Network Working Group                                      Y. Lee (ed.)
Internet Draft                                                   Huawei
Intended status: Informational                       G. Bernstein (ed.)
Expires: August 2011                                  Grotto Networking
                                                         Wataru Imajuku

                                                       February 7, 8, 2011

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


   This document 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, it examines Routing and Wavelength
   Assignment (RWA) of optical paths.

   This document 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.

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Table of Contents

   1. Introduction...................................................4
   2. Terminology....................................................5
   3. Wavelength Switched Optical Networks...........................6
      3.1. WDM and CWDM Links........................................6
      3.2. Optical Transmitters and Receivers........................8
      3.3. Optical Signals in WSONs..................................9
         3.3.1. Optical Tributary Signals...........................10
         3.3.2. WSON Signal Characteristics.........................10
      3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs............11
         3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs.......11
         3.4.2. Splitters...........................................14
         3.4.3. Combiners...........................................15
         3.4.4. Fixed Optical Add/Drop Multiplexers.................15
      3.5. Electro-Optical Systems..................................16
         3.5.1. Regenerators........................................16
         3.5.2. OEO Switches........................................19
      3.6. Wavelength Converters....................................19
         3.6.1. Wavelength Converter Pool Modeling..................21
      3.7. Characterizing Electro-Optical Network Elements..........25
         3.7.1. Input Constraints...................................26
         3.7.2. Output Constraints..................................26
         3.7.3. Processing Capabilities.............................27
   4. Routing and Wavelength Assignment and the Control Plane.......28
      4.1. Architectural Approaches to RWA..........................28
         4.1.1. Combined RWA (R&WA).................................29
         4.1.2. Separated R and WA (R+WA)...........................29
         4.1.3. Routing and Distributed WA (R+DWA)..................30
      4.2. Conveying information needed by RWA......................30
   5. Modeling Examples and Control Plane Use Cases.................31
      5.1. Network Modeling for GMPLS/PCE Control...................31
         5.1.1. Describing the WSON nodes...........................32
         5.1.2. Describing the links................................34
      5.2. RWA Path Computation and Establishment...................35
      5.3. Resource Optimization....................................36
      5.4. Support for Rerouting....................................37
      5.5. Electro-Optical Networking Scenarios.....................37
         5.5.1. Fixed Regeneration Points...........................37
         5.5.2. Shared Regeneration Pools...........................38
         5.5.3. Reconfigurable Regenerators.........................38
         5.5.4. Relation to Translucent Networks....................38
   6. GMPLS and PCE Implications....................................39
      6.1. Implications for GMPLS signaling.........................39
         6.1.1. Identifying Wavelengths and Signals.................39
         6.1.2. WSON Signals and Network Element Processing.........40
         6.1.3. Combined RWA/Separate Routing WA support............40
         6.1.4. Distributed Wavelength Assignment: Unidirectional, No
         6.1.5. Distributed Wavelength Assignment: Unidirectional,
         Limited Converters.........................................41
         6.1.6. Distributed Wavelength Assignment: Bidirectional, No
      6.2. Implications for GMPLS Routing...........................42
         6.2.1. Electro-Optical Element Signal Compatibility........42
         6.2.2. Wavelength-Specific Availability Information........43
         6.2.3. WSON Routing Information Summary....................43
      6.3. Optical Path Computation and Implications for PCE........45
         6.3.1. Optical path Constraints and Characteristics........45
         6.3.2. Electro-Optical Element Signal Compatibility........45
         6.3.3. Discovery of RWA Capable PCEs.......................46
   7. Security Considerations.......................................46
   8. IANA Considerations...........................................47
   9. Acknowledgments...............................................47
   10. References...................................................48
      10.1. Normative References....................................48
      10.2. Informative References..................................49
   11. Contributors.................................................51
   Author's Addresses...............................................52
   Intellectual Property Statement..................................52
   Disclaimer of Validity...........................................53

1. Introduction

   Wavelength Switched Optical Networks (WSONs) are constructed from
   subsystems that include Wavelength Division Multiplexed (WDM) links,
   tunable transmitters and receivers, Reconfigurable Optical Add/Drop
   Multiplexers (ROADM), wavelength converters, and electro-optical
   network elements.  A WSON is a WDM-based optical network in which
   switching is performed selectively based on the center wavelength of
   an optical signal.

   WSONs can differ from other types of GMPLS networks in that many
   types of WSON nodes are highly asymmetric with respect to their
   switching capabilities, compatibility of signal types and network
   elements may need to be considered, and label assignment can be non-
   local. In order to provision an optical connection (an optical path)
   through a WSON certain wavelength continuity and resource
   availability constraints must be met to determine viable and optimal
   paths through the WSON. The determination of paths is known as
   Routing and Wavelength Assignment (RWA).

   Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] includes
   an architecture and a set of control plane protocols that can be used
   to operate data networks ranging from packet switch capable networks,
   through those networks that use time division multiplexing, to WDM
   networks.  The Path Computation Element (PCE) architecture [RFC4655]
   defines functional components that can be used to compute and suggest
   appropriate paths in connection-oriented traffic-engineered networks.

   This document provides a framework for applying the GMPLS
   architecture and protocols [RFC3945], and the PCE architecture
   [RFC4655] to the control and operation of WSONs.  To aid in this
   process this document also provides an overview of the subsystems and
   processes that comprise WSONs, and describes RWA so that the
   information requirements, both static and dynamic, can be identified
   to explain how the information can be modeled for use by GMPLS and
   PCE systems. This work will facilitate the development of protocol
   solution models and protocol extensions within the GMPLS and PCE
   protocol families.

   Different WSONs such as access, metro, and long haul may apply
   different techniques for dealing with optical impairments hence this
   document does not address optical impairments in any depth. Note that
   this document focuses on the generic properties of links, switches
   and path selection constraints that occur in many types of WSONs.
   See [WSON-Imp] for more information on optical impairments and GMPLS.

2. Terminology

   Add/Drop Multiplexers (ADM): An optical device used in WDM networks
   composed of one or more line side ports and typically many tributary

   CWDM: Coarse Wavelength Division Multiplexing.

   DWDM: Dense Wavelength Division Multiplexing.

   Degree: The degree of an optical device (e.g., ROADM) is given by a
   count of its line side ports.

   Drop and continue: A simple multi-cast feature of some ADM where a
   selected wavelength can be switched out of both a tributary (drop)
   port and a line side port.

   FOADM: Fixed Optical Add/Drop Multiplexer.

   GMPLS: Generalized Multi-Protocol Label Switching.

   Line side: In WDM system line side ports and links typically can
   carry the full multiplex of wavelength signals, as compared to
   tributary (add or drop ports) that typically carry a few (typically
   one) wavelength signals.

   OXC: Optical cross connect. An optical switching element in which a
   signal on any input port can reach any output port.

   PCC: Path Computation Client.  Any client application requesting a
   path computation to be performed by the Path Computation Element.

   PCE: Path Computation Element.  An entity (component, application, or
   network node) that is capable of computing a network path or route
   based on a network graph and applying computational constraints.

   PCEP: PCE Communication Protocol. The communication protocol between
   a Path Computation Client and Path Computation Element.

   ROADM: Reconfigurable Optical Add/Drop Multiplexer. A wavelength
   selective switching element featuring input and output line side
   ports as well as add/drop tributary 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.

   Tributary: A link or port on a WDM system that can carry
   significantly less than the full multiplex of wavelength signals
   found on the line side links/ports. Typical tributary ports are the
   add and drop ports on an ADM and these support only a single
   wavelength channel.

   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 (WSONs): 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 range in size from continent spanning long haul networks, to
   metropolitan networks, to residential access networks. In all these
   cases, the main concern is 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. The
   subsequent sections review and model some of the major subsystems of
   a WSON with an emphasis on those aspects that are of relevance to the
   control plane. In particular, WDM links, optical transmitters,
   ROADMs, and wavelength converters are examined.

   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 examples
   applications. Examples include access networks, metro, long haul, and
   submarine links. International Telecommunication Union -
   Telecommunication Standardization Sector (ITU-T) standards exist for
   various types of fibers. Although fiber can be categorized into
   Single mode fibers (SMF) and Multi-mode fibers (MMF), the latter are
   typically used for short-reach campus and premise applications. SMF
   are used for longer-reach applications and therefore are the primary
   concern of this document. 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 a discontinuous acceptable
   wavelength range for a particular link may be needed and is modeled.
   Also some systems will utilize more than one band. This is
   particularly true for CWDM systems.

   Current technology subdivides 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, Spectral grids for WDM applications: DWDM
   frequency grid [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, Spectral grids for WDM
   applications: CWDM wavelength grid [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 defined for
   GMPLS, see [RFC3471].  A label representation for these ITU-T grids
   is given in [Otani] and provides a common label format to be used in
   signaling optical paths. 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.

   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 significant system
   engineering and a fairly limited range of wavelengths. Hence the
   following information is needed as parameters to perform basic,
   impairment unaware, modeling of a WDM link:

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

   o  Channel spacing: Currently there are five channel spacings used in
      DWDM systems and a single channel spacing defined for CWDM

   For a particular link this information is relatively static, as
   changes to these properties generally require hardware upgrades. Such
   information may be used locally during wavelength assignment via
   signaling, similar to label restrictions in MPLS or used by a PCE in
   providing combined RWA.

   3.2. Optical Transmitters and Receivers

   WDM optical systems make use of optical transmitters and receivers
   utilizing different wavelengths (frequencies). Some transmitters are
   manufactured for a specific wavelength of operation, that is, the
   manufactured frequency cannot be changed. First introduced to reduce
   inventory costs, tunable optical transmitters and receivers are
   deployed in some systems, and allow flexibility in the wavelength
   used for optical transmission/reception.  Such tunable optics aid in
   path selection.

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

   o  Tunable: Do the transmitter and receivers operate at variable or
      fixed wavelength.

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

   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 usable for fast protection applications.

   o  Spectral characteristics and stability: The spectral shape of a
      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 closest channel spacing with
      which the transmitter can be used.

   Note that ITU-T recommendations specify many aspects of an optical
   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 the Label Switched Path (LSP) provisioning in a properly
   designed system.

   Also note that optical components can degrade and fail over time.
   This presents the possibility of the failure of a LSP (optical path)
   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 optical transmitter will
   still be failed on the alternate optical path.

   3.3. Optical Signals in WSONs

   In WSONs the 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
   multichannel DWDM networks with single channel interfaces are the
   prime focus of this document general concern as opposed to multi-
   channel multi-channel interfaces.
   Interfaces of this type are defined in ITU-T recommendations
   [G.698.1] and [G.698.2]. 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

   For the purposes of modeling the WSON in the control plane, (a) and
   (b) are considered 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 currently a number of different types of optical tributary
   signals, which are 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
   development 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).

   According to [G.698.2] it is important to fully specify the bit rate
   of the optical tributary signal. Hence it is seen 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

   An optical tributary signal referenced in ITU-T [G.698.1] and
   [G.698.2] is referred to as the "signal" in this document. This
   corresponds to the "lambda" LSP in GMPLS. For signal compatibility
   purposes with electro-optical network elements, the following signal
   characteristics are considered:

  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 the optical network with elements that include
   regenerators, Optical-to-Electrical (OEO) switches, or wavelength

   Bit rate and G-PID 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 non-standard or proprietary modulation formats
   and FEC codes are commonly used in WSONs. For some digital bit
   streams the presence of Forward Error Correction (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 Optical Channel Transport
   Unit-k (OTUk) is all zeros or not.

   3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs

   Definitions of various optical devices such as ROADMs, Optical Cross-
   connects (OXCs), splitters, combiners and Fixed Optical Add-Drop
   Multiplexers (FOADMs) and their parameters can be found in [G.671].
   Only a subset of these relevant to the control plane and their non-
   impairment related properties are considered in the following

      3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs

   ROADMs are available in different forms and technologies. This is a
   key technology that allows wavelength based optical switching. A
   classic degree-2 ROADM is shown in Figure 1.

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

                  Figure 1. Degree-2 unidirectional ROADM

   The key feature across all ROADM types is their highly asymmetric
   switching capability. In the ROADM of Figure 1, signals introduced
   via the add ports can only be sent on the line side output port and
   not on any of the drop ports. The term "degree" is used to refer to
   the number of line side ports (input and output) of a ROADM, and does
   not include the number of "add" or "drop" ports. The add and drop
   ports are sometimes 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 it is necessary to know the
   switched connectivity offered by such a network element to
   effectively utilize it. A straightforward way to represent this is
   via a "switched connectivity" matrix A where Amn = 0 or 1, depending
   upon whether a wavelength on input port m can be connected to output
   port n [Imajuku]. For the ROADM shown in Figure 1 the switched
   connectivity matrix can be expressed as:

               Input    Output 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 input ports 2-5 are add ports, output ports 2-5 are drop ports
   and input port #1 and output port #1 are the line side (WDM) ports.

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

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

                  Figure 2. Degree-4 bidirectional ROADM

   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 "bidirectional", i.e. if input port X can be connected to output
   port Y, typically input port Y can be connected to output port X,
   assuming the numbering is done in such a way that input X and output
   X correspond to the same line side direction or the same add/drop
   port. This makes the connectivity matrix symmetrical as shown below.

     Input     Output 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 loopback is not supported in
   the example. If ports support loopback, diagonal elements would be
   set to one.

   Additional constraints may also apply to the various ports in a
   ROADM/OXC. The following restrictions and terms may be used:

   Colored port: an input or more typically an output (drop) port
   restricted to a single channel of fixed wavelength.

   Colorless port: an input or more typically an output (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 it is necessary to have 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 input port and two or more
   output ports. The input optical signaled is essentially copied (with
   power loss) to all output ports.

   Using the modeling notions of Section 3.4.1. (Reconfigurable Add/Drop
   Multiplexers and OXCs) the input and output ports of a splitter would
   have the same wavelength restrictions. In addition a splitter is
   modeled by a connectivity matrix Amn as follows:

               Input    Output 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
   connectivity matrix but the fixed connectivity matrix of the device.

      3.4.3. Combiners

   An optical combiner is a device that combines the optical wavelengths
   carried by multiple input ports into a single multi-wavelength output
   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 output port.
   The fixed connectivity matrix Amn for a combiner would look like:

               Input    Output 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 input
   wavelength in a preset way. In particular a given wavelength (or
   waveband) from a line side input port would be dropped to a fixed
   "tributary" output port. Depending on the device's construction that
   same wavelength may or may not also be sent out the line side output
   port.  This is commonly referred to as "drop and continue" operation.
   There also may exist tributary input ports ("add" ports) whose
   signals are combined with each other and other line side signals.

   In general, to represent the routing properties of an FOADM it is
   necessary to have both a fixed connectivity matrix Amn as previously
   discussed and the precise wavelength restrictions for all input and
   output ports. From the wavelength restrictions on the tributary
   output ports, what wavelengths have been selected can be derived.
   From the wavelength restrictions on the tributary input ports, it can
   be seen which wavelengths have been added to the line side output
   port. Finally from the added wavelength information and the line side
   output wavelength restrictions it can be inferred which wavelengths
   have been continued.

   To summarize, the modeling methodology introduced in Section 3.4.1.
   (Reconfigurable Add/Drop Multiplexers and OXCs) 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 listed in Section 3.3.2. (WSON Signal
   Characteristics) 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 and hence their properties can be described first.

      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 this table it is seen 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.  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

   It is common for regenerators to modify the digital bit stream for
   performance monitoring and fault management purposes. Synchronous
   Optical Networking (SONET), Synchronous Digital Hierarchy (SDH) and
   Interfaces for the Optical Transport Network (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.  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 below.

       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 it is seen that frame alignment, signal
   identification, and FEC are supported. What table 2 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 depending upon the regenerator technology the following
   constraints may be 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 the limited wavelength range constraint can be modeled for
   GMPLS signaling with the label set defined in [RFC3471] and that the
   modulation type restriction constraint includes FEC.

      3.5.2. OEO Switches

   A common place where OEO processing may take place is within WSON
   switches that utilize (or contain) regenerators. This may be to
   convert the signal to an electronic form for switching then
   reconverting to an optical signal prior to output from the switch.
   Another common technique is to add regenerators to restore signal
   quality either before or after optical processing (switching).   In
   the former 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 which are described for
   regenerators in Table 3.

   3.6. Wavelength Converters

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

   Another approach performs the wavelength conversion, 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 fixed or
     tunable optics. In this case there are typically multiple
     converters available since each on the use of an OEO switch can be thought
     of as a potential wavelength converter.

  2. Wavelength conversion associated with ROADMs/OXCs. In this case
     there may be 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 there may be a limited amount of conversion. Also in
     this case the conversion may be used as part of optical path

   Based on the above considerations, wavelength converters are modeled
   as follows:

   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 input 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 they can be associated with input ports.

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

   In WSONs where wavelength converters are sparse an optical path may
   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 input to the wavelength converter would be different
   from the lambda coming back from 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 it is necessary 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 input wavelength on a particular input port
      to a desired output wavelength on a particular output port.

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

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

   A three stage model is used as shown schematically in Figure 3.
   (Schematic diagram of wavelength converter pool model). This model
   represents N input ports (fibers), P wavelength converters, and M
   output ports (fibers). Since not all input ports can necessarily
   reach the converter pool, the model starts with a wavelength pool
   input matrix WI(i,p) = {0,1} where input port i can reach potentially reach
   wavelength converter p.

   Since not all wavelengths can necessarily reach all the converters or
   the converters may have limited input wavelength range there is a set
   of input port constraints for each wavelength converter. Currently it
   is assumed that a wavelength converter can only take a single
   wavelength on input. Each wavelength converter input port constraint
   can be modeled via a wavelength set mechanism.

   Next 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 [Gen-

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

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

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

                    Input wavelength    Output wavelength
                    constraints for       constraints for
                    each converter        each converter

      Figure 3. Schematic diagram of wavelength converter pool model.

   Figure 4 below shows a simple optical switch in a four wavelength
   DWDM system sharing wavelength converters in a general shared "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 input and output pool matrices are simply:

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

   Figure 5 shows a different wavelength pool architecture known as
   "shared per fiber". In this case the input and output 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 electro-optical WSON network elements are
   characterized 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. (Wavelength Switched Optical Networks) discussed the basic
   properties regenerators, OEO switches and wavelength converters. From
   these the following possible types of input constraints and
   properties are derived:

   1. Acceptable Modulation formats.

   2. Client Signal (G-PID) restrictions.

   3. Bit Rate restrictions.

   4. FEC coding restrictions.

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

   These constraints are represented 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 may be
   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 item 5 has
   been added, which describes the devices configurability.

   Note that such input constraints also apply to the 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 the following types
   of output constraints are seen:

   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.

   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 it is necessary to 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 (input and output restrictions, availability).

   Note that the properties of shared regenerator pools would be
   essentially the same at as that of wavelength converter pools modeled in
   section 3.6.1. (Wavelength Pool Convertor Modeling).

   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 on 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

   From a control plane perspective, a wavelength-convertible network
   with full wavelength-conversion capability at each node can be
   controlled much like a packet MPLS-labeled network or a circuit-
   switched Time-division multiplexing (TDM) network with full time slot
   interchange capability is controlled.  In this case, the path
   selection process needs to identify the Traffic Engineered (TE) links
   to be used by an optical path, and wavelength assignment can be made
   on a hop-by-hop basis.

   However, in the case of an optical network without wavelength
   converters, an optical path needs to be routed from source to
   destination and must use a single wavelength that is available along
   that path without "colliding" with a wavelength used by any other
   optical path that may share an optical fiber. This is sometimes
   referred to as a "wavelength continuity constraint".

   In the general case of limited or no wavelength converters the
   computation of both the links and wavelengths is known as RWA.

   The inputs to basic RWA are the requested optical path's source and
   destination, the network topology, the locations and capabilities of
   any wavelength converters, and the wavelengths available on each
   optical link. The output from an algorithm providing RWA is an
   explicit route through ROADMs, a wavelength for 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 the choice of specific RWA algorithm is out of
   the scope for this document. However there are a number of different
   approaches to dealing with RWA algorithm that can affect the division
   of effort between path computation/routing and signaling.

   4.1. Architectural Approaches to RWA

   Two general computational approaches are taken to performing RWA.
   Some algorithms utilize a two-step procedure of path selection
   followed by wavelength assignment, and others perform RWA 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. The approaches
   are provided for reference purposes only, and other approaches are

      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 places:

   o  In a PCE which maintains a complete and updated view of network
      state and provides path computation services to nodes (PCCs).

   o  In an ingress node, in which case all nodes have the R&WA
      functionality and 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, one entity performs routing, while a second performs
   wavelength assignment. The first entity furnishes one or more paths
   to the second entity which will perform wavelength assignment and
   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 wavelength 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. Hence, while 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 specific network node capabilities.

      4.1.3. Routing and Distributed WA (R+DWA)

   In this case, one entity performs routing, while wavelength
   assignment is performed on a hop-by-hop, distributed, distributed manner along the
   previously computed path. 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. GMPLS, per [RFC3471], includes
   support for the communication of the set of labels (wavelengths) that
   may be used between nodes via a Label Set. When conversion is not
   performed at an intermediate node, a hop generates the Label Set it
   sends to the next hop based on the intersection of the Label Set
   received from the previous hop and the wavelengths available on the
   node's switch and ongoing interface. The generation of the outgoing
   Label Set 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 node selects one label
   in the Label Set which it received; additionally the node can apply
   local policy during label selection. GMPLS also provides support for
   the signaling of bidirectional optical paths.

   Depending on these policies a wavelength assignment may not be found
   or one consuming may be found that consumes 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.

   This solution may be facilitated via signaling extensions which ease
   its functioning and possibly enhance its performance relatively with respect to
   blocking probability. Note that this approach requires less
   information dissemination than the other techniques described.

   The first entity may be a PCE or the ingress node of the LSP.

   4.2. Conveying information needed by RWA

   The previous sections have characterized WSONs and optical path
   requests. In particular, high level models of the information used by
   RWA process were presented. This information can be viewed as either
   relatively static, i.e., changing with hardware changes (including
   possibly failures), or relatively dynamic, i.e., those that can
   change with optical path provisioning. The time requirement in which
   an entity involved in RWA process needs to be 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, i.e., GMPLS routing and
      signaling. Note that routing protocols can be used to convey both
      static and dynamic information.

   o  Management protocols such as NetConf, SNMPv3, CLI, and CORBA.

   o  Directory services and accompanying protocols. These are typically
      used for the dissemination of relatively static information.
      Directory services are not suited to manage information in dynamic
      and fluid environments.

   o  Other techniques for dynamic information, e.g., sending
      information directly 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 There may be other ways to limit flooding to
      "interested" NEs.

   Possible 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.

   o  Utilize incremental updates if feasible.

5. Modeling Examples and Control Plane Use Cases

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

   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
                                              |   |
                                             ++-+ |

     Figure 7. Routers and WSON nodes in a GMPLS and PCE Environment.

      5.1.1. Describing the WSON nodes

   The eight WSON nodes described in Figure 7 have the following

   o  Nodes N1, N2, N3 have 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 output links (L5,
      L7 and L12 in this case).

   o  The links from the routers are 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 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 output 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 output 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 document. In general optical impairment feasible routes
   serve as an input to 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 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 RWA algorithm yields 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 RWA algorithm yields WL2 and the path L2 L4 L6 L7 L9
   for the establishment of the new LSP.

   A 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

   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 a RWA

   Given the above example again, assume that a RWA algorithm should
   identify 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. An RWA algorithm can now
   compute the following alternate path 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 various networking scenarios are considered
   involving regenerators, OEO switches and wavelength converters. These
   scenarios can be grouped 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,
   regeneration is associated with a WDM link or an 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 may be input constraints and output constraints on the
   regenerators. Hence the path selection process will need to know from
   routing 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 it is necessary 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

   This scenario is concerned with regenerators that require
   configuration prior to use on an optical signal. As discussed
   previously, 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 it is necessary to have information
   concerning regenerator properties for selection of compatible paths
   and for IA-RWA computations. In addition during LSP setup it is
   necessary 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

   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.

   Three main types of translucent optical networks have been discussed:

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

   2. 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.

   3. 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 types of translucent networks fit within the networking
   scenarios of Section 5.5.1.  and Section 5.5.2.  above. And hence,
   can be accommodated by the GMPLS extensions envisioned in this

6. GMPLS and 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] provides such a
   fixed mapping for communication between PCE and WSON PCCs.

      6.1.2. WSON Signals and Network Element Processing

   As discussed in Section 3.3.2.  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 described in Section 5.5.1.
   (Fixed Regeneration Points) no enhancements are required to signaling
   since there are no additional configuration options for the LSP at a

   In the case of shared regeneration pools described in Section 5.5.2.
   (Shared Regeneration Pools) it is necessary to indicate to a node
   that it should perform regeneration on a particular signal. Viewed
   another way, for an LSP, it is desirable 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 described in Section 5.5.3.
   (Reconfigurable Regenerators) is very similar to the previous except
   that now there are potentially many more items that can be configured
   on a per node basis for an LSP.

   Note that the techniques of [RFC5420] which allow for additional LSP
   attributes and their recording in a Record Route Object (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 used 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 interpreted appropriately.

      6.1.4. Distributed Wavelength Assignment: Unidirectional, No

   GMPLS signaling for a unidirectional optical path LSP allows for the
   use of a label set object in the Resource Reservation Protocol -
   Traffic Engineering (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.

      6.1.5. Distributed Wavelength Assignment: Unidirectional, Limited

   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 the output 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 is processed. The node will pass on an enlarged label
   set reflecting only the limitations of the wavelength converter and
   the output link. The record route option in RSVP-TE signaling can be
   used to show where wavelength conversion has taken place.

      6.1.6. Distributed Wavelength Assignment: Bidirectional, No

   There are cases of a bidirectional optical path which requires the
   use of the same lambda in both directions. The above procedure can be
   used to determine the available bidirectional lambda set if it is
   interpreted that the available label set is available in both
   directions. In bidirectional LSPs setup, according to [RFC3471]
   Section 4.1. (Architectural Approaches to RWA), is indicated by the
   presence of an upstream label in the path message.

   However, until the intersection of the available label sets is
   determined along the path and at the destination node the upstream
   label information may not be correct.   This case can be supported
   using current GMPLS mechanisms, but may not be as efficient as an
   optimized bidirectional single-label allocation mechanism.

   6.2. Implications for GMPLS Routing

   GMPLS routing [RFC4202] currently defines an interface capability
   descriptor for "lambda switch capable" (LSC) which can be used 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, it would be necessary to convey the following
   subsystem properties to minimally characterize a WSON:

  1. WDM Link properties (allowed wavelengths).

  2. Optical 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 it is
   necessary 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

   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.
   This can be communicated as an LSP parameter and hence this
   information would be available for any NE that needs to use it for
   configuration. Hence it is not necessary to have "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) G-PID particular
      capabilities, (b) optical performance monitoring capabilities.

   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, see, basis; see
   the GMPLS interface switching capability descriptor [RFC4202].

      6.2.2. Wavelength-Specific Availability Information

   For wavelength assignment it is necessary to know which specific
   wavelengths are available and which are occupied if a combined RWA
   process or separate WA process is run 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. RWA 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 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 the
   approach of a global wavelength to label mapping or furnishing the
   local mappings to the PCEs is taken then representing the use of
   wavelengths via a simple bit-map is feasible [Gen-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
      Optical transmitter range           Static               Link(2)
      Wavelength conversion capabilities  Static(3)            Node
      Maximum bandwidth per wavelength    Static               Link
      Wavelength availability             Dynamic(4)           Link
      Signal compatibility and 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 it may be desirable 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 + distributed WA via signaling
   only the following information is needed:

      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], [Gen-Encode] and [WSON-Encode].

   6.3. Optical Path Computation and Implications for PCE

   As previously noted RWA can be computationally intensive. Such
   computationally intensive path computations and optimizations were
   part of the impetus for the PCE architecture [RFC4655].

   The Path Computation Element Protocol (PCEP) defines the procedures
   necessary to support both sequential [RFC5440] and global concurrent
   path computations (PCE-GCO) [RFC5557], PCE [RFC5557]. The PCEP is well positioned to
   support WSON-enabled RWA computation with some protocol enhancement.

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

      6.3.1. Optical path Constraints and Characteristics

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

   o  Batch optimization, multiple optical paths requested at one time

   o  Optical path(s) and backup optical path(s) requested at one time

   o  Single optical path requested at a time (PCEP).

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

   Optical path 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.

      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 G-PID 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 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 RWA. 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.

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 may make 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 RWA represents a disclosure of network capabilities that an
   operator may wish to keep private. Consideration should be given to
   securing this information. For a general discussion on MPLS and GMPLS
   related security issues, see the MPLS/GMPLS security framework

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.

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

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

   [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.

   [RFC4655] Farrel, A., Vasseur, JP., and Ash, J., "A Path Computation
             Element (PCE)-Based Architecture ", RFC 4655, August 2006.

   [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

   10.2. Informative References

   [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.

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

   [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-

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

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

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

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


   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


   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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