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Versions: 00                                                            
Network Working Group                                       Fatai Zhang
Internet-Draft                                                Young Lee
Intended status: Informational                                   Huawei
                                                    O. Gonzalez de Dios
                                                         Ramon Casellas
                                                          D. Ceccarelli
Expires: September 05, 2012                              March 05, 2012

         Framework for GMPLS and PCE Control of Spectrum Switched
                             Optical Networks


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
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   The list of current Internet-Drafts can be accessed at

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

   This Internet-Draft will expire on September 05,2012.

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   A new flexible grid of DWDM has been developed within the ITU-T
   Study Group 15 to allow a more efficient spectrum allocation. In
   such environment a data plane connection is switched based on the
   allocated variable width optical spectrum frequency slot. This new
   switching capability is referred to as Spectrum Switched Optical
   Networks (SSON). This draft describes the framework for the
   application of a GMPLS control plane to a SSON.

Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC-2119 [RFC2119].

Table of Contents

   1. Introduction ................................................. 3
   2. Terminology .................................................. 4
   3. New characteristics of SSON .................................. 5
   3.1. Overview of Flexible Grid .................................. 6
   3.2. ROADM ...................................................... 7
   3.3. Optical Transmitters and Receivers ......................... 8
   4. Routing and Spectrum Assignment .............................. 9
   4.1. Architectural Approaches to RSA ........................... 10
   4.1.1. Combined RSA (R&SA) ..................................... 10
   4.1.2. Separated RSA (R+SA) .................................... 11
   4.1.3. Routing and Distributed SA (R+DSA) ...................... 11
   5. Requirements for GMPLS Control Plane ........................ 11
   5.1. Routing ................................................... 11
   5.1.1. Available Frequency Ranges of DWDM Links ................ 12
   5.1.2. Available Slot Width Ranges of DWDM Links ............... 12
   5.1.3. Tunable Optical Transmitters and Receivers .............. 12
   5.2. Signaling ................................................. 12
   5.2.1. Slot Width Requirement .................................. 13
   5.2.2. Frequency Slot Representation ........................... 13
   5.3. PCE ....................................................... 13
   5.3.1. RSA Computation Type .................................... 13
   5.3.2. RSA path re-optimization request/reply .................. 14
   5.3.3. Frequency Constraints ................................... 14
   6. Security Considerations ..................................... 15
   7. References .................................................. 15
   7.1. Normative References ...................................... 15
   7.2. Informative References .................................... 15
   8. Authors' Addresses .......................................... 16

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1. Introduction

   [G.694.1v1] defines the DWDM frequency grids for WDM applications. A
   frequency grid is a reference set of frequencies used to denote
   allowed nominal central frequencies that may be used for defining
   applications. The channel spacing, i.e. the frequency spacing
   between two allowed nominal central frequencies could be 12.5 GHz,
   25 GHz, 50 GHz, 100 GHz or integer multiples of 100 GHz as defined
   in [G.694.1v1]. The frequency spacing of the channels on a fiber is

   The data rate of optical signals becomes higher and higher with the
   advancement of the optical technology. In the near future, it is
   anticipated that high data rate signals (beyond 100 Gbit/s or even
   400 Gbit/s) will be deployed in optical networks. These signals may
   not be accommodated in the channel spacing specified in old
   [G.694.1v1]. Moreover, ''mixed rate'' scenarios will be prevalent, and
   the optical signals with different rates may require different
   spectrum width. As a result, when the optical signals with different
   rates are mixed to be transmitted on the same fiber, the frequency
   allocation needs to be more flexible so as to improve spectral

   An updated version of [G.694.1v1], i.e., [G.FLEXIGRID] has been
   consented in December 2011 in support of flexible grids. The terms
   ''frequency slot (the frequency range allocated to a channel and
   unavailable to other channels within a flexible grid)'' and ''slot
   width'' (the full width of a frequency slot in a flexible grid) are
   introduced to address flexible grid extensions. A channel is
   represented as a LSC (Lambda Switching Capable) LSP in the control
   plane, and it means that a LSC LSP should occupy a frequency slot on
   each fiber it traverses. In the case of flexible grid, different LSC
   LSPs may have different slot widths on a fiber.

   Thus the concept of Wavelength Switched Optical Network(WSON) is
   extended to Spectrum Switched Optical Network (SSON) which includes
   flexible capabilities (i.e. flexi-grid). In SSON, a data plane
   connection is switched based on an optical spectrum frequency slot
   of a variable (flexible) slot width, rather than based on a single
   wavelength within a fixed grid and with a fixed channel spacing as
   is the case for WSON. In this sense, a WSON can be seen as a
   particular case of a SSON in which all slot widths are equal and
   central frequencies depend on the used channel spacing.

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   WSON related documents are currently being developed with the focus
   of the GMPLS control of fixed grid optical networks. This document
   describes the new characteristics of SSON and provides the framework
   of GMPLS control for the new features of SSON beyond WSON.

   Note that this document focuses on the general properties of SSON.
   Information related to optical impairments is out of its scope and
   will be addressed in a separate draft.

2. Terminology

   Flexible Grid: a new WDM frequency grid defined with the aim of
   allowing flexible optical spectrum management, in which the Slot
   Width of the frequency ranges allocated to different channels are
   flexible (variable size).

   Frequency Range: a frequency range is defined as the portion of
   frequency spectrum included between a lowest and a highest frequency.

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

   Slot Width: the full width (in Hz) of a frequency slot. A slot width
   can be expressed as a multiple (m) of a basic slot width (e.g. 12.5

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

   Flexi-LSP: a control plane construct that represents a data plane
   connection in which the switching involves a frequency slot of a
   variable (flexible) slot width. The mapped client signal is
   transported over the frequency slot, using spectrum efficient
   modulations such as Coherent Optical Orthogonal Frequency Division
   Multiplexing (CO-OFDM) and Forward Error Correction (FEC) techniques.
   Although still in the scope of LSC, the term flexi-LSP is used, when
   needed, to differentiate from regular WSON LSP in which switching is
   based on a nominal wavelength.

   RSA: Routing and Spectrum Assignment. As opposed to the typical
   Routing and Wavelength Assignment (RWA) problem of traditional WDM

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   networks, the flexibility in SSON leads to spectral contiguous
   constraint, which means that when assigning the spectral resources
   to single connections, the resources assigned to them must be
   contiguous over the entire connections in the spectrum domain. RSA
   is introduced to describe the routing and spectrum assignment

3. New characteristics of SSON

   Wavelength Switched Optical Networks (WSONs) are constructed from
   subsystems that include Wavelength Division Multiplexing (WDM) links,
   tunable transmitters and receivers, Reconfigurable Optical Add/Drop
   Multiplexers (ROADMs), wavelength converters, and electro-optical
   network elements. WSON framework is described in [RFC6163]. The
   introduced flexible grid brings some changes on GMPLS controlled
   optical networks.

   The concept of WSON is extended to SSON, to highlight that such
   subsystems are extended with flexible capabilities (i.e. flexi-grid).
   Note that, when modeling SSONs, a WSON can be seen as a particular
   case of SSON where all LSC LSPs use a fixed (and equal) slot width
   which depends on the used channel spacing.

   In WSON, the joint determination of an optical path (physical route)
   along with the nominal wavelength on a fiber is known as Routing and
   Wavelength Assignment (RWA). Wavelength Assignment (WA) is the
   determination of which wavelength can be used for a specific optical
   path. In analogy with WSON, in SSON, the determination of a path and
   a frequency slot (including both central frequency and slot width)
   is referred to as Routing and Spectrum Assignment (RSA). Spectrum
   Assignment (SA) is the process of determining the spectrum range
   that can be used for one specific flex-LSP given a physical route.

   Compared to WSON, flexibility needs to be introduced in optical
   network devices such as ROADMs or optical transponders in order to
   fully benefit from SSON (flexible grid) improved spectrum management.
   Consequently, transceivers may be able to fully leverage flexible
   optical channels with advanced modulation formats, and ROADMs may
   need to be extended to allow flexible spectrum switching.

   A flexible grid is defined for the DWDM system in [G.FLEXIGRID].
   Compared to fixed grids a flexible grid has a smaller granularity
   for the central frequencies and the slot width may range from say,
   12.5 GHz to hundreds of GHz, in order to accommodate different
   client data rates. The subsequent sections analyze the new
   characteristics of flexible grid based on standard [G.FLEXIGRID],

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   and then model ROADMs, and optical transponders in SSON with an
   emphasis on those aspects that are of relevance to the control plane.

3.1. Overview of Flexible Grid

   o Central Frequency

     According to the definition of flexible DWDM grid in [G.FLEXIGRID],
     the allowed nominal central frequencies are calculated as in the
     case of flexible grid:

               Central Frequency = 193.1 THz + n * 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 and
     0.00625 THz is the nominal central frequency granularity.

   o Slot Width

     A slot width is defined by:

                                12.5 GHz * m

     Where m is a positive integer and 12.5 GHz is the slot width

     Note that, when flexi-grid is supported on a WDM link, the slot
     width of different flexi-LSPs may be different.

   The WDM link for flexible grid can be represented as shown in figure

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


                Figure 1 Fiber link model for flexible grid

   The symbol'+' represents the allowed nominal central frequencies.
   The symbol ''--" represents the basic 6.25 GHz frequency slot. The
   number on the top of the line represents the 'n' in the frequency
   calculation formula. The nominal central frequency is 193.1 THz when
   n equals zero.

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   As Described in [G.FLEXIGRID], 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, may not have to be capable of supporting
   every possible slot width or central frequency granularity. For
   example, ROADM and transceivers in SSON may support subset of all
   possible slot width or posit defined in [G.FLEXIGRID].

3.2. ROADM

   To support flexi grid, a ROADM is a key device which allows
   spectrum-based optical switching. A classic degree-4 ROADM is shown
   in Figure 2.

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

                   Figure 2 Degree-4 Bidirectional ROADM

   The key feature of ROADMs is their highly asymmetric switching
   capability which is described in [RFC6163] in detail. The asymmetric
   switching feature of flexible ROADM in SSON is similar to fixed
   ROADM in WSON. The ports on ROADM include line side port which is
   connected to WDM link, tributary side input/output port which is
   connected to transmitter/receiver. The main difference between
   ROADMs in SSON and WSON is the capability of ports on ROADM, which
   are characterized as follows:

   From a SSON control plane perspective (in terms of path computation
   and resource allocation), ROADMs line side ports are characterized
   by the following aspects:

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   o Available frequency ranges: the set or union of frequency ranges
      that are not allocated (i.e. available or unused. 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 ROADM. It includes the following information:

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

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

   These properties can be injected into the link parameters from the
   control plane perspective, which is described in Section 5.

   Since the tributary side port is connected to a transmitter and
   receiver, the characterization of tributary side ports is described
   in the next section.

3.3. Optical Transmitters and Receivers

   In WSON, the optical transmitter is the wavelength source and the
   optical receiver is the wavelength sink of the WDM system. In each
   direction, the wavelength used by the transmitter and receiver along
   a path shall be consistent if no wavelength converter is available.
   The central frequency used by a transmitter or receiver may be fixed
   or tunable.

   In SSON the optical spectrum (frequency slot width) used by
   different flexi-LSPs may be variable. Optical transmitters/receivers
   may have different restriction on the following properties:

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

   o Slot width: The slot width needed by a transmitter/receiver.

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

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   Similarly, other information on transmitters and receivers
   capabilities, in regard to signal processing is needed to perform
   efficient RSA, much like in WSON [WSON-ENCODE].

4. Routing and Spectrum Assignment

   A LSC flexi-LSP occupies a frequency slot, i.e. a range of
   frequencies, on each link the LSP traverses.

   Much like in WSON, in which 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]), in SSON if the
   capability of shifting or converting the whole optical spectrum
   allocated to a flex-LSP is not available, the flexi-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

   The RSA process determines a route and frequency slot for a flexi-
   LSP. Note that the mapping between client signals data rates (10, 40,
   100... Gbps) and optical slot widths (which are dependent on
   modulation formats and other physical layer parameters) is out of
   the scope of this document. The frequency slot can be deduced from
   the central frequency and slot width parameters as follows:

   Lowest frequency = (central frequency) - (slot width)/2;

   Highest frequency = (central frequency) + (slot width)/2.

   Hence, when a route is computed the spectrum assignment process (SA)
   should determine the central frequency for a flexi-LSP 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.

   Figure 2 shows two LSC LSPs that traverse a link.

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                           Frequency Slot 1     Frequency Slot 2
                           -------------     -------------------
                           |           |     |                 |
     -9 -8 -7 -6 -5 -4 -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 Two LSC LSPs traverse a Link

   The two wavelengths shown in figure 2 have the following meaning:

   Flexi-LSP 1: central frequency = 193.1 THz, slot width = 25 GHz. It
   means the frequency slot [193.0875 THz, 193.1125 THz] is assigned to
   this LSC LSP.

   Flexi-LSP 2: central frequency = 193.14375 THz, slot width = 37.5
   GHz. It means the frequency slot [193.125 THz, 193.1625 THz] is
   assigned to this LSC LSP.

   Note that the frequency slots of two LSC flexi-LSPs on a fiber do
   not overlap with each other, and a guard band may be considered to
   counteract inter-channel detrimental effects.

4.1. 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.

4.1.1. 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 capability, etc.

   The computation entity could reside on the following elements, which
   depends on the implementation:

   o PCE: PCE gets the detailed network information and implements the
      RSA algorithm for RSA requests from the PCCs.

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   o Ingress node: Ingress node gets the detailed network information
      (e.g. through routing protocol) and implements the RSA algorithm
      when a LSC LSP request is received.

4.1.2. 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.

4.1.3. 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 wavelength
   continuity constraint should be collected hop by hop along the route.
   This procedure can be implemented by the GMPLS signaling protocol.

   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 central frequencies that meet the slot width
   requirement of the LSC LSP, i.e. the frequency slot which is
   determined by the central frequency and slot width MUST NOT overlap
   with the existing LSC LSPs.

5. Requirements for GMPLS Control Plane

   According to the different architecture approaches to RSA some
   additional requirements have to be considered for the GMPLS control
   of SSONs.

5.1. Routing

   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.

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   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.

5.1.1. Available Frequency Ranges 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 LSC LSPs could make use of different slot
   widths on the same link. Hence, the available frequency ranges
   should be advertised.

5.1.2. Available Slot Width Ranges of DWDM Links

   The available slot width ranges needs to be advertised in order to
   understand whether a LSC LSCP with a given slot width can be set up
   or not.

   Whether a LSC LSP with a certain slot width can be set up or not is
   constrained by the available slot width ranges of flexible ROADM. So
   the available slot width ranges should be advertised.

5.1.3. Tunable Optical Transmitters and Receivers

   The slot width of a LSC 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.

5.2. Signaling

   Compared with [RFC6163], except identifying the resource (i.e.,
   fixed wavelength for WSON and frequency resource for flexible grids),
   the other signaling requirements (e.g., unidirectional or
   bidirectional, with or without converters) are the same as WSON
   described in the section 6.1 of [RFC6163].

   In the case of routing and distributed SA, GMPLS signaling can be
   used to allocate the frequency slot to a LSC LSP. This brings the
   following changes to the GMPLS signaling.

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5.2.1. Slot Width Requirement

   In order to allocate a proper frequency slot for a LSC LSP, the
   signaling should specify the slot width requirement of a LSC LSP.
   Then 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 LSC LSP to
   assign the proper frequency resource. Hence, the slot width
   requirement should be specified in the signaling message when a LSC
   LSP is being set up.

5.2.2. Frequency Slot Representation

   The frequency slot can be determined by the central frequency (n
   value) and slot width (m value) as described in section 5. Such
   parameters should be able to be specified by the signaling protocol.

5.3. PCE

   [WSON-PCE] describes the architecture and requirements of PCE for
   WSON. In the case of flexible grid, RSA instead of RWA is used for
   routing and frequency slot assignment. Hence PCE should implement
   RSA for flexible grids. The architecture and requirements of PCE for
   flexible grids are similar to what is described in [WSON-PCE]. This
   section describes the changes brought by flexible grids.

5.3.1. RSA Computation Type

   A PCEP request within a PCReq message MUST be able to specify the
   computation type of the request:

   o Combined RSA: Both the route and frequency slot should be provided
      by PCE.

   o Routing Only: Only the route is requested to be provided by PCE.

   The PCEP response within a PCRep Message MUST be able to specify the
   route and the frequency slot assigned to the route.

   RSA in SSON MAY include the check of signal processing capabilities,
   which MAY be provided by the IGP. A PCC should be able to indicate
   additional restrictions for such signal compatibility, either on the
   endpoint or any given link (such as regeneration points).

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   A PCC MUST be able to specify whether the PCE MUST also assign a
   Modulation list and/or a FEC list, as defined in [WSON-ENCODE] and

   A PCC MUST be able to specify whether the PCE MUST or SHOULD include
   or exclude specific modulation formats and FEC mechanisms.

   In the case where a valid path is not found, the response MUST be
   able to specify the reason (e.g., no route, spectrum not found, etc.)

5.3.2. RSA path re-optimization request/reply

   For a re-optimization request, the PCEP request MUST provide the
   path to be re-optimized and include the following options:

   o Re-optimize the path keeping the same frequency slot.

   o Re-optimize spectrum keeping the same path.

   o Re-optimize allowing both frequency slot and the path to change.

   The corresponding PCEP response for the re-optimized request MUST
   provide the Re-optimized path and frequency slot.

   In case a path is not found, the response MUST include the reason
   (e.g., no route, frequency slot not found, both of route and
   frequency slot not found, etc.)

5.3.3. Frequency Constraints

   A PCE should consider the following constraints brought by the
   transmitters and receivers:

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

   o Slot width: The slot width needed by a transmitter or receiver.

   These constraints may be provided by the requester (PCC) in the PCEP
   request or reside within the PCE's TEDB which stores the
   transponder's capabilities.

   A PCC may also specify the frequency constraints for policy reasons.
   In this case, the constraints should be specified in the request
   sent to the PCE. In any case, the PCE will compute the route and
   assign the frequency slot to meet the constraints specified in

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   theafore mentioned request and it will then return the result of the
   path computation to the PCC in the corresponding response.

6. Security Considerations

   This document does not introduce any further security issues other
   than those described in [RFC6163] and [RFC5920].

7. References

7.1. Normative References

   [RFC2119] S. Bradner, "Key words for use in RFCs to indicate
             requirements levels", RFC 2119, March 1997.

   [WSON-PCE] Y. Lee, G. Bernstein, Jonas Martensson, T. Takeda and T.
             Tsuritani, "PCEP Requirements for WSON Routing and
             Wavelength Assignment", draft-ietf-pce-wson-routing-
             wavelength-05, July 2011.

   [WSON-ENCODE] G. Bernstein, Y. Lee, Dan Li and W. Imajuku, "Routing
             and Wavelength Assignment Information Encoding for
             Wavelength Switched Optical Networks", draft-ietf-ccamp-
             rwa-wson-encode, August 2011.

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

   [G.FLEXIGRID]Draft revised G.694.1 version 1.6, Consented in
             December 2011, ITU-T Study Group 15.

7.2. Informative References

   [G.694.1v1]ITU-T Recommendation G.694.1, Spectral grids for WDM
             applications: DWDM frequency grid, June 2002.

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

   [SSON-RSA]Yawei Yin, Ke Wen, David J. Geisler, Ruiting Liu, and S. J.
             B. Yoo, ''Dynamic on-demand defragmentation in flexible
             bandwidth elastic optical networks'', 2012 Optical Society
             of America.

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8. Authors' Addresses

   Fatai Zhang
   Huawei Technologies
   F3-5-B R&D Center, Huawei Base
   Bantian, Longgang District
   Shenzhen 518129 P.R.China
   Phone: +86-755-28972912
   Email: zhangfatai@huawei.com

   Young Lee
   1700 Alma Drive, Suite 100
   Plano, TX  75075

   Phone: +1 972 509 5599 x2240
   Fax:   +1 469 229 5397
   EMail: ylee@huawei.com

   Oscar Gonzalez de Dios
   Telefonica Investigacion y Desarrollo
   Emilio Vargas 6
   Madrid,   28045
   Phone: +34 913374013
   Email: ogondio@tid.es

   Ramon Casellas
   Av. Carl Friedrich Gauss, 7
   Castelldefels, 08860, Spain
   Phone: +34 936452900
   Email: ramon.casellas@cttc.es

   Daniele Ceccarelli
   Via A. Negrone 1/A
   Genova - Sestri Ponente

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   Email: daniele.ceccarelli@ericsson.com

   Xiaobing Zi
   Huawei Technologies
   F3-5-B R&D Center, Huawei Base
   Bantian, Longgang District
   Shenzhen 518129 P.R.China
   Phone: +86-755-28973229
   Email: zixiaobing@huawei.com

   Jianrui Han
   Huawei Technologies
   F3-5-B R&D Center, Huawei Base
   Bantian, Longgang District
   Shenzhen 518129 P.R.China
   Phone: +86-755-28973229
   Email: hanjianrui@huawei.com

   Felipe Jimenez Arribas
   Telefonica Investigacion y Desarrollo
   Emilio Vargas 6
   Madrid,   28045
   Email: felipej@tid.es

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