CCAMP G. Martinelli, Ed.
Internet-Draft Cisco
Intended status: Informational X. Zhang, Ed.
Expires: January 14, 2014 Huawei Technologies
G. Galimberti
Cisco
A. Zanardi
D. Siracusa
CREATE-NET
July 13, 2013
Information Model for Wavelength Switched Optical Networks (WSONs) with
Impairments Validation
draft-martinelli-ccamp-wson-iv-info-02
Abstract
This document defines an information model to support Impairment-
Aware (IA) Routing and Wavelength Assignment (RWA) function. This
operation might be required in Wavelength Switched Optical Networks
(WSON) that already support RWA and the information model defined
here goes in addition and it is fully compatible with the already
defined information model for impairment-free RWA process in WSON.
This information model shall support all control plane architectural
options defined for WSON with impairment validation.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 14, 2014.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Applicability . . . . . . . . . . . . . . . . . . . . . . 3
2. Properties of an Impairment Information Model . . . . . . . . 3
3. Background from WSON Information Model . . . . . . . . . . . 5
4. Optical Impairment Information Model . . . . . . . . . . . . 6
4.1. The Optical Impairment Vector . . . . . . . . . . . . . . 7
4.2. Node Information . . . . . . . . . . . . . . . . . . . . 7
4.3. Link Information . . . . . . . . . . . . . . . . . . . . 9
4.4. Path Information . . . . . . . . . . . . . . . . . . . . 9
5. Encoding Considerations . . . . . . . . . . . . . . . . . . . 10
6. Control Plane Architectures . . . . . . . . . . . . . . . . . 10
6.1. IV-Centralized . . . . . . . . . . . . . . . . . . . . . 11
6.2. IV-Distributed . . . . . . . . . . . . . . . . . . . . . 11
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
8. Contributing Authors . . . . . . . . . . . . . . . . . . . . 11
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
10. Security Considerations . . . . . . . . . . . . . . . . . . . 13
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
11.1. Normative References . . . . . . . . . . . . . . . . . . 13
11.2. Informative References . . . . . . . . . . . . . . . . . 13
Appendix A. G.680 Essential information . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
In the context of Wavelength Switched Optical Network (WSON),
[RFC6163] describes the basic framework for a GMPLS and PCE-based
Routing and Wavelength Assignment (RWA) control plane. The
associated information model [I-D.ietf-ccamp-rwa-info] defines all
information/parameters required by an RWA process.
There are cases of WSON where optical impairments plays a significant
role and are considered as important constraints. The framework
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document [RFC6566] defines problem scope and related control plane
architectural options for the Impairment Aware Routing and Wavelength
Assignment (IA-RWA) operation. Options include different
combinations of Impairment Validation (IV) and RWA functions in term
of different combination of control plane functions (i.e., PCE,
Routing, Signaling).
This document provides an information model for the impairment aware
case to allow the impairment validation function implemented in the
control plane or enabled by control plane available information.
This model goes in addition to [I-D.ietf-ccamp-rwa-info] and it shall
support any control plane architectural option described by the
framework document (see sections 4.2 and 4.3 of [RFC6566]) where a
set of control plane combinations of control plane functions vs. IV
functions is provided.
1.1. Applicability
This document targets at Scenario C defined in [RFC6566] section
4.1.1., i.e., approximate impairment estimation. The usage of
"Approximate" concept helps to clarify that a path resulting from a
IV-RWA process are not guaranteed to work from an optical perspective
however, has better chance to be feasible than other(s). Setting up
the ligth-path, there is still a possibility to fail but this is an
acceptable in term of GMPLS control plane.
The information model defined in this document strictly relates to a
control plane information model hence it does not define any new
Optical Computational Model. Optical Computational Models are
defined by ITU-T, [ITU.G680] defines transfer functions for some
linear optical parameters while there's no general optical
computational model for non-linear effects. This information model
uses the available optical computational model as a reference, and
identify GMPLS WSON control plane extensions to allow IV functions to
perform its task.
Following here above considerations, scope of this information model
is to provide a generic mechanism so will easily support additional
impairment parameters and/or additional optical computational models.
2. Properties of an Impairment Information Model
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An information model may have several attributes or properties that
need to be defined for each optical parameter made available to the
control plane. The properties will help to determine how the control
plane can deal with a specific impairment parameter, depending on
architectural options chosen within the overall impairment framework
[RFC6566]. In some case, properties value will help to identify the
level of approximation supported by the IV process.
o Time Dependency
This identifies how an impairment parameter may vary with time.
There could be cases where there is no time dependency, while in
other cases there may be need of re-evaluation after a certain
time. In this category, variations in impairments due to
environmental factors such as those discussed in [G.sup47] are
considered. In some cases, an impairment parameter that has time
dependency may be considered as a constant for approximation. In
this information model, we do neglect this property.
o Wavelength Dependency
This property identifies if an impairment parameter can be
considered as constant over all the wavelength spectrum of
interest or not. Also in this case a detailed impairment
evaluation might lead to consider the exact value while an
approximation IV might take a constant value for all wavelengths.
In this information model, we consider both case: dependency / no
dependency on a specific wavelength. This property appears
directly in the information model definitions and related
encoding.
o Linearity
As impairments are representation of physical effects, there are
some that have a linear behavior while other are non-linear.
Linear approximation is in scope of Scenario C of [RFC6566].
During the impairment validation process, this property implies
that the optical effect (or quantity) satisfies the superposition
principle, thus a final result can be calculated by the sum of
each component. The linearity implies the additivity of optical
quantities considered during an impairment validation process.
The non-linear effects in general does not satisfy this property.
The information model presented in this document however, easily
allow introduction of non-linear optical effects with a linear
approximated contribution to the linear ones.
o Multi-Channel
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There are cases where a channel's impairments take different
values depending on the aside wavelengths already in place, this
is mostly due to non-linear impairments. The result would be a
dependency among different LSPs sharing the same path. This
information model do not cosider this kind of property.
The following table summarize the above considerations where in the
first column reports the list of properties to be considered for each
optical parameter, while the second column states if this property is
taken into account or not by this information model.
+-----------------------+----------------------+
| Property | Info Model Awareness |
+-----------------------+----------------------+
| Time Dependency | no |
| Wavelength Dependency | yes |
| Linearity | yes |
| Multi-channel | no |
+-----------------------+----------------------+
Table 1: Optical Impairment Properties
3. Background from WSON Information Model
In this section we report terms already defined for the WSON-RWA
(impairment free) as in [I-D.ietf-ccamp-rwa-info] and
[I-D.ietf-ccamp-general-constraint-encode]. The purpose is to
provide essential information that will be reused or extended for the
impairment case.
In particular [I-D.ietf-ccamp-rwa-info] defines the connectivity
matrix as the following:
ConnectivityMatrix ::= <MatrixID> <ConnType> <Matrix>
According to [I-D.ietf-ccamp-general-constraint-encode], this
definition is further detailed as:
ConnectivityMatrix ::=
<MatrixID> <ConnType> ((<LinkSet> <LinkSet>) ...)
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This second formula highlights how the connectivity matrix is built
by pairs of LinkSet objects identifying the internal connectivity
capability due to internal optical node constraint(s). It's
essentially binary information and tell if a wavelength or a set of
wavelengths can go from an input port to an output port.
As an additional note, connectivity matrix belongs to node
information and is purely static. Dynamic information related to the
actual usage of the connections is available through specific
extension to link information.
4. Optical Impairment Information Model
The idea behind this information model is to categorize the
impairment parameters into three types and extend the information
model already defined for impairment-free WSONs. The three
categories are:
o Node Information. The concept of connectivity matrix is reused
and extended to introduce an impairment matrix.
o Link Information representing impairment information related to a
specific link or hop.
o Path Information representing the impairment information related
to the whole path.
All the above three categories will make use of a generic container,
the Impairment Vector, to transport optical impairment information.
In term of optical parameters, this document is not to rephrase
content from [ITU.G680] but only provide necessary building blocks
that allow the IA-RWA process to apply the specific Optical
Computational Model (i.e. transfer functions). Section 9 of
[ITU.G680] defines the optical computational models and provides
information to calculate the following optical parameters:
o OSNR. Section 9.1
o Optical Power. As per Section 9.1, required by Optical
Computation Model for OSNR calculation.
o Chromatic Dispersion (CD). Section 9.2
o Polarization Mode Dispersion (PMD). Section 9.3
o Polarization Dependent Loss (PDL). Section 9.3
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This information model however will allow however to add additional
parameters beyond the one defined by [ITU.G680] in order to support
additional computational models. This mechanism could eventually
applicable to both linear and non-linear parameters.
This information model makes the assumption that the each optical
node in the network is able to provide the control plane protocols
with its own parameter values however, no assumption is made on how
the optical node gets those value information (e.g. internally
computed, provisioned by a network management system, etc.). To this
extent, the information model intentionally ignores all internal
detailed parameters that are used by the formulas of the Optical
Computational Model (i.e., "transfer function") and simply provides
the object containers to carry results of the formulas.
4.1. The Optical Impairment Vector
Optical Impairment Vector (OIV) is defined as a list of optical
parameters to be associated to a WSON node or a WSON link. It is
defined as:
<OIV> ::= ([<LabelSet>] <OPTICAL_PARAM>) ...
The optional LabelSet object enables wavelength dependency property
as per Table 1. LabelSet has its definition in
[I-D.ietf-ccamp-general-constraint-encode].
OPTICAL_PARAM. This object represents an optical parameter. The
Impairment vector can contain a set of parameters as identified by
[ITU.G697] since those parameters match the terms of the linear
impairments computational models provided by [ITU.G680]. This
information model does not speculate about the set of parameters
(since defined elsewhere, e.g. ITU-T), however it does not preclude
extentions by adding new parameters.
4.2. Node Information
Impairment matrix describes a list of the optical parameters that
applies to a network element as a whole or ingress/egress port pairs
of a network element. Wavelength dependency property of optical
paramters is also considered.
ImpairmentMatrix ::= <MatrixID> <ConnType>
((<LinkSet> <LinkSet> <OIV>) ...)
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Where:
MatrixID. This ID is a unique identifier for the matrix. It
shall be unique in scope among connectivity matrices defined in
[I-D.ietf-ccamp-rwa-info] and impairment matrices defined here.
ConnType. This number identifies the type of matrix and it shall
be unique in scope with other values defined by impairment-free
WSON documents.
LinkSet. Same object definition and usage as
[I-D.ietf-ccamp-general-constraint-encode]. The pairs of LinkSet
identify one or more internal node constrain.
OIV. The Optical Impairment Vector defined above.
The model can be represented as a multidimensional matrix shown in
the following picture
_________________________________________
/ / / / / /|
/ / / / / / |
/________/_______/_______/_______/_______/ |
/ / / / / /| /|
/ / / / / / | |
/________/_______/_______/_______/_______/ | /|
/ / / / / /| /| |
/ / / / / / | | /|
/________/_______/_______/_______/_______/ | /| |
/ / / / / /| /| | /|
/ / / / / / | | /| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | /| | / PDL
<LinkSet#1> | - | | | | | /| | /|/
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | /| /
<linkSet#2> | | - | | | | /| | / PND
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | /|/
<linkSet#3> | | | - | | | /| /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | / Chr.Disp.
<linkSet#4> | | | | - | | /|/
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ /
<linkSet#5> | | | | | - | / OSNR
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
<LS#1> <LS#2> <LS#3> <LS#4> <LS#5>
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The connectivity matrix from
[I-D.ietf-ccamp-general-constraint-encode] is only a two dimensional
matrix, containing only binary information, through the LinkSet
pairs. In this model, a third dimension is added by generalizing the
binary information through the Optical Impairment Vector associated
with each LinkSet pair. Optical parameters in the picture are
reported just as examples while details go into specific encoding
draft [I-D.martinelli-ccamp-wson-iv-encode].
This representation shows the most general case however, the total
amount of information transported by control plane protocols can be
greatly reduced by proper encoding when the same set of values apply
to all LinkSet pairs.
[EDITOR NODE: first run of the information model does looks for
generality not for optimizing the quantity of information. We'll
deal with optimization in a further step.]
4.3. Link Information
For the list of optical parameters associated to the link, the same
approach used for the node-specific impairment information can be
applied. The link-specific impairment information is extended from
[I-D.ietf-ccamp-rwa-info] as the following:
<DynamicLinkInfo> ::= <LinkID> <AvailableLabels>
[<SharedBackupLabels>] [<OIV>]
DynamicLinkInfo is already defined in [I-D.ietf-ccamp-rwa-info] while
OIV is the Optical Impairment Vector is defined in the previous
section.
4.4. Path Information
There are cases where the optical impariments can only be described
as a contrains on the overall end to end path. In such case, the
optical impariment and/or parameter, cannot be derived (using a
simple function) from the set of node / link contributions.
An equivalent case is the option reported by [RFC6566] on IV-
Candidate paths where, the control plane knows a list of optically
feasible paths so a new path setup can be selected among that list.
Independent from the protocols and functions combination (i.e. RWA
vs. Routing vs. PCE), the IV-Candidates imply a path property stating
that a path is optically feasible.
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<PathInfo> ::= <OIV>
[EDITOR NOTE: section to be completed, especially to evaluate
protocol implications. Likely resemble to RSVP ADSPEC].
5. Encoding Considerations
Details about encoding will be defined in a separate document
[I-D.martinelli-ccamp-wson-iv-encode] however worth remembering that,
within [ITU.G697] Appending V, ITU already provides a guideline for
encoding some optical parameters.
In particular [ITU.G697] indicates that each parameter shall be
represented by a 32 bit floating point number.
As an additional consideration, actual values for each optical
parameter are provided by each optical node and it could provide by
direct measurement or from some internal computation starting from
indirect measurement. In any case the encoding shall provide the
possibility to associate a variance with the parameter. This
information will enable the function implementing IA-RWA process to
make some additional considerations on wavelength feasibility.
[RFC6566] Section 4.1.3 reports some considerations regarding this
degree of confidence during the impairment validation process.
6. Control Plane Architectures
This section briefly describes how the defintions contained in this
information model will match the architectural options described by
[RFC6566].
The first assumption is that the WSON GMPLS extentions are available
and operational. To such extent, the WSON-RWA will provide the
following information through its path computation (and RWA process):
o The wavelengths connectivity, considering also the connectivity
constraints limited by reconfigurable optics, and wavelengths
availability.
o The interface compatibility at the physical level.
o The Optical-Elettro-Optical (OEO) availability within the network
(and related physical interface compatibility). As already stated
by the framework this information it's very important for
impairment validation:
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a. If the IV functions fail (path optically infeasible), the path
computation function may use an available OEO point to find a
feasible path. In normally operated networks OEO are mainly
uses to support optically unfeasible path than mere wavelength
conversion.
b. The OEO points reset the optical impairment information since
a new light is generated.
6.1. IV-Centralized
Centralized IV process is performed by a single entity (e.g., a PCE).
Given sufficient impairment information, it can either be used to
provide a list of paths between two nodes, which are valid in terms
of optical impairments. Alternatively, it can help validate whether
a particular selected path and wavelength is feasiable or not. This
requires distribution of impairment information to the entity
performing the IV process.
[EDITOR NOTE: to be completed]
6.2. IV-Distributed
For the distributed IV process, common computational models are
needed together with the information model defined in this document.
Computational models for the optical impairments are defined by ITU
standard body. The currently available computation models are
reported in [ITU.G680] and only cover the linear impairment case.
This does not require the distribution of impairment information
since they can be collected hop-by-hop using a control plane
signaling protocol.
[EDITOR NOTE: to be completed]
7. Acknowledgements
TBD
8. Contributing Authors
This document was the collective work of several authors. The text
and content of this document was contributed by the editors and the
co-authors listed below (the contact information for the editors
appears in appropriate section and is not repeated below):
Moustafa Kattan
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Cisco
DUBAI, 500321
UNITED ARAB EMIRATES
Email: mkattan@cisco.com
Tim Gibbon
Department of Physics
Nelson Mandela Metropolitan University
SOUTH AFRICA
Email: Tim.Gibbon@nmmu.ac.za
Young Lee
Huawei
1700 Alma Drive, Suite 100
Plano, TX 75075
USA
Greg M. Bernstein
Grotto Networking
Fremont, CA
USA
Phone: +1 510 573 2237
Email: gregb@grotto-networking.com
Phone: +1 972 509 5599 x2240
Fax: +1 469 229 5397
Email: ylee@huawei.com
Fatai Zhang
Huawei
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
P.R. China
Phone: +86-755-28972912
Email: zhangfatai@huawei.com
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9. IANA Considerations
This document does not contain any IANA requirement.
10. Security Considerations
This document defines an information model for impairments in optical
networks. If such a model is put into use within a network it will
by its nature contain details of the physical characteristics of an
optical network. Such information would need to be protected from
intentional or unintentional disclosure.
11. References
11.1. Normative References
[ITU.G680]
International Telecommunications Union, "Physical transfer
functions of optical network elements ", ITU-T
Recommendation G.680, July 2007.
[ITU.G697]
International Telecommunications Union, "Optical
monitoring for dense wavelength division multiplexing
systems ", ITU-T Recommendation G.697, February 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
11.2. Informative References
[I-D.ietf-ccamp-general-constraint-encode]
Bernstein, G., Lee, Y., Li, D., and W. Imajuku, "General
Network Element Constraint Encoding for GMPLS Controlled
Networks", draft-ietf-ccamp-general-constraint-encode-11
(work in progress), May 2013.
[I-D.ietf-ccamp-rwa-info]
Lee, Y., Bernstein, G., Li, D., and W. Imajuku, "Routing
and Wavelength Assignment Information Model for Wavelength
Switched Optical Networks", draft-ietf-ccamp-rwa-info-18
(work in progress), May 2013.
[I-D.martinelli-ccamp-wson-iv-encode]
Martinelli, G., Kattan, M., Galimberti, G., and A.
Zanardi, "Encoding for WSON Information Model with
Impairments Validation.", draft-martinelli-ccamp-wson-iv-
encode-01 (work in progress), February 2013.
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[I-D.narten-iana-considerations-rfc2434bis]
Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", draft-narten-iana-
considerations-rfc2434bis-09 (work in progress), March
2008.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
June 1999.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552, July
2003.
[RFC6163] Lee, Y., Bernstein, G., and W. Imajuku, "Framework for
GMPLS and Path Computation Element (PCE) Control of
Wavelength Switched Optical Networks (WSONs)", RFC 6163,
April 2011.
[RFC6566] Lee, Y., Bernstein, G., Li, D., and G. Martinelli, "A
Framework for the Control of Wavelength Switched Optical
Networks (WSONs) with Impairments", RFC 6566, March 2012.
Appendix A. G.680 Essential information
TBD if we need some info instead of reading [ITU.G680]
[Xian's note]: I thought about listing paramters to show different
categories. but it seems to contradict to the idea of providing a
general enough information model. Any suggestions?
Authors' Addresses
Giovanni Martinelli (editor)
Cisco
via Philips 12
Monza 20900
Italy
Phone: +39 039 2092044
Email: giomarti@cisco.com
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Xian Zhang (editor)
Huawei Technologies
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzen 518129
P.R. China
Phone: +86 755 28972913
Email: zhang.xian@huawei.com
Gabriele M. Galimberti
Cisco
Via Philips,12
Monza 20900
Italy
Phone: +39 039 2091462
Email: ggalimbe@cisco.com
Andrea Zanardi
CREATE-NET
via alla Cascata 56 C, Povo
Trento 38100
Italy
Email: andrea.zanardi@create-net.org
Domenico Siracusa
CREATE-NET
via alla Cascata 56 C, Povo
Trento 38100
Italy
Email: domenico.siracusa@create-net.org
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