ALTO WG LM. Contreras
Internet-Draft Telefonica
Intended status: Informational October 25, 2021
Expires: April 28, 2022
Considering ALTO as IETF Network Exposure Function
draft-contreras-alto-ietf-nef-00
Abstract
This document proposes ALTO as the means for exposure of underlay
network capabilities for multiple overlays on top of the network.
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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. Visibility of underlying network information in
overlay networks . . . . . . . . . . . . . . . . . . 6
4.2.2.1. Cellular case . . . . . . . . . . . . . . . . . . 6
4.2.2.2. Media distribution case . . . . . . . . . . . . . 6
5. ALTO as IETF Network Exposure Function . . . . . . . . . . . 6
6. TODO for next versions of this document . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10
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
mission of aggregating, processing and securely exposing such
information.
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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
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
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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. 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.
4.2.2.1. 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.
4.2.2.2. 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].
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.
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Figure 1 illustrates the role of ALTO as IETF Network Exposure
Function.
+--------------+ +--------------+
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.
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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.
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.
(TODO: elaborate on data-related security issues as NEF).
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-03 (work in progress),
July 2021.
[I-D.ietf-alto-path-vector]
Gao, K., Lee, Y., Randriamasy, S., Yang, Y. R., and J. J.
Zhang, "ALTO Extension: Path Vector", draft-ietf-alto-
path-vector-18 (work in progress), October 2021.
[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-19 (work in progress),
October 2021.
[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.
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[I-D.ryan-cdni-capacity-insights-extensions]
Ryan, A., Rosenblum, B., and N. B. Sopher, "CDNI Capacity
Insights Capability Advertisment Extensions", draft-ryan-
cdni-capacity-insights-extensions-01 (work in progress),
October 2021.
[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>.
[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>.
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[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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