GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc6566

Internet Engineering Task Force (IETF) Y. Lee, Ed. Request for Comments: 6566 Huawei Category: Informational G. Bernstein, Ed. ISSN: 2070-1721 Grotto Networking

                                                                 D. Li
                                                                Huawei
                                                         G. Martinelli
                                                                 Cisco
                                                            March 2012
                   A Framework for the Control of
   Wavelength Switched Optical Networks (WSONs) with Impairments

Abstract

 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,
 these processes are usually referred to as "impairments".  These
 physical characteristics may be important constraints to consider
 when using a GMPLS control plane to support path setup and
 maintenance in wavelength switched optical networks.
 This document provides a framework for applying GMPLS protocols and
 the Path Computation Element (PCE) architecture to support
 Impairment-Aware Routing and Wavelength Assignment (IA-RWA) in
 wavelength switched optical networks.  Specifically, this document
 discusses key computing constraints, scenarios, and architectural
 processes: routing, wavelength assignment, and impairment validation.
 This document does not define optical data plane aspects; impairment
 parameters; or measurement of, or assessment and qualification of, a
 route; rather, it describes the architectural and information
 components for protocol solutions.

Lee, et al. Informational [Page 1] RFC 6566 Framework for Optical Impairments March 2012

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6566.

Copyright Notice

 Copyright (c) 2012 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Lee, et al. Informational [Page 2] RFC 6566 Framework for Optical Impairments March 2012

Table of Contents

 1. Introduction ....................................................3
 2. Terminology .....................................................4
 3. Applicability ...................................................6
 4. Impairment-Aware Optical Path Computation .......................7
    4.1. Optical Network Requirements and Constraints ...............8
         4.1.1. Impairment-Aware Computation Scenarios ..............9
         4.1.2. Impairment Computation and
                Information-Sharing Constraints ....................10
         4.1.3. Impairment Estimation Process ......................11
    4.2. IA-RWA Computation and Control Plane Architectures ........13
         4.2.1. Combined Routing, WA, and IV .......................15
         4.2.2. Separate Routing, WA, or IV ........................15
         4.2.3. Distributed WA and/or IV ...........................16
    4.3. Mapping Network Requirements to Architectures .............16
 5. Protocol Implications ..........................................19
    5.1. Information Model for Impairments .........................19
    5.2. Routing ...................................................20
    5.3. Signaling .................................................21
    5.4. PCE .......................................................21
         5.4.1. Combined IV & RWA ..................................21
         5.4.2. IV-Candidates + RWA ................................22
         5.4.3. Approximate IA-RWA + Separate Detailed-IV ..........24
 6. Manageability and Operations ...................................25
 7. Security Considerations ........................................26
 8. References .....................................................27
    8.1. Normative References ......................................27
    8.2. Informative References ....................................27
 9. Contributors ...................................................29

1. Introduction

 Wavelength Switched Optical Networks (WSONs) are constructed from
 subsystems that may include wavelength division multiplexed links,
 tunable transmitters and receivers, Reconfigurable Optical Add/Drop
 Multiplexers (ROADMs), wavelength converters, and electro-optical
 network elements.  A WSON is a Wavelength Division Multiplexing
 (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,
 these processes are usually referred to as "impairments".  Optical
 impairments accumulate along the path (without 3R regeneration
 [G.680]) traversed by the signal.  They are influenced by the type of
 fiber used, the types and placement of various optical devices, and

Lee, et al. Informational [Page 3] RFC 6566 Framework for Optical Impairments March 2012

 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.
 In order to provision an optical connection (an optical path) through
 a WSON, a combination of path continuity, resource availability, and
 impairment constraints must be met to determine viable and optimal
 paths through the network.  The determination of appropriate paths is
 known as Impairment-Aware Routing and Wavelength Assignment (IA-RWA).
 Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] provides
 a set of control plane protocols that can be used to operate networks
 ranging from packet switch capable networks to those networks that
 use time division multiplexing and WDM.  The Path Computation Element
 (PCE) architecture [RFC4655] defines functional computation
 components that can be used in cooperation with the GMPLS control
 plane to compute and suggest appropriate paths.  [RFC4054] provides
 an overview of optical impairments and their routing (path selection)
 implications for GMPLS.  This document uses [G.680] and other ITU-T
 Recommendations as references for the optical data plane aspects.
 This document provides a framework for applying GMPLS protocols and
 the PCE architecture to the control and operation of IA-RWA for
 WSONs.  To aid in this evaluation, this document provides an overview
 of the subsystems and processes that comprise WSONs and describes
 IA-RWA models based on the corresponding ITU-T Recommendations, so
 that the information requirements for use by GMPLS and PCE systems
 can be identified.  This work will facilitate the development of
 protocol extensions in support of IA-RWA within the GMPLS and PCE
 protocol families.

2. Terminology

 ADM: Add/Drop Multiplexer.  An optical device used in WDM networks
    and composed of one or more line side ports and, typically, many
    tributary ports.
 Black Links: Black links refer to tributary interfaces where only
    link characteristics are defined.  This approach enables
    transverse compatibility at the single-channel point using a
    direct wavelength-multiplexing configuration.
 CWDM: Coarse Wavelength Division Multiplexing
 DGD: Differential Group Delay
 DWDM: Dense Wavelength Division Multiplexing

Lee, et al. Informational [Page 4] RFC 6566 Framework for Optical Impairments March 2012

 FOADM: Fixed Optical Add/Drop Multiplexer
 GMPLS: Generalized Multi-Protocol Label Switching
 IA-RWA: Impairment-Aware Routing and Wavelength Assignment
 Line Side: In a WDM system, line side ports and links typically can
    carry the full multiplex of wavelength signals, as compared to
    tributary (add or drop ports), which typically carry a few
    (typically one) wavelength signals.
 NEs: Network Elements
 OADMs: Optical Add/Drop Multiplexers
 OSNR: Optical Signal-to-Noise Ratio
 OXC: Optical Cross-Connect.  An optical switching element in which a
    signal on any input port can reach any output port.
 PCC: Path Computation Client.  Any client application requesting that
    a path computation be performed by the Path Computation Element.
 PCE: Path Computation Element.  An entity (component, application, or
    network node) that is capable of computing a network path or route
    based on a network graph and application of computational
    constraints.
 PCEP: PCE Communication Protocol.  The communication protocol between
    a Path Computation Client and Path Computation Element.
 PXC: Photonic Cross-Connect
 Q-Factor: The Q-factor provides a qualitative description of the
    receiver performance.  It is a function of the optical signal-to-
    noise ratio.  The Q-factor suggests the minimum SNR (Signal-to-
    Noise Ratio) required to obtain a specific bit error rate (BER)
    for a given signal.
 ROADM: Reconfigurable Optical Add/Drop Multiplexer.  A wavelength-
    selective switching element featuring input and output line side
    ports as well as add/drop tributary ports.
 RWA: Routing and Wavelength Assignment
 Transparent Network: A Wavelength Switched Optical Network that does
    not contain regenerators or wavelength converters.

Lee, et al. Informational [Page 5] RFC 6566 Framework for Optical Impairments March 2012

 Translucent Network:  A Wavelength Switched Optical Network that is
    predominantly transparent but may also contain limited numbers of
    regenerators and/or wavelength converters.
 Tributary: A link or port on a WDM system that can carry
    significantly less than the full multiplex of wavelength signals
    found on the line side links/ports.  Typical tributary ports are
    the add and drop ports on an ADM, and these support only a single
    wavelength channel.
 Wavelength Conversion/Converters: The process of converting an
    information-bearing optical signal centered at a given wavelength
    to information 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 WSONs where not all possible paths
 will yield suitable signal quality.  There are multiple reasons;
 below is a non-exhaustive list of examples:
 o  WSONs are evolving and are using multi-degree optical cross-
    connects in such a way that network topologies are changing from
    rings (and interconnected rings) to general mesh.  Adding network
    equipment such as amplifiers or regenerators to ensure that all
    paths are 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's life; e.g., the optical interfaces might be
    upgraded to higher bitrates.  Such changes could result in paths
    being unsuitable for the optical signal.  Moreover, the optical
    physical interfaces 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.

Lee, et al. Informational [Page 6] RFC 6566 Framework for Optical Impairments March 2012

 o  With the recent bitrate increases from 10G to 40G and 100G over a
    single wavelength, WSONs will likely be operated with a mix of
    wavelengths at different bitrates.  This operational scenario will
    impose impairment constraints due to different physical behavior
    of different bitrates and associated modulation formats.
 Not having an impairment-aware control plane for such networks will
 require a more complex network design phase that needs to take into
 account the evolving network status in terms of equipment and traffic
 at the beginning stage.  In addition, network operations such as path
 establishment will require significant pre-design via non-control-
 plane processes, resulting in significantly slower network
 provisioning.
 It should be highlighted that the impact of impairments and use in
 determination of path viability is not sufficiently well established
 for general applicability [G.680]; it will depend on network
 implementations.  The use of an impairment-aware control plane, and
 the set of information distributed, will need to be evaluated on a
 case-by-case scenario.

4. Impairment-Aware Optical Path Computation

 The basic criterion 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 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.
 Impairment-aware path calculation also needs to take into account
 when regeneration is used along the path.  [RFC6163] provides
 background on the concept of optical translucent networks that
 contain transparent elements and electro-optical elements such as OEO
 regenerations.  In such networks, a generic light path can go through
 a number of regeneration points.

Lee, et al. Informational [Page 7] RFC 6566 Framework for Optical Impairments March 2012

 Regeneration points could happen for two reasons:
  (i) Wavelength conversion is performed in order to assist RWA in
      avoiding wavelength blocking.  This is the impairment-free case
      covered by [RFC6163].
 (ii) The optical signal without regeneration would be too degraded to
      meet end-to-end BER requirements.  This is the case when RWA
      takes into consideration impairment estimation covered by this
      document.
 In the latter case, an optical path can be seen as a set of
 transparent segments.  The calculation of optical impairments needs
 to be reset at each regeneration point so each transparent segment
 will have its own impairment evaluation.
       +---+    +----+   +----+     +-----+     +----+    +---+
       | I |----| N1 |---| N2 |-----| REG |-----| N3 |----| E |
       +---+    +----+   +----+     +-----+     +----+    +---+
       |<----------------------------->|<-------------------->|
                  Segment 1                    Segment 2
       Figure 1.  Optical Path as a Set of Transparent Segments
 For example, Figure 1 represents an optical path from node I to
 node E with a regeneration point, REG, in between.  This is feasible
 from an impairment validation perspective if both segments (I, N1,
 N2, REG) and (REG, N3, E) are feasible.

4.1. Optical Network Requirements and Constraints

 This section examines the various optical network requirements and
 constraints under which an impairment-aware optical control plane may
 have to operate.  These requirements and constraints motivate the
 IA-RWA architectural alternatives presented in Section 4.2.
 Different optical network contexts 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.

Lee, et al. Informational [Page 8] RFC 6566 Framework for Optical Impairments March 2012

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; after that -- for example, during optical
    path computation -- they can be ignored.  This is the case
    discussed in [RFC6163] 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 where there is a sufficient
    margin such that impairment effects can be estimated via such
    approximation techniques as link budgets and 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 generally known as the
    linear case, where only linear effects are taken into account.
    Note that adding or removing an optical signal on the path should
    not render any of the existing signals in the network non-viable.
    For example, one form of non-viability is the occurrence in
    existing links of transients of sufficient magnitude to impact the
    BER of existing signals.
    Much work at ITU-T has gone into developing impairment models at
    this level and at more detailed levels.  Impairment
    characterization of network elements may be used to calculate
    which paths are conformant with a specified BER for a particular
    signal type.  In such a case, the impairment-aware (IA) path
    computation can be combined with the RWA process to permit more
    optimal IA-RWA computations.  Note that the IA path computation
    may also take place in a separate entity, i.e., a PCE.

Lee, et al. Informational [Page 9] RFC 6566 Framework for Optical Impairments March 2012

 D. Accurate 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 need 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.

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.  However, note that 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 in order 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 in the path could not be
 performed by a general-purpose 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 IA computation entity.  Such
 a vendor-specific IA computation entity could utilize standardized
 impairment information imported from other network elements in these
 proprietary computations.
 In the following, the term "black links" will be used to describe
 these computation and information-sharing constraints in optical
 networks.  From the control plane perspective, the following options
 are considered:

Lee, et al. Informational [Page 10] RFC 6566 Framework for Optical Impairments March 2012

 1. The authority in control of the black links can furnish a list of
    all viable paths between all viable node pairs to a computation
    entity.  This information would be particularly useful as an input
    to RWA optimization to be performed by another computation entity.
    The difficulty here is that such a list of paths, along with any
    wavelength constraints, could get unmanageably large as the size
    of the network increases.
 2. The authority in control of the black links could provide a
    PCE-like entity 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.
 3. The authority in control of the black links provides a PCE that
    performs full IA-RWA services.  The difficulty here is that this
    option requires the one authority to also become the sole source
    of all RWA optimization algorithms.
 In all of 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.

4.1.3. Impairment Estimation Process

 The impairment estimation process can be modeled through the
 following functional blocks.  These blocks are independent of any
 control plane architecture; that is, they can be implemented by the
 same or by different control plane functions, as detailed in the
 following sections.

Lee, et al. Informational [Page 11] RFC 6566 Framework for Optical Impairments March 2012

                                             +-----------------+
      +------------+        +-----------+    |  +------------+ |
      |            |        |           |    |  |            | |
      | Optical    |        | Optical   |    |  | Optical    | |
      | Interface  |------->| Impairment|--->|  | Channel    | |
      | (Transmit/ |        | Path      |    |  | Estimation | |
      |  Receive)  |        |           |    |  |            | |
      +------------+        +-----------+    |  +------------+ |
                                             |        ||       |
                                             |        ||       |
                                             |    Estimation   |
                                             |        ||       |
                                             |        \/       |
                                             |  +------------+ |
                                             |  |  BER/      | |
                                             |  |  Q Factor  | |
                                             |  +------------+ |
                                             +-----------------+
 Starting from the functional block on the left, the optical interface
 represents where the optical signal is transmitted or received and
 defines the properties at the path endpoints.  Even the impairment-
 free case, such as scenario B in Section 4.1.1, needs to consider a
 minimum set of interface characteristics.  In such a case, only a few
 parameters used to assess the signal compatibility will be taken into
 account (see [RFC6163]).  For the impairment-aware case, 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
 the impairment validation process.
 The "Optical Impairment Path" block represents the types of
 impairments affecting a wavelength as it traverses the networks
 through links and nodes.  In the case of a network where there are no
 impairments (scenario A), this block will not be present.  Otherwise,
 this function must be implemented in some way via the control plane.
 Architectural alternatives to accomplish this are provided in
 Section 4.2.  This block implementation (e.g., through routing,
 signaling, or a 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 the case of no IA approximation,
 only the signal class compatibility will be verified.  In addition to
 a feasible/not-feasible result, it may be worthwhile for decision
 functions to consider the case in which paths would likely be
 feasible within some degree of confidence.  The optical impairments

Lee, et al. Informational [Page 12] RFC 6566 Framework for Optical Impairments March 2012

 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 the
 impairment validation process may lead to marking some paths as not
 feasible, while they are very likely to be, in reality, feasible.

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 [RFC6163].  In IA-RWA, there are conceptually three general
 classes of processes to be considered: Routing (R), Wavelength
 Assignment (WA), and Impairment Validation (IV), i.e., estimation.
 Impairment validation may come in many forms and may be invoked at
 different levels of detail in the IA-RWA process.  All of the
 variations of impairment validation discussed in this section are
 based on scenario C ("Approximated Impairment Estimation") as
 discussed in Section 4.1.1.  From a process point of view, the
 following three forms of impairment validation will be considered:
 o  IV-Candidates
    In this case, an 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 actually be available in the network, due to
    its current usage state.  This set of paths 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 also that this
    case includes any paths between the source and destination that
    may have been "pre-validated".
    In this case, the control plane simply makes use of candidate
    paths but does not have 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.

Lee, et al. Informational [Page 13] RFC 6566 Framework for Optical Impairments March 2012

 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 from a decision-making point of view.
 o  IV-Centralized
    In this case, impairments to a path are computed at a single
    entity.  The information concerning impairments, however, may
    still be gathered from network elements.  Depending on how
    information is gathered, this may put additional requirements on
    routing protocols.  This topic will be detailed in later sections.
 o  IV-Distributed
    In the distributed IV process, approximate degradation measures
    such as OSNR, dispersion, DGD, etc., may be accumulated along the
    path via signaling.  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
    distributing optical parameters to the entire network.
 The control plane must not preclude the possibility of concurrently
 performing one or all of the above cases in the same network.  For
 example, there could be cases where a certain number of paths are
 already pre-validated (IV-Candidates), so the control plane may set
 up one of those paths 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 review some of their respective
 advantages and disadvantages.

Lee, et al. Informational [Page 14] RFC 6566 Framework for Optical Impairments March 2012

4.2.1. Combined Routing, WA, and IV

 From the point of view of optimality, reasonably good IA-RWA
 solutions can be achieved if the 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 information as discussed in [RFC6163] and (b)
 impairment information to validate potential paths.

4.2.2. Separate Routing, WA, or IV

 Separating the processes of routing, WA, and/or IV can reduce the
 need for the sharing of different types of information used in path
 computation.  This was discussed for routing, separate from WA, in
 [RFC6163].  In addition, as was discussed in Section 4.1.2, some
 impairment information may not be shared, and this may lead to the
 need to separate IV from RWA.  In addition, 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 improved efficiency.
 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.

Lee, et al. Informational [Page 15] RFC 6566 Framework for Optical Impairments March 2012

4.2.3. Distributed WA and/or IV

 In the non-impairment RWA situation [RFC6163], it was shown that a
 distributed WA process carried out via signaling can eliminate the
 need to distribute wavelength availability information via an
 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 by routing protocols or by other means.  Therefore, the
 following conceptual options belong to this category:
 o  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.
 Distributed impairment validation for a prescribed network path
 requires that the effects of impairments be calculated by approximate
 models with cumulative quality measures such as those given in
 [G.680].  The protocol encoding of the impairment-related information
 from [G.680] would need to be agreed upon.
 If distributed WA is being done at the same time as distributed IV,
 then it is necessary to accumulate impairment-related information for
 all wavelengths that could be used.  The amount of information is
 reduced somewhat as potential wavelengths are discovered to be in use
 but could be a significant burden for lightly loaded networks with
 high channel counts.

4.3. Mapping Network Requirements to Architectures

 Figure 2 shows process flows for the three main architectural
 alternatives to IA-RWA that apply when approximate impairment
 validation is sufficient.  Figure 3 shows process flows for the two
 main architectural alternatives that apply when detailed impairment
 verification is required.

Lee, et al. Informational [Page 16] RFC 6566 Framework for Optical Impairments March 2012

                +-----------------------------------+
                |   +--+     +-------+     +--+     |
                |   |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 computation entity
    have 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 computation entities while still maintaining a high degree of
    potential optimality and efficiency in IA-RWA.  The IV-Candidates
    process needs to have impairment information from all optical
    network elements, while the RWA process needs to have

Lee, et al. Informational [Page 17] RFC 6566 Framework for Optical Impairments March 2012

    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 conducive to specialization.
 o  Routing + Distributed WA and IV
    In this alternative, a signaling protocol may be extended and
    leveraged in the wavelength assignment and impairment validation
    processes.  Although this doesn't enable as high a potential
    degree 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 the highest potential optimality and
    efficiency in IA-RWA while keeping 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.

Lee, et al. Informational [Page 18] RFC 6566 Framework for Optical Impairments March 2012

 o  IV-Candidates + RWA + Detailed-IV
    This alternative allows separation of approximate impairment
    information into a computation 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.

5. Protocol Implications

 The previous IA-RWA architectural alternatives and process flows make
 differing demands on a GMPLS/PCE-based control plane.  This section
 discusses the use of (a) an impairment information model, (b) the PCE
 as computation entity assuming the various process roles and
 consequences for PCEP, (c) possible extensions to signaling, and
 (d) possible extensions to routing.  This document is providing this
 evaluation to aid protocol solutions work.  The protocol
 specifications may deviate from this assessment.  The assessment of
 the impacts to the control plane for IA-RWA is 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 |     |     |            |         |
     +--------------------+-----+-----+------------+---------+
   Figure 4.  IA-RWA Architectural Options and Control Plane Impacts

5.1. Information Model for Impairments

 As previously discussed, most IA-RWA scenarios rely, to a greater or
 lesser extent, on a common impairment information model.  A number of
 ITU-T Recommendations cover both detailed and approximate impairment
 characteristics of fibers, a variety of devices, and a variety of
 subsystems.  An impairment model that can be used as a guideline for
 optical network elements and assessment of path viability is given
 in [G.680].

Lee, et al. Informational [Page 19] RFC 6566 Framework for Optical Impairments March 2012

 It should be noted that the current version of [G.680] is limited to
 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
 planned 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].
 For the case of distributed IV, this would require more than an
 impairment information model.  It would need 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,
 and effects of channel uniformity.  However, specifics of what
 intermediate results are kept and in what form would need to be
 standardized for interoperability.  As noted in [G.680], this
 information may possibly not be sufficient, and in such a case, the
 applicability would be network dependent.

5.2. Routing

 Different approaches to path/wavelength impairment validation give
 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 the impairment validation
 process.  This can potentially cause scalability issues, due to the
 high volume of data that need to be advertised.  Such issues can be
 addressed by separating data that need to be advertised only rarely
 from data that need to be advertised more frequently, or by adopting
 other forms of awareness solutions as described in previous sections
 (e.g., a centralized and/or external IV entity).
 In terms of scenario C in Section 4.1.1, the model defined by [G.680]
 will apply, and the routing protocol will need to gather information
 required for such computations.
 In the case of distributed IV, no new demands would be placed on the
 routing protocol.

Lee, et al. Informational [Page 20] RFC 6566 Framework for Optical Impairments March 2012

5.3. Signaling

 The largest impacts on signaling occur in the cases where distributed
 impairment validation is performed.  In this case, it is necessary 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 whether 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 IV scenarios.

5.4. PCE

 In Section 4.2, a number of computational architectural alternatives
 were given that could be used to meet the various requirements and
 constraints of Section 4.1.  Here, the focus is on 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.  This
 document provides this evaluation to aid solutions work.  The
 protocol specifications may deviate from this assessment.

5.4.1. Combined IV & RWA

 In this situation, shown in Figure 2(a), a single PCE performs all of
 the computations needed for IA-RWA.
 o  Traffic Engineering (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, and 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 why.  At a minimum, it is
    of interest to know if this was due to lack of wavelength
    availability, impairment considerations, or both.  The information
    to be conveyed is for further study.

Lee, et al. Informational [Page 21] RFC 6566 Framework for Optical Impairments March 2012

5.4.2. IV-Candidates + RWA

 In this situation, as shown in Figure 2(b), two separate processes
 are involved in the IA-RWA computation.  This requires two
 cooperating path computation entities: one for the IV-Candidates
 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 this functionality could be added to one of a number of
 previously defined entities.  This later option requires that the RWA
 entity also act as the overall process coordinator.  The roles,
 responsibilities, and information requirements for these two
 entities, when instantiated as PCEs, are given below.
 RWA and Coordinator PCE (RWA-Coord PCE):
    The RWA-Coord PCE is responsible for interacting with the PCC and
    for utilizing the IV-Candidates PCE as needed during RWA
    computations.  In particular, it needs to know that it is to use
    the IV-Candidates PCE to obtain a 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 IV-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 need not take into account current link
    wavelength utilization, but this is not prohibited.  The
    IV-Candidates PCE is only required to interact with the RWA PCE as
    indicated above, and not the initiating PCC.  Note: The
    RWA-Coord PCE is also a PCC with respect to the IV-Candidate.

Lee, et al. Informational [Page 22] RFC 6566 Framework for Optical Impairments March 2012

    o  TE Database requirements: WSON topology and switching
       capabilities, and WSON impairment information (no information
       link wavelength utilization required).
 Figure 5 shows a sequence diagram for the possible interactions
 between the PCC, RWA-Coord PCE, and IV-Candidates PCE.
    +---+                +-------------+          +-----------------+
    |PCC|                |RWA-Coord PCE|          |IV-Candidates PCE|
    +-+-+                +------+------+          +---------+-------+
      ...___     (a)            |                           |
      |     ````---...____      |                           |
      |                   ```-->|                           |
      |                         |                           |
      |                         |--..___    (b)             |
      |                         |       ```---...___        |
      |                         |                   ```---->|
      |                         |                           |
      |                         |                           |
      |                         |           (c)       ___...|
      |                         |       ___....---''''      |
      |                         |<--''''                    |
      |                         |                           |
      |                         |                           |
      |          (d)      ___...|                           |
      |      ___....---'''      |                           |
      |<--'''                   |                           |
      |                         |                           |
      |                         |                           |
   Figure 5.  Sequence Diagram for the Interactions between the PCC,
                 RWA-Coord PCE, and IV-Candidates PCE
 In step (a), the PCC requests a path that meets 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-Coord PCE requests up to
 K candidate paths between nodes A and Z, and associated acceptable
 wavelengths.  The term "K candidate paths" is associated with the k
 shortest path algorithm.  It refers to an algorithm that finds
 multiple k short paths connecting the source and the destination in a
 graph allowing repeated vertices and edges in the paths.  See details
 in [Eppstein].

Lee, et al. Informational [Page 23] RFC 6566 Framework for Optical Impairments March 2012

 In step (c), the IV-Candidates PCE returns this list to the
 RWA-Coord 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-Coord PCE returns the overall IA-RWA computation results to
 the PCC.

5.4.3. Approximate IA-RWA + Separate Detailed-IV

 Previously, Figure 3 showed two cases where a separate detailed
 impairment validation process could be utilized.  It is possible to
 place the detailed validation process into a separate PCE.  Assuming
 that a different PCE assumes a coordinating role and interacts with
 the PCC, it is possible to keep the interactions with this separate
 IV-Detailed PCE very simple.  Note that, from a message flow
 perspective, there is some inefficiency as a result of separating the
 IV-Candidates PCE from the IV-Detailed PCE in order to achieve a high
 degree of potential optimality.
 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  RWA-Coord PCE to IV-Detailed PCE request: The RWA-Coord PCE will
    furnish signal characteristics, quality requirements, path, and
    wavelength to the IV-Detailed PCE.
 o  IV-Detailed PCE to RWA-Coord PCE reply: The reply is essentially a
    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 the cause or to
    quantify the failure, e.g., so that a judgment can be made
    regarding whether to try a different signal or adjust signal
    parameters.
 Figure 6 shows a sequence diagram for the interactions corresponding
 to the process shown in Figure 3(b).  This involves interactions
 between the PCC, RWA PCE (acting as coordinator), IV-Candidates PCE,
 and IV-Detailed PCE.
 In step (a), the PCC requests a path that meets 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-Coord 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

Lee, et al. Informational [Page 24] RFC 6566 Framework for Optical Impairments March 2012

 the RWA-Coord 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-Coord PCE requests 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-Coord PCE.  Finally,
 in step (f), the RWA-Coord PCE returns the final results (either a
 path and wavelength, or a 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 the PCC,
         RWA-Coord PCE, IV-Candidates PCE, and IV-Detailed PCE

6. Manageability and Operations

 The issues concerning manageability and operations are beyond the
 scope of this document.  The details of manageability and operational
 issues will have to be deferred to future protocol implementations.

Lee, et al. Informational [Page 25] RFC 6566 Framework for Optical Impairments March 2012

 On a high level, the GMPLS-routing-based architecture discussed in
 Section 5.2 may have to deal with how to resolve potential scaling
 issues associated with disseminating a large amount of impairment
 characteristics of the network elements and links.
 From a scaling point of view, the GMPLS-signaling-based architecture
 discussed in Section 5.3 would be more scalable than other
 alternatives, as this architecture would avoid the dissemination of a
 large amount of data to the networks.  This benefit may come,
 however, at the expense of potentially inefficient use of network
 resources.
 The PCE-based architectures discussed in Section 5.4 would have to
 consider operational complexity when implementing options that
 require the use of multiple PCE servers.  The most serious case is
 the option discussed in Section 5.4.3 ("Approximate IA-RWA + Separate
 Detailed-IV").  The combined IV & RWA option (which was discussed in
 Section 5.4.1), on the other hand, is simpler to operate than are
 other alternatives, as one PCE server handles all functionality;
 however, this option may suffer from a heavy computation and
 processing burden compared to other alternatives.
 Interoperability may be a hurdle to overcome when trying to agree on
 some impairment parameters, especially those that are associated with
 the black links.  This work has been in progress in ITU-T and needs
 some more time to mature.

7. Security Considerations

 This document discusses a number of control plane architectures that
 incorporate knowledge of impairments in optical networks.  If such an
 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, similar to other network
 information used within intra-domain protocols.
 This document does not require changes to the security models within
 GMPLS and associated protocols.  That is, the OSPF-TE, RSVP-TE, and
 PCEP security models could be operated unchanged.  However,
 satisfying the requirements for impairment information dissemination
 using the existing protocols may significantly affect the loading of
 those protocols and may make the operation of the network more
 vulnerable to active attacks such as injections, impersonation, and
 man-in-the-middle attacks.  Therefore, additional care may be
 required to ensure that the protocols are secure in the impairment-
 aware WSON environment.

Lee, et al. Informational [Page 26] RFC 6566 Framework for Optical Impairments March 2012

 Furthermore, the additional information distributed in order to
 address impairment information represents a disclosure of network
 capabilities that an operator may wish to keep private.
 Consideration should be given to securing this information.  For a
 general discussion on MPLS- and GMPLS-related security issues, see
 the MPLS/GMPLS security framework [RFC5920] and, in particular, text
 detailing security issues when the control plane is physically
 separated from the data plane.

8. References

8.1. Normative References

 [G.680]     ITU-T Recommendation G.680, "Physical transfer functions
             of optical network elements", July 2007.
 [RFC3945]   Mannie, E., Ed., "Generalized Multi-Protocol Label
             Switching (GMPLS) Architecture", RFC 3945, October 2004.
 [RFC4655]   Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
             Computation Element (PCE)-Based Architecture", RFC 4655,
             August 2006.

8.2. Informative References

 [Eppstein]  Eppstein, D., "Finding the k shortest paths", 35th IEEE
             Symposium on Foundations of Computer Science, Santa Fe,
             pp. 154-165, 1994.
 [G.698.1]   ITU-T Recommendation G.698.1, "Multichannel DWDM
             applications with single-channel optical interfaces",
             November 2009.
 [G.698.2]   ITU-T Recommendation G.698.2, "Amplified multichannel
             dense wavelength division multiplexing applications with
             single channel optical interfaces", November 2009.
 [G.Sup39]   ITU-T Series G Supplement 39, "Optical system design and
             engineering considerations", February 2006.
 [RFC4054]   Strand, J., Ed., and A. Chiu, Ed., "Impairments and Other
             Constraints on Optical Layer Routing", RFC 4054,
             May 2005.

Lee, et al. Informational [Page 27] RFC 6566 Framework for Optical Impairments March 2012

 [RFC5920]   Fang, L., Ed., "Security Framework for MPLS and GMPLS
             Networks", RFC 5920, July 2010.
 [RFC6163]   Lee, Y., Ed., Bernstein, G., Ed., and W. Imajuku,
             "Framework for GMPLS and Path Computation Element (PCE)
             Control of Wavelength Switched Optical Networks (WSONs)",
             RFC 6163, April 2011.

Lee, et al. Informational [Page 28] RFC 6566 Framework for Optical Impairments March 2012

9. Contributors

 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

Lee, et al. Informational [Page 29] RFC 6566 Framework for Optical Impairments March 2012

 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
 Sweden
 EMail: elisa.bellagamba@ericsson.com
 Diego Caviglia
 Ericsson
 Via A. Negrone 1/A
 Genova - Sestri Ponente
 Italy
 EMail: diego.caviglia@ericsson.com

Lee, et al. Informational [Page 30] RFC 6566 Framework for Optical Impairments March 2012

Authors' Addresses

 Young Lee (editor)
 Huawei Technologies
 5340 Legacy Drive, Building 3
 Plano, TX  75024
 USA
 Phone: (469) 277-5838
 EMail: leeyoung@huawei.com
 Greg M. Bernstein (editor)
 Grotto Networking
 Fremont, CA
 USA
 Phone: (510) 573-2237
 EMail: gregb@grotto-networking.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

Lee, et al. Informational [Page 31]

/data/webs/external/dokuwiki/data/pages/rfc/rfc6566.txt · Last modified: 2012/03/12 22:19 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki