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Versions: (draft-qin-netslices-use-cases) 00 01 02

none                                                        K. Makhijani
Internet-Draft                                                    J. Qin
Intended status: Informational                              R. Ravindran
Expires: December 3, 2017                            Huawei Technologies
                                                                 L. Geng
                                                            China Mobile
                                                                L. Qiang
                                                                 S. Peng
                                                     Huawei Technologies
                                                               X. de Foy
                                                               A. Rahman
                                                       InterDigital Inc.
                                                                A. Galis
                                               University College London
                                                            June 1, 2017

  Network Slicing Use Cases: Network Customization and Differentiated


   Network Slicing is meant to enable creating (end-to-end) partitioned
   network infrastructure which may include the user equipment, access/
   core transport networks, edge and central data center resources to
   provide differentiated connectivity behaviors to fulfill the
   requirements of distinct services, applications and customers.  In
   this context, connectivity is not restricted to differentiated
   forwarding capabilities but it covers also advanced service functions
   that will be invoked when transferring data within a given domain.

   The purpose of this document is to focus on use cases that benefit
   from the usefulness of network slicing.

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

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   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 3, 2017.

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  A Generalized Network Slice as a Service  . . . . . . . . . .   6
     3.1.  Resource Centric Service Concept  . . . . . . . . . . . .   6
     3.2.  Strict Resource Demand  . . . . . . . . . . . . . . . . .   7
     3.3.  Network Customization . . . . . . . . . . . . . . . . . .   7
     3.4.  NSaaS of Different Granularities  . . . . . . . . . . . .   7
     3.5.  Challenges in NSaaS . . . . . . . . . . . . . . . . . . .   8
   4.  Network Slicing in 3GPP Mobile Network  . . . . . . . . . . .   8
     4.1.  Network Slices in 3GPP Systems  . . . . . . . . . . . . .   8
     4.2.  Challenges  . . . . . . . . . . . . . . . . . . . . . . .   9
     4.3.  Creating 3GPP Network Slices  . . . . . . . . . . . . . .   9
     4.4.  Managing 3GPP Network Slices  . . . . . . . . . . . . . .  10
     4.5.  Operating 3GPP Network Slices . . . . . . . . . . . . . .  12
   5.  Role of NFV in Network slicing  . . . . . . . . . . . . . . .  13
     5.1.  Virtualized Customer Premise Equipment  . . . . . . . . .  13
       5.1.1.  Traditional Customer premise equipments(CPEs) . . . .  13
       5.1.2.  Trends in CPE infrastructure  . . . . . . . . . . . .  14
       5.1.3.  vCPE as a network slice . . . . . . . . . . . . . . .  15
   6.  Services with Resource Assurance  . . . . . . . . . . . . . .  17
     6.1.  Enhanced Broadband  . . . . . . . . . . . . . . . . . . .  17
       6.1.1.  Media delivery networks . . . . . . . . . . . . . . .  17
       6.1.2.  Enhanced Media Streaming Description  . . . . . . . .  17
       6.1.3.  eMBB Type Slices  . . . . . . . . . . . . . . . . . .  18

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       6.1.4.  Required Characteristics  . . . . . . . . . . . . . .  19
     6.2.  Massive machine to machine communication  . . . . . . . .  21
       6.2.1.  Wireless Sensor Networks  . . . . . . . . . . . . . .  21
       6.2.2.  Massive Internet of Things Description  . . . . . . .  22
       6.2.3.  mMTC Type Slices  . . . . . . . . . . . . . . . . . .  23
       6.2.4.  Required Characteristics  . . . . . . . . . . . . . .  24
     6.3.  Ultra-reliable low latency communication  . . . . . . . .  24
       6.3.1.  Brief introduction  . . . . . . . . . . . . . . . . .  24
       6.3.2.  Challenges  . . . . . . . . . . . . . . . . . . . . .  24
       6.3.3.  New service verticals . . . . . . . . . . . . . . . .  24
       6.3.4.  Required Characteristics  . . . . . . . . . . . . . .  26
     6.4.  Critical Communications . . . . . . . . . . . . . . . . .  28
       6.4.1.  Public Safety Infrastructure  . . . . . . . . . . . .  29
       6.4.2.  Enhanced Critical Service Type Slices . . . . . . . .  30
   7.  Network Infrastructure for new technologies . . . . . . . . .  31
     7.1.  ICN as a Network Slice  . . . . . . . . . . . . . . . . .  32
       7.1.1.  Information Centric Networks Description  . . . . . .  32
       7.1.2.  ICN Type Slices Asks  . . . . . . . . . . . . . . . .  33
       7.1.3.  Required Characteristics  . . . . . . . . . . . . . .  33
     7.2.  Network Slices in Communication Endpoints . . . . . . . .  34
       7.2.1.  Connected Vehicle . . . . . . . . . . . . . . . . . .  34
       7.2.2.  Sliced Terminal . . . . . . . . . . . . . . . . . . .  35
       7.2.3.  Required Characteristics  . . . . . . . . . . . . . .  35
   8.  Overall Use case Analysis . . . . . . . . . . . . . . . . . .  35
     8.1.  Requirements Reference  . . . . . . . . . . . . . . . . .  35
     8.2.  Mapping Common characteristics to Requirements  . . . . .  36
       8.2.1.  Req.1 Network Slicing Resource Specification  . . . .  36
       8.2.2.  Req.2 Cross-Network Segment & Cross-Domain
               Negotiation . . . . . . . . . . . . . . . . . . . . .  36
       8.2.3.  Req.3 Guaranteed Slice Performance and Isolation  . .  37
       8.2.4.  Req.4 Slice Identification  . . . . . . . . . . . . .  37
       8.2.5.  Req.5 NS Domain-Abstraction . . . . . . . . . . . . .  38
       8.2.6.  Req.6 OAM Operations with Customized Granularity  . .  38
     8.3.  Mapping Common Characteristics to Requirements  . . . . .  38
     8.4.  Other Challenges and Considerations . . . . . . . . . . .  40
   9.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . .  40
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  41
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  41
   12. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  41
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  41
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  41
     13.2.  Informative References . . . . . . . . . . . . . . . . .  42
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  44

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1.  Introduction

   Network Slicing enables the creation of (end-to-end) partitioned
   network infrastructure which may include the user equipment, access/
   core transport networks, edge and central data center resources to
   provide differentiated connectivity behaviors to fulfill the
   requirements of distinct services, applications and customers.  In
   this context, connectivity is not restricted to differentiated
   forwarding capabilities but it also spans service, management and
   control plane support offered to a slice instance.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119.

1.2.  Terminology

   Please refer to [ns-architecture] for related terminologies and

   Additionally, the following terms are used -

   o  V2X (Vehicle-to-everything): Is a communication of information
      from a vehicle to any other entity that may be a another vehicle,
      road-side network element or application end point.

   o  ITS (Intelligent Transportation Systems): Considered as an aspect
      of how using Internet of Things resource like road sensors can
      creates a smart transport network.  The network offers services
      related to transport and traffic management systems through flow
      of information between road-side sensors, vehicles, smart devices
      and humans.

   o  Over-the-top (OTT): A service, e.g., content delivery using a CDN
      or a social networking service, operated by a different service
      providers to which the users of the NSP service are attached to,
      and to whom it serves as a communication (or bit pipe) provider

   o  Industry vertical: A collection of services or tools specific to
      an industry, trade or market sector. also, referred to as Service
      Verticals in this document.

   o  TETRA: Terrestrial trunked radio is a digital trunked mobile radio
      standard to meet needs of public safety, transportation and
      utilities like organizations.

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   o  SLA: Service Level Agreement - A contract between a service
      provider and an end user that stipulates a specified level of
      service, support option, a guaranteed level of system performance
      as relates to downtime or uptime.

2.  Scope

   To maximize resource utilization and minimize infrastructure cost,
   services will need to operate over a shared network infrastructure,
   as against the traditional monolithic model operated either as
   dedicated network or as an overlay.  Service operators can utilize or
   benefit from Network Slicing through multi-tenancy, enabling
   different customized network infrastructures for different group of
   services across different network segments and operating them

   In this document, multi-domain refers to combination of different
   kinds of connection-technology network domains.  For example, it may
   be a RAN, DSL etc in access, mobile core network, Internet Service
   Provider (ISP) or different domains in transport networks such as
   carrier ethernet, optical, MPLS, TE-tunnel etc.  Often, different
   technology domains are under the same administrator's control as but
   may also require coordination across different administrations.

   Although 5G will drive NS based deployments, the document also covers
   generalized scenarios that can be applied to existing

   The remaining document is organized as below:

   o  In Section 3, Network Slice as a Service(NSaaS) delivery model is

   o  In Section 4, 3GPP architecture for 5G is discussed as a use case
      so that any requirements arising from current 5G based
      architecture are taken into consideration during slicing
      activities in IETF.

   o  Use cases are discussed from 2 perspectives

      a  Existing scenarios: Several already deployed or existing
         examples that would further benefit when deployed through
         Network Slice paradigm are discussed in Section 5.

      b  Differentiated service scenarios: that must absolutely meet
         strict resource requirements, as if they use a dedicated
         infrastructure.  The example use cases are categorized in
         Section 6.

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   o  End-to-end slicing requires awareness in a terminal to select a
      specific or many slices.  This is discussed in Section 7.2.

   o  In Section 8, the use case requirements are summarized and mapped
      to the [I-D.qiang-netslices-gap-analysis].

3.  A Generalized Network Slice as a Service

   Network slicing instances share a common infrastructure, which
   provide flexible design of specific network functions, customized to
   support differentiated performance requirements of vertical industry,
   logical or physical system isolation and certain OAM tools.

   Traditionally, vertical industries run their services in a shared
   network environment upon which infrastructure owner and service
   provider offers standalone network capabilities including
   connections, storage and etc.  Network slicing shall support the
   requirements of a network slicing tenant to be met individually.
   Hence it is anticipated that this type of new business model where
   network slice instances are leased to industry verticals as a service
   (i.e.  Network Slcing as a Service, NSaaS) may become a norm in the
   near future).

3.1.  Resource Centric Service Concept

   Network services specify a set of resource requirements to offer
   desired Quality of Experience (QoE) to it consumers, using features
   offered by the control and forwarding plane Traditional service
   guarantees are associated with resource attributes such as
   throughput, packet loss, latency, network bandwidth/burst or other
   bit rates and security.  In addition, redundancy and reliability are
   provided by the infrastructure to improve over all QoE.  More
   recently, newer concepts such as edge computing allows opportunistic
   placement of services to meet diverse requirments of low latency and/
   or high bandwidth applications.

   Clearly the description of service delivery is more diverse than
   before and demands higher degree of engineering and agility.  The
   motivation behind Network slicing paradigm is to enable new service
   deployments without having to build new network infrastructures or
   causing disruptions to other already deployed services in the
   network.  In this regard, there are two primary characteristics NS
   should satisfy, a) Strict demand for network resource, b) Network

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3.2.  Strict Resource Demand

   Several services are sensitive to response times and/or amount of
   bandwidth, e.g. realtime interactive multimedia, high bandwidth video
   feed or remote access to an enterprise network.  Failure to meet
   these criteria leads to service degradation.  Moreover, new industry
   verticals are evolving due to technological advancements in sensors,
   IoT, robotics and multi-media, along with new type of network
   interactions (both human-human or human-machine).  These impose even
   stricter resource and connectivity requirements.  The challenge lies
   in utilizing common network infrastructure and judiciously allocating
   available infrastructure resources.

3.3.  Network Customization

   Network slicing requires ability to customize.  Customization gives
   control to the operator of a slice to create, provision and change
   network resources to suit their service demands.  Customization
   enables decomposition of resources from an underlying network
   infrastructure and logically aggregate them as part of a slice.
   These customizations also include placement and logical connection of
   the network functions based on the service requirements.

3.4.  NSaaS of Different Granularities

   In order to meet various requirements from the network slice tenant,
   NSaaS should be be provided with different granularities.  Some
   typical examples of granularities are as follows.

   o  Network Segments - Network slice instances of different network
      segment, i.e.  radio access network, transport network and core

   o  SLA requirements - Network slice instances of different SLA
      requirements, i.e. low-latency network, legacy best-effort network
      and network with guaranteed-bandwidth.

   o  Vertical applications - Network slice instances of different
      industry verticals. i.e. manufacturing site, V2X, industrial IoT
      and smart city.

   o  Access technologies - Network slice instances of different
      generations of cellular and fixed network technologies, i.e. 4G,
      enhanced Mobile Broadband(eMBB), Ultra-Reliable and Low Latency
      Communication(URLLC), WiFi, Passive Optical Network (PON) and DSL.

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   o  OTT services - Network slice instances of different applications
      provided by OTT, i.e. messaging, payment, video streaming and

   During the realization of network slicing, it is also very important
   that sub-instance of a more general one can be provided with a finer
   granularity.  In practice, it is up to the provider to decide the
   granularity to lease the network slice instances.

   Editor's note: please revisit definitions for consistency.

3.5.  Challenges in NSaaS

   The flexibility and customization of different network slicing
   granularity introduce many challenges, especially in terms of network
   management and orchestration.  As a network slice provider (provider
   of end-to-end slice orchestration), it is essential to have a
   comprehensive understanding of the network capability.  This requires
   that network connectivity and resources can be exposed to the network
   slice tenants - the differentiated services offerers.  Accordingly,
   network slice provider is able to orchestrate specific instances
   based on these exposed capabilities.

4.  Network Slicing in 3GPP Mobile Network

   Network Slicing is a core feature of the currently under development
   3GPP 5G phase 1 mobile system, because it makes it possible for
   different vertical applications, such as IoT and broadband
   applications, to be deployed over a common infrastructure.  More
   details can be found in [TS_3GPP.23.501], [TS_3GPP.23.502],
   [TR_3GPP.38.801], [TR_3GPP.33.899] and [TS_3GPP.28.500].

4.1.  Network Slices in 3GPP Systems

   In 3GPP systems a network slice is a complete logical network which
   provides telecommunication services and network capabilities.
   Distinct Radio Access Network (RAN) network slices and core network
   slices will interwork with each other to provide mobile connectivity.
   A device may access multiple network slices simultaneously through a
   single RAN.

   3GPP defines slice IDs (named (S-)NSSAI in the standard) composed of
   a Slice Service Type (SST) and optionally a Slice Differentiator
   (SD).  SST refers to an expected network behavior in terms of
   features and services (e.g. specialized for broadband or massive
   IoT), while SD helps distinguishing among several network slice

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   Figure 1 describes the general layout of Network Slicing in mobile
   networks.  A core network slice is composed, on the control plane
   side, of a Session Management Function (SMF), which manages PDU
   sessions, and, on the user plane side, of a User Plane Function (UPF)
   and possibly other functions.  It is interconnected with a RAN Slice
   to complete the user plane.  Some functions on the control plane are
   common and shared between multiple RAN and core network slices.  A
   primary example of such a shared function is the Access and Mobility
   management Function (AMF).

              Common Functions   Core Network Slice Instance
             |   +--------+    |     +--------+      |
             |   | Control|    |     | Control|      |
        +--------+ Plane  +----------+ Plane  |      |
        |    |   | AMF... |    |     | SMF... |      |
    +---+--+ |   +--------+    |     +----+---+      |
    |Device| +-----------------+          |          |
    +---+--+ |   +--------+    |   +------+-----+    |
        |    |   |        |    |   | User Plane |    | +---------------+
        +--------+  RAN   +--------+ Functions  +------+Data Network or|
             |   |        |    |   | UPF...     |    | | The Internet  |
             |   +--------+    |   +------------+    | +---------------+
             RAN Slice Instance

                       Figure 1: 3GPP Network Slices

4.2.  Challenges

   A core challenge here is to identify or develop a set of technologies
   suitable to implement the infrastructure over which 3GPP Network
   Slicing will be built, without requiring major rework of the 3GPP
   specifications.  Among the specific challenges that an IETF NS
   framework will need to address, it will need to support sharing
   network functions between several slices, building slices recursively
   from smaller slices, implementing roaming across different domains,
   etc.  The following subsections describe creation, management and
   operation of 3GPP network slices as currently planned in the
   specifications, in order to better understand those challenges.

4.3.  Creating 3GPP Network Slices

   To create a network slice instance, mobile network operators will
   start by describing it by assembling together "Network Slice
   Subnets", which are smaller components included in a RAN or core

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   network slice.  Network slice subnets include NFs and reserved
   network resources, in term of KPIs such as minimum and maximum
   throughput, delay, packet loss, etc.  Network slice subnets can be
   shared between several network slices.  Both network slices and their
   subnets are described by the operator through the OSS/BSS management
   system.  The OSS/BSS translates this input from the operator into
   descriptors that are sent to an orchestrator.  The orchestrator,
   through the rest of the NFV-MANO system, configures compute and
   network elements to create network slice subnets and compose them as
   a network slice.  Beyond creation, RAN or core network slice
   activation is orchestrated as the activation of individual subnets,
   possibly in a given order.

   Network slices are isolated from each other to avoid control plane
   congestion on one slice (e.g. using one SMF in slice dedicated for
   broadband applications) to affect the control plane of other slices
   (e.g. to affect potentially critical IoT applications).  Since some
   common core network functions (AMF, PCF, UDM, etc.) are shared
   between multiple dedicated core network slices, the interaction
   between shared NFs and NFs in dedicated network slices should be
   isolated from each other as well.

   Network slices creation will support different combinations of "n"
   network services, "m" client devices and "p" interconnections with
   external (sliced or non-sliced) networks and services.  In 3GPP, RAN
   and core network slices are typically dedicated to a certain type of
   network services such as broadband or IoT, but may serve one or more
   network services of this type.  Additionally, in some mobile
   networks, parts of the core network may not be implemented over a
   slice, while others are (e.g.  SMF could be in a slice, while common
   functions are not).  While this can lead to a sub-optimal isolation
   between slices, this effect can be partially compensated by over-
   provisioning non-sliced sections of the network.

4.4.  Managing 3GPP Network Slices

   Mobile network operators can modify the configuration of a RAN or
   core network slices, while it is in use.  Example of such operations

   o  Increase or decrease compute capacity of NFs

   o  Increase or decrease network capacity

   o  Update the configuration of NFs

   o  Add, replace or remove a NFs

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   o  Add, replace or remove a Network Slice Subnet

   Some operations affecting a shared slice may not be possible without
   affecting other network slices, and in this case may be replaced by
   other operations: for example, instead of changing the configuration
   of a shared AMF to accommodate the needs of a SMF, another network
   slice subnet with an AMF may be created, and replace the original
   AMF's slice for this SMF.  The management system monitors performance
   of individual network slice components and coalesce performance data
   and events for the whole RAN or core network slice.  This includes
   user and control traffic load data, QoS/SLA data, e.g. indicating
   whether services were provided at expected QoS/SLA level.  The
   management system uses this information for example to decide to
   scale up or down NFs.  Performance data and events from a shared
   network slice component will be attributed by the 3GPP management
   system to one of the RAN or core network slices that contain or
   interact with this shared component.  To support roaming, mobile
   network operators will need to configure the interconnection between
   network slices on the home network and network slices on the visited
   network.  On the visited side, the operator ensures that the proper
   network slice is selected for a roaming device.  User traffic will
   flow through the visited network slice either directly to an external
   data network, or through the interconnected home network slice (both
   cases will need to be supported).  From the end user perspective only
   the performance of the whole (visited + home) network slice is
   important.  Mobile network operators may expose limited 3GPP network
   slice management to third party communication service providers
   (CSP), who may in turn consume this service or provide it to their
   own customers, as a form of "Slice as a Service" described
   in Section 3.  Using this interface, a CSP can request the creation
   of a network slice using specifications of NFs, isolation, security,
   performance requirements (such as traffic demand requirements for the
   coverage areas, QoS for service).  When an operator exposes
   management data (e.g. fault management data, performance data) about
   a network slice shared by multiple customers of a CSP, exposed
   management data of each customer can be isolated from each other.

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                                              Limited NS |        |
                   Limited NS                 Instance   |Customer|
        +-------+  Instance   +-------------+ Management |        |
        |Mobile |  Management |Communication+<-----------+--------+
        |Network+<------------+Service      |
        |       |             |Provider     +<-----------+--------+
        +-------+             +-------------+ Limited NS |        |
                                              Instance   |Customer|
                                              Management |        |

         Figure 2: 3GPP Limited Network Slice Management Exposure

4.5.  Operating 3GPP Network Slices

   Slice selection occurs in 2 phases: first, when initially registering
   with the network, the device lists the slice IDs it wishes support
   for.  This list could be part of the configuration of the device.
   The network uses it, among other information like device
   capabilities, subscription information and local operator policies,
   to pre-select one or more RAN slices and core network slices.  In
   this process, a set of 5G Common Control Plane Functions (CCNF) are
   selected to process future requests from the device.  No resource
   reservation occurs at this stage.  Later on, a particular application
   is started on the device.  Using a slice ID associated with the
   application, the device requests from the network the establishment
   of flows for this application.  For example, this slice ID can be
   associated to the application by the application service provider.
   This slice ID is used by the network to select the actual RAN slice
   and core network slice that will host user and control plane flows
   and network functions.  In the user plane, network resource
   reservation (in term of KPIs such as maximum throughput, delay, etc.)
   is applied at the individual application flow level (e.g. at the PDU
   Session level in 3GPP terms).  In the control plane, resource
   reservation can be performed in a less granular fashion, e.g.
   reservation may occur once for a given slice.  During the lifetime of
   a device connection to a network, application flows will be
   established and maintained through a given set of common control
   plane function (CCNF), which may rarely change.  In general, a single
   device and a single CCNF will therefore interoperate with multiple
   slices simultaneously (e.g. a broadband and a Tactile Internet

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                    RAN uses Slide IDs |Device |
                        to select CCNF +---+---+
                                      \    |(Slide IDs, a.k.a. NSSAI)
                   CCNF uses Slide IDs |  RAN  +-------------+
                    to select slices   +---+---+---------+   |
                                  \        |(Slide IDs ) |   |
                                   +-------+--------+    |   |
                                   | Common Control |    |   |
                                   | Plane Network  |    |   |
                                   |    Functions   |    |   |
                                   |    (CCNF)      |    |   |
                                   +-----+----+-----+    |   |
                                         |    |          |   |
                            +------------|---------------|-------+   |
                            |  +---------++        +-----+----+  |   |
                            |  | +------+ |        | +------+ |  |   |
                            |  | |CP NF1| |        | |UP NF1| |  |   |
                            |  | +------+ |        | +------+ |  |   |
                            |  |    ...   |        |    ...   |  |   |
                            |  | +------+ |        | +------+ |  |   |
                            |  | |CP NFn| |        | |UP NFn| |  |   |
                            |  | +------+ |        | +------+ |  +---+
                            |  +----------+        +----------+  |
                                 Core Network Slice Instances

                  Figure 3: 3GPP Network Slice Selection

5.  Role of NFV in Network slicing

   Virtualization is a key enabler of network slices; Many network
   services can be easily deployed using components of NFV framework
   like network functions, hardware decoupling and resource placement
   [#?NFVSLICE].  When deployed as a network slice, the resources
   associated with virtualized network services are managed uniformly by
   infrastructure provider.  One such use case is described below.

5.1.  Virtualized Customer Premise Equipment

5.1.1.  Traditional Customer premise equipments(CPEs)

   A CPE is an equipment that connects the customer premises to the
   provider's network.  A CPE may either be a layer-2 or a layer-3
   device (the routing gateway) performing different network functions
   depending on the access technology (DSL modem, PON modem, etc.).  Any

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   services provided such as Internet access, IPTV, VoIP, etc. or
   network functions for example, local NAT, local DHCP, IGMP proxy-
   routing, PPP sessions, routing, etc. are also part of CPE.  The
   installation of different on premise devices, entails a high cost for
   service providers in terms of both initial installation and
   operational support, since they are typically responsible for the
   end-to-end service.

                                        +-----+      campus
                                   |----| CPEx | -----[     ]
                                   |    +-----+
            -----        Broadband |    +-----+      branch
           (     ) ----------------|--->| CPEy |------[     ]
           ( CSP  )           MPLS |    +-----+
           (____)            access|    +------+      main site
                                   |--->| CPEz |----- [     ]

                  Figure 4: Traditional CPE architecture

   Traditional CPE deployments are shown in figure Figure 4.  These are
   service provider network functions installed on customer site to
   provide above mentioned functionalities along with remote site
   connectivity.  Communication Service provider (CSP) is responsible
   for management and administration of connections and state with
   proper policy, bandwidth, security and QoS requirements.

5.1.2.  Trends in CPE infrastructure

   A virtualized CPE architecture moves several network functions from
   on premise to the service provider network to facilitate provisioning
   of new services to customers based on a lean CPE functions on
   premises such as minimizing number of network functions on customer
   premises, perhaps only layer-2 visibility among them with no need for
   routing gateways in the home network is suppressed.  Several routing,
   NAT, firewall capabilities may be performed in the service provider's
   cloud.  A customer's site is highly simplified with vCPE solution,
   perhaps requiring only access level connectivity on premise and
   moving other network functions to ISP's cloud.

   A vCPE when combined with SD-WAN technology provides service
   guarantees for different enterprise applications and with a
   generalized sliced approach, the solution can be customized on per
   enterprise basis using a standard approach to delivery of WAN
   solutions to multiple enterprises.

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     |              +------+ |------------------+-------+       campus
     |           |--|      | |                  | vCPEx | -----[     ]
     |           |  |      | |------------------+-------+
     |           |  |      | | <====Broadband ==>
     |    -----  |  | vCPE | | -----------------+-------+       branch
     |  (      ) |->|      | |                  | vCPEy |------[     ]
     | (   CSP  )|  |      | |------------------+-------+
     |  (_____)  |  |      | |<===  MPLS/4G. ==>
     |           |  |      | |------------------+-------+    main site
     |           |->|      | |                  | vCPEz |----- [     ]
     |              +------+ |------------------+-------+

          Figure 5: irtualized CPE, with distributed architecture

   Figure 5 shows a virtualized architecture in which many functions are
   moved to CSP's cloud simplifying CPE on premises tremendously.
   Additional details of deployment architecture models are captured in
   [I-D.pularikkal-virtual-cpe] where full dissemination of data path
   and control plane functions is described.  Here only a high-level
   relevance of virtualized CPE is shown.  The figure shows vCPEx,
   vCPEy, vCPEz are virtualized CPEs on multiple sites of a specific
   customer, there may be set of different network functions in each x,
   y and z CPE.  The vCPE instance in CSP cloud is integrated to each
   site performing service chains of network functions and resource
   allocations specific for ingress and egress path of each site.  Challenges

   A vCPE is a well-known concept[VCPEBBF] which when combined with WAN
   technologies provides end to end visibility and reachability to
   remote sites.  It has been solved using network function
   virtualization (NFV) approaches and via offload of compute intensive
   functions to the CSP cloud for ease of management by CSP.  However,
   there is no standard approach to connectivity or management of
   various CPE functions.  Furthermore, it is highly desirable for
   customers to control and monitor their own network resources at both
   remote and local sites.  Using network slicing, a greater level of
   agility can be achieved, with each customer dynamically managing its
   own network with the assistance of network slicing framework.

5.1.3.  vCPE as a network slice

   The benefit of self-managing a vCPE network slice is the capability
   to move network functions on premise of to the cloud.  An obvious use
   case will be customer initiated gradual migration of network
   functions from a site to CSP cloud.

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              +-------------+       +-------------+
              | E2E Slice   |       | Slice       |
              | Orchestrator|       | Resource Mgr|
              +-------------+       +-------------+
                    |                     ^
                    | NS protocol or i/f  |
                    V                     V
            |                                                  |
            |   +-------------+       +-------------+          |
            |   | vCPE Slice  |       | CSP         |          |
            |   | Mgr/Monitor |       | vCPE subnet |          |
            |   +-------------+       +-------------+          |
            |                                                  |
            |  +--------+  +--------+  +--------+  +--------+  |
            |  | vCPEy  |  | vCPEy  |  | trans  |  | vCPEz  |  |
            |  | subnet |  | subnet |  | subnet |  | subnet |  |
            |  +--------+  +--------+  +--------+  +--------+  |
            |                                                  |
                    |                               |
                    | NS transport protocol or i/f  |
                    V                               V
               [Campus]    [branch]    [Transport] [main site]

                     Figure 6: vCPE as a Network Slice

   Editor's Note: TODO: here we have inconsistencies between the drafts
   and more importantly with the 3GPPP and TM forum.

   In Figure 6, a slice for vCPE is shown.  Using slice subnet approach,
   each vCPE site instance may be considered as a subnet, along with the
   WAN transport as another subnet.  The network functions are chained
   in a distributed fashion between site vCPEs and CSP vCPE subnet.  A
   monitoring function interfaces with CSP's global slice manager for
   resource management and an interface to physical infrastructure
   through network slice transport protocol, realizes these functions on
   the infrastructure.  Required Characteristics

   Having a dedicated sliced network catering to dynamic customization
   of network functions with guaranteed resource method, simplifies
   network operations.  In case of such vCPE type solutions, it is
   common for each customer to have its own private IP address space,
   therefore, the resource isolation must include address isolations as
   well.  This may be achieved based on existing label techniques or
   through new network slicing data path protocol.

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6.  Services with Resource Assurance

6.1.  Enhanced Broadband

   Today, video consumes the largest amount of bandwidth over the
   Internet.  As the higher resolution formats enter mainstream, even
   more bandwidth will be needed to stream 4K/8K/360 degree formats.
   The scenario in this section are discussed in regards to need for
   demands beyond best-effort network delivery, in particular
   requirements due to growth in data rate capacity, connection density
   and interactive media.  These are equally applicable to both fixed
   and mobile networks.

6.1.1.  Media delivery networks

                                                             |=>| DASH|
                                                             |  +-----+
     +------------+    +-------------+     -----     +-----+ |  +-----+
     | Content    |<==>| Transcoding |<=> (     ) ==>| CDN |=|=>| HDS |
     | Aquisition |    | Function    |   (  ISP  )   +-----+ |  +-----+
     +------------+    +-------------+    (____)             |  +-----+
                                                             |=>| HLS |
                                              Media delivery formats

           Figure 7: Traditional Streaming Media Infrastructure

6.1.2.  Enhanced Media Streaming Description

   Today the video output format is HD with 1080p resolution with few
   services delivering up to 4K.  Both Video-on-demand and live-linear
   channels (streaming live event feed) can be supported.  Most often
   media services are delivered using streaming platforms.  Factors Influencing Enhanced Broadband Use Cases

   Media delivery comprises of different functional components, as shown
   in Figure 7 above and often an overlay or OTT infrastructure is used.
   The deployment requires acquiring content, transcoders and CDN
   servers and decoders to support different delivery formats All these
   may be considered specialized service functions in media streaming
   infrastructure.  The entire operation is (a) not flexible in terms of
   resources placement (on premise vs cloud vs proximity to destination)
   (b) is built on best-effort of available resources, (c) Is reactive
   when the congestion occurs leading to client-server based end to end
   stream optimization derived from network conditions.

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Internet-Draft               Network slicing                   June 2017  Traditional Media Streaming Service Verticals

   There are 3 categories of media or content distribution

   a  Video on Demand (VOD)

   b  Live streaming/Linear channels

   c  Video conferencing

   While a and b are one way content consumption, Video conferencing
   requires 2-way or multi-way connection.  It may consist of either
   person-person or person-group video communication.  New Verticals - Virtual Reality (VR)/Augmented Reality (AR)

   Virtual Reality(VR)/Augmented Reality(AR) is the future use case of
   eMBB services.  A 360-degree video is mostly low resolution,
   requiring ~25 Mbps network bandwidth for streaming.  For a network
   based AR/VR bandwidth required will be in the order of Gbps and
   latency less than 10 milliseconds for a fully immersive experience
   such as cloud-based VR gaming, fully-interactive media experience.
   However, media processing for AR/VR will still be identical to in-
   network processing functions as shown in figure 1 and corresponding
   latencies could lead to downgrade of user experience.  Therefore,
   upon request for an AR/VR stream a special infrastructure is required
   that differs from best-effort network.

6.1.3.  eMBB Type Slices

   A purpose-built network slice for eMBB streaming shall ensure to
   minimize processing overheads, it may be done by placement of network
   functions closer to subscribers.

   o  Resource scaling: eMBB resources should be allocated dynamically
      because bandwidth is expensive and requirements are high, such
      vertical service operators may not want to pay for unutilized
      bandwidth.  Therefore, slices should adjust in negotiated chunks
      of scale both bandwidth and service functions.  For example, if a
      stream is viewed by 8 people initially, the resource for 20 users
      is allocated.  It will subsequently grow or shrink in chunks of
      resource for 20 subscribers.

   o  Transport resource constraints are different for the Fan-out
      network between user and distribution network; and content
      acquisition to distribution network.

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   o  Latency Guarantee varies for live streaming, on-demand streaming
      and connected AR/VR streaming

          |     E2E Slice Orchestrator       |
          |                                  |
          |       +------------------+       |
          |       | eMBB Resource    |       |
          |  +--> |    Spec Guard    |---+   |
          |  |    +------------------+   |   |
          |  |                           |   |
          |  |    +----------+-------+   |   |
          |  +--->|  Resource Monitor|<--+   |
          |       +---------+--------+       |
          |           ^             |        |
                      |             |
                      | Real time feed|back
                      |             |
          eMBB        |             |
          Network     |             v dynamic resource adjustment
       | +----------+-------+    +-----------+ |
       | |  Acquired Content|<-->| eMBB slice| |
       | |      subnet      |    | Customizer| |
       | +---------+--------+    +-----------+ |
       |         |       |                     |       +-+
       |         |       |                   =======>  | |
       |  +--------+  +-------+              | |       +-+  handheld
       |  | CDN1   |  | CDN2  |              | |      +---+
       |  | subnet |  | subnet|              ========>|   |
       |  +--------+  +-------+              | |      +---+ PC
       |      |          |                   | |
       |  +-----------------+                | |     +---------+
       |  | Encoders subnet |================+=+====>|         |
       |  +-----------------+                  |     +---------+ TV

                      Figure 8: Reference eMBB slice

   See Figure 8 above for a reference slice.

6.1.4.  Required Characteristics

   A typical eMBB slice flow from a network operator is as follows

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   o  There is an eMBB slice offering template/form.  A service vertical
      provider requests

      1.  Regional network locations of CDN and location of acquired

      2.  Describes transport requirements for its own distribution
          network comprising of connectivity between content acquisition
          and Fan-out points.

      3.  A granularity of transport resource chunk.

      4.  It may request access to subscriber database from multiple
          access network types (mobile, fixed) creating value add for
          both service provider.

      5.  For each access type resource requirement is specified.

   o  Registers self with access rights to resource monitoring and
      negotiation loop.  Slice operator has an abstracted view of its
      own slice instance topology.

   o  Network operator has end to end (acquired content to cached
      content to user) visibility across different domain segments and
      corresponding transport resources.  A well-coordinated network
      slice protocol enables resource allocation across different

   Note in addition to eMBB, traditional CDN use cases can be deployed
   in a slice as well, see examples in [RFC6770].

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      |                    +-----------------------+                |
      |          +-------->| E2E Slice Orchestrator|<----+          |
      |          |         +-----------------------+     |          |
      |          |                                       |          |
      |   +------+-----------+               +-----------+-------+  |
      |   |     Global       |               |     eMBB Slice    |  |
      |   | Resource Manager |<------------> | Resource Allocator|  |
      |   +------------------+               +-------------------+  |
      |                                                             |
                   |                        |
           -------  NS control -------------- NS control--
                   |                        |
         ------------------          -----------------
        |  --------------  |        |  -------------- |
        | | eMBB Manager | |        | | eMBB Manager ||
        |  --------------  |        |  -------------- |
        |                  |        |                 |
        |                  |        |                 |
        |  --------------  |        |  -------------- |
        | | eMBB Network | |        | | eMBB Network ||
        | |--------------  |        |  -------------- |
        --------------------         -----------------
                 | |                       | |
                 V V                       V V
       ------------------NS transport ----------------
               |                  |             |
               V                  V             V
         ----------------  ----------------  -----------
        | Infrastructure | |Infrastructure | | DC       |
        |  Domain A      | | Domain B      | | Domain C |
         ----------------  ----------------  -----------

    Figure 9: Transport provider network operator view.  shows deployed
                   eMBB slice components for reference.

6.2.  Massive machine to machine communication

6.2.1.  Wireless Sensor Networks

   Sensor networks are widely deployed in industries such as
   agriculture, environmental monitoring and manufacturing.  The general
   workflow of wireless sensor network is provided in Figure 10.

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           6.Decided Behavior
          |                   |
     +----v------+            |
     |  Sensor   |            |
     |(1. Data   |            |
     |Collection)|            |
     +----+------+            |
          |2.Collected Data   |  3.Aggregated  +---------------------+
          +------------->+----------+ Data     |     Data Center     |
                      |  Sink Node/ |----------> (4. Data Analysis   |
                      | Base Station|          |         &           |
          +---------->+--------------+--<------|  Behavior Decision) |
          |2.Collected Data   |  5. Decided    +---------------------+
     +----+------+            |     Behavior
     |  Sensor   |            |
     |(1. Data   |            |
     |Collection)|            |
     +----^------+            |
          |                   |
           6.Decided Behavior

              Figure 10: Workflow of wireless sensor network

   As figure Figure 10 shows, sensors mainly collect data & behavior;
   rarely communicate with each other in traditional wireless sensor
   network.  While in the scenarios discussed in this section, sensors
   or embedded devices will be more intelligent and carry out more
   frequent interactions that raises more challenges for mobile

6.2.2.  Massive Internet of Things Description

   Machine-to-machine type communication will dominate communication
   paradigm in various industries such as healthcare, manufacturing,
   transportation, etc.  In order to support the massive internet of
   things, traditional mobile networks have to be redefined -- by
   creating the connectivity fabric for everything and bringing new
   levels of on-device intelligence.  Factors Influencing Massive Internet of Things Use Cases

   There are three main challenges raised by Massive Internet of Things
   use cases:

   o  Scalable connectivity: there will be billions of smart devices
      connect to mobile networks worldwide by 2020;

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   o  Wide area coverage: sensor could be embedded into various
      household equipments, medical instruments, vehicles, or even
      public facilities;

   o  Frequent small amount data transmission: due to limited power,
      most of the embedded sensors work intermittently rather than
      continuously.  New Massive Machine Type Communications (mMTC) Verticals

   A few examples of new types of scenarios that require unique
   infrastructure are mentioned below.  Smart City

   Smart city networks is an integration of several public
   infrastructures together through M2M communications.  For example

   o  Automatic metering for gas, energy, water, etc;

   o  Environment monitoring for pollution, temperature, humidity, etc;

   o  Light management inside buildings or even the whole city;

   o  Traffic signal control;

   o  Public safety alerting for natural disaster.

   Building a smart city requires a variety of IoT networks to inter-
   operate together; these IoT networks are run by different departments
   with different access privileges for administration and access
   control.  A smart-city network should be isolated from the public
   Internet.  E-Health

   E-health refers to the application that remote monitor the physical
   conditions (e.g., heart rate, pulse, blood pressure etc.), and
   accordingly take necessary medical measures remotely.  Being a life-
   critical service, e-health communication network must be reliable and
   fast but small-size of data exchange.  In addition, the privacy and
   security of user's data must be guaranteed.

6.2.3.  mMTC Type Slices

   mMTC involves potentially a large number of small and power-
   constrained devices, therefore, resource allocation at scale is of
   particular importance in mMTC type slices.  Furthermore, different

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   kind of IoT devices may exhibit quite different traffic patterns
   e.g., continuous (heart rate monitors) & periodic delay tolerant
   (temperature sensors), delay sensitive (e.g., weather forecast &
   disaster alerting), mobility mode, security awareness etc.  The mMTC
   type slices should be conscious of various requirements of scale,
   data pattern, reliability, security and energy efficient

6.2.4.  Required Characteristics

   Different from eMBB and uRLLC type services, mMTC service does not
   have so much strict requirements on bandwidth and latency.  Massive
   and ubiquitous connectivity support would become the biggest
   challenge of mMTC service.  That is, for an network operator, mMTC is
   mainly concentrated in the access network side and most of the
   information flow should not pass through the transmission or core
   network, both for security and communication efficiency.  The
   mobility management IoT gateway functions could be placed closer to
   terminals (e.g., base-stations, edge clouds, etc.).  Consequently, an
   mMTC type slice should consist of plentiful access network resource,
   as well as normal yet reliable transmission network and core network
   resources in general.

6.3.  Ultra-reliable low latency communication

6.3.1.  Brief introduction

   Not only, mission critical communication services but industrial
   manufacturing, production processes, remote medical surgery, and
   transportation safety (high mobility cases), etc scenarios require
   ultra-reliable communications with no packet loss.

6.3.2.  Challenges

   In uRLLC scenarios, both data and control planes may require
   significant enhancements to transmission or information distribution
   protocols.  [TR_3GPP_38.913] specifies generic KPIs for access
   network user plane latency as 1ms and reliability factor of 99.999%
   for transmission of a packet of size 32 bytes.  Although KPIs vary
   for different scenarios such as V2X(3-10ms, 99.999%), eMBB (4ms UL/DL
   each), In order to meet these, latency and reliability of the
   transport in mobile networks should also be considered.

6.3.3.  New service verticals

   In the following sections three new uRLLC scenarios are described.

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   Operations in remote industry sites usually need the support of
   mobile transport network.  Accurately operating machinery (low
   latency and jitter) from remote locations requires high-quality
   communication links between the control site.  Factors to consider *
   low latency and low jtter in communication path * Short time interval
   between an operator sending control signal tp equipment response.

   In an industrial closed control loop (Sensor -Controller - Actuator)
   as shown in figure Figure 11, a typical control cycle time where
   network is involved should be below 10ms [White-paper-5GAA].

    ++++++++++   +++++++++++++++
    + Sensor +-->+ Transmitter +---+
    ++++++++++   +++++++++++++++   |
                                   |   ++++++++++++     ++++++++++++++
                                   +-->+   Base   +---->+ Controller +
                                   +---+ Station  +<----+            +
                                   |   ++++++++++++     ++++++++++++++
    ++++++++++   +++++++++++++++   |
    +Actuator+<--+   Receiver  +<--+
    ++++++++++   +++++++++++++++

                 Figure 11: Industrial closed control loop  Remote Surgery

   Remote surgery which enables surgeons to perform critical specialized
   medical procedures remotely, allowing their vital expertise to be
   applied globally.  Providing accurate control and feedback for the
   surgeon entails very strict requirements in terms of latency,
   reliability and security.  Vehicle-To-Everything (V2X)

   Vehicle-To-Everything (V2X) network uses precise knowledge of the
   traffic situation across the entire road/highway network to optimize
   traffic flows, reduce congestion, and minimize accidents.  For uRLLC

   o  V2X in access network uses Vehicular Ad Hoc Network (VANET) type
      protocols for vehicle-to-vehicle and an access medium
      communication (either ITS-band or commercial-cellular).  The
      topologies are dynamic and mobility is high.  In order to support
      fully autonomous reliable driving, a highly reliable communication
      channel is required.

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   o  Often, V2X may involve a part transport and core networks for
      functions such as subscriber/vehicle admission and intensive
      computational resource for aggregating information from multiple
      traffic zones.

6.3.4.  Required Characteristics

   A uRLLC network slice only accepts service specifc traffic and
   discards any other type of traffic to avoid negative impact on uRLLC
   service operation.  Even within the same vertical different kind of
   services should be isolated.  For example, in the V2X vertical, the
   network slice used for autonomous driving should not be used for in-
   vehicle infotainment.  Capabilities required by uRLLC service
   provider include

   o  Locations of the access nodes for terminals (devices, vehicles) to
      the transport network and locations of the controller to construct
      its own network topology within the network slice.  In high
      mobility scenario such as automotive verticals, the dynamic
      topology adjustments are required without loss of data.

   o  Each service vertical has different performance requirements in
      terms of latency, reliability and data rate etc., therefore, the
      uRLLC network slice should allow customization for these

   o  A uRLLC service provider should be able to registers self with
      access rights to resource monitoring and negotiation loop.

   From a network operator provides a uRLLC Slice with following

   o  Should support/provide specific data and control planes protocols
      with significant enhancements for deterministic latency and
      reliability (e.g.  DetNet[I-D.dt-detnet-dp-sol] in data plane).

   o  Allow uRLLC provider to access user admission and authentication
      to its network slice in advance.

   o  The network coverage for a uRLLC service provisioning may be
      limited to a confined area, either indoor or outdoor, network
      operator needs to be able to coordinate resource allocation across
      different access types and network segments.

   The Figure 12, shows provider and operator view of the network.  The
   monitoring of resources is done in the context of performance.  A
   performance degradation would require resource adjustment.  As shown
   in Figure 12, in one possible sliced model will have its own

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   customizer that uses internal performance observing logic with in its
   slice by coordinating with different subnets/domains using southbound
   NS transport protocol and transfers this information to operator via
   a northbound NS protocol for resource adjustment.

   It is implied that domains maybe different access technologies and
   need for a common performance metric propagation and resource
   allocation is important for a uRLLC slice to function properly.

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         |    E2E  Slice Orchestrator  |
         |                             |
         |       +---------+ +-----+   | uRLLC service +---------+
         |       | Resource| | Perf| <-|---------------| uRLLC   |
         |  +--- | view    | | Spec|   |  template     | service |
         |  |    +---------+ +-----+   |               +---------+
         |  |    +----------+--------+ |
         |  +--->|Performance Monitor| |
         |       +---------+------^--+ |
         |                        | |  |
                                  | | resource adjustment
                                  | |
              performance  metrics| |
                                  | |
           uRLLC slice            | v
         | +--------+--+    +-----------+      |
         | |  Subs     |<-->|uRLLC slice|      |
         | |  Mgmt     |    |Customizer |      |
         | +-------+---+    +---------^-+      |
         |       +-------+------------|        |
         |       |       |        +---v-----+  +
         |  +--------+  +-------+ | micro   |  |
         |  | GC-1   |  | GC-2  | | resource|  |
         |  | subnet |  | subnet| | mgr     |  |
         |  +--------+  +-------+ +---------+  |
         |     |          |                    |
              | |        | |
              V V        V V
         ------------NS transport --------------
         |                  |             |
         V                  V             V
         +--------------+  +------------+ +----------+
         |  Domain A    |  | Domain B   | | Domain C |
         +--------------+  +------------+ +----------+

               Figure 12: Reference for uRLLC Network Slice.

6.4.  Critical Communications

   Critical communications are used during emergency situations.  Often
   referred to as mission critical, the communication has to be reliable
   and non-disruptive.  Different scenarios of critical communications
   relate to public safety responders, military, utility or commercial
   applications, mainly using reliable voice or short data messaging

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   over wireless communication systems.  First responders such as
   firefighters, paramedics and other responders, for their daily and
   emergency communications needs to be able to communicate without

6.4.1.  Public Safety Infrastructure  Current Improvements over traditional services

   Traditional technologies for emergency communications are narrow band
   radio networks such as Land Mobile Radio (LMR) systems.  They are
   terrestrially-based professional push to talk wireless communications
   systems commonly used for critical communications by public safety
   organizations such as police, firefighters, and other emergency
   response organization.  LMR and related systems such as TETRA or P25
   have dedicated frequencies and channels assigned to individual groups
   of users for instant connection through a simple interface.  Next-
   generation public safety communications are planned to be built with
   enhanced broadband voice, data and video communications services
   beyond narrowband LMR with broadband LTE networks for high speed data
   (ref 22.179 and FirstNet).  Challenges for Enhanced Critical communication

   3GPP defined on-network critical communication can be established
   with the help of a network infrastructure to manage the call.  It can
   also be off-network, where the terminals communicate directly to each
   other.  The scope here does not discuss point to point off-network
   communication as it is not relevant to the topic.

   Most important challenges for on-network communications include:

   o  Expensive to deploy a separate broadband network: The coverage of
      a separate network at the scale of area, state or nationwide that
      is interoperable is not cost effective, especially as new
      communication technologies emerge, public safety systems should be
      able to adapt easily to state of the art.

   o  Lack of flexibility: in terms of adding new value added services
      or ability to take advantage of commercial services.

   o  Ability to reliable support of basic mission critical services
      such as voice: loss of information in voice communication is no
      acceptable in emergency services, if common infrastructure is to
      be used, it must assure no loss of information.

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6.4.2.  Enhanced Critical Service Type Slices

   The traditional critical communications use dedicated separate
   infrastructures in order to be reliable and non-disruptive.  In
   contrast, LTE based mechanisms acquire different bearer QoS Class
   Identifier (QCI) for different type of barriers (data, voice, video).
   The eMC (enhanced mission critical) network slices benefit from the

   o  Insertion and authorization of subscribers in a group
      communication: In a critical infrastructure, the subscriber
      authentication may be done earlier at the entry point
      automatically through slice selection functional entity.

   o  Pre-allocated QCIs: Generally, QCIs are requested on per session
      basis which could slow down overall call control setup and is
      undesirable for emergency services.  When operating in a slice,
      these resources maybe reserved ahead of time in a coarse-grained
      manner instead of per session.

   MC Network slices are relatively straight forward as it only concerns
   with guaranteed bit rate (GBR) on per media basis and management of
   groups.  The MC network slice need an ability to request transport
   services based on GBR for reliable communication.  A reference
   network slice below shows a mission critical (MC) organization
   providing service agreement through a network slice template with
   resource specification.  The eMC slice sets up different subnetworks
   of different subscriber groups and manages its membership.  These
   subnets are realized into the infrastructure across different domains
   through a network slice transport mechanism.  The MC network slice
   must be capable of active resource monitoring to prevent congestions
   to ever occur as well as request additional transport resources in
   case of emergency event occurrence.

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   |     E2E Slice Orchestrator       |
   |                                  |
   |       +------------------+       |  service   +------------------+
   |       | eMBB Resource    |       |<-----------| Mission Critical |
   |  +--> |    Spec Guard    |---+   |  agreement |    Organization  |
   |  |    +------------------+   |   |            +------------------+
   |  |                           |   |
   |  |    +----------+-------+   |   |
   |  +--->|  Resource Monitor|<--+   |
   |       +---------+--------+       |
   |           ^             |        |
               |             |
               | Resource request
               |             | prioritized resource adjustment
     MC Network|Slice        v dynamic group management
   | +----------+-------+    +-----------+ |
   | |  Group Subs Mgmt |<-->| MC slice  | |
   | |                  |    | Customizer| |
   | +---------+--------+    +-----------+ |
   |         |       |                     |     +-+
   |         |       |        +---------+  + +-->| |
   |  +--------+  +-------+   | GRP     |  |     +-+ MC-UE
   |  | GC-1   |  | GC-2  |   | selector|  |     +-+
   |  | subnet |  | subnet|   +---------+  | --->| |
   |  +--------+  +-------+                |     +-+ MC-UE
   |      |          |                     |
     | |                       | |
     V V                       V V
   ------------NS transport ----------------
   |                  |             |
   V                  V             V
   ----------------  ----------------  -----------
   | Infrastructure | |Infrastructure | | MC server|
   |  Domain A      | | Domain B      | | Domain C |
   ----------------  ----------------  -----------

         Figure 13: Reference for Mission Critical Network Slice.

7.  Network Infrastructure for new technologies

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7.1.  ICN as a Network Slice

   ICN as in Information-Centric Networking is a culmination of multiple
   future Internet research efforts in various parts of the world, now
   being pursued under IRTF's research task group called [ICNRG].

7.1.1.  Information Centric Networks Description

   Information-Centric Networking (ICN) addresses Internet's network
   architectural design gaps based on evolving applications requirements
   and end user behavior which is significantly different from what IP
   was designed for, which was optimized for host-to-host communication
   paradigm.  ICN is a non-IP paradigm based on name-based routing and
   offers many desirable networking features to applications such as,
   caching, mobility, multicasting and computing in a manner different
   from traditional host-centric communication model.  With respect to
   5G and network slicing, ICN paradigm is in line with the move towards
   service-centric architectures enabled through frameworks like SDN,
   NFV, and Edge Computing.  At a high level, ICN offers a name-based
   abstraction to application that doesn't require further translation
   (as in domain names to IP mapping in current IP networking), making
   it suitable to several communication modalities such as multi-point-
   to-multi-point, D2D and Ad hoc communication.  New Verticals - ICN based service delivery

   Services over ICN slices can take advantage of its features such as:

   (1)  In ICN, applications, services and content are addressed using
        names, hence end host resolution services like DNS can be
        avoided, this achieves name resolution to edge content or
        services without incurring additional RTT delays.

   (2)  Service flows will be offered mobility and multicasting support,
        as the networking is session-less and optimized towards
        efficient movement of named data or networking named services
        and host level communication.

   (3)  Services can be deployed at the very edges with ease as ICN
        routers are compute friendly, this is because states in the
        forwarding table can be that of either content or service

   (4)  Further saving bandwidth in the upstream link through
        opportunistic caching is an inherent feature of ICN, this also
        leads to energy efficient networking.

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   When offered as a programmable and customizable logical network
   slice, ICN based services can be offered as a network slice in
   parallel with traditional IP based services.  ICN can be realized as
   a slice [_5GICN_] based on the choice of data plane resource offered
   by the operators in different segments of the network such as the
   access, core network or main data centers.  While the same resources
   can be used to support services over IP, proper resource isolation
   shall allow it to co-exist with ICN slices as well.  ICN though
   initially was aimed to serve CDN applications such as video-on-demand
   or general web content distribution, it is equally adept to server
   real-time applications such as audio/video conferencing [ICN-AV], AR/
   VR applications, or IoT services.  ICN slices can be offered over a
   network slicing framework built upon a programmable pool of software
   and/or hardware based data plane resources.  Heterogeneous mix of
   pool of infrastructure resourcesis possible such as : Hardware
   decoupled network functions as in containers or VMs.  Deeply
   programmable hardware resources include GPU, FPGAs [ClickNP], Smart
   NIC [Netronome] operated using P4 abstractions, that are supported
   over x-86 platform.  Programmable hardware may also include
   commercial chips supported using P4 or POF allowing one to realize
   high performing novel data planes, e.g.  [Barefoot]

7.1.2.  ICN Type Slices Asks

   In ICN, applications use Interest/Data abstractions over named
   resources resolved by ICN's routing plane.  An ICN slice shall be a
   programmable ICN-domain, in which content learning and distribution
   will be done using existing or new ICN aware routing and data plane
   protocols.  As a result, it should be possible to deploy network
   functions such as ICN routers and content producers and distributors
   that serve and speak ICN protocols.  Just as multiple service
   instances can be part of a slice, an ICN slices can multiplex
   heterogeneous services; on the other hand an ICN slice can be as
   granular as a service instance too.  The latter approach has
   implications with respect to consumer privacy, access control of name
   data objects, and granularity of mobility handling.

7.1.3.  Required Characteristics

   A basic ICN slice can be manifested as a resource isolated logical
   network while sharing resources with other connectivity or service
   slices.  An ICN slice relies on programmability and virtualization
   framework to manage the service slices, to allow maximum flexibility
   through ICN aware logically centralized control plane for icn service
   and slice management.

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   o  Through a network slice template -ICN service providing entity
      could specify specific locations (edge of network domains) to
      deploy ICN-routers or other ICN-NFs (ICN aware network functions).
      Its service definition varies with the type of service, for e.g.
      in case of a VoD service, it can include the demand with respect
      user popularity distribution for a particular set of content,
      distributed cache or storage resource, and compute resources to
      execute video-centric service functions.

   o  An ability to establish connectivity between ICN network elements
      in all segments and create an ICN based virtual topology.  This
      can be done using specific service control plane based on
      application events arriving in a dynamic manner.

   o  Mechanism to carry ICN user traffic over the infrastructure, ICN
      slice can be made aware to the RAN explicitly by integrating ICN
      NF with the eNodeB or implicitly using traffic classification
      function at the edge and tunneled to ICN user plane functin (UPF)
      or can be enabled in an overlay manner.  The close the ICN network
      is to the UE, better will be the affect on overall efficiency in
      terms of bandwidth, latency and energy consumption.

   o  In addition, bandwidth and other network resources may be
      requested from the underlay depending on its capability of
      providing deterministic or statisticaly guarnatees.

   How multiple services will be deployed within an ICN aware slice may
   or may not be exposed to the network operator, depending on if the
   ICN slices are natively managed by it or a by other service

7.2.  Network Slices in Communication Endpoints

   In this section connected endpoint use case are described to
   highlight significance of slicing in an end point.

7.2.1.  Connected Vehicle

   Connected vehicles are example of scenarios where a communication end
   point is split into 3 different type of services that vary in in
   terms of topology, bandwidth, latency, mobility and security.

   a  V2I in short-range: requires ad hoc routing protocol, reliable
      data plane and higher layer security and authentication;

   b  Traditional broadband for Infotainment: requires high speed
      connection bandwidth.

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   c  In network assistance for localized services: low speed, reliable
      connection for a short period of time.  This service need to be
      highly secure and isolated because it connects vehicle to
      manufacturers who can alter component settings.

7.2.2.  Sliced Terminal

   a terminal, if authorized may be allocated dedicated resource for
   mission critical services and best-effort slice for normal

7.2.3.  Required Characteristics

   A network operator that registers a subscriber is required to know
   how a terminal is used and which services, offered as a slice it is
   part of.  A highly secure 3-way authentication between an operator,
   service provider and terminal is required to enable a slice on a

8.  Overall Use case Analysis

   The discussion in above use cases can be summarized as following in
   terms of the requirements for network slicing framework.

8.1.  Requirements Reference

   The following functional requirements are derived from discussions in
   above sections.  They are described in details in
   [I-D.qiang-netslices-gap-analysis] document:

   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 Identification

   o  Req.5 NS Domain-Abstraction:

   o  Req.6 OAM Operations with Customized Granularity

   The differentiated services described in this document are to be
   supported on a common network infrastructure.  They also demonstrate
   several common functionalities.  Therefore, a homogenous approach
   towards deployment and management is absolutely necessary.

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8.2.  Mapping Common characteristics to Requirements

8.2.1.  Req.1 Network Slicing Resource Specification

   1.  Resource Reservation: compute and network resources are reserved
       as part of initial creation and later maintenance of a slice.
       For example, a service may initially reserve resources for its
       own control plane, and then later it may reserve user plane flows
       for applications on demand.  Reference use cases: Differentiated
       services discussed in section "Services with Resource Assurance".

   2.  Transparency: Network slicing does not change the functionality
       of a scenario; It only facilitates creation of an isolated, an
       independently run infrastructure for that use case over a common
       network.  Transparency promotes inter-operability and a common
       resource specification enables it.

   3.  Multi-access knowledge: Many services are scoped within an access
       domain that could be either wireless technologies or different
       cellular spectrum.  Each network domain or segment has different
       characteristics, for example, it may use layer-2, layer-3 or MPLS
       connectivity or cellular network.  Dissemination of resource
       characteristics should be done uniformly across all networks to
       simplify slice deployment.

   4.  Multi-dimensional service vertical: Network slicing supports
       dynamic multi-services, multi-tenancy and the means for backing
       vertical market players

8.2.2.  Req.2 Cross-Network Segment & Cross-Domain Negotiation

   1.  Multi-domain coordination: Multi-domain refers to different
       technology related network domains.  For example, it may be RAN,
       DSL etc, mobile core network, ISP or different domains in
       transport networks such as carrier ethernet, MPLS, TE-tunnel etc.
       Often, they are under same administrator's control but may
       require coordination across different administration.  All
       scenarios mentioned require multi-domain coordination to connect
       and administer different subnets.

   2.  Automated Network Slice Management: Network slicing would need to
       be self-managed with automated deployment in order to cope with

   3.  Resource Assurance: Meet low latency or bandwidth demands: All
       scenarios require agile resource adjustments. it may not be
       possible to achieve this using centralize or API approach.  It
       can also be difficult to coordinate across different domains.

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       Therefore, a network slice transport protocol that standardizes
       resource propagation in different subnets is needed.  It is
       important for protocol (or interface) to be lightweight and

8.2.3.  Req.3 Guaranteed Slice Performance and Isolation

   1.  Performance Isolation: resource or traffic congestion in a slice
       should not affect traffic on other slices sharing the same

   2.  Secure Isolation: network services hosted on a slice should not
       be able to breach into other slices deployed over the same
       infrastructure, e.g. a network function should not be able to
       intercept or inject traffic on another slice it is not connected

   3.  Operational Isolation: Each network slice may have its own
       operator that sees this slice as a complete network (i.e router
       instances, programmability, using any appropriate communication
       protocol, caches, provide dynamic placement of virtual network
       functions according to traffic patterns, to use its own
       controller, finally it can manage its network as its own).

   4.  Reliability: It is an important resource attribute in the type of
       service verticals described above.  Many services verticals
       cannot deliver functionality unless the network is reliable (See
       remote industry operation, remote surgery and other uRLLC

8.2.4.  Req.4 Slice Identification

   1.  Agile resource adjustment: all scenarios require meeting low
       latency or bandwidth demands.  It may not be always possible to
       achieve this using centralize or API approach in all deployment
       scenario.  It can also be difficult to coordinate across
       different domains.  Therefore, a network slice transport protocol
       that standardizes resource propagation in different subnets is
       needed.  It is important for protocol (or interface) to be
       lightweight and distributed.

   2.  Function Sharing: a given physical or virtual function or
       possibly slice subnet may be interconnected with more than one
       slice simultaneously.  Examples include a client device or, in
       3GPP systems, the AMF.  An auto discovery of such attributes is
       necessary as an exception to isolation.

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   3.  Slice identification: It is needed to uniquely specify and
       resolve resources and for slice-lifecycle in management plane.
       In control and data plane identification isolates and secures
       resources among the slices.

8.2.5.  Req.5 NS Domain-Abstraction

   1.  Abstraction: Network slicing introduces an additional layer of
       abstraction by the creation of logically or physically isolated
       groups of network resources and network function/virtual network
       functions configurations separating its behavior from the
       underlying physical network.

   2.  Subnet Concept: Functionality of each use case can be logically
       split into slice subnets.  Each subnet supports only a part of
       functionality or interconnection.  For example, a segment is
       dedicated to virtualized function chain using NFV, another
       segment maybe radio-based and third segment may be an edge cloud
       node in cellular network.  The total resource consumption of a
       slice is sum of resources in each of these segments.  Therefore,
       a proper abstract or logical representation of these subnets is
       mandatory.  A provider transport network with assured network
       resources will be required to inter-connect these subnets.

   3.  Virtualization of Network Functions: NFV plays an important role
       in terms of dynamic placement of services, partitioning of
       network resource and configuring the network (physical/virtual)
       functions.  For example, Ability to run own control and data
       plane as needed in mMTC or ICN case.

8.2.6.  Req.6 OAM Operations with Customized Granularity

   1.  Independent per slice management plane: Since a sliced network is
       purpose-built, the intelligence to run, control, manage, operate
       and administer a slice is with the provider of service in a

8.3.  Mapping Common Characteristics to Requirements

   The above discussion is summarized in Figure 14 as below:

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   | Scenario/   |          driving factors           |     Mapped     |
   | service     |                                    |  Requirements  |
   |  eMBB,uRLLC,| (a) uniform resource reservation   |    REQ.1       |
   |  mMTC       | (b) multi-access  connectivity     |                |
   |             | (c) transparency for portability   |                |
   |  3GPP       |   and inter-operability to support |                |
   |  NSaaS      |   differentiated service verticals.|                |
   |  AR/VR,V2X  |  Total resource required is sum of |    REQ.2       |
   |             |  resource in each network segment  |                |
   |             |  and a coordination of what is     |                |
   |             |  available or not and dynamic      |                |
   |             |  adjustment is necessary.          |                |
   |  NSaaS, 3GPP|  Need mechanisms to ensure         |    REQ.3       |
   |  e.g remote |   (a) E2E resource Isolation       |                |
   |  surgery,   |   (b) Secure Isolation             |                |
   |  industry   |   (c) Operational Isolation        |                |
   |emergency    |                                    |                |
   |             | mechanisms to support              |    REQ.4       |
   |  e.g core   |   (a) agile resource adjustment    |                |
   |  network,   |   (b) Function sharing             |                |
   |  V2X, emer- |   (c) Operational Isolation        |                |
   | gency servcs|   (d) slice identification         |                |
   |             | To offer a service and             |    REQ.5       |
   |  NSaaS      | coordinate across different tech-  |                |
   |             |  nologies:                         |                |
   |             | (a) Abstraction is important       |                |
   |             |  both for network and resource.    |                |
   |             | (b) abstract each partitioned net- |                |
   |             |  work via logical sub-network      |                |
   |             |  concept.                          |                |
   |             | (a) Independent per slice manage-  |    REQ.6       |
   |  NSaaS      | ment plane                         |                |
   |             | (b) E2E orchestration              |                |

                                 Figure 14

   Table: Mapping Common Characteristics to Requirements

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8.4.  Other Challenges and Considerations

   These observations impose several challenges on network transport.

   (1)  Within each domain different traffic engineering techniques may
        be deployed, for example, FlexE, MPLS, RSVP-TE, DETNET or SDN
        based TE.  2(1) Within each domain different transport
        techniques may be deployed, for example L2 or L3 virtual
        networks such as VLAN, GUE, VxLAN, etc. or Software Function
        Chaining (SFC) such as NSH.

   (2)  No two network infrastructures are alike, technologies such as,
        edge computing, NFV, SDN, cloud are partially deployed today.
        There is no uniformity about whether a service is available as a
        physical node or a virtual node.  A network slice framework need
        to be able to cater to all cases.

   (3)  Optimal placement of resources on-demand is only possible when
        infrastructure supports it.  A capability exposure of a domain
        could facilitate such functions.

   (4)  At a massive scale, it is extremely complex to centralize global
        view of resources and be able to distribute on-demand.
        Considerations may be made to incorporate domain-to-domain
        communication about data and control for a specific network

   Network operators would exploit network slicing for:

   o  Significantly reducing operational expenditures, allowing
      programmability necessary to enrich the offered tailored services.

   o  Providing the means for network programmability

   o  Additional business offerings to OTT and other vertical market
      players without changing the physical infrastructure (i.e.  Health
      Vertical Sector, Energy Vertical Sector, Automotive Vertical
      Sector, Media and Entertainment Vertical Sector, Factory-of-the-
      Future Vertical Sector, Smart Home Vertical Sector, Smart City
      Vertical Sector, Additional Specialized Services Vertical Sector.

9.  Conclusion

   A service should typically need a network slice for one of those

   (1)  The service cannot provide optimal experience on a best-effort

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   (2)  It is inefficient and expensive to build a separate

   The separation from a generalized network, should allow new services
   to use newer or different protocols in network, transport and
   management layer/plane for that service (as in the case of ICN, mMTC,
   uRLL).  The goal of Network slices is to offer enriched service
   verticals with very different network capability and performance
   demands but also simplify from the traditional service delivery

   There is need for a uniform framework for end to end network slicing
   specifications that spans across multiple technology domains and can
   drive extensions in those technolgy-areas for support of Network

10.  Security Considerations

   The security considerations apply to each slice.  In addition general
   security considerations of underlying infrastructure whether isolated
   communication with in a slice apply for links using wireless

11.  IANA Considerations

   There are no IANA actions requested at this time.

12.  Acknowledgements

   Thanks to the following reviewers for providing details for several
   use cases and for helping with review of the document.

   Stewart Bryant (stewart.bryant@gmail.com, Hannu Flinck
   (hannu.flinck@nokia-bell-labs.com), Med Boucadair
   (mohamed.boucadair@orange.com), Dong Jie (dong.jie@huawei.com).

13.  References

13.1.  Normative References

              Korhonen, J., Andersson, L., Jiang, Y., Varga, B., Farkas,
              J., Bernardos, C., and T. Mizrahi, "DetNet Data Plane
              solution", draft-dt-detnet-dp-sol-00 (work in progress),
              March 2017.

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              Pularikkal, B., Fu, Q., Hui, D., Sundaram, G., and S.
              Gundavelli, "Virtual CPE Deployment Considerations",
              draft-pularikkal-virtual-cpe-02 (work in progress),
              February 2017.

              Qiang, L., Martinez-Julia, P., 67, 4., Dong, J.,
              kiran.makhijani@huawei.com, k., Galis, A., Hares, S., and
              S. Slawomir, "Gap Analysis for Network Slicing", draft-
              qiang-netslices-gap-analysis-00 (work in progress), June

   [RFC6770]  Bertrand, G., Ed., Stephan, E., Burbridge, T., Eardley,
              P., Ma, K., and G. Watson, "Use Cases for Content Delivery
              Network Interconnection", RFC 6770, DOI 10.17487/RFC6770,
              November 2012, <http://www.rfc-editor.org/info/rfc6770>.

13.2.  Informative References

   [_5GICN_]  IEEE Communication, "Delivering ICN Services in 5G using
              Network Slicing.  'Asit Chakraborti, Syed Obaid Amin,
              Aytac Azgin, Ravi Ravindran, G.Q.Wang'", May 2017,

              Barefoot, "Barefoot", 2017,

   [ClickNP]  ACM SIGCOMM, "ClickNP: Highly Flexible and High
              Performance Network Processing with Reconfigurable
              Hardware.  'B. Li, et al'", 2017,

   [ICN-AV]   IEEE Transaction on Emerging Network Architecture (under
              submission),, "SRMCA: Scalable and Realiable Multimedia
              Communication Architecture.  'Asit Chakraborti, Syed Obaid
              Amin, Aytac Azgin, Ravi Ravindran, G.Q.Wang.'", 2017,

   [ICNRG]    IRTF, "ICN Routing Group", November 2016,

              Netronome, "Netronome", 2017,

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              3GPP, "Study on the security aspects of the next
              generation system", 3GPP TR 33.899 0.6.0, November 2016,

              3GPP, "Study on new radio access technology Radio access
              architecture and interfaces", 3GPP TR 38.801 1.0.0, March
              2017, <http://www.3gpp.org/ftp/Specs/html-info/38801.htm>.

              3GPP, "Study on scenarios and requirements for next
              generation access technologies", 3GPP TR 38.913 14.2.0,
              March 2017,

              3GPP, "System Architecture for the 5G System", 3GPP
              TS 23.501 0.2.0, February 2017,

              3GPP, "Procedures for the 5G System", 3GPP TS 23.502
              0.2.0, February 2017,

              3GPP, "Telecommunication management; Management concept,
              architecture and requirements for mobile networks that
              include virtualized network functions", 3GPP TS 28.500
              1.3.0, 11 2016,

   [VCPEBBF]  Broadband Forum, "TR-345 Broadband Network Gateway and
              Network Function Virtualization", Dec 2016,

              5G Automotive Association, "The Case for Cellular V2X for
              Safety and Cooperative Driving", November 2016,

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Authors' Addresses

   Kiran Makhijani
   Huawei Technologies
   2890 Central Expressway
   Santa Clara  CA 95050

   Email: kiran.makhijani@huawei.com

   Jun Qin
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing   100095

   Email: qinjun4@huawei.com

   Ravi Ravindran
   Huawei Technologies
   2890 Central Expressway
   Santa Clara  CA 95050

   Email: ravi.ravindran@huawei.com

   Liang Geng
   China Mobile
   Beijing   100095

   Email: gengliang@chinamobile.com

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

   Email: qiangli3@huawei.com

   Shuping Peng
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing   100095

   Email: pengshuping@huawei.com

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   Xavier de Foy
   InterDigital Inc.
   1000 Sherbrooke West

   Email: Xavier.Defoy@InterDigital.com

   Akbar Rahman
   InterDigital Inc.
   1000 Sherbrooke West

   Email: Akbar.Rahman@InterDigital.com

   Alex Galis
   University College London

   Email: a.galis@ucl.ac.uk

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