Applicability of Path Computation Element (PCE) for Abstraction and Control of TE Networks (ACTN)
draft-dhody-pce-applicability-actn-00

PCE Working Group                                               D. Dhody
Internet-Draft                                                    Y. Lee
Intended status: Informational                       Huawei Technologies
Expires: January 8, 2017                                   D. Ceccarelli
                                                                Ericsson
                                                            July 7, 2016

  Applicability of Path Computation Element (PCE) for Abstraction and
                     Control of TE Networks (ACTN)
                 draft-dhody-pce-applicability-actn-00

Abstract

   Abstraction and Control of TE Networks (ACTN) refers to the set of
   virtual network operations needed to orchestrate, control and manage
   large-scale multi-domain TE networks so as to facilitate network
   programmability, automation, efficient resource sharing, and end-to-
   end virtual service aware connectivity and network function
   virtualization services.

   The Path Computation Element Communication Protocol (PCEP) provides
   mechanisms for Path Computation Elements (PCEs) to perform path
   computations in response to Path Computation Clients (PCCs) requests.

   This document examines the applicability of PCE to the ACTN
   framework.

Status of This Memo

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   This Internet-Draft will expire on January 8, 2017.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Path Computation Element (PCE)  . . . . . . . . . . . . .   2
       1.1.1.  Role of PCE in SDN  . . . . . . . . . . . . . . . . .   3
       1.1.2.  PCE in multi-domain and multi-layer deployments . . .   4
     1.2.  Abstraction and Control of TE Networks (ACTN) . . . . . .   5
     1.3.  PCE and ACTN  . . . . . . . . . . . . . . . . . . . . . .   5
   2.  Architectural Considerations  . . . . . . . . . . . . . . . .   6
     2.1.  Multi domain coordination via Hierarchy . . . . . . . . .   6
     2.2.  Virtualization/Abstraction function . . . . . . . . . . .   6
     2.3.  Customer mapping function . . . . . . . . . . . . . . . .   7
     2.4.  Virtual Network Operations  . . . . . . . . . . . . . . .   8
   3.  Interface Considerations  . . . . . . . . . . . . . . . . . .   8
   4.  Realizining ACTN with PCE (and PCEP)  . . . . . . . . . . . .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  11
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

1.1.  Path Computation Element (PCE)

   The Path Computation Element communication Protocol (PCEP) [RFC5440]
   provides mechanisms for Path Computation Elements (PCEs) [RFC4655] to
   perform path computations in response to Path Computation Clients
   (PCCs) requests.

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   The ability to compute shortest constrained TE LSPs in Multiprotocol
   Label Switching (MPLS) and Generalized MPLS (GMPLS) networks across
   multiple domains has been identified as a key motivation for PCE
   development.

   A stateful PCE is capable of considering, for the purposes of path
   computation, not only the network state in terms of links and nodes
   (referred to as the Traffic Engineering Database or TED) but also the
   status of active services (previously computed paths, and currently
   reserved resources, stored in the Label Switched Paths Database
   (LSPDB).

   [I-D.ietf-pce-stateful-pce-app] describes general considerations for
   a stateful PCE deployment and examines its applicability and
   benefits, as well as its challenges and limitations through a number
   of use cases.

   [I-D.ietf-pce-stateful-pce] describes a set of extensions to PCEP to
   provide stateful control.  A stateful PCE has access to not only the
   information carried by the network's Interior Gateway Protocol (IGP),
   but also the set of active paths and their reserved resources for its
   computations.  The additional state allows the PCE to compute
   constrained paths while considering individual LSPs and their
   interactions.  [I-D.ietf-pce-pce-initiated-lsp] describes the setup,
   maintenance and teardown of PCE-initiated LSPs under the stateful PCE
   model.

   [I-D.ietf-pce-stateful-pce] also describes the active stateful PCE.
   The active PCE functionality allows a PCE to reroute an existing LSP
   or make changes to the attributes of an existing LSP, or delegate
   control of specific LSPs to a new PCE.

1.1.1.  Role of PCE in SDN

   Software-Defined Networking (SDN) refers to a separation between the
   control elements and the forwarding components so that software
   running in a centralized system called a controller, can act to
   program the devices in the network to behave in specific ways.  A
   required element in an SDN architecture is a component that plans how
   the network resources will be used and how the devices will be
   programmed.  It is possible to view this component as performing
   specific computations to place flows within the network given
   knowledge of the availability of network resources, how other
   forwarding devices are programmed, and the way that other flows are
   routed.  It is concluded in [RFC7399], that this is the same function
   that a PCE might offer in a network operated using a dynamic control
   plane.  This is the function and purpose of a PCE, and the way that a

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   PCE integrates into a wider network control system including SDN is
   presented in Application-Based Network Operation (ABNO) [RFC7491].

   [I-D.zhao-teas-pce-control-function] introduces the architecture for
   PCE as a central controller, examines the motivations and
   applicability for PCEP as a southbound interface, and introduces the
   implications for the protocol.

1.1.2.  PCE in multi-domain and multi-layer deployments

   Computing paths across large multi-domain environments require
   special computational components and cooperation between entities in
   different domains capable of complex path computation.  The PCE
   provides an architecture and a set of functional components to
   address this problem space.  A PCE may be used to compute end-to-end
   paths across multi-domain environments using a per-domain path
   computation technique [RFC5152].  The Backward recursive PCE based
   path computation (BRPC) mechanism [RFC5441] defines a PCE-based path
   computation procedure to compute inter-domain constrained MPLS and
   GMPLS TE networks.  However, both per-domain and BRPC techniques
   assume that the sequence of domains to be crossed from source to
   destination is known, either fixed by the network operator or
   obtained by other means.

   [RFC6805] describes a Hierarchical PCE (H-PCE) architecture which can
   be used for computing end-to-end paths for inter-domain MPLS Traffic
   Engineering (TE) and GMPLS Label Switched Paths (LSPs) when the
   domain sequence is not known.  Within the Hierarchical PCE (H-PCE)
   architecture, the Parent PCE (P-PCE) is used to compute a multi-
   domain path based on the domain connectivity information.  A Child
   PCE (C-PCE) may be responsible for a single domain or multiple
   domains, it is used to compute the intra-domain path based on its
   domain topology information.

   [I-D.dhodylee-pce-stateful-hpce] state the considerations for
   stateful PCE(s) in hierarchical PCE architecture.  In particular, the
   behavior changes and additions to the existing stateful PCE
   mechanisms (including PCE- initiated LSP setup and active PCE usage)
   in the context of networks using the H-PCE architecture.

   [RFC5623] describes a framework for applying the PCE-based
   architecture to inter-layer to (G)MPLS TE.  It provides suggestions
   for the deployment of PCE in support of multi-layer networks.  It
   also describes the relationship between PCE and a functional
   component in charge of the control and management of the VNT, called
   the Virtual Network Topology Manager (VNTM).

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1.2.  Abstraction and Control of TE Networks (ACTN)

   [I-D.ietf-teas-actn-requirements] describes the high-level ACTN
   requirements.  [I-D.ceccarelli-teas-actn-framework] describes the
   architecture model for ACTN including the entities (Customer Network
   Controller(CNC), Mult-domain Service Coordinator(MDSC), and Physical
   Network Controller(PNC)) and their interfaces.

   The ACTN reference architecture identified a three-tier control
   hierarchy as depicted in Figure 1:

      +-------+                 +-------+                   +-------+
      | CNC-A |                 | CNC-B |                   | CNC-C |
      +-------+                 +-------+                   +-------+
            \                       |                           /
             ----------             | CMI          ------------
                        \           |            /
                         +-----------------------+
                         |         MDSC          |
                         +-----------------------+
                        /           |            \
               --------             | MPI          ------------
              /                     |                          \
      +-------+                 +-------+                   +-------+
      |  PNC  |                 |  PNC  |                   |  PNC  |
      +-------+                 +-------+                   +-------+

                         Figure 1: ACTN Hierarchy

   The two interfaces with respect to the MDSC, one north of the MDSC
   and the other south of the MDSC are referred to as CMI (CNC-MDSC
   Interface) and MPI (MDSC-PNC Interface), respectively.

   [I-D.leebelotti-teas-actn-info] provides an information model for
   ACTN interfaces.

1.3.  PCE and ACTN

   This document examines the PCE and ACTN architecture and describes
   how the PCE architecture is applicable to ACTN.  It also list the
   PCEP extensions that are needed to use PCEP as an ACTN interface.
   This documents also identify any gaps in PCEP, that exist at the time
   of publication of this document.

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2.  Architectural Considerations

   ACTN [I-D.ceccarelli-teas-actn-framework] architecture is based on
   hierarchy and recursiveness of controllers.  It defines three types
   of controllers (depending on the functionalities they implement).
   The main functionalities are -

   o  Multi domain coordination function

   o  Virtualization/Abstraction function

   o  Customer mapping function

   o  Virtual service coordination

2.1.  Multi domain coordination via Hierarchy

   With the definition of domain being "everything that is under the
   control of the same controller", as per
   [I-D.ceccarelli-teas-actn-framework], it is needed to have a control
   entity that oversees the specific aspects of the different domains
   and to build a single abstracted end-to-end network topology in order
   to coordinate end-to-end path computation and path/service
   provisioning.

   The MDSC in ACTN framework realizes this function by coordinating the
   per-domain PNCs in a hierarchy of controllers.  It also needs to
   detach from the underlying network technology and express customer
   concerns by business needs.

   [RFC6805] and [I-D.dhodylee-pce-stateful-hpce] describes a hierarchy
   of PCE with Parent PCE coordinating multi-domain path computation
   function between Child PCE(s).  It is easy to see how these
   principles align, and thus how H-PCE architecture can be used to
   realize ACTN.

   The Per domain stitched LSP in the Hierarchical stateful PCE
   architecture, described in Section 3.3.1 of
   [I-D.dhodylee-pce-stateful-hpce].  This is also applicable to multi-
   layer coordination.

2.2.  Virtualization/Abstraction function

   To realize ACTN, the MDSC needs to build an multi-domain topology.
   This topology is best served, if this is an abstracted view of the
   underlying network resources of each domain.  It is also important to
   provide a customer view of network slice for each customer.

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   In order to compute and provide optimal paths, PCEs require an
   accurate and timely Traffic Engineering Database (TED).
   Traditionally this TED has been obtained from a link state (LS)
   routing protocol supporting traffic engineering extensions.  PCE may
   construct its TED by participating in the IGP ([RFC3630]  and
   [RFC5305]  for MPLS-TE; [RFC4203]  and [RFC5307] for GMPLS).  An
   alternative is offered by BGP-LS [RFC7752].

   In case of H-PCE [RFC6805], the parent PCE needs to build the domain
   topology map of the child domains and their interconnectivity.
   [RFC6805] and [I-D.ietf-pce-inter-area-as-applicability] suggest that
   BGP-LS could be used as a "northbound" TE advertisement from the
   child PCE to the parent PCE.

   [I-D.leedhody-teas-pcep-ls] proposes some other approaches for
   learning and maintaining the Link-State and TE information as an
   alternative to IGPs and BGP flooding using PCEP.  The child PCE can
   use this mechanism to transport Link-State and TE information from
   child PCE to a Parent PCE using PCEP itself.

   In ACTN, there is a need to control the level of abstraction based on
   the deployment scenario and business relationship between the
   controllers.  The mechanism used to disseminate information from PNC
   (child PCE) to MDSC (parent PCE) should support abstraction.
   [I-D.dhodylee-pce-pcep-ls] supports this function.

2.3.  Customer mapping function

   In ACTN, there is a need to map customer virtual network (VN)
   requirements into network provisioning request to the PNC.

   [I-D.ietf-pce-pce-initiated-lsp] describes the setup, maintenance and
   teardown of PCE-initiated LSPs under the stateful PCE model, without
   the need for local configuration on the PCC, thus allowing for a
   dynamic network that is centrally controlled and deployed.  To
   instantiate or delete an LSP, the PCE sends the Path Computation LSP
   Initiate Request (PCInitiate) message to the PCC.  As described in
   [I-D.dhodylee-pce-stateful-hpce], for inter-domain LSP in
   Hierarchical PCE architecture, the initiation operations can be
   carried out at the parent PCE.  In which case after parent PCE
   finishes the E2E path computation, it can send the PCInitiate message
   to the child PCE, the PCE further propagates the initiate request to
   the PCC.

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2.4.  Virtual Network Operations

   Virtual service coordination function in ACTN incorporates customer
   service-related knowledge into the virtual network operations in
   order to seamlessly operate virtual networks while meeting customer's
   service requirements.

   [I-D.leedhody-pce-vn-association] describes the need for associating
   a set of LSPs with a VN "construct" to facilitate VN operations in
   PCE architecture.  This association allows the PCEs to identify which
   LSPs belong to a certain VN.

3.  Interface Considerations

   As per [I-D.ceccarelli-teas-actn-framework], to allow virtualization
   and multi domain coordination, the network has to provide open,
   programmable interfaces, in which customer applications can create,
   replace and modify virtual network resources and services in an
   interactive, flexible and dynamic fashion while having no impact on
   other customers.  The 2 ACTN interfaces are -

   o  The CNC-MDSC Interface (CMI) is an interface between a Customer
      Network Controller and a Multi Domain Service Coordinator.  It
      requests the creation of the network resources, topology or
      services for the applications.  The MDSC may also report potential
      network topology availability if queried for current capability
      from the Customer Network Controller.

   o  The MDSC-PNC Interface (MPI) is an interface between a Multi
      Domain Service Coordinator and a Physical Network Controller.  It
      communicates the creation request, if required, of new
      connectivity of bandwidth changes in the physical network, via the
      PNC.  In multi-domain environments, the MDSC needs to establish
      multiple MPIs, one for each PNC, as there are multiple PNCs
      responsible for its domain control.

   PCEP is especially suitable on the MPI, as it meets the requirement
   and the functions as set out in the ACTN framework
   [I-D.ceccarelli-teas-actn-framework].  The Section 4 describe how PCE
   and PCEP could help realize ACTN.

4.  Realizining ACTN with PCE (and PCEP)

   As per the example in the Figure 2, there are 4 domains, each with
   its own PNC and a MDSC at top.  The PNC and MDSC need PCE as a
   important function.  The PNC (or child PCE) uses PCEP to communicate
   to the network device already.  It can utilize the PCEP as the MPI to
   communicate between controllers too.

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                             ******
                   ..........*MDSC*..............................
                .            ****** ..                   MPI    .
             .                .        .                        .
          .                   .          .                      .
        .                    .             .                    .
       .                    .                .                  .
      .                    .                  .                 .
     .                    .                    .                .
     v                    v                    v                .
   ******               ******               ******             .
   *PNC1*               *PNC2*               *PNC4*             .
   ******               ******               ******             .
   +---------------+    +---------------+    +---------------+  .
   |A              |----|               |----|              C|  .
   |               |    |               |    |               |  .
   |DOMAIN 1       |----|DOMAIN 2       |----|DOMAIN 4       |  .
   +------------B13+    +---------------+    +B43------------+  .
                   \                         /                  .
                    \   ******              /                   .
                     \  *PNC3*<............/.....................
                      \ ******            /
                       \+---------------+/
                        B31           B34
                        |               |
                        |DOMAIN 3      B|
                        +---------------+

   MDSC -> Parent PCE
   PNC  -> Child  PCE
   MPI  -> PCEP

                          Figure 2: ACTN with PCE

   o  Building Domain Topology at MDSC: PNC (or child PCE) needs to have
      the TED to compute path in its domain.  As described in
      Section 2.2, it can learn the topology via IGP or BGP-LS.  PCEP-LS
      is also a proposed mechanism to carry link state and traffic
      engineering information within PCEP.  A mechanism to carry
      abstracted topology while hiding technology specific information
      between PNC and MDSC is described in [I-D.dhodylee-pce-pcep-ls].
      At the end of this step the MDSC (or parent PCE) has the
      abstracted topology from each of its PNC (or child PCE).  This
      could as simple as a domain topology map as described in [RFC6805]
      or it can have full topology information of all domains.  The
      latter is not scalable and thus an abstracted topology of each

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      domain interconnected by inter-domain links is the most common
      case.

      *  Topology Change: When the PNC learns of any topology change,
         the PNC needs to decide if the change needs to be notified to
         the MDSC.  This is dependent on the level abstraction between
         the MDSC and the PNC.

   o  VN Instantiate: MDSC is requested to instantiate a VN, the minimal
      information that is required would be a VN identifier, a set of
      end points.  Various path computation and setup constraints and
      objective functions may also be provided.  In PCE terms, a VN
      Instantiate can be considered as a set of Path belonging to the
      same VN.  As described in Section 2.4 and
      [I-D.leedhody-pce-vn-association] the VN association can help in
      identifying the set of paths that belong to a VN.  The rest of the
      information like the endpoints, constraints and objective function
      is already defined in PCEP in terms of a single path.

      *  Path Computation: As per the example in the Figure 2, the VN
         instantiate requires two end to end paths between (A in Domain
         1 to B in Domain 3) and (A in Domain 1 to C in Domain 4).  The
         MDSC (or parent PCE) triggers the end to end path computation
         for these two paths.  MDSC can do path computation based on the
         abstracted domain topology that it already has or it may use
         the H-PCE procedures (Section 2.1) using the PCReq and PCRep
         messages to get the end to end path with the help of PNC.
         Either way, the resulted E2E paths may be broken into per-
         domain paths.

      *  A-B: (A-B13,B13-B31,B31-B)

      *  A-C: (A-B13,B13-B31,B34-B43,B43-C)

      *  Per Domain Path Instantiation: Based on the above path
         computation, MDSC can issue the path instantiation request to
         each PNC via PCInitiate message (see
         [I-D.dhodylee-pce-stateful-hpce] and
         [I-D.leedhody-pce-vn-association]).  The message from MDSC to
         PNC can contain a partial path, in which case the PNC computes
         the full path in the domain.  A suitable stitching mechanism
         would be use to stitch these per domain LSPs.

      *  Per Domain Path Report: Each PNC should report the status of
         the per-domain LSP to the MDSC via PCRpt message, as per the
         Hierarchy of stateful PCE ([I-D.dhodylee-pce-stateful-hpce]).
         The status of the end to end LSP (A-B and A-C) is made up when
         all the per domain LSP are reported up by the PNCs.

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      *  Delegation: It is suggested that the per domain LSPs are
         delegated to respective PNC, so that they can control the path
         and attributes based on each domain network conditions.

   o  VN Modify: MDSC is requested to modify a VN, for example the
      bandwidth for VN is increased.  This may trigger path computation
      at MDSC as described in the previous step and can trigger an
      update to existing per-intra-domain path (via PCUpd message) or
      creation (or deletion) of a per-domain path (via PCInitiate
      message).

   o  VN Delete: MDSC is requested to delete a VN, in this case, based
      on the E2E paths and the resulting per-domain paths need to be
      removed (via PCInitiate message).

   o  VN Update (based on network changes): Any change in the per-domain
      LSP are reported to the MDSC (via PCRpt message) as per
      [I-D.dhodylee-pce-stateful-hpce].  This may result in changes in
      the E2E path or VN status.  This may also trigger a reoptimization
      leading to a new per-domain path, update to existing path, or
      deletion of the path.

   o  VN Protection: The VN protection/restoration requirements, need to
      applied to each E2E path as well as each per domain path.  The
      MDSC needs to play a crucial role in coordinating the right
      protection/restoration policy across each PNC.  The existing
      protection/resoration mechanism of PCEP can be applied on each
      path.

5.  IANA Considerations

   This is an informational document and thus does not have any IANA
   allocations to be made.

6.  Security Considerations

7.  Acknowledgments

8.  References

8.1.  Normative References

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <http://www.rfc-editor.org/info/rfc5440>.

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8.2.  Informative References

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630,
              DOI 10.17487/RFC3630, September 2003,
              <http://www.rfc-editor.org/info/rfc3630>.

   [RFC4203]  Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in
              Support of Generalized Multi-Protocol Label Switching
              (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,
              <http://www.rfc-editor.org/info/rfc4203>.

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <http://www.rfc-editor.org/info/rfc4655>.

   [RFC5152]  Vasseur, JP., Ed., Ayyangar, A., Ed., and R. Zhang, "A
              Per-Domain Path Computation Method for Establishing Inter-
              Domain Traffic Engineering (TE) Label Switched Paths
              (LSPs)", RFC 5152, DOI 10.17487/RFC5152, February 2008,
              <http://www.rfc-editor.org/info/rfc5152>.

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, DOI 10.17487/RFC5305, October
              2008, <http://www.rfc-editor.org/info/rfc5305>.

   [RFC5307]  Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions
              in Support of Generalized Multi-Protocol Label Switching
              (GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008,
              <http://www.rfc-editor.org/info/rfc5307>.

   [RFC5441]  Vasseur, JP., Ed., Zhang, R., Bitar, N., and JL. Le Roux,
              "A Backward-Recursive PCE-Based Computation (BRPC)
              Procedure to Compute Shortest Constrained Inter-Domain
              Traffic Engineering Label Switched Paths", RFC 5441,
              DOI 10.17487/RFC5441, April 2009,
              <http://www.rfc-editor.org/info/rfc5441>.

   [RFC5623]  Oki, E., Takeda, T., Le Roux, JL., and A. Farrel,
              "Framework for PCE-Based Inter-Layer MPLS and GMPLS
              Traffic Engineering", RFC 5623, DOI 10.17487/RFC5623,
              September 2009, <http://www.rfc-editor.org/info/rfc5623>.

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   [RFC6805]  King, D., Ed. and A. Farrel, Ed., "The Application of the
              Path Computation Element Architecture to the Determination
              of a Sequence of Domains in MPLS and GMPLS", RFC 6805,
              DOI 10.17487/RFC6805, November 2012,
              <http://www.rfc-editor.org/info/rfc6805>.

   [RFC7399]  Farrel, A. and D. King, "Unanswered Questions in the Path
              Computation Element Architecture", RFC 7399,
              DOI 10.17487/RFC7399, October 2014,
              <http://www.rfc-editor.org/info/rfc7399>.

   [RFC7491]  King, D. and A. Farrel, "A PCE-Based Architecture for
              Application-Based Network Operations", RFC 7491,
              DOI 10.17487/RFC7491, March 2015,
              <http://www.rfc-editor.org/info/rfc7491>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,
              <http://www.rfc-editor.org/info/rfc7752>.

   [I-D.ietf-pce-stateful-pce-app]
              Zhang, X. and I. Minei, "Applicability of a Stateful Path
              Computation Element (PCE)", draft-ietf-pce-stateful-pce-
              app-05 (work in progress), October 2015.

   [I-D.ietf-pce-stateful-pce]
              Crabbe, E., Minei, I., Medved, J., and R. Varga, "PCEP
              Extensions for Stateful PCE", draft-ietf-pce-stateful-
              pce-14 (work in progress), March 2016.

   [I-D.ietf-pce-pce-initiated-lsp]
              Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "PCEP
              Extensions for PCE-initiated LSP Setup in a Stateful PCE
              Model", draft-ietf-pce-pce-initiated-lsp-05 (work in
              progress), October 2015.

   [I-D.dhodylee-pce-stateful-hpce]
              Dhody, D., Lee, Y., Ceccarelli, D., Shin, J., and D. King,
              "Hierarchical Stateful Path Computation Element (PCE).",
              draft-dhodylee-pce-stateful-hpce-00 (work in progress),
              February 2016.

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   [I-D.zhao-teas-pce-control-function]
              Farrel, A., Zhao, Q., Li, Z., and C. Zhou, "An
              Architecture for Use of PCE and PCEP in a Network with
              Central Control", draft-zhao-teas-pce-control-function-01
              (work in progress), May 2016.

   [I-D.ietf-teas-actn-requirements]
              Lee, Y., Dhody, D., Belotti, S., Pithewan, K., and D.
              Ceccarelli, "Requirements for Abstraction and Control of
              TE Networks", draft-ietf-teas-actn-requirements-03 (work
              in progress), July 2016.

   [I-D.ceccarelli-teas-actn-framework]
              Ceccarelli, D. and Y. Lee, "Framework for Abstraction and
              Control of Traffic Engineered Networks", draft-ceccarelli-
              teas-actn-framework-02 (work in progress), April 2016.

   [I-D.leebelotti-teas-actn-info]
              Lee, Y., Belotti, S., Ceccarelli, D., and B. Yoon,
              "Information Model for Abstraction and Control of TE
              Networks (ACTN)", draft-leebelotti-teas-actn-info-02 (work
              in progress), March 2016.

   [I-D.ietf-pce-inter-area-as-applicability]
              King, D., Meuric, J., Dugeon, O., Zhao, Q., and O. Dios,
              "Applicability of the Path Computation Element to Inter-
              Area and Inter-AS MPLS and GMPLS Traffic Engineering",
              draft-ietf-pce-inter-area-as-applicability-05 (work in
              progress), July 2015.

   [I-D.leedhody-teas-pcep-ls]
              Lee, Y., Dhody, D., and D. Ceccarelli, "Architecture and
              Requirement for Distribution of Link-State and TE
              Information via PCEP.", draft-leedhody-teas-pcep-ls-02
              (work in progress), March 2016.

   [I-D.dhodylee-pce-pcep-ls]
              Dhody, D., Lee, Y., and D. Ceccarelli, "PCEP Extension for
              Distribution of Link-State and TE Information.", draft-
              dhodylee-pce-pcep-ls-03 (work in progress), March 2016.

   [I-D.leedhody-pce-vn-association]
              Lee, Y., Dhody, D., and D. Ceccarelli, "PCEP Extensions
              for Establishing Relationships Between Sets of LSPs and
              Virtual Networks", draft-leedhody-pce-vn-association-00
              (work in progress), February 2016.

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Authors' Addresses

   Dhruv Dhody
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560066
   India

   EMail: dhruv.ietf@gmail.com

   Young Lee
   Huawei Technologies
   5340 Legacy Drive, Building 3
   Plano, TX  75023
   USA

   EMail: leeyoung@huawei.com

   Daniele Ceccarelli
   Ericsson
   Torshamnsgatan,48
   Stockholm
   Sweden

   EMail: daniele.ceccarelli@ericsson.com

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