SDN Research Group LM. Contreras Internet-Draft Telefonica I+D Intended status: Standards Track CJ. Bernardos Expires: August 13, 2014 UC3M February 9, 2014 Cooperating Layered Architecture for SDN draft-contreras-sdnrg-layered-sdn-00 Abstract The Software Defined Networking paradigm proposes the separation of the control plane from the data plane in the network nodes and its logical centralization on a control entity. All the network intelligence is moved to this central entity. Typically, such central 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 services and transport control. This document describes a new 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 evolutionary way. 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 http://datatracker.ietf.org/drafts/current/. 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 August 13, 2014. Contreras & Bernardos Expires August 13, 2014 [Page 1] Internet-Draft Layered SDN Architecture February 2014 Copyright Notice Copyright (c) 2014 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 (http://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 . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Architecture overview . . . . . . . . . . . . . . . . . . . . 4 3.1. Functional strata . . . . . . . . . . . . . . . . . . . . 6 3.1.1. Transport stratum . . . . . . . . . . . . . . . . . . 6 3.1.2. Service stratum . . . . . . . . . . . . . . . . . . . 6 3.1.3. Recursiveness . . . . . . . . . . . . . . . . . . . . 7 3.2. Plane separation . . . . . . . . . . . . . . . . . . . . 7 3.2.1. Control Plane . . . . . . . . . . . . . . . . . . . . 7 3.2.2. Management Plane . . . . . . . . . . . . . . . . . . 7 3.2.3. Resource Plane . . . . . . . . . . . . . . . . . . . 7 4. Deployment scenarios . . . . . . . . . . . . . . . . . . . . 8 4.1. Full SDN environments . . . . . . . . . . . . . . . . . . 8 4.1.1. Multiple Service strata associated to a single Transport stratum . . . . . . . . . . . . . . . . . . 8 4.1.2. Single service stratum associated to multiple Transport strata . . . . . . . . . . . . . . . . . . 8 4.2. Hybrid environments . . . . . . . . . . . . . . . . . . . 8 4.2.1. SDN Service stratum associated to a legacy Transport stratum . . . . . . . . . . . . . . . . . . . . . . . 8 4.2.2. Legacy Service stratum associated to an SDN Transport stratum . . . . . . . . . . . . . . . . . . . . . . . 9 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 6. Security Considerations . . . . . . . . . . . . . . . . . . . 9 7. Normative References . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 Contreras & Bernardos Expires August 13, 2014 [Page 2] Internet-Draft Layered SDN Architecture February 2014 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 now simplified to purely perform traffic forwarding. Through that interface, the central control entity instructs the nodes and modifies their traffic forwarding behavior. All the intelligence is moved to such central entity. Typically, such central 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. 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 services and transport control. This document describes a new 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 evolutionary way. 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. Contreras & Bernardos Expires August 13, 2014 [Page 3] Internet-Draft Layered SDN Architecture February 2014 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]. Additionally, the following acronyms are used in this document. CLAS: Cooperating Layered Architecture for SDN SDN: Software Defined Networking SLA: Service Level Agreement 3. Architecture overview Current operator networks support multiple services (e.g., mobile, fixed, enterprise, 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, ideally, an abstraction of the transport network to hide the particularities of each technology while offering a common set of capabilities. Such separation can provide configuration flexibility and adaptability either from the point of view of the services or the transport network. Multiple services can be provided on top of a common transport network, and similarly, different technologies can support a certain service. A close coordination among them is required for a consistent service delivery. An example of that could be the guarantee of some Quality of Service (QoS) level. Different QoS 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. This document presents a proposal called Cooperating Layered Architecture for SDN (CLAS). In this architecture the logically centralized control functions are separated in two blocks or layers. One of the layers 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 open, 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]. Two strata of functionality are defined, namely the Service Stratum, Contreras & Bernardos Expires August 13, 2014 [Page 4] Internet-Draft Layered SDN Architecture February 2014 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. 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 Contreras & Bernardos Expires August 13, 2014 [Page 5] Internet-Draft Layered SDN Architecture February 2014 In the CLAS architecture both the control and management functions are the ones logically centralized in an SDN controller, in such a way that separated SDN controllers are present 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 an 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 a North Bound Interface towards external applications to expose network service capabilities to those applications. 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. 3.1.1. Transport stratum The Transport stratum comprises the functions focused on the pure transfer of end user data between the communication end points. The data forwarding nodes are part of the Resource plane. These nodes are controlled and managed by the Transport SDN controller. 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. Finally, the Management plane performs management functions 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 Contreras & Bernardos Expires August 13, 2014 [Page 6] Internet-Draft Layered SDN Architecture February 2014 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). 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. 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. 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. 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 Contreras & Bernardos Expires August 13, 2014 [Page 7] Internet-Draft Layered SDN Architecture February 2014 from the transport resources (e.g., one database keeping some register for the end user). 4. Deployment scenarios Different situations can be found depending on the characteristics of the networks involved in a given deployment. 4.1. Full SDN environments This case considers the fact that the networks involved in the provision and delivery of a given service have SDN capabilities. 4.1.1. 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, independent routing, etc. 4.1.2. 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. 4.2. Hybrid environments This case considers scenarios where one of the strata is legacy totally or in part. 4.2.1. 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. Contreras & Bernardos Expires August 13, 2014 [Page 8] Internet-Draft Layered SDN Architecture February 2014 4.2.2. 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. 5. IANA Considerations TBD. 6. Security Considerations TBD. Security in the communication between strata to be addressed. 7. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [Y.2011] "General principles and general reference model for Next Generation Networks", ITU-T Recommendation Y.2011 , October 2004. Authors' Addresses Luis M. Contreras Telefonica I+D Ronda de la Comunicacion, s/n Sur-3 building, 3rd floor Madrid 28050 Spain Email: lmcm@tid.es 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/ Contreras & Bernardos Expires August 13, 2014 [Page 9]