draft-ietf-ccamp-rwa-wson-framework-06.txt   draft-ietf-ccamp-rwa-wson-framework-07.txt 
Network Working Group Y. Lee (ed.) Network Working Group Y. Lee (ed.)
Internet Draft Huawei Internet Draft Huawei
Intended status: Informational G. Bernstein (ed.) Intended status: Informational G. Bernstein (ed.)
Expires: October 2010 Grotto Networking Expires: April 2011 Grotto Networking
Wataru Imajuku Wataru Imajuku
NTT NTT
April 5, 2010 October 8, 2010
Framework for GMPLS and PCE Control of Wavelength Switched Optical Framework for GMPLS and PCE Control of Wavelength Switched Optical
Networks (WSON) Networks (WSON)
draft-ietf-ccamp-rwa-wson-framework-06.txt draft-ietf-ccamp-rwa-wson-framework-07.txt
Abstract
This document provides a framework for applying Generalized Multi-
Protocol Label Switching (GMPLS) and the Path Computation Element
(PCE) architecture to the control of wavelength switched optical
networks (WSON). In particular, it examines the Routing and
Wavelength Assignment (RWA) problem.
This document focuses on topological elements and path selection
constraints that are common across different WSON environments as
such it does not address optical impairments in any depth.
Status of this Memo Status of this Memo
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Abstract
This memo provides a framework for applying Generalized Multi-
Protocol Label Switching (GMPLS) and the Path Computation Element
(PCE) architecture to the control of wavelength switched optical
networks (WSON). In particular we provide control plane models for
key wavelength switched optical network subsystems and processes. The
subsystems include wavelength division multiplexed links, tunable
laser transmitters, reconfigurable optical add/drop multiplexers
(ROADM) and wavelength converters. In addition, electro-optical
network elements and their compatibility constraints relative to
optical signal parameters are characterized.
Lightpath provisioning, in general, requires the routing and
wavelength assignment (RWA) process. This process is reviewed and the
information requirements, both static and dynamic for this process
are presented, along with alternative implementation architectures
that could be realized via various combinations of extended GMPLS and
PCE protocols.
This memo focuses on topological elements and path selection
constraints that are common across different WSON environments as
such it does not address optical impairments in any depth.
Table of Contents Table of Contents
1. Introduction...................................................4 1. Introduction..................................................4
1.1. Revision History..........................................5 2. Terminology....................................................4
1.1.1. Changes from 00......................................5 3. Wavelength Switched Optical Networks...........................6
1.1.2. Changes from 01......................................5 3.1. WDM and CWDM Links........................................6
1.1.3. Changes from 02......................................5 3.2. Optical Transmitters and Receivers........................8
1.1.4. Changes from 03......................................6 3.3. Optical Signals in WSONs..................................9
1.1.5. Changes from 04......................................6 3.3.1. Optical Tributary Signals...........................10
1.1.6. Changes from 05......................................6 3.3.2. WSON Signal Characteristics.........................10
2. Terminology....................................................6 3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs............11
3. Wavelength Switched Optical Networks...........................7 3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs.......11
3.1. WDM and CWDM Links........................................7 3.4.2. Splitters...........................................14
3.2. Optical Transmitters......................................9 3.4.3. Combiners...........................................15
3.3. Optical Signals in WSONs.................................10 3.4.4. Fixed Optical Add/Drop Multiplexers.................15
3.3.1. Optical Tributary Signals...........................11 3.5. Electro-Optical Systems..................................16
3.3.2. WSON Signal Characteristics.........................12 3.5.1. Regenerators........................................16
3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs............12 3.5.2. OEO Switches........................................19
3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs.......13 3.6. Wavelength Converters....................................19
3.4.2. Splitters...........................................16 3.6.1. Wavelength Converter Pool Modeling..................21
3.4.3. Combiners...........................................16 3.7. Characterizing Electro-Optical Network Elements..........25
3.4.4. Fixed Optical Add/Drop Multiplexers.................17 3.7.1. Input Constraints...................................26
3.5. Electro-Optical Systems..................................17 3.7.2. Output Constraints..................................26
3.5.1. Regenerators........................................17 3.7.3. Processing Capabilities.............................27
3.5.2. OEO Switches........................................20 4. Routing and Wavelength Assignment and the Control Plane.......28
3.6. Wavelength Converters....................................20 4.1. Architectural Approaches to RWA..........................28
3.6.1. Wavelength Converter Pool Modeling..................22 4.1.1. Combined RWA (R&WA).................................29
3.7. Characterizing Electro-Optical Network Elements..........26 4.1.2. Separated R and WA (R+WA)...........................29
3.7.1. Input Constraints...................................27 4.1.3. Routing and Distributed WA (R+DWA)..................30
3.7.2. Output Constraints..................................27 4.2. Conveying information needed by RWA......................30
3.7.3. Processing Capabilities.............................28 5. Modeling Examples and Control Plane Use Cases.................31
4. Routing and Wavelength Assignment and the Control Plane.......29 5.1. Network Modeling for GMPLS/PCE Control...................31
4.1. Architectural Approaches to RWA..........................30 5.1.1. Describing the WSON nodes...........................32
4.1.1. Combined RWA (R&WA).................................30 5.1.2. Describing the links................................34
4.1.2. Separated R and WA (R+WA)...........................30 5.2. RWA Path Computation and Establishment...................35
4.1.3. Routing and Distributed WA (R+DWA)..................31 5.3. Resource Optimization....................................36
4.2. Conveying information needed by RWA......................32 5.4. Support for Rerouting....................................37
5. Modeling Examples and Control Plane Use Cases.................33 5.5. Electro-Optical Networking Scenarios.....................37
5.1. Network Modeling for GMPLS/PCE Control...................33 5.5.1. Fixed Regeneration Points...........................37
5.1.1. Describing the WSON nodes...........................33 5.5.2. Shared Regeneration Pools...........................38
5.1.2. Describing the links................................35 5.5.3. Reconfigurable Regenerators.........................38
5.2. RWA Path Computation and Establishment...................36 5.5.4. Relation to Translucent Networks....................38
5.3. Resource Optimization....................................37 6. GMPLS and PCE Implications....................................39
5.4. Support for Rerouting....................................38 6.1. Implications for GMPLS signaling.........................39
5.5. Electro-Optical Networking Scenarios.....................38 6.1.1. Identifying Wavelengths and Signals.................39
5.5.1. Fixed Regeneration Points...........................38 6.1.2. WSON Signals and Network Element Processing.........40
5.5.2. Shared Regeneration Pools...........................39 6.1.3. Combined RWA/Separate Routing WA support............40
5.5.3. Reconfigurable Regenerators.........................39
5.5.4. Relation to Translucent Networks....................39
6. GMPLS & PCE Implications......................................40
6.1. Implications for GMPLS signaling.........................40
6.1.1. Identifying Wavelengths and Signals.................41
6.1.2. WSON Signals and Network Element Processing.........41
6.1.3. Combined RWA/Separate Routing WA support............41
6.1.4. Distributed Wavelength Assignment: Unidirectional, No 6.1.4. Distributed Wavelength Assignment: Unidirectional, No
Converters.................................................42 Converters.................................................41
6.1.5. Distributed Wavelength Assignment: Unidirectional, 6.1.5. Distributed Wavelength Assignment: Unidirectional,
Limited Converters.........................................42 Limited Converters.........................................41
6.1.6. Distributed Wavelength Assignment: Bidirectional, No 6.1.6. Distributed Wavelength Assignment: Bidirectional, No
Converters.................................................42 Converters.................................................41
6.2. Implications for GMPLS Routing...........................43 6.2. Implications for GMPLS Routing...........................42
6.2.1. Electro-Optical Element Signal Compatibility........43 6.2.1. Electro-Optical Element Signal Compatibility........42
6.2.2. Wavelength-Specific Availability Information........44 6.2.2. Wavelength-Specific Availability Information........43
6.2.3. WSON Routing Information Summary....................45 6.2.3. WSON Routing Information Summary....................43
6.3. Optical Path Computation and Implications for PCE........46 6.3. Optical Path Computation and Implications for PCE........45
6.3.1. Lightpath Constraints and Characteristics...........46 6.3.1. Lightpath Constraints and Characteristics...........45
6.3.2. Electro-Optical Element Signal Compatibility........47 6.3.2. Electro-Optical Element Signal Compatibility........46
6.3.3. Discovery of RWA Capable PCEs.......................47 6.3.3. Discovery of RWA Capable PCEs.......................46
7. Security Considerations.......................................48 7. Security Considerations.......................................47
8. IANA Considerations...........................................48 8. IANA Considerations...........................................47
9. Acknowledgments...............................................48 9. Acknowledgments...............................................47
10. References...................................................49 10. References...................................................48
10.1. Normative References....................................49 10.1. Normative References....................................48
10.2. Informative References..................................50 10.2. Informative References..................................49
11. Contributors.................................................53 11. Contributors.................................................51
Author's Addresses...............................................54 Author's Addresses...............................................52
Intellectual Property Statement..................................54 Intellectual Property Statement..................................52
Disclaimer of Validity...........................................55 Disclaimer of Validity...........................................53
12. Appendix A Revision History..................................53
1. Introduction 1. Introduction
This memo provides a framework for applying GMPLS and the Path Wavelength Switched Optical Networks (WSONs) are constructed from
Computation Element (PCE) architecture to the control of WSONs. In subsystems that include Wavelength Division Multiplexed (WDM) links,
particular we provide control plane models for key wavelength tunable transmitters and receivers, Reconfigurable Optical Add/Drop
switched optical network subsystems and processes. The subsystems Multiplexers (ROADM), wavelength converters, and electro-optical
include wavelength division multiplexed links, tunable laser network elements. A WSON is a WDM-based optical network in which
transmitters, reconfigurable optical add/drop multiplexers (ROADM) switching is performed selectively based on the center wavelength of
and wavelength converters. In addition, electro-optical network an optical signal.
elements and their compatibility constraints relative to optical
signal parameters are characterized.
Lightpath provisioning, in general, requires the routing and
wavelength assignment (RWA) process. This process is reviewed and the
information requirements, both static and dynamic for this process
are presented, along with alternative implementation architectures
that could be realized via various combinations of extended GMPLS and
PCE protocols.
This document will focus on the unique properties of links, switches
and path selection constraints that occur in WSONs. Different WSONs
such as access, metro and long haul may apply different techniques
for dealing with optical impairments hence this document will not
address optical impairments in any depth, but instead focus on
properties that are common across a variety of WSONs. For more on how
the GMPLS control plane can aid in dealing with optical impairments
see [WSON-Imp].
1.1. Revision History
1.1.1. Changes from 00
o Added new first level section on modeling examples and control
plane use cases.
o Added new third level section on wavelength converter pool
modeling
o Editorial clean up of English and updated references.
1.1.2. Changes from 01
Fixed error in wavelength converter pool example.
1.1.3. Changes from 02
Updated the abstract to emphasize the focus of this draft and
differentiate it from WSON impairment [WSON-Imp] and WSON
compatibility [WSON-Compat] drafts.
Added references to [WSON-Imp] and [WSON-Compat].
Updated the introduction to explain the relationship between this
document and the [WSON-Imp] and [WSON-Compat] documents.
In section 3.1 removed discussion of optical impairments in fibers.
Merged section 3.2.2 and section 3.2.3. Deferred much of the
discussion of signal types and standards to [WSON-Compat].
In section 3.4 on Wavelength converters removed paragraphs dealing
with signal compatibility discussion as this is addressed in [WSON-
Compat].
In section 6.1 removed discussion of signaling extensions to deal
with different WSON signal types. This is deferred to [WSON-Compat].
In section 6 removed discussion of "Need for Wavelength Specific
Maximum Bandwidth Information".
In section 6 removed discussion of "Relationship to link bundling and
layering".
In section 6 removed discussion of "Computation Architecture
Implications" as this material was redundant with text that occurs
earlier in the document.
In section 6 removed discussion of "Scaling Implications" as this
material was redundant with text that occurs earlier in the document.
1.1.4. Changes from 03
In Section 3.3.1 added 4-degree ROADM example and its connectivity In order to provision an optical connection (a lightpath) through a
matrix. WSON certain path continuity and resource availability constraints
must be met to determine viable and optimal paths through the
network. The generic problem of determining such paths is known as
the Routing and Wavelength Assignment (RWA) problem.
1.1.5. Changes from 04 Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] includes
a set of control plane protocols that can be used to operate data
networks ranging from packet switch capable networks, through those
networks that use time division multiplexing, to WDM networks. The
Path Computation Element (PCE) architecture [RFC4655] defines
functional components that can be used to compute and suggest
appropriate paths in connection-oriented traffic-engineered networks.
Added and enhanced sections on signal type and network element This document provides a framework for applying GMPLS protocols and
compatibility. the PCE architecture to the control and operation of WSONs. To aid
in this process this document also provides an overview of the
subsystems and processes that comprise WSONs, and describes the RWA
problem so that the information requirements, both static and
dynamic, can be identified to explain how the information can be
modeled for use by GMPLS and PCE systems. This work will facilitate
the development of protocol solution models and protocol extensions
within the GMPLS and PCE protocol families.
Merged section 3.2.1 into section 3.2. Note that this document focuses on the generic properties of links,
switches and path selection constraints that occur in WSONs.
Different WSONs such as access, metro, and long haul may apply
different techniques for dealing with optical impairments hence this
document does not address optical impairments in any depth. See
[WSON-Imp] for more information on optical impairments and GMPLS.
Created new section 3.3 on Optical signals with material from [WSON- 2. Terminology
Compat].
Created new section 3.5 on Electro-Optical systems with material from Add/Drop Multiplexers (ADM): An optical device used in WDM networks
[WSON-Compat]. composed of one or more line side ports and typically many tributary
ports.
Created new section 3.7 on Characterizing Electro-Optical Network CWDM: Coarse Wavelength Division Multiplexing.
Elements with material from [WSON-Compat].
Created new section 5.5 on Electro-Optical Networking Scenarios with DWDM: Dense Wavelength Division Multiplexing.
material from [WSON-Compat].
Created new section 6.1.2 on WSON Signals and Network Element Degree: The degree of an optical device (e.g., ROADM) is given by a
Processing with material from [WSON-Compat]. count of its line side ports.
Created new section 6.3.2. Electro-Optical Related PCEP Extensions Drop and continue: A simple multi-cast feature of some ADM where a
with material from [WSON-Compat]. selected wavelength can be switched out of both a tributary (drop)
port and a line side port.
1.1.6. Changes from 05 FOADM: Fixed Optical Add/Drop Multiplexer.
Removal of Section 1.2; Removal of section on lightpath temporal GMPLS: Generalized Multi-Protocol Label Switching.
characteristics; Removal of details on wavelength assignment
algorithms; Removal of redundant summary in section 6.
2. Terminology Line side: In WDM system line side ports and links typically can
carry the full multiplex of wavelength signals, as compared to
tributary (add or drop ports) that typically carry a few (typically
one) wavelength signals.
CWDM: Coarse Wavelength Division Multiplexing. OXC: Optical cross connect. An optical switching element in which a
signal on any input port can reach any output port.
DWDM: Dense Wavelength Division Multiplexing. PCC: Path Computation Client. Any client application requesting a
path computation to be performed by the Path Computation Element.
FOADM: Fixed Optical Add/Drop Multiplexer. PCE: Path Computation Element. An entity (component, application, or
network node) that is capable of computing a network path or route
based on a network graph and applying computational constraints.
OXC: Optical cross connect. A symmetric optical switching element in PCEP: PCE Communication Protocol. The communication protocol between
which a signal on any ingress port can reach any egress port. a Path Computation Client and Path Computation Element.
ROADM: Reconfigurable Optical Add/Drop Multiplexer. An asymmetric ROADM: Reconfigurable Optical Add/Drop Multiplexer. An wavelength
wavelength selective switching element featuring ingress and egress selective switching element featuring input and output line side
line side ports as well as add/drop side ports. ports as well as add/drop side ports.
RWA: Routing and Wavelength Assignment. RWA: Routing and Wavelength Assignment.
Transparent Network: a wavelength switched optical network that does Transparent Network: A wavelength switched optical network that does
not contain regenerators or wavelength converters. not contain regenerators or wavelength converters.
Translucent Network: a wavelength switched optical network that is Translucent Network: A wavelength switched optical network that is
predominantly transparent but may also contain limited numbers of predominantly transparent but may also contain limited numbers of
regenerators and/or wavelength converters. 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 Wavelength Conversion/Converters: The process of converting an
information bearing optical signal centered at a given wavelength to information bearing optical signal centered at a given wavelength to
one with "equivalent" content centered at a different wavelength. one with "equivalent" content centered at a different wavelength.
Wavelength conversion can be implemented via an optical-electronic- Wavelength conversion can be implemented via an optical-electronic-
optical (OEO) process or via a strictly optical process. optical (OEO) process or via a strictly optical process.
WDM: Wavelength Division Multiplexing. WDM: Wavelength Division Multiplexing.
Wavelength Switched Optical Networks (WSON): WDM based optical Wavelength Switched Optical Networks (WSONs): WDM based optical
networks in which switching is performed selectively based on the networks in which switching is performed selectively based on the
center wavelength of an optical signal. center wavelength of an optical signal.
3. Wavelength Switched Optical Networks 3. Wavelength Switched Optical Networks
WSONs come in a variety of shapes and sizes from continent spanning WSONs range in size from continent spanning long haul networks, to
long haul networks, to metropolitan networks, to residential access metropolitan networks, to residential access networks. In all these
networks. In all these cases we are concerned with those properties cases, the main concern is those properties that constrain the choice
that constrain the choice of wavelengths that can be used, i.e., of wavelengths that can be used, i.e., restrict the wavelength label
restrict the wavelength label set, impact the path selection process, set, impact the path selection process, and limit the topological
and limit the topological connectivity. In addition, if electro- connectivity. In addition, if electro-optical network elements are
optical network elements are used in the WSON, additional used in the WSON, additional compatibility constraints may be imposed
compatibility constraints may be imposed by the network elements on by the network elements on various optical signal parameters. The
various optical signal parameters. In the following we examine and subsequent sections review and model some of the major subsystems of
model some major subsystems of a WSON with an emphasis on those a WSON with an emphasis on those aspects that are of relevance to the
aspects that are of relevance to the control plane. In particular we control plane. In particular, WDM links, optical transmitters,
look at WDM links, Optical Transmitters, ROADMs, and Wavelength ROADMs, and wavelength converters are examined.
Converters.
3.1. WDM and CWDM Links 3.1. WDM and CWDM Links
WDM and CWDM links run over optical fibers, and optical fibers come WDM and CWDM links run over optical fibers, and optical fibers come
in a wide range of types that tend to be optimized for various in a wide range of types that tend to be optimized for various
applications from access networks, metro, long haul, and submarine applications examples include access networks, metro, long haul, and
links to name a few. ITU-T standards exist for various types of submarine links. International Telecommunication Union -
fibers. For the purposes here we are concerned only with single mode Telecommunication Standardization Sector (ITU-T) standards exist for
fibers (SMF). The following SMF fiber types are typically encountered various types of fibers. Although fiber can be categorized into
in optical networks: Single mode fibers (SMF) and Multi-mode fibers (MMF), the latter are
typically used for short-reach campus and premise applications. SMF
are used for longer-reach applications and therefore are the primary
concern of this document. The following SMF fiber types are typically
encountered in optical networks:
ITU-T Standard | Common Name ITU-T Standard | Common Name
------------------------------------------------------------ ------------------------------------------------------------
G.652 [G.652] | Standard SMF | G.652 [G.652] | Standard SMF |
G.653 [G.653] | Dispersion shifted SMF | G.653 [G.653] | Dispersion shifted SMF |
G.654 [G.654] | Cut-off shifted SMF | G.654 [G.654] | Cut-off shifted SMF |
G.655 [G.655] | Non-zero dispersion shifted SMF | G.655 [G.655] | Non-zero dispersion shifted SMF |
G.656 [G.656] | Wideband non-zero dispersion shifted SMF | G.656 [G.656] | Wideband non-zero dispersion shifted SMF |
------------------------------------------------------------ ------------------------------------------------------------
Typically WDM links operate in one or more of the approximately Typically WDM links operate in one or more of the approximately
defined optical bands [G.Sup39]: defined optical bands [G.Sup39]:
Band Range (nm) Common Name Raw Bandwidth (THz) Band Range (nm) Common Name Raw Bandwidth (THz)
O-band 1260-1360 Original 17.5 O-band 1260-1360 Original 17.5
E-band 1360-1460 Extended 15.1 E-band 1360-1460 Extended 15.1
S-band 1460-1530 Short 9.4 S-band 1460-1530 Short 9.4
C-band 1530-1565 Conventional 4.4 C-band 1530-1565 Conventional 4.4
L-band 1565-1625 Long 7.1 L-band 1565-1625 Long 7.1
U-band 1625-1675 Ultra-long 5.5 U-band 1625-1675 Ultra-long 5.5
skipping to change at page 8, line 31 skipping to change at page 7, line 27
Band Range (nm) Common Name Raw Bandwidth (THz) Band Range (nm) Common Name Raw Bandwidth (THz)
O-band 1260-1360 Original 17.5 O-band 1260-1360 Original 17.5
E-band 1360-1460 Extended 15.1 E-band 1360-1460 Extended 15.1
S-band 1460-1530 Short 9.4 S-band 1460-1530 Short 9.4
C-band 1530-1565 Conventional 4.4 C-band 1530-1565 Conventional 4.4
L-band 1565-1625 Long 7.1 L-band 1565-1625 Long 7.1
U-band 1625-1675 Ultra-long 5.5 U-band 1625-1675 Ultra-long 5.5
Not all of a band may be usable, for example in many fibers that Not all of a band may be usable, for example in many fibers that
support E-band there is significant attenuation due to a water support E-band there is significant attenuation due to a water
absorption peak at 1383nm. Hence we can have a discontinuous absorption peak at 1383nm. Hence a discontinuous acceptable
acceptable wavelength range for a particular link. Also some systems wavelength range for a particular link may be needed and is modeled.
will utilize more than one band. This is particularly true for coarse Also some systems will utilize more than one band. This is
WDM (CWDM) systems. particularly true for CWDM systems.
Current technology breaks up the bandwidth capacity of fibers into Current technology subdivides the bandwidth capacity of fibers into
distinct channels based on either wavelength or frequency. There are distinct channels based on either wavelength or frequency. There are
two standards covering wavelengths and channel spacing. ITU-T two standards covering wavelengths and channel spacing. ITU-T
recommendation [G.694.1] describes a DWDM grid defined in terms of Recommendation G.694.1, Spectral grids for WDM applications: DWDM
frequency grid [G.694.1] describes a DWDM grid defined in terms of
frequency grids of 12.5GHz, 25GHz, 50GHz, 100GHz, and other multiples frequency grids of 12.5GHz, 25GHz, 50GHz, 100GHz, and other multiples
of 100GHz around a 193.1THz center frequency. At the narrowest of 100GHz around a 193.1THz center frequency. At the narrowest
channel spacing this provides less than 4800 channels across the O channel spacing this provides less than 4800 channels across the O
through U bands. ITU-T recommendation [G.694.2] describes a CWDM grid through U bands. ITU-T Recommendation G.694.2, Spectral grids for WDM
applications: CWDM wavelength grid [G.694.2] describes a CWDM grid
defined in terms of wavelength increments of 20nm running from 1271nm defined in terms of wavelength increments of 20nm running from 1271nm
to 1611nm for 18 or so channels. The number of channels is to 1611nm for 18 or so channels. The number of channels is
significantly smaller than the 32 bit GMPLS label space allocated to significantly smaller than the 32 bit GMPLS label space defined for
lambda switching. A label representation for these ITU-T grids is GMPLS, see [RFC3471]. A label representation for these ITU-T grids
given in [Otani] and allows a common vocabulary to be used in is given in [Otani] and provides a common label format to be used in
signaling lightpaths. Further, these ITU-T grid based labels can also signaling lightpaths. Further, these ITU-T grid based labels can also
be used to describe WDM links, ROADM ports, and wavelength converters be used to describe WDM links, ROADM ports, and wavelength converters
for the purposes of path selection. for the purposes of path selection.
With a tremendous existing base of fiber many WDM links are designed Many WDM links are designed to take advantage of particular fiber
to take advantage of particular fiber characteristics or to try to characteristics or to try to avoid undesirable properties. For
avoid undesirable properties. For example dispersion shifted SMF example dispersion shifted SMF [G.653] was originally designed for
[G.653] was originally designed for good long distance performance in good long distance performance in single channel systems, however
single channel systems, however putting WDM over this type of fiber putting WDM over this type of fiber requires significant system
requires much system engineering and a fairly limited range of engineering and a fairly limited range of wavelengths. Hence the
wavelengths. Hence for our basic, impairment unaware, modeling of a following information is needed as parameters to perform basic,
WDM link we will need the following information: impairment unaware, modeling of a WDM link:
o Wavelength range(s): Given a mapping between labels and the ITU-T o Wavelength range(s): Given a mapping between labels and the ITU-T
grids each range could be expressed in terms of a doublet grids each range could be expressed in terms of a tuple (lambda1,
(lambda1, lambda2) or (freq1, freq1) where the lambdas or lambda2) or (freq1, freq1) where the lambdas or frequencies can be
frequencies can be represented by 32 bit integers. represented by 32 bit integers.
o Channel spacing: currently there are about five channel spacings o Channel spacing: Currently there are five channel spacings used in
used in DWDM systems 12.5GHz to 200GHz and one defined CWDM DWDM systems and a single channel spacing defined for CWDM
spacing. systems.
For a particular link this information is relatively static, i.e., For a particular link this information is relatively static, as
changes to these properties generally require hardware upgrades. Such changes to these properties generally require hardware upgrades. Such
information could be used locally during wavelength assignment via information may be used locally during wavelength assignment via
signaling, similar to label restrictions in MPLS or used by a PCE in signaling, similar to label restrictions in MPLS or used by a PCE in
solving the combined routing and wavelength assignment problem. solving the combined RWA problem.
3.2. Optical Transmitters 3.2. Optical Transmitters and Receivers
WDM optical systems make use of laser transmitters utilizing WDM optical systems make use of optical transmitters and receivers
different wavelengths (frequencies). Some laser transmitters were and utilizing different wavelengths (frequencies). Some transmitters are
are manufactured for a specific wavelength of operation, that is, the manufactured for a specific wavelength of operation, that is, the
manufactured frequency cannot be changed. First introduced to reduce manufactured frequency cannot be changed. First introduced to reduce
inventory costs, tunable optical laser transmitters are becoming inventory costs, tunable optical transmitters and receivers are
widely deployed in some systems [Coldren04], [Buus06]. This allows deployed in some systems, and allow flexibility in the wavelength
flexibility in the wavelength used for optical transmission and aids used for optical transmission/reception. Such tunable optics aid in
in path selection. path selection.
Fundamental modeling parameters from the control plane perspective Fundamental modeling parameters from the control plane perspective
optical transmitters are: optical transmitters and receivers are:
o Tunable: Is this transmitter tunable or fixed. o Tunable: Do the transmitter and receivers operate at variable or
fixed wavelength.
o Tuning range: This is the frequency or wavelength range over which o Tuning range: This is the frequency or wavelength range over which
the laser can be tuned. With the fixed mapping of labels to the optics can be tuned. With the fixed mapping of labels to
lambdas of [Otani] this can be expressed as a doublet (lambda1, lambdas as proposed in [Otani] this can be expressed as a tuple
lambda2) or (freq1, freq2) where lambda1 and lambda2 or freq1 and (lambda1, lambda2) or (freq1, freq2) where lambda1 and lambda2 or
freq2 are the labels representing the lower and upper bounds in freq1 and freq2 are the labels representing the lower and upper
wavelength or frequency. bounds in wavelength.
o Tuning time: Tuning times highly depend on the technology used. o Tuning time: Tuning times highly depend on the technology used.
Thermal drift based tuning may take seconds to stabilize, whilst Thermal drift based tuning may take seconds to stabilize, whilst
electronic tuning might provide sub-ms tuning times. Depending on electronic tuning might provide sub-ms tuning times. Depending on
the application this might be critical. For example, thermal drift the application this might be critical. For example, thermal drift
might not be applicable for fast protection applications. might not be usable for fast protection applications.
o Spectral Characteristics and stability: The spectral shape of the o Spectral characteristics and stability: The spectral shape of a
laser's emissions and its frequency stability put limits on laser's emissions and its frequency stability put limits on
various properties of the overall WDM system. One relatively easy various properties of the overall WDM system. One relatively easy
to characterize constraint is the finest channel spacing on which to characterize constraint is the closest channel spacing with
the transmitter can be used. which the transmitter can be used.
Note that ITU-T recommendations specify many aspects of a laser Note that ITU-T recommendations specify many aspects of an optical
transmitter. Many of these parameters, such as spectral transmitter. Many of these parameters, such as spectral
characteristics and stability, are used in the design of WDM characteristics and stability, are used in the design of WDM
subsystems consisting of transmitters, WDM links and receivers subsystems consisting of transmitters, WDM links and receivers
however they do not furnish additional information that will however they do not furnish additional information that will
influence label switched path (LSP) provisioning in a properly influence the Label Switched Path (LSP) provisioning in a properly
designed system. designed system.
Also note that lasers transmitters as a component can degrade and Also note that optical components can degrade and fail over time.
fail over time. This presents the possibility of the failure of a LSP This presents the possibility of the failure of a LSP (lightpath)
(lightpath) without either a node or link failure. Hence, additional without either a node or link failure. Hence, additional mechanisms
mechanisms may be necessary to detect and differentiate this failure may be necessary to detect and differentiate this failure from the
from the others, e.g., one doesn't not want to initiate mesh others, e.g., one doesn't not want to initiate mesh restoration if
restoration if the source transmitter has failed, since the laser the source transmitter has failed, since the optical transmitter will
transmitter will still be failed on the alternate optical path. still be failed on the alternate optical path.
3.3. Optical Signals in WSONs 3.3. Optical Signals in WSONs
In wavelength switched optical networks (WSONs) our fundamental unit In WSONs the fundamental unit of switching is intuitively that of a
of switching is intuitively that of a "wavelength". The transmitters "wavelength". The transmitters and receivers in these networks will
and receivers in these networks will deal with one wavelength at a deal with one wavelength at a time, while the switching systems
time, while the switching systems themselves can deal with multiple themselves can deal with multiple wavelengths at a time. Hence
wavelengths at a time. Hence we are generally concerned with multichannel DWDM networks with single channel interfaces are the
multichannel dense wavelength division multiplexing (DWDM) networks prime focus of this document general concern as opposed to multi-
with single channel interfaces. Interfaces of this type are defined channel interfaces. Interfaces of this type are defined in ITU-T
in ITU-T recommendations [G.698.1] and [G.698.1]. Key non-impairment recommendations [G.698.1] and [G.698.2]. Key non-impairment related
related parameters defined in [G.698.1] and [G.698.2] are: parameters defined in [G.698.1] and [G.698.2] are:
(a) Minimum Channel Spacing (GHz) (a) Minimum channel spacing (GHz)
(b) Minimum and Maximum central frequency
(c) Bit-rate/Line coding (modulation) of optical tributary signals (b) Minimum and maximum central frequency
In for the purposes of modeling the WSON in the control plane we can (c) Bit-rate/Line coding (modulation) of optical tributary signals
consider (a) and (b) as properties of the link and restrictions on For the purposes of modeling the WSON in the control plane, (a) and
the GMPLS labels while (c) is a property of the "signal". (b) are considered as properties of the link and restrictions on the
GMPLS labels while (c) is a property of the "signal".
3.3.1. Optical Tributary Signals 3.3.1. Optical Tributary Signals
The optical interface specifications [G.698.1], [G.698.2], and The optical interface specifications [G.698.1], [G.698.2], and
[G.959.1] all use the concept of an Optical Tributary Signal which is [G.959.1] all use the concept of an optical tributary signal which is
defined as "a single channel signal that is placed within an optical defined as "a single channel signal that is placed within an optical
channel for transport across the optical network". Note the use of channel for transport across the optical network". Note the use of
the qualifier "tributary" to indicate that this is a single channel the qualifier "tributary" to indicate that this is a single channel
entity and not a multichannel optical signal. entity and not a multichannel optical signal.
There are a currently a number of different "flavors" of optical There are currently a number of different types of optical tributary
tributary signals, known as "optical tributary signal classes". These signals, which are known as "optical tributary signal classes". These
are currently characterized by a modulation format and bit rate range are currently characterized by a modulation format and bit rate range
[G.959.1]: [G.959.1]:
(a) optical tributary signal class NRZ 1.25G (a) Optical tributary signal class NRZ 1.25G
(b) optical tributary signal class NRZ 2.5G (b) Optical tributary signal class NRZ 2.5G
(c) optical tributary signal class NRZ 10G (c) Optical tributary signal class NRZ 10G
(d) optical tributary signal class NRZ 40G (d) Optical tributary signal class NRZ 40G
(e) optical tributary signal class RZ 40G (e) Optical tributary signal class RZ 40G
Note that with advances in technology more optical tributary signal Note that with advances in technology more optical tributary signal
classes may be added and that this is currently an active area for classes may be added and that this is currently an active area for
deployment and standardization. In particular at the 40G rate there development and standardization. In particular at the 40G rate there
are a number of non-standardized advanced modulation formats that are a number of non-standardized advanced modulation formats that
have seen significant deployment including Differential Phase Shift have seen significant deployment including Differential Phase Shift
Keying (DPSK) and Phase Shaped Binary Transmission (PSBT)[Winzer06]. Keying (DPSK) and Phase Shaped Binary Transmission (PSBT).
Note that according to [G.698.2] it is important to fully specify the
bit rate of the optical tributary signal:
"When an optical system uses one of these codes, therefore, it is According to [G.698.2] it is important to fully specify the bit rate
necessary to specify both the application code and also the exact bit of the optical tributary signal. Hence it is seen that modulation
rate of the system. In other words, there is no requirement for format (optical tributary signal class) and bit rate are key
equipment compliant with one of these codes to operate over the parameters in characterizing the optical tributary signal.
complete range of bit rates specified for its optical tributary
signal class."
Hence we see that modulation format (optical tributary signal class)
and bit rate are key parameters in characterizing the optical
tributary signal.
3.3.2. WSON Signal Characteristics 3.3.2. WSON Signal Characteristics
We refer an optical tributary signal defined in ITU-T G.698.1 and .2 An optical tributary signal defined in ITU-T [G.698.1] and [G.698.2]
to as the signal in this document. This is an "entity" that can be is referred to as the "signal" in this document. This corresponds to
put on an optical communications channel formed from links and the "lambda" LSP in GMPLS. For signal compatibility purposes with
network elements in a WSON. This corresponds to the "lambda" LSP in electro-optical network elements, the following signal
GMPLS. For signal compatibility purposes with electro-optical network characteristics are considered:
elements we will be interested in the following signal
characteristics:
List 1. WSON Signal Characteristics
1. Optical tributary signal class (modulation format). 1. Optical tributary signal class (modulation format).
2. FEC: whether forward error correction is used in the digital stream 2. FEC: whether forward error correction is used in the digital stream
and what type of error correcting code is used and what type of error correcting code is used.
3. Center frequency (wavelength) 3. Center frequency (wavelength).
4. Bit rate 4. Bit rate.
5. G-PID: General Protocol Identifier for the information format 5. G-PID: general protocol identifier for the information format.
The first three items on this list can change as a WSON signal The first three items on this list can change as a WSON signal
traverses a network with regenerators, OEO switches, or wavelength traverses the optical network with elements that include
regenerators, Optical-to-Electrical (OEO) switches, or wavelength
converters. converters.
Bit rate and GPID would not change since they describe the encoded Bit rate and G-PID would not change since they describe the encoded
bit stream. A set of G-PID values is already defined for lambda bit stream. A set of G-PID values is already defined for lambda
switching in [RFC3471] and [RFC4328]. switching in [RFC3471] and [RFC4328].
Note that a number of "pre-standard" or proprietary modulation Note that a number of non-standard or proprietary modulation formats
formats and FEC codes are commonly used in WSONs. For some digital and FEC codes are commonly used in WSONs. For some digital bit
bit streams the presence of FEC can be detected, e.g., in [G.707] streams the presence of Forwarding Equivalence Class (FEC) can be
this is indicated in the signal itself via the FEC status indication detected, e.g., in [G.707] this is indicated in the signal itself via
(FSI) byte, while in [G.709] this can be inferred from whether the the FEC Status Indication (FSI) byte, while in [G.709] this can be
FEC field of the OTUk is all zeros or not. inferred from whether the FEC field of the Optical Channel Transport
Unit-k (OTUk) is all zeros or not.
3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs 3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs
Definitions of various optical devices and their parameters can be Definitions of various optical devices such as ROADMs, Optical Cross-
found in [G.671], we only look at a subset of these and their non- connects (OXCs), splitters, combiners and Fixed Optical Add-Drop
impairment related properties. Multiplexers (FOADMs) and their parameters can be found in [G.671].
Only a subset of these and their non-impairment related properties
are considered in the following sections.
3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs 3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs
Reconfigurable add/drop optical multiplexers (ROADM) have matured and ROADMs are available in different forms and technologies. This is a
are available in different forms and technologies [Basch06]. This is key technology that allows wavelength based optical switching. A
a key technology that allows wavelength based optical switching. A
classic degree-2 ROADM is shown in Figure 1. classic degree-2 ROADM is shown in Figure 1.
Line side ingress +---------------------+ Line side egress Line side input +---------------------+ Line side output
--->| |---> --->| |--->
| | | |
| ROADM | | ROADM |
| | | |
| | | |
+---------------------+ +---------------------+
| | | | o o o o | | | | o o o o
| | | | | | | | | | | | | | | |
O O O O | | | | O O O O | | | |
Tributary Side: Drop (egress) Add (ingress) Tributary Side: Drop (output) Add (input)
Figure 1 Degree-2 ROADM Figure 1. Degree-2 ROADM
The key feature across all ROADM types is their highly asymmetric The key feature across all ROADM types is their highly asymmetric
switching capability. In the ROADM of Figure 1, the "add" ingress switching capability. In the ROADM of Figure 1, signals introduced
ports can only egress on the line side egress port and not on any of via the add ports can only be sent on the line side output port and
the "drop" egress ports. The degree of a ROADM or switch is given by not on any of the drop ports. The term "degree" is used to refer to
the number of line side ports (ingress and egress) and does not the number of line side ports (input and output) of a ROADM, and does
include the number of "add" or "drop" ports. Sometimes the "add" not include the number of "add" or "drop" ports. The add and drop
"drop" ports are also called tributary ports. As the degree of the ports are sometimes also called tributary ports. As the degree of the
ROADM increases beyond two it can have properties of both a switch ROADM increases beyond two it can have properties of both a switch
(OXC) and a multiplexer and hence we must know the switched (OXC) and a multiplexer and hence it is necessary to know the
connectivity offered by such a network element to effectively utilize switched connectivity offered by such a network element to
it. A straight forward way to do this is via a "switched effectively utilize it. A straightforward way to represent this is
connectivity" matrix A where Amn = 0 or 1, depending upon whether a via a "switched connectivity" matrix A where Amn = 0 or 1, depending
wavelength on ingress port m can be connected to egress port n upon whether a wavelength on input port m can be connected to output
[Imajuku]. For the ROADM of Figure 1 the switched connectivity matrix port n [Imajuku]. For the ROADM shown in Figure 1 the switched
can be expressed as connectivity matrix can be expressed as:
Ingress Egress Port
Input Output Port
Port #1 #2 #3 #4 #5 Port #1 #2 #3 #4 #5
-------------- --------------
#1: 1 1 1 1 1 #1: 1 1 1 1 1
#2 1 0 0 0 0 #2 1 0 0 0 0
A = #3 1 0 0 0 0 A = #3 1 0 0 0 0
#4 1 0 0 0 0 #4 1 0 0 0 0
#5 1 0 0 0 0 #5 1 0 0 0 0
Where ingress ports 2-5 are add ports, egress ports 2-5 are drop Where input ports 2-5 are add ports, output ports 2-5 are drop ports
ports and ingress port #1 and egress port #1 are the line side (WDM) and input port #1 and output port #1 are the line side (WDM) ports.
ports.
For ROADMs this matrix will be very sparse, and for OXCs the For ROADMs, this matrix will be very sparse, and for OXCs the matrix
complement of the matrix will be very sparse, compact encodings and will be very dense, compact encodings and examples, including high
examples, including high degree ROADMs/OXCs, are given in [WSON- degree ROADMs/OXCs, are given in [WSON-Encode]. A degree-4 ROADM is
Encode]. A classic degree-4 ROADM is shown in Figure 2. shown in Figure 2.
+-----------------------+ +-----------------------+
Line side-1 --->| |---> Line side-2 Line side-1 --->| |---> Line side-2
ingress (I1) | | egress (E2) Input (I1) | | Output (E2)
Line side-1 <---| |<--- Line side-2 Line side-1 <---| |<--- Line side-2
Egress (E1) | | Ingress (I2) Output (E1) | | Input (I2)
| ROADM | | ROADM |
Line side-3 --->| |---> Line side-4 Line side-3 --->| |---> Line side-4
ingress (I3) | | egress (E4) Input (I3) | | Output (E4)
Line side-3 <---| |<--- Line side-4 Line side-3 <---| |<--- Line side-4
Egress (E3) | | Ingress (I4) Output (E3) | | Input (I4)
| | | |
+-----------------------+ +-----------------------+
| O | O | O | O | O | O | O | O
| | | | | | | | | | | | | | | |
O | O | O | O | O | O | O | O |
Tributary Side: E5 I5 E6 I6 E7 I7 E8 I8 Tributary Side: E5 I5 E6 I6 E7 I7 E8 I8
Figure 2 Degree-4 ROADM Figure 2. Degree-4 ROADM
Note that this example is 4-degree example with one (potentially Note that this example is 4-degree example with one (potentially
multi-channel) add/drop per line side port. multi-channel) add/drop per line side port.
Note also that the connectivity constraints for typical ROADM designs Note also that the connectivity constraints for typical ROADM designs
are "bi-directional", i.e. if ingress port X can be connected to are "bidirectional", i.e. if input port X can be connected to output
egress port Y, typically ingress port Y can be connected to egress port Y, typically input port Y can be connected to output port X,
port X, assuming the numbering is done in such a way that ingress X assuming the numbering is done in such a way that input X and output
and egress X correspond to the same line side direction or the same X correspond to the same line side direction or the same add/drop
add/drop port. This makes the connectivity matrix symmetrical as port. This makes the connectivity matrix symmetrical as shown below.
shown below.
Ingress Egress Port Input Output Port
Port E1 E2 E3 E4 E5 E6 E7 E8 Port E1 E2 E3 E4 E5 E6 E7 E8
----------------------- -----------------------
I1 0 1 1 1 0 1 0 0 I1 0 1 1 1 0 1 0 0
I2 1 0 1 1 0 0 1 0 I2 1 0 1 1 0 0 1 0
A = I3 1 1 0 1 1 0 0 0 A = I3 1 1 0 1 1 0 0 0
I4 1 1 1 0 0 0 0 1 I4 1 1 1 0 0 0 0 1
I5 0 0 1 0 0 0 0 0 I5 0 0 1 0 0 0 0 0
I6 1 0 0 0 0 0 0 0 I6 1 0 0 0 0 0 0 0
I7 0 1 0 0 0 0 0 0 I7 0 1 0 0 0 0 0 0
I8 0 0 0 1 0 0 0 0 I8 0 0 0 1 0 0 0 0
where I5/E5 are add/drop ports to/from line side-3, I6/E6 are Where I5/E5 are add/drop ports to/from line side-3, I6/E6 are
add/drop ports to/from line side-1, I7/E7 are add/drop ports to/from add/drop ports to/from line side-1, I7/E7 are add/drop ports to/from
line side-2 and I8/E8 are add/drop ports to/from line side-4. Note line side-2 and I8/E8 are add/drop ports to/from line side-4. Note
that diagonal elements are zero since it is assumed that loopback is that diagonal elements are zero since loopback is not supported in
not supported. If ports support loopback, diagonal elements would be the example. If ports support loopback, diagonal elements would be
one. set to one.
Additional constraints may also apply to the various ports in a Additional constraints may also apply to the various ports in a
ROADM/OXC. In the literature of optical switches and ROADMs the ROADM/OXC. The following restrictions and terms may be used:
following restrictions/terms are used:
Colored port: An ingress or more typically an egress (drop) port Colored port: an input or more typically an output (drop) port
restricted to a single channel of fixed wavelength. restricted to a single channel of fixed wavelength.
Colorless port: An ingress or more typically an egress (drop) port Colorless port: an input or more typically an output (drop) port
restricted to a single channel of arbitrary wavelength. restricted to a single channel of arbitrary wavelength.
In general a port on a ROADM could have any of the following In general a port on a ROADM could have any of the following
wavelength restrictions: wavelength restrictions:
o Multiple wavelengths, full range port o Multiple wavelengths, full range port.
o Single wavelength, full range port o Single wavelength, full range port.
o Single wavelength, fixed lambda port o Single wavelength, fixed lambda port.
o Multiple wavelengths, reduced range port (for example wave band o Multiple wavelengths, reduced range port (for example wave band
switching) switching).
To model these restrictions we need two pieces of information for To model these restrictions it is necessary to have two pieces of
each port: (a) number of wavelengths, (b) wavelength range and information for each port: (a) number of wavelengths, (b) wavelength
spacing. Note that this information is relatively static. More range and spacing. Note that this information is relatively static.
complicated wavelength constraints are modeled in [WSON-Info]. More complicated wavelength constraints are modeled in [WSON-Info].
3.4.2. Splitters 3.4.2. Splitters
An optical splitter consists of a single ingress port and two or more An optical splitter consists of a single input port and two or more
egress ports. The ingress optical signaled is essentially copied output ports. The input optical signaled is essentially copied (with
(with power loss) to all egress ports. power loss) to all output ports.
Using the modeling notions of section 3.4.1. the ingress and egress Using the modeling notions of Section 3.4.1. (Reconfigurable Add/Drop
ports of a splitter would have the same wavelength restrictions. In Multiplexers and OXCs) the input and output ports of a splitter would
addition we can describe a splitter by a connectivity matrix Amn as have the same wavelength restrictions. In addition a splitter is
follows: modeled by a connectivity matrix Amn as follows:
Ingress Egress Port Input Output Port
Port #1 #2 #3 ... #N Port #1 #2 #3 ... #N
----------------- -----------------
A = #1 1 1 1 ... 1 A = #1 1 1 1 ... 1
The difference from a simple ROADM is that this is not a switched The difference from a simple ROADM is that this is not a switched
(potential) connectivity matrix but the fixed connectivity matrix of connectivity matrix but the fixed connectivity matrix of the device.
the device.
3.4.3. Combiners 3.4.3. Combiners
A optical combiner is somewhat the dual of a splitter in that it has An optical combiner is a device that combines the optical wavelengths
a single multi-wavelength egress port and multiple ingress ports. carried by multiple input ports into a single multi-wavelength output
The contents of all the ingress ports are copied and combined to the output port. The various ports may have different wavelength
single egress port. The various ports may have different wavelength
restrictions. It is generally the responsibility of those using the restrictions. It is generally the responsibility of those using the
combiner to assure that wavelength collision does not occur on the combiner to assure that wavelength collision does not occur on the
egress port. The fixed connectivity matrix Amn for a combiner would output port. The fixed connectivity matrix Amn for a combiner would
look like: look like:
Ingress Egress Port Input Output Port
Port #1 Port #1
--- ---
#1: 1 #1: 1
#2 1 #2 1
A = #3 1 A = #3 1
... 1 ... 1
#N 1 #N 1
3.4.4. Fixed Optical Add/Drop Multiplexers 3.4.4. Fixed Optical Add/Drop Multiplexers
A fixed optical add/drop multiplexer can alter the course of an A fixed optical add/drop multiplexer can alter the course of an input
ingress wavelength in a preset way. In particular a given wavelength wavelength in a preset way. In particular a given wavelength (or
(or waveband) from a line side ingress port would be dropped to a waveband) from a line side input port would be dropped to a fixed
fixed "tributary" egress port. Depending on the device's construction "tributary" output port. Depending on the device's construction that
that same wavelength may or may not be "continued" to the line side same wavelength may or may not also be sent out the line side output
egress port ("drop and continue" operation). Further there may exist port. This is commonly referred to as "drop and continue" operation.
tributary ingress ports ("add" ports) whose signals are combined with There also may exist tributary input ports ("add" ports) whose
each other and "continued" line side signals. signals are combined with each other and other line side signals.
In general to represent the routing properties of an FOADM we need a In general, to represent the routing properties of an FOADM it is
fixed connectivity matrix Amn as previously discussed and we need the necessary to have both a fixed connectivity matrix Amn as previously
precise wavelength restrictions for all ingress and egress ports. discussed and the precise wavelength restrictions for all input and
From the wavelength restrictions on the tributary egress ports (drop output ports. From the wavelength restrictions on the tributary
ports) we can see what wavelengths have been dropped. From the output ports, what wavelengths have been selected can be derived.
wavelength restrictions on the tributary ingress (add) ports we can From the wavelength restrictions on the tributary input ports, it can
see which wavelengths have been added to the line side egress port. be seen which wavelengths have been added to the line side output
Finally from the added wavelength information and the line side port. Finally from the added wavelength information and the line side
egress wavelength restrictions we can infer which wavelengths have output wavelength restrictions it can be inferred which wavelengths
been continued. have been continued.
To summarize, the modeling methodology introduced in section 3.4.1. To summarize, the modeling methodology introduced in Section 3.4.1.
consisting of a connectivity matrix and port wavelength restrictions (Reconfigurable Add/Drop Multiplexers and OXCs) consisting of a
can be used to describe a large set of fixed optical devices such as connectivity matrix and port wavelength restrictions can be used to
combiners, splitters and FOADMs. Hybrid devices consisting of both describe a large set of fixed optical devices such as combiners,
switched and fixed parts are modeled in [WSON-Info]. splitters and FOADMs. Hybrid devices consisting of both switched and
fixed parts are modeled in [WSON-Info].
3.5. Electro-Optical Systems 3.5. Electro-Optical Systems
This section describes how Electro-Optical Systems (e.g., OEO This section describes how Electro-Optical Systems (e.g., OEO
switches, wavelength converters, and regenerators) interact with the switches, wavelength converters, and regenerators) interact with the
WSON signal characteristics defined in List 1 in Section 2.3. OEO WSON signal characteristics listed in Section 3.3.2. (WSON Signal
switches, wavelength converters and regenerators all share a similar Characteristics) OEO switches, wavelength converters and regenerators
property: they can be more or less "transparent" to an "optical all share a similar property: they can be more or less "transparent"
signal" depending on their functionality and/or implementation. to an "optical signal" depending on their functionality and/or
Regenerators have been fairly well characterized in this regard so we implementation. Regenerators have been fairly well characterized in
start by describing their properties. this regard and hence their properties can be described first.
3.5.1. Regenerators 3.5.1. Regenerators
The various approaches to regeneration are discussed in ITU-T G.872 The various approaches to regeneration are discussed in ITU-T G.872
Annex A [G.872]. They map a number of functions into the so-called Annex A [G.872]. They map a number of functions into the so-called
1R, 2R and 3R categories of regenerators as summarized in Table 1 1R, 2R and 3R categories of regenerators as summarized in Table 1
below: below:
Table 1 Regenerator functionality mapped to general regenerator Table 1. Regenerator functionality mapped to general regenerator
classes from [G.872]. classes from [G.872].
--------------------------------------------------------------------- ---------------------------------------------------------------------
1R | Equal amplification of all frequencies within the amplification 1R | Equal amplification of all frequencies within the amplification
| bandwidth. There is no restriction upon information formats. | bandwidth. There is no restriction upon information formats.
+----------------------------------------------------------------- +-----------------------------------------------------------------
| Amplification with different gain for frequencies within the | Amplification with different gain for frequencies within the
| amplification bandwidth. This could be applied to both single- | amplification bandwidth. This could be applied to both single-
| channel and multi-channel systems. | channel and multi-channel systems.
+----------------------------------------------------------------- +-----------------------------------------------------------------
skipping to change at page 18, line 31 skipping to change at page 17, line 4
+----------------------------------------------------------------- +-----------------------------------------------------------------
| Digital reshaping (Schmitt Trigger function) with no clock | Digital reshaping (Schmitt Trigger function) with no clock
| recovery. This is applicable to individual channels and can be | recovery. This is applicable to individual channels and can be
| used for different bit rates but is not transparent to line | used for different bit rates but is not transparent to line
| coding (modulation). | coding (modulation).
-------------------------------------------------------------------- --------------------------------------------------------------------
3R | Any or all 1R and 2R functions. Complete regeneration of the 3R | Any or all 1R and 2R functions. Complete regeneration of the
| pulse shape including clock recovery and retiming within | pulse shape including clock recovery and retiming within
| required jitter limits. | required jitter limits.
-------------------------------------------------------------------- --------------------------------------------------------------------
From this table it is seen that 1R regenerators are generally
From the previous table we can see that 1R regenerators are generally
independent of signal modulation format (also known as line coding), independent of signal modulation format (also known as line coding),
but may work over a limited range of wavelength/frequencies. We see but may work over a limited range of wavelength/frequencies. 2R
that 2R regenerators are generally applicable to a single digital regenerators are generally applicable to a single digital stream and
stream and are dependent upon modulation format (line coding) and to are dependent upon modulation format (line coding) and to a lesser
a lesser extent are limited to a range of bit rates (but not a extent are limited to a range of bit rates (but not a specific bit
specific bit rate). Finally, 3R regenerators apply to a single rate). Finally, 3R regenerators apply to a single channel, are
channel, are dependent upon the modulation format and generally dependent upon the modulation format and generally sensitive to the
sensitive to the bit rate of digital signal, i.e., either are bit rate of digital signal, i.e., either are designed to only handle
designed to only handle a specific bit rate or need to be programmed a specific bit rate or need to be programmed to accept and regenerate
to accept and regenerate a specific bit rate. In all these types of a specific bit rate. In all these types of regenerators the digital
regenerators the digital bit stream contained within the optical or bit stream contained within the optical or electrical signal is not
electrical signal is not modified. modified.
However, in the most common usage of regenerators the digital bit It is common for regenerators to modify the digital bit stream for
stream may be slightly modified for performance monitoring and fault performance monitoring and fault management purposes. Synchronous
management purposes. SONET, SDH and G.709 all have digital signal Optical Networking (SONET), Synchronous Digital Hierarchy (SDH) and
"envelopes" designed to be used between "regenerators" (in this case Interfaces for the Optical Transport Network (G.709) all have digital
3R regenerators). In SONET this is known as the "section" signal, in signal "envelopes" designed to be used between "regenerators" (in
SDH this is known as the "regenerator section" signal, in G.709 this this case 3R regenerators). In SONET this is known as the "section"
is known as an OTUk (Optical Channel Transport Unit-k). These signal, in SDH this is known as the "regenerator section" signal, in
signals reserve a portion of their frame structure (known as G.709 this is known as an OTUk. These signals reserve a portion of
overhead) for use by regenerators. The nature of this overhead is their frame structure (known as overhead) for use by regenerators.
summarized in Table 2. The nature of this overhead is summarized in Table 2 below.
Table 2. SONET, SDH, and G.709 regenerator related overhead. Table 2. SONET, SDH, and G.709 regenerator related overhead.
+-----------------------------------------------------------------+ +-----------------------------------------------------------------+
|Function | SONET/SDH | G.709 OTUk | |Function | SONET/SDH | G.709 OTUk |
| | Regenerator | | | | Regenerator | |
| | Section | | | | Section | |
|------------------+----------------------+-----------------------| |------------------+----------------------+-----------------------|
|Signal | J0 (section | Trail Trace | |Signal | J0 (section | Trail Trace |
|Identifier | trace) | Identifier (TTI) | |Identifier | trace) | Identifier (TTI) |
skipping to change at page 19, line 35 skipping to change at page 18, line 32
|Fault Management | A1, A2 framing | FAS (frame alignment | |Fault Management | A1, A2 framing | FAS (frame alignment |
| | bytes | signal), BDI(backward| | | bytes | signal), BDI(backward|
| | | defect indication)BEI| | | | defect indication)BEI|
| | | (backward error | | | | (backward error |
| | | indication) | | | | indication) |
+------------------+----------------------+-----------------------| +------------------+----------------------+-----------------------|
|Forward Error | P1,Q1 bytes | OTUk FEC | |Forward Error | P1,Q1 bytes | OTUk FEC |
|Correction (FEC) | | | |Correction (FEC) | | |
+-----------------------------------------------------------------+ +-----------------------------------------------------------------+
In the previous table we see support for frame alignment, signal In the previous table it is seen that frame alignment, signal
identification, and FEC. What this table also shows by its omission identification, and FEC are supported. What this table also shows by
is that no switching or multiplexing occurs at this layer. This is a its omission is that no switching or multiplexing occurs at this
significant simplification for the control plane since control plane layer. This is a significant simplification for the control plane
standards require a multi-layer approach when there are multiple since control plane standards require a multi-layer approach when
switching layers, but not for "layering" to provide the management there are multiple switching layers, but not for "layering" to
functions of Table 2. That is, many existing technologies covered by provide the management functions of Table 2. That is, many existing
GMPLS contain extra management related layers that are essentially technologies covered by GMPLS contain extra management related layers
ignored by the control plane (though not by the management plane!). that are essentially ignored by the control plane (though not by the
Hence, the approach here is to include regenerators and other devices management plane!). Hence, the approach here is to include
at the WSON layer unless they provide higher layer switching and then regenerators and other devices at the WSON layer unless they provide
a multi-layer or multi-region approach [RFC5212] is called for. higher layer switching and then a multi-layer or multi-region
However, this can result in regenerators having a dependence on the approach [RFC5212] is called for. However, this can result in
client signal type. regenerators having a dependence on the client signal type.
Hence we see that depending upon the regenerator technology we may Hence depending upon the regenerator technology the following
have the following constraints imposed by a regenerator device: constraints may be imposed by a regenerator device:
Table 3. Regenerator Compatibility Constraints Table 3. Regenerator Compatibility Constraints.
+--------------------------------------------------------+ +--------------------------------------------------------+
| Constraints | 1R | 2R | 3R | | Constraints | 1R | 2R | 3R |
+--------------------------------------------------------+ +--------------------------------------------------------+
| Limited Wavelength Range | x | x | x | | Limited Wavelength Range | x | x | x |
+--------------------------------------------------------+ +--------------------------------------------------------+
| Modulation Type Restriction | | x | x | | Modulation Type Restriction | | x | x |
+--------------------------------------------------------+ +--------------------------------------------------------+
| Bit Rate Range Restriction | | x | x | | Bit Rate Range Restriction | | x | x |
+--------------------------------------------------------+ +--------------------------------------------------------+
| Exact Bit Rate Restriction | | | x | | Exact Bit Rate Restriction | | | x |
+--------------------------------------------------------+ +--------------------------------------------------------+
| Client Signal Dependence | | | x | | Client Signal Dependence | | | x |
+--------------------------------------------------------+ +--------------------------------------------------------+
Note that Limited Wavelength Range constraint is already modeled in Note that the limited wavelength range constraint can be modeled for
GMPLS for WSON and that Modulation Type Restriction constraint GMPLS signaling with the label set defined in [RFC3471] and that the
includes FEC. modulation type restriction constraint includes FEC.
3.5.2. OEO Switches 3.5.2. OEO Switches
A common place where optical-to-electrical-to-optical (OEO) A common place where OEO processing may take place is within WSON
processing may take place is in WSON switches that utilize (or switches that utilize (or contain) regenerators. Regenerators may be
contain) regenerators. A vendor may add regenerators to a switching added to a switching system for a number of reasons. One common
system for a number of reasons. One obvious reason is to restore reason is to restore signal quality either before or after optical
signal quality either before or after optical processing (switching). processing (switching). Another reason may be to convert the signal
Another reason may be to convert the signal to an electronic form for to an electronic form for switching then reconverting to an optical
switching then reconverting to an optical signal prior to egress from signal prior to output from the switch. In this later case the
the switch. In this later case the regeneration is applied to adapt regeneration is applied to adapt the signal to the switch fabric
the signal to the switch fabric regardless of whether or not it is regardless of whether or not it is needed from a signal quality
needed from a signal quality perspective. perspective.
In either case these optical switches have essentially the same In either case these optical switches have essentially the same
compatibility constraints as those we described for regenerators in compatibility constraints as those which are described for
Table 3. regenerators in Table 3.
3.6. Wavelength Converters 3.6. Wavelength Converters
Wavelength converters take an ingress optical signal at one Wavelength converters take an input optical signal at one wavelength
wavelength and emit an equivalent content optical signal at another and emit an equivalent content optical signal at another wavelength
wavelength on egress. There are currently two approaches to building on output. There are multiple approaches to building wavelength
wavelength converters. One approach is based on optical to electrical converters. One approach is based on OEO conversion with fixed or
to optical (OEO) conversion with tunable lasers on egress. This tunable optics on output. This approach can be dependent upon the
approach can be dependent upon the signal rate and format, i.e., this signal rate and format, i.e., this is basically an electrical
is basically an electrical regenerator combined with a tunable laser. regenerator combined with a laser/receiver. Hence, this type of
Hence, this type wavelength converter has signal processing wavelength converter has signal processing restrictions that are
restrictions that are essentially the same as those we described for essentially the same as those described for regenerators in Table 3
regenerators in Table 3 of section 3.5.1. of section 3.5.1.
The other approach performs the wavelength conversion, optically via Another approach performs the wavelength conversion, optically via
non-linear optical effects, similar in spirit to the familiar non-linear optical effects, similar in spirit to the familiar
frequency mixing used in radio frequency systems, but significantly frequency mixing used in radio frequency systems, but significantly
harder to implement. Such processes/effects may place limits on the harder to implement. Such processes/effects may place limits on the
range of achievable conversion. These may depend on the wavelength of range of achievable conversion. These may depend on the wavelength of
the input signal and the properties of the converter as opposed to the input signal and the properties of the converter as opposed to
only the properties of the converter in the OEO case. Different WSON only the properties of the converter in the OEO case. Different WSON
system designs may choose to utilize this component to varying system designs may choose to utilize this component to varying
degrees or not at all. degrees or not at all.
Current or envisioned contexts for wavelength converters are: Current or envisioned contexts for wavelength converters are:
1. Wavelength conversion associated with OEO switches and tunable 1. Wavelength conversion associated with OEO switches and fixed or
laser transmitters. In this case there are plenty of converters to tunable optics. In this case there are typically multiple
go around since we can think of each tunable output laser converters available since each on the use of an OEO switch can be
transmitter on an OEO switch as a potential wavelength converter. thought of as a potential wavelength converter.
2. Wavelength conversion associated with ROADMs/OXCs. In this case we 2. Wavelength conversion associated with ROADMs/OXCs. In this case
may have a limited pool of wavelength converters available. there may be a limited pool of wavelength converters available.
Conversion could be either all optical or via an OEO method. Conversion could be either all optical or via an OEO method.
3. Wavelength conversion associated with fixed devices such as FOADMs. 3. Wavelength conversion associated with fixed devices such as FOADMs.
In this case we may have a limited amount of conversion. Also in In this case there may be a limited amount of conversion. Also in
this case the conversion may be used as part of light path routing. this case the conversion may be used as part of light path routing.
Based on the above considerations we model wavelength converters as Based on the above considerations, wavelength converters are modeled
follows: as follows:
1. Wavelength converters can always be modeled as associated with 1. Wavelength converters can always be modeled as associated with
network elements. This includes fixed wavelength routing elements. network elements. This includes fixed wavelength routing elements.
2. A network element may have full wavelength conversion capability, 2. A network element may have full wavelength conversion capability,
i.e., any ingress port and wavelength, or a limited number of i.e., any input port and wavelength, or a limited number of
wavelengths and ports. On a box with a limited number of wavelengths and ports. On a box with a limited number of
converters there also may exist restrictions on which ports can converters there also may exist restrictions on which ports can
reach the converters. Hence regardless of where the converters reach the converters. Hence regardless of where the converters
actually are we can associate them with ingress ports. actually are they can be associated with input ports.
3. Wavelength converters have range restrictions that are either 3. Wavelength converters have range restrictions that are either
independent or dependent upon the ingress wavelength. independent or dependent upon the input wavelength.
In WSONs where wavelength converters are sparse we may actually see a In WSONs where wavelength converters are sparse a light path may
light path appear to loop or "backtrack" upon itself in order to appear to loop or "backtrack" upon itself in order to reach a
reach a wavelength converter prior to continuing on to its wavelength converter prior to continuing on to its destination. The
destination. The lambda used on the "detour" out to the wavelength lambda used on input to the wavelength converter would be different
converter would be different from that coming back from the "detour" the lambda coming back from the wavelength converter.
to the wavelength converter.
A model for an individual O-E-O wavelength converter would consist A model for an individual O-E-O wavelength converter would consist
of: of:
o Input lambda or frequency range o Input lambda or frequency range.
o Output lambda or frequency range o Output lambda or frequency range.
3.6.1. Wavelength Converter Pool Modeling 3.6.1. Wavelength Converter Pool Modeling
A WSON node may include multiple wavelength converters. These are A WSON node may include multiple wavelength converters. These are
usually arranged into some type of pool to promote resource sharing. usually arranged into some type of pool to promote resource sharing.
There are a number of different approaches used in the design of There are a number of different approaches used in the design of
switches with converter pools. However, from the point of view of switches with converter pools. However, from the point of view of
path computation we need to know the following: path computation it is necessary to know the following:
1. The nodes that support wavelength conversion. 1. The nodes that support wavelength conversion.
2. The accessibility and availability of a wavelength converter to 2. The accessibility and availability of a wavelength converter to
convert from a given ingress wavelength on a particular ingress convert from a given input wavelength on a particular input port
port to a desired egress wavelength on a particular egress port. to a desired output wavelength on a particular output port.
3. Limitations on the types of signals that can be converted and the 3. Limitations on the types of signals that can be converted and the
conversions that can be performed. conversions that can be performed.
To model point 2 above we can use a similar technique as used to To model point 2 above, a similar technique can be used to model
model ROADMs and optical switches, i.e., matrices to indicate ROADMs and optical switches, i.e., matrices to indicate possible
possible connectivity along with wavelength constraints for connectivity along with wavelength constraints for links/ports. Since
links/ports. Since wavelength converters are considered a scarce wavelength converters are considered a scarce resource it will be
resource we will also want our model to include as a minimum the desirable to include as a minimum the usage state of individual
usage state of individual wavelength converters in the pool. wavelength converters in the pool.
We utilize a three stage model as shown schematically in Figure 3. In A three stage model is used as shown schematically in Figure 3.
this model we assume N ingress ports (fibers), P wavelength (Schematic diagram of wavelength converter pool model). In this model
converters, and M egress ports (fibers). Since not all ingress ports it is assumed N input ports (fibers), P wavelength converters, and M
can necessarily reach the converter pool, the model starts with a output ports (fibers). Since not all input ports can necessarily
wavelength pool ingress matrix WI(i,p) = {0,1} whether ingress port i reach the converter pool, the model starts with a wavelength pool
can reach potentially reach wavelength converter p. input matrix WI(i,p) = {0,1} where input port i can reach potentially
reach wavelength converter p.
Since not all wavelength can necessarily reach all the converters or Since not all wavelength can necessarily reach all the converters or
the converters may have limited input wavelength range we have a set the converters may have limited input wavelength range there is a set
of ingress port constraints for each wavelength converter. Currently of input port constraints for each wavelength converter. Currently it
we assume that a wavelength converter can only take a single is assumed that a wavelength converter can only take a single
wavelength on input. We can model each wavelength converter ingress wavelength on input. Each wavelength converter input port constraint
port constraint via a wavelength set mechanism. can be modeled via a wavelength set mechanism.
Next we have a state vector WC(j) = {0,1} dependent upon whether Next a state vector WC(j) = {0,1} dependent upon whether wavelength
wavelength converter j in the pool is in use. This is the only state converter j in the pool is in use. This is the only state kept in the
kept in the converter pool model. This state is not necessary for converter pool model. This state is not necessary for modeling
modeling "fixed" transponder system, i.e., systems where there is no "fixed" transponder system, i.e., systems where there is no sharing.
sharing. In addition, this state information may be encoded in a In addition, this state information may be encoded in a much more
much more compact form depending on the overall connectivity compact form depending on the overall connectivity structure [WSON-
structure [WSON-Encode]. Encode].
After that, we have a set of wavelength converter egress wavelength After that, a set of wavelength converter output wavelength
constraints. These constraints indicate what wavelengths a particular constraints is used. These constraints indicate what wavelengths a
wavelength converter can generate or are restricted to generating due particular wavelength converter can generate or are restricted to
to internal switch structure. generating due to internal switch structure.
Finally, we have a wavelength pool egress matrix WE(p,k) = {0,1} Finally, a wavelength pool output matrix WE(p,k) = {0,1} indicating
depending on whether the output from wavelength converter p can reach whether the output from wavelength converter p can reach output port
egress port k. Examples of this method being used to model wavelength k. Examples of this method being used to model wavelength converter
converter pools for several switch architectures from the literature pools for several switch architectures are given in reference [WSON-
are given in reference [WSON-Encode]. Encode].
I1 +-------------+ +-------------+ E1 I1 +-------------+ +-------------+ E1
----->| | +--------+ | |-----> ----->| | +--------+ | |----->
I2 | +------+ WC #1 +-------+ | E2 I2 | +------+ WC #1 +-------+ | E2
----->| | +--------+ | |-----> ----->| | +--------+ | |----->
| Wavelength | | Wavelength | | Wavelength | | Wavelength |
| Converter | +--------+ | Converter | | Converter | +--------+ | Converter |
| Pool +------+ WC #2 +-------+ Pool | | Pool +------+ WC #2 +-------+ Pool |
| | +--------+ | | | | +--------+ | |
| Ingress | | Egress | | Input | | Output |
| Connection | . | Connection | | Connection | . | Connection |
| Matrix | . | Matrix | | Matrix | . | Matrix |
| | . | | | | . | |
| | | | | | | |
IN | | +--------+ | | EM IN | | +--------+ | | EM
----->| +------+ WC #P +-------+ |-----> ----->| +------+ WC #P +-------+ |----->
| | +--------+ | | | | +--------+ | |
+-------------+ ^ ^ +-------------+ +-------------+ ^ ^ +-------------+
| | | |
| | | |
| | | |
| | | |
Ingress wavelength Egress wavelength Input wavelength Output wavelength
constraints for constraints for constraints for constraints for
each converter each converter each converter each converter
Figure 3 Schematic diagram of wavelength converter pool model. Figure 3. Schematic diagram of wavelength converter pool model.
Example: Shared Per Node
In Figure 4 below we show a simple optical switch in a four Figure 4 below shows a simple optical switch in a four wavelength
wavelength DWDM system sharing wavelength converters in a general DWDM system sharing wavelength converters in a general shared "per
"per node" fashion. node" fashion.
+-----------+ ___________ +------+ +-----------+ ___________ +------+
| |--------------------------->| | | |--------------------------->| |
| |--------------------------->| C | | |--------------------------->| C |
/| | |--------------------------->| o | E1 /| | |--------------------------->| o | E1
I1 /D+--->| |--------------------------->| m | I1 /D+--->| |--------------------------->| m |
+ e+--->| | | b |====> + e+--->| | | b |====>
====>| M| | Optical | +-----------+ +----+ | i | ====>| M| | Optical | +-----------+ +----+ | i |
+ u+--->| Switch | | WC Pool | |O S|-->| n | + u+--->| Switch | | WC Pool | |O S|-->| n |
\x+--->| | | +-----+ | |p w|-->| e | \x+--->| | | +-----+ | |p w|-->| e |
skipping to change at page 25, line 28 skipping to change at page 24, line 28
I2 /D+--->| +----+->|WC #2|--+->|l |-->| C | E2 I2 /D+--->| +----+->|WC #2|--+->|l |-->| C | E2
+ e+--->| | | +-----+ | | | | o | + e+--->| | | +-----+ | | | | o |
====>| M| | | +-----------+ +----+ | m |====> ====>| M| | | +-----------+ +----+ | m |====>
+ u+--->| | | b | + u+--->| | | b |
\x+--->| |--------------------------->| i | \x+--->| |--------------------------->| i |
\| | |--------------------------->| n | \| | |--------------------------->| n |
| |--------------------------->| e | | |--------------------------->| e |
|___________|--------------------------->| r | |___________|--------------------------->| r |
+-----------+ +------+ +-----------+ +------+
Figure 4 An optical switch featuring a shared per node wavelength Figure 4. An optical switch featuring a shared per node wavelength
converter pool architecture. converter pool architecture.
In this case the ingress and egress pool matrices are simply: In this case the input and output pool matrices are simply:
+-----+ +-----+ +-----+ +-----+
| 1 1 | | 1 1 | | 1 1 | | 1 1 |
WI =| |, WE =| | WI =| |, WE =| |
| 1 1 | | 1 1 | | 1 1 | | 1 1 |
+-----+ +-----+ +-----+ +-----+
Example: Shared Per Link Figure 5 shows a different wavelength pool architecture known as
"shared per fiber". In this case the input and output pool matrices
In Figure 5 we show a different wavelength pool architecture know as
"shared per fiber". In this case the ingress and egress pool matrices
are simply: are simply:
+-----+ +-----+ +-----+ +-----+
| 1 1 | | 1 0 | | 1 1 | | 1 0 |
WI =| |, WE =| | WI =| |, WE =| |
| 1 1 | | 0 1 | | 1 1 | | 0 1 |
+-----+ +-----+ +-----+ +-----+
+-----------+ +------+ +-----------+ +------+
| |--------------------------->| | | |--------------------------->| |
| |--------------------------->| C | | |--------------------------->| C |
/| | |--------------------------->| o | E1 /| | |--------------------------->| o | E1
I1 /D+--->| |--------------------------->| m | I1 /D+--->| |--------------------------->| m |
+ e+--->| | | b |====> + e+--->| | | b |====>
====>| M| | Optical | +-----------+ | i | ====>| M| | Optical | +-----------+ | i |
+ u+--->| Switch | | WC Pool | | n | + u+--->| Switch | | WC Pool | | n |
\x+--->| | | +-----+ | | e | \x+--->| | | +-----+ | | e |
\| | +----+->|WC #1|--+---------->| r | \| | +----+->|WC #1|--+---------->| r |
skipping to change at page 26, line 33 skipping to change at page 25, line 26
/| | | | +-----+ | | | /| | | | +-----+ | | |
I2 /D+--->| +----+->|WC #2|--+---------->| C | E2 I2 /D+--->| +----+->|WC #2|--+---------->| C | E2
+ e+--->| | | +-----+ | | o | + e+--->| | | +-----+ | | o |
====>| M| | | +-----------+ | m |====> ====>| M| | | +-----------+ | m |====>
+ u+--->| | | b | + u+--->| | | b |
\x+--->| |--------------------------->| i | \x+--->| |--------------------------->| i |
\| | |--------------------------->| n | \| | |--------------------------->| n |
| |--------------------------->| e | | |--------------------------->| e |
|___________|--------------------------->| r | |___________|--------------------------->| r |
+-----------+ +------+ +-----------+ +------+
Figure 5 An optical switch featuring a shared per fiber wavelength Figure 5. An optical switch featuring a shared per fiber wavelength
converter pool architecture. converter pool architecture.
3.7. Characterizing Electro-Optical Network Elements 3.7. Characterizing Electro-Optical Network Elements
In this section we characterize Electro-Optical WSON network elements In this section electro-optical WSON network elements are
by the three key functional components: Input constraints, Output characterized by the three key functional components: input
constraints and Processing Capabilities. constraints, output constraints and processing capabilities.
WSON Network Element WSON Network Element
+-----------------------+ +-----------------------+
WSON Signal | | | | WSON Signal WSON Signal | | | | WSON Signal
| | | | | | | |
---------------> | | | | -----------------> ---------------> | | | | ----------------->
| | | | | | | |
+-----------------------+ +-----------------------+
<-----> <-------> <-----> <-----> <-------> <----->
Input Processing Output Input Processing Output
Figure 6 WSON Network Element Figure 6. WSON Network Element
3.7.1. Input Constraints 3.7.1. Input Constraints
Section 3 discussed the basic properties regenerators, OEO switches Section 3. (Wavelength Switched Optical Networks) discussed the basic
and wavelength converters from these we have the following possible properties regenerators, OEO switches and wavelength converters. From
types of input constraints and properties: these the following possible types of input constraints and
properties are derived:
1. Acceptable Modulation formats 1. Acceptable Modulation formats.
2. Client Signal (GPID) restrictions 2. Client Signal (G-PID) restrictions.
3. Bit Rate restrictions 3. Bit Rate restrictions.
4. FEC coding restrictions 4. FEC coding restrictions.
5. Configurability: (a) none, (b) self-configuring, (c) required 5. Configurability: (a) none, (b) self-configuring, (c) required.
We can represent these constraints via simple lists. Note that the These constraints are represented via simple lists. Note that the
device may need to be "provisioned" via signaling or some other means device may need to be "provisioned" via signaling or some other means
to accept signals with some attributes versus others. In other cases to accept signals with some attributes versus others. In other cases
the devices maybe relatively transparent to some attributes, e.g., the devices maybe relatively transparent to some attributes, e.g.,
such as a 2R regenerator to bit rate. Finally, some devices maybe such as a 2R regenerator to bit rate. Finally, some devices maybe
able to auto-detect some attributes and configure themselves, e.g., a able to auto-detect some attributes and configure themselves, e.g., a
3R regenerator with bit rate detection mechanisms and flexible phase 3R regenerator with bit rate detection mechanisms and flexible phase
locking circuitry. To account for these different cases we've added locking circuitry. To account for these different cases item 5 has
item 5, which describes the devices configurability. been added, which describes the devices configurability.
Note that such input constraints also apply to the final destination, Note that such input constraints also apply to the termination of the
sink or termination, of the WSON signal. WSON signal.
3.7.2. Output Constraints 3.7.2. Output Constraints
None of the network elements considered here modifies either the bit None of the network elements considered here modifies either the bit
rate or the basic type of the client signal. However, they may modify rate or the basic type of the client signal. However, they may modify
the modulation format or the FEC code. Typically we'd see the the modulation format or the FEC code. Typically the following types
following types of output constraints: of output constraints are seen:
1. Output modulation is the same as input modulation (default) 1. Output modulation is the same as input modulation (default).
2. A limited set of output modulations is available 2. A limited set of output modulations is available.
3. Output FEC is the same as input FEC code (default) 3. Output FEC is the same as input FEC code (default).
4. A limited set of output FEC codes is available 4. A limited set of output FEC codes is available.
Note that in cases (2) and (4) above, where there is more than one Note that in cases (2) and (4) above, where there is more than one
choice in the output modulation or FEC code then the network element choice in the output modulation or FEC code then the network element
will need to be configured on a per LSP basis as to which choice to will need to be configured on a per LSP basis as to which choice to
use. use.
3.7.3. Processing Capabilities 3.7.3. Processing Capabilities
A general WSON network element (NE) can perform a number of signal A general WSON network element (NE) can perform a number of signal
processing functions including: processing functions including:
(A) Regeneration (possibly different types) (A) Regeneration (possibly different types).
(B) Fault and Performance Monitoring
(C) Wavelength Conversion (B) Fault and Performance Monitoring.
(D) Switching (C) Wavelength Conversion.
Item(D) can be modeled with existing GMPLS mechanisms. (D) Switching.
An NE may or may not have the ability to perform regeneration (of the An NE may or may not have the ability to perform regeneration (of the
one of the types previously discussed). In addition some nodes may one of the types previously discussed). In addition some nodes may
have limited regeneration capability, i.e., a shared pool, which may have limited regeneration capability, i.e., a shared pool, which may
be applied to selected signals traversing the NE. Hence to describe be applied to selected signals traversing the NE. Hence to describe
the regeneration capability of a link or node we have at a minimum: the regeneration capability of a link or node it is necessary to have
at a minimum:
1. Regeneration capability: (a)fixed, (b) selective, (c) none 1. Regeneration capability: (a)fixed, (b) selective, (c) none.
2. Regeneration type: 1R, 2R, 3R 2. Regeneration type: 1R, 2R, 3R.
3. Regeneration pool properties for the case of selective 3. Regeneration pool properties for the case of selective
regeneration (ingress & egress restrictions, availability) regeneration (input and output restrictions, availability).
Note that the properties of shared regenerator pools would be Note that the properties of shared regenerator pools would be
essentially the same at that of wavelength converter pools modeled in essentially the same at that of wavelength converter pools modeled in
section 3.6.1. section 3.6.1. (Wavelength Pool Convertor Modeling).
Item (B), fault and performance monitoring, is typically outside the Item (B), fault and performance monitoring, is typically outside the
scope of the control plane. However, when the operations are to be scope of the control plane. However, when the operations are to be
performed on an LSP basis or as part of an LSP then the control plane performed on an LSP basis or on part of an LSP then the control plane
can be of assistance in their configuration. Per LSP, per node, fault can be of assistance in their configuration. Per LSP, per node, fault
and performance monitoring examples include setting up a "section and performance monitoring examples include setting up a "section
trace" (a regenerator overhead identifier) between two nodes, or trace" (a regenerator overhead identifier) between two nodes, or
intermediate optical performance monitoring at selected nodes along a intermediate optical performance monitoring at selected nodes along a
path. path.
4. Routing and Wavelength Assignment and the Control Plane 4. Routing and Wavelength Assignment and the Control Plane
In wavelength switched optical networks consisting of tunable lasers A wavelength-convertible network with full wavelength-conversion
and wavelength selective switches with wavelength converters on every capability at each node is equivalent to packet MPLS-labeled network
interface, path selection is similar to the MPLS and TDM circuit or a circuit-switched Time-division multiplexing (TDM) network with
switched cases in that the labels, in this case wavelengths full time slot interchange capability. In this case, the routing
(lambdas), have only local significance. That is, a wavelength- problem needs to be addressed only at the level of the Traffic
convertible network with full wavelength-conversion capability at Engineered (TE) link choice, and wavelength assignment can be
each node is equivalent to a circuit-switched TDM network with full resolved locally by the switches on a hop-by-hop basis.
time slot interchange capability; thus, the routing problem needs to
be addressed only at the level of the traffic engineered (TE) link
choice, and wavelength assignment can be resolved locally by the
switches on a hop-by-hop basis.
However, in the limiting case of an optical network with no However, in the limiting case of an optical network with no
wavelength converters, a light path (optical signal) needs a route wavelength converters, a light path (optical signal) needs a route
from source to destination and must pick a single wavelength that can from source to destination and must pick a single wavelength that can
be used along that path without "colliding" with the wavelength used be used along that path without "colliding" with the wavelength used
by any other light path that may share an optical fiber. This is by any other light path that may share an optical fiber. This is
sometimes referred to as a "wavelength continuity constraint". To sometimes referred to as a "wavelength continuity constraint".
ease up on this constraint while keeping network costs in check a
limited number of wavelength converters may be introduced at key
points in the network [Chu03].
In the general case of limited or no wavelength converters this In the general case of limited or no wavelength converters this
computation is known as the Routing and Wavelength Assignment (RWA) computation is known as the RWA problem.
problem [HZang00]. The "hardness" of this problem is well documented.
There, however, exist a number of reasonable approximate methods for
its solution [HZang00].
The inputs to the basic RWA problem are the requested light paths The inputs to the basic RWA problem are the requested light path's
source and destination, the network's topology, the locations and source and destination, the network topology, the locations and
capabilities of any wavelength converters, and the wavelengths capabilities of any wavelength converters, and the wavelengths
available on each optical link. The output from an algorithm solving available on each optical link. The output from an algorithm solving
the RWA problem is an explicit route through ROADMs, a wavelength for the RWA problem is an explicit route through ROADMs, a wavelength for
the optical transmitter, and a set of locations (generally associated the optical transmitter, and a set of locations (generally associated
with ROADMs or switches) where wavelength conversion is to occur and with ROADMs or switches) where wavelength conversion is to occur and
the new wavelength to be used on each component link after that point the new wavelength to be used on each component link after that point
in the route. in the route.
It is to be noted that choice of specific RWA algorithm is out of the It is to be noted that the choice of specific RWA algorithm is out of
scope for this document. However there are a number of different the scope for this document. However there are a number of different
approaches to dealing with the RWA algorithm that can affect the approaches to dealing with the RWA algorithm that can affect the
division of effort between signaling, routing and PCE. division of effort between path computation/routing and signaling.
4.1. Architectural Approaches to RWA 4.1. Architectural Approaches to RWA
Two general computational approaches are taken to solving the RWA Two general computational approaches are taken to solving the RWA
problem. Some algorithms utilize a two step procedure of path problem. Some algorithms utilize a two step procedure of path
selection followed by wavelength assignment, and others solve the selection followed by wavelength assignment, and others solve the
problem in a combined fashion. problem in a combined fashion.
In the following, three different ways of performing RWA in In the following, three different ways of performing RWA in
conjunction with the control plane are considered. The choice of one conjunction with the control plane are considered. The choice of one
skipping to change at page 30, line 35 skipping to change at page 29, line 18
wavelength assignment. This approach relies on a sufficient knowledge wavelength assignment. This approach relies on a sufficient knowledge
of network topology, of available network resources and of network of network topology, of available network resources and of network
nodes capabilities. This solution is compatible with most known RWA nodes capabilities. This solution is compatible with most known RWA
algorithms, and in particular those concerned with network algorithms, and in particular those concerned with network
optimization. On the other hand, this solution requires up-to-date optimization. On the other hand, this solution requires up-to-date
and detailed network information. and detailed network information.
Such a computational entity could reside in two different logical Such a computational entity could reside in two different logical
places: places:
o In a separate Path Computation Element (PCE) which owns the o The PCE, which maintains a complete and updated view of network
complete and updated knowledge of network state and provides path state, provides path computation services to nodes (PCCs).
computation services to nodes.
o In the Ingress node, in that case all nodes have the R&WA o In the ingress node, in that case all nodes have the R&WA
functionality; the knowledge of the network state is obtained by a functionality; the knowledge of the network state is obtained by a
periodic flooding of information provided by the other nodes. periodic flooding of information provided by the other nodes.
4.1.2. Separated R and WA (R+WA) 4.1.2. Separated R and WA (R+WA)
In this case a first entity performs routing, while a second performs In this case a first entity performs routing, while a second performs
wavelength assignment. The first entity furnishes one or more paths wavelength assignment. The first entity furnishes one or more paths
to the second entity that will perform wavelength assignment and to the second entity that will perform wavelength assignment and
possibly final path selection. possibly final path selection.
As the entities computing the path and the wavelength assignment are As the entities computing the path and the wavelength assignment are
separated, this constrains the class of RWA algorithms that may be separated, this constrains the class of RWA algorithms that may be
implemented. Although it may seem that algorithms optimizing a joint implemented. Although it may seem that algorithms optimizing a joint
usage of the physical and spectral paths are excluded from this usage of the physical and spectral paths are excluded from this
solution, many practical optimization algorithms only consider a solution, many practical optimization algorithms only consider a
limited set of possible paths, e.g., as computed via a k-shortest limited set of possible paths, e.g., as computed via a k-shortest
path algorithm [Ozdaglar03]. Hence although there is no guarantee path algorithm. Hence although there is no guarantee that the
that the selected final route and wavelength offers the optimal selected final route and wavelength offers the optimal solution, by
solution, by allowing multiple routes to pass to the wavelength allowing multiple routes to pass to the wavelength selection process
selection process reasonable optimization can be performed. reasonable optimization can be performed.
The entity performing the routing assignment needs the topology The entity performing the routing assignment needs the topology
information of the network, whereas the entity performing the information of the network, whereas the entity performing the
wavelength assignment needs information on the network's available wavelength assignment needs information on the network's available
resources and on network node capabilities. resources and specific network node capabilities.
4.1.3. Routing and Distributed WA (R+DWA) 4.1.3. Routing and Distributed WA (R+DWA)
In this case a first entity performs routing, while wavelength In this case a first entity performs routing, while wavelength
assignment is performed on a hop-by-hop manner along the previously assignment is performed on a hop-by-hop, distributed, manner along
computed route. This mechanism relies on updating of a list of the previously computed route. This mechanism relies on updating of a
potential wavelengths used to ensure conformance with the wavelength list of potential wavelengths used to ensure conformance with the
continuity constraint. wavelength continuity constraint.
As currently specified, the GMPLS protocol suite signaling protocol As currently specified, the GMPLS protocol suite signaling protocol
can accommodate such an approach. Per [RFC3471], the Label Set can accommodate such an approach. Per [RFC3471], the Label Set
selection works according to an AND scheme. Each hop restricts the selection works according to an AND scheme. Each hop restricts the
Label Set sent to the next hop from the one received from the Label Set sent to the next hop from the one received from the
previous hop by performing an AND operation between the wavelength previous hop by performing an AND operation between the wavelength
referred by the labels the message includes with the one available on referred by the labels the message includes with the one available on
the ongoing interface. The constraint to perform this AND operation the ongoing interface. The constraint to perform this AND operation
is up to the node local policy (even if one expects a consistent is up to the node local policy (even if one expects a consistent
policy configuration throughout a given transparency domain). When policy configuration throughout a given transparency domain). When
wavelength conversion is performed at an intermediate node, a new wavelength conversion is performed at an intermediate node, a new
Label Set is generated. The egress nodes selects one label in the Label Set is generated. The output node selects one label in the
Label Set received at the node, which is also up to the node local Label Set which it received; additionally the node can apply local
policy. policy during label selection.
Depending on these policies a spectral assignment may not be found or Depending on these policies a spectral assignment may not be found or
one consuming too many conversion resources relative to what a one consuming too many conversion resources relative to what a
dedicated wavelength assignment policy would have achieved. Hence, dedicated wavelength assignment policy would have achieved. Hence,
this approach may generate higher blocking probabilities in a heavily this approach may generate higher blocking probabilities in a heavily
loaded network. loaded network.
On the one hand, this solution may be empowered with some signaling On the one hand, this solution may be empowered with some signaling
extensions to ease its functioning and possibly enhance its extensions to ease its functioning and possibly enhance its
performances relatively to blocking. Note that this approach requires performance relatively to blocking. Note that this approach requires
less information dissemination than the others. less information dissemination than the other techniques described.
The first entity may be a PCE or the ingress node of the LSP. This The first entity may be a PCE or the ingress node of the LSP. This
solution is applicable inside networks where resource optimization is solution is applicable inside networks where resource optimization is
not as critical. not as critical.
4.2. Conveying information needed by RWA 4.2. Conveying information needed by RWA
The previous sections have characterized WSONs and lightpath The previous sections have characterized WSONs and lightpath
requests. In particular, high level models of the information used by requests. In particular, high level models of the information used by
the RWA process were presented. We can view this information as the RWA process were presented. This information can be viewed as
either static, changing with hardware changes (including possibly either static, changing with hardware changes (including possibly
failures), or dynamic, those that can change with subsequent failures), or dynamic, those that can change with subsequent
lightpath provisioning. The timeliness in which an entity involved in lightpath provisioning. The timeliness in which an entity involved in
the RWA process is notified of such changes is fairly situational. the RWA process is notified of such changes is fairly situational.
For example, for network restoration purposes, learning of a hardware For example, for network restoration purposes, learning of a hardware
failure or of new hardware coming online to provide restoration failure or of new hardware coming online to provide restoration
capability can be critical. capability can be critical.
Currently there are various methods for communicating RWA relevant Currently there are various methods for communicating RWA relevant
information, these include, but are not limited to: information, these include, but are not limited to:
o Existing control plane protocols such as GMPLS routing and o Existing control plane protocols such as GMPLS routing and
signaling. Note that routing protocols can be used to convey both signaling. Note that routing protocols can be used to convey both
static and dynamic information. Static information currently static and dynamic information.
conveyed includes items like router options and such.
o Management protocols such as NetConf, SNMPv3, CLI, CORBA, or o Management protocols such as NetConf, SNMPv3, CLI, CORBA, or
others. others.
o Directory services and accompanying protocols. These are good for o Directory services and accompanying protocols. These are good for
the dissemination of relatively static information. Not intended the dissemination of relatively static information. Directory
for dynamic information. services are not suited to manage information in dynamic and fluid
environments.
o Other techniques for dynamic information: messaging straight from o Other techniques for dynamic information: messaging straight from
NEs to PCE to avoid flooding. This would be useful if the number NEs to PCE to avoid flooding. This would be useful if the number
of PCEs is significantly less than number of WSON NEs. Or other of PCEs is significantly less than number of WSON NEs. Or other
ways to limit flooding to "interested" NEs. ways to limit flooding to "interested" NEs.
Mechanisms to improve scaling of dynamic information: Mechanisms to improve scaling of dynamic information:
o Tailor message content to WSON. For example the use of wavelength o Tailor message content to WSON. For example the use of wavelength
ranges, or wavelength occupation bit maps. ranges, or wavelength occupation bit maps.
Utilize incremental updates if feasible. o Utilize incremental updates if feasible.
5. Modeling Examples and Control Plane Use Cases 5. Modeling Examples and Control Plane Use Cases
This section provides examples of the fixed and switch optical node This section provides examples of the fixed and switch optical node
and wavelength constraint models of section 3. and WSON control plane and wavelength constraint models of Section 3. and WSON control
use cases related to path computation, establishment, rerouting, and plane use cases related to path computation, establishment,
optimization. rerouting, and optimization.
5.1. Network Modeling for GMPLS/PCE Control 5.1. Network Modeling for GMPLS/PCE Control
Consider a network containing three routers (R1 through R3), eight Consider a network containing three routers (R1 through R3), eight
WSON nodes (N1 through N8) and 18 links (L1 through L18) and one OEO WSON nodes (N1 through N8) and 18 links (L1 through L18) and one OEO
converter (O1) in a topology shown below. converter (O1) in a topology shown below.
+--+ +--+ +--+ +--------+ +--+ +--+ +--+ +--------+
+-L3-+N2+-L5-+ +--------L12--+N6+--L15--+ N8 +-- +-L3-+N2+-L5-+ +--------L12--+N6+--L15--+ N8 +
| +--+ |N4+-L8---+ +--+ ++--+---++ | +--+ |N4+-L8---+ +--+ ++--+---++
| | +-L9--+| | | | | | +-L9--+| | | |
+--+ +-+-+ ++-+ || | L17 L18 +--+ +-+-+ ++-+ || | L17 L18
| ++-L1--+ | | ++++ +----L16---+ | | | ++-L1--+ | | ++++ +----L16---+ | |
|R1| | N1| L7 |R2| | | | |R1| | N1| L7 |R2| | | |
| ++-L2--+ | | ++-+ | ++---++ | ++-L2--+ | | ++-+ | ++---++
+--+ +-+-+ | | | + R3 | +--+ +-+-+ | | | + R3 |
| +--+ ++-+ | | +-----+ | +--+ ++-+ | | +-----+
+-L4-+N3+-L6-+N5+-L10-+ ++----+ +-L4-+N3+-L6-+N5+-L10-+ ++----+
+--+ | +--------L11--+ N7 +---- +--+ | +--------L11--+ N7 +
+--+ ++---++ +--+ ++---++
| | | |
L13 L14 L13 L14
| | | |
++-+ | ++-+ |
|O1+-+ |O1+-+
+--+ +--+
Figure 7. Routers and WSON nodes in a GMPLS and PCE Environment.
5.1.1. Describing the WSON nodes 5.1.1. Describing the WSON nodes
The eight WSON nodes in this example have the following properties: The eight WSON nodes described in Figure 7 have the following
properties:
o Nodes N1, N2, N3 have fixed OADMs (FOADMs) installed and can o Nodes N1, N2, N3 have FOADMs installed and can therefore only
therefore only access a static and pre-defined set of wavelengths access a static and pre-defined set of wavelengths.
o All other nodes contain ROADMs and can therefore access all o All other nodes contain ROADMs and can therefore access all
wavelengths. wavelengths.
o Nodes N4, N5, N7 and N8 are multi-degree nodes, allowing any o Nodes N4, N5, N7 and N8 are multi-degree nodes, allowing any
wavelength to be optically switched between any of the links. Note wavelength to be optically switched between any of the links. Note
however, that this does not automatically apply to wavelengths however, that this does not automatically apply to wavelengths
that are being added or dropped at the particular node. that are being added or dropped at the particular node.
o Node N4 is an exception to that: This node can switch any o Node N4 is an exception to that: This node can switch any
wavelength from its add/drop ports to any of its outgoing links wavelength from its add/drop ports to any of its outgoing links
(L5, L7 and L12 in this case) (L5, L7 and L12 in this case).
o The links from the routers are always only able to carry one o The links from the routers are always only able to carry one
wavelength with the exception of links L8 and L9 which are capable wavelength with the exception of links L8 and L9 which are capable
to add/drop any wavelength. to add/drop any wavelength.
o Node N7 contains an OEO transponder (O1) connected to the node via o Node N7 contains an OEO transponder (O1) connected to the node via
links L13 and L14. That transponder operates in 3R mode and does links L13 and L14. That transponder operates in 3R mode and does
not change the wavelength of the signal. Assume that it can not change the wavelength of the signal. Assume that it can
regenerate any of the client signals, however only for a specific regenerate any of the client signals, however only for a specific
wavelength. wavelength.
skipping to change at page 36, line 16 skipping to change at page 35, line 16
wavelengths designated WL1 through WL4. wavelengths designated WL1 through WL4.
o It is assumed that the impairment feasibility of a path or path o It is assumed that the impairment feasibility of a path or path
segment is independent from the wavelength chosen. segment is independent from the wavelength chosen.
For the discussion of the RWA operation to build LSPs between two For the discussion of the RWA operation to build LSPs between two
routers, the wavelength constraints on the links between the routers routers, the wavelength constraints on the links between the routers
and the WSON nodes as well as the connectivity matrix of these links and the WSON nodes as well as the connectivity matrix of these links
needs to be specified: needs to be specified:
+Link+WLs supported +Possible egress links+ +Link+WLs supported +Possible output links+
| L1 | WL1 | L3 | | L1 | WL1 | L3 |
+----+-----------------+---------------------+ +----+-----------------+---------------------+
| L2 | WL2 | L4 | | L2 | WL2 | L4 |
+----+-----------------+---------------------+ +----+-----------------+---------------------+
| L8 | WL1 WL2 WL3 WL4 | L5 L7 L12 | | L8 | WL1 WL2 WL3 WL4 | L5 L7 L12 |
+----+-----------------+---------------------+ +----+-----------------+---------------------+
| L9 | WL1 WL2 WL3 WL4 | L5 L7 L12 | | L9 | WL1 WL2 WL3 WL4 | L5 L7 L12 |
+----+-----------------+---------------------+ +----+-----------------+---------------------+
| L10| WL2 | L6 | | L10| WL2 | L6 |
+----+-----------------+---------------------+ +----+-----------------+---------------------+
| L13| WL1 WL2 WL3 WL4 | L11 L14 | | L13| WL1 WL2 WL3 WL4 | L11 L14 |
+----+-----------------+---------------------+ +----+-----------------+---------------------+
| L14| WL1 WL2 WL3 WL4 | L13 L16 | | L14| WL1 WL2 WL3 WL4 | L13 L16 |
+----+-----------------+---------------------+ +----+-----------------+---------------------+
| L17| WL2 | L16 | | L17| WL2 | L16 |
+----+-----------------+---------------------+ +----+-----------------+---------------------+
| L18| WL1 | L15 | | L18| WL1 | L15 |
+----+-----------------+---------------------+ +----+-----------------+---------------------+
Note that the possible egress links for the links connecting to the Note that the possible output links for the links connecting to the
routers is inferred from the Switched Connectivity Matrix and the routers is inferred from the switched connectivity matrix and the
Fixed Connectivity Matrix of the Nodes N1 through N8 and is show here fixed connectivity matrix of the Nodes N1 through N8 and is show here
for convenience, i.e., this information does not need to be repeated. for convenience, i.e., this information does not need to be repeated.
5.2. RWA Path Computation and Establishment 5.2. RWA Path Computation and Establishment
The calculation of optical impairment feasible routes is outside the The calculation of optical impairment feasible routes is outside the
scope of this framework document. In general impairment feasible scope of this framework document. In general impairment feasible
routes serve as an input to the RWA algorithm. routes serve as an input to the RWA algorithm.
For the example use case shown here, assume the following feasible For the example use case shown here, assume the following feasible
routes: routes:
skipping to change at page 37, line 49 skipping to change at page 36, line 49
Assume now that the RWA chooses WL2 and the path L2 L4 L6 L7 L9 for Assume now that the RWA chooses WL2 and the path L2 L4 L6 L7 L9 for
the establishment of the new LSP. the establishment of the new LSP.
Faced with another LSP request -this time from R2 to R3 - can not be Faced with another LSP request -this time from R2 to R3 - can not be
fulfilled since the only four possible paths (starting at L8 and L9) fulfilled since the only four possible paths (starting at L8 and L9)
are already in use. are already in use.
5.3. Resource Optimization 5.3. Resource Optimization
The preceding example gives rise to another use case: The The preceding example gives rise to another use case: the
optimization of network resources. Optimization can be achieved on a optimization of network resources. Optimization can be achieved on a
number of layers (e.g. through electrical or optical multiplexing of number of layers (e.g. through electrical or optical multiplexing of
client signals) or by re-optimizing the solutions found by the RWA client signals) or by re-optimizing the solutions found by the RWA
algorithm. algorithm.
Given the above example again, assume that the RWA algorithm should Given the above example again, assume that the RWA algorithm should
find a path between R2 and R3. The only possible path to reach R3 find a path between R2 and R3. The only possible path to reach R3
from R2 needs to use L9. L9 however is blocked by one of the LSPs from R2 needs to use L9. L9 however is blocked by one of the LSPs
from R1. from R1.
skipping to change at page 38, line 36 skipping to change at page 37, line 36
R1 -> N7 -> R2 R1 -> N7 -> R2
Level 3 regeneration will take place at N7, so that the complete path Level 3 regeneration will take place at N7, so that the complete path
looks like this: looks like this:
R1 -> L2 L4 L6 L11 L13 -> O1 -> L14 L16 L15 L12 L9 -> R2 R1 -> L2 L4 L6 L11 L13 -> O1 -> L14 L16 L15 L12 L9 -> R2
5.5. Electro-Optical Networking Scenarios 5.5. Electro-Optical Networking Scenarios
In the following we look at various networking scenarios involving In the following various networking scenarios are considered
regenerators, OEO switches and wavelength converters. We group these involving regenerators, OEO switches and wavelength converters. These
scenarios roughly by type and number of extensions to the GMPLS scenarios can be grouped roughly by type and number of extensions to
control plane that would be required. the GMPLS control plane that would be required.
5.5.1. Fixed Regeneration Points 5.5.1. Fixed Regeneration Points
In the simplest networking scenario involving regenerators, the In the simplest networking scenario involving regenerators, the
regeneration is associated with a WDM link or entire node and is not regeneration is associated with a WDM link or entire node and is not
optional, i.e., all signals traversing the link or node will be optional, i.e., all signals traversing the link or node will be
regenerated. This includes OEO switches since they provide regenerated. This includes OEO switches since they provide
regeneration on every port. regeneration on every port.
There maybe input constraints and output constraints on the There maybe input constraints and output constraints on the
skipping to change at page 39, line 28 skipping to change at page 38, line 28
the network in addition to fixed regenerators of the previous the network in addition to fixed regenerators of the previous
scenario. These regenerators are shared within a node and their scenario. These regenerators are shared within a node and their
application to a signal is optional. There are no reconfigurable application to a signal is optional. There are no reconfigurable
options on either input or output. The only processing option is to options on either input or output. The only processing option is to
"regenerate" a particular signal or not. "regenerate" a particular signal or not.
Regenerator information in this case is used in path computation to Regenerator information in this case is used in path computation to
select a path that ensures signal compatibility and IA-RWA criteria. select a path that ensures signal compatibility and IA-RWA criteria.
To setup an LSP that utilizes a regenerator from a node with a shared To setup an LSP that utilizes a regenerator from a node with a shared
regenerator pool we need to be able to indicate that regeneration is regenerator pool one should be able to indicate that regeneration is
to take place at that particular node along the signal path. Such a to take place at that particular node along the signal path. Such a
capability currently does not exist in GMPLS signaling. capability currently does not exist in GMPLS signaling.
5.5.3. Reconfigurable Regenerators 5.5.3. Reconfigurable Regenerators
In this scenario we have regenerators that require configuration This scenario is concerned with regenerators that require
prior to use on an optical signal. We discussed previously that this configuration prior to use on an optical signal. As discussed
could be due to a regenerator that must be configured to accept previously, this could be due to a regenerator that must be
signals with different characteristics, for regenerators with a configured to accept signals with different characteristics, for
selection of output attributes, or for regenerators with additional regenerators with a selection of output attributes, or for
optional processing capabilities. regenerators with additional optional processing capabilities.
As in the previous scenarios we will need information concerning As in the previous scenarios it is necessary to have information
regenerator properties for selection of compatible paths and for IA- concerning regenerator properties for selection of compatible paths
RWA computations. In addition during LSP setup we need to be able and for IA-RWA computations. In addition during LSP setup it is
configure regenerator options at a particular node along the path. necessary to be able configure regenerator options at a particular
Such a capability currently does not exist in GMPLS signaling. node along the path. Such a capability currently does not exist in
GMPLS signaling.
5.5.4. Relation to Translucent Networks 5.5.4. Relation to Translucent Networks
In the literature, networks that contain both transparent network Networks that contain both transparent network elements such as
elements such as reconfigurable optical add drop multiplexers reconfigurable optical add drop multiplexers (ROADMs) and electro-
(ROADMs) and electro-optical network elements such regenerators or optical network elements such regenerators or OEO switches are
OEO switches are frequently referred to as Translucent optical frequently referred to as translucent optical networks.
networks [Trans07]. Earlier work suggesting GMPLS extensions for
translucent optical networks can be found in [Yang05] while a more
comprehensive evaluation of differing GMPLS control plane approaches
to translucent networks can be found in [Sambo09].
Three main types of translucent optical networks have been discussed: Three main types of translucent optical networks have been discussed:
4. Transparent "islands" surrounded by regenerators. This is 1. Transparent "islands" surrounded by regenerators. This is
frequently seen when transitioning from a metro optical sub- frequently seen when transitioning from a metro optical sub-
network to a long haul optical sub-network. network to a long haul optical sub-network.
5. Mostly transparent networks with a limited number of OEO 2. Mostly transparent networks with a limited number of OEO
("opaque") nodes strategically placed. This takes advantage of the ("opaque") nodes strategically placed. This takes advantage of the
inherent regeneration capabilities of OEO switches. In the inherent regeneration capabilities of OEO switches. In the
planning of such networks one has to determine the optimal planning of such networks one has to determine the optimal
placement of the OEO switches [Sen08]. placement of the OEO switches.
6. Mostly transparent networks with a limited number of optical 3. Mostly transparent networks with a limited number of optical
switching nodes with "shared regenerator pools" that can be switching nodes with "shared regenerator pools" that can be
optionally applied to signals passing through these switches. optionally applied to signals passing through these switches.
These switches are sometimes called translucent nodes. These switches are sometimes called translucent nodes.
All three of these types of translucent networks fit within either All three of these types of translucent networks fit within the
the networking scenarios of sections 5.5.1. and 5.5.2. above. And networking scenarios of Section 5.5.1. and Section 5.5.2. above.
hence, can be accommodated by the GMPLS extensions suggested in this And hence, can be accommodated by the GMPLS extensions suggested in
document. this document.
6. GMPLS & PCE Implications 6. GMPLS and PCE Implications
The presence and amount of wavelength conversion available at a The presence and amount of wavelength conversion available at a
wavelength switching interface has an impact on the information that wavelength switching interface has an impact on the information that
needs to be transferred by the control plane (GMPLS) and the PCE needs to be transferred by the control plane (GMPLS) and the PCE
architecture. Current GMPLS and PCE standards can address the full architecture. Current GMPLS and PCE standards can address the full
wavelength conversion case so the following will only address the wavelength conversion case so the following will only address the
limited and no wavelength conversion cases. limited and no wavelength conversion cases.
6.1. Implications for GMPLS signaling 6.1. Implications for GMPLS signaling
skipping to change at page 41, line 9 skipping to change at page 40, line 4
lambda (value 9) LSP encoding type [RFC3471], or for G.709 compatible lambda (value 9) LSP encoding type [RFC3471], or for G.709 compatible
optical channels, the LSP encoding type (value = 13) "G.709 Optical optical channels, the LSP encoding type (value = 13) "G.709 Optical
Channel" from [RFC4328]. However a number of practical issues arise Channel" from [RFC4328]. However a number of practical issues arise
in the identification of wavelengths and signals, and distributed in the identification of wavelengths and signals, and distributed
wavelength assignment processes which are discussed below. wavelength assignment processes which are discussed below.
6.1.1. Identifying Wavelengths and Signals 6.1.1. Identifying Wavelengths and Signals
As previously stated a global fixed mapping between wavelengths and As previously stated a global fixed mapping between wavelengths and
labels simplifies the characterization of WDM links and WSON devices. labels simplifies the characterization of WDM links and WSON devices.
Furthermore such a mapping as described in [Otani] eases Furthermore such a mapping as described in [Otani] eases
communication between PCE and WSON PCCs. communication between PCE and WSON PCCs.
6.1.2. WSON Signals and Network Element Processing 6.1.2. WSON Signals and Network Element Processing
We saw in section 3.3.2. 3.3.2. that a WSON signal at any point along It was seen in Section 3.3.2. that a WSON signal at any point along
its path can be characterized by the (a) modulation format, (b) FEC, its path can be characterized by the (a) modulation format, (b) FEC,
(c) wavelength, (d)bit rate, and (d)G-PID. (c) wavelength, (d)bit rate, and (d)G-PID.
Currently G-PID, wavelength (via labels), and bit rate (via bandwidth Currently G-PID, wavelength (via labels), and bit rate (via bandwidth
encoding) are supported in [RFC3471] and [RFC3473]. These RFCs can encoding) are supported in [RFC3471] and [RFC3473]. These RFCs can
accommodate the wavelength changing at any node along the LSP and can accommodate the wavelength changing at any node along the LSP and can
thus provide explicit control of wavelength converters. thus provide explicit control of wavelength converters.
In the fixed regeneration point scenario (section 5.5.1. ) no In the fixed regeneration point scenario described in Section 5.5.1.
enhancements are required to signaling since there are no additional (Fixed Regeneration Points) no enhancements are required to signaling
configuration options for the LSP at a node. since there are no additional configuration options for the LSP at a
node.
In the case of shared regeneration pools (section 5.5.2. ) we need to In the case of shared regeneration pools described in Section 5.5.2.
be able to indicate to a node that it should perform regeneration on (Shared Regeneration Pools) it is necessary to indicate to a node
a particular signal. Viewed another way, for an LSP we want to that it should perform regeneration on a particular signal. Viewed
specify that certain nodes along the path perform regeneration. Such another way, for an LSP, it is desirable to specify that certain
a capability currently does not exist in GMPLS signaling. nodes along the path perform regeneration. Such a capability
currently does not exist in GMPLS signaling.
The case of configurable regenerators (section 5.5.3. ) is very The case of configurable regenerators described in Section 5.5.3.
similar to the previous except that now there are potentially many (Reconfigurable Regenerators) is very similar to the previous except
more items that we may want to configure on a per node basis for an that now there are potentially many more items that can be configured
LSP. on a per node basis for an LSP.
Note that the techniques of [RFC5420] which allow for additional LSP Note that the techniques of [RFC5420] which allow for additional LSP
attributes and their recording in an RRO object could be extended to attributes and their recording in an Record Route Object (RRO) object
allow for additional LSP attributes in an ERO. This could allow one could be extended to allow for additional LSP attributes in an ERO.
to indicate where optional 3R regeneration should take place along a This could allow one to indicate where optional 3R regeneration
path, any modification of LSP attributes such as modulation format, should take place along a path, any modification of LSP attributes
or any enhance processing such as performance monitoring. such as modulation format, or any enhance processing such as
performance monitoring.
6.1.3. Combined RWA/Separate Routing WA support 6.1.3. Combined RWA/Separate Routing WA support
In either the combined RWA or separate routing WA cases, the node In either the combined RWA or separate routing WA cases, the node
initiating the signaling will have a route from the source to initiating the signaling will have a route from the source to
destination along with the wavelengths (generalized labels) to be destination along with the wavelengths (generalized labels) to be
used along portions of the path. Current GMPLS signaling supports an used along portions of the path. Current GMPLS signaling supports an
explicit route object (ERO) and within an ERO an ERO Label subobject Explicit Route Object (ERO) and within an ERO an ERO Label subobject
can be use to indicate the wavelength to be used at a particular can be use to indicate the wavelength to be used at a particular
node. In case the local label map approach is used the label sub- node. In case the local label map approach is used the label sub-
object entry in the ERO has to be translated appropriately. object entry in the ERO has to be translated appropriately.
6.1.4. Distributed Wavelength Assignment: Unidirectional, No 6.1.4. Distributed Wavelength Assignment: Unidirectional, No
Converters Converters
GMPLS signaling for a uni-directional lightpath LSP allows for the GMPLS signaling for a uni-directional lightpath LSP allows for the
use of a label set object in the RSVP-TE path message. The processing use of a label set object in the Resource Reservation Protocol -
of the label set object to take the intersection of available lambdas Traffic Engineering (RSVP-TE) path message. The processing of the
along a path can be performed resulting in the set of available label set object to take the intersection of available lambdas along
lambda being known to the destination that can then use a wavelength a path can be performed resulting in the set of available lambda
being known to the destination that can then use a wavelength
selection algorithm to choose a lambda. selection algorithm to choose a lambda.
6.1.5. Distributed Wavelength Assignment: Unidirectional, Limited 6.1.5. Distributed Wavelength Assignment: Unidirectional, Limited
Converters Converters
The previous outlined the case with no wavelength converters. In the In the case of wavelength converters, nodes with wavelength
case of wavelength converters, nodes with wavelength converters would converters would need to make the decision as to whether to perform
need to make the decision as to whether to perform conversion. One conversion. One indicator for this would be that the set of available
indicator for this would be that the set of available wavelengths wavelengths which is obtained via the intersection of the incoming
which is obtained via the intersection of the incoming label set and label set and the output links available wavelengths is either null
the egress links available wavelengths is either null or deemed too or deemed too small to permit successful completion.
small to permit successful completion.
At this point the node would need to remember that it will apply At this point the node would need to remember that it will apply
wavelength conversion and will be responsible for assigning the wavelength conversion and will be responsible for assigning the
wavelength on the previous lambda-contiguous segment when the RSVP-TE wavelength on the previous lambda-contiguous segment when the RSVP-TE
RESV message passes by. The node will pass on an enlarged label set RESV message passes by. The node will pass on an enlarged label set
reflecting only the limitations of the wavelength converter and the reflecting only the limitations of the wavelength converter and the
egress link. The record route option in RVSP-TE signaling can be used output link. The record route option in RVSP-TE signaling can be used
to show where wavelength conversion has taken place. to show where wavelength conversion has taken place.
6.1.6. Distributed Wavelength Assignment: Bidirectional, No 6.1.6. Distributed Wavelength Assignment: Bidirectional, No
Converters Converters
There are potential issues in the case of a bi-directional lightpath There are potential issues in the case of a bi-directional lightpath
which requires the use of the same lambda in both directions. We can which requires the use of the same lambda in both directions. The
try to use the above procedure to determine the available above procedure can be used to determine the available bidirectional
bidirectional lambda set if we use the interpretation that the lambda set if it is interpreted that the available label set is
available label set is available in both directions. However, a available in both directions. However, a problem, arises in that
problem, arises in that bidirectional LSPs setup, according to bidirectional LSPs setup, according to [RFC3471] Section 4.1.
[RFC3471] section 4.1, is indicated by the presence of an upstream (Architectural Approaches to RWA), is indicated by the presence of an
label in the path message. upstream label in the path message.
However, until the intersection of the available label sets is However, until the intersection of the available label sets is
obtained, e.g., at the destination node and the wavelength assignment obtained, e.g., at the destination node and the wavelength assignment
algorithm has been run the upstream label information will not be algorithm has been run the upstream label information will not be
available. Hence currently distributed wavelength assignment with available. Hence currently distributed wavelength assignment with
bidirectional lightpaths is not supported. bidirectional lightpaths is not supported.
6.2. Implications for GMPLS Routing 6.2. Implications for GMPLS Routing
GMPLS routing [RFC4202] currently defines an interface capability GMPLS routing [RFC4202] currently defines an interface capability
descriptor for "lambda switch capable" (LSC) which we can use to descriptor for "lambda switch capable" (LSC) which can be used to
describe the interfaces on a ROADM or other type of wavelength describe the interfaces on a ROADM or other type of wavelength
selective switch. In addition to the topology information typically selective switch. In addition to the topology information typically
conveyed via an IGP, we would need to convey the following subsystem conveyed via an IGP, it would be necessary to convey the following
properties to minimally characterize a WSON: subsystem properties to minimally characterize a WSON:
1. WDM Link properties (allowed wavelengths). 1. WDM Link properties (allowed wavelengths).
2. Laser Transmitters (wavelength range). 2. Optical transmitters (wavelength range).
3. ROADM/FOADM properties (connectivity matrix, port wavelength 3. ROADM/FOADM Properties (connectivity matrix, port wavelength
restrictions). restrictions).
4. Wavelength Converter properties (per network element, may change if 4. Wavelength converter properties (per network element, may change if
a common limited shared pool is used). a common limited shared pool is used).
This information is modeled in detail in [WSON-Info] and a compact This information is modeled in detail in [WSON-Info] and a compact
encoding is given in [WSON-Encode]. encoding is given in [WSON-Encode].
6.2.1. Electro-Optical Element Signal Compatibility 6.2.1. Electro-Optical Element Signal Compatibility
In network scenarios where signal compatibility is a concern we need In network scenarios where signal compatibility is a concern it is
to add parameters to our existing node and link models to take into necessary to add parameters to our existing node and link models to
account electro-optical input constraints, output constraints, and take into account electro-optical input constraints, output
the signal processing capabilities of a NE in path computations. constraints, and the signal processing capabilities of a NE in path
computations.
Input Constraints: Input constraints:
1. Permitted optical tributary signal classes: A list of optical 1. Permitted optical tributary signal classes: A list of optical
tributary signal classes that can be processed by this network tributary signal classes that can be processed by this network
element or carried over this link. [configuration type] element or carried over this link. (configuration type)
2. Acceptable FEC codes [configuration type] 2. Acceptable FEC codes. (configuration type)
3. Acceptable Bit Rate Set: A list of specific bit rates or bit rate 3. Acceptable Bit Rate Set: a list of specific bit rates or bit rate
ranges that the device can accommodate. Coarse bit rate info is ranges that the device can accommodate. Coarse bit rate info is
included with the optical tributary signal class restrictions. included with the optical tributary signal class restrictions.
4. Acceptable G-PID list: A list of G-PIDs corresponding to the 4. Acceptable G-PID list: a list of G-PIDs corresponding to the
"client" digital streams that is compatible with this device. "client" digital streams that is compatible with this device.
Note that since the bit rate of the signal does not change over the Note that since the bit rate of the signal does not change over the
LSP. We can make this an LSP parameter and hence this information LSP. This can be made as an LSP parameter and hence this information
would be available for any NE that needs to use it for configuration. would be available for any NE that needs to use it for configuration.
Hence we do not need "configuration type" for the NE with respect to Hence it is not necessary to have "configuration type" for the NE
bit rate. with respect to bit rate.
Output Constraints: Output constraints:
1. Output modulation: (a)same as input, (b) list of available types 1. Output modulation: (a)same as input, (b) list of available types
2. FEC options: (a) same as input, (b) list of available codes 2. FEC options: (a) same as input, (b) list of available codes
Processing Capabilities: Processing capabilities:
1. Regeneration: (a) 1R, (b) 2R, (c) 3R, (d)list of selectable 1. Regeneration: (a) 1R, (b) 2R, (c) 3R, (d)list of selectable
regeneration types regeneration types
2. Fault and Performance Monitoring (a)GPID particular capabilities 2. Fault and performance monitoring: (a) G-PID particular
TBD, (b) optical performance monitoring capabilities TBD. capabilities, (b) optical performance monitoring capabilities.
Note that such parameters could be specified on an (a) Network Note that such parameters could be specified on an (a) Network
element wide basis, (b) a per port basis, (c) on a per regenerator element wide basis, (b) a per port basis, (c) on a per regenerator
basis. Typically such information has been on a per port basis, basis. Typically such information has been on a per port basis,
e.g., the GMPLS interface switching capability descriptor [RFC4202]. e.g., the GMPLS interface switching capability descriptor [RFC4202].
6.2.2. Wavelength-Specific Availability Information 6.2.2. Wavelength-Specific Availability Information
For wavelength assignment we need to know which specific wavelengths For wavelength assignment it is necessary to know which specific
are available and which are occupied if we are going to run a wavelengths are available and which are occupied if a combined RWA
combined RWA process or separate WA process as discussed in sections process or separate WA process is run as discussed in sections 4.1.1.
4.1.1. 4.1.2. This is currently not possible with GMPLS routing 4.1.2. This is currently not possible with GMPLS routing extensions.
extensions.
In the routing extensions for GMPLS [RFC4202], requirements for In the routing extensions for GMPLS [RFC4202], requirements for
layer-specific TE attributes are discussed. The RWA problem for layer-specific TE attributes are discussed. The RWA problem for
optical networks without wavelength converters imposes an additional optical networks without wavelength converters imposes an additional
requirement for the lambda (or optical channel) layer: that of requirement for the lambda (or optical channel) layer: that of
knowing which specific wavelengths are in use. Note that current knowing which specific wavelengths are in use. Note that currentDWDM
dense WDM (DWDM) systems range from 16 channels to 128 channels with systems range from 16 channels to 128 channels with advanced
advanced laboratory systems with as many as 300 channels. Given these laboratory systems with as many as 300 channels. Given these channel
channel limitations and if we take the approach of a global limitations and if the approach of a global wavelength to label
wavelength to label mapping or furnishing the local mappings to the mapping or furnishing the local mappings to the PCEs is taken then
PCEs then representing the use of wavelengths via a simple bit-map is representing the use of wavelengths via a simple bit-map is feasible
feasible [WSON-Encode]. [WSON-Encode].
6.2.3. WSON Routing Information Summary 6.2.3. WSON Routing Information Summary
The following table summarizes the WSON information that could be The following table summarizes the WSON information that could be
conveyed via GMPLS routing and attempts to classify that information conveyed via GMPLS routing and attempts to classify that information
as to its static or dynamic nature and whether that information would as to its static or dynamic nature and whether that information would
tend to be associated with either a link or a node. tend to be associated with either a link or a node.
Information Static/Dynamic Node/Link Information Static/Dynamic Node/Link
------------------------------------------------------------------ ------------------------------------------------------------------
Connectivity matrix Static Node Connectivity matrix Static Node
Per port wavelength restrictions Static Node(1) Per port wavelength restrictions Static Node(1)
WDM link (fiber) lambda ranges Static Link WDM link (fiber) lambda ranges Static Link
WDM link channel spacing Static Link WDM link channel spacing Static Link
Laser Transmitter range Static Link(2) Optical transmitter range Static
Link(2)
Wavelength conversion capabilities Static(3) Node Wavelength conversion capabilities Static(3) Node
Maximum bandwidth per Wavelength Static Link Maximum bandwidth per wavelength Static Link
Wavelength Availability Dynamic(4) Link Wavelength availability Dynamic(4) Link
Signal Compatibility & Processing Static/Dynamic Node Signal compatibility and processing Static/Dynamic Node
Notes: Notes:
1. These are the per port wavelength restrictions of an optical 1. These are the per port wavelength restrictions of an optical
device such as a ROADM and are independent of any optical device such as a ROADM and are independent of any optical
constraints imposed by a fiber link. constraints imposed by a fiber link.
2. This could also be viewed as a node capability. 2. This could also be viewed as a node capability.
3. This could be dynamic in the case of a limited pool of converters 3. This could be dynamic in the case of a limited pool of converters
where the number available can change with connection where the number available can change with connection
establishment. Note we may want to include regeneration establishment. Note it may be desirable to include regeneration
capabilities here since OEO converters are also regenerators. capabilities here since OEO converters are also regenerators.
4. Not necessarily needed in the case of distributed wavelength 4. Not necessarily needed in the case of distributed wavelength
assignment via signaling. assignment via signaling.
While the full complement of the information from the previous table While the full complement of the information from the previous table
is needed in the Combined RWA and the separate Routing and WA is needed in the Combined RWA and the separate Routing and WA
architectures, in the case of Routing + distribute WA via signaling architectures, in the case of Routing + distributed WA via signaling
we only need the following information: only the following information is needed:
Information Static/Dynamic Node/Link Information Static/Dynamic Node/Link
------------------------------------------------------------------ ------------------------------------------------------------------
Connectivity matrix Static Node Connectivity matrix Static Node
Wavelength conversion capabilities Static(3) Node Wavelength conversion capabilities Static(3) Node
Information models and compact encodings for this information is Information models and compact encodings for this information is
provided in [WSON-Info], [Gen-Encode] and [WSON-Encode]. provided in [WSON-Info], [Gen-Encode] and [WSON-Encode].
6.3. Optical Path Computation and Implications for PCE 6.3. Optical Path Computation and Implications for PCE
As previously noted the RWA problem can be computationally intensive As previously noted the RWA problem can be computationally intensive.
[HZang00]. Such computationally intensive path computations and Such computationally intensive path computations and optimizations
optimizations were part of the impetus for the PCE (path computation were part of the impetus for the PCE architecture [RFC4655].
element) architecture.
As the PCEP defines the procedures necessary to support both The Path Computation Element Protocol (PCEP) defines the procedures
sequential [RFC5440] and global concurrent path computations necessary to support both sequential [RFC5440] and global concurrent
[RFC5557], PCE is well positioned to support WSON-enabled RWA path computations (PCE-GCO) [RFC5557], PCE is well positioned to
computation with some protocol enhancement. support WSON-enabled RWA computation with some protocol enhancement.
Implications for PCE generally fall into two main categories: (a) Implications for PCE generally fall into two main categories: (a)
lightpath constraints and characteristics, (b) computation lightpath constraints and characteristics, (b) computation
architectures. architectures.
6.3.1. Lightpath Constraints and Characteristics 6.3.1. Lightpath Constraints and Characteristics
For the varying degrees of optimization that may be encountered in a For the varying degrees of optimization that may be encountered in a
network the following models of bulk and sequential lightpath network the following models of bulk and sequential lightpath
requests are encountered: requests are encountered:
o Batch optimization, multiple lightpaths requested at one time. o Batch optimization, multiple lightpaths requested at one time
(PCE-GCO).
o Lightpath(s) and backup lightpath(s) requested at one time. o Lightpath(s) and backup lightpath(s) requested at one time (PCEP).
o Single lightpath requested at a time. o Single lightpath requested at a time (PCEP).
PCEP and PCE-GCO can be readily enhanced to support all of the PCEP and PCE-GCO can be readily enhanced to support all of the
potential models of RWA computation. potential models of RWA computation.
Lightpath constraints include: Lightpath constraints include:
o Bidirectional Assignment of wavelengths o Bidirectional Assignment of wavelengths.
o Possible simultaneous assignment of wavelength to primary and o Possible simultaneous assignment of wavelength to primary and
backup paths. backup paths.
o Tuning range constraint on optical transmitter. o Tuning range constraint on optical transmitter.
6.3.2. Electro-Optical Element Signal Compatibility 6.3.2. Electro-Optical Element Signal Compatibility
When requesting a path computation to PCE, the PCC should be able to When requesting a path computation to PCE, the PCC should be able to
indicate the following: indicate the following:
o The GPID type of an LSP o The G-PID type of an LSP.
o The signal attributes at the transmitter (at the source): (i) o The signal attributes at the transmitter (at the source): (i)
modulation type; (ii) FEC type modulation type; (ii) FEC type.
o The signal attributes at the receiver (at the sink): (i) o The signal attributes at the receiver (at the sink): (i)
modulation type; (ii) FEC type modulation type; (ii) FEC type.
The PCE should be able to respond to the PCC with the following: The PCE should be able to respond to the PCC with the following:
o The conformity of the requested optical characteristics associated o The conformity of the requested optical characteristics associated
with the resulting LSP with the source, sink and NE along the LSP. with the resulting LSP with the source, sink and NE along the LSP.
o Additional LSP attributes modified along the path (e.g., o Additional LSP attributes modified along the path (e.g.,
modulation format change, etc.) modulation format change, etc.).
6.3.3. Discovery of RWA Capable PCEs 6.3.3. Discovery of RWA Capable PCEs
The algorithms and network information needed for solving the RWA are The algorithms and network information needed for solving the RWA are
somewhat specialized and computationally intensive hence not all PCEs somewhat specialized and computationally intensive hence not all PCEs
within a domain would necessarily need or want this capability. within a domain would necessarily need or want this capability.
Hence, it would be useful via the mechanisms being established for Hence, it would be useful via the mechanisms being established for
PCE discovery [RFC5088] to indicate that a PCE has the ability to PCE discovery [RFC5088] to indicate that a PCE has the ability to
deal with the RWA problem. Reference [RFC5088] indicates that a sub- deal with the RWA problem. Reference [RFC5088] indicates that a sub-
TLV could be allocated for this purpose. TLV could be allocated for this purpose.
skipping to change at page 49, line 18 skipping to change at page 48, line 18
[RFC3471] Berger, L., "Generalized Multi-Protocol Label Switching [RFC3471] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Functional Description", RFC 3471, (GMPLS) Signaling Functional Description", RFC 3471,
January 2003. January 2003.
[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label [RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol- Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 3473, Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
January 2003. January 2003.
[RFC3945] Mannie, E. "Generalized Multi-Protocol Label Switching
(GMPLS) Architecture", RFC 3945, October 2004.
[RFC4202] Kompella, K. and Y. Rekhter, "Routing Extensions in Support [RFC4202] Kompella, K. and Y. Rekhter, "Routing Extensions in Support
of Generalized Multi-Protocol Label Switching (GMPLS)", RFC of Generalized Multi-Protocol Label Switching (GMPLS)", RFC
4202, October 2005. 4202, October 2005.
[RFC4328] Papadimitriou, D., "Generalized Multi-Protocol Label [RFC4328] Papadimitriou, D., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Extensions for G.709 Optical Switching (GMPLS) Signaling Extensions for G.709 Optical
Transport Networks Control", RFC 4328, January 2006. Transport Networks Control", RFC 4328, January 2006.
[G.694.1] ITU-T Recommendation G.694.1, "Spectral grids for WDM [G.694.1] ITU-T Recommendation G.694.1, "Spectral grids for WDM
applications: DWDM frequency grid", June, 2002. applications: DWDM frequency grid", June, 2002.
skipping to change at page 50, line 37 skipping to change at page 49, line 41
(WSON) with Impairments", draft-ietf-ccamp-wson- (WSON) with Impairments", draft-ietf-ccamp-wson-
impairments, work in progress. impairments, work in progress.
[WSON-Info] Y. Lee, G. Bernstein, D. Li, W. Imajuku, "Routing and [WSON-Info] Y. Lee, G. Bernstein, D. Li, W. Imajuku, "Routing and
Wavelength Assignment Information for Wavelength Switched Wavelength Assignment Information for Wavelength Switched
Optical Networks", draft-bernstein-ccamp-wson-info, work in Optical Networks", draft-bernstein-ccamp-wson-info, work in
progress progress
10.2. Informative References 10.2. Informative References
[HZang00] H. Zang, J. Jue and B. Mukherjeee, "A review of routing and [RFC4655] Farrel, A., Vasseur, JP., and Ash, J., "A Path Computation
wavelength assignment approaches for wavelength-routed Element (PCE)-Based Architecture ", RFC 4655, August 2006.
optical WDM networks", Optical Networks Magazine, January
2000.
[Coldren04] Larry A. Coldren, G. A. Fish, Y. Akulova, J. S.
Barton, L. Johansson and C. W. Coldren, "Tunable
Seiconductor Lasers: A Tutorial", Journal of Lightwave
Technology, vol. 22, no. 1, pp. 193-202, January 2004.
[Chu03] Xiaowen Chu, Bo Li and Chlamtac I, "Wavelength converter
placement under different RWA algorithms in wavelength-
routed all-optical networks", IEEE Transactions on
Communications, vol. 51, no. 4, pp. 607-617, April 2003.
[Buus06] Jens Buus EJM, "Tunable Lasers in Optical Networks",
Journal of Lightware Technology, vol. 24, no. 1, pp. 5-11,
January 2006.
[Basch06] E. Bert Bash, Roman Egorov, Steven Gringeri and Stuart
Elby, "Architectural Tradeoffs for Reconfigurable Dense
Wavelength-Division Multiplexing Systems", IEEE Journal of
Selected Topics in Quantum Electronics, vol. 12, no. 4, pp.
615-626, July/August 2006.
[Otani] T. Otani, H. Guo, K. Miyazaki, D. Caviglia, "Generalized [Otani] T. Otani, H. Guo, K. Miyazaki, D. Caviglia, "Generalized
Labels of Lambda-Switching Capable Label Switching Routers Labels of Lambda-Switching Capable Label Switching Routers
(LSR)", work in progress: draft-otani-ccamp-gmpls-g-694- (LSR)", work in progress: draft-otani-ccamp-gmpls-g-694-
lambda-labels, work in progress. lambda-labels, work in progress.
[Winzer06] Peter J. Winzer and Rene-Jean Essiambre, "Advanced
Optical Modulation Formats", Proceedings of the IEEE, vol.
94, no. 5, pp. 952-985, May 2006.
[G.652] ITU-T Recommendation G.652, Characteristics of a single-mode [G.652] ITU-T Recommendation G.652, Characteristics of a single-mode
optical fibre and cable, June 2005. optical fibre and cable, June 2005.
[G.653] ITU-T Recommendation G.653, Characteristics of a dispersion- [G.653] ITU-T Recommendation G.653, Characteristics of a dispersion-
shifted single-mode optical fibre and cable, December 2006. shifted single-mode optical fibre and cable, December 2006.
[G.654] ITU-T Recommendation G.654, Characteristics of a cut-off [G.654] ITU-T Recommendation G.654, Characteristics of a cut-off
shifted single-mode optical fibre and cable, December 2006. shifted single-mode optical fibre and cable, December 2006.
[G.655] ITU-T Recommendation G.655, Characteristics of a non-zero [G.655] ITU-T Recommendation G.655, Characteristics of a non-zero
skipping to change at page 52, line 19 skipping to change at page 51, line 5
engineering considerations, February 2006. engineering considerations, February 2006.
[G.Sup43] ITU-T Series G Supplement 43, Transport of IEEE 10G base-R [G.Sup43] ITU-T Series G Supplement 43, Transport of IEEE 10G base-R
in optical transport networks (OTN), November 2006. in optical transport networks (OTN), November 2006.
[Imajuku] W. Imajuku, Y. Sone, I. Nishioka, S. Seno, "Routing [Imajuku] W. Imajuku, Y. Sone, I. Nishioka, S. Seno, "Routing
Extensions to Support Network Elements with Switching Extensions to Support Network Elements with Switching
Constraint", work in progress: draft-imajuku-ccamp-rtg- Constraint", work in progress: draft-imajuku-ccamp-rtg-
switching-constraint. switching-constraint.
[Ozdaglar03] Asuman E. Ozdaglar and Dimitri P. Bertsekas, "Routing 11. Contributors
and wavelength assignment in optical networks," IEEE/ACM
Transactions on Networking, vol. 11, 2003, pp. 259 -272.
[Sambo09] N. Sambo, N. Andriolli, A. Giorgetti, L. Valcarenghi, I.
Cerutti, P. Castoldi, and F. Cugini, "GMPLS-controlled
dynamic translucent optical networks," Network, IEEE, vol.
23, 2009, pp. 34-40.
[Sen08] A. Sen, S. Murthy, and S. Bandyopadhyay, "On Sparse Placement
of Regenerator Nodes in Translucent Optical Network,"
Global Telecommunications Conference, 2008. IEEE GLOBECOM
2008. IEEE, 2008, pp. 1-6.
[Trans07] Gangxiang Shen and Rodney S. Tucker, "Translucent optical
networks: the way forward [Topics in Optical
Communications]," Communications Magazine, IEEE, vol. 45,
2007, pp. 48-54.
[Yang05] Xi Yang and B. Ramamurthy, "Dynamic routing in translucent
WDM optical networks: the intradomain case," Lightwave
Technology, Journal of, vol. 23, 2005, pp. 955-971.
11. Contributors
Snigdho Bardalai Snigdho Bardalai
Fujitsu Fujitsu
Email: Snigdho.Bardalai@us.fujitsu.com Email: Snigdho.Bardalai@us.fujitsu.com
Diego Caviglia Diego Caviglia
Ericsson Ericsson
Via A. Negrone 1/A 16153 Via A. Negrone 1/A 16153
Genoa Italy Genoa Italy
Phone: +39 010 600 3736 Phone: +39 010 600 3736
Email: diego.caviglia@(marconi.com, ericsson.com) Email: diego.caviglia@(marconi.com, ericsson.com)
skipping to change at page 53, line 22 skipping to change at page 51, line 23
Ericsson Ericsson
Via A. Negrone 1/A 16153 Via A. Negrone 1/A 16153
Genoa Italy Genoa Italy
Phone: +39 010 600 3736 Phone: +39 010 600 3736
Email: diego.caviglia@(marconi.com, ericsson.com) Email: diego.caviglia@(marconi.com, ericsson.com)
Daniel King Daniel King
Old Dog Consulting Old Dog Consulting
UK UK
Aria Networks
Email: daniel@olddog.co.uk Email: daniel@olddog.co.uk
Itaru Nishioka Itaru Nishioka
NEC Corp. NEC Corp.
1753 Simonumabe, Nakahara-ku, Kawasaki, Kanagawa 211-8666 1753 Simonumabe, Nakahara-ku
Kawasaki, Kanagawa 211-8666
Japan Japan
Phone: +81 44 396 3287 Phone: +81 44 396 3287
Email: i-nishioka@cb.jp.nec.com Email: i-nishioka@cb.jp.nec.com
Lyndon Ong Lyndon Ong
Ciena Ciena
Email: Lyong@Ciena.com Email: Lyong@Ciena.com
Pierre Peloso Pierre Peloso
Alcatel-Lucent Alcatel-Lucent
Route de Villejust - 91620 Nozay - France Route de Villejust, 91620 Nozay
France
Email: pierre.peloso@alcatel-lucent.fr Email: pierre.peloso@alcatel-lucent.fr
Jonathan Sadler Jonathan Sadler
Tellabs Tellabs
Email: Jonathan.Sadler@tellabs.com Email: Jonathan.Sadler@tellabs.com
Dirk Schroetter Dirk Schroetter
Cisco Cisco
Email: dschroet@cisco.com Email: dschroet@cisco.com
skipping to change at line 2406 skipping to change at page 53, line 36
IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL
WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY
WARRANTY THAT THE USE OF THE INFORMATION THEREIN WILL NOT INFRINGE WARRANTY THAT THE USE OF THE INFORMATION THEREIN WILL NOT INFRINGE
ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS
FOR A PARTICULAR PURPOSE. FOR A PARTICULAR PURPOSE.
Acknowledgment Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
12. Appendix A Revision History
This appendix to be removed before publication as an RFC.
A.1 Changes from 00
o Added new first level section on modeling examples and control
plane use cases.
o Added new third level section on wavelength converter pool
modeling
o Editorial clean up of English and updated references.
A.2 Changes from 01
Fixed error in wavelength converter pool example.
A.3 Changes from 02
Updated the abstract to emphasize the focus of this draft and
differentiate it from WSON impairment [WSON-Imp] and WSON
compatibility [WSON-Compat] drafts.
Added references to [WSON-Imp] and [WSON-Compat].
Updated the introduction to explain the relationship between this
document and the [WSON-Imp] and [WSON-Compat] documents.
In section 3.1 removed discussion of optical impairments in fibers.
Merged section 3.2.2 and section 3.2.3. Deferred much of the
discussion of signal types and standards to [WSON-Compat].
In section 3.4 on Wavelength converters removed paragraphs dealing
with signal compatibility discussion as this is addressed in [WSON-
Compat].
In section 6.1 removed discussion of signaling extensions to deal
with different WSON signal types. This is deferred to [WSON-Compat].
In section 6 removed discussion of "Need for Wavelength Specific
Maximum Bandwidth Information".
In section 6 removed discussion of "Relationship to link bundling and
layering".
In section 6 removed discussion of "Computation Architecture
Implications" as this material was redundant with text that occurs
earlier in the document.
In section 6 removed discussion of "Scaling Implications" as this
material was redundant with text that occurs earlier in the document.
A.4 Changes from 03
In Section 3.3.1 added 4-degree ROADM example and its connectivity
matrix.
A.5 Changes from 04
Added and enhanced sections on signal type and network element
compatibility.
Merged section 3.2.1 into section 3.2.
Created new section 3.3 on Optical signals with material from [WSON-
Compat].
Created new section 3.5 on Electro-Optical systems with material from
[WSON-Compat].
Created new section 3.7 on Characterizing Electro-Optical Network
Elements with material from [WSON-Compat].
Created new section 5.5 on Electro-Optical Networking Scenarios with
material from [WSON-Compat].
Created new section 6.1.2 on WSON Signals and Network Element
Processing with material from [WSON-Compat].
Created new section 6.3.2. Electro-Optical Related PCEP Extensions
with material from [WSON-Compat].
A.6 Changes from 05
Removal of Section 1.2; Removal of section on lightpath temporal
characteristics; Removal of details on wavelength assignment
algorithms; Removal of redundant summary in section 6.
 End of changes. 272 change blocks. 
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