CCAMP Working Group                             O. Gonzalez de Dios, Ed.
Internet-Draft                                            Telefonica I+D
Intended status: Informational                          R. Casellas, Ed.
Expires: February 26, March 2, 2016                                              CTTC
                                                         August 25, 30, 2015

 Framework and Requirements for GMPLS-based control of Flexi-grid DWDM


   To allow efficient allocation of optical spectral bandwidth for high
   bit-rate systems, the International Telecommunication Union
   Telecommunication Standardization Sector (ITU-T) has extended its
   Recommendations G.694.1 and G.872 to include a new dense wavelength
   division multiplexing (DWDM) grid by defining a set of nominal
   central frequencies, channel spacings and the concept of "frequency
   slot".  In such an environment, a data plane connection is switched
   based on allocated, variable-sized frequency ranges within the
   optical spectrum creating what is known as a flexible grid (flexi-

   Given the specific characteristics of flexi-grid optical networks and
   their associated technology, this document defines a framework and
   the associated control plane requirements for the application of the
   existing GMPLS architecture and control plane protocols to the
   control of flexi-grid DWDM networks.  The actual extensions to the
   GMPLS protocols will be defined in companion documents.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
     2.2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Overview of Flexi-grid Networks . . . . . . . . . . . . . . .   5
     3.1.  Flexi-grid in the Context of OTN  . . . . . . . . . . . .   5
     3.2.  Flexi-grid Terminology  . . . . . . . . . . . . . . . . .   6
       3.2.1.  Frequency Slots . . . . . . . . . . . . . . . . . . .   6
       3.2.2.  Media Layer Elements  . . . . . . . . . . . . . . . .   8
       3.2.3.  Media Channels  . . . . . . . . . . . . . . . . . . .   8
       3.2.4.  Optical Tributary Signals . . . . . . . . . . . . . .   9
       3.2.5.  Composite Media Channels  . . . . . . . . . . . . . .   9
     3.3.  Hierarchy in the Media Layer  . . . . . . . . . . . . . .  10
     3.4.  Flexi-grid Layered Network Model  . . . . . . . . . . . .  10
       3.4.1.  DWDM Flexi-grid Enabled Network Element Models  . . .  12
   4.  GMPLS Applicability . . . . . . . . . . . . . . . . . . . . .  12
     4.1.  General Considerations  . . . . . . . . . . . . . . . . .  12
     4.2.  Consideration of TE Links . . . . . . . . . . . . . . . .  13
     4.3.  Consideration of LSPs in Flexi-grid . . . . . . . . . . .  15
     4.4.  Control Plane Modeling of Network Elements  . . . . . . .  20
     4.5.  Media Layer Resource Allocation Considerations  . . . . .  20
     4.6.  Neighbor Discovery and Link Property Correlation  . . . .  24
     4.7.  Path Computation / Routing and Spectrum Assignment (RSA)   25
       4.7.1.  Architectural Approaches to RSA . . . . . . . . . . .  25
     4.8.  Routing and Topology Dissemination  . . . . . . . . . . .  26
       4.8.1.  Available Frequency Ranges/Slots of DWDM Links  . . .  27
       4.8.2.  Available Slot Width Ranges of DWDM Links . . . . . .  27
       4.8.3.  Spectrum Management . . . . . . . . . . . . . . . . .  27
       4.8.4.  Information Model . . . . . . . . . . . . . . . . . .  28
   5.  Control Plane Requirements  . . . . . . . . . . . . . . . . .  29
     5.1.  Support for Media Channels  . . . . . . . . . . . . . . .  29
       5.1.1.  Signaling . . . . . . . . . . . . . . . . . . . . . .  30
       5.1.2.  Routing . . . . . . . . . . . . . . . . . . . . . . .  30
     5.2.  Support for Media Channel Resizing  . . . . . . . . . . .  31
     5.3.  Support for Logical Associations of Multiple Media
           Channels  . . . . . . . . . . . . . . . . . . . . . . . .  31
     5.4.  Support for Composite Media Channels  . . . . . . . . . .  31
     5.5.  Support for Neighbor Discovery and Link Property
           Correlation . . . . . . . . . . . . . . . . . . . . . . .  32
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  32
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  32
   8.  Manageability Considerations  . . . . . . . . . . . . . . . .  33
   9.  Authors . . . . . . . . . . . . . . . . . . . . . . . . . . .  34
   10. Contributing Authors  . . . . . . . . . . . . . . . . . . . .  34
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  37
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  37
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  37
     12.2.  Informative References . . . . . . . . . . . . . . . . .  38
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  40

1.  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 spacing 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 and its slot width which, as per
   [G.694.1], is constrained to be a multiple of a given slot width

   Compared to a traditional fixed grid network, which uses fixed size
   optical spectrum frequency ranges or frequency slots with typical
   channel separations of 50 GHz, a flexible grid network can select its
   media channels with a more flexible choice of slot widths, allocating
   as much optical spectrum as required.

   From a networking perspective, a flexible grid network is assumed to
   be a layered network [G.872][G.800] in which the media layer is the
   server layer and the optical 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, a media channel can
   transport more than one Optical Tributary Signals (OTSi), as defined
   later in this document.

   A Wavelength Switched Optical Network (WSON), addressed in [RFC6163],
   is a term commonly used to refer to the application/deployment of a
   GMPLS-based control plane for the control (provisioning/recovery,
   etc.) of a fixed grid wavelength division multiplexing (WDM) network
   in which media (spectrum) and signal are jointly considered.

   This document defines the framework for a GMPLS-based control of
   flexi-grid enabled dense wavelength division multiplexing (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.

2.  Terminology

   Further terminology specific to flexi-grid networks can be found in
   Section 3.2.

2.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

   While [RFC2119] describes interpretations of these key words in terms
   of protocol specifications and implementations, they are used in this
   document to describe design requirements for protocol extensions.

2.2.  Abbreviations

   FS: Frequency Slot

   FSC: Fiber-Switch Capable

   LSR: Label Switching Router

   NCF: Nominal Central Frequency

   OCh: Optical Channel

   OCh-P: Optical Channel Payload

   OTN: Optical Transport Network
   OTSi: Optical Tributary Signal

   OTSiG: OTSi Group is a set of OTSi

   OCC: Optical Channel Carrier

   PCE: Path Computation Element

   ROADM: Reconfigurable Optical Add-Drop Multiplexer

   SSON: Spectrum-Switched Optical Network

   SWG: Slot Width Granularity

3.  Overview of Flexi-grid Networks

3.1.  Flexi-grid in the Context of OTN

   [G.872] describes, from a network level, the functional architecture
   of an OTN.  It is decomposed into independent layer networks with
   client/layer relationships among them.  A simplified view of the OTN
   layers is shown in Figure 1.

   | Digital Layer  |
   | Signal Layer   |
   |  Media Layer   |

                      Figure 1: Generic OTN Overview

   In the OTN layering context, the media layer is the server layer of
   the optical signal layer.  The optical signal is guided to its
   destination by the media layer by means of a network media channel.
   In the media layer, switching is based on a frequency slot.

   In this scope, this document uses the term flexi-grid enabled DWDM
   network to refer to a network in which switching is based on
   frequency slots defined using the flexible grid, and covers mainly
   the Media Layer as well as the required adaptations from the Signal
   layer.  The present document is thus focused on the control and
   management of the media layer.

3.2.  Flexi-grid Terminology

   This section presents the definition of the terms used in flexi-grid
   networks.  More detail about these terms can be found in the ITU-T
   Recommendations [G.694.1], [G.872]), [G.870], [G.8080], and

   Where appropriate, this documents also uses terminology and
   lexicography from [RFC4397].

3.2.1.  Frequency Slots

   This subsection is focused on the frequency slot and related terms.

   o  Frequency Slot [G.694.1]: The frequency range allocated to a slot
      within the flexible grid and unavailable to other slots.  A
      frequency slot is defined by its nominal central frequency and its
      slot width.

   o  Nominal Central Frequency: Each of the allowed frequencies as per
      the definition of flexible DWDM grid in [G.694.1].  The set of
      nominal central frequencies can be built using the following

   f = 193.1 THz + n x 0.00625 THz

      where 193.1 THz is ITU-T "anchor frequency" for transmission over
      the C band, and 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

     Figure 2: Anchor Frequency and Set of Nominal Central Frequencies

   o  Nominal Central Frequency Granularity: This is the spacing between
      allowed nominal central frequencies and it is set to 6.25 GHz

   o  Slot Width Granularity (SWG): 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.

          Frequency Slot 1     Frequency Slot 2
           -------------     -------------------
           |           |     |                 |
       -3 -2 -1  0  1  2  3  4  5  6  7  8  9 10 11
           -------------     -------------------
                 ^                    ^
       Slot NCF = 193.1THz     Slot NCF = 193.14375 THz
       Slot width = 25 GHz     Slot width = 37.5 GHz
         n=0, m=2                n=7, m=3

                     Figure 3: Example Frequency Slots

      *  The symbol '+' represents the allowed nominal central

      *  The '--' represents the nominal central frequency granularity
         in units of 6.25 GHz

      *  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 to

   o  Effective Frequency Slot [G.870]: The effective frequency slot of
      a media channel is that part of the frequency slots of the filters
      along the media channel that is common to all of the filters'
      frequency slots.  Note that both the Frequency Slot and Effective
      Frequency Slot are local terms.

   o  Figure 4 shows the effect of combining two filters along a
      channel.  The combination of frequency slot 1 and frequency slot 2
      applied to the media channel is effective frequency slot shown.

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

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

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

                    Figure 4: Effective Frequency Slot

3.2.2.  Media Layer Elements

   o  Media Element: A media element directs an optical signal or
      affects the properties of an optical signal.  It does not modify
      the properties of the information that has been modulated to
      produce the optical signal [G.870].  Examples of media elements
      include fibers, amplifiers, filters, and switching matrices.

   o  Media Channel Matrixes: The media channel matrix provides flexible
      connectivity for the media channels.  That is, it represents a
      point of flexibility where relationships between the media ports
      at the edge of a media channel matrix may be created and broken.
      The relationship between these ports is called a matrix channel.
      (Network) Media Channels are switched in a Media Channel Matrix.

3.2.3.  Media Channels

   This section defines concepts such as (Network) Media Channel; the
   mapping to GMPLS constructs (i.e., LSP) is detailed in Section 4.

   o  Media Channel: A media association that represents both the
      topology (i.e., path through the media) and the resource
      (frequency slot) that it occupies.  As a topological construct, it
      represents a frequency slot (an effective frequency slot)
      supported by a concatenation of media elements (fibers,
      amplifiers, filters, switching matrices...).  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

   o  Network Media Channel: [G.870] defines the Network Media Channel
      as a media channel that transports a single OTSi, defined next.

3.2.4.  Optical Tributary Signals

   o  Optical Tributary Signal (OTSi) [G.959.1-2013]: The optical signal
      that is placed within a network media channel for transport across
      the optical network.  This may consist of a single modulated
      optical carrier or a group of modulated optical carriers or
      subcarriers.  To provide a connection between the OTSi source and
      the OTSi sink the optical signal must be assigned to a network
      media channel.

   o  OTSi Group (OTSiG): The set of OTSi that are carried by a group of
      network media channels.  Each OTSi is carried by one network media
      channel.  From a management perspective it SHOULD be possible to
      manage both the OTSiG and a group of Network Media Channels as
      single entities.

3.2.5.  Composite Media Channels

   o  It is possible to construct an end-to-end media channel as a
      composite of more than one network media channels.  A composite
      media channel carries a group of OTSi (i.e., OTSiG).  Each OTSi is
      carried by one network media channel.  This group of OTSi are
      carried over a single fibre.

   o  In this case, the effective frequency slots may be contiguous
      (i.e., there is no spectrum between them that can be used for
      other media channels) or non-contiguous.

   o  It is not currently envisaged that such composite media channels
      may be constructed from slots carried on different fibers whether
      those fibers traverse the same hop-by-hop path through the network
      or not.

   o  Furthermore, it is not considered likely that a media channel may
      be constructed from a different variation of slot composition on
      each hop.  That is, the slot composition (i.e., the group of OTSi
      carried by the composite media channel) must be the same from one
      end to the other of the media channel even if the specific slot
      for each OTSi and the spacing among slots may vary hop by hop.

   o  How the signal is carried across such groups of network media
      channels is out of scope for this document.

3.3.  Hierarchy in the Media Layer

   In summary, the concept of frequency slot is a logical abstraction
   that represents a frequency range, while the media layer represents
   the underlying media support.  Media Channels are media associations,
   characterized by their (effective) frequency slot, respectively; and
   media channels are switched in media channel matrixes.  From the
   control and management perspective, a media channel can be logically
   split into network media channels.

   In Figure 5, a media channel has been configured and dimensioned to
   support two network media channels, each of them carrying one OTSi.

                             Media Channel Frequency Slot
     |                                                              |
     |       Frequency Slot                  Frequency Slot         |
     |   +-----------X-----------+       +----------X-----------+   |
     |   |         OTSi          |       |         OTSi         |   |
     |   |           o           |       |          o           |   |
     |   |           |           |       |          |           |   |
    -4  -3  -2  -1   0   1   2   3   4   5   6   7  8   9  10  11  12

          <- Network Media Channel->     <- Network Media Channel->

      <------------------------ Media Channel ----------------------->

         X - Frequency Slot Central Frequency

         o - Signal Central Frequency

      Figure 5: Example of Media Channel / Network Media Channels and
                        Associated Frequency Slots

3.4.  Flexi-grid Layered Network Model

   In the OTN layered network, the network media channel transports a
   single OTSi (see Figure 6)
     |                            OTSi                                 |
     O - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O
     |                                                                 |
     | Channel Port         Network Media Channel         Channel Port |
     O - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O
     |                                                                 |
   +--------+                 +-----------+                   +--------+
   |  \ (1) |                 |    (1)    |                   | (1)  / |
   |   \----|-----------------|-----------|-------------------|-----/  |
   +--------+ Link Channel    +-----------+  Link Channel     +--------+
     Media Channel            Media Channel                Media Channel
     Matrix                   Matrix                       Matrix

   The symbol (1) indicates a Matrix Channel

                Figure 6: Simplified Layered Network Model

   Note that a particular example of OTSi is the OCh-P.  Figure 7 shows
   this specific example as defined in G.805 [G.805].

    OCh AP                     Trail (OCh)                    OCh AP
     O- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O
     |                                                              |
    --- OCh-P                                                OCh-P ---
    \ / source                                               sink  \ /
     +                                                              +
     | OCh-P               OCh-P Network Connection           OCh-P |
     O TCP - - - - - - - - - - - - - - - - - - - - - - - - - - -TCP O
     |                                                              |
     |Channel Port          Network Media Channel      Channel Port |
     O - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  O
     |                                                              |
   +--------+                 +-----------+                 +---------+
   |  \ (1) |  OCh-P LC       |    (1)    |  OCh-P LC       |  (1)  / |
   |   \----|-----------------|-----------|-----------------|------/  |
   +--------+ Link Channel    +-----------+  Link Channel   +---------+
   Media Channel              Media Channel                Media Channel
     Matrix                     Matrix                        Matrix

    The symbol (1) indicates a Matrix Channel

            Figure 7: Layered Network Model According to G.805

3.4.1.  DWDM Flexi-grid Enabled Network Element Models

   A flexible grid network is constructed from subsystems that include
   WDM links, tunable transmitters, and receivers, (i.e, media elements
   including media layer switching elements that are media matrices) as
   well as electro-optical network elements.  This is just the same as
   in a fixed grid network except that each element has flexible grid

   As stated in Clause 7 of [G.694.1] the flexible DWDM grid 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 might 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).

4.  GMPLS Applicability

   The goal of this section is to provide an insight into the
   application of GMPLS as a control mechanism in flexi-grid networks.
   Specific control plane requirements for the support of flexi-grid
   networks are covered in Section 5.  This framework is aimed at
   controlling the media layer within the OTN hierarchy, and controlling
   the required adaptations of the signal layer.  This document also
   defines the term Spectrum-Switched Optical Network (SSON) to refer to
   a Flexi-grid enabled DWDM network that is controlled by a GMPLS/PCE
   control plane.

   This section provides a mapping of the ITU-T G.872 architectural
   aspects to GMPLS/Control plane terms, and considers the relationship
   between the architectural concept/construct of media channel and its
   control plane representations (e.g., as a TE link, as defined in

4.1.  General Considerations

   The GMPLS control of the media layer deals with the establishment of
   media channels that are switched in media channel matrices.  GMPLS
   labels are used to locally represent the media channel and its
   associated frequency slot.  Network media channels are considered a
   particular case of media channels when the end points are
   transceivers (that is, source and destination of an OTSi).

4.2.  Consideration of TE Links

   From a theoretical / abstract point of view, a fiber can be modeled
   as having a frequency slot that ranges from minus infinity to plus
   infinity.  This representation helps understand the relationship
   between frequency slots and ranges.

   The frequency slot is a local concept that applies within a component
   or element.  When applied to a media channel, we are referring to its
   effective frequency slot as defined in [G.872].

   The association sequence of the three components (i.e., a filter, a
   fiber, and a filter), is a media channel in its most basic form.
   From the control plane perspective this may modeled as a (physical)
   TE-link with a contiguous optical spectrum.  This can be represented
   by saying that the portion of spectrum available at time t0 depends
   on which filters are placed at the ends of the fiber and how they
   have been configured.  Once filters are placed we have a one-hop
   media channel.  In practical terms, associating a fiber with the
   terminating filters determines the usable optical spectrum.

   ---------------+                             +-----------------+
                  |                             |
         +--------+                             +--------+
         |        |                             |        |  +---------
     ---o|        ===============================        o--|
         |        |             Fiber           |        |  | --\  /--
     ---o|        |                             |        o--|    \/
         |        |                             |        |  |    /\
     ---o|        ===============================        o--| --/  \--
         | Filter |                             | Filter |  |
         |        |                             |        |  +---------
         +--------+                             +--------+
                  |                             |
               |------- Basic Media Channel  ---------|
   ---------------+                             +-----------------+

       --------+                                      +--------
        LSR    |               TE link                |  LSR
      +--------+                                      +--------

                Figure 8: (Basic) Media Channel and TE Link

   Additionally, when a cross-connect for a specific frequency slot is
   considered, the resulting media support of joining basic media
   channels is still a media channel, i.e., a longer association
   sequence of media elements and its effective frequency slot.  In
   other words, It is possible to "concatenate" several media channels
   (e.g., patch on intermediate nodes) to create a single media channel.

   The architectural construct resulting of the association sequence of
   basic media channels and media layer matrix cross-connects can be
   represented as (i.e., corresponds to) a Label Switched Path (LSP)
   from a control plane perspective.

   ----------+       +------------------------------+       +---------
             |       |                              |       |
      +------+       +------+                +------+       +------+
      |      |       |      |  +----------+  |      |       |      |
   --o|      =========      o--|          |--o      =========      o--
      |      | Fiber |      |  | --\  /-- |  |      | Fiber |      |
   --o|      |       |      o--|    \/    |--o      |       |      o--
      |      |       |      |  |    /\    |  |      |       |      |
   --o|      =========      o--***********|--o      =========      o--
      |Filter|       |Filter|  |          |  |Filter|       |Filter|
      |      |       |      |                |      |       |      |
      +------+       +------+                +------+       +------+
             |       |                              |       |
         <- Basic Media ->    <- Matrix ->       <- Basic Media->
             |Channel|           Channel            |Channel|
   ----------+       +------------------------------+       +---------

         <--------------------  Media Channel  ---------------->

   ------+                  +---------------+                  +------
         |------------------|               |------------------|
    LSR  |       TE link    |      LSR      |   TE link        |  LSR
         |------------------|               |------------------|
   ------+                  +---------------+                  +------

                     Figure 9: Extended Media Channel

   Furthermore, if appropriate, the media channel can also be
   represented as a TE link or Forwarding Adjacency (FA) [RFC4206],
   augmenting the control plane network model.

   ----------+       +------------------------------+       +---------
             |       |                              |       |
      +------+       +------+                +------+       +------+
      |      |       |      |  +----------+  |      |       |      |
   --o|      =========      o--|          |--o      =========      o--
      |      | Fiber |      |  | --\  /-- |  |      | Fiber |      |
   --o|      |       |      o--|    \/    |--o      |       |      o--
      |      |       |      |  |    /\    |  |      |       |      |
   --o|      =========      o--***********|--o      =========      o--
      |Filter|       |Filter|  |          |  |Filter|       |Filter|
      |      |       |      |                |      |       |      |
      +------+       +------+                +------+       +------+
             |       |                              |       |
   ----------+       +------------------------------+       +---------

          <------------------------  Media Channel  ----------->

   ------+                                                      +-----
    LSR  |                               TE link                | LSR
   ------+                                                      +-----

             Figure 10: Extended Media Channel / TE Link / FA

4.3.  Consideration of LSPs in Flexi-grid

   The flexi-grid LSP is a control plane representation of a media
   channel.  Since network media channels are media channels, an LSP may
   also be the control plane representation of a network media channel
   (without considering the adaptation functions).  From a control plane
   perspective, the main difference (regardless of the actual effective
   frequency slot which may be dimensioned arbitrarily) is that the LSP
   that represents a network media channel also includes the endpoints
   (transceivers), including the cross-connects at the ingress and
   egress nodes.  The ports towards the client can still be represented
   as interfaces from the control plane perspective.

   Figure 11 shows an LSP routed between 3 nodes.  The LSP is terminated
   before the optical matrix of the ingress and egress nodes and can
   represent a media channel.  This case does not (and cannot) represent
   a network media channel because it does not include (and cannot
   include) the transceivers.

   ---------+       +--------------------------------+       +--------
            |       |                                |       |
     +------+       +------+                  +------+       +------+
     |      |       |      |   +----------+   |      |       |      |
   -o|      =========      o---|          |---o      =========      o-
     |      | Fiber |      |   | --\  /-- |   |      | Fiber |      |
     |      |       |      |   |    /\    |   |      |       |      |
   -o|      =========      o---***********|---o      =========      o-
     |Filter|       |Filter|   |          |   |Filter|       |Filter|
     |      |       |      |                  |      |       |      |
     +------+       +------+                  +------+       +------+
            |       |                                |       |
   ---------+       +--------------------------------+       +--------

          >>>>>>>>>>>>>>>>>>>>>>>>>>>> LSP >>>>>>>>>>>>>>>>>>>>>>>>
     -----+                  +---------------+                +-----
          |------------------|               |----------------|
     LSR  |       TE link    |     LSR       |      TE link   | LSR
          |------------------|               |----------------|
     -----+                  +---------------+                +-----

   Figure 11: Flex-grid LSP Representing a Media Channel that Starts at
    the Filter of the Outgoing Interface of the Ingress LSR and ends at
          the Filter of the Incoming Interface of the Egress LSR

   In Figure 12 a Network Media Channel is represented as terminated at
   the network side of the transceivers.  This is commonly named an
   OTSi-trail connection.

   |--------------------- Network Media Channel ----------------------|

        +----------------------+           +----------------------+
        |                                  |                      |
        +------+        +------+           +------+        +------+
        |      | +----+ |      |           |      | +----+ |      |OTSi
    OTSi|      o-|    |-o      |  +-----+  |      o-|    |-o      |sink
    src |      | |    | |      ===+-+ +-+==|      | |    | |      O---|R
        |      | |\  /| |         | | | |  |      | |\  /| |      |
        |      o-| \/ |-o      ===| | | |==|      o-| \/ |-o      |
        |      | | /\ | |      |  +-+ +-+  |      | | /\ | |      |
        |      o-|/  \|-o      |  |  \/ |  |      o-|/  \|-o      |
        |Filter| |    | |Filter|  |  /\ |  |Filter| |    | |Filter|
        +------+ |    | +------+  +-----+  +------+ |    | +------+
        |        |    |        |           |        |    |        |
        +----------------------+           +----------------------+

         +-----+                   +--------+                +-----+
    o--- |     |-------------------|        |----------------|     |---o
         | LSR |       TE link     |  LSR   |   TE link      | LSR |
         |     |-------------------|        |----------------|     |
         +-----+                   +--------+                +-----+

     Figure 12: LSP Representing a Network Media Channel (OTSi Trail)

   In a third case, a Network Media Channel is terminated on the Filter
   ports of the Ingress and Egress nodes.  This is named in G.872 as
   OTSi Network Connection.  As can be seen from the figures, there is
   no difference from a GMPLS modelling perspective between these cases,
   but they are shown as distinct examples to highlight the differences
   in the data plane.

     |---------------------  Network Media Channel --------------------|

     +------------------------+               +------------------------+
     +------+        +------+                 +------+          +------+
     |      | +----+ |      |                 |      | +----+ |      |
     |      o-|    |-o      |    +------+     |      o-|    |-o      |
     |      | |    | |      =====+-+  +-+=====|      | |    | |      |
     |      | |\  /| |           | |  | |     |      | |\  /| |      |
     |      o-| \/ |-o      =====| |  | |=====|      o-| \/ |-o      |
     |      | | /\ | |      |    +-+  +-+     |      | | /\ | |      |
     |      o-|/  \|-o      |    |  \/  |     |      o-|/  \|-o      |
     |Filter| |    | |Filter|    |  /\  |     |Filter| |    | |Filter|
     +------+ |    | +------+    +------+     +------+ |    | +------+
     |        |    |        |                 |        |    |        |
     +----------------------+                 +----------------------+

      +-----+                    +--------+                   +-----+
   o--|     |--------------------|        |-------------------|     |--o
      | LSR |       TE link      |  LSR   |      TE link      | LSR |
      |     |--------------------|        |-------------------|     |
      +-----+                    +--------+                   +-----+

     Figure 13: LSP Representing a Network Media Channel (OTSi Network

   Applying the notion of hierarchy at the media layer, by using the LSP
   as an FA (i.e., by using hierarchical LSPs), the media channel
   created can support multiple (sub-)media channels.

   +--------------+                      +--------------+
   | Media Channel|           TE         | Media Channel|  Virtual TE
   |              |          link        |              |    link
   |    Matrix    |o- - - - - - - - - - o|    Matrix    |o- - - - - -
   +--------------+                      +--------------+
                  |     +---------+      |
                  |     |  Media  |      |
                  |o----| Channel |-----o|
                        |         |
                        | Matrix  |

                Figure 14: Topology View with TE Link / FA

   Note that there is only one media layer switch matrix (one
   implementation is a FlexGrid ROADM) in SSON, while a signal layer LSP
   (Network Media Channel) is established mainly for the purpose of
   management and control of individual optical signals.  Signal layer
   LSPs with the same attributes (such as source and destination) can be
   grouped into one media-layer LSP (media channel): this has advantages
   in spectral efficiency (reduce guard band between adjacent OChs in
   one FSC channel) and LSP management.  However, assuming some network
   elements perform signal layer switching in an SSON, there must be
   enough guard band between adjacent OTSis in any media channel to
   compensate for the filter concatenation effects and other effects
   caused by signal layer switching elements.  In such a situation, the
   separation of the signal layer from the media layer does not bring
   any benefit in spectral efficiency or in other aspects, but makes the
   network switch and control more complex.  If two OTSis must be
   switched to different ports, it is better to carry them by diferent
   FSC channels, and the media layer switch is enough in this scenario.

   As discussed in Section 3.2.5, a media channel may be constructed
   from a compsite of network media channels.  This may be achieved in
   two ways using LSPs.  These mechanisms may be compared to the
   techniques used in GMPLS to support inverse multiplexing in Time
   Division Multiplexing (TDM) networks and in OTN [RFC4606], [RFC6344],
   and [RFC7139].

   o  In the first case, a single LSP may be established in the control
      plane.  The signaling messages include information for all of the
      component network media channels that make up the composite media

   o  In the second case, each component network media channel is
      established using a separate control plane LSP, and these LSPs are
      associated within the control plane so that the end points may see
      them as a single media channel.

4.4.  Control Plane Modeling of Network Elements

   Optical transmitters and receivers may have different tunability
   constraints, and media channel matrixes may have switching
   restrictions.  Additionally, a key feature of their implementation is
   their highly asymmetric switching capability which is described in
   detail in [RFC6163].  Media matrices include line side ports that are
   connected to DWDM links, and tributary side input/output ports that
   can be connected to transmitters/receivers.

   A set of common constraints can be defined:

   o  Slot widths: The minimum and maximum slot width.

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

   o  Available frequency ranges: The set or union of frequency ranges
      that have not been allocated (i.e., are available).  The relative
      grouping and distribution of available frequency ranges in a fiber
      is usually referred to as "fragmentation".

   o  Available slot width ranges: The set or union of slot width ranges
      supported by media matrices.  It includes the following

      *  Slot width threshold: The minimum and maximum Slot Width
         supported by the media matrix.  For example, the slot width
         could be from 50GHz to 200GHz.

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

4.5.  Media Layer Resource Allocation Considerations

   A media channel has an associated effective frequency slot.  From the
   perspective of network control and management, this effective slot is
   seen as the "usable" end-to-end frequency slot.  The establishment of
   an LSP is related to the establishment of the media channel and the
   configuration of the effective frequency slot.

   A "service request" is characterized (at a minimum) by its required
   effective frequency slot width.  This does not preclude that the request may
   add additional constraints such as also imposing the nominal central
   frequency.  A given effective frequency slot may be requested for the
   media channel in the control plane LSP setup messages, and a specific
   frequency slot can be requested on any specific hop of the LSP setup.
   Regardless of the actual encoding, the LSP setup message specifies a
   minimum effective frequency slot width that needs to be fulfilled in
   order to successful establish the requsted LSP.

   An effective frequency slot must equally be described in terms of a
   central nominal frequency and its slot width (in terms of usable
   spectrum of the effective frequency slot).  That is, it must be
   possible to determine the end-to-end values of the n and m
   parameters.  We refer to this by saying that the "effective frequency
   slot of the media channel/LSP must be valid".

   In GMPLS the requested effective frequency slot is represented to the
   TSpec present in the RSVP-TE Path message, and the effective
   frequency slot is mapped to the FlowSpec carried in the RSVP-TE Resv

   In GMPLS-controlled systems, the switched element corresponds to the
   'label'.  In flexi-grid where the switched element is a frequency
   slot, the label represents a frequency slot.  In consequence, the
   label in flexi-grid conveys the necessary information to obtain the
   frequency slot characteristics (i.e, central frequency and slot
   width: the n and m parameters).  The frequency slot is locally
   identified by the label.

   The local frequency slot may change at each hop, given hardware
   constraints and capabilities (e.g., a given node might not support
   the finest granularity).  This means that the values of n and m may
   change at each hop.  As long as a given downstream node allocates
   enough optical spectrum, m can be different along the path.  This
   covers the issue where media matrices can have different slot width
   granularities.  Such variations in the local value of m will appear
   in the allocated label that encodes the frequency slot as well as the
   in the FlowSpec that describes the flow.

   Different operational modes can be considered.  For Routing and
   Spectrum Assignment (RSA) with explicit label control, and for
   Routing and Distributed Spectrum Assignment (R+DSA), the GMPLS
   signaling procedures are similar to those described in section 4.1.3
   of [RFC6163] for Routing and Wavelength Assignment (RWA) and for
   Routing and Distributed Wavelength Assignment (R+DWA).  The main
   difference is that the label set specifies the available nominal
   central frequencies that meet the slot width requirements of the LSP.

   The intermediate nodes use the control plane to 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
   an LSP to assign the proper frequency resource.  Except for
   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 for WSON as described in section 6.1 of

   Regarding how a GMPLS control plane can assign n and m hop-by-hop
   along the path of an LSP, different cases can apply:

   a.  n and m can both change.  It is the effective frequency slot that
       matters, it needs to remain valid along the path.

   b.  m can change, but n needs to remain the same along the path.
       This ensures that the nominal central frequency stays the same,
       but the width of the slot can vary along the path.  Again, the
       important thing is that the effective frequency slot remains
       valid and satisfies the requested parameters along the whole path
       of the LSP.

   c.  n and m need to be unchanging along the path.  This ensures that
       the frequency slot is well-known end-to-end, and is a simple way
       to ensure that the effective frequency slot remains valid for the
       whole LSP.

   d.  n can change, but m needs to remain the same along the path.
       This ensures that the effective frequency slot remains valid, but
       allows the frequency slot to be moved within the spectrum from
       hop to hop.

   The selection of a path that ensures n and m continuity can be
   delegated to a dedicated entity such as a Path Computation Element
   (PCE).  Any constraint (including frequency slot and width
   granularities) can be taken into account during path computation.
   Alternatively, A PCE can compute a path leaving the actual frequency
   slot assignment to be done, for example, with a distributed
   (signaling) procedure:

   o  Each downstream node ensures that m is >= requested_m.

   o  A downstream node cannot foresee what an upstream node will
      allocate.  A way to ensure that the effective frequency slot is
      valid along the length of the LSP is to ensure that the same value
      of n is allocated at each hop.  By forcing the same value of n we
      avoid cases where the effective frequency slot of the media
      channel is invalid (that is, the resulting frequency slot cannot
      be described by its n and m parameters).

   o  This may be too restrictive, since a node (or even a centralized/
      combined RSA entity) may be able to ensure that the resulting end-
      to-end effective frequency slot is valid even if n varies locally.
      That means, the effective frequency slot that characterizes the
      media channel from end to end is consistent and is determined by
      its n and m values, but that the effective frequency slot and
      those values are logical (i.e., do not map direct to the
      physically assigned spectrum) in the sense that they are the
      result of the intersection of locally-assigned frequency slots
      applicable at local components (such as filters) each of which may
      have assigned different frequency slots.

   For Figure 15 the effective slot is made valid by ensuring that the
   minimum m is greater than the requested m.  The effective slot
   (intersection) is the lowest m (bottleneck).

   For Figure 16 the effective slot is made valid by ensuring that it is
   valid at each hop in the upstream direction.  The intersection needs
   to be computed because invalid slots could result otherwise.

                            C                B                A
             |Path(m_req)   |                ^                |
             |--------->    |                #                |
             |              |                #                ^
   Effective #              #                #                #
   FS n, m   # . . . . . . .#. . . . . . . . # . . . . . . . .# <-fixed
             #              #                #                #   n
             |              |                #                v
             |              |                #          Resv  |
             |              |                v        <------ |
             |              |                |FlowSpec(n, m_a)|
             |              |       <--------|                |
             |              |  FlowSpec (n,  |
                   <--------|      min(m_a, m_b))
             FlowSpec (n,   |
               min(m_a, m_b, m_c))

               m_a, m_b, m_c: Selected frequency slot widths

       Figure 15: Distributed Allocation with Different m and Same n
                           C                B                 A
             |Path(m_req)  ^                |                 |
             |--------->   #                |                 |
             |             #                ^                 ^
   Effective #             #                #                 #
   FS n, m   #             #                #                 #
             #             #                #                 #
             |             |                #                 v
             |             |                #           Resv  |
             |             |                v         <------ |
             |             |                |FlowSpec(n_a, m_a)
             |             |       <--------|                 |
             |             |  FlowSpec (FSb [intersect] FSa)
            FlowSpec ([intersect] FSa,FSb,FSc)

             n_a: Selected nominal central frequencyfr by node A
             m_a: Selected frequency slot widths by node A
             FSa, FSb, FSc: Frequency slot at each hop A, B, C

    Figure 16: Distributed Allocation with Different m and Different n

   Note, when a media channel is bound to one OTSi (i.e., is a network
   media channel), the effective FS must be the one of the OTSi.  The
   media channel setup by the LSP may contain the effective FS of the
   network media channel effective FS.  This is an endpoint property:
   the egress and ingress have to constrain the Effective FS to be the
   OTSi Effective FS.

4.6.  Neighbor Discovery and Link Property Correlation

   There are potential interworking problems between fixed-grid DWDM and
   flexi-grid DWDM nodes.  Additionally, even two flexi-grid nodes may
   have different grid properties, leading to link property conflict
   with resulting limited interworking.

   Devices or applications that make use of the flexi-grid might not be
   able to support every possible slot width.  In other words, different
   applications may be defined where each supports a different grid
   granularity.  In this case the link between two optical nodes with
   different grid granularities must be configured to align with the
   larger of both granularities.  Furthermore, different nodes may have
   different slot-width tuning ranges.

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

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

   o  Grid granularity - Between two flexi-grid nodes.

   o  Slot width tuning range - Between two flexi-grid nodes.

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

   In WSON, if there is no (available) wavelength converter in an
   optical network, an LSP is subject to the "wavelength continuity
   constraint" (see section 4 of [RFC6163]).  Similarly in flexi-grid,
   if the capability to shift or convert an allocated frequency slot is
   absent, the LSP is subject to the "Spectrum Continuity Constraint".

   Because of the limited availability of wavelength/spectrum converters
   (in what is called a "sparse translucent optical network") the
   wavelength/spectrum continuity constraint always has to be
   considered.  When available, information regarding spectrum
   conversion capabilities at the optical nodes may be used by RSA

   The RSA process determines a route and frequency slot for an LSP.
   Hence, when a route is computed the spectrum assignment process (SA)
   determines the central frequency and slot width based on the slot
   width and available central frequencies information of the
   transmitter and receiver, and utilizing the available frequency
   ranges information and available slot width ranges of the links that
   the route traverses.

4.7.1.  Architectural Approaches to RSA

   Similar to RWA for fixed grids [RFC6163], 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

   Note that all of these models allow the concept of a composite media
   channel supported by a single control plane LSP or by a set of
   associated LSPs.  Combined RSA (R&SA)

   In this case, a computation entity performs both routing and
   frequency slot assignment.  The computation entity needs access to
   detailed network information, e.g., the connectivity topology of the
   nodes and links, the available frequency ranges on each link, the
   node capabilities, etc.

   The computation entity could reside on a dedicated PCE server, in the
   provisioning application that requests the service, or on the ingress
   node.  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 needs the connectivity topology to compute the
   proper routes.  The second entity needs information about the
   available frequency ranges of the links and the capabilities of the
   nodes in order to assign the spectrum.  Routing and Distributed SA (R+DSA)

   In this case an 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 need to be collected hop-by-hop along the
   route.  This procedure can be implemented by the GMPLS signaling

4.8.  Routing and Topology Dissemination

   In the case of the combined RSA architecture, the computation entity
   needs 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 topology and
   node capabilities, while spectrum assignment is performed based on
   the available frequency ranges of the links.  The computation entity
   may get the detailed network information via the GMPLS routing

   For WSON, the connectivity topology and node capabilities can be
   advertised by the GMPLS routing protocol (refer to section 6.2 of
   [RFC6163].  Except for wavelength-specific availability information,
   the information for flexi-grid is the same as for WSON and can
   equally be distributed by the GMPLS routing protocol.

   This section analyses the necessary changes on link information
   brought by flexible grids.

4.8.1.  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 need to be

4.8.2.  Available Slot Width Ranges of DWDM Links

   The available slot width ranges need to be advertised in combination
   with the available frequency ranges, in order that the computing
   entity can verify whether an LSP with a given slot width can be set
   up or not.  This is constrained by the available slot width ranges of
   the media matrix.  Depending on the availability of the slot width
   ranges, it is possible to allocate more spectrum than strictly needed
   by the LSP.

4.8.3.  Spectrum Management

   The total available spectrum on a fiber can be described as a
   resource that can be partitioned.  For example, a part of the
   spectrum could be assigned to a third party to manage, or parts of
   the spectrum could be assigned by the operator for different classes
   of traffic.  This partitioning creates the impression that spectrum
   is a hierarchy in view of Management and Control Plane: each
   partition could be itself be partitioned.  However, the hierarchy is
   created purely within a management system: it defines a hierarchy of
   access or management rights, but there is no corresponding resource
   hierarchy within the 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.  Thus, while there is a hierarchy of ownership (the
   Link Channel Port and corresponding LSP are located on a fiber and so
   associated with a fiber port) there is no continued nesting hierarchy
   of frequency slots within larger frequency slots.  In its way, this
   mirrors the fixed grid behavior where a wavelength is associated with
   a port/fiber, but cannot be subdivided even though it is a partition
   of the total spectrum available on the fiber.

4.8.4.  Information Model

   This section defines an information model to describe the data that
   represents the capabilities and resources available in an flexi-grid
   network.  It is not a data model and is not intended to limit any
   protocol solution such as an encoding for an IGP.  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 is for further study in an IGP encoding document.

   Fixed DWDM 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.  Thus, the
   information model needs to enable:

      exchange of information to enable RSA in a flexi-grid network

      representation of a fixed grid device participating in a flexi-
      grid network

      full interworking of fixed and flexible grid devices within the
      same network

      interworking of flexgrid devices with different capabilities.

   The information model is represented using Routing Backus-Naur Format
   (RBNF) as defined in [RFC5511].

   <Available Spectrum> ::=
     <Available Frequency Range-List>
     <Available NCFs>
     <Available Slot Widths>


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

   <Available Frequency Range> ::=
     ( <Start NCF> <End NCF> ) |
     <FS defined by (n, m) containing  contiguous available NCFs>


   <Available NCFs> ::=
     <Available NCF Granularity> [<Offset>]
     -- Subset of supported n values given by p x n + q
     -- where p is a positive integer
     -- and q (offset) belongs to 0,..,p-1.


   <Available Slot Widths> ::=
     <Available Slot Width Granularity>
     <Min Slot Width>
     -- given by j x 12.5GHz, with j a positive integer
     <Max Slot Width>
     -- given by k x 12.5GHz, with k a positive integer (k >= j)

                   Figure 17: Routing Information Model

5.  Control Plane Requirements

   The control of a flexi-grid networks places additional requirements
   on the GMPLS protocols.  This section summarizes those requirements
   for signaling and routing.

5.1.  Support for Media Channels

   The control plane SHALL be able to support Media Channels,
   characterized by a single frequency slot.  The representation of the
   Media Channel in the GMPLS control plane is the so-called flexi-grid
   LSP.  Since network media channels are media channels, an LSP may
   also be the control plane representation of a network media channel.

   Consequently, the control plane will also be able to support Network
   Media Channels.

5.1.1.  Signaling

   The signaling procedure SHALL be able to configure the nominal
   central frequency (n) of a flexi-grid LSP.

   The signaling procedure SHALL allow a flexible range of values for
   the frequency slot width (m) parameter.  Specifically, the control
   plane SHALL allow setting up a media channel with frequency slot
   width (m) ranging from a minimum of m=1 (12.5GHz) to a maximum of the
   entire C-band (the wavelength range 1530 nm to 1565 nm, which
   corresponds to the amplification range of erbium doped fiber
   amplifiers) with a slot width granularity of 12.5GHz.

   The signaling procedure SHALL be able to configure the minimum width
   (m) of a flexi-grid LSP.  In addition, the signaling procedure SHALL
   be able to configure local frequency slots.

   The control plane architecture SHOULD allow for the support of L-band
   (the wavelength range 1565 nm to 1625 nm) and S-band (the wavelength
   range 1460 nm to 1530 nm).

   The signalling process SHALL be able to collect the local frequency
   slot assigned at each link along the path.

   The signaling procedures SHALL support all of the RSA architectural
   models (R&SA, R+SA, and R+DSA) within a single set of protocol
   objects although some objects may only be applicable within one of
   the models.

5.1.2.  Routing

   The routing protocol will support all functions as described in
   [RFC4202] and extend them to a flexi-grid data plane.

   The routing protocol SHALL distribute sufficient information to
   compute paths to enable the signaling procedure to establish LSPs as
   described in the previous sections.  This includes, at a minimum the
   data described by the Information Model in Figure 17.

   The routing protocol SHALL update its advertisements of available
   resources and capabilities as the usage of resources in the network
   varies with the establishment or tear-down of LSPs.  These updates
   SHOULD be amenable to damping and thresholds as in other traffic
   engineering routing advertisements.

   The routing protocol SHALL support all of the RSA architectural
   models (R&SA, R+SA, and R+DSA) without any configuration or change of
   behavior.  Thus, the routing protocols SHALL be agnostic to the
   computation and signaling model that is in use.

5.2.  Support for Media Channel Resizing

   The signaling procedures SHALL allow resizing (grow or shrink) the
   frequency slot width of a media channel/network media channel.  The
   resizing MAY imply resizing the local frequency slots along the path
   of the flexi-grid LSP.

   The routing protocol SHALL update its advertisements of available
   resources and capabilities as the usage of resources in the network
   varies with the resizing of LSP.  These updates SHOULD be amenable to
   damping and thresholds as in other traffic engineering routing

5.3.  Support for Logical Associations of Multiple Media Channels

   A set of media channels can be used to transport signals that have a
   logical association between them.  The control plane architecture
   SHOULD allow multiple media channels to be logically associated.  The
   control plane SHOULD allow the co-routing of a set of media channels
   that are logically associated.

5.4.  Support for Composite Media Channels

   As described in Section 3.2.5 and Section 4.3, a media channel may be
   composed of multiple network media channels.

   The signaling procedures SHOULD include support for signaling a
   single control plane LSP that includes information about multiple
   network media channels that will comprise the single compound media

   The signaling procedures SHOULD include a mechanism to associate
   separately signaled control plane LSPs so that the end points may
   correlate them into a single compound media channel.

   The signaling procedures MAY include a mechanism to dynamically vary
   the composition of a composite media channel by allowing network
   media channels to be added to or removed from the whole.

   The routing protocols MUST provide sufficient information for the
   computation of paths and slots for composite media channels using any
   of the three RSA architectural models (R&SA, R+SA, and R+DSA).

5.5.  Support for Neighbor Discovery and Link Property Correlation

   The control plane MAY include support for neighbor discovery such
   that an flexi-grid network can be constructed in a "plug-and-play"
   manner.  Note, however, that in common operational practice
   validation processes are used rather than automatic discovery.

   The control plane SHOULD allow the nodes at opposite ends of a link
   to correlate the properties that they will apply to the link.  Such
   correlation SHOULD include at least the identities of the node and
   the identities they apply to the link.  Other properties such as the
   link characteristics described for the routing information model in
   Figure 17 SHOULD also be correlated.

   Such neighbor discovery and link property correlation, if provided,
   MUST be able to operate in both an out-of-band and an out-of-fiber
   control channel.

6.  IANA Considerations

   This framework document makes no requests for IANA action.

7.  Security Considerations

   The control plane and data plane aspects of a flexi-grid system are
   fundamentally the same as a fixed grid system and there is no
   substantial reason to expect the security considerations to be any

   A good overview of the security considerations for a GMPLS-based
   control plane can be found in [RFC5920].

   [RFC6163] includes a section describing security considerations for
   WSON, and it is reasonable to infer that these considerations apply
   and may be exacerbated in a flexi-grid SSON system.  In particular,
   the detailed and granular information describing a flexi- grid
   network and the capabilities of nodes in that network could put
   stress on the routing protocol or the out-of-band control channel
   used by the protocol.  An attacker might be able to cause small
   variations in the use of the network or the available resources
   (perhaps by modifying the environment of a fiber) and so trigger the
   routing protocol to make new flooding announcements.  This situation
   is explicitly mitigated in the requirements for the routing protocol
   extensions where it is noted that the protocol must include damping
   and configurable thresholds as already exist in the core GMPLS
   routing protocols.

8.  Manageability Considerations

   GMPLS systems already contain a number of management tools.

   o  MIB modules exist to model the control plane protocols and the
      network elements [RFC4802], [RFC4803], and there is early work to
      provide similar access through YANG.  The features described in
      these models are currently designed to represent fixed-label
      technologies such as optical networks using the fixed grid:
      extensions may be needed in order to represent bandwidth,
      frequency slots, and effective frequency slots in flexi- grid

   o  There are protocol extensions within GMPLS signaling to allow
      control plane systems to report the presence of faults that affect
      LSPs [RFC4783], although it must be carefully noted that these
      mechanisms do not constitute an alarm mechanism that could be used
      to rapidly propagate information about faults in a way that would
      allow the data plane to perform protection switching.  These
      mechanisms could easily be enhanced with the addition of
      technology-specific reasons codes if any are needed.

   o  The GMPLS protocols, themselves, already include fault detection
      and recovery mechanisms (such as the PathErr and Notify messages
      in RSVP-TE signaling as used by GMPLS [RFC3473].  It is not
      anticipated that these mechanisms will need enhancement to support
      flexi-grid although additional reason codes may be needed to
      describe technology-specific error cases.

   o  [RFC7260] describes a framework for the control and configuration
      of data plane Operations, Administration, and Management (OAM).
      It would not be appropriate for the IETF to define or describe
      data plane OAM for optical systems, but the framework described in
      RFC 7260 could be used (with minor protocol extensions) to enable
      data plane OAM that has been defined by the originators of the
      flexi-grid data plane technology (the ITU-T).

   o  The Link Management Protocol [RFC4204] is designed to allow the
      two ends of a network link to coordinate and confirm the
      configuration and capabilities that they will apply to the link.
      This protocol is particularly applicable to optical links where
      the characteristics of the network devices may considerably affect
      how the link is used and where misconfiguration of mis-fibering
      could make physical interoperability impossible.  LMP could easily
      be extended to collect and report information between the end
      points of links in a flexi-grid network.

9.  Authors

      Fatai Zhang
      Huawei Base, Longgang District, Chine

      Xihua Fu
      ZTE Plaza,No.10,Tangyan South Road, Gaoxin District, China

      Daniele Ceccarelli
      Via Calda 5, Genova, Italy

      Iftekhar Hussain
      140 Caspian Ct, Sunnyvale, 94089, USA

10.  Contributing Authors

      Adrian Farrel
      Old Dog Consulting

      Daniel King
      Old Dog Consulting

      Xian Zhang

      Cyril Margaria
      Juniper Networks
      Qilei Wang
      Ruanjian Avenue, Nanjing, China

      Malcolm Betts

      Sergio Belotti
      Alcatel Lucent
      Optics CTO
      Via Trento 30 20059 Vimercate (Milano) Italy
      +39 039 6863033

      Yao Li
      Nanjing University

      Fei Zhang

      Lei Wang

      Guoying Zhang
      China Academy of Telecom Research
      No.52 Huayuan Bei Road, Beijing, China

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

      Lei Liu
      U.C.  Davis, USA
      Eve Varma
      +1 732 239 7656

      Young Lee

      Jianrui Han

      Sharfuddin Syed

      Rajan Rao

      Marco Sosa

      Biao Lu

      Abinder Dhillon

      Felipe Jimenez Arribas
      Telefonica I+D

      Andrew G.  Malis

      Huub van Helvoort
      Hai Gaoming BV
      The Neterlands

11.  Acknowledgments

   The authors would like to thank Pete Anslow for his insights and
   clarifications, and to Matt Hartley and Jonas Maertensson for their

   This work was supported in part by the FP-7 IDEALIST project under
   grant agreement number 317999.

12.  References

12.1.  Normative References

   [G.694.1]  International Telecomunications Union, "ITU-T
              Recommendation G.694.1, Spectral grids for WDM
              applications: DWDM frequency grid", November 2012.

   [G.800]    International Telecomunications Union, "ITU-T
              Recommendation G.800, Unified functional architecture of
              transport networks.", February 2012.

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

   [G.8080]   International Telecomunications Union, "ITU-T
              Recommendation G.8080/Y.1304, Architecture for the
              automatically switched optical network", 2012.

   [G.870]    International Telecomunications Union, "ITU-T
              Recommendation G.870/Y.1352, Terms and definitions for
              optical transport networks", November 2012.

   [G.872]    International Telecomunications Union, "ITU-T
              Recommendation G.872, Architecture of optical transport
              networks, draft v0.16 2012/09 (for discussion)", 2012.

              International Telecomunications Union, "Update of ITU-T
              Recommendation G.959.1, Optical transport network physical
              layer interfaces", 2013.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC3945]  Mannie, E., Ed., "Generalized Multi-Protocol Label
              Switching (GMPLS) Architecture", RFC 3945,
              DOI 10.17487/RFC3945, October 2004,

   [RFC4202]  Kompella, K., Ed. and Y. Rekhter, Ed., "Routing Extensions
              in Support of Generalized Multi-Protocol Label Switching
              (GMPLS)", RFC 4202, DOI 10.17487/RFC4202, October 2005,

   [RFC4206]  Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
              Hierarchy with Generalized Multi-Protocol Label Switching
              (GMPLS) Traffic Engineering (TE)", RFC 4206,
              DOI 10.17487/RFC4206, October 2005,

   [RFC5511]  Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
              Used to Form Encoding Rules in Various Routing Protocol
              Specifications", RFC 5511, DOI 10.17487/RFC5511, April
              2009, <>.

12.2.  Informative References

   [RFC3473]  Berger, L., Ed., "Generalized Multi-Protocol Label
              Switching (GMPLS) Signaling Resource ReserVation Protocol-
              Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
              DOI 10.17487/RFC3473, January 2003,

   [RFC4204]  Lang, J., Ed., "Link Management Protocol (LMP)", RFC 4204,
              DOI 10.17487/RFC4204, October 2005,

   [RFC4397]  Bryskin, I. and A. Farrel, "A Lexicography for the
              Interpretation of Generalized Multiprotocol Label
              Switching (GMPLS) Terminology within the Context of the
              ITU-T's Automatically Switched Optical Network (ASON)
              Architecture", RFC 4397, DOI 10.17487/RFC4397, February
              2006, <>.

   [RFC4606]  Mannie, E. and D. Papadimitriou, "Generalized Multi-
              Protocol Label Switching (GMPLS) Extensions for
              Synchronous Optical Network (SONET) and Synchronous
              Digital Hierarchy (SDH) Control", RFC 4606,
              DOI 10.17487/RFC4606, August 2006,

   [RFC4783]  Berger, L., Ed., "GMPLS - Communication of Alarm
              Information", RFC 4783, DOI 10.17487/RFC4783, December
              2006, <>.

   [RFC4802]  Nadeau, T., Ed., Farrel, A., and , "Generalized
              Multiprotocol Label Switching (GMPLS) Traffic Engineering
              Management Information Base", RFC 4802,
              DOI 10.17487/RFC4802, February 2007,

   [RFC4803]  Nadeau, T., Ed. and A. Farrel, Ed., "Generalized
              Multiprotocol Label Switching (GMPLS) Label Switching
              Router (LSR) Management Information Base", RFC 4803,
              DOI 10.17487/RFC4803, February 2007,

   [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS
              Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,

   [RFC6163]  Lee, Y., Ed., Bernstein, G., Ed., and W. Imajuku,
              "Framework for GMPLS and Path Computation Element (PCE)
              Control of Wavelength Switched Optical Networks (WSONs)",
              RFC 6163, DOI 10.17487/RFC6163, April 2011,

   [RFC6344]  Bernstein, G., Ed., Caviglia, D., Rabbat, R., and H. van
              Helvoort, "Operating Virtual Concatenation (VCAT) and the
              Link Capacity Adjustment Scheme (LCAS) with Generalized
              Multi-Protocol Label Switching (GMPLS)", RFC 6344,
              DOI 10.17487/RFC6344, August 2011,

   [RFC7139]  Zhang, F., Ed., Zhang, G., Belotti, S., Ceccarelli, D.,
              and K. Pithewan, "GMPLS Signaling Extensions for Control
              of Evolving G.709 Optical Transport Networks", RFC 7139,
              DOI 10.17487/RFC7139, March 2014,

   [RFC7260]  Takacs, A., Fedyk, D., and J. He, "GMPLS RSVP-TE
              Extensions for Operations, Administration, and Maintenance
              (OAM) Configuration", RFC 7260, DOI 10.17487/RFC7260, June
              2014, <>.

Authors' Addresses

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

   Phone: +34913128832

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

   Phone: +34 93 645 29 00