Internet DRAFT - draft-contreras-sdnrg-layered-sdn
draft-contreras-sdnrg-layered-sdn
SDN Research Group LM. Contreras
Internet-Draft Telefonica
Intended status: Standards Track CJ. Bernardos
Expires: April 21, 2016 UC3M
D. Lopez
Telefonica
M. Boucadair
France Telecom
P. Iovanna
Ericsson
October 19, 2015
Cooperating Layered Architecture for SDN
draft-contreras-sdnrg-layered-sdn-04
Abstract
Software Defined Networking proposes the separation of the control
plane from the data plane in the network nodes and its logical
centralization on a control entity. Most of the network intelligence
is moved to this functional entity. 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 a proposal named Cooperating Layered
Architecture for SDN. 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
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This Internet-Draft will expire on April 21, 2016.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Architecture overview . . . . . . . . . . . . . . . . . . . . 5
3.1. Functional strata . . . . . . . . . . . . . . . . . . . . 8
3.1.1. Transport stratum . . . . . . . . . . . . . . . . . . 8
3.1.2. Service stratum . . . . . . . . . . . . . . . . . . . 9
3.1.3. Recursiveness . . . . . . . . . . . . . . . . . . . . 9
3.2. Plane separation . . . . . . . . . . . . . . . . . . . . 9
3.2.1. Control Plane . . . . . . . . . . . . . . . . . . . . 9
3.2.2. Management Plane . . . . . . . . . . . . . . . . . . 10
3.2.3. Resource Plane . . . . . . . . . . . . . . . . . . . 10
4. Required features . . . . . . . . . . . . . . . . . . . . . . 10
5. Communication between SDN Controllers . . . . . . . . . . . . 11
6. Deployment scenarios . . . . . . . . . . . . . . . . . . . . 11
6.1. Full SDN environments . . . . . . . . . . . . . . . . . . 11
6.1.1. Multiple Service strata associated to a single
Transport stratum . . . . . . . . . . . . . . . . . . 11
6.1.2. Single service stratum associated to multiple
Transport strata . . . . . . . . . . . . . . . . . . 12
6.2. Hybrid environments . . . . . . . . . . . . . . . . . . . 12
6.2.1. SDN Service stratum associated to a legacy Transport
stratum . . . . . . . . . . . . . . . . . . . . . . . 12
6.2.2. Legacy Service stratum associated to an SDN Transport
stratum . . . . . . . . . . . . . . . . . . . . . . . 12
6.3. Multi-domain scenarios in Transport Stratum . . . . . . . 12
7. Use cases . . . . . . . . . . . . . . . . . . . . . . . . . . 13
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7.1. Network Function Virtualization . . . . . . . . . . . . . 13
7.2. Abstraction and Control of Transport Networks . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
9. Security Considerations . . . . . . . . . . . . . . . . . . . 13
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
10.1. Normative References . . . . . . . . . . . . . . . . . . 13
10.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
Software Defined Networking (SDN) proposes the separation of the
control plane from the data plane in the network nodes and its
logical centralization on a control entity. A programmatic interface
is defined between such entity and the network nodes, which
functionality is supposed to perform traffic forwarding (only).
Through that interface, the control entity instructs the nodes
involved in the forwarding plane and modifies their traffic
forwarding behavior accordingly.
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.
This approach presents a number of issues:
o Unclear responsibilities between actors involved in a 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.
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 solutions do not provide a clear separation between
services and transport control.
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This document describes a proposal 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 and associated components to
provide an efficient usage of the resources.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119 [RFC2119].
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: denote a logical construct that make 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 SDN intelligence: refers to the decision-making process that is
hosted by a node or a set of nodes. 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
SDN: Software Defined Networking
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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 requires 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 external 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 blocks or layers. One of
the functional blocks comprises the service-related functions,
whereas the other one contains the transport-related functions. The
cooperation between the two layers is considered to be implemented
through standard interfaces.
Figure 1 shows the CLAS architecture. It is based on functional
separation in the NGN architecture defined by the ITU-T in [Y.2011].
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Two strata of functionality are defined, namely the Service Stratum,
comprising the service-related functions, and the Transport Stratum,
covering the transport ones. The functions on each of these layers
are further grouped on control, management and user (or data) planes.
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North Bound Interface
/\
||
+-------------------------------------||-------------+
| Service Stratum || |
| \/ |
| ........................... |
| . SDN Controller . |
| . . |
| +--------------+ . +--------------+ . |
| | Resource Pl. | . | Mngmt. Pl. | . |
| | |<===>. +--------------+ | . |
| | | . | Control Pl. | | . |
| +--------------+ . | |-----+ . |
| . | | . |
| . +--------------+ . |
| ........................... |
| /\ |
| || |
+-------------------------------------||-------------+
||
||
||
+-------------------------------------||-------------+
| Transport Stratum || |
| \/ |
| ........................... |
| . SDN Controller . |
| . . |
| +--------------+ . +--------------+ . |
| | Resource Pl. | . | Mngmt. Pl. | . |
| | |<===>. +--------------+ | . |
| | | . | Control Pl. | | . |
| +--------------+ . | |-----+ . |
| . | | . |
| . +--------------+ . |
| ........................... |
| |
| |
+----------------------------------------------------+
Figure 1: Cooperating Layered Architecture for SDN
In the CLAS architecture both the control and management functions
are the ones logically centralized in one or a set of SDN
controllers, in such a way that separated SDN controllers are present
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in the Service and Transport strata. 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 controller through a standard
interface.
The SDN controllers cooperate for the provision and delivery of
services. There is a hierarchy in which the Service SDN controller
requests transport capabilities to the Transport SDN controller.
Furthermore, the Transport SDN controller interacts with the Service
SDN controller to inform it about events in the transport network
that can motivate actions in the service layer.
The Service SDN controller acts as a client of the Transport SDN
controller.
Despite it is not shown in the figure, 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 external applications to expose network service capabilities
to those applications or customers.
This document does assume that SDN techniques can be enabled jointly
with other distributed means (e.g., IGP).
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.
Consistecy is determined and characterized by the service layer.
Communication between these two components could be implemented using
a variety of means (such as
[I-D.boucadair-connectivity-provisioning-protocol], Intermediate-
Controller Plane Interface (I-CPI) [ONFArch], etc).
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 controller 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
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entries; dynamic means can be enabled so that involved nodes can
build dynamically routing and forwarding paths. 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
services complemented with advanced capabilities additional to the
pure data transport (e.g., maintenance of a given SLA [RFC7297]).
3.2. Plane separation
The CLAS architecture leverages on the SDN proposition of 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.
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 controller, and can interact with other
control planes in the same or different strata for accomplishing
control functions.
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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
controller, 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
A number of features are required to be supported by the CLAS
architecture.
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,
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.
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5. Communication between SDN Controllers
The SDN Controller 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 controller needs to
easily access transport resources through well defined APIs to access
the capabilities offered by the Transport Stratum. There could be
different ways of obtainign such transport-aware information, i.e.,
by discovering or publishing mechanisms. In the former case the
Service SDN Controller 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 should be also secure,
preventing denial of service.
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 the fact that the networks involved in the
provision and delivery of a given service have SDN capabilities.
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 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.
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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
controller 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.
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.
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Multi-domain situations can happen in both single-operator and multi-
operator scenarios. Multi-operator scenarios will be addressed in
future versions of the document.
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.
7. Use cases
This section presents a number of use cases as examples of
applicability of this proposal
7.1. Network Function Virtualization
To be completed
7.2. Abstraction and Control of Transport Networks
To be completed.
8. IANA Considerations
TBD.
9. Security Considerations
TBD. Security in the communication between strata to be addressed.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[Y.2011] "General principles and general reference model for Next
Generation Networks", ITU-T Recommendation Y.2011 ,
October 2004.
10.2. Informative References
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[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-10 (work in progress), September
2015.
[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>.
[RFC7297] Boucadair, M., Jacquenet, C., and N. Wang, "IP
Connectivity Provisioning Profile (CPP)", RFC 7297,
DOI 10.17487/RFC7297, July 2014,
<http://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, <http://www.rfc-editor.org/info/rfc7426>.
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://people.tid.es/LuisM.Contreras/
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/
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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
France Telecom
Rennes 35000
France
Email: mohamed.boucadair@orange.com
Paola Iovanna
Ericsson
Pisa
Italy
Email: paola.iovanna@ericsson.com
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