TEAS Working Group                                        Haomian Zheng
Internet Draft                                             Xianlong Luo
Category: Informational                             Huawei Technologies
                                                              Yang Zhao
                                                           China Mobile
                                                              Yunbin Xu
                                                         Sergio Belotti
                                                          Dieter Beller
Expires: June 6, 2019                                  December 6, 2018

     Interworking of GMPLS Control and Centralized Controller System



   Generalized Multi-Protocol Label Switching (GMPLS) control allows
   each network element (NE) to perform local resource discovery,
   routing and signaling in a distributed manner.

   On the other hand, with the development of software-defined
   transport networking technology, a set of NEs can be controlled via
   centralized controller hierarchies to address the issue from multi-
   domain, multi-vendor and multi-technology. An example of such
   centralized architecture is ACTN controller hierarchy described in
   RFC 8453.

   Instead of competing with each other, both the distributed and the
   centralized control plane have their own advantages, and should be
   complementary in the system. This document describes how the GMPLS
   distributed control plane can interwork with a centralized
   controller system in a 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.

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   months and may be updated, replaced, or obsoleted by other documents

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   at any time.  It is inappropriate to use Internet-Drafts as
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Conventions used in this document

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 ................................................ 7
      4.3. Netconf/RESTconf ....................................... 7
   5. Path Computation ............................................ 7
      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
   7. Interworking Scenarios ...................................... 8

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      7.1. Topology Collection & Synchronization .................. 8
      7.2. Multi-domain/layer Service Provisioning ................ 9
      7.3. Recovery ............................................... 9
      7.4. Controller Reliability ................................ 10
   8. Manageability Considerations ............................... 10
   9. Security Considerations .................................... 10
   10. IANA Considerations........................................ 10
   11. References ................................................ 11
      11.1. Normative References ................................. 11
      11.2. Informative References ............................... 12
   12. Authors' Addresses ........................................ 14

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 GMPLS control plane collects network
   information from other NEs and supports service provisioning through
   signaling in a distributed manner. More generic description for
   Traffic-engineering networking information exchange can be found in

   On the other hand, Software-Defined Networking (SDN) technologies
   have been introduced to control the transport network in a
   centralized manner. Central controllers 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) [RFC8453], which defines a hierarchical
   architecture with Provisioning Network Controller(PNC), Multi-domain
   Service Coordinator(MDSC) and Customer Network Controller(CNC) as
   central controllers for different network abstraction levels. A Path
   Computation Element (PCE) based approach has been proposed as
   Application-Based Network Operations (ABNO) in [RFC7491].

   In such centralized controller architectures, GMPLS can be applied
   for the NE-level control. A central controller may support GMPLS
   enabled domains and may interact with a GMPLS enabled domain where
   the GMPLS control plane does the service provisioning from ingress
   to egress. In this case the centralized controller sends the request
   to the ingress node and does not have to configure all NEs along the
   path through the domain from ingress to egress thus leveraging the
   GMPLS control plane. This document describes how GMPLS control
   interworks with centralized controller system in transport network.

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2. Overview

   In this section, overviews of GMPLS control plane and centralized
   controller system are discussed as well as the interactions between
   the GMPLS control plane and centralized controllers.

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 runs a GMPLS control plane instance.
   Functionalities such as service provisioning, protection, and
   restoration can be performed via GMPLS communication among multiple
   NEs.  At the same time, the controller 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 Label Switched Paths (LSPs). In this way,
   controllers in different nodes in the network have the same view of
   the network topology and provision services based on local policies.

2.2. Overview of Centralized Controller System

   With the development of SDN technologies, a centralized controller
   architecture has been introduced to transport networks such as ACTN
   [RFC8453]. In centralized controller systems, 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 provides a topological view of the
   domain it controls, which can be abstracted, to the MDSC, so that
   the MDSC learns the topology of the network encompassing multiple
   domains. When a multi-domain service request arrives at the MDSC,
   the MDSC first computes an end-to-end path based on the abstracted
   topology view provided by the PNCs. 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. When each PNC has reported the establishment of its
   LSP segment, the multi-domain service is established.

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2.3. GMPLS Control Interwork with Centralized Controller System

   The ACTN framework [RFC8453] defines a hierarchical controller
   architecture and describes how these controllers communicate with
   each other in order to control a multi-domain transport network. The
   controllers at the different levels in the hierarchy typically
   perform network abstraction of the domain they control and provide
   an abstracted view of their domain to the controller at the next
   level in the hierarchy. The controllers at the different
   hierarchical levels also interact with each other during end-to-end
   service establishment, which can span 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. Figure 1 shows an example of GMPLS
   interworking with ACTN.

                        |   MDSC   |
                          ^      ^
                          |      |
                +---------+      +---------+
                |  RESTConf / YANG models  |
                V                          V
           +---------+                +---------+
           |   PNC   |                |   PNC   |
           +---------+                +---------+
              ^   ^                      ^   ^
              |   |                      |   |
       OSPF-TE|   |PCEP           OSPF-TE|   |PCEP
       Netconf|   |               Netconf|   |
              V   V                      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 has the GMPLS control plane enabled at the
   physical network level. The PNC can listen to the IGP routing
   protocol messages (OSPF LSAs for example) that the GMPLS control

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   plane instances are disseminating into the network and thus learn
   the network topology. For path computation in the domain with PNC
   implementing a PCE, PCCs (e.g. NEs, other controller/PCE) use PCEP
   to ask the PNC for a path and get replies. The MDSC communicates
   with PNCs using for example REST/RESTConf based on YANG data models.
   As a PNC has learned its domain topology, it can report the topology
   to the MDSC. When a service arrives, the MDSC computes the path and
   coordinates PNCs to establish the corresponding LSP segment.

   Alternatively, the NETCONF protocol can be used to retrieve topology
   information utilizing the [TE-topo] Yang model and the technology-
   specific YANG model augmentations required for the specific network
   technology. The PNC can retrieve topology information from any NE
   (the GMPLS control plane instance of each NE in the domain has the
   same topological view), construct the topology of the domain and
   export an abstracted view to the MDSC. Based on the topology
   retrieved from multiple PNCs, the MDSC can create topology graph of
   the multi-domain network, and can use it for path computation. To
   setup a service, the MDSC can exploit Yang tunnel model together
   with the technology-specific YANG model augmentations.

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 the setup and
   maintenance of 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

   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.

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   The routing protocol for OTN, WSON and optical flexi-grid network
   are defined in [RFC7138], [RFC7688] and [RFC8363], 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.

4.3. Netconf/RESTconf

   Netconf [RFC6241] and RESTconf [RFC8040] protocols are originally
   used for network configuration. Besides, these protocols can also be
   used for topology retrieval by using topology-related YANG models,
   such as [RFC8345] and [TE-topo]. These protocols provide a powerful
   mechanism for notification that permits to notify the client about
   topology changes.

5. Path Computation

   Once a controller learns the network topology, it can utilize the
   available resources to serve service requests by performing path
   computation. Due to abstraction, the MDSC may not have sufficient
   information to compute the optimal path. In this case, the MDSC can
   interact with different domain controllers by sending Yang Path
   Computation requests [PAT-COMP] to compute a set of potential
   optimal paths and then, based on its own constraints, policy and
   specific knowledge (e.g. cost of access link) can choose the more
   feasible path for service e2e path setup.

   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

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   computed path may be infeasible if there is a diversity requirement,
   because stateless PCE has no knowledge about the former computed

   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

   In PCE Initiation [RFC8281], 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.

6. Signaling Options

   Signaling mechanisms are 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] have been extended to support different
   interfaces in GMPLS.

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.

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

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   or abstracted. Three different abstraction methods have been
   described in [RFC8453], and different controllers can select the
   corresponding method depending on application.

   When there are changes in the network topology, the impacted network
   element(s) need to report changes 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 NEs and
   controllers can either be achieved by routing protocols OSPF-
   TE/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

   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. Similarly, the interaction between the controller and the
   ingress node of a domain can be achieved by Netconf protocol with
   corresponding YANG models, and then completed by running RSVP among
   the network elements.

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].

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   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.

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. Manageability Considerations

   Each entity in the network, including both controllers and network
   elements, should be managed properly as it will interact with other
   entities. The manageability considerations in controller hierarchies
   and network elements still apply respectively. For the protocols
   applied in the network, manageability is also requested.

   The responsibility of each entity should be clarified. The control
   of function and policy among different controllers should be
   consistent via proper negotiation process.

9. Security Considerations

   This document provides the interwork between the GMPLS and
   controller hierarchies. The security requirements in both system
   still applies respectively. Protocols referenced in this document
   also have various security considerations, which is also expected to
   be satisfied.

   Other considerations on the interface between the controller and the
   network element are also important. Such security includes the
   functions to authenticate and authorize the control access to the
   controller from multiple network elements. Security mechanisms on
   the controller are also required to safeguard the underlying network
   elements against attacks on the control plane and/or unauthorized
   usage of data transport resources.

10. IANA Considerations

   This document requires no IANA actions.

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11. References

11.1. Normative References

   [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.

   [RFC3473]  Berger, L., Ed., "Generalized Multi-Protocol Label
             Switching (GMPLS) Signaling Resource ReserVation Protocol-
             Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
             January 2003.

   [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.

   [RFC4203]  Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions
             in Support of Generalized Multi-Protocol Label Switching
             (GMPLS)", RFC 4203, October 2005.

   [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.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
             Element (PCE) Communication Protocol (PCEP)", RFC 5440,
             March 2009.

   [RFC6241]  Enns, R., Bjorklund, M., Schoenwaelder J., Bierman A.,
             "Network Configuration Protocol (NETCONF)", RFC 6241, June

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   [RFC7074]  Berger, L. and J. Meuric, "Revised Definition of the
             GMPLS Switching Capability and Type Fields", RFC 7074,
             November 2013.

   [RFC7491] King, D., Farrel, A., "A PCE-Based Architecture for
             Application-Based Network Operations", RFC7491, March

   [RFC7926] Farrel, A., Drake, J., Bitar, N., Swallow, G., Ceccarelli,
             D. and Zhang, X., "Problem Statement and Architecture for
             Information Exchange between Interconnected Traffic-
             Engineered Networks", RFC7926, July 2016.

   [RFC8040]  Bierman, A., Bjorklund, M., Watsen, K., "RESTCONF
             Protocol", RFC 8040, January 2017.

   [RFC8453]  Ceccarelli, D. and Y. Lee, "Framework for Abstraction and
             Control of Traffic Engineered Networks", RFC 8453, August

11.2. Informative References

   [RFC3471]  Berger, L., Ed., "Generalized Multi-Protocol Label
             Switching (GMPLS) Signaling Functional Description", RFC
             3471, January 2003.

   [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.

   [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.

   [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.

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   [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.

   [RFC8281]  Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "PCEP
             Extensions for PCE-initiated LSP Setup in a Stateful PCE
             Model", RFC 8281, October 2017.

   [RFC8345] Clemm, A., Medved, J., Varga, R., Bahadur, N.,
             Ananthakrishnan, H., Liu, X., "A YANG Data Model for
             Network Topologies", RFC 8345, March 2018.

   [RFC8363]  Zhang, X., Zheng, H., Casellas, R., Dios, O., and D.
             Ceccarelli, "GMPLS OSPF-TE Extensions in support of Flexi-
             grid DWDM networks", RFC8363, February 2017.

   [TE-topo]  Liu, X., Bryskin, I., Beeram, V., Saad, T., Shah, H.,
             Gonzalez De Dios, O., "YANG Data Model for Traffic
             Engineering (TE) Topologies", draft-ietf-teas-yang-te-
             topo-18, work in progress.

   [PAT-COMP] Busi, I., Belotti, S., Lopez, V., Gonzalez de Dios, O.,
             Sharma, A., Shi, Y., Vilalta, R., Setheraman, K., "Yang
             model for requesting Path Computation", draft-ietf-teas-
             yang-path-computation-04, work in progress.

   [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.

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Internet-Draft        GMPLS and Controller Interwork        December 2018

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
   Email: xuyunbin@ritt.cn

   Yang Zhao
   China Mobile
   Email: zhaoyangyjy@chinamobile.com

   Sergio Belotti
   Email: sergio.belotti@nokia.com

   Dieter Beller
   Email: Dieter.Beller@nokia.com

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