Internet DRAFT - draft-contreras-alto-ietf-nef

draft-contreras-alto-ietf-nef







ALTO WG                                                    LM. Contreras
Internet-Draft                                                Telefonica
Intended status: Informational                             July 11, 2022
Expires: January 12, 2023


           Considering ALTO as IETF Network Exposure Function
                    draft-contreras-alto-ietf-nef-01

Abstract

   This document proposes ALTO as the means for exposure of underlay
   network capabilities for multiple overlays on top of the network.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on January 12, 2023.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Exposing network capabilities for enhancing service delivery    2
   3.  ALTO versus network controller conceptualization  . . . . . .   3
   4.  Modes of usage  . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Existing use cases  . . . . . . . . . . . . . . . . . . .   4
       4.1.1.  Network topology and reachability . . . . . . . . . .   4
       4.1.2.  Network performance metrics per path  . . . . . . . .   4
       4.1.3.  Segmented paths and associated characteristics  . . .   5
       4.1.4.  In-time view of dynamic IP addressing allocation  . .   5
     4.2.  Prospective use cases . . . . . . . . . . . . . . . . . .   5
       4.2.1.  Determination of optimal compute facility taking into
               account network information . . . . . . . . . . . . .   5
       4.2.2.  Information related to Service Functions and Service
               Function chains . . . . . . . . . . . . . . . . . . .   6
       4.2.3.  Visibility of underlying network information in
               overlay networks  . . . . . . . . . . . . . . . . . .   6
         4.2.3.1.  Cellular case . . . . . . . . . . . . . . . . . .   6
         4.2.3.2.  Media distribution case . . . . . . . . . . . . .   6
   5.  ALTO as IETF Network Exposure Function  . . . . . . . . . . .   7
   6.  TODO for next versions of this document . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  11
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Networks are turning on consumable objects by external applications
   and services.  In order to facilitate that, it is necessary to expose
   the capabilities offered by the networks in such a way that the
   applications and services can produce informed decisions that assist
   in the improvement of the service delivery.

   Thus it is convenient to define mechanisms for capabilities exposure
   that could provide required information for IETF networks.  ALTO
   [RFC7285] can play such a role.  This memo describes existing and
   foreseen capabilities that can be exposed by leveraging on ALTO.

2.  Exposing network capabilities for enhancing service delivery

   More and more, services and applications rely on information
   retrieved from the network in order to make decisions positively
   affecting the service delivery, by adapting the applications to the
   reality observed through the retrieved information.  This information
   is typically offered by specific components in the network with the



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   mission of aggregating, processing and securely exposing such
   information.

   Several initiatives are being developed in order to facilitate such
   exposure of capabilities and information at different network levels.
   For example, 3GPP defines the Network Exposure function (NEF)
   [TS29.522] as a secure, scalable and simplified exposing tool for
   capabilities (as well as events) supported by the 5G Core (5GC)
   network.  Main capabilities of NEF are the following:

   o  Securely expose 3GPP Network Functions (NFs) capabilities to
      Application Functions (AF).

   o  Secure provision of information to 5GC, including authentication
      and authorization to AF.

   o  Rate limit AF access to 5GC functions and information, including
      charging functions.

   o  Translation of internal-external information, e.g. identities.

   This is done though a number of APIs defined in [TS29.522].  A
   specific NEF instance may support only a subset of the APIs specified
   for capability exposure.

   Further examples are present in other network concerns.  Thus, in
   ETSI Multi-Access Edge Computing (MEC) group a number of APIs allow
   the retrieval of specific network information at the edge (e.g.,
   location API [MEC-013]), or the O-RAN Alliance which is working on
   exposing information to applications running on top of the non-real
   time Radio Informacion Controller (RIC) [O-RAN].

   The purpose of this document is to consider ALTO as the means for
   exposure of underlay network capabilities to multiple overlays on top
   of the network.  In other words, serve as "ground truth" from the
   network provider perspective to the applications consuming network
   capabilities in the scope of IETF.

3.  ALTO versus network controller conceptualization

   A relevant question that could arise is about the difference on
   purpose between ALTO and a network controller in the network.

   Primarily, the final purpose of these components is quite different.
   In this respect, a network controller (i.e., SDN controller
   [RFC7149]) can be seen as the element devoted to orchestration,
   control and management of the network assets, that is, the component
   in charge of administering network objects.  Typically, a network



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   controller leverages on another IETF functional component used for
   network control, such as the Path Computation Element (PCE)
   [RFC4655], which is used to compute paths for forwarding purposes
   based on network constraints.  In contrast to these two elements,
   ALTO acts as a "one-stop-shop" for retrieving (and correlating)
   network related information, potentially leveraging on the
   capabilities of the othe rtow (i.e., SDN controller and/or PCE).

   Moreover, ALTO has been included as part of some architectural
   frameworks, such ABNO [RFC7491], with the mission of allowing joint
   network and application-layer optimization precisely by exposing to
   applications an abstract network topology containing only information
   relevant to such application.  In this manner the application can
   take an informed decision and request specific control actions in the
   network.

4.  Modes of usage

   This section presents different modes of usage of ALTO network
   exposure capabilities to improve network operations.  Some of these
   usages can be implemented nowadays based on existing specifications,
   while a set of other use cases is considered as prospective since
   more specification work is yet needed in IETF.

4.1.  Existing use cases

   This subsection presents a number of use cases already described that
   can leverage on ALTO as IETF Network Exposure Function.

4.1.1.  Network topology and reachability

   The basic ALTO capabilities [RFC7285] provide network maps associated
   with costs in a manner that for any pair of source and destination
   can be retrieved information about topology and reachability.  This
   can be considered as the fundamental or baseline information on top
   of which the other modes of usage are built on.

4.1.2.  Network performance metrics per path

   Extensions defined in [I-D.ietf-alto-performance-metrics] permit the
   reporting of standard-based performance metrics associated to the
   paths generated in the network map.  With that view, applications
   consuming ALTO (i.e., ALTO clients) can determine the performance
   expectation for the possible paths between an origin and a
   destination.  Thus, not only puere cost but also performance can be
   considered as an element for decision.





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4.1.3.  Segmented paths and associated characteristics

   Original ALTO concentrates on end-to-end paths.  However it may
   result of interest to get knowledge of specific parts of the end-to-
   end paths that could produce problems such as e.g. congestion.  Then,
   having means of segmenting the end-to-end paths becomes useful.
   [I-D.ietf-alto-path-vector] allows for that defining a new
   abstraction called Abstract Network Element (ANE) to represent
   components constituting an entire end-to-end network path as a vector
   of ANEs.

4.1.4.  In-time view of dynamic IP addressing allocation

   Some architectures allow for dynamic allocation of IP address subnets
   across the network.  An example of that is the Control and User Plane
   Separation (CUPS) architecture for Broadband Network Gateways (BNGs)
   [I-D.wadhwa-rtgwg-bng-cups], [TR-459].  In that architecture, the
   control place of the BNG has the possibility of dynamically assigning
   IP address subnets to different elements distributed in the network,
   acting as user plane functions of the BNG.  This dynamic allocation
   implies that certain IP prefixes could be allocated in different
   parts of the network along the time.  By means of ALTO and its
   network map is it possible to obtain an up-to-date view of the
   topological location of each subnet in runtime, facilitating the
   optimization of some services (e.g. media distribution) in an
   automated manner.

4.2.  Prospective use cases

   This subsection presents a number of use cases that could be enabled
   by ALTO as IETF Network Exposure Function.

4.2.1.  Determination of optimal compute facility taking into account
        network information

   ALTO can be used as a component to provide insights on the
   reachability of suitable compute facilities.  An initial case has
   been documented in [I-D.contreras-alto-service-edge].  The rationale
   for this case is that ALTO receives information of connected compute
   capabilities in terms of e.g.  CPU, memory and storage.  This
   information can be put together with the network map, in a way that
   the cost of reaching those capabilities can be easily determined.

   Note that if further information apart of cost is included in the map
   (e.g., performance metrics) then the resulting information provided
   to applications becomes enriched.





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4.2.2.  Information related to Service Functions and Service Function
        chains

   ALTO can provide information relative to the paths characteristics
   associated with a single Service Function or with a number of chained
   Service Functions.  This can be useful at the definition phase of a
   network service, either considering specific instances of the
   constituent Service Functions, or as a mean of identifying the more
   appropriate Service Functions to compose a service.

   [I-D.lcsr-alto-service-functions] proposes different situations of
   interest and explores augmentations in ALTO to support the retrieval
   of information associated to Service Functions.  Internal IETF
   solutions as the ones for Service Function Chaining or SRv6
   programmability can benefit of this insight, but also other solutions
   like ETSI NFV, 3GPP, O-RAN or any other requiring efficient decisions
   in relation with chains of Service Functions can be benefitted for
   their own automation, management and control processes.

4.2.3.  Visibility of underlying network information in overlay networks

   Different overlay networks run today leveraging the connectivity
   provided by the basic underlying transport network.  Since specific
   situations on the transport network can result in relevance for the
   service being provided by the overlays, it is crucial to facilitate
   the observation of such situations from the underlay to the overlay.

4.2.3.1.  Cellular case

   Mobile networks leverage transport networks to connect mobile access
   nodes with core management and control entities (e.g., for mobility
   management, policing, etc), running in an overlay mode through
   tunneling (i.e., the GTP protocol).  [I-D.li-alto-cellular-use-cases]
   presents the benefits of exposing network information for
   applications running on access devices of a cellular network.

4.2.3.2.  Media distribution case

   Media delivery systems, as traditional CDNs, deliver content to end-
   users in an over-the-top fashion.  The key aspect for an efficient
   and optimal delivery of the content is to select the proper delivery
   point for whatever end-user requesting it is to have a clear view of
   the network topology (including the associated costs or any other
   information that could enrich the decision, such as performance
   metrics).  In this respect, the information exposed by ALTO in
   reference to the requesting end-user can be consumed by CDN control
   elements for improving the decision on what delivery point to select
   [RFC7971].



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   Further than that, additional scenarios can benefit from ALTO network
   information exposure capabilities.  For instance, in scenarios of
   interconnection of CDNs, such as the one described in
   [I-D.ryan-cdni-capacity-insights-extensions] for advertising capacity
   associated with the CDN internal to an operator, could leverage on
   ALTO capabilities for that purpose (with the necessary
   augmentations).

5.  ALTO as IETF Network Exposure Function

   From its inception, ALTO was defined as a way of informing
   applications about network-related aspects for improving the overall
   service.

   The applications under scope can be either internal or external to
   the operator of the network.  The implications can differ in the
   level of aggregating, abstracting and securely exposing the
   information, but the purpose keeps being the same.

   Figure 1 illustrates the role of ALTO as IETF Network Exposure
   Function.






























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                    +--------------+            +--------------+
 External           |   External   |            |    Cloud     |
 Applications     / |   CDN logic  |     ...    | Application  |
 (as ALTO        /  |              |            | Orchestrator |
 clients)       /   +--------------+            +--------------+
               /                                 /
       -------/---------------------------------/-----------------------
             /                                 /
            v                                 /
    +--------------+                         /
    |   ALTO as    |<-----------------------/               Internal
    |   Network    |                                        Applications
    |Exposure Func.|<-----------------------\               (as ALTO
    +--------------+                         \              clients)
         A  A                                 \
         |   \                                 \
         |    \                                 \
         |     \    +--------------+            +--------------+
         |      \   |SDN Controller|            |   Internal   |
         |       \  | (e.g., ABNO) |     ...    |   CDN logic  |
         |        \ |              |            |              |
         |          +--------------+            +--------------+
         \                  |                           |
          \                 |                           |
           >                v                           v
            ^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^
           (                                                   )
          (                                                     )
         (                       Network                         )
          (                                                     )
           (                                                   )
            ^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^v^


             Figure 1: ALTO as IETF Network Exposure Function

   Each particular ALTO instance in a certain network could support only
   a subset of the capabilities discussed in the use cases described
   before.  In this respect, ways of advertising supported capabilities
   should be defined.

6.  TODO for next versions of this document

   This version is a work-in-progress.  Next versions of the document
   will address somo further aspects such as:

   o  Identification of further network capabilities of interest for
      being exposed by ALTO.



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   o  Complete security aspects when exposing information to internal
      and external applications.

7.  Security Considerations

   ALTO security considerations as reflected in [RFC7285] apply to this
   document.

   Apart from that, the following aspects should be taken into
   consideration:

   o  Authentication between ALTO and any external entitiy consuming
      ALTO, to prevent malicious behaviors.

   o  Privacy of the information shared between components, especially
      when those components pertain to different administrative domain
      (e.g., an external CDN retieving network information from a
      network of a different administrative domain).

   o  Secure transport of the information in the communication with ALTO
      Server (e.g., TLS, etc).

8.  IANA Considerations

   This draft does not include any IANA considerations

9.  References

   [I-D.contreras-alto-service-edge]
              Contreras, L. M., Lachos, D. A., Rothenberg, C. E., and S.
              Randriamasy, "Use of ALTO for Determining Service Edge",
              draft-contreras-alto-service-edge-05 (work in progress),
              July 2022.

   [I-D.ietf-alto-path-vector]
              Gao, K., Lee, Y., Randriamasy, S., Yang, Y. R., and J. J.
              Zhang, "An ALTO Extension: Path Vector", draft-ietf-alto-
              path-vector-25 (work in progress), March 2022.

   [I-D.ietf-alto-performance-metrics]
              Wu, Q., Yang, Y. R., Lee, Y., Dhody, D., Randriamasy, S.,
              and L. M. C. Murillo, "ALTO Performance Cost Metrics",
              draft-ietf-alto-performance-metrics-28 (work in progress),
              March 2022.







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   [I-D.lcsr-alto-service-functions]
              Contreras, L. M. and S. Randriamasy, "ALTO extensions for
              handling Service Functions", draft-lcsr-alto-service-
              functions-00 (work in progress), July 2022.

   [I-D.li-alto-cellular-use-cases]
              Gang, L., Randriamasy, S., and C. Xiong, "ALTO Uses Cases
              for Cellular Networks", draft-li-alto-cellular-use-
              cases-00 (work in progress), July 2021.

   [I-D.ryan-cdni-capacity-insights-extensions]
              Ryan, A., Rosenblum, B., and N. B. Sopher, "CDNI Capacity
              Capability Advertisment Extensions", draft-ryan-cdni-
              capacity-insights-extensions-02 (work in progress), March
              2022.

   [I-D.wadhwa-rtgwg-bng-cups]
              Wadhwa, S., Shinde, R., Newton, J., Hoffman, R., Muley,
              P., and S. Pani, "Architecture for Control and User Plane
              Separation on BNG", draft-wadhwa-rtgwg-bng-cups-03 (work
              in progress), March 2019.

   [MEC-013]  "GS MEC 013 Location API V2.1.1", ETSI GS MEC 013 V2.1.1 ,
              September 2019.

   [O-RAN]    "Non-RT RIC Architecture", O-RAN.WG2.Non-RT-RIC-ARCH-TS-
              v01.00.02 , July 2021.

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <https://www.rfc-editor.org/info/rfc4655>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC7149]  Boucadair, M. and C. Jacquenet, "Software-Defined
              Networking: A Perspective from within a Service Provider
              Environment", RFC 7149, DOI 10.17487/RFC7149, March 2014,
              <https://www.rfc-editor.org/info/rfc7149>.

   [RFC7285]  Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S.,
              Previdi, S., Roome, W., Shalunov, S., and R. Woundy,
              "Application-Layer Traffic Optimization (ALTO) Protocol",
              RFC 7285, DOI 10.17487/RFC7285, September 2014,
              <https://www.rfc-editor.org/info/rfc7285>.



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   [RFC7491]  King, D. and A. Farrel, "A PCE-Based Architecture for
              Application-Based Network Operations", RFC 7491,
              DOI 10.17487/RFC7491, March 2015,
              <https://www.rfc-editor.org/info/rfc7491>.

   [RFC7971]  Stiemerling, M., Kiesel, S., Scharf, M., Seidel, H., and
              S. Previdi, "Application-Layer Traffic Optimization (ALTO)
              Deployment Considerations", RFC 7971,
              DOI 10.17487/RFC7971, October 2016,
              <https://www.rfc-editor.org/info/rfc7971>.

   [TR-459]   "Control and User Plane Separation for a disaggrgated
              BNG", Broadband Forum TR-459 , June 2020.

   [TS29.522]
              "TS 29.522 Network Exposure Function Northbound APIs
              V16.9.0.", 3GPP TS 29.522 V16.9.0 , September 2021.

Acknowledgments

   ...

Author's Address

   Luis M. Contreras
   Telefonica
   Ronda de la Comunicacion, s/n
   Sur-3 building, 3rd floor
   Madrid  28050
   Spain

   Email: luismiguel.contrerasmurillo@telefonica.com
   URI:   http://lmcontreras.com/


















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