TEAS Working Group                                               J. Dong
Internet-Draft                                                    Huawei
Intended status: Informational                                 S. Bryant
Expires: 8 September 2022                           University of Surrey
                                                                   Z. Li
                                                            China Mobile
                                                             T. Miyasaka
                                                        KDDI Corporation
                                                                  Y. Lee
                                                            7 March 2022

    A Framework for Enhanced Virtual Private Network (VPN+) Services


   This document describes the framework for Enhanced Virtual Private
   Network (VPN+) services.  The purpose of enhanced VPNs is to support
   the needs of new applications, particularly applications that are
   associated with 5G services, by utilizing an approach that is based
   on the VPN and Traffic Engineering (TE) technologies and adds
   characteristics that specific services require over those provided by
   traditional VPNs.

   Typically, VPN+ will be used to underpin network slicing, but could
   also be of use in its own right providing enhanced connectivity
   services between customer sites.

   It is envisaged that enhanced VPNs will be delivered using a
   combination of existing, modified, and new networking technologies.
   This document provides an overview of relevant technologies and
   identifies some areas for potential new work.

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 https://datatracker.ietf.org/drafts/current/.

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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on 8 September 2022.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   6
   3.  Overview of the Requirements  . . . . . . . . . . . . . . . .   7
     3.1.  Performance Guarantees  . . . . . . . . . . . . . . . . .   7
     3.2.  Isolation between Enhanced VPN Services . . . . . . . . .   8
       3.2.1.  A Pragmatic Approach to Isolation . . . . . . . . . .  10
     3.3.  Integration . . . . . . . . . . . . . . . . . . . . . . .  11
       3.3.1.  Abstraction . . . . . . . . . . . . . . . . . . . . .  11
     3.4.  Dynamic Changes . . . . . . . . . . . . . . . . . . . . .  12
     3.5.  Customized Control  . . . . . . . . . . . . . . . . . . .  12
     3.6.  Applicability to Overlay Technologies . . . . . . . . . .  13
     3.7.  Inter-Domain and Inter-Layer Network  . . . . . . . . . .  13
   4.  Architecture of Enhanced VPNs . . . . . . . . . . . . . . . .  14
     4.1.  Layered Architecture  . . . . . . . . . . . . . . . . . .  16
     4.2.  Multi-Point to Multi-Point (MP2MP) Connectivity . . . . .  18
     4.3.  Application Specific Data Types . . . . . . . . . . . . .  18
     4.4.  Scaling Considerations  . . . . . . . . . . . . . . . . .  18
   5.  Candidate Technologies  . . . . . . . . . . . . . . . . . . .  19
     5.1.  Packet Forwarding Plane Technologies  . . . . . . . . . .  20
       5.1.1.  Flexible Ethernet . . . . . . . . . . . . . . . . . .  20
       5.1.2.  Dedicated Queues  . . . . . . . . . . . . . . . . . .  20
       5.1.3.  Time Sensitive Networking . . . . . . . . . . . . . .  21
     5.2.  Layer Three Data Plane  . . . . . . . . . . . . . . . . .  21
       5.2.1.  Deterministic Networking  . . . . . . . . . . . . . .  21
       5.2.2.  MPLS Traffic Engineering (MPLS-TE)  . . . . . . . . .  22

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       5.2.3.  Segment Routing . . . . . . . . . . . . . . . . . . .  22
     5.3.  Non-Packet Data Plane . . . . . . . . . . . . . . . . . .  23
     5.4.  Control Plane . . . . . . . . . . . . . . . . . . . . . .  23
     5.5.  Management Plane  . . . . . . . . . . . . . . . . . . . .  24
     5.6.  Applicability of Service Data Models to Enhanced VPN  . .  26
   6.  Applicability to Network Slice Realization  . . . . . . . . .  26
     6.1.  VTN Planning  . . . . . . . . . . . . . . . . . . . . . .  27
     6.2.  VTN Instantiation . . . . . . . . . . . . . . . . . . . .  27
     6.3.  VPN+ Service Provisioning . . . . . . . . . . . . . . . .  27
     6.4.  Network Slice Traffic Steering and Forwarding . . . . . .  28
   7.  Scalability Considerations  . . . . . . . . . . . . . . . . .  28
     7.1.  Maximum Stack Depth of SR . . . . . . . . . . . . . . . .  29
     7.2.  RSVP-TE Scalability . . . . . . . . . . . . . . . . . . .  29
     7.3.  SDN Scaling . . . . . . . . . . . . . . . . . . . . . . .  29
   8.  OAM Considerations  . . . . . . . . . . . . . . . . . . . . .  30
   9.  Telemetry Considerations  . . . . . . . . . . . . . . . . . .  30
   10. Enhanced Resiliency . . . . . . . . . . . . . . . . . . . . .  31
   11. Operational Considerations  . . . . . . . . . . . . . . . . .  32
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  32
   13. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  33
   14. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  33
   15. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  33
   16. References  . . . . . . . . . . . . . . . . . . . . . . . . .  34
     16.1.  Normative References . . . . . . . . . . . . . . . . . .  34
     16.2.  Informative References . . . . . . . . . . . . . . . . .  34
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  40

1.  Introduction

   Virtual private networks (VPNs) have served the industry well as a
   means of providing different groups of users with logically isolated
   connectivity over a common network.  The common or base network that
   is used to provide the VPNs is often referred to as the underlay, and
   the VPN is often called an overlay.

   Customers of a network operator may request a connectivity services
   with advanced characteristics such as low latency guarantees, bounded
   jitter, or isolation from other services or customers so that changes
   in some other service (such as changes in network load, or events
   such as congestion or outages) have no or only acceptable effect on
   the throughput or latency of the services provided to the customer.
   These services are referred to as "enhanced VPNs" (known as VPN+) in
   that they are similar to VPN services providing the customer with the
   required connectivity, but in addition they have enhanced

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   The concept of network slicing has gained traction driven largely by
   needs surfacing from 5G [NGMN-NS-Concept] [TS23501] [TS28530].
   According to [TS28530], a 5G end-to-end network slice consists of
   three major types of network segments: Radio Access Network (RAN),
   Transport Network (TN), and Mobile Core Network (CN).  The transport
   network provides the connectivity between different entities in RAN
   and CN segments of a 5G end-to-end network slice, with specific
   performance commitment.

   [I-D.ietf-teas-ietf-network-slices] defines the terminologies and the
   characteristics of IETF network slices.  It also discusses the
   general framework, the components and interfaces for requesting and
   operating IETF network slices.  An IETF Network Slice Service enables
   connectivity between a set of CEs with specific Service Level
   Objectives (SLOs) and Service Level Expectations (SLEs) over a common
   underlay network.  An IETF Network Slice can be realized as a logical
   network connecting a number of endpoints and is associated with a set
   of shared or dedicated network resources that are used to satisfy the
   Service Level Objectives (SLOs) and Service Level Expectations (SLEs)
   requirements.  In this document (which is solely about IETF
   technologies) we refer to an "IETF network slice" simply as a
   "network slice": a network slice is considered one possible use case
   of an enhanced VPN.

   A network slice could span multiple technologies (such as IP or
   Optical) and multiple administrative domains.  Depending on the
   customer's requirement, a network slice could be isolated from other
   network slices in terms of data plane, control plane, and management
   plane resources.

   Network slicing builds on the concepts of resource management,
   network virtualization, and abstraction to provide performance
   assurance, flexibility, programmability, and modularity.  It may use
   techniques such as Software Defined Networking (SDN) [RFC7149],
   network abstraction [RFC7926] and Network Function Virtualization
   (NFV) [RFC8172] [RFC8568] to create multiple logical (virtual)
   networks, each tailored for use by a set of services or by a
   particular tenant or a group of tenants that share the same or
   similar requirements.  These logical networks are created on top of a
   common underlay network.  How the network slices are engineered can
   be deployment-specific.

   The requirements of enhanced VPN services cannot be met by simple
   overlay networks, as these services require tighter coordination and
   integration between the underlay and the overlay network.  VPN+ is
   built from a VPN overlay and an underlying Virtual Transport Network
   (VTN) which has a customized network topology and a set of dedicated
   or shared resources in the underlay network.  The enhanced VPN may

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   also include a set of invoked service functions located within the
   underlay network.  Thus, an enhanced VPN can achieve greater
   isolation with strict performance guarantees.  These new properties,
   which have general applicability, are also of interest as part of a
   network slicing solution.

   VPN+ can be used to instantiate a network slice service, and the
   technique can also be of use in general cases to provide enhanced
   connectivity services between customer sites or service end points.
   [I-D.ietf-teas-ietf-network-slices] introduces the concept Network
   Resource Partition (NRP) as a set of network resources that are
   available to carry traffic and meet the SLOs and SLEs.  An NRP is
   associated with a network topology to define the set of links and
   nodes.  Thus VTN and NRP are considered as similar concepts, and NRP
   can be seen as an instantiation of VTN in the context of network

   It is not envisaged that VPN+ services will replace traditional VPN
   services.  Traditional VPN services will continue to be delivered
   using pre-existing mechanisms and can co-exist with VPN+ services.

   This document describes a framework for using existing, modified, and
   potential new technologies as components to provide a VPN+ service.
   Specifically, we are concerned with:

   *  The functional requirements and service characteristics of an
      enhanced VPN.

   *  The design of the enhanced data plane.

   *  The necessary control and management protocols in both the
      underlay and the overlay of the enhanced VPN.

   *  The mechanisms to achieve integration between overlay and

   *  The necessary Operation, Administration, and Management (OAM)
      methods to instrument an enhanced VPN to make sure that the
      required Service Level Agreement (SLA) between the customer and
      the network operator is met, and to take any corrective action
      (such as switching traffic to an alternate path) to avoid SLA

   The required layered network structure to achieve this is shown in
   Section 4.1.

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2.  Terminology

   In this document, the relationship of the four terms "VPN", "VPN+",
   "VTN", and "Network Slice" are as follows:

   *  A Virtual Private Network (VPN) refers to the overlay network
      service that provides the connectivity between different customer
      sites, and that maintains traffic separation between different
      customers.  The typical VPN technologies are: IPVPN [RFC2764],
      L2VPN [RFC4664], L3VPN [RFC4364], and EVPN [RFC7209].

   *  An enhanced VPN (VPN+) is an evolution of the VPN service that
      makes additional service-specific commitments.  An enhanced VPN is
      made by integrating an overlay VPN with a set of network resources
      allocated in the underlay network.

   *  A Virtual Transport Network (VTN) is a virtual underlay network
      which consists of a set of dedicated or shared network resources
      allocated from the physical underlay network, and is associated
      with a customized logical network topology.  VTN has the
      capability to deliver the performance characteristics required by
      the VPN+ customers and to provide isolation between different VPN+

   *  A network slice could be provided by provisioning an enhanced VPN
      in the network.  Other mechanisms for delivering network slices
      may exist but are not in scope for this document.

   The term "tenant" is used in this document to refer to the customers
   and all of their associated enhanced VPNs.

   The following terms are also used in this document.  Some of them are
   newly defined, some others reference existing definitions.

   ACTN:  Abstraction and Control of Traffic Engineered Networks

   DetNet:  Deterministic Networking.  See [DETNET] and [RFC8655]

   FlexE:  Flexible Ethernet [FLEXE]

   TSN:  Time Sensitive Networking [TSN]

   VN:  Virtual Network [I-D.ietf-teas-actn-vn-yang]

   VTP:  Virtual Transport Path.  A VTP is a path through the VTN which
      provides the required connectivity and performance between two or
      more customer sites.

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3.  Overview of the Requirements

   This section provides an overview of the requirements of an enhanced
   VPN service.

3.1.  Performance Guarantees

   Performance guarantees are made by network operators to their
   customers in relation to the services provided to the customers.
   They are usually expressed in SLAs as a set of SLOs.

   There are several kinds of performance guarantee, including
   guaranteed maximum packet loss, guaranteed maximum delay, and
   guaranteed delay variation.  Note that these guarantees apply to
   conformance traffic, out-of-profile traffic will be handled according
   to a separate agreement with the customer.

   Guaranteed maximum packet loss is usually addressed by setting packet
   priorities, queue size, and discard policy.  However this becomes
   more difficult when the requirement is combined with latency
   requirements.  The limiting case is zero congestion loss, and that is
   the goal of DetNet [DETNET] and TSN [TSN].  In modern optical
   networks, loss due to transmission errors already approaches zero,
   but there is the possibility of failure of the interface or the fiber
   itself.  This type of fault can only be addressed by some form of
   signal duplication and transmission over diverse paths.

   Guaranteed maximum latency is required by a number of applications
   particularly real-time control applications and some types of virtual
   reality applications.  DetNet [DETNET] is relevant, however
   additional methods of enhancing the underlay to better support the
   delay guarantees may be needed, and these methods will need to be
   integrated with the overall service provisioning mechanisms.

   Guaranteed maximum delay variation is a performance guarantee that
   may also be needed.  [RFC8578] calls up a number of cases that need
   this guarantee, for example in electrical utilities.  Time transfer
   is an example service that needs a performance guarantee, although it
   is in the nature of time that the service might be delivered by the
   underlay as a shared service and not provided through different
   enhanced VPNs.  Alternatively, a dedicated enhanced VPN might be used
   to provide this as a shared service.

   This suggests that a spectrum of service guarantees need to be
   considered when deploying an enhanced VPN.  As a guide to
   understanding the design requirements we can consider four types of

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   *  Best effort

   *  Assured bandwidth

   *  Guaranteed latency

   *  Enhanced delivery

   The best effort service is the basic service as provided by current

   An assured bandwidth service is one in which the bandwidth over some
   period of time is assured.  This can be achieved either simply based
   on a best effort service with over-capacity provisioning, or it can
   be based on MPLS traffic engineered label switching paths (TE-LSPs)
   with bandwidth reservations.  Depending on the technique used,
   however, the bandwidth is not necessarily assured at any instant.
   Providing assured bandwidth to VPNs, for example by using per-VPN TE-
   LSPs, is not widely deployed at least partially due to scalability
   concerns.  VPN+ aims to provide a more scalable approach for such

   A guaranteed latency service has an upper bound to edge-to-edge
   latency.  Assuring the upper bound is sometimes more important than
   minimizing latency.  There are several new technologies that provide
   some assistance with this performance guarantee.  Firstly, the IEEE
   TSN project [TSN] introduces the concept of scheduling of delay- and
   loss-sensitive packets.  The DetNet work [DETNET] is also of
   relevance in assuring an upper bound of end-to-end packet latency.
   FlexE [FLEXE] is also useful to help provide these guarantees.  The
   use of such underlying technologies to deliver VPN+ services needs to
   be considered.

   An enhanced delivery service is one in which the underlay network (at
   Layer 3) attempts to deliver the packet through multiple paths in the
   hope of eliminating packet loss due to equipment or media failures.
   Such a mechanism may need to be used for VPN+ service.

3.2.  Isolation between Enhanced VPN Services

   One element of the SLA demanded for an enhanced VPN may be a
   guarantee that the service offered to the customer will not be
   affected by any other traffic flows in the network.  This is termed
   "isolation" and a customer may express the requirement for isolation
   as an SLE [I-D.ietf-teas-ietf-network-slices].

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   One way for a network operator to meet the requirement for isolation
   is simply by setting and conforming to all the SLOs.  For example,
   traffic congestion (interference from other services) might impact on
   the latency experienced by a VPN+ customer.  Thus, in this example,
   conformance to a latency SLO would be the primary requirement for
   delivery of the VPN+ service, and isolation from other services might
   be only a means to that end.

   Another way for a service provider to meet this SLE is to control the
   degree to which traffic from one service is isolated from other
   services in the network.

   There is a fine distinction between how isolation is requested by a
   customer and how it is delivered by the service provider.  In
   general, the customer is interested in service performance and not
   how it is delivered.  Thus, for example, the customer wants specific
   quality guarantees and is not concerned about how the service
   provider delivers them.  However, it should be noted that some
   aspects of isolation might be directly measurable by a customer if
   they have information about the traffic patterns on a number services
   supported by the same service provider.  Furthermore, a customer may
   be nervous about disruption caused by other services, contamination
   by other traffic, or delivery of their traffic to the wrong
   destinations.  In this way, the customer may want to specify (and pay
   for) the level of isolation provided by the service provider.

   Isolation is achieved in the realization of a VPN+ through existing
   technologies that may be supplemented by new mechanisms.  The service
   provider chooses which processes to use to meet this SLE just as they
   choose how to meet all other SLOs and SLEs.  Isolation may be
   achieved in the network by various forms of resource partitioning
   ranging from simple separation of service traffic on delivery
   (ensuring that traffic is not delivered to the wrong customer),
   through sharing of resources with some form of safeguards, to
   dedicated allocation of resources for a specific enhanced VPN.  For
   example, interference avoidance may be achieved by network capacity
   planning, allocating dedicated network resources, traffic policing or
   shaping, prioritizing in using shared network resources, etc.

   The terms hard and soft isolation are used to indicate different
   levels of isolation.  A service has soft isolation if the traffic of
   one service cannot be received by the customers of another service.
   The existing IP and MPLS VPNs are examples of services with soft
   isolation: the network delivers the traffic only to the required
   customer endpoints.  However, with soft isolation, as the network
   resources are shared, traffic from some services may congest the
   network, resulting in packet loss and delay for other services.  The
   ability for a service or a group of services to be sheltered from

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   this effect is called hard isolation.  Hard isolation may be needed
   so that applications with exacting requirements can function
   correctly, despite other demands (perhaps a burst of traffic in
   another service) competing for the underlying resources.  A customer
   may request different degrees of isolation ranging from soft
   isolation to hard isolation.  In practice isolation may be delivered
   on a spectrum between soft and hard, and in some cases soft and hard
   isolation may be used in a hierarchical manner with one enhanced VPN
   being built on another.

   To provide the required level of isolation, resources may need to be
   reserved in the data plane of the underlay network and dedicated to
   traffic from a specific enhanced VPN or a specific group of enhanced
   VPNs.  This may introduce scalability concerns both in the
   implementation (as each enhanced VPN would need to be tracked in the
   network) and in how many resources need to be reserved and may be
   under-used (see Section 4.4).  Thus, some trade-off needs to be
   considered to provide the isolation between enhanced VPNs while still
   allowing reasonable resource sharing.

   An optical underlay can offer a high degree of isolation, at the cost
   of allocating resources on a long-term and end-to-end basis.  On the
   other hand, where adequate isolation can be achieved at the packet
   layer, this permits the resources to be shared amongst a group of
   services and only dedicated to a service on a temporary basis.

   The next section explores a pragmatic approach to isolation in packet

3.2.1.  A Pragmatic Approach to Isolation

   A key question is whether it is possible to achieve hard isolation in
   packet networks that were designed to provide statistical
   multiplexing through sharing of data plane resources, a significant
   economic advantage when compared to a dedicated, or a Time Division
   Multiplexing (TDM) network.  Clearly, there is no need to provide
   more isolation than is required by the applications, and an
   approximation to full hard isolation is sufficient in most cases.
   For example, pseudowires [RFC3985] emulate services that would have
   had hard isolation in their native form.

        |          \---------------v---------------/
    Statistical                Pragmatic             Absolute
    Multiplexing               Isolation            Isolation
   (Traditional VPNs)        (Enhanced VPN)     (Dedicated Network)

                    Figure 1: The Spectrum of Isolation

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   Figure 1 shows a spectrum of isolation that may be delivered by a
   network.  At one end of the spectrum, we see statistical multiplexing
   technologies that support traditional VPNs.  This is a service type
   that has served the industry well and will continue to do so.  At the
   opposite end of the spectrum, we have the absolute isolation provided
   by dedicated transport networks.  The goal of enhanced VPNs is
   "pragmatic isolation".  This is isolation that is better than what is
   obtainable from pure statistical multiplexing, more cost effective
   and flexible than a dedicated network, but is a practical solution
   that is good enough for the majority of applications.  Mechanisms for
   both soft isolation and hard isolation are needed to meet different
   levels of service requirement.

3.3.  Integration

   The way to achieve the characteristics demanded by an enhanced VPN
   (such as guaranteed or predictable performance) is by integrating the
   overlay VPN with a particular set of resources in the underlay
   network which are allocated to meet the service requirement.  This
   needs be done in a flexible and scalable way so that it can be widely
   deployed in operators' networks to support a reasonable number of
   enhanced VPN customers.

   Taking mobile networks and in particular 5G into consideration, the
   integration of the network with service functions is likely a
   requirement.  The IETF's work on service function chaining (SFC)
   [SFC] provides a foundation for this.  Service functions can be
   considered as part of enhanced VPN services.  The detailed mechanisms
   about the integration between service functions and enhanced VPNs are
   out of the scope of this document.

3.3.1.  Abstraction

   Integration of the overlay VPN and the underlay network resources
   does not always need to be a direct mapping.  As described in
   [RFC7926], abstraction is the process of applying policy to a set of
   information about a traffic engineered (TE) network to produce
   selective information that represents the potential ability to
   connect across the network.  The process of abstraction presents the
   connectivity graph in a way that is independent of the underlying
   network technologies, capabilities, and topology so that the graph
   can be used to plan and deliver network services in a uniform way.

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   Virtual networks can be built on top of an abstracted topology that
   represents the connectivity capabilities of the underlay TE based
   network as described in the framework for Abstraction and Control of
   TE Networks (ACTN) [RFC8453] as discussed further in Section 5.5.
   [I-D.ietf-teas-applicability-actn-slicing] describes the
   applicability of ACTN to network slicing and is, therefore, relevant
   to the consideration of using ACTN to enable enhanced VPNs.

3.4.  Dynamic Changes

   Enhanced VPNs need to be created, modified, and removed from the
   network according to service demands.  An enhanced VPN that requires
   hard isolation (Section 3.2) must not be disrupted by the
   instantiation or modification of another enhanced VPN.  Determining
   whether modification of an enhanced VPN can be disruptive to that
   VPN, and whether the traffic in flight will be disrupted can be a
   difficult problem.

   The data plane aspects of this problem are discussed further in
   Section 5.1,Section 5.2, and Section 5.3.

   The control plane aspects of this problem are discussed further in
   Section 5.4.

   The management plane aspects of this problem are discussed further in
   Section 5.5.

   Dynamic changes both to the enhanced VPN and to the underlay network
   need to be managed to avoid disruption to services that are sensitive
   to changes in network performance.

   In addition to non-disruptively managing the network during changes
   such as the inclusion of a new VPN endpoint or a change to a link,
   VPN traffic might need to be moved because of changes to traffic
   patterns and volumes.

3.5.  Customized Control

   In many cases the customers are delivered with enhanced VPN services
   without knowing the information about the underlying VTNs.  However,
   depends on the agreement between the operator and the customer, in
   some cases the customer may also be provided with some information
   about the underlying VTNs.  Such information can be filtered or
   aggregated according to the operator's policy.  This allows the
   customer of the enhanced VPN to have some visibility and even control
   over how the underlying topology and resources of the VTN are used.
   For example, the customers may be able to specify the service paths
   within the VTN for specific traffic flows of their enhanced VPNs.

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   Depending on the requirements, an enhanced VPN customer may have his
   own network controller, which may be provided with an interface to
   the control or management system run by the network operator.  Note
   that such control is within the scope of the customer's enhanced VPN,
   any additional changes beyond this would require some intervention by
   the network operator.

   A description of the control plane aspects of this problem are
   discussed further in Section 5.4.  A description of the management
   plane aspects of this feature can be found in Section 5.5.

3.6.  Applicability to Overlay Technologies

   The concept of enhanced VPN can be applied to any existing and future
   multi-tenancy overlay technologies including but not limited to :

   *  Layer-2 point-to-point services such as pseudowires [RFC3985]

   *  Layer-2 VPNs [RFC4664]

   *  Ethernet VPNs [RFC7209]

   *  Layer-3 VPNs [RFC4364], [RFC2764]

   Where such VPN service types need enhanced isolation and delivery
   characteristics, the technologies described in Section 5 can be used
   to provide an underlay with the required enhanced performance.

3.7.  Inter-Domain and Inter-Layer Network

   In some scenarios, an enhanced VPN service may span multiple network
   domains.  A domain is considered to be any collection of network
   elements within a common realm of address space or path computation
   responsibility [RFC5151] for example, an Autonomous System.  In some
   domains the network operator may manage a multi-layered network, for
   example, a packet network over an optical network.  When VPN+
   services are provisioned in such network scenarios, the technologies
   used in different network planes (data plane, control plane, and
   management plane) need to provide mechanisms to support multi-domain
   and multi-layer coordination and integration, so as to provide the
   required service characteristics for different enhanced VPNs, and
   improve network efficiency and operational simplicity.

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4.  Architecture of Enhanced VPNs

   A number of VPN+ services will typically be provided by a common
   network infrastructure.  Each VPN+ service is provisioned with an
   overlay VPN and a corresponding VTN, which has a specific set of
   network resources and functions allocated in the underlay to satisfy
   the needs of the customer.  One VTN may support one of more VPN+
   services.  The integration between the overlay connectivity and the
   underlay resources ensures the required isolation between different
   VPN+ services, and achieves the guaranteed performance for different

   The VPN+ architecture needs to be designed with consideration given

   *  An enhanced data plane.

   *  A control plane to create enhanced VPNs, making use of the data
      plane isolation and performance guarantee techniques.

   *  A management plane for enhanced VPN service life-cycle management.

   These topics are expanded below.

   *  The enhanced data plane:

      -  Provides the required packet latency and jitter

      -  Provides the required packet loss characteristics.

      -  Provides the required resource isolation capability, e.g.,
         bandwidth guarantee.

      -  Provides the mechanism to associate a packet with the set of
         resources allocated to a VTN which the VPN+ service packet is
         mapped to.

   *  The control plane:

      -  Collects information about the underlying network topology and
         network resources, and exports this to network nodes and/or a
         centralized controller as required.

      -  Creates VTNs with the network resource and topology properties
         needed by the VPN+ services.

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      -  Distribute the attributes of VTNs to network nodes which
         participate in the VTNs and/or a centralized controller.

      -  Compute and set up network paths in each VTN.

      -  Map VPN+ services to an appropriate VTN.

      -  Determines the risk of SLA violation and takes appropriate
         avoiding action.

      -  Consider the right balance of per-packet and per-node state
         according to the needs of the VPN+ services to scale to the
         required size.

   *  The management plane:

      -  Provides an interface between the VPN+ service provider (e.g.,
         operator's network management system ) and the VPN+ customer
         (e.g., an organization or a service with enhanced VPN
         requirement) such that some of the operation requests can be
         met without interfering with other VPN+ customers.

      -  Provides an interface between the VPN+ service provider and the
         VPN+ customers to expose the network capability information
         toward the customer.

      -  Provides the service life-cycle management and operation of
         VPN+ services (e.g., creation, modification, assurance/
         monitoring, and decommissioning).

   *  Operations, Administration, and Maintenance (OAM)

      -  Provides the tools to verify the connectivity and performance
         of the VPN+ service.

      -  Provides the tools to verify whether the underlay network
         resources are correctly allocated and operating properly.

   *  Telemetry

      -  Provides the mechanisms to collect network information about
         the operation of the data plane, control plane, and management
         plane.  More specifically, telemetry provides the mechanisms to
         collect network data:

         o  from the underlay network for overall performance evaluation
            and for the planning VPN+ services.

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         o  from each VPN+ service for monitoring and analytics of the
            characteristics and SLA fulfillment of the VPN+ services.

4.1.  Layered Architecture

   The layered architecture of VPN+ is shown in Figure 2.

   Underpinning everything is the physical network infrastructure layer
   which provide the underlying resources used to provision the
   separated VTNs.  This layer is responsbile for the partitioning of
   link and/or node resources for different VTNs.  Each subset of link
   or node resource can be considered as a virtual link or virtual node
   used to build the VTNs.

                      +-------------------+       Centralized
                      | Network Controller|   Control & Management
                  o---------------------------o    VPN Service 1
                  o____________/______________o    VPN Service 2
                  o___/     \_________________o    VPN Service 3
                             ......                    ...
                  o-----------\ /-------------o
                  o____________X______________o    VPN Service n

                    /       o----o-----o      /
                   /       /          /      /        VTN-1
                  / o-----o-----o----o----o /
                    /       o----o            /
                   /       /    / \          /        VTN-2
                  / o-----o----o---o------o /
                           ......                      ...
                   /             o----o       /
                  /             /    /       /        VTN-m
                 /  o-----o----o----o-----o /

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                   ++++   ++++   ++++
                   ++++   +++\\  ++++
                    ||     || \\  ||             Physical
                    ||     ||  \\ ||              Network
            ++++   ++++   ++++  \\+++   ++++  Infrastructure
            ++++   ++++   ++++   ++++   ++++

       o    Virtual Node     ++++
                             +--+  Physical Node with resource partition
       --   Virtual Link     +--+
       ==  Physical Link with resource partition

                Figure 2: The Layered Architecture of VPN+

   Various components and techniques discussed in Section 5 can be used
   to enable resource partitioning, such as FlexE, TSN, DetNet,
   dedicated queues, etc.  These partitions may be physical or virtual
   so long as the SLA required by the higher layers is met.

   Based on the network resource partitions provided by the physical
   network infrastructure, multiple VTNs can be created, each with a set
   of dedicated or shared network resources allocated from the physical
   underlay network, and is associated with a customized logical network
   topology, so as to meet the requirements of different VPN+ services
   or different groups of VPN+ services.  According to the associated
   logical network topology, each VTN needs to be instantiated on a set
   of network nodes and links which are involved in the logical
   topology.  And on each node or link, each VTN is associated with a
   set of local resources which are allocated for the processing of
   traffic in the VTN.  The VTN provides the integration between the
   virtual network topology and the required underlying network

   According to the service requirements on connectivity, performance
   and isolation, etc., VPN services can be mapped to the appropriate
   VTNs in the network.  Different VPN services can be mapped to
   different VTNs, while it is also possible that multiple VPNs are
   mapped to the same VTN.  Thus VTN is an essential scaling technique,
   as it has the potential of eliminating per-path state from the
   network.  In addition, when a group of VPN+ services are mapped to a
   single VTN, only the network state of the single VTN needs to be
   maintained in the network (see Section 4.4 for more information).

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   The centralized network controller is responsible for creating a VTN,
   instructing the involved network nodes to allocate network resources
   to the VTN, and provisioning the VPN services on the VTN.  A
   distributed control plane may be used for distributing the VTN
   resource and topology attributes among nodes in the VTN.

   The process used to create VTNs and to allocate network resources for
   use by the VTNs needs to take a holistic view of the needs of all of
   its customers and to partition the resources accordingly.  However,
   within a VTN these resources can, if required, be managed via a
   dynamic control plane.  This provides the required scalability and
   isolation with some flexibility.

4.2.  Multi-Point to Multi-Point (MP2MP) Connectivity

   At the VPN service level, the required connectivity for an MP2MP VPN
   service is usually full or partial mesh.  To support such VPN
   services, the corresponding VTN also needs to provide MP2MP
   connectivity among the end points.

   Other service requirements may be expressed at different
   granularities, some of which can be applicable to the whole service,
   while some others may only be applicable to some pairs of end points.
   For example, when a particular level of performance guarantee is
   required, the point-to-point path through the underlying VTN of the
   VPN+ service may need to be specifically engineered to meet the
   required performance guarantee.

4.3.  Application Specific Data Types

   Although a lot of the traffic that will be carried over VPN+ will
   likely be IP based, the design must be capable of carrying other
   traffic types, in particular Ethernet traffic.  This is easily
   accomplished through the various pseudowire (PW) techniques
   [RFC3985].  Where the underlay is MPLS, Ethernet traffic can be
   carried over VPN+ encapsulated according to the method specified in
   [RFC4448].  Where the underlay is IP, Layer Two Tunneling Protocol -
   Version 3 (L2TPv3) [RFC3931] can be used with Ethernet traffic
   carried according to [RFC4719].  Encapsulations have been defined for
   most of the common Layer-2 types for both PW over MPLS and for

4.4.  Scaling Considerations

   VPNs are instantiated as overlays on top of an operator's network and
   offered as services to the operator's customers.  An important
   feature of overlays is that they can deliver services without placing
   per-service state in the core of the underlay network.

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   VPN+ may need to install some additional state within the network to
   achieve the features that they require.  Solutions must consider
   minimizing and controlling the scale of such state, and deployment
   architectures should constrain the number of VPN+ services so that
   the additional state introduced to the network is acceptable and
   under control.  It is expected that the number of VPN+ services will
   be small at the beginning, and even in future the number of VPN+
   services will be fewer than traditional VPNs because pre-existing VPN
   techniques are good enough to meet the needs of most existing VPN-
   type services.

   In general, it is not required that the state in the network be
   maintained in a 1:1 relationship with the VPN+ services.  It will
   usually be possible to aggregate a set or group of VPN+ services so
   that they share the same VTN and the same set of network resources
   (much in the same way that current VPNs are aggregated over transport
   tunnels) so that collections of VPN+ services that require the same
   behavior from the network in terms of resource reservation, latency
   bounds, resiliency, etc. can be grouped together.  This is an
   important feature to assist with the scaling characteristics of VPN+

   [I-D.dong-teas-nrp-scalability] provides more details of scalability
   considerations for the network resource partitions used to
   instantiate VTNs, and Section 7 includes a greater discussion of
   scalability considerations.

5.  Candidate Technologies

   A VPN is a network created by applying a demultiplexing technique to
   the underlying network (the underlay) to distinguish the traffic of
   one VPN from that of another.  A VPN path that travels by other than
   the shortest path through the underlay normally requires state in the
   underlay to specify that path.  State is normally applied to the
   underlay through the use of the RSVP-TE signaling protocol, or
   directly through the use of an SDN controller, although other
   techniques may emerge as this problem is studied.  This state gets
   harder to manage as the number of VPN paths increases.  Furthermore,
   as we increase the coupling between the underlay and the overlay to
   support the VPN+ service, this state will increase further.  Thus, a
   VPN+ solution needs tighter coupling with the underlay than is the
   case with existing VPN techniques.  We cannot, for example, share the
   network resource between VPN+ services which require hard isolation.

   In a VPN+ solution, different subsets of the underlay resources can
   be dedicated to different VPN+ services or different groups of VPN+
   services through the use of VTNs.

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5.1.  Packet Forwarding Plane Technologies

   Several candidate Layer 2 packet- or frame-based data plane solutions
   which provide the required isolation and guarantees are described in
   the following sections.

5.1.1.  Flexible Ethernet

   FlexE [FLEXE] provides the ability to multiplex channels over an
   Ethernet link to create point-to-point fixed- bandwidth connections
   in a way that provides hard isolation.  FlexE also supports bonding
   links to create larger links out of multiple low capacity links.

   However, FlexE is only a link level technology.  When packets are
   received by the downstream node, they need to be processed in a way
   that preserves that isolation in the downstream node.  This in turn
   requires a queuing and forwarding implementation that preserves the
   end-to-end isolation.

   If different FlexE channels are used for different services, then no
   sharing is possible between the FlexE channels.  This means that it
   may be difficult to dynamically redistribute unused bandwidth to
   lower priority services in another FlexE channel.  If one FlexE
   channel is used by one customer, the customer can use some methods to
   manage the relative priority of their own traffic in the FlexE

5.1.2.  Dedicated Queues

   DiffServ based queuing systems are described in [RFC2475] and
   [RFC4594].  This approach is not sufficient to provide isolation for
   VPN+ services because DiffServ does not provide enough markers to
   differentiate between traffic of a large number of VPN+ services.
   Nor does DiffServ offer the range of service classes that each VPN+
   service needs to provide to its tenants.  This problem is
   particularly acute with an MPLS underlay, because MPLS only provides
   eight traffic classes.

   In addition, DiffServ, as currently implemented, mainly provides per-
   hop priority-based scheduling, and it is difficult to use it to
   achieve quantitative resource reservation for different VPN+

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   To address these problems and to reduce the potential interference
   between VPN+ services, it would be necessary to steer traffic to
   dedicated input and output queues per VPN+ service or per group of
   VPN+ services: some routers have a large number of queues and
   sophisticated queuing systems which could support this, while some
   routers may struggle to provide the granularity and level of
   isolation required by the applications of VPN+.

5.1.3.  Time Sensitive Networking

   Time Sensitive Networking (TSN) [TSN] is an IEEE project to provide a
   method of carrying time sensitive information over Ethernet.  It
   introduces the concept of packet scheduling where a packet stream may
   be given a time slot guaranteeing that it experiences no queuing
   delay or increase in latency beyond the very small scheduling delay.
   The mechanisms defined in TSN can be used to meet the requirements of
   time sensitive traffic flows of VPN+ service.

   Ethernet can be emulated over a Layer 3 network using an IP or MPLS
   pseudowire.  However, a TSN Ethernet payload would be opaque to the
   underlay and thus not treated specifically as time sensitive data.
   The preferred method of carrying TSN over a Layer 3 network is
   through the use of deterministic networking as explained in
   Section 5.2.1.

5.2.  Layer Three Data Plane

   This section considers the problem of VPN+ service differentiation
   and the representation of underlying network resources in the network
   layer.  More specifically, it describes the possible data plane
   mechanisms to determine the network resources and the logical network
   topology or paths associated with a VTN.

5.2.1.  Deterministic Networking

   Deterministic Networking (DetNet) [RFC8655] is a technique being
   developed in the IETF to enhance the ability of Layer-3 networks to
   deliver packets more reliably and with greater control over the
   delay.  The design cannot use re-transmission techniques such as TCP
   since that can exceed the delay tolerated by the applications.  Even
   the delay improvements that are achieved with Stream Control
   Transmission Protocol Partial Reliability Extension (SCTP-PR)
   [RFC3758] may not meet the bounds set by application demands.  DetNet
   pre-emptively sends copies of the packet over various paths to
   minimize the chance of all copies of a packet being lost.  It also
   seeks to set an upper bound on latency, but the goal is not to
   minimize latency.  Detnet can be realized over IP data plane
   [RFC8939] or MPLS data plane [RFC8964], and may be used to provide

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   Virtual Transport Path (VTP) for VPN+ services.

5.2.2.  MPLS Traffic Engineering (MPLS-TE)

   MPLS-TE [RFC2702][RFC3209] introduces the concept of reserving end-
   to-end bandwidth for a TE-LSP, which can be used to provide a point-
   to-point Virtual Transport Path (VTP) across the underlay network to
   support VPN services.  VPN traffic can be carried over dedicated TE-
   LSPs to provide reserved bandwidth for each specific connection in a
   VPN, and VPNs with similar behavior requirements may be multiplexed
   onto the same TE-LSPs.  Some network operators have concerns about
   the scalability and management overhead of MPLS-TE system, especially
   with regard to those systems that use an active control plane, and
   this has lead them to consider other solutions for traffic
   engineering in their networks.

5.2.3.  Segment Routing

   Segment Routing (SR) [RFC8402] is a method that prepends instructions
   to packets at the head-end of a path.  These instructions are used to
   specify the nodes and links to be traversed, and allow the packets to
   be routed on paths other than the shortest path.  By encoding the
   state in the packet, per-path state is transitioned out of the

   An SR traffic engineered path operates with a granularity of a link.
   Hints about priority are provided using the Traffic Class (TC) or
   Differentiated Services Code Point (DSCP) field in the packet header.
   However, to achieve the performance and isolation characteristics
   that are sought by VPN+ customers, it will be necessary to steer
   packets through specific virtual links and/or queues on the same link
   and direct them to use specific resources.  With SR, it is possible
   to introduce such fine-grained packet steering by specifying the
   queues and the associated resources through an SR instruction list.

   Note that the concept of a queue is a useful abstraction for
   different types of underlay mechanism that may be used to provide
   enhanced isolation and performance support.  How the queue satisfies
   the requirement is implementation specific and is transparent to the
   layer-3 data plane and control plane mechanisms used.

   With Segment Routing, the SR instruction list could be used to build
   a P2P path, and a group of SR SIDs could also be used to represent an
   MP2MP network.  Thus, the SR based mechanism could be used to provide
   both a Virtual Transport Path (VTP) and a Virtual Transport Network
   (VTN) for VPN+ services.

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5.3.  Non-Packet Data Plane

   Non-packet underlay data plane technologies often have TE properties
   and behaviors, and meet many of the key requirements in particular
   for bandwidth guarantees, traffic isolation (with physical isolation
   often being an integral part of the technology), highly predictable
   latency and jitter characteristics, measurable loss characteristics,
   and ease of identification of flows.  The cost is that the resources
   are allocated on a long-term and end-to-end basis.  Such an
   arrangement means that the full cost of the resources has to be borne
   by the service that is allocated with the resources.

5.4.  Control Plane

   The control plane of VPN+ would likely be based on a hybrid control
   mechanism that takes advantage of a logically centralized controller
   for on-demand provisioning and global optimization, whilst still
   relying on a distributed control plane to provide scalability, high
   reliability, fast reaction, automatic failure recovery, etc.
   Extension to and optimization of the centralized and distributed
   control plane is needed to support the enhanced properties of VPN+.

   As described in section 4, the VPN+ control plane needs to provide
   the following functions:

   *  Collects information about the underlying network topology and
      network resources, and exports this to network nodes and/or a
      centralized controller as required.

   *  Creates VTNs with the network resource and topology properties
      needed by the VPN+ services.

   *  Distribute the attributes of VTNs to network nodes which
      participate in the VTNs and/or the centralized controller.

   *  Compute and set up VTPs in each VTN.

   *  Map VPN+ services to an appropriate VTN.

   The collection of underlying network topology and resource
   information can be done using existing the IGP and BGP-LS based
   mechanisms.  The creation of VTN and the distribution of VTN
   attributes may need further control protocol extensions.  The
   computation of VTPs based on the attributes and constraints of the
   VTN can be performed either by the headend node of the path or a
   centralized Path Computation Element (PCE).

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   There are two candidate mechanisms for the setup of VTPs in the VTN:
   RSVP-TE and Segment Routing (SR).

   *  RSVP-TE [RFC3209] provides the signaling mechanism for
      establishing a TE-LSP in an MPLS network with end-to-end resource
      reservation.  This can be seen as an approach of providing a
      Virtual Transport Path (VTP) which could be used to bind the VPN
      to specific network resources allocated within the underlay, but
      there remain scalability concerns as mentioned in Section 5.2.2.

   *  The SR control plane [RFC8665] [RFC8667] [RFC9085] does not have
      the capability of signaling resource reservations along the path.
      On the other hand, the SR approach provides a potential way of
      binding the underlay network resource and the VTNs without
      requiring per-path state to be maintained in the network.  A
      centralized controller can perform resource planning and
      reservation for VTNs, and it needs to instruct the network nodes
      to ensure that resources are correctly allocated for the VTN.  The
      controller could provision the SR paths based on the mechanism in
      [I-D.ietf-spring-segment-routing-policy] to the headend nodes of
      the paths.

   According to the service requirements on connectivity, performance
   and isolation, one VPN+ service may be mapped a dedicated VTN, or a
   group of VPN+ services may be mapped to the same VTN.  The mapping of
   VPN+ services to VTN can be achieved using existing control
   mechanisms with possible extensions, and it can be based on either
   the characteristics of the data packet or the attributes of the VPN
   service routes.

5.5.  Management Plane

   The management plane provides the interface between the VPN+ service
   provider and the customers for life-cycle management of the VPN+
   service (i.e., creation, modification, assurance/monitoring, and
   decommissioning).  It relies on a set of service data models for the
   description of the information and operations needed on the

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   As an example, in the context of 5G end-to-end network slicing
   [TS28530], the management of VPN+ services is considered as the
   management of the transport network segment of the 5G end-to-end
   network slice.  The 3GPP management system may provide the
   connectivity and performance related parameters as requirements to
   the management plane of the transport network.  It may also require
   the transport network to expose the capabilities and status of the
   network slice.  Thus, an interface between the VPN+ management plane
   and the 5G network slice management system, and relevant service data
   models are needed for the coordination of 5G end-to-end network slice

   The management plane interface and data models for VPN+ services can
   be based on the service models described in Section 5.6.

   It is important that the management life-cycle supports in-place
   modification of VPN+ services.  That is, it should be possible to add
   and remove end points, as well as to change the requested
   characteristics of the service that is delivered.  The management
   system needs to be able to assess the revised VPN+ requests and
   determine whether they can be provided by the existing VTNs or
   whether changes must be made, and it will additionally need to
   determine whether those changes to the VTN are possible.  If not,
   then the customer's modification request may be rejected.

   When the modification of a VPN+ service is possible, the management
   system should make every effort to make the changes in a non-
   disruptive way.  That is, the modification of the VPN+ service or the
   underlying VTN should not perturbate traffic on the VPN+ service in a
   way that causes the service level to drop below the agreed levels.
   Furthermore, in the spirit of isolation, changes to one VPN+ service
   should not cause disruption to other VPN+ services.

   The network operator for the underlay network (i.e., the provider of
   the VPN+ service) may delegate some operational aspects of the
   overlay VPN and the underlying VTN to the customer.  In this way, the
   VPN+ is presented to the customer as a virtual network, and the
   customer can choose how to use that network.  The customer cannot
   exceed the capabilities of the virtual links and nodes, but can
   decide how to load traffic onto the network, for example, by
   assigning different metrics to the virtual links so that the customer
   can control how traffic is routed through the virtual network.  This
   approach requires a management system for the virtual network, but
   does not necessarily require any coordination between the management
   systems of the virtual network and the physical network, except that
   the virtual network management system might notice when the VTN is
   close to capacity or considerably under-used and automatically
   request changes in the service provided by the underlay network.

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5.6.  Applicability of Service Data Models to Enhanced VPN

   This section describes the applicability of the existing and in-
   progress service data models to VPN+. [RFC8309] describes the the
   scope and purpose of service models and shows where a service model
   might fit into a SDN based network management architecture.  New
   service models may also be introduced for some of the required
   management functions.

   Service data models are used to represent, monitor, and manage the
   virtual networks and services enabled by VPN+. The VPN customer
   service models (e.g., the layer 3 VPN service model (L3SM) [RFC8299],
   the layer 2 VPN service model (L2SM) [RFC8466]), or the ACTN Virtual
   Network (VN) model [I-D.ietf-teas-actn-vn-yang]) are service models
   which can provide the customer's view of the VPN+ service.  The layer
   3 VPN network model (L3NM) [I-D.ietf-opsawg-l3sm-l3nm], the layer 2
   VPN network model (L2NM) [I-D.ietf-opsawg-l2nm] provide the
   operator's view of the managed infrastructure as a set of virtual
   networks and the associated resources.  The NRP model
   [I-D.wd-teas-nrp-yang] further provides the management of the virtual
   underlay network topology and resources both in the controller and in
   the network devices to instantiate the VTNs needed for the VPN+

   The ACTN framework[RFC8453] supports operators in viewing and
   controlling different domains and presenting virtualized networks to
   their customers.  [I-D.ietf-teas-applicability-actn-slicing]
   discusses the applicability of the ACTN approach in the context of
   network slicing.  Since there is a strong correlation between network
   slices and enhanced VPNs, that document also give guidance on how
   ACTN can be applied to enhanced VPNs.

6.  Applicability to Network Slice Realization

   One of the typical use cases of enhanced VPN is to deliver IETF
   network slice service.  This section describes the applicability of
   enhanced VPN to network slice realization.

   In order to provide IETF network slices to customers, a technology-
   agnostic network slice service Northbound Interface (NBI) data model
   [I-D.ietf-teas-ietf-network-slice-nbi-yang] is needed for the
   customers to communicate the requirements of IETF network slices (end
   points, connectivity, SLOs, and SLEs).  These requirements may be
   realized using technology specified in this document to instruct the
   network to instantiate a VPN+ service to meet the requirements of the
   IETF network slice customers.

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6.1.  VTN Planning

   According to the network operators' network resource planning policy,
   or based on the requirement of one or a group of customers or
   services, a VTN may need to be created.  One of the basic
   requirements for a VTN is to provide a set of dedicated network
   resources to avoid unexpected interference from other services in the
   same network.  Other possible requirements may include the required
   topology and connectivity, bandwidth, latency, reliability, etc.

   A centralized network controller can be responsible for calculating a
   subset of the underlay network topology (which is called a logical
   topology) to support the VTN requirement.  And on the network nodes
   and links within the logical topology, the set of network resources
   to be allocated to the VTN can also be determined by the controller.
   Normally such calculation needs to take the underlay network
   connectivity information and the available network resource
   information of the underlay network into consideration.  The network
   controller may also take the status of the existing VTNs into
   consideration in the planning and calculation of a new VTN.

6.2.  VTN Instantiation

   According to the result of the VTN planning, the network nodes and
   links involved in the logical topology of the VTN are instructed to
   allocated the required set of network resources for the VTN.  One or
   multiple mechanisms as specified in section 5.1 can be used to
   partition the forwarding plane network resources and allocate
   different subsets of resources to different VTNs.  In addition, the
   data plane identifiers which are used to identify the set of network
   resources allocated to the VTN are also provisioned on the network
   nodes.  Depends on the data plane technologies used, the set of
   network resources of a VTN can be identified using either resource
   aware SR segments as specified in
   [I-D.ietf-spring-resource-aware-segments], or a dedicated VTN
   resource ID as specified in [I-D.dong-6man-enhanced-vpn-vtn-id] can
   be introduced.  The network nodes involved in a VTN may distribute
   the logical topology information, the VTN specific network resource
   information and the VTN resource identifiers using the control plane.
   Such information could be used by the controller and the network
   nodes to compute the TE or shortest paths within the VTN, and install
   the VTN specific forwarding entries to network nodes.

6.3.  VPN+ Service Provisioning

   According to the connectivity requirements of an IETF network slice
   service, an overlay VPN can be created using the existing or future
   multi-tenancy overlay technologies as described in Section 3.6.

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   Then according to the SLOs and SLEs requirements of the network
   slice, the overlay VPN is mapped to an appropriate VTN as the virtual
   underlay.  The integration of the overlay VPN and the underlay VTN
   together provide an enhanced VPN service which can meet the network
   slice service requirements.

6.4.  Network Slice Traffic Steering and Forwarding

   At the edge of the operator's network, traffic of IETF network slices
   can be classified based on the rules defined by operator's policy, so
   that the traffic is treated as a specific VPN+ service, which is
   further mapped to a underlay VTN.  Packets belonging to the VPN+
   service will be processed and forwarded by network nodes based the TE
   or shortest path forwarding entries and the set of network resources
   of the corresponding VTN.

7.  Scalability Considerations

   VPN+ provides performance guaranteed services in packet networks, but
   with the potential cost of introducing additional state into the
   network.  There are at least three ways that this additional state
   might be brought into the network:

   *  Introduce the complete state into the packet, as is done in SR.
      This allows the controller to specify the detailed series of
      forwarding and processing instructions for the packet as it
      transits the network.  The cost of this is an increase in the
      packet header size.  The cost is also that systems will have
      capabilities enabled in case they are called upon by a service.
      This is a type of latent state, and increases as the path and
      resources that need to be exclusively available to a VPN are
      specified more precisely.

   *  Introduce the state to the network.  This is normally done by
      creating a path using signaling such as RSVP-TE.  This could be
      extended to include any element that needs to be specified along
      the path, for example explicitly specifying queuing policy.  It is
      also possible to use other methods to introduce path state, such
      as via an SDN controller, or possibly by modifying a routing
      protocol.  With this approach there is state per path: per-path
      characteristic that needs to be maintained over the life of the
      path.  This is more network state than is needed using SR, but the
      packets are usually shorter.

   *  Provide a hybrid approach.  One example is based on using binding
      SIDs [RFC8402] to create path fragments, and bind them together
      with SR.  Dynamic creation of a VPN service path using SR requires
      less state maintenance in the network core at the expense of

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      larger packet headers.  The packet size can be lower if a form of
      loose source routing is used (using a few nodal SIDs), and it will
      be lower if no specific functions or resources on the routers are

   Reducing the state in the network is important to VPN+, as it
   requires the overlay to be more closely integrated with the underlay
   than with traditional VPNs.  This tighter coupling would normally
   mean that more state needs to be created and maintained in the
   network, as the state about fine granularity processing would need to
   be loaded and maintained in the routers.  However, an SR approach
   allows much of this state to be spread amongst the network ingress
   nodes, and transiently carried in the packets as SIDs.

   Further discussion of the scalability considerations of the
   underlaying network resource partitions of VPN+ can be found in

7.1.  Maximum Stack Depth of SR

   One of the challenges with SR is the stack depth that nodes are able
   to impose on packets [RFC8491].  This leads to a difficult balance
   between adding state to the network and minimizing stack depth, or
   minimizing state and increasing the stack depth.

7.2.  RSVP-TE Scalability

   The traditional method of creating a resource allocated path through
   an MPLS network is to use the RSVP-TE protocol.  However, there have
   been concerns that this requires significant continuous state
   maintenance in the network.  Work to improve the scalability of RSVP-
   TE LSPs in the control plane can be found in [RFC8370].

   There is also concern at the scalability of the forwarder footprint
   of RSVP-TE as the number of paths through a label switching router
   (LSR) grows.  [RFC8577] addresses this by employing SR within a
   tunnel established by RSVP-TE.

7.3.  SDN Scaling

   The centralized approach of SDN requires state to be stored in the
   network, but does not have the overhead of also requiring control
   plane state to be maintained.  Each individual network node may need
   to maintain a communication channel with the SDN controller, but that
   compares favorably with the need for a control plane to maintain
   communication with all neighbors.

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   However, SDN may transfer some of the scalability concerns from the
   network to the centralized controller.  In particular, there may be a
   heavy processing burden at the controller, and a heavy load in the
   network surrounding the controller.  A centralized controller also
   presents a single point of failure within the network.

8.  OAM Considerations

   The design of OAM for VPN+ services needs to consider the following

   *  Instrumentation of the underlay so that the network operator can
      be sure that the resources committed to a tenant are operating
      correctly and delivering the required performance.

   *  Instrumentation of the overlay by the tenant.  This is likely to
      be transparent to the network operator and to use existing
      methods.  Particular consideration needs to be given to the need
      to verify the isolation and the various committed performance

   *  Instrumentation of the overlay by the network provider to
      proactively demonstrate that the committed performance is being
      delivered.  This needs to be done in a non-intrusive manner,
      particularly when the tenant is deploying a performance sensitive

   *  Verification of the conformity of the path to the service
      requirement.  This may need to be done as part of a commissioning

   A study of OAM in SR networks has been documented in [RFC8403].

9.  Telemetry Considerations

   Network visibility is essential for network operation.  Network
   telemetry has been considered as an ideal means to gain sufficient
   network visibility with better flexibility, scalability, accuracy,
   coverage, and performance than conventional OAM technologies.

   As defined in [I-D.ietf-opsawg-ntf], the objective of Network
   Telemetry is to acquire network data remotely for network monitoring
   and operation.  It is a general term for a large set of network
   visibility techniques and protocols.  Network telemetry addresses the
   current network operation issues and enables smooth evolution toward
   intent-driven autonomous networks.  Telemetry can be applied on the
   forwarding plane, the control plane, and the management plane in a

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   How the telemetry mechanisms could be used or extended for the VPN+
   service is out of the scope of this document.

10.  Enhanced Resiliency

   Each VPN+ service has a life cycle, and may need modification during
   deployment as the needs of its tenant change.  This is discussed in
   Section 5.5.  Additionally, as the network evolves, there may need to
   be garbage collection performed to consolidate resources into usable

   Systems in which the path is imposed, such as SR or some form of
   explicit routing, tend to do well in these applications, because it
   is possible to perform an atomic transition from one path to another.
   That is, a single action by the head-end that changes the path
   without the need for coordinated action by the routers along the
   path.  However, implementations and the monitoring protocols need to
   make sure that the new path is operational and meets the required SLA
   before traffic is transitioned to it.  It is possible for deadlocks
   to arise as a result of the network becoming fragmented over time,
   such that it is impossible to create a new path or to modify an
   existing path without impacting the SLA of other paths.  Resolution
   of this situation is as much a commercial issue as it is a technical
   issue and is outside the scope of this document.

   There are, however, two manifestations of the latency problem that
   are for further study in any of these approaches:

   *  The problem of packets overtaking one another if a path latency
      reduces during a transition.

   *  The problem of transient variation in latency in either direction
      as a path migrates.

   There is also the matter of what happens during failure in the
   underlay infrastructure.  Fast reroute is one approach, but that
   still produces a transient loss with a normal goal of rectifying this
   within 50ms [RFC5654].  An alternative is some form of N+1 delivery
   such as has been used for many years to support protection from
   service disruption.  This may be taken to a different level using the
   techniques of DetNet with multiple in-network replication and the
   culling of later packets [RFC8655].

   In addition to the approach used to protect high priority packets,
   consideration should be given to the impact of best effort traffic on
   the high priority packets during a transition.  Specifically, if a
   conventional re-convergence process is used there will inevitably be
   micro-loops and whilst some form of explicit routing will protect the

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   high priority traffic, lower priority traffic on best effort shortest
   paths will micro-loop without the use of a loop prevention
   technology.  To provide the highest quality of service to high
   priority traffic, either this traffic must be shielded from the
   micro-loops, or micro-loops must be prevented completely.

11.  Operational Considerations

   It is likely that VPN+ services will be introduced in networks which
   already have traditional VPN services deployed.  Depending on service
   requirements, the tenants or the operator may choose to use a
   traditional VPN or an enhanced VPN to fulfill a service requirement.
   The information and parameters to assist such a decision needs to be
   reflected on the management interface between the tenant and the

12.  Security Considerations

   All types of virtual network require special consideration to be
   given to the isolation of traffic belonging to different tenants.
   That is, traffic belonging to one VPN must not be delivered to end
   points outside that VPN.  In this regard VPN+ neither introduce, nor
   experience a greater security risks than other VPNs.

   However, in a VPN+ service the additional service requirements need
   to be considered.  For example, if a service requires a specific
   upper bound to latency then it can be damaged by simply delaying the
   packets through the activities of another tenant, i.e., by
   introducing bursts of traffic for other services.  In some respects
   this makes the enhanced VPN more susceptible to attacks since the SLA
   may be broken.  But another view is that the operator must, in any
   case, preform monitoring of the enhanced VPN to ensure that the SLA
   is met, and this means that the operator may be more likely to spot
   the early onset of a security attack and be able to take pre-emptive
   protective action.

   The measures to address these dynamic security risks must be
   specified as part to the specific solution are form part of the
   isolation requirements of a service.

   While a VPN+ service may be sold as offering encryption and other
   security features as part of the service, customers would be well
   advised to take responsibility for their own security requirements
   themselves possibly by encrypting traffic before handing it off to
   the service provider.

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   The privacy of VPN+ service customers must be preserved.  It should
   not be possible for one customer to discover the existence of another
   customer, nor should the sites that are members of an VPN+ be
   externally visible.

13.  IANA Considerations

   There are no requested IANA actions.

14.  Contributors

      Daniel King
      Email: daniel@olddog.co.uk

      Adrian Farrel
      Email: adrian@olddog.co.uk

      Jeff Tansura
      Email: jefftant.ietf@gmail.com

      Zhenbin Li
      Email: lizhenbin@huawei.com

      Qin Wu
      Email: bill.wu@huawei.com

      Bo Wu
      Email: lana.wubo@huawei.com

      Daniele Ceccarelli
      Email: daniele.ceccarelli@ericsson.com

      Mohamed Boucadair
      Email: mohamed.boucadair@orange.com

      Sergio Belotti
      Email: sergio.belotti@nokia.com

      Haomian Zheng
      Email: zhenghaomian@huawei.com

15.  Acknowledgements

   The authors would like to thank Charlie Perkins, James N Guichard,
   John E Drake, Shunsuke Homma, and Luis M.  Contreras for their review
   and valuable comments.

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   This work was supported in part by the European Commission funded
   H2020-ICT-2016-2 METRO-HAUL project (G.A. 761727).

16.  References

16.1.  Normative References

   [RFC2764]  Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A.
              Malis, "A Framework for IP Based Virtual Private
              Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000,

   [RFC3985]  Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
              Edge-to-Edge (PWE3) Architecture", RFC 3985,
              DOI 10.17487/RFC3985, March 2005,

   [RFC4664]  Andersson, L., Ed. and E. Rosen, Ed., "Framework for Layer
              2 Virtual Private Networks (L2VPNs)", RFC 4664,
              DOI 10.17487/RFC4664, September 2006,

16.2.  Informative References

   [DETNET]   "Deterministic Networking", March ,

   [FLEXE]    "Flex Ethernet Implementation Agreement", March 2016,

              Dong, J., Li, Z., Xie, C., Ma, C., and G. Mishra,
              "Carrying Virtual Transport Network (VTN) Identifier in
              IPv6 Extension Header", Work in Progress, Internet-Draft,
              draft-dong-6man-enhanced-vpn-vtn-id-06, 24 October 2021,

              Dong, J., Li, Z., Gong, L., Yang, G., Guichard, J. N.,
              Mishra, G., Qin, F., Saad, T., and V. P. Beeram,
              "Scalability Considerations for Network Resource
              Partition", Work in Progress, Internet-Draft, draft-dong-
              teas-nrp-scalability-01, 7 February 2022,

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              Barguil, S., Dios, O. G. D., Boucadair, M., and L. A.
              Munoz, "A Layer 2 VPN Network YANG Model", Work in
              Progress, Internet-Draft, draft-ietf-opsawg-l2nm-12, 22
              November 2021, <https://www.ietf.org/archive/id/draft-

              Barguil, S., Dios, O. G. D., Boucadair, M., Munoz, L. A.,
              and A. Aguado, "A YANG Network Data Model for Layer 3
              VPNs", Work in Progress, Internet-Draft, draft-ietf-
              opsawg-l3sm-l3nm-18, 8 October 2021,

              Song, H., Qin, F., Martinez-Julia, P., Ciavaglia, L., and
              A. Wang, "Network Telemetry Framework", Work in Progress,
              Internet-Draft, draft-ietf-opsawg-ntf-13, 3 December 2021,

              Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li,
              Z., and F. Clad, "Introducing Resource Awareness to SR
              Segments", Work in Progress, Internet-Draft, draft-ietf-
              spring-resource-aware-segments-03, 12 July 2021,

              Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture", Work in
              Progress, Internet-Draft, draft-ietf-spring-segment-
              routing-policy-18, 17 February 2022,

              Lee, Y., Dhody, D., Ceccarelli, D., Bryskin, I., and B. Y.
              Yoon, "A YANG Data Model for VN Operation", Work in
              Progress, Internet-Draft, draft-ietf-teas-actn-vn-yang-13,
              23 October 2021, <https://www.ietf.org/archive/id/draft-

              Lee, Y., Zheng, H., Ceccarelli, D., Yoon, B. Y., and S.
              Belotti, "Applicability of YANG models for Abstraction and

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              Control of Traffic Engineered Networks", Work in Progress,
              Internet-Draft, draft-ietf-teas-actn-yang-08, 8 September
              2021, <https://www.ietf.org/archive/id/draft-ietf-teas-

              King, D., Drake, J., Zheng, H., and A. Farrel,
              "Applicability of Abstraction and Control of Traffic
              Engineered Networks (ACTN) to Network Slicing", Work in
              Progress, Internet-Draft, draft-ietf-teas-applicability-
              actn-slicing-00, 21 September 2021,

              Wu, B., Dhody, D., Rokui, R., Saad, T., and L. Han, "IETF
              Network Slice Service YANG Model", Work in Progress,
              Internet-Draft, draft-ietf-teas-ietf-network-slice-nbi-
              yang-01, 4 March 2022, <https://www.ietf.org/archive/id/

              Farrel, A., Drake, J., Rokui, R., Homma, S., Makhijani,
              K., Contreras, L. M., and J. Tantsura, "Framework for IETF
              Network Slices", Work in Progress, Internet-Draft, draft-
              ietf-teas-ietf-network-slices-08, 6 March 2022,

              Wu, B., Dhody, D., and Y. Cheng, "A YANG Data Model for
              Network Resource Partition (NRP)", Work in Progress,
              Internet-Draft, draft-wd-teas-nrp-yang-00, 30 January
              2022, <https://www.ietf.org/archive/id/draft-wd-teas-nrp-

              hao ,, "NGMN NS Concept", 2016,

   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
              and W. Weiss, "An Architecture for Differentiated
              Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,

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   [RFC2702]  Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
              McManus, "Requirements for Traffic Engineering Over MPLS",
              RFC 2702, DOI 10.17487/RFC2702, September 1999,

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,

   [RFC3758]  Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P.
              Conrad, "Stream Control Transmission Protocol (SCTP)
              Partial Reliability Extension", RFC 3758,
              DOI 10.17487/RFC3758, May 2004,

   [RFC3931]  Lau, J., Ed., Townsley, M., Ed., and I. Goyret, Ed.,
              "Layer Two Tunneling Protocol - Version 3 (L2TPv3)",
              RFC 3931, DOI 10.17487/RFC3931, March 2005,

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

   [RFC4448]  Martini, L., Ed., Rosen, E., El-Aawar, N., and G. Heron,
              "Encapsulation Methods for Transport of Ethernet over MPLS
              Networks", RFC 4448, DOI 10.17487/RFC4448, April 2006,

   [RFC4594]  Babiarz, J., Chan, K., and F. Baker, "Configuration
              Guidelines for DiffServ Service Classes", RFC 4594,
              DOI 10.17487/RFC4594, August 2006,

   [RFC4719]  Aggarwal, R., Ed., Townsley, M., Ed., and M. Dos Santos,
              Ed., "Transport of Ethernet Frames over Layer 2 Tunneling
              Protocol Version 3 (L2TPv3)", RFC 4719,
              DOI 10.17487/RFC4719, November 2006,

   [RFC5151]  Farrel, A., Ed., Ayyangar, A., and JP. Vasseur, "Inter-
              Domain MPLS and GMPLS Traffic Engineering -- Resource
              Reservation Protocol-Traffic Engineering (RSVP-TE)
              Extensions", RFC 5151, DOI 10.17487/RFC5151, February
              2008, <https://www.rfc-editor.org/info/rfc5151>.

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   [RFC5654]  Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
              Sprecher, N., and S. Ueno, "Requirements of an MPLS
              Transport Profile", RFC 5654, DOI 10.17487/RFC5654,
              September 2009, <https://www.rfc-editor.org/info/rfc5654>.

   [RFC7149]  Boucadair, M. and C. Jacquenet, "Software-Defined
              Networking: A Perspective from within a Service Provider
              Environment", RFC 7149, DOI 10.17487/RFC7149, March 2014,

   [RFC7209]  Sajassi, A., Aggarwal, R., Uttaro, J., Bitar, N.,
              Henderickx, W., and A. Isaac, "Requirements for Ethernet
              VPN (EVPN)", RFC 7209, DOI 10.17487/RFC7209, May 2014,

   [RFC7926]  Farrel, A., Ed., Drake, J., Bitar, N., Swallow, G.,
              Ceccarelli, D., and X. Zhang, "Problem Statement and
              Architecture for Information Exchange between
              Interconnected Traffic-Engineered Networks", BCP 206,
              RFC 7926, DOI 10.17487/RFC7926, July 2016,

   [RFC8172]  Morton, A., "Considerations for Benchmarking Virtual
              Network Functions and Their Infrastructure", RFC 8172,
              DOI 10.17487/RFC8172, July 2017,

   [RFC8299]  Wu, Q., Ed., Litkowski, S., Tomotaki, L., and K. Ogaki,
              "YANG Data Model for L3VPN Service Delivery", RFC 8299,
              DOI 10.17487/RFC8299, January 2018,

   [RFC8309]  Wu, Q., Liu, W., and A. Farrel, "Service Models
              Explained", RFC 8309, DOI 10.17487/RFC8309, January 2018,

   [RFC8370]  Beeram, V., Ed., Minei, I., Shakir, R., Pacella, D., and
              T. Saad, "Techniques to Improve the Scalability of RSVP-TE
              Deployments", RFC 8370, DOI 10.17487/RFC8370, May 2018,

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

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   [RFC8403]  Geib, R., Ed., Filsfils, C., Pignataro, C., Ed., and N.
              Kumar, "A Scalable and Topology-Aware MPLS Data-Plane
              Monitoring System", RFC 8403, DOI 10.17487/RFC8403, July
              2018, <https://www.rfc-editor.org/info/rfc8403>.

   [RFC8453]  Ceccarelli, D., Ed. and Y. Lee, Ed., "Framework for
              Abstraction and Control of TE Networks (ACTN)", RFC 8453,
              DOI 10.17487/RFC8453, August 2018,

   [RFC8466]  Wen, B., Fioccola, G., Ed., Xie, C., and L. Jalil, "A YANG
              Data Model for Layer 2 Virtual Private Network (L2VPN)
              Service Delivery", RFC 8466, DOI 10.17487/RFC8466, October
              2018, <https://www.rfc-editor.org/info/rfc8466>.

   [RFC8491]  Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
              "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
              DOI 10.17487/RFC8491, November 2018,

   [RFC8568]  Bernardos, CJ., Rahman, A., Zuniga, JC., Contreras, LM.,
              Aranda, P., and P. Lynch, "Network Virtualization Research
              Challenges", RFC 8568, DOI 10.17487/RFC8568, April 2019,

   [RFC8577]  Sitaraman, H., Beeram, V., Parikh, T., and T. Saad,
              "Signaling RSVP-TE Tunnels on a Shared MPLS Forwarding
              Plane", RFC 8577, DOI 10.17487/RFC8577, April 2019,

   [RFC8578]  Grossman, E., Ed., "Deterministic Networking Use Cases",
              RFC 8578, DOI 10.17487/RFC8578, May 2019,

   [RFC8655]  Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", RFC 8655,
              DOI 10.17487/RFC8655, October 2019,

   [RFC8665]  Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler,
              H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
              Extensions for Segment Routing", RFC 8665,
              DOI 10.17487/RFC8665, December 2019,

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   [RFC8667]  Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C.,
              Bashandy, A., Gredler, H., and B. Decraene, "IS-IS
              Extensions for Segment Routing", RFC 8667,
              DOI 10.17487/RFC8667, December 2019,

   [RFC8939]  Varga, B., Ed., Farkas, J., Berger, L., Fedyk, D., and S.
              Bryant, "Deterministic Networking (DetNet) Data Plane:
              IP", RFC 8939, DOI 10.17487/RFC8939, November 2020,

   [RFC8964]  Varga, B., Ed., Farkas, J., Berger, L., Malis, A., Bryant,
              S., and J. Korhonen, "Deterministic Networking (DetNet)
              Data Plane: MPLS", RFC 8964, DOI 10.17487/RFC8964, January
              2021, <https://www.rfc-editor.org/info/rfc8964>.

   [RFC9085]  Previdi, S., Talaulikar, K., Ed., Filsfils, C., Gredler,
              H., and M. Chen, "Border Gateway Protocol - Link State
              (BGP-LS) Extensions for Segment Routing", RFC 9085,
              DOI 10.17487/RFC9085, August 2021,

   [SFC]      "Service Function Chaining", March ,

   [TS23501]  "3GPP TS23.501", 2016,

   [TS28530]  "3GPP TS28.530", 2016,

   [TSN]      "Time-Sensitive Networking", March ,

Authors' Addresses

   Jie Dong
   Email: jie.dong@huawei.com

   Stewart Bryant
   University of Surrey
   Email: stewart.bryant@gmail.com

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   Zhenqiang Li
   China Mobile
   Email: lizhenqiang@chinamobile.com

   Takuya Miyasaka
   KDDI Corporation
   Email: ta-miyasaka@kddi.com

   Young Lee
   Email: younglee.tx@gmail.com

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