SFC WG                                                     CJ. Bernardos
Internet-Draft                                                      UC3M
Intended status: Experimental                                  A. Mourad
Expires: September 23, 2021                                 InterDigital
                                                          March 22, 2021

             Service Function discovery in fog environments


   Service function chaining (SFC) allows the instantiation of an
   ordered set of service functions and subsequent "steering" of traffic
   through them.  Service functions provide an specific treatment of
   received packets, therefore they need to be known so they can be used
   in a given service composition via SFC.  This document discusses the
   need for service function discovery mechanisms and propose some
   solutions for sfc-aware nodes to discover available service functions
   in fog environments.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Problem statement . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Discovery of SF in a multi-provider fog/edge environment    4
   4.  Network-based SF discovery  . . . . . . . . . . . . . . . . .   6
     4.1.  ICMPv6-based SF discovery . . . . . . . . . . . . . . . .   8
     4.2.  DHCPv6-based SF discovery . . . . . . . . . . . . . . . .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   8.  Informative References  . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Virtualization of functions 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.

   Service Functions are widely deployed and essential in many networks.
   These Service Functions provide a range of features such as security,
   WAN acceleration, and server load balancing.  Service Functions may

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   be instantiated at different points in the network infrastructure
   such as data center, the WAN, the RAN, and even on mobile nodes.

   Service functions (SFs), also referred to as VNFs, or just functions,
   are hosted on compute, storage and networking resources.  The hosting
   environment of a function is called Service Function Provider or
   NFVI-PoP (using ETSI NFV terminology).

   With the arrival of virtualization, the deployment model for service
   function is evolving to one where the traffic is steered through the
   functions wherever they are deployed (functions do not need to be
   deployed in the traffic path anymore).  For a given service, the
   abstracted view of the required service functions and the order in
   which they are to be applied is called a Service Function Chain
   (SFC).  An SFC is instantiated through selection of specific service
   function instances on specific network nodes to form a service graph:
   this is called a Service Function Path (SFP).  The service functions
   may be applied at any layer within the network protocol stack
   (network layer, transport layer, application layer, etc.).

   A mobile terminal can benefit from using service function chaining at
   the edge/fog to enhance existing applications or to enable new ones.
   In order to do so, discovery of available service functions is
   required.  This document focuses on this aspect.

2.  Terminology

   The following terms used in this document are defined by the IETF in
   [RFC7665] and [I-D.ietf-bess-nsh-bgp-control-plane]:

      Service Function (SF): a function that is responsible for specific
      treatment of received packets (e.g., firewall, load balancer).

      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 Forwarder (SFF): A service function forwarder is
      responsible for forwarding traffic to one or more connected
      service functions according to information carried in the SFC
      encapsulation, as well as handling traffic coming back from the

      SFI: SF instance.

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      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.

      A Service Function Type (SFT) that is the category of Service
      Function that is provided (such as "firewall").

3.  Problem statement

   [RFC7665] describes an architecture for the specification, creation,
   and ongoing maintenance of Service Function Chains (SFCs) in a
   network.  It includes architectural concepts, principles, and
   components used in the construction of composite services through
   deployment of SFCs.  In this architecture, a key element is the
   service function (SF), which is a function that is responsible for
   specific treatment of received packets (e.g., a firewall).

   So far, how the SFs are discovered and composed has been out of the
   scope of discussions in IETF.  There is however a need to define
   mechanisms that allow SF discovery in fog environments
   [I-D.bernardos-sfc-fog-ran].  Note that the mechanisms described in
   this document address fog environments.  There are other mechanisms
   described, like [I-D.ietf-bess-nsh-bgp-control-plane], that cover
   generic SF discovery in more traditional environments.  Some of the
   solutions described in the present document might be of applicable to
   other scenarios as well.

3.1.  Discovery of SF in a multi-provider fog/edge environment

   The need to provide networking, computing, and storage capabilities
   closer to the users has recently emerged, due to the demands from 5G
   applications of very low latency, leading to what is known today as
   the concept of intelligent edge.  ETSI has been the first to address
   this need recently by developing the framework of mobile edge
   computing (MEC).  Such an intelligent edge could not be envisaged
   without virtualization.  Beyond applications, it raises a clear
   opportunity for networking functions to execute at the edge
   benefiting from inherent low latencies.  Being in close proximity to
   the access, the edge becomes an attractive place for hosting
   different functions, saving bandwidth in their respective domains and
   offering local breakout options where required.  Whilst it is
   appreciated the particular challenge for the intelligent edge concept
   in dealing with mobile users, the edge virtualization substrate has
   been largely assumed to be fixed or stationary.  Although little
   developed, the intelligent edge concept is being extended further to
   scenarios where for example the edge computing substrate is on the
   move, e.g., on-board a car or a train, or that it is distributed

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   further down the edge, even integrating resources from different
   stakeholders, into what is known as the fog.

   Service composition is a powerful tool which can provide significant
   benefits when applied in a softwarized network environment.  While it
   is being explored in the core part of networks to compose services
   using DPIs (Deep Packet Inspections), firewalls, parental control,
   video accelerators, etc., its applicability to the RAN (Radio Access
   Network), and in particular to the edge and the fog, has not been
   explored yet.

   Running functions (standalone functions or service function chains)
   at the edge of the network has clear advantages.  For example, it
   enables offloading functions from the end-user terminal so that it
   can become more efficient in terms of cost and energy consumption.

   A mobile terminal can benefit from using service function chaining at
   the edge/fog to enhance existing applications or to enable new ones.
   Some examples of such applications are: privacy enhancement by local
   anchoring, opportunistic local breakout, assisted encryption, video
   transcoding, personal firewalling, etc.  The mobile terminal might
   look for function hosting opportunities at the edge for various
   reasons such as:

   o  to increase battery life in critical situations by offloading
      energy demanding operations (e.g., video transcoding, augmented
      reality) to the edge/cloud;

   o  to reduce communications latency (e.g., by using local breakout at
      the edge for selected applications demanding low latency);

   o  to enable new functions (e.g., privacy improvements, personal
      firewalling) which demand additional intelligence/resources at the

   o  to benefit from context information available at the edge (e.g.,
      enrich networking decisions by executing functions at the edge
      using RAN information);

   Several key challenges need to be addressed to enable controlled
   service function chaining for a mobile terminal, and one of them is
   the discovery of the functions available for use at the Fog/Edge/

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4.  Network-based SF discovery

   In this section we describe several mechanisms for a mobile SFC-aware
   node to discover what SFs are available in the network.  Different
   alternatives (protocol containers) are considered to enable the
   mobile node to obtain the following information per SF available:

   o  Service Function Type, identifying the category of SF provided.

   o  SFC-aware: Yes/No.  Indicates if the SF is SFC-aware.

   o  Route Distinguisher (RD): IP address indicating the location of
      the SF(I).

   o  Pricing/costs details.

   o  Migration capabilities of the SF: whether a given function can be
      moved to another provider (potentially including information about
      compatible providers topologically close).

   o  Mobility of the device hosting the SF, with e.g. the following

         Level: no, low, high; or a corresponding scale (e.g., 1 to 10).

         Current geographical area (e.g., GPS coordinates, post code).

         Target moving area (e.g., GPS coordinates, post code).

   o  Power source of the device hosting the SF, with e.g. the following

         Battery: Yes/No.  If Yes, the following sub-options could be

         Capacity of the battery (e.g., mmWh).

         Charge status (e.g., %).

         Lifetime (e.g., minutes).

   Figure 1 shows the generic mechanism for SF discovery, with network
   support.  In this scenario, SFs (which might belong to different
   administrative domains) are previously registered at the network,
   which can then reply to requests sent from mobile nodes that have
   just attached to the network.  A request might optionally include the
   SFs of interest for the terminal, instead of a request for all known

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   The network might also send periodic advertisements in addition to
   responses to solicited requests.  These responses/advertisements
   include the information about known SFs (or only about the ones
   queried by the terminal), which can then be used by the terminal to
   decide whether to use (some of) them in a certain SFC.  How the
   mobile terminal then configures this SFC is not covered in this

                                                    _(           )_
                                                  _(  SF1    SF2   )_
    ------------                   -----------  _(        SF3        )_
    | terminal |                   | network |-(_  SF4         SF5    _)
    ------------                   -----------   (_   SF6   SF7     _)
        |                               |          (_    SF8      _)
       XXX (1. attachment)              |            (___________)
        |                               |
        +---2. Request (optional)------>|
        |                               |
        |<--------3. Response/Advert.---|
        |            (SF1,SF2...,SF8)   |
        |                               |

                     Figure 1: SF (network) discovery

   In addition to the discovery of SFs at the infrastructure, mobile
   terminals can also host SF(I)s, and therefore they also need to be
   discovered.  A similar approach can be followed, as showin in
   Figure 2.

                   |    SF3   |
    ------------   | terminal |    ------------
    | SF1  SF2 |   ------------    | SF4  SF5 |
    | terminal |        |          | terminal |
    ------------        |          ------------
         |              |               |
         +--1. Request->+-------------->|
         |    (SF1,SF2) |               |
         |<----------------2. Response--+
         |            (SF4,SF5)         |
         |<-2. Response-+               |
         |      (SF3)   |               |
         |              |               |

                     Figure 2: SF (mobiles) discovery

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   SFs might belong to different administrative domains.  This might
   require the use of additional security and authentication mechanisms.
   Policies can be used (both in single and multi-domain scenarios) to
   adapt/limit the type and number of SFs that are advertised, depending
   on the relationship of the requester and the advertiser.

   Next sections describe different protocol alternatives for this SF
   discovery in fog environments.

4.1.  ICMPv6-based SF discovery


4.2.  DHCPv6-based SF discovery


5.  IANA Considerations


6.  Security Considerations


7.  Acknowledgments

   The work in this draft will be further developed and explored under
   the framework of the H2020 5G-DIVE project (Grant 859881).

8.  Informative References

              Bernardos, C., Rahman, A., and A. Mourad, "Service
              Function Chaining Use Cases in Fog RAN", draft-bernardos-
              sfc-fog-ran-08 (work in progress), September 2020.

              Farrel, A., Drake, J., Rosen, E., Uttaro, J., and L.
              Jalil, "BGP Control Plane for the Network Service Header
              in Service Function Chaining", draft-ietf-bess-nsh-bgp-
              control-plane-18 (work in progress), August 2020.

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,

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Authors' Addresses

   Carlos J. Bernardos
   Universidad Carlos III de Madrid
   Av. Universidad, 30
   Leganes, Madrid  28911

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

   Alain Mourad
   InterDigital Europe

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

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