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Versions: 00 01 02 03 draft-ietf-ccamp-flexi-grid-fwk

Network Working Group                           O. Gonzalez de Dios, Ed.
Internet-Draft                                            Telefonica I+D
Intended status: Standards Track                        R. Casellas, Ed.
Expires: January 7, 2013                                            CTTC
                                                                F. Zhang
                                                                  Huawei
                                                                   X. Fu
                                                                     ZTE
                                                           D. Ceccarelli
                                                                Ericsson
                                                              I. Hussain
                                                                Infinera
                                                            July 6, 2012


     Framework for GMPLS based control of Flexi-grid DWDM networks
                 draft-ogrcetal-ccamp-flexi-grid-fwk-00

Abstract

   This document defines a framework and the associated control plane
   requirements for the GMPLS based control of flexi-grid DWDM networks.
   To allow efficient allocation of optical spectral bandwidth for high
   bit-rate systems, the International Telecommunication Union
   Telecommunication Standardization Sector (ITU-T) is extending the
   standard [G.694.1] to include the concept of flexible grid: a new
   DWDM grid has been developed within the ITU-T Study Group 15, by
   defining a set of nominal central frequencies, smaller channel
   spacings and the concept of "frequency slot".  In such environment, a
   data plane connection is switched based on the allocated, variable-
   width optical spectrum frequency slot.

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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 7, 2013.



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Copyright Notice

   Copyright (c) 2012 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
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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.





































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Table of Contents

   1.  Requirements Language  . . . . . . . . . . . . . . . . . . . .  4
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  DWDM flexi-grid enabled network element models . . . . . . . . 11
     5.1.  Switched Resources and Labels  . . . . . . . . . . . . . . 11
     5.2.  Physical links . . . . . . . . . . . . . . . . . . . . . . 12
     5.3.  Transceivers . . . . . . . . . . . . . . . . . . . . . . . 12
     5.4.  ROADMs . . . . . . . . . . . . . . . . . . . . . . . . . . 13
   6.  Layered Network Model  . . . . . . . . . . . . . . . . . . . . 14
   7.  Topology view in Control Plane . . . . . . . . . . . . . . . . 15
   8.  Control Plane Requirements . . . . . . . . . . . . . . . . . . 15
     8.1.  Neighbor Discovery and Link Property Correlation . . . . . 16
     8.2.  Path Computation / Routing and Spectrum Assignment
           (RSA)  . . . . . . . . . . . . . . . . . . . . . . . . . . 16
       8.2.1.  Architectural Approaches to RSA  . . . . . . . . . . . 17
     8.3.  Routing / Topology dissemination . . . . . . . . . . . . . 17
       8.3.1.  Available Frequency Ranges/slots of DWDM Links . . . . 18
       8.3.2.  Available Slot Width Ranges of DWDM Links  . . . . . . 18
       8.3.3.  Tunable Optical Transmitters and Receivers . . . . . . 18
       8.3.4.  Hierarchical Spectrum Management . . . . . . . . . . . 18
       8.3.5.  Information Model  . . . . . . . . . . . . . . . . . . 19
     8.4.  Signaling requirements . . . . . . . . . . . . . . . . . . 20
       8.4.1.  Slot Width Requirement . . . . . . . . . . . . . . . . 20
       8.4.2.  Frequency Slot Representation  . . . . . . . . . . . . 20
       8.4.3.  Relationship with MRN/MLN  . . . . . . . . . . . . . . 20
   9.  Control Plane Procedures . . . . . . . . . . . . . . . . . . . 20
   10. Backwards (fixed-grid) compatibility, and WSON interworking  . 21
   11. Misc & Summary of open Issues [To be removed at later
       versions]  . . . . . . . . . . . . . . . . . . . . . . . . . . 22
   12. Security Considerations  . . . . . . . . . . . . . . . . . . . 23
   13. Contributing Authors . . . . . . . . . . . . . . . . . . . . . 23
   14. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 25
   15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
     15.1. Normative References . . . . . . . . . . . . . . . . . . . 25
     15.2. Informative References . . . . . . . . . . . . . . . . . . 26
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26












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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.  Introduction

   The term "Flexible grid" (flexi-grid for short) as defined by the
   International Telecommunication Union Telecommunication
   Standardization Sector (ITU-T) study group 15 in the latest version
   of [G.694.1], refers to the updated set of nominal central
   frequencies (a frequency grid), channel spacings and optical spectrum
   management/allocation considerations that have been defined in order
   to allow an efficient and flexible allocation and configuration of
   optical spectral bandwidth for high bit-rate systems.

   A key concept of flexi-grid is the "frequency slot"; a variable-sized
   optical frequency range that can be allocated to a data connection.
   As detailed later in the document, a frequency slot is characterized
   by its nominal central frequency, selected from the set of reference
   frequencies, and its slot width which, as per [G.694.1], is
   constrained to be a multiple of a given slot width granularity.

   Compared to a traditional fixed grid network, which uses fixed size
   optical spectrum frequency ranges or "frequency slots" with typical
   channel separations of 100 or 50 GHz, a flexible grid network can
   select its data channels with with a more flexible choice of slot
   widths, allocating as much optical spectrum as required, and allowing
   higher bitrates (e.g., 100G or 400G or higher).

   From a networking perspective, a flexible grid network is assumed to
   be a layered network [G.872][G.805], extending the OTN architecture
   and interfaces [G.709], in which the flexi-grid layer (also referred
   to as the media layer) is the server layer and the OCh Layer (also
   referred to as the signal layer) is the client layer.  In the media
   layer, switching is based on a frequency slot, and the size of a
   media channel is given by the properties of the associated frequency
   slot.  In this layered network, the media channel itself can be
   dimensioned to contain one or more Optical Channels.

   As described in [RFC3945], GMPLS extends MPLS from supporting only
   Packet Switching Capable (PSC) interfaces and switching to also
   support four new classes of interfaces and switching that include
   Lambda Switch Capable (LSC).

   A Wavelength Switched Optical Network (WSON), addressed in [RFC6163],



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   is a term commonly used to refer to the application/deployment of a
   Generalized Multi-Protocol Label Switching (GMPLS)-based control
   plane for the control (provisioning/recovery, etc) of a fixed grid
   WDM network. [editors' note: we need to think of the relationship of
   WSON and OCh switching.  Are they equivalent?  WSON includes
   regeneration, OCh does not? decoupling of lambda/OCh/OCC]

   This document defines the framework for a GMPLS-based control of
   flexi-grid enabled DWDM networks (in the scope defined by ITU-T
   layered Optical Transport Networks [G.872], as well as a set of
   associated control plane requirements.  An important design
   consideration relates to the decoupling of the management of the
   optical spectrum resource and the client signals to be transported.
   [Editor's note: a point was raised during the meeting that WSON has
   not made separation between Och and Lambda (spectrum and signal are
   bundled).  This needs to be confirmed.]  A direct consequence of this
   "separation of concerns" is that, although not in scope of the
   present document, single-carrier / multi-carrier and related
   modulation formats, etc. could be supported.  [Editor's note: the
   concept of frequency slot channel supporting multiple OCHs is defined
   in an ITU contribution.  It is not a standard document yet.]

   [Editors' note: this document will track changes and evolutions of
   [G.694.1] [G.872] documents until their final publication.  This
   document is not expected to become RFC until then.  Likewise, as
   agreed during IETF83, the consideration of the concepts of Super-
   channel (a collection of one or more frequency slots to be treated as
   unified entity for management and control plane) and consequently
   Contiguous Spectrum Super-channel (a super-channel with a single
   frequency slot) and Split-Spectrum super-channel (a super-channel
   with multiple frequency slots) is postponed until the ITU-T data
   plane includes such physical layer entities, e.g., an ITU-T
   contribution exists]


3.  Acronyms

   FS: Frequency Slot

   FSCh: Frequency Slot Channel

   NCF: Nominal Central Frequency

   OCG: Optical Carrier Group

   OCh: Optical Channel

   OCC: Optical Channel Carrier



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   OTUk: Optical channel Transport Unit level k

   ODUk: Optical channel Data Unit Level k

   ODUj: Optical channel Data Unit Level j

   SWG: Slot Width Granularity


4.  Terminology

   The following is a list of terms (see [G.694.1] and [G.872])
   reproduced here for completeness.  [Editors' note: regarding
   wavebands, we agreed NOT to use the term in flexigrid.  The term has
   been used inconsistently in fixed-grid networks and overlaps with the
   definition of frequency slot.  If need be, a question will be sent to
   ITU-T asking for clarification regarding wavebands.]

   [Editors' note: *important* these terms are not yet final and they
   may change / be replaced or obsoleted at any time.]

   o  Optical Channel Slot (definition in the scope of a fixed grid DWDM
      network, to be adapted to a flexi-grid).  The optical spectrum
      frequency range (portion of optical spectrum) allocated / occupied
      by a single optical channel.  Each optical channel signal has a
      defined carrier central frequency and required frequency slot
      width (the supported optical channel signal bandwidth plus source
      stability).  Optical Channel slots within an optical multiplex
      section may be allocated (in-service) or may be unallocated (out-
      of-service).  An in-service Optical Channel Slot may be carrying
      an Optical Channel Signal or not.  Optical Channel Slots are
      switched in an Optical Channel Matrix.

   o  Nominal Central Frequency Granularity: 6.25 GHz (note: sometimes
      referred to as 0.00625 THz).

   o  Nominal Central Frequency: each of the allowed frequences as per
      the definition of flexible DWDM grid in [G.694.1].  The set of
      nominal central frequencies can be built using the following
      expression f = 193.1 THz + n x 0.00625 THz, where 193.1 THz is
      ITU-T ''anchor frequency'' for transmission over the C band, n is
      a positive or negative integer including 0.


      -5 -4 -3 -2 -1  0  1  2  3  4  5     <- values of n
    ...+--+--+--+--+--+--+--+--+--+--+-
                      ^
                      193.1 THz <- anchor frequency



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      Figure 1. Anchor frequency and set of nominal central frequencies

   o  Slot Width Granularity: 12.5 GHz, as defined in [G.694.1].

   o  Slot Width: The slot width determines the "amount" of optical
      spectrum regardless of its actual "position" in the frequency
      axis.  A slot width is constrained to be m x SWG (that is, m x
      12.5 GHz), where m is an integer greater than or equal to 1.

   o  Frequency Slot: The frequency range allocated to a slot within the
      flexible grid.  A frequency slot is defined by its nominal central
      frequency and its slot width.  Assuming a fixed and known central
      nominal frequency granularity, and assuming a fixed and known slot
      width granularity, a frequency slot is fully characterized by the
      values of 'n' and 'm'.  Note that an equivalent characterization
      of a frequency slot is given by the start and end frequencies
      (i.e., a frequency range) which can, in turn, be defined by their
      respective values of 'n'.  Note that a bidirectional optical
      transmission section layer network connection may be supported by
      one optical fiber for both directions (single fiber), or each
      direction of the connection may be supported by different fibers
      (pair of fibers).  Since a frequency slot is a unidirectional
      entity (the same nominal central frequency cannot be used in two
      directions of transmission), the single fiber case is carried out
      by a pair of unidirectional frequency slots on the same fiber, and
      the pair of fibers case may have frequency slots that use the same
      nominal central frequencies.


         Frequency Slot 1     Frequency Slot 2
          -------------     -------------------
          |           |     |                 |
      -3 -2 -1  0  1  2  3  4  5  6  7  8  9 10 11
   ..--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--...
          -------------     -------------------
                ^                    ^
        Central F = 193.1THz    Central F = 193.14375 THz
        Slot width = 25 GHz     Slot width = 37.5 GHz


                      Figure 2. Example Frequency slots

      The symbol '+' represents the allowed nominal central frequencies,
      the '--' represents the nominal central frequency granularity, and
      the '^' represents the slot nominal central frequency.  The number
      on the top of the '+' symbol represents the 'n' in the frequency
      calculation formula.  The nominal central frequency is 193.1 THz
      when n equals zero.  Note that over a single frequency slot, one



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      or multiple Optical Channels may be transported.

   o  Fiber Frequency Slot: the total allocable spectrum on a fiber (n=0
      and m= infinity?).  [Editors' note/CM: is this useful? is the
      spectrum bounded/symmetric w.r.t anchor frequency?]

   o  Frequency Slot Channel: a topological construct that represents a
      piece of spectrum supported by a concatenation of media elements
      (fiber, amplifiers, filters..).  This term is used to identify the
      end-to-end physical layer entity with its corresponding (one or
      more) frequency slots local at each link.  [Editors' note:

      *  MB: a frequency slot is a local (i.e., to the link) concept,
         while a frequency slot channel has an end to end meaning.

      *  IH: the FSCh is the CTP layer that is defining the frequency
         slot connection matrix.

      *  CM: the CTP is the Frequency Slot and the Frequency Slot
         Channel the trail, the OCh being on top of the Channel.

      *  ITU-T mailing list defines Common Frequency Slot which may
         replace Frequency Slot Channel (?).

      ]

   o  Common Frequency Slot: the optical frequency range that is common
      to all of the devices in a particular path through the optical
      network.  It is a logical construct derived from the frequency
      slots allocated to each device in the path (intersection).  As an
      example, if there are two devices having slots with the same n but
      different m, then the common frequency slot has the smaller of the
      two m values.  [Editors' note: this definition overlaps with
      Effective Frequency Slot] [Editors' note: clarify what happens
      when the resulting slot cannot be characterized with n and m, see
      Figure.  Are we assuming that the same "n" applies?].















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         Frequency Slot 1
          -------------
          |           |
      -3 -2 -1  0  1  2  3  4  5  6  7  8  9 10 11
      ..--+--+--X--+--+--+--+--+--+--+--+--+--+--+--+--+--...

             Frequency Slot 2
             -------------------
             |                 |
      -3 -2 -1  0  1  2  3  4  5  6  7  8  9 10 11
      ..--+--+--+--+--X--+--+--+--+--+--+--+--+--+--+--+--...

   =============================================== Common
           Common Frequency Slot (valid?, CF?)
             ----------
             |        |
      -3 -2 -1  0  1  2  3  4  5  6  7  8  9 10 11
      ..--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--...


                       Figure 4. Common Frequency Slot

   o  [Note: Following terminology is copied from ITU-T WP3 Q12 interim
      meeting [WD12R2]].

   o  [Editors' note: if we accept that a frequency slot can support one
      or more optical channel signals do we need the following two
      definitions?).

   o  Single-Channel Frequency Slot: a frequency slot associated with a
      single optical channel signal ((that carries a single OCh
      payload).

   o  Multi-Channel Frequency Slot: a frequency slot associated with
      multiple optical channel signals (i.e. multiple OChs).  Note that
      if there are multiple optical signals within frequency slot, then
      each signal still has its own central frequency.  That is, the
      term "central frequency" applies to an Optical signal and the term
      "nominal central frequency" applies to a frequency slot.  In other
      words, the Frequency Slot central frequency is independent of the
      signals central frequencies.










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                    Frequency Slot
        -----------------------------------+
        |  Optical           Optical       |
        |  Channel           Channel       |
        |  Signal            Signal        |
        |  +-----+        +-----------+    |
        |  |     |        |           |    |
        |  |  o  |        |     o     |    |
       -4 -3 -2 -1  0  1  2  3  4  5  6  7 8
   ...  +--+--+--+--+--X--+--+--+--+--+--+-+--...
                       ^
                       +-- Frequency Slot
                            Central Frequency

        o - signal central frequency


           Figure 3. Frequency slot with 2 Optical channel signals

   o  Network Channel (NCh): An end-to-end path through an optical
      network from a port on an OCh termination source to a port on an
      OCh termination sink (i.e. one OEO to another OEO).  It is
      constructed from a concatenation of link channels and subnetwork
      channels.

   o  Link Channel (LCh): A partial path through an optical network that
      provides a fixed relationship between the ports on a "subnetwork"
      or "access group" and the ports on another "subnetwork" or "access
      group".  [Note: the terms subnetwork and access group are defined
      in G.805].

   o  Subnetwork Channel (SNCh): A path through an optical subnetwork
      that provides a relationship across a subnetwork.  It is formed by
      the association of "ports" on the boundary of the subnetwork.

   o  Matrix Channel (MCh): A path through an optical matrix that
      provides a relationship across a matrix.  It is formed by the
      association of "ports" on the boundary of the matrix.

   o  Effective Frequency Slot: An attribute of a channel which
      identifies that part of the frequency slots allocated to the
      devices along the channel that is common to all

   The following terms are defined in the scope of a GMPLS control
   plane.  [Editors' note: the following ones were *not* agreed during
   IETF83 but are put here to be discussed.]





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   o  SSON: Spectrum-Switched Optical Network.  An optical network in
      which a data plane connection is switched based on an optical
      spectrum frequency slot of a variable slot width, rather than
      based on a fixed grid and fixed slot width.  Please note that a
      Wavelength Switched Optical Network (WSON) can be seen as a
      particular case of SSON in which all slot widths are equal and
      depend on the used channel spacing.

   o  Flexi-LSP: a control plane construct that represents a data plane
      connection in which the switching involves a frequency slot.
      Different Flexi-LSPs may have different slot widths.  The term
      flexi-LSP is used when needed to differentiate from regular WSON
      LSP in which switching is based on a nominal wavelength.

   o  RSA: Routing and Spectrum Assignment.  As opposed to the typical
      Routing and Wavelength Assignment (RWA) problem of traditional WDM
      networks, the flexibility in SSON leads to spectral contiguous
      constraint, which means that when assigning the spectral resources
      to single connections, the resources assigned to them must be
      contiguous over the entire connections in the spectrum domain.


5.  DWDM flexi-grid enabled network element models

   Similar to fixed grid networks, a flexible grid network is also
   constructed from subsystems that include Wavelength Division
   Multiplexing (WDM) links, tunable transmitters and receivers,
   Reconfigurable Optical Add/Drop Multiplexers (ROADMs), wavelength
   converters, and electro-optical network elements, all of them with
   flexible grid characteristics.

   As stated in [G.694.1] the flexible DWDM grid defined in Clause 7 has
   a nominal central frequency granularity of 6.25 GHz and a slot width
   granularity of 12.5 GHz.  However, devices or applications that make
   use of the flexible grid may not be capable of supporting every
   possible slot width or position.  In other words, applications may be
   defined where only a subset of the possible slot widths and positions
   are required to be supported.  For example, an application could be
   defined where the nominal central frequency granularity is 12.5 GHz
   (by only requiring values of n that are even) and that only requires
   slot widths as a multiple of 25 GHz (by only requiring values of m
   that are even).

5.1.  Switched Resources and Labels

   As per [G.872] [Editor's note/CM: we need to better distinguish
   between G.872 and contributions, it would help to see what is agreed
   and what is still open, the list below contains items as per MB/XF



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   slides]:

   o  OCh Slots are switched in an Optical Channel Matrix.

   o  The (link) physical layer entity, as defined by ITU-T is the
      Frequency Slot.

   o  A frequency slot channel may be switched in a Frequency Slot
      Matrix [ITU-T contribution draft].

   o  The frequency slot matrix connection cannot modify the center
      frequency or increase the bandwidth of the frequency slots present
      at its ports [Editors' note: this text comes from G.872 updated.
      This seems to constrain / limit to only a transparent segment? the
      "m" must be the same end to end while "n" can be change by the
      equivalent of a wavelength converter, but WC are not defined.
      Currently, we only consider the case that the frequency slot
      matrix connection cannot modify the center frequency or the
      bandwidth of the frequency slots present at its ports.  The use
      cases of dynamically modifying the center frequency or the
      bandwidth of the frequency slots are for further study after the
      clear definition by ITU-T].

   o  [Editors' note: we are not discarding O/E/O. If defined in a ITU-T
      network reference model with trail/terminations, considering
      optical channels i.e. with well-defined interfaces, reference
      points, and architectures.  The implications of O/E/O will be also
      addressed once we have another context that includes them.  In OTN
      from an OCh point of view end to end means from transponder to
      transponder, so if there is a 3R from ingress to egress there are
      2 OCh which can have different 'n' and 'm'].

5.2.  Physical links

5.3.  Transceivers

   Optical transmitters/receivers may have different restrictions on the
   following properties:

   o  Available central frequencies: The set of central frequencies
      which can be used by an optical transmitter/receiver.

   o  Slot width: The slot width needed by a transmitter/receiver.  The
      slot width is dependent on bit rate and modulation format.  For
      one specific transmitter, the bit rate and modulation format may
      be tunable, so slot width would be determined by the modulation
      format used at a given bit rate.




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   o  The minimum and maximum slot width.

   o  The step granularity: the optical hardare may not be able to
      select parameters with the lowest granulairy (e.g. 6.25 GHz for
      nominal central frequencies or 12.5 GHz for slot width
      granularity).

5.4.  ROADMs


                 Tributary Side:        E5 I5 E6 I6
                                         O |   O |
                                         | |   | |
                                         | O   | O
                               +-----------------------+
                               |+-----+         +-----+|
               Line side-1 --->||Split|         |WSS-2||---> Line side-2
               Input (I1)      |+-----+         +-----+|     Output (E2)
               Line side-1 <---||WSS-1|         |Split||<--- Line side-2
               Output  (E1)    |+-----+         +-----+|     Input (I2)
                               |         ROADM         |
                               |+-----+         +-----+|
               Line side-3 --->||Split|         |WSS-4||---> Line side-4
               Input (I3)      |+-----+         +-----+|     Output (E4)
               Line side-3 <---||WSS-3|         |Split||<--- Line side-4
               Output (E3)     |+-----+         +-----+|     Input (I4)
                               +-----------------------+
                                        | O   | O
                                        | |   | |
                                        O |   O |
                 Tributary Side:        E7 I7 E8 I8

     Figure 5. Simplified ROADM model with Line Sides and Tributaries

   [Editor's note: different ROADM configuration such as C/CD/CDC will
   be added later.]

   A Frequency slot matrix may have switching restrictions, for example
   , when it is realized using flexi-grid enabled ROADMs.  A key feature
   of ROADMs is their highly asymmetric switching capability which is
   described in [RFC6163] in detail.  The ports on ROADM include line
   side ports which are connected to DWDM links and tributary side
   input/output ports which can be connected to transmitters/receivers.
   The capability of ports on ROADM, which are characterized as follows:

   o  Available frequency ranges: the set or union of frequency ranges
      that are not allocated (i.e. available).  The relative grouping
      and distribution of available frequency ranges in a fiber is



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      usually referred to as ''fragmentation''.

   o  Available slot width ranges: the set or union of slot width ranges
      supported by ROADM.  It includes the following information.

      *  Slot width threshold: the minimum and maximum Slot Width
         supported by ROADM.  For example, the slot width can be from
         50GHz to 200GHz.

      *  Step granularity: the minimum step by which the optical filter
         bandwidth of ROADM can be increased or decreased.  This
         parameter is typically equal to slot width granularity (i.e.
         12.5GHz) or integer multiples of 12.5GHz.


6.  Layered Network Model

   [Editors' note: OTN hierarchy is not fully covered.  It is important
   to understand, where the FSC sits in the OTN hierarchy.  This is also
   important from control plane perspective as this layer becomes the
   connection end points of optical layer service].  OCh / flexi-grid
   layered model.

  AP                       Trail (OCh)                               AP
  O- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O
  TCP                 Link Connection (OCh)                          TCP
  o------------o-------------------------------------------o---------o
    Subnetwork                                              Subnetwork
    Connection                                              Connection
               |            Media Path                     |
           AP  O- - - - - - - - - - - - - - - - - - - - - -O AP
               |                                           |
               |                Link (Fiber)               |
           TCP o---------------o-----------o---------------o
                Subnet. channel Link channel   Subnet. chan
               (freq slot)      (freq slot)      (freq slot)


                   Figure 6. Layered Network Model G.805

   [Editors' note: we are replicating the figure here for reference,
   until the ITU-T document is official.

   The media path is a piece of spectrum that has been allocated to a
   path between two ports of a media device.  [Editors'note/CM/IH: it
   seems the media path is equivalent to the FSC (freq.slot channel is
   between the AP?.  Why use a new term media path?]




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7.  Topology view in Control Plane

   [Note: the frequency slot matrix connection may interconnect one or
   more frequency slot channels which in turn may carry one or more Och
   signals.]


+--------------+                            +--------------+
| Signal (OCh) |             TE             | Signal (OCh) |  Virtual TE
|              |            link            |              |    link
|    Matrix    |o- - - - - - - - - - - - - o|    Matrix    |o- - - - - -
|              |                            |              |
+--------------+                            +--------------+
               |       +---------+          |
               |       |Freq Slot|          |
               |o------| Matrix  |---------o|
                       |         |
                       +---------+


             Figure 7. MRN/MLN topology view with TE link / FA


8.  Control Plane Requirements

   [Editor's note: The considered topology view is a layered network, in
   which the media layer corresponds to the server layer (flexigrid) and
   the signal layer corresponds to the client layer (Och).  This data
   plane modeling considers the flexigrid and the OCh as separate
   layers, especially considering both the single and multi-channel
   frequency slots.  However, this has implications on the interop/
   interworking with WSON and OCh switching.  We need to manage a MRN
   for OCh and stitching for WSON?  In other words, a key part of the
   fwk is to define how can we have MRN/MLN hierarchical relationship
   with Och/FS and yet stitching 1:1 between WSON and SSON?  In this
   line: how does OCh switching and WSON relate, actually?]

   [Editor's note: formal requirements such as noted in the comments
   will be added in a later version of the document].

   Hierarchy spectrum management decouples media and signal, but from
   the point of view of the control plane, such separation of concerns
   implies the management of a MRN/MLN network.  So Control Plane needs
   to differentiate signal LSP and media LSP.  It should also need to
   support Hierarchy-LSP [RFC4206] The central frequency of each hop
   should be same along end-to-end media or signal LSP because of
   Spectrum Continuity Constraint.  Otherwise some nodes need to convert
   the central frequency along media or signal LSP.



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8.1.  Neighbor Discovery and Link Property Correlation

   [Editors' note: text from draft-li-ccamp-grid-property-lmp-01]

   During the practical deployment procedure, fixed-grid optical nodes
   will be gradually replaced by flexible nodes.  This will lead to an
   interworking problem between fixed-grid DWDM and flexible-grid DWDM
   nodes.  Additionally, even two flexible-grid optical nodes may have
   different grid properties, leading to link property conflict.

   Devices or applications that make use of the flexible-grid may not be
   able to support every possible slot width.  In other words,
   applications may be defined where different grid granularity can be
   supported.  Taking node F as an example, an application could be
   defined where the nominal central frequency granularity is 12.5 GHz
   requiring slot widths being multiple of 25 GHz.  Therefore the link
   between two optical nodes with different grid granularity must be
   configured to align with the larger of both granularities.  Besides,
   different nodes may have different slot width tuning ranges.

   In summary, in a DWDM Link between two nodes, at least the following
   properties should be negotiated:

      Grid capability (channel spacing) - Between fixed-grid and
      flexible-grid nodes.

      Grid granularity - Between two flexible-grid nodes.

      Slot width tuning range - Between two flexible-grid nodes.

8.2.  Path Computation / Routing and Spectrum Assignment (RSA)

   Much like in WSON, in which if there is no (available) wavelength
   converters in an optical network, an LSP is subject to the
   ''wavelength continuity constraint'' (see section 4 of [RFC6163]), if
   the capability of shifting or converting an allocated frequency slot,
   the LSP is subject to the Optical ''Spectrum Continuity Constraint''.

   Because of the limited availability of wavelength/spectrum converters
   (sparse translucent optical network) the wavelength/spectrum
   continuity constraint should always be considered.  When available,
   information regarding spectrum conversion capabilities at the optical
   nodes may be used by RSA mechanisms.

   The RSA process determines a route and frequency slot for a LSP.
   Hence, when a route is computed the spectrum assignment process (SA)
   should determine the central frequency and slot width based on the
   slot width and available central frequencies information of the



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   transmitter and receiver, and the available frequency ranges
   information and available slot width ranges of the links that the
   route traverses.

8.2.1.  Architectural Approaches to RSA

   Similar to RWA for fixed grids, different ways of performing RSA in
   conjunction with the control plane can be considered.  The approaches
   included in this document are provided for reference purposes only;
   other possible options could also be deployed.

8.2.1.1.  Combined RSA (R&SA)

   In this case, a computation entity performs both routing and
   frequency slot assignment.  The computation entity should have the
   detailed network information, e.g. connectivity topology constructed
   by nodes/links information, available frequency ranges on each link,
   node capabilities, etc.

   The computation entity could reside either on a PCE or the ingress
   node.

8.2.1.2.  Separated RSA (R+SA)

   In this case, routing computation and frequency slot assignment are
   performed by different entities.  The first entity computes the
   routes and provides them to the second entity; the second entity
   assigns the frequency slot.

   The first entity should get the connectivity topology to compute the
   proper routes; the second entity should get the available frequency
   ranges of the links and nodes' capabilities information to assign the
   spectrum.

8.2.1.3.   Routing and Distributed SA (R+DSA)

   In this case, one entity computes the route but the frequency slot
   assignment is performed hop-by-hop in a distributed way along the
   route.  The available central frequencies which meet the spectrum
   continuity constraint should be collected hop by hop along the route.
   This procedure can be implemented by the GMPLS signaling protocol.

8.3.  Routing / Topology dissemination

   In the case of combined RSA architecture, the computation entity
   needs to get the detailed network information, i.e. connectivity
   topology, node capabilities and available frequency ranges of the
   links.  Route computation is performed based on the connectivity



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   topology and node capabilities; spectrum assignment is performed
   based on the available frequency ranges of the links.  The
   computation entity may get the detailed network information by the
   GMPLS routing protocol.  Compared with [RFC6163], except wavelength-
   specific availability information, the connectivity topology and node
   capabilities are the same as WSON, which can be advertised by GMPLS
   routing protocol (refer to section 6.2 of [RFC6163].  This section
   analyses the necessary changes on link information brought by
   flexible grids.

8.3.1.  Available Frequency Ranges/slots of DWDM Links

   In the case of flexible grids, channel central frequencies span from
   193.1 THz towards both ends of the C band spectrum with 6.25 GHz
   granularity.  Different LSPs could make use of different slot widths
   on the same link.  Hence, the available frequency ranges should be
   advertised.

8.3.2.  Available Slot Width Ranges of DWDM Links

   The available slot width ranges needs to be advertised, in
   combination with the Available frequency ranges, in order to verify
   whether a LSP with a given slot width can be set up or not; this is
   is constrained by the available slot width ranges of the flexi-grid
   enabled ROADMs (the flexi-grid Frequency slot matrix).  Depending on
   the availability of the slot width ranges, it is possible to allocate
   more spectrum than strictly needed by the LSP.

8.3.3.  Tunable Optical Transmitters and Receivers

   The slot width of a LSP is determined by the transmitter and receiver
   that could be mapped to ADD/DROP interfaces in WSON.  Moreover their
   central frequency could be fixed or tunable, hence, both the slot
   width of an ADD/DROP interface and the available central frequencies
   should be advertised.

8.3.4.  Hierarchical Spectrum Management

   [Editors' note: the part on the hierarchy of the optical spectrum
   could be confusing, we can discuss it].  The total available spectrum
   on a fiber could be described as a resource that can be divided by a
   media device into a set of Frequency Slots.  In terms of managing
   spectrum, it is necessary to be able to speak about different
   granularities of managed spectrum.  For example, a part of the
   spectrum could be assigned to a third party to manage.  This need to
   partition creates the impression that spectrum is a hierarchy in view
   of Management and Control Plane.  The hierarchy is created within a
   management system, and it is an access right hierarchy only.  It is a



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   management hierarchy without any actual resource hierarchy within
   fiber.  The end of fiber is a link end and presents a fiber port
   which represents all of spectrum available on the fiber.  Each
   spectrum allocation appears as Link Channel Port (i.e., frequency
   slot port) within fiber.

8.3.5.  Information Model

   Fixed DM grids can also be described via suitable choices of slots in
   a flexible DWDM grid.  However, devices or applications that make use
   of the flexible grid may not be capable of supporting every possible
   slot width or central frequency position.  Following is the
   definition of information model, not intended to limit any IGP
   encoding implementation.  For example, information required for
   routing/path selection may be the set of available nominal central
   frequencies from which a frequency slot of the required width can be
   allocated.  A convenient encoding for this information (may be as a
   frequency slot or sets of contiguous slices) is further study in IGP
   encoding document.

   [Editor's note: to be discussed]

   <Available Spectrum in Fiber for frequency slot> ::=
       <Available Frequency Range-List>
       <Available Central Frequency Granularity >
       <Available Slot Width Granularity>
       <Minimal Slot Width>
       <Maximal Slot Width>

   <Available Frequency Range-List> ::=
       <Available Frequency Range >[< Available Frequency Range-List>]

   <Available Frequency Range >::=
     <Start Spectrum Position><End Spectrum Position> |
     <Sets of contiguous slices>

   <Available Central Frequency Granularity> ::= n x 6.25GHz,
     where n is positive integer, such as 6.25GHz, 12.5GHz, 25GHz, 50GHz
     or 100GHz

   <Available Slot Width Granularity> ::= m x 12.5GHz,
     where m is positive integer

   <Minimal Slot Width> ::= j x 12.5GHz,
     j is a positive integer

   <Maximal Slot Width> ::= k x 12.5GHz,
       k is a positive integer (k >= j)



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                    Figure 8. Routing Information model

8.4.  Signaling requirements

   Note on explicit label control

   Compared with [RFC6163], except identifying the resource (i.e., fixed
   wavelength for WSON and frequency resource for flexible grids), the
   other signaling requirements (e.g., unidirectional or bidirectional,
   with or without converters) are the same as WSON described in the
   section 6.1 of [RFC6163].  In the case of routing and distributed SA,
   GMPLS signaling can be used to allocate the frequency slot to a LSP.

   For R+DSA, the GMPLS signaling procedure is similar to the one
   described in section 4.1.3 of [RFC6163] except that the label set
   should specify the available nominal central frequencies that meet
   the slot width requirement of the LSP.

8.4.1.  Slot Width Requirement

   [Editors' note: the signaling requirements need to be discussed.
   This is just preliminary text].

   In order to allocate a proper frequency slot for a LSP, the signaling
   should specify its slot width requirement.  The intermediate nodes
   can collect the acceptable central frequencies that meet the slot
   width requirement hop by hop.  The tail-end node also needs to know
   the slot width of a LSP to assign the proper frequency resource.
   Hence, the slot width requirement should be specified in the
   signaling message when a LSP is being set up.  [Note: other methods
   may not need to collect availability]

8.4.2.  Frequency Slot Representation

   The frequency slot can be determined by the central frequency (n
   value) and slot width (m value).  Such parameters should be able to
   be specified by the signaling protocol.

8.4.3.  Relationship with MRN/MLN

8.4.3.1.  OCh Layer

8.4.3.2.  Media (frequency slot) layer


9.  Control Plane Procedures

   Resizing existing LSP(s) without deletion: refers to increase or



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   decrease of slot width value 'm' without changing the value of 'n'

   [Editor's note: Restoration / Resizing a single LSP without deletion
   as well as timing constraints.  As per ITU-T clarification on service
   affecting or non-service affecting (i.e., hitless) restoration, at
   present no hitless resizing protocol has been defined for OCh.
   Hitless resizing is defined for an ODU entity only.]


10.  Backwards (fixed-grid) compatibility, and WSON interworking

   o  SSON as evolution of WSON, same LSC, different Swcap?

   o  Potential problems with having the same swcap but the label format
      changes w.r.t. wson

   o  A new SwCap may need to be defined, LSC swcap already defined ISCD
      which can not be modified

   o  Role of LSP encoding type?

   o  Notion of hierarchy?  There is no notion of hierarchy between WSON
      and flexi-grid / SSON - only interop / interwork.

   Arguments for LSC switching capability

   [QW] A LSP for an optical signal which has a bandwidth of 50GHz
   passes through both a fixed grid network and a flexible grid network.
   We assume that no OEOs exist in the LSP, so both the fixed grid path
   and flexible grid path occupy 50GHz.  From the perspective of data
   plane, there is no change of the signal and no multiplexing when the
   fixed grid path interconnects with flexible grid path.  From this
   scenario we can conclude that both fixed grid network path and
   flexible grid network path belong to the same layer.  No notion of
   hierarchy exists between them.

   [QW] stitching LSP which is described in [RFC5150] can be applied in
   one layer.  LSP hierarchy allows more than one LSP to be mapped to an
   H-LSP, but in case of S-LSP, at most one LSP may be associated with
   an S-LSP.  This is similar to the scenario of interconnection between
   fixed grid LSP and flexible grid LSP.  Similar to an H-LSP, an S-LSP
   could be managed and advertised, although it is not required, as a TE
   link, either in the same TE domain as it was provisioned or a
   different one.  Path setup procedure of stitching LSP can be applied
   in the scenario of interconnection between fixed grid path and
   flexible grid path.





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           e2e LSP
           +++++++++++++++++++++++++++++++++++> (LSP1-2)

                     LSP segment (flexi-LSP)
                   ====================> (LSP-AB)
                       C --- E --- G
                      /|\    |   / |\
                     / | \   |  /  | \
           R1 ---- A \ |  \  | /   | / B --- R2
                      \|   \ |/    |/
                       D --- F --- H

      fixed grid --A-- flexi-grid    --B-- fixed grid


    Figure 9. LSP Stitching [RFC5150] and relationship with fixed-flexi


11.  Misc & Summary of open Issues [To be removed at later versions]

   o  Will reuse a lot of work / procedures / encodings defined in the
      context of WSON

   o  At data rates of GBps / TBps, encoding bandwidths with bytes per
      second unit and IEEE 32-bit floating may be problematic / non
      scalable.

   o  Bandwidth fields not relevant since there is not a 1-to-1 mapping
      between bps and Hz, since it depends on the modulation format,
      fec, either there is an agreement on assuming best / worst case
      modulations and spectral efficiency.

   o  Label I: "m" is inherent part of the label, part of the switching,
      allows encode the "lightpath" in a ERO using Explicit Label
      Control, Still maintains that feature a cross-connect is defined
      by the tuple (port-in, label-in, port-out, label-out), allows a
      kind-of "best effort LSP"

   o  Label II: "m" is not part of the label but of the TSPEC, neds to
      be in the TSPEC to decouple client signal traffic specification
      and management of the optical spectrum, having in both places is
      redundant and open to incoherences, extra error checking.

   o  Label III: both, It reflects both the concept of resource request
      allocation / reservation and the concept of being inherent part of
      the switching.





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12.  Security Considerations

   TBD


13.  Contributing Authors

      Qilei Wang
      ZTE
      Ruanjian Avenue, Nanjing, China
      wang.qilei@zte.com.cn

      Malcolm Betts
      ZTE
      malcolm.betts@zte.com.cn

      Sergio Belotti
      Alcatel Lucent
      Optics CTO
      Via Trento 30 20059 Vimercate (Milano) Italy
      +39 039 6863033
      sergio.belotti@alcatel-lucent.com

      Cyril Margaria
      Nokia Siemens Networks
      St Martin Strasse 76, Munich, 81541, Germany
      +49 89 5159 16934
      cyril.margaria@nsn.com

      Xian Zhang
      Huawei
      zhang.xian@huawei.com

      Yao Li
      ZTE
      Zijinghua Road, Nanjing, China
      li.yao3@zte.com.cn

      Fei Zhang
      ZTE
      Zijinghua Road, Nanjing, China
      zhang.fei3@zte.com.cn

      Lei Wang
      ZTE
      East Huayuan Road, Haidian district, Beijing, China
      wang.lei131@zte.com.cn




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      Guoying Zhang
      China Academy of Telecom Research
      No.52 Huayuan Bei Road, Beijing, China
      zhangguoying@ritt.cn

      Takehiro Tsuritani
      KDDI R&D Laboratories Inc.
      2-1-15 Ohara, Fujimino, Saitama, Japan
      tsuri@kddilabs.jp

      Lei Liu
      KDDI R&D Laboratories Inc.
      2-1-15 Ohara, Fujimino, Saitama, Japan
      le-liu@kddilabs.jp

      Eve Varma
      Alcatel-Lucent
      +1 732 239 7656
      eve.varma@alcatel-lucent.com

      Young Lee
      Huawei

      Jianrui Han
      Huawei

      Sharfuddin Syed
      Infinera

      Rajan Rao
      Infinera

      Marco Sosa
      Infinera

      Biao Lu
      Infinera

      Abinder Dhillon
      Infinera

      Felipe Jimenez Arribas
      Telefonica I+D

      Andrew G. Malis
      Verizon





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      Adrian Farrel
      Old Dog Consulting

      Daniel King
      Old Dog Consulting


14.  Acknowledgments

   The authors would like to thank Pete Anslow for his insights and
   clarifications.


15.  References

15.1.  Normative References

   [G.709]    International Telecomunications Union, "ITU-T
              Recommendation G.709: Interfaces for the Optical Transport
              Network (OTN).", March 2009.

   [G.805]    International Telecomunications Union, "ITU-T
              Recommendation G.805: Generic functional architecture of
              transport networks.", March 2000.

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

   [RFC3945]  Mannie, E., "Generalized Multi-Protocol Label Switching
              (GMPLS) Architecture", RFC 3945, October 2004.

   [RFC4206]  Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
              Hierarchy with Generalized Multi-Protocol Label Switching
              (GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.

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

   [RFC6163]  Lee, Y., Bernstein, G., and W. Imajuku, "Framework for
              GMPLS and Path Computation Element (PCE) Control of
              Wavelength Switched Optical Networks (WSONs)", RFC 6163,
              April 2011.







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15.2.  Informative References

   [G.694.1]  International Telecomunications Union, "ITU-T
              Recommendation G.694.1, Spectral grids for WDM
              applications: DWDM frequency grid, draft v1.6 2011/12",
              2011.

   [G.872]    International Telecomunications Union, "ITU-T
              Recommendation G.872, Architecture of optical transport
              networks, draft v0.12 2012/03 (for discussion)", 2012.

   [WD12R2]   International Telecomunications Union, WD12R2, Q12-SG15,
              ZTE, Ciena WP3, "Proposed media layer terminology for
              G.872", 05 2012.


Authors' Addresses

   Oscar Gonzalez de Dios (editor)
   Telefonica I+D
   Don Ramon de la Cruz 82-84
   Madrid,   28045
   Spain

   Phone: +34913128832
   Email: ogondio@tid.es


   Ramon Casellas (editor)
   CTTC
   Av. Carl Friedrich Gauss n.7
   Castelldefels,   Barcelona
   Spain

   Phone: +34 93 645 29 00
   Email: ramon.casellas@cttc.es


   Fatai Zhang
   Huawei
   Huawei Base, Bantian, Longgang District
   Shenzhen,   518129
   China

   Phone: +86-755-28972912
   Email: zhangfatai@huawei.com





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   Xihua Fu
   ZTE
   Ruanjian Avenue
   Nanjing,
   China

   Email: fu.xihua@zte.com.cn


   Daniele Ceccarelli
   Ericsson
   Via Calda 5
   Genova,
   Italy

   Phone: +39 010 600 2512
   Email: daniele.ceccarelli@ericsson.com


   Iftekhar Hussain
   Infinera
   140 Caspian Ct.
   Sunnyvale,   94089
   USA

   Phone: 408-572-5233
   Email: ihussain@infinera.com
























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