draft-ietf-ccamp-rwa-wson-framework-02.txt   draft-ietf-ccamp-rwa-wson-framework-03.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: September 2009 Grotto Networking Expires: March 2010 Grotto Networking
Wataru Imajuku Wataru Imajuku
NTT NTT
March 4, 2009 September 8, 2009
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-02.txt draft-ietf-ccamp-rwa-wson-framework-03.txt
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Abstract Abstract
This memo provides a framework for applying Generalized Multi- This memo provides a framework for applying Generalized Multi-
Protocol Label Switching (GMPLS) and the Path Computation Element Protocol Label Switching (GMPLS) and the Path Computation Element
(PCE) architecture to the control of wavelength switched optical (PCE) architecture to the control of wavelength switched optical
networks (WSON). In particular we provide control plane models for networks (WSON). In particular we provide control plane models for
key wavelength switched optical network subsystems and processes. The key wavelength switched optical network subsystems and processes. The
subsystems include wavelength division multiplexed links, tunable subsystems include wavelength division multiplexed links, tunable
laser transmitters, reconfigurable optical add/drop multiplexers laser transmitters, reconfigurable optical add/drop multiplexers
(ROADM) and wavelength converters. (ROADM) and wavelength converters.
Lightpath provisioning, in general, requires the routing and Lightpath provisioning, in general, requires the routing and
wavelength assignment (RWA) process. This process is reviewed and the wavelength assignment (RWA) process. This process is reviewed and the
information requirements, both static and dynamic for this process information requirements, both static and dynamic for this process
are presented, along with alternative implementation scenarios that are presented, along with alternative implementation architectures
could be realized via GMPLS/PCE and/or extended GMPLS/PCE protocols. that could be realized via various combinations of extended GMPLS and
This memo does NOT address optical impairments in any depth and PCE protocols.
focuses on topological elements and path selection constraints that
are common across different WSON environments. It is expected that a This memo focuses on topological elements and path selection
variety of different techniques will be applied to optical constraints that are common across different WSON environments as
impairments depending on the type of WSON, such as access, metro or such it does not address optical impairments in any depth nor does it
long haul. address potential incompatibilities between some types of optical
signals and some types of network elements and links.
Table of Contents Table of Contents
1. Introduction...................................................4 1. Introduction...................................................4
1.1. Revision History..........................................5 1.1. Revision History..........................................4
1.1.1. Changes from 00......................................5 1.1.1. Changes from 00......................................4
1.1.2. Changes from 01......................................5 1.1.2. Changes from 01......................................5
2. Terminology....................................................5 1.1.3. Changes from 02......................................5
3. Wavelength Switched Optical Networks...........................6 1.2. Related Documents ........................................5
3.1. WDM and CWDM Links........................................6 2. Terminology....................................................6
3.2. Optical Transmitters......................................8 3. Wavelength Switched Optical Networks...........................7
3.2.1. Lasers...............................................8 3.1. WDM and CWDM Links........................................7
3.2.2. Spectral Characteristics & Modulation Type...........9 3.2. Optical Transmitters......................................9
3.2.3. Signal Rates and Error Correction...................10 3.2.1. Lasers...............................................9
3.2.2. WSON Signal Parameters..............................10
3.3. ROADMs, OXCs, Splitters, Combiners and FOADMs............10 3.3. ROADMs, OXCs, Splitters, Combiners and FOADMs............10
3.3.1. Reconfigurable Add/Drop Multiplexers and OXCs.......11 3.3.1. Reconfigurable Add/Drop Multiplexers and OXCs.......10
3.3.2. Splitters...........................................13 3.3.2. Splitters...........................................12
3.3.3. Combiners...........................................13 3.3.3. Combiners...........................................13
3.3.4. Fixed Optical Add/Drop Multiplexers.................13 3.3.4. Fixed Optical Add/Drop Multiplexers.................13
3.4. Wavelength Converters....................................14 3.4. Wavelength Converters....................................14
3.4.1. Wavelength Converter Pool Modeling..................16 3.4.1. Wavelength Converter Pool Modeling..................15
4. Routing and Wavelength Assignment and the Control Plane.......20 4. Routing and Wavelength Assignment and the Control Plane.......19
4.1. Architectural Approaches to RWA..........................21 4.1. Architectural Approaches to RWA..........................20
4.1.1. Combined RWA (R&WA).................................22 4.1.1. Combined RWA (R&WA).................................21
4.1.2. Separated R and WA (R+WA)...........................22 4.1.2. Separated R and WA (R+WA)...........................21
4.1.3. Routing and Distributed WA (R+DWA)..................23 4.1.3. Routing and Distributed WA (R+DWA)..................22
4.2. Conveying information needed by RWA......................23 4.2. Conveying information needed by RWA......................22
4.3. Lightpath Temporal Characteristics.......................24 4.3. Lightpath Temporal Characteristics.......................23
5. Modeling Examples and Control Plane Use Cases.................25 5. Modeling Examples and Control Plane Use Cases.................24
5.1. Network Modeling for GMPLS/PCE Control...................25 5.1. Network Modeling for GMPLS/PCE Control...................24
5.1.1. Describing the WSON nodes...........................26 5.1.1. Describing the WSON nodes...........................25
5.1.2. Describing the links................................28 5.1.2. Describing the links................................27
5.2. RWA Path Computation and Establishment...................29 5.2. RWA Path Computation and Establishment...................28
5.3. Resource Optimization....................................30 5.3. Resource Optimization....................................29
5.4. Support for Rerouting....................................31 5.4. Support for Rerouting....................................30
6. GMPLS & PCE Implications......................................31 6. GMPLS & PCE Implications......................................30
6.1. Implications for GMPLS signaling.........................31 6.1. Implications for GMPLS signaling.........................30
6.1.1. Identifying Wavelengths and Signals.................32 6.1.1. Identifying Wavelengths and Signals.................31
6.1.2. Combined RWA/Separate Routing WA support............32 6.1.2. Combined RWA/Separate Routing WA support............31
6.1.3. Distributed Wavelength Assignment: Unidirectional, No 6.1.3. Distributed Wavelength Assignment: Unidirectional, No
Converters.................................................32 Converters.................................................31
6.1.4. Distributed Wavelength Assignment: Unidirectional, 6.1.4. Distributed Wavelength Assignment: Unidirectional,
Limited Converters.........................................33 Limited Converters.........................................32
6.1.5. Distributed Wavelength Assignment: Bidirectional, No 6.1.5. Distributed Wavelength Assignment: Bidirectional, No
Converters.................................................34 Converters.................................................32
6.2. Implications for GMPLS Routing...........................34 6.2. Implications for GMPLS Routing...........................33
6.2.1. Need for Wavelength-Specific Maximum Bandwidth 6.2.1. Wavelength-Specific Availability Information........33
Information................................................35 6.2.2. WSON Routing Information Summary....................34
6.2.2. Need for Wavelength-Specific Availability Information35 6.3. Optical Path Computation and Implications for PCE........35
6.2.3. Relationship to Link Bundling and Layering..........36 6.3.1. Lightpath Constraints and Characteristics...........35
6.2.4. WSON Routing Information Summary....................36 6.3.2. Discovery of RWA Capable PCEs.......................36
6.3. Optical Path Computation and Implications for PCE........37 6.4. Summary of Impacts by RWA Architecture...................36
6.3.1. Lightpath Constraints and Characteristics...........37 7. Security Considerations.......................................37
6.3.2. Computation Architecture Implications...............38 8. IANA Considerations...........................................38
6.3.3. Discovery of RWA Capable PCEs.......................38 9. Acknowledgments...............................................38
6.4. Scaling Implications.....................................39 10. References...................................................39
6.4.1. Routing.............................................39 10.1. Normative References....................................39
6.4.2. Signaling...........................................39 10.2. Informative References..................................40
6.4.3. Path computation....................................39 11. Contributors.................................................43
6.5. Summary of Impacts by RWA Architecture...................40 Author's Addresses...............................................43
7. Security Considerations.......................................41 Intellectual Property Statement..................................44
8. IANA Considerations...........................................41 Disclaimer of Validity...........................................45
9. Acknowledgments...............................................41
10. References...................................................42
10.1. Normative References....................................42
10.2. Informative References..................................43
11. Contributors.................................................46
Author's Addresses...............................................46
Intellectual Property Statement..................................47
Disclaimer of Validity...........................................48
1. Introduction 1. Introduction
From its beginning Generalized Multi-Protocol Label Switching (GMPLS)
was intended to control wavelength switched optical networks (WSON)
with the GMPLS architecture document [RFC3945] explicitly mentioning
both wavelength and waveband switching and equating wavelengths
(lambdas) with GMPLS labels. In addition a discussion of optical
impairments and other constraints on optical routing can be found in
[RFC4054]. However, optical technologies have advanced in ways that
make them significantly different from other circuit switched
technologies such as Time Division Multiplexing (TDM). Service
providers have already deployed many of these new optical
technologies such as ROADMs and tunable lasers and desire the same
automation and restoration capabilities that GMPLS has provided to
TDM and packet switched networks. Another important application of an
automated control plane such as GMPLS is the possibility to improve,
via recovery schemes, the availability of the network. One of the
key points of GMPLS based recovery schemes is the capability to
survive multiple failures while legacy protection mechanism such as
1+1 path protection can survive from a single failure. Moreover this
improved availability can be obtained using less network resources.
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.
This memo provides a framework for applying GMPLS and the Path This memo provides a framework for applying GMPLS and the Path
Computation Element (PCE) architecture to the control of WSONs. In Computation Element (PCE) architecture to the control of WSONs. In
particular we provide control plane models for key wavelength particular we provide control plane models for key wavelength
switched optical network subsystems and processes. The subsystems switched optical network subsystems and processes. The subsystems
include wavelength division multiplexed links, tunable laser include wavelength division multiplexed links, tunable laser
transmitters, reconfigurable optical add/drop multiplexers (ROADM) transmitters, reconfigurable optical add/drop multiplexers (ROADM)
and wavelength converters. and wavelength converters.
Lightpath provisioning, in general, requires the routing and Lightpath provisioning, in general, requires the routing and
wavelength assignment (RWA) process. This process is reviewed and the wavelength assignment (RWA) process. This process is reviewed and the
information requirements, both static and dynamic for this process information requirements, both static and dynamic for this process
are presented, along with alternative implementation architectures are presented, along with alternative implementation architectures
that could be realized via various combinations of extended GMPLS and that could be realized via various combinations of extended GMPLS and
PCE protocols. 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].
For the purposes of this document we assume that all signals used in
a WSON are compatible with all network elements and links within the
WSON. This can arise in practice for a number of reasons including:
(a) in some WSONs only one class of signal is used throughout the
network, or (b) only "relatively" transparent network elements are
utilized in the WSON. How the GMPLS control plane can deal with
situations where this assumption is not true (i.e., where not all of
the optical signals in the network are compatible with all network
elements and limited to processing only certain types of WSON
signals) is addressed in a separate draft [WSON-Compat].
1.1. Revision History 1.1. Revision History
1.1.1. Changes from 00 1.1.1. Changes from 00
o Added new first level section on modeling examples and control o Added new first level section on modeling examples and control
plane use cases. plane use cases.
o Added new third level section on wavelength converter pool o Added new third level section on wavelength converter pool
modeling modeling
o Editorial clean up of English and updated references. o Editorial clean up of English and updated references.
1.1.2. Changes from 01 1.1.2. Changes from 01
Fixed error in wavelength converter pool example. 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.
1.2. Related Documents
This framework document covers essential concepts and models for the
application and extension of the control plane to WSONs. The
following documents address specific aspects of WSONs and complement
this draft.
o [WSON-Info] This document provides an information model needed by
the routing and wavelength assignment (RWA) process in WSON.
o [WSON-Encode] This document provides efficient, protocol-agnostic
encodings for the information elements necessary to support the
routing and wavelength assignment (RWA) process in WSONs.
o [WSON-Imp] This document provides a framework for the support of
impairment aware Routing and Wavelength Assignment (RWA) in WSON.
o [WSON-Compat] This document provides an overview of signal
compatibility constraints associated with WSON network elements
including regenerators.
o [PCEP-RWA] This document provides application-specific
requirements for the Path Computation Element communication
Protocol (PCEP) for the support of RWA in WSON.
2. Terminology 2. Terminology
CWDM: Coarse Wavelength Division Multiplexing. CWDM: Coarse Wavelength Division Multiplexing.
DWDM: Dense Wavelength Division Multiplexing. DWDM: Dense Wavelength Division Multiplexing.
FOADM: Fixed Optical Add/Drop Multiplexer. FOADM: Fixed Optical Add/Drop Multiplexer.
OXC: Optical cross connect. A symmetric optical switching element in OXC: Optical cross connect. A symmetric optical switching element in
which a signal on any ingress port can reach any egress port. which a signal on any ingress port can reach any egress port.
skipping to change at page 6, line 23 skipping to change at page 7, line 23
and model some major subsystems of a WSON with an emphasis on those and model some major subsystems of a WSON with an emphasis on those
aspects that are of relevance to the control plane. In particular we aspects that are of relevance to the control plane. In particular we
look at WDM links, Optical Transmitters, ROADMs, and Wavelength look at WDM links, Optical Transmitters, ROADMs, and Wavelength
Converters. 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 from access networks, metro, long haul, and submarine
links to name a few. ITU-T and IEC standards exist for various types links to name a few. ITU-T standards exist for various types of
of fibers. For the purposes here we are concerned only with single fibers. For the purposes here we are concerned only with single mode
mode fibers (SMF). The following SMF fiber types are typically fibers (SMF). The following SMF fiber types are typically encountered
encountered in optical networks: 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 |
------------------------------------------------------------ ------------------------------------------------------------
These fiber types are differentiated by their optical impairment
characteristics such as attenuation, chromatic dispersion,
polarization mode dispersion, four wave mixing, etc. Since these
effects can be dependent upon wavelength, channel spacing and input
power level, the net effect for our modeling purposes here is to
restrict the range of wavelengths that can be used.
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
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 we can have a discontinuous
acceptable wavelength range for a particular link. Also some systems acceptable wavelength range for a particular link. Also some systems
will utilize more than one band. This is particularly true for coarse will utilize more than one band. This is particularly true for coarse
WDM (CWDM) systems. WDM (CWDM) systems.
[Editor's note: the previous text is primarily tutorial in nature and
maybe deleted or moved to an appendix in a future draft]
Current technology breaks up the bandwidth capacity of fibers into Current technology breaks up 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] 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] 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 allocated to
lambda switching. A label representation for these ITU-T grids is lambda switching. A label representation for these ITU-T grids is
given in [Otani] and allows a common vocabulary to be used in given in [Otani] and allows a common vocabulary to be used in
signaling lightpaths. Further, these ITU-T grid based labels can and signaling lightpaths. Further, these ITU-T grid based labels can also
also be used to describe WDM links, ROADM ports, and wavelength be used to describe WDM links, ROADM ports, and wavelength converters
converters for the purposes path selection. for the purposes path selection.
With a tremendous existing base of fiber many WDM links are designed With a tremendous existing base of fiber many WDM links are designed
to take advantage of particular fiber characteristics or to try to to take advantage of particular fiber characteristics or to try to
avoid undesirable properties. For example dispersion shifted SMF avoid undesirable properties. For example dispersion shifted SMF
[G.653] was originally designed for good long distance performance in [G.653] was originally designed for good long distance performance in
single channel systems, however putting WDM over this type of fiber single channel systems, however putting WDM over this type of fiber
requires much system engineering and a fairly limited range of requires much system engineering and a fairly limited range of
wavelengths. Hence for our basic, impairment unaware, modeling of a wavelengths. Hence for our basic, impairment unaware, modeling of a
WDM link we will need the following information: WDM link we will need the following information:
skipping to change at page 8, line 31 skipping to change at page 9, line 16
3.2.1. Lasers 3.2.1. Lasers
WDM optical systems make use of laser transmitters utilizing WDM optical systems make use of laser transmitters utilizing
different wavelengths (frequencies). Some laser transmitters were and different wavelengths (frequencies). Some laser transmitters were and
are manufactured for a specific wavelength of operation, that is, the are 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 laser transmitters are becoming
widely deployed in some systems [Coldren04], [Buus06]. This allows widely deployed in some systems [Coldren04], [Buus06]. This allows
flexibility in the wavelength used for optical transmission and aids flexibility in the wavelength used for optical transmission and aids
in the control of path selection. in path selection.
Fundamental modeling parameters from the control plane perspective Fundamental modeling parameters from the control plane perspective
optical transmitters are: optical transmitters are:
o Tunable: Is this transmitter tunable or fixed. o Tunable: Is this transmitter tunable or fixed.
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 laser can be tuned. With the fixed mapping of labels to
lambdas of [Otani] this can be expressed as a doublet (lambda1, lambdas of [Otani] this can be expressed as a doublet (lambda1,
lambda2) or (freq1, freq2) where lambda1 and lambda2 or freq1 and lambda2) or (freq1, freq2) where lambda1 and lambda2 or freq1 and
skipping to change at page 9, line 11 skipping to change at page 9, line 42
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 applicable for fast protection applications.
o Spectral Characteristics and stability: The spectral shape of the o Spectral Characteristics and stability: The spectral shape of the
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 finest channel spacing on which
the transmitter can be used. the transmitter can be used.
Note that ITU-T recommendations specify many other aspects of a Note that ITU-T recommendations specify many aspects of a laser
laser's such as spectral characteristics and stability. Many of these transmitter.. Many of these parameters, such as spectral
parameters are used in the design of WDM subsystems consisting of characteristics and stability, are used in the design of WDM
transmitters, WDM links and receivers however they do not furnish subsystems consisting of transmitters, WDM links and receivers
additional information that will influence label switched path (LSP) however they do not furnish additional information that will
provisioning in a properly designed system. influence label switched path (LSP) provisioning in a properly
designed system.
Also note that lasers transmitters as a component can degrade and Also note that lasers transmitters as a component can degrade and
fail over time. This presents the possibility of the failure of a LSP fail over time. This presents the possibility of the failure of a LSP
(lightpath) without either a node or link failure. Hence, additional (lightpath) without either a node or link failure. Hence, additional
mechanisms may be necessary to detect and differentiate this failure mechanisms may be necessary to detect and differentiate this failure
from the others, e.g., one doesn't not want to initiate mesh from the others, e.g., one doesn't not want to initiate mesh
restoration if the source transmitter has failed, since the laser restoration if the source transmitter has failed, since the laser
transmitter will still be failed on the alternate optical path. transmitter will still be failed on the alternate optical path.
3.2.2. Spectral Characteristics & Modulation Type 3.2.2. WSON Signal Parameters
Contrary to some marketing claims optical systems are not truly
"transparent" to the content of the signals that they carry. Each
lightpath will have spectral characteristics based on its content,
and the spacing of wavelengths in a WDM link will ultimately put
constraints on that spectrum.
For analog signals such as used in closed access television (CATV) or
"radio over fiber" links spectral characteristics are given in terms
of various bandwidth measures. However digital signals consist of our
main focus here and in the ITU-T G series optical specifications. In
this case the spectral characteristics can be more accurately
inferred from the modulation format and the bit rate.
Although Non-Return to Zero (NRZ) is currently the dominant form of
optical modulation, new modulation formats are being researched
[Winzer06] and deployed. With a choice in modulation formats we no
longer have a one to one relationship between digital bandwidth in
bytes or bits per second and the amount of optical spectrum (optical
bandwidth) consumed. To simplify the specification of optical signals
the ITU-T, in recommendation G.959.1, combined a rate bound and
modulation format designator [G.959.1]. For example, two of the
signal classes defined in [G.959.1] are:
Optical tributary signal class NRZ 1.25G:
"Applies to continuous digital signals with non-return to zero line
coding, from nominally 622 Mbit/s to nominally 1.25 Gbit/s. Optical
tributary signal class NRZ 1.25G includes a signal with STM-4 bit
rate according to ITU-T Rec. G.707/Y.1322." Note that Gigabit
Ethernet falls into this signaling class as well.
Optical tributary signal class RZ 40G:
"Applies to continuous digital signals with return to zero line
coding, from nominally 9.9 Gbit/s to nominally 43.02 Gbit/s.
Optical tributary signal class RZ 40G includes a signal with STM-
256 bit rate according to ITU-T Rec. G.707/Y.1322 and OTU3 bit rate
according to ITU-T Rec. G.709/Y.1331."
From a modeling perspective we have:
o Analog signals: bandwidth parameters, e.g., 3dB parameters and
similar.
o Digital signals: there are predefined modulation bit rate classes
that we can encode.
This information can be important in constraining route selection,
for example some signals may not be compatible with some links or
wavelength converters. In addition it lets the endpoints understand
if it can process the signal.
3.2.3. Signal Rates and Error Correction As pointed out in the introduction, for the purposes of this document
we assume that all optical signals used in a WSON are compatible with
all links, network elements, and receivers in that WSON. In [WSON-
Compat] we discuss how the GMPLS control plane can be extended to
deal with incompatibilities between signals and network elements.
Although, the spectral characteristics of a signal determine its Key WSON signal parameters include modulation type, bit rate and
basic compatibility with a WDM system, more information is generally forward error correction coding technique. Multiple modulation
needed for various processing activities such as regeneration and formats have been standardized [G.959.1] and many others are used
reception. Many digital signals such as Ethernet, G.709, and SDH have industry and discussed in the literature [Winzer06]. When signals
well defined encoding which includes forward error correction (FEC). with different modulation types are used in a WSON then it can be
However many subsystem vendors offer additional FEC options for a important to check these signals for compatibility with network
given signal type. The use of different FECs can lead to different elements such as regenerators, OEO switches, wavelength converters
overall signal rates. If the FEC and rate used is not compatible and receivers [WSON-Compat].
between the sender and receiver the signal can not be correctly
processed. Note that the rates of "standard" signals may be extended
to accommodate different payloads. For example there are
transmitters capable of directly mapping 10GE LAN-PHY traffic into
G.709 ODU2 frame with slightly higher clock rate [G.Sup43].
3.3. ROADMs, OXCs, Splitters, Combiners and FOADMs 3.3. ROADMs, OXCs, Splitters, Combiners and FOADMs
Definitions of various optical devices and their parameters can be Definitions of various optical devices and their parameters can be
found in [G.671], we only look at a subset of these and their non- found in [G.671], we only look at a subset of these and their non-
impairment related properties. impairment related properties.
3.3.1. Reconfigurable Add/Drop Multiplexers and OXCs 3.3.1. Reconfigurable Add/Drop Multiplexers and OXCs
Reconfigurable add/drop optical multiplexers (ROADM) have matured and Reconfigurable add/drop optical multiplexers (ROADM) have matured and
skipping to change at page 12, line 19 skipping to change at page 11, line 50
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 ingress ports 2-5 are add ports, egress ports 2-5 are drop
ports and ingress port #1 and egress port #1 are the line side (WDM) ports and ingress port #1 and egress 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
complement of the matrix will be very sparse, compact encodings and complement of the matrix will be very sparse, compact encodings and
usage including high degree ROADMs/OXCs are given in [WSON-Encode]. examples, including high degree ROADMs/OXCs, are given in [WSON-
Encode].
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. In the literature of optical switches and ROADMs the
following restrictions/terms are used: following restrictions/terms are used:
Colored port: An ingress or more typically an egress (drop) port Colored port: An ingress or more typically an egress (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 ingress or more typically an egress (drop) port
restricted to a single channel of arbitrary wavelength. restricted to a single channel of arbitrary wavelength.
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ports of a splitter would have the same wavelength restrictions. In ports of a splitter would have the same wavelength restrictions. In
addition we can describe a splitter by a connectivity matrix Amn as addition we can describe a splitter by a connectivity matrix Amn as
follows: follows:
Ingress Egress Port Ingress Egress 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
connectivity matrix but the fixed connectivity matrix of the device. (potential) connectivity matrix but the fixed connectivity matrix of
the device.
3.3.3. Combiners 3.3.3. Combiners
A optical combiner is somewhat the dual of a splitter in that it has A optical combiner is somewhat the dual of a splitter in that it has
a single multi-wavelength egress port and multiple ingress ports. a single multi-wavelength egress port and multiple ingress ports.
The contents of all the ingress ports are copied and combined to the The contents of all the ingress ports are copied and combined to the
single egress 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 egress port. The fixed connectivity matrix Amn for a combiner would
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--- ---
#1: 1 #1: 1
#2 1 #2 1
A = #3 1 A = #3 1
... 1 ... 1
#N 1 #N 1
3.3.4. Fixed Optical Add/Drop Multiplexers 3.3.4. 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
ingress wavelength in a preset way. In particular a particular ingress wavelength in a preset way. In particular a given wavelength
wavelength (or waveband) from a line side ingress port would be (or waveband) from a line side ingress port would be dropped to a
dropped to a particular "tributary" egress port. Depending on the fixed "tributary" egress port. Depending on the device's construction
device's fixed configuration that same wavelength may or may not be that same wavelength may or may not be "continued" to the line side
"continued" to the line side egress port ("drop and continue" egress port ("drop and continue" operation). Further there may exist
operation). Further there may exist tributary ingress ports ("add" tributary ingress ports ("add" ports) whose signals are combined with
ports) whose signals are combined with each other and "continued" each other and "continued" line side signals.
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 we need a
fixed connectivity matrix Amn as previously discussed and we need the fixed connectivity matrix Amn as previously discussed and we need the
precise wavelength restrictions for all ingress and egress ports. precise wavelength restrictions for all ingress and egress ports.
From the wavelength restrictions on the tributary egress ports (drop From the wavelength restrictions on the tributary egress ports (drop
ports) we can see what wavelengths have been dropped. From the ports) we can see what wavelengths have been dropped. From the
wavelength restrictions on the tributary ingress (add) ports we can wavelength restrictions on the tributary ingress (add) ports we can
see which wavelengths have been added to the line side egress port. see which wavelengths have been added to the line side egress port.
Finally from the added wavelength information and the line side Finally from the added wavelength information and the line side
egress wavelength restrictions we can infer which wavelengths have egress wavelength restrictions we can infer which wavelengths have
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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 tunable
laser transmitters. In this case there are plenty of converters to laser transmitters. In this case there are plenty of converters to
go around since we can think of each tunable output laser go around since we can think of each tunable output laser
transmitter on an OEO switch as a potential wavelength converter. transmitter on an OEO switch 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 we
may have a limited amount of conversion available. Conversion could may have a limited pool of wavelength converters available.
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 we may have 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 contexts a tentative modeling approach for Based on the above contexts a modeling approach for wavelength
wavelength converters could be as follows: converters could be 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 ingress 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 we can associate them with ingress 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. [TBD: for independent or dependent upon the ingress wavelength.
those that depend on ingress wavelength can we have a standard
formula? Also note that this type of converter introduces
additional optical impairments.]
4. Wavelength converters that are O-E-O based will have a restriction
based on the modulation format and transmission speed.
Note that since O-E-O wavelength converters also serve as
regenerators we can include regenerators in our model of wavelength
converters. O-E-O Regenerators come in three general types known as
1R, 2R, and 3R regenerators. 1R regenerators re-amplify the signal to
combat attenuation, 2R regenerators reshape as well as amplify the
signal, 3R regenerators amplify, reshape and retime the signal. As we
go from 1R to 3R regenerators the signal is ''cleaned up'' better but
at the same time the regeneration process becomes more dependent on
the signal characteristics such as format and rate.
In WSONs where wavelength converters are sparse we may actually see a In WSONs where wavelength converters are sparse we may actually see a
light path appear to loop or ''backtrack'' upon itself in order to light path appear to loop or "backtrack" upon itself in order to
reach a wavelength converter prior to continuing on to its reach a wavelength converter prior to continuing on to its
destination. The lambda used on the "detour" out to the wavelength destination. The lambda used on the "detour" out to the wavelength
converter would be different from that coming back from the "detour" converter would be different from that coming back from the "detour"
to 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
o Equivalent regeneration level (1R, 2R, 3R)
o Signal restrictions if a 2R or 3R regeneration: formats and rates
[FFS: Model for an all optical wavelength converter]
3.4.1. Wavelength Converter Pool Modeling 3.4.1. 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 we need 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 ingress wavelength on a particular ingress
port to a desired egress wavelength on a particular egress port. port to a desired egress wavelength on a particular egress 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 we can use a similar technique as used to
model ROADMs and optical switches, i.e., a matrices to indicate model ROADMs and optical switches, i.e., matrices to indicate
possible connectivity along with wavelength constraints for possible connectivity along with wavelength constraints for
links/ports. Since wavelength converters are considered a scarce links/ports. Since wavelength converters are considered a scarce
resource we will also want our model to include as a minimum the resource we will also want our model to include as a minimum the
usage state of individual wavelength converters in the pool. Models usage state of individual wavelength converters in the pool.
that incorporate more state to further reveal blocking conditions on
ingress or egress to particular converters are for further study.
We utilize a three stage model as shown schematically in Figure 2. In We utilize a three stage model as shown schematically in Figure 2. In
this model we assume N ingress ports (fibers), P wavelength this model we assume N ingress ports (fibers), P wavelength
converters, and M egress ports (fibers). Since not all ingress ports converters, and M egress ports (fibers). Since not all ingress ports
can necessarily reach the converter pool, the model starts with a can necessarily reach the converter pool, the model starts with a
wavelength pool ingress matrix WI(i,p) = {0,1} whether ingress port i wavelength pool ingress matrix WI(i,p) = {0,1} whether ingress port i
can reach potentially reach wavelength converter p. 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 we have a set
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switched cases in that the labels, in this case wavelengths switched cases in that the labels, in this case wavelengths
(lambdas), have only local significance. That is, a wavelength- (lambdas), have only local significance. That is, a wavelength-
convertible network with full wavelength-conversion capability at convertible network with full wavelength-conversion capability at
each node is equivalent to a circuit-switched TDM network with full each node is equivalent to a circuit-switched TDM network with full
time slot interchange capability; thus, the routing problem needs to time slot interchange capability; thus, the routing problem needs to
be addressed only at the level of the traffic engineered (TE) link be addressed only at the level of the traffic engineered (TE) link
choice, and wavelength assignment can be resolved locally by the choice, and wavelength assignment can be resolved locally by the
switches on a hop-by-hop basis. 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 channel - OCh -) needs a wavelength converters, a light path (optical signal) needs a route
route from source to destination and must pick a single wavelength from source to destination and must pick a single wavelength that can
that can be used along that path without "colliding" with the be used along that path without "colliding" with the wavelength used
wavelength used by any other light path that may share an optical by any other light path that may share an optical fiber. This is
fiber. This is sometimes referred to as a "wavelength continuity sometimes referred to as a "wavelength continuity constraint". To
constraint". To ease up on this constraint while keeping network ease up on this constraint while keeping network costs in check a
costs in check a limited number of wavelength converters maybe limited number of wavelength converters may be introduced at key
introduce at key points in the network [Chu03]. 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 Routing and Wavelength Assignment (RWA)
problem [HZang00]. The "hardness" of this problem is well documented. problem [HZang00]. The "hardness" of this problem is well documented.
There, however, exist a number of reasonable approximate methods for There, however, exist a number of reasonable approximate methods for
its solution [HZang00]. 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 paths
source and destination, the networks topology, the locations and source and destination, the network's 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 choice of specific RWA algorithm is out of the
scope for this document. However there are a number of different scope for this document. However there are a number of different
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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
of these architectural approaches over another generally impacts the of these architectural approaches over another generally impacts the
demands placed on the various control plane protocols. demands placed on the various control plane protocols.
4.1.1. Combined RWA (R&WA) 4.1.1. Combined RWA (R&WA)
In this case, a unique entity is in charge of performing routing and In this case, a unique entity is in charge of performing routing and
wavelength assignment. This choice assumes that computational entity wavelength assignment. This approach relies on a sufficient knowledge
has sufficient WSON network link/nodal information and topology to be
able to compute RWA. This solution 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 knowledge has to be accessible to the entity nodes capabilities. This solution is compatible with most known RWA
performing the routing and wavelength assignment. algorithms, and in particular those concerned with network
optimization. On the other hand, this solution requires up-to-date
This solution is compatible with most known RWA algorithms, and in and detailed network information.
particular those concerned with network optimization. On the other
hand, this solution requires up-to-date and detailed network
information dissemination.
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 hence owns the o In a separate Path Computation Element (PCE) which hence owns the
complete and updated knowledge of network state and provides path complete and updated knowledge of network state and provides path
computation services to node. computation services to node.
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
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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 [Ozdaglar03]. Hence although there is no guarantee
that the selected final route and wavelength offers the optimal that the selected final route and wavelength offers the optimal
solution by allowing multiple routes to pass to the wavelength solution, by allowing multiple routes to pass to the wavelength
selection process reasonable optimization can be performed. selection process 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 on 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
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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.
An alternative to a global network map of labels to wavelengths would
be to use LMP to assign the map for each link then convey that
information to any path computation entities, e.g., label switch
routers or stand alone PCEs. The local label map approach will
require the label-set contents in the RSVP-TE Path message to be
translated every time the map changes between an incoming link and
the outgoing link.
In the future, it maybe worthwhile to define traffic parameters for
lambda LSPs that include a signal type field that includes modulation
format/rate information. This is similar to what was done in
reference [RFC4606] for SONET/SDH signal types.
6.1.2. Combined RWA/Separate Routing WA support 6.1.2. 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.
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4. Least Loaded: the available wavelength set and information 4. Least Loaded: the available wavelength set and information
concerning the wavelength dependent loading for each link (this concerning the wavelength dependent loading for each link (this
applies to multi-fiber links). This could be obtained via global applies to multi-fiber links). This could be obtained via global
information or via supplemental information passed via the information or via supplemental information passed via the
signaling protocol. signaling protocol.
In case (3) above the global information needed by the wavelength In case (3) above the global information needed by the wavelength
assignment could be derived from suitably enhanced GMPLS routing. assignment could be derived from suitably enhanced GMPLS routing.
Note however this information need not be accurate enough for Note however this information need not be accurate enough for
combined RWA computation. Currently, GMPLS signaling does not provide combined RWA computation. GMPLS signaling does not provide a way to
a way to indicate that a particular wavelength assignment algorithm indicate that a particular wavelength assignment algorithm should be
should be used. used.
6.1.4. Distributed Wavelength Assignment: Unidirectional, Limited 6.1.4. Distributed Wavelength Assignment: Unidirectional, Limited
Converters Converters
The previous outlined the case with no wavelength converters. In the The previous outlined the case with no wavelength converters. In the
case of wavelength converters, nodes with wavelength converters would case of wavelength converters, nodes with wavelength converters would
need to make the decision as to whether to perform conversion. One need to make the decision as to whether to perform conversion. One
indicator for this would be that the set of available wavelengths indicator for this would be that the set of available wavelengths
which is obtained via the intersection of the incoming label set and which is obtained via the intersection of the incoming label set and
the egress links available wavelengths is either null or deemed too the egress links available wavelengths is either null or deemed too
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1. WDM Link properties (allowed wavelengths). 1. WDM Link properties (allowed wavelengths).
2. Laser Transmitters (wavelength range). 2. Laser 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).
In most cases we should be able to combine items (1) and (2) into the This information is modeled in detail in [WSON-Info] and a compact
information in item (3). Except for the number of wavelength encoding is given in [WSON-Encode].
converters that are available in a shared pool, and the previous
information is fairly static. In the next two sections we discuss
dynamic available link bandwidth information.
6.2.1. Need for Wavelength-Specific Maximum Bandwidth Information
Difficulties are encountered when trying to use the bandwidth
accounting methods of [RFC4202] and [RFC3630] to describe the
availability of wavelengths on a WDM link. The current RFCs give
three link resource measures: Maximum Bandwidth, Maximum Reservable
Bandwidth, and Unreserved Bandwidth. Although these can be used to
describe a WDM span they do not provide the fundamental information
needed for RWA. We are not given the maximum bandwidth per wavelength
for the span. If we did then we could use the aforementioned measures
to tell us the maximum wavelength count and the number of available
wavelengths.
For example, suppose we have a 32 channel WDM span, and that the
system in general supports ITU-T NRZ signals up to NRZ 10Gbps.
Further suppose that the first 20 channels are carrying 1Gbps
Ethernet, then the maximum bandwidth would be 320Gbps and the maximum
reservable bandwidth would be 120Gbps (12 wavelengths).
Alternatively, consider the case where the first 8 channels are
carrying 2.5Gbps SDH STM-16 channels, then the maximum bandwidth
would still be 320Gbps and the maximum reservable bandwidth would be
240Gbps (24 wavelengths).
Such information would be useful in the routing with distributed WA
approach of section 4.1.3.
6.2.2. Need for Wavelength-Specific Availability Information 6.2.1. Wavelength-Specific Availability Information
Even if we know the number of available wavelengths on a link, we For wavelength assignment we need to know which specific wavelengths
actually need to know which specific wavelengths are available and are available and which are occupied if we are going to run a
which are occupied if we are going to run a combined RWA process or combined RWA process or separate WA process as discussed in sections
separate WA process as discussed in sections 4.1.1. 4.1.2. This is 4.1.1. 4.1.2. This is currently not possible with GMPLS routing
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 current
dense WDM (DWDM) systems range from 16 channels to 128 channels with dense WDM (DWDM) systems range from 16 channels to 128 channels with
advanced laboratory systems with as many as 300 channels. Given these advanced laboratory systems with as many as 300 channels. Given these
channel limitations and if we take the approach of a global channel limitations and if we take the approach of a global
wavelength to label mapping or furnishing the local mappings to the wavelength to label mapping or furnishing the local mappings to the
PCEs then representing the use of wavelengths via a simple bit-map is PCEs then representing the use of wavelengths via a simple bit-map is
feasible. feasible [WSON-Encode].
6.2.3. Relationship to Link Bundling and Layering
When dealing with static DWDM systems, particularly from a SONET/SDH
or G.709 digital wrapper layer, each lambda looks like a separate
link. Typically a bunch of unnumbered links, as supported in GMPLS
routing extensions [RFC4202], would be used to describe a static DWDM
system. In addition these links can be bundled into a TE link
([RFC4202], [RFC4201]) for more efficient dissemination of resource
information. However, in the case discussed here we want to control a
dynamic WDM layer and must deal with wavelengths as labels and not
just as links or component links from the perspective of an upper
(client) layer. In addition, a typical point to point optical cable
contains many optical fibers and hence it may be desirable to bundle
these separate fibers into a TE link. Note that in the no wavelength
conversion or limited wavelength conversion situations that we will
need information on wavelength usage on the individual component
links.
6.2.4. WSON Routing Information Summary 6.2.2. 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)
skipping to change at page 37, line 24 skipping to change at page 35, line 13
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 + distribute WA via signaling
we only need the following information: we only need the following information:
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]. provided in [WSON-Info] 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 [HZang00]. Such computationally intensive path computations and
optimizations were part of the impetus for the PCE (path computation optimizations were part of the impetus for the PCE (path computation
element) architecture. element) architecture.
As the PCEP defines the procedures necessary to support both As the PCEP defines the procedures necessary to support both
sequential [PCEP] and global concurrent path computations [PCE-GCO], sequential [RFC5440] and global concurrent path computations
PCE is well positioned to support WSON-enabled RWA computation with [RFC5557], PCE is well positioned to support WSON-enabled RWA
some protocol enhancement. 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:
skipping to change at page 38, line 30 skipping to change at page 36, line 16
o Tuning range constraint on optical transmitter. o Tuning range constraint on optical transmitter.
Lightpath characteristics can include: Lightpath characteristics can include:
o Duration information (how long this connection may last) o Duration information (how long this connection may last)
o Timeliness/Urgency information (how quickly is this connection o Timeliness/Urgency information (how quickly is this connection
needed) needed)
6.3.2. Computation Architecture Implications 6.3.2. Discovery of RWA Capable PCEs
When a PCE performs a combined RWA computation per section 4.1.1. it
requires accurate an up to date wavelength utilization on all links
in the network.
When a PCE is used to perform wavelength assignment (WA) in the
separate routing WA architecture then the entity requesting WA needs
to furnish the pre-selected route to the PCE as well as any of the
lightpath constraints/characteristics previously mentioned. This
architecture also requires the PCE performing WA to have accurate and
up to date network wavelength utilization information.
When a PCE is used to perform routing in a routing with distribute WA
architecture, then the PCE does not necessarily need the most up to
date network wavelength utilization information, however timely
information can contributed to reducing failed signaling attempts
related to blocking.
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.
Recent progress on objective functions in PCE [PCE-OF] would allow Recent progress on objective functions in PCE [RFC5541] would allow
the operators to flexibly request differing objective functions per the operators to flexibly request differing objective functions per
their need and applications. For instance, this would allow the their need and applications. For instance, this would allow the
operator to choose an objective function that minimizes the total operator to choose an objective function that minimizes the total
network cost associated with setting up a set of paths concurrently. network cost associated with setting up a set of paths concurrently.
This would also allow operators to choose an objective function that This would also allow operators to choose an objective function that
results in a most evenly distributed link utilization. results in a most evenly distributed link utilization.
This implies that PCEP would easily accommodate wavelength selection This implies that PCEP would easily accommodate wavelength selection
algorithm in its objective function to be able to optimize the path algorithm in its objective function to be able to optimize the path
computation from the perspective of wavelength assignment if chosen computation from the perspective of wavelength assignment if chosen
by the operators. by the operators.
6.4. Scaling Implications 6.4. Summary of Impacts by RWA Architecture
This section provides a summary of the scaling issue for WSON
routing, signaling and path computation introduced by the concepts
discussed in this document.
6.4.1. Routing
In large WSONs label availability and cross connect capability
information being advertised may generate a significant amount of
routing information.
6.4.2. Signaling
When dealing with a large number of simultaneous end-to-end
wavelength service requests and service deletions the network may
have to process a significant number of forward and backward service
messages. Also, similar situation possibly happens in the case of
link or node failure, if the WSON support dynamic restoration
capability.
6.4.3. Path computation
If a PCE is handling path computation requests for end-to-end
wavelength services within the WSON, then the complexity of the
network and number of service path computation requests being sent to
the PCE may have an impact on the PCEs ability to process requests in
a timely manner.
6.5. Summary of Impacts by RWA Architecture
The following table summarizes for each RWA strategy the list of The following table summarizes for each RWA strategy the list of
mandatory ("M") and optional ("O") control plane features according mandatory ("M") and optional ("O") control plane features according
to GMPLS architectural blocks: to GMPLS architectural blocks:
o Information required by the path computation entity, o Information required by the path computation entity,
o LSP request parameters used in either PCC to PCE situations or in o LSP request parameters used in either PCC to PCE situations or in
signaling, signaling,
o RSVP-TE LSP signaling parameters used in LSP establishment. o RSVP-TE LSP signaling parameters used in LSP establishment.
The table shows which enhancements are common to all architectures The table shows which enhancements are common to all architectures
(R&WA, R+WA, R+DWA), which apply only to R&WA and R+WA (R+&WA), and (R&WA, R+WA, R+DWA), which apply only to R&WA and R+WA (R+&WA), and
which apply only to R+DWA. which apply only to R+DWA. Note that this summary serves for the
purpose of a generic reference.
+-------------------------------------+-----+-------+-------+-------+ +-------------------------------------+-----+-------+-------+-------+
| | |Common | R+&WA | R+DWA | | | |Common | R+&WA | R+DWA |
| Feature | ref +---+---+---+---+---+---+ | Feature | ref +---+---+---+---+---+---+
| | | M | O | M | O | M | O | | | | M | O | M | O | M | O |
+-------------------------------------+-----+---+---+---+---+---+---+ +-------------------------------------+-----+---+---+---+---+---+---+
| Generalized Label for Wavelength |5.1.1| x | | | | | | | Generalized Label for Wavelength |5.1.1| x | | | | | |
+-------------------------------------+-----+---+---+---+---+---+---+ +-------------------------------------+-----+---+---+---+---+---+---+
| Flooding of information for the | | | | | | | | | Flooding of information for the | | | | | | | |
| routing phase | | | | | | | | | routing phase | | | | | | | |
skipping to change at page 42, line 38 skipping to change at page 39, line 38
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.
[RFC5088] J.L. Le Roux, J.P. Vasseur, Yuichi Ikejiri, and Raymond [RFC5088] J.L. Le Roux, J.P. Vasseur, Yuichi Ikejiri, and Raymond
Zhang, "OSPF protocol extensions for Path Computation Zhang, "OSPF protocol extensions for Path Computation
Element (PCE) Discovery", January 2008. Element (PCE) Discovery", January 2008.
[PCE-GCO] Y. Lee, J.L. Le Roux, D. King, and E. Oki, "Path [RFC5557] Y. Lee, J.L. Le Roux, D. King, and E. Oki, "Path
Computation Element Communication Protocol (PCECP) Computation Element Communication Protocol (PCECP)
Requirements and Protocol Extensions In Support of Global Requirements and Protocol Extensions In Support of Global
Concurrent Optimization", work in progress, draft-ietf-pce- Concurrent Optimization", RFC 5557, July 2009.
global-concurrent-optimization-08.txt, January 2009.
[PCEP] J.P. Vasseur and J.L. Le Roux (Editors), "Path Computation [RFC5440] J.P. Vasseur and J.L. Le Roux (Editors), "Path Computation
Element (PCE) Communication Protocol (PCEP)", work in Element (PCE) Communication Protocol (PCEP)", RFC 5440, May
progress, draft-ietf-pce-pcep-19.txt, November 2008. 2009.
[PCE-OF] J.L. Le Roux, J.P. Vasseur, and Y. Lee, "Encoding of [RFC5541] J.L. Le Roux, J.P. Vasseur, and Y. Lee, "Encoding of
Objective Functions in Path Computation Element (PCE) Objective Functions in Path Computation Element (PCE)
communication and discovery protocols", work in progress, communication and discovery protocols", RFC 5541, July
draft-ietf-pce-of-06.txt, December 2008. 2009.
[WSON-Compat] G. Bernstein, Y. Lee, B. Mack-Crane, "WSON Signal
Characteristics and Network Element Compatibility
Constraints for GMPLS", draft-bernstein-ccamp-wson-
compatibility, work in progress.
[WSON-Encode] G. Bernstein, Y. Lee, D. Li, and W. Imajuku, "Routing [WSON-Encode] G. Bernstein, Y. Lee, D. Li, and W. Imajuku, "Routing
and Wavelength Assignment Information Encoding for and Wavelength Assignment Information Encoding for
Wavelength Switched Optical Networks", draft-bernstein- Wavelength Switched Optical Networks", draft-bernstein-
ccamp-wson-encode-01.txt, November 2008. ccamp-wson-encode, work in progress.
[WSON-Info] G. Bernstein, Y. Lee, D. Li, W. Imajuku," Routing and [WSON-Imp] Y. Lee, G. Bernstein, D. Li, G. Martinelli, "A Framework
for the Control of Wavelength Switched Optical Networks
(WSON) with Impairments", draft-ietf-ccamp-wson-
impairments, work in progress.
[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-03.txt, Optical Networks", draft-bernstein-ccamp-wson-info, work in
July, 2008. progress
[PCEP-RWA] Y. Lee, G. Bernstein, J. Martensson, T. Takeda, T. Otani,
"PCEP Requirements for WSON Routing and Wavelength
Assignment", draft-lee-pce-wson-routing-wavelength, work in
progress.
10.2. Informative References 10.2. Informative References
[HZang00] H. Zang, J. Jue and B. Mukherjeee, "A review of routing and [HZang00] H. Zang, J. Jue and B. Mukherjeee, "A review of routing and
wavelength assignment approaches for wavelength-routed wavelength assignment approaches for wavelength-routed
optical WDM networks", Optical Networks Magazine, January optical WDM networks", Optical Networks Magazine, January
2000. 2000.
[Coldren04] Larry A. Coldren, G. A. Fish, Y. Akulova, J. S. [Coldren04] Larry A. Coldren, G. A. Fish, Y. Akulova, J. S.
Barton, L. Johansson and C. W. Coldren, "Tunable Barton, L. Johansson and C. W. Coldren, "Tunable
skipping to change at page 43, line 44 skipping to change at page 41, line 13
January 2006. January 2006.
[Basch06] E. Bert Bash, Roman Egorov, Steven Gringeri and Stuart [Basch06] E. Bert Bash, Roman Egorov, Steven Gringeri and Stuart
Elby, "Architectural Tradeoffs for Reconfigurable Dense Elby, "Architectural Tradeoffs for Reconfigurable Dense
Wavelength-Division Multiplexing Systems", IEEE Journal of Wavelength-Division Multiplexing Systems", IEEE Journal of
Selected Topics in Quantum Electronics, vol. 12, no. 4, pp. Selected Topics in Quantum Electronics, vol. 12, no. 4, pp.
615-626, July/August 2006. 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-lambda- (LSR)", work in progress: draft-otani-ccamp-gmpls-g-694-
labels-02.txt, November 2007. lambda-labels, work in progress.
[Winzer06] Peter J. Winzer and Rene-Jean Essiambre, "Advanced [Winzer06] Peter J. Winzer and Rene-Jean Essiambre, "Advanced
Optical Modulation Formats", Proceedings of the IEEE, vol. Optical Modulation Formats", Proceedings of the IEEE, vol.
94, no. 5, pp. 952-985, May 2006. 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.
skipping to change at page 44, line 45 skipping to change at page 42, line 16
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-02.txt, July 2007. switching-constraint-02.txt, July 2007.
[Ozdaglar03] Asuman E. Ozdaglar and Dimitri P. Bertsekas, ''Routing [Ozdaglar03] Asuman E. Ozdaglar and Dimitri P. Bertsekas, "Routing
and wavelength assignment in optical networks,'' IEEE/ACM and wavelength assignment in optical networks," IEEE/ACM
Transactions on Networking, vol. 11, 2003, pp. 259 -272. Transactions on Networking, vol. 11, 2003, pp. 259 -272.
[RFC4054] Strand, J. and A. Chiu, "Impairments and Other Constraints [RFC4054] Strand, J. and A. Chiu, "Impairments and Other Constraints
on Optical Layer Routing", RFC 4054, May 2005. on Optical Layer Routing", RFC 4054, May 2005.
[RFC4606] Mannie, E. and D. Papadimitriou, "Generalized Multi- [RFC4606] Mannie, E. and D. Papadimitriou, "Generalized Multi-
Protocol Label Switching (GMPLS) Extensions for Synchronous Protocol Label Switching (GMPLS) Extensions for Synchronous
Optical Network (SONET) and Synchronous Digital Hierarchy Optical Network (SONET) and Synchronous Digital Hierarchy
(SDH) Control", RFC 4606, August 2006. (SDH) Control", RFC 4606, August 2006.
skipping to change at page 46, line 36 skipping to change at page 43, line 36
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
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