[Teas-ns-dt] John's Proposed NS-DT Framework Starting Point

[Eric Gray <[e-mail]>]

Hopefully for addition to today's agenda...



John will be unable to attend today's meeting and asked me to talk about his proposal to augment the Framework draft.



In John's E-Mail, he added references to places in the Enhanced VPN draft where we could "lift" the text to fill in sections in the Framework skeleton Jari provided (at: https://github.com/teas-wg/teas-ns-dt/blob/master/notes/notes-2019-12-23-framework-skeleton.md).



I have reformatted this in order to clarify what were "section headers" in Jari's proposed skeleton.  I also added a note that the underlying technologies section is not expected to be all inclusive.  Finally, I have added some of the proposed section text explicitly in order to make it easier to see what John has proposed adding



All that John appears to have added (or changed) otherwise is the URLs referring to specific sections (which is what we asked him to do).





Introduction



... Refer to [definitions] ...



.... Relation to existing IETF technologies ...



......JD  https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#section-1



   Virtual private networks (VPNs) have served the industry well as a

   means of providing different groups of users with logically isolated

   access to 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 enhanced overlay services

   with advanced characteristics such as complete isolation from other

   services so that changes in one service (such as changes in network

   load, or events such as congestion or outages) have no effect on the

   throughput or latency of other services provided to the customer.



While this paragraph may be (and probably is) true for some set of customers, it is not particularly relevant to this work.



I recommend omitting the paragraph.



   Driven largely by needs surfacing from 5G, the concept of network

   slicing has gained traction [NGMN-NS-Concept<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-NGMN-NS-Concept>] [TS23501<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-TS23501>] [TS28530<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-TS28530>]

   [BBF-SD406<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-BBF-SD406>].  In [TS23501<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-TS23501>], Network Slice is defined as "a logical

   network that provides specific network capabilities and network

   characteristics", and Network Slice Instance is defined as "A set of

   Network Function instances and the required resources (e.g. compute,

   storage and networking resources) which form a deployed Network

   Slice".  According to [TS28530<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-TS28530>], an end-to-end network slice consists

   of three major network segments: Radio Access Network (RAN),

   Transport Network (TN) and Core Network (CN).  Transport network

   provides the required connectivity within and between RAN and CN

   parts, with specific performance commitment.  For each end-to-end

   network slice, the topology and performance requirement on transport

   network can be very different, which requires transport network to

   have the capability of supporting multiple different transport

   network slices.



This should probably refer to "types of network segments," as it is clear from prior DT discussions that there may be multiple instances of (for example) "Transport Slices."



   A transport network slice is a virtual (logical) network with a

   particular network topology and a set of shared or dedicated network

   resources, which are used to provide the network slice consumer with

   the required connectivity, appropriate isolation and specific Service

   Level Agreement (SLA).  A transport network slice could span multiple

   technology (IP, Optical) and multiple administrative domains.

   Depends on the consumer's requirement, a transport network slice

   could be isolated from other, often concurrent transport network

   slices in terms of data plane, control plane and management plane.



   In the following sections of this document, network slice refers to

   transport network slice, and is interchangeable with enhanced VPN.          (spelling)

   End-to-end network slice is used to refer to the 5G network slice.



In the above paragraph, we would (obviously) not include the phrase claiming that a "transport network slice" being interchangeable with VPN+; in addition there are the following issues:

1)  We have agreed (I am fairly certain) to use the expression "Transport Slice" to refer to what this text refers to as a "transport network slice" hence - if we include this text (and subsequent text using either "transport network slice" or just "network slice" we will need to revise that text to be consistent with the definitions draft;

2)  We have also (again, I am fairly certain) agreed that the scope for transport (network) slices is not limited to 5G.



I recommend omitting this paragraph and - instead - making sure that the remainder of the subsequent text becomes consistent with the definitions draft.



   Network abstraction is a technique that can be applied to a network

   domain to select network resources by policy to obtain a view of

   potential connectivity and a set of service functions.



   Network slicing builds on the concept 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<https://tools.ietf.org/html/rfc7149>] and Network

   Function Virtualization (NFV) [RFC8172<https://tools.ietf.org/html/rfc8172>][RFC8568] to create multiple

   logical (virtual) networks, each tailored for a set of services or a

   particular tenant or a group of tenants that share the same set of

   requirements, on top of a common network.  How the network slices are

   engineered can be deployment-specific.



   Thus, there is a need to create virtual networks with enhanced

   characteristics.  The tenant of such a virtual network can require a

   degree of isolation and performance that previously could not be

   satisfied by traditional overlay VPNs.  Additionally, the tenant may

   ask for some level of control to their virtual networks, e.g., to

   customize the service paths in a network slice.



This usage of "could (not)" has been a target for extensive objections in the VPN+ draft and should not be included in this work.



I recommend replacing "could" with "might."



   These enhanced properties cannot be met with pure overlay networks,

   as they require tighter coordination and integration between the

   underlay and the overlay network.  This document introduces a new

   network service called Enhanced VPN: VPN+. VPN+ is built from a

   virtual network which has a customized network topology and a set of

   dedicated or shared network resources, including invoked service

   functions, allocated from the underlay network.  Unlike a traditional

   VPN, an enhanced VPN can achieve greater isolation with strict

   performance guarantees.  These new properties, which have general

   applicability, may also be of interest as part of a network slicing







Dong, et al.             Expires March 15, 2020                 [Page 4]

________________________________

 <https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#page-5>

Internet-Draft               VPN+ Framework               September 2019





   solution, but it is not envisaged that VPN+ techniques will be

   applied to normal VPN services that can continue to be deployed using

   pre-existing mechanisms.  Furthermore, it is not intended that large

   numbers of VPN+ instances will be deployed within a single network.

   See Section 5<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#section-5> for a discussion of scalability considerations.



The above paragraph is specific to VPN+ (or enhanced VPN) and therefore has no place in this NS-DT Framework Introduction.



I recommend omitting this paragraph.



   This document specifies a framework for using existing, modified and

   potential new technologies as components to provide a VPN+ service.

   Specifically we are concerned with:



I recommend replacing "VPN+" with "Transport Slice."



   o  The design of the enhanced data plane.



I recommend replacing "enhanced" with "Transport Slice."



   o  The necessary protocols in both the underlay and the overlay of

      the enhanced VPN.



I recommend replacing "enhanced VPN" with "Transport Slice."



   o  The mechanisms to achieve integration between overlay and

      underlay.



   o  The necessary Operation, Administration, and Management (OAM)

      methods to instrument an enhanced VPN to make sure that the

      required Service Level Agreement (SLA) is met, and to take any

      corrective action to avoid SLA violation, such as switching to an

      alternate path.



I recommend replacing "enhanced VPN" with "Transport Slice."



In addition, we have settled on using "Service Level Objectives in our work, so this should be aligned with that usage.



I receommend replacing "Agreement (SLA)" with "Objective (SLO)" and further modifying subsequent text as needed to be consistent with the definitions draft.



   The required layered network structure to achieve this is shown in

   Section 3.1<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#section-3.1>.



This reference - if this sentence is included - must be corrected to refer to a section (or figure) in this draft.



   Note that, in this document, the four terms "VPN", "Enhanced VPN" (or

   "VPN+"), "Virtual Network (VN)", and "Network Slice" may be

   considered as describing similar concepts dependent on the viewpoint

   from which they are used.



I recommend omitting this paragraph.



   o  An enhanced VPN can be considered as a form of VPN, but with

      additional service-specific commitments.  Thus, care must be taken

      with the term "VPN" to distinguish normal or legacy VPNs from VPN+

      instances.



I recommend replacing "enhanced VPN" with "Transport Slice" and omitting the second sentence.



   o  A Virtual Network is a type of service that connects customer edge

      points with the additional possibility of requesting further

      service characteristics in the manner of an enhanced VPN.



I recommend omitting this bullet.



   o  An enhanced VPN or VN is made by creating a slice through the

      resources of the underlay network.



I recommend omitting this bullet.



   o  The general concept of network slicing in a TE network is a larger

      problem space than is addressed by VPN+ or VN, but those concepts

      are tools to address some aspects or realizations of network

      slicing.



I recommend replacing the highlighted  text above with "existing concepts (e.g. - VPN/VPN+)."



Requirements



....



.... clarify scoping is only networking ...



.... add some discussion of scalability ...



......JD  https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#section-2,  https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#section-5



The text in section 2 of the enhanced VPN draft is entirely about the contentious concept of hard and soft isolation, which that draft is explicitly aimed at providing.  Including the text from section 2 of the enhanced VPN draft MUST be seen as an explicit endorsement of that draft as a solution to "Transport Slicing."



I recommend providing a reference to section 2 of the enhanced VPN draft as an example of a set of requirements that may apply to "Transport Slices."



Similarly, the text in section 5 addresses state scalability issues related to use of Segment Routing, RSVP-TE or some mix of the two. This text would require extensive modification to emphasize the generic issues associated with state information (in packets, or in the network) required for a number of currently proposed solutions for supporting "Transport Slicing."  Note that the section concludes that a solution to the scalability issues it discusses is for further study.



I recommend making the modifications to the text from section 5 to discuss the generic scalability issues only.  A reference to section 5 of the enhanced VPN draft may be included for further information about example technologies.



Framework



......JD  https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#section-3



Note that this section of the enhanced VPN draft is named "Architecture of Enhanced VPN."   The text (and figure) in this section extends from page 13 to page 16 (4 pages).



It is not the purpose of this Framework section  in our draft to provide a specific solution architecture, and the subsections of this section do not align well with the subsections in this framework skeleton.  Specifically, section 3 has the following subsections:



   3.  Architecture of Enhanced VPN

     3.1.  Layered Architecture

     3.2.  Multi-Point to Multi-Point (MP2MP)

     3.3.  Application Specific Network Types

     3.4.  Scaling Considerations



I recommend reviewing the contents of this section and providing a recommendation based on it as a starting point for filling in at least the leading text for the framework (as well as evaluating the included figure (Figure 2) as a possible starting point for the diagram suggested below.



.... diagram ...



            Applications



.... the transport slice system is used by an application. in most likely, that application is just another level slice orchestrator, e.g., the end-to-end slice orchestrator. but in theory it could also be an actual application that wants to manage some specific connectivity through the transport slice system. ...



              Expressing connectivity intents



......JD  I would replace the term 'applications' w/ 'overlay services'



.... northbound interface ...



.... data models ...



.... SLOs as intents ...



.... (most of this comes from the definitions draft) ...



              Mapping



.... the requirements get mapped by a piece of software, the controller, to concrete technologies and the connectivity is set up ...



              Controller



....



            Underlying technology (examples)



.... such as MPLS or VPNs or even physical cables ...



......JD  https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#section-4



   A VPN is a network created by applying a multiplexing technique to

   the underlying network (the underlay) in order 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 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 enhanced VPN service, this state will increase

   further.



   In an enhanced VPN different subsets of the underlay resources can be

   dedicated to different enhanced VPNs or different groups of enhanced

   VPNs.  An enhanced VPN solution thus needs tighter coupling with

   underlay than is the case with existing VPNs.  We cannot, for

   example, share the network resource between enhanced VPNs which

   require hard isolation.



       Layer-Two Data Plane

   A number of candidate Layer-2 packet or frame-based data plane

   solutions which can be used provide the required isolation and

   guarantee are described in following sections.



   o  FlexE



   o  Time Sensitive Networking



   o  Dedicated Queues



       FlexE



   FlexE [FLEXE<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-FLEXE>] is a method of creating a point-to-point Ethernet with

   a specific fixed bandwidth.  FlexE provides the ability to multiplex

   multiple channels over an Ethernet link in a way that provides hard

   isolation.  FlexE also supports the bonding of multiple links, which

   can be used to create larger links out of multiple low capacity links

   in a more efficient way that traditional link aggregation.  FlexE

   also supports the sub-rating of links, which allows an operator to

   only use a portion of a link.  However it is a 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 in turn means

   that it may be difficult to dynamically redistribute unused bandwidth

   to lower priority services.  This may increase the cost of providing

   services on the network.  On the other hand, FlexE can be used to

   provide hard isolation between different tenants on a shared

   interface.  The tenant can then use other methods to manage the

   relative priority of their own traffic in each FlexE channel.



   Methods of dynamically re-sizing FlexE channels and the implication

   for enhanced VPN are for further study.



       Dedicated Queues



   In order to provide multiple isolated virtual networks for enhanced

   VPN, the conventional DiffServ based queuing system [RFC2475<https://tools.ietf.org/html/rfc2475>]

   [RFC4594<https://tools.ietf.org/html/rfc4594>] is considered insufficient, as DiffServ does not always

   provide enough queues to differentiate between traffic of different

   enhanced VPNs, or the range of service classes that each need to

   provide to their tenants.  This problem is particularly acute with an

   MPLS underlay, because MPLS only provides 8 Traffic Classes (TC), and

   it's highly likely that there will be more than eight enhanced VPN

   instances supported by a network.  In addition, DiffServ, as

   currently implemented, mainly provides relative priority-based

   scheduling, and is difficult to achieve quantitive resource

   reservation.  In order to address this problem and reduce the

   interference between enhanced VPNs, it is necessary to steer traffic

   of enhanced VPNs to dedicated input and output queues.  Some routers

   have large amount of queues and sophisticated queuing systems, which

   could be used or enhanced to provide the granularity and level of

   isolation required by the applications of enhanced VPN.  For example,

   on one physical interface, the queuing system can provide a set of

   virtual sub-interfaces, each allocated with dedicated queueing and

   buffer resources.  Sophisticated queuing systems of this type may be

   used to provide end-to-end virtual isolation between traffic of

   different enhanced VPNs.



       Time-Sensitive Networking



   Time Sensitive Networking (TSN) [TSN<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-TSN>] is an IEEE project that is

   designing a method of carrying time sensitive information over

   Ethernet.  It introduces the concept of packet scheduling where a

   high priority packet stream may be given a scheduled time slot

   thereby guaranteeing that it experiences no queuing delay and hence a

   reduced latency.  However, when no scheduled packet arrives, its

   reserved time-slot is handed over to best effort traffic, thereby

   improving the economics of the network.  The mechanisms defined in

   TSN can be used to meet the requirements of time sensitive services

   of an enhanced VPN.



   Ethernet can be emulated over a Layer 3 network using a pseudowire.

   However the TSN 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 the following section of

   this document.

       Layer-Three Data Plane

   We now consider the problem of slice differentiation and resource

   representation in the network layer.  The candidate technologies are:



   o  Deterministic Networking



   o  MPLS-TE



   o  Segment Routing



       Deterministic Networking



   Deterministic Networking (DetNet) [I-D.ietf-detnet-architecture<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-I-D.ietf-detnet-architecture>] 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 Extenstion

   (SCTP-PR) [RFC3758<https://tools.ietf.org/html/rfc3758>] do 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, and trims duplicate packets to prevent excessive flooding of

   the network and to prevent multiple packets being delivered to the

   destination.  It also seeks to set an upper bound on latency.  The

   goal is not to minimize latency; the optimum upper bound paths may

   not be the minimum latency paths.



   DetNet is based on flows.  It currently does not specify the use of

   underlay topology other than the base topology.  To be of use for

   enhanced VPN, DetNet needs to be integrated with different virtual

   topologies of enhanced VPNs.



   The detailed design that allows the use DetNet in a multi-tenant

   network, and how to improve the scalability of DetNet in a multi-

   tenant network are topics for further study.



       MPLS Traffic Engineering



   MPLS-TE introduces the concept of reserving end-to-end bandwidth for

   a TE-LSP, which can be used as the underlay of VPNs.  It also

   introduces the concept of non-shortest path routing through the use

   of the Explicit Route Object [RFC3209<https://tools.ietf.org/html/rfc3209>].  VPN traffic can be run over

   dedicated TE-LSPs to provide reserved bandwidth for each specific

   connection in a VPN.  Some network operators have concerns about the

   scalability and management overhead of RSVP-TE system, and this has

   lead them to consider other solutions for their networks.



       Segment Routing



   Segment Routing [RFC8402<https://tools.ietf.org/html/rfc8402>] is a method that prepends instructions to

   packets at the head-end node and optionally at various points as it

   passes though the network.  These instructions allow the packets to

   be routed on paths other than the shortest path for various traffic

   engineering reasons.  With SR, a path needs to be dynamically created

   through a set of segments by simply specifying the Segment

   Identifiers (SIDs), i.e. instructions rooted at a particular point in

   the network.  By encoding the state in the packet, per-path state is

   transitioned out of the network.



   With current segment routing, the instructions are used to specify

   the nodes and links to be traversed.  An SR traffic engineered path

   operates with a granularity of a link with hints about priority

   provided through the use of the traffic class (TC) or Differentiated

   Services Code Point (DSCP) field in the header.  However to achieve

   the latency and isolation characteristics that are sought by the

   enhanced VPN users, steering packets through specific queues and

   resources will likely be required.  With SR, it is possible to

   introduce such fine-grained packet steering by specifying the queues

   and resources through an SR instruction list.



   Note that the concept of a queue is a useful abstraction for many

   types of underlay mechanism that may be used to provide enhanced

   isolation and latency support.  How the queue satisfies the

   requirement is implementation specific and is transparent to the

   layer-3 data plane and control plane mechanisms used.



   Both SR-MPLS and SRv6 are candidate data plane technologies for

   enhanced VPN.  In some cases they can further be used for DetNet to

   meet the packet loss, delay and jitter requirement of particular

   service.  How to provide the DetNet enhanced delivery in an SRv6

   environment is specified in [I-D.geng-spring-srv6-for-detnet<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-I-D.geng-spring-srv6-for-detnet>].



       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 (and hence slices).



   The control and management planes for non-packet data plane

   technologies have most in common with MPLS-TE (Section 4.2.2<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#section-4.2.2>) and

   offer the same set of advanced features [RFC3945<https://tools.ietf.org/html/rfc3945>].  Furthermore,

   management techniques such as ACTN ([RFC8453<https://tools.ietf.org/html/rfc8453>] and Section 4.6<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#section-4.6> can be

   used to aid in the reporting of underlying network topologies, and

   the creation of virtual networks with the resource and properties

   needed by the enhanced VPN services.



       Control Plane



   Enhanced VPN would likely be based on a hybrid control mechanism,

   which takes advantage of the logically centralized controller for on-

   demand provisioning and global optimization, whilst still relies on

   distributed control plane to provide scalability, high reliability,

   fast reaction, automatic failure recovery etc.  Extension and

   optimization to the distributed control plane is needed to support

   the enhanced properties of VPN+.



   RSVP-TE provides the signaling mechanism of establishing a TE-LSP

   with end-to-end resource reservation.  It can be used to bind the VPN

   to specific network resource allocated within the underlay, but there

   are the above mentioned scalability concerns.



   SR does not have the capability of signaling the resource reservation

   along the path, nor do its currently specified distributed link state

   routing protocols.  On the other hand, the SR approach provides a way

   of efficiently binding the network underlay and the enhanced VPN

   overlay, as it reduces the amount of state to be maintained in the

   network.  An SR-based approach with per-slice resource reservation

   can easily create dedicated SR network slices, and the VPN services

   can be bound to a particular SR network slice.  A centralized

   controller can perform resource planning and reservation from the

   controller's point of view, but this does not ensure resource

   reservation is actually done in the network nodes.  Thus, if a

   distributed control plane is needed, either in place of an SDN

   controller or as an assistant to it, the design of the control system

   needs to ensure that resources are uniquely allocated in the network

   nodes for the correct services, and not allocated to other services

   causing unintended resource conflict.



   In addition, in multi-domain and multi-layer networks, the

   centralized and distributed control mechanisms will be used for

   inter-domain coordination and inter-layer optimization, so that the

   diverse and customized enhanced VPN service requirement could be met.

   The detailed mechanisms will be described in a future version.



       Management Plane



   In the context of 5G end-to-end network slicing, the management of

   enhanced VPN is considered as the management of transport network

   part of the end-to-end network slice. 3GPP management system may

   provide the topology and QoS parameters as requirement to the

   management plane of transport network.  It may also require the

   transport network to expose the capability and status of the

   transport network slice.  Thus an interface between enhanced VPN

   management plane and 3GPP network slice management system and

   relevant service data models are needed for the coordination of end-

   to-end network slice management.



   The management plane interface and data models for enhanced VPN can

   be based on the service models such as:



   o  VPN service models defined in [RFC8299<https://tools.ietf.org/html/rfc8299>] and [RFC8466<https://tools.ietf.org/html/rfc8466>]



   o  Possible augmentations and extensions

      (e.g.,[I-D.ietf-teas-te-service-mapping-yang<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-I-D.ietf-teas-te-service-mapping-yang>]) to VPN service

      models

   o  ACTN related service models such as [I-D.ietf-teas-actn-vn-yang<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-I-D.ietf-teas-actn-vn-yang>]

      and [I-D.ietf-teas-actn-pm-telemetry-autonomics<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-I-D.ietf-teas-actn-pm-telemetry-autonomics>].



   o  VPN network model as defined in [I-D.aguado-opsawg-l3sm-l3nm<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-I-D.aguado-opsawg-l3sm-l3nm>].



   o  TE Tunnel model as defined in [I-D.ietf-teas-yang-te<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-I-D.ietf-teas-yang-te>].



   These data models can be applicable in the provisioning of enhanced

   VPN service.  The details are described in Section 4.6<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#section-4.6>.



       Applicability of Service Data Models to Enhanced VPN



   ACTN supports operators in viewing and controlling different domains

   and presenting virtualized networks to their customers.  The ACTN

   framework [RFC8453<https://tools.ietf.org/html/rfc8453>] highlights how:



   o  Abstraction of the underlying network resources are provided to

      higher-layer applications and customers.



   o  Virtualization of underlying resources, whose selection criterion

      is the allocation of those resources for the customer,

      application, or service.



   o  Creation of a virtualized environment allowing operators to view

      and control multi-domain networks as a single virtualized network.



   o  The presentation to customers of networks as a virtual network via

      open and programmable interfaces.



   The infrastructure managed through the Service Data models comprises

   traffic engineered network resources (e.g. bandwidth, time slot,

   wavelength) and VPN service related resources (e.g.  Route Target

   (RT) and Route Distinguisher (RD)).



   The type of network virtualization enabled by ACTN managed

   infrastructure provides customers and applications (tenants) with the

   capability to utilize and independently control allocated virtual

   network resources as if they were physically their own resources.



   The Customer VPN model (e.g.  L3SM) or an ACTN Virtual Network (VN)

   model is a customer view of the ACTN managed infrastructure, and is

   presented by the ACTN provider as a set of abstracted services or

   resources.



   L3VPN network model or TE tunnel model is a network view of the ACTN

   managed infrastructure, and is presented by the ACTN provider as a

   set of transport resources.



   Depending on the agreement between customer and provider, various

   VPN/VN operations and VPN/VN views are possible.



   o  Virtual Network Creation: A VPN/VN could be pre-configured and

      created via static or dynamic request and negotiation between

      customer and provider.  It must meet the specified SLA attributes

      which satisfy the customer's objectives.



   o  Virtual Network Operations: The virtual network may be further

      modified and deleted based on customer request to request changes

      in the network resources reserved for the customer, and used to

      construct the network slice.  The customer can further act upon

      the virtual network to manage traffic flow across the virtual

      network.



   o  Virtual Network View: The VPN/VN topology from a customer point of

      view.  These may be a variety of tunnels, or an entire VN

      topology, or an VPN service topology.  Such connections may

      comprise of customer end points, access links, intra-domain paths,

      and inter-domain links.



   Dynamic VPN/VN Operations allow a customer to modify or delete the

   VPN/VN.  The customer can further act upon the virtual network to

   create/modify/delete virtual links and nodes or VPN sites.  These

   changes will result in subsequent tunnel management or VPN service

   management in the operator's networks.



       Enhanced VPN Delivery in ACTN Architecture



   ACTN provides VPN connections or VN connections between multiple

   sites as requested via a VPN requestor enabled by the Customer

   Network Controller (CNC).  The CNC is managed by the customer

   themselves, and interacts with the network provider's Multi-Domain

   Service Controller (MDSC).  The Provisioning Network Controllers

   (PNC) are responible for network resource management, thus the PNCs

   are remain entirely under the management of the network provider and

   are not visible to the customer.



   The benefits of this model include:



   o  Provision of edge-to-edge VPN multi-access connectivity.



   o  Management is mostly performed by the network provider, with some

      flexibility delegated to the customer-managed CNC.



   Figure 3 presents a more general representation of how multiple

   enhanced VPNs may be created from the resources of multiple physical

   networks using the CNC, MDSC, and PNC components of the ACTN

   architecture.  Each enhanced VPN is controlled by its own CNC.  The

   CNCs send requests to the provider's MDSC.  The provider manages two

   different physical networks each under the control of PNC.  The MDSC

   asks the PNCs to allocate and provision resources to achieve the

   enhanced VPNs.  In this figure, one enhanced VPN is constructed

   solely from the resources of one of the physical networks, while the

   the VPN uses resources from both physical networks.



                                              ___________

                   ---------------           (           )

                   |    CNC      |---------->(    VPN+   )

                   --------^------           (           )

                           |                _(_________ _)

                ---------------            (           ) ^

                |    CNC      |----------->(    VPN+   ) :

                ------^--------            (           ) :

                      |    |               (___________) :

                      |    |                   ^    ^    :

    Boundary          |    |                   :    :    :

    Between ==========|====|===================:====:====:========

    Customer &        |    |                   :    :    :

    Network Provider  |    |                   :    :    :

                      v    v                   :    :    :

                ---------------                :    :....:

                |    MDSC     |                :         :

                ---------------                :         :

                      ^                     ---^------    ...

                      |                    (          )      .

                      v                   (  Physical  )      .

                  ----------------         ( Network  )        .

                  |     PNC      |<-------->(        )      ---^------

                ---------------- |           --------      (          )

                |              |--                        (  Physical  )

                |    PNC       |<------------------------->( Network  )

                ---------------                             (        )

                                                             --------



         Figure 3: Generic VPN+ Delivery in the ACTN Architecture



       Enhanced VPN Features with Service Data Models



   This section discusses how the service data models can fulfill the

   enhanced VPN requirements described earlier in this document.  As

   previously noted, key requirements of the enhanced VPN include:



   1.  Isolation between VPNs/VNs



   2.  Guaranteed Performance



   3.  Integration



   4.  Dynamic Management



   5.  Customized Control



   The subsections that follow outline how each requirement is met using

   ACTN.



       Isolation Between VPNs/VNs



   The VN YANG model [I-D.ietf-teas-actn-vn-yang<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-I-D.ietf-teas-actn-vn-yang>] and the TE-service

   mapping model [I-D.ietf-teas-te-service-mapping-yang<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-I-D.ietf-teas-te-service-mapping-yang>] fulfill the

   VPN/VN isolation requirement by providing the following features for

   the VPN/VNs:



   o  Each VN is identified with a unique identifier (vn-id and vn-name)

      and so is each VN member that belongs to the VN (vn-member-id).



   o  Each VPN is identified with a unique identifier (vpn-id) and can

      be mapped to one specific VN.  While multiple VPNs may mapped to

      the same VN according to service requirement and operator's

      policy.



   o  Each VPN and the corresponding VN is managed and controlled

      independent of other VPNs/VNs in the network with proper

      availability level.



   o  Each VPN/VN is instantiated with an isolation requirement

      described by the TE-service mapping model

      [I-D.ietf-teas-te-service-mapping-yang<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-I-D.ietf-teas-te-service-mapping-yang>].  This mapping supports:



      *  Hard isolation with deterministic characteristics (e.g., this

         case may need an optical bypass tunnel or a DetNet/TSN tunnel

         to guarantee latency with no jitter)



      *  Hard isolation (i.e., dedicated TE resources in all underlays)



      *  Soft isolation (i.e., resource in some layer may be shared

         while in some other layers is dedicated).



      *  No isolation (i.e., sharing with other VPN/VN).



       Guaranteed Performance



   Performance objectives of a VN need first to be expressed in order to

   assure the performance guarantee.



   Performance objectives of a VPN [RFC8299<https://tools.ietf.org/html/rfc8299>][RFC8466] are expressed with

   QoS profile, either standard profile or customer profile.  The

   customer QoS profile include the following properties:



   o  Rate-limit



   o  Bandwidth



   o  Latency



   o  Jitter



   [I-D.ietf-teas-actn-vn-yang] and [I-D.ietf-teas-yang-te-topo<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-I-D.ietf-teas-yang-te-topo>] allow

   configuration of several TE parameters that may affect the VN

   performance objectives as follows:



   o  Bandwidth



   o  Objective function (e.g., min cost path, min load path, etc.)



   o  Metric Types and their threshold:



      *  TE cost, IGP cost, Hop count, or Unidirectional Delay (e.g.,

         can set all path delay <= threshold)



   Once these requests are instantiated, the resources are committed and

   guaranteed through the life cycle of the VPN/VN.



       Integration



   L3VPN network model provides mechanism to correlate customer's VPN

   and the VPN service related resources (e.g.RT and RD) allocated in

   the provider's network.



   VPN/Network performance monitoring model

   [I-D.www-bess-yang-vpn-service-pm<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-I-D.www-bess-yang-vpn-service-pm>] provides mechanisms to monitor and

   manage network Performance on the topology at different layer or the

   overlay topology between VPN sites.



   VN model and Performance Monitoring Telemetry model provides

   mechanisms to correlate customer's VN and the actual TE tunnels

   instantiated in the provider's network.  Specifically:



   o  Link each VN member to actual TE tunnel.



   o  Each VN can be monitored on a various level such as VN level, VN

      member level, TE-tunnel level, and link/node level.



   Service function integration with network topology (L3 and TE

   topology) is in progress in [I-D.ietf-teas-sf-aware-topo-model<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-I-D.ietf-teas-sf-aware-topo-model>].

   Specifically, [I-D.ietf-teas-sf-aware-topo-model<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-I-D.ietf-teas-sf-aware-topo-model>] addresses a number

   of use-cases that show how TE topology supports various service

   functions.



       Dynamic Management



   ACTN provides an architecture that allows the CNC to interact with

   the MDSC which is network provider's SDN controller.  This gives the

   customer control of their VPN or VNs.



   e.g., the ACTN VN model [I-D.ietf-teas-actn-vn-yang<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-I-D.ietf-teas-actn-vn-yang>] allows the VN to

   life-cycle management such as create, modify, and delete VNs on

   demand.  Another example is L3VPN servicel model [RFC8299<https://tools.ietf.org/html/rfc8299>] which

   allows the VPN lifecycle management such as VPN creation,

   modification and deletion on demand.



       Customized Control



   ACTN provides a YANG model that allows the CNC to control a VN as a

   "Type 2 VN" that allows the customer to provision tunnels that

   connect their endpoints over the customized VN topology.



   For some VN members, the customers are allowed to configure the path

   (i.e., the sequence of virtual nodes and virtual links) over the VN/

   abstract topology.



       5G Transport Service Delivery via Coordinated Data Modules



   The overview of network slice structure as defined in the 3GPP 5GS is

   shown in Figure 5.  The terms are described in specific 3GPP

   documents (e.g.  [TS23501<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-TS23501>] and [TS28530<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-TS28530>].)



   <==================          E2E-NSI         =======================>

                 :                 :                  :           :  :

                 :                 :                  :           :  :

    <======  RAN-NSSI  ======><=TRN-NSSI=><====== CN-NSSI  ======>VL[APL]

        :        :        :        :         :       :        :   :  :

        :        :        :        :         :       :        :   :  :

    RW[NFs ]<=TRN-NSSI=>[NFs ]<=TRN-NSSI=>[NFs ]<=TRN-NSSI=>[NFs ]VL[APL]



     . . . . . . . . . . . . ..          . . . . . . . . . . . . ..

     .,----.   ,----.   ,----..  ,----.  .,----.   ,----.   ,----..

  UE--|RAN |---| TN |---|RAN |---| TN |---|CN  |---| TN |---|CN  |--[APL]

     .|NFs |   `----'   |NFs |.  `----'  .|NFs |   `----'   |NFs |.

     .`----'            `----'.          .`----'            `----'.

     . . . . . . . . . . . . ..          . . . . . . . . . . . . ..



    RW         RAN                MBH               CN               DN



 *Legends

   UE: User Equipment

   RAN: Radio Access Network

   CN: Core Network

   DN: Data Network

   TN: Transport Network

   MBH: Mobile Backhaul

   RW: Radio Wave

   NF: Network Function

   APL: Application Server

   NSI: Network Slice Instance

   NSSI: Network Slice Subnet Instance



       Figure 4: Overview of Structure of Network Slice in 3GPP 5GS



   To support 5G service (e.g., 5G MBB service), L3VPN service model

   [RFC8299<https://tools.ietf.org/html/rfc8299>] and TEAS VN model [I-D.ietf-teas-actn-vn-yang<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-I-D.ietf-teas-actn-vn-yang>] can be both

   provided to describe 5G MBB Transport Service or connectivity

   service.  L3VPN service model is used to describe end-to-end IP

   connectivity service while TEAS VN model is used to describe TE

   connectivity service between VPN sites or between RAN NFs and Core

   network NFs.



   VN in TEAS VN model and support point-to-point or multipoint-to-

   multipoint connectivity service and can be seen as one example of

   network slice.



   TE Service mapping model can be used to map L3VPN service requests

   onto underlying network resource and TE models to get TE network

   setup.



   For IP VPN service provision, the service parameters in the L3VPN

   service model [RFC8299<https://tools.ietf.org/html/rfc8299>] can be decomposed into a set of configuration

   parameters described in the L3VPN network model

   [I-D.aguado-opsawg-l3sm-l3nm<https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#ref-I-D.aguado-opsawg-l3sm-l3nm>] which will get VPN network setup.



Much of this text (and at least one of the figures) will be usable in the NS-DT Framework draft.  It will be necessary to comb through the text to make it generically applicable to Transport Slicing, consistent with the definitions draft, etc. - and some text may not be directly usable (we could include the less relevant concepts by reference).



Considerations

              Monitoring



.... we need to instrument the slice realization to know how it is doing + update the slice as situation changes + dynamic reconfig...           (spelling)



              How to deal with hierarchy



......JD  https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#section-6,  https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#section-7,  https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#section-8



Sections 6 and 7 of the enhanced VPN draft are (respectively) OAM and Telemetry Considerations, and - as such - are a better fit for the "Monitoring" subsection above.  It is not clear how section 8 ("Enhanced Resiliency") applies here.



....



              Security model



.... accidental or malicous interaction between slices raises new security concerns ...



......JD  https://tools.ietf.org/html/draft-ietf-teas-enhanced-vpn-03#section-10



The text in this section would - after some modification - provide a good basis for a security considerations section of this draft.  Note that "Security Model" and "Security Considerations" are not the same thing.