Network Working Group                                            Y. Lee
Internet Draft
                                                                 Huawei
                                                           G. Bernstein
                                                      Grotto Networking
                                                                  D. Li
                                                                 Huawei
                                                          G. Martinelli
                                                                  Cisco

Internet Draft
Intended status: Informational                         October 21, 2010                            March 9, 2011
Expires: April September 2011

    A Framework for the Control of Wavelength Switched Optical Networks
                          (WSON) with Impairments
                 draft-ietf-ccamp-wson-impairments-04.txt
                 draft-ietf-ccamp-wson-impairments-05.txt

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Abstract

   The operation of

   As an optical networks requires information on signal progresses along its path it may be altered by
   the various physical characterization of processes in the optical network elements, subsystems,
   devices, fibers and cabling. devices it
   encounters. When such alterations result in signal degradation, we
   usually refer to these processes as "impairments". These physical
   characteristics may be important constraints to consider when using a
   GMPLS control plane to support path setup and maintenance. maintenance in
   wavelength switched optical networks.

   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 provides a framework for applying GMPLS control plane protocols and mechanisms
   the PCE architecture to support Impairment Aware Routing and
   Wavelength Assignment (IA-RWA) in wavelength switched optical
   networks.

Table of Contents

   1. Introduction...................................................4
      1.1. Revision History..........................................5 Introduction...................................................3
   2. Motivation.....................................................5 Terminology....................................................4
   3. Applicability..................................................5
   4. Impairment Aware Optical Path Computation......................6
      3.1.
      4.1. Optical Network Requirements and Constraints..............7
         3.1.1.
         4.1.1. Impairment Aware Computation Scenarios...............7
         3.1.2.
         4.1.2. Impairment Computation and Information Sharing
         Constraints.................................................8
         3.1.3.
         4.1.3. Impairment Estimation Process.......................10
      3.2.
      4.2. IA-RWA Computation and Control Plane Architectures.......11
         3.2.1.
         4.2.1. Combined Routing, WA, and IV........................13
         3.2.2.
         4.2.2. Separate Routing, WA, or IV.........................13
         3.2.3.
         4.2.3. Distributed WA and/or IV............................13
      3.3. IV............................14
      4.3. Mapping Network Requirements to Architectures............14

   4. Architectures............15
   5. Protocol Implications.........................................17
      4.1.
      5.1. Information Model for Impairments........................17
      4.2.
      5.2. Routing..................................................18
      4.3. Signaling................................................18
      4.4.
      5.3. Signaling................................................19
      5.4. PCE......................................................19
         4.4.1.
         5.4.1. Combined IV & RWA...................................19
         4.4.2.
         5.4.2. IV-Candidates + RWA.................................19
         4.4.3. Approximate IA-RWA + Separate Detailed IV...........21
   5. Security Considerations.......................................23 RWA.................................20
   6. IANA Considerations...........................................23 Security Considerations.......................................22
   7. Acknowledgments...............................................23 IANA Considerations...........................................22
   8. References....................................................31 References....................................................22
      8.1. Normative References.....................................31 References.....................................22
      8.2. Informative References...................................33 References...................................24
   9. Acknowledgments...............................................24

1. Introduction

   Wavelength Switched Optical Networks (WSONs) are constructed from
   subsystems that may 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 wavelength division
   multiplexed (WDM)-based optical network in which switching is
   performed selectively based on the center wavelength of an optical
   signal.

   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 are usually referred to as "impairments".
      An overview of some critical optical impairments and their routing
      (path selection) implications can be found in [RFC4054]. Roughly
      speaking, optical 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

   In order to the egress
      point with provision an acceptable signal quality.

      Some optical subnetworks are designed such that over any path the
      degradation to an connection (an optical signal due to path) through
   a WSON certain path continuity, resource availability and impairments never exceeds
      prescribed bounds. This may
   constraints must be due met to determine viable and optimal paths through
   the limited geographic
      extent network. The determination 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 paths is known as Impairment Aware
   Routing and Wavelength Assignment
      problem). These (IA-RWA).

   Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] includes
   a set of control plane protocols that can be used to operate data
   networks are discussed in [WSON-Frame]. In other
      optical ranging from packet switch capable networks, impairments are important through those
   networks that use time division multiplexing, and the path selection
      process must be impairment-aware.

      Although WDM. [RFC4054] describes a number of key optical impairments,
      a more complete description
   gives an overview of some critical optical impairments and processes their
   routing (path selection) implications for GMPLS. The Path Computation
   Element (PCE) architecture [RFC4655] defines functional components
   that can be found used to compute and suggest appropriate paths in
   connection-oriented traffic-engineered networks.

   This document provides a framework for applying GMPLS protocols and
   the ITU-T Recommendations. Appendix A PCE architecture to the control and operation of IA-RWA for
   WSONs.  To aid in this process this document also provides an
   overview of the extensive ITU-T documentation
      in this area.

      The benefits of operating networks using 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
      [RFC4655].

      Based on the existing ITU-T standards covering optical
      characteristics (impairments) subsystems and processes that comprise WSONs, and
   describes IA-RWA so that the knowledge of information requirements can be
   identified to explain how the impact
      of impairments may information can be estimated along a path, this document
      provides a framework modeled for impairment aware path computation and
      establishment utilizing use by
   GMPLS protocols and the PCE architecture.
      As in systems. This work will facilitate the impairment free case covered in [WSON-Frame], a number
      of different control plane architectural options are described.

   1.1. Revision History

      Changes from 00 to 01:

      Added discussion of regenerators to section 3.

      Added to discussion of interface parameters in section 3.1.3.

      Added to discussion development of IV Candidates function in section 3.2.

      Changes from 01 to 02:

      Correct
   protocol solution models and refine use of "black link" concept based on liaison
      with ITU-T and WG feedback.

      Changes from 02 to 03:

      Insert additional information on use protocol extensions within the GMPLS and considerations for
      regenerators in section 3.
   PCE protocol families.

2. Motivation

      There are deployment scenarios for WSON Terminology

   Add/Drop Multiplexers (ADM): An optical device used in WDM networks where not all
      possible paths will yield suitable signal quality. There are
      multiple reasons behind this choice; here below is a non-
      exhaustive list
   composed of examples:

     o WSON is evolving using multi-degree optical one or more line side ports and typically many tributary
   ports.

   CWDM: Coarse Wavelength Division Multiplexing.

   DWDM: Dense Wavelength Division Multiplexing.

   FOADM: Fixed Optical Add/Drop Multiplexer.

   GMPLS: Generalized Multi-Protocol Label Switching.

   IA-RWA: Impairment Aware Routing and Wavelength Assignment

   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 connects connect. An optical switching element in which a
        way that network topologies are changing from rings (and
        interconnected rings)
   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 full mesh. Adding network equipment
        such as amplifiers path or regenerators, to make all paths feasible,
        leads to an over-provisioned network. Indeed, even with over
        provisioning, the route
   based on a network could still have some infeasible
        paths.

     o Within graph and applying computational constraints.

   PCEP: PCE Communication Protocol. The communication protocol between
   a given network, the 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 physical interface may
        change over the network life, e.g., the 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
   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. Applicability

   There are deployment scenarios for WSON networks where not all
   possible paths will yield suitable signal quality. There are
   multiple reasons behind this choice; here below is a non-exhaustive
   list of examples:

   o  WSON is evolving using multi-degree optical cross connects in a
      way that network topologies are changing from rings (and
      interconnected rings) to general mesh. Adding network equipment
      such as amplifiers or regenerators, to make all paths feasible,
      leads to an over-provisioned network. Indeed, even with over
      provisioning, the network could still have some infeasible paths.

   o  Within a given network, the optical physical interface may change
      over the network life, e.g., the optical interfaces might be
      upgraded to higher bit-rates. Such changes could result in paths
      being unsuitable for the optical signal. Although the same
        considerations may apply to other network equipment upgrades, Moreover, the optical
      physical interfaces are a typical case because they
        are typically provisioned at various stages of
      the network's life span as needed by traffic demands.

   o  There are cases where a network is upgraded by adding new optical
      cross connects to increase network flexibility. In such cases
      existing paths will have their feasibility modified while new
      paths will need to have their feasibility assessed.

   o  With the recent bit rate increases from 10G to 40G and 100G over a
      single wavelength, WSON networks will likely be operated with a
      mix of wavelengths at different bit rates. This operational
      scenario will impose some impairment considerations constraints due to different
      physical behavior of different bit rates and associated modulation
      formats.

   Not having an impairment aware control plane for such networks will
   require a more complex network design phase that, since the
      beginning, that takes into account
   evolving network status in term of equipments and traffic. traffic at the
   beginning stage. This could result in over-engineering the DWDM
   network with additional regenerators nodes and optical amplifiers. Optical impairment awareness allows for the concept of
      photonic switching where possible and provides regeneration when
      it is a must. In
   addition, network operations such as path establishment, will
   require significant pre-design via non-control plane processes
   resulting in significantly slower network provisioning.

   3.

4. Impairment Aware Optical Path Computation

   The basic criteria for path selection is whether one can successfully
   transmit the signal 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 a
   signal on a particular end-to-end path. This could
      include parameters such as the Q factor to correlate both linear
      and non-linear parameters into one value.

      The impairment-aware

   Impairment-aware path calculation needs also needs to take into account
   when regeneration happens is used along the path. [WSON-Frame]
      introduces provides
   background on the concept of Optical optical translucent network that networks which
   contains transparent elements and electro-optical elements such as
   OEO regenerations. In such networks a generic light path can go
   through a certain number of regeneration points.

   Regeneration points could happen for two reasons:

  (i)  wavelength conversion to assist the RWA process to avoid wavelength blocking.
     This is the impairment free case covered
        by[WSON-Frame]. by [WSON-Frame].

  (ii)  the optical signal is without regeneration would be too degraded. degraded
     to meet end to end BER requirements. This is the case when
        the RWA take
     takes into consideration impairment estimation covered by this
     document.

In the latter case a light an optical path can be seen as a set of transparent
segments. The optical impairments calculation needs to be reset at each
regeneration point so each transparent segment will have its own
impairment evaluation.

   +---+    +----+   +----+     +---+     +-----+     +----+    +---+
   | I |----| N1 |---| N2 |-----| R REG |-----| N3 |----| E |
      +--+
   +---+    +----+   +----+     +---+     +-----+     +----+    +---+

      |.--------------------------.|.------------------.|

   |<----------------------------->|<-------------------->|
           Segment 1                      Segment 2

          Figure 1 Light Optical path as a set of transparent segments

For example, Figure 1 represents a Light an optical path from node I to node E
with a regeneration point R REG in between. It is feasible from an
impairment validation perspective if both segments (I, N1, N2, R) REG) and
   (R,
(REG, N3, E) are feasible.

   3.1.

4.1. Optical Network Requirements and Constraints

   This section examines the various optical network requirements and
   constraints that an impairment aware optical control plane may have
   to operate under. These requirements and constraints motivate the IA-RWA IA-
   RWA architectural alternatives to be presented in the following
   section. We can break the different Different optical networks contexts up along can be broken into two
   main criteria: (a) the accuracy required in the estimation of
   impairment effects, and (b) the constraints on the impairment
   estimation computation and/or sharing of impairment information.

   3.1.1.

4.1.1. Impairment Aware Computation Scenarios

   A. No concern for impairments or Wavelength Continuity Constraints

   This situation is covered by existing GMPLS with local wavelength
   (label) assignment.

   B. No concern for impairments but Wavelength Continuity Constraints

   This situation is applicable to networks designed such that every
   possible path is valid 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 may be ignored by the control plane and only optical
   parameters related to signal compatibility are considered.

   C. Approximated Impairment Estimation

   This situation is applicable to networks in which impairment effects
   need to be considered but there is sufficient margin such that they
   can be estimated via approximation techniques such as link budgets
   and dispersion[G.680],[G.sup39]. dispersion [G.680],[G.sup39]. The viability of optical paths for
   a particular class of signals can be estimated using well defined
   approximation techniques [G.680], [G.sup39]. This is the generally
   known as linear case where only linear effects are taken into
   account. Adding Note that adding or removing an optical signal on the path will
   should not render any of the existing signals in the network as non-viable. non-
   viable.  For example, one form of non-viability is the occurrence of
   transients in existing links of sufficient magnitude to impact the
   BER of those existing signals.

   Much work at ITU-T has gone into developing impairment models at this
   and more detailed levels. Impairment characterization of network
   elements could then may be used to calculate which paths are conformant with a
   specified BER for a particular signal type. In such a case, we can
   combine the impairment aware (IA) path computation with the RWA
   process to permit more optimal IA-RWA computations. Note, Note that the IA
   path computation may also take place in a separate entity, i.e., a
   PCE.

   D. Detailed Impairment Computation

   This situation is applicable to networks in which impairment effects
   must be more accurately computed. For these networks, a full
   computation and evaluation of the impact to any existing paths needs
   to be performed prior to the addition of a new path. Currently no
   impairment models are available from ITU-T and this scenario is
   outside the scope of this document.

   3.1.2.

4.1.2. Impairment Computation and Information Sharing Constraints

   In GMPLS, information used for path computation is standardized for
   distribution amongst the elements participating in the control plane
   and any appropriately equipped PCE can perform path computation. For
   optical systems this may not be possible. This is typically due to
   only portions of an optical system being subject to standardization.
   In ITU-T recommendations [G.698.1] and [G.698.2] which specify single
   channel interfaces to multi-channel DWDM systems only the single
   channel interfaces (transmit and receive) are specified while the
   multi-channel links are not standardized. These DWDM links are
   referred to as "black links" since their details are not generally
   available. Note however the overall impact of a black link at the
   single channel interface points is limited by [G.698.1] and
   [G.698.2].

   Typically a vendor might use proprietary impairment models for DWDM
   spans and to estimate the validity of optical paths. For example,
   models of optical nonlinearities are not currently standardized.
   Vendors may also choose not to publish impairment details for links
   or a set of network elements in order not to divulge their optical
   system designs.

   In general, the impairment estimation/validation of an optical path
   for optical networks with "black links" (path) could not be performed
   by a general purpose impairment aware (IA) computation entity since
   it would not have access to or understand the "black link" impairment
   parameters. However, impairment estimation (optical path validation)
   could be performed by a vendor specific impairment aware computation
   entity. Such a vendor specific IA computation, could utilize
   standardized impairment information imported from other network
   elements in these proprietary computations.

   In the following we will use the term "black links" will be used to describe
   these computation and information sharing constraints in optical
   networks. From the control plane perspective we have the following
      options:

      A. options
   are considered:

   1. The authority in control of the "black links" can furnish a list
      of all viable paths between all viable node pairs to a
      computational entity. This information would be particularly
      useful as an input to RWA optimization to be performed by another
      computation entity. The difficulty here is for larger networks
      such a list of paths along with any wavelength constraints could
      get unmanageably large.

      B.

   2. The authority in control of the "black links" could provide a PCE
      like entity that would furnish a list of viable paths/wavelengths
      between two requested nodes. This is useful as an input to RWA
      optimizations and can reduce the scaling issue previously
      mentioned. Such a PCE like entity would not need to perform a full
      RWA computation, i.e., it would not need to take into account
      current wavelength availability on links. Such an approach may
      require PCEP extensions for both the request and response
      information.

      C.

   3. The authority in control of the "black links" can provide a PCE
      that performs full IA-RWA services. The difficulty is this
      requires the one authority to also become the sole source of all
      RWA optimization algorithms and such.

   In all the above cases it would be the responsibility of the
   authority in control of the "black links" to import the shared
   impairment information from the other NEs via the control plane or
   other means as necessary.

   3.1.3.

4.1.3. Impairment Estimation Process

   The Impairment Estimation Process can be modeled through the
   following functional blocks. These blocks are independent from of any
   Control Plane architecture, that is, they can be implemented by the
   same or by different control plane functions as detailed in following
   sections.

                                              +-----------------+
       +------------+        +-----------+    |  +------------+ |
       |            |        |           |    |  |            | |
       | Optical    |        | Optical   |    |  | Optical    | |
       | Interface  |------->| Impairment|--->|  | Channel    | |
       | (Transmit/ |        | Path      |    |  | Estimation | |
       |  Receive)  |        |           |    |  |            | |
       +------------+        +-----------+    |  +------------+ |
                                              |        ||       |
                                              |        ||       |
                                              |    Estimation   |
                                              |        ||       |
                                              |        \/       |
                                              |  +------------+ |
                                              |  |  BER /     | |
                                              |  |  Q Factor  | |
                                              |  +------------+ |
                                              +-----------------+

   Starting from functional block on the left the Optical Interface
   represents where the optical signal is transmitted or received and
   defines the properties at the end points path. Even the no-
      impairment no-impairment
   case like scenario B in section 3.1.1 4.1.1 needs to consider a minimum set
   of interface characteristics. In such case only a few parameters used
   to assess the signal compatibility will be taken into account (see
   [WSON-Frame]). For the impairment-awareness impairment-aware case
      signal compatibility these parameters may be
   sufficient or not depending on the accepted level of approximation
   (scenarios C and D). This functional block highlights the need to
   consider a set of interface parameters during an Impairment
   Validation Process.

   The block "Optical Impairment Path" represents all kinds of
   impairments affecting a wavelength as it traverses the networks
   through links and nodes. In the case where the control plane has no
   IV this block will not be present. Otherwise, this function must be
   implemented in some way via the control plane. Options for this will
   be given in the next section on architectural alternatives. This
   block implementation (e.g. through routing, signaling or PCE) may
   influence the way the control plane distributes impairment
   information within the network.

   The last block implements the decision function for path feasibility.
   Depending on the IA level of approximation this function can be more
   or less complex. For example in case of no IA only the signal class
   compatibility will be verified. In addition to feasible/not-feasible
   result, it may be worth worthwhile for decision functions to consider the
   case in which paths can be likely-to-be-
      feasible likely-to-be-feasible within some degree
   of confidence. The optical impairments are usually not fixed values
   as they may vary within ranges of values according to the approach
   taken in the physical modeling (worst-case, statistical or based on
   typical values). For example, the utilization of the worst-case value
   for each parameter within impairment validation process may lead to
   marking some paths as not-feasible while they are very likely to be
   feasible in reality.

   3.2.

4.2. IA-RWA Computation and Control Plane Architectures

   From a control plane point of view optical impairments are additional
   constraints to the impairment-free RWA process described in [WSON-Frame]. [WSON-
   Frame]. In impairment aware routing and wavelength assignment (IA-RWA), (IA-
   RWA), there are conceptually three general classes of processes to be
   considered: Routing (R), Wavelength Assignment (WA), and Impairment
   Validation (estimation) (IV).

   Impairment validation may come in many forms, and maybe invoked at
   different levels of detail in the IA-RWA process. From a process
   point of view we will consider the following three forms of
   impairment validation:

   o  IV-Candidates

   In this case an Impairment Validation (IV) process furnishes a set of
   paths between two nodes along with any wavelength restrictions such
   that the paths are valid with respect to optical impairments. These
   paths and wavelengths may not be actually available in the network
   due to its current usage state. This set of paths would could be returned
   in response to a request for a set of at most K valid paths between
   two specified nodes. Note that such a process never directly
   discloses optical impairment information. Note that that this case
   includes any paths between source and destination that may have been
   "pre-validated".

   In this case the control plane simply makes use of candidate paths
   but does not know any optical impairment information. Another option
   is when the path validity is assessed within the control plane. The
   following cases highlight this situation.

   o  IV-Approximate Verification

   Here approximation methods are used to estimate the impairments
   experienced by a signal. Impairments are typically approximated by
   linear and/or statistical characteristics of individual or combined
   components and fibers along the signal path.

   o  IV-Detailed Verification

   In this case an IV process is given a particular path and wavelength
   through an optical network and is asked to verify whether the overall
   quality objectives for the signal over this path can be met. Note
   that such a process never directly discloses optical impairment
   information.

   The next two cases refer to the way an impairment validation
   computation can be performed.

   o  IV-Centralized

   In this case impairments to a path are computed at a single entity.
   The information concerning impairments impairments, however, may still be
   gathered from network elements however. elements. Depending how information
      are is gathered
   this may put additional requirements on routing protocols. This will
   be detailed in following later sections.

   o  IV-Distributed

   In the distributed IV process, impairment approximate degradation measures such
   as OSNR, dispersion, DGD, etc. are accumulated along the path via a
   signaling like protocol. Each node on the path may already perform
   some part of the impairment computation (i.e. distributed). When the
   accumulated measures reach the destination node a decision on the
   impairment validity of the path can be made. Note that such a process
   would entail revealing an individual network element's impairment
   information but it does not generally require spreading distributing optical
   parameters at network
      level. to the entire network.

   The Control Plane must not preclude the possibility to operate one or
   all the above cases concurrently in the same network. For example
   there could be cases where a certain number of paths are already pre-validates pre-
   validated (IV-Candidates) so the control plane may setup one of those
   path without requesting any impairment validation procedure. On the
   same network however the control plane may compute a path outside the
   set of IV-Candidates for which an impairment evaluation can be
   necessary.

   The following subsections present three major classes of IA-RWA path
   computation architectures and reviews some of their respective
   advantages and disadvantages.

   3.2.1.

4.2.1. Combined Routing, WA, and IV

   From the point of view of optimality, the "best" reasonably good IA-RWA
   solutions can be achieved if the path computation entity (PCE) can
   conceptually/algorithmically combine the processes of routing,
   wavelength assignment and impairment validation.

   Such a combination can take place if the PCE is given: (a) the
   impairment-free WSON network information as discussed in [WSON-
      Frame] [WSON-Frame]
   and (b) impairment information to validate potential paths.

   3.2.2.

4.2.2. Separate Routing, WA, or IV

   Separating the processes of routing, WA and/or IV can reduce the need
   for sharing of different types of information used in path
   computation. This was discussed for routing separate from WA in
   [WSON-Frame]. In addition, as will be was discussed in the section on
      network contexts some impairment
   information may not be shared and this may lead to the need to
   separate IV from RWA.  In addition,
      as also discussed in the section on network contexts, if IV needs to be done at a high
   level of precision it may be advantageous to offload this computation
   to a specialized server.

   The following conceptual architectures belong in this general
   category:

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

   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.

   Note that the IV process may come before or after the RWA processes.
   If RWA comes first then IV is just rendering a yes/no decision on the
   selected path and wavelength. If IV comes first it would need to
   furnish a list of possible (valid with respect to impairments) routes
   and wavelengths to the RWA processes.

   3.2.3.

4.2.3. Distributed WA and/or IV

   In the non-impairment RWA situation [WSON-Frame] it was shown that a
   distributed wavelength assignment (WA) process carried out via
   signaling can eliminate the need to distribute wavelength
   availability information via an IGP. interior gateway protocol (IGP). A
   similar approach can allow for the distributed computation of
   impairment effects and avoid the need to distribute impairment
   characteristics of network elements and links via route routing protocols
   or by other means. An example of such an approach is given in
   [Martinelli] and utilizes enhancements to RSVP signaling to carry
   accumulated impairment related information. So the following
   conceptual options belong to this category:

   o RWA+D(IV)  RWA + D(IV) - Combined routing and wavelength assignment and
      distributed impairment validation.

   o  R + D(WA & IV) -- routing separate from a distributed wavelength
      assignment and impairment validation process.

      A distributed

    Distributed impairment validation for a prescribed network path
   requires that the effects of impairments can be calculated by approximate
   models with cumulative quality measures such as those given in
   [G.680]. For such a system to be interoperable the various
      impairment measures to be accumulated exact encoding of
   the techniques from [G.680] would need to be agreed
      according to [G.680]. upon.

   If distributed WA is being done at the same time as distributed 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.

   3.3.

4.3. Mapping Network Requirements to Architectures

      In

   Figure 2 we show shows process flows for three main architectural
   alternatives to IA-RWA when approximate impairment validation
   suffices. In Figure 3 we show shows process flows for two main architectural
   alternatives when detailed impairment verification is required.

                  +-----------------------------------+
                  |   +--+     +-------+     +--+     |
                  |   |IV|     |Routing|     |WA|     |
                  |   +--+     +-------+     +--+     |
                  |                                   |
                  |        Combined Processes         |
                  +-----------------------------------+
                                  (a)

           +--------------+      +----------------------+
           | +----------+ |      | +-------+    +--+    |
           | |    IV    | |      | |Routing|    |WA|    |
           | |candidates| |----->| +-------+    +--+    |
           | +----------+ |      |  Combined Processes  |
           +--------------+      +----------------------+
                                  (b)

            +-----------+        +----------------------+
            | +-------+ |        |    +--+    +--+      |
            | |Routing| |------->|    |WA|    |IV|      |
            | +-------+ |        |    +--+    +--+      |
            +-----------+        | Distributed Processes|
                                 +----------------------+
                                  (c)
     Figure 2 Process flows for the three main approximate impairment
                        architectural alternatives.

   The advantages, requirements and suitability of these options are as
   follows:

   o  Combined IV & RWA process

   This alternative combines RWA and IV within a single computation
   entity enabling highest potential optimality and efficiency in IA-
   RWA. This alternative requires that the computational entity knows
   impairment information as well as non-impairment RWA information.
   This alternative can be used with "black links", but would then need
   to be provided by the authority controlling the "black links".

   o  IV-Candidates + RWA process
   This alternative allows separation of impairment information into two
   computational entities while still maintaining a high degree of
   potential optimality and efficiency in IA-RWA. The candidates IV
   process needs to know impairment information from all optical network
   elements, while the RWA process needs to know non-
      impairment non-impairment RWA
   information from the network elements. This alternative can be used
   with "black links", but the authority in control of the "black links"
   would need to provide the functionality of the IV-candidates process.
   Note that this is still very useful since the algorithmic areas of IV
   and RWA are very different and prone to specialization.

   o  Routing + Distributed WA and IV

   In this alternative a signaling protocol is extended and leveraged in
   the wavelength assignment and impairment validation processes.
   Although this doesn't enable as high a potential degree of optimality
   of optimality as (a) or (b), it does not require distribution of
   either link wavelength usage or link/node impairment information.
   Note that this is most likely not suitable for "black links".

          +-----------------------------------+     +------------+
          | +-----------+  +-------+    +--+  |     | +--------+ |
          | |    IV     |  |Routing|    |WA|  |     | |  IV    | |
          | |approximate|  +-------+    +--+  |---->| |Detailed| |
          | +-----------+                     |     | +--------+ |
          |        Combined Processes         |     |            |
          +-----------------------------------+     +------------+
                                   (a)

    +--------------+      +----------------------+     +------------+
    | +----------+ |      | +-------+    +--+    |     | +--------+ |
    | |    IV    | |      | |Routing|    |WA|    |---->| |  IV    | |
    | |candidates| |----->| +-------+    +--+    |     | |Detailed| |
    | +----------+ |      |  Combined Processes  |     | +--------+ |
    +--------------+      +----------------------+     |            |
                                   (b)                 +------------+
        Figure 3 Process flows for the two main detailed impairment
                     validation architectural options.

   The advantages, requirements and suitability of these detailed
   validation options are as follows:

   o  Combined approximate IV & RWA + Detailed-IV

   This alternative combines RWA and approximate IV within a single
   computation entity enabling highest potential optimality and
   efficiency in IA-RWA; then has a separate entity performing detailed
   impairment validation. In the case of "black links" the authority
   controlling the "black links" would need to provide all
   functionality.

   o  Candidates-IV + RWA + Detailed-IV

   This alternative allows separation of approximate impairment
   information into a computational entity while still maintaining a
   high degree of potential optimality and efficiency in IA-RWA; then a
   separate computation entity performs detailed impairment validation.
   Note that detailed impairment estimation is not standardized.

   4.

5. Protocol Implications

   The previous IA-RWA architectural alternatives and process flows make
   differing demands on a GMPLS/PCE based control plane. In this section
   we discuss the use of (a) an impairment information model, (b) PCE as
   computational entity assuming the various process roles and
   consequences for PCEP, (c)any needed extensions to signaling, and (d)
   extensions to routing. The impacts to the control plane for IA-RWA
   are summarized in Figure 4.

        +-------------------+----+----+----------+--------+
        | IA-RWA Option     |PCE |Sig |Info Model| Routing|
        +-------------------+----+----+----------+--------+
        |          Combined |Yes | No |  Yes     |  Yes   |
        |          IV & RWA |    |    |          |        |
        +-------------------+----+----+----------+--------+-
        |     IV-Candidates |Yes | No |  Yes     |  Yes   |
        |         + RWA     |    |    |          |        |
        +-------------------+----+----+----------+--------+
        |    Routing +      |No  | Yes|  Yes     |  No    |
        |Distributed IV, RWA|    |    |          |        |
        +-------------------+----+----+----------+--------+
           |       Detailed IV |Yes | No |  Yes     |  Yes   |
           +-------------------+----+----+----------+--------+

     Figure 4 IA-RWA architectural options and control plane impacts.

   4.1.

5.1. Information Model for Impairments

   As previously discussed all IA-RWA scenarios to a greater or lesser
   extent rely on a common impairment information model. 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].

   It should be noted that the current version of [G.680] is limited to
   the networks composed of a single WDM line system vendor combined
   with OADMs and/or PXCs from potentially multiple other vendors, this
   is known as situation 1 and is shown in Figure 1-1 of [G.680]. It is
   planed in the future that [G.680] will include networks incorporating
   line systems from multiple vendors as well as OADMs and/or PXCs from
   potentially multiple other vendors, this is known as situation 2 and
   is shown in Figure 1-2 of [G.680].

   The case of distributed impairment validation actually requires a bit
   more than an impairment information model. In particular, it needs a
   common impairment "computation" model. In the distributed IV case one
   needs to standardize the accumulated impairment measures that will be
   conveyed and updated at each node. Section 9 of [G.680] provides
   guidance in this area with specific formulas given for OSNR, residual
   dispersion, polarization mode dispersion/polarization dependent loss,
   effects of channel uniformity, etc... However, specifics of what
   intermediate results are kept and in what form would need to be
   standardized.

   4.2.

5.2. Routing

   Different approaches to path/wavelength impairment validation gives
   rise to different demands placed on GMPLS routing protocols. 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 based on the
   impairment information model previously discussed.

   Depending on the computational alternative the routing protocol may
   need to advertise information necessary to impairment validation
   process. This can potentially cause scalability issues due to the
   high amount of data that need to be advertised. Such issue can be
   addressed separating data that need to be advertised rarely and data
   that need to be advertised more frequently or adopting other form of
   awareness solutions described in previous sections (e.g. centralized
   and/or external IV entity).

   In term of approximated scenario (see Section 3.1.1. 4.1.1. ) the model
   defined by [G.680] will apply and routing protocol will need to
   gather information required for such computation.

   In the case of distributed-IV no new demands would be placed on the
   routing protocol.

   4.3.

5.3. Signaling

   The largest impacts on signaling occur in the cases where distributed
   impairment validation is performed. In this we need to accumulate
   impairment information as previously discussed. 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 so that
   an impairment validation decision can be made at the destination
   node.

   It remains for further study if it may be beneficial to include
   additional information to a connection request such as desired egress
   signal quality (defined in some appropriate sense) in non-
      distributed non-distributed
   IV scenarios.

   4.4.

5.4. PCE

   In section 3.3. 4.3. we gave a number of computation architectural
   alternatives that could be used to meet the various requirements and
   constraints of section 3.1. 4.1.  Here we look at how these alternatives
   could be implemented via either a single PCE or a set of two or more
   cooperating PCEs, and the impacts on the PCEP protocol.

   4.4.1.

5.4.1. Combined IV & RWA

   In this situation, shown in Figure 2(a), a single PCE performs all
   the computations needed for IA-RWA.

   o  TE Database Requirements

     WSON Topology and switching capabilities, WSON WDM link wavelength
     utilization, and WSON impairment information

   o  PCC to PCE Request Information

     Signal characteristics/type, required quality, source node,
     destination node

   o  PCE to PCC Reply Information
     If the computations completed successfully then the PCE returns
     the path and its assigned wavelength. If the computations could
     not complete successfully it would be potentially useful to know
     the reason why. At a very crude level we'd like to know if this
     was due to lack of wavelength availability or impairment
     considerations or a bit of both. The information to be conveyed is
     for further study.

   4.4.2.

5.4.2. IV-Candidates + RWA

   In this situation, shown in Figure 2(b), we have two separate
   processes involved in the IA-RWA computation. This requires at
      least two
   cooperating PCEs: one for the Candidates-IV process and another for
   the RWA process. In addition, the overall process needs to be
   coordinated. This could be done with yet another PCE or we can add
   this functionality to one of previously defined PCEs. We choose this
   later option and require the RWA PCE to also act as the overall
   process coordinator. The roles, responsibilities and information
   requirements for these two PCEs are given below.

   RWA and Coordinator PCE (RWA-Coord-PCE):

   Responsible for interacting with PCC and for utilizing Candidates-
      PCE Candidates-PCE
   as needed during RWA computations. In particular it needs to know to
   use the Candidates-PCE to obtain potential set of routes and
   wavelengths.

   o  TE Database Requirements

     WSON Topology and switching capabilities and WSON WDM link
     wavelength utilization (no impairment information).

   o  PCC to RWA-PCE request: same as in the combined case.

   o  RWA-PCE to PCC reply: same as in the combined case.

   o  RWA-PCE to IV-Candidates-PCE request

  The RWA-PCE asks for a set of at most K routes along with acceptable
     wavelengths between nodes specified in the original PCC request.

   o  IV-Candidates-PCE reply to RWA-PCE

  The Candidates-PCE returns a set of at most K routes along with
     acceptable wavelengths between nodes specified in the RWA-PCE
     request.

  IV-Candidates-PCE:

     The IV-Candidates-PCE is responsible for impairment aware path
     computation. It needs not take into account current link
     wavelength utilization, but this is not prohibited. The
     Candidates-PCE is only required to interact with the RWA-PCE as
     indicated above and not the PCC.

   o  TE Database Requirements

     WSON Topology and switching capabilities and WSON impairment
     information (no information link wavelength utilization required).

   In Figure 5 we show a sequence diagram for the interactions between
   the PCC, RWA-PCE RWA-Coord PCE and IV-Candidates-PCE. IV-Candidates PCE.

    +---+                +-------------+          +-----------------
      +          +-----------------+
    |PCC|                |RWA-Coord-PCE|          |IV-Candidates-                |RWA-Coord PCE|          |IV-Candidates PCE|
    +-+-+                +------+------+          +---------+-------
      +          +---------+-------+
       ...___     (a)            |                           |
       |     ````---...____      |                           |
       |                   ```-->|                           |
       |                         |                           |
       |                         |--..___    (b)             |
       |                         |       ```---...___        |
       |                         |                   ```---->|
       |                         |                           |
       |                         |                           |
       |                         |           (c)       ___...|
       |                         |       ___....---''''      |
       |                         |<--''''                    |
       |                         |                           |
       |                         |                           |
       |          (d)      ___...|                           |
       |      ___....---'''      |                           |
       |<--'''                   |                           |
       |                         |                           |
       |                         |                           |

     Figure 5 Sequence diagram for the interactions between PCC, RWA-
                Coordinating-PCE and the IV-Candidates-PCE.

   In step (a) the PCC requests a path meeting specified quality
   constraints between two nodes (A and Z) for a given signal
   represented either by a specific type or a general class with
   associated parameters. In step (b) the RWA-Coordinating-PCE requests
   up to K candidate paths between nodes A and Z and associated
   acceptable wavelengths. In step (c) The IV-Candidates- IV-Candidates PCE returns
   this list to the RWA-Coordinating PCE which then uses
      this set of paths and wavelengths as input (e.g. a constraint) to
      its RWA computation. In step (d) the RWA-Coordinating-PCE returns
      the overall IA-RWA computation results to the PCC.

   4.4.3. Approximate IA-RWA + Separate Detailed IV

      In Figure 3 we showed two cases where a separate detailed
      impairment validation process could be utilized. We can place the
      detailed validation process into a separate PCE. Assuming that a
      different PCE assumes a coordinating role and interacts with the
      PCC we can keep the interactions with this separate IV-Detailed-
      PCE very simple.

      IV-Detailed-PCE:

     o TE Database Requirements

     The IV-Detailed-PCE will need optical impairment information, WSON
        topology, and possibly WDM link wavelength usage information.
        This document puts no restrictions on the type of information
        that may be used in these computations.

     o Coordinating-PCE to IV-Detailed-PCE request

     The coordinating-PCE will furnish signal characteristics, quality
        requirements, path and wavelength to the IV-Detailed-PCE.

     o IV-Detailed-PCE to Coordinating-PCE reply

     The reply is essential an yes/no decision as to whether the
        requirements could actually be met. In the case where the
        impairment validation fails it would be helpful to convey
        information related to cause or quantify the failure, e.g., so a
        judgment can be made whether to try a different signal or adjust
        signal parameters.

      In Figure 6 we show a sequence diagram for the interactions for
      the process shown in Figure 3(b). This involves interactions
      between the PCC, RWA-PCE (acting as coordinator), IV-Candidates-
      PCE and the IV-Detailed-PCE.

      In step (a) the PCC requests a path meeting specified quality
      constraints between two nodes (A and Z) for a given signal
      represented either by a specific type or a general class with
      associated parameters. In step (b) the RWA-Coordinating-PCE
      requests up to K candidate paths between nodes A and Z and
      associated acceptable wavelengths. In step (c) The IV-Candidates-
      PCE returns this list to the RWA-Coordinating PCE which then uses
      this set of paths and wavelengths as input (e.g. a constraint) to
      its RWA computation. In step (d) the RWA-Coordinating-PCE request
      a detailed verification of the path and wavelength that it has
      computed. In step (e) the IV-Detailed-PCE returns the results of
      the validation to the RWA-Coordinating-PCE. Finally in step (f)IA-
      RWA-Coordinating PCE returns the final results (either a path and
      wavelength or cause for the failure to compute a path and
      wavelength) to the PCC.

                   +----------+      +--------------+      +------------
      +
       +---+       |RWA-Coord |      |IV-Candidates |      |IV-Detailed
      |
       |PCC|       |   PCE    |      |     PCE      |      |    PCE
      |
       +-+-+       +----+-----+      +------+-------+      +-----+------
      +
         |.._   (a)     |                   |                    |
         |   ``--.__    |                   |                    |
         |          `-->|                   |                    |
         |              |        (b)        |                    |
         |              |--....____         |                    |
         |              |          ````---.>|                    |
         |              |                   |                    |
         |              |         (c)  __..-|                    |
         |              |     __..---''     |                    |
         |              |<--''              |                    |
         |              |                                        |
         |              |...._____          (d)                  |
         |              |         `````-----....._____           |
         |              |                             `````----->|
         |              |                                        |
         |              |                 (e)          _____.....+
         |              |          _____.....-----'''''          |
         |              |<----'''''                              |
         |     (f)   __.|                                        |
         |    __.--''   |
         |<-''          |
         |              |
       Figure 6 Sequence diagram for the interactions between PCC, RWA-
           Coordinating-PCE, IV-Candidates-PCE and IV-Detailed-PCE.

   5. 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.

   6. IANA Considerations

      This draft does not currently require any consideration from IANA.

   7. Acknowledgments

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

   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
        [G.650.3]

      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, 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:

      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
      difference).

      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 [G.666]

     o Characteristics of Adaptive Chromatic Dispersion Compensators
        [G.667]

      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
      [G.959.1].

   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.

      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);

     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 segments.

      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 uses this set of the optical fiber,
      line amplifiers
   paths and any embedded dispersion compensators.
      Similarly wavelengths as input (e.g. a constraint) to its RWA
   computation. In step (d) the OADM/PXC network element may consist of RWA-Coordinating PCE returns the basic
      OADM component and optionally included optical amplifiers. The
      parameters for these overall
   IA-RWA computation results to the PCC.

6. 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 elements (ONE) are given
      under it will by its nature
   contain details of the following circumstances:

     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 physical characteristics of an optical amplifiers
   network. Such information would need to be protected from intentional
   or unintentional disclosure.

7. IANA Considerations

   This draft does not currently require any consideration from IANA.

8. References

8.1. Normative References

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

      [650.2]

   [G.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]

   [G.650.3] ITU-T Recommendation G.650.3

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

   [G.653] ITU-T Recommendation G.653, Characteristics of a
               dispersion-shifted 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
             1998.

   [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.698.1] ITU-T Recommendation G.698.1, Multichannel DWDM
             applications with Single-Channel optical interface,
             December 2006.

   [G.698.2] ITU-T Recommendation G.698.2, Amplified multichannel DWDM
             applications with Single-Channel optical interface, July
             2007.

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

   [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.

8.2. Informative References

   [WSON-Frame] G. Bernstein, Y. Lee, G. Bernstein, W. Imajuku, "Framework for GMPLS
             and PCE Control of Wavelength Switched Optical Networks",
             work in progress: draft-ietf-ccamp-
               wavelength-switched-framework-02.txt, March 2009.

   8.2. Informative References draft-ietf-ccamp-wavelength-switched-
             framework.

   [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. draft-
             bernstein-wson-impairment-info.

   [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-02.txt, February 2008.

      [WSON-Comp] G. Bernstein, Y. Lee, Ben Mack-Crane, "WSON Signal
               Characteristics draft-martinelli-ccamp-optical-
             imp-signaling.

9. Acknowledgments

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

   Copyright (c) 2011 IETF Trust and Network Element Compatibility
               Constraints for GMPLS", work the persons identified as authors
   of the code. All rights reserved.

   Redistribution and use in progress: draft-
               bernstein-ccamp-wson-signal.

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   modification, are permitted provided that the following conditions
   are met:

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   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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Authors' Addresses

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

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

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

   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

   Giovanni Martinelli
   Cisco
   Via Philips 12
   20052 Monza, Italy

   Phone: +39 039 2092044
   Email: giomarti@cisco.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

   Gabriele Galimberti
   Cisco
   Via Philips 12,
   20052 Monza, Italy

   Phone: +39 039 2091462
   Email: ggalimbe@cisco.com

   Alberto Tanzi
   Cisco
   Via Philips 12,
   20052 Monza, Italy

   Phone: +39 039 2091469
   Email: altanzi@cisco.com

   David Bianchi
   Cisco
   Via Philips 12,
   20052 Monza, Italy

   Email: davbianc@cisco.com

   Moustafa Kattan
   Cisco
   Dubai  500321
   United Arab Emirates

   Email: mkattan@cisco.com

   Dirk Schroetter
   Cisco

   Email: dschroet@cisco.com

   Daniele Ceccarelli
   Ericsson
   Via A. Negrone 1/A
   Genova - Sestri Ponente
   Italy
   Email: daniele.ceccarelli@ericsson.com

   Elisa Bellagamba
   Ericsson
   Farogatan 6,
   Kista   164 40
   Sweeden

   Email: elisa.bellagamba@ericcson.com

   Diego Caviglia
   Ericsson
   Via A. negrone 1/A
   Genova - Sestri Ponente
   Italy

   Email: diego.caviglia@ericcson.com

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