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NFV RG                                                CJ. Bernardos, Ed.
Internet-Draft                                                      UC3M
Intended status: Informational                             LM. Contreras
Expires: March 7, 2019                                               TID
                                                            I. Vaishnavi
                                                                  Huawei
                                                                R. Szabo
                                                                Ericsson
                                                              J. Mangues
                                                                    CTTC
                                                                   X. Li
                                                                     NEC
                                                             F. Paolucci
                                                          A. Sgambelluri
                                                              B. Martini
                                                          L. Valcarenghi
                                                                    SSSA
                                                                G. Landi
                                                               Nextworks
                                                            D. Andrushko
                                                                MIRANTIS
                                                               A. Mourad
                                                            InterDigital
                                                       September 3, 2018


                  Multi-domain Network Virtualization
                  draft-bernardos-nfvrg-multidomain-05

Abstract

   This document analyzes the problem of multi-provider multi-domain
   orchestration, by first scoping the problem, then looking into
   potential architectural approaches, and finally describing the
   solutions being developed by the European 5GEx and 5G-TRANSFORMER
   projects.

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
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on March 7, 2019.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (https://trustee.ietf.org/license-info) in effect on the date of
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Background: the ETSI NFV
       architecture  . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Multi-domain problem statement  . . . . . . . . . . . . . . .   8
   5.  Multi-domain architectural approaches . . . . . . . . . . . .   9
     5.1.  ETSI NFV approaches . . . . . . . . . . . . . . . . . . .   9
     5.2.  Hierarchical  . . . . . . . . . . . . . . . . . . . . . .  17
     5.3.  Cascading . . . . . . . . . . . . . . . . . . . . . . . .  20
   6.  Virtualization and Control for Multi-Provider Multi-Domain  .  20
     6.1.  Interworking interfaces . . . . . . . . . . . . . . . . .  22
     6.2.  5GEx Multi Architecture . . . . . . . . . . . . . . . . .  23
     6.3.  5G-TRANSFORMER Architecture . . . . . . . . . . . . . . .  26
       6.3.1.  So-Mtp Interface (IF3)  . . . . . . . . . . . . . . .  28
       6.3.2.  So-So Interface (IF2) . . . . . . . . . . . . . . . .  29
       6.3.3.  Vs-So Interface (IF1) . . . . . . . . . . . . . . . .  30
   7.  Multi-domain orchestration and Open Source  . . . . . . . . .  31
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  32
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  32
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  32
   11. Informative References  . . . . . . . . . . . . . . . . . . .  33
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  33





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1.  Introduction

   The telecommunications sector is experiencing a major revolution that
   will shape the way networks and services are designed and deployed
   for the next decade.  We are witnessing an explosion in the number of
   applications and services demanded by users, which are now really
   capable of accessing them on the move.  In order to cope with such a
   demand, some network operators are looking at the cloud computing
   paradigm, which enables a potential reduction of the overall costs by
   outsourcing communication services from specific hardware in the
   operator's core to server farms scattered in datacenters.  These
   services have different characteristics if compared with conventional
   IT services that have to be taken into account in this cloudification
   process.  Also the transport network is affected in that it is
   evolving to a more sophisticated form of IP architecture with trends
   like separation of control and data plane traffic, and more fine-
   grained forwarding of packets (beyond looking at the destination IP
   address) in the network to fulfill new business and service goals.

   Virtualization of functions also provides operators with tools to
   deploy new services much faster, as compared to the traditional use
   of monolithic and tightly integrated dedicated machinery.  As a
   natural next step, mobile network operators need to re-think how to
   evolve their existing network infrastructures and how to deploy new
   ones to address the challenges posed by the increasing customers'
   demands, as well as by the huge competition among operators.  All
   these changes are triggering the need for a modification in the way
   operators and infrastructure providers operate their networks, as
   they need to significantly reduce the costs incurred in deploying a
   new service and operating it.  Some of the mechanisms that are being
   considered and already adopted by operators include: sharing of
   network infrastructure to reduce costs, virtualization of core
   servers running in data centers as a way of supporting their load-
   aware elastic dimensioning, and dynamic energy policies to reduce the
   monthly electricity bill.  However, this has proved to be tough to
   put in practice, and not enough.  Indeed, it is not easy to deploy
   new mechanisms in a running operational network due to the high
   dependency on proprietary (and sometime obscure) protocols and
   interfaces, which are complex to manage and often require configuring
   multiple devices in a decentralized way.

   Furthermore, 5G networks are being designed to be capable of
   fulfilling the needs of a plethora of vertical industries (e.g.,
   automotive, eHealth, media), which have a wide variety of
   requirements [ngmn_5g_whitepaper].  The slicing concept tries to make
   the network of the provider aware of the business needs of tenants
   (e.g., vertical industries) by customizing the share of the network
   assigned to them.  The term network slice was coined to refer to a



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   complete logical network composed of network functions and the
   resources to run them [ngmn_slicing].  These resources include
   network, storage, and computing.  The way in which services requested
   by customers of the provider are assigned to slices depends on
   customer needs and provider policies.  The system must be flexible to
   accommodate a variety of options.

   Another characteristic of current and future telecommunication
   networks is complexity.  It comes from three main aspects.  First,
   heterogeneous technologies are often separated in multiple domains
   under the supervision of different network managers, which exchange
   provisioning orders that are manually handled.  This does not only
   happen between different operators, but also inside the network of
   the same operator.  Second, the different regional scope of each
   operator requires peering with others to extend their reach.  And
   third, the increasing variety of interaction among specialized
   providers (e.g., mobile operator, cloud service provider, transport
   network provider) that complement each other to satisfy the service
   requests from customers.  In conclusion, realizing the slicing vision
   to adapt the network to needs of verticals will require handling
   multi-provider and multi-domain aspects.

   Additionally, Network Function Virtualization (NFV) and Software
   Defined Networking (SDN) are changing the way the telecommunications
   sector will deploy, extend and operate its networks.  Together, they
   bring the required programmability and flexibility.  Moreover, these
   concepts and network slicing are tightly related.  In fact, slices
   may be implemented as NFV network services.  However, building a
   complete end-to-end logical network will likely require stitching
   services offered by multiple domains from multiple providers.  This
   is why multi-domain network virtualization is crucial in 5G networks.

2.  Terminology

   The following terms used in this document are defined by the ETSI NVF
   ISG, and the ONF and the IETF:

      NFV Infrastructure (NFVI): totality of all hardware and software
      components which build up the environment in which VNFs are
      deployed

      NFV Management and Orchestration (NFV-MANO): functions
      collectively provided by NFVO, VNFM, and VIM.

      NFV Orchestrator (NFVO): functional block that manages the Network
      Service (NS) lifecycle and coordinates the management of NS
      lifecycle, VNF lifecycle (supported by the VNFM) and NFVI




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      resources (supported by the VIM) to ensure an optimized allocation
      of the necessary resources and connectivity.

      Network Service Orchestration (NSO): function responsible for the
      Network Service lifecycle management, including operations such
      as: On-board Network Service, Instantiate Network Service, Scale
      Network Service, Update Network Service, etc.

      OpenFlow protocol (OFP): allowing vendor independent programming
      of control functions in network nodes.

      Resource Orchestration (RO): subset of NFV Orchestrator functions
      that are responsible for global resource management governance.

      Service Function Chain (SFC): for a given service, the abstracted
      view of the required service functions and the order in which they
      are to be applied.  This is somehow equivalent to the Network
      Function Forwarding Graph (NF-FG) at ETSI.

      Service Function Path (SFP): the selection of specific service
      function instances on specific network nodes to form a service
      graph through which an SFC is instantiated.

      Virtualized Infrastructure Manager (VIM): functional block that is
      responsible for controlling and managing the NFVI compute, storage
      and network resources, usually within one operator's
      Infrastructure Domain.

      Virtualized Network Function (VNF): implementation of a Network
      Function that can be deployed on a Network Function Virtualization
      Infrastructure (NFVI).

      Virtualized Network Function Manager (VNFM): functional block that
      is responsible for the lifecycle management of VNF.

3.  Background: the ETSI NFV architecture

   The ETSI ISG NFV is a working group which, since 2012, aims to evolve
   quasi-standard IT virtualization technology to consolidate many
   network equipment types into industry standard high volume servers,
   switches, and storage.  It enables implementing network functions in
   software that can run on a range of industry standard server hardware
   and can be moved to, or loaded in, various locations in the network
   as required, without the need to install new equipment.  To date,
   ETSI NFV is by far the most accepted NFV reference framework and
   architectural footprint [etsi_nvf_whitepaper].  The ETSI NFV
   framework architecture framework is composed of three domains
   (Figure 1):



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   o  Virtualized Network Function, running over the NFVI.

   o  NFV Infrastructure (NFVI), including the diversity of physical
      resources and how these can be virtualized.  NFVI supports the
      execution of the VNFs.

   o  NFV Management and Orchestration, which covers the orchestration
      and life-cycle management of physical and/or software resources
      that support the infrastructure virtualization, and the life-cycle
      management of VNFs.  NFV Management and Orchestration focuses on
      all virtualization specific management tasks necessary in the NFV
      framework.

   +-------------------------------------------+  +---------------+
   |   Virtualized Network Functions (VNFs)    |  |               |
   |  -------   -------   -------   -------    |  |               |
   |  |     |   |     |   |     |   |     |    |  |               |
   |  | VNF |   | VNF |   | VNF |   | VNF |    |  |               |
   |  |     |   |     |   |     |   |     |    |  |               |
   |  -------   -------   -------   -------    |  |               |
   +-------------------------------------------+  |               |
                                                  |               |
   +-------------------------------------------+  |               |
   |         NFV Infrastructure (NFVI)         |  |      NFV      |
   | -----------    -----------    ----------- |  |  Management   |
   | | Virtual |    | Virtual |    | Virtual | |  |      and      |
   | | Compute |    | Storage |    | Network | |  | Orchestration |
   | -----------    -----------    ----------- |  |               |
   | +---------------------------------------+ |  |               |
   | |         Virtualization Layer          | |  |               |
   | +---------------------------------------+ |  |               |
   | +---------------------------------------+ |  |               |
   | | -----------  -----------  ----------- | |  |               |
   | | | Compute |  | Storage |  | Network | | |  |               |
   | | -----------  -----------  ----------- | |  |               |
   | |          Hardware resources           | |  |               |
   | +---------------------------------------+ |  |               |
   +-------------------------------------------+  +---------------+

                       Figure 1: ETSI NFV framework

   The NFV architectural framework identifies functional blocks and the
   main reference points between such blocks.  Some of these are already
   present in current deployments, whilst others might be necessary
   additions in order to support the virtualization process and
   consequent operation.  The functional blocks are (Figure 2):

   o  Virtualized Network Function (VNF).



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   o  Element Management (EM).

   o  NFV Infrastructure, including: Hardware and virtualized resources,
      and Virtualization Layer.

   o  Virtualized Infrastructure Manager(s) (VIM).

   o  NFV Orchestrator.

   o  VNF Manager(s).

   o  Service, VNF and Infrastructure Description.

   o  Operations and Business Support Systems (OSS/BSS).





































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                                                  +--------------------+
   +-------------------------------------------+  | ----------------   |
   |                 OSS/BSS                   |  | | NFV          |   |
   +-------------------------------------------+  | | Orchestrator +-- |
                                                  | ---+------------ | |
   +-------------------------------------------+  |    |             | |
   |  ---------     ---------     ---------    |  |    |             | |
   |  | EM 1  |     | EM 2  |     | EM 3  |    |  |    |             | |
   |  ----+----     ----+----     ----+----    |  | ---+----------   | |
   |      |             |             |        |--|-|    VNF     |   | |
   |  ----+----     ----+----     ----+----    |  | | manager(s) |   | |
   |  | VNF 1 |     | VNF 2 |     | VNF 3 |    |  | ---+----------   | |
   |  ----+----     ----+----     ----+----    |  |    |             | |
   +------|-------------|-------------|--------+  |    |             | |
          |             |             |           |    |             | |
   +------+-------------+-------------+--------+  |    |             | |
   |         NFV Infrastructure (NFVI)         |  |    |             | |
   | -----------    -----------    ----------- |  |    |             | |
   | | Virtual |    | Virtual |    | Virtual | |  |    |             | |
   | | Compute |    | Storage |    | Network | |  |    |             | |
   | -----------    -----------    ----------- |  | ---+------       | |
   | +---------------------------------------+ |  | |        |       | |
   | |         Virtualization Layer          | |--|-| VIM(s) +-------- |
   | +---------------------------------------+ |  | |        |         |
   | +---------------------------------------+ |  | ----------         |
   | | -----------  -----------  ----------- | |  |                    |
   | | | Compute |  | Storage |  | Network | | |  |                    |
   | | | hardware|  | hardware|  | hardware| | |  |                    |
   | | -----------  -----------  ----------- | |  |                    |
   | |          Hardware resources           | |  |  NFV Management    |
   | +---------------------------------------+ |  | and Orchestration  |
   +-------------------------------------------+  +--------------------+

                 Figure 2: ETSI NFV reference architecture

4.  Multi-domain problem statement

   Market fragmentation results from having a multitude of
   telecommunications network and cloud operators each with a footprint
   focused to a specific region.  This makes it difficult to deploy cost
   effective infrastructure services, such as virtual connectivity or
   compute resources, spanning multiple countries as no single operator
   has a big enough footprint.  Even if operators largely aim to provide
   the same infrastructure services (VPN connectivity, compute resources
   based on virtual machines and block storage), inter-operator
   collaboration tools for providing a service spanning several
   administrative boundaries are very limited and cumbersome.  This
   makes service development and provisioning very time consuming.  For



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   example, having a VPN with end-points in several countries, in order
   to connect multiple sites of a business (such as a hotel chain),
   requires contacting several network operators.  Such an approach is
   possible only with significant effort and integration work from the
   side of the business.  This is not only slow, but also inefficient
   and expensive, since the business also needs to employ networking
   specialists to do the integration instead of focusing on its core
   business

   Technology fragmentation also represents a major bottleneck
   internally for an operator.  Different networks and different parts
   of a network may be built as different domains using separate
   technologies, such as optical or packet switched (with different
   packet switching paradigms included); having equipment from different
   vendors; having different control paradigms, etc.  Managing and
   integrating these separate technology domains requires substantial
   amount of effort, expertise, and time.  The associated costs are paid
   by both network operators and vendors alike, who need to design
   equipment and develop complex integration features.  In addition to
   technology domains, there are other reasons for having multiple
   domains within an operator, such as, different geographies, different
   performance characteristics, scalability, policy or simply historic
   (e.g., result of a merge or an acquisition).  Multiple domains in a
   network are a necessary and permanent feature however, these should
   not be a roadblock towards service development and provisioning,
   which should be fast and efficient.

   A solution is needed to deal with both the multi-operator
   collaboration issue, and address the multi-domain problem within a
   single network operator.  While these two problems are quite
   different, they also share a lot of common aspects and can benefit
   from having a number of common tools to solve them.

5.  Multi-domain architectural approaches

   This section summarizes different architectural options that can be
   considered to tackle the multi-domain orchestration problem.

5.1.  ETSI NFV approaches

   Recently, the ETSI NFV ISG has started to look into viable
   architectural options supporting the placement of functions in
   different administrative domains.  In the document [etsi_nvf_ifa009],
   different approaches are considered, which we summarize next.

   The first option (shown in Figure 3) is based on a split of the NFVO
   into Network Service Orchestrator (NSO) and Resource Orchestrator
   (RO).  A use case that this separation could enable is the following:



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   a network operator offering its infrastructure to different
   departments within the same operator, as well as to a different
   network operator like in cases of network sharing agreements.  In
   this scenario, an administrative domain can be defined as one or more
   data centers and VIMs, providing an abstracted view of the resources
   hosted in it.

   A service is orchestrated out of VNFs that can run on infrastructure
   provided and managed by another Service Provider.  The NSO manages
   the lifecycle of network services, while the RO provides an overall
   view of the resources present in the administrative domain to which
   it provides access and hides the interfaces of the VIMs present below
   it.

                             -------
                             | NSO |
                            /-------\
                           /         \
               --------   /  -------- \    --------
               | VNFM |   |  | VNFM |  |   | VNFM |
               --------  /   --------   \  --------
                  / ____/      /  \      \____ \
                 / / _________/    \_________ \ \
                / / /                        \ \ \
   +-----------/-/-/---------+     +----------\-\-\----------+
   |        ---------        |     |        ---------        |
   |        |  RO   |        |     |        |  RO   |        |
   |        ---------        |     |        ---------        |
   |       /    |    \       |     |       /    |    \       |
   |      /     |     \      |     |      /     |     \      |
   |     /      |      \     |     |     /      |      \     |
   | ------- ------- ------- |     | ------- ------- ------- |
   | |VIM 1| |VIM 2| |VIM 3| |     | |VIM 1| |VIM 2| |VIM 3| |
   | ------- ------- ------- |     | ------- ------- ------- |
   | Administrative domain A |     | Administrative domain B |
   +-------------------------+     +-------------------------+

      Figure 3: Infrastructure provided using multiple administrative
                 domains (from ETSI GS NFV-IFA 009 V1.1.1)

   The second option (shown in Figure 4) is based on having an umbrella
   NFVO.  A use case enabled by this is the following: a Network
   Operator offers Network Services to different departments within the
   same operator, as well as to a different network operator like in
   cases of network sharing agreements.  In this scenario, an
   administrative domain is compose of one or more Datacentres, VIMs,
   VNFMs (together with their related VNFs) and NFVO, allowing distinct
   specific sets of network services to be hosted and offered on each.



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   A top Network Service can include another Network Service.  A Network
   Service containing other Network Services might also contain VNFs.
   The NFVO in each admin domain provides visibility of the Network
   Services specific to this admin domain.  The umbrella NFVO is
   providing the lifecycle management of umbrella network services
   defined in this NFVO.  In each admin domain, the NFVO is providing
   standard NFVO functionalities, with a scope limited to the network
   services, VNFs and resources that are part of its admin domain.

                           ------------
                           | Umbrella |
                           |   NFVO   |
                           ------------
                              / |  \
                            /   |    \
                           / -------- \
                          /  | VNFM |  \
                        /    --------    \
                       /        |         \
                     /       -------        \
                    /        |VIM 1|         \
                  /          -------           \
   --------------/------------     -------------\-------------
   |        --------         |     |        --------         |
   |        | NFVO |         |     |        | NFVO |         |
   |        --------         |     |        --------         |
   |          | | |          |     |          | | |          |
   | -------- | | | -------- |     | -------- | | | -------- |
   | | VNFM | | | | | VNFM | |     | | VNFM | | | | | VNFM | |
   | -------- | | | -------- |     | -------- | | | -------- |
   |   |  \__/__|__\_/_   |  |     |   |  \__/__|__\_/_   |  |
   |   |  __/___|___/\ \  |  |     |   |  __/___|___/\ \  |  |
   |   | / /    |     \ \ |  |     |   | / /    |     \ \ |  |
   | ------- ------- ------- |     | ------- ------- ------- |
   | |VIM 1| |VIM 2| |VIM 3| |     | |VIM 1| |VIM 2| |VIM 3| |
   | ------- ------- ------- |     | ------- ------- ------- |
   | Administrative domain A |     | Administrative domain B |
   +-------------------------+     +-------------------------+

     Figure 4: Network services provided using multiple administrative
                 domains (from ETSI GS NFV-IFA 009 V1.1.1)

   More recently, ETSI NFV has released a new whitepaper, titled
   "Network Operator Perspectives on NFV priorities for 5G"
   [etsi_nvf_whitepaper_5g], which provides network operator
   perspectives on NFV priorities for 5G and identifies common technical
   features in terms of NFV.  This whitepaper identifies multi-site/
   multi-tenant orchestration as one key priority.  ETSI highlights the



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   support of Infrastructure as a Service (IaaS), NFV as a Service
   (NFVaaS) and Network Service (NS) composition in different
   administrative domains (for example roaming scenarios in wireless
   networks) as critical for the 5G work.

   In January 2018 ETSI NFV released a report about NFV MANO
   architectural options to support multiple administrative domains
   [etsi_nvf_ifa028].  This report presents two use cases: the NFVI as a
   Service (NFVIaaS) case, where a service provider runs VNFs inside an
   NFVI operated by a different service provider, and the case of
   Network Services (NS) offered by multiple administrative domains,
   where an organization uses NS(s) offered by another organization.

   In the NFVIaaS use case, the NFVIaaS consumer runs VNF instances
   inside an NFVI provided by a different service provider, called
   NFVIaaS provider, that offers computing, storage, and networking
   resources to the NFVIaaS consumer.  Therefore, the NFVIaaS consumer
   has the control on the applications that run on the virtual
   resources, but has not the control of the underlying infrastructure,
   which is instead managed by the NFVIaaS provider.  In this scenario,
   the NFVIaaS provider's domain is composed of one or more NFVI-PoPs
   and VIMs, while the NFVIaaS consumer's domain includes one or more
   NSs and VNFs managed by its own NFVO and VNFMs, as depicted in
   Figure 5.



























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   +------------------------------------------------+
   |    NFVIaaS consumer's administrative domain    |
   |                                                |
   |  +----------+                                  |
   |  |   NS(s)  |                                  |
   |  +----------+                                  |
   |                                                |
   |  +----------+   +----------+   +----------+    |
   |  |  VNF(s)  |   | VNFM(s)  |   |   NFVO   |    |
   |  +----------+   +----------+   +----------+    |
   |                                                |
   +-------------------------+----------------------+
                             +
    Administrative domain    +
   ++++++++++++++++++++++++++++++++++++++++++++++++++
    boundary                 + NFVIaaS
                             +
   +-------------------------+----------------------+
   |                                                |
   |  +----------+   +-----------+                  |
   |  |  NFVI    |   |   VIM(s)  |                  |
   |  +----------+   +-----------+                  |
   |                                                |
   +------------------------------------------------+

                          Figure 5: NFVI use case

   The ETSI IFA 028 defines two main options to model the interfaces
   between NFVIaaS provider and consumer for NFVIaaS service requests,
   as follows:

   1.  Access to Multiple Logical Points of Contacts (MLPOC) in the
       NFVIaaS provider's administrative domain.  In this case the
       NFVIaaS consumer has visibility of the NFVIaaS provider's VIMs
       and it interacts with each of them to issue NFVIaaS service
       requests, through Or-Vi (IFA 005) or Vi-Vnfm (IFA 006) reference
       points.

   2.  Access to a Single Logical Point of Contact (SLPOC) in the
       NFVIaaS provider's administrative domain.  In this case the
       NFVIaaS provider's VIMs are hidden from the NFVIaaS consumer and
       a single unified interface is exposed by the SLPOC to the NFVIaaS
       consumer.  The SLPOC manages the information about the
       organization, the availability and the utilization of the
       infrastructure resources, forwarding the requests from the
       NFVIaaS consumer to the VIMs.  The interaction between SLPOC and
       NFVIaaS consumer is based on IFA 005 or IFA 006 interfaces, while




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       the interface between the SLPOC and the underlying VIMs is based
       on the IFA 005.

   The two options are shown in Figure 6 and Figure 7 respectively,
   where we assume the direct mode for the management of VNF resources.
   In addition, the ETSI IFA 028 includes the possibility of an indirect
   management mode of the VNF resources through the consumer NFVIaaS
   NFVO and the IFA 007 interface.  In this latter case between the
   consumer NFVIaaS NFVO and the provider NFVIaaS NFVO only the IFA 005
   interface is utilized.

        +------------------------------------------------+
        |    NFVIaaS consumer's administrative domain    |
        |                                                |
        |  +-----------+               +------------+    |
        |  |   VNFM    |---+           |   NFVO     |    |
        |  +-+---------+   |---+       +-+--+-------+    |
        |    + +-+---------+   |        +   +            |
        |    +   + +----+----+-+       +    +            |
        |    +   +     +     +        +    +             |
        +----+---+----+------+-------+----+--------------+
             +   +    +      +      +    +
   IFA 006 --+---+---+-------+--  --+----+-- IFA 005
             +   +  +        +     +    +
        +----+---+--+--------+----+----+-----------------+
        |    +   +  +   ++++++++++    +                  |
        |  +-+---+--+-+ +    +       +                   |
        |  |   VIM    |-+-+  +      +                    |
        |  +----------+   |--+-+   +                     |
        |      +----------+    ++++                      |
        |          |    VIM    |                         |
        |          +-----------+                         |
        |    NFVIaaS provider's administrative domain    |
        +------------------------------------------------+

               Figure 6: NFVIaaS architecture: MLPOC option















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        +------------------------------------------------+
        |    NFVIaaS consumer's administrative domain    |
        |                                                |
        |  +-----------+               +------------+    |
        |  |   VNFM    |---+           |   NFVO     |    |
        |  +-+---------+   |---+       +-+----------+    |
        |    + +-----------+   |        +                |
        |    +     |   VNFM    |        +                |
        |     +    +---------+-+       +                 |
        |      +             +        +                  |
        +-------+------------+-------+-------------------+
                 +           +      +
   IFA 006 -------+----------+--  --+-- IFA 005
                   +         +     +
        +-----------+--------+----+----------------------+
        |            +       +   +                       |
        |         +---+------+--+--+                     |
        |         | SLPOC function |                     |
        |         +-+---+---+------+                     |
        |          +    +   +                            |
        |      ---+-----+---+--- IFA 005                 |
        |        +      +   +                            |
        |  +----+-----+ +   +                            |
        |  |   VIM    |-+-+ +                            |
        |  +----------+   |-+-+                          |
        |      +----------+   |                          |
        |          |   VIM    |                          |
        |          +----------+                          |
        |    NFVIaaS provider's administrative domain    |
        +------------------------------------------------+

               Figure 7: NFVIaaS architecture: SLPOC option

   In the use case related to Network Services provided using multiple
   administrative domains, each domain includes an NFVO and one or more
   NFVI PoPs, VIMs and VNFMs.  The NFVO in each domain offers a
   catalogue of Network Services that can be used to deploy nested NSs,
   which in turn can be composed into composite NSs, as shown in
   Figure 8.  Nested NSs can be also shared among different composite
   NSs.











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                |
     ***********+***************************************
     *          |                                      *
     *  +-------+------+                               *
     *  |              |                               *
   --+--+ Nested NS A  +-------+                       *
     *  |              |       +--------+              *
     *  +-------+------+                |              *
     *          |                       |              *
     *          |                 +-----+--------+     *
     *          |                 |              |     *
     *          +-----------------+ Nested NS B  +-----+---
     *                            |              |     *
     *                            +-------+------+     *
     *        Composite NS C              |            *
     *                                    |            *
     *************************************+*************
                                          |

                    Figure 8: Composite and nested NSs

   The management of the NS hierarchy is handled through a hierarchy of
   NFVOs, with one of them responsible for the instantiation and
   lifecycle management of the composite NS, coordinating the actions of
   the other NFVOs that manage the nested NSs.  These two different
   kinds of NFVOs interact through a new reference point, named Or-Or,
   as shown in Figure 9, where NFVO-1 manages composite NSs and NFVO-2
   manages nested NSs.  To build the composite NSs, the responsible NFVO
   consult its own catalogue and may subscribe to the NSD notifications
   sent by other NFVOs.





















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            +---------------------------------------------+
            |                                             |
            |                             +-------------+ |
            |                       +++++++   VNFM1-1   | |
            |    +-----------+     +      +-------------+ |
            |    |  NFVO-1   ++++++                       |
            |    +---+-------+     +      +-------------+ |
            |        +              +++++++   VNFM1-2   | |
            |        +                    +-------------+ |
            |        +    Administrative domain C         |
            +--------+------------------------------------+
                     +
                     +
                     +   Or-Or
                     +
            +--------+------------------------------------+
            |        +                                    |
            |        +                    +-------------+ |
            |        +              +++++++   VNFM2-1   | |
            |    +---+-------+     +      +-------------+ |
            |    |  NFVO-2   ++++++                       |
            |    +-----------+     +      +-------------+ |
            |                       +++++++   VNFM2-2   | |
            |                             +-------------+ |
            |             Administrative domain A         |
            +---------------------------------------------+

     Figure 9: Architecture for management of composite and nested NS

5.2.  Hierarchical

   Considering the potential split of the NFVO into a Network Service
   Orchestrator (NSO) and a Resource Orchestrator (RO), multi-provider
   hierarchical interfaces may exist at their northbound APIs.
   Figure 10 illustrates the various interconnection options, namely:

      E/NSO (External NSO): an evolved NFVO northbound API based on
      Network Service (NS).

      E/RO (External RO): VNF-FG oriented resource embedding service.  A
      received VNF-FG that is mapped to the northbound resource view is
      embedded into the distributed resources collected from southbound,
      i.e., VNF-FG_in = VNF-FG_out_1 + VNF-FG_out_2 + ... + VNF-
      FG_out_N, where VNF-FG_out_j corresponds to a spatial embedding to
      subordinate domain "j".  For example, Provider 3's MP-NFVO/RO
      creates VNF-FG corresponding to its E/RO and E/VIM sub-domains.





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      E/VIM (External VIM): a generic VIM interface offered to an
      external consumer.  In this case the NFVI-PoP may be shared for
      multiple consumers, each seeing a dedicated NFVI-PoP.  This
      corresponds to IaaS interface.

      I/NSO (Internal NSO): if a Multi-provider NSO (MP-NSO) is
      separated from the provider's operational NSO, e.g., due to
      different operational policies, the MP-NSO may need this interface
      to realize its northbound E/NSO requests.  Provider 1 illustrates
      a scenario the MP-NSO and the NSO are logically separated.
      Observe that Provider 1's tenants connect to the NSO and MP-NSO
      corresponds to "wholesale" services.

      I/RO (Internal RO): VNF-FG oriented resource embedding service.  A
      received VNF-FG that is mapped to the northbound resource view is
      embedded into the distributed resources collected from southbound,
      i.e., VNF-FG_in = VNF-FG_out_1 + VNF-FG_out_2 + ... + VNF-
      FG_out_N, where VNF-FG_out_j corresponds to a spatial embedding to
      subordinate domain "j".  For example, Provider 1's MP-NFVO/RO
      creates VNF-FG corresponding to its I/RO and I/VIM sub-domains.

      I/VIM (Internal VIM): a generic VIM interface at an NFVI-PoP.

      Nfvo-Vim: a generic VIM interface between a (monolithic) NFVO and
      a VIM.

   Some questions arise from this.  It would be good to explore use-
   cases and potential benefits for the above multi-provider interfaces
   as well as to learn how much they may differ from their existing
   counterparts.  For example, are (E/RO, I/RO), (E/NSO, I/NSO), (E/VIM,
   I/VIM) pairs different?




















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                                             Tenants
                             *    Provider      |
      *                       *   Domain 4   +--+-----------+
       *                       *             |MP-NFVO/NSO:  |
        *                       *            |Network Serv. |
         *   Provider            *           |Orchestrator  |
          *  Domain 3             *          +--+-----------+
           *              Tenants  *            |E/RO
            *                |      ************|*************
             *              ++-------------+    |
              *             |MP-NFVO/NSO:  |    |
      Provider *            |Network Serv. |    |
      Domain 1  *           |Orchestrator  |    |
                 *          +-+-----+------+    |
                  *      E/NSO|     | I/RO     /
                   *.---------'   +-+---------+--+
                   /*             |MP-NFVO/RO:   |
                  /  *            |Resource      |
   Tenants       /    *           |Orchestrator  |
   |             |     *          +--+---+-------+
   | +-----------+--+   *************|***|********************
   | |MP-NFVO/NSO:  |                |  * \           Provider
   | |Network Serv. |         E/RO  /   *  \ E/VIM    Domain 2
   | |Orchestrator  |  .-----------'    *   `-------.
   | +-+------+-----+  |                *           |
   |   |I/NSO |I/RO    |                *           |
   |   |   +--+--------+--+             *           |
   |   |   |MP-NFVO/RO:   |             *           |
   |   |   |Resource      |             *           |
    \  |   |Orchestrator  |             *    +------+-------+
     \ |   +----+---- --+-+             *    |VIM:          |
    +--+-----+  |I/RO   |I/VIM          *    |Virtualized   |
    |NFVO/NSO|  |       |               *    |Pys mapping   |
    +------+-+  |       |               *    +--------------+
       I/RO|    |       |               *
    +------+----+---+   |               *
    |    NFVO/RO    |   |               *
    ++-------------++   |               *
     |Nfvo-Vim     |    |               *
    ++-------+    ++----+--+            *
    |WIM|VIM ||   |VIM|WIM |            *
    +--------+|   +--------+            *
     +--------+                         *

        Figure 10: NSO-RO Split: possible multi-provider APIs - an
                               illustration





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5.3.  Cascading

   Cascading is an alternative way of relationship among providers, from
   the network service point of view.  In this case, service
   decomposition is implemented in a paired basis.  This can be extended
   in a recursive manner, then allowing for a concatenation of cascaded
   relations between providers.

   As a complement to this, from a service perspective, the cascading of
   two remote providers (i.e., providers not directly interconnected)
   could require the participation of a third provider (or more)
   facilitating the necessary communication among the other two.  In
   that sense, the final service involves two providers while the
   connectivity imposes the participation of more parties at resource
   level.

6.  Virtualization and Control for Multi-Provider Multi-Domain

   Orchestration operation in multi-domain is somewhat different from
   that in a single domain as the assumption in single domain single
   provider orchestration is that the orchestrator is aware of the
   entire topology and resource availability within its domain as well
   as has complete control over those resources.  This assumption of
   technical control cannot be made in a multi domain scenario,
   furthermore the assumption of the knowledge of the resources and
   topologies cannot be made across providers.  In such a scenario
   solutions are required that enable the exchange of relevant
   information across these orchestrators.  This exchange needs to be
   standardized as shown in Figure 11.

                   |                               |
                   + IF1                           +
              _____|____                       ____|_____
             |   Multi  |        IF2          |   Multi  |
             | Provider |<--------+---------->| Provider |
             |___Orch___|                     |___Orch___|
                  /\                               /\
                 /  \                             /  \
                /    \ IF3                       /    \
        _______/__   _\_________        ________/_    _\________
       |  Domain  | |  Domain  |       |  Domain  |  |  Domain  |
       |___Orch___| |___Orch___|       |___Orch___|  |___Orch___|

       Figure 11: Multi Domain Multi Provider reference architecture

   The figure shows the Multi Provider orchestrator exposing an
   interface 1 (IF1) to the tenant, interface 2 (IF2) to other Multi
   Provider Orchestrator (MPO) and an interface 3 (IF3) to individual



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   domain orchestratrators.  Each one of these interfaces could be a
   possible standardization candidate.  Interface 1 is exposed to the
   tenant who could request his specific services and/or slices to be
   deployed.  Interface 2 is between the orchestrator and is a key
   interface to enable multi-provider operation.  Interface 3 focuses on
   abstracting the technology or vendor dependent implementation details
   to support orchestration.

   The proposed operation of the MPO follows three main technical steps.
   First, over interface 2 various functions such as abstracted topology
   discovery, pricing and service details are detected.  Second, once a
   request for deploying a service is received over interface 1 the
   Multi Provider Orchestrator evaluates the best orchestrators to
   implement parts of this request.  The request to deploy these parts
   are sent to the different domain orchestrators over IF2 and IF3 and
   the acknowledgement that these are deployed in different domain are
   received back over those interfaces.  Third, on receipt of the
   acknowledgement the slice specific assurance management is started
   within the MPO.  This assurance function collects the appropriate
   information over IF2 and IF3 and reports the performance back to the
   tenant over IF1.  The assurance is also responsible for detecting any
   failures in the service and violations in the SLA and recommending to
   the orchestration engine the reconfiguration of the service or slice
   which again needs to be performed over IF2 and IF3.

   Each of the three steps is assigned to a specific block in our high
   level architecture shown in Figure 12.

                   |                                    |
                   + IF1                                +
     ______________|______________                  ____|_____
    |      Multi Provider Orch    |                |  Multi   |
    | ______   ________   _______ |<------+------->| Provider |
    ||Assur-| |        | | Catal-||      IF2       |___Orch___|
    ||-ance | |  NFVO  | | logue ||
    || Mgmt.| |        | | Topo. ||
    ||______| |________| |_Mgmt._||
    |_____________________________|
                  /\
                 /  \ IF3

              Figure 12: Detailed MPO reference architecture

   The catalogue and topology management system is responsible for step
   1.  It discovers the service as well as the resources exposed by the
   other domains both on IF2 and IF3.  The combination of these services
   with coverage over the detected topology is provided to the user over
   IF1.  In turn the catalogue and topology management system is also



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   responsible for exposing the topology and service deployment
   capabilities to the other domain.  The exposure over interface 2 to
   other MPO maybe abstracted and the mapping of this abstracted view to
   the real view when requested by the NFVO.

   The NFVO (Network Function Virtualization Orchestrator) is
   responsible for the second step.  It deploys the service or slice as
   is received from the tenant over IF2 and IF3.  It then hands over the
   deployment decisions to the Assurance management subsystem which use
   this information to collect the periodic monitoring tickets in step
   3.  On the other end it is responsible for receiving the request over
   IF2 to deploy a part of the service, consult with the catalogue and
   topology management system on the translation of the abstraction to
   the received request and then for the actual deployment over the
   domains using IF3.  The result of this deployment and the management
   and control handles to access the deployed slice or service is then
   returned to the requesting MPO.

   The assurance management component periodically studies the collected
   results to report the overall service performance to the tenant or
   the requesting MPO as well as to ensure that the service is
   functioning within the specified parameters.  In case of failures or
   violations the Assurance management system recommends
   reconfigurations to the NFVO.

6.1.  Interworking interfaces

   In this section we provide more details on the interworking
   interfaces of the MPO reference architecture.  Each interface IF1,
   IF2 and IF3 is broken down into several sub-interfaces.  Each of them
   has a clear scope and functionality.

   For multi provider Network Service orchestration, the Multi-domain
   Orchestrator (MdO) offers Network Services by exposing an OSS/BSS -
   NFVO interface to other MPOs belonging to other providers.  For
   multi-provider resource orchestration, the MPO presents a VIM-like
   view and exposes an extended NFVO - VIM interface to other MPOs.  The
   MPO exposes a northbound sub-interface (IF1-S) through which an MPO
   customer sends the initial request for services.  It handles command
   and control functions to instantiate network services.  Such
   functions include requesting the instantiation and interconnection of
   Network Functions (NFs).  A sub-interface IF2-S is defined to perform
   similar operations between MPOs of different administrative domains.
   A set of sub-interfaces -- IF3-R and IF2-R -- are used to keep an
   updated global view of the underlying infrastructure topology exposed
   by domain orchestrators.  The service catalogue exposes available
   services to customers on a sub-interface IF1-C and to other MPO
   service operators on sub-interface IF2-C.  Resource orchestration



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   related interfaces are broken up to IF2-RC, IF2-RT, IF2-RMon to
   reflect resource control, resource topology and resource monitoring
   respectively.  Furthermore, the sub-interfaces introduced before are
   generalised and also used for interfaces IF3 and IF1.

6.2.  5GEx Multi Architecture

   The 5G-PPP H2020 5GEx projects addresses the proposal and the
   deployment of a complete Multi-Provider Orchestrator providing,
   besides network and service orchestration, service exposition to
   other providers.  The main assumptions of the 5GEx functional
   architecture are a) a multi-operator wholesale relationship, b) a
   full multi-vendor inter-operability and c) technology-agnostic
   approach for physical resources.  The proposed functional
   architecture of the 5GEx MPO is depicted in Figure 13.

                         ^                          ^
                    I1-S |                          |
                    I1-F |                     I1-C |
                    I1-RM|                          |
   +----------------------------------------------------+
   |          +-------------------------------------|--+|
   |          |          |                          |  ||     I2-S
   |          | +--------------------+              |  ||     I2-F
   |+---+     | | +-----+ +---+ IP-  |              |  ||     I2-RC
   ||OSS|<----|-| | NSO | |RO | NFVO +<-------------|--+|-------------->
   |+---+     | | +-----+ +---+      |<-------------+  ||
   |  ^       | +---^----------------+              |  ||
   |  |       |     |     ^ ^    ^^ ^               |  ||
   |  |       | +---+---+ | |    || |               |  ||
   |  +---------| VNF   | | |    || |  Multi-       |  ||
   |          | |Manager| | |    || |  Provider     |  ||
   |          | ++------+ | |    || |  Orchestrator |  ||
   |          |  ^        | |    || |  (MPO)        |  ||
   |          |  +--------+ |    || |               |  ||
   |          |  |     +-------+ || |               |  ||    I2-Mon
   |          |  |     |SLA    |<-|-|---------------|--+|-------------->
   |          |  |     |Manager| || |               |  ||
   |          |  |     +-------+ || |               |  ||
   |          |  |       ^       || +------------+  |  ||I2-RT-advertise
   |          |  |       |       || |Topology    |  |  ||I2-RT-bilateral
   |          |  |       |       || |Distribution|<-|--+|-------------->
   |          |  |       |       || |Repository  |  |  ||
   |          |  |       |       || +--------^+--+  |  ||
   |          |  |       |       ||   ^      ||     |  ||
   |          |  |       |       ||   |  +---+v-+   |  ||I2-RC-network
   |          |  |       |       |+---|--+MD-PCE|<--|--+|-------------->
   |          |  |       |       |    |  +------+   |  ||



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   |          |  |       |       |    |   ^ +-------+-+||I2-C-advertise
   |          |  |       |       |    |   | |Service  |||I2-C-bilateral
   |          |  |       |       |    |   | |Catalogue+<|-------------->
   |          |  |       |       |    |   | +---------+||
   |          |  |       |       |    |   |      ^     ||
   |          +--|----- -|-------|----|---|------|-----+|
   |             |       |            |   |      |      |
   |             |I3-RC  |   I3-S|    |   |I3-RC-network|
   |          +--+--+    |   +----+   | +---+    |      |
   |          | VIM |    |   |NFVO|   | |PCE|    |      |
   |          +-----+    |   +----+   | +---+    |      |
   |                     |            |          |      |
   |                     |       I3-RT|          |I3-C  |
   |              I3-Mon |     +------+----+ +---+-----+|
   |           +---------+-+   |Topology   | |Service  ||
   |Operator   | Monitoring|   |Abstraction| |Catalogue||
   |Domain     +-----------+   +-----------+ +---------+|
   +----------------------------------------------------+

                Figure 13: 5GEx MPO functional architecture

   Providers expose MPOs service specification API allowing OSS/BSS or
   external business customers to perform and select their requirements
   for a service.  Interface I1-x is exploited as a northbound API for
   business client requests.  Peer MPO-MPO communications implementing
   multi-operator orchestration operate with specific interfaces
   referred to as I2-x interfaces.  A number of I2-based interfaces are
   provided for communication between specific MPO modules: I2-S for
   service orchestration, I2-RC for network resource control, I2-F for
   management lifecycle, I2-Mon for inter-operator monitoring messages,
   I2-RT for resource advertisement, I2-C for service catalogue
   exchange, I2-RC-network for the QoS connectivity resource control.
   Some I2 interfaces are bilateral, involving direct relationship
   between two operators, and utilized to exchange business/SLA
   agreements before entering the federation of inter-operator
   orchestrators.  Each MPO communicates through a set of southbound
   interface, I3-x, with local orchestrators/controllers/VIM, in order
   to set/modify/release resources identified by the MPO or during
   inter-MPO orchestration phase.  A number of I3 interfaces are
   defined: I3-S for service orchestration towards local NFVO, I3-RC for
   resource orchestration towards local VIM, I3-C towards local service
   catalogue, I3-RT towards local abstraction topology module, I3-RC-
   network towards local PCE or network controller, I3-Mon towards local
   Resource Monitoring agent.  All the considered interfaces are
   provided to cover either flat orchestration or layered/hierarchical
   orchestration.  The possibility of hierarchical inter-provider MPO
   interaction is enabled at a functional level, e.g., in the case of




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   operators managing a high number of large administrative domains.
   The main MPO modules are the following:

      The Inter-provider NFVO, including the RO and the NSO,
      implementing the multi-provider service decomposition

      the VNF/Element manager, managing VNF lifecycle, scaling and
      responsible for FCAPS (Fault, Configuration, Accounting,
      Performance and Security management)

      the SLA Manager, in charge of reporting monitoring and performance
      alerts on the service graph

      the Service Catalogue, exposing available services to external
      client and operators

      the Topology and Resource Distribution module and Repository,
      exchanging operators topologies (both IT and network resources)
      and providing abstracted view of the own operator topology

      the Multi-domain Path Computation Element (PCE implementing inter-
      operator path computation to allow QoS-based connectivity serving
      VNF-VNF link).

   The Inter-provider NVFO selects providers to be involved in the
   service chained request, according to policy-based decisions and
   resorting to Inter-Provider topologies and service catalogues
   advertised through interfaces I2-RT-advertise and I2-C-advertise,
   respectively.  Network/service requests are sent to other providers
   using the I2-RC and I2-S interfaces, respectively.  Policy
   enforcement for authorized providers running resource orchestration
   and lifecycle management are exploited through interfaces I2-RC and
   I2-F, respectively.  The VNF/Element Manager is in charge of managing
   the lifecycle of the VNFs part of the services.  More specifically,
   it is in charge to perform: the configuration of the VNFs, also in
   terms of security aspects, the fault recovery and the scaling
   according to their performance.  The SLA Manager collects and
   aggregates quality measurement reports from probes deployed by the
   Inter-Provider NFVO as part of the service setup.  Measurements
   results at the Manager represent aggregated results and are computed
   and stored utilizing the I2-Mon interface between Inter-Provider MPOs
   sharing the same service.  Faults and alarms are moreover correlated
   to raise SLA violation to remote inter-provider MPOs and, optionally,
   to detect the source and the location of the violation, triggering
   service re-computation/rerouting procedures.  The Service Catalogue
   stores information on network services and available VNFs and uses
   I2-C interfaces (either bilateral or advertised) to advertise and
   updating such offered services to other operators.  To enable inter-



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   provider service decomposition, multi-operator topology and peering
   relationships need to be advertised.  Providers advertise basic
   inter-provider topologies using the I2-RT-advertse interface
   including, optionally, abstracted network resources, overall IT
   resource capabilities, MPO entry-point and MD-PCE IP address.  Basic
   advertisement takes place between adjacent operators.  These
   information are collected, filtered by policy rules and propagated
   hop-by-hop.  In 5GEx, the I2-RT-advertise interfaces utilizes BGP-LS
   protocol.  Moreover, providers establish point-to-point bilateral
   (i.e., direct and exclusive) communications to exchange additional
   topology and business information, using the I2-RT-bilateral
   interface.  Service decomposition may imply the instantiation of
   traffic-engineered multi-provider connectivity, subject to
   constraints such as guaranteed bandwidth, latency or minimum TE
   metric.  The multi-domain PCE (MD-PCE) receives the connectivity
   request from the inter-provider NFVO and performs inter-operator path
   computation to instantiate QoS-based connectivity between two VNFs
   (e.g., Label Switched Paths).  Two procedures are run sequentially:

      operators/domain sequence computation, based on the topology
      database, provided by Topology Distribution module, and on
      specific policies (e.g., business, bilateral),

      per-operator connectivity computation and instantiation.

   In 5GEx, MD-PCE is stateful (i.e., current connectivity information
   is stored inside the PCE) and inter-operator detailed computation is
   performed resorting to the stateful Backward Recursive PCE-based
   computation (BRPC) [draft-stateful-BRPC], deploying a chain of PCEP
   sessions among adjacent operators, each one responsible of computing
   and deploying its segment.  Backward recursive procedure allows
   optimal e2e constrained path computation results.

6.3.  5G-TRANSFORMER Architecture

   5G-TRANSFORMER project proposes a flexible and adaptable SDN/NFV-
   based design of the next generation Mobile Transport Networks,
   capable of simultaneously supporting the needs of various vertical
   industries with diverse range of requirements by offering customized
   slices.  In this design, multi-domain orchestration and federation
   are considered as the key concepts to enable end-to-end orchestration
   of services and resources across multiple administrative domains.

   The 5G-TRANSFORMER solution consists of three novel building blocks,
   namely:

   1.  Vertical Slicer (VS) as the common entry point for all verticals
       into the system.  The VS dynamically creates and maps the



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       vertical services onto network slices according to their
       requirements, and manages their lifecycle.  It also translates
       the vertical and slicing requests into ETSI defined NFV network
       services (NFV-NS) sent towards the SO.  Here a network slice is
       deployed as a NFV-NS instance.

   2.  Service Orchestrator (SO).  It offers service or resource
       orchestration and federation, depending on the request coming
       from the VS.  This includes all tasks related with coordinating
       and offering to the vertical an integrated view of services and
       resources from multiple administrative domains.  Orchestration
       entails managing end-to-end services or resources that were split
       into multiple administrative domains based on requirements and
       availability.  Federation entails managing administrative
       relations at the interface between SOs belonging to different
       domains and handling abstraction of services and resources.

   3.  Mobile Transport and Computing Platform (MTP) as the underlying
       unified transport stratum, responsible for providing the
       resources required by the NFV-NS orchestrated by the SO.  This
       includes their instantiation over the underlying physical
       transport network, computing and storage infrastructure.  It also
       may (de)abstract de MTP resources offered to the SO.

   The 5G-TRANSFROMER architecture is quite in line with the general
   Multi Domain Multi Provider reference architecture depicted in
   Figure 11.  Its mapping to the reference architecture is illustrated
   in the figure below.

               _________                       _________
              |         |                     |         |
              |   VS    |                     |   VS    |
              |_________|                     |_________|
                   |                               |
                   + IF1                           +
               ____|____                       ____|____
              |         |        IF2          |         |
              |   SO    |<--------+---------->|   SO    |
              |_________|                     |_________|
                  /\                               /\
                 /  \                             /  \
                /    \ IF3                       /    \
         ______/__   _\_______           _______/_    _\_______
        |   MTP   | |   MTP   |         |   MTP   |  |   MTP   |
        |_________| |_________|         |_________|  |_________|

      Figure 14: 5G-TRANSFORMER architecture mapped to the reference
                               architecture



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   The MTP would be mapped to the individual domain orchestrators, which
   only provides the resource orchestration for the local administrative
   domain.  The role of the SO is the Multi Provider orchestrator (MPO)
   responsible for multi-domain service or resource orchestration and
   federation.  The operation of the SO follows three main technical
   steps handled by the three function components of the MPO shown in
   Figure 14, namely (i) the catalogue and topology management system;
   (ii) the NFVO (Network Function Virtualization Orchestrator); and the
   assurance management component.

   Correspondingly, the interface between the SO and the VS (So-Vs) is
   the interface 1 (IF1), through which the VS requests the
   instantiation and deployment of various network services to support
   individual vertical service slices.  The interface between the SOs
   (So-So) of different domains is the interface 2 (IF2), enabling multi
   domain orchestration and federation operations.  The interface
   between the SO and the MTP (So-Mtp) is the interface 3 (IF3).  It, on
   the one hand, provides the SO the updated global view of the
   underlying infrastructure topology abstraction exposed by the MTP
   domain orchestrators, while on the other hand it also handles command
   and control functions to allow the SO request each MTP domain for
   virtual resource allocation.

   In 5G-TRANSFOMER, a set of sub-interfaces have been defined for the
   So-Mtp, So-So and Vs-So interfaces.

6.3.1.  So-Mtp Interface (IF3)

   This interface is based on ETSI GS-NFV IFA 005 and ETSI GS-NFV IFA
   006 for the request of virtual resource allocation, management and
   monitoring.  Accordingly, the 5G-TRANSFORMER identified the following
   sub-interfaces at the level of So-Mtp interactions (i.e., IF3-x
   interfaces regulating MPO-DO interactions).

      So-Mtp(-RAM).  It provides the Resource Advertisement Management
      (RAM) functions to allow updates or reporting about virtualized
      resources and network topologies in the MTP that will accommodate
      the requested NFVO component network services.

      So-Mtp(-RM).  It provides the Resource Management (RM) operations
      over the virtualized resources used for reserving, allocating,
      updating (in terms of scaling up or down) and terminating (i.e.,
      release) the virtualized resources handled by each MTP and
      triggered by NFVO component (in Figure 14) to accommodate network
      services.

      So-Mtp(-RMM).  It provides the required primitives and parameters
      for supporting the SO resource monitoring management (RMM)



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      capability for the purpose of fault management and SLA assurance
      handled by assurance management component in Figure 14.

   In the reference architecture (Fig. 6), the IF3-RC, IF3-RT, IF3-RMon
   sub-interface are defined for resource control, resource topology and
   resource monitoring respectively.  The IF3-RT, IF3-RC and IF3-RMon
   sub-interfaces map to So-Mtp(-RAM), So-Mtp(-RM) and So-Mtp(-RMM) sub-
   interfaces from 5G-TRANSFORMER.

6.3.2.  So-So Interface (IF2)

   This interface is based ETSI GS-NFV IFA 013 and ETSI GS-NFV IFA 005
   for the service and resource federation between the domains.  The 5G-
   TRANSFORMER identified the following sub-interfaces at the level of
   So-So interactions (i.e., IF2-x interfaces regulating MPO
   interactions) to provide service and resource federation and enable
   NSaaS and NFVIaaS provision, respectively, across different
   administrative domains.

      So-So(-LCM), for the operation of NFV network services.  The
      reference point is used to instantiate, terminate, query, update
      or re-configure network services or receive notifications for
      federated NFV network services.  The SO NFVO-NSO uses this
      reference point.

      So-So(-MON), for the monitoring of network services through
      queries or subscriptions/notifications about performance metrics,
      VNF indicators and network service failures.  The SO NFVO-NSO uses
      this reference point.

      So-So(-CAT), for the management of Network Service Descriptors
      (NSDs) flavors together with VNF/VA and MEC Application Packages,
      including their Application Descriptors (AppDs).  This reference
      point offers primitives for on-boarding, removal, updates, queries
      and enabling/disabling of descriptors and packages.  The SO NFVO-
      NSO uses this reference point.

   Furthermore, resource orchestration related operations are broken up
   to the following sub-interfaces to reflect resource control, resource
   topology and resource monitoring respectively.

      So-So(-RM), for allocating, configuring, updating and releasing
      resources.  The Resource Management reference point offers
      operations such as configuration of the resources, configuration
      of the network paths for connectivity of VNFs.  These operations
      mainly depend of the level of abstraction applied to the actual
      resources.  The SO NFVO-RO uses this reference point.




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      So-So(-RMM), for monitoring of different resources, computing
      power, network bandwidth or latency, storage capacity, VMs, MEC
      hosts provided by the peering administrative domain.  The details
      level depends on the agreed abstraction level.  The SO NFVO-RO
      uses this reference point.

      So-So(-RAM), for advertising available resource abstractions to/
      from other SOs.  It broadcasts available resources or resource
      abstractions upon capability calculation and periodic updates for
      near real-time availability of resources.  The SO-SO Resource
      Advertisement uses this reference point.

      So-So(-RMM), for monitoring of different resources, computing
      power, network bandwidth or latency, storage capacity, VMs, MEC
      hosts provided by the peering administrative domain.  The details
      level depends on the agreed abstraction level.  The SO NFVO-RO
      uses this reference point.

   In the reference architecture (Figure 11), the sub-interface IF2-S
   and IF2-C are defined to perform network service-related operations
   between MPOs of different administrative domains.  The IF2-RC,
   IF2-RT, IF2-RMon sub-interfaces are defined to regulated interactions
   between Catalogue and Topology Management components.  Their mapping
   to the sub-interfaces defined in 5G-TRANSFORMER are summarized as
   follows:

      The IF2-S sub-interface maps to So-So(-LCM) and So-So(-MON).

      The IF2-C sub-interface maps to So-So(-CAT).

      The IF2-RC, IF2-RT, IF2-RMon sub-interfaces map to So-So-RM, So-
      So-RAM, So-So-RT respectively.

6.3.3.  Vs-So Interface (IF1)

   This interface is based on ETSI GS-NFV IFA 013 for the VS requesting
   network services from the SO.  Accordingly, the 5G-TRANSFORMER
   identified the following sub-interfaces at the level of Vs-So
   interactions (i.e., IF1-x interfaces regulating tenant-MPO
   interactions).

      Vs-So(-LCM).  It deals with the NFV network service lifecycle
      management (LCM) and it is based on the IFA 013 NS Lifecycle
      Management Interface.  It offers primitives to instantiate,
      terminate, query, update or re-configure network services or
      receive notifications about their lifecycle.





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      Vs-So(-MON).  It deals with the monitoring (MON) of network
      services and VNFs through queries or subscriptions and
      notifications about performance metrics, VNF indicators and
      network services or VNFs failures.  It maps to IF1-S sub-interface
      of the reference architecture.

      Vs-So(-CAT).  It deals with the catalogue (CAT) management of
      Network Service Descriptors (NSDs), VNF packages, including their
      VNF Descriptors (VNFDs), and Application Packages, including their
      Application Descriptors (AppDs).  It offers primitives for on-
      boarding, removal, updates, queries and enabling/disabling of
      descriptors and packages.  It maps to IF1-C sub-interface of the
      reference architecture.

   In the reference architecture (Figure 11), the sub-interface IF1-S
   and IF1-C are defined to build request to perform network service-
   related operations including requesting the instantiation, update and
   termination of the requested network services.  The IF1-S sub-
   interface maps to Vs-So(-LCM) and Vs-So(-MON), while the IF1-C sub-
   interface maps to Vs-So(-CAT) defined in 5G-TRANSFORMER architecture.

7.  Multi-domain orchestration and Open Source

   Before reviewing current state of the open source projects it should
   be explicitly mentioned that term "federation" is quite ambiguous and
   used in multiple contexts across the industry.  For example,
   federation is the approach used at certain software projects to
   achieve high availability and enable reliable non-interrupted
   operation and service delivery.  One of the distinguishing features
   of this federation type is that all federated instances are managing
   the same piece of the infrastructure or resources set.  However, this
   document is focused on another federation type, where multiples
   independent instances of the orchestration/management software
   establish certain relationships and expose available resources and
   capabilities in the particular domain to consumers at another domain.
   Besides sharing resource details, multi-domain federation requires
   various management information synchronization, such authentication/
   authorization data, run-time policies, connectivity details and so
   on.  This kind of functionality and appropriate implementation
   approaches at the relevant open source projects are in scope of
   current section.

   At this moment several open source industry projects were formed to
   develop integrated NFV orchestration platform.  The most known of
   them are ONAP [onap], OSM [osm] and Cloudify [cloudify].  While all
   these projects have different drivers, motivations, implementation
   approach and technology stack under the hood, all of them are
   considering multi-VIM deployment scenario, i.e. all these software



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   platforms are capable to deploy NFV service over different
   virtualized infrastructures, like public or private providers.
   Additionally OSM and Cloudify orchestration platforms have
   capabilities to manage interconnection among managed VIMs using
   appropriate plugins or drivers.  However, despite the fact that
   typical Telco/Carrier infrastructure has multiple domains (both
   technology and administrative), none of these orchestration projects
   is focused on a service federation use case development.

   In the meantime, as an acknowledgement of the challenges, emerged
   during exploitation of the federation use cases Multisite project
   emerged under OPNFV umbrella [opnfv].  Considering OpenStack-based
   VIM deployments spanned across multiple regions as a general use
   case, this project initially was focusing on a gaps identification in
   the key OpenStack projects which lacks capabilities for multi-site
   deployment.  During several development phases of this OPNFV project,
   number of gaps were identified and submitted as a blueprints for the
   development into the appropriate OpenStack projects.  Further several
   demo scenarios were delivered to trial OpenStack as the open source
   VIM which is capable to support multisite NFV clouds.  While
   Multisite OPNFV project was focusing on a resource and VIM layer
   only, there are multiple viable outputs which might be considered
   during implementation of the federation use cases on the upper
   layers.

   As a summary it can be stated that it is still early days for the
   technology implemented in a referenced NFV orchestration projects and
   federation use case in not on a radar for these projects for the
   moment.  However, it is expected that upon maturity of the federation
   as a viable market use case appropriate feature set in the reviewed
   projects will be developed.

8.  IANA Considerations

   N/A.

9.  Security Considerations

   TBD.

10.  Acknowledgments

   This work is supported by 5G-PPP 5GEx, an innovation action project
   partially funded by the European Community under the H2020 Program
   (grant agreement no.  671636).  This work is also supported by 5G-PPP
   5G-TRANSFORMER, a research and innovation action project partially
   funded by the European Community under the H2020 Program (grant
   agreement no. 761536).  The views expressed here are those of the



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   authors only.  The European Commission is not liable for any use that
   may be made of the information in this presentation.

11.  Informative References

   [cloudify]
              "Cloudify", <https://cloudify.co/>.

   [etsi_nvf_ifa009]
              "Report on Architectural Options, ETSI GS NFV-IFA 009
              V1.1.1", July 2016.

   [etsi_nvf_ifa028]
              "Report on architecture options to support multiple
              administrative domains, ETSI GR NFV-IFA 028 V3.1.1",
              January 2018.

   [etsi_nvf_whitepaper]
              "Network Functions Virtualisation (NFV). White Paper 2",
              October 2014.

   [etsi_nvf_whitepaper_5g]
              "Network Functions Virtualisation (NFV). White Paper on
              "Network Operator Perspectives on NFV priorities for 5G"",
              February 2017.

   [ngmn_5g_whitepaper]
              "5G White Paper", February 2015.

   [ngmn_slicing]
              "Description of Network Slicing Concept", January 2016.

   [onap]     "ONAP project", <https://www.onap.org/>.

   [opnfv]    "OPNFV Multisite project",
              <https://wiki.opnfv.org/display/multisite/Multisite>.

   [osm]      "Open Source MANO project", <https://osm.etsi.org/>.

Authors' Addresses











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   Carlos J. Bernardos (editor)
   Universidad Carlos III de Madrid
   Av. Universidad, 30
   Leganes, Madrid  28911
   Spain

   Phone: +34 91624 6236
   Email: cjbc@it.uc3m.es
   URI:   http://www.it.uc3m.es/cjbc/


   Luis M. Contreras
   Telefonica I+D
   Ronda de la Comunicacion, S/N
   Madrid  28050
   Spain

   Email: luismiguel.conterasmurillo@telefonica.com


   Ishan Vaishnavi
   Huawei Technologies Dusseldorf GmBH
   Riesstrasse 25,
   Munich  80992
   Germany

   Email: Ishan.vaishnavi@huawei.com


   Robert Szabo
   Ericsson
   Konyves Kaman krt. 11
   Budapest, EMEA  1097
   Hungary

   Phone: +36703135738
   Email: robert.szabo@ericsson.com


   Josep Mangues-Bafalluy
   CTTC
   Av. Carl Friecrish Gauss, 7
   Castelldefels, EMEA  08860
   Spain

   Email: josep.mangues@cttc.cat





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   Xi Li
   NEC
   Kurfuersten-Anlage 36
   Heidelberg  69115
   Germany

   Email: Xi.Li@neclab.eu


   Francesco Paolucci
   SSSA
   Via Giuseppe Moruzzi, 1
   Pisa  56121
   Italy

   Phone: +395492124
   Email: fr.paolucci@santannapisa.it


   Andrea Sgambelluri
   SSSA
   Via Giuseppe Moruzzi, 1
   Pisa  56121
   Italy

   Phone: +395492132
   Email: a.sgambelluri@santannapisa.it


   Barbara Martini
   SSSA
   Via Giuseppe Moruzzi, 1
   Pisa  56121
   Italy

   Email: barbara.martini@cnit.it


   Luca Valcarenghi
   SSSA
   Via Giuseppe Moruzzi, 1
   Pisa  56121
   Italy

   Email: luca.valcarenghi@santannapisa.it






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   Giada Landi
   Nextworks
   Via Livornese, 1027
   Pisa  56122
   Italy

   Email: g.landi@nextworks.it


   Dmitriy Andrushko
   MIRANTIS

   Email: dandrushko@mirantis.com


   Alain Mourad
   InterDigital Europe

   Email: Alain.Mourad@InterDigital.com
   URI:   http://www.InterDigital.com/































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