draft-ietf-ccamp-wson-impairments-01.txt   draft-ietf-ccamp-wson-impairments-02.txt 
Network Working Group Y. Lee Network Working Group Y. Lee
Internet Draft Huawei Internet Draft Huawei
G. Bernstein G. Bernstein
Grotto Networking Grotto Networking
D. Li D. Li
Huawei Huawei
G. Martinelli G. Martinelli
Cisco Cisco
Intended status: Informational October 22, 2009 Intended status: Informational May 20, 2010
Expires: April 2010 Expires: November 2010
A Framework for the Control of Wavelength Switched Optical Networks A Framework for the Control of Wavelength Switched Optical Networks
(WSON) with Impairments (WSON) with Impairments
draft-ietf-ccamp-wson-impairments-01.txt draft-ietf-ccamp-wson-impairments-02.txt
Status of this Memo Status of this Memo
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Abstract Abstract
The operation of optical networks requires information on the The operation of optical networks requires information on the
physical characterization of optical network elements, subsystems, physical characterization of optical network elements, subsystems,
devices, and cabling. These physical characteristics may be important devices, and cabling. These physical characteristics may be important
to consider when using a GMPLS control plane to support path setup to consider when using a GMPLS control plane to support path setup
and maintenance. This document discusses how the definition and and maintenance. This document discusses how the definition and
characterization of optical fiber, devices, subsystems, and network characterization of optical fiber, devices, subsystems, and network
elements contained in various ITU-T recommendations can be combined elements contained in various ITU-T recommendations can be combined
with GMPLS control plane protocols and mechanisms to support with GMPLS control plane protocols and mechanisms to support
Impairment Aware Routing and Wavelength Assignment (IA-RWA) in Impairment Aware Routing and Wavelength Assignment (IA-RWA) in
optical networks. optical networks.
Table of Contents Table of Contents
1. Introduction...................................................3 1. Introduction...................................................3
1.1. Revision History..........................................4 1.1. Revision History..........................................4
2. Motivation.....................................................4 2. Motivation.....................................................5
3. Impairment Aware Optical Path Computation......................5 3. Impairment Aware Optical Path Computation......................5
3.1. Optical Network Requirements and Constraints..............6 3.1. Optical Network Requirements and Constraints..............6
3.1.1. Categories of Impairment Aware Computation...........6 3.1.1. Categories of Impairment Aware Computation...........6
3.1.2. Impairment Computation and Information Sharing 3.1.2. Impairment Computation and Information Sharing
Constraints.................................................7 Constraints.................................................7
3.1.3. Impairment Estimation Functional Blocks..............8 3.1.3. Impairment Estimation Functional Blocks..............8
3.2. IA-RWA Computing and Control Plane Architectures.........10 3.2. IA-RWA Computing and Control Plane Architectures.........10
3.2.1. Combined Routing, WA, and IV........................11 3.2.1. Combined Routing, WA, and IV........................11
3.2.2. Separate Routing, WA, or IV.........................11 3.2.2. Separate Routing, WA, or IV.........................11
3.2.3. Distributed WA and/or IV............................12 3.2.3. Distributed WA and/or IV............................12
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1.1. Revision History 1.1. Revision History
Changes from 00 to 01: Changes from 00 to 01:
Added discussion of regenerators to section 3. Added discussion of regenerators to section 3.
Added to discussion of interface parameters in section 3.1.3. Added to discussion of interface parameters in section 3.1.3.
Added to discussion of IV Candidates function in section 3.2. Added to discussion of IV Candidates function in section 3.2.
Changes from 01 to 02:
Correct and refine use of "black link" concept based on liaison with
ITU-T and WG feedback.
2. Motivation 2. Motivation
There are deployment scenarios for WSON networks where not all There are deployment scenarios for WSON networks where not all
possible paths will yield suitable signal quality. There are possible paths will yield suitable signal quality. There are
multiple reasons behind this choice; here below is a non-exhaustive multiple reasons behind this choice; here below is a non-exhaustive
list of examples: list of examples:
o WSON is evolving using multi-degree optical cross connects in a o WSON is evolving using multi-degree optical cross connects in a
way that network topologies are changing from rings (and way that network topologies are changing from rings (and
interconnected rings) to a full mesh. Adding network equipment interconnected rings) to a full mesh. Adding network equipment
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approximation techniques [G.680], [G.sup39]. Also, adding or removing approximation techniques [G.680], [G.sup39]. Also, adding or removing
an optical signal on the path will not render any of the existing an optical signal on the path will not render any of the existing
signals in the network as non-viable. For example, one form of non- signals in the network as non-viable. For example, one form of non-
viability is the occurrence of transients in existing links of viability is the occurrence of transients in existing links of
sufficient magnitude to impact the BER of those existing signals. sufficient magnitude to impact the BER of those existing signals.
Much work at ITU-T has gone into developing impairment models at this Much work at ITU-T has gone into developing impairment models at this
and more detailed levels. Impairment characterization of network and more detailed levels. Impairment characterization of network
elements could then may be used to calculate which paths are elements could then may be used to calculate which paths are
conformant with a specified BER for a particular signal type. In such conformant with a specified BER for a particular signal type. In such
a case, we can combine the impairment aware (IA) path computation a case, we can combine the impairment aware (IA) path computation
with the RWA process to permit more optimal IA-RWA computations. with the RWA process to permit more optimal IA-RWA computations.
Note, the IA path computation may also take place in a separate Note, the IA path computation may also take place in a separate
entity, i.e., a PCE. entity, i.e., a PCE.
D. Detailed Impairment Computation D. Detailed Impairment Computation
This situation is applicable to networks in which impairment effects This situation is applicable to networks in which impairment effects
must be more accurately computed. For these networks, a full must be more accurately computed. For these networks, a full
computation and evaluation of the impact to any existing paths needs computation and evaluation of the impact to any existing paths needs
to be performed prior to the addition of a new path. This scenario is to be performed prior to the addition of a new path. This scenario is
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distribution amongst the elements participating in the control plane distribution amongst the elements participating in the control plane
and any appropriately equipped PCE can perform path computation. For and any appropriately equipped PCE can perform path computation. For
optical systems this may not be possible. This is typically due to optical systems this may not be possible. This is typically due to
only portions of an optical system being subject to standardization. only portions of an optical system being subject to standardization.
In ITU-T recommendations [G.698.1] and [G.698.2] which specify single In ITU-T recommendations [G.698.1] and [G.698.2] which specify single
channel interfaces to multi-channel DWDM systems only the single channel interfaces to multi-channel DWDM systems only the single
channel interfaces (transmit and receive) are specified while the channel interfaces (transmit and receive) are specified while the
multi-channel links are not standardized. These DWDM links are multi-channel links are not standardized. These DWDM links are
referred to as "black links" since their details are not generally referred to as "black links" since their details are not generally
available. Note however the overall impact of a black link at the available. Note however the overall impact of a black link at the
single channel interface points typically can be characterized single channel interface points is limited by [G.698.1] and
[G.698.1] and [G.698.2]. [G.698.2].
Typically a vendor might use proprietary impairment models for DWDM Typically a vendor might use proprietary impairment models for DWDM
spans and to estimate the validity of optical paths. For example, spans and to estimate the validity of optical paths. For example,
models of optical nonlinearities are not currently standardized. models of optical nonlinearities are not currently standardized.
Vendors may also choose not to publish impairment details for links Vendors may also choose not to publish impairment details for links
or a set of network elements in order not to divulge their optical or a set of network elements in order not to divulge their optical
system designs. system designs.
In general, the impairment estimation/validation of an optical path In general, the impairment estimation/validation of an optical path
for optical networks with "black links" (path) could not be performed for optical networks with "black links" (path) could not be performed
by a general purpose impairment aware (IA) computation entity since by a general purpose impairment aware (IA) computation entity since
it would not have access to or understand the "black link" impairment it would not have access to or understand the "black link" impairment
parameters. However, impairment estimation (optical path validation) parameters. However, impairment estimation (optical path validation)
but could be performed by a vendor specific impairment aware could be performed by a vendor specific impairment aware computation
computation entity. Such a vendor specific IA computation, could entity. Such a vendor specific IA computation, could utilize
utilize standardized impairment information imported from other standardized impairment information imported from other network
network elements in these proprietary computations. In section 3.2. elements in these proprietary computations.
In the following we will use the term "black links" to describe these In the following we will use the term "black links" to describe these
computation and information sharing constraints in optical networks. computation and information sharing constraints in optical networks.
From the control plane perspective we have the following options: From the control plane perspective we have the following options:
A. The vendor in control of the "black links" can furnish a list of A. The authority in control of the "black links" can furnish a list
all viable paths between all viable node pairs to a computational of all viable paths between all viable node pairs to a
entity. This information would be particularly useful as an input computational entity. This information would be particularly
to RWA optimization to be performed by another computation entity. useful as an input to RWA optimization to be performed by another
The difficulty here is for larger networks such a list of paths computation entity. The difficulty here is for larger networks
along with any wavelength constraints could get unmanageably such a list of paths along with any wavelength constraints could
large. get unmanageably large.
B. The vendor in control of the "black links" could furnish a PCE B. The authority in control of the "black links" could provide a PCE
like entity that would furnish a list of viable paths/wavelengths like entity that would furnish a list of viable paths/wavelengths
between two requested nodes. This is useful as an input to RWA between two requested nodes. This is useful as an input to RWA
optimizations and can reduce the scaling issue previously optimizations and can reduce the scaling issue previously
mentioned. Such a PCE like entity would not need to perform a full mentioned. Such a PCE like entity would not need to perform a full
RWA computation, i.e., it would not need to take into account RWA computation, i.e., it would not need to take into account
current wavelength availability on links. Such an approach may current wavelength availability on links. Such an approach may
require PCEP extensions for both the request and response require PCEP extensions for both the request and response
information. information.
C. The vendor in control of the "black links" can furnish a PCE that C. The authority in control of the "black links" can provide a PCE
performs full IA-RWA services. The difficulty is this requires the that performs full IA-RWA services. The difficulty is this
one vendor to also become the sole source of all RWA optimization requires the one authority to also become the sole source of all
algorithms and such. RWA optimization algorithms and such.
In all the above cases it would be the responsibility of the vendor In all the above cases it would be the responsibility of the
in control of the "black links" to import the shared impairment authority in control of the "black links" to import the shared
information from the other NEs via the control plane or other means impairment information from the other NEs via the control plane or
as necessary. other means as necessary.
3.1.3. Impairment Estimation Functional Blocks 3.1.3. Impairment Estimation Functional Blocks
The Impairment Estimation process can be modeled by the following The Impairment Estimation process can be modeled by the following
functional blocks. These blocks are independent of any Control Plane functional blocks. These blocks are independent of any Control Plane
architecture, that is, they can be implemented by the same or by architecture, that is, they can be implemented by the same or by
different control plane functional blocks. different control plane functional blocks.
+-----------------+ +-----------------+
+------------+ +-----------+ | +------------+ | +------------+ +-----------+ | +------------+ |
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In this case an Impairment Validation (IV) process furnishes a set of In this case an Impairment Validation (IV) process furnishes a set of
paths between two nodes along with any wavelength restrictions such paths between two nodes along with any wavelength restrictions such
that the paths are valid with respect to optical impairments. These that the paths are valid with respect to optical impairments. These
paths and wavelengths may not be actually available in the network paths and wavelengths may not be actually available in the network
due to its current usage state. This set of paths would be returned due to its current usage state. This set of paths would be returned
in response to a request for a set of at most K valid paths between in response to a request for a set of at most K valid paths between
two specified nodes. Note that such a process never directly two specified nodes. Note that such a process never directly
discloses optical impairment information. discloses optical impairment information.
In this case the control plane simply make use of candidate paths but In this case the control plane simply makes use of candidate paths
does not know any optical impairment information. Another option is but does not know any optical impairment information. Another option
when the path validity is assessed within the control plane. The is when the path validity is assessed within the control plane. The
following cases highlight this situation. following cases highlight this situation.
o IV-Detailed Verification o IV-Detailed Verification
In this case an IV process is given a particular path and wavelength In this case an IV process is given a particular path and wavelength
through an optical network and is asked to verify whether the overall through an optical network and is asked to verify whether the overall
quality objectives for the signal over this path can be met. Note quality objectives for the signal over this path can be met. Note
that such a process never directly discloses optical impairment that such a process never directly discloses optical impairment
information. information.
o IV-Distributed o IV-Distributed
In this distributed IV process impairment approximate degradation In this distributed IV process, impairment approximate degradation
measures such as OSNR, dispersion, DGD, etc. are accumulated along measures such as OSNR, dispersion, DGD, etc. are accumulated along
the path via a signaling like protocol. When the accumulated measures the path via a signaling like protocol. When the accumulated measures
reach the destination node a decision on the impairment validity of reach the destination node a decision on the impairment validity of
the path can be made. Note that such a process would entail revealing the path can be made. Note that such a process would entail revealing
an individual network element's impairment information. an individual network element's impairment information.
The following subsections present three major classes of IA-RWA path The following subsections present three major classes of IA-RWA path
computation architectures and their respective advantages and computation architectures and their respective advantages and
disadvantages. disadvantages.
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The advantages, requirements and suitability of these options are as The advantages, requirements and suitability of these options are as
follows: follows:
o Combined IV & RWA process o Combined IV & RWA process
This alternative combines RWA and IV within a single computation This alternative combines RWA and IV within a single computation
entity enabling highest potential optimality and efficiency in IA- entity enabling highest potential optimality and efficiency in IA-
RWA. This alternative requires that the computational entity knows RWA. This alternative requires that the computational entity knows
impairment information as well as non-impairment RWA information. impairment information as well as non-impairment RWA information.
This alternative can be used with "black links", but would then need This alternative can be used with "black links", but would then need
to be provided by the vendor controlling the "black links". to be provided by the authority controlling the "black links".
o IV-Candidates + RWA process o IV-Candidates + RWA process
This alternative allows separation of impairment information into two This alternative allows separation of impairment information into two
computational entities while still maintaining a high degree of computational entities while still maintaining a high degree of
potential optimality and efficiency in IA-RWA. The candidates IV potential optimality and efficiency in IA-RWA. The candidates IV
process needs to know impairment information from all optical network process needs to know impairment information from all optical network
elements, while the RWA process needs to know non-impairment RWA elements, while the RWA process needs to know non-impairment RWA
information from the network elements. This alternative can be used information from the network elements. This alternative can be used
with "black links", but the vendor in control of the "black links" with "black links", but the authority in control of the "black links"
would need to provide the functionality of the IV-candidates process. would need to provide the functionality of the IV-candidates process.
Note that this is still very useful since the algorithmic areas of IV Note that this is still very useful since the algorithmic areas of IV
and RWA are very different and prone to specialization. and RWA are very different and prone to specialization.
o Routing + Distributed WA and IV o Routing + Distributed WA and IV
In this alternative a signaling protocol is extended and leveraged in In this alternative a signaling protocol is extended and leveraged in
the wavelength assignment and impairment validation processes. the wavelength assignment and impairment validation processes.
Although this doesn't enable as high a potential degree of optimality Although this doesn't enable as high a potential degree of optimality
of optimality as (a) or (b), it does not require distribution of of optimality as (a) or (b), it does not require distribution of
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validation architectural options. validation architectural options.
The advantages, requirements and suitability of these detailed The advantages, requirements and suitability of these detailed
validation options are as follows: validation options are as follows:
o Combined approximate IV & RWA + Detailed-IV o Combined approximate IV & RWA + Detailed-IV
This alternative combines RWA and approximate IV within a single This alternative combines RWA and approximate IV within a single
computation entity enabling highest potential optimality and computation entity enabling highest potential optimality and
efficiency in IA-RWA; then has a separate entity performing detailed efficiency in IA-RWA; then has a separate entity performing detailed
impairment validation. In the case of "black links" the vendor impairment validation. In the case of "black links" the authority
controlling the "black links" would need to provide all controlling the "black links" would need to provide all
functionality. functionality.
o Candidates-IV + RWA + Detailed-IV o Candidates-IV + RWA + Detailed-IV
This alternative allows separation of approximate impairment This alternative allows separation of approximate impairment
information into a computational entity while still maintaining a information into a computational entity while still maintaining a
high degree of potential optimality and efficiency in IA-RWA; then a high degree of potential optimality and efficiency in IA-RWA; then a
separate computation entity performs detailed impairment validation. separate computation entity performs detailed impairment validation.
Note that detailed impairment estimation is not standardized. Note that detailed impairment estimation is not standardized.
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[WSON-Frame] G. Bernstein, Y. Lee, W. Imajuku, "Framework for GMPLS [WSON-Frame] G. Bernstein, Y. Lee, W. Imajuku, "Framework for GMPLS
and PCE Control of Wavelength Switched Optical Networks", and PCE Control of Wavelength Switched Optical Networks",
work in progress: draft-ietf-ccamp-wavelength-switched- work in progress: draft-ietf-ccamp-wavelength-switched-
framework-02.txt, March 2009. framework-02.txt, March 2009.
8.2. Informative References 8.2. Informative References
[Imp-Info] G. Bernstein, Y. Lee, D. Li, "A Framework for the Control [Imp-Info] G. Bernstein, Y. Lee, D. Li, "A Framework for the Control
and Measurement of Wavelength Switched Optical Networks and Measurement of Wavelength Switched Optical Networks
(WSON) with Impairments", work in progress: draft- (WSON) with Impairments", work in progress: draft-
bernstein-wson-impairment-info-01.txt, March 2009. bernstein-wson-impairment-info.
[Martinelli] G. Martinelli (ed.) and A. Zanardi (ed.), "GMPLS [Martinelli] G. Martinelli (ed.) and A. Zanardi (ed.), "GMPLS
Signaling Extensions for Optical Impairment Aware Lightpath Signaling Extensions for Optical Impairment Aware Lightpath
Setup", Work in Progress: draft-martinelli-ccamp-optical- Setup", Work in Progress: draft-martinelli-ccamp-optical-
imp-signaling-02.txt, February 2008. imp-signaling-02.txt, February 2008.
[WSON-Comp] G. Bernstein, Y. Lee, Ben Mack-Crane, "WSON Signal [WSON-Comp] G. Bernstein, Y. Lee, Ben Mack-Crane, "WSON Signal
Characteristics and Network Element Compatibility Characteristics and Network Element Compatibility
Constraints for GMPLS", work in progress: draft-bernstein- Constraints for GMPLS", work in progress: draft-bernstein-
ccamp-wson-signal. ccamp-wson-signal.
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