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Versions: (draft-farrkingel-ccamp-flexigrid-lambda-label) 00 01 02 03 04 05 RFC 7699

Network Working Group                                          A. Farrel
Internet Draft                                                   D. King
Updates: 3471, 6205 (if approved)                     Old Dog Consulting
Intended Status: Standards Track                                   Y. Li
Expires: 10 March 2016                                Nanjing University
                                                                F. Zhang
                                                     Huawei Technologies

                                                       10 September 2015

                Generalized Labels for the Flexi-Grid in
          Lambda Switch Capable (LSC) Label Switching Routers



   GMPLS supports the description of optical switching by identifying
   entries in fixed lists of switchable wavelengths (called grids)
   through the encoding of lambda labels.  Work within the ITU-T Study
   Group 15 has defined a finer granularity grid, and the facility to
   flexibly select different widths of spectrum from the grid.  This
   document defines a new GMPLS lambda label format to support this

   This document updates RFC 3471 and RFC 6205 by introducing a new
   label format.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as Internet-Drafts.

   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."

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

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Copyright Notice

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

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

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   1.1.  Conventions Used in This Document  . . . . . . . . . . . . .  4
   2.  Overview of Flexi-Grid . . . . . . . . . . . . . . . . . . . .  4
   2.1.  Composite Labels . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Fixed Grid Lambda Label Encoding . . . . . . . . . . . . . . .  5
   4.  Flexi-Grid Label Format and Values . . . . . . . . . . . . . .  5
   4.1 Flexi-Grid Label Encoding  . . . . . . . . . . . . . . . . . .  5
   4.2.  Considerations of Bandwidth  . . . . . . . . . . . . . . . .  7
   4.3.  Composite Labels . . . . . . . . . . . . . . . . . . . . . .  7
   5.  Manageability and Backward Compatibility Considerations  . . .  8
   5.1.  Control Plane Backward Compatibility . . . . . . . . . . . .  9
   5.2.  Manageability Considerations . . . . . . . . . . . . . . . .  9
   6.  Implementation Status  . . . . . . . . . . . . . . . . . . . . 10
   6.1. Centre Tecnologic de Telecomunicacions de Catalunya (CTTC)  . 10
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   8.1.  Grid Subregistry . . . . . . . . . . . . . . . . . . . . . . 12
   8.2.  DWDM Channel Spacing Subregistry . . . . . . . . . . . . . . 12
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 12
   10.  References  . . . . . . . . . . . . . . . . . . . . . . . . . 13
   10.1.  Normative References  . . . . . . . . . . . . . . . . . . . 13
   10.2.  Informative References  . . . . . . . . . . . . . . . . . . 13
   Appendix A.  Flexi-Grid Example  . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
   Contributors' Addresses  . . . . . . . . . . . . . . . . . . . . . 16

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1.  Introduction

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

   A functional description of the extensions to MPLS signaling needed
   to support this new class of interface and switching is provided in

   Section of [RFC3471] states that wavelength labels "only have
   significance between two neighbors": global wavelength semantics are
   not considered.  [RFC6205] defines a standard lambda label format
   that has a global semantic and which is compliant with both the Dense
   Wavelength Division Multiplexing (DWDM) grid [G.694.1] and the Coarse
   Wavelength Division Multiplexing (CWDM) grid [G.694.2].  The terms
   DWDM and CWDM are defined in [G.671].

   A flexible grid network selects its data channels as arbitrarily
   assigned pieces of the spectrum.  Mixed bitrate transmission systems
   can allocate their channels with different spectral bandwidths so
   that the channels can be optimized for the bandwidth requirements of
   the particular bit rate and modulation scheme of the individual
   channels.  This technique is regarded as a promising way to improve
   the network utilization efficiency and fundamentally reduce the cost
   of the core network.

   The "flexi-grid" has been developed within the ITU-T Study Group 15
   to allow selection and switching of pieces of the optical spectrum
   chosen flexibly from a fine granularity grid of wavelengths with
   variable spectral bandwidth [G.694.1].

   [RFC3471] defines several basic label types including the lambda
   label.  [RFC3471] states that wavelength labels "only have
   significance between two neighbors" (Section; global
   wavelength semantics are not considered.  In order to facilitate
   interoperability in a network composed of LSC equipment, [RFC6205]
   defines a standard lambda label format and is designated an update of
   RFC 3471.

   This document continues the theme of defining global semantics for
   the wavelength label by adding support for the flexi-grid.  Thus,
   this document updates [RFC6205] and [RFC3471].

   This document relies on [G.694.1] for the definition of the optical
   data plane and does not make any updates to the work of the ITU-T.

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1.1.  Conventions Used in This Document

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

2.  Overview of Flexi-Grid

   [G.694.1] defines DWDM fixed grids.  The latest version of that
   document extends the DWDM fixed grids to add support for flexible
   grids.  The basis of the work is to allow a data channel to be formed
   from an abstract grid anchored at 193.1 THz and selected on a channel
   spacing of 6.25 GHz with a variable slot width measured in units of
   12.5 GHz.  Individual allocations may be made on this basis from
   anywhere in the spectrum, subject to allocations not overlapping.

   [G.694.1] provides clear guidance on the support of flexible grid by
   implementations in Section 2 of Appendix I:

      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 have to 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).

   Some additional background on the use of GMPLS for flexible grids
   can be found in [FLEXFWRK].

2.1.  Composite Labels

   It is possible to construct an end-to-end connection as a composite
   of more than one flexi-grid slot.  The mechanism used in GMPLS is
   similar to that used to support inverse multiplexing familiar in
   time-division multiplexing (TDM) and optical transport networks
   (OTN).  The slots in the set could potentially be contiguous or non-
   contiguous (only as allowed by the definitions of the data plane) and
   could be signaled as a single LSP or constructed from a group of
   LSPs.  For more details, refer to Section 4.3.

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

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3.  Fixed Grid Lambda Label Encoding

   [RFC6205] defines an encoding for a global semantic for a DWDM label
   based on four fields:

   - Grid: used to select which grid the lambda is selected from.
     Values defined in [RFC6205] identify DWDM [G.694.1] and CWDM

   - C.S. (Channel Spacing): used to indicate the channel spacing.
     [RFC6205] defines values to represent spacing of 100, 50, 25 and
     12.5 GHz.

   - Identifier: a local-scoped integer used to distinguish different
     lasers (in one node) when they can transmit the same frequency

   - n: a two's-complement integer to take a positive, negative, or zero
     value.  This value is used to compute the frequency as defined in
     [RFC6205] and based on [G.694.1].  The use of n is repeated here
     for ease of reading the rest of this document: in case of
     discrepancy, the definition in [RFC6205] is normative.

        Frequency (THz) = 193.1 THz + n * frequency granularity (THz)

     where the nominal central frequency granularity for the flexible
     grid is 0.00625 THz

4.  Flexi-Grid Label Format and Values

4.1 Flexi-Grid Label Encoding

   This document defines a generalized label encoding for use in flexi-
   grid systems.  As with the other GMPLS lambda label formats defined
   in [RFC3471] and [RFC6205], the use of this label format is known a
   priori.  That is, since the interpretation of all lambda labels is
   determined hop-by-hop, the use of this label format requires that all
   nodes on the path expect to use this label format.

   For convenience, however, the label format is modeled on the fixed
   grid label defined in [RFC6205] and briefly described in Section 3.

   Figure 1 shows the format of the Flexi-Grid Label. It is a 64 bit

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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |Grid | C.S.  |    Identifier   |              n                |
   |              m                |          Reserved             |

              Figure 1 : The Flexi-Grid Label Encoding

   This document defines a new Grid value to supplement those in

    |   Grid   |  Value  |
    |ITU-T Flex|    3    |

   Within the fixed grid network, the C.S. value is used to represent
   the channel spacing, as the spacing between adjacent channels is
   constant.  For the flexible grid situation, this field is used to
   represent the nominal central frequency granularity.

   This document defines a new C.S. value to supplement those in

    | C.S(GHz) |  Value  |
    |     6.25 |    5    |

   The meaning of the Identifier field is maintained from [RFC6205] (see
   also Section 3).

   The meaning of n is maintained from [RFC6205] (see also Section 3).

   The m field is used to identify the slot width according to the
   formula given in [G.694.1] as follows.  It is a 16 bit integer value
   encoded in line format.

         Slot Width (GHz) = 12.5 GHz * m

   The Reserved field MUST be set to zero on transmission and SHOULD be
   ignored on receipt.

   An implementation that wishes to use the flexi-grid label encoding

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   MUST follow the procedures of [RFC3473] and of [RFC3471] as updated
   by [RFC6205].  It MUST set Grid to 3 and C.S. to 5.  It MUST set
   Identifier to indicate the local identifier of the laser in use as
   described in [RFC6205].  It MUST also set n according to the formula
   in Section 3 (inherited unchanged from [RFC6205]).  Finally, the
   implementation MUST set m as described in the formula stated above.

4.2.  Considerations of Bandwidth

   There is some overlap between the concepts of bandwidth and label in
   many GMPLS-based systems where a label indicates a physical switching
   resource.  This overlap is increased in a flexi-grid system where a
   label value indicates the slot width and so affects the bandwidth
   supported by an LSP.  Thus the 'm' parameter is both a property of
   the label (i.e., it helps define exactly what is switched) and of the

   In GMPLS signaling [RFC3473], bandwidth is requested in the TSpec
   object and confirmed in the Flowspec object.  The 'm' parameter that
   is a parameter of the GMPLS flexi-grid label as described above, is
   also a parameter of the flexi-grid TSpec and Flowspec as described in

4.3.  Composite Labels

   The creation of a composite of multiple channels to support inverse
   multiplexing is already supported in GMPLS for TDM and OTN [RFC4606],
   [RFC6344], [RFC7139].  The mechanism used for flexi-grid is similar.

   To signal an LSP that uses multiple flexi-grid slots a "compound
   label" is constructed.  That is, the LABEL object is constructed from
   a concatenation of the 64-bit Flexi-Grid Labels shown in Figure 1.
   The number of elements in the label can be determined from the length
   of the LABEL object.  The resulting LABEL object is shown in Figure
   2 including the object header that is not normally shown in
   diagrammatic representations of RSVP-TE objects.  Note that r is the
   count of component labels, and this is backward compatible with the
   label shown in Figure 1 where the value of r is 1.

   The order of component labels MUST be presented in increasing order
   of the value n.  Implementations MUST NOT infer anything about the
   encoding of a signal into the set of slots represented by a compound
   label from the label itself.  Information about the encoding MAY be
   handled in other fields in signaling messages or through an out of
   band system, but such considerations are out of the scope of this

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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |   Object Length (4 + 8r)      | Class-Num (16)|  C-Type (2)   |
   |Grid | C.S.  |    Identifier   |              n                |
   |              m                |          Reserved             |
   ~                                                               ~
   |Grid | C.S.  |    Identifier   |              n                |
   |              m                |          Reserved             |

       Figure 2 : A Compound Label for Virtual Concatenation

   Note that specific rules must be applied as follows:

   - Grid MUST show "ITU-T Flex" value 3 in each component label.
   - C.S. MUST have the same value in each component label.
   - Identifier in each component label may identify different physical
   - Values of n and m in each component label define the slots that
     are concatenated.

   At the time of writing [G.694.1] only supports only groupings of
   adjacent slots (i.e., without intervening unused slots that could be
   used for other purposes) of identical width (same value of m), and
   the component slots must be in increasing order of frequency (i.e.,
   increasing order of the value n).  The mechanism defined here MUST
   NOT be used for other forms of grouping unless and until those forms
   are defined and documented in Recommendations published by the ITU-T.

   Note further that while the mechanism described here naturally means
   that all component channels are corouted, a composite channel can
   also be achieved by constructing individual LSPs from single flexi-
   grid slots and managing those LSPs as a group.  A mechanism for
   achieving this for TDM is described in [RFC6344], but is out of scope
   for discussion in this document because the labels used are normal,
   single slot labels and require no additional definitions.

5.  Manageability and Backward Compatibility Considerations

   This section briefly considers issues of manageability and backward

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5.1.  Control Plane Backward Compatibility

   Labels are carried in two ways in GMPLS: for immediate use on the
   next hop and for use at remote hops.

   It is an assumption of GMPLS that both ends of a link know what
   label types are supported and only use appropriate label types.  If
   a label of an unknown type is received it will be processed as if it
   was of a known type since the Label Object and similar label-carrying
   objects do not contain a type identifier.  Thus the introduction of a
   flexi-grid label in this document does not change the compatibility
   issues and a legacy node that does not support the new flexi-grid
   label should not expect to receive or handle such labels.  If one is
   incorrectly used in communication with a legacy node it will attempt
   to process it as an expected label type with a potentially poor

   It is possible that a GMPLS message transitting a legacy node will
   contain a flexi-grid label destined for or reported by a remote node.
   For example, an LSP that transits links of different technologies
   might record flexi-grid labels in a Record Route Object that is
   subsequently passed to a legacy node.  Such labels will not have any
   impact on legacy implementations except as noted in the manageability
   considerations in the next section.

5.2.  Manageability Considerations

   This document introduces no new elements for management.  That is,
   labels can continue to be used in the same way by the GMPLS protocols
   and where those labels were treated as opaque quantities with local
   or global significance, no change is needed to the management

   However, this document introduces some changes to the nature of a
   label that may require changes to management systems.  Although
   Section 3.2 of [RFC3471] makes clear that a label is of variable
   length according to the type and that the type is supposed to be
   known a priori by both ends of a link, a management system is not
   guaranteed to be updated in step with upgrades or installations of
   new flexi-grid functionality in the network.

   But an implementation expecting a 32 bit lambda label would not fail
   ungracefully because the first 32 bits follow the format of
   [RFC6205].  It would look at theses labels and read but not recognize
   the new grid type value.  It would then give up trying to parse the
   label and (presumably) the whole of the rest of the message.

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   The management system can be upgraded in two steps:

   - Firstly, systems that handle lambda labels as 32 bit quantities
     need to be updated to handle the increase length (64 bits) of
     labels as described in this document.  These "unknown" 64 bit
     labels could be displayed as opaque 64 bit quantities and still add
     a lot of value for the operator (who might need to parse the label
     by hand).  However, an implementation that already supports lambda
     labels as defined in [RFC6205] can safely continue to process the
     first 32 bits and display the fields defined in RFC 6205 as before
     leaving just the second 32 bits as opaque data.

   - Second, a more sophisticated upgrade to a management system would
     fully parse the flex-gird labels and display them field-by-field as
     described in this document.

6.  Implementation Status

[RFC Editor Note: Please remove this entire section prior to publication
 as an RFC.]

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in RFC 6982
   [RFC6982].  The description of implementations in this section is
   intended to assist the IETF in its decision processes in progressing
   drafts to RFCs.  Please note that the listing of any individual
   implementation here does not imply endorsement by the IETF.
   Furthermore, no effort has been spent to verify the information
   presented here that was supplied by IETF contributors.  This is not
   intended as, and must not be construed to be, a catalog of available
   implementations or their features.  Readers are advised to note that
   other implementations may exist.

   According to RFC 6982, "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit."

6.1. Centre Tecnologic de Telecomunicacions de Catalunya (CTTC)

   Organization Responsible for the Implementation:
      Centre Tecnologic de Telecomunicacions de Catalunya (CTTC)
      Optical Networks and Systems Department

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   Implementation Name and Details:
      ADRENALINE testbed

   Brief Description:
      Experimental testbed implementation of GMPLS/PCE control plane.

   Level of Maturity:
      Implemented as extensions to a mature GMLPS/PCE control plane.
      It is limited to research / prototyping stages but it has been
      used successfully for more than the last five years.

      Support for the 64 bit label as described version 07 of this
      This affects mainly the implementation of RSVP-TE and PCEP

      - Generalized Label Support
      - Suggested Label Support
      - Upstream Label Support
      - ERO Label Subobjects and Explicit Label Control
      It is expected that this implementation will evolve to follow the
      evolution of this document.


   Implementation Experience:
      Implementation of this document reports no issues.
      General implementation experience has been reported in a number of
      journal papers. Contact Ramon Casellas for more information or see

   Contact Information:
      Ramon Casellas: ramon.casellas@cttc.es

      No report.

7.  Security Considerations

   [RFC6205] notes that the definition of a new label encoding does not
   introduce any new security considerations to [RFC3471] and [RFC3473].
   That statement applies equally to this document.

   For a general discussion on MPLS and GMPLS-related security issues,

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   see the MPLS/GMPLS security framework [RFC5920].

8.  IANA Considerations

   IANA maintains the "Generalized Multi-Protocol Label Switching
   (GMPLS) Signaling Parameters" registry that contains several

8.1.  Grid Subregistry

   IANA is requested to allocate a new entry in this subregistry as

   Value   Grid                         Reference
   -----   -------------------------    ----------
     3     ITU-T Flex                   [This.I-D]

8.2.  DWDM Channel Spacing Subregistry

   IANA is requested to allocate a new entry in this subregistry as

   Value   Channel Spacing (GHz)        Reference
   -----   -------------------------    ----------
     5     6.25                         [This.I-D]

9.  Acknowledgments

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

   Very many thanks to Lou Berger for discussions of labels of more than
   32 bits.  Many thanks to Sergio Belotti and Pietro Vittorio Grandi
   for their support of this work.  Thanks to Gabriele Galimberti for
   discussion of the size of the "m" field, and to Iftekhar Hussain for
   discussion of composite labels.  Robert Sparks, Carlos Pignataro, and
   Paul Wouters provided review comments during IETF last call.

   Special thanks to the Vancouver 2012 Pool Party for discussions and
   rough consensus: Dieter Beller, Ramon Casellas, Daniele Ceccarelli,
   Oscar Gonzalez de Dios, Iftekhar Hussain, Cyril Margaria, Lyndon Ong,
   Fatai Zhang, and Adrian Farrel.

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10.  References

10.1.  Normative References

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

   [RFC3471]  Berger, L., Ed., "Generalized Multi-Protocol Label
              Switching (GMPLS) Signaling Functional Description", RFC
              3471, January 2003.

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

   [RFC6205]  Otani, T., and Li, D., "Generalized Labels for Lambda-
              Switch-Capable (LSC) Label Switching Routers", RFC 6205,
              October 2011.

   [G.694.1]  ITU-T Recommendation G.694.1 (revision 2), "Spectral grids
              for WDM applications: DWDM frequency grid", February 2012.

10.2.  Informative References

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

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

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

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

   [RFC6982]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", RFC 6982, July
[RFC Editor Note: This reference can be removed when Section 6 is

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

   [G.671]    ITU-T Recommendation G.671, "Transmission characteristics
              of optical components and subsystems", 2009.

   [G.694.2]  ITU-T Recommendation G.694.2, "Spectral grids for WDM
              applications: CWDM wavelength grid", December 2003.

   [FLEXFWRK] O. Gonzalez de Dios, et al., "Framework and Requirements
              for GMPLS based control of Flexi-grid DWDM networks",
              draft-ogrcetal-ccamp-flexi-grid-fwk, work in progress.

   [FLEXRSVP] Zhang, F., Gonzalez de Dios, O., and D. Ceccarelli,
              "RSVP-TE Signaling Extensions in support of Flexible
              Grid", draft-zhang-ccamp-flexible-grid-rsvp-te-ext, work
              in progress.

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Appendix A.  Flexi-Grid Example

   Consider a fragment of an optical LSP between node A and node B using
   the flexible grid.  Suppose that the LSP on this hop is formed:
   - using the ITU-T Flexi-Grid
   - the nominal central frequency of the slot 193.05 THz
   - the nominal central frequency granularity is 6.25 GHz
   - the slot width is 50 GHz.

   In this case the label representing the switchable quantity that is
   the flexi-grid quantity is encoded as described in Section 4.1 with
   the following parameter settings.  The label can be used in signaling
   or in management protocols to describe the LSP.

     Grid = 3 : ITU-T Flexi-Grid

     C.S. = 5 : 6.25 GHz nominal central frequency granularity

     Identifier = local value indicating the laser in use

     n = -8 :

          Frequency (THz) = 193.1 THz + n * frequency granularity (THz)

          193.05 (THz) = 193.1 (THz) + n * 0.00625 (THz)

          n = (193.05-193.1)/0.00625 = -8

     m = 4 :

          Slot Width (GHz) = 12.5 GHz * m

          50 (GHz) = 12.5 (GHz) * m

          m = 50 / 12.5 = 4

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Authors' Addresses

   Adrian Farrel
   Old Dog Consulting
   EMail: adrian@olddog.co.uk

   Daniel King
   Old Dog Consulting
   EMail: daniel@olddog.co.uk

   Yao Li
   Nanjing University
   EMail: wsliguotou@hotmail.com

   Fatai Zhang
   Huawei Technologies
   EMail: zhangfatai@huawei.com

Contributors' Addresses

   Zhang Fei
   Huawei Technologies
   EMail: zhangfei7@huawei.com

   Ramon Casellas
   EMail: ramon.casellas@cttc.es

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