Network Working Group                                      Y. Lee (ed.)
Internet Draft                                                   Huawei
Intended status: Informational                       G. Bernstein (ed.)
Expires: August October 2010                                 Grotto Networking
                                                         Wataru Imajuku

                                                       February 1,

                                                          April 5, 2010

    Framework for GMPLS and PCE Control of Wavelength Switched Optical
                              Networks (WSON)

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   This memo provides a framework for applying Generalized Multi-
   Protocol Label Switching (GMPLS) and the Path Computation Element
   (PCE) architecture to the control of wavelength switched optical
   networks (WSON).  In particular we provide control plane models for
   key wavelength switched optical network subsystems and processes. The
   subsystems include wavelength division multiplexed links, tunable
   laser transmitters, reconfigurable optical add/drop multiplexers
   (ROADM) and wavelength converters. In addition, electro-optical
   network elements and their compatibility constraints relative to
   optical signal parameters are characterized.

   Lightpath provisioning, in general, requires the routing and
   wavelength assignment (RWA) process. This process is reviewed and the
   information requirements, both static and dynamic for this process
   are presented, along with alternative implementation architectures
   that could be realized via various combinations of extended GMPLS and
   PCE protocols.

   This memo focuses on topological elements and path selection
   constraints that are common across different WSON environments as
   such it does not address optical impairments in any depth.

Table of Contents

   1. Introduction..................................................4 Introduction...................................................4
      1.1. Revision History..........................................5
         1.1.1. Changes from 00......................................5
         1.1.2. Changes from 01......................................5
         1.1.3. Changes from 02......................................5
         1.1.4. Changes from 03......................................6
         1.1.5. Changes from 04......................................6
      1.2. Related Documents.........................................6
         1.1.6. Changes from 05......................................6
   2. Terminology....................................................7 Terminology....................................................6
   3. Wavelength Switched Optical Networks...........................7
      3.1. WDM and CWDM Links........................................8 Links........................................7
      3.2. Optical Transmitters......................................9
      3.3. Optical Signals in WSONs.................................10
         3.3.1. Optical Tributary Signals...........................11
         3.3.2. WSON Signal Characteristics.........................12
      3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs............13 FOADMs............12
         3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs.......13
         3.4.2. Splitters...........................................16
         3.4.3. Combiners...........................................16
         3.4.4. Fixed Optical Add/Drop Multiplexers.................17
      3.5. Electro-Optical Systems..................................17
         3.5.1. Regenerators........................................17
         3.5.2. OEO Switches........................................20
      3.6. Wavelength Converters....................................20
         3.6.1. Wavelength Converter Pool Modeling..................22
      3.7. Characterizing Electro-Optical Network Elements..........26
         3.7.1. Input Constraints...................................27
         3.7.2. Output Constraints..................................27
         3.7.3. Processing Capabilities.............................28
   4. Routing and Wavelength Assignment and the Control Plane.......29
      4.1. Architectural Approaches to RWA..........................30
         4.1.1. Combined RWA (R&WA).................................30
         4.1.2. Separated R and WA (R+WA)...........................30
         4.1.3. Routing and Distributed WA (R+DWA)..................31
      4.2. Conveying information needed by RWA......................32
      4.3. Lightpath Temporal Characteristics.......................33
   5. Modeling Examples and Control Plane Use Cases.................34 Cases.................33
      5.1. Network Modeling for GMPLS/PCE Control...................34 Control...................33
         5.1.1. Describing the WSON nodes...........................34 nodes...........................33
         5.1.2. Describing the links................................36 links................................35
      5.2. RWA Path Computation and Establishment...................37 Establishment...................36
      5.3. Resource Optimization....................................38 Optimization....................................37
      5.4. Support for Rerouting....................................39 Rerouting....................................38
      5.5. Electro-Optical Networking Scenarios.....................39 Scenarios.....................38
         5.5.1. Fixed Regeneration Points...........................39 Points...........................38
         5.5.2. Shared Regeneration Pools...........................40 Pools...........................39
         5.5.3. Reconfigurable Regenerators.........................40 Regenerators.........................39
         5.5.4. Relation to Translucent Networks....................40 Networks....................39
   6. GMPLS & PCE Implications......................................41 Implications......................................40
      6.1. Implications for GMPLS signaling.........................41 signaling.........................40
         6.1.1. Identifying Wavelengths and Signals.................42 Signals.................41
         6.1.2. WSON Signals and Network Element Processing.........42 Processing.........41
         6.1.3. Combined RWA/Separate Routing WA support............42 support............41
         6.1.4. Distributed Wavelength Assignment: Unidirectional, No
         6.1.5. Distributed Wavelength Assignment: Unidirectional,
         Limited Converters.........................................44 Converters.........................................42
         6.1.6. Distributed Wavelength Assignment: Bidirectional, No
      6.2. Implications for GMPLS Routing...........................44 Routing...........................43
         6.2.1. Electro-Optical Element Signal Compatibility........45 Compatibility........43
         6.2.2. Wavelength-Specific Availability Information........46 Information........44
         6.2.3. WSON Routing Information Summary....................46 Summary....................45
      6.3. Optical Path Computation and Implications for PCE........48 PCE........46
         6.3.1. Lightpath Constraints and Characteristics...........48 Characteristics...........46
         6.3.2. Electro-Optical Element Signal Compatibility........49 Compatibility........47
         6.3.3. Discovery of RWA Capable PCEs.......................49
      6.4. Summary of Impacts by RWA Architecture...................50 PCEs.......................47
   7. Security Considerations.......................................51 Considerations.......................................48
   8. IANA Considerations...........................................51 Considerations...........................................48
   9. Acknowledgments...............................................51 Acknowledgments...............................................48
   10. References...................................................52 References...................................................49
      10.1. Normative References....................................52 References....................................49
      10.2. Informative References..................................53 References..................................50
   11. Contributors.................................................56 Contributors.................................................53
   Author's Addresses...............................................57 Addresses...............................................54
   Intellectual Property Statement..................................57 Statement..................................54
   Disclaimer of Validity...........................................58 Validity...........................................55

1. Introduction

   This memo provides a framework for applying GMPLS and the Path
   Computation Element (PCE) architecture to the control of WSONs.  In
   particular we provide control plane models for key wavelength
   switched optical network subsystems and processes. The subsystems
   include wavelength division multiplexed links, tunable laser
   transmitters, reconfigurable optical add/drop multiplexers (ROADM)
   and wavelength converters. In addition, electro-optical network
   elements and their compatibility constraints relative to optical
   signal parameters are characterized.

   Lightpath provisioning, in general, requires the routing and
   wavelength assignment (RWA) process. This process is reviewed and the
   information requirements, both static and dynamic for this process
   are presented, along with alternative implementation architectures
   that could be realized via various combinations of extended GMPLS and
   PCE protocols.

   This document will focus on the unique properties of links, switches
   and path selection constraints that occur in WSONs.  Different WSONs
   such as access, metro and long haul may apply different techniques
   for dealing with optical impairments hence this document will not
   address optical impairments in any depth, but instead focus on
   properties that are common across a variety of WSONs. For more on how
   the GMPLS control plane can aid in dealing with optical impairments
   see [WSON-Imp].

   1.1. Revision History

      1.1.1. Changes from 00

   o  Added new first level section on modeling examples and control
      plane use cases.

   o  Added new third level section on wavelength converter pool

   o  Editorial clean up of English and updated references.

      1.1.2. Changes from 01

   Fixed error in wavelength converter pool example.

      1.1.3. Changes from 02

   Updated the abstract to emphasize the focus of this draft and
   differentiate it from WSON impairment [WSON-Imp] and WSON
   compatibility [WSON-Compat] drafts.

   Added references to [WSON-Imp] and [WSON-Compat].

   Updated the introduction to explain the relationship between this
   document and the [WSON-Imp] and [WSON-Compat] documents.

   In section 3.1 removed discussion of optical impairments in fibers.

   Merged section 3.2.2 and section 3.2.3. Deferred much of the
   discussion of signal types and standards to [WSON-Compat].

   In section 3.4 on Wavelength converters removed paragraphs dealing
   with signal compatibility discussion as this is addressed in [WSON-

   In section 6.1 removed discussion of signaling extensions to deal
   with different WSON signal types. This is deferred to [WSON-Compat].

   In section 6 removed discussion of "Need for Wavelength Specific
   Maximum Bandwidth Information".

   In section 6 removed discussion of "Relationship to link bundling and

   In section 6 removed discussion of "Computation Architecture
   Implications" as this material was redundant with text that occurs
   earlier in the document.

   In section 6 removed discussion of "Scaling Implications" as this
   material was redundant with text that occurs earlier in the document.

      1.1.4. Changes from 03

   In Section 3.3.1 added 4-degree ROADM example and its connectivity

      1.1.5. Changes from 04

   Added and enhanced sections on signal type and network element

   Merged section 3.2.1 into section 3.2.

   Created new section 3.3 on Optical signals with material from [WSON-

   Created new section 3.5 on Electro-Optical systems with material from

   Created new section 3.7 on Characterizing Electro-Optical Network
   Elements with material from [WSON-Compat].

   Created new section 5.5 on Electro-Optical Networking Scenarios with
   material from [WSON-Compat].

   Created new section 6.1.2 on WSON Signals and Network Element
   Processing with material from [WSON-Compat].

   Created new section 6.3.2. Electro-Optical Related PCEP Extensions
   with material from [WSON-Compat].

   1.2. Related Documents

   This framework document covers essential concepts and models for the
   application and extension

      1.1.6. Changes from 05

   Removal of the control plane to WSONs. The
   following documents address specific aspects Section 1.2; Removal of WSONs and complement
   this draft.

   o  [WSON-Info] This document provides an information model needed by
      the routing and wavelength assignment (RWA) process in WSON.

   o  [WSON-Encode] This document provides efficient, protocol-agnostic
      encodings for the information elements necessary to support the
      routing and section on lightpath temporal
   characteristics; Removal of details on wavelength assignment (RWA) process in WSONs.

   o  [WSON-Imp] This document provides a framework for the support of
      impairment aware Routing and Wavelength Assignment (RWA) in WSON.

   o  [PCEP-RWA] This document provides application-specific
      requirements for the Path Computation Element communication
      Protocol (PCEP) for the support
   algorithms; Removal of RWA redundant summary in WSON. section 6.

2. Terminology

   CWDM: Coarse Wavelength Division Multiplexing.

   DWDM: Dense Wavelength Division Multiplexing.

   FOADM: Fixed Optical Add/Drop Multiplexer.

   OXC: Optical cross connect. A symmetric optical switching element in
   which a signal on any ingress port can reach any egress port.

   ROADM: Reconfigurable Optical Add/Drop Multiplexer. An asymmetric
   wavelength selective switching element featuring ingress and egress
   line side ports as well as add/drop side ports.

   RWA: Routing and Wavelength Assignment.

   Transparent Network: a wavelength switched optical network that does
   not contain regenerators or wavelength converters.

   Translucent Network:  a wavelength switched optical network that is
   predominantly transparent but may also contain limited numbers of
   regenerators and/or wavelength converters.

   Wavelength Conversion/Converters: The process of converting an
   information bearing optical signal centered at a given wavelength to
   one with "equivalent" content centered at a different wavelength.
   Wavelength conversion can be implemented via an optical-electronic-
   optical (OEO) process or via a strictly optical process.

   WDM: Wavelength Division Multiplexing.

   Wavelength Switched Optical Networks (WSON): WDM based optical
   networks in which switching is performed selectively based on the
   center wavelength of an optical signal.

3. Wavelength Switched Optical Networks

   WSONs come in a variety of shapes and sizes from continent spanning
   long haul networks, to metropolitan networks, to residential access
   networks. In all these cases we are concerned with those properties
   that constrain the choice of wavelengths that can be used, i.e.,
   restrict the wavelength label set, impact the path selection process,
   and limit the topological connectivity. In addition, if electro-
   optical network elements are used in the WSON, additional
   compatibility constraints may be imposed by the network elements on
   various optical signal parameters. In the following we examine and
   model some major subsystems of a WSON with an emphasis on those
   aspects that are of relevance to the control plane. In particular we
   look at WDM links, Optical Transmitters, ROADMs, and Wavelength

   3.1. WDM and CWDM Links

   WDM and CWDM links run over optical fibers, and optical fibers come
   in a wide range of types that tend to be optimized for various
   applications from access networks, metro, long haul, and submarine
   links to name a few. ITU-T standards exist for various types of
   fibers. For the purposes here we are concerned only with single mode
   fibers (SMF). The following SMF fiber types are typically encountered
   in optical networks:

      ITU-T Standard |  Common Name
      G.652 [G.652]  |  Standard SMF                              |
      G.653 [G.653]  |  Dispersion shifted SMF                    |
      G.654 [G.654]  |  Cut-off shifted SMF                       |
      G.655 [G.655]  |  Non-zero dispersion shifted SMF           |
      G.656 [G.656]  |  Wideband non-zero dispersion shifted SMF  |
   Typically WDM links operate in one or more of the approximately
   defined optical bands [G.Sup39]:

      Band     Range (nm)     Common Name    Raw Bandwidth (THz)
      O-band   1260-1360      Original       17.5
      E-band   1360-1460      Extended       15.1
      S-band   1460-1530      Short          9.4
      C-band   1530-1565      Conventional   4.4
      L-band   1565-1625      Long           7.1
      U-band   1625-1675      Ultra-long     5.5

   Not all of a band may be usable, for example in many fibers that
   support E-band there is significant attenuation due to a water
   absorption peak at 1383nm. Hence we can have a discontinuous
   acceptable wavelength range for a particular link. Also some systems
   will utilize more than one band. This is particularly true for coarse
   WDM (CWDM) systems.

   Current technology breaks up the bandwidth capacity of fibers into
   distinct channels based on either wavelength or frequency. There are
   two standards covering wavelengths and channel spacing. ITU-T
   recommendation [G.694.1] describes a DWDM grid defined in terms of
   frequency grids of 12.5GHz, 25GHz, 50GHz, 100GHz, and other multiples
   of 100GHz around a 193.1THz center frequency. At the narrowest
   channel spacing this provides less than 4800 channels across the O
   through U bands. ITU-T recommendation [G.694.2] describes a CWDM grid
   defined in terms of wavelength increments of 20nm running from 1271nm
   to 1611nm for 18 or so channels. The number of channels is
   significantly smaller than the 32 bit GMPLS label space allocated to
   lambda switching.  A label representation for these ITU-T grids is
   given in [Otani] and allows a common vocabulary to be used in
   signaling lightpaths. Further, these ITU-T grid based labels can also
   be used to describe WDM links, ROADM ports, and wavelength converters
   for the purposes of path selection.

   With a tremendous existing base of fiber many WDM links are designed
   to take advantage of particular fiber characteristics or to try to
   avoid undesirable properties.  For example dispersion shifted SMF
   [G.653] was originally designed for good long distance performance in
   single channel systems, however putting WDM over this type of fiber
   requires much system engineering and a fairly limited range of
   wavelengths. Hence for our basic, impairment unaware, modeling of a
   WDM link we will need the following information:

   o  Wavelength range(s): Given a mapping between labels and the ITU-T
      grids each range could be expressed in terms of a doublet
      (lambda1, lambda2) or (freq1, freq1) where the lambdas or
      frequencies can be represented by 32 bit integers.

   o  Channel spacing: currently there are about five channel spacings
      used in DWDM systems 12.5GHz to 200GHz and one defined CWDM

   For a particular link this information is relatively static, i.e.,
   changes to these properties generally require hardware upgrades. Such
   information could be used locally during wavelength assignment via
   signaling, similar to label restrictions in MPLS or used by a PCE in
   solving the combined routing and wavelength assignment problem.

   3.2. Optical Transmitters

   WDM optical systems make use of laser transmitters utilizing
   different wavelengths (frequencies). Some laser transmitters were and
   are manufactured for a specific wavelength of operation, that is, the
   manufactured frequency cannot be changed. First introduced to reduce
   inventory costs, tunable optical laser transmitters are becoming
   widely deployed in some systems [Coldren04], [Buus06]. This allows
   flexibility in the wavelength used for optical transmission and aids
   in path selection.

   Fundamental modeling parameters from the control plane perspective
   optical transmitters are:

   o  Tunable: Is this transmitter tunable or fixed.

   o  Tuning range: This is the frequency or wavelength range over which
      the laser can be tuned. With the fixed mapping of labels to
      lambdas of [Otani] this can be expressed as a doublet (lambda1,
      lambda2) or (freq1, freq2) where lambda1 and lambda2 or freq1 and
      freq2 are the labels representing the lower and upper bounds in
      wavelength or frequency.

   o  Tuning time: Tuning times highly depend on the technology used.
      Thermal drift based tuning may take seconds to stabilize, whilst
      electronic tuning might provide sub-ms tuning times. Depending on
      the application this might be critical. For example, thermal drift
      might not be applicable for fast protection applications.

   o  Spectral Characteristics and stability: The spectral shape of the
      laser's emissions and its frequency stability put limits on
      various properties of the overall WDM system. One relatively easy
      to characterize constraint is the finest channel spacing on which
      the transmitter can be used.

   Note that ITU-T recommendations specify many aspects of a laser
   transmitter. Many of these parameters, such as spectral
   characteristics and stability, are used in the design of WDM
   subsystems consisting of transmitters, WDM links and receivers
   however they do not furnish additional information that will
   influence label switched path (LSP) provisioning in a properly
   designed system.

   Also note that lasers transmitters as a component can degrade and
   fail over time. This presents the possibility of the failure of a LSP
   (lightpath) without either a node or link failure. Hence, additional
   mechanisms may be necessary to detect and differentiate this failure
   from the others, e.g., one doesn't not want to initiate mesh
   restoration if the source transmitter has failed, since the laser
   transmitter will still be failed on the alternate optical path.

   3.3. Optical Signals in WSONs

   In wavelength switched optical networks (WSONs) our fundamental unit
   of switching is intuitively that of 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. Hence we are generally concerned with
   multichannel dense wavelength division multiplexing (DWDM) networks
   with single channel interfaces. Interfaces of this type are defined
   in ITU-T recommendations [G.698.1] and [G.698.1]. Key non-impairment
   related parameters defined in [G.698.1] and [G.698.2] are:

   (a)   Minimum Channel Spacing (GHz)
   (b)   Minimum and Maximum central frequency

   (c)   Bit-rate/Line coding (modulation) of optical tributary signals

   In for the purposes of modeling the WSON in the control plane we can
   consider (a) and (b) as properties of the link and restrictions on
   the GMPLS labels while (c) is a property of the "signal".

      3.3.1. Optical Tributary Signals

   The optical interface specifications [G.698.1], [G.698.2], and
   [G.959.1] all use the concept of an Optical Tributary Signal which is
   defined as "a single channel signal that is placed within an optical
   channel for transport across the optical network". Note the use of
   the qualifier "tributary" to indicate that this is a single channel
   entity and not a multichannel optical signal.

   There are a currently a number of different "flavors" of optical
   tributary signals, known as "optical tributary signal classes". These
   are currently characterized by a modulation format and bit rate range

   (a)   optical tributary signal class NRZ 1.25G

   (b)   optical tributary signal class NRZ 2.5G

   (c)   optical tributary signal class NRZ 10G

   (d)   optical tributary signal class NRZ 40G

   (e)   optical tributary signal class RZ 40G

   Note that with advances in technology more optical tributary signal
   classes may be added and that this is currently an active area for
   deployment and standardization. In particular at the 40G rate there
   are a number of non-standardized advanced modulation formats that
   have seen significant deployment including Differential Phase Shift
   Keying (DPSK) and Phase Shaped Binary Transmission (PSBT)[Winzer06].

   Note that according to [G.698.2] it is important to fully specify the
   bit rate of the optical tributary signal:

   "When an optical system uses one of these codes, therefore, it is
   necessary to specify both the application code and also the exact bit
   rate of the system. In other words, there is no requirement for
   equipment compliant with one of these codes to operate over the
   complete range of bit rates specified for its optical tributary
   signal class."
   Hence we see that modulation format (optical tributary signal class)
   and bit rate are key parameters in characterizing the optical
   tributary signal.

      3.3.2. WSON Signal Characteristics

   We refer an optical tributary signal defined in ITU-T G.698.1 and .2
   to as the signal in this document. This is an "entity" that can be
   put on an optical communications channel formed from links and
   network elements in a WSON. This corresponds to the "lambda" LSP in
   GMPLS. For signal compatibility purposes with electro-optical network
   elements we will be interested in the following signal

                    List 1. WSON Signal Characteristics

  1. Optical tributary signal class (modulation format).
  2. FEC: whether forward error correction is used in the digital stream
     and what type of error correcting code is used
  3. Center frequency (wavelength)
  4. Bit rate
  5. G-PID: General Protocol Identifier for the information format

   The first three items on this list can change as a WSON signal
   traverses a network with regenerators, OEO switches, or wavelength

   Bit rate and GPID would not change since they describe the encoded
   bit stream. A set of G-PID values is already defined for lambda
   switching in [RFC3471] and [RFC4328].

   Note that a number of "pre-standard" or proprietary modulation
   formats and FEC codes are commonly used in WSONs. For some digital
   bit streams the presence of FEC can be detected, e.g., in [G.707]
   this is indicated in the signal itself via the FEC status indication
   (FSI) byte, while in [G.709] this can be inferred from whether the
   FEC field of the OTUk is all zeros or not.

   3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs

   Definitions of various optical devices and their parameters can be
   found in [G.671], we only look at a subset of these and their non-
   impairment related properties.

      3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs

   Reconfigurable add/drop optical multiplexers (ROADM) have matured and
   are available in different forms and technologies [Basch06]. This is
   a key technology that allows wavelength based optical switching. A
   classic degree-2 ROADM is shown in Figure 1.

        Line side ingress    +---------------------+  Line side egress
                         --->|                     |--->
                             |                     |
                             |        ROADM        |
                             |                     |
                             |                     |
                                 | | | |  o o o o
                                 | | | |  | | | |
                                 O O O O  | | | |
         Tributary Side:   Drop (egress)  Add (ingress)

                          Figure 1 Degree-2 ROADM

   The key feature across all ROADM types is their highly asymmetric
   switching capability. In the ROADM of Figure 1, the "add" ingress
   ports can only egress on the line side egress port and not on any of
   the "drop" egress ports. The degree of a ROADM or switch is given by
   the number of line side ports (ingress and egress) and does not
   include the number of "add" or "drop" ports. Sometimes the "add"
   "drop" ports are also called tributary ports. As the degree of the
   ROADM increases beyond two it can have properties of both a switch
   (OXC) and a multiplexer and hence we must know the switched
   connectivity offered by such a network element to effectively utilize
   it. A straight forward way to do this is via a "switched
   connectivity" matrix A where Amn = 0 or 1, depending upon whether a
   wavelength on ingress port m can be connected to egress port n
   [Imajuku]. For the ROADM of Figure 1 the switched connectivity matrix
   can be expressed as
               Ingress  Egress Port
               Port     #1 #2 #3 #4 #5
               #1:      1  1  1  1  1
               #2       1  0  0  0  0
         A =   #3       1  0  0  0  0
               #4       1  0  0  0  0
               #5       1  0  0  0  0

   Where ingress ports 2-5 are add ports, egress ports 2-5 are drop
   ports and ingress port #1 and egress port #1 are the line side (WDM)

   For ROADMs this matrix will be very sparse, and for OXCs the
   complement of the matrix will be very sparse, compact encodings and
   examples, including high degree ROADMs/OXCs, are given in [WSON-
   Encode]. A classic degree-4 ROADM is shown in Figure 2.

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

                          Figure 2 Degree-4 ROADM

   Note that this example is 4-degree example with one (potentially
   multi-channel) add/drop per line side port.

   Note also that the connectivity constraints for typical ROADM designs
   are "bi-directional", i.e. if ingress port X can be connected to
   egress port Y, typically ingress port Y can be connected to egress
   port X, assuming the numbering is done in such a way that ingress X
   and egress X correspond to the same line side direction or the same
   add/drop port. This makes the connectivity matrix symmetrical as
   shown below.

   Ingress  Egress Port
      Port     E1 E2 E3 E4 E5 E6 E7 E8
         I1    0  1  1  1  0  1  0  0
         I2    1  0  1  1  0  0  1  0
     A = I3    1  1  0  1  1  0  0  0
         I4    1  1  1  0  0  0  0  1
         I5    0  0  1  0  0  0  0  0
         I6    1  0  0  0  0  0  0  0
         I7    0  1  0  0  0  0  0  0
         I8    0  0  0  1  0  0  0  0

   where I5/E5 are add/drop ports to/from line side-3, I6/E6 are
   add/drop ports to/from line side-1, I7/E7 are add/drop ports to/from
   line side-2 and I8/E8 are add/drop ports to/from line side-4. Note
   that diagonal elements are zero since it is assumed that loopback is
   not supported. If ports support loopback, diagonal elements would be

   Additional constraints may also apply to the various ports in a
   ROADM/OXC. In the literature of optical switches and ROADMs the
   following restrictions/terms are used:

   Colored port: An ingress or more typically an egress (drop) port
   restricted to a single channel of fixed wavelength.

   Colorless port: An ingress or more typically an egress (drop) port
   restricted to a single channel of arbitrary wavelength.

   In general a port on a ROADM could have any of the following
   wavelength restrictions:

   o  Multiple wavelengths, full range port

   o  Single wavelength, full range port

   o  Single wavelength, fixed lambda port

   o  Multiple wavelengths, reduced range port (for example wave band

   To model these restrictions we need two pieces of information for
   each port: (a) number of wavelengths, (b) wavelength range and
   spacing.  Note that this information is relatively static. More
   complicated wavelength constraints are modeled in [WSON-Info].

      3.4.2. Splitters

   An optical splitter consists of a single ingress port and two or more
   egress ports. The ingress optical signaled is essentially copied
   (with power loss) to all egress ports.

   Using the modeling notions of section 3.4.1. the ingress and egress
   ports of a splitter would have the same wavelength restrictions. In
   addition we can describe a splitter by a connectivity matrix Amn as

               Ingress  Egress Port
               Port     #1 #2 #3 ...   #N
         A =   #1       1  1  1  ...   1

   The difference from a simple ROADM is that this is not a switched
   (potential) connectivity matrix but the fixed connectivity matrix of
   the device.

      3.4.3. Combiners

   A optical combiner is somewhat the dual of a splitter in that it has
   a single multi-wavelength egress port and multiple ingress ports.
   The contents of all the ingress ports are copied and combined to the
   single egress port.  The various ports may have different wavelength
   restrictions. It is generally the responsibility of those using the
   combiner to assure that wavelength collision does not occur on the
   egress port. The fixed connectivity matrix Amn for a combiner would
   look like:

               Ingress  Egress Port
               Port     #1
               #1:      1
               #2       1
         A =   #3       1
               ...      1
               #N       1
      3.4.4. Fixed Optical Add/Drop Multiplexers

   A fixed optical add/drop multiplexer can alter the course of an
   ingress wavelength in a preset way. In particular a given wavelength
   (or waveband) from a line side ingress port would be dropped to a
   fixed "tributary" egress port. Depending on the device's construction
   that same wavelength may or may not be "continued" to the line side
   egress port ("drop and continue" operation).  Further there may exist
   tributary ingress ports ("add" ports) whose signals are combined with
   each other and "continued" line side signals.

   In general to represent the routing properties of an FOADM we need a
   fixed connectivity matrix Amn as previously discussed and we need the
   precise wavelength restrictions for all ingress and egress ports.
   From the wavelength restrictions on the tributary egress ports (drop
   ports) we can see what wavelengths have been dropped. From the
   wavelength restrictions on the tributary ingress (add) ports we can
   see which wavelengths have been added to the line side egress port.
   Finally from the added wavelength information and the line side
   egress wavelength restrictions we can infer which wavelengths have
   been continued.

   To summarize, the modeling methodology introduced in section 3.4.1.
   consisting of a connectivity matrix and port wavelength restrictions
   can be used to describe a large set of fixed optical devices such as
   combiners, splitters and FOADMs. Hybrid devices consisting of both
   switched and fixed parts are modeled in [WSON-Info].

   3.5. Electro-Optical Systems

   This section describes how Electro-Optical Systems (e.g., OEO
   switches, wavelength converters, and regenerators) interact with the
   WSON signal characteristics defined in List 1 in Section 2.3. 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.
   Regenerators have been fairly well characterized in this regard so we
   start by describing their properties.

      3.5.1. Regenerators

   The various approaches to regeneration are discussed in ITU-T G.872
   Annex A [G.872]. They map a number of functions into the so-called
   1R, 2R and 3R categories of regenerators as summarized in Table 1

   Table 1 Regenerator functionality mapped to general regenerator
   classes from [G.872].

   1R | Equal amplification of all frequencies within the amplification
      | bandwidth. There is no restriction upon information formats.
      | Amplification with different gain for frequencies within the
      | amplification bandwidth. This could be applied to both single-
      | channel and multi-channel systems.
      | Dispersion compensation (phase distortion). This analogue
      | process can be applied in either single-channel or multi-
      | channel systems.
   2R | Any or all 1R functions. Noise suppression.
      | Digital reshaping (Schmitt Trigger function) with no clock
      | recovery. This is applicable to individual channels and can be
      | used for different bit rates but is not transparent to line
      | coding (modulation).
   3R | Any or all 1R and 2R functions. Complete regeneration of the
      | pulse shape including clock recovery and retiming within
      | required jitter limits.

   From the previous table we can see that 1R regenerators are generally
   independent of signal modulation format (also known as line coding),
   but may work over a limited range of wavelength/frequencies.  We see
   that 2R regenerators are generally applicable to a single digital
   stream and are dependent upon modulation format (line coding) and to
   a lesser extent are limited to a range of bit rates (but not a
   specific bit rate). Finally, 3R regenerators apply to a single
   channel, are dependent upon the modulation format and generally
   sensitive to the bit rate of digital signal, i.e., either are
   designed to only handle a specific bit rate or need to be programmed
   to accept and regenerate a specific bit rate.  In all these types of
   regenerators the digital bit stream contained within the optical or
   electrical signal is not modified.

   However, in the most common usage of regenerators the digital bit
   stream may be slightly modified for performance monitoring and fault
   management purposes. SONET, SDH and G.709 all have digital signal
   "envelopes" designed to be used between "regenerators" (in this case
   3R regenerators). In SONET this is known as the "section" signal, in
   SDH this is known as the "regenerator section" signal, in G.709 this
   is known as an OTUk (Optical Channel Transport Unit-k).  These
   signals reserve a portion of their frame structure (known as
   overhead) for use by regenerators. The nature of this overhead is
   summarized in Table 2.

       Table 2. SONET, SDH, and G.709 regenerator related overhead.

    |Function          |       SONET/SDH      |     G.709 OTUk        |
    |                  |       Regenerator    |                       |
    |                  |       Section        |                       |
    |Signal            |       J0 (section    |  Trail Trace          |
    |Identifier        |       trace)         |  Identifier (TTI)     |
    |Performance       |       BIP-8 (B1)     |  BIP-8 (within SM)    |
    |Monitoring        |                      |                       |
    |Management        |       D1-D3 bytes    |  GCC0 (general        |
    |Communications    |                      |  communications       |
    |                  |                      |  channel)             |
    |Fault Management  |       A1, A2 framing |  FAS (frame alignment |
    |                  |       bytes          |  signal), BDI(backward|
    |                  |                      |  defect indication)BEI|
    |                  |                      |  (backward error      |
    |                  |                      |  indication)          |
    |Forward Error     |       P1,Q1 bytes    |  OTUk FEC             |
    |Correction (FEC)  |                      |                       |

   In the previous table we see support for frame alignment, signal
   identification, and FEC. What this table also shows by its omission
   is that no switching or multiplexing occurs at this layer. This is a
   significant simplification for the control plane since control plane
   standards require a multi-layer approach when there are multiple
   switching layers, but not for "layering" to provide the management
   functions of Table 2. That is, many existing technologies covered by
   GMPLS contain extra management related layers that are essentially
   ignored by the control plane (though not by the management plane!).
   Hence, the approach here is to include regenerators and other devices
   at the WSON layer unless they provide higher layer switching and then
   a multi-layer or multi-region approach [RFC5212] is called for.
   However, this can result in regenerators having a dependence on the
   client signal type.

   Hence we see that depending upon the regenerator technology we may
   have the following constraints imposed by a regenerator device:

              Table 3. Regenerator Compatibility Constraints

   |      Constraints            |   1R   |   2R   |   3R   |
   | Limited Wavelength Range    |    x   |    x   |    x   |
   | Modulation Type Restriction |        |    x   |    x   |
   | Bit Rate Range Restriction  |        |    x   |    x   |
   | Exact Bit Rate Restriction  |        |        |    x   |
   | Client Signal Dependence    |        |        |    x   |

   Note that Limited Wavelength Range constraint is already modeled in
   GMPLS for WSON and that Modulation Type Restriction constraint
   includes FEC.

      3.5.2. OEO Switches

   A common place where optical-to-electrical-to-optical (OEO)
   processing may take place is in WSON switches that utilize (or
   contain) regenerators. A vendor may add regenerators to a switching
   system for a number of reasons. One obvious reason is to restore
   signal quality either before or after optical processing (switching).
   Another reason may be to convert the signal to an electronic form for
   switching then reconverting to an optical signal prior to egress from
   the switch. In this later case the regeneration is applied to adapt
   the signal to the switch fabric regardless of whether or not it is
   needed from a signal quality perspective.

   In either case these optical switches have essentially the same
   compatibility constraints as those we described for regenerators in
   Table 3.

   3.6. Wavelength Converters

   Wavelength converters take an ingress optical signal at one
   wavelength and emit an equivalent content optical signal at another
   wavelength on egress. There are currently two approaches to building
   wavelength converters. One approach is based on optical to electrical
   to optical (OEO) conversion with tunable lasers on egress. This
   approach can be dependent upon the signal rate and format, i.e., this
   is basically an electrical regenerator combined with a tunable laser.
   Hence, this type wavelength converter has signal processing
   restrictions that are essentially the same as those we described for
   regenerators in Table 3 of section 3.5.1.

   The other approach performs the wavelength conversion, optically via
   non-linear optical effects, similar in spirit to the familiar
   frequency mixing used in radio frequency systems, but significantly
   harder to implement.  Such processes/effects may place limits on the
   range of achievable conversion. These may depend on the wavelength of
   the input signal and the properties of the converter as opposed to
   only the properties of the converter in the OEO case. Different WSON
   system designs may choose to utilize this component to varying
   degrees or not at all.

   Current or envisioned contexts for wavelength converters are:

  1. Wavelength conversion associated with OEO switches and tunable
     laser transmitters. In this case there are plenty of converters to
     go around since we can think of each tunable output laser
     transmitter on an OEO switch as a potential wavelength converter.

  2. Wavelength conversion associated with ROADMs/OXCs. In this case we
     may have a limited pool of wavelength converters available.
     Conversion could be either all optical or via an OEO method.

  3. Wavelength conversion associated with fixed devices such as FOADMs.
     In this case we may have a limited amount of conversion. Also in
     this case the conversion may be used as part of light path routing.

   Based on the above considerations we model wavelength converters as

   1. Wavelength converters can always be modeled as associated with
      network elements. This includes fixed wavelength routing elements.

   2. A network element may have full wavelength conversion capability,
      i.e., any ingress port and wavelength, or a limited number of
      wavelengths and ports. On a box with a limited number of
      converters there also may exist restrictions on which ports can
      reach the converters. Hence regardless of where the converters
      actually are we can associate them with ingress ports.

   3. Wavelength converters have range restrictions that are either
      independent or dependent upon the ingress wavelength.

   In WSONs where wavelength converters are sparse we may actually see a
   light path appear to loop or "backtrack" upon itself in order to
   reach a wavelength converter prior to continuing on to its
   destination. The lambda used on the "detour" out to the wavelength
   converter would be different from that coming back from the "detour"
   to the wavelength converter.

   A model for an individual O-E-O wavelength converter would consist

   o  Input lambda or frequency range

   o  Output lambda or frequency range

      3.6.1. Wavelength Converter Pool Modeling

   A WSON node may include multiple wavelength converters. These are
   usually arranged into some type of pool to promote resource sharing.
   There are a number of different approaches used in the design of
   switches with converter pools. However, from the point of view of
   path computation we need to know the following:

   1. The nodes that support wavelength conversion.

   2. The accessibility and availability of a wavelength converter to
      convert from a given ingress wavelength on a particular ingress
      port to a desired egress wavelength on a particular egress port.

   3. Limitations on the types of signals that can be converted and the
      conversions that can be performed.

   To model point 2 above we can use a similar technique as used to
   model ROADMs and optical switches, i.e., matrices to indicate
   possible connectivity along with wavelength constraints for
   links/ports. Since wavelength converters are considered a scarce
   resource we will also want our model to include as a minimum the
   usage state of individual wavelength converters in the pool.

   We utilize a three stage model as shown schematically in Figure 3. In
   this model we assume N ingress ports (fibers), P wavelength
   converters, and M egress ports (fibers). Since not all ingress ports
   can necessarily reach the converter pool, the model starts with a
   wavelength pool ingress matrix WI(i,p) = {0,1} whether ingress port i
   can reach potentially reach wavelength converter p.

   Since not all wavelength can necessarily reach all the converters or
   the converters may have limited input wavelength range we have a set
   of ingress port constraints for each wavelength converter. Currently
   we assume that a wavelength converter can only take a single
   wavelength on input. We can model each wavelength converter ingress
   port constraint via a wavelength set mechanism.

   Next we have a state vector WC(j) = {0,1} dependent upon whether
   wavelength converter j in the pool is in use. This is the only state
   kept in the converter pool model. This state is not necessary for
   modeling "fixed" transponder system, i.e., systems where there is no
   sharing.  In addition, this state information may be encoded in a
   much more compact form depending on the overall connectivity
   structure [WSON-Encode].

   After that, we have a set of wavelength converter egress wavelength
   constraints. These constraints indicate what wavelengths a particular
   wavelength converter can generate or are restricted to generating due
   to internal switch structure.

   Finally, we have a wavelength pool egress matrix WE(p,k) = {0,1}
   depending on whether the output from wavelength converter p can reach
   egress port k. Examples of this method being used to model wavelength
   converter pools for several switch architectures from the literature
   are given in reference [WSON-Encode].

      I1   +-------------+                       +-------------+ E1
     ----->|             |      +--------+       |             |----->
      I2   |             +------+ WC #1  +-------+             | E2
     ----->|             |      +--------+       |             |----->
           | Wavelength  |                       |  Wavelength |
           | Converter   |      +--------+       |  Converter  |
           | Pool        +------+ WC #2  +-------+  Pool       |
           |             |      +--------+       |             |
           | Ingress     |                       |  Egress     |
           | Connection  |           .           |  Connection |
           | Matrix      |           .           |  Matrix     |
           |             |           .           |             |
           |             |                       |             |
      IN   |             |      +--------+       |             | EM
     ----->|             +------+ WC #P  +-------+             |----->
           |             |      +--------+       |             |
           +-------------+   ^               ^   +-------------+
                             |               |
                             |               |
                             |               |
                             |               |

                    Ingress wavelength    Egress wavelength
                    constraints for       constraints for
                    each converter        each converter

      Figure 3 Schematic diagram of wavelength converter pool model.

   Example: Shared Per Node

   In Figure 4 below we show a simple optical switch in a four
   wavelength DWDM system sharing wavelength converters in a general
   "per node" fashion.

                +-----------+ ___________                +------+
                |           |--------------------------->|      |
                |           |--------------------------->|  C   |
          /|    |           |--------------------------->|  o   | E1
    I1   /D+--->|           |--------------------------->|  m   |
        + e+--->|           |                            |  b   |====>
   ====>| M|    |  Optical  |    +-----------+  +----+   |  i   |
        + u+--->|   Switch  |    |  WC Pool  |  |O  S|-->|  n   |
         \x+--->|           |    |  +-----+  |  |p  w|-->|  e   |
          \|    |           +----+->|WC #1|--+->|t  i|   |  r   |
                |           |    |  +-----+  |  |i  t|   +------+
                |           |    |           |  |c  c|   +------+
          /|    |           |    |  +-----+  |  |a  h|-->|      |
    I2   /D+--->|           +----+->|WC #2|--+->|l   |-->|  C   | E2
        + e+--->|           |    |  +-----+  |  |    |   |  o   |
   ====>| M|    |           |    +-----------+  +----+   |  m   |====>
        + u+--->|           |                            |  b   |
         \x+--->|           |--------------------------->|  i   |
          \|    |           |--------------------------->|  n   |
                |           |--------------------------->|  e   |
                |___________|--------------------------->|  r   |
                +-----------+                            +------+

     Figure 4 An optical switch featuring a shared per node wavelength
                       converter pool architecture.

   In this case the ingress and egress pool matrices are simply:

              +-----+       +-----+
              | 1 1 |       | 1 1 |
          WI =|     |,  WE =|     |
              | 1 1 |       | 1 1 |
              +-----+       +-----+

   Example: Shared Per Link

   In Figure 5 we show a different wavelength pool architecture know as
   "shared per fiber". In this case the ingress and egress pool matrices
   are simply:

              +-----+       +-----+
              | 1 1 |       | 1 0 |
          WI =|     |,  WE =|     |
              | 1 1 |       | 0 1 |
              +-----+       +-----+

                +-----------+                            +------+
                |           |--------------------------->|      |
                |           |--------------------------->|  C   |
          /|    |           |--------------------------->|  o   | E1
    I1   /D+--->|           |--------------------------->|  m   |
        + e+--->|           |                            |  b   |====>
   ====>| M|    |  Optical  |    +-----------+           |  i   |
        + u+--->|   Switch  |    |  WC Pool  |           |  n   |
         \x+--->|           |    |  +-----+  |           |  e   |
          \|    |           +----+->|WC #1|--+---------->|  r   |
                |           |    |  +-----+  |           +------+
                |           |    |           |           +------+
          /|    |           |    |  +-----+  |           |      |
    I2   /D+--->|           +----+->|WC #2|--+---------->|  C   | E2
        + e+--->|           |    |  +-----+  |           |  o   |
   ====>| M|    |           |    +-----------+           |  m   |====>
        + u+--->|           |                            |  b   |
         \x+--->|           |--------------------------->|  i   |
          \|    |           |--------------------------->|  n   |
                |           |--------------------------->|  e   |
                |___________|--------------------------->|  r   |
                +-----------+                            +------+
    Figure 5 An optical switch featuring a shared per fiber wavelength
                       converter pool architecture.

   3.7. Characterizing Electro-Optical Network Elements

   In this section we characterize Electro-Optical WSON network elements
   by the three key functional components: Input constraints, Output
   constraints and Processing Capabilities.

                             WSON Network Element
          WSON Signal     |      |         |      |    WSON Signal
                          |      |         |      |
        --------------->  |      |         |      | ----------------->
                          |      |         |      |
                          <-----> <-------> <----->

                          Input   Processing Output

                       Figure 6 WSON Network Element

      3.7.1. Input Constraints

   Section 3 discussed the basic properties regenerators, OEO switches
   and wavelength converters from these we have the following possible
   types of input constraints and properties:

   1. Acceptable Modulation formats

   2. Client Signal (GPID) restrictions

   3. Bit Rate restrictions

   4. FEC coding restrictions

   5. Configurability: (a) none, (b) self-configuring, (c) required

   We can represent these constraints via simple lists. Note that the
   device may need to be "provisioned" via signaling or some other means
   to accept signals with some attributes versus others. In other cases
   the devices maybe relatively transparent to some attributes, e.g.,
   such as a 2R regenerator to bit rate. Finally, some devices maybe
   able to auto-detect some attributes and configure themselves, e.g., a
   3R regenerator with bit rate detection mechanisms and flexible phase
   locking circuitry. To account for these different cases we've added
   item 5, which describes the devices configurability.

   Note that such input constraints also apply to the final destination,
   sink or termination, of the WSON signal.

      3.7.2. Output Constraints

   None of the network elements considered here modifies either the bit
   rate or the basic type of the client signal. However, they may modify
   the modulation format or the FEC code. Typically we'd see the
   following types of output constraints:

   1. Output modulation is the same as input modulation (default)

   2. A limited set of output modulations is available

   3. Output FEC is the same as input FEC code (default)

   4. A limited set of output FEC codes is available

   Note that in cases (2) and (4) above, where there is more than one
   choice in the output modulation or FEC code then the network element
   will need to be configured on a per LSP basis as to which choice to

      3.7.3. Processing Capabilities

   A general WSON network element (NE) can perform a number of signal
   processing functions including:

     (A) Regeneration (possibly different types)

     (B) Fault and Performance Monitoring

     (C) Wavelength Conversion

     (D) Switching

   Item(D) can be modeled with existing GMPLS mechanisms.

   An NE may or may not have the ability to perform regeneration (of the
   one of the types previously discussed). In addition some nodes may
   have limited regeneration capability, i.e., a shared pool, which may
   be applied to selected signals traversing the NE. Hence to describe
   the regeneration capability of a link or node we have at a minimum:

   1. Regeneration capability: (a)fixed, (b) selective, (c) none

   2. Regeneration type: 1R, 2R, 3R

   3. Regeneration pool properties for the case of selective
      regeneration (ingress & egress restrictions, availability)

   Note that the properties of shared regenerator pools would be
   essentially the same at that of wavelength converter pools modeled in
   section 3.6.1.

   Item (B), fault and performance monitoring, is typically outside the
   scope of the control plane. However, when the operations are to be
   performed on an LSP basis or as part of an LSP then the control plane
   can be of assistance in their configuration. Per LSP, per node, fault
   and performance monitoring examples include setting up a "section
   trace" (a regenerator overhead identifier) between two nodes, or
   intermediate optical performance monitoring at selected nodes along a

4. Routing and Wavelength Assignment and the Control Plane

   In wavelength switched optical networks consisting of tunable lasers
   and wavelength selective switches with wavelength converters on every
   interface, path selection is similar to the MPLS and TDM circuit
   switched cases in that the labels, in this case wavelengths
   (lambdas), have only local significance. That is, a wavelength-
   convertible network with full wavelength-conversion capability at
   each node is equivalent to a circuit-switched TDM network with full
   time slot interchange capability; thus, the routing problem needs to
   be addressed only at the level of the traffic engineered (TE) link
   choice, and wavelength assignment can be resolved locally by the
   switches on a hop-by-hop basis.

   However, in the limiting case of an optical network with no
   wavelength converters, a light path (optical signal) needs a route
   from source to destination and must pick a single wavelength that can
   be used along that path without "colliding" with the wavelength used
   by any other light path that may share an optical fiber. This is
   sometimes referred to as a "wavelength continuity constraint". To
   ease up on this constraint while keeping network costs in check a
   limited number of wavelength converters may be introduced at key
   points in the network [Chu03].

   In the general case of limited or no wavelength converters this
   computation is known as the Routing and Wavelength Assignment (RWA)
   problem [HZang00]. The "hardness" of this problem is well documented.
   There, however, exist a number of reasonable approximate methods for
   its solution [HZang00].

   The inputs to the basic RWA problem are the requested light paths
   source and destination, the network's topology, the locations and
   capabilities of any wavelength converters, and the wavelengths
   available on each optical link. The output from an algorithm solving
   the RWA problem is an explicit route through ROADMs, a wavelength for
   the optical transmitter, 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.

   It is to be noted that choice of specific RWA algorithm is out of the
   scope for this document. However there are a number of different
   approaches to dealing with the RWA algorithm that can affect the
   division of effort between signaling, routing and PCE.

   4.1. Architectural Approaches to RWA

   Two general computational approaches are taken to solving the RWA
   problem. Some algorithms utilize a two step procedure of path
   selection followed by wavelength assignment, and others solve the
   problem in a combined fashion.

   In the following, three different ways of performing RWA in
   conjunction with the control plane are considered. The choice of one
   of these architectural approaches over another generally impacts the
   demands placed on the various control plane protocols.

      4.1.1. Combined RWA (R&WA)

   In this case, a unique entity is in charge of performing routing and
   wavelength assignment. This approach relies on a sufficient knowledge
   of network topology, of available network resources and of network
   nodes capabilities. This solution is compatible with most known RWA
   algorithms, and in particular those concerned with network
   optimization. On the other hand, this solution requires up-to-date
   and detailed network information.

   Such a computational entity could reside in two different logical

   o  In a separate Path Computation Element (PCE) which owns the
      complete and updated knowledge of network state and provides path
      computation services to nodes.

   o  In the Ingress node, in that case all nodes have the R&WA
      functionality; the knowledge of the network state is obtained by a
      periodic flooding of information provided by the other nodes.

      4.1.2. Separated R and WA (R+WA)

   In this case a first entity performs routing, while a second performs
   wavelength assignment. The first entity furnishes one or more paths
   to the second entity that will perform wavelength assignment and
   possibly final path selection.

   As the entities computing the path and the wavelength assignment are
   separated, this constrains the class of RWA algorithms that may be
   implemented. Although it may seem that algorithms optimizing a joint
   usage of the physical and spectral paths are excluded from this
   solution, many practical optimization algorithms only consider a
   limited set of possible paths, e.g., as computed via a k-shortest
   path algorithm [Ozdaglar03]. Hence although there is no guarantee
   that the selected final route and wavelength offers the optimal
   solution, by allowing multiple routes to pass to the wavelength
   selection process reasonable optimization can be performed.

   The entity performing the routing assignment needs the topology
   information of the network, whereas the entity performing the
   wavelength assignment needs information on the network's available
   resources and on network node capabilities.

      4.1.3. Routing and Distributed WA (R+DWA)

   In this case a first entity performs routing, while wavelength
   assignment is performed on a hop-by-hop manner along the previously
   computed route. This mechanism relies on updating of a list of
   potential wavelengths used to ensure conformance with the wavelength
   continuity constraint.

   As currently specified, the GMPLS protocol suite signaling protocol
   can accommodate such an approach. Per [RFC3471], the Label Set
   selection works according to an AND scheme. Each hop restricts the
   Label Set sent to the next hop from the one received from the
   previous hop by performing an AND operation between the wavelength
   referred by the labels the message includes with the one available on
   the ongoing interface. The constraint to perform this AND operation
   is up to the node local policy (even if one expects a consistent
   policy configuration throughout a given transparency domain). When
   wavelength conversion is performed at an intermediate node, a new
   Label Set is generated. The egress nodes selects one label in the
   Label Set received at the node, which is also up to the node local

   Depending on these policies a spectral assignment may not be found or
   one consuming too many conversion resources relative to what a
   dedicated wavelength assignment policy would have achieved. Hence,
   this approach may generate higher blocking probabilities in a heavily
   loaded network.

   On the one hand, this solution may be empowered with some signaling
   extensions to ease its functioning and possibly enhance its
   performances relatively to blocking. Note that this approach requires
   less information dissemination than the others.

   The first entity may be a PCE or the ingress node of the LSP. This
   solution is applicable inside networks where resource optimization is
   not as critical.

   4.2. Conveying information needed by RWA

   The previous sections have characterized WSONs and lightpath
   requests. In particular, high level models of the information used by
   the RWA process were presented. We can view this information as
   either static, changing with hardware changes (including possibly
   failures), or dynamic, those that can change with subsequent
   lightpath provisioning. The timeliness in which an entity involved in
   the RWA process is notified of such changes is fairly situational.
   For example, for network restoration purposes, learning of a hardware
   failure or of new hardware coming online to provide restoration
   capability can be critical.
   Currently there are various methods for communicating RWA relevant
   information, these include, but are not limited to:

   o  Existing control plane protocols such as GMPLS routing and
      signaling. Note that routing protocols can be used to convey both
      static and dynamic information. Static information currently
      conveyed includes items like router options and such.

   o  Management protocols such as NetConf, SNMPv3, CLI, CORBA, or

   o  Directory services and accompanying protocols. These are good for
      the dissemination of relatively static information. Not intended
      for dynamic information.

   o  Other techniques for dynamic information: messaging straight from
      NEs to PCE to avoid flooding. This would be useful if the number
      of PCEs is significantly less than number of WSON NEs. Or other
      ways to limit flooding to "interested" NEs.

   Mechanisms to improve scaling of dynamic information:

   o  Tailor message content to WSON. For example the use of wavelength
      ranges, or wavelength occupation bit maps.

   Utilize incremental updates if feasible.

   4.3. Lightpath Temporal Characteristics

   The temporal characteristics

5. Modeling Examples and Control Plane Use Cases

   This section provides examples of a light path connection can affect the choice fixed and switch optical node
   and wavelength constraint models of solution section 3. and WSON control plane
   use cases related to the RWA process. For our purposes here we
   look at the timeliness of connection establishment/teardown, path computation, establishment, rerouting, and the
   duration of the connection.

   Connection Establishment/Teardown Timeliness can be thought of in
   approximately three time frames:

  1. Time Critical:  For example those lightpath establishments used for
     restoration of service or other high priority real time service

  2. Soft time bounds: This is a more typical new connection request.
     While expected to be responsive, there should be more time to take
     into account network optimization.

  3. Scheduled or Advanced reservations. Here lightpath connections are
     requested significantly ahead of their intended "in service" time.
     There is the potential for significant network optimization if
     multiple lightpaths can be computed concurrently to achieve network
     optimization objectives.

  Lightpath connection duration has typically been thought of as
     approximately three time frames:

  1. Dynamic: those lightpaths with relatively short duration (holding

  2. Pseudo-static: lightpaths with moderately long durations.

  3. Static: lightpaths with long durations.

   Different types of RWA algorithms have been developed for dealing
   with dynamic versus pseudo-static conditions.  These can address
   service provider's needs for: (a) network optimization, (b)
   restoration, and (c) highly dynamic lightpath provisioning.

   Hence we can model timescale related lightpath requirements via the
   following notions:

   o  Batch or Sequential light path connection requests

   o  Timeliness of Connection establishment

   o  Duration of lightpath connection

5. Modeling Examples and Control Plane Use Cases

   This section provides examples of the fixed and switch optical node
   and wavelength constraint models of section 3. and WSON control plane
   use cases related to path computation, establishment, rerouting, and

   5.1. Network Modeling

   5.1. Network Modeling for GMPLS/PCE Control

   Consider a network containing three routers (R1 through R3), eight
   WSON nodes (N1 through N8) and 18 links (L1 through L18) and one OEO
   converter (O1) in a topology shown below.

                    +--+    +--+             +--+       +--------+
               +-L3-+N2+-L5-+  +--------L12--+N6+--L15--+   N8   +--
               |    +--+    |N4+-L8---+      +--+       ++--+---++
               |            |  +-L9--+|                  |  |   |
   +--+      +-+-+          ++-+     ||                  | L17 L18
   |  ++-L1--+   |           |      ++++      +----L16---+  |   |
   |R1|      | N1|           L7     |R2|      |             |   |
   |  ++-L2--+   |           |      ++-+      |            ++---++
   +--+      +-+-+           |       |        |            +  R3 |
               |    +--+    ++-+     |        |            +-----+
               +-L4-+N3+-L6-+N5+-L10-+       ++----+
                    +--+    |  +--------L11--+ N7  +----
                            +--+             ++---++
                                              |   |
                                             L13 L14
                                              |   |
                                             ++-+ |
      5.1.1. Describing the WSON nodes

   The eight WSON nodes in this example have the following properties:

   o  Nodes N1, N2, N3 have fixed OADMs (FOADMs) installed and can
      therefore only access a static and pre-defined set of wavelengths

   o  All other nodes contain ROADMs and can therefore access all

   o  Nodes N4, N5, N7 and N8 are multi-degree nodes, allowing any
      wavelength to be optically switched between any of the links. Note
      however, that this does not automatically apply to wavelengths
      that are being added or dropped at the particular node.

   o  Node N4 is an exception to that: This node can switch any
      wavelength from its add/drop ports to any of its outgoing links
      (L5, L7 and L12 in this case)

   o  The links from the routers are always only able to carry one
      wavelength with the exception of links L8 and L9 which are capable
      to add/drop any wavelength.

   o  Node N7 contains an OEO transponder (O1) connected to the node via
      links L13 and L14. That transponder operates in 3R mode and does
      not change the wavelength of the signal. Assume that it can
      regenerate any of the client signals, however only for a specific

   Given the above restrictions, the node information for the eight
   nodes can be expressed as follows: (where ID == identifier, SCM ==
   switched connectivity matrix, and FCM == fixed connectivity matrix).

   +ID+SCM                    +FCM                    +
   |  |   |L1 |L2 |L3 |L4 |   |   |L1 |L2 |L3 |L4 |   |
   |  |L1 |0  |0  |0  |0  |   |L1 |0  |0  |1  |0  |   |
   |N1|L2 |0  |0  |0  |0  |   |L2 |0  |0  |0  |1  |   |
   |  |L3 |0  |0  |0  |0  |   |L3 |1  |0  |0  |1  |   |
   |  |L4 |0  |0  |0  |0  |   |L4 |0  |1  |1  |0  |   |
   |  |   |L3 |L5 |   |   |   |   |L3 |L5 |   |   |   |
   |N2|L3 |0  |0  |   |   |   |L3 |0  |1  |   |   |   |
   |  |L5 |0  |0  |   |   |   |L5 |1  |0  |   |   |   |
   |  |   |L4 |L6 |   |   |   |   |L4 |L6 |   |   |   |
   |N3|L4 |0  |0  |   |   |   |L4 |0  |1  |   |   |   |
   |  |L6 |0  |0  |   |   |   |L6 |1  |0  |   |   |   |
   |  |   |L5 |L7 |L8 |L9 |L12|   |L5 |L7 |L8 |L9 |L12|
   |  |L5 |0  |1  |1  |1  |1  |L5 |0  |0  |0  |0  |0  |
   |N4|L7 |1  |0  |1  |1  |1  |L7 |0  |0  |0  |0  |0  |
   |  |L8 |1  |1  |0  |1  |1  |L8 |0  |0  |0  |0  |0  |
   |  |L9 |1  |1  |1  |0  |1  |L9 |0  |0  |0  |0  |0  |
   |  |L12|1  |1  |1  |1  |0  |L12|0  |0  |0  |0  |0  |
   |  |   |L6 |L7 |L10|L11|   |   |L6 |L7 |L10|L11|   |
   |  |L6 |0  |1  |0  |1  |   |L6 |0  |0  |1  |0  |   |
   |N5|L7 |1  |0  |0  |1  |   |L7 |0  |0  |0  |0  |   |
   |  |L10|0  |0  |0  |0  |   |L10|1  |0  |0  |0  |   |
   |  |L11|1  |1  |0  |0  |   |L11|0  |0  |0  |0  |   |
   |  |   |L12|L15|   |   |   |   |L12|L15|   |   |   |
   |N6|L12|0  |1  |   |   |   |L12|0  |0  |   |   |   |
   |  |L15|1  |0  |   |   |   |L15|0  |0  |   |   |   |
   |  |   |L11|L13|L14|L16|   |   |L11|L13|L14|L16|   |
   |  |L11|0  |1  |0  |1  |   |L11|0  |0  |0  |0  |   |
   |N7|L13|1  |0  |0  |0  |   |L13|0  |0  |1  |0  |   |
   |  |L14|0  |0  |0  |1  |   |L14|0  |1  |0  |0  |   |
   |  |L16|1  |0  |1  |0  |   |L16|0  |0  |1  |0  |   |
   |  |   |L15|L16|L17|L18|   |   |L15|L16|L17|L18|   |
   |  |L15|0  |1  |0  |0  |   |L15|0  |0  |0  |1  |   |
   |N8|L16|1  |0  |0  |0  |   |L16|0  |0  |1  |0  |   |
   |  |L17|0  |0  |0  |0  |   |L17|0  |1  |0  |0  |   |
   |  |L18|0  |0  |0  |0  |   |L18|1  |0  |1  |0  |   |

      5.1.2. Describing the links

   For the following discussion some simplifying assumptions are made:

   o   It is assumed that the WSON node support a total of four
      wavelengths designated WL1 through WL4.

   o   It is assumed that the impairment feasibility of a path or path
      segment is independent from the wavelength chosen.

   For the discussion of the RWA operation to build LSPs between two
   routers, the wavelength constraints on the links between the routers
   and the WSON nodes as well as the connectivity matrix of these links
   needs to be specified:

   +Link+WLs supported    +Possible egress links+
   | L1 | WL1             | L3                  |
   | L2 | WL2             | L4                  |
   | L8 | WL1 WL2 WL3 WL4 | L5 L7 L12           |
   | L9 | WL1 WL2 WL3 WL4 | L5 L7 L12           |
   | L10| WL2             | L6                  |
   | L13| WL1 WL2 WL3 WL4 | L11 L14             |
   | L14| WL1 WL2 WL3 WL4 | L13 L16             |
   | L17| WL2             | L16                 |
   | L18| WL1             | L15                 |

   Note that the possible egress links for the links connecting to the
   routers is inferred from the Switched Connectivity Matrix and the
   Fixed Connectivity Matrix of the Nodes N1 through N8 and is show here
   for convenience, i.e., this information does not need to be repeated.

   5.2. RWA Path Computation and Establishment

   The calculation of optical impairment feasible routes is outside the
   scope of this framework document. In general impairment feasible
   routes serve as an input to the RWA algorithm.

   For the example use case shown here, assume the following feasible

   +Endpoint 1+Endpoint 2+Feasible Route        +
   |  R1      | R2       | L1 L3 L5 L8          |
   |  R1      | R2       | L1 L3 L5 L9          |
   |  R1      | R2       | L2 L4 L6 L7 L8       |
   |  R1      | R2       | L2 L4 L6 L7 L9       |
   |  R1      | R2       | L2 L4 L6 L10         |
   |  R1      | R3       | L1 L3 L5 L12 L15 L18 |
   |  R1      | N7       | L2 L4 L6 L11         |
   |  N7      | R3       | L16 L17              |
   |  N7      | R2       | L16 L15 L12 L9       |
   |  R2      | R3       | L8 L12 L15 L18       |
   |  R2      | R3       | L8 L7 L11 L16 L17    |
   |  R2      | R3       | L9 L12 L15 L18       |
   |  R2      | R3       | L9 L7 L11 L16 L17    |

   Given a request to establish a LSP between R1 and R2 the RWA
   algorithm finds the following possible solutions:

   +WL  + Path          +
   | WL1| L1 L3 L5 L8   |
   | WL1| L1 L3 L5 L9   |
   | WL2| L2 L4 L6 L7 L8|
   | WL2| L2 L4 L6 L7 L9|
   | WL2| L2 L4 L6 L10  |

   Assume now that the RWA chooses WL1 and the Path L1 L3 L5 L8 for the
   requested LSP.

   Next, another LSP is signaled from R1 to R2. Given the established
   LSP using WL1, the following table shows the available paths:

   +WL  + Path          +
   | WL2| L2 L4 L6 L7 L9|
   | WL2| L2 L4 L6 L10  |

   Assume now that the RWA chooses WL2 and the path L2 L4 L6 L7 L9 for
   the establishment of the new LSP.

   Faced with another LSP request -this time from R2 to R3 - can not be
   fulfilled since the only four possible paths (starting at L8 and L9)
   are already in use.

   5.3. Resource Optimization

   The preceding example gives rise to another use case: The
   optimization of network resources. Optimization can be achieved on a
   number of layers (e.g. through electrical or optical multiplexing of
   client signals) or by re-optimizing the solutions found by the RWA

   Given the above example again, assume that the RWA algorithm should
   find a path between R2 and R3. The only possible path to reach R3
   from R2 needs to use L9. L9 however is blocked by one of the LSPs
   from R1.

   5.4. Support for Rerouting

   It is also envisioned that the extensions to GMPLS and PCE support
   rerouting of wavelengths in case of failures.

   Assume for this discussion that the only two LSPs in use in the
   system are:

   LSP1: WL1 L1 L3 L5 L8

   LSP2: WL2 L2 L4 L6 L7 L9

   Assume furthermore that the link L5 fails. The RWA can now find the
   following alternate path and and establish that path:

   R1 -> N7 -> R2

   Level 3 regeneration will take place at N7, so that the complete path
   looks like this:

   R1 -> L2 L4 L6 L11 L13 -> O1 -> L14 L16 L15 L12 L9 -> R2

   5.5. Electro-Optical Networking Scenarios

   In the following we look at various networking scenarios involving
   regenerators, OEO switches and wavelength converters. We group these
   scenarios roughly by type and number of extensions to the GMPLS
   control plane that would be required.

      5.5.1. Fixed Regeneration Points

   In the simplest networking scenario involving regenerators, the
   regeneration is associated with a WDM link or entire node and is not
   optional, i.e., all signals traversing the link or node will be
   regenerated. This includes OEO switches since they provide
   regeneration on every port.

   There maybe input constraints and output constraints on the
   regenerators. Hence the path selection process will need to know from
   an IGP or other means the regenerator constraints so that it can
   choose a compatible path. For impairment aware routing and wavelength
   assignment (IA-RWA) the path selection process will also need to know
   which links/nodes provide regeneration. Even for "regular" RWA, this
   regeneration information is useful since wavelength converters
   typically perform regeneration and the wavelength continuity
   constraint can be relaxed at such a point.

   Signaling does not need to be enhanced to include this scenario since
   there are no reconfigurable regenerator options on input, output or
   with respect to processing.

      5.5.2. Shared Regeneration Pools

   In this scenario there are nodes with shared regenerator pools within
   the network in addition to fixed regenerators of the previous
   scenario. These regenerators are shared within a node and their
   application to a signal is optional. There are no reconfigurable
   options on either input or output. The only processing option is to
   "regenerate" a particular signal or not.

   Regenerator information in this case is used in path computation to
   select a path that ensures signal compatibility and IA-RWA criteria.

   To setup an LSP that utilizes a regenerator from a node with a shared
   regenerator pool we need to be able to indicate that regeneration is
   to take place at that particular node along the signal path. Such a
   capability currently does not exist in GMPLS signaling.

      5.5.3. Reconfigurable Regenerators

   In this scenario we have regenerators that require configuration
   prior to use on an optical signal. We discussed previously that this
   could be due to a regenerator that must be configured to accept
   signals with different characteristics, for regenerators with a
   selection of output attributes, or for regenerators with additional
   optional processing capabilities.

   As in the previous scenarios we will need information concerning
   regenerator properties for selection of compatible paths and for IA-
   RWA computations. In addition during LSP setup we need to be able
   configure regenerator options at a particular node along the path.
   Such a capability currently does not exist in GMPLS signaling.

      5.5.4. Relation to Translucent Networks

   In the literature, networks that contain both transparent network
   elements such as reconfigurable optical add drop multiplexers
   (ROADMs) and electro-optical network elements such regenerators or
   OEO switches are frequently referred to as Translucent optical
   networks [Trans07]. Earlier work suggesting GMPLS extensions for
   translucent optical networks can be found in [Yang05] while a more
   comprehensive evaluation of differing GMPLS control plane approaches
   to translucent networks can be found in [Sambo09].

   Three main types of translucent optical networks have been discussed:

   4. Transparent "islands" surrounded by regenerators. This is
      frequently seen when transitioning from a metro optical sub-
      network to a long haul optical sub-network.

   5. Mostly transparent networks with a limited number of OEO
      ("opaque") nodes strategically placed. This takes advantage of the
      inherent regeneration capabilities of OEO switches. In the
      planning of such networks one has to determine the optimal
      placement of the OEO switches [Sen08].

   6. Mostly transparent networks with a limited number of optical
      switching nodes with "shared regenerator pools" that can be
      optionally applied to signals passing through these switches.
      These switches are sometimes called translucent nodes.

   All three of these types of translucent networks fit within either
   the networking scenarios of sections 5.5.1. and 5.5.2.  above. And
   hence, can be accommodated by the GMPLS extensions suggested in this

6. GMPLS & PCE Implications

   The presence and amount of wavelength conversion available at a
   wavelength switching interface has an impact on the information that
   needs to be transferred by the control plane (GMPLS) and the PCE
   architecture. Current GMPLS and PCE standards can address the full
   wavelength conversion case so the following will only address the
   limited and no wavelength conversion cases.

   6.1. Implications for GMPLS signaling

   Basic support for WSON signaling already exists in GMPLS with the
   lambda (value 9) LSP encoding type [RFC3471], or for G.709 compatible
   optical channels, the LSP encoding type (value = 13) "G.709 Optical
   Channel" from [RFC4328]. However a number of practical issues arise
   in the identification of wavelengths and signals, and distributed
   wavelength assignment processes which are discussed below.

      6.1.1. Identifying Wavelengths and Signals

   As previously stated a global fixed mapping between wavelengths and
   labels simplifies the characterization of WDM links and WSON devices.
   Furthermore such a mapping as described in [Otani] eases
   communication between PCE and WSON PCCs.

      6.1.2. WSON Signals and Network Element Processing

   We saw in section 3.3.2. 3.3.2. that a WSON signal at any point along
   its path can be characterized by the (a) modulation format, (b) FEC,
   (c) wavelength, (d)bit rate, and (d)G-PID.

   Currently G-PID, wavelength (via labels), and bit rate (via bandwidth
   encoding) are supported in [RFC3471] and [RFC3473]. These RFCs can
   accommodate the wavelength changing at any node along the LSP and can
   thus provide explicit control of wavelength converters.

   In the fixed regeneration point scenario (section 5.5.1. ) no
   enhancements are required to signaling since there are no additional
   configuration options for the LSP at a node.

   In the case of shared regeneration pools (section 5.5.2. ) we need to
   be able to indicate to a node that it should perform regeneration on
   a particular signal. Viewed another way, for an LSP we want to
   specify that certain nodes along the path perform regeneration.  Such
   a capability currently does not exist in GMPLS signaling.

   The case of configurable regenerators (section 5.5.3. ) is very
   similar to the previous except that now there are potentially many
   more items that we may want to configure on a per node basis for an

   Note that the techniques of [RFC5420] which allow for additional LSP
   attributes and their recording in an RRO object could be extended to
   allow for additional LSP attributes in an ERO. This could allow one
   to indicate where optional 3R regeneration should take place along a
   path, any modification of LSP attributes such as modulation format,
   or any enhance processing such as performance monitoring.

      6.1.3. Combined RWA/Separate Routing WA support

   In either the combined RWA or separate routing WA cases, the node
   initiating the signaling will have a route from the source to
   destination along with the wavelengths (generalized labels) to be
   used along portions of the path. Current GMPLS signaling supports an
   explicit route object (ERO) and within an ERO an ERO Label subobject
   can be use to indicate the wavelength to be used at a particular
   node. In case the local label map approach is used the label sub-
   object entry in the ERO has to be translated appropriately.

      6.1.4. Distributed Wavelength Assignment: Unidirectional, No

   GMPLS signaling for a uni-directional lightpath LSP allows for the
   use of a label set object in the RSVP-TE path message. The processing
   of the label set object to take the intersection of available lambdas
   along a path can be performed resulting in the set of available
   lambda being known to the destination that can then use a wavelength
   selection algorithm to choose a lambda. For example,

      6.1.5. Distributed Wavelength Assignment: Unidirectional, Limited

   The previous outlined the following is
   a non-exhaustive subset case with no wavelength converters. In the
   case of wavelength assignment (WA) approaches
   discussed in [HZang00]:

   1. Random: Looks at all available wavelengths converters, nodes with wavelength converters would
   need to make the decision as to whether to perform conversion. One
   indicator for this would be that the light path then
      chooses from those available at random.

   2. First Fit: Wavelengths are ordered, first set of available (on all links) wavelengths
   which is chosen.

   3. Most Used: Out obtained via the intersection of the wavelengths available on the path attempts
      to select most use wavelength in network.

   4. Least Loaded: For multi-fiber networks. Chooses the wavelength j
      that maximizes minimum of the difference between the number of
      fibers on link l and the number of fibers on link l with
      wavelength j occupied.

   As can be seen from the above short list, wavelength assignment
   methods have differing information or processing requirements. The
   information requirements of these methods are as follows:

  1. Random: nothing more than the available wavelength set.

  2. First Fit: nothing more than the available wavelength set.

  3. Most Used: the available wavelength set and information on global
     wavelength use in the network.

  4. Least Loaded: the available wavelength set and information
     concerning the wavelength dependent loading for each link (this
     applies to multi-fiber links). This could be obtained via global
     information or via supplemental information passed via the
     signaling protocol.

   In case (3) above the global information needed by the wavelength
   assignment could be derived from suitably enhanced GMPLS routing.

   Note however this information need not be accurate enough for
   combined RWA computation. GMPLS signaling does not provide a way to
   indicate that a particular wavelength assignment algorithm should be

      6.1.5. Distributed Wavelength Assignment: Unidirectional, Limited

   The previous outlined the case with no wavelength converters. In the
   case of wavelength converters, nodes with wavelength converters would
   need to make the decision as to whether to perform conversion. One
   indicator for this would be that the set of available wavelengths
   which is obtained via the intersection of the incoming label set and incoming label set and
   the egress links available wavelengths is either null or deemed too
   small to permit successful completion.

   At this point the node would need to remember that it will apply
   wavelength conversion and will be responsible for assigning the
   wavelength on the previous lambda-contiguous segment when the RSVP-TE
   RESV message passes by. The node will pass on an enlarged label set
   reflecting only the limitations of the wavelength converter and the
   egress link. The record route option in RVSP-TE signaling can be used
   to show where wavelength conversion has taken place.

      6.1.6. Distributed Wavelength Assignment: Bidirectional, No

   There are potential issues in the case of a bi-directional lightpath
   which requires the use of the same lambda in both directions. We can
   try to use the above procedure to determine the available
   bidirectional lambda set if we use the interpretation that the
   available label set is available in both directions. However, a
   problem, arises in that bidirectional LSPs setup, according to
   [RFC3471] section 4.1, is indicated by the presence of an upstream
   label in the path message.

   However, until the intersection of the available label sets is
   obtained, e.g., at the destination node and the wavelength assignment
   algorithm has been run the upstream label information will not be
   available. Hence currently distributed wavelength assignment with
   bidirectional lightpaths is not supported.

   6.2. Implications for GMPLS Routing

   GMPLS routing [RFC4202] currently defines an interface capability
   descriptor for "lambda switch capable" (LSC) which we can use to
   describe the interfaces on a ROADM or other type of wavelength
   selective switch. In addition to the topology information typically
   conveyed via an IGP, we would need to convey the following subsystem
   properties to minimally characterize a WSON:

  1. WDM Link properties (allowed wavelengths).

  2. Laser Transmitters (wavelength range).

  3. ROADM/FOADM properties (connectivity matrix, port wavelength

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

   This information is modeled in detail in [WSON-Info] and a compact
   encoding is given in [WSON-Encode].

      6.2.1. Electro-Optical Element Signal Compatibility

   In network scenarios where signal compatibility is a concern we need
   to add parameters to our existing node and link models to take into
   account electro-optical input constraints, output constraints, and
   the signal processing capabilities of a NE in path computations.

   Input Constraints:

  1. Permitted optical tributary signal classes: A list of optical
     tributary signal classes that can be processed by this network
     element or carried over this link. [configuration type]
  2. Acceptable FEC codes [configuration type]
  3. Acceptable Bit Rate Set: A list of specific bit rates or bit rate
     ranges that the device can accommodate. Coarse bit rate info is
     included with the optical tributary signal class restrictions.
  4. Acceptable G-PID list: A list of G-PIDs corresponding to the
     "client" digital streams that is compatible with this device.

   Note that since the bit rate of the signal does not change over the
   LSP. We can make this an LSP parameter and hence this information
   would be available for any NE that needs to use it for configuration.
   Hence we do not need "configuration type" for the NE with respect to
   bit rate.

   Output Constraints:

   1. Output modulation: (a)same as input, (b) list of available types

   2. FEC options: (a) same as input, (b) list of available codes

   Processing Capabilities:

   1. Regeneration: (a) 1R, (b) 2R, (c) 3R, (d)list of selectable
      regeneration types

   2. Fault and Performance Monitoring (a)GPID particular capabilities
      TBD, (b) optical performance monitoring capabilities TBD.

   Note that such parameters could be specified on an (a) Network
   element wide basis, (b) a per port basis, (c) on a per regenerator
   basis.  Typically such information has been on a per port basis,
   e.g., the GMPLS interface switching capability descriptor [RFC4202].

      6.2.2. Wavelength-Specific Availability Information

   For wavelength assignment we need to know which specific wavelengths
   are available and which are occupied if we are going to run a
   combined RWA process or separate WA process as discussed in sections
   4.1.1. 4.1.2.  This is currently not possible with GMPLS routing

   In the routing extensions for GMPLS [RFC4202], requirements for
   layer-specific TE attributes are discussed. The RWA problem for
   optical networks without wavelength converters imposes an additional
   requirement for the lambda (or optical channel) layer: that of
   knowing which specific wavelengths are in use. Note that current
   dense WDM (DWDM) systems range from 16 channels to 128 channels with
   advanced laboratory systems with as many as 300 channels. Given these
   channel limitations and if we take the approach of a global
   wavelength to label mapping or furnishing the local mappings to the
   PCEs then representing the use of wavelengths via a simple bit-map is
   feasible [WSON-Encode].

      6.2.3. WSON Routing Information Summary

   The following table summarizes the WSON information that could be
   conveyed via GMPLS routing and attempts to classify that information
   as to its static or dynamic nature and whether that information would
   tend to be associated with either a link or a node.

      Information                         Static/Dynamic       Node/Link
      Connectivity matrix                 Static               Node
      Per port wavelength restrictions    Static               Node(1)
      WDM link (fiber) lambda ranges      Static               Link
      WDM link channel spacing            Static               Link
      Laser Transmitter range             Static               Link(2)
      Wavelength conversion capabilities  Static(3)            Node
      Maximum bandwidth per Wavelength    Static               Link
      Wavelength Availability             Dynamic(4)           Link
      Signal Compatibility & Processing   Static/Dynamic       Node


   1. These are the per port wavelength restrictions of an optical
      device such as a ROADM and are independent of any optical
      constraints imposed by a fiber link.

   2. This could also be viewed as a node capability.

   3. This could be dynamic in the case of a limited pool of converters
      where the number available can change with connection
      establishment. Note we may want to include regeneration
      capabilities here since OEO converters are also regenerators.

   4. Not necessarily needed in the case of distributed wavelength
      assignment via signaling.

   While the full complement of the information from the previous table
   is needed in the Combined RWA and the separate Routing and WA
   architectures, in the case of Routing + distribute WA via signaling
   we only need the following information:

      Information                         Static/Dynamic       Node/Link
      Connectivity matrix                 Static               Node
      Wavelength conversion capabilities  Static(3)            Node

   Information models and compact encodings for this information is
   provided in [WSON-Info] [WSON-Info], [Gen-Encode] and [WSON-Encode].

   6.3. Optical Path Computation and Implications for PCE

   As previously noted the RWA problem can be computationally intensive
   [HZang00]. Such computationally intensive path computations and
   optimizations were part of the impetus for the PCE (path computation
   element) architecture.

   As the PCEP defines the procedures necessary to support both
   sequential [RFC5440] and global concurrent path computations
   [RFC5557], PCE is well positioned to support WSON-enabled RWA
   computation with some protocol enhancement.

   Implications for PCE generally fall into two main categories: (a)
   lightpath constraints and characteristics, (b) computation

      6.3.1. Lightpath Constraints and Characteristics

   For the varying degrees of optimization that may be encountered in a
   network the following models of bulk and sequential lightpath
   requests are encountered:

   o  Batch optimization, multiple lightpaths requested at one time.

   o  Lightpath(s) and backup lightpath(s) requested at one time.

   o  Single lightpath requested at a time.

   PCEP and PCE-GCO can be readily enhanced to support all of the
   potential models of RWA computation.

   Lightpath constraints include:

   o  Bidirectional Assignment of wavelengths

   o  Possible simultaneous assignment of wavelength to primary and
      backup paths.

   o  Tuning range constraint on optical transmitter.

   Lightpath characteristics can include:

   o  Duration information (how long this connection may last)

   o  Timeliness/Urgency information (how quickly is this connection

      6.3.2. Electro-Optical Element Signal Compatibility

   When requesting a path computation to PCE, the PCC should be able to
   indicate the following:

   o  The GPID type of an LSP

   o  The signal attributes at the transmitter (at the source): (i)
      modulation type; (ii) FEC type

   o  The signal attributes at the receiver (at the sink): (i)
      modulation type; (ii) FEC type

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

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

   o  Additional LSP attributes modified along the path (e.g.,
      modulation format change, etc.)

      6.3.3. Discovery of RWA Capable PCEs

   The algorithms and network information needed for solving the RWA are
   somewhat specialized and computationally intensive hence not all PCEs
   within a domain would necessarily need or want this capability.
   Hence, it would be useful via the mechanisms being established for
   PCE discovery [RFC5088] to indicate that a PCE has the ability to
   deal with the RWA problem. Reference [RFC5088] indicates that a sub-
   TLV could be allocated for this purpose.

   Recent progress on objective functions in PCE [RFC5541] would allow
   the operators to flexibly request differing objective functions per
   their need and applications. For instance, this would allow the
   operator to choose an objective function that minimizes the total
   network cost associated with setting up a set of paths concurrently.
   This would also allow operators to choose an objective function that
   results in a most evenly distributed link utilization.

   This implies that PCEP would easily accommodate wavelength selection
   algorithm in its objective function to be able to optimize the path
   computation from the perspective of wavelength assignment if chosen
   by the operators.

   6.4. Summary of Impacts by RWA Architecture

   The following table summarizes for each RWA strategy the list of
   mandatory ("M") and optional ("O") control plane features according
   to GMPLS architectural blocks:

   o  Information required by the path computation entity,

   o  LSP request parameters used in either PCC to PCE situations or in

   o  RSVP-TE LSP signaling parameters used in LSP establishment.

   The table shows which enhancements are common to all architectures
   (R&WA, R+WA, R+DWA), which apply only to R&WA and R+WA (R+&WA), and
   which apply only to R+DWA. Note that this summary serves for the
   purpose of a generic reference.

   |                                     |     |Common | R+&WA | R+DWA |
   |               Feature               | ref +---+---+---+---+---+---+
   |                                     |     | M | O | M | O | M | O |
   | Generalized Label for Wavelength    |5.1.1| x |   |   |   |   |   |
   | Flooding of information for the     |     |   |   |   |   |   |   |
   | routing phase                       |     |   |   |   |   |   |   |
   |   Node features                     | 3.3 |   |   |   |   |   |   |
   |     Node type                       |     |   | x |   |   |   |   |
   |     spectral X-connect constraint   |     |   |   | x |   |   |   |
   |     port X-connect constraint       |     |   |   | x |   |   |   |
   |   Transponders availability         |     |   | x |   |   |   |   |
   |   Transponders features             | 3.2 |   | x |   |   |   |   |
   |   Converter availability            |     |   |   | x |   |   |   |
   |   Converter features                | 3.4 |   |   | x |   |   | x |
   |   TE-parameters of WDM links        | 3.1 | x |   |   |   |   |   |
   |   Total Number of wavelength        |     | x |   |   |   |   |   |
   |   Number of wavelengths available   |     | x |   |   |   |   |   |
   |   Grid spacing                      |     | x |   |   |   |   |   |
   |   Wavelength availability on links  | 5.2 |   |   | x |   |   |   |
   | LSP request parameters              |     |   |   |   |   |   |   |
   |   Signal features                   | 5.1 |   | x |   |   | x |   |
   |   Modulation format                 |     |   | x |   |   | x |   |
   |   Modulation parameters             |     |   | x |   |   | x |   |
   |   Specification of RWA method       | 5.1 |   | x |   |   | x |   |
   |   LSP time features                 | 4.3 |   | x |   |   |   |   |
   | Enriching signaling messages        |     |   |   |   |   |   |   |
   |   Signal features                   | 5.1 |   |   |   |   | x |   |

7. Security Considerations

   This document has no requirement for a change to the security models
   within GMPLS and associated protocols. That is the OSPF-TE, RSVP-TE,
   and PCEP security models could be operated unchanged.

   However satisfying the requirements for RWA using the existing
   protocols may significantly affect the loading of those protocols.
   This makes the operation of the network more vulnerable to denial of
   service attacks. Therefore additional care maybe required to ensure
   that the protocols are secure in the WSON environment.

   Furthermore the additional information distributed in order to
   address the RWA problem represents a disclosure of network
   capabilities that an operator may wish to keep private. Consideration
   should be given to securing this information.

8. IANA Considerations

   This document makes no request for IANA actions.

9. Acknowledgments

   The authors would like to thank Adrian Farrel for many helpful
   comments that greatly improved the contents of this draft.

   This document was prepared using

10. References

   10.1. Normative References

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

   [RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
             (TE) Extensions to OSPF Version 2", RFC 3630, September

   [RFC3945] Mannie, E.,

   [RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
             Switching (GMPLS) Architecture", RFC 3945, October 2004.

   [RFC4201] Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling in
             MPLS Signaling Resource ReserVation Protocol-
             Traffic Engineering (TE)", (RSVP-TE) Extensions", RFC 4201, October 2005. 3473,
             January 2003.

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

   [RFC4328] Papadimitriou, D., "Generalized Multi-Protocol Label
             Switching (GMPLS) Signaling Extensions for G.709 Optical
             Transport Networks Control", RFC 4328, January 2006.

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

   [RFC5088] J.L. Le Roux, J.P. Vasseur, Yuichi Ikejiri, and Raymond
             Zhang, "OSPF protocol extensions for Path Computation
             Element (PCE) Discovery", January 2008.

   [RFC5212] Shiomoto, K., Papadimitriou, D., Le Roux, JL., Vigoureux,
             M., and D. Brungard, "Requirements for GMPLS-Based Multi-
             Region and Multi-Layer Networks (MRN/MLN)", RFC 5212, July

   [RFC5557] Y. Lee, J.L. Le Roux, D. King, and E. Oki, "Path
             Computation Element Communication Protocol (PCECP)
             Requirements and Protocol Extensions In Support of Global
             Concurrent Optimization", RFC 5557, July 2009.

   [RFC5420] Farrel, A., Ed., Papadimitriou, D., Vasseur, JP., and A.
             Ayyangarps, "Encoding of Attributes for MPLS LSP
             Establishment Using Resource Reservation Protocol Traffic
             Engineering (RSVP-TE)", RFC 5420, February 2009.

   [RFC5440] J.P. Vasseur and J.L. Le Roux (Editors), "Path Computation
             Element (PCE) Communication Protocol (PCEP)", RFC 5440, May

   [RFC5541] J.L. Le Roux, J.P. Vasseur, and Y. Lee, "Encoding of
             Objective Functions in Path Computation Element (PCE)
             communication and discovery protocols", RFC 5541, July

   [WSON-Compat]  G. Bernstein, Y. Lee, B. Mack-Crane, "WSON Signal
             Characteristics and Network Element Compatibility
             Constraints for GMPLS", draft-bernstein-ccamp-wson-
             compatibility, work in progress.

   [WSON-Encode]  G. Bernstein, Y. Lee, D. Li, and W. Imajuku, "Routing
             and Wavelength Assignment Information Encoding for
             Wavelength Switched Optical Networks", draft-bernstein-
             ccamp-wson-encode, draft-ietf-ccamp-
             wson-encode, work in progress.

   [Gen-Encode] G. Bernstein, Y. Lee, D. Li, and W. Imajuku, "General
             Network Element Constraint Encoding for GMPLS Controlled
             Networks", draft-ietf-ccamp-general-constraint-encode, work
             in progress.

   [WSON-Imp]  Y. Lee, G. Bernstein, D. Li, G. Martinelli, "A Framework
             for the Control of Wavelength Switched Optical Networks
             (WSON) with Impairments", draft-ietf-ccamp-wson-
             impairments, work in progress.

   [WSON-Info] Y. Lee, G. Bernstein, D. Li, W. Imajuku, "Routing and
             Wavelength Assignment Information for Wavelength Switched
             Optical Networks", draft-bernstein-ccamp-wson-info, work in

   [PCEP-RWA] Y. Lee, G. Bernstein, J. Martensson, T. Takeda, T. Otani,
             "PCEP Requirements for WSON Routing and Wavelength
             Assignment", draft-lee-pce-wson-routing-wavelength, work in

   10.2. Informative References

   [HZang00] H. Zang, J. Jue and B. Mukherjeee, "A review of routing and
             wavelength assignment approaches for wavelength-routed
             optical WDM networks", Optical Networks Magazine, January

   [Coldren04]    Larry A. Coldren, G. A. Fish, Y. Akulova, J. S.
             Barton, L. Johansson and C. W. Coldren, "Tunable
             Seiconductor Lasers: A Tutorial", Journal of Lightwave
             Technology, vol. 22, no. 1, pp. 193-202, January 2004.

   [Chu03]   Xiaowen Chu, Bo Li and Chlamtac I, "Wavelength converter
             placement under different RWA algorithms in wavelength-
             routed all-optical networks", IEEE Transactions on
             Communications, vol. 51, no. 4, pp. 607-617, April 2003.

   [Buus06]    Jens Buus EJM, "Tunable Lasers in Optical Networks",
             Journal of Lightware Technology, vol. 24, no. 1, pp. 5-11,
             January 2006.

   [Basch06] E. Bert Bash, Roman Egorov, Steven Gringeri and Stuart
             Elby, "Architectural Tradeoffs for Reconfigurable Dense
             Wavelength-Division Multiplexing Systems", IEEE Journal of
             Selected Topics in Quantum Electronics, vol. 12, no. 4, pp.
             615-626, July/August 2006.

   [Otani]  T. Otani, H. Guo, K. Miyazaki, D. Caviglia, "Generalized
             Labels of Lambda-Switching Capable Label Switching Routers
             (LSR)", work in progress: draft-otani-ccamp-gmpls-g-694-
             lambda-labels, work in progress.

   [Winzer06]    Peter J. Winzer and Rene-Jean Essiambre, "Advanced
             Optical Modulation Formats", Proceedings of the IEEE, vol.
             94, no. 5, pp. 952-985, May 2006.

   [G.652] ITU-T Recommendation G.652, Characteristics of a single-mode
             optical fibre and cable, June 2005.

   [G.653] ITU-T Recommendation G.653, Characteristics of a dispersion-
             shifted single-mode optical fibre and cable, December 2006.

   [G.654] ITU-T Recommendation G.654, Characteristics of a cut-off
             shifted single-mode optical fibre and cable, December 2006.

   [G.655] ITU-T Recommendation G.655, Characteristics of a non-zero
             dispersion-shifted single-mode optical fibre and cable,
             March 2006.

   [G.656] ITU-T Recommendation G.656, Characteristics of a fibre and
             cable with non-zero dispersion for wideband optical
             transport, December 2006.

   [G.671]  ITU-T Recommendation G.671, Transmission characteristics of
             optical components and subsystems, January 2005.

   [G.872]  ITU-T Recommendation G.872, Architecture of optical
             transport networks, November 2001.

   [G.959.1] ITU-T Recommendation G.959.1, Optical Transport Network
             Physical Layer Interfaces, March 2006.

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

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

   [G.Sup39] ITU-T Series G Supplement 39, Optical system design and
             engineering considerations, February 2006.

   [G.Sup43] ITU-T Series G Supplement 43, Transport of IEEE 10G base-R
             in optical transport networks (OTN), November 2006.

   [Imajuku] W. Imajuku, Y. Sone, I. Nishioka, S. Seno, "Routing
             Extensions to Support Network Elements with Switching
             Constraint", work in progress: draft-imajuku-ccamp-rtg-
             switching-constraint-02.txt, July 2007.

   [Ozdaglar03]   Asuman E. Ozdaglar and Dimitri P. Bertsekas, "Routing
             and wavelength assignment in optical networks," IEEE/ACM
             Transactions on Networking,  vol. 11, 2003, pp. 259 -272.

   [RFC4054] Strand, J.

   [Sambo09] N. Sambo, N. Andriolli, A. Giorgetti, L. Valcarenghi, I.
             Cerutti, P. Castoldi, and F. Cugini, "GMPLS-controlled
             dynamic translucent optical networks," Network, IEEE,  vol.
             23, 2009, pp. 34-40.

   [Sen08] A. Chiu, "Impairments Sen, S. Murthy, and Other Constraints
             on S. Bandyopadhyay, "On Sparse Placement
             of Regenerator Nodes in Translucent Optical Layer Routing", RFC 4054, May 2005.

   [RFC4606] Mannie, E. Network,"
             Global Telecommunications Conference, 2008. IEEE GLOBECOM
             2008. IEEE, 2008, pp. 1-6.

   [Trans07] Gangxiang Shen and D. Papadimitriou, "Generalized Multi-
             Protocol Label Switching (GMPLS) Extensions for Synchronous Rodney S. Tucker, "Translucent optical
             networks: the way forward [Topics in Optical Network (SONET)
             Communications]," Communications Magazine, IEEE,  vol. 45,
             2007, pp. 48-54.

   [Yang05]  Xi Yang and Synchronous Digital Hierarchy
             (SDH) Control", RFC 4606, August 2006. B. Ramamurthy, "Dynamic routing in translucent
             WDM optical networks: the intradomain case," Lightwave
             Technology, Journal of,  vol. 23, 2005, pp. 955-971.

11. Contributors

   Snigdho Bardalai

   Diego Caviglia
   Via A. Negrone 1/A 16153
   Genoa Italy

   Phone: +39 010 600 3736
   Email: diego.caviglia@(,

   Daniel King
   Old Dog Consulting
   Aria Networks

   Itaru Nishioka
   NEC Corp.
   1753 Simonumabe, Nakahara-ku, Kawasaki, Kanagawa 211-8666
   Phone: +81 44 396 3287

   Lyndon Ong

   Pierre Peloso
   Route de Villejust - 91620 Nozay - France

   Jonathan Sadler

   Dirk Schroetter

   Jonas Martensson
   Electrum 236
   16440 Kista, Sweden

Author's Addresses

   Greg M. Bernstein (ed.)
   Grotto Networking
   Fremont California, USA

   Phone: (510) 573-2237

   Young Lee (ed.)
   Huawei Technologies
   1700 Alma Drive, Suite 100
   Plano, TX 75075

   Phone: (972) 509-5599 (x2240)

   Wataru Imajuku
   NTT Network Innovation Labs
   1-1 Hikari-no-oka, Yokosuka, Kanagawa

   Phone: +81-(46) 859-4315

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