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Versions: 00 01 02 03 04                                                
NFV Research Group                                            G. Bernini
Internet-Draft                                               V. Maffione
Intended status: Informational                                 Nextworks
Expires: January 4, 2016                                        D. Lopez
                                                     P. Aranda Gutierrez
                                                          Telefonica I+D
                                                            July 3, 2015

      VNF Orchestration For Automated Resiliency in Service Chains


   Network Function Virtualization (NFV) aims at evolving the way
   network operators design, deploy and provision their networks by
   leveraging standard IT virtualization technologies to move and
   consolidate a wide range of network functions and services onto
   industry standard high volume servers, switches and storage.  Primary
   area of impact for operators is the network edge, being stimulated by
   the recent updates on NFV and SDN.  In fact, operators are looking at
   their future datacenters and Points of Presence (PoPs) as
   increasingly dynamic infrastructures to deploy Virtualized Network
   Functions (VNFs) and on-demand chained services with high elasticity.

   This document presents an orchestration framework for automated
   deployment of highly available VNF chains.  Resiliency of VNFs and
   chained services is a key requirement for operators to improve, ease,
   automate and speed up services lifecycle management.  The proposed
   VNFs orchestration framework is also positioned with respect to
   current NFV and Service Function Chaining (SFC) architectures and

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
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

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

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   This Internet-Draft will expire on January 4, 2016.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  VNF Orchestration for Resilient Virtual Appliances  . . . . .   4
     3.1.  Problem Statement . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Orchestration Framework . . . . . . . . . . . . . . . . .   6
       3.2.1.  Orchestrator  . . . . . . . . . . . . . . . . . . . .   8
       3.2.2.  SDN Controller  . . . . . . . . . . . . . . . . . . .   8
       3.2.3.  VNF Chain Configurator  . . . . . . . . . . . . . . .   9
       3.2.4.  Edge Configurator . . . . . . . . . . . . . . . . . .  10
     3.3.  Resiliency Control Functions for Chained VNFs . . . . . .  10
   4.  Positioning in Existing NFV and SFC Frameworks  . . . . . . .  12
     4.1.  Mapping into NFV Architecture . . . . . . . . . . . . . .  12
     4.2.  Mapping into SFC Architecture . . . . . . . . . . . . . .  12
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   Current Telco infrastructures are facing the rapid development of the
   cloud market, which includes a broad range of emerging virtualized
   services and distributed applications.  Network Function
   Virtualization (NFV) is gaining wide interest across operators to
   evolve the way networks are operated and provisioned, with the

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   execution in virtualized environments of those network functions and
   services traditionally integrated in hardware devices.

   A Virtualized Network Function (VNF) provides the same function as
   the equivalent network function (e.g. firewall, load balancer) but is
   deployed as a software instance running on general purpose servers
   via a virtualization technology.  The main idea is therefore to run
   network functions in either datacenters or commodity network nodes
   that are, in some cases, close to the end user premises.  With NFV,
   network functions that were traditionally implemented on specialized
   hardware devices are moved to general purpose servers, running in
   self-contained virtual machines.  These virtualized functions can be
   deployed in multiple instances or moved to various locations in the
   network, adapting themselves to traffic dynamicity and customer
   demands without the overhead cost and management of installing new
   equipment.  Moreover, operators' networks are populated with a large
   and increasing variety of proprietary software and hardware tools and
   appliances.  The deployment of new network services in operational
   environments is often a complex and costly procedure, requiring
   additional space and power to accommodate new boxes.  Moreover,
   current hardware-based appliances rapidly reach end of life,
   requiring much of the design integration and deployment cycle to be
   repeated with little revenue benefit.  In this context, the
   transition of network functions and appliances from hardware to
   software solutions by means of NFV promises to address and overcome
   these hindrances for network operators.

   While the above considerations are valid for stand-alone VNFs running
   independently, additional challenges and requirements raise for
   network operators when services offered to customers are built by the
   composition of multiple VNFs.  In this case, the deployment and
   provisioning of each VNF composing the service for the customer needs
   to be coordinated with the other VNFs, applying control functions to
   steer the traffic through them following the proper order (i.e.
   according to the specific service function path).  An orchestration
   framework capable of coordinating the automated deployment,
   configuration, provisioning and chaining of multiple VNFs would ease
   the management of the whole lifecycle of services offered to
   customers.  Additionally, when dealing with virtualized functions,
   resiliency and high availability of chained services pose additional
   requirements for a VNF orchestration framework, in terms of detection
   of software failure at various levels, including hypervisors and
   virtual machines, hardware failure, and virtual appliance migration.

   This document presents an orchestration framework for automated
   deployment of high available VNF chains, and introduces its
   architecture and building blocks.  Resiliency for both stand-alone
   VNFs and chained services is considered in this document as a key

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   control function based on VNF pool concepts.  The proposed VNF
   orchestration framework is also positioned with respect to approaches
   and architectures currently defined for Network Function
   Virtualization and Service Function Chaining (SFC).

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

   The following acronyms are used in this document:

   NFV:  Network Function Virtualization.

   SDN:  Software Defined Networking.

   VNF:  Virtualized Network Function.

   SFC:  Service Function Chaining.

   CPE:  Customer Premise Equipment.

   VPN:  Virtual Private Network.

   EMS:  Element Management System.

   PoP:  Point of Presence.

   VM:  Virtual Machine.

3.  VNF Orchestration for Resilient Virtual Appliances

   The telco market is rapidly moving towards an Everything as a Service
   model, where the virtualization of traditionally in-the-box network
   functions can benefit from Software Defined Networking (SDN) tools
   and technologies.  As said, the recent updates and proposed solutions
   on NFV and SDN is practically bringing, from an operator perspective,
   a deep evolution on how the network edge is architected, operated and
   provisioned, since that is the place where VNFs and virtual services
   can be deployed and provisioned close to the customers.  Operators
   target to evolve their datacenters and PoPs into more and more
   dynamic infrastructures where VNFs and chained services can be
   deployed with high availability and high elasticity to scale up and
   down while optimizing performances and resources utilization.

   This section introduces the VNF orchestration framework proposed in
   this document for the deployment, provisioning and chaining of

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   resilient virtual appliances and services within operators'

3.1.  Problem Statement

   The orchestration framework proposed in this document aims at solving
   some of the challenges that operators face when, trying to apply the
   base NFV concepts, they replace hardware devices implementing well-
   known network functions with software-based virtual appliances.  In
   particular, this VNF orchestration framework targets an automated,
   flexible and elastic provisioning of service chains within operators'

   When operators need to compose and chain multiple VNFs to provision a
   given service to the customer, they need to operate network and
   computing resources in a coordinated way, and above all to implement
   control mechanisms and procedures to steer the traffic through the
   different VNFs and the customer sites.  As an example, the
   virtualization of the Customer Premises Equipment (CPE) is emerging
   as one of the first applications of the Network Functions
   Virtualization (NFV) architecture that is currently being
   commercialized by several software (and hardware) vendors.  It has
   the potential to generate a significant impact on the operators
   businesses.  The term virtual CPE (vCPE) refers to the execution in a
   virtual environment of the network functions that traditionally
   integrated in hardware gears at customer premises, like BGP speakers,
   firewall, NAT, etc.  Different scenarios and use cases exist for the
   vCPE.  Currently, the typical scenario is the vCPE in the PoP, that
   actually provides softwarization and shift to the first PoP of the
   operator for those network functions normally deployed at customer
   premises (e.g.  NAT, Firewall, etc.).  The goal is to manage the
   whole LAN environment of the customer, while preserving QoE of its
   services, providing added value services to users not willing to get
   involved with technology issues, and reducing maintenance trouble
   tickets and the need for in-house problem solving.  In addition, the
   vCPE can be used in the operator's datacenter to implement in
   software those chained network functions to provision automated VPN
   services for customers [VCPE-T2], in order to dynamically and
   automatically extend existing L3 VPNs (e.g. connecting remote
   customer sites) to incorporate new virtual assets (like virtual
   machines) into a private cloud.

   As additional requirements for the proposed orchestration framework,
   the use of VNFs opens new challenges concerning the reliability of
   provided virtual services.  When network functions are deployed on
   monolithic hardware platforms, the lifecycle of individual services
   is strictly bound to the availability of the physical device, and
   management tools may detect outages and migrate affected services to

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   new instances deployed on backup hardware.  When introducing VNFs,
   individual network functions may still fail, but with more risk
   factors such as software failure at various levels, including
   hypervisors and virtual machines, hardware failure, and virtual
   appliance migration.  Moreover, when considering chains of VNFs, the
   management and control tools used by the operators have to consider
   and apply reliability mechanisms at the service level, including
   transparent migration to backup VNFs and synchronization of state
   information.  In this context, VNF pooling mechanisms and concepts
   are valid and applicable, thus considering VNF instances grouped as
   pools to provide the same function in a reliable way.

3.2.  Orchestration Framework

   The VNF orchestration framework proposed in this document aims to
   provide automated functions for the deployment, provisioning and
   composition of resilient VNFs within operators' datacenters.
   Figure 1 presents the high level architecture, including building
   blocks and functional components.

   This VNF orchestration framework is built around two key components:
   the orchestrator and the SDN controller.  The orchestrator includes
   all the functions related to the management, coordination, and
   control of VNFs instantiation, configuration and composition.  It is
   the component at the highest level of the architecture and represents
   the access point to the VNF orchestration framework for the operator.
   On the other hand, the SDN controller provides dynamic traffic
   steering and flexible network provisioning within the datacenter as
   needed by the VNF chains.  The basic controller functions are
   augmented by a set of enhanced network applications deployed on top,
   that might be themselves control and management VNFs for operator use
   (i.e. not related to customers and users functions).

   Therefore, the architecture depicted in Figure 1 is a practical
   demonstration of how SDN and NFV technologies and concepts can be
   integrated to provide substantial benefits to network operators in
   terms of robustness, ease of management, control and provisioning of
   their network infrastructures and services.  SDN and NFV are clearly
   complementary solutions for enabling virtualization of network
   infrastructures, services and functions while supporting dynamic and
   flexible network traffic engineering.  SDN focuses on network
   programmability, traffic steering and multi-tenancy by means of a
   common, open, and dynamic abstraction of network resources.  NFV
   targets a progressive migration of network elements, network
   appliances and fixed function boxes into VMs that can be ran on
   commodity hardware, enabling the benefits of cloud and datacenters to
   be applied to network functions.

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                     |                Orchestrator                  |
                           |                |                |
                           V                V                V
                     +------------+  +-------------+  +-------------+
                     |            |  |             |  |             |
                     |  VNF Pool  |  | VNF Chain   |  |    Edge     |
                     |  Manager   |  |Configurator |  |Configurator |
                     |            |  |             |  |             |
                     +-----+------+  +------+------+  +------+------+
                           |                |                |
                           V                V                V
                     |                 SDN Controller               |
+.......................+           |   |    |              |
:           +--------+  \           |   |    |              +-----+
:           |+-------++ :|    +-----+---+----+----+               |
:           +|       || :\    | +-----------------+-+         +---+----+
:          /|| VNF1  || : |   | | +---------------+-+-+       |        |
:         / ||       || :..+  | | |    Virtual    | | +-------+  Edge  |
:        /  ++-------+| :  :  | | |   Switche(s)  | | +-------+ Router |
:       /    +---+----+ :  :| +-+-+---------------+ | |       |        |
:      /         |      :  :\   +-+-----------------+ |       +--------+
:  +--+-----+    |      :  : |    +-----+---+---+-----+
:  |+-------++   |      :  : \          |   |   |
:  ||       ||   |      :  :  |         |   |   |
:  || VNF2  ||   |      :  :  \---------+---+---+------+
:  ||       ||   |      :  :  |                        |
:  ++-------+|   |      :  :  |                        |
:   +--+-+---+   |      :  :  |     Virtual Compute    |
:         \ +----+---+  :  :  |     Infrastructure     |
:          \|+-------++ :  :  |                        |
:           +|       || :  :  |                        |
:           || VNF3  || :  :  /------------------------+
:           ||       || :  : |
:           ++-------+| :  : |
:            +--------+ :  : |
:Service Chain "X"      :  : /
+.......................+  : |
  :Service Chain "Y"       :/

            Figure 1: VNF Orchestration Framework Architecture.

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3.2.1.  Orchestrator

   The VNF orchestrator implements a set of functions to seamlessly
   control and manage in a coordinated way the instantiation and
   deployment of VNFs on one hand, and their composition and chaining to
   steer the traffic through them on the other.  It is fully controlled
   and operated by the network operator, and basically it is the highest
   control and orchestration layer that sits above all the softwarized
   and virtualized components in the proposed architecture.

   Therefore the VNF orchestrator provides a consistent way to access
   the system and provision chains of VNFs to the operator.  It exposes
   a set of primitives to instantiate, configure VNFs and compose them
   according to the specific service chain requirements.  Practically,
   it aims at enabling an efficient and dynamic management of operator's
   infrastructure resources with great flexibility by means of a
   consistent set of APIs.

   To enable this, the orchestrator can be seen as a composition of
   several internal functionalities, each providing a given coordination
   function needed to orchestrate the lower layer control and management
   functions depicted in Figure 1 (i.e.  VNF chain configuration, VNF
   pool provisioning, etc.).  In practice, the orchestrator needs to
   include at least an internal component to manage the instantiation
   and configuration of stand-alone VNFs (e.g. implemented by a self-
   contained VM) that might be directly interfaced with the physical
   servers in the datacenter.  And also a dedicated component for
   programmatic coordination and provisioning of VNF chains is needed to
   properly orchestrate the traffic steering through VNFs belonging to
   the same service chain.  This should also provide multi-tenant
   functionalities and maintain isolation across VNF chains deployed for
   different customers.  It is then clear that the VNF orchestrator is
   the overall coordinator of the proposed framework, and it drives all
   the lower layer components that implement the actual control logic.

3.2.2.  SDN Controller

   The SDN controller provides the logic for network control,
   provisioning and monitoring.  It is the component where the SDN
   abstraction happens.  This means it exposes a set of primitives to
   configure the datacenter network according to the requirements of the
   VNF chains to be provisioned, while hiding the specific technology
   constraints and capabilities of the software switches and edge
   routers underneath.  The deployment of an SDN controller allows to
   implement a software driven VNF orchestration, with flexible and
   programmable network functions for service chaining and resilient
   virtual appliances.

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   At its southbound interface, the SDN controller interfaces with
   software switches running in servers, physical switches
   interconnecting them and edge routers connecting the datacenter with
   external networks.  Multiple control protocols can be used at this
   southbound interface to actually provision the datacenter network and
   enable traffic steering through VNFs, including OpenFlow, OVSDB,
   NETCONF and others.

   Therefore the SDN controller provides the basic network provisioning
   functions needed by upper layer coordination functions to perform
   service chain and VNF pool-wide actions.  Indeed, the logic and the
   state at the service level is only maintained and coordinated by
   network applications on top of the SDN controller.

3.2.3.  VNF Chain Configurator

   The VNF chain configurator is deployed as a bridging component
   between the orchestrator and the SDN controller, and it is mostly
   dedicated to the implementation of VNF chaining and composition
   logic.  It computes a suitable path to interconnect the involved VNFs
   (already instantiated and identified by the orchestrator) and
   forwards the network configuration request to the SDN controller for
   each new VNF chain requested by the orchestrator.

   Following the datacenter service chains and related traffic types
   defined in [I-D.ietf-sfc-dc-use-cases], the VNF chain configurator
   should implement its coordination logic to support both north-south
   and east-west chains.  The former refer to network traffic staying
   within the datacenter but coming from a remote datacenter or a user
   through the edge router connecting to an external network.  In this
   case, the VNF chain configurator should also coordinate with the edge
   configurator to properly provision the datacenter edge router.
   Moreover, this north-south case may also refer to VNF chains spanning
   multiple datacenters, thus requiring a further inter-datacenter
   coordination between VNF chain configurators and orchestrators.
   These coordination functions are out of the scope of this document.
   On the other hand, the east-west chains refer to VNFs treating
   network traffic that do not exit the datacenter.  For both cases, the
   VNF chain configurator (in combination with the SDN controller)
   should implement and support proper service chains encapsulation
   solutions [I-D.ietf-sfc-nsh] to isolate and segregate traffic related
   to VNF chains belonging to different tenants.

   Different deployment models may exist for the VNF chain configurator:
   a dedicated configurator for each chain, or a single configurator for
   all the VNF chains.  In the first approach, the orchestrator needs to
   implement some coordination logic related to the dynamic
   instantiation of configurators when new VNF chains are provisioned.

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3.2.4.  Edge Configurator

   The edge configurator is a network control application deployed on
   top of the SDN controller.  Its main role is to coordinate the
   provisioning and configuration of the edge router for those north-
   south VNF chains exiting the datacenter.  In particular, it keeps the
   binding between the traffic steered through the VNFs and the related
   network service outside the datacenter terminated at the edge router
   (e.g. a L3 VPN, VLAN, VXLAN, VRF etc), possibly considering the
   service chain encapsulation implemented within the VNF chain.  The
   mediation of the SDN controller allows to support a variety of
   control and management protocols for the actual configuration of the
   datacenter edge router.

3.3.  Resiliency Control Functions for Chained VNFs

   In the proposed orchestration architecture, the resiliency control
   functions that have been identified as a key feature for a flexible
   and dynamic provisioning of chained VNF services, are implemented by
   the VNF pool manager depicted in Figure 1.  It is the entity that
   manages and coordinates VNFs reliability providing high availability
   and resiliency features at both stand-alone and chained VNFs level.

   The deployment of VNF based services requires a transition of
   resiliency capabilities and mechanisms from physical network devices
   typically highly available (and often specialized) to entities (like
   self-contained VMs) running VNFs in the context of pools of
   virtualized resources.

   When moving towards a resilient approach for VNFs deployment and
   operation, the generic high availability requirements to be matched
   are translated into the following ones:

   Service continuity:  when a hardware failure or capacity limits
      (memory and CPU) occur on platforms hosting VMs (and therefore
      VNFs), it is necessary to migrate VNFs to other VMs and/or
      hardware platforms to guarantee service continuity with minimum
      impact on the users

   Topological transparency:  the hand-over between live and backup VNFs
      must be implemented in a transparent way for the user and also for
      the service chain itself.  The backup VNF instances need to
      replicate the necessary information (configuration, addressing,
      etc.) so that the network function is taken over without any
      topological disruption (i.e. at the VNF chain level)

   Load balancing or scaling:  migration of VNF instances may also
      happen for load-balancing purposes (e.g. for CPU, memory overload

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      in virtualized platforms) or scaling of network services (with
      VNFs moved to new hardware platforms).  In both cases the working
      network function is moved to a new VNF instance and the service
      continuity must be maintained.

   Auto scale of VNFs instances:  when a VNF requires increased resource
      allocation to improve overall service performance, the network
      function could be distributed across multiple VMs, and to
      guarantee the performance improvement dedicated pooling mechanisms
      for scaling up or down resources to each VNF in a consistent way
      are needed.

   Multiple VNF resiliency classes:  each type of end-to-end service
      (e.g. web, financial backend, video streaming, etc.) has its own
      specific resiliency requirements for the related VNFs.  While for
      operators it is not easy to achieve service resiliency SLAs
      without building to peak, a basic set of VNF resiliency classes
      can be defined to identify some metrics, such as: if a VNF needs
      status synchronization; fault detection and restoration time
      objective (e.g. real-time); service availability metrics; service
      quality metrics; service latency metrics for VNF chain components.

   The aim of the VNF orchestration presented in this document is to
   address the above requirements by introducing the VNF pool manager
   that follows the principles of the IETF VNFPOOL architecture [I-
   D.zong-vnfpool-arch], where a pool manager coordinates the
   reliability of stand-alone VNFs, by selecting the active instance and
   interacting with the Service Control Entity for consistent end-to-end
   service chain reliability and provisioning.  In the VNF orchestration
   architecture illustrated in Figure 1, the Service Control Entity is
   implemented by the combination of the orchestrator (for overall
   coordination of service chains) and the VNF chain configuration (for
   actual provisioning and coordination of individual service chains).

   Different deployment models may exist for the VNF pool manager: a
   dedicated manager for each VNF chain, or a single one for all the

   In terms of offered resiliency functionalities, the VNF pool manager
   provides some post-configuration functions to instantiate VNFs (as
   self-contained VMs) with the desired degree of reliability and
   redundancy.  This translates into further actions to create and
   configure additional VMs as backups, therefore building a pool for
   each VNF in the chain.

   The VNF pool manager is conceived to offer several types and degrees
   of reliability functions.  First, it provides specific functions for
   the persistence of VNFs configuration, including making periodic

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   snapshots of the VMs running the VNF.  Moreover, at runtime (i.e.
   with the service chain in place), it monitors the operational status
   and performances of the master VNFs VMs, and collects notifications
   about VMs status, e.g. by registering as an observer to dedicated
   services offered by the virtualization platform used within the
   virtual compute infrastructure.  Moreover, VNF pool manager reacts to
   any failure condition by autonomously replacing the master VNF with
   one of its backup on the pool, basically implementing a swap of VMs
   for service chain recovery purposes.  Thus, the VNF pool manager also
   takes care in coordination with the VNF chain configurator of
   implementing those resiliency mechanisms at the chain level.  Two
   options have been identified so far: cold recovery and hot recovery.
   In the former, backup VNFs, properly configured with the same master
   configuration, are kept ready (but switched off) to be started when
   the master dies.  In this case the recovery time depends on the
   specific VNF and its type of function, e.g. it may depend on
   convergence time for a virtual BGP router.  In the hot recovery,
   active backup VNFs are kept synchronized with the master ones, and
   the recovery of the service chain (mostly performed at the VNF chain
   configurator) in case of failure is faster than cold recovery.

4.  Positioning in Existing NFV and SFC Frameworks

4.1.  Mapping into NFV Architecture

   For the presented solution to be integrated in the ETSI NFV reference
   architecture, some modifications need to be applied to it.  The VNF
   pools replace the VNFs in the architecture.  They are then controlled
   by the Element Management System (EMS) on the northbound.  So the EMS
   has to be made VNFPOOL aware.  Additional elements that need to
   support the mechanisms proposed by VNFPOOL are the VNF managers,
   which need to implement the resiliency and VNF scaling
   (up-/downscale) functions.  This has also implications on the
   orchestrator, which has to be aware of the augmented functionality
   offered by the VNF Manager.  In fact, the orchestrator also provides
   primitives for VNFs chaining, matching the Service Control Entity in
   the VNFPool architecture.

4.2.  Mapping into SFC Architecture

   [I-D.ietf-sfc-architecture] describes the Service Function Chaining
   (SFC) architecture.  It describes the concept of a service function
   (SF) and how to chain SFs and provides only little detail of the SFC
   control plane, which is responsible with the coordination of the SFs
   and their stitching into SFCs.  The combination of orchestrator, VNF
   chain configurator and VNF pool manager functionalities described in
   this document cover most of the functions expected from the SFC
   control plane.

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5.  IANA Considerations

   This draft does not have any IANA consideration.

6.  Security Considerations

   Security issues related to VNF orchestration and resiliency of
   service chains are left for further study.

7.  Acknowledgements

   This work has been partially supported by the European Commission
   through the FP7 ICT Trilogy2 project (Building the Liquid Net, grant
   agreement no:317756).

   The views expressed here are those of the author only.  The European
   Commission is not liable for any use that may be made of the
   information in this document.

   Authors would like to thank G.  Carrozzo and G.  Landi from Nextworks
   for valuable discussions and contributions to the topics addressed in
   this document.

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

8.2.  Informative References

              Surendra, S., Tufail, M., Majee, S., Captari, C., and S.
              Homma, "Service Function Chaining Use Cases In Data
              Centers", draft-ietf-sfc-dc-use-cases-02 (work in
              progress), January 2015.

              Halpern, J. and C. Pignataro, "Service Function Chaining
              (SFC) Architecture", draft-ietf-sfc-architecture-09 (work
              in progress), June 2015.

              Quinn, P. and U. Elzur, "Network Service Header", draft-
              ietf-sfc-nsh-00 (work in progress), March 2015.

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              Zong, N., Dunbar, L., Shore, M., Lopez, D., and G.
              Karagiannis, "Virtualized Network Function (VNF) Pool
              Problem Statement", draft-zong-vnfpool-problem-
              statement-06 (work in progress), July 2014.

   [VCPE-T2]  G. Bernini, G. Carrozzo, P. A. Gutierrez, D. R. Lopez, ,
              "Virtualizing the Network Edge: Virtual CPE for the
              datacenter and the PoP", European Conference on Networks
              and Communications , June 2014.

Authors' Addresses

   Giacomo Bernini
   via Livornese 1027
   San Piero a Grado, Pisa  56122

   Phone: +39 050 3871600
   Email: g.bernini@nextworks.it

   Vincenzo Maffione
   via Livornese 1027
   San Piero a Grado, Pisa  56122

   Phone: +39 050 3871600
   Email: v.maffione@nextworks.it

   Diego R. Lopez
   Telefonica I+D
   Calle Zubaran, 12
   Madrid  28010

   Email: diego.r.lopez@telefonica.com

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   Pedro Andres Aranda Gutierrez
   Telefonica I+D
   Calle Zubaran, 12
   Madrid  28010

   Email: pedroa.aranda@telefonica.com

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