draft-ietf-ccamp-rwa-wson-framework-04.txt   draft-ietf-ccamp-rwa-wson-framework-05.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: April 2010 Grotto Networking Expires: August 2010 Grotto Networking
Wataru Imajuku Wataru Imajuku
NTT NTT
October 9, 2009 February 1, 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-04.txt draft-ietf-ccamp-rwa-wson-framework-05.txt
Status of this Memo Status of this Memo
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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. 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 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 memo focuses on topological elements and path selection This memo focuses on topological elements and path selection
constraints that are common across different WSON environments as constraints that are common across different WSON environments as
such it does not address optical impairments in any depth nor does it such it does not address optical impairments in any depth.
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..........................................4 1.1. Revision History..........................................5
1.1.1. Changes from 00......................................4 1.1.1. Changes from 00......................................5
1.1.2. Changes from 01......................................5 1.1.2. Changes from 01......................................5
1.1.3. Changes from 02......................................5 1.1.3. Changes from 02......................................5
1.2. Related Documents ........................................6 1.1.4. Changes from 03......................................6
2. Terminology....................................................6 1.1.5. Changes from 04......................................6
1.2. Related Documents.........................................6
2. Terminology....................................................7
3. Wavelength Switched Optical Networks...........................7 3. Wavelength Switched Optical Networks...........................7
3.1. WDM and CWDM Links........................................7 3.1. WDM and CWDM Links........................................8
3.2. Optical Transmitters......................................9 3.2. Optical Transmitters......................................9
3.2.1. Lasers...............................................9 3.3. Optical Signals in WSONs.................................10
3.2.2. WSON Signal Parameters..............................10 3.3.1. Optical Tributary Signals...........................11
3.3. ROADMs, OXCs, Splitters, Combiners and FOADMs............10 3.3.2. WSON Signal Characteristics.........................12
3.3.1. Reconfigurable Add/Drop Multiplexers and OXCs.......10 3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs............13
3.3.2. Splitters...........................................13 3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs.......13
3.3.3. Combiners...........................................14 3.4.2. Splitters...........................................16
3.3.4. Fixed Optical Add/Drop Multiplexers.................14 3.4.3. Combiners...........................................16
3.4. Wavelength Converters....................................15 3.4.4. Fixed Optical Add/Drop Multiplexers.................17
3.4.1. Wavelength Converter Pool Modeling..................16 3.5. Electro-Optical Systems..................................17
4. Routing and Wavelength Assignment and the Control Plane.......20 3.5.1. Regenerators........................................17
4.1. Architectural Approaches to RWA..........................21 3.5.2. OEO Switches........................................20
4.1.1. Combined RWA (R&WA).................................22 3.6. Wavelength Converters....................................20
4.1.2. Separated R and WA (R+WA)...........................22 3.6.1. Wavelength Converter Pool Modeling..................22
4.1.3. Routing and Distributed WA (R+DWA)..................23 3.7. Characterizing Electro-Optical Network Elements..........26
4.2. Conveying information needed by RWA......................23 3.7.1. Input Constraints...................................27
4.3. Lightpath Temporal Characteristics.......................24 3.7.2. Output Constraints..................................27
5. Modeling Examples and Control Plane Use Cases.................25 3.7.3. Processing Capabilities.............................28
5.1. Network Modeling for GMPLS/PCE Control...................25 4. Routing and Wavelength Assignment and the Control Plane.......29
5.1.1. Describing the WSON nodes...........................26 4.1. Architectural Approaches to RWA..........................30
5.1.2. Describing the links................................28 4.1.1. Combined RWA (R&WA).................................30
5.2. RWA Path Computation and Establishment...................29 4.1.2. Separated R and WA (R+WA)...........................30
5.3. Resource Optimization....................................30 4.1.3. Routing and Distributed WA (R+DWA)..................31
5.4. Support for Rerouting....................................31 4.2. Conveying information needed by RWA......................32
6. GMPLS & PCE Implications......................................31 4.3. Lightpath Temporal Characteristics.......................33
6.1. Implications for GMPLS signaling.........................31 5. Modeling Examples and Control Plane Use Cases.................34
6.1.1. Identifying Wavelengths and Signals.................32 5.1. Network Modeling for GMPLS/PCE Control...................34
6.1.2. Combined RWA/Separate Routing WA support............32 5.1.1. Describing the WSON nodes...........................34
6.1.3. Distributed Wavelength Assignment: Unidirectional, No 5.1.2. Describing the links................................36
Converters.................................................32 5.2. RWA Path Computation and Establishment...................37
6.1.4. Distributed Wavelength Assignment: Unidirectional, 5.3. Resource Optimization....................................38
Limited Converters.........................................33 5.4. Support for Rerouting....................................39
6.1.5. Distributed Wavelength Assignment: Bidirectional, No 5.5. Electro-Optical Networking Scenarios.....................39
Converters.................................................33 5.5.1. Fixed Regeneration Points...........................39
6.2. Implications for GMPLS Routing...........................34 5.5.2. Shared Regeneration Pools...........................40
6.2.1. Wavelength-Specific Availability Information........34 5.5.3. Reconfigurable Regenerators.........................40
6.2.2. WSON Routing Information Summary....................35 5.5.4. Relation to Translucent Networks....................40
6.3. Optical Path Computation and Implications for PCE........36 6. GMPLS & PCE Implications......................................41
6.3.1. Lightpath Constraints and Characteristics...........36 6.1. Implications for GMPLS signaling.........................41
6.3.2. Discovery of RWA Capable PCEs.......................37 6.1.1. Identifying Wavelengths and Signals.................42
6.4. Summary of Impacts by RWA Architecture...................37 6.1.2. WSON Signals and Network Element Processing.........42
7. Security Considerations.......................................38 6.1.3. Combined RWA/Separate Routing WA support............42
8. IANA Considerations...........................................39 6.1.4. Distributed Wavelength Assignment: Unidirectional, No
9. Acknowledgments...............................................39 Converters.................................................43
10. References...................................................40 6.1.5. Distributed Wavelength Assignment: Unidirectional,
10.1. Normative References....................................40 Limited Converters.........................................44
10.2. Informative References..................................41 6.1.6. Distributed Wavelength Assignment: Bidirectional, No
11. Contributors.................................................44 Converters.................................................44
Author's Addresses...............................................45 6.2. Implications for GMPLS Routing...........................44
Intellectual Property Statement..................................45 6.2.1. Electro-Optical Element Signal Compatibility........45
Disclaimer of Validity...........................................46 6.2.2. Wavelength-Specific Availability Information........46
6.2.3. WSON Routing Information Summary....................46
6.3. Optical Path Computation and Implications for PCE........48
6.3.1. Lightpath Constraints and Characteristics...........48
6.3.2. Electro-Optical Element Signal Compatibility........49
6.3.3. Discovery of RWA Capable PCEs.......................49
6.4. Summary of Impacts by RWA Architecture...................50
7. Security Considerations.......................................51
8. IANA Considerations...........................................51
9. Acknowledgments...............................................51
10. References...................................................52
10.1. Normative References....................................52
10.2. Informative References..................................53
11. Contributors.................................................56
Author's Addresses...............................................57
Intellectual Property Statement..................................57
Disclaimer of Validity...........................................58
1. Introduction 1. Introduction
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. 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 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 This document will focus on the unique properties of links, switches
and path selection constraints that occur in WSONs. Different WSONs and path selection constraints that occur in WSONs. Different WSONs
such as access, metro and long haul may apply different techniques such as access, metro and long haul may apply different techniques
for dealing with optical impairments hence this document will not for dealing with optical impairments hence this document will not
address optical impairments in any depth, but instead focus on address optical impairments in any depth, but instead focus on
properties that are common across a variety of WSONs. For more on how properties that are common across a variety of WSONs. For more on how
the GMPLS control plane can aid in dealing with optical impairments the GMPLS control plane can aid in dealing with optical impairments
see [WSON-Imp]. 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 1.1.3. Changes from 02
Updated the abstract to emphasize the focus of this draft and Updated the abstract to emphasize the focus of this draft and
differentiate it from WSON impairment [WSON-Imp] and WSON differentiate it from WSON impairment [WSON-Imp] and WSON
compatibility [WSON-Compat] drafts. compatibility [WSON-Compat] drafts.
Added references to [WSON-Imp] and [WSON-Compat]. Added references to [WSON-Imp] and [WSON-Compat].
Updated the introduction to explain the relationship between this Updated the introduction to explain the relationship between this
document and the [WSON-Imp] and [WSON-Compat] documents. document and the [WSON-Imp] and [WSON-Compat] documents.
skipping to change at page 5, line 45 skipping to change at page 6, line 8
In section 6 removed discussion of "Relationship to link bundling and In section 6 removed discussion of "Relationship to link bundling and
layering". layering".
In section 6 removed discussion of "Computation Architecture In section 6 removed discussion of "Computation Architecture
Implications" as this material was redundant with text that occurs Implications" as this material was redundant with text that occurs
earlier in the document. earlier in the document.
In section 6 removed discussion of "Scaling Implications" as this In section 6 removed discussion of "Scaling Implications" as this
material was redundant with text that occurs earlier in the document. material was redundant with text that occurs earlier in the document.
1.1.4. Changes from 03 1.1.4. Changes from 03
In Section 3.3.1 added 4-degree ROADM example and its connectivity In Section 3.3.1 added 4-degree ROADM example and its connectivity
matrix. matrix.
1.1.5. 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].
1.2. Related Documents 1.2. Related Documents
This framework document covers essential concepts and models for the This framework document covers essential concepts and models for the
application and extension of the control plane to WSONs. The application and extension of the control plane to WSONs. The
following documents address specific aspects of WSONs and complement following documents address specific aspects of WSONs and complement
this draft. this draft.
o [WSON-Info] This document provides an information model needed by o [WSON-Info] This document provides an information model needed by
the routing and wavelength assignment (RWA) process in WSON. the routing and wavelength assignment (RWA) process in WSON.
o [WSON-Encode] This document provides efficient, protocol-agnostic o [WSON-Encode] This document provides efficient, protocol-agnostic
encodings for the information elements necessary to support the encodings for the information elements necessary to support the
routing and wavelength assignment (RWA) process in WSONs. routing and wavelength assignment (RWA) process in WSONs.
o [WSON-Imp] This document provides a framework for the support of o [WSON-Imp] This document provides a framework for the support of
impairment aware Routing and Wavelength Assignment (RWA) in WSON. 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 o [PCEP-RWA] This document provides application-specific
requirements for the Path Computation Element communication requirements for the Path Computation Element communication
Protocol (PCEP) for the support of RWA in WSON. 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.
skipping to change at page 7, line 18 skipping to change at page 7, line 48
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 come in a variety of shapes and sizes from continent spanning
long haul networks, to metropolitan networks, to residential access long haul networks, to metropolitan networks, to residential access
networks. In all these cases we are concerned with those properties networks. In all these cases we are concerned with those properties
that constrain the choice of wavelengths that can be used, i.e., that constrain the choice of wavelengths that can be used, i.e.,
restrict the wavelength label set, impact the path selection process, restrict the wavelength label set, impact the path selection process,
and limit the topological connectivity. In the following we examine and limit the topological connectivity. In addition, if electro-
and model some major subsystems of a WSON with an emphasis on those optical network elements are used in the WSON, additional
compatibility constraints may be imposed by the network elements on
various optical signal parameters. In the following we examine 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 standards exist for various types of links to name a few. ITU-T standards exist for various types of
skipping to change at page 8, line 27 skipping to change at page 9, line 13
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 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 path selection. for the purposes of 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 9, line 7 skipping to change at page 9, line 41
spacing. spacing.
For a particular link this information is relatively static, i.e., For a particular link this information is relatively static, i.e.,
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 could 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 routing and wavelength assignment problem.
3.2. Optical Transmitters 3.2. Optical Transmitters
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 path selection. in path selection.
Fundamental modeling parameters from the control plane perspective Fundamental modeling parameters from the control plane perspective
skipping to change at page 9, line 43 skipping to change at page 10, line 27
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 aspects of a laser Note that ITU-T recommendations specify many aspects of a laser
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 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 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. WSON Signal Parameters 3.3. Optical Signals in WSONs
As pointed out in the introduction, for the purposes of this document In wavelength switched optical networks (WSONs) our fundamental unit
we assume that all optical signals used in a WSON are compatible with of switching is intuitively that of a "wavelength". The transmitters
all links, network elements, and receivers in that WSON. In [WSON- and receivers in these networks will deal with one wavelength at a
Compat] we discuss how the GMPLS control plane can be extended to time, while the switching systems themselves can deal with multiple
deal with incompatibilities between signals and network elements. wavelengths at a time. Hence we are generally concerned with
multichannel dense wavelength division multiplexing (DWDM) networks
with single channel interfaces. Interfaces of this type are defined
in ITU-T recommendations [G.698.1] and [G.698.1]. Key non-impairment
related parameters defined in [G.698.1] and [G.698.2] are:
Key WSON signal parameters include modulation type, bit rate and (a) Minimum Channel Spacing (GHz)
forward error correction coding technique. Multiple modulation
formats have been standardized [G.959.1] and many others are used
industry and discussed in the literature [Winzer06]. When signals
with different modulation types are used in a WSON then it can be
important to check these signals for compatibility with network
elements such as regenerators, OEO switches, wavelength converters
and receivers [WSON-Compat].
3.3. ROADMs, OXCs, Splitters, Combiners and FOADMs (b) Minimum and Maximum central frequency
(c) Bit-rate/Line coding (modulation) of optical tributary signals
In for the purposes of modeling the WSON in the control plane we can
consider (a) and (b) 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
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
defined as "a single channel signal that is placed within an optical
channel for transport across the optical network". Note the use of
the qualifier "tributary" to indicate that this is a single channel
entity and not a multichannel optical signal.
There are a currently a number of different "flavors" of optical
tributary signals, known as "optical tributary signal classes". These
are currently characterized by a modulation format and bit rate range
[G.959.1]:
(a) optical tributary signal class NRZ 1.25G
(b) optical tributary signal class NRZ 2.5G
(c) optical tributary signal class NRZ 10G
(d) optical tributary signal class NRZ 40G
(e) optical tributary signal class RZ 40G
Note that with advances in technology more optical tributary signal
classes may be added and that this is currently an active area for
deployment and standardization. In particular at the 40G rate there
are a number of non-standardized advanced modulation formats that
have seen significant deployment including Differential Phase Shift
Keying (DPSK) and Phase Shaped Binary Transmission (PSBT)[Winzer06].
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
necessary to specify both the application code and also the exact bit
rate of the system. In other words, there is no requirement for
equipment compliant with one of these codes to operate over the
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
We refer an optical tributary signal defined in ITU-T G.698.1 and .2
to as the signal in this document. This is an "entity" that can be
put on an optical communications channel formed from links and
network elements in a WSON. This corresponds to the "lambda" LSP in
GMPLS. For signal compatibility purposes with electro-optical network
elements we will be interested in the following signal
characteristics:
List 1. WSON Signal Characteristics
1. Optical tributary signal class (modulation format).
2. FEC: whether forward error correction is used in the digital stream
and what type of error correcting code is used
3. Center frequency (wavelength)
4. Bit rate
5. G-PID: General Protocol Identifier for the information format
The first three items on this list can change as a WSON signal
traverses a network with regenerators, OEO switches, or wavelength
converters.
Bit rate and GPID would not change since they describe the encoded
bit stream. A set of G-PID values is already defined for lambda
switching in [RFC3471] and [RFC4328].
Note that a number of "pre-standard" or proprietary modulation
formats and FEC codes are commonly used in WSONs. For some digital
bit streams the presence of FEC can be detected, e.g., in [G.707]
this is indicated in the signal itself via the FEC status indication
(FSI) byte, while in [G.709] this can be inferred from whether the
FEC field of the OTUk is all zeros or not.
3.4. 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 3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs
Reconfigurable add/drop optical multiplexers (ROADM) have matured and Reconfigurable add/drop optical multiplexers (ROADM) have matured and
are available in different forms and technologies [Basch06]. This is are available in different forms and technologies [Basch06]. This is
a 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 ingress +---------------------+ Line side egress
--->| |---> --->| |--->
| | | |
| ROADM | | ROADM |
skipping to change at page 13, line 5 skipping to change at page 15, line 23
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 I assume that loopback is not that diagonal elements are zero since it is assumed that loopback is
supported. If ports support loopback, diagonal elements would be one. not supported. If ports support loopback, diagonal elements would be
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. 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.
skipping to change at page 13, line 35 skipping to change at page 16, line 7
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 we need two pieces of information for
each port: (a) number of wavelengths, (b) wavelength range and each port: (a) number of wavelengths, (b) wavelength range and
spacing. Note that this information is relatively static. More spacing. Note that this information is relatively static. More
complicated wavelength constraints are modeled in [WSON-Info]. complicated wavelength constraints are modeled in [WSON-Info].
3.3.2. 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 ingress port and two or more
egress ports. The ingress optical signaled is essentially copied egress ports. The ingress optical signaled is essentially copied
(with loss) to all egress ports. (with power loss) to all egress ports.
Using the modeling notions of section 3.3.1. the ingress and egress Using the modeling notions of section 3.4.1. the ingress and egress
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
(potential) connectivity matrix but the fixed connectivity matrix of (potential) connectivity matrix but the fixed connectivity matrix of
the device. the device.
3.3.3. Combiners 3.4.3. 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
look like: look like:
Ingress Egress Port Ingress Egress 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
3.3.4. 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
ingress wavelength in a preset way. In particular a given wavelength ingress wavelength in a preset way. In particular a given wavelength
(or waveband) from a line side ingress port would be dropped to a (or waveband) from a line side ingress port would be dropped to a
fixed "tributary" egress port. Depending on the device's construction fixed "tributary" egress port. Depending on the device's construction
that same wavelength may or may not be "continued" to the line side that same wavelength may or may not be "continued" to the line side
egress port ("drop and continue" operation). Further there may exist egress port ("drop and continue" operation). Further there may exist
tributary ingress ports ("add" ports) whose signals are combined with tributary ingress ports ("add" ports) whose signals are combined with
each other and "continued" line side signals. each other and "continued" line side signals.
skipping to change at page 15, line 9 skipping to change at page 17, line 27
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
been continued. been continued.
To summarize, the modeling methodology introduced in section 3.3.1. To summarize, the modeling methodology introduced in section 3.4.1.
consisting of a connectivity matrix and port wavelength restrictions consisting of a connectivity matrix and port wavelength restrictions
can be used to describe a large set of fixed optical devices such as can be used to describe a large set of fixed optical devices such as
combiners, splitters and FOADMs. Hybrid devices consisting of both combiners, splitters and FOADMs. Hybrid devices consisting of both
switched and fixed parts are modeled in [WSON-Info]. switched and fixed parts are modeled in [WSON-Info].
3.4. Wavelength Converters 3.5. Electro-Optical Systems
This section describes how Electro-Optical Systems (e.g., OEO
switches, wavelength converters, and regenerators) interact with the
WSON signal characteristics defined in List 1 in Section 2.3. OEO
switches, wavelength converters and regenerators all share a similar
property: they can be more or less "transparent" to an "optical
signal" depending on their functionality and/or implementation.
Regenerators have been fairly well characterized in this regard so we
start by describing their properties.
3.5.1. Regenerators
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
1R, 2R and 3R categories of regenerators as summarized in Table 1
below:
Table 1 Regenerator functionality mapped to general regenerator
classes from [G.872].
---------------------------------------------------------------------
1R | Equal amplification of all frequencies within the amplification
| bandwidth. There is no restriction upon information formats.
+-----------------------------------------------------------------
| Amplification with different gain for frequencies within the
| amplification bandwidth. This could be applied to both single-
| channel and multi-channel systems.
+-----------------------------------------------------------------
| Dispersion compensation (phase distortion). This analogue
| process can be applied in either single-channel or multi-
| channel systems.
---------------------------------------------------------------------
2R | Any or all 1R functions. Noise suppression.
+-----------------------------------------------------------------
| Digital reshaping (Schmitt Trigger function) with no clock
| recovery. This is applicable to individual channels and can be
| used for different bit rates but is not transparent to line
| coding (modulation).
--------------------------------------------------------------------
3R | Any or all 1R and 2R functions. Complete regeneration of the
| pulse shape including clock recovery and retiming within
| required jitter limits.
--------------------------------------------------------------------
From the previous table we can see that 1R regenerators are generally
independent of signal modulation format (also known as line coding),
but may work over a limited range of wavelength/frequencies. We see
that 2R regenerators are generally applicable to a single digital
stream and are dependent upon modulation format (line coding) and to
a lesser extent are limited to a range of bit rates (but not a
specific bit rate). Finally, 3R regenerators apply to a single
channel, are dependent upon the modulation format and generally
sensitive to the bit rate of digital signal, i.e., either are
designed to only handle a specific bit rate or need to be programmed
to accept and regenerate a specific bit rate. In all these types of
regenerators the digital bit stream contained within the optical or
electrical signal is not modified.
However, in the most common usage of regenerators the digital bit
stream may be slightly modified for performance monitoring and fault
management purposes. SONET, SDH and G.709 all have digital signal
"envelopes" designed to be used between "regenerators" (in this case
3R regenerators). In SONET this is known as the "section" signal, in
SDH this is known as the "regenerator section" signal, in G.709 this
is known as an OTUk (Optical Channel Transport Unit-k). These
signals reserve a portion of their frame structure (known as
overhead) for use by regenerators. The nature of this overhead is
summarized in Table 2.
Table 2. SONET, SDH, and G.709 regenerator related overhead.
+-----------------------------------------------------------------+
|Function | SONET/SDH | G.709 OTUk |
| | Regenerator | |
| | Section | |
|------------------+----------------------+-----------------------|
|Signal | J0 (section | Trail Trace |
|Identifier | trace) | Identifier (TTI) |
|------------------+----------------------+-----------------------|
|Performance | BIP-8 (B1) | BIP-8 (within SM) |
|Monitoring | | |
|------------------+----------------------+-----------------------|
|Management | D1-D3 bytes | GCC0 (general |
|Communications | | communications |
| | | channel) |
|------------------+----------------------+-----------------------|
|Fault Management | A1, A2 framing | FAS (frame alignment |
| | bytes | signal), BDI(backward|
| | | defect indication)BEI|
| | | (backward error |
| | | indication) |
+------------------+----------------------+-----------------------|
|Forward Error | P1,Q1 bytes | OTUk FEC |
|Correction (FEC) | | |
+-----------------------------------------------------------------+
In the previous table we see support for frame alignment, signal
identification, and FEC. What this table also shows by its omission
is that no switching or multiplexing occurs at this layer. This is a
significant simplification for the control plane since control plane
standards require a multi-layer approach when there are multiple
switching layers, but not for "layering" to provide the management
functions of Table 2. That is, many existing technologies covered by
GMPLS contain extra management related layers that are essentially
ignored by the control plane (though not by the management plane!).
Hence, the approach here is to include regenerators and other devices
at the WSON layer unless they provide higher layer switching and then
a multi-layer or multi-region approach [RFC5212] is called for.
However, this can result in regenerators having a dependence on the
client signal type.
Hence we see that depending upon the regenerator technology we may
have the following constraints imposed by a regenerator device:
Table 3. Regenerator Compatibility Constraints
+--------------------------------------------------------+
| Constraints | 1R | 2R | 3R |
+--------------------------------------------------------+
| Limited Wavelength Range | x | x | x |
+--------------------------------------------------------+
| Modulation Type Restriction | | x | x |
+--------------------------------------------------------+
| Bit Rate Range Restriction | | x | x |
+--------------------------------------------------------+
| Exact Bit Rate Restriction | | | x |
+--------------------------------------------------------+
| Client Signal Dependence | | | x |
+--------------------------------------------------------+
Note that Limited Wavelength Range constraint is already modeled in
GMPLS for WSON and that Modulation Type Restriction constraint
includes FEC.
3.5.2. OEO Switches
A common place where optical-to-electrical-to-optical (OEO)
processing may take place is in WSON switches that utilize (or
contain) regenerators. A vendor may add regenerators to a switching
system for a number of reasons. One obvious reason is to restore
signal quality either before or after optical processing (switching).
Another reason may be to convert the signal to an electronic form for
switching then reconverting to an optical signal prior to egress from
the switch. In this later case the regeneration is applied to adapt
the signal to the switch fabric regardless of whether or not it is
needed from a signal quality perspective.
In either case these optical switches have essentially the same
compatibility constraints as those we described for regenerators in
Table 3.
3.6. Wavelength Converters
Wavelength converters take an ingress optical signal at one Wavelength converters take an ingress optical signal at one
wavelength and emit an equivalent content optical signal at another wavelength and emit an equivalent content optical signal at another
wavelength on egress. There are currently two approaches to building wavelength on egress. There are currently two approaches to building
wavelength converters. One approach is based on optical to electrical wavelength converters. One approach is based on optical to electrical
to optical (OEO) conversion with tunable lasers on egress. This to optical (OEO) conversion with tunable lasers on egress. This
approach can be dependent upon the signal rate and format, i.e., this approach can be dependent upon the signal rate and format, i.e., this
is basically an electrical regenerator combined with a tunable laser. is basically an electrical regenerator combined with a tunable laser.
Hence, this type wavelength converter has signal processing
restrictions that are essentially the same as those we described for
regenerators in Table 3 of section 3.5.1.
The other approach performs the wavelength conversion, optically via The other 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.
skipping to change at page 15, line 49 skipping to change at page 21, line 37
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 pool of wavelength converters available. may have 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 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 modeling approach for wavelength Based on the above considerations we model wavelength converters as
converters could be as follows: 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.
skipping to change at page 16, line 32 skipping to change at page 22, line 19
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
3.4.1. 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 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
skipping to change at page 17, line 29 skipping to change at page 23, line 18
we assume that a wavelength converter can only take a single we assume that a wavelength converter can only take a single
wavelength on input. We can model each wavelength converter ingress wavelength on input. We can model each wavelength converter ingress
port constraint via a wavelength set mechanism. port constraint via a wavelength set mechanism.
Next we have a state vector WC(j) = {0,1} dependent upon whether Next we have a state vector WC(j) = {0,1} dependent upon whether
wavelength converter j in the pool is in use. This is the only state wavelength converter j in the pool is in use. This is the only state
kept in the converter pool model. This state is not necessary for kept in the converter pool model. This state is not necessary for
modeling "fixed" transponder system, i.e., systems where there is no modeling "fixed" transponder system, i.e., systems where there is no
sharing. In addition, this state information may be encoded in a sharing. In addition, this state information may be encoded in a
much more compact form depending on the overall connectivity much more compact form depending on the overall connectivity
structure [WC-Pool]. structure [WSON-Encode].
After that, we have a set of wavelength converter egress wavelength After that, we have a set of wavelength converter egress wavelength
constraints. These constraints indicate what wavelengths a particular constraints. These constraints indicate what wavelengths a particular
wavelength converter can generate or are restricted to generating due wavelength converter can generate or are restricted to generating due
to internal switch structure. to internal switch structure.
Finally, we have a wavelength pool egress matrix WE(p,k) = {0,1} Finally, we have a wavelength pool egress matrix WE(p,k) = {0,1}
depending on whether the output from wavelength converter p can reach depending on whether the output from wavelength converter p can reach
egress port k. Examples of this method being used to model wavelength egress port k. Examples of this method being used to model wavelength
converter pools for several switch architectures from the literature converter pools for several switch architectures from the literature
are given in reference [WC-Pool]. are given in reference [WSON-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 | | Ingress | | Egress |
skipping to change at page 19, line 5 skipping to change at page 25, line 5
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 Example: Shared Per Node
In Figure 4 below we show a simple optical switch in a four In Figure 4 below we show a simple optical switch in a four
wavelength DWDM system sharing wavelength converters in a general wavelength DWDM system sharing wavelength converters in a general
"per node" fashion. "per 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 |
\| | +----+->|WC #1|--+->|t i| | r | \| | +----+->|WC #1|--+->|t i| | r |
| | | +-----+ | |i t| +------+ | | | +-----+ | |i t| +------+
| | | | |c c| +------+ | | | | |c c| +------+
/| | | | +-----+ | |a h|-->| | /| | | | +-----+ | |a h|-->| |
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 ingress and egress pool matrices are simply:
+-----+ +-----+ +-----+ +-----+
| 1 1 | | 1 1 | | 1 1 | | 1 1 |
WI =| |, WE =| | WI =| |, WE =| |
| 1 1 | | 1 1 | | 1 1 | | 1 1 |
skipping to change at page 20, line 11 skipping to change at page 26, line 11
In Figure 5 we show a different wavelength pool architecture know as In Figure 5 we show a different wavelength pool architecture know as
"shared per fiber". In this case the ingress and egress pool matrices "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 |
| | | +-----+ | +------+ | | | +-----+ | +------+
| | | | +------+ | | | | +------+
/| | | | +-----+ | | | /| | | | +-----+ | | |
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
In this section we characterize Electro-Optical WSON network elements
by the three key functional components: Input constraints, Output
constraints and Processing Capabilities.
WSON Network Element
+-----------------------+
WSON Signal | | | | WSON Signal
| | | |
---------------> | | | | ----------------->
| | | |
+-----------------------+
<-----> <-------> <----->
Input Processing Output
Figure 6 WSON Network Element
3.7.1. Input Constraints
Section 3 discussed the basic properties regenerators, OEO switches
and wavelength converters from these we have the following possible
types of input constraints and properties:
1. Acceptable Modulation formats
2. Client Signal (GPID) restrictions
3. Bit Rate restrictions
4. FEC coding restrictions
5. Configurability: (a) none, (b) self-configuring, (c) required
We can represent these constraints via simple lists. Note that the
device may need to be "provisioned" via signaling or some other means
to accept signals with some attributes versus others. In other cases
the devices maybe relatively transparent to some attributes, e.g.,
such as a 2R regenerator to bit rate. Finally, some devices maybe
able to auto-detect some attributes and configure themselves, e.g., a
3R regenerator with bit rate detection mechanisms and flexible phase
locking circuitry. To account for these different cases we've added
item 5, which describes the devices configurability.
Note that such input constraints also apply to the final destination,
sink or termination, of the WSON signal.
3.7.2. Output Constraints
None of the network elements considered here modifies either the bit
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
following types of output constraints:
1. Output modulation is the same as input modulation (default)
2. A limited set of output modulations is available
3. Output FEC is the same as input FEC code (default)
4. A limited set of output FEC codes is available
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
will need to be configured on a per LSP basis as to which choice to
use.
3.7.3. Processing Capabilities
A general WSON network element (NE) can perform a number of signal
processing functions including:
(A) Regeneration (possibly different types)
(B) Fault and Performance Monitoring
(C) Wavelength Conversion
(D) Switching
Item(D) can be modeled with existing GMPLS mechanisms.
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
have limited regeneration capability, i.e., a shared pool, which may
be applied to selected signals traversing the NE. Hence to describe
the regeneration capability of a link or node we have at a minimum:
1. Regeneration capability: (a)fixed, (b) selective, (c) none
2. Regeneration type: 1R, 2R, 3R
3. Regeneration pool properties for the case of selective
regeneration (ingress & egress restrictions, availability)
Note that the properties of shared regenerator pools would be
essentially the same at that of wavelength converter pools modeled in
section 3.6.1.
Item (B), fault and performance monitoring, is typically outside the
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
can be of assistance in their configuration. Per LSP, per node, fault
and performance monitoring examples include setting up a "section
trace" (a regenerator overhead identifier) between two nodes, or
intermediate optical performance monitoring at selected nodes along a
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 In wavelength switched optical networks consisting of tunable lasers
and wavelength selective switches with wavelength converters on every and wavelength selective switches with wavelength converters on every
interface, path selection is similar to the MPLS and TDM circuit interface, path selection is similar to the MPLS and TDM circuit
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
skipping to change at page 22, line 5 skipping to change at page 30, line 22
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
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 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 hence owns the o In a separate Path Computation Element (PCE) which 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 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
skipping to change at page 23, line 5 skipping to change at page 31, line 21
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
assignment is performed on a hop-by-hop manner along the previously assignment is performed on a hop-by-hop manner along the previously
computed route. This mechanism relies on updating of a list of computed route. This mechanism relies on updating of a list of
potential wavelengths used to ensure conformance with the wavelength potential wavelengths used to ensure conformance with the wavelength
continuity constraint. 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
skipping to change at page 26, line 24 skipping to change at page 34, line 37
| +--+ ++-+ | | +-----+ | +--+ ++-+ | | +-----+
+-L4-+N3+-L6-+N5+-L10-+ ++----+ +-L4-+N3+-L6-+N5+-L10-+ ++----+
+--+ | +--------L11--+ N7 +---- +--+ | +--------L11--+ N7 +----
+--+ ++---++ +--+ ++---++
| | | |
L13 L14 L13 L14
| | | |
++-+ | ++-+ |
|O1+-+ |O1+-+
+--+ +--+
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 in this example have the following properties:
o Nodes N1, N2, N3 have fixed OADMs (FOADMs) installed and can o Nodes N1, N2, N3 have fixed OADMs (FOADMs) installed and can
therefore only access a static and pre-defined set of wavelengths therefore only 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
skipping to change at page 28, line 50 skipping to change at page 36, line 50
| |L14|0 |0 |0 |1 | |L14|0 |1 |0 |0 | | | |L14|0 |0 |0 |1 | |L14|0 |1 |0 |0 | |
| |L16|1 |0 |1 |0 | |L16|0 |0 |1 |0 | | | |L16|1 |0 |1 |0 | |L16|0 |0 |1 |0 | |
+--+---+---+---+---+---+---+---+---+---+---+---+---+ +--+---+---+---+---+---+---+---+---+---+---+---+---+
| | |L15|L16|L17|L18| | |L15|L16|L17|L18| | | | |L15|L16|L17|L18| | |L15|L16|L17|L18| |
| |L15|0 |1 |0 |0 | |L15|0 |0 |0 |1 | | | |L15|0 |1 |0 |0 | |L15|0 |0 |0 |1 | |
|N8|L16|1 |0 |0 |0 | |L16|0 |0 |1 |0 | | |N8|L16|1 |0 |0 |0 | |L16|0 |0 |1 |0 | |
| |L17|0 |0 |0 |0 | |L17|0 |1 |0 |0 | | | |L17|0 |0 |0 |0 | |L17|0 |1 |0 |0 | |
| |L18|0 |0 |0 |0 | |L18|1 |0 |1 |0 | | | |L18|0 |0 |0 |0 | |L18|1 |0 |1 |0 | |
+--+---+---+---+---+---+---+---+---+---+---+---+---+ +--+---+---+---+---+---+---+---+---+---+---+---+---+
5.1.2. Describing the links 5.1.2. Describing the links
For the following discussion some simplifying assumptions are made: For the following discussion some simplifying assumptions are made:
o It is assumed that the WSON node support a total of four o It is assumed that the WSON node support a total of four
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
skipping to change at page 31, line 34 skipping to change at page 39, line 34
Assume furthermore that the link L5 fails. The RWA can now find the Assume furthermore that the link L5 fails. The RWA can now find the
following alternate path and and establish that path: following alternate path and and establish that path:
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
In the following we look at various networking scenarios involving
regenerators, OEO switches and wavelength converters. We group these
scenarios roughly by type and number of extensions to the GMPLS
control plane that would be required.
5.5.1. Fixed Regeneration Points
In the simplest networking scenario involving regenerators, the
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
regenerated. This includes OEO switches since they provide
regeneration on every port.
There maybe input constraints and output constraints on the
regenerators. Hence the path selection process will need to know from
an IGP or other means the regenerator constraints so that it can
choose a compatible path. For impairment aware routing and wavelength
assignment (IA-RWA) the path selection process will also need to know
which links/nodes provide regeneration. Even for "regular" RWA, this
regeneration information is useful since wavelength converters
typically perform regeneration and the wavelength continuity
constraint can be relaxed at such a point.
Signaling does not need to be enhanced to include this scenario since
there are no reconfigurable regenerator options on input, output or
with respect to processing.
5.5.2. Shared Regeneration Pools
In this scenario there are nodes with shared regenerator pools within
the network in addition to fixed regenerators of the previous
scenario. These regenerators are shared within a node and their
application to a signal is optional. There are no reconfigurable
options on either input or output. The only processing option is to
"regenerate" a particular signal or not.
Regenerator information in this case is used in path computation to
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
regenerator pool we need to be able to indicate that regeneration is
to take place at that particular node along the signal path. Such a
capability currently does not exist in GMPLS signaling.
5.5.3. Reconfigurable Regenerators
In this scenario we have regenerators that require configuration
prior to use on an optical signal. We discussed previously that this
could be due to a regenerator that must be configured to accept
signals with different characteristics, for regenerators with a
selection of output attributes, or for regenerators with additional
optional processing capabilities.
As in the previous scenarios we will need information concerning
regenerator properties for selection of compatible paths and for IA-
RWA computations. In addition during LSP setup we need to be able
configure regenerator options at a particular node along the path.
Such a capability currently does not exist in GMPLS signaling.
5.5.4. Relation to Translucent Networks
In the literature, networks that contain both transparent network
elements such as reconfigurable optical add drop multiplexers
(ROADMs) and electro-optical network elements such regenerators or
OEO switches are frequently referred to as Translucent optical
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:
4. Transparent "islands" surrounded by regenerators. This is
frequently seen when transitioning from a metro optical sub-
network to a long haul optical sub-network.
5. Mostly transparent networks with a limited number of OEO
("opaque") nodes strategically placed. This takes advantage of the
inherent regeneration capabilities of OEO switches. In the
planning of such networks one has to determine the optimal
placement of the OEO switches [Sen08].
6. Mostly transparent networks with a limited number of optical
switching nodes with "shared regenerator pools" that can be
optionally applied to signals passing through these switches.
These switches are sometimes called translucent nodes.
All three of these types of translucent networks fit within either
the networking scenarios of sections 5.5.1. and 5.5.2. above. And
hence, can be accommodated by the GMPLS extensions suggested in this
document.
6. GMPLS & PCE Implications 6. GMPLS & 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
Basic support for WSON signaling already exists in GMPLS with the Basic support for WSON signaling already exists in GMPLS with the
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. Combined RWA/Separate Routing WA support 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
its path can be characterized by the (a) modulation format, (b) FEC,
(c) wavelength, (d)bit rate, and (d)G-PID.
Currently G-PID, wavelength (via labels), and bit rate (via bandwidth
encoding) are supported in [RFC3471] and [RFC3473]. These RFCs can
accommodate the wavelength changing at any node along the LSP and can
thus provide explicit control of wavelength converters.
In the fixed regeneration point scenario (section 5.5.1. ) no
enhancements are required to signaling 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
be able to indicate to a node that it should perform regeneration on
a particular signal. Viewed another way, for an LSP we want to
specify that certain 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
similar to the previous except that now there are potentially many
more items that we may want to configure on a per node basis for an
LSP.
Note that the techniques of [RFC5420] which allow for additional LSP
attributes and their recording in an RRO object could be extended to
allow for additional LSP attributes in an ERO. This could allow one
to indicate where optional 3R regeneration should take place along a
path, any modification of LSP attributes such as modulation format,
or any enhance processing such as performance monitoring.
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.
6.1.3. 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 RSVP-TE path message. The processing
of the label set object to take the intersection of available lambdas of the label set object to take the intersection of available lambdas
along a path can be performed resulting in the set of available along a path can be performed resulting in the set of available
lambda being known to the destination that can then use a wavelength lambda being known to the destination that can then use a wavelength
selection algorithm to choose a lambda. For example, the following is selection algorithm to choose a lambda. For example, the following is
a non-exhaustive subset of wavelength assignment (WA) approaches a non-exhaustive subset of wavelength assignment (WA) approaches
discussed in [HZang00]: discussed in [HZang00]:
skipping to change at page 33, line 24 skipping to change at page 44, line 4
wavelength use in the network. wavelength use in the network.
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. GMPLS signaling does not provide a way to combined RWA computation. GMPLS signaling does not provide a way to
indicate that a particular wavelength assignment algorithm should be indicate that a particular wavelength assignment algorithm should be
used. used.
6.1.4. 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 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
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 egress 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.
6.1.5. 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. We can
try to use the above procedure to determine the available try to use the above procedure to determine the available
bidirectional lambda set if we use the interpretation that the bidirectional lambda set if we use the interpretation that the
available label set is available in both directions. However, a available label set is available in both directions. However, a
problem, arises in that bidirectional LSPs setup, according to problem, arises in that bidirectional LSPs setup, according to
[RFC3471] section 4.1, is indicated by the presence of an upstream [RFC3471] section 4.1, is indicated by the presence of an upstream
label in the path message. label in the path message.
skipping to change at page 34, line 39 skipping to change at page 45, line 21
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. Wavelength-Specific Availability Information 6.2.1. Electro-Optical Element Signal Compatibility
In network scenarios where signal compatibility is a concern we need
to add parameters to our existing node and link models to take into
account electro-optical input constraints, output constraints, and
the signal processing capabilities of a NE in path computations.
Input Constraints:
1. Permitted optical tributary signal classes: A list of optical
tributary signal classes that can be processed by this network
element or carried over this link. [configuration type]
2. Acceptable FEC codes [configuration type]
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
included with the optical tributary signal class restrictions.
4. Acceptable G-PID list: A list of G-PIDs corresponding to the
"client" digital streams that is compatible with this device.
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
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
bit rate.
Output Constraints:
1. Output modulation: (a)same as input, (b) list of available types
2. FEC options: (a) same as input, (b) list of available codes
Processing Capabilities:
1. Regeneration: (a) 1R, (b) 2R, (c) 3R, (d)list of selectable
regeneration types
2. Fault and Performance Monitoring (a)GPID particular capabilities
TBD, (b) optical performance monitoring capabilities TBD.
Note that such parameters could be specified on an (a) Network
element wide basis, (b) a per port basis, (c) on a per regenerator
basis. Typically such information has been on a per port basis,
e.g., the GMPLS interface switching capability descriptor [RFC4202].
6.2.2. Wavelength-Specific Availability Information
For wavelength assignment we need to know which specific wavelengths For wavelength assignment we need to know which specific wavelengths
are available and which are occupied if we are going to run a are available and which are occupied if we are going to run a
combined RWA process or separate WA process as discussed in sections combined RWA process or separate WA process as discussed in sections
4.1.1. 4.1.2. This is currently not possible with GMPLS routing 4.1.1. 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 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 [WSON-Encode]. feasible [WSON-Encode].
6.2.2. 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) Laser 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
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
skipping to change at page 36, line 31 skipping to change at page 48, line 21
As the PCEP defines the procedures necessary to support both As the PCEP defines the procedures necessary to support both
sequential [RFC5440] and global concurrent path computations sequential [RFC5440] and global concurrent path computations
[RFC5557], PCE is well positioned to support WSON-enabled RWA [RFC5557], PCE is well positioned to support WSON-enabled RWA
computation with 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:
o Batch optimization, multiple lightpaths requested at one time. o Batch optimization, multiple lightpaths requested at one time.
o Lightpath(s) and backup lightpath(s) requested at one time. o Lightpath(s) and backup lightpath(s) requested at one time.
o Single lightpath requested at a time. o Single lightpath requested at a time.
skipping to change at page 37, line 15 skipping to change at page 49, line 4
backup paths. backup paths.
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. Electro-Optical Element Signal Compatibility
6.3.2. Discovery of RWA Capable PCEs When requesting a path computation to PCE, the PCC should be able to
indicate the following:
o The GPID type of an LSP
o The signal attributes at the transmitter (at the source): (i)
modulation type; (ii) FEC type
o The signal attributes at the receiver (at the sink): (i)
modulation type; (ii) FEC type
The PCE should be able to respond to the PCC with the following:
o The conformity of the requested optical characteristics associated
with the resulting LSP with the source, sink and NE along the LSP.
o Additional LSP attributes modified along the path (e.g.,
modulation format change, etc.)
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 [RFC5541] would allow Recent progress on objective functions in PCE [RFC5541] would allow
skipping to change at page 43, line 28 skipping to change at page 56, line 5
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.
[WC-Pool] G. Bernstein, Y. Lee, "Modeling WDM Switching Systems
including Wavelength Converters" to appear www.grotto-
networking.com, 2008.
11. Contributors 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)
Daniel King Daniel King
Old Dog Consulting
UK
Aria Networks Aria Networks
Email: daniel.king@aria-networks.com 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
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