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rfc:rfc4054

Network Working Group J. Strand, Ed. Request for Comments: 4054 A. Chiu, Ed. Category: Informational AT&T

                                                              May 2005
    Impairments and Other Constraints on Optical Layer Routing

Status of This Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2005).

Abstract

 Optical networking poses a number challenges for Generalized Multi-
 Protocol Label Switching (GMPLS).  Fundamentally, optical technology
 is an analog rather than digital technology whereby the optical layer
 is lowest in the transport hierarchy and hence has an intimate
 relationship with the physical geography of the network.  This
 contribution surveys some of the aspects of optical networks that
 impact routing and identifies possible GMPLS responses for each:  (1)
 Constraints arising from the design of new software controllable
 network elements, (2) Constraints in a single all-optical domain
 without wavelength conversion, (3) Complications arising in more
 complex networks incorporating both all-optical and opaque
 architectures, and (4) Impacts of diversity constraints.

Table of Contents

 1.  Introduction .................................................  2
 2.  Sub-IP Area Summary and Justification of Work ................  3
 3.  Reconfigurable Network Elements ..............................  3
     3.1.  Technology Background ..................................  3
     3.2.  Implications for Routing ...............................  6
 4.  Wavelength Routed All-Optical Networks .......................  6
     4.1.  Problem Formulation ....................................  7
     4.2.  Polarization Mode Dispersion (PMD) .....................  8
     4.3.  Amplifier Spontaneous Emission .........................  9
     4.4.  Approximating the Effects of Some Other
           Impairments Constraints ................................ 10
     4.5.  Other Impairment Considerations ........................ 13

Strand & Chiu Informational [Page 1] RFC 4054 Optical Layer Routing May 2005

     4.6.  An Alternative Approach - Using Maximum
           Distance as the Only Constraint ........................ 13
     4.7.  Other Considerations ................................... 15
     4.8.  Implications for Routing and Control Plane Design ...... 15
 5.  More Complex Networks ........................................ 17
 6.  Diversity .................................................... 19
     6.1.  Background on Diversity ................................ 19
     6.2.  Implications for Routing ............................... 23
 7.  Security Considerations ...................................... 23
 8.  Acknowledgements ............................................. 24
 9.  References ................................................... 25
     9.1.  Normative References ................................... 25
     9.2.  Informative References ................................. 26
 10. Contributing Authors ......................................... 26

1. Introduction

 Generalized Multi-Protocol Label Switching (GMPLS) [Mannie04] aims to
 extend MPLS to encompass a number of transport architectures,
 including optical networks that incorporate a number of all-optical
 and opto-electronic elements, such as optical cross-connects with
 both optical and electrical fabrics, transponders, and optical add-
 drop multiplexers.  Optical networking poses a number of challenges
 for GMPLS.  Fundamentally, optical technology is an analog rather
 than digital technology whereby the optical layer is lowest in the
 transport hierarchy and hence has an intimate relationship with the
 physical geography of the network.
 GMPLS already has incorporated extensions to deal with some of the
 unique aspects of the optical layer.  This contribution surveys some
 of the aspects of optical networks that impact routing and identifies
 possible GMPLS responses for each.  Routing constraints and/or
 complications arising from the design of network elements, the
 accumulation of signal impairments, and the need to guarantee the
 physical diversity of some circuits are discussed.
 Since the purpose of this document is to further the specification of
 GMPLS, alternative approaches to controlling an optical network are
 not discussed.  For discussions of some broader issues, see
 [Gerstel2000] and [Strand02].
 The organization of the contribution is as follows:
  1. Section 2 is a section requested by the sub-IP Area management for

all new documents. It explains how this document fits into the

    Area and into the IPO WG, and why it is appropriate for these
    groups.

Strand & Chiu Informational [Page 2] RFC 4054 Optical Layer Routing May 2005

  1. Section 3 describes constraints arising from the design of new

software controllable network elements.

  1. Section 4 addresses the constraints in a single all-optical domain

without wavelength conversion.

  1. Section 5 extends the discussion to more complex networks and

incorporates both all-optical and opaque architectures.

  1. Section 6 discusses the impacts of diversity constraints.
  1. Section 7 deals with security requirements.
  1. Section 8 contains acknowledgments.
  1. Section 9 contains references.
  1. Section 10 contains contributing authors' addresses.

2. Sub-IP Area Summary and Justification of Work

 This document merges and extends two previous expired Internet-Drafts
 that were made IPO working group documents to form a basis for a
 design team at the Minneapolis IETF meeting, where it was also
 requested that they be merged to create a requirements document for
 the WG.
 In the larger sub-IP Area structure, this merged document describes
 specific characteristics of optical technology and the requirements
 they place on routing and path selection.  It is appropriate for the
 IPO working group because the material is specific to optical
 networks.  It identifies and documents the characteristics of the
 optical transport network that are important for selecting paths for
 optical channels, which is a work area for the IPO WG.  The material
 covered is directly aimed at establishing a framework and
 requirements for routing in an optical network.

3. Reconfigurable Network Elements

3.1. Technology Background

 Control plane architectural discussions (e.g., [Awduche99]) usually
 assume that the only software reconfigurable network element is an
 optical layer cross-connect (OLXC).  There are however other software
 reconfigurable elements on the horizon, specifically tunable lasers
 and receivers and reconfigurable optical add-drop multiplexers

Strand & Chiu Informational [Page 3] RFC 4054 Optical Layer Routing May 2005

 (OADM).  These elements are illustrated in the following simple
 example, which is modeled on announced Optical Transport System (OTS)
 products:
             +                                       +
 ---+---+    |\                                     /|    +---+---
 ---| A |----|D|          X              Y         |D|----| A |---
 ---+---+    |W|     +--------+     +--------+     |W|    +---+---
      :      |D|-----|  OADM  |-----|  OADM  |-----|D|      :
 ---+---+    |M|     +--------+     +--------+     |M|    +---+---
 ---| A |----| |      |      |       |      |      | |----| A |---
 ---+---+    |/       |      |       |      |       \|    +---+---
             +      +---+  +---+   +---+  +---+      +
              D     | A |  | A |   | A |  | A |     E
                    +---+  +---+   +---+  +---+
                     | |    | |     | |    | |
     Figure 3-1: An OTS With OADMs - Functional Architecture
 In Fig. 3-1, the part that is on the inner side of all boxes labeled
 "A" defines an all-optical subnetwork.  From a routing perspective
 two aspects are critical:
  1. Adaptation: These are the functions done at the edges of the

subnetwork that transform the incoming optical channel into the

    physical wavelength to be transported through the subnetwork.
  1. Connectivity: This defines which pairs of edge Adaptation

functions can be interconnected through the subnetwork.

 In Fig. 3-1, D and E are DWDMs and X and Y are OADMs.  The boxes
 labeled "A" are adaptation functions.  They map one or more input
 optical channels assumed to be standard short reach signals into a
 long reach (LR) wavelength or wavelength group that will pass
 transparently to a distant adaptation function.  Adaptation
 functionality that affects routing includes:
  1. Multiplexing: Either electrical or optical TDM may be used to

combine the input channels into a single wavelength. This is done

    to increase effective capacity:  A typical DWDM might be able to
    handle 100 2.5 Gb/sec signals (250 Gb/sec total) or 50 10 Gb/sec
    (500 Gb/sec total); combining the 2.5 Gb/sec signals together thus
    effectively doubles capacity.  After multiplexing the combined
    signal must be routed as a group to the distant adaptation
    function.

Strand & Chiu Informational [Page 4] RFC 4054 Optical Layer Routing May 2005

  1. Adaptation Grouping: In this technique, groups of k (e.g., 4)

wavelengths are managed as a group within the system and must be

    added/dropped as a group.  We will call such a group an
    "adaptation grouping".  Examples include so called "wave group"
    and "waveband" [Passmore01].  Groupings on the same system may
    differ in basics such as wavelength spacing, which constrain the
    type of channels that can be accommodated.
  1. Laser Tunability: The lasers producing the LR wavelengths may have

a fixed frequency, may be tunable over a limited range, or may be

    tunable over the entire range of wavelengths supported by the
    DWDM.  Tunability speeds may also vary.
 Connectivity between adaptation functions may also be limited:
  1. As pointed out above, TDM multiplexing and/or adaptation grouping

by the adaptation function forces groups of input channels to be

    delivered together to the same distant adaptation function.
  1. Only adaptation functions whose lasers/receivers are tunable to

compatible frequencies can be connected.

  1. The switching capability of the OADMs may also be constrained.
 For example:
 o  There may be some wavelengths that can not be dropped at all.
 o  There may be a fixed relationship between the frequency dropped
    and the physical port on the OADM to which it is dropped.
 o  OADM physical design may put an upper bound on the number of
    adaptation groupings dropped at any single OADM.
 For a fixed configuration of the OADMs and adaptation functions
 connectivity will be fixed: Each input port will essentially be
 hard-wired to some specific distant port.  However this connectivity
 can be changed by changing the configurations of the OADMs and
 adaptation functions.  For example, an additional adaptation grouping
 might be dropped at an OADM or a tunable laser retuned.  In each case
 the port-to-port connectivity is changed.
 These capabilities can be expected to be under software control.
 Today the control would rest in the vendor-supplied Element
 Management system (EMS), which in turn would be controlled by the
 operator's OSes.  However in principle the EMS could participate in
 the GMPLS routing process.

Strand & Chiu Informational [Page 5] RFC 4054 Optical Layer Routing May 2005

3.2. Implications for Routing

 An OTS of the sort discussed in Sec. 3.1 is essentially a
 geographically distributed but blocking cross-connect system.  The
 specific port connectivity is dependent on the vendor design and also
 on exactly what line cards have been deployed.
 One way for GMPLS to deal with this architecture would be to view the
 port connectivity as externally determined.  In this case the links
 known to GMPLS would be groups of identically routed wavebands.  If
 these were reconfigured by the external EMS the resulting
 connectivity changes would need to be detected and advertised within
 GMPLS.  If the topology shown in Fig. 3-1 became a tree or a mesh
 instead of the linear topology shown, the connectivity changes could
 result in Shared Risk Link Group (SRLG - see Section 6.2) changes.
 Alternatively, GMPLS could attempt to directly control this port
 connectivity.  The state information needed to do this is likely to
 be voluminous and vendor specific.

4. Wavelength Routed All-Optical Networks

 The optical networks deployed until recently may be called "opaque"
 ([Tkach98]): each link is optically isolated by transponders doing
 O/E/O conversions.  They provide regeneration with retiming and
 reshaping, also called 3R, which eliminates transparency to bit rates
 and frame format.  These transponders are quite expensive and their
 lack of transparency also constrains the rapid introduction of new
 services.  Thus there are strong motivators to introduce "domains of
 transparency" - all-optical subnetworks - larger than an OTS.
 The routing of lightpaths through an all-optical network has received
 extensive attention.  (See [Yates99] or [Ramaswami98]).  When
 discussing routing in an all-optical network it is usually assumed
 that all routes have adequate signal quality.  This may be ensured by
 limiting all-optical networks to subnetworks of limited geographic
 size that are optically isolated from other parts of the optical
 layer by transponders.  This approach is very practical and has been
 applied to date, e.g., when determining the maximum length of an
 Optical Transport System (OTS).  Furthermore operational
 considerations like fault isolation also make limiting the size of
 domains of transparency attractive.
 There are however reasons to consider contained domains of
 transparency in which not all routes have adequate signal quality.
 From a demand perspective, maximum bit rates have rapidly increased
 from DS3 to OC-192 and soon OC-768 (40 Gb/sec).  As bit rates
 increase it is necessary to increase power.  This makes impairments

Strand & Chiu Informational [Page 6] RFC 4054 Optical Layer Routing May 2005

 and nonlinearities more troublesome.  From a supply perspective,
 optical technology is advancing very rapidly, making ever-larger
 domains possible.  In this section, we assume that these
 considerations will lead to the deployment of a domain of
 transparency that is too large to ensure that all potential routes
 have adequate signal quality for all circuits.  Our goal is to
 understand the impacts of the various types of impairments in this
 environment.
 Note that, as we describe later in the section, there are many types
 of physical impairments.  Which of these needs to be dealt with
 explicitly when performing on-line distributed routing will vary
 considerably and will depend on many variables, including:
  1. Equipment vendor design choices,
  2. Fiber characteristics,
  3. Service characteristics (e.g., circuit speeds),
  4. Network size,
  5. Network operator engineering and deployment strategies.
 For example, a metropolitan network that does not intend to support
 bit rates above 2.5 Gb/sec may not be constrained by any of these
 impairments, while a continental or international network that wished
 to minimize O/E/O regeneration investment and support 40 Gb/sec
 connections might have to explicitly consider many of them.  Also, a
 network operator may reduce or even eliminate their constraint set by
 building a relatively small domain of transparency to ensure that all
 the paths are feasible, or by using some proprietary tools based on
 rules from the OTS vendor to pre-qualify paths between node pairs and
 put them in a table that can be accessed each time a routing decision
 has to be made through that domain.

4.1. Problem Formulation

 We consider a single domain of transparency without wavelength
 translation.  Additionally, due to the proprietary nature of DWDM
 transmission technology, we assume that the domain is either single
 vendor or architected using a single coherent design, particularly
 with regard to the management of impairments.
 We wish to route a unidirectional circuit from ingress client node X
 to egress client node Y.  At both X and Y, the circuit goes through
 an O/E/O conversion that optically isolates the portion within our
 domain.  We assume that we know the bit rate of the circuit.  Also,
 we assume that the adaptation function at X may apply some Forward
 Error Correction (FEC) method to the circuit.  We also assume we know
 the launch power of the laser at X.

Strand & Chiu Informational [Page 7] RFC 4054 Optical Layer Routing May 2005

 Impairments can be classified into two categories, linear and
 nonlinear.  (See [Tkach98] or [Kaminow02] for more on impairment
 constraints.)  Linear effects are independent of signal power and
 affect wavelengths individually.  Amplifier spontaneous emission
 (ASE), polarization mode dispersion (PMD), and chromatic dispersion
 are examples.  Nonlinearities are significantly more complex: they
 generate not only impairments on each channel, but also crosstalk
 between channels.
 In the remainder of this section we first outline how two key linear
 impairments (PMD and ASE) might be handled by a set of analytical
 formulae as additional constraints on routing.  We next discuss how
 the remaining constraints might be approached.  Finally we take a
 broader perspective and discuss the implications of such constraints
 on control plane architecture and also on broader constrained domain
 of transparency architecture issues.

4.2. Polarization Mode Dispersion (PMD)

 For a transparent fiber segment, the general PMD requirement is that
 the time-average differential group delay (DGD) between two
 orthogonal state of polarizations should be less than some fraction a
 of the bit duration, T=1/B, where B is the bit rate.  The value of
 the parameter a depends on three major factors: 1) margin allocated
 to PMD, e.g., 1dB; 2) targeted outage probability, e.g., 4x10-5, and
 3) sensitivity of the receiver to DGD.  A typical value for a is 10%
 [ITU].  More aggressive designs to compensate for PMD may allow
 values higher than 10%.  (This would be a system parameter dependent
 on the system design.  It would need to be known to the routing
 process.)
 The PMD parameter (Dpmd) is measured in pico-seconds (ps) per
 sqrt(km).  The square of the PMD in a fiber span, denoted as span-
 PMD-square is then given by the product of Dpmd**2 and the span
 length.  (A fiber span in a transparent network refers to a segment
 between two optical amplifiers.)  If Dpmd is constant, this results
 in a upper bound on the maximum length of an M-fiber-span transparent
 segment, which is inversely proportional to the square of the product
 of bit rate and Dpmd (the detailed equation is omitted due to the
 format constraint - see [Strand01] for details).
 For older fibers with a typical PMD parameter of 0.5 picoseconds per
 square root of km, based on the constraint, the maximum length of the
 transparent segment should not exceed 400km and 25km for bit rates of
 10Gb/s and 40Gb/s, respectively.  Due to recent advances in fiber
 technology, the PMD-limited distance has increased dramatically.  For
 newer fibers with a PMD parameter of 0.1 picosecond per square root
 of km, the maximum length of the transparent segment (without PMD

Strand & Chiu Informational [Page 8] RFC 4054 Optical Layer Routing May 2005

 compensation) is limited to 10000km and 625km for bit rates of 10Gb/s
 and 40Gb/, respectively.  Still lower values of PMD are attainable in
 commercially available fiber today, and the PMD limit can be further
 extended if a larger value of the parameter a (ratio of DGD to the
 bit period) can be tolerated.  In general, the PMD requirement is not
 an issue for most types of fibers at 10Gb/s or lower bit rate.  But
 it will become an issue at bit rates of 40Gb/s and higher.
 If the PMD parameter varies between spans, a slightly more
 complicated equation results (see [Strand01]), but in any event the
 only link dependent information needed by the routing algorithm is
 the square of the link PMD, denoted as link-PMD-square.  It is the
 sum of the span-PMD-square of all spans on the link.
 Note that when one has some viable PMD compensation devices and
 deploy them ubiquitously on all routes with potential PMD issues in
 the network, then the PMD constraint disappears from the routing
 perspective.

4.3. Amplifier Spontaneous Emission

 ASE degrades the optical signal to noise ratio (OSNR).  An acceptable
 optical SNR level (SNRmin), which depends on the bit rate,
 transmitter-receiver technology (e.g., FEC), and margins allocated
 for the impairments, needs to be maintained at the receiver.  In
 order to satisfy this requirement, vendors often provide some general
 engineering rule in terms of maximum length of the transparent
 segment and number of spans.  For example, current transmission
 systems are often limited to up to 6 spans each 80km long.  For
 larger transparent domains, more detailed OSNR computations will be
 needed to determine whether the OSNR level through a domain of
 transparency is acceptable.  This would provide flexibility in
 provisioning or restoring a lightpath through a transparent
 subnetwork.
 Assume that the average optical power launched at the transmitter is
 P.  The lightpath from the transmitter to the receiver goes through M
 optical amplifiers, with each introducing some noise power.  Unity
 gain can be used at all amplifier sites to maintain constant signal
 power at the input of each span to minimize noise power and
 nonlinearity.  A constraint on the maximum number of spans can be
 obtained [Kaminow97] which is proportional to P and inversely
 proportional to SNRmin, optical bandwidth B, amplifier gain G-1 and
 spontaneous emission factor n of the optical amplifier, assuming all
 spans have identical gain and noise figure.  (Again, the detailed
 equation is omitted due to the format constraint - see [Strand01] for
 details.)  Let's take a typical example.  Assuming P=4dBm,
 SNRmin=20dB with FEC, B=12.5GHz, n=2.5, G=25dB, based on the

Strand & Chiu Informational [Page 9] RFC 4054 Optical Layer Routing May 2005

 constraint, the maximum number of spans is at most 10.  However, if
 FEC is not used and the requirement on SNRmin becomes 25dB, the
 maximum number of spans drops down to 3.
 For ASE the only link-dependent information needed by the routing
 algorithm is the noise of the link, denoted as link-noise, which is
 the sum of the noise of all spans on the link.  Hence the constraint
 on ASE becomes that the aggregate noise of the transparent segment
 which is the sum of the link-noise of all links can not exceed
 P/SNRmin.

4.4. Approximating the Effects of Some Other Impairment Constraints

 There are a number of other impairment constraints that we believe
 could be approximated with a domain-wide margin on the OSNR, plus in
 some cases a constraint on the total number of networking elements
 (OXC or OADM) along the path.  Most impairments generated at OXCs or
 OADMs, including polarization dependent loss, coherent crosstalk, and
 effective passband width, could be dealt with using this approach.
 In principle, impairments generated at the nodes can be bounded by
 system engineering rules because the node elements can be designed
 and specified in a uniform manner.  This approach is not feasible
 with PMD and noise because neither can be uniformly specified.
 Instead, they depend on node spacing and the characteristics of the
 installed fiber plant, neither of which are likely to be under the
 system designer's control.
 Examples of the constraints we propose to approximate with a domain-
 wide margin are given in the remaining paragraphs in this section.
 It should be kept in mind that as optical transport technology
 evolves it may become necessary to include some of these impairments
 explicitly in the routing process.  Other impairments not mentioned
 here at all may also become sufficiently important to require
 incorporation either explicitly or via a domain-wide margin.
 Other Polarization Dependent Impairments
    Other polarization-dependent effects besides PMD influence system
    performance.  For example, many components have polarization-
    dependent loss (PDL) [Ramaswami98], which accumulates in a system
    with many components on the transmission path.  The state of
    polarization fluctuates with time and its distribution is very
    important also.  It is generally required that the total PDL on
    the path be maintained within some acceptable limit, potentially
    by using some compensation technology for relatively long
    transmission systems, plus a small built-in margin in OSNR.  Since
    the total PDL increases with the number of components in the data
    path, it must be taken into account by the system vendor when
    determining the maximum allowable number of spans.

Strand & Chiu Informational [Page 10] RFC 4054 Optical Layer Routing May 2005

 Chromatic Dispersion
    In general this impairment can be adequately (but not optimally)
    compensated for on a per-link basis, and/or at system initial
    setup time.  Today most deployed compensation devices are based on
    Dispersion Compensation Fiber (DCF).  DCF provides per fiber
    compensation by means of a spool of fiber with a CD coefficient
    opposite to the fiber.  Due to the imperfect matching between the
    CD slope of the fiber and the DCF some lambdas can be over
    compensated while others can be under compensated.  Moreover DCF
    modules may only be available in fixed lengths of compensating
    fiber; this means that sometimes it is impossible to find a DCF
    module that exactly compensates the CD introduced by the fiber.
    These effects introduce what is known as residual CD.  Residual CD
    varies with the frequency of the wavelength.  Knowing the
    characteristics of both of the fiber and the DCF modules along the
    path, this can be calculated with a sufficient degree of
    precision.  However this is a very challenging task.  In fact the
    per-wavelength residual dispersion needs to be combined with other
    information in the system (e.g., types fibers to figure out the
    amount of nonlinearities) to obtain the net effect of CD either by
    simulation or by some analytical approximation.  It appears that
    the routing/control plane should not be burdened by such a large
    set of information while it can be handled at the system design
    level.  Therefore it will be assumed until proven otherwise that
    residual dispersion should not be reported.  For high bit rates,
    dynamic dispersion compensation may be required at the receiver to
    clean up any residual dispersion.
 Crosstalk
    Optical crosstalk refers to the effect of other signals on the
    desired signal.  It includes both coherent (i.e., intrachannel)
    crosstalk and incoherent (i.e., interchannel) crosstalk.  Main
    contributors of crosstalk are the OADM and OXC sites that use a
    DWDM multiplexer/demultiplexer (MUX/DEMUX) pair.  For a relatively
    sparse network where the number of OADM/OXC nodes on a path is
    low, crosstalk can be treated with a low margin in OSNR without
    being a binding constraint.  But for some relatively dense
    networks where crosstalk might become a binding constraint, one
    needs to propagate the per-link crosstalk information to make sure
    that the end-to-end path crosstalk which is the sum of the
    crosstalks on all the corresponding links to be within some limit,
    e.g., -25dB threshold with 1dB penalty ([Goldstein94]).  Another
    way to treat it without having to propagate per-link crosstalk
    information is to have the system evaluate what the maximum number
    of OADM/OXC nodes that has a MUX/DEMUX pair for the worst route in
    the transparent domain for a low built-in margin.  The latter one
    should work well where all the OXC/OADM nodes have similar level
    of crosstalk.

Strand & Chiu Informational [Page 11] RFC 4054 Optical Layer Routing May 2005

 Effective Passband
    As more and more DWDM components are cascaded, the effective
    passband narrows.  The number of filters along the link, their
    passband width and their shape will determine the end-to-end
    effective passband.  In general, this is a system design issue,
    i.e., the system is designed with certain maximum bit rate using
    the proper modulation format and filter spacing.  For linear
    systems, the filter effect can be turned into a constraint on the
    maximum number of narrow filters with the condition that filters
    in the systems are at least as wide as the one in the receiver.
    Because traffic at lower bit rates can tolerate a narrower
    passband, the maximum allowable number of narrow filters will
    increase as the bit rate decreases.
 Nonlinear Impairments
    It seems unlikely that these can be dealt with explicitly in a
    routing algorithm because they lead to constraints that can couple
    routes together and lead to complex dependencies, e.g., on the
    order in which specific fiber types are traversed [Kaminow97].
    Note that different fiber types (standard single mode fiber,
    dispersion shifted fiber, dispersion compensated fiber, etc.) have
    very different effects from nonlinear impairments.  A full
    treatment of the nonlinear constraints would likely require very
    detailed knowledge of the physical infrastructure, including
    measured dispersion values for each span, fiber core area and
    composition, as well as knowledge of subsystem details such as
    dispersion compensation technology.  This information would need
    to be combined with knowledge of the current loading of optical
    signals on the links of interest to determine the level of
    nonlinear impairment.  Alternatively, one could assume that
    nonlinear impairments are bounded and result in X dB margin in the
    required OSNR level for a given bit rate, where X for performance
    reasons would be limited to 1 or 2 dB, consequently setting a
    limit on the maximum number of spans.  For the approach described
    here to be useful, it is desirable for this span length limit to
    be longer than that imposed by the constraints which can be
    treated explicitly.  When designing a DWDM transport system, there
    are tradeoffs between signal power launched at the transmitter,
    span length, and nonlinear effects on BER that need to be
    considered jointly.  Here, we assume that an X dB margin is
    obtained after the transport system has been designed with a fixed
    signal power and maximum span length for a given bit rate.  Note
    that OTSs can be designed in very different ways, in linear,
    pseudo-linear, or nonlinear environments.  The X-dB margin
    approach may be valid for some but not for others.  However, it is
    likely that there is an advantage in designing systems that are

Strand & Chiu Informational [Page 12] RFC 4054 Optical Layer Routing May 2005

    less aggressive with respect to nonlinearities, and therefore
    somewhat sub-optimal, in exchange for improved scalability,
    simplicity and flexibility in routing and control plane design.

4.5. Other Impairment Considerations

 There are many other types of impairments that can degrade
 performance.  In this section, we briefly mention one other type of
 impairment, which we propose be dealt with by either the system
 designer or by the transmission engineers at the time the system is
 installed.  If dealt with successfully in this manner they should not
 need to be considered in the dynamic routing process.
 Gain Nonuniformity and Gain Transients For simple noise estimates to
 be of use, the amplifiers must be gain-flattened and must have
 automatic gain control (AGC).  Furthermore, each link should have
 dynamic gain equalization (DGE) to optimize power levels each time
 wavelengths are added or dropped.  Variable optical attenuators on
 the output ports of an OXC or OADM can be used for this purpose, and
 in-line devices are starting to become commercially available.
 Optical channel monitors are also required to provide feedback to the
 DGEs.  AGC must be done rapidly if signal degradation after a
 protection switch or link failure is to be avoided.
 Note that the impairments considered here are treated more or less
 independently.  By considering them jointly and varying the tradeoffs
 between the effects from different components may allow more routes
 to be feasible.  If that is desirable or the system is designed such
 that certain impairments (e.g., nonlinearities) need to be considered
 by a centralized process, then distributed routing is not the one to
 use.

4.6. An Alternative Approach - Using Maximum Distance as the Only

    Constraint
 Today, carriers often use maximum distance to engineer point-to-point
 OTS systems given a fixed per-span length based on the OSNR
 constraint for a given bit rate.  They may desire to keep the same
 engineering rule when they move to all-optical networks.  Here, we
 discuss the assumptions that need to be satisfied to keep this
 approach viable and how to treat the network elements between two
 adjacent links.
 In order to use the maximum distance for a given bit rate to meet an
 OSNR constraint as the only binding constraint, the operators need to
 satisfy the following constraints in their all-optical networks:

Strand & Chiu Informational [Page 13] RFC 4054 Optical Layer Routing May 2005

  1. All the other non-OSNR constraints described in the previous

subsections are not binding factors as long as the maximum

    distance constraint is met.
  1. Specifically for PMD, this means that the whole all-optical

network is built on top of sufficiently low-PMD fiber such that

    the upper bound on the mean aggregate path DGD is always satisfied
    for any path that does not exceed the maximum distance, or PMD
    compensation devices might be used for routes with high-PMD
    fibers.
  1. In terms of the ASE/OSNR constraint, in order to convert the ASE

constraint into a distance constraint directly, the network needs

    to have a fixed fiber distance D for each span (so that ASE can be
    directly mapped by the gain of the amplifier which equals to the
    loss of the previous fiber span), e.g., 80km spacing which is
    commonly chosen by carriers.  However, when spans have variable
    lengths, certain adjustment and compromise need to be made in
    order to avoid treating ASE explicitly as in section 4.3.  These
    include: 1) Unless a certain mechanism is built in the OTS to take
    advantage of shorter spans, spans shorter than a typical span
    length D need to be treated as a span of length D instead of with
    its real length.  2) Spans that are longer than D would have a
    higher average span loss.  In general, the maximum system reach
    decreases when the average span loss increases.  Thus, in order to
    accommodate longer spans in the network, the maximum distance
    upper bound has to be set with respect to the average span loss of
    the worst path in the network.  This sub-optimality may be
    acceptable for some networks if the variance is not too large, but
    may be too conservative for others.
 If these assumptions are satisfied, the second issue we need to
 address is how to treat a transparent network element (e.g., MEMS-
 based switch) between two adjacent links in terms of a distance
 constraint since it also introduces an insertion loss.  If the
 network element cannot somehow compensate for this OSNR degradation,
 one approach is to convert each network element into an equivalent
 length of fiber based on its loss/ASE contribution.  Hence, in
 general, introducing a set of transparent network elements would
 effectively result in reducing the overall actual transmission
 distance between the OEO edges.
 With this approach, the link-specific state information is link-
 distance, the length of a link.  It equals the distance sum of all
 fiber spans on the link and the equivalent length of fiber for the
 network element(s) on the link.  The constraint is that the sum of

Strand & Chiu Informational [Page 14] RFC 4054 Optical Layer Routing May 2005

 all the link-distance over all links of a path should be less than
 the maximum-path-distance, the upper bound of all paths.

4.7. Other Considerations

 Routing in an all-optical network without wavelength conversion
 raises several additional issues:
  1. Since the route selected must have the chosen wavelength available

on all links, this information needs to be considered in the

    routing process.  One approach is to propagate information
    throughout the network about the state of every wavelength on
    every link in the network.  However, the state required and the
    overhead involved in processing and maintaining this information
    is proportional to the total number of links (thus, number of
    nodes squared), maximum number of wavelengths (which keeps
    doubling every couple of years), and the frequency of wavelength
    availability changes, which can be very high.  Instead
    [Hjalmtysson00], proposes an alternative method which probes along
    a chosen path to determine which wavelengths (if any) are
    available.  This would require a significant addition to the
    routing logic normally used in OSPF.  Others have proposed
    simultaneously probing along multiple paths.
  1. Choosing a path first and then a wavelength along the path is

known to give adequate results in simple topologies such as rings

    and trees ([Yates99]).  This does not appear to be true in large
    mesh networks under realistic provisioning scenarios, however.
    Instead significantly better results are achieved if wavelength
    and route are chosen simultaneously ([Strand01b]).  This approach
    would however also have a significant effect on OSPF.

4.8. Implications For Routing and Control Plane Design

 If distributed routing is desired, additional state information will
 be required by the routing to deal with the impairments described in
 Sections 4.2 - 4.4:
  1. As mentioned earlier, an operator who wants to avoid having to

provide impairment-related parameters to the control plane may

    elect not to deal with them at the routing level, instead treating
    them at the system design and planning level if that is a viable
    approach for their network.  In this approach the operator can
    pre-qualify all or a set of feasible end-to-end optical paths
    through the domain of transparency for each bit rate.  This
    approach may work well with relatively small and sparse networks,
    but it may not be scalable for large and dense networks where the
    number of feasible paths can be very large.

Strand & Chiu Informational [Page 15] RFC 4054 Optical Layer Routing May 2005

  1. If the optical paths are not pre-qualified, additional link-

specific state information will be required by the routing

    algorithm for each type of impairment that has the potential of
    being limiting for some routes.  Note that for one operator, PMD
    might be the only limiting constraint while for another, ASE might
    be the only one, or it could be both plus some other constraints
    considered in this document.  Some networks might not be limited
    by any of these constraints.
  1. For an operator needing to deal explicitly with these constraints,

the link-dependent information identified above for PMD is link-

    PMD-square which is the square of the total PMD on a link.  For
    ASE the link-dependent information identified is link-noise which
    is the total noise on a link.  Other link-dependent information
    includes link-span-length which is the total number of spans on a
    link, link-crosstalk or OADM-OXC-number which is the total
    crosstalk or the number of OADM/OXC nodes on a link, respectively,
    and filter-number which is the number of narrow filters on a link.
    When the alternative distance-only approach is chosen, the link-
    specific information is link-distance.
  1. In addition to the link-specific information, bounds on each of

the impairments need to be quantified. Since these bounds are

    determined by the system designer's impairment allocations, these
    will be system dependent.  For PMD, the constraint is that the sum
    of the link-PMD-square of all links on the transparent segment is
    less than the square of (a/B) where B is the bit rate.  Hence, the
    required information is the parameter "a".  For ASE, the
    constraint is that the sum of the link-noise of all links is no
    larger than P/SNRmin.  Thus, the information needed include the
    launch power P and OSNR requirement SNRmin.  The minimum
    acceptable OSNR, in turn, depends on the strength of the FEC being
    used and the margins reserved for other types of impairments.
    Other bounds include the maximum span length of the transmission
    system, the maximum path crosstalk or the maximum number of
    OADM/OXC nodes, and the maximum number of narrow filters, all are
    bit rate dependent.  With the alternative distance-only approach,
    the upper bound is the maximum-path-distance.  In single-vendor
    "islands" some of these parameters may be available in a local or
    EMS database and would not need to be advertised
  1. It is likely that the physical layer parameters do not change

value rapidly and could be stored in some database; however these

    are physical layer parameters that today are frequently not known
    at the granularity required.  If the ingress node of a lightpath
    does path selection these parameters would need to be available at
    this node.

Strand & Chiu Informational [Page 16] RFC 4054 Optical Layer Routing May 2005

  1. The specific constraints required in a given situation will depend

on the design and engineering of the domain of transparency; for

    example it will be essential to know whether chromatic dispersion
    has been dealt with on a per-link basis, and whether the domain is
    operating in a linear or nonlinear regime.
  1. As optical transport technology evolves, the set of constraints

that will need to be considered either explicitly or via a

    domain-wide margin may change.  The routing and control plane
    design should therefore be as open as possible, allowing
    parameters to be included as necessary.
  1. In the absence of wavelength conversion, the necessity of finding

a single wavelength that is available on all links introduces the

    need to either advertise detailed information on wavelength
    availability, which probably doesn't scale, or have some mechanism
    for probing potential routes with or without crankback to
    determine wavelength availability.  Choosing the route first, and
    then the wavelength, may not yield acceptable utilization levels
    in mesh-type networks.

5. More Complex Networks

 Mixing optical equipment in a single domain of transparency that has
 not been explicitly designed to interwork is beyond the scope of this
 document.  This includes most multi-vendor all-optical networks.
 An optical network composed of multiple domains of transparency
 optically isolated from each other by O/E/O devices (transponders) is
 more plausible.  A network composed of both "opaque" (optically
 isolated) OLXCs and one or more all-optical "islands" isolated by
 transponders is of particular interest because this is most likely
 how all-optical technologies (such as that described in Sec. 2) are
 going to be introduced.  (We use the term "island" in this discussion
 rather than a term like "domain" or "area" because these terms are
 associated with specific approaches like BGP or OSPF.)
 We consider the complexities raised by these alternatives now.
 The first requirement for routing in a multi-island network is that
 the routing process needs to know the extent of each island.  There
 are several reasons for this:
  1. When entering or leaving an all-optical island, the regeneration

process cleans up the optical impairments discussed in Sec. 3.

  1. Each all-optical island may have its own bounds on each

impairment.

Strand & Chiu Informational [Page 17] RFC 4054 Optical Layer Routing May 2005

  1. The routing process needs to be sensitive to the costs associated

with "island-hopping".

 This last point needs elaboration.  It is extremely important to
 realize that, at least in the short to intermediate term, the
 resources committed by a single routing decision can be very
 significant: The equipment tied up by a single coast-to-coast OC-192
 can easily have a first cost of $10**6, and the holding times on a
 circuit once established is likely to be measured in months.
 Carriers will expect the routing algorithms used to be sensitive to
 these costs.  Simplistic measures of cost such as the number of
 "hops" are not likely to be acceptable.
 Taking the case of an all-optical island consisting of an "ultra
 long-haul" system like that in Fig. 3-1 embedded in an OEO network of
 electrical fabric OLXCs as an example: It is likely that the ULH
 system will be relatively expensive for short hops but relatively
 economical for longer distances.  It is therefore likely to be
 deployed as a sort of "express backbone".  In this scenario a carrier
 is likely to expect the routing algorithm to balance OEO costs
 against the additional costs associated with ULH technology and route
 circuitously to make maximum use of the backbone where appropriate.
 Note that the metrics used to do this must be consistent throughout
 the routing domain if this expectation is to be met.
 The first-order implications for GMPLS seem to be:
  1. Information about island boundaries needs to be advertised.
  1. The routing algorithm needs to be sensitive to island transitions

and to the connectivity limitations and impairment constraints

    particular to each island.
  1. The cost function used in routing must allow the balancing of

transponder costs, OXC and OADM costs, and line haul costs across

    the entire routing domain.
 Several distributed approaches to multi-island routing seem worth
 investigating:
  1. Advertise the internal topology and constraints of each island

globally; let the ingress node compute an end-to-end strict

    explicit route sensitive to all constraints and wavelength
    availabilities.  In this approach the routing algorithm used by
    the ingress node must be able to deal with the details of routing
    within each island.

Strand & Chiu Informational [Page 18] RFC 4054 Optical Layer Routing May 2005

  1. Have the EMS or control plane of each island determine and

advertise the connectivity between its boundary nodes together

    with additional information such as costs and the bit rates and
    formats supported.  As the spare capacity situation changes,
    updates would be advertised.  In this approach impairment
    constraints are handled within each island and impairment-related
    parameters need not be advertised outside of the island.  The
    ingress node would then do a loose explicit route and leave the
    routing and wavelength selection within each island to the island.
  1. Have the ingress node send out probes or queries to nearby gateway

nodes or to an NMS to get routing guidance.

6. Diversity

6.1. Background on Diversity

 "Diversity" is a relationship between lightpaths.  Two lightpaths are
 said to be diverse if they have no single point of failure.  In
 traditional telephony the dominant transport failure mode is a
 failure in the interoffice plant, such as a fiber cut inflicted by a
 backhoe.
 Why is diversity a unique problem that needs to be considered for
 optical networks?  Traditionally, data network operators have relied
 on their private line providers to ensure diversity and so have not
 had to deal directly with the problem.  GMPLS makes the complexities
 handled by the private line provisioning process, including
 diversity, part of the common control plane and so visible to all.
 To determine whether two lightpath routings are diverse it is
 necessary to identify single points of failure in the interoffice
 plant.  To do so we will use the following terms: A fiber cable is a
 uniform group of fibers contained in a sheath.  An Optical Transport
 System will occupy fibers in a sequence of fiber cables.  Each fiber
 cable will be placed in a sequence of conduits - buried honeycomb
 structures through which fiber cables may be pulled - or buried in a
 right of way (ROW).  A ROW is land in which the network operator has
 the right to install his conduit or fiber cable.  It is worth noting
 that for economic reasons, ROWs are frequently obtained from
 railroads, pipeline companies, or thruways.  It is frequently the
 case that several carriers may lease ROW from the same source; this
 makes it common to have a number of carriers' fiber cables in close
 proximity to each other.  Similarly, in a metropolitan network,
 several carriers might be leasing duct space in the same RBOC
 conduit.  There are also "carrier's carriers" - optical networks
 which provide fibers to multiple carriers, all of whom could be
 affected by a single failure in the "carrier's carrier" network.  In

Strand & Chiu Informational [Page 19] RFC 4054 Optical Layer Routing May 2005

 a typical intercity facility network there might be on the order of
 100 offices that are candidates for OLXCs.  To represent the inter-
 office fiber network accurately a network with an order of magnitude
 more nodes is required.  In addition to Optical Amplifier (OA) sites,
 these additional nodes include:
  1. Places where fiber cables enter/leave a conduit or right of way;
  1. Locations where fiber cables cross; Locations where fiber splices

are used to interchange fibers between fiber cables.

 An example of the first might be:
                                  A                 B
    A-------------B                 \             /
                                      \         /
                                        X-----Y
                                      /         \
    C-------------D                 /             \
                                  C                 D
    (a) Fiber Cable Topology      (b) Right-Of-Way/Conduit Topology
           Figure 6-1:  Fiber Cable vs. ROW Topologies
 Here the A-B fiber cable would be physically routed A-X-Y-B and the
 C-D cable would be physically routed C-X-Y-D.  This topology might
 arise because of some physical bottleneck: X-Y might be the Lincoln
 Tunnel, for example, or the Bay Bridge.
 Fiber route crossing (the second case) is really a special case of
 this, where X and Y coincide.  In this case the crossing point may
 not even be a manhole; the fiber routes might just be buried at
 different depths.
 Fiber splicing (the third case) often occurs when a major fiber route
 passes near to a small office.  To avoid the expense and additional
 transmission loss only a small number of fibers are spliced out of
 the major route into a smaller route going to the small office.  This
 might well occur in a manhole or hut.  An example is shown in Fig.
 6-2(a), where A-X-B is the major route, X the manhole, and C the
 smaller office.  The actual fiber topology would then look like Fig.
 6-2(b), where there would typically be many more A-B fibers than A-C
 or C-B fibers, and where A-C and C-B might have different numbers of
 fibers.  (One of the latter might even be missing.)

Strand & Chiu Informational [Page 20] RFC 4054 Optical Layer Routing May 2005

                    C                             C
                    |                           /   \
                    |                         /       \
                    |                       /           \
             A------X------B              A---------------B
             (a) Fiber Cable Topology     (b) Fiber Topology
               Figure 6-2.  Fiber Cable vs Fiber Topologies
 The imminent deployment of ultra-long (>1000 km) Optical Transport
 Systems introduces a further complexity: Two OTSes could interact a
 number of times.  To make up a hypothetical example: A New York -
 Atlanta OTS and a Philadelphia - Orlando OTS might ride on the same
 right of way for x miles in Maryland and then again for y miles in
 Georgia.  They might also cross at Raleigh or some other intermediate
 node without sharing right of way.
 Diversity is often equated to routing two lightpaths between a single
 pair of points, or different pairs of points so that no single route
 failure will disrupt them both.  This is too simplistic, for a number
 of reasons:
  1. A sophisticated client of an optical network will want to derive

diversity needs from his/her end customers' availability

    requirements.  These often lead to more complex diversity
    requirements than simply providing diversity between two
    lightpaths.  For example, a common requirement is that no single
    failure should isolate a node or nodes.  If a node A has single
    lightpaths to nodes B and C, this requires A-B and A-C to be
    diverse.  In real applications, a large data network with N
    lightpaths between its routers might describe their needs in an
    NxN matrix, where (i,j) defines whether lightpaths i and j must be
    diverse.
  1. Two circuits that might be considered diverse for one application

might not be considered diverse for in another situation.

    Diversity is usually thought of as a reaction to interoffice route
    failures.  High reliability applications may require other types
    of failures to be taken into account.  Some examples:
    o  Office Outages: Although less frequent than route failures,
       fires, power outages, and floods do occur.  Many network
       managers require that diverse routes have no (intermediate)
       nodes in common.  In other cases an intermediate node might be
       acceptable as long as there is power diversity within the
       office.

Strand & Chiu Informational [Page 21] RFC 4054 Optical Layer Routing May 2005

    o  Shared Rings: Many applications are willing to allow "diverse"
       circuits to share a SONET ring-protected link; presumably they
       would allow the same for optical layer rings.
    o  Disasters: Earthquakes and floods can cause failures over an
       extended area.  Defense Department circuits might need to be
       routed with nuclear damage radii taken into account.
  1. Conversely, some networks may be willing to take somewhat larger

risks. Taking route failures as an example: Such a network might

    be willing to consider two fiber cables in heavy duty concrete
    conduit as having a low enough chance of simultaneous failure to
    be considered "diverse".  They might also be willing to view two
    fiber cables buried on opposite sides of a railroad track as being
    diverse because there is minimal danger of a single backhoe
    disrupting them both even though a bad train wreck might
    jeopardize them both.  A network seeking N mutually diverse paths
    from an office with less than N diverse ROWs will need to live
    with some level of compromise in the immediate vicinity of the
    office.
 These considerations strongly suggest that the routing algorithm
 should be sensitive to the types of threat considered unacceptable by
 the requester.  Note that the impairment constraints described in the
 previous section may eliminate some of the long circuitous routes
 sometimes needed to provide diversity.  This would make it harder to
 find many diverse paths through an all-optical network than an opaque
 one.
 [Hjalmtysson00] introduced the term "Shared Risk Link Group" (SRLG)
 to describe the relationship between two non-diverse links.  The
 above examples and discussion given at the start of this section
 suggests that an SRLG should be characterized by 2 parameters:
  1. Type of Compromise: Examples would be shared fiber cable, shared

conduit, shared ROW, shared optical ring, shared office without

    power sharing, etc.)
  1. Extent of Compromise: For compromised outside plant, this would

be the length of the sharing.

 A CSPF algorithm could then penalize a diversity compromise by an
 amount dependent on these two parameters.

Strand & Chiu Informational [Page 22] RFC 4054 Optical Layer Routing May 2005

 Two links could be related by many SRLGs.  (AT&T's experience
 indicates that a link may belong to over 100 SRLGs, each
 corresponding to a separate fiber group.)  Each SRLG might relate a
 single link to many other links.  For the optical layer, similar
 situations can be expected where a link is an ultra-long OTS.
 The mapping between links and different types of SRLGs is in general
 defined by network operators based on the definition of each SRLG
 type.  Since SRLG information is not yet ready to be discoverable by
 a network element and does not change dynamically, it need not be
 advertised with other resource availability information by network
 elements.  It could be configured in some central database and be
 distributed to or retrieved by the nodes, or advertised by network
 elements at the topology discovery stage.

6.2. Implications For Routing

 Dealing with diversity is an unavoidable requirement for routing in
 the optical layer.  It requires dealing with constraints in the
 routing process, but most importantly requires additional state
 information (e.g., the SRLG relationships).  The routings of any
 existing circuits from which the new circuit must be diverse must
 also be available to the routing process.
 At present SRLG information cannot be self-discovered.  Indeed, in a
 large network it is very difficult to maintain accurate SRLG
 information.  The problem becomes particularly daunting whenever
 multiple administrative domains are involved, for instance after the
 acquisition of one network by another, because there normally is a
 likelihood that there are diversity violations between the domains.
 It is very unlikely that diversity relationships between carriers
 will be known any time in the near future.
 Considerable variation in what different customers will mean by
 acceptable diversity should be anticipated.  Consequently we suggest
 that an SRLG should be defined as follows: (i) It is a relationship
 between two or more links, and (ii) it is characterized by two
 parameters, the type of compromise (shared conduit, shared ROW,
 shared optical ring, etc.) and the extent of the compromise (e.g.,
 the number of miles over which the compromise persisted).  This will
 allow the SRLGs appropriate to a particular routing request to be
 easily identified.

7. Security Considerations

 We are assuming OEO interfaces to the domain(s) covered by our
 discussion (see, e.g., Sec. 4.1 above).  If this assumption were to
 be relaxed and externally generated optical signals allowed into the

Strand & Chiu Informational [Page 23] RFC 4054 Optical Layer Routing May 2005

 domain, network security issues would arise.  Specifically,
 unauthorized usage in the form of signals at improper wavelengths or
 with power levels or impairments inconsistent with those assumed by
 the domain would be possible.  With OEO interfaces, these types of
 layer one threats should be controllable.
 A key layer one security issue is resilience in the face of physical
 attack.  Diversity, as describe in Sec. 6, is a part of the solution.
 However, it is ineffective if there is not sufficient spare capacity
 available to make the network whole after an attack.  Several major
 related issues are:
  1. Defining the threat: If, for example, an electro-magnetic

interference (EMI) burst is an in-scope threat, then (in the

    terminology of Sec. 6) all of the links sufficiently close
    together to be disrupted by such a burst must be included in a
    single SRLG.  Similarly for other threats: For each in-scope
    threat, SRLGs must be defined so that all links vulnerable to a
    single incident of the threat must be grouped together in a single
    SRLG.
  1. Allocating responsibility for responding to a layer one failure

between the various layers (especially the optical and IP layers):

    This must be clearly specified to avoid churning and unnecessary
    service interruptions.
 The whole proposed process depends on the integrity of the impairment
 characterization information (PMD parameters, etc.) and also the SRLG
 definitions.  Security of this information, both when stored and when
 distributed, is essential.
 This document does not address control plane issues, and so control-
 plane security is out of scope.  IPO control plane security
 considerations are discussed in [Rajagopalam04].  Security
 considerations for GMPLS, a likely control plane candidate, are
 discussed in [Mannie04].

8. Acknowledgments

 This document has benefited from discussions with Michael Eiselt,
 Jonathan Lang, Mark Shtaif, Jennifer Yates, Dongmei Wang, Guangzhi
 Li, Robert Doverspike, Albert Greenberg, Jim Maloney, John Jacob,
 Katie Hall, Diego Caviglia, D. Papadimitriou, O. Audouin, J. P.
 Faure, L. Noirie, and with our OIF colleagues.

Strand & Chiu Informational [Page 24] RFC 4054 Optical Layer Routing May 2005

9. References

9.1. Normative References

 [Goldstein94]   Goldstein, E. L., Eskildsen, L., and Elrefaie, A. F.,
                 Performance Implications of Component Crosstalk in
                 Transparent Lightwave Networks", IEEE Photonics
                 Technology Letters, Vol.6, No.5, May 1994.
 [Hjalmtysson00] Gsli Hjalmtysson, Jennifer Yates, Sid Chaudhuri and
                 Albert Greenberg, "Smart Routers - Simple Optics: An
                 Architecture for the Optical Internet, IEEE/OSA
                 Journal of Lightwave Technology, December 2000, Vo
                 18, Issue 12, Dec. 2000, pp. 1880-1891.
 [ITU]           ITU-T Doc. G.663, Optical Fibers and Amplifiers,
                 Section II.4.1.2.
 [Kaminow97]     Kaminow, I. P. and Koch, T. L., editors, Optical
                 Fiber Telecommunications IIIA, Academic Press, 1997.
 [Mannie04]      Mannie, E., Ed., "Generalized Multi-Protocol Label
                 Switching (GMPLS) Architecture", RFC 3945, October
                 2004.
 [Rajagopalam04]  Rajagopalan, B., Luciani, J., and D. Awduche, "IP
                 over Optical Networks: A Framework", RFC 3717, March
                 2004.
 [Strand01]      Strand, J., Chiu, A., and R. Tkach, "Issues for
                 Routing in the Optical Layer", IEEE Communications
                 Magazine, Feb. 2001, vol. 39 No. 2, pp. 81-88.
 [Strand01b]     Strand, J., Doverspike, R., and G. Li, "Importance of
                 Wavelength Conversion In An Optical Network", Optical
                 Networks Magazine, May/June 2001, pp. 33-44.
 [Yates99]       Yates, J. M., Rumsewicz, M. P., and J. P. R. Lacey,
                 "Wavelength Converters in Dynamically-Reconfigurable
                 WDM Networks", IEEE Communications Surveys, 2Q1999
                 (online at
                 www.comsoc.org/pubs/surveys/2q99issue/yates.html).

Strand & Chiu Informational [Page 25] RFC 4054 Optical Layer Routing May 2005

9.2. Informative References

 [Awduche99]     Awduche, D. O., Rekhter, Y., Drake, J., R. and
                 Coltun, "Multi-Protocol Lambda Switching: Combining
                 MPLS Traffic Engineering Control With Optical
                 Crossconnects", Work in Progress.
 [Gerstel2000]   Gorstel, O., "Optical Layer Signaling: How Much Is
                 Really Needed?" IEEE Communications Magazine, vol. 38
                 no. 10, Oct. 2000, pp. 154-160
 [Kaminow02]     Ivan P. Kaminow and Tingye Li (editors), "Optical
                 Fiber Communications IV: Systems and Impairments",
                 Elsevier Press, 2002.
 [Passmore01]    Passmore, D., "Managing Fatter Pipes," Business
                 Communications Review, August 2001, pp. 20-21.
 [Ramaswami98]   Ramaswami, R. and K. N. Sivarajan, Optical Networks:
                 A Practical Perspective, Morgan Kaufmann Publishers,
                 1998.
 [Strand02]      John Strand, "Optical Network Architecture
                 Evolution", in [Kaminow02].
 [Tkach98]       Tkach, R., Goldstein, E., Nagel, J., and J. Strand,
                 "Fundamental Limits of Optical Transparency", Optical
                 Fiber Communication Conf., Feb. 1998, pp. 161-162.

10. Contributing Authors

 This document was a collective work of a number of people. The text
 and content of this document was contributed by the editors and the
 co-authors listed below.
 Ayan Banerjee
 Calient Networks
 6620 Via Del Oro
 San Jose, CA 95119
 EMail: abanerjee@calient.net
 Prof. Dan Blumenthal
 Eng. Science Bldg., Room 2221F
 Department of Electrical and Computer Engineering
 University of California
 Santa Barbara, CA 93106-9560
 EMail: danb@ece.ucsb.edu

Strand & Chiu Informational [Page 26] RFC 4054 Optical Layer Routing May 2005

 Dr. John Drake
 Boeing
 2260 E Imperial Highway
 El Segundo, Ca 90245
 EMail: John.E.Drake2@boeing.com
 Andre Fredette
 Hatteras Networks
 PO Box 110025
 Research Triangle Park, NC 27709
 EMail: afredette@hatterasnetworks.com
 Change Nan Froberg's reach info to:
 Dr. Nan Froberg
 Photonic Systems, Inc.
 900 Middlesex Turnpike, Bldg #5
 Billerica, MA 01821
 EMail: nfroberg@photonicsinc.com
 Dr. Taha Landolsi
 King Fahd University
 KFUPM Mail Box 1026
 Dhahran 31261, Saudi Arabia
 EMail: landolsi@kfupm.edu.sa
 James V. Luciani
 900 Chelmsford St.
 Lowell, MA 01851
 EMail: james_luciani@mindspring.com
 Dr. Robert Tkach
 32 Carriage House Lane
 Little Silver, NJ 07739
 908 246 5048
 EMail: tkach@ieee.org

Strand & Chiu Informational [Page 27] RFC 4054 Optical Layer Routing May 2005

 Yong Xue
 Dr. Yong Xue
 DoD/DISA
 5600 Columbia Pike
 Falls Church VA 22041
 EMail: yong.xue@disa.mil

Editors' Addresses

 Angela Chiu
 AT&T Labs
 200 Laurel Ave., Rm A5-1F13
 Middletown, NJ 07748
 Phone: (732) 420-9061
 EMail: chiu@research.att.com
 John Strand
 AT&T Labs
 200 Laurel Ave., Rm A5-1D33
 Middletown, NJ 07748
 Phone: (732) 420-9036
 EMail: jls@research.att.com

Strand & Chiu Informational [Page 28] RFC 4054 Optical Layer Routing May 2005

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Strand & Chiu Informational [Page 29]

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