Internet DRAFT - draft-wang-ccamp-gmpls-flexigrid-framework

draft-wang-ccamp-gmpls-flexigrid-framework






Network Working Group                                         Qilei Wang
Internet-Draft                                                  Xihua Fu
Intended status: Standards Track                         ZTE Corporation
Expires: September 12, 2012                                 Mar 11, 2012


          Framework for GMPLS Control of Flexible Grid Network
           draft-wang-ccamp-gmpls-flexigrid-framework-01.txt

Abstract

   This document provides a framework for applying Generalized Multi-
   Protocol Label Switching (GMPLS) and the Path Computation Element
   (PCE) architecture to control the flexible grid network base on the
   Wavelength Switched Optical Networks (WSONs).  GMPLS control of WSON
   which is addressed in RFC6163 is out of the scope of this document.

   This document focuses on the topological elements changes and new
   path selection constraints that flexible grid technology takes.
   Impairments related technology is not covered in this document.

Status of this Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on September 12, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



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   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  . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Flexible Grid Networks . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Flexible Grid Network  . . . . . . . . . . . . . . . . . .  4
     3.2.  WDM Links  . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.3.  Optical Transmitters and Receivers . . . . . . . . . . . .  5
     3.4.  Optical Signals in Flexible Grid Network . . . . . . . . .  6
       3.4.1.  Optical Tributary Signals  . . . . . . . . . . . . . .  7
       3.4.2.  WSON Signal Characteristics  . . . . . . . . . . . . .  7
     3.5.  ROADMs, OXCs, Splitters, Combiners, and FOADMs . . . . . .  7
       3.5.1.  Reconfigurable Optical Add/Drop Multiplexers, OXCs
               and FOADM  . . . . . . . . . . . . . . . . . . . . . .  8
       3.5.2.  Splitters and Combiners  . . . . . . . . . . . . . . .  9
     3.6.  Electro-Optical Systems  . . . . . . . . . . . . . . . . .  9
   4.  Routing and wavelength Assignment in flexible grid network . . 10
   5.  GMPLS and PCE Control  . . . . . . . . . . . . . . . . . . . . 11
     5.1.  Extension to GMPLS Signaling . . . . . . . . . . . . . . . 11
     5.2.  Extension to GMPLS Routing . . . . . . . . . . . . . . . . 11
       5.2.1.  Available Wavelength Range . . . . . . . . . . . . . . 12
       5.2.2.  Port Label Restriction . . . . . . . . . . . . . . . . 12
     5.3.  Optical Path Computation and Implications for PCE  . . . . 13
       5.3.1.  Optical Path Constraints and Electro-Optical
               Element Signal Compatibility . . . . . . . . . . . . . 13
       5.3.2.  Discovery of RWA-Capable PCEs  . . . . . . . . . . . . 14
       5.3.3.  Use of GCO . . . . . . . . . . . . . . . . . . . . . . 14
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15












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1.  Introduction

   Flexible grid is a new DWDM application which is defined in the
   newest version of [G.694.1].  Compared to traditional fixed grid
   network, a flexible grid network can select its data channels with
   arbitrary slot width, and mainly be used to setup path with higher
   bitrates (e.g., 100G or 400G or higher). whereas traditional fixed
   grid DWDM technology always uses fixed slot width and is mainly used
   to setup path with lower bitrates signals.  Flexible grid network is
   also a WDM-based optical network in which switching is performed
   selectively based on the center wavelength of optical channels ,which
   means flexible grid channels can be represented as a lambda capable
   switching LSP by center wavelength and slot width from the control
   plane perspective.

   Wavelength Switched Optical Network (WSON) which is addressed in
   [RFC6163] is the application of Generalized Multi-Protocol Label
   Switching (GMPLS) [RFC3945] operation to traditional fixed grid WDM
   network.  As flexible grid network is a new WDM network which evolves
   from traditional fixed grid network, GMPLS also can be used to
   operate flexible grid network.  Similar to fixed grid network,
   flexible grid network is also constructed from subsystems that
   include Wavelength Division Multiplexing (WDM) links, tunable
   transmitters and receivers, Reconfigurable Optical Add/Drop
   Multiplexers (ROADMs), wavelength converters, and electro-optical
   network elements, which have flexible grid characteristics.  WSON
   specific descriptions are addressed in [RFC6163] and are out of the
   scope of this document.  People who are interested in this document
   are supposed to be familiar with [RFC6163].

   This document provides a framework for applying the GMPLS
   architecture and protocols [RFC3945] and the PCE architecture
   [RFC4655] to the control and operation of flexible grid networks.  In
   order to help GMPLS and PCE use for flexible grid network, this
   document first focuses on the subsystems and characteristics
   information that flexible grid network brings and then modeled the
   characteristics information by GMPLS and PCE.  This work will help
   facilitate the development of protocol solution models and protocol
   extensions within the GMPLS and PCE protocol families.

1.1.  Conventions used in this document

   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].






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2.  Terminology

   o  Flexible Grid: a new WDM technology different from traditional
      fixed grid DWDM technology defined with the aim of allowing
      flexible optical spectrum management, in which the Slot Width of
      the wavelength ranges allocated to different channels are flexible
      (variable sized).

   o  Wavelength Range: [RFC6163] gives a description of this
      terminology.Wavelength range given a mapping between labels and
      the ITU-T grids, each range could be expressed in terms of a
      tuple, (lambda1, lambda2) or (freq1, freq2), where the lambdas or
      frequencies can be represented by 32-bit integers.

   o  Frequency slot: The definition in [G.694.1] is shown here.  The
      frequency range allocated to a channel and unavailable to other
      channels within a flexible grid.  A frequency slot is defined by
      its nominal central frequency and its slot width.

   o  Slot width: The full width of a frequency slot in a flexible grid.


3.  Flexible Grid Networks

   Wavelength Switched Optical Network (WSON) related documents cover
   the constraints information that needs to be considered in the
   process of path computation.  Emergence of flexible grid DWDM
   technology raises some new characteristics and these new
   characteristics should be modeled by GMPLS and PCE from the
   perspective of contral plane in order to help path computation.  This
   document mainly focus on the flexible grid subsystems'
   characteristics information and constraints information that impact
   the flexible grid path selection process (i.e. wavelength selection).
   Subsequent sections review and model flexible grid characteristics
   that need to be emphasized by control plane and these sections follow
   the sequence of the section addressed in [RFC6163].

3.1.  Flexible Grid Network

   As described in the newest version of [G.694.1], flexible DWDM grid
   allows frequency slots have a nominal central frequency (in THz)
   defined by: 193.1 + n x 0.00625 where n is a positive or negative
   integer including 0 and 0.00625 is the nominal central frequency
   granularity in THz and a slot width defined by: 12.5 x m where m is a
   positive integerand 12.5 is the slot width granularity in GHz.  Any
   combination of frequency slots is allowed as long as no two frequency
   slots overlap.




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3.2.  WDM Links

   According to the review of the newest version of [G.694.1], the
   nominal central frequencies for the flexible grid network are defined
   with a granularity of 6.25 GHz and the frequency slot widths are
   defined as a multiple of 12.5 GHz.  A label representation which
   includes the information of central frequency and slot width is
   needed to provides a common label format to be used in signaling
   optical paths.  The flexible grid labels can also be used to describe
   WDM links, ROADM ports, and wavelength converters for the purposes of
   path selection.

   As described in section 3.1 of [RFC 6163], putting WDM over different
   types of fiber require significant engineering and a fairly limited
   range of wavelengths.  Parameters that include wavelength range and
   channel spacing is needed to perform basic, impairment-unaware
   modeling of a WDM link.


   o  Wavelength range: wavelength range can be used to give a mapping
      between labels and the flexible grid and each range could be
      expressed in terms of a tuple,(lambda1, lambda2) or (freq1,
      freq2).  Maybe new label representation is needed to describe
      wavelength range.

   o  Channel Spacing: since flexible grid can provide a granularity of
      6.25GHz, this new channel spacing value needs to be added.

   In addition to the wavelength range and channel spacing, indication
   SHOULD also be added to indicate the link support flexible grid DWDM
   technology.

   As indicated in [RFC6163], this information is relatively statically
   for a particular link as changes to these properties generally
   require hardware upgrades.  Such information may be used locally
   during wavelength assignment via signaling.

3.3.  Optical Transmitters and Receivers

   Similar to WSON, flexible grid WDM optical systems make use of
   coupled optical transmitters and receivers to setup LSC LSP.  In the
   case of an optical network without wavelength converters, an optical
   path needs to be routed from source transmitter to sink receiver and
   must use a single wavelength.  Flexible grid brings some new
   characteristics to transmitters and receivers compare to traditional
   fixed grid characteristics like "Tunable", "Tuning range", "Tuning
   time" and "Spectral characteristics and stability" which are
   addressed in [RFC6163] for fixed grid.  This section examines the new



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   characteristics that would impact optical transmitters and receivers
   in the process of control plane path computation.  Modeling
   parameters for flexible grid optical transmitters and receivers from
   the control plane perspective are:


   o  Tuning range: As described in [RFC6163], this is the frequency or
      wavelength range over which the optics can be tuned. (lambda1,
      lambda2) or (freq1, freq2) can be used to represent the wavelength
      range, where lambda1 and lambda2 or freq1 and freq2 are the labels
      representing the lower and upper bounds in wavelength.  As nominal
      central frequencies can't be figured out before the path setup in
      flexible grid network and flexible grid label may be different
      from fixed grid label, "Tuning range" may be encode with some
      different format from traditional fixed grid technology.

   o  Slot width: this parameter indicates slot width needed by a
      transmitter or receiver and SHOULD be considered in the process of
      path computation.

   When an end-to-end LSC LSP needs be setup, operator first sends a
   path setup command which convey some characteristics information of
   the LSP, such as bitrates, to the source node.  Path setup request is
   sent to path computation element to computes an end-to-end LSC LSP
   with specific slot width information, which bases on the bitrates and
   modulation format that transceiver and receiver support.

3.4.  Optical Signals in Flexible Grid Network

   Similar to the fixed grid swithing (e.g., WSON), the fundamental unit
   of switching in flexible grid is also a "wavelength".  The
   transmitters and receivers in these networks will deal with one
   wavelength at a time, while the switching systems themselves can deal
   with multiple wavelengths at a time.  Key non-impairment-related
   parameters which are listed in [RFC6163] are shown below:


   o  (a) Minimum channel spacing (GHz)

   o  (b) Minimum and maximum central frequency

   o  (c) Bitrates/Line coding (modulation) of optical tributary signals


   As described in [RFC6163], (a) and (b) are considered properties of
   the link and restrictions on the GMPLS Labels while (c) is a property
   of the "signal".  For the purposes of modeling the flexible grid, new
   parameters which are related to the properities of the link and



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   restrictions and property of "signal" SHOULD be considered:


   o  (d) Minimum and Maximum Slot Width

   o  (e) Slot Width


   (d) is considered properties of the link and restrictions on the
   GMPLS Labels, and description can be found in the following section.
   (e) is a property of the "signal" and this property is determined by
   the transmitter and may be changed if signal traverse an OEO.

3.4.1.  Optical Tributary Signals

   In [RFC6163], "optical tributary signal classes" are characterized by
   a modulation format and bitrates range and both of them are key
   parameters in characterizing the optical tributary signal.  Note
   that, with advances in technology, optical tributary signal classes
   that support flexible grid would be added.

   For optical tributary signals in flexible grid, bitrates range and
   modulation format are still two key parameters, as a single
   wavelength with central frequency and slot width used by a signal
   sent from transmitter can be deduced from these two parameters base
   on the available wavelength and slot width range from the source to
   the destination.

3.4.2.  WSON Signal Characteristics

   Description about WSON signal characteristics in [RFC6163] also can
   be applied to this document.  Fundamental unit of switching in
   flexible grid network is also "wavelength".  WSON signal
   characteristics like optical tributary signal class (modulation
   format), forward error correction (FEC), central frequency
   (wavelength), bitrates and general protocol identifier (G-PID) are
   still used in flexible grid network in the process of path
   computation and some more modulation formats and FECs may be added to
   describe flexible grid network signal characteristics.

   Except the parameter that have been included in [RFC6163], the
   parameter slot width is also needed here to specify the slot width
   that signal occupies.

3.5.  ROADMs, OXCs, Splitters, Combiners, and FOADMs

   This section mainly focuses on optical devices such as ROADMs,
   Optical Cross-Connects (OXCs), splitters, combiners, and Fixed



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   Optical Add/Drop Multiplexers (FOADMs) which can be used in flexible
   grid network and examines their parameters of these devices that can
   be used in the process of control plane path computation.

3.5.1.  Reconfigurable Optical Add/Drop Multiplexers, OXCs and FOADM



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


                              Figure 1: ROADM


   A picture is shown here to facilitate the description of ROADM.
   ROADM is composed of WSSes (wavelength selective switch) and
   splitters which are used massively in current WDM network.  WSS can
   be used to select the wavelength on the line side output port and
   splitter can be used on the line side input port to split the income
   wavelength.

   Switched connectivity matrix is needed to show whether a wavelength
   on input port can be connected to an output port internal.

   Besides the switched connectivity matrix which is applied to line
   side port and tributary side port included in [RFC6163], new
   wavelength restriction of the line side port on a ROADM which are
   brought by flexible grid are considered below:



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   o  (a) Available wavelength range:

      This parameter indicates the available wavelength that can be
      allocated to a LSP. (lambda1, lambda2) or (freq1, freq2) can be
      used to represent the available wavelength range.

   o  (b) Maximum/Minimum slot width that a port support

      This is an inherent attribution of the network subsystems, like
      WSS, and can be treated as port label restriction.  Requirements
      and descriptions about the restrictions information can be found
      in [draft-wangl-ccamp-ospf-ext-constraint-flexi-grid].  For
      flexible grid subsystems' ports, the possible values of slot width
      are within the range [Minimum Slot Width, Maximum Slot Width] and
      with the slot width granularity of 2 * C.S. (Channel Spacing).
      The combination of C.S. and [Minimum Slot Width, Maximum Slot
      Width] can represent any slot width that ROADM support.

   o  (c) Wavelength Range allocation

      The whole wavelength that ROADM support can be partitioned into
      several wavelength ranges, and one wavelength range can only be
      used for paths setup with the specific bit rate and/or modulation
      format.  The advertisement of this restrictions information will
      help reduce fragments in flexible grid network.  Requirements
      related description can be found in
      [draft-wang-ccamp-flexible-grid-wavelength-range-ospf-te].  This
      is an optional requirement.


   These restrictions information can also be applied to fixed optical
   Add/Drop Multiplexers.

3.5.2.  Splitters and Combiners

   Nothing is new except switched connectivity matrix and this has been
   addressed in [RFC6163].

3.6.  Electro-Optical Systems

   Some words can be found in [RFC6163].  OEO switches, wavelength
   converters, and regenerators all share a similar property: they can
   be more or less "transparent" to an "optical signal" depending on
   their functionality and/or implementation.  Properties can be applied
   to flexible grid, and these properties can satisfy path computation
   without taking any new characteristics into consideration.  Modeling
   of OEO switches, wavelength converters and regenerators can also be
   applied to flexible grid.



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   Regenerator can be used to restore signal quality.  Bitrates range
   and modulation formats that the regenerator support need to be taken
   into consideration to help path computation, whereas slot width do
   not (May be someone will talk about slot width).  If one regenerator
   is designed to handle signal with specific bitrates and modulation
   formats, then it would support the corresponding slot width because
   slot width can be derived by modulation format and bitrates.  Even if
   the slot width is changed by the electro-optical systems due to the
   change of modulation format, the slot width that has already changed
   may not be explicitly specified because bitrates and modulation
   format are explicitly specified.


4.  Routing and wavelength Assignment in flexible grid network

   This section briefly describes the constraints information of routing
   and wavelength assignment in the flexible grid network.  Similar to
   WSON, the input to basic RWA in flexible grid network are the
   requested optical path's source and destination, the network
   topology, the locations and capabilities of any wavelength
   converters, the wavelengths available on each optical link and port
   label constraints information such as slot width range that a port
   support and wavelength range partition information by bitrates and/or
   modulation formats.  The output that provided by RWA in flexible grid
   network are an explicit route through ROADMs, a wavelength for
   optical transmitter, the slot width that this wavelength occupies,
   and a set of locations (generally associated with ROADMs or switches)
   where wavelength conversion is to occur and the new wavelength to be
   used on each component link after that point in the route.Similar to
   WSON, an optical flexible grid path that from source to destination
   also must use a single wavelength that is available along that path
   without "colliding" with a wavelength used by any other optical path
   that may share an optical fiber.

   In [RFC6163], three different ways of performing RWA in conjunction
   with the control plane are shown here:

   1)  Combined RWA

   2)  Separated R and WA (R + WA)

   3)  Routing and Distributed WA (R + DWA)

   These ways can also be applied to flexible grid control plane path
   computation.  Related description about these three architectures can
   be found in section 4.1 of [RFC6163].





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5.  GMPLS and PCE Control

   Flexible grid brings some new characteristics to WDM network, and
   consequently WSON would add some extensions or change in order to
   control the flexible grid network.  Extensions to GMPLS signaling,
   routing and PCE are described in this section.

5.1.  Extension to GMPLS Signaling

   Support for WSON signaling exists in [RFC3471], [RFC4328] and
   [draft-ietf-ccamp-wson-signaling].  However, a number of practical
   issues arise in the identification of wavelengths and signals in
   wavelength assignment in flexible grid.

   A mapping between label and wavelength is needed to simplify the
   characterization of WDM links and WSON devices.  The mapping like the
   one described in [draft-farrkingel-ccamp-flexigrid-lambda-label]
   provides label and wavelength mapping for communication between PCE
   and WSON PCCs.  Different LSP may occupy different slot width if
   paths have different bitrates and modulation format in flexible grid
   network.  So in the flexible grid network, not only central frequency
   is needed, but also slot width SHOULD be included to identify a
   channel in the process of path setup in flexible grid network.

   GMPLS Signaling should be able to convey the central frequency and
   slot width information that a LSC LSP occupies.  If the slot width is
   changed due to the change of modulation format, signaling should also
   be able to express this.  Except methods that are specified in
   [draft-farrkingel-ccamp-flexigrid-lambda-label],
   [draft-hussain-ccamp-super-channel-label] and
   [draft-zhang-ccamp-flexible-grid-rsvp-te-ext] also provide methods to
   carry central frequency and slot width information in the process of
   signaling.

   Note: extension to GMPLS signaling SHOULD be compatible with current
   signaling protocol.

5.2.  Extension to GMPLS Routing

   The following subsystem's properties are needed by IGP to minimally
   characterize WSON, also these properties are needed to characterize
   flexible grid control plane.  This section addresses the constraints
   information needed to model flexible grid from the control plane
   perspective base on the Wavelength Switched Optical Network (WSON).







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   1)  WDM link properties (allowed wavelengths)

   2)  Optical transmitters (wavelength range)

   3)  ROADM/FOADM properties (connectivity matrix, port wavelength
       restrictions)

   4)  Wavelength converter properties (per network element, may change
       if a common limited shared pool is used)

   Here 1, 2 and 3 are re-considered in the flexible grid network.

5.2.1.  Available Wavelength Range

   Wavelengths available on WDM link and port of optical transmitters
   are advertised through routing protocol, the wavelengths available
   information can be used by path computation element to compute a
   suitable end-to-end LSP.  As different flexible grid channels always
   have different slot widths and channels' central frequency position
   and slot width can't be decided in advance, so mapping between label
   and wavelength may not be able to use the representation similar to
   [RFC6205] to represent every channel.  Maybe new label formats and
   representation of wavelength available are needed in routing protocol
   to transfer IGP information between nodes and PCEs.  Extensions to
   label set field SHOULD be able to represent the wavelength available
   validly in flexible grid network.  Allowed wavelengths on WDM link
   and wavelength range on optical transmitters neede to adapt to this
   change.[draft-dhillon-ccamp-super-channel-ospfte-ext],
   [draft-wangl-ccamp-ospf-ext-constraint-flexi-grid] and
   [draft-zhang-ccamp-flexible-grid-ospf-ext] give some different
   methods to represent the available wavelengths.

5.2.2.  Port Label Restriction

   Some new ROADM/FOADM properties brought by flexible grid need to be
   advertised by routing protocol in order to help path computation.  In
   the section 3, properties of ROADM/FOADM are described as the port
   label restrictions information.

   The first one, maximum/minimum slot width supported on one port need
   to be advertised.  This slot width constraint information of a port
   (i.e., available slot width range of a WSS) SHOULD be known by path
   computation element in order to compute a suitable path.  According
   to [draft-wangl-ccamp-ospf-ext-constraint-flexi-grid], combination of
   C.S. and [Minimum Slot Width, Maximum Slot Width] can represent any
   slot width that ROADM support.  LMP can be run between two neighbor
   nodes to negotiate these attributes and related extension can be
   found in [draft-li-ccamp-grid-property-lmp].  This is optional



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   because routing protocol can also be used to deal with it.

   The second one, wavelength range allocation information of ROADM/
   FOADM needs to be advertised through routing protocol.  Grouping of
   wavelength of the same bitrates and/or modulation formats would help
   reduce fragments.  Channels in the same wavelength range with the
   same bitrates looks almost like fixed grid technology, and they won't
   generate much fragment in the path setup and release because every
   channel use the same slot width.  Requirements of wavelength range
   allocation and protocol extensions can be found in
   [draft-wang-ccamp-flexible-grid-wavelength-range-ospf-te].

5.3.  Optical Path Computation and Implications for PCE

   Extensions to PCEP can be found in [draft-lee-pce-wson-rwa-ext] base
   on Wavelength Switched Optical Network.  Emergence of flexible grid
   brings some extension to current draft.  PCEP SHOULD be able to
   support flexible grid path computation.

5.3.1.  Optical Path Constraints and Electro-Optical Element Signal
        Compatibility

   Flexible grid may not change the computation architectures of WSON,
   but new constraints information SHOULD be taken into consideration in
   the process of path computation.  According to the description in
   [RFC6163], when requesting a path computation to PCE, the PCC should
   be able to indicate:


   1)  The G-PID type of an LSP

   2)  The signal attributes at the transmitter and receiver.


   And the PCE should be able to respond to the PCC with the following:

   1)  The conformity of the requested optical characteristics
       associated with the resulting LSP with the source, sink, and NE
       along the LSP.

   2)  Additional LSP attributes modified along the path.

   3)  Slot width of the LSP.  This should be respond to the PCC as
       flexible grid channels always have different slot widths.  Slot
       width information may be contained in the wavelength object which
       is carried in PCRep message from PCE to PCC.





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5.3.2.   Discovery of RWA-Capable PCEs

   Not all PCEs within a domain would necessarily need the capability of
   flexible grid path computation.  Therefore, it would be useful to
   indicate that a PCE has the ability to deal with flexible grid via
   the discovery mechanisms being established for PCE discovery in
   [RFC5088].  Extensions to [RFC5088] are needed to achieve this goal.

5.3.3.  Use of GCO

   Though GCO is able to reduce the fragment of the wavelength or
   spectrum, it is hard to be implemented in the network, because GCO
   would involve massive LSPs and distrub current service.  As fragment
   can be reduced through early wavelength or spectrum allocation
   planning, GCO maybe avoided.


6.  Security Considerations

   TBD


7.  References

7.1.  Normative References

   [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.

7.2.  Informative References

   [G.694.1 v1]
              International Telecommunications Union, "Draft revised
              G.694.1 version 1.3".

   [flexible-grid-ospf-ext]
              Fatai Zhang, Xiaobing Zi, Ramon Casellas, O. Gonzalez de
              Dios, and D. Ceccarelli, "GMPLS OSPF-TE Extensions in
              support of Flexible-Grid in DWDM Networks",
              draft-zhang-ccamp-flexible-grid-ospf-ext-00.txt .

   [flexible-grid-requirements]
              Fatai Zhang, Xiaobing Zi, O. Gonzalez de Dios, and Ramon
              Casellas, "Requirements for GMPLS Control of Flexible
              Grids",



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              draft-zhang-ccamp-flexible-grid-requirements-01.txt .

   [flexible-grid-rsvp-te]
              Fatai Zhang, O. Gonzalez de Dios, and D. Ceccarelli,
              "RSVP-TE Signaling Extensions in support of Flexible
              Grid",
              draft-zhang-ccamp-flexible-grid-rsvp-te-ext-00.txt .

   [flexigrid-lambda-label]
              D. King, A. Farrel, Y. Li, F. Zhang, and R. Casellas,
              "Generalized Labels for the Flexi-Grid in Lambda-Switch-
              Capable (LSC) Label Switching Routers",
              draft-farrkingel-ccamp-flexigrid-lambda-label-01.txt .

   [ospf-ext-constraint-flexi-grid]
              L Wang, Y Li, "OSPF Extensions for Routing Constraint
              Encoding in Flexible-Grid Networks",
              draft-wangl-ccamp-ospf-ext-constraint-flexi-grid-00.txt .

   [super-channel-label]
              Iftekhar Hussain, Abinder Dhillon, Zhong Pan, Marco Sosa
              and Bert Basch, Steve Liu, Andrew G. Malis, "Generalized
              Label for Super-Channel Assignment on Flexible Grid",
              draft-hussain-ccamp-super-channel-label-02.txt .

   [super-channel-ospfte]
              Abinder Dhillon, Iftekhar Hussain, Rajan Rao, Marco Sosa,
              "OSPFTE extension to support GMPLS for Flex Grid",
              draft-dhillon-ccamp-super-channel-ospfte-ext-02.txt .


Authors' Addresses

   Qilei Wang
   ZTE Corporation

   Email: wang.qilei@zte.com.cn


   Xihua Fu
   ZTE Corporation
   ZTE Plaza, No.10, Tangyan South Road, Gaoxin District
   Xi'an
   P.R.China

   Email: fu.xihua@zte.com.cn





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