Slice Provider
                                     |
   +---------------------------------v---------------------------------+
   |  Slice Manager                                                    |
   |                                                                   |
   | +---------------------------------------------------------------+ |
   | |   Data model: network slice composed of NS subnet 1 and 2     | |
   | |                                                               | |
   | |      Network Slice Subnet 1            Network Slice Subnet 2 | |
   | | +---------------------------+  +----------------------------+ | |
   | | |     cross-subnet link     |  |   cross-subnet             | | |
   | | |    +----------------+     |  |       link    +------+     | | |
   | | |    |                |     |  |      +--------o node |     | | |
   | | |    |                |Interconnection|        +---o--+     | | |
   | | |+---o--+     +-------|-----+--+------|------+     |        | | |
   | | || node |     |       |     |  |      |      |     |        | | |
   | | |+---o--+     | +-----|---+ |  | +----|----+ |     |        | | |
   | | |    |        | |     |   | |  | |    |    | |     |        | | |
   | | |    |        | |     o - - - - - - - o    | |     |        | | |
   | | |    |        | |         | |  | |         | |     |        | | |
   | | |    |        | | logical | |  | | logical | |     |        | | |
   | | |    |        | |  node   | |  | |  node   | |     |        | | |
   | | |    |        | |         | |  | |         | |     +---+    | | |
   | | |    |        | |     o - - - - - - - o    | |         |    | | |
   | | |    |        | |     |   | |  | |    |    | |         |    | | |
   | | |    |        | +-----|---+ |  | +----|----+ |     +---o--+ | | |
   | | |    |        |       |     |  |      |      |     | node | | | |
   | | |    |        +-------|-----+--+------|------+     +---o--+ | | |
   | | |    | +------+       |     |  |      |                |    | | |
   | | |    +-o node o-------+     |  |      +----------------+    | | |
   | | |      +------+ cross-subnet|  |         cross-subnet       | | |
   | | |                link       |  |           link             | | |
   | | +---------------------------+  +----------------------------+ | |
   | +---------------------------------------------------------------+ |
   +--------------------------------+----------------------------------+
                                    |
                                    v
                            Network Infrastructure

              Figure 1: Network Slice Subnets Interconnection

   Network slice interconnection information in data models can be used
   for different related purposes:

   o  Anchoring interconnections at logical termination points: a NS
      subnet model should specify which link termination points are the
      "network slice subnet boundaries" that need to be interconnected.




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   o  Programming interconnections: a NS provider may set attributes in
      a NS subnet model to configure the interconnection with another NS
      subnet.  For example, constraints on the interconnection (on
      throughput, latency, etc.) may be programmed to trigger an alarm
      that may be lead the NS operator to disable NS subnets, replace NS
      subnets by others, etc. to maintain overall service performance.

   o  Describing the state of interconnection (once NS subnets are
      interconnected).

3.  Information Model

3.1.  Representing Interconnections

   A fairly minimal way to represent an interconnection is:

   o  To represent an interconnection anchor in a subnet: a "logical
      termination point" in this subnet.

   o  To program or represent an interconnection between subnets: a pair
      of logical termination points, one in each subnet.

   Some form of grouping of logical termination points (for example, in
   logical nodes) may tell the NS manager to treat those termination
   points as a single unit for placement, implementation, etc.

   Additional information may be useful to complement the description of
   an interconnections.  Some attributes may be useful to describe an
   interconnection point anchor, while others may be useful to program
   or represent the state of an interconnection.  For example, logical
   termination points may be associated with information that
   facilitates placement or stitching operations.  Future work should
   determine what type of information would be useful to specify or
   represent a NS interconnection.

3.2.  Relation to NS Information Model

   The network slice information model defined in
   [I-D.qiang-coms-netslicing-information-model] will be used as a base.
   This model is itself based on the "ietf-network" model defined in
   [I-D.ietf-i2rs-yang-network-topo]

   Individual network slice data model instances ("network" attributes
   of the "ietf-network" model) can represent network slice subnets.  If
   there is a need to tie multiple subnets together, a parent network
   slice may be added to the model if necessary, but this is out of
   scope of the present draft.  A "network" attribute may also represent




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   a full, end-to-end slice, in which case it does not need be
   interconnected using the mechanisms described in the present draft.

   Interconnection anchors are logical termination points (TP) included
   in logical nodes.  The base model can be augmented as described
   below.  Those new logical node and logical TP attributes will
   typically be used only for nodes and termination points used as
   interconnection anchors.  Logical nodes should be as simple as
   possible (e.g. should not include any compute or storage unit), so
   that they can be abstracted away in underlying networks during the
   interconnection operation, if needed.

   module: ietf-network
   +--rw networks
      +--rw network* [network-id]
         +--rw network-id
         +--rw network-types
         +--rw supporting-network* [network-ref]
         |  +--rw network-ref
         +--rw node* [node-id]
         |  +--... (augmented with new attributes of logical nodes)
         |  +--rw nt:termination-point* [tp-id]
         |  |  ... (augmented with new attributes of logical TP)
       ...

4.  Operations

   Stitching may occur when network slice subnets are initially
   instantiated, or later after instantiation.

5.  Security Considerations

   Access control mechanisms for managing network slices can likely be
   reused for network slice subnets, since their models should be
   similar to each other.

   Stitching 2 NS subnets together may be subject to some form of
   authorization by a NS tenant.

6.  Next Steps

   The present draft investigates one aspect of a non-technology
   specific representation of a network slice.  It may therefore be part
   of the larger discussion on the need for such a representation.

   Beyond this, next steps can include the following:





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   o  Discussing the definition and need for NS subnets.  Is "NS with
      unconnected links" an adequate simple definition?  Is there an
      agreement on the use cases?  Should NS subnet interconnection be
      standardized?

   o  Assuming there is some interest in this, further work is needed to
      better understand what attributes and operations are needed, and
      how to integrate them in a baseline NS model.

   o  Additionally, we can also further study NS composition mechanisms,
      beyond the simple connect/disconnect mechanism in the present
      draft.

7.  IANA Considerations

   This document has no actions for IANA.

8.  Informative References

   [I-D.geng-coms-problem-statement]
              67, 4., Slawomir, S., Qiang, L., Matsushima, S., Galis,
              A., and L. Contreras, "Problem Statement of Supervised
              Heterogeneous Network Slicing", draft-geng-coms-problem-
              statement-00 (work in progress), September 2017.

   [I-D.ietf-i2rs-yang-network-topo]
              Clemm, A., Medved, J., Varga, R., Bahadur, N.,
              Ananthakrishnan, H., and X. Liu, "A Data Model for Network
              Topologies", draft-ietf-i2rs-yang-network-topo-17 (work in
              progress), October 2017.

   [I-D.qiang-coms-netslicing-information-model]
              Qiang, L., Galis, A., 67, 4., kiran.makhijani@huawei.com,
              k., Martinez-Julia, P., Flinck, H., and X. Foy,
              "Technology Independent Information Model for Network
              Slicing", draft-qiang-coms-netslicing-information-model-01
              (work in progress), October 2017.

   [NGMN_Network_Slicing]
              NGMN, "Description of Network Slicing Concept", 10 2016,
              <https://www.ngmn.org/uploads/
              media/161010_NGMN_Network_Slicing_framework_v1.0.8.pdf>.

Authors' Addresses







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   Xavier de Foy
   InterDigital Inc.
   1000 Sherbrooke West
   Montreal
   Canada

   Email: Xavier.Defoy@InterDigital.com


   Akbar Rahman
   InterDigital Inc.
   1000 Sherbrooke West
   Montreal
   Canada

   Email: Akbar.Rahman@InterDigital.com


   Alex Galis
   University College London

   Email: a.galis@ucl.ac.uk


   Kiran Makhijani
   Huawei Technologies
   2890 Central Expressway
   Santa Clara  CA 95050
   USA

   Email: kiran.makhijani@huawei.com


   Li Qiang
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095

   Email: qiangli3@huawei.com












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