Cooperating Layered Architecture for Software-Defined Networking (CLAS)
draft-contreras-layered-sdn-03
The information below is for an old version of the document that is already published as an RFC.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 8597.
|
|
|---|---|---|---|
| Authors | Luis M. Contreras , Carlos J. Bernardos , Diego Lopez , Mohamed Boucadair , Paola Iovanna | ||
| Last updated | 2019-05-15 (Latest revision 2018-11-22) | ||
| RFC stream | Independent Submission | ||
| Intended RFC status | Informational | ||
| Formats | |||
| IETF conflict review | conflict-review-contreras-layered-sdn | ||
| Stream | ISE state | Published RFC | |
| Consensus boilerplate | Unknown | ||
| Document shepherd | Eliot Lear | ||
| Shepherd write-up | Show Last changed 2018-11-26 | ||
| IESG | IESG state | Became RFC 8597 (Informational) | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | Adrian Farrel <rfc-ise@rfc-editor.org> | ||
| IANA | IANA review state | IANA OK - No Actions Needed | |
| IANA action state | No IANA Actions |
draft-contreras-layered-sdn-03
Network Working Group LM. Contreras
Internet-Draft Telefonica
Intended status: Informational CJ. Bernardos
Expires: May 25, 2019 UC3M
D. Lopez
Telefonica
M. Boucadair
Orange
P. Iovanna
Ericsson
November 21, 2018
Cooperating Layered Architecture for Software Defined Networking (CLAS)
draft-contreras-layered-sdn-03
Abstract
Software Defined Networking adheres to 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 sevice intelligence is moved to these control
entities. Typically, such entity is seen as a compendium of
interacting control functions in a vertical, tight 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 relies
upon transport capabilities.
This document describes an approach named Cooperating Layered
Architecture for Software Defined Networking. The idea behind that
is to differentiate the control functions associated to transport
from those related to services, in such a way that they can be
provided and maintained independently, and can follow their own
evolution path.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Contreras, et al. Expires May 25, 2019 [Page 1]
Internet-Draft Layered SDN Architecture November 2018
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 25, 2019.
Copyright Notice
Copyright (c) 2018 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. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
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 . . . . . . . . . . . . . . . . . . 12
6.1.1. Multiple Service Strata Associated to a Single
Transport Stratum . . . . . . . . . . . . . . . . . . 13
6.1.2. Single Service Stratum associated to multiple
Transport Strata . . . . . . . . . . . . . . . . . . 13
6.2. Hybrid Environments . . . . . . . . . . . . . . . . . . . 13
6.2.1. SDN Service Stratum associated to a Legacy Transport
Stratum . . . . . . . . . . . . . . . . . . . . . . . 13
6.2.2. Legacy Service Stratum Associated to an SDN Transport
Stratum . . . . . . . . . . . . . . . . . . . . . . . 13
Contreras, et al. Expires May 25, 2019 [Page 2]
Internet-Draft Layered SDN Architecture November 2018
6.3. Multi-domain Scenarios in Transport Stratum . . . . . . . 13
7. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.1. Network Function Virtualization (NFV) . . . . . . . . . . 14
7.2. Abstraction and Control of Transport Networks . . . . . . 14
8. Challenges for Implementing Actions Between Service and
Transport Strata . . . . . . . . . . . . . . . . . . . . . . 15
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
10. Security Considerations . . . . . . . . . . . . . . . . . . . 16
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
12.1. Normative References . . . . . . . . . . . . . . . . . . 17
12.2. Informative References . . . . . . . . . . . . . . . . . 17
Appendix A. Relationship with RFC7426 . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
Network softwarization advances are facilitating the introduction of
programmability in services and infrastructures of telco operators.
This is achieved generically through the introduction of Software
Defined Networking (SDN, [RFC7149][RFC7426]) capabilities in the
network, including controllers and orchestrators.
However, there are concerns of different nature that these SDN
capabilities have to resolve. In one hand there is a need for
actions focused on programming the network for handle the
connectivity or forwarding of digital data between distant nodes. On
the other hand, there is a need for actions devoted to program the
functions or services that process (or manipulate) such digital data.
SDN adheres to the separation of the control plane from the data
plane in the network nodes by introducing abstraction among both
planes, allowing to centralize the control logic on a functional
entity which is commonly referred as SDN Controller; 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. Additional capabilities (e.g.,
performance monitoring, fault management, etc.) could be expected to
be supported through such kind of programmatic interface [RFC7149].
Most of the intelligence is moved to such functional entity.
Typically, such entity is seen as a compendium of interacting control
functions in a vertical, tight integrated fashion.
The approach of considering an omnipotent control entity governing
the overall aspects of a network, especially both the transport
Contreras, et al. Expires May 25, 2019 [Page 3]
Internet-Draft Layered SDN Architecture November 2018
network and the services to be supported on top of it, presents a
number of issues:
o From a provider perspective, where usually different departments
are responsible of 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.
o Difficult interoperability and interchangeability of functional
components.
o Blurred business boundaries among providers, especially in
situations where a provider provides just 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 segment 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 also
defined in Section 2 of this document.
This document describes an approach named Cooperating Layered
Architecture for SDN (CLAS). The idea behind that is to
differentiate the control functions associated to transport 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 it is required a close cooperation
between service and transport layers (or strata in [Y.2011]) and
associated components to provide an efficient usage of the resources.
Contreras, et al. Expires May 25, 2019 [Page 4]
Internet-Draft Layered SDN Architecture November 2018
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 assumption on the functional
perimeter of a service that can be built above a transport
infrastructure. As such, a service can be an offering that is
offered to customers or be invoked for the delivery of another
(added-value) service.
o Layer: refers to the set of elements comprised for enabling either
transport or service capabilities as defined before. In [Y.2011],
this is referred to as stratum, and both are used interchangeably.
o Domain: is a set of elements which share a common property or
characteristic. In this document this applies to administrative
domain (i.e., elements pertaining to the same organization),
technological domain (elements implementing the same kind of
technology, as for example 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.
The SDN intelligence relies on inputs form 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 in this document, is out of scope.
Additionally, the following acronyms are used in this document:
CLAS: Cooperating Layered Architecture for SDN
FCAPS: Fault, Configuration, Accounting, Performance and Security
Contreras, et al. Expires May 25, 2019 [Page 5]
Internet-Draft Layered SDN Architecture November 2018
SDN: Software Defined Networking
SLA: Service Level Agreement
3. Architecture Overview
Current operator networks support multiple services (e.g., VoIP,
IPTV, mobile VoIP, critical mission applications, etc.) on a variety
of transport technologies. The provision and delivery of a service
independently of the underlying transport capabilities require a
separation of the service related functionalities and an abstraction
of the transport network to hide the specificities of underlying
transfer techniques while offering a common set of capabilities.
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, and similarly, different
technologies can accommodate the connectivity requirements of a
certain service. A close coordination among them is required for a
consistent service delivery (inter-layer cooperation).
This document focuses particularly on:
o Means to expose transport capabilities to services.
o Means to capture service requirements of services.
o Means to notify service intelligence with underlying transport
events, for example to adjust service decision-making process with
underlying transport events.
o Means to instruct the underlying transport capabilities to
accommodate new requirements, etc.
An example is to guarantee some Quality of Service (QoS) levels.
Different QoS-based offerings could be present at both service and
transport layers. Vertical mechanisms for linking both service and
transport QoS mechanisms should be in place to provide the quality
guarantees to the end user.
CLAS architecture assumes that the logically centralized control
functions are separated in 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.
Contreras, et al. Expires May 25, 2019 [Page 6]
Internet-Draft Layered SDN Architecture November 2018
Figure 1 shows the CLAS architecture. It is based on functional
separation in the NGN architecture defined by the ITU-T in [Y.2011],
where two strata of functionality are defined, namely the Service
Stratum, comprising the service-related functions, and the
Connectivity Stratum, covering the transport ones. The functions on
each of these layers are further grouped on control, management and
user (or data) planes.
CLAS adopts the same structured model described in [Y.2011] but
applying it to the objectives of programmability through SDN
[RFC7149]. To this respect, CLAS advocates for addressing services
and transport in a separated manner because of their differentiated
concerns.
Contreras, et al. Expires May 25, 2019 [Page 7]
Internet-Draft Layered SDN Architecture November 2018
Applications
/\
||
||
+-------------------------------------||-------------+
| Service Stratum || |
| \/ |
| ........................... |
| . SDN Intelligence . |
| . . |
| +--------------+ . +--------------+ . |
| | Resource Pl. | . | Mngmt. Pl. | . |
| | |<===>. +--------------+ | . |
| | | . | Control Pl. | | . |
| +--------------+ . | |-----+ . |
| . | | . |
| . +--------------+ . |
| ........................... |
| /\ |
| || |
+-------------------------------------||-------------+
|| Standard
-- || -- API
||
+-------------------------------------||-------------+
| Transport Stratum || |
| \/ |
| ........................... |
| . SDN Intelligence . |
| . . |
| +--------------+ . +--------------+ . |
| | Resource Pl. | . | Mngmt. Pl. | . |
| | |<===>. +--------------+ | . |
| | | . | Control Pl. | | . |
| +--------------+ . | |-----+ . |
| . | | . |
| . +--------------+ . |
| ........................... |
| |
| |
+----------------------------------------------------+
Figure 1: Cooperating Layered Architecture for SDN
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, e.g., scalability, reliability) providing the SDN
Contreras, et al. Expires May 25, 2019 [Page 8]
Internet-Draft Layered SDN Architecture November 2018
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 the
effective operation in a service provider ecosystem [RFC7149] despite
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 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 for the provision and delivery of
services. There is a hierarchy in which the Service SDN Intelligence
requests transport capabilities to the Transport SDN Intelligence.
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 it is not 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
towards applications to expose network service capabilities to those
applications or customers.
3.1. Functional Strata
As described before, the functional split separates transport-related
functions from service-related functions. Both strata cooperate for
a 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 end points (e.g., between end-user
devices, between two service gateways, etc.). The data forwarding
nodes are controlled and managed by the Transport SDN component.
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 forwarding service is appropriately
setup. Forwarding may not be rely on the sole pre-configured
Contreras, et al. Expires May 25, 2019 [Page 9]
Internet-Draft Layered SDN Architecture November 2018
entries; dynamic means can be enabled so that involved nodes can
build dynamically 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 for requesting 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 for
a cooperating management between layers.
3.1.3. Recursiveness
Recursive layering can happen in some usage scenarios in which the
Transport Stratum is itself structured in Service and Transport
Stratum. This could be the case of the provision of a transport
service complemented with advanced capabilities additional to the
pure data transport (e.g., maintenance of a given SLA [RFC7297]).
Recursiveness has been also discussed in [ONFArch] as a way of
reaching scalability and modularity, when each higher level can
provide greater abstraction capabilities. Additionally,
recursiveness can allow some scenarios for multi-domain where single
or multiple administrative domains are involved, as the ones
described in Section 6.3.
3.2. Plane Separation
The CLAS architecture leverages on plane separation. As mentioned
before, three different planes are considered for each stratum. The
communication among these three planes (and with the corresponding
plane in other strata) is based on open, standard interfaces.
Contreras, et al. Expires May 25, 2019 [Page 10]
Internet-Draft Layered SDN Architecture November 2018
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 a SDN architecture. This
plane is part of an SDN Intelligence, and can interact with other
control planes in the same or different strata for accomplishing
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 a 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) whereas in other cases it can be decoupled
from the transport resources (e.g., one database keeping some
register for the end user). Both 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: 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
taking in to account, e.g., the traffic load.
o Resource computation: functions able to decide which resources
will be used for a given service request. As an example,
Contreras, et al. Expires May 25, 2019 [Page 11]
Internet-Draft Layered SDN Architecture November 2018
functions like PCE could be used to compute/select/decide a
certain path.
o Orchestration: 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, e.g.,
DoS attacks.
5. Communication Between SDN Controllers
The SDN controllers residing respectively in the Service and the
Transport Stratum need to establish a tight coordination. Mechanisms
for transfer 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 of handling
complete information about the transport capabilities (including
resources) offered by the Transport Stratum. In the latter case, the
Transport Stratum exposes available capabilities, e.g., through a
catalog, reducing the amount of detail of the underlying network.
On the other hand, the Transport Stratum requires to properly capture
Service requirements. These can include SLA requirements with
specific metrics (such as delay), level of protection to be provided,
max/min capacity, applicable resource constraints, etc.
The communication between controllers must be also secure, e.g., by
preventing denial of service or any other kind of threats (similarly,
the 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.
6.1. Full SDN Environments
This case considers that the networks involved in the provision and
delivery of a given service have SDN capabilities.
Contreras, et al. Expires May 25, 2019 [Page 12]
Internet-Draft Layered SDN Architecture November 2018
6.1.1. Multiple Service Strata Associated to a Single Transport Stratum
A single Transport Stratum can provide transfer functions to more
than one Service strata. 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 to multiple Transport Strata
A single Service stratum can make use of different Transport Strata
for the provision of a certain service. The Service stratum
interfaces each of the Transport Strata with standard protocols, 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 legacy
totally or in part.
6.2.1. SDN Service Stratum associated to a Legacy Transport Stratum
An SDN service stratum can interact with a legacy Transport Stratum
through some interworking function 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 to an SDN Transport Stratum
A legacy Service stratum can work with an SDN-enabled Transport
Stratum through the mediation of and interworking function capable to
interpret commands from the legacy service functions and translate
them into SDN protocols for operating with the SDN-enabled Transport
Stratum.
6.3. Multi-domain Scenarios in Transport Stratum
The Transport Stratum can be composed by transport resources being
part of different administrative, topological or technological
domains. The Service Stratum can yet 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.
Contreras, et al. Expires May 25, 2019 [Page 13]
Internet-Draft Layered SDN Architecture November 2018
Those abstraction capabilities constitute a service itself offered by
the Transport Stratum to the services making use of it. This service
is focused on the provision of transport capabilities, then different
of the final communication service using such capabilities.
In this particular case this recursion allows multi-domain scenarios
at 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 an 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. This could be accomplished, for example, by
the exchange of traffic-engineered information of each of the
administrative domains [RFC7926].
7. Use Cases
This section presents a number of use cases as examples of
applicability of the CLAS approach.
7.1. Network Function Virtualization (NFV)
NFV environments offer two possible levels of SDN control
[ETSI_NFV_EVE005]. One level is the need for controlling the NFV
Infrastructure (NFVI) to provide connectivity end-to- end 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), taking profit of the
programmability brought by SDN. Both control concerns are separated
in nature. However, interaction between both could be expected in
order to optimize, scale or influence each other.
7.2. Abstraction and Control of Transport Networks
Abstraction and Control of Transport Networks (ACTN) [RFC8453]
presents a framework to allow 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.
Contreras, et al. Expires May 25, 2019 [Page 14]
Internet-Draft Layered SDN Architecture November 2018
ACTN defines a hierarchy of controllers for facilitating the creation
and operation of the virtual networks. An interface is defined for
the relation of the customers requesting these virtual networks
services with the controller in charge of orchestrating and serving
such request. Such interface is equivalent to the one defined in
Figure 1 (Section 3) between 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 both strata. The following
is a work-in-progress list reflecting 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 them could be solutions like the Connectivity Provisioning
Protocol [I-D.boucadair-connectivity-provisioning-protocol] or the
Intermediate-Controller Plane Interface (I-CPI) [ONFArch].
Other potential candidates could be the Transport API [TAPI] or
the Transport Transport Northbound Interface
[I-D.ietf-ccamp-transport-nbi-app-statement]. Each of these
options has a different status of maturity and scope.
o Multi-provider awareness: In multi-domain scenarios involving more
than one provider at transport level, the service stratum could
have or not awareness of such multiplicity of domains.
If the service stratum is unaware of the multi-domain situation,
then the Transport Stratum acting as entry point of the service
stratum request should be responsible of managing the multi-domain
issue.
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 for
composing the final end-to-end path among service end-points
(i.e., service functions).
o SLA mapping: Both strata will handle SLAs but the nature of those
SLAs could differ. Then it is required for the entities in each
stratum to map service SLAs to connectivity SLAs in order to
ensure proper service delivery.
Contreras, et al. Expires May 25, 2019 [Page 15]
Internet-Draft Layered SDN Architecture November 2018
o Association between strata: The association between strata could
be configured beforehand, or could be dynamic following mechanisms
of discovery, that could be required to be supported by both
strata with this purpose.
o Security: As reflected before, the communication between strata
must be secure preventing attacks and threats. Additionally,
privacy should be enforced, especially when addressing multi-
provider scenarios at 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 does not request any action from IANA.
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 which 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 about the
set of information (and granularity) that can be disclosed to a peer
controller. Means to prevent leaking 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.
A corrupted controller may induce some disruption on another
controller. Guards against such attacks should be enabled.
Security in the communication between the strata here described
should apply on the APIs (and/or protocols) to be defined among them.
In consequence, security concerns will correspond to the specific
solution.
Contreras, et al. Expires May 25, 2019 [Page 16]
Internet-Draft Layered SDN Architecture November 2018
11. Acknowledgements
This document was previously discussed and adopted in the IRTF SDN RG
as [I-D.irtf-sdnrg-layered-sdn]. After the closure of the IRTF SDN
RG this document is being progressed as Individual Submission to
record (some of) that group's disucussions.
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.
12. References
12.1. Normative References
[Y.2011] "General principles and general reference model for Next
Generation Networks", ITU-T Recommendation Y.2011 ,
October 2004.
12.2. Informative References
[ETSI_NFV_EVE005]
"Report on SDN Usage in NFV Architectural Framework",
December 2015.
[I-D.boucadair-connectivity-provisioning-protocol]
Boucadair, M., Jacquenet, C., Zhang, D., and P.
Georgatsos, "Connectivity Provisioning Negotiation
Protocol (CPNP)", draft-boucadair-connectivity-
provisioning-protocol-15 (work in progress), December
2017.
[I-D.ietf-ccamp-transport-nbi-app-statement]
Busi, I., King, D., Zheng, H., and Y. Xu, "Transport
Northbound Interface Applicability Statement", draft-ietf-
ccamp-transport-nbi-app-statement-04 (work in progress),
November 2018.
[I-D.irtf-sdnrg-layered-sdn]
Contreras, L., Bernardos, C., Lopez, D., Boucadair, M.,
and P. Iovanna, "Cooperating Layered Architecture for
SDN", draft-irtf-sdnrg-layered-sdn-01 (work in progress),
October 2016.
Contreras, et al. Expires May 25, 2019 [Page 17]
Internet-Draft Layered SDN Architecture November 2018
[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>.
[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>.
[TAPI] "Functional Requirements for Transport API", June 2016.
Appendix A. Relationship with RFC7426
[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 among them. A number of
planes are defined, namely:
o Forwarding Plane: focused on delivering packets in the data path
based on the instructions received from the control plane.
Contreras, et al. Expires May 25, 2019 [Page 18]
Internet-Draft Layered SDN Architecture November 2018
o Operational Plane: centered on managing the operational state of
the network device.
o Control Plane: devoted to instruct 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 that, [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 strata.
From this point of view, CLAS planes can be seen as a superset of
[RFC7426], even though in some cases not all the planes as considered
in [RFC7426] could not be totally present in CLAS representation
(e.g., forwarding plane in Service Stratum).
Being said that, internal structure of CLAS strata could follow the
taxonomy defined in [RFC7426]. Which is differential is the
specialization of the SDN environments, through the distinction
between service and transport.
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
Contreras, et al. Expires May 25, 2019 [Page 19]
Internet-Draft Layered SDN Architecture November 2018
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
Mohamed Boucadair
Orange
Rennes 35000
France
Email: mohamed.boucadair@orange.com
Paola Iovanna
Ericsson
Pisa
Italy
Email: paola.iovanna@ericsson.com
Contreras, et al. Expires May 25, 2019 [Page 20]