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Versions: 00 01 02 03 04 05 draft-ietf-ccamp-wson-impairments

Network Working Group                                      G. Bernstein
Internet Draft                                        Grotto Networking
                                                                 Y. Lee
                                                                  D. Li
Intended status: Informational                         October 29, 2008
Expires: April 2009

    A Framework for the Control and Measurement of Wavelength Switched
                 Optical Networks (WSON) with Impairments

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Copyright Notice

   Copyright (C) The IETF Trust (2008).

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   The operation of optical networks can require a level of detail in
   the characterization of network elements, subsystems, devices, and
   cabling not typically encountered with other networking technologies.
   In addition, these physical characteristics may be important to
   consider during typical day-to-day operations such as optical path
   establishment and connection monitoring, as well as during the
   network planning, installation, and turn-up phases. This document
   discusses how the definition and characterization of optical fiber,
   devices, subsystems, and network elements contained in various ITU-T
   recommendations can be combined with common control and measurement
   plane and path computation element technologies to support impairment
   aware Routing and Wavelength Assignment (RWA) in optical networks.

Table of Contents

   1. Introduction...................................................3
   2. Impairment Aware Optical Path Computation......................4
      2.1. IA-RWA Computing Architectures............................6
         2.1.1. Combined Routing, WA, and IV.........................7
         2.1.2. Separate Routing, WA, or IV..........................7
         2.1.3. Distributed WA and/or IV.............................7
      2.2. Information Model for Impairments.........................8
      2.3. Protocol Extension Implications...........................8
         2.3.1. Routing..............................................8
         2.3.2. Signaling............................................9
         2.3.3. PCE..................................................9
   3. Security Considerations........................................9
   4. IANA Considerations............................................9
   5. Acknowledgments...............................................10
   APPENDIX A: Overview of Optical Layer ITU-T Recommendations......11
      A.1. Fiber and Cables.........................................11
      A.2. Devices..................................................12
         A.2.1. Optical Amplifiers..................................12
         A.2.2. Dispersion Compensation.............................13
         A.2.3. Optical Transmitters................................14
         A.2.4. Optical Receivers...................................14
      A.3. Components and Subsystems................................15
      A.4. Network Elements.........................................16
   6. References....................................................18
      6.1. Normative References.....................................18
      6.2. Informative References...................................20
   Author's Addresses...............................................20

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   Intellectual Property Statement..................................21
   Disclaimer of Validity...........................................22

1. Introduction

   As an optical signal progresses along its path it may be altered by
   the various physical processes in the optical fibers and devices it
   encounters. When such alterations result in signal degradation, we
   usually refer to these processes as "impairments". An overview of
   some critical optical impairments and their routing (path selection)
   implications can be found in [RFC4054]. Roughly speaking, optical
   impairments accumulate along the path (without 3R regeneration)
   traversed by the signal. They are influenced by the type of fiber
   used, the types and placement of various optical devices and the
   presence of other optical signals that may share a fiber segment
   along the signal's path. The degradation of the optical signals due
   to impairments can result in unacceptable bit error rates or even a
   complete failure to demodulate and/or detect the received signal.
   Therefore, path selection in any WSON requires consideration of
   optical impairments so that the signal will be propagated from the
   network ingress point to the egress point with acceptable amount of

   Some optical subnetworks are designed such that over any path the
   degradation to an optical signal due to impairments never exceeds
   prescribed bounds. This may be due to the limited geographic extent
   of the network, the network topology, and/or the quality of the
   fiber and devices employed. In such networks the path selection
   problem reduces to determining a continuous wavelength from source
   to destination (the Routing and Wavelength Assignment problem).
   These networks are discussed in [WSON-Frame]. In other optical
   networks, impairments are important and the path selection process
   must be impairment-aware.

   Although [RFC4054] describes a number of key optical impairments, a
   more complete description of optical impairments and the processes
   that spawn them can be found in textbooks or reference books on
   optical communications [Agrawal02], [Agrawal07]. To be useful to
   consumers and producers of optical fiber, components, and subsystems,
   optical characteristics need to be precisely defined along with
   methods for their measurement, estimation and approximation. The ITU-
   T and other SDOs have assumed this responsibility and as optical
   technology has advanced these documents have been updated.  Appendix
   A of this document provides an overview of the extensive ITU-T
   documentation in this area.

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   The benefits of operating networks of different technologies using an
   intelligent control plane have been described in many places, and the
   Generalized Multiprotocol Label Switching (GMPLS) control plane is
   described in [RFC3945]. The advantages of using a path computation
   element (PCE) to perform complex path computations are discussed in

   Given the existing standards covering optical characteristics
   (impairments) and the knowledge how the impact of impairments may be
   estimated along a path, this document provides a framework for
   impairment aware path computation and establishment utilizing GMPLS
   protocols and the PCE architecture. As in the impairment free case
   covered in [WSON-Frame] a number of different control plane
   architectural options are described.

2. Impairment Aware Optical Path Computation

   One of the most basic questions in communications is whether one can
   successfully transmit information from a transmitter to a receiver
   within a prescribed error tolerance, usually specified as a maximum
   permissible bit error ratio (BER). This generally depends on the
   nature of the signal transmitted between the sender and receiver and
   the nature of the communications channel between the sender and
   receiver. The optical path utilized (along with the wavelength)
   determines the communications channel.

   The optical impairments incurred by the signal along the fiber and at
   each optical network element along the path determine whether the BER
   performance or any other measure of signal quality can be met for
   this particular signal on this particular path.

   From a control plane perspective it is useful to classify optical
   networks into categories based on how one determines whether a
   particular optical signal on a particular optical path can meet
   desired signal quality objectives such as BER [WD24],[WD05]. In the
   following we say a path is "conformant" for a particular type of
   signal if the signal quality objectives are achieved at the receiver.
   The four classes of optical networks with regards to impairments are:

   1. Networks designed such that every possible path is conformant for
      the signal types permitted on the network. In this case
      impairments are only taken into account during network design and
      after that, for example during optical path computation, they can
      be ignored. This is the case discussed in [WSON-Frame] where
      impairments could be ignored by the control plane.

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   2. Networks in which a limited number of pre-calculated paths are
      conformant for each type of signal permitted in the network. In
      this case the control plane is not have any detailed information
      about optical impairments. Instead we are given a list of
      qualified paths for each permitted signal in the network. This
      might occur if proprietary impairment models are used to evaluate
      paths or a vendor chooses not to publish impairment information.
      For example if a single WDM line system vendor is used within an
      optical subnetwork and chooses not to publish optical impairment
      information, that vendor with knowledge of the characteristics of
      the ROADMS and PXCs used in the network could pre-calculate a list
      of valid paths. Note that the structure of such a qualified
      path/wavelength list could be useful to standardize as part of an
      impairment aware information model.

   3. Networks in which impairment effects can be estimated via
      approximation techniques such as link budgets and dispersion (rise
      time) budgets [Agrawal02],[G.680],[G.sup39]. As networks grow
      larger listing all useable paths for each signal type can
      encounter scaling issues. Instead the viability of most optical
      paths for a particular class of signals is performed using well
      defined approximation techniques [G.680], [G.sup39]. Much work at
      ITU-T has gone into developing impairment models at this and more
      detailed levels. Impairment characterization of network elements
      could then made available via the control plane and then used to
      calculate which paths are conformant with a specified BER for a
      particular signal type. This case requires that all relevant
      impairment information is available from all optical subsystems.

   4. Networks in which impairment effects must be more accurately
      estimated. This typically includes detailed dispersion,
      interference and/or nonlinear effect simulations. This includes
      evaluation of the impact to any existing paths prior to the
      addition of a new path. This is currently performed via methods
      that solve the partial differential equations describing signal
      propagation in fiber along with more detail models for the other
      network elements [Agrawal02],[Agrawal07]. The
      estimation/simulation time required can be very situation
      dependent. The implication is that a significant amount of time
      could be required to "qualify" a path and this would need to be
      taken into account in a PCE architecture that includes impaired
      path validation. ITU-T recommendations contain a good deal of more
      detailed optical characteristics (see Appendix A) for fibers and
      devices, however these are not currently assembled into a single
      modeling document as was done for the approximate analysis model
      in [G.680].

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2.1. IA-RWA Computing Architectures

   As previously stated from the point of view of RWA we may take
   optical impairments into account by being given:

   1. A list of valid paths with corresponding wavelength constraints;

   2. Sufficient approximate impairment information to determine valid

   3. A validation decision from an estimation incorporating more
      complete impairment models;

   Hence to take into account optical impairments we add additional
   constraints to the impairment-free RWA process described in [WSON-
   Frame]. In IA-RWA, there are conceptually three functions to be
   considered in path computation.

  o  Routing (R): finding a route for the given source-destination.

  o  Wavelength Assignment (WA): assigning a wavelength for the route

  o  Impairment Validation (IV): applying a set of impairment
     constraints to the route and selected wavelength to see whether
     they would provide signal quality satisfaction.

   The IA-RWA architecture options can be built from the non-IA RWA
   computation architectures defined in the WSON framework document
   [WSON Frame]. Recall that the following three RWA computation
   architecture options [WSON-Frame].

  o  Combined RWA --- Both routing and wavelength assignment are
     performed at a single computational entity.  This choice assumes
     that computational entity has sufficient WSON network link/nodal
     and topology information to be able to compute RWA.

  o  Separate Routing and WA --- Separate entities perform routing and
     wavelength assignment.  The path obtained from the routing
     computational entity must be furnished to the entity performing
     wavelength assignment.

  o  Routing with Distributed WA --- Routing is performed at a
     computational entity while wavelength assignment is performed in a
     distributed fashion across the nodes along the path.

   The following subsections consider three major classes of IA-RWA path
   computation architectures.

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      2.1.1. Combined Routing, WA, and IV

   We can conceptually or algorithmically combine the processes of
   routing, wavelength assignment and impairment validation if we are
   given: (a) the impairment-free WSON network information as discussed
   in [WSON-Frame] and (b) either a list of validated paths/wavelengths
   or sufficient approximate impairment information to perform
   calculations to validate potential paths. In this case routing (R)
   and wavelength assignment (WA) and impairment validation (IV) are
   performed at a single computational entity.

   This situation could benefit from an information model that compactly
   describes a list of valid paths/wavelengths or characterizes
   impairments at a level similar to that in [G.680].

      2.1.2. Separate Routing, WA, or IV

   As was discussed in [WSON-Frame] there can be advantages to
   separating routing from WA. In addition, as previously described in
   the case of detailed impairment modeling we may want to logically
   separate IV from RWA. In addition for systems operating closer to
   physical limits the validation computations could be proprietary and
   hence by necessity may be logically separated.

   The following conceptual architectures belong in this general

  o  R+WA+IV -- separate routing, wavelength assignment, and impairment

  o  R + (WA & IV) -- routing separate from a combined wavelength
     assignment and impairment validation process. Note that impairment
     validation is typically wavelength dependent hence combining WA
     with IV can lead to efficiencies.

  o  (RWA)+IV - combined routing and wavelength assignment with a
     separate impairment validation process.

      2.1.3. Distributed WA and/or IV

   In the case where the effects of impairments can be calculated via
   approximate models such as those in [G.680] standard methods can be
   applied to calculate the combined potential impairment effects on a
   signal following a prescribed network path. This can allow for the
   distributed computation of impairment effects and avoid the need to
   distribute impairment characteristics of network elements and links
   via route protocols or by other means. An example of such an approach

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   is given in [Martinelli] and utilizes enhancements to RSVP signaling
   to carry accumulated impairment related information. For such a
   system to be interoperable the various impairment measures to be
   accumulated would need to be agreed upon. Section 9 of [G.680] can be
   useful in deriving such cumulative measures but doesn't explicitly
   state how a distributed computation would take place. For example in
   the computation of the optical signal to noise ratio along a path
   (see equation 9-3 of [G.680]) one could accumulate the linear sum
   terms and convert to dBs at the destination or one could convert in
   and out of dBs at each intermediate point along the path.

   If distributed WA is being done at the same time as distribute IV
   then we may need to accumulate impairment related information for all
   wavelengths that could be used. This is somewhat winnowed down as
   potential wavelengths are discovered to be in use, but could be a
   significant burden for lightly loaded high channel count networks.

2.2. Information Model for Impairments

   As previously discussed we are either given a list of conformant
   optical paths through a network or we are given information
   concerning the impairments for each network element which we can use
   to validate a path for a particular signal type.

   GMPLS and other IETF protocols have included descriptions of paths in
   the past and methods for compact representations of available
   wavelengths have been discussed in [WSON-Info]. A number of ITU-T
   recommendations cover detailed as well as approximate impairment
   characteristics of fibers and a variety of devices and subsystems. A
   well integrated impairment model for optical network elements is
   given in [G.680] and is used to form the basis for an optical
   impairment model in a companion document [Imp-Info].

2.3. Protocol Extension Implications

   Given the previous architectures and information models we have the
   following implications for routing, signaling and PCE related

      2.3.1. Routing

   Different approaches to path/wavelength impairment validation gives
   rise to different demands placed on GMPLS routing protocols.

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   In the case where a list of conformant paths/lambdas needs to be
   distributed to PCEs (or network elements with co-located PCEs) the
   routing protocol might be expected to help distribute this list.

   In the case where approximate impairment information is used to
   validate paths GMPLS routing may be used to distribute the impairment
   characteristics of the network elements and links.

   In the case where a separate path/wavelength validation server is
   used no additional demands may be require of GMPLS routing.

      2.3.2. Signaling

   Although we see impacts on signaling in cases where distributed
   impairment validation is performed, we may also want to add
   information to a connection request such as desired egress signal
   quality (defined in some appropriate sense). In addition, since the
   characteristics of the signal itself, such as modulation type, can
   play a major role in the tolerance of impairments, this type of
   information will need to be implicitly or explicitly signaled.

   In the cases of distributed validation of path/wavelength and
   distributed wavelength assignment and validation we need to
   accumulate impairment information as discussed in section 2.1.3.

      2.3.3. PCE

   For a PCE involved with impairment related computations we have two
   potential areas of impact: (a) impairment information model, (b) PCEP
   extensions for dealing with impairment related requests.

3. Security Considerations

   This document discusses a number of control plane architectures that
   incorporate knowledge of impairments in optical networks. If such
   architecture is put into use within a network it will by its nature
   contain details of the physical characteristics of an optical
   network. Such information would need to be protected from intentional
   or unintentional disclosure.

4. IANA Considerations

   This draft does not currently require any consideration from IANA.

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5. Acknowledgments

   This document was prepared using 2-Word-v2.0.template.dot.

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APPENDIX A: Overview of Optical Layer ITU-T Recommendations

   For optical fiber, devices, subsystems and network elements the ITU-T
   has a variety of recommendations that include definitions,
   characterization parameters and test methods. In the following we
   take a bottom up survey to emphasize the breadth and depth of the
   existing recommendations.  We focus on digital communications over
   single mode optical fiber.

A.1. Fiber and Cables

   Fibers and cables form a key component of what from the control plane
   perspective could be termed an optical link. Due to the wide range of
   uses of optical networks a fairly wide range of fiber types are used
   in practice. The ITU-T has three main recommendations covering the
   definition of attributes and test methods for single mode fiber:

  o  Definitions and test methods for linear, deterministic attributes
     of single-mode fibre and cable  [G.650.1]

  o  Definitions and test methods for statistical and non-linear
     related attributes of single-mode fibre and cable [G.650.2]

  o  Test methods for installed single-mode fibre cable sections

   General Definitions[G.650.1]: Mechanical Characteristics (numerous),
   Mode field characteristics(mode field, mode field diameter, mode
   field centre, mode field concentricity error, mode field non-
   circularity), Glass geometry characteristics, Chromatic dispersion
   definitions (chromatic dispersion, group delay, chromatic dispersion
   coefficient, chromatic dispersion slope, zero-dispersion wavelength,
   zero-dispersion slope), cut-off wavelength, attenuation. Definition
   of equations and fitting coefficients for chromatic dispersion (Annex
   A). [G.650.2] polarization mode dispersion (PMD) - phenomenon of PMD,
   principal states of polarization (PSP), differential group delay
   (DGD), PMD value, PMD coefficient, random mode coupling, negligible
   mode coupling, mathematical definitions in terms of Stokes or Jones
   vectors. Nonlinear attributes: Effective area, correction factor k,
   non-linear coefficient (refractive index dependent on intensity),
   Stimulated Billouin scattering.

   Tests defined [G.650.1]: Mode field diameter, cladding diameter, core
   concentricity error, cut-off wavelength, attenuation, chromatic
   dispersion. [G.650.2]: test methods for polarization mode dispersion.
   [G.650.3] Test methods for characteristics of fibre cable sections
   following installation: attenuation, splice loss, splice location,

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   fibre uniformity and length of cable sections (these are OTDR based),
   PMD, Chromatic dispersion.

   With these definitions a variety of single mode fiber types are
   defined as shown in the table below:

      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  |

A.2. Devices

A.2.1. Optical Amplifiers

   Optical amplifiers greatly extend the transmission distance of
   optical signals in both single channel and multi channel (WDM)
   subsystems. The ITU-T has the following recommendations:

  o  Definition and test methods for the relevant generic parameters of
     optical amplifier devices and subsystems [G.661]

  o  Generic characteristics of optical amplifier devices and
     subsystems [G.662]

  o  Application related aspects of optical amplifier devices and
     subsystems [G.663]

  o  Generic characteristics of Raman amplifiers and Raman amplified
     subsystems [G.665]

   Reference [G.661] starts with general classifications of optical
   amplifiers based on technology and usage, and include a near
   exhaustive list of over 60 definitions for optical amplifier device
   attributes and parameters. In references [G.662] and [G.665] we have
   characterization of specific devices, e.g., semiconductor optical
   amplifier, used in a particular setting, e.g., line amplifier. For
   example reference[G.662] gives the following minimum list of relevant
   parameters for the specification of an optical amplifier device used
   as line amplifier in a multichannel application:

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   a) Channel allocation.

   b) Total input power range.

   c) Channel input power range.

   d) Channel output power range.

   e) Channel signal-spontaneous noise figure.

   f) Input reflectance.

   g) Output reflectance.

   h) Maximum reflectance tolerable at input.

   i) Maximum reflectance tolerable at output.

   j) Maximum total output power.

   k) Channel addition/removal (steady-state) gain response.

   l) Channel addition/removal (transient) gain response.

   m) Channel gain.

   n) Multichannel gain variation (inter-channel gain difference).

   o) Multichannel gain-change difference (inter-channel gain-change

   p) Multichannel gain tilt (inter-channel gain-change ratio).

   q) Polarization Mode Dispersion (PMD).

A.2.2. Dispersion Compensation

   In optical systems two forms of dispersion are commonly encountered
   [RFC4054] chromatic dispersion and polarization mode dispersion
   (PMD). There are a number of techniques and devices used for
   compensating for these effects. The following ITU-T recommendations
   characterize such devices:

  o  Characteristics of PMD compensators and PMD compensating receivers

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  o  Characteristics of Adaptive Chromatic Dispersion Compensators

   The above furnish definitions as well as parameters and
   characteristics. For example in [G.667] adaptive chromatic dispersion
   compensators are classified as being receiver, transmitter or line
   based, while in [G.666] PMD compensators are only defined for line
   and receiver configurations. Parameters that are common to both PMD
   and chromatic dispersion compensators include: line fiber type,
   maximum and minimum input power, maximum and minimum bit rate, and
   modulation type. In addition there are a great many parameters that
   apply to each type of device and configuration.

A.2.3.  Optical Transmitters

   The definitions of the characteristics of optical transmitters can be
   found in references [G.957], [G.691], [G.692] and [G.959.1]. In
   addition references [G.957], [G.691], and [G.959.1] define specific
   parameter values or parameter ranges for these characteristics for
   interfaces for use in particular situations.

   We generally have the following types of parameters

   Wavelength related: Central frequency, Channel spacing, Central
   frequency deviation[G.692].

   Spectral characteristics of the transmitter: Nominal source type
   (LED, MLM lasers, SLM lasers) [G.957], Maximum spectral width, Chirp
   parameter, Side mode suppression ratio, Maximum spectral power
   density [G.691].

   Power related: Mean launched power, Extinction ration, Eye pattern
   mask [G.691], Maximum and minimum mean channel output power

A.2.4. Optical Receivers

   References [G.959.1], [G.691], [G.692] and [G.957], define optical
   receiver characteristics and [G.959.1], [G.691] and [G.957]give
   specific values of these parameters for particular interface types
   and network contexts.

   The receiver parameters include:

   Receiver sensitivity: minimum value of average received power to
   achieve a 1x10-10 BER [G.957] or 1x10-12 BER [G.691]. See [G.957] and
   [G.691] for assumptions on signal condition.

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   Receiver overload: Receiver overload is the maximum acceptable value
   of the received average power for a 1x10.10 BER [G.957] or a 1x10-12
   BER [G.691].

   Receiver reflectance: "Reflections from the receiver back to the
   cable plant are specified by the maximum permissible reflectance of
   the receiver measured at reference point R."

   Optical path power penalty: "The receiver is required to tolerate an
   optical path penalty not exceeding X dB to account for total
   degradations due to reflections, intersymbol interference, mode
   partition noise, and laser chirp."

   When dealing with multi-channel systems or systems with optical
   amplifiers we may also need:

   Optical signal-to-noise ratio: "The minimum value of optical SNR
   required to obtain a 1x10-12 BER."[G.692]

   Receiver wavelength range: "The receiver wavelength range is defined
   as the acceptable range of wavelengths at point Rn. This range must
   be wide enough to cover the entire range of central frequencies over
   the OA passband." [G.692]

   Minimum equivalent sensitivity: "This is the minimum sensitivity that
   would be required of a receiver placed at MPI-RM in multichannel
   applications to achieve the specified maximum BER of the application
   code if all except one of the channels were to be removed (with an
   ideal loss-less filter) at point MPI-RM." [G.959.1]

A.3. Components and Subsystems

   Reference [G.671] "Transmission characteristics of optical components
   and subsystems" covers the following components:

  o  optical add drop multiplexer (OADM) subsystem;

  o  asymmetric branching component;

  o  optical attenuator;

  o  optical branching component (wavelength non-selective);

  o  optical connector;

  o  dynamic channel equalizer (DCE);

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  o  optical filter;

  o  optical isolator;

  o  passive dispersion compensator;

  o  optical splice;

  o  optical switch;

  o  optical termination;

  o  tuneable filter;

  o  optical wavelength multiplexer (MUX)/demultiplexer (DMUX);

       - coarse WDM device;

       - dense WDM device;

       - wide WDM device.

   Reference [G.671] then specifies applicable parameters for these
   components. For example an OADM subsystem will have parameters such
   as: insertion loss (input to output, input to drop, add to output),
   number of add, drop and through channels, polarization dependent
   loss, adjacent channel isolation, allowable input power, polarization
   mode dispersion, etc...

A.4. Network Elements

   The previously cited ITU-T recommendations provide a plethora of
   definitions and characterizations of optical fiber, devices,
   components and subsystems. Reference [G.Sup39] "Optical system design
   and engineering considerations" provides useful guidance on the use
   of such parameters.

   In many situations the previous models while good don't encompass the
   higher level network structures that one typically deals with in the
   control plane, i.e, "links" and "nodes". In addition such models
   include the full range of network applications from planning,
   installation, and possibly day to day network operations, while with
   the control plane we are generally concerned with a subset of the
   later. In particular for many control plane applications we are
   interested in formulating the total degradation to an optical signal
   as it travels through multiple optical subsystems, devices and fiber

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   In reference [G.680] "Physical transfer functions of optical networks
   elements", a degradation function is currently defined for the
   following optical network elements: (a) DWDM Line segment, (b)
   Optical Add/Drop Multiplexers (OADM), and (c) Photonic cross-connect
   (PXC). The scope of [G.680] is currently for optical networks
   consisting of one vendors DWDM line systems along with another
   vendors OADMs or PXCs.

   The DWDM line system of [G.680] consists of the optical fiber, line
   amplifiers and any embedded dispersion compensators. Similarly the
   OADM/PXC network element may consist of the basic OADM component and
   optionally included optical amplifiers. The parameters for these
   optical network elements (ONE) are given under the following

  o  General ONE without optical amplifiers

  o  General ONE with optical amplifiers

  o  OADM without optical amplifiers

  o  OADM with optical amplifiers

  o  Reconfigurable OADM (ROADM) without optical amplifiers

  o  ROADM with optical amplifiers

  o  PXC without optical amplifiers

  o  PXC with optical amplifiers

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6. References

6.1. Normative References

   [G.650.1] ITU-T Recommendation G.650.1, Definitions and test methods
             for linear, deterministic attributes of single-mode fibre
             and cable, June 2004.

   [650.2]  ITU-T Recommendation G.650.2, Definitions and test methods
             for statistical and non-linear related attributes of
             single-mode fibre and cable, July 2007.

   [650.3]  ITU-T Recommendation G.650.3

   [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.661]  ITU-T Recommendation G.661, Definition and test methods for
             the relevant generic parameters of optical amplifier
             devices and subsystems, March 2006.

   [G.662]  ITU-T Recommendation G.662, Generic characteristics of
             optical amplifier devices and subsystems, July 2005.

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

   [G.680]  ITU-T Recommendation G.680, Physical transfer functions of
             optical network elements, July 2007.

   [G.691]  ITU-T Recommendation G.691, Optical interfaces for
             multichannel systems with optical amplifiers, November

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   [G.692]  ITU-T Recommendation G.692, Optical interfaces for single
             channel STM-64 and other SDH systems with optical
             amplifiers, March 2006.

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

   [G.957]  ITU-T Recommendation G.957, Optical interfaces for
             equipments and systems relating to the synchronous digital
             hierarchy, March 2006.

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

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

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

   [RFC4054] Strand, J., Ed., and A. Chiu, Ed., "Impairments and Other
             Constraints on Optical Layer Routing", RFC 4054, May 2005.

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

   [WSON-Frame] G. Bernstein, Y. Lee, W. Imajuku, "Framework for GMPLS
             and PCE Control of Wavelength Switched Optical Networks",
             work in progress: draft-ietf-ccamp-wavelength-switched-
             framework-00.txt, July 2008.

   [WSON-Info] G. Bernstein, Y. Lee, D. Li, W. Imajuku, "Routing and
             Wavelength Assignment Information Model for Wavelength
             Switched Optical Networks", work in progress: draft-ietf-
             ccamp-rwa-info-00.txt, August 2008.

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6.2. Informative References

   [Agrawal02] Govind P. Agrawal, Fiber-Optic Communications Systems -
             Third Edition, Wiley-Interscience, 2002.

   [Agrawal07] Govind P. Agrawal, Nonlinear Fiber Optics - Fourth
             Edition, Academic Press, 2007.

   [Imp-Info]  G. Bernstein, Y. Lee, D. Li, "A Framework for the Control
             and Measurement of Wavelength Switched Optical Networks
             (WSON) with Impairments", work in progress: draft-
             bernstein-wson-impairment-info-00.txt, October 2008.

   [Martinelli]   G. Martinelli (ed.) and A. Zanardi (ed.), "GMPLS
             Signaling Extensions for Optical Impairment Aware Lightpath
             Setup", Work in Progress: draft-martinelli-ccamp-optical-
             imp-signaling-01.txt, February 2008.

   [WD05]   Malcolm Betts, Hing-Kam Lam, " Report of Q12/15 and Q14/15
             Joint Interregnum Meeting in Beijing, 22 - 26 September
             2008", Study Group 15, Question 12 & 14, WD 05r2, September

   [WD24]   Malcolm Betts, "Considerations on the model of media layer
             networks", Study Group 15, Question 12, WD 24, September

Author's Addresses

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

   Phone: (510) 573-2237
   Email: gregb@grotto-networking.com

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

   Phone: (972) 509-5599 (x2240)
   Email: ylee@huawei.com

   Dan Li
   Huawei Technologies Co., Ltd.
   F3-5-B R&D Center, Huawei Base,
   Bantian, Longgang District
   Shenzhen 518129 P.R.China

   Phone: +86-755-28973237
   Email: danli@huawei.com

Contributor's Addresses

   Ming Chen
   Huawei Technologies Co., Ltd.
   F3-5-B R&D Center, Huawei Base,
   Bantian, Longgang District
   Shenzhen 518129 P.R.China

   Phone: +86-755-28973237
   Email: mchen@huawei.com

   Rebecca Han
   Huawei Technologies Co., Ltd.
   F3-5-B R&D Center, Huawei Base,
   Bantian, Longgang District
   Shenzhen 518129 P.R.China

   Phone: +86-755-28973237
   Email: hanjianrui@huawei.com

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   We thank Chen Ming of DICONNET Project who provided valuable
   information relevant to this document.

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