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Versions: 00 01 02

Network Working Group                                            L. Geng
Internet-Draft                                              China Mobile
Intended status: Informational                                   J. Dong
Expires: December 4, 2017                                      S. Bryant
                                                            K. Makhijani
                                                     Huawei Technologies
                                                                A. Galis
                                               University College London
                                                               X. de Foy
                                                       InterDigital Inc.
                                                             S. Kuklinsk
                                                                  Orange
                                                            June 2, 2017


                      Network Slicing Architecture
                  draft-geng-netslices-architecture-01

Abstract

   This document defines the overall architecture of network slicing.
   Based on the general architecture, basic concepts of network slicing
   and examples of network slicing instances are introduced for
   clarification purposes.  Some architectural considerations about the
   data plane, control plane, management and orchestration of network
   slicing are described to give a general view of network slicing
   implementation principles.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 4, 2017.







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Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Demand for Network Slicing  . . . . . . . . . . . . . . . . .   7
     2.1.  Guaranteed Service Performance  . . . . . . . . . . . . .   7
     2.2.  End-to-end Customization  . . . . . . . . . . . . . . . .   8
     2.3.  Network Slicing as a Service  . . . . . . . . . . . . . .   8
   3.  Network Slicing Architecture  . . . . . . . . . . . . . . . .   8
     3.1.  Requirements  . . . . . . . . . . . . . . . . . . . . . .   8
     3.2.  High-Level Functional Components  . . . . . . . . . . . .   9
       3.2.1.  Service Component . . . . . . . . . . . . . . . . . .  11
       3.2.2.  Network Slicing Management and Orchestration  . . . .  11
       3.2.3.  Resource Component  . . . . . . . . . . . . . . . . .  14
     3.3.  Network Slicing Capabilities  . . . . . . . . . . . . . .  15
       3.3.1.  Reclusiveness . . . . . . . . . . . . . . . . . . . .  15
       3.3.2.  Protection  . . . . . . . . . . . . . . . . . . . . .  15
       3.3.3.  Elasticity  . . . . . . . . . . . . . . . . . . . . .  15
       3.3.4.  Extensibility . . . . . . . . . . . . . . . . . . . .  16
       3.3.5.  Safety  . . . . . . . . . . . . . . . . . . . . . . .  16
       3.3.6.  Isolation . . . . . . . . . . . . . . . . . . . . . .  16
     3.4.  Network Slices Capability Exposure  . . . . . . . . . . .  16
   4.  Data Plane of Network Slicing . . . . . . . . . . . . . . . .  17
     4.1.  Propagation of Guarantees . . . . . . . . . . . . . . . .  17
     4.2.  The Underlying Physical Layer . . . . . . . . . . . . . .  17
     4.3.  Hard vs Soft Slicing in the Data-plane  . . . . . . . . .  18
     4.4.  The Role of Deterministic Networking  . . . . . . . . . .  18
     4.5.  The Role of VPNs  . . . . . . . . . . . . . . . . . . . .  19
     4.6.  Dynamic Reprovisioning  . . . . . . . . . . . . . . . . .  19
     4.7.  Non-IP Data Plane . . . . . . . . . . . . . . . . . . . .  19
   5.  Control Plane of Network Slicing  . . . . . . . . . . . . . .  19
     5.1.  NS Infrastructure Control Plane . . . . . . . . . . . . .  20



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     5.2.  NS Infrastructure Control Operations and Protocols  . . .  20
     5.3.  Programmability of the NS Infrastructure Control Plane  .  21
     5.4.  Intra-Slice Control Plane . . . . . . . . . . . . . . . .  21
   6.  Management Plane of Network Slicing . . . . . . . . . . . . .  22
     6.1.  Network Slice Creation - Reservation / Release Messages
           Flow  . . . . . . . . . . . . . . . . . . . . . . . . . .  22
     6.2.  Self- Management Operations . . . . . . . . . . . . . . .  23
     6.3.  Programmability of the Management Plane . . . . . . . . .  24
     6.4.  Management plane slicing protocols  . . . . . . . . . . .  24
   7.  Service Functions and Mappings  . . . . . . . . . . . . . . .  24
   8.  OAM and Telemetry . . . . . . . . . . . . . . . . . . . . . .  24
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  25
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  25
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  25
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  25
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  25
     12.2.  Informative References . . . . . . . . . . . . . . . . .  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

1.  Introduction

   The Internet has always been designed to support a variety of
   services.  The emerging 5G market is expected to bring this diversity
   of services to a new level [NS_WP].  Typical examples of new
   bandwidth-hungry services enabled by 5G include high definition (HD)
   video, virtual reality (VR) and augmented reality (AR).  The high
   bandwidth requirement of these services is not particularly
   challenging thanks to the continuing advancing technologies.
   However, the guarantee of high bandwidth performance of these
   services based-on a spontaneous on-demand pattern is fairly
   challenging.  Moreover, providing high bandwidth with strict packet
   loss tolerances and high mobility is also difficult for the current
   networks which are commonly designed for best effort purposes.

   Given that most Internet protocols are designed to comply with a best
   effort, or enhanced best effort paradigm, it is inevitable that the
   network will suffer from performance degradation in case of
   congestion.  Recent work on deterministic networking (DetNet)
   [I-D.finn-detnet-architecture] aims to improve this situation by
   providing a ceiling on latency for a particular traffic flow, which
   significant improves packet error rate for specific DetNet services.
   This pioneering work gives a great example that new approaches are
   investigated to make the Internet aware of certain performance
   requirement other than the bandwidth.

   Taking a look at the network infrastructure, service provider used to
   build dedicated network and resources for services requiring
   guaranteed performance.  This is simply not cost-effective, neither



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   is it flexible.  The emergence of virtualization and VPN technologies
   make it possible to set up logically isolated computing and network
   instances from shared infrastructures.  This can be used dedicatedly
   by specific services for improved performances.  However, many
   questions are still to be answered as different technologies in
   various domains need to be combined to build network slices, which
   may require the separation of different resources and various types
   of performance guarantees.

1.1.  Requirements Language

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

1.2.  Terminology

   I.  Networking Servicing Terms

   Service - A piece of software that performs one or more functions and
   provides one or more APIs to applications or other services of the
   same or different layers to make use of said functions and returns
   one or more results.  Services can be combined with other services,
   or called in a certain serialized manner, to create a new service.

   Service Instance - An instance of an end-user service or a business
   service that is realized within or by a network slice.  Each service
   is represented by a service instance.  Services and service instances
   would be provided by the network operator or by third parties.

   Administrative domain - A collection of systems and networks operated
   by a single organization or administrative authority.  Infrastructure
   domain is an administrative domain that provides virtualized
   infrastructure resources such as compute, network, and storage, or a
   composition of those resources via a service abstraction to another
   Administrative Domain, and is responsible for the management and
   orchestration of those resources.

   II.  Network Resource Terms

   Resource - A physical or virtual (network, compute, storage)
   component available within a system.  Resources can be very simple or
   fine-grained (e.g., a port or a queue) or complex, comprised of
   multiple resources (e.g., a network device).

   Logical Resource - An independently manageable partition of a
   physical resource, which inherits the same characteristics as the




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   physical resource and whose capability is bound to the capability of
   the physical resource.

   Virtual Resource - An abstraction of a physical or logical resource,
   which may have different characteristics from that resource, and
   whose capability may not be bound to the capability of that resource.

   Network Function (NF) - A processing function in a network.  It
   includes but is not limited to network nodes functionality, e.g.
   session management, mobility management, switching, routing
   functions, which has defined functional behaviour and interfaces.
   Network functions can be implemented as a network node on a dedicated
   hardware or as a virtualized software functions.  Data, Control,
   Management, Orchestration planes functions are Network Functions.

   Virtual Network Function (VNF) - A network function whose functional
   software is decoupled from hardware.  One or more virtual machines
   running different software and processes on top of industry-standard
   high-volume servers, switches and storage, or cloud computing
   infrastructure, and capable of implementing network functions
   traditionally implemented via custom hardware appliances and middle-
   boxes (e.g. router, NAT, firewall, load balancer, etc.)

   Network Element - A network element is defined as a manageable
   logical entity uniting one or more network devices.  This allows
   distributed devices to be managed in a unified way using one
   management system.  It means also a facility or equipment used in the
   provision of a communication service.  Such term also includes
   features, functions, and capabilities that are provided by means of
   such facility or equipment, including subscriber numbers, databases,
   signalling systems, and information sufficient for billing and
   collection or used in the transmission, routing, or other provision
   of a telecommunications service.

   III.  Network Slicing Terms used in this draft

   Resource Slice - A grouping of physical or virtual (network, compute,
   storage) resources.  It inherits the characteristics of the resources
   which are also bound to the capability of the resource.  A resource
   slice could be one of the components of Network Slice, however on its
   own does not represent fully a Network Slice.

   Network Slice - A Network slice is a managed group of subsets of
   resources, network functions / network virtual functions at the data,
   control, management/orchestration planes and services at a given
   time.  Network slice is programmable and has the ability to expose
   its capabilities.  The behaviour of the network slice realized via
   network slice instance(s).



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   Network Slice Instance - An activated network slice.  It is created
   based on network template.  A set of managed run-time network
   functions, and resources to run these network functions, forming a
   complete instantiated logical network to meet certain network
   characteristics required by the service instance(s).  It provides the
   network characteristics that are required by a service instance.  A
   network slice instance may also be shared across multiple service
   instances provided by the network operator.  The network slice
   instance may be composed by none, one or more sub-network instances,
   which may be shared by another network slice instance.

   Network Slice Template - A complete description of the structure,
   configuration and the plans/work flows for how to instantiate and
   control the Network Slice Instance during its life cycle.

   Network Slice Type - Network slices are categorized into different
   types according to the abstraction of characteristics of the services
   they facilitate.  The methodology used for defining network slice
   types may be different for the network slice provider.  Some typical
   examples of network slice types according to 5G implementation
   include eMMB, mMTC and URLLC.  Network slice type may be used to map
   specific network resources, VPNs, QoS categories according to real
   implementation.  It is advised that mutual types should be defined
   according to existing main-stream service implementation scenarios.
   Extensions should be allowed for network slicing service provider to
   make according to new requirements.

   Network Slice Provider - A network slicing provider, typically a
   telecommunication service provider, is the owner or tenant of the
   network infrastructures from which network slices are created.  The
   network slicing provider takes the responsibilities of managing and
   orchestrating corresponding resources that the network slicing
   consists of.

   Network Slice Terminal - A terminal that is network-slice-aware,
   typically subscribed to the service which is hosted within a network
   slice instance.  A network slice terminal may be capable of
   subscribing to multiple network slice instance simultaneously.

   Network Slice Tenant - A network slice tenant is the user of specific
   NSIs, with which specific services can be provided to end customers.
   Network slice tenants can make requests of the creation of new
   network slice instances.  Certain level of management capability
   should be exposed to network slice tenant from network slice service
   provider.

   Network Slice Repository - A repository that in each domain consists
   of a list of active Network Slices with their identifiers and



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   description.  This description defines also the rules that have to be
   fulfilled in order to access a slice.  Network Slice Repository is
   updated by slice orchestrator.  In case of recursive slicing the
   Network Slice Repository keeps information about all slices that
   compose a higher level slice but such slice has its own identifier
   and descriptors.

   Slice Border Control - A functional entity that is used for users to
   slice attachment and in recursive slicing, in which an end-to-end
   slice is a horizontal combination of per domain slices.  It's role is
   to expose information about a slice to other slices in order to
   provide efficient slice connection (i.e. topology information
   exchange, etc.) and to perform necessary protocol translations.

   Slice Selection Function - A functional entity that is used by the
   end-users in order to attach to a slice.  It provides mechanisms
   related to slice advertisement, on request passes information related
   to slice attachment to the end-users and optionally authenticate
   users.  In case of lack of an active slice as described in user
   request it may provide slice matching and also trigger the creation
   of a slice on-demand.

2.  Demand for Network Slicing

   It is expected that a diversity of new services will emerge in both
   mobile/5G and fixed networks.[I-D.qin-netslices-use-cases] describes
   many of the differentiated services (e.g. smart home, industrial
   control, remote healthcare, Vehicle-to-Everything (V2X) etc.) and
   their relevance to the Network Slicing.  These use cases are typical
   examples of service verticals requiring features beyond connectivity
   such as uRLL, high-bandwidth, and isolation.

2.1.  Guaranteed Service Performance

   One of the most challenging requirements for future network is to
   provide guaranteed performance for varieties of new services whilst
   maintaining the economies of scale that accrue through resource
   sharing.  It has been foreseen that the requirements of different
   services would be diversified and complex.

   Network slicing can deal with these challenges by mapping the
   performance requirements to physically or logically dedicated
   resources.








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2.2.  End-to-end Customization

   Customization is another significant feature of future services.
   Many vertical industries are expected to offer customization
   capabilities as a service to both internal manufacturing processes
   and specific end users.  Meanwhile, these customized services need to
   be deployed with short time-to-market.  The network needs to adapt to
   this challenge since customers may frequently adjust and refine their
   customization requirements.

   There is ongoing work such as network orchestration, software defined
   networks and network function virtualization that aims to address
   this problem.  In principle, these new technologies share a common
   request for the network to provide the ability to provide agile
   resource allocation.

2.3.  Network Slicing as a Service

   It is anticipated that the operation of 5G and future networks will
   involve new business models.  Given that the network is more
   flexible, elastic, modularized and customized, the shared network
   infrastructure can be sliced and offered as a service to the
   customer.  For instance, dedicated, isolated, end-to-end network
   resources with a customized topology can be provided as a network
   slice service to the tenant of this network slice.The tenants are
   allowed to have a certain level of provisioning of their network
   slices.

3.  Network Slicing Architecture

   This section introduces the general system architecture of network
   slicing.

3.1.  Requirements

   To meet the diversified Quality of Experience (QoE) demands of
   different vertical industries, the gap analysis document has
   identified the following requirements:

   o  Req.1 Network Slicing Resource Specification

   o  Req.2 Cross-Network Segment; Cross-Domain Negotiation

   o  Req.3 Guaranteed Slice Performance and Isolation

   o  Req.4 Slice Discovery and Identification

   o  Req.5 NS Domain-Abstraction



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   o  Req.6 OAM Operations with Customized Granularity

   In the following sections, these requirements will be addressed and
   associated with different aspects of the Network Slicing
   architecture.

3.2.  High-Level Functional Components

   End-to-end network slice is a broad area and comprises of several
   functional components.  In the context of distribution of role and
   responsibilities, a network slice consists of the following
   components as shown in Figure 1.  It can be seen that two network
   slice instances are created from the shared network infrastructures.
   In principle, the network slicing subnets (NS Subnets) represent any
   general physical and logical network resources for demonstration
   purposes.  The two network slice instances created share the
   computing, connectivity and storage resources, whether they are in
   physical or virtual forms.

   It is fundamental to network slicing that slices may be created, the
   topology and/or its resources modified, and that the slices may be
   decommissioned in a timely manner with minimum work by the network
   slicing provider or the customer.  This is not however unique to
   network slicing, it is a goal of modern classical networks to be able
   to do this.

   The descriptions of functional components are introduced in the
   following sections.























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   +------------------------------------------------------------------+
   |                      Service Component                           |
   +------------------------------------------------------------------+
   +------------------------------------------------------------------+
   |         Network Slice Management and Orchestration               |
   |       +---------------+ +-----------+  +----------------+        |
   |       |    Template   | |    NS     |  |Life cycle Mngt.|        |
   |       |  Management   | |Repository.|  |and monitoring  |        |
   |       +---------------+ +-----------+  +----------------+        |
   |     +-------------++---------------++---------++----------+      |
   |     | E2E         || Domain        || NS      || Resource |      |
   |     |Orchestration|| Orchestration || Manager || Registrar|      |
   |     +-------------++---------------++---------++----------+      |
   +------------------------------------------------------------------+
   +------------------------------------------------------------------+
   |                      Resource Component                          |
   |    +---+         +---+             +---+      +---+              |
   |    |NE1+----+    |NE3+------+   +--+NE5+------+NE6|              |
   |    +---+    |    +-+-+      |   |  +-+-+      +---+              |
   |           +-+-+    |      +-+-+ |    |                           |
   |           |NE2+----+      |NE4+-+    |                           |
   |           +-+-+           +-+-+      |                           |
   |             |               |        |                           |
   |             +------------------------+                           |
   +------------------------------------------------------------------+
                                  |
                                  |
                                  \/
   +------------------------------------------------------------------+
   |              Created Network Slice Instance                      |
   | +--------------------------------------------------------------+ |
   | |  +-----------+      +-----------+   +-----------+    +-----+ | |
   | |  |NS-Subnet 1+----+ |NS-Subnet 3|   |NS-Subnet 6|----| SBC | | |
   | |  +-----------+ |    +-----------+   +-----------+    +-----+ | |
   | |                |                      |                      | |
   | |         +-----------+     |+-----------+                     | |
   | |         |NS-Subnet 2+-----| NS-Subnet 4|                     | |
   | |         +-----------+     +------------+   Network Slice     | |
   | |           |                      |          Instance 1       | |
   | |           +----------------------+                           | |
   | +--------------------------------------------------------------+ |
   | +--------------------------------------------------------------+ |
   | |                                             Network Slice    | |
   | |                                              Instance N      | |
   | +--------------------------------------------------------------+ |
   +------------------------------------------------------------------+

                  Figure 1: Network Slicing Architecture



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3.2.1.  Service Component

   A service represents an end-user's business logic.  It is realized
   within or by Network slice instance.  A service may demand a set of
   network resources and attributes in form of a network slice.  A
   service is either mapped to a network slice instance or an ordered
   chain of network slice instances.

3.2.2.  Network Slicing Management and Orchestration

   As seen in Figure 1, The management and orchestration layer of
   network slicing system consist of the following functional
   components.

   1.  NS Template Management

   2.NS Repository

   To provide mechanism that will allow the end-user selection and
   attachment to a slice instance or, if required, to multiple slice
   instances at the same time, a NS repository (or repositories) is
   needed, in which there are stored slices with the description of
   their properties and access rules.

   The service component should have an access to such repository in
   order to check if the required slice exists.  If such a slice doesn't
   exist a matching procedure should allow an attachment of the service
   to a slice which properties are the most similar ones to the
   requested slice (under certain policies agreement between network
   slice provider and tenant).  Optionally the service may trigger the
   deployment of a new slice.  During the attachment of the service
   component to a slice the slice data forwarding mechanisms are
   configured in way that will redirect a selected part of the end-user
   traffic to the slice.

   3.Lifecycle management and monitoring

   Network slicing enables the operator to create logically partitioned
   networks at a given time customized to provide optimized services for
   different market scenarios.  These scenarios demand diverse
   requirements in terms of service characteristics, required customized
   network and virtual network functionality (at the data, control,
   management planes), required network resources, performance,
   isolation, elasticity and QoS issues.  A network slice is created
   only with the necessary network functions and network resources at a
   given time.  They are gathered from a complete set of resources and
   network /virtual network functions and orchestrated for the
   particular services and purposes.



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   A network slice is a dynamic entity therefore its lifecycle has to be
   managed.  The network slice lifecycle management is (creation,
   update, deletion) is managed by the network slice orchestrator.  The
   slice orchestrator according to requests that can be send by the
   orchestrator operator, 3rd parties or even by the end-users creates a
   new slice instance that is based on slice template that is stored is
   slice template repository however it takes into account slice
   operator (owner) preferences (policies).

   4.E2E Orchestration

   This section describes E2E Slices Orchestration and its
   functionality.  Orchestration refers to the system functions in a
   domain that automate and autonomically co-ordination of network
   functions in slices autonomically coordinate the slices lifecycle and
   all the components that are part of the slice (i.e.  Service
   Instances, Network Slice Instances, Resources, Capabilities exposure)
   to ensure an optimized allocation of the necessary resources across
   the network.  The main functionality of E2E slice orchestration may
   include the following aspects.

   (1)  Coordinate a number of interrelated resources, often distributed
        across a number of subordinate domains, and to assure
        transactional integrity as part of the process.

   (2)  Autonomically control of slice life cycle management, including
        concatenation of slices in each segment of the infrastructure
        including the data pane, the control plane, and the management
        plane.

   (3)  Autonomically coordinate and trigger of slice elasticity and
        placement of logical resources in slices.

   (4)  Coordinates and (re)-configure logical resources in the slice by
        taking over the control of all the virtualized network functions
        assigned to the slice.

   It is the continuous process of allocating resources to satisfy
   contending demands in an optimal manner.  The idea of optimization
   would include at least prioritized SLA commitments , and factors such
   as customer endpoint location, geographic or topological proximity,
   delay, aggregate or fine-grained load, monetary cost, fate- sharing
   or affinity.  The word continuing incorporates recognition that the
   environment and the service demands constantly change over the course
   of time, so that orchestration is a continuous, multi-dimensional
   optimization feedback loop.  The E2E slice orchestration should have
   the following characteristics.




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   o  It protects the infrastructure from instabilities and side effects
      due to the presence of many slice components running in parallel.

   o  It ensures the proper triggering sequence of slice functionality
      and their stable operation.

   o  It defines conditions/constraints under which service components
      will be activated, taking into account operator service and
      network requirements (inclusive of optimize the use of the
      available network; compute resources and avoid situations that can
      lead to sub-par performance and even unstable and oscillatory
      behaviors.

            + ------------------------------------------------+
            |              E2E Slice Orchestration            |
            +-------------------------------------------------+
              |               |                           |
      +----------+       +-----------+                 +----------+
      | Network   |      | Network   |                 | Network  |
      | Slice 1   |      | Slice 2   |                 | Slice N  |
      |  NS Mngr  |------|  NS Mngr  |------  ...  --  |  NS Mngr |
      +-----------+      +-----------+                 +----------+
           |                    |                          |
      +-------------------------------------------------------------+
      |              Resources / Network Functions                  |
      +-------------------------------------------------------------+

                     Figure 2: E2E Slice Orchestration

   5.  Domain Orchestration

   Another value that the network slicing brings is fast, automated and
   dynamic deployment services in end-to-end manner, even in
   heterogeneous environment.  In order to achieve that goal the problem
   of providing a slice that spans multiple domains has to be solved.
   There two possible solutions.  The first one lies on appropriate
   allocation of resources in each domain (i.e. creation of the resource
   slice instance), their aggregation and using of a single orchestrator
   in order to deploy a slice.  Another possibility is to use per domain
   orchestrators with domain specific template and provide the chaining
   of domain slices in order to obtain the end-to-end slice.  In such a
   case the orchestration is hierarchical one, i.e. the domain
   orchestration is driven by a high level orchestrator that interacts
   with orchestrators of all domains that are involved in end-to-end
   slice instance creation.  The slice that is composed of multiple
   domain level slices requires specific mechanisms for inter-slice
   operations like topology information exchange and/or appropriate
   protocol conversion/adaptation.



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   The approach may lead to recursive slicing (or sub-slicing) in which
   higher level slice instances are composed of lower level ones.  The
   creation of end-to-end slice composed of several slices may require
   specific description of such slice and changes of functions of domain
   slices.  For example the traffic redirection can be implemented only
   in this domain slice which is an ingress slice.

   6.  NS Manager

   NS Manager mangement entity for a specific network slice instance. it
   manages all access permissions and all interaction between a Network
   Slice and external functions (i.e. other Network Slices,
   Orchestrators, etc).  Each NS Manager maps requirements from
   orchestrator into network resources and manages these resources of a
   specific network slice instance.

      Allow 3rd parties to access via APIs information regarding
      services provided by the slice (e.g. connectivity information,
      QoS, mobility, autonomicity, etc.)

      Allow dynamical customization of the network characteristics for
      different diverse use cases within the limits set of functions by
      the operator.  Network slice enables the operator to create
      networks customized to provide flexible solutions for different
      market scenarios, which have diverse requirements, with respect to
      the functionality, performance and resource separation.

      It includes a description of the structure (and contained
      components) and configuration of the slice instance.

   7.  Resource Registration

   Resource registration component manages the exposed capability of the
   network infrastructure.  Details description is TBD.

3.2.3.  Resource Component

   Resource component includes physical, logical and virtual resources
   (defined in Section 2).  An abstraction of resources is required in
   order to consistently map the requirements such as latency,
   reliability, band-width.  Resource component may need interfaces with
   elements in network slice functional component as well as NS manager
   for that purpose of discovering capabilities.








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3.3.  Network Slicing Capabilities

3.3.1.  Reclusiveness

   Recursion is a property of some functional blocks: a larger
   functional block can be created by aggregating a number of a smaller
   functional block and interconnecting them with a specific topology.
   As such one could summarize the concept of recursive network slice
   definition as the ability to build a new network slice out of
   existing network slice (s).  A certain resource or network function
   /virtual network function could scale recursively, meaning that a
   certain pattern could replace part of itself.  This leads to a more
   elastic network slice definition, where a network slice template,
   describing the functionality, can be filled by a specific pattern or
   implementation, depending on the required performance, required QoS
   or available infrastructure.  If a certain part of a network slice
   can be replaced by different patterns, this can offer some
   advantages:

   o  Each pattern might have its own capabilities in terms of
      performance.Depending on the required workload, a network function
      /virtual network function might be replaced by a pattern able to
      process at higher performance.  Similarly, a service or network
      function /virtual network function can be decomposed so it can be
      deployed on the available infrastructure.

   o  From an orchestrating point of view, above way of using recursive
      network slice templates, can be beneficial for the placement
      algorithm used by the orchestrator.  The success rate, solution
      quality and/or runtime of such an embedding algorithm benefits
      from information on both possible scaling or decomposition
      topologies and available infrastructure.

   o  Enabling methods for network slice template segmentation allowing
      a slicing hierarchy with parent - child relationships.

3.3.2.  Protection

   Protection refers to the related capability and mechanisms so that
   events within one network slice, such as congestion, do not have a
   negative impact on another slice.

3.3.3.  Elasticity

   Elasticity refers to the capability, mechanisms and triggers for the
   growth /shrinkage of network resources, and/or network and service
   functions in an Network Slice as function of service needs.




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3.3.4.  Extensibility

   Extensibility refers to the capability and ability to expand a
   network slice with additional functionality and/or characteristics,
   or through the modification of existing network function / virtual
   network function while minimizing impact to existing functions.

3.3.5.  Safety

   Safety refers to the conditions in within one network slice of being
   protected against different types and the consequences of failure,
   error harm or any other event, which could be considered non-
   desirable in an other network slice.

3.3.6.  Isolation

   Efficient slice creation is expected to guarantee the isolation and
   non interference between network slices in the Data /Control
   /Management planes as well as safety and security for multi-tenancy
   in slices.

3.4.  Network Slices Capability Exposure

   An important value of network slicing is the capability of a slice to
   be tightly coupled with services, i.e. the slice instance can be
   designed that way that it support a specific service or limited
   number of services only, but not all of them in the same slice.  The
   property means that not only the slice data plane operations are
   properly tuned, but also the control plane can be designed according
   to the requirements of slice specific services.  In general it is
   possible that a single slice instance may support a single service
   only, however it is more scalable to provide more than a single
   service per slice.  Such approach has important implications.  First
   of all in order to add services to a slice each slice should expose
   its functions to services/applications.  Moreover the service
   lifecycle management is different than slice lifecycle management.
   This is similar to the existing networks, however in opposite to them
   the deployment of a new service may lead to important reconfiguration
   of a slice to which the service is attached (the slice is
   programmable what means that we are going beyond the API approach -
   the services templates are melted with the slice template).  The goal
   is to have tightly coupled services with networks and providing joint
   optimization of networks and services at the level that is impossible
   to achieve in present, hardware based solutions.







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4.  Data Plane of Network Slicing

   In the network slicing architecture, the data plane in the edge and
   core of the network will likely be one or more of the standard IETF
   data planes: IPv4/IPv6, MPLS or Pseudo-wires (PW).  This section
   assumes that the IETF protocol stack exists as-is, and describes the
   performance consideration in different layers of the data plane.

4.1.  Propagation of Guarantees

   Guarantees of delay start at the physical layer and propagate up the
   stack layer by layer.  Any layer can add delay, and can take various
   steps to minimize the impact of delay on its layer, but no layer can
   reduce the delay introduced by a lower layer.

   Guarantees of loss and jitter can, by contrast be upheld or improved
   at any layer of the protocol stack, but usually at a cost of
   increased delay.  Where delay is a constrain as it is in some 5G
   applications the option of trading delay for better loss or jitter
   characteristics is not an option.  In these circumstances it is
   critical that the quality characteristics start at the physical layer
   and be maintained at each layer of the protocol stack.

4.2.  The Underlying Physical Layer

   A point to point dedicated physical channel provides the delay,
   jitter and loss characteristics limited only by the media itself.
   This does not fulfill the need for rapid reconfiguration of the
   network to provision new services.

   To address the need to provision a slice of the data-plane one
   approach that can be deployed is to time-slice access to the physical
   service.  Ignoring many of the classic TDM offering as being too
   slow, a number of technologies are available that might be applied
   including OTN and FlexE.  Whilst the provisioning of the channel
   provided by underlays such as FlexE and the interconnection of FlexE
   channels is within the scope of this architecture the operation of
   the underlay is outside its scope.

   The logical sub-division of a physical channel be that a single
   channel with the full bandwidth available or a channel multiplexed at
   the physical layer such as is provided by FlexE we will consider in
   the following section.








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4.3.  Hard vs Soft Slicing in the Data-plane

   Hard slicing refers to the provision of resources in such a way that
   they are dedicated to a specific NSI.  Data-plane resources are
   provided in the data-plane through the allocation of a lambda,
   through the allocation of a time domain multiplexed resource such as
   a FlexE channel or through a service such as an MPLS hard-pipe.  Note
   that although hard-pipes can be used to allocate dedicated, non-
   shared resources to an NSI, the using of allocation is bandwidth,
   which can result in more "lumpiness" in the physical channel that
   would not be present with a true physical layer multiplexing scheme.

   Soft slicing refers to the provision of resources in such a way that
   whilst the slices are separated such that they cannot statically
   interfere with each other (one cannot receive the others packets or
   observe or interfere with the other's storage), they can interact
   dynamically (one may find the other is sending a packet just when it
   wants to, or the other may be using CPU cycles just when the other
   needs to process some information), which means they may compete for
   some particular resource at some specific time.  Soft slicing is
   achieved through logically multiplexing the data-plane over a
   physical channel include various types of tunnel (IP or MPLS) or
   various types of pseudo-wire (again IP or MPLS).  Although the design
   of deterministic networking techniques helps, it is not possible to
   achieve the same degree of isolation with these techniques as it is
   possible to achieve with pure physical layer multiplexing techniques.
   However where such techniques provide sufficient isolation their use
   leads to a network design that may be deployed on existing equipment
   designs and which can make unused bandwidth available to best effort
   traffic.

4.4.  The Role of Deterministic Networking

   Deterministic networking is a technology under development in the
   IETF that aims to both minimize congestion loss and set an upper
   bound on per hop latency.  It allows a packet layer to emulate the
   behaviour of a fully partitioned underlay such might be provided
   through some physical layer multiplexing system such as FlexE.

   Deterministic networking works by policing the ingress rate of a flow
   to an agreed maximum and then scheduling the transmission time of
   each flow to reduce the "lumpiness" and hence the possible buildup of
   queues and hence congestion loss.

   Whilst deterministic networking is not as perfect as physical layer
   multiplexing in terms of latency minimization, because the scheduling
   is hop by hop and not end to end meaning that at each hop a packet
   has to wait for the transmission slot allocated to its flow, it has



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   the advantage that it is able to allocate slots not needed by the
   allocated traffic to best effort traffic.  This reallocation of the
   unused transmission slots to background traffic significantly
   improves the efficiency of the network by amortizing the cost between
   the scheduled high priority users and the best effort users.

4.5.  The Role of VPNs

   VPNs are considered candidate technologies for network slicing.  The
   existing VPN technologies mainly focus on the isolation of forwarding
   tables between different tenants and provide a virtual topology for
   the connectivity between different sites of a tenant.  The VPN layer
   and the underlying network resources are usually loosely coupled, and
   statistical multiplexing is adopted to improve network utilization.

   Although VPNs have been widely used to provide enterprise services in
   service provide networks, it is unclear that whether VPNs along with
   existing underlying tunnel technologies can meet the performance and
   isolation requirements of critical services in the vertical
   industries.

4.6.  Dynamic Reprovisioning

   A requirement of the network slicing system is that it can be
   dynamically and non-disruptively reprovisioned.  That is not an
   unusual requirement of a modern network.  However the frequency of
   reprovisioning with network slicing will be relatively high, such
   that it in many cases it is not possible to hide any disruption
   during a "quiet" time.

   Physical multiplexing methods such as FlexE have the ability to
   seamlessly reprovision multiplex slots.  At the network layer
   techniques such as make-before-break, segment routing, and loop-free-
   convergence can be used to provide uninterrupted operation during a
   topology change.

4.7.  Non-IP Data Plane

   Non-IP data plane in support of Information Centric Networking (ICN),
   some of the IoT services and other similar requirements will be added
   in a future version.

5.  Control Plane of Network Slicing

   There are two control plane systems that need to be considered.  The
   first is the control plane of the slicing infrastructure itself (NS
   Infrastructure Control Plane), the second is the control plane of an
   individual slice (Intra-Slice Control Plane).



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5.1.  NS Infrastructure Control Plane

   The NS infrastructure control plane receives the instruction of
   creating a network slice with particular requirements from the
   orchestration layer.  It then creates the network slice by allocating
   a set of network resources in the corresponding network
   infrastructure.  This set of network resources is associated with the
   network slice during this operation.

   The NS infrastructure control plane is also responsible, with the
   support of the orchestration layer, for dynamically adjusting the
   network according to slice change requests (e.g. from slice tenants),
   and to changes in network infrastructure.  As it is critical to meet
   the service requirements of a network slice independently from
   activity and changes occurred in other network slices or in
   infrastructure, appropriate service assurance mechanisms should be
   deployed in the network.  The control plane, with the support of the
   orchestration layer, MUST be able to react within a pre-determined
   (possibly system-specific) time to any network events, such as
   resource addition and failure.  The orchestration layer SHOULD be
   involved, directly or indirectly, to take reactive decisions, e.g. to
   re-route a flow, to ensure that other network slices are not
   affected.  Indirect involvement includes, for example, reactive
   programming by the orchestration layer to address foreseeable events
   or cases where connection to the orchestration layer is lost.

   The NS infrastructure control plane can be implemented as an
   extension of the Virtual Infrastructure Manager (VIM), in cases where
   the NFV-MANO architecture is used for the management and control
   architecture of the system.  Especially, the VNF Manager is
   considered part of the management plane and not control plane.  From
   technology standpoint, NS infrastructure control plane can be an
   extension of Cloud infrastructure technology (e.g.  OpenStack), which
   itself can integrate SDN technology for network control.  This
   logically centralized control can be supplemented or replaced with
   distributed control protocols, that can provide some benefits in
   scenarios which require fast reaction, robustness and efficient
   information distribution.  A hybrid architecture is anticipated,
   where distributed protocols complement and simplify a centralized
   control system.

5.2.  NS Infrastructure Control Operations and Protocols

   The following operations should be supported.  Different control
   protocols can be used to control different types of resources.
   Multiple control protocols can be supported simultaneously.





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   o  Setting up or tearing down network function instances within a
      slice.  Set, increase or decrease compute capacity of NFs.

      *  Control protocols can be based on openstack APIs and other
         Cloud infrastructure control protocols.

   o  Setting up, tearing down, increase or decrease capacity of
      connectivity between network function instances within a slice,
      e.g. as L2-L3 virtual network or software function chain.

      *  Control protocols can include NVO3 control protocol, SFC
         control protocol and NetConf.

   o  Reservation/release of traffic flows within a slice, possibly with
      associated QoS and routing requirements.

      *  Control protocols can include DETNET, MPLS-TE, etc.

      *  Interconnect slices or slice flows, including across domains

      *  Control protocols are TBD.

5.3.  Programmability of the NS Infrastructure Control Plane

   The NS Control Plane exposes a Northbound API, typically for use by
   the orchestration layer.  A higher-than-physical representation level
   of abstraction can be used, enabling the manipulation of a logical
   network, that is translated down to physical resource manipulation by
   the NS infrastructure control plane.  The level of this abstraction
   and of its associated logical network is TBD.  Programmability should
   include programming reactions to events, which reduces the dynamic
   involvement of the orchestration layer, and therefore reaction time
   to events.

5.4.  Intra-Slice Control Plane

   Intra-slice control plane maintains proper connectivity and
   networking characteristics within the slice.  A full range of
   existing control plane technologies needs to be permissible.  Intra-
   slice control plane technologies can include existing IGP protocols
   (such as IS-IS or OSPF), BGP, overlay control (such as NVO3 or SFC).
   Some slices may be controlled by their own SDN controllers.  Intra-
   slice control plane can span across multiple domains (since NS
   infrastructure control deals with slice interconnection).







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6.  Management Plane of Network Slicing

   It is expected that the management and orchestration layer would use
   state of the art management technologies to support short time-to-
   market, and help the operators to build an open ecosystem for new
   services in vertical industries.  In multi-tenant environment the
   slice tenants can trigger the creation of slice instances for them by
   interacting with the E2E Orchestrator.  After the creation of the
   slice the slice tenant is able to monitor slice KPIs (performance,
   faults) and send slice reconfiguration requests to E2E Orchestrator.

   The basic functional architecture of management and orchestration
   layer of network slicing system has been discussed in section 3.
   This section further introduces some essential characteristics.

6.1.  Network Slice Creation - Reservation / Release Messages Flow

   The establishment of Network slices is both business-driven (i.e.
   slices are in support for different types and service characteristics
   and business cases) and technology-driven as network slice is a
   grouping of physical or virtual resources (network, compute, storage)
   and a grouping network functions and virtual network functions (at
   the data, control and management planes) which can act as a sub
   network at a given time.  A network slice can accommodate service
   components and network functions (physical or virtual) in all network
   segments: access, core and edge / enterprise networks.

   The management plane creates the grouping of network resources
   (physical, virtual or a combination thereof), it connects with the
   physical and virtual network and service functions and it
   instantiates all of the network and service functions assigned to the
   slice.

   Once a network slice is created, the slice control plane takes over
   the control, slice operations and governing of all the network
   resources, network functions, and service functions assigned to the
   slice.  It (re-) configures them as appropriate and as per elasticity
   needs, in order to provide an end-to-end service.  In particular,
   ingress routers are configured so that appropriate traffic is bound
   to the relevant slice.  Identification means for the traffic may be
   simple (relying on a subset of the transport coordinate, DSCP/traffic
   class, or flow label), or identification may be a more sophisticated
   one.  Also, the traffic capacity that is specified for a slice can be
   changed dynamically, based on some events (e.g. triggered by a
   service request).  The slice control plane is responsible for
   instructing the involved elements to guarantee such needs.





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    Inter Network Slice  Slice Element      Element           Network
      Orchestrator       Manager            Manager           Function
            |                 |               |                |
            |   Discovery -   |  Discovery -  |   Discovery    |
            |   -Response     |  Response     |   Response     |
            |   <------------>|<------------->|<-------------> |
            |                 |               |                |
            |                 |               |                |
            |      Request    |               |                |
            |     Net Slice   |               |                |
            |---------------->|   Request     |                |
            |                 |  Net Sice     |                |
            |                 |----------->   |  Request       |
            |                 |               |  Net Slice     |
            |                 |               |------------>   |
            |                 |Confirm-Waiting|                |
            |                 |<--------------|                |
            |                 |               |  Negotiation   |
            |                 |               |(Single/Multiple|
            |                 |               |         Rounds)|
            |                 |               |<-------------> |
            |Confirm-Waiting  |               |                |
            |<----------------|               |                |
            |                 | Negotiation   |                |
            |                 |Single/Multiple|                |
            |                 | Rounds        |                |
            |     Negotiation | <-----------> |                |
            |Single/Multiple  |               |                |
            |  Rounds         |               |                |
            | <-------------> |               |                |

        Figure 3: Network Slice Reservation / Release Messages Flow

6.2.  Self- Management Operations

   Self-management operations are focused on self-optimization and self-
   healing of network slice instances (including intra-slice functions
   management), network slice instance services and resources that are
   used for all slice instances.  All these operations are combined with
   efficient and economical monitoring and reconfigurations at
   appropriate level.  In order to make the management scalable and
   environment aware the management architecture is composed of many
   functional entities that follows the feedback loop management
   paradigm (aka autonomic management).  The self-management functions
   may realize different goals and have to be coordinated according to
   slice instance and infrastructure operator policies.  The self-
   management deals with dynamic (1) allocation of resources to slice
   instances in a economical way that provides required slice instances



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   performance, (2) self-optimization and self-healing of slice
   instances during their deployment (lifecycle management) and
   operations (3) self-optimization and self-healing of services of each
   slice instance.  Their lifecycle, that is typically different than
   slice instance lifecycle should also be managed in the autonomous
   way.  Despite the self-managed functions may have different goals and
   involved entities the slice instance self-management should be
   coordinated with self-management of their services and self-
   management of resources (inter-slice operations) should be aligned
   with in-slice self-management operations.  In the implementation the
   self-management functionality is split between NS manager (that is a
   part of slice template) and slice orchestrator in case of slice
   management and between service specific management and NS manager in
   case of services that use a specific slice.

6.3.  Programmability of the Management Plane

   The Management Plane is composed of multiple functional entities and
   is responsible for resource, slice instance and slice service
   management.  In case of slice instances and services their management
   comes as a part of appropriate slice or service template
   respectively.  That way slice or service related management functions
   are instantiated for each slice and/or service.  The Management Plane
   may expose a set of APIs which can be used by additional management
   services that are added independently on service or slice instance
   lifecycle.  Using these APIs and allocation additional resource the
   slice or service operator can add advanced and new management
   functions.  That way the Management Plane programmability is
   provided.

6.4.  Management plane slicing protocols

   At this stage it is too early do define protocols (IMHO).  We have to
   define the management architecture first with functional entities and
   reference points/interfaces.  Having them we could define which
   protocol(s) we want to use for each of them.  Maybe we can mention
   some protocols but generally they should be a part of separate
   specification.

7.  Service Functions and Mappings

8.  OAM and Telemetry

   OAM and telemetry to instrument the system need to be provided for
   each NSI so that the NSI provider can monitor the health of the NSI
   and so that the NSI owner can independently verify the health of
   their NSI.




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   Running OAM on the NSI from the perspective of its owner can be
   undertaken by the owner using the native tools for the NSI network
   type.  For example if the NSI is IP, tools like ICMP [RFC792], ICMPv6
   [RFC4443], or IPFIX [RFC7011] can be used.  Similarly the native OAM
   tools for MPLS and Ethernet can be used.  If the NSI provides a
   partial emulation of the network type that limits the ability to
   operate such native instrumentation tools, then this needs to be made
   clear to the NSI owner.

   Similarly running OAM on the underlay will also use the native tools
   for the network type providing the underlay.  Care must be taken that
   any OAM run by the NS provider does not impinge on the operation of
   the NSI, and SHOULD be undetectable in the NSI.

   Telemetry will need to be provided to both the NS provider and the
   NSI owner.  Telemetry of the underlay will use the NS providers pub-
   sub system of choice.

   Telemetry of the NSI may be provided purely by the NSI owner
   installing a telemetry collection system.  However significant
   efficiencies may be realised by if the NS provider exports relevant
   telemetry to the NSI owner's pub-sub system.  Where this is done,
   consideration must be given to the security of the measurement and
   export system so to no information is leaked between NSIs.

9.  IANA Considerations

   This document makes no request of IANA.

10.  Security Considerations

   Each layer of the system has its own security requirements.

11.  Acknowledgements

12.  References

12.1.  Normative References

   [I-D.finn-detnet-architecture]
              Finn, N. and P. Thubert, "Deterministic Networking
              Architecture", draft-finn-detnet-architecture-08 (work in
              progress), August 2016.








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   [I-D.qin-netslices-use-cases]
              Qin, J., kiran.makhijani@huawei.com, k., Dong, J., Qiang,
              L., and S. Peng, "Network Slicing Use Cases: Network
              Customization for Different Services", draft-qin-
              netslices-use-cases-00 (work in progress), March 2017.

12.2.  Informative References

   [NS_WP]    China Mobile Communication Corporation, Huawei
              Technologies Co. Deutsche Telekom AG,Volkswagen, "5G
              Service-Guaranteed Network Slicing White Paper", 2016,
              <http://labs.chinamobile.com/
              pdf/5GService-GuaranteedNetworkSlicingWhitePaper.pdf>.

Authors' Addresses

   Liang Geng
   China Mobile
   Beijing
   China

   Email: gengliang@chinamobile.com


   Jie Dong
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing   100095

   Email: jie.dong@huawei.com


   Stewart Bryant
   Huawei Technologies
   U.K.

   Email: stewart.bryant@gmail.com


   Kiran Makhijani
   Huawei Technologies
   2890 Central Expressway
   Santa Clara  CA 95050

   Email: kiran.makhijani@huawei.com






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   Alex Galis
   University College London
   London
   U.K.

   Email: a.galis@ucl.ac.uk


   Xavier de Foy
   InterDigital Inc.
   1000 Sherbrooke West
   Montreal
   Canada

   Email: Xavier.Defoy@InterDigital.com


   Slawomir Kuklinski
   Orange

   Email: slawomir.kuklinski@gmail.com






























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