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PCE Working Group                                               D. Dhody
Internet-Draft                                                    Y. Lee
Intended status: Informational                       Huawei Technologies
Expires: July 25, 2015                                     LM. Contreras
                                                     O. Gonzalez de Dios
                                                          Telefonica I+D
                                                               N. Ciulli
                                                               Nextworks
                                                        January 21, 2015


          Cross Stratum Optimization enabled Path Computation
            draft-dhody-pce-cso-enabled-path-computation-07

Abstract

   Applications like cloud computing, video gaming, HD Video streaming,
   Live Concerts, Remote Medical Surgery, etc are offered by Data
   Centers.  These data centers are geographically distributed and
   connected via a network.  Many decisions are made in the Application
   space without any concern of the underlying network.  Cross stratum
   application/network optimization focus on the challenges and
   opportunities presented by data center based applications and
   carriers networks together [CSO-DATACNTR].

   Constraint-based path computation is a fundamental building block for
   traffic engineering systems such as Multiprotocol Label Switching
   (MPLS) and Generalized Multiprotocol Label Switching (GMPLS)
   networks.  [RFC4655] explains the architecture for a Path Computation
   Element (PCE)-based model to address this problem space.

   This document explains the architecture for CSO enabled Path
   Computation.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."



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   This Internet-Draft will expire on July 25, 2015.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   5
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  CSO enabled PCE Architecture  . . . . . . . . . . . . . . . .   6
   4.  Path Computation and Setup Procedure  . . . . . . . . . . . .  10
     4.1.  Path Setup Using NMS  . . . . . . . . . . . . . . . . . .  11
     4.2.  Path Setup Using a Network Control Plane  . . . . . . . .  12
     4.3.  Path Setup using PCE  . . . . . . . . . . . . . . . . . .  13
     4.4.  Path Setup Using a Software Defined Network controller  .  14
   5.  Other Consideration . . . . . . . . . . . . . . . . . . . . .  15
     5.1.  Inter-domain  . . . . . . . . . . . . . . . . . . . . . .  15
       5.1.1.  One Application Domain with Multiple Network Domains   15
       5.1.2.  Multiple Application Domains with Multiple Network
               Domains . . . . . . . . . . . . . . . . . . . . . . .  16
         5.1.2.1.  ACG talks to multiple NCGs  . . . . . . . . . . .  16
         5.1.2.2.  ACG talks to the primary NCG, which talks to the
                   other NCG of different domains  . . . . . . . . .  17
       5.1.3.  Federation of SDN domains . . . . . . . . . . . . . .  18
       5.1.4.  Nesting of multi-layer SDN domains  . . . . . . . . .  19
     5.2.  Bottleneck  . . . . . . . . . . . . . . . . . . . . . . .  20
     5.3.  Relationship to ABNO  . . . . . . . . . . . . . . . . . .  21
     5.4.  Relationship to ACTN  . . . . . . . . . . . . . . . . . .  21
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
   8.  Manageability Considerations  . . . . . . . . . . . . . . . .  21
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  21
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  22
     10.2.  Informative References . . . . . . . . . . . . . . . . .  22



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1.  Introduction

   Many application services offered by Data Center to end-users make
   significant use of the underlying networks resources in the form of
   bandwidth consumption used to carry the actual traffic between data
   centers and/or among data center and end-users.  There is a need for
   cross optimization for both network and application resources.
   [CSO-PROBLEM] describes the problem space for cross stratum
   optimization.

   [NS-QUERY] describes the general problem of network stratum (NS)
   query in Data Center environments.  Network Stratum (NS) query is an
   ability to query the network from application controller in Data
   Centers so that decision would be jointly performed based on both the
   application needs and the network status.  Figure 1 shows typical
   data center architecture.

                             ---------------
       ----------           |         DC 1  |
      | End-user |. . . . .>|      o o o    |
      |          |          |       \|/     |
       ----------           |        O      |
            |                ----- --|------
            |                        |
            |                        |
            |       -----------------|-----------
            |      /                 |           \
            |     /        ..........O PE1        \     --------------
            |    |       .                         |   | o o o   DC 2 |
            |    | PE4 .                      PE2  |   |  \|/         |
             ----|---O.........................O---|---|---O          |
                 |     .                           |   |              |
                 |      .           PE3            |    --------------
                  \      ..........O   Carrier    /
                   \               |   Network   /
                    ---------------|-------------
                                   |
                           --------|------
                          |        O      |
                          |       /|\     |
                          |      o o o    |
                          |          DC 3 |
                           ---------------

                    Figure 1: Data Center Architecture

   Figure 2 shows the context of NS Query within the overarching data
   center architecture shown in Figure 1.



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                        --------------------------------------------
                       |                    Application Overlay     |
                       |                    (Data Centers)          |
                       |                                            |
     ----------        |    --------------         --------------   |
    | End-User |       |   | Application  |. . . .| Application  |  |
    |          |. . . >|   | Control      |       |  Processes   |  |
     ----------        |   | Gateway (ACG)|        --------------   |
                       |   |              |        --------------   |
                       |    ------------- . . . . | Application  |  |
                       |          /\              | Related Data |  |
                       |          ||               --------------   |
                        ----------||--------------------------------
                                  ||
                                  ||  Network Stratum Query (First
                                  ||                         Stage)
                                  ||
                        ----------||--------------------------------
                       |          \/         Network Underlay       |
                       |                                            |
                       |    --------------        ----------------  |
                       |   | Network      |. . . |    Network     | |
                       |   | Control      |      |    Processes   | |
                       |   | Gateway (NCG)|       ----------------
                       |   |              |       ----------------  |
                       |    -------------        |    Network     | |
                       |          |------------->|  Related Data  | |
                       |         (Second Stage)   ----------------  |
                        -------------------------------------------

                      Figure 2: NS Query Architecture

   NS Query is a two-stage query that consists of two stages:

   o  A vertical query capability where an external point (i.e., the
      Application Control Gateway (ACG) in Data Center) will query the
      network (i.e., the Network Control Gateway (NCG)).  The query can
      be initiated either by ACG to NCG or NCG to ACG depending on the
      mode of operation.  ACG initiated query is an application-centric
      mode while NCG initiated query is a network-centric mode.  It is
      anticipated that either ACG or NCG can be a final decision making
      point that chooses the end-to-end resources (i.e., both
      application IT resources and the network connectivity) depending
      on the mode of operation.

   o  A horizontal query capability where the NCG gathers the collective
      information of a variety of horizontal schemes implemented in the
      network stratum.



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   As an example for vertical query (1st stage), [ALTO-APPNET] describes
   Application Layer Traffic Optimization (ALTO) information model and
   protocol extensions to support application and network resource
   information exchange for high bandwidth applications in partially
   controlled and controlled environments as part of the infrastructure
   to application information exposure (i2aex) initiative.

   For the horizontal query (2nd stage), PCE can be an ideal choice,
   [CSO-PCE-REQT] describes the general requirement PCE should support
   in order to accommodate CSO capability.  This document is intended to
   fulfill the general PCE requirements discussed in the aforementioned
   reference.

   This document describes how PCE Architecture as described in
   [RFC4655] can help in the second stage of NS query.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.  Terminology

   The following terminology is used in this document.

   ACG:  Application Control Gateway.

   Application Stratum:  The application stratum is the functional block
      which manages and controls application resources and provides
      application resources to a variety of clients/end-users.
      Application resources are non-network resources critical to
      achieving the application service functionality.  Examples
      include: application specific servers, storage, content, large
      data sets, and computing power.  Data Centers are regarded as
      tangible realization of the application stratum architecture.

   ALTO:  Application Layer Traffic Optimization.

   CSO:  Cross Stratum Optimization.

   GMPLS:  Generalized Multiprotocol Label Switching.

   i2aex:  Infrastructure to application information exposure.

   LSR:  Label Switch Router.

   MPLS:  Multiprotocol Label Switching.



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   NCG:  Network Control Gateway.

   Network Stratum:  The network stratum is the functional block which
      manages and controls network resources and provides transport of
      data between clients/end-users to and among application resources.
      Network Resources are resources of any layer 3 or below (L1/L2/L3)
      such as bandwidth, links, paths, path processing (creation,
      deletion, and management), network databases, path computation,
      admission control, and resource reservation capability.

   NMS:  Network Management System

   PCC:  Path Computation Client: any client application requesting a
      path computation to be performed by a Path Computation Element.

   PCE:  Path Computation Element.  An entity (component, application,
      or network node) that is capable of computing a network path or
      route based on a network graph and applying computational
      constraints.

   PCEP:  Path Computation Element Communication Protocol.

   TE:  Traffic Engineering.

   TED:  Traffic Engineering Database.

   UNI:  User Network Interface.

3.  CSO enabled PCE Architecture

   In the network stratum, the Network Control Gateway (NCG) serves as
   the proxy gateway to the network.  The NCG receives the query request
   from the ACG, probes the network to test the capabilities for data
   flows to/from particular points in the network, and gathers the
   collective information of a variety of horizontal schemes implemented
   in the network stratum.  This is a horizontal query (Stage 2 in
   Figure 2).

   In this section we will describe how PCE fits in this horizontal
   scheme.

   A Path Computation Element (PCE) is an entity that is capable of
   computing a network path or route based on a network graph, and of
   applying computational constraints during the computation.

   (1) NCG and PCE are co-located.





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   In this composite solution, the same node implements functionality of
   both NCG and PCE.  When a network stratum query is received from the
   ACG (stage 1), this query is broken into one or more Path computation
   requests and handled by the PCE functionality co-located with the
   NCG.  There is no need for PCEP protocol here.  In this case, an
   external PCE interface (e.g., CLI, SNMP, proprietary) needs to be
   supported.  This is out of the scope of this document.


          +--------------------------------------------------+
          |   --   --   --   --   --   --   --   --   --     |
          |  |  | |  | |  | |  | |  | |  | |  | |  | |  |    |
          |   --   --   --   --   --   --   --   --   --     |
          |                                                  |
          |               Application Stratum                |
          |                                                  |
          |    +---------------------------------------+     |
          |    |                                       |     |
          +----+                  ACG                  +-----+
               |                                       |
               +------*---*----------------------------+
                      |   |
                      |   |
                      |   |
               +------*---*----------------------------+
               |   +----------+          +----------+  |
          +----+   +          *----------*          *  +-----+
          |    |   |   NCG    |          |   PCE    |  |     |
          |    |   |          *----------*          *  |     |
          |    |   +----------+          +----------+  |     |
          |    |                                       |     |
          |    +---------------------------------------+     |
          |                                                  |
          |                Network Stratum                   |
          |   --   --   --   --   --   --   --   --   --     |
          |  |  | |  | |  | |  | |  | |  | |  | |  | |  |    |
          |   --   --   --   --   --   --   --   --   --     |
          +--------------------------------------------------+

                     Figure 3: NCG and PCE Collocated

   (2) NCG and external PCE

   In this solution, an external node implements PCE functionality.
   Network stratum query received from the ACG (stage 1) is converted
   into Path computation requests at the NCG and relayed to the external
   PCE using the PCEP [RFC5440].  In this case the NCG includes Path
   Computation Client (PCC) functionalities.



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          +--------------------------------------------------+
          |   --   --   --   --   --   --   --   --   --     |
          |  |  | |  | |  | |  | |  | |  | |  | |  | |  |    |
          |   --   --   --   --   --   --   --   --   --     |
          |                                                  |
          |               Application Stratum                |
          |                                                  |
          |    +---------------------------------------+     |
          |    |                                       |     |
          +----+                  ACG                  +-----+
               |                                       |
               +------*---*----------------------------+
                      |   |
                      |   |
                      |   |
               +------*---*-------+
               |   +----------+   |      +----------+
          +----+   |          |   *------*          *--------+
          |    |   |   NCG    |   |      |   PCE    |        |
          |    |   |          |   *------*          *        |
          |    |   +----------+   |      +----------+        |
          |    |                  |                          |
          |    +------------------+                          |
          |                                                  |
          |                Network Stratum                   |
          |   --   --   --   --   --   --   --   --   --     |
          |  |  | |  | |  | |  | |  | |  | |  | |  | |  |    |
          |   --   --   --   --   --   --   --   --   --     |
          +--------------------------------------------------+


                      Figure 4: NCG and external PCE

   PCE has the capability to compute constrained paths between a source
   and one or more destination(s), optionally providing the value of the
   metrics associated to the computed path(s).  Thus it can fit very
   well in the horizontal query stage of CSO.  A PCE MAY have further
   capability to do multi-layer and/or inter-domain path computation
   which can be further utilized.  NCG which understands the vertical
   query and the presence of applications constraints can break the
   application request into suitable path computation request which PCE
   understands.  In this scenario, the PCE MAY have no knowledge of
   applications and provide only network related metrics to the NCG: the
   NCG (or the ACG for an application-centric model) is in charge of
   correlating the network quotations with the application layer
   information to achieve the global CSO objective.





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   With this architecture, NCG can request PCE different sets of
   computation mode that are not currently supported by PCE.  For
   instance, NCG may request PCE a multi-destination and multi-source
   path computation request.  This scenario arises when there are many
   possible Data Center choices for a given application request and
   there could be multiple sources for this request.  Multi-destination
   with a single source (aka., anycast) is a default case for multi-
   destination and multi-source path computation.

   In addition, with this architecture, NCG may have different sets of
   objectives and constraints than typical path computation requests.
   For instance, multi-criteria objective functions that combine the
   bandwidth requirement and latency may be very useful for some
   applications.  [PCE-SERVICE-AWARE] describes the extension to PCEP to
   carry Latency, Latency-Variation and Loss as constraints for end to
   end path computation.

   In a Stateful PCE (refer [PCE-STATEFUL]), there is a strict
   synchronization of the network states (in term of topology and
   resource information), and the set of computed paths and reserved
   resources in use in the network.  In other words, the PCE utilizes
   information from the TED as well as information about existing paths
   (for example, TE LSPs) in the network when processing new requests.
   Stateful PCE will be very important tool to achieve the goals of
   cross stratum optimization as maintains the status of final path
   selected after cross (application and network) optimization.

   As Stateful PCE would keep both LSP ID and the application ID
   associated with the LSP, it will make path computation more efficient
   in terms of resource usage and computation time.  Moreover, Stateful
   PCE would have an accurate snapshot of network resource information
   and as such it can increase adaptability to the changes.  This may be
   important for some application that requires a stringent performance
   objective.

   In conclusion -

   o  NCG can use the PCE to do path computation based on constrains
      from multiple sources and destinations.

   o  Stateful PCE can help in maintaining the status of the final cross
      optimized path.  It can also help NCG in maintaining the
      relationship of application request and setup path.  In case of
      any change of the path, the Stateful PCE and NCG and cooperate and
      take suitable action.






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4.  Path Computation and Setup Procedure

   Path computation flow is shown in Figure 5.

   1.  User for application would contact the application gateway ACG
       with its requirements.

   2.  ACG would further query the NCG to obtain the underlying network
       Status and quotations (offers) for the network connectivity
       services.

   3.  NCG would break the vertical request into suitable horizontal
       path computation request(s).

   4.  PCE would provide the result to NCG.

   5.  NCG would abstract the computation result and provide to ACG.

   6.  NCG and ACG would cooperate to finalize the path that needs to be
       setup.

   7.  Note that that the final decision can be made either in ACG or
       NCG depending on the mode of operation.  With application centric
       mode, minimal data center/IT resource information would flow from
       ACG to NCG while ACG collects network abstracted information from
       NCG to choose the optimal application-network resources.  With
       network centric mode, ACG would supply maximal data center/IT
       resource information to NCG so that NCG in conjunction with PCE
       would determine the optimal mixed set of application and network
       resources.  In the latter case, the PCE COULD support
       application/IT- based constrained computation capability beyond
       network path computation.  This requires further PCE capabilities
       to receive and process data center/IT resource information,
       possibly in conjunction with network information.

















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    +----------+    1    +---------------------------------------+
    |          |-------->|                                       |
    |   User   |         |                  ACG                  |
    |          |<--------|                                       |
    +----------+    6    +---------------------------------------+
                           ^  |
                           | 2|
                           |  |  +----------+    3     +----------+
                           |  +->|          |--------->|          |
                           |     |   NCG    |          |   PCE    |
                           +-----|          |<---------|          |
                             5   +----------+    4     +----------+

                      Figure 5: Path Computation Flow

   In this section we would analyze the mechanisms to finally setup the
   cross stratum optimized path.

4.1.  Path Setup Using NMS

   After ACG and NCG have decided the path that needs to be set, NCG can
   send a request to NMS asking it relay the message to the head end LSR
   (also a PCC) to setup the pre computed path.  Once the path signaling
   is completed and the LSP is setup, PCC should relay the status of the
   LSP to the Stateful PCE.

   In this mechanism we can reuse the existing NMS to establish the
   path.  Any updates or deletion of such path would be made via the
   NMS.

   Head end LSR (PCC) 'H' is always the owner of the path.

   See Figure 6 for this scenario.


















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    +----------+         +---------------------------------------+
    |          |-------->|                                       |
    |   User   |         |                  ACG                  |
    |          |<--------|                                       |
    +----------+         +---------------------------------------+
                          ^  |
        +-----------------+--+------------------------------------+
        |+----------+     |  |  +----------+          +----------+|
        ||          |     |  +->|          |--------->|          ||
        ||   NMS    |     +-----|   NCG    |          |   PCE    ||
        ||          |<----------|          |<---------|          ||
        |+----------+           +----------+          +----------+|
        |    |                                             ^      |
        |    |        +------------------------------------+      |
        |    |        |         Network Stratum                   |
        |    |       --   --   --   --   --   --   --   --   --   |
        |    +----->|H | |  | |  | |  | |  | |  | |  | |  | |  |  |
        |            --   --   --   --   --   --   --   --   --   |
        +---------------------------------------------------------+

                      Figure 6: Path Setup Using NMS

4.2.  Path Setup Using a Network Control Plane

   A network control plane (e.g.  GMPLS) MAY be used to automatically
   establish the cross optimized path between the selected end points.
   This control plane MAY be triggered via -

   o  NCG to Control Plane: GMPLS UNI or other protocols

   o  Control Plane to Head end Router: GMPLS Control Channel Interface
      (CCI).  Suitable protocol extensions are needed to achieve this.

   See Figure 7 for this scenario.

















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    +----------+         +---------------------------------------+
    |          |-------->|                                       |
    |   User   |         |                  ACG                  |
    |          |<--------|                                       |
    +----------+         +---------------------------------------+
                          ^  |
        +-----------------+--+------------------------------------+
        |+----------+     |  |  +----------+          +----------+|
        || GMPLS    |     |  +->|          |--------->|          ||
        || Control  |     +-----|   NCG    |          |   PCE    ||
        ||  plane   |<----------|          |<---------|          ||
        |+----------+           +----------+          +----------+|
        |    |                                             ^      |
        |    |        +------------------------------------+      |
        |    |        |         Network Stratum                   |
        |    |       --   --   --   --   --   --   --   --   --   |
        |    +----->|H | |  | |  | |  | |  | |  | |  | |  | |  |  |
        |            --   --   --   --   --   --   --   --   --   |
        +---------------------------------------------------------+

           Figure 7: Path Setup Using Centralized Control Plane

   After cross optimization, ACG and NCG will select the suitable end
   points, (the path is already calculated by PCE), this path is
   conveyed to the head end LSR which signals the path and notify the
   status to the Stateful PCE.  Later NCG can send suitable message to
   tear down the path.

   Using centralized control plane can make the NCG responsible for the
   LSP.  Head end LSR signals and maintains the status but the
   establishment and tear-down are initiated by the control plane.  This
   would have an obvious advantage in managing the setup paths.  The
   Stateful PCE will maintain the TED as well as the status of setup
   LSP.  NCG through centralized control plane can further
   setup/teardown/modify/re-optimize those paths.

4.3.  Path Setup using PCE

   A Stateful PCE extension MAY be developed to communicate the cross
   optimized path to the head end LSR.  Current PCEP protocol requires
   PCC to trigger Path request and PCE to provide reply.  Even in
   Stateful PCE, PCC must delegate the LSP to a PCE, a PCE never
   initiate path setup.  An extension to PCEP protocol MAY let PCE
   notify to PCC (Head end LSR) to establish the path.

   NCG via PCE and PCEP protocol can establish and tear-down LSP as
   shown in Figure 8.  [PCE_INITIATED] is one such attempt to extend
   PCEP.



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    +----------+         +---------------------------------------+
    |          |-------->|                                       |
    |   User   |         |                  ACG                  |
    |          |<--------|                                       |
    +----------+         +---------------------------------------+
                          ^  |
        +-----------------+--+------------------------------------+
        |                 |  |  +----------+          +----------+|
        |                 |  +->|          |--------->|          ||
        |                 |     |   NCG    |          |   PCE    ||
        |                 +-----|          |<---------|          ||
        |                       +----------+          +----------+|
        |        +---------------------------------------+ ^      |
        |        |    +------------------------------------+      |
        |        |    |         Network Stratum                   |
        |        |   --   --   --   --   --   --   --   --   --   |
        |        +->|H | |  | |  | |  | |  | |  | |  | |  | |  |  |
        |            --   --   --   --   --   --   --   --   --   |
        +---------------------------------------------------------+

                      Figure 8: Path Setup using PCE

4.4.  Path Setup Using a Software Defined Network controller

   A logically centralized Software Defined Network (SDN) controller MAY
   be used to properly configure in an automatic way the traffic
   forwarding rules that allow the end to end communication across the
   Network Stratum.

   Figure 9 shows this scenario.





















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      +----------+         +---------------------------------------+
      |          |-------->|                                       |
      |   User   |         |                  ACG                  |
      |          |<--------|                                       |
      +----------+         +---------------------------------------+
                            ^  |
          +-----------------+--+------------------------------------+
          |                 |  |  +----------+          +----------+|
          |                 |  +->|          |--------->|          ||
          |                 |     |   NCG    |          |   PCE    ||
          |                 +-----|          |<---------|          ||
          |                       +----------+          +----------+|
          |                           |   ^                         |
          |                           v   |                         |
          |               +----------------------------+            |
          |             +-|       SDN Controller       |--+         |
          |             | +----------------------------+  |         |
          |             |    |    |    |    |    |    |   |         |
          |             v    v    v    v    v    v    v   v         |
          |            --   --   --   --   --   --   --   --        |
          |           |  | |  | |  | |  | |  | |  | |  | |  |       |
          |            --   --   --   --   --   --   --   --        |
          |                                                         |
          |                       Network Stratum                   |
          |                                                         |
          +---------------------------------------------------------+

                      Figure 9: Path Setup using SDN

   A direct interface between the SDN Controller and the PCE could be
   present in the architecture shown in Figure 9.

   As result of the interaction between ACG and NCG (including the PCE
   processing), the NCG is able to instruct the SDN Controller to
   populate a number of forwarding rules to the network devices for
   building the end to end path.

5.  Other Consideration

5.1.  Inter-domain

5.1.1.  One Application Domain with Multiple Network Domains

   Underlying network connecting the datacenters MAYBE made up of
   multiple domains (AS and Area).  In this case an inter-domain path
   computation is required.





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    +----------+         +---------------------------------------+
    |          |-------->|                                       |
    |   User   |         |                  ACG                  |
    |          |<--------|                                       |
    +----------+         +---------------------------------------+
                          ^  |
                          |  |
    +--------------+   +--+--+------------------------------------+
    |  +----------+|   |  |  |  +----------+          +----------+|
    |  |          ||   |  |  +->|          |--------->|          ||
    |  |   PCE    ||   |  |     |   NCG    |          |   PCE    ||
    |  |          ||   |  +-----|          |<---------|          ||
    |  +----+-----+|   |        +----------+          +----+-----+|
    |       |      |   |                                   |      |
    +-------+------+   +-----------------------------------+------+
            |                                              |
            |                                              |
            |<---------------pcep session----------------->|
            |                                              |


                     Figure 10: Multi-domain Scenario

   [RFC5441] describes an inter-domain path computation with cooperating
   PCEs which can be enhanced and utilized in CSO enabled path
   computation.

5.1.2.  Multiple Application Domains with Multiple Network Domains

   Underlying network connecting the datacenters MAY be made up of
   multiple domains (AS and Area) as well as applications domains and
   ACG MAY be distributed.  In such case multiple ACG and NCG will be
   involved in cross optimizing.  This needs to be analyzed further.

5.1.2.1.  ACG talks to multiple NCGs

   As shown in Figure 11, ACG where the request originates may
   communicate with multiple NCG to get the network information from
   multiple domains to be cross optimized.












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     Application stratum
    +---------------------------+  +---------------------------+
    |                           |  |                           |
    |                           |  |                           |
    |                           |  |                           |
    |                           |  |                           |
    |                           |  |                           |
    |  +----------------------+ |  |  +----------------------+ |
    |  |                      | |  |  |                      | |
    +--+        ACG           +-+  +--+       ACG            +-+
       |                      |       |                      |
       +-+-+-------------+-+--+       +-------+-+------------+
         | |             | +------------+     | |
         | |             +------------+ |     | |
       +-+-+--------+   +-----+       +-+-----+-+--+    +-----+
    +--+            +---+     +-+  +--+            +----+     ++
    |  |    NCG     |---|     | |  |  |     NCG    |----|     ||
    |  |            |---|     | |  |  |            |----|     ||
    |  +------------+   | PCE | |  |  +------------+    | PCE ||
    |                   |     | |  |                    |     ||
    |                   |     |<+--+------------------->|     ||
    |                   +-----+ |  |                    +-----+|
    |Domain 1                   |  |Domain 2                   |
    +---------------------------+  +---------------------------+
                                            Network Stratum

                   Figure 11: ACG talks to multiple NCG

5.1.2.2.  ACG talks to the primary NCG, which talks to the other NCG of
          different domains

   As shown in Figure 12, ACG communicated only to the primary NCG,
   which may gather network information from multiple NCG and then
   communicate consolidated information to ACG.

















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     Application stratum
    +---------------------------+  +---------------------------+
    |                           |  |                           |
    |                           |  |                           |
    |                           |  |                           |
    |                           |  |                           |
    |                           |  |                           |
    |  +----------------------+ |  |  +----------------------+ |
    |  |                      | |  |  |                      | |
    +--+        ACG           +-+  +--+       ACG            +-+
       |                      |       |                      |
       +-+-+------------------+       +-------+-+------------+
         | |                                  | |
         | |                                  | |
       +-+-+--------+   +-----+       +-------+-+--+    +-----+
    +--+            +---+     +-+  +--+            +----+     ++
    |  |    NCG     |---|     | |  |  |     NCG    |----|     ||
    |  |            |---|     | |  |  |            |----|     ||
    |  +------+-----+   | PCE | |  |  +---+--------+    | PCE ||
    |         |         |     | |  |      |             |     ||
    |         |         |     |<+--+------+------------>|     ||
    |         |         +-----+ |  |      |             +-----+|
    |Domain 1 |                 |  |Domain|2                   |
    +---------+-----------------+  +------+--------------------+
              |                           | Network Stratum
              |                           |
              |<------------------------->|
              |                           |

                 Figure 12: Primary NCG talks to other NCG

5.1.3.  Federation of SDN domains

   In this case, the Data Centers are federated building a community
   cloud.  In each Data Center, the connection to the network stratum
   that interconnects the Data Center federation is done by means of one
   or more devices controllable through an SDN controller particular for
   that Data Center.

   The NCG, then, interacts with a number of separated SDN controllers,
   orchestrating their operation in order to perform the service
   requested by the ACG in an optimized way.

   Figure 13 shows this scenario.







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     +----------+         +---------------------------------------+
      |          |-------->|                                       |
      |   User   |         |                  ACG                  |
      |          |<--------|                                       |
      +----------+         +---------------------------------------+
                                      |  ^
                                      |  |
                           +----------+--+-------------------------+
                           |          |  |                         |
                           |          v  |                         |
                           |      +----------+         +----------+|
                           |      |          |-------->|          ||
                           |      |   NCG    |         |   PCE    ||
                           |      |          |<--------|          ||
                           |      +----------+         +----------+|
                           |       | ^    | ^                      |
                           |       | |    | |                      |
                           +-------+-+----+-+----------------------+
                                   | |    | |
                     +-------------+ |    | +-------------+
                     | +-------------+    +-------------+ |
                     | |                                | |
                     v |                                v |
           +--------------------+           +--------------------+
       +-  | SDN Controller DC1 |   . . .   | SDN Controller DCN |  -+
       |   +--------------------+           +--------------------+   |
       |                                                             |
       |                   Federated Data Centers                    |
       +-------------------------------------------------------------+

           Figure 13: NCG orchestration of separated SDN domains

5.1.4.  Nesting of multi-layer SDN domains

   A different scenario for multi-domain interconnection could be due to
   the deployment of multi-layered multi-domain networks (and these
   domains may be technology, administrative or vendor specific (vendor
   islands))for supporting end-to-end connectivity at the Network
   Stratum.  Each of those domains can be controlled by a distinct SDN
   controller adapted to the specifics of the technology under control.

   The NCG requests path calculation to a multi-layer PCE which takes
   into consideration such diversity providing an integrated computation
   for the best path according to application constraints.  The NCG
   instruct a primary SDN controller which apart of configuring the
   elements directly controlled by itself, it is able to communicate
   with other SDN controllers with responsibility over other domains.
   Such communication can be done through the usage of specific methods



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   through pre-defined South Bound Interface or East/West Interface (out
   of the scope of this document).

   The following figure shows this scenario.

          +----------+        +---------------------------------------+
         |          |------->|                                       |
         |   User   |        |                  ACG                  |
         |          |<-------|                                       |
         +----------+        +---------------------------------------+
                                        |  ^
                                        |  |
                             +----------+--+-------------------------+
                             |          |  |                         |
                             |          v  |                         |
                             |      +----------+       +----------+  |
                             |      |          |------>|  Multi-  |  |
                             |      |   NCG    |       |  Layer   |  |
                             |      |          |<------|   PCE    |  |
                             |      +----------+       +----------+  |
                             |          |  ^                         |
                             |          |  |                         |
                             +----------+--+-------------------------+
                                        |  |
                                        v  |
                                    +----------+
                                    |   SDN    |----------+
                                    |Controller|          |
                                    +----------+          |
                                         ^          +----------+
                                         |          |   SDN    |
                                         v          |Controller|
                                      Layer-N       +----------+
                                     Resources           ^
                                                         |
                                                         v
                                                     Layer-N-1
                                                     Resources

                 Figure 14: Nested multi-layer SDN domains

5.2.  Bottleneck

   In optical networks all PCE messages are sent over control channel,
   in Stateful PCE cases its observed that in case of a major link or
   node failure lot of PCEP messages are sent from all PCC to PCE.  This
   use lot of bandwidth of the control channel.




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   PCE MAY become a common point of failure and bottleneck.  PCE/NCG/ACG
   failure as well as the link-failure disrupting connectivity could be
   highly disruptive to the system.

   The solution should focus on reducing such bottleneck.

5.3.  Relationship to ABNO

   [ABNO] demonstrates cross-stratum application/network optimization
   for the data center use case with PCE as the heart of Application-
   Based Network Operations (ABNO) architecture.  It further highlights
   the interaction between various ABNO components and PCE to achieve
   this use-case.

5.4.  Relationship to ACTN

   [ACTN] describes the framework for abstraction and control of
   transport networks (ACTN) using hierarchy of controllers.  The
   Physical Network Controller (PNC) or Virtual Network Controller (VNC)
   is equivalent to the NCG in the CSO framework, both rely on PCE for
   the network optimization.

6.  IANA Considerations

   None, This is an informational document.

7.  Security Considerations

   TBD

8.  Manageability Considerations

   TBD

9.  Acknowledgements

   Part of the work in this document has been funded by the European
   Community's Seventh Framework Programme projects XIFI (L.M.
   Contreras and O.  Gonzalez), under grant agreement n. 604590, and
   GEYSERS (N.  Ciulli and L.M.  Contreras), under grant agreement n.
   248657.

10.  References








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10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

10.2.  Informative References

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655, August 2006.

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

   [RFC5441]  Vasseur, JP., 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, April 2009.

   [CSO-DATACNTR]
              Lee, Y., Bernstein, G., So, N., Kim, T., Shiomoto, K., and
              O. Gonzalez-de-Dios, "Research Proposal for Cross Stratum
              Optimization (CSO) between Data Centers and Networks.
              (draft-lee-cross-stratum-optimization-datacenter-00)",
              March 2011.

   [CSO-PROBLEM]
              Lee, Y., Bernstein, G., So, N., Hares, S., Xia, F.,
              Shiomoto, K., and O. Gonzalez-de-Dios, "Problem Statement
              for Cross-Layer Optimization. (draft-lee-cross-layer-
              optimization-problem-02)", January 2011.

   [NS-QUERY]
              Lee, Y., Bernstein, G., So, N., McDysan, D., Kim, T.,
              Shiomoto, K., and O. Gonzalez-de-Dios, "Problem Statement
              for Network Stratum Query. (draft-lee-network-stratum-
              query-problem-02)", April 2011.

   [CSO-PCE-REQT]
              Tovar, A., Contreras, L., Landi, G., and N. Ciulli, "Path
              Computation Requirements for Cross-Stratum-Optimization.
              (draft-tovar-cso-path-computation-requirements-00)",
              October 2011.








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   [PCE-SERVICE-AWARE]
              Dhody, D., Wu, Q., Manral, V., Ali, Z., and K. Kumaki,
              "Extensions to the Path Computation Element Communication
              Protocol (PCEP) to compute service aware Label Switched
              Path (LSP). (draft-ietf-pce-pcep-service-aware-06)",
              December 2014.

   [PCE-STATEFUL]
              Crabbe, E., Medved, J., Varga, R., and I. Minei, "PCEP
              Extensions for Stateful PCE. (draft-ietf-pce-stateful-pce-
              10)", October 2014.

   [ALTO-APPNET]
              Lee, Y., Bernstein, G., Varga, T., Madhavan, S., Dhody,
              D., and Q. Wu, "ALTO Extensions to Support Application and
              Network Resource Information Exchange for High Bandwidth
              Applications. (draft-lee-alto-app-net-info-exchange-04)",
              October 2013.

   [PCE_INITIATED]
              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-02)", July 2013.

   [ACTN]     Ceccarelli, D., Fang, L., Lee, Y., Lopez, D., Belotti, S.,
              and D. King, "Framework for Abstraction and Control of
              Transport Networks", draft-ceccarelli-actn-framework-06
              (work in progress), December 2014.

   [ABNO]     King, D. and A. Farrel, "A PCE-based Architecture for
              Application-based Network Operations", draft-farrkingel-
              pce-abno-architecture-15 (work in progress), January 2015.

Authors' Addresses

   Dhruv Dhody
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560037
   India

   EMail: dhruv.ietf@gmail.com









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   Young Lee
   Huawei Technologies
   1700 Alma Drive, Suite 500
   Plano, TX  75075
   USA

   EMail: leeyoung@huawei.com


   Luis M. Contreras
   Telefonica I+D
   Ronda de la Comunicacion, s/n
   Sur-3 building, 3rd floor
   Madrid  28050
   Spain

   EMail: lmcm@tid.es


   Oscar Gonzalez de Dios
   Telefonica I+D
   Ronda de la Comunicacion, s/n
   Sur-3 building, 3rd floor
   Madrid  28050
   Spain

   EMail: ogondio@tid.es


   Nicola Ciulli
   Nextworks

   EMail: n.ciulli@nextworks.it


















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