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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: April 25, 2013                                             CTTC
                                                                F. Zhang
                                                                  Huawei
                                                                   X. Fu
                                                                     ZTE
                                                           D. Ceccarelli
                                                                Ericsson
                                                              I. Hussain
                                                                Infinera
                                                        October 22, 2012


     Framework for GMPLS based control of Flexi-grid DWDM networks
                 draft-ogrcetal-ccamp-flexi-grid-fwk-01

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
   recommendations [G.694.1] and [G.872] 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
   allocated, variable-sized frequency ranges within the ptical
   spectrum.

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




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   This Internet-Draft will expire on April 25, 2013.

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
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   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
     4.1.  Frequency Slots  . . . . . . . . . . . . . . . . . . . . .  6
     4.2.  Media Layer, Elements and Channels . . . . . . . . . . . .  9
     4.3.  Media Layer Switching  . . . . . . . . . . . . . . . . . . 10
     4.4.  Control Plane Terms  . . . . . . . . . . . . . . . . . . . 11
   5.  GMPLS applicability  . . . . . . . . . . . . . . . . . . . . . 12
   6.  DWDM flexi-grid enabled network element models . . . . . . . . 12
     6.1.  Network element constraints  . . . . . . . . . . . . . . . 13
   7.  Layered Network Model  . . . . . . . . . . . . . . . . . . . . 14
   8.  Topology view in Control Plane . . . . . . . . . . . . . . . . 14
   9.  Control Plane Requirements . . . . . . . . . . . . . . . . . . 16
     9.1.  Neighbor Discovery and Link Property Correlation . . . . . 16
     9.2.  Path Computation / Routing and Spectrum Assignment
           (RSA)  . . . . . . . . . . . . . . . . . . . . . . . . . . 17
       9.2.1.  Architectural Approaches to RSA  . . . . . . . . . . . 17
     9.3.  Routing / Topology dissemination . . . . . . . . . . . . . 18
       9.3.1.  Available Frequency Ranges/slots of DWDM Links . . . . 19
       9.3.2.  Available Slot Width Ranges of DWDM Links  . . . . . . 19
       9.3.3.  Tunable Optical Transmitters and Receivers . . . . . . 19
       9.3.4.  Hierarchical Spectrum Management . . . . . . . . . . . 19
       9.3.5.  Information Model  . . . . . . . . . . . . . . . . . . 19
     9.4.  Signaling requirements . . . . . . . . . . . . . . . . . . 20
       9.4.1.  Slot Width Requirement . . . . . . . . . . . . . . . . 21
       9.4.2.  Frequency Slot Representation  . . . . . . . . . . . . 21
       9.4.3.  Relationship with MRN/MLN  . . . . . . . . . . . . . . 21
   10. Control Plane Procedures . . . . . . . . . . . . . . . . . . . 21
   11. Backwards (fixed-grid) compatibility, and WSON interworking  . 21
   12. Misc & Summary of open Issues [To be removed at later
       versions]  . . . . . . . . . . . . . . . . . . . . . . . . . . 23
   13. Security Considerations  . . . . . . . . . . . . . . . . . . . 24
   14. Contributing Authors . . . . . . . . . . . . . . . . . . . . . 24
   15. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 26
   16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
     16.1. Normative References . . . . . . . . . . . . . . . . . . . 26
     16.2. Informative References . . . . . . . . . . . . . . . . . . 27
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27










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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 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 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, and allowing higher bit rates
   (e.g., 400G, 1T or higher).

   From a networking perspective, a flexible grid network is assumed to
   be a layered network [G.872][G.800] 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],
   is a term commonly used to refer to the application/deployment of a



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   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 the separation between Och and Lambda (spectrum and signal
   are bundled)].

   [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.]

   [Editor's note: -00 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.  ITU-T is still discussing B100G
   Architecture]

   [Editors' note: -01 this version reflects the agreements made during
   IETF84, notably concerning the focus in the media layer, terminology
   updates post ITU-T September meeting in Geneva and the deprecation of
   the ROADM term, in favor of the more concrete media layer switching
   element (media channel matrix).]

   [Editors' note: -01 in partial answer to Gert question on the layered
   model, [G.872] footnote explains that this separation is necessary to
   allow the description of media elements that may act on more than a
   single OCh-P signal.  See appendix IV within.]


3.  Acronyms

   FS: Frequency Slot

   NCF: Nominal Central Frequency




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   OCh: Optical Channel

   OCh-P: Optical Channel Payload

   OCh-O: Optical Channel Overhead

   OCC: Optical Channel Carrier

   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.]

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

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

4.1.  Frequency Slots

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

   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
      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


      Figure 1: Anchor frequency and set of nominal central frequencies





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   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 and unavailable to other slots.  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'.


         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
      or multiple Optical Channels may be transported.  Note that when
      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.

   o  Effective Frequency Slot: the effective frequency slot of a media
      channel is the common part of the frequency slots of the filter
      components along the media channel through a particular path



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      through the optical network.  It is a logical construct derived
      from the (intersection of) frequency slots allocated to each
      device in the path.  The effective frequency slot is an attribute
      of a media channel and, being a frequencly slot, it is described
      by its nominal central frequency and slot width.  As an example,
      if there are two filters having slots with the same n but
      different m, then the common frequency slot has the smaller of the
      two m values.  [Editor's note: within the GMPLS label swapping
      paradigm, the switched resource corresponds to the local frequency
      slot defined by the observable filters of the media layer
      switching element.  The GMPLS label MUST identify the switched
      resource locally, and (as agreed during IETF84) is locally scoped
      to a link, even if the same frequency slot is allocated at all the
      hops of the path.  Note that the requested slot width and the
      finally allocated slot witdh by a given node may be different,
      e.g., due to restrictions in the slot width granularity of the
      nodes.  Due to the symmetric definition of frequency slot,
      allocations seem to be constrained to have the same nominal
      central frequency.  It is important to note that if n changes
      along the path, it cannot be guaranteed that there is a valid
      common frequency slot.  We must determine if different n's are
      allowed.  We need to explain this rationale. e.g. what happens
      when the resulting slot cannot be characterized with n and m, see
      Figure 3 and Figure 4.].


                        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--+--+--+--+--+--+--+--+--+--+--+--...

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


                      Figure 3: Effective Frequency Slot




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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--+--+--+--+--+--+--+--+--+--+--+--...

   ===============================================
           Invalid Effective Frequency Slot - (n, m?)
             ----------
             |        |
      -3 -2 -1  0  1  2  3  4  5  6  7  8  9 10 11
      ..--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--...


                  Figure 4: Invalid Effective Frequency Slot

4.2.  Media Layer, Elements and Channels

   o  Media Element: a media element only directs the 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.  Examples of media elements include
      fibers, amplifiers, filters, switching matrices[Note: the data
      plane component of a LSR in the media layer is a media element,
      but not all media elements correspond to data plane nodes in the
      GMPLS network model.

   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 (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 filters.

   o  Network Media Channel: a media channel (media association) that
      supports a single OCh-P network connection.  It represents the
      concatenation of all media elements between an OCh-P source and an
      OCh-P sink.  [TODO: |Malcolm| explain the use case rationale to
      support a hierarchy of media channels, where a media channel acts
      as "pipe" for one or more network media channels and they are both



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      separate entities (IETF84).  This may be tied to the concept of a
      "waveband" or express channel, as stated in [G.872] footnote 4.]

   o  OCh-P Frequency Slot: The spectrum allocated to a single OCh
      signal supported on a Network Media Channel.

4.3.  Media Layer Switching

   [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'].

   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.

   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.  In Figure 5 ,
   a Media Channel has been configured and dimensioned to support two
   OCh-P, each transported in its own OCh-P frequency slot.




















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                         Media Channel Frequency Slot
     +-------------------------------X------------------------------+
     |                                                              |
     |      OCh-P Frequency Slot             OCh-P Frequency Slot   |
     |  +------------X-----------+       +----------X-----------+   |
     |   |       OCh-P           |       |      OCh-P           |   |
     |   |           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

4.4.  Control Plane Terms

   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.]

   o  SSON: Spectrum-Switched Optical Network.  An optical network in
      which a LSP is switched based on an frequency slot of a variable
      slot width of a media channel, 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 with
      variable slot width.  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



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      to single connections, the resources assigned to them must be
      contiguous over the entire connections in the spectrum domain.


5.  GMPLS applicability

   The GMPLS control of the media layer deals with the establishment of
   media channels, which are switched in media channel matrixes.  GMPLS
   labels locally represent the media channel and its associated
   frequency slot.

   [Editors'note: As agreed during IETF84, current focus is on the media
   layer.  Preliminaty agreement on the "m" parameter should appear in
   the label *and* the traffic parameters.]


6.  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, i.e,
   media elements including media layer switching elements (media
   matrices), as well as electro-optical network elements, all of them
   with flexible grid characteristics.

   [Editors' Note: In the scope of this document, and despite is
   informal use, the term Reconfigurable Optical Add / Drop Multiplexer,
   (ROADM) is avoided, in favor on media matrix.  This avoid ambiguity.
   A ROADM can be implemented in terms on media matrices.
   Informationally, this document may provide an appendix on possible
   implementations of flexi-ROADMs in terms of media layer switching
   elements or matrices.  XF: Whether ROADM is used or not doesn't
   matter with GMPLS Control Plane.  I suggest to delete this statement.
   We may check G.798.  Likewise, modeling of filters is out of scope of
   the current document IETF84, and is also considered implementation
   specific.]

   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).



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6.1.  Network element constraints

   [TODO: section needs to be rewritten, remove redundancy].

   Optical transmitters/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
   [RFC6163] in detail.  Media matrices include line side ports which
   are connected to DWDM links and tributary side input/output ports
   which can be connected to transmitters/receivers.

   A set of common constraints can be defined :

   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.

   o  The minimum and maximum slot width.

   o  Granularity: the optical hardware may not be able to select
      parameters with the lowest granularityy (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 are not allocated (i.e. 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
      information.

      *  Slot width threshold: the minimum and maximum Slot Width
         supported by the media matrix.  For example, the slot width can
         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.

   [Editor's note: different configurations such as C/CD/CDC will be



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   added later.  This section should state specifics to media channel
   matrices, ROADM models need to be moved to an appendix].


7.  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.


 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

(1) - Matrix Channel

                   Figure 6: Layered Network Model G.805

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


8.  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.]






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


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

   A SSON (network) refers to the GMPLS control of flexi-grid enabled
   DWDM optical networks and it encompasses both the signal and media
   layers.  The WSON also encompasses the signal and media layers but,
   since there is no formal separation between OCh and OCC (1:1) this
   layer separation is often not considered.  A WSON is a particular
   case of SSON in the which all slot widths are equal and depend on the
   channel spacing.  In other words, since there is only a 1:1
   relationship between OCh : OCC there is no need to have separate
   controlled layers, as if both layers are collapsed into one.

   +=======================================+
   |     WSON         |          SSON      |
   +=======================================+
   |      OCh         |         OCh        | Signal Layer
   +------------------+--------------------+
   |                  |  Frequency Slot    |
   | Optical Channel  |                    | Media Layer
   | Carrier          |                    |
   +------------------+--------------------+
   |     1:1          |       N:1          | Relationship
   | single layer     |    MRN/MLN         |  SL : ML
   |   network        |     (* see note)   |
   +------------------+--------------------+

                   Figure 8: Table Comparison WSON/SSON

   Note that there is only one media layer switch matrix (one
   implementation is FlexGrid ROADM) in SSON, while "signal layer LSP is
   mainly for the purpose of management and control of individual
   optical signal".  Signal layer LSPs (OChs) with the same attributions
   (such as source and destination) could be grouped into one media-
   layer LSP (media channel), which has advantages in spectral
   efficiency (reduce guard band between adjacent OChs in one FSC) and



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   LSP management.  However, assuming some network elements indeed
   perform signal layer switch in SSON, there must be enough guard band
   between adjacent OChs in one media channel, in order to compensate
   filter concatenation effect and other effects caused by signal layer
   switching elements.  In such condition, the separation of signal
   layer from media layer cannot bring any benefit in spectral
   efficiency and in other aspects, but make the network switch and
   control more complex.  If two OChs must switch to different ports, it
   is better to carry them by diferent FSCs and the media layer switch
   is enough in this scenario.


9.  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, 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.

9.1.  Neighbor Discovery and Link Property Correlation

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

   Potential interworking problems between fixed-grid DWDM and flexible-
   grid DWDM nodes, may appear.  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,



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   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.

9.2.  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
   transmitter and receiver, and the available frequency ranges
   information and available slot width ranges of the links that the
   route traverses.

9.2.1.  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.





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9.2.1.1.  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.

9.2.1.2.  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.

9.2.1.3.   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.

9.3.  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
   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.





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9.3.1.  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.

9.3.2.  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 media matrix
   Depending on the availability of the slot width ranges, it is
   possible to allocate more spectrum than strictly needed by the LSP.

9.3.3.  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.

9.3.4.  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
   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.

9.3.5.  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



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   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)


                    Figure 9: Routing Information model

9.4.  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,



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   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.

9.4.1.  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]

9.4.2.  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.

9.4.3.  Relationship with MRN/MLN

9.4.3.1.  OCh Layer

9.4.3.2.  Media (frequency slot) layer


10.  Control Plane Procedures

   FFS.  Postpone procedures such as resizing existing LSP(s) without
   deletion, which refers to increase or decrease of slot width value
   'm' without changing the value of 'n', etc. until requirements have
   been identified.  At present no hitless resizing protocol has been
   defined for OCh.  Hitless resizing is defined for an ODU entity only.


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





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   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 10: LSP Stitching [RFC5150] and relationship with fixed-flexi


12.  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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13.  Security Considerations

   TBD


14.  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
      Nanjing University
      wsliguotou@hotmail.com

      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


15.  Acknowledgments

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


16.  References

16.1.  Normative References

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

   [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.

   [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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16.2.  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 v0.16 2012/09 (for discussion)", 2012.

   [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, February 2006.

   [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









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

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


   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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