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Versions: (draft-zheng-teas-gmpls-controller-inter-work) 00 01

TEAS Working Group                                        Haomian Zheng
Internet Draft                                             Xianlong Luo
Category: Informational                             Huawei Technologies
                                                              Yang Zhao
                                                           China Mobile
                                                              Yunbin Xu
                                                                  CAICT
                                                         Sergio Belotti
                                                          Dieter Beller
                                                                  Nokia
Expires: January 8, 2020                                   July 8, 2019


    Interworking of GMPLS Control and Centralized Controller System


              draft-ietf-teas-gmpls-controller-inter-work-01


Abstract

   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.

   Internet-Drafts are working documents of the Internet Engineering
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   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



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   at any time.  It is inappropriate to use Internet-Drafts as
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   The list of current Internet-Drafts can be accessed at
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   This Internet-Draft will expire on January 8, 2020.

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   Copyright (c) 2019 IETF Trust and the persons identified as the
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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...4
   3. Link Management Protocol............Error! Bookmark not defined.
   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 Service Provisioning.........................9
      7.3. Multi-layer Service Provisioning.........................11
      7.4. Recovery.................................................11
      7.5. Controller Reliability...................................11
   8. Manageability Considerations..................................12
   9. Security Considerations.......................................12
   10. IANA Considerations..........................................12
   11. References...................................................12
      11.1. Normative References....................................12
      11.2. Informative References..................................14
   12. Authors' Addresses ...........................................16



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
   [RFC7926].

   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. One example
   architecture can be found in ACTN [RFC8453]. In such systems, a
   controller is aware of the network topology and is responsible for
   provisioning incoming service requests.

   Multiple hierarchies of controllers are designed at different levels
   implementing different functions. This kind of architecture enables
   multi-vendor, multi-domain, and multi-technology control. For
   example, a higher-level controller coordinates several lower-level
   controllers controlling different domains, for topology collection
   and service provisioning. Vendor-specific features can be abstracted
   between controllers, and standard API (e.g., generated from
   RESTconf/YANG) is used.

2.3. GMPLS Control Interwork with Centralized Controller System

   Besides the GMPLS and the interactions among the controller
   hierarchies, it is also necessary for the controllers to communicate
   with the network elements. Within each domain, GMPLS control can be
   applied to each NE. The bottom-level central controller can act as a
   NE to collect network information and initiate LSP. Figure 1 shows

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   an example of GMPLS interworking with centralized controllers (ACTN
   terminologies are used in the figure).

                              +--------------------+
                              |    Orchestrator    |
                              +--------------------+
                              ^       ^         ^
                              |       |         |
                +-------------+       |         +------------+
                |                     | RESTConf/YANG models |
                V                     V                      V
           +----------+           +----------+          +----------+
           |Controller|           |Controller|          |Controller|
           +----------+           +----------+          +----------+
              ^   ^                  ^   ^                     ^
              |   |                  |   |                     |
       Netconf|   |PCEP       Netconf|   |PCEP                 | IF*
        /YANG |   |            /YANG |   |                     |
              V   V                  V   V                     V
         .------------.  Inter-  .-----------.  Inter-   .-----------.
        /              \ domain /             \ domain  /             \
       |                | link |     LMP       | link  |     LMP      |
       |                |======|  OSPF-TE      |=======|   OSPF-TE    |
       |                |      |   RSVP-TE     |       |   RSVP-TE    |
        \              /        \             /         \            /
          `-----------`          `------------`          `----------`
       non-GMPLS domain 1      GMPLS domain 2            GMPLS domain 3


       Figure 1: Example of GMPLS/non-GMPLS interworks with Controllers

   Figure 1 shows the scenario with two GMPLS domains and one non-GMPLS
   domain. This system supports the interworking among non-GMPLS
   domain, GMPLS domain and the controller hierarchies. For domain 1,
   the network element were not enabled with GMPLS so the control can
   be purely from the controller, via Netconf/YANG and/or PCEP. For
   domain 2 and 3, each domain has the GMPLS control plane enabled at
   the physical network level. The PNC can exploit GMPLS capability
   implemented in the domain to listen to the IGP routing protocol
   messages (OSPF LSAs for example) that the GMPLS control 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


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   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 e.g.[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 e.g.[TE-
   Tunnel] Yang model together with the technology-specific YANG model
   augmentations.

3. Discovery Options

   In GMPLS control, the link connectivity need to be verified between
   each pair of nodes. In this way, link resources, which are
   fundamental resources in the network, are discovered by both ends of
   the link.

3.1. LMP

   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.

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.

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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 controllers may not have
   sufficient information to compute the optimal path. In this case,
   the controller can interact with other 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
   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 [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 implemented 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. One of the reference
   architecture can be found at [RFC7491].

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

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   information, while the topology on the controller can be either raw
   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 notifications with YANG
   model.



7.2. Multi-domain 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 service provisioning would request coordination among
   the controller hierarchies. Given the service request, the end-to-
   end delivery procedure may include interactions at any level (i.e.
   interface) in the hierachy of the controllers (e.g. MPI and SBI for
   ACTN). The computation for a cross-domain path is usually completed
   by controllers who have a global view of the topologies. Then the
   configuration is decomposed into lower layer controllers, 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. Several methods can be used to create the inter-domain
   path:

   1) One end-to-end RSVP-TE session:

   In this method, an end-to-end RSVP-TE session from the source NE to
   the destination NE will be used to create the inter-domain path. 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.



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   This method requires the interworking of RSVP-TE protocols between
   different domains.

   2) Multiple RSVP-TE sessions for multiple path segments:

   In this method, each SDN controller is responsible to create the
   path segment within its domain.

   Note that path segments in the source domain and the destination
   domain are "asymmetrical" segments, because the configuration of
   client signal mapping into server layer tunnel is needed at only one
   end of the segment, while configuration of server layer cross-
   connect is needed at the other end of the segment. For example, the
   path segment 1 and 3 in Figure 3 are asymmetrical segments, because
   one end of the segment requires mapping GE into ODU0, while the
   other end of the segment requires setting up ODU0 cross-connect.

   +-----------------+   +----------------+   +-----------------+
   |Client           |   |                |   |           Client|
   |Signal   Domain 1|   |    Domain 2    |   |Domain 3   Signal|
   |(GE)             |   |                |   |            (GE) |
   |  |   ODU0 tunnel|   |                |   |              |  |
   |+-+-+       ^    |   |                |   |            +-+-+|
   || | |  +--+ |+--+|   |+--+  +--+  +--+|   |+--+  +--+  | | ||
   || | |  |  | ||  ||   ||  |  |  |  |  ||   ||  |  |  |  | | ||
   || ******************************************************** ||
   ||   |  |  |  |  || . ||  |  |  |  |  || . ||  |  |  |  |   ||
   |+---+  +--+  +--+| . |+--+  +--+  +--+| . |+--+  +--+  +---+|
   +-----------------+ . +----------------+ . +-----------------+
    .                  .                    .                  .
    .<-Path Segment 1->.<--Path Segment 2-->.<-Path Segment 3->.
    .                  .                    .                  .

              Figure 3: Example of asymmetrical path segment

   The PCEP / GMPLS protocols should support creation of such
   asymmetrical segment.

   Note also that mechanisms to assign the labels in the inter-domain
   links are also needed to be considered. There are two possible
   methods:

   2.1) Inter-domain labels assigned by NEs:

   The concept of Stitching Label that allows stitching local path
   segments was introduced in [RFC5150] and [sPCE-ID], in order to form
   the inter-domain path crossing several different domains. It also
   describes the BRPC and H-PCE PCInitiate procedure, i.e., the ingress
   boarder node of each downstream domain assigns the stitching label
   for the inter-domain link between the downstream domain and its

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   upstream neighbor domain, and this stitching label will be passed to
   the upstream neighbor domain by PCE protocol, which will be used for
   the path segment creation in the upstream neighbor domain.

   2.2) Inter-domain labels assigned by SDN controller:

   If the resource of inter-domain links are managed by the multi-
   domain SDN controller, each single-domain SDN controller can provide
   to the multi-domain SDN controller the list of available labels
   (e.g. timeslots if OTN is the scenario) using IETF Topology model
   and related technology specific extension. Once that multi-domain
   SDN controller has computed e2e path RSVP-TE or PCEP can be used in
   the different domains to setup related segment tunnel consisting
   with label inter-domain information, e.g. for PCEP the label ERO can
   be included in the PCInitiate message to indicate the inter-domain
   labels, so that each boarder node of each domain can configure the
   correct cross-connect within itself.

7.3. Multi-layer Service Provisioning

   For further study. Plan to be updated in the next version.

7.4. 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.

7.5. 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


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   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.

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.




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   [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
             2011.

   [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
             2015.

   [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.


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   [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
             2018.





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.

   [RFC5150]  Ayyangar, A., Kompella, K., Vasseur, J.P., Farrel, A.,
             "Label Switched Path Stitching with Generalized
             Multiprotocol Label Switching Traffic Engineering (GMPLS
             TE)", RFC 5150, February, 2008.

   [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.




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   [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-19, 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.

   [TE-Tunnel] Saad, T. et al., "A YANG Data Model for Traffic
             Engineering Tunnels and Interfaces", draft-ietf-teas-yang-
             te, work in progress.




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   [sPCE-ID] Dugeon, O. et al., "PCEP Extension for Stateful Inter-
             Domain Tunnels", draft-dugeon-pce-stateful-interdomain,
             work in progress.



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

   Sergio Belotti
   Nokia
   Email: sergio.belotti@nokia.com

   Dieter Beller
   Nokia
   Email: Dieter.Beller@nokia.com












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