CCAMP Working Group . Internet Draft Haomian Zheng Category: Informational Xianlong Luo Huawei Technologies Yang Zhao China Mobile Yunbin Xu CAICT Expires: September 5, 2018 March 5, 2018 Interworking of GMPLS Control and Centralized Controller System draft-zheng-ccamp-gmpls-controller-inter-work-01 Abstract Generalized Multi-Protocol Label Switching (GMPLS) control allows each network element (NE) to perform resource discovery, routing and signaling in a distributed manner. On the other hand, with the development of software-defined transport networking technology, central controllers are introduced to transport networks to control a set of NEs. In transport networks, the GMPLS control has many mature mechanisms such as RSVP-TE, OSPF-TE, and LMP, so that GMPLS can be applied for the NE-level control in the centralized controller systems. This document describes how GMPLS control interworks with centralized controller systems (e.g. ACTN) in transport network. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. Zheng, et al. Expires September 2018 [Page 1] Internet-Draft GMPLS and Controller Interwork March 2018 The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on September 5, 2018. 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 (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. Conventions used in this document 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]. Table of Contents 1. Introduction ................................................ 3 2. Overview .................................................... 4 2.1. Overview of GMPLS Control Plane ............................ 4 2.2. Overview of Centralized Controller System .................. 4 2.3. GMPLS Control Interwork with Centralized Controller System . 5 3. Link Management Protocol ..................................... 6 4. Routing Options ............................................. 6 4.1. OSPF-TE ................................................ 6 4.2. ISIS-TE ................................................ 6 5. Path Computation ............................................ 6 5.1. Constraint-based Path Computing in GMPLS Control........ 7 5.2. Path Computation Element (PCE) ......................... 7 6. Signaling Options ........................................... 8 6.1. RSVP-TE ................................................ 8 6.2. CR-LDP ................................................. 8 Zheng Expires September 2018 [Page 2] Internet-Draft GMPLS and Controller Interwork March 2018 7. Interworking Scenarios....................................... 8 7.1. Topology Collection & Synchronization .................. 8 7.2. Multi-domain/layer Service Provisioning ................ 9 7.3. Recovery ............................................... 9 7.4. Controller Reliability................................. 10 8. Network Management ......................................... 10 9. Security Considerations..................................... 10 10. IANA Considerations........................................ 10 11. References ................................................ 10 11.1. Normative References.................................. 10 11.2. Informative References ................................ 13 12. Authors' Addresses ......................................... 13 1. Introduction Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] extends MPLS to support different classes of interfaces and switching capabilities such as Time-Division Multiplex Capable (TDM), Lambda Switch Capable (LSC), and Fiber-Switch Capable (FSC). Each network element (NE) running a control plane collects network information from other NEs and provisions services through signaling in a distributed manner. On the other hand, Software-Defined Networking (SDN) technologies have been introduced to control the transport network in a centralized manner. Central controllers, which can locate outside of the network, can collect network information from each node and provision services to corresponding nodes. One of the examples is the Abstraction and Control of Traffic Engineered Networks (ACTN) [I-D.ietf-teas-actn-framework], which defines a hierarchical architecture with PNC, MDSC and CNC as central controllers for different network abstraction levels. In such centralized controller systems, GMPLS can be applied for the NE-level control. Introducing GMPLS in centralized controller system can reuse the mature mechanisms defined for GMPLS and be practical for legacy transport networks. This document describes how GMPLS control interworks with centralized controller system in transport network. Zheng Expires September 2018 [Page 3] Internet-Draft GMPLS and Controller Interwork March 2018 2. Overview In this section, overviews of GMPLS control plane and centralized controller system are discussed as well as the cooperation between GMPLS control plane and centralized controller system. 2.1. Overview of GMPLS Control Plane GMPLS separates the control plane and the data plane to support time-division, wavelength, and spatial switching, which are significant in transport networks. For the NE level control in GMPLS, each node has its controller to perform service provisioning, protection, and restoration. At the same time, the controller can negotiate available link resources with controllers in adjacent nodes, and it can also collect node and link resources in the network to construct the network topology and compute routing paths for serving service requests. Several protocols have been designed for GMPLS control [RFC3945] including link management [RFC4204], signaling [RFC3471], and routing [RFC4202] protocols. The controllers applying these protocols communicate with each other to exchange resource information and establish LSP. In this way, controllers in different nodes in the network have the same network topology and provision services by their local policies. 2.2. Overview of Centralized Controller System With the development of SDN technologies, centralized controller system has been introduced to transport networks such as ACTN. In centralized controller system, a controller is aware of the network topology and is responsible for provisioning incoming service requests. In ACTN, multiple abstraction levels are designed and controllers at different levels implement different functions. This kind of abstraction enables multi-vendor, multi-domain, and multi- technology control. For example in ACTN, an MDSC coordinates several PNCs controlling different domains. Each PNC reports its topology, which can be abstracted, to the MDSC, so that the MDSC learns the picture of multiple domains. When a multi-domain service arrives at the MDSC, the MDSC first computes an end-to-end routing path. Then the MDSC splits this path to multiple segment according to domain boundaries and allocate each segment to corresponding PNC for detailed path computation and LSP segment setup. After each PNC reporting the establishment of corresponding LSP segment, this multi-domain service is accommodated. Zheng Expires September 2018 [Page 4] Internet-Draft GMPLS and Controller Interwork March 2018 2.3. GMPLS Control Interwork with Centralized Controller System Centralized controller system as ACTN provides the architecture and communication between central controllers of different abstraction levels to coordinate multiple domains. Within each domain, GMPLS control can be applied to each NE. The bottom-level central controller like PNC can act as a NE to collect network information and initiate LSP. Following figure shows an example of GMPLS interworking with ACTN. +----------+ | MDSC | +----------+ ^ ^ | | +---------+ +---------+ | RESTConf / YANG models | V V +---------+ +---------+ | PNC | | PNC | +---------+ +---------+ ^ ^ ^ ^ | | | | OSPF-TE| |PCEP OSPF-TE| |PCEP | | | | | V | V .-------------. Inter- .-------------. / \ domain / \ | LMP | link | LMP | | OSPF-TE ========== OSPF-TE | | RSVP-TE | | RSVP-TE | \ / \ / `------------` `------------` GMPLS domain GMPLS domain Figure 1: Example of GMPLS interworks with ACTN In Figure 1, each domain runs GMPLS control. The PNC listens LSAs flooded in the domain and learns the topology. For path computation in the domain with PNC implementing a PCE, NEs use PCEP to ask the PNC for a path and get replies. The MDSC communicates with PNCs using RESTConf or YANG models. As a PNC has learned its domain topology, it can report the topology to the MDSC. When a service Zheng Expires September 2018 [Page 5] Internet-Draft GMPLS and Controller Interwork March 2018 arrives, the MDSC computes the path and coordinates PNCs to establish the corresponding LSP segment. 3. Link Management Protocol Link management protocol (LMP) [RFC4204] runs between a pair of nodes and is used to manage TE links. In addition to setup and maintain control channels, LMP can be used to verify the data link connectivity and correlate the link property. In this way, link resources, which are fundamental resources in the network, are discovered by both ends of the link. 4. Routing Options In GMPLS control, link state information is flooded within the network as defined in [RFC4202]. Each node in the network can build the network topology according to the flooded link state information. Routing protocols such as OSPF-TE [RFC4203] and ISIS-TE [RFC5307] have been extended to support different interfaces in GMPLS. In centralized controller system, central controller can be placed at the GMPLS network and passively receive the information flooded in the network. In this way, the central controller can construct and update the network topology. 4.1. OSPF-TE OSPF-TE is introduced for TE networks in [RFC3630]. OSPF extensions have been defined in [RFC4203] to enable the capability of link state information for GMPLS network. Based on this work, OSPF protocol has been extended to support technology-specific routing. The routing protocol for OTN, WSON and optical flexi-grid network are defined in [RFC7138], [RFC7688] and [I-D.ietf-ccamp-flexible- grid-ospf-ext], respectively. 4.2. ISIS-TE ISIS-TE is introduced for TE networks in [RFC5305] and is extended to support GMPLS routing functions [RFC5307], and has been updated to [RFC7074] to support the latest GMPLS switching capability and Types fields. 5. Path Computation Once a controller learn the network topology, it can utilize the available resources to serve service requests by performing path Zheng Expires September 2018 [Page 6] Internet-Draft GMPLS and Controller Interwork March 2018 computation. Path computation is one of the key objectives in various types of controllers. In the given architecture, it is possible for different components that have the capability to compute the path. 5.1. Constraint-based Path Computing in GMPLS Control In GMPLS control, a routing path is computed by the ingress node [RFC3473] and is based on the ingress node TED. Constraint-based path computation is performed according to the local policy of the ingress node. 5.2. Path Computation Element (PCE) PCE has been introduced in [RFC4655] as a functional component that provides services to compute path in a network. In [RFC5440], the path computation is accomplished by using the Traffic Engineering Database (TED), which maintains the link resources in the network. The emergence of PCE efficiently improve the quality of network planning and offline computation, but there is a risk that the computed path may be infeasible if there is a diversity requirement, because stateless PCE has no knowledge about the former computed paths. To address this issue, stateful PCE has been proposed in [RFC8231]. Besides the TED, an additional LSP Database (LSP-DB) is introduced to archive each LSP computed by the PCE. In this way, PCE can easily figure out the relationship between the computing path and former computed paths. In this approach, PCE provides computed paths to PCC, and then PCC decides which path is deployed and when to be established. In PCE Initiation [I-D.ietf-pce-pce-initiated-lsp], PCE is allowed to trigger the PCC to setup, maintenance, and teardown of the PCE- initiated LSP under the stateful PCE model. This would allow a dynamic network that is centrally controlled and deployed. In centralized controller system, the PCE can be implement in a central controller, and the central controller performs path computation according to its local policies. On the other hand, the PCE can also be placed outside of the central controller. In this case, the central controller acts as a PCC to request path computation to the PCE through PCEP. Zheng Expires September 2018 [Page 7] Internet-Draft GMPLS and Controller Interwork March 2018 6. Signaling Options Signaling mechanism is used to setup LSPs in GMPLS control. Messages are sent hop by hop between the ingress node and the egress node of the LSP to allocate labels. Once the labels are allocated along the path, the LSP setup is accomplished. Signaling protocols such as RSVP-TE [RFC3473] and CR-LDP [RFC3472] have been extended to support different interfaces in GMPLS. In centralized controller system, the central controller can manage LSPs by using PCE-initiation [I-D.ietf-pce-pce-initiated-lsp] to notify the corresponding ingress node. The ingress node will maintain the LSP through GMPLS signaling. 6.1. RSVP-TE RSVP-TE is introduced in [RFC3209] and extended to support GMPLS signaling in [RFC3473]. Several label formats are defined for a generalized label request, a generalized label, suggested label and label sets. Based on [RFC3473], RSVP-TE has been extended to support technology-specific signaling. The RSVP-TE extensions for OTN, WSON, optical flexi-grid network are defined in [RFC7139], [RFC7689], and [RFC7792], respectively. 6.2. CR-LDP In order to support the label formats and signaling mechanism defined in [RFC3471], CR-LDP is extended in [RFC3472]. Several label formats are defined and bidirectional LSPs are supported. 7. Interworking Scenarios 7.1. Topology Collection & Synchronization Topology information is necessary on both network elements and controllers. The topology on network element is usually raw information, while the topology on the controller can be either raw or abstracted. Three different abstraction method has been described in [I-D.ietf-teas-actn-framework], and different controllers can select the corresponding method depending on application. When there are changes in the network topology, the related network element(s) need to report to all the other network elements, together with the controller, to sync up the topology information. The inter-NE synchronization can be achieved via protocols mentioned in section 3 and 4. The topology synchronization between NE can Zheng Expires September 2018 [Page 8] Internet-Draft GMPLS and Controller Interwork March 2018 controllers can either be achieved by PCEP-LS in [PCEP-LS] or netconf protocol with YANG model. 7.2. Multi-domain/layer Service Provisioning Based on the topology information on controllers and network elements, service provisioning can be deployed. Plenty of methods have been specified for single domain service provisioning, such as using PCEP and RSVP-TE. Multi-domain/layer service provisioning would request coordination among the controller hierarchies. Given the service request, the end-to-end delivery procedure may include interactions on MPI and SBI. The computation for a cross-domain/layer path is usually completed by MDSC, who has a global view of the topologies. Then the configuration is decomposed into lower layer controllers, including both MDSC and PNCs, to configure the network elements to set up the path. A combination of the centralized and distributed protocols may be necessary for the interaction between network elements and controller. A typical example would be the PCE Initiation scenario, in which a PCE message (PCInitiate) is sent from the controller to the first-end node, and then trigger a RSVP procedure along the path. 7.3. Recovery The GMPLS recovery functions are described in [RFC4426]. Two models, span protection and end-to-end protection and restoration, are discussed with different protection schemes and message exchange requirements. Related RSVP-TE extensions to support end-to-end recovery is described in [RFC4872]. The extensions in [RFC4872] include protection, restoration, preemption, and rerouting mechanisms for an end-to-end LSP. Besides end-to-end recovery, a GMPLS segment recovery mechanism is defined in [RFC4873]. By introducing secondary record route objects, LSP segment can be switched to another path like fast reroute [RFC4090]. For the recovery with controllers, timely interaction between controller and network elements are required. Usually the re-routing can be decomposed into path computation and delivery, the controller can take some advantage in the path computation due to the global topology view. And the delivery can be achieved by the procedure described in section 7.2. Zheng Expires September 2018 [Page 9] Internet-Draft GMPLS and Controller Interwork March 2018 7.4. Controller Reliability Given the important role in the network, the reliability of controller is critical. Once a controller is shut down, the network should operate as well. It can be either achieved by controller back up or functionality back up. There are several of controller backup or federation mechanisms in the literature. It is also more reliable to have some function back up in the network element, to guarantee the performance in the network. 8. Network Management TBD. 9. Security Considerations TBD. 10. IANA Considerations This document requires no IANA actions. 11. References 11.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, December 2001. [RFC3471] Berger, L., Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description", RFC 3471, January 2003. [RFC3472] Ashwood-Smith, P., Ed. and L. Berger, Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Constraint-based Routed Label Distribution Protocol (CR- LDP) Extensions", RFC 3472, January 2003. [RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation Protocol- Traffic Engineering (RSVP-TE) Extensions", RFC 3473, January 2003. Zheng Expires September 2018 [Page 10] Internet-Draft GMPLS and Controller Interwork March 2018 [RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering (TE) Extensions to OSPF Version 2", RFC 3630, September 2003. [RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Architecture", RFC 3945, October 2004. [RFC4090] Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090, May 2005. [RFC4202] Kompella, K., Ed. and Y. Rekhter, Ed., "Routing Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4202, October 2005. [RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4203, October 2005. [RFC4204] Lang, J., Ed., "Link Management Protocol (LMP)", RFC 4204, October 2005. [RFC4426] Lang, J., Ed., Rajagopalan, B., Ed., and D. Papadimitriou, Ed., "Generalized Multi-Protocol Label witching (GMPLS) Recovery Functional Specification", RFC 4426, March 2006. [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, August 2006. [RFC4872] Lang, J., Ed., Rekhter, Y., Ed., and D. Papadimitriou, Ed., "RSVP-TE Extensions in Support of End-to-End Generalized Multi-Protocol Label Switching (GMPLS) Recovery", RFC 4872, May 2007. [RFC4873] Berger, L., Bryskin, I., Papadimitriou, D., and A. Farrel, "GMPLS Segment Recovery", RFC 4873, May 2007. [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic Engineering", RFC 5305, October 2008. [RFC5307] Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 5307, October 2008. Zheng Expires September 2018 [Page 11] Internet-Draft GMPLS and Controller Interwork March 2018 [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, March 2009. [RFC7074] Berger, L. and J. Meuric, "Revised Definition of the GMPLS Switching Capability and Type Fields", RFC 7074, November 2013. [RFC7138] Ceccarelli, D., Ed., Zhang, F., Belotti, S., Rao, R., and J. Drake, "Traffic Engineering Extensions to OSPF for GMPLS Control of Evolving G.709 Optical Transport Networks", RFC 7138, March 2014. [RFC7139] Zhang, F., Ed., Zhang, G., Belotti, S., Ceccarelli, D., and K. Pithewan, "GMPLS Signaling Extensions for Control of Evolving G.709 Optical Transport Networks", RFC 7139, March 2014. [RFC7688] Lee, Y., Ed. and G. Bernstein, Ed., "GMPLS OSPF Enhancement for Signal and Network Element Compatibility for Wavelength Switched Optical Networks", RFC 7688, November 2015. [RFC7689] Bernstein, G., Ed., Xu, S., Lee, Y., Ed., Martinelli, G., and H. Harai, "Signaling Extensions for Wavelength Switched Optical Networks", RFC 7689, November 2015. [RFC7792] Zhang, F., Zhang, X., Farrel, A., Gonzalez de Dios, O., and D. Ceccarelli, "RSVP-TE Signaling Extensions in Support of Flexi-Grid Dense Wavelength Division Multiplexing (DWDM) Networks", RFC 7792, March 2016. [RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path Computation Element Communication Protocol (PCEP) Extensions for Stateful PCE", RFC 8231, September 2017. [I-D.ietf-ccamp-flexible-grid-ospf-ext] Zhang, X., Zheng, H., Casellas, R., Dios, O., and D. Ceccarelli, "GMPLS OSPF-TE Extensions in support of Flexi-grid DWDM networks", draft- ietf-ccamp-flexible-grid-ospf-ext-09 (work in progress), February 2017. [RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "PCEP Extensions for PCE-initiated LSP Setup in a Stateful PCE Model", October 2017. Zheng Expires September 2018 [Page 12] Internet-Draft GMPLS and Controller Interwork March 2018 [I-D.ietf-teas-actn-framework] Ceccarelli, D. and Y. Lee, "Framework for Abstraction and Control of Traffic Engineered Networks", draft-ietf-teas-actn-framework work in progress. [I-D. dhodylee-pce-pcep-ls] Dhody, D., Lee, Y., Ceccarelli, D., "PCEP Extensions for Distribution of Link-State and TE Information", draft-dhodylee-pce-pcep-ls, work in progress. 11.2. Informative References 12. Authors' Addresses Haomian Zheng Huawei Technologies F3 R&D Center, Huawei Industrial Base, Bantian, Longgang District, Shenzhen 518129 P.R.China Email: zhenghaomian@huawei.com Xianlong Luo Huawei Technologies F3 R&D Center, Huawei Industrial Base, Bantian, Longgang District, Shenzhen 518129 P.R.China Email: luoxianlong@huawei.com Yunbin Xu CAICT Email: xuyunbin@ritt.cn Yang Zhao China Mobile Email: zhaoyangyjy@chinamobile.com Zheng Expires September 2018 [Page 13]