Independent Submission LM. Contreras
Request for Comments: 8597 Telefonica
Category: Informational CJ. Bernardos
ISSN: 2070-1721 UC3M
D. Lopez
Telefonica
M. Boucadair
Orange
P. Iovanna
Ericsson
May 2019
Cooperating Layered Architecture for Software-Defined Networking (CLAS)
Abstract
Software-Defined Networking (SDN) advocates for the separation of the
control plane from the data plane in the network nodes and its
logical centralization on one or a set of control entities. Most of
the network and/or service intelligence is moved to these control
entities. Typically, such an entity is seen as a compendium of
interacting control functions in a vertical, tightly integrated
fashion. The relocation of the control functions from a number of
distributed network nodes to a logical central entity conceptually
places together a number of control capabilities with different
purposes. As a consequence, the existing solutions do not provide a
clear separation between transport control and services that rely
upon transport capabilities.
This document describes an approach called Cooperating Layered
Architecture for Software-Defined Networking (CLAS), wherein the
control functions associated with transport are differentiated from
those related to services in such a way that they can be provided and
maintained independently and can follow their own evolution path.
Contreras, et al. Informational [Page 1]
RFC 8597 Layered SDN Architecture May 2019
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This is a contribution to the RFC Series, independently of any other
RFC stream. The RFC Editor has chosen to publish this document at
its discretion and makes no statement about its value for
implementation or deployment. Documents approved for publication by
the RFC Editor are not candidates for any level of Internet Standard;
see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8597.
Copyright Notice
Copyright (c) 2019 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
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
Contreras, et al. Informational [Page 2]
RFC 8597 Layered SDN Architecture May 2019
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Architecture Overview . . . . . . . . . . . . . . . . . . . . 6
3.1. Functional Strata . . . . . . . . . . . . . . . . . . . . 9
3.1.1. Transport Stratum . . . . . . . . . . . . . . . . . . 9
3.1.2. Service Stratum . . . . . . . . . . . . . . . . . . . 10
3.1.3. Recursiveness . . . . . . . . . . . . . . . . . . . . 10
3.2. Plane Separation . . . . . . . . . . . . . . . . . . . . 10
3.2.1. Control Plane . . . . . . . . . . . . . . . . . . . . 11
3.2.2. Management Plane . . . . . . . . . . . . . . . . . . 11
3.2.3. Resource Plane . . . . . . . . . . . . . . . . . . . 11
4. Required Features . . . . . . . . . . . . . . . . . . . . . . 11
5. Communication between SDN Controllers . . . . . . . . . . . . 12
6. Deployment Scenarios . . . . . . . . . . . . . . . . . . . . 12
6.1. Full SDN Environments . . . . . . . . . . . . . . . . . . 13
6.1.1. Multiple Service Strata Associated with a Single
Transport Stratum . . . . . . . . . . . . . . . . . . 13
6.1.2. Single Service Stratum Associated with Multiple
Transport Strata . . . . . . . . . . . . . . . . . . 13
6.2. Hybrid Environments . . . . . . . . . . . . . . . . . . . 13
6.2.1. SDN Service Stratum Associated with a Legacy
Transport Stratum . . . . . . . . . . . . . . . . . . 13
6.2.2. Legacy Service Stratum Associated with an SDN
Transport Stratum . . . . . . . . . . . . . . . . . . 13
6.3. Multi-domain Scenarios in the Transport Stratum . . . . . 14
7. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.1. Network Function Virtualization (NFV) . . . . . . . . . . 14
7.2. Abstraction and Control of TE Networks . . . . . . . . . 15
8. Challenges for Implementing Actions between Service and
Transport Strata . . . . . . . . . . . . . . . . . . . . . . 15
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
10. Security Considerations . . . . . . . . . . . . . . . . . . . 16
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
11.1. Normative References . . . . . . . . . . . . . . . . . . 17
11.2. Informative References . . . . . . . . . . . . . . . . . 17
Appendix A. Relationship with RFC 7426 . . . . . . . . . . . . . 19
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
Contreras, et al. Informational [Page 3]
RFC 8597 Layered SDN Architecture May 2019
1. Introduction
Network softwarization advances are facilitating the introduction of
programmability in the services and infrastructures of
telecommunications operators. This is generally achieved through the
introduction of Software-Defined Networking (SDN) [RFC7149] [RFC7426]
capabilities in the network, including controllers and orchestrators.
However, there are concerns of a different nature that these SDN
capabilities have to resolve. On the one hand, actions focused on
programming the network to handle the connectivity or forwarding of
digital data between distant nodes are needed. On the other hand,
actions devoted to programming the functions or services that process
(or manipulate) such digital data are also needed.
SDN advocates for the separation of the control plane from the data
plane in the network nodes by introducing abstraction among both
planes, allowing the control logic on a functional entity, which is
commonly referred as SDN Controller, to be centralized; one or
multiple controllers may be deployed. A programmatic interface is
then defined between a forwarding entity (at the network node) and a
control entity. Through that interface, a control entity instructs
the nodes involved in the forwarding plane and modifies their
traffic-forwarding behavior accordingly. Support for additional
capabilities (e.g., performance monitoring, fault management, etc.)
could be expected through this kind of programmatic interface
[RFC7149].
Most of the intelligence is moved to this kind of functional entity.
Typically, such an entity is seen as a compendium of interacting
control functions in a vertical, tightly integrated fashion.
The approach of considering an omnipotent control entity governing
the overall aspects of a network, especially both the transport
network and the services to be supported on top of it, presents a
number of issues:
o From a provider perspective, where different departments usually
are responsible for handling service and connectivity (i.e.,
transport capabilities for the service on top), the mentioned
approach offers unclear responsibilities for complete service
provision and delivery.
o Complex reuse of functions for the provision of services.
o Closed, monolithic control architectures.
Contreras, et al. Informational [Page 4]
RFC 8597 Layered SDN Architecture May 2019
o Difficult interoperability and interchangeability of functional
components.
o Blurred business boundaries among providers, especially in
situations where one provider provides only connectivity while
another provider offers a more sophisticated service on top of
that connectivity.
o Complex service/network diagnosis and troubleshooting,
particularly to determine which layer is responsible for a
failure.
The relocation of the control functions from a number of distributed
network nodes to another entity conceptually places together a number
of control capabilities with different purposes. As a consequence,
the existing SDN solutions do not provide a clear separation between
services and transport control. Here, the separation between service
and transport follows the distinction provided by [Y.2011] and as
defined in Section 2 of this document.
This document describes an approach called Cooperating Layered
Architecture for SDN (CLAS), wherein the control functions associated
with transport are differentiated from those related to services in
such a way that they can be provided and maintained independently and
can follow their own evolution path.
Despite such differentiation, close cooperation between the service
and transport layers (or strata in [Y.2011]) and the associated
components are necessary to provide efficient usage of the resources.
2. Terminology
This document makes use of the following terms:
o Transport: denotes the transfer capabilities offered by a
networking infrastructure. The transfer capabilities can rely
upon pure IP techniques or other means, such as MPLS or optics.
o Service: denotes a logical construct that makes use of transport
capabilities.
This document does not make any assumptions about the functional
perimeter of a service that can be built above a transport
infrastructure. As such, a service can be offered to customers or
invoked for the delivery of another (added-value) service.
Contreras, et al. Informational [Page 5]
RFC 8597 Layered SDN Architecture May 2019
o Layer: refers to the set of elements that enable either transport
or service capabilities, as defined previously. In [Y.2011], this
is referred to as a "stratum", and the two terms are used
interchangeably.
o Domain: is a set of elements that share a common property or
characteristic. In this document, it applies to the
administrative domain (i.e., elements pertaining to the same
organization), technological domain (elements implementing the
same kind of technology, such as optical nodes), etc.
o SDN Intelligence: refers to the decision-making process that is
hosted by a node or a set of nodes. These nodes are called SDN
controllers.
The intelligence can be centralized or distributed. Both schemes
are within the scope of this document.
An SDN Intelligence relies on inputs from various functional
blocks, such as: network topology discovery, service topology
discovery, resource allocation, business guidelines, customer
profiles, service profiles, etc.
The exact decomposition of an SDN Intelligence, apart from the
layering discussed here, is out of the scope of this document.
Additionally, the following acronyms are used in this document:
CLAS: Cooperating Layered Architecture for SDN
FCAPS: Fault, Configuration, Accounting, Performance, and Security
SDN: Software-Defined Networking
SLA: Service Level Agreement
3. Architecture Overview
Current operator networks support multiple services (e.g., Voice over
IP (VoIP), IPTV, mobile VoIP, critical mission applications, etc.) on
a variety of transport technologies. The provision and delivery of a
service independent of the underlying transport capabilities require
a separation of the service-related functionalities and an
abstraction of the transport network to hide the specifics of the
underlying transfer techniques while offering a common set of
capabilities.
Contreras, et al. Informational [Page 6]
RFC 8597 Layered SDN Architecture May 2019
Such separation can provide configuration flexibility and
adaptability from the point of view of either the services or the
transport network. Multiple services can be provided on top of a
common transport infrastructure; similarly, different technologies
can accommodate the connectivity requirements of a certain service.
Close coordination among these elements is required for consistent
service delivery (inter-layer cooperation).
This document focuses particularly on the means to:
o expose transport capabilities to services.
o capture transport requirements of services.
o notify service intelligence of underlying transport events, for
example, to adjust a service decision-making process with
underlying transport events.
o instruct the underlying transport capabilities to accommodate new
requirements, etc.
An example is guaranteeing some Quality-of-Service (QoS) levels.
Different QoS-based offerings could be present at both the service
and transport layers. Vertical mechanisms for linking both service
and transport QoS mechanisms should be in place to provide quality
guarantees to the end user.
CLAS architecture assumes that the logically centralized control
functions are separated into two functional layers. One of the
functional layers comprises the service-related functions, whereas
the other one contains the transport-related functions. The
cooperation between the two layers is expected to be implemented
through standard interfaces.
Figure 1 shows the CLAS architecture. It is based on functional
separation in the Next Generation Network (NGN) architecture defined
by the ITU-T in [Y.2011], where two strata of functionality are
defined. These strata are the Service Stratum, comprising the
service-related functions, and the Transport Stratum, covering the
transport-related functions. The functions of each of these layers
are further grouped into the control, management, and user (or data)
planes.
CLAS adopts the same structured model described in [Y.2011] but
applies it to the objectives of programmability through SDN
[RFC7149]. In this respect, CLAS advocates for addressing services
and transport in a separated manner because of their differentiated
concerns.
Contreras, et al. Informational [Page 7]
RFC 8597 Layered SDN Architecture May 2019
Applications
/\
||
||
+-------------------------------------||-------------+
| Service Stratum || |
| \/ |
| ........................... |
| . SDN Intelligence . |
| . . |
| +--------------+ . +--------------+ . |
| | Resource Pl. | . | Mgmt. Pl. | . |
| | |<===>. +--------------+ | . |
| | | . | Control Pl. | | . |
| +--------------+ . | |-----+ . |
| . | | . |
| . +--------------+ . |
| ........................... |
| /\ |
| || |
+-------------------------------------||-------------+
|| Standard
-- || -- API
||
+-------------------------------------||-------------+
| Transport Stratum || |
| \/ |
| ........................... |
| . SDN Intelligence . |
| . . |
| +--------------+ . +--------------+ . |
| | Resource Pl. | . | Mgmt. Pl. | . |
| | |<===>. +--------------+ | . |
| | | . | Control Pl. | | . |
| +--------------+ . | |-----+ . |
| . | | . |
| . +--------------+ . |
| ........................... |
| |
| |
+----------------------------------------------------+
Figure 1: Cooperating Layered Architecture for SDN
Contreras, et al. Informational [Page 8]
RFC 8597 Layered SDN Architecture May 2019
In the CLAS architecture, both the control and management functions
are considered to be performed by one or a set of SDN controllers
(due to, for example, scalability, reliability), providing the SDN
Intelligence in such a way that separated SDN controllers are present
in the Service and Transport Strata. Management functions are
considered to be part of the SDN Intelligence to allow for effective
operation in a service provider ecosystem [RFC7149], although some
initial propositions did not consider such management as part of the
SDN environment [ONFArch].
Furthermore, the generic user- or data-plane functions included in
the NGN architecture are referred to here as resource-plane
functions. The resource plane in each stratum is controlled by the
corresponding SDN Intelligence through a standard interface.
The SDN controllers cooperate in the provision and delivery of
services. There is a hierarchy in which the Service SDN Intelligence
makes requests of the Transport SDN Intelligence for the provision of
transport capabilities.
The Service SDN Intelligence acts as a client of the Transport SDN
Intelligence.
Furthermore, the Transport SDN Intelligence interacts with the
Service SDN Intelligence to inform it about events in the transport
network that can motivate actions in the service layer.
Despite not being shown in Figure 1, the resource planes of each
stratum could be connected. This will depend on the kind of service
provided. Furthermore, the Service Stratum could offer an interface
to applications to expose network service capabilities to those
applications or customers.
3.1. Functional Strata
As aforementioned, there is a functional split that separates
transport-related functions from service-related functions. Both
strata cooperate for consistent service delivery.
Consistency is determined and characterized by the service layer.
3.1.1. Transport Stratum
The Transport Stratum comprises the functions focused on the transfer
of data between the communication endpoints (e.g., between end-user
devices, between two service gateways, etc.). The data-forwarding
nodes are controlled and managed by the Transport SDN component.
Contreras, et al. Informational [Page 9]
RFC 8597 Layered SDN Architecture May 2019
The control plane in the SDN Intelligence is in charge of instructing
the forwarding devices to build the end-to-end data path for each
communication or to make sure the forwarding service is appropriately
set up. Forwarding may not be rely solely on the preconfigured
entries; means can be enabled so that involved nodes can dynamically
build routing and forwarding paths (this would require that the nodes
retain some of the control and management capabilities for enabling
this). Finally, the management plane performs management functions
(i.e., FCAPS) on those devices, like fault or performance management,
as part of the Transport Stratum capabilities.
3.1.2. Service Stratum
The Service Stratum contains the functions related to the provision
of services and the capabilities offered to external applications.
The resource plane consists of the resources involved in the service
delivery, such as computing resources, registries, databases, etc.
The control plane is in charge of controlling and configuring those
resources as well as interacting with the control plane of the
Transport Stratum in client mode to request transport capabilities
for a given service. In the same way, the management plane
implements management actions on the service-related resources and
interacts with the management plane in the Transport Stratum to
ensure management cooperation between layers.
3.1.3. Recursiveness
Recursive layering can happen in some usage scenarios in which the
Transport Stratum is itself structured in the Service and Transport
Strata. This could be the case in the provision of a transport
service complemented with advanced capabilities in addition to the
pure data transport (e.g., maintenance of a given SLA [RFC7297]).
Recursiveness has also been discussed in [ONFArch] as a way of
reaching scalability and modularity, where each higher level can
provide greater abstraction capabilities. Additionally,
recursiveness can allow some multi-domain scenarios where single or
multiple administrative domains are involved, such as those described
in Section 6.3.
3.2. Plane Separation
The CLAS architecture leverages plane separation. As mentioned in
Sections 3.1.1 and 3.1.2, three different planes are considered for
each stratum. The communication among these three planes (with the
corresponding plane in other strata) is based on open, standard
interfaces.
Contreras, et al. Informational [Page 10]
RFC 8597 Layered SDN Architecture May 2019
3.2.1. Control Plane
The control plane logically centralizes the control functions of each
stratum and directly controls the corresponding resources. [RFC7426]
introduces the role of the control plane in an SDN architecture.
This plane is part of an SDN Intelligence and can interact with other
control planes in the same or different strata to perform control
functions.
3.2.2. Management Plane
The management plane logically centralizes the management functions
for each stratum, including the management of the control and
resource planes. [RFC7426] describes the functions of the management
plane in an SDN environment. This plane is also part of the SDN
Intelligence and can interact with the corresponding management
planes residing in SDN controllers of the same or different strata.
3.2.3. Resource Plane
The resource plane comprises the resources for either the transport
or the service functions. In some cases, the service resources can
be connected to the transport ones (e.g., being the terminating
points of a transport function); in other cases, it can be decoupled
from the transport resources (e.g., one database keeping a register
for the end user). Both the forwarding and operational planes
proposed in [RFC7426] would be part of the resource plane in this
architecture.
4. Required Features
Since the CLAS architecture implies the interaction of different
layers with different purposes and responsibilities, a number of
features are required to be supported:
o Abstraction: the mapping of physical resources into the
corresponding abstracted resources.
o Service-Parameter Translation: the translation of service
parameters (e.g., in the form of SLAs) to transport parameters (or
capabilities) according to different policies.
o Monitoring: mechanisms (e.g., event notifications) available in
order to dynamically update the (abstracted) resources' status
while taking into account, for example, the traffic load.
Contreras, et al. Informational [Page 11]
RFC 8597 Layered SDN Architecture May 2019
o Resource Computation: functions able to decide which resources
will be used for a given service request. As an example,
functions like PCE could be used to compute/select/decide a
certain path.
o Orchestration: the ability to combine diverse resources (e.g., IT
and network resources) in an optimal way.
o Accounting: record of resource usage.
o Security: secure communication among components, preventing, for
example, DoS attacks.
5. Communication between SDN Controllers
The SDN controllers residing respectively in the Service and
Transport Strata need to establish tight coordination. Mechanisms
for transferring relevant information for each stratum should be
defined.
From the service perspective, the Service SDN Intelligence needs to
easily access transport resources through well-defined APIs to
retrieve the capabilities offered by the Transport Stratum. There
could be different ways of obtaining such transport-aware
information, i.e., by discovering or publishing mechanisms. In the
former case, the Service SDN Intelligence could be able to handle
complete information about the transport capabilities (including
resources) offered by the Transport Stratum. In the latter case, the
Transport Stratum reveals the available capabilities, for example,
through a catalog, reducing the amount of detail of the underlying
network.
On the other hand, the Transport Stratum must properly capture the
Service requirements. These can include SLA requirements with
specific metrics (such as delay), the level of protection to be
provided, maximum/minimum capacity, applicable resource constraints,
etc.
The communication between controllers must also be secure, e.g., by
preventing denial of service or any other kind of threat (similarly,
communications with the network nodes must be secure).
6. Deployment Scenarios
Different situations can be found depending on the characteristics of
the networks involved in a given deployment.
Contreras, et al. Informational [Page 12]
RFC 8597 Layered SDN Architecture May 2019
6.1. Full SDN Environments
This case considers that the networks involved in the provision and
delivery of a given service have SDN capabilities.
6.1.1. Multiple Service Strata Associated with a Single Transport
Stratum
A single Transport Stratum can provide transfer functions to more
than one Service Stratum. The Transport Stratum offers a standard
interface(s) to each of the Service Strata. The Service Strata are
the clients of the Transport Stratum. Some of the capabilities
offered by the Transport Stratum can be isolation of the transport
resources (slicing), independent routing, etc.
6.1.2. Single Service Stratum Associated with Multiple Transport Strata
A single Service Stratum can make use of different Transport Strata
for the provision of a certain service. The Service Stratum invokes
standard interfaces to each of the Transport Strata, and orchestrates
the provided transfer capabilities for building the end-to-end
transport needs.
6.2. Hybrid Environments
This case considers scenarios where one of the strata is totally or
partly legacy.
6.2.1. SDN Service Stratum Associated with a Legacy Transport Stratum
An SDN service Stratum can interact with a legacy Transport Stratum
through an interworking function that is able to adapt SDN-based
control and management service-related commands to legacy transport-
related protocols, as expected by the legacy Transport Stratum.
The SDN Intelligence in the Service Stratum is not aware of the
legacy nature of the underlying Transport Stratum.
6.2.2. Legacy Service Stratum Associated with an SDN Transport Stratum
A legacy Service Stratum can work with an SDN-enabled Transport
Stratum through the mediation of an interworking function capable of
interpreting commands from the legacy service functions and
translating them into SDN protocols for operation with the SDN-
enabled Transport Stratum.
Contreras, et al. Informational [Page 13]
RFC 8597 Layered SDN Architecture May 2019
6.3. Multi-domain Scenarios in the Transport Stratum
The Transport Stratum can be composed of transport resources that are
part of different administrative, topological, or technological
domains. The Service Stratum can interact with a single entity in
the Transport Stratum in case some abstraction capabilities are
provided in the transport part to emulate a single stratum.
Those abstraction capabilities constitute a service itself offered by
the Transport Stratum to the services making use of this stratum.
This service is focused on the provision of transport capabilities,
which is different from the final communication service using such
capabilities.
In this particular case, this recursion allows multi-domain scenarios
at the transport level.
Multi-domain situations can happen in both single-operator and multi-
operator scenarios.
In single-operator scenarios, a multi-domain or end-to-end
abstraction component can provide a homogeneous abstract view of the
underlying heterogeneous transport capabilities for all the domains.
Multi-operator scenarios at the Transport Stratum should support the
establishment of end-to-end paths in a programmatic manner across the
involved networks. For example, this could be accomplished by each
of the administrative domains exchanging their traffic-engineered
information [RFC7926].
7. Use Cases
This section presents a number of use cases as examples of the
applicability of the CLAS approach.
7.1. Network Function Virtualization (NFV)
NFV environments offer two possible levels of SDN control
[GSNFV-EVE005]. One level is the need to control the NFV
Infrastructure (NFVI) to provide end-to-end connectivity among VNFs
(Virtual Network Functions) or among VNFs and PNFs (Physical Network
Functions). A second level is the control and configuration of the
VNFs themselves (in other words, the configuration of the network
service implemented by those VNFs), which benefits from the
programmability brought by SDN. The two control concerns are
separate in nature. However, interaction between the two can be
expected in order to optimize, scale, or influence one another.
Contreras, et al. Informational [Page 14]
RFC 8597 Layered SDN Architecture May 2019
7.2. Abstraction and Control of TE Networks
Abstraction and Control of TE Networks (ACTN) [RFC8453] presents a
framework that allows the creation of virtual networks to be offered
to customers. The concept of "provider" in ACTN is limited to the
offering of virtual network services. These services are essentially
transport services and would correspond to the Transport Stratum in
CLAS. On the other hand, the Service Stratum in CLAS can be
assimilated as a customer in the context of ACTN.
ACTN defines a hierarchy of controllers to facilitate the creation
and operation of the virtual networks. An interface is defined for
the relationship between the customers requesting these virtual
network services and the controller in charge of orchestrating and
serving such a request. Such an interface is equivalent to the one
defined in Figure 1 (Section 3) between the Service and Transport
Strata.
8. Challenges for Implementing Actions between Service and Transport
Strata
The distinction of service and transport concerns raises a number of
challenges in the communication between the two strata. The
following list reflects some of the identified challenges:
o Standard mechanisms for interaction between layers: Nowadays,
there are a number of proposals that could accommodate requests
from the Service Stratum to the Transport Stratum.
Some of the proposals could be solutions like the Connectivity
Provisioning Negotiation Protocol [CPNP] or the Intermediate-
Controller Plane Interface (I-CPI) [ONFArch].
Other potential candidates could be the Transport API [TAPI] or
the Transport Northbound Interface [TRANS-NORTH]. Each of these
options has a different scope.
o Multi-provider awareness: In multi-domain scenarios involving more
than one provider at the transport level, the Service Stratum may
or may not be aware of such multiplicity of domains.
If the Service Stratum is unaware of the multi-domain situation,
then the Transport Stratum acting as the entry point of the
Service Stratum request should be responsible for managing the
multi-domain issue.
Contreras, et al. Informational [Page 15]
RFC 8597 Layered SDN Architecture May 2019
On the contrary, if the Service Stratum is aware of the multi-
domain situation, it should be in charge of orchestrating the
requests to the different underlying Transport Strata to compose
the final end-to-end path among service endpoints (i.e., service
functions).
o SLA mapping: Both strata will handle SLAs, but the nature of those
SLAs could differ. Therefore, it is required for the entities in
each stratum to map service SLAs to connectivity SLAs in order to
ensure proper service delivery.
o Association between strata: The association between strata could
be configured beforehand, or both strata could require the use of
a discovery mechanism that dynamically establishes the association
between the strata.
o Security: As reflected before, the communication between strata
must be secure to prevent attacks and threats. Additionally,
privacy should be enforced, especially when addressing multi-
provider scenarios at the transport level.
o Accounting: The control and accountancy of resources used and
consumed by services should be supported in the communication
among strata.
9. IANA Considerations
This document has no IANA actions.
10. Security Considerations
The CLAS architecture relies upon the functional entities that are
introduced in [RFC7149] and [RFC7426]. As such, security
considerations discussed in Section 5 of [RFC7149], in particular,
must be taken into account.
The communication between the service and transport SDN controllers
must rely on secure means that achieve the following:
o Mutual authentication must be enabled before taking any action.
o Message integrity protection.
Each of the controllers must be provided with instructions regarding
the set of information (and granularity) that can be disclosed to a
peer controller. Means to prevent the leaking of privacy data (e.g.,
from the Service Stratum to the Transport Stratum) must be enabled.
The exact set of information to be shared is deployment specific.
Contreras, et al. Informational [Page 16]
RFC 8597 Layered SDN Architecture May 2019
A corrupted controller may induce some disruption on another
controller. Protection against such attacks should be enabled.
Security in the communication between the strata described here
should apply to the APIs (and/or protocols) to be defined among them.
Consequently, security concerns will correspond to the specific
solution.
11. References
11.1. Normative References
[Y.2011] International Telecommunication Union, "General principles
and general reference model for Next Generation Networks",
ITU-T Recommendation Y.2011, October 2004,
<https://www.itu.int/rec/T-REC-Y.2011-200410-I/en>.
11.2. Informative References
[CPNP] Boucadair, M., Jacquenet, C., Zhang, D., and
P. Georgatsos, "Connectivity Provisioning Negotiation
Protocol (CPNP)", Work in Progress, draft-boucadair-
connectivity-provisioning-protocol-15, December 2017.
[GSNFV-EVE005]
ETSI, "Network Functions Virtualisation (NFV); Ecosystem;
Report on SDN Usage in NFV Architectural Framework", ETSI
GS NFV-EVE 005, V1.1.1, December 2015,
<https://www.etsi.org/deliver/etsi_gs/
NFV-EVE/001_099/005/01.01.01_60/
gs_nfv-eve005v010101p.pdf>.
[ONFArch] Open Networking Foundation, "SDN Architecture, Issue 1",
June 2014, <https://www.opennetworking.org/images/stories/
downloads/sdn-resources/technical-reports/
TR_SDN_ARCH_1.0_06062014.pdf>.
[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>.
[RFC7297] Boucadair, M., Jacquenet, C., and N. Wang, "IP
Connectivity Provisioning Profile (CPP)", RFC 7297,
DOI 10.17487/RFC7297, July 2014,
<https://www.rfc-editor.org/info/rfc7297>.
Contreras, et al. Informational [Page 17]
RFC 8597 Layered SDN Architecture May 2019
[RFC7426] Haleplidis, E., Ed., Pentikousis, K., Ed., Denazis, S.,
Hadi Salim, J., Meyer, D., and O. Koufopavlou, "Software-
Defined Networking (SDN): Layers and Architecture
Terminology", RFC 7426, DOI 10.17487/RFC7426, January
2015, <https://www.rfc-editor.org/info/rfc7426>.
[RFC7926] Farrel, A., Ed., Drake, J., Bitar, N., Swallow, G.,
Ceccarelli, D., and X. Zhang, "Problem Statement and
Architecture for Information Exchange between
Interconnected Traffic-Engineered Networks", BCP 206,
RFC 7926, DOI 10.17487/RFC7926, July 2016,
<https://www.rfc-editor.org/info/rfc7926>.
[RFC8453] Ceccarelli, D., Ed. and Y. Lee, Ed., "Framework for
Abstraction and Control of TE Networks (ACTN)", RFC 8453,
DOI 10.17487/RFC8453, August 2018,
<https://www.rfc-editor.org/info/rfc8453>.
[SDN-ARCH] Contreras, LM., Bernardos, CJ., Lopez, D., Boucadair, M.,
and P. Iovanna, "Cooperating Layered Architecture for
SDN", Work in Progress, draft-irtf-sdnrg-layered-sdn-01,
October 2016.
[TAPI] Open Networking Foundation, "Functional Requirements for
Transport API", June 2016,
<https://www.opennetworking.org/wp-content/uploads/
2014/10/TR-527_TAPI_Functional_Requirements.pdf>.
[TRANS-NORTH]
Busi, I., King, D., Zheng, H., and Y. Xu, "Transport
Northbound Interface Applicability Statement", Work in
Progress, draft-ietf-ccamp-transport-nbi-app-statement-05,
March 2019.
Contreras, et al. Informational [Page 18]
RFC 8597 Layered SDN Architecture May 2019
Appendix A. Relationship with RFC 7426
[RFC7426] introduces an SDN taxonomy by defining a number of planes,
abstraction layers, and interfaces or APIs among them as a means of
clarifying how the different parts constituent of SDN (network
devices, control and management) relate. A number of planes are
defined, including:
o Forwarding Plane: focused on delivering packets in the data path
based on the instructions received from the control plane.
o Operational Plane: centered on managing the operational state of
the network device.
o Control Plane: dedicated to instructing the device on how packets
should be forwarded.
o Management Plane: in charge of monitoring and maintaining network
devices.
o Application Plane: enabling the usage for different purposes (as
determined by each application) of all the devices controlled in
this manner.
Apart from these, [RFC7426] proposes a number of abstraction layers
that permit the integration of the different planes through common
interfaces. CLAS focuses on control, management, and resource planes
as the basic pieces of its architecture. Essentially, the control
plane modifies the behavior and actions of the controlled resources.
The management plane monitors and retrieves the status of those
resources. And finally, the resource plane groups all the resources
related to the concerns of each stratum.
From this point of view, CLAS planes can be seen as a superset of
those defined in [RFC7426]. However, in some cases, not all the
planes considered in [RFC7426] may be totally present in CLAS
representation (e.g., the forwarding plane in the Service Stratum).
That being said, the internal structure of CLAS strata could follow
the taxonomy defined in [RFC7426]. What is different is the
specialization of the SDN environments through the distinction
between service and transport.
Contreras, et al. Informational [Page 19]
RFC 8597 Layered SDN Architecture May 2019
Acknowledgements
This document was previously discussed and adopted in the IRTF SDN RG
as [SDN-ARCH]. After the closure of the IRTF SDN RG, this document
was progressed as an Independent Submission to record (some of) that
group's discussions.
The authors would like to thank (in alphabetical order) Bartosz
Belter, Gino Carrozzo, Ramon Casellas, Gert Grammel, Ali Haider,
Evangelos Haleplidis, Zheng Haomian, Giorgios Karagianis, Gabriel
Lopez, Maria Rita Palatella, Christian Esteve Rothenberg, and Jacek
Wytrebowicz for their comments and suggestions.
Thanks to Adrian Farrel for the review.
Authors' Addresses
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
Carlos J. Bernardos
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/
Diego R. Lopez
Telefonica
Ronda de la Comunicacion, s/n
Sur-3 building, 3rd floor
Madrid 28050
Spain
Email: diego.r.lopez@telefonica.com
Contreras, et al. Informational [Page 20]
RFC 8597 Layered SDN Architecture May 2019
Mohamed Boucadair
Orange
Rennes 35000
France
Email: mohamed.boucadair@orange.com
Paola Iovanna
Ericsson
Pisa
Italy
Email: paola.iovanna@ericsson.com
Contreras, et al. Informational [Page 21]