draft-ietf-ccamp-wson-impairments-07.txt   draft-ietf-ccamp-wson-impairments-08.txt 
Network Working Group Y. Lee Network Working Group Y. Lee
Huawei Huawei
G. Bernstein G. Bernstein
Grotto Networking Grotto Networking
D. Li D. Li
Huawei Huawei
G. Martinelli G. Martinelli
Cisco Cisco
Internet Draft Internet Draft
Intended status: Informational April 29, 2011 Intended status: Informational November 23, 2011
Expires: October 2011 Expires: May 2012
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-07.txt draft-ietf-ccamp-wson-impairments-08.txt
Abstract
As an optical signal progresses along its path, it may be altered by
the various physical processes in the optical fibers and devices it
encounters. When such alterations result in signal degradation,
these processes are usually referred to as "impairments". These
physical characteristics may be important constraints to consider
when using a GMPLS control plane to support path setup and
maintenance in wavelength switched optical networks.
This document provides a framework for applying GMPLS protocols and
the PCE architecture to support Impairment Aware Routing and
Wavelength Assignment (IA-RWA) in wavelength switched optical
networks. Specifically, this document discusses key computing
constraints, scenarios and architectural processes: Routing,
Wavelength Assignment, and Impairment Validation. This document does
not define optical data plane aspects; impairment parameters,
measurement of, or assessment and qualification of a route, but
rather it describes the architectural and information components for
protocol solutions.
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Abstract
As an optical signal progresses along its path it may be altered by
the various physical processes in the optical fibers and devices it
encounters. When such alterations result in signal degradation, these
processes are usually referred to as "impairments". These physical
characteristics may be important constraints to consider when using a
GMPLS control plane to support path setup and maintenance in
wavelength switched optical networks.
This document provides a framework for applying GMPLS protocols and
the PCE architecture to support Impairment Aware Routing and
Wavelength Assignment (IA-RWA) in wavelength switched optical
networks. This document does not define optical data plane aspects;
impairment parameters, measurement of, or assessment and
qualification of a route, but rather it describes the architectural
and information components for protocol solutions.
Table of Contents Table of Contents
1. Introduction...................................................3 1. Introduction...................................................3
2. Terminology....................................................3 2. Terminology....................................................4
3. Applicability..................................................5 3. Applicability..................................................6
4. Impairment Aware Optical Path Computation......................6 4. Impairment Aware Optical Path Computation......................7
4.1. Optical Network Requirements and Constraints..............7 4.1. Optical Network Requirements and Constraints..............8
4.1.1. Impairment Aware Computation Scenarios...............8 4.1.1. Impairment Aware Computation Scenarios...............8
4.1.2. Impairment Computation and Information Sharing 4.1.2. Impairment Computation and Information Sharing
Constraints.................................................9 Constraints.................................................9
4.1.3. Impairment Estimation Process.......................10 4.1.3. Impairment Estimation Process.......................11
4.2. IA-RWA Computation and Control Plane Architectures.......12 4.2. IA-RWA Computation and Control Plane Architectures.......12
4.2.1. Combined Routing, WA, and IV........................14 4.2.1. Combined Routing, WA, and IV........................14
4.2.2. Separate Routing, WA, or IV.........................14 4.2.2. Separate Routing, WA, or IV.........................14
4.2.3. Distributed WA and/or IV............................14 4.2.3. Distributed WA and/or IV............................15
4.3. Mapping Network Requirements to Architectures............15 4.3. Mapping Network Requirements to Architectures............16
5. Protocol Implications.........................................18 5. Protocol Implications.........................................18
5.1. Information Model for Impairments........................18 5.1. Information Model for Impairments........................19
5.2. Routing..................................................19 5.2. Routing..................................................20
5.3. Signaling................................................20 5.3. Signaling................................................20
5.4. PCE......................................................20 5.4. PCE......................................................21
5.4.1. Combined IV & RWA...................................20 5.4.1. Combined IV & RWA...................................21
5.4.2. IV-Candidates + RWA.................................21 5.4.2. IV-Candidates + RWA.................................21
5.4.3. Approximate IA-RWA + Separate Detailed IV...........23 5.4.3. Approximate IA-RWA + Separate Detailed IV...........24
6. Security Considerations.......................................24 6. Security Considerations.......................................25
7. IANA Considerations...........................................25 7. IANA Considerations...........................................26
8. References....................................................25 8. References....................................................26
8.1. Normative References.....................................25 8.1. Normative References.....................................26
8.2. Informative References...................................25 8.2. Informative References...................................26
9. Acknowledgments...............................................25 9. Acknowledgments...............................................27
1. Introduction 1. Introduction
Wavelength Switched Optical Networks (WSONs) are constructed from Wavelength Switched Optical Networks (WSONs) are constructed from
subsystems that may include Wavelength Division Multiplexed (WDM) subsystems that may include Wavelength Division Multiplexed (WDM)
links, tunable transmitters and receivers, Reconfigurable Optical links, tunable transmitters and receivers, Reconfigurable Optical
Add/Drop Multiplexers (ROADM), wavelength converters, and electro- Add/Drop Multiplexers (ROADM), wavelength converters, and electro-
optical network elements. A WSON is a wavelength division optical network elements. A WSON is a wavelength division
multiplexed (WDM)-based optical network in which switching is multiplexed (WDM)-based optical network in which switching is
performed selectively based on the center wavelength of an optical performed selectively based on the center wavelength of an optical
signal. signal.
As an optical signal progresses along its path it may be altered by As an optical signal progresses along its path, it may be altered by
the various physical processes in the optical fibers and devices it the various physical processes in the optical fibers and devices it
encounters. When such alterations result in signal degradation, these encounters. When such alterations result in signal degradation,
processes are usually referred to as "impairments". Optical these processes are usually referred to as "impairments". Optical
impairments accumulate along the path (without 3R regeneration) impairments accumulate along the path (without 3R regeneration)
traversed by the signal. They are influenced by the type of fiber traversed by the signal. They are influenced by the type of fiber
used, the types and placement of various optical devices and the used, the types and placement of various optical devices, and the
presence of other optical signals that may share a fiber segment presence of other optical signals that may share a fiber segment
along the signal's path. The degradation of the optical signals due along the signal's path. The degradation of the optical signals due
to impairments can result in unacceptable bit error rates or even a to impairments can result in unacceptable bit error rates or even a
complete failure to demodulate and/or detect the received signal. complete failure to demodulate and/or detect the received signal.
In order to provision an optical connection (an optical path) through In order to provision an optical connection (an optical path)
a WSON, a combination of path continuity, resource availability and through a WSON, a combination of path continuity, resource
impairments constraints must be met to determine viable and optimal availability, and impairments constraints must be met to determine
paths through the network. The determination of appropriate paths is viable and optimal paths through the network. The determination of
known as Impairment Aware Routing and Wavelength Assignment (IA-RWA). appropriate paths is known as Impairment Aware Routing and
Wavelength Assignment (IA-RWA).
Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] provides Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945]
a set of control plane protocols that can be used to operate networks provides a set of control plane protocols that can be used to
ranging from packet switch capable networks, through those networks operate networks ranging from packet switch capable networks,
that use time division multiplexing, and WDM. The Path Computation through those networks that use time division multiplexing and WDM.
Element (PCE) architecture [RFC4655] defines functional computation The Path Computation Element (PCE) architecture [RFC4655] defines
components that can be used in cooperation with the GMPLS control functional computation components that can be used in cooperation
plane to compute and suggest appropriate paths. [RFC4054] provides an with the GMPLS control plane to compute and suggest appropriate
overview of optical impairments and their routing (path selection) paths. [RFC4054] provides an overview of optical impairments and
implications for GMPLS. This document uses as reference [G.680] and their routing (path selection) implications for GMPLS. This document
other ITU-T Recommendations for the optical data plane aspects. uses as reference [G.680] and other ITU-T Recommendations for the
optical data plane aspects.
This document provides a framework for applying GMPLS protocols and This document provides a framework for applying GMPLS protocols and
the PCE architecture to the control and operation of IA-RWA for the PCE architecture to the control and operation of IA-RWA for
WSONs. To aid in this evaluation, this document provides an overview WSONs. To aid in this evaluation, this document provides an
of the subsystems and processes that comprise WSONs and describes IA- overview of the subsystems and processes that comprise WSONs and
RWA models based on the corresponding ITU-T Recommendations, so that describes IA-RWA models based on the corresponding ITU-T
the information requirements for use by GMPLS and PCE systems can be Recommendations, so that the information requirements for use by
identified. This work will facilitate the development of protocol GMPLS and PCE systems can be identified. This work will facilitate
extensions in support of IA-RWA within the GMPLS and PCE protocol the development of protocol extensions in support of IA-RWA within
families. the GMPLS and PCE protocol families.
2. Terminology 2. Terminology
Add/Drop Multiplexers (ADM): An optical device used in WDM networks ADM: Add/Drop Multiplexers - An optical device used in WDM networks
composed of one or more line side ports and typically many tributary composed of one or more line side ports and typically many tributary
ports. ports.
CWDM: Coarse Wavelength Division Multiplexing. Black links: Black links refer to tributary interfaces where only
link characteristics are defined. This approach enables transverse
compatibility at the single-channel point using a direct wavelength-
multiplexing configuration.
DWDM: Dense Wavelength Division Multiplexing. CWDM: Coarse Wavelength Division Multiplexing
FOADM: Fixed Optical Add/Drop Multiplexer. DGD: Differential Group Delay
GMPLS: Generalized Multi-Protocol Label Switching. DWDM: Dense Wavelength Division Multiplexing
FOADM: Fixed Optical Add/Drop Multiplexer
GMPLS: Generalized Multi-Protocol Label Switching
IA-RWA: Impairment Aware Routing and Wavelength Assignment IA-RWA: Impairment Aware Routing and Wavelength Assignment
Line side: In WDM system line side ports and links typically can Line side: In WDM system line side ports and links typically can
carry the full multiplex of wavelength signals, as compared to carry the full multiplex of wavelength signals, as compared to
tributary (add or drop ports) that typically carry a few (typically tributary (add or drop ports) that typically carry a few (typically
one) wavelength signals. one) wavelength signals.
OXC: Optical cross connect. An optical switching element in which a NEs: Network Elements
OADMs: Optical Add Drop Multiplexers
OSNR: Optical Signal to Noise Ratio
OXC: Optical cross connect - An optical switching element in which a
signal on any input port can reach any output port. signal on any input port can reach any output port.
PCC: Path Computation Client. Any client application requesting a PCC: Path Computation Client - Any client application requesting a
path computation to be performed by the Path Computation Element. path computation to be performed by the Path Computation Element.
PCE: Path Computation Element. An entity (component, application, or PCE: Path Computation Element - An entity (component, application,
network node) that is capable of computing a network path or route or network node) that is capable of computing a network path or
based on a network graph and applying computational constraints. route based on a network graph and applying computational
constraints.
PCEP: PCE Communication Protocol. The communication protocol between PCEP: PCE Communication Protocol - The communication protocol
a Path Computation Client and Path Computation Element. between a Path Computation Client and Path Computation Element.
ROADM: Reconfigurable Optical Add/Drop Multiplexer. A wavelength PXC: Photonic Cross Connects
Q-factor: The Q-factor provides a qualitative description of the
receiver performance. It is a function of the signal to optical
noise ratio. The Q-factor suggests the minimum SNR (Signal Noise
Ratio) required to obtain a specific BER for a given signal.
ROADM: Reconfigurable Optical Add/Drop Multiplexer - A wavelength
selective switching element featuring input and output line side selective switching element featuring input and output line side
ports as well as add/drop tributary ports. ports as well as add/drop tributary ports.
RWA: Routing and Wavelength Assignment. RWA: Routing and Wavelength Assignment
Transparent Network: A wavelength switched optical network that does Transparent Network: A wavelength switched optical network that does
not contain regenerators or wavelength converters. not contain regenerators or wavelength converters.
Translucent Network: A wavelength switched optical network that is Translucent Network: A wavelength switched optical network that is
predominantly transparent but may also contain limited numbers of predominantly transparent but may also contain limited numbers of
regenerators and/or wavelength converters. regenerators and/or wavelength converters.
Tributary: A link or port on a WDM system that can carry Tributary: A link or port on a WDM system that can carry
significantly less than the full multiplex of wavelength signals significantly less than the full multiplex of wavelength signals
found on the line side links/ports. Typical tributary ports are the found on the line side links/ports. Typical tributary ports are the
add and drop ports on an ADM and these support only a single add and drop ports on an ADM and these support only a single
wavelength channel. wavelength channel.
Wavelength Conversion/Converters: The process of converting Wavelength Conversion/Converters: The process of converting
information bearing optical signal centered at a given wavelength to information bearing optical signal centered at a given wavelength to
one with "equivalent" content centered at a different wavelength. one with "equivalent" content centered at a different wavelength.
Wavelength conversion can be implemented via an optical-electronic- Wavelength conversion can be implemented via an optical-electronic-
optical (OEO) process or via a strictly optical process. optical (OEO) process or via a strictly optical process.
WDM: Wavelength Division Multiplexing. WDM: Wavelength Division Multiplexing
Wavelength Switched Optical Networks (WSONs): WDM based optical Wavelength Switched Optical Networks (WSONs): WDM based optical
networks in which switching is performed selectively based on the networks in which switching is performed selectively based on the
center wavelength of an optical signal. center wavelength of an optical signal.
3. Applicability 3. Applicability
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; below is a non-exhaustive list of examples: multiple reasons; below is a non-exhaustive list of examples:
skipping to change at page 6, line 9 skipping to change at page 6, line 41
interconnected rings) to general mesh. Adding network equipment interconnected rings) to general mesh. Adding network equipment
such as amplifiers or regenerators, to ensure all paths are such as amplifiers or regenerators, to ensure all paths are
feasible, leads to an over-provisioned network. Indeed, even with feasible, leads to an over-provisioned network. Indeed, even with
over provisioning, the network could still have some infeasible over provisioning, the network could still have some infeasible
paths. paths.
o Within a given network, the optical physical interface may change o Within a given network, the optical physical interface may change
over the network life, e.g., the optical interfaces might be over the network life, e.g., the optical interfaces might be
upgraded to higher bit-rates. Such changes could result in paths upgraded to higher bit-rates. Such changes could result in paths
being unsuitable for the optical signal. Moreover, the optical being unsuitable for the optical signal. Moreover, the optical
physical interfaces are typically provisioned at various stages of physical interfaces are typically provisioned at various stages
the network's life span as needed by traffic demands. of the network's life span as needed by traffic demands.
o There are cases where a network is upgraded by adding new optical o There are cases where a network is upgraded by adding new optical
cross connects to increase network flexibility. In such cases cross connects to increase network flexibility. In such cases,
existing paths will have their feasibility modified while new existing paths will have their feasibility modified while new
paths will need to have their feasibility assessed. paths will need to have their feasibility assessed.
o With the recent bit rate increases from 10G to 40G and 100G over a o With the recent bit rate increases from 10G to 40G and 100G over
single wavelength, WSON networks will likely be operated with a a single wavelength, WSON networks will likely be operated with a
mix of wavelengths at different bit rates. This operational mix of wavelengths at different bit rates. This operational
scenario will impose impairment constraints due to different scenario will impose impairment constraints due to different
physical behavior of different bit rates and associated modulation physical behavior of different bit rates and associated
formats. modulation formats.
Not having an impairment aware control plane for such networks will Not having an impairment aware control plane for such networks will
require a more complex network design phase that needs to take into require a more complex network design phase that needs to take into
account the evolving network status in term of equipments and account the evolving network status in term of equipments and
traffic at the beginning stage. In addition, network operations such traffic at the beginning stage. In addition, network operations such
as path establishment, will require significant pre-design via non- as path establishment, will require significant pre-design via non-
control plane processes resulting in significantly slower network control plane processes resulting in significantly slower network
provisioning. provisioning.
It should be highlighted that the impact of impairments and use in It should be highlighted that the impact of impairments and use in
determination of path viability is not sufficiently well established determination of path viability is not sufficiently well established
for general applicability [G.680]; it will depend on network for general applicability [G.680]; it will depend on network
implementations. The use of an impairment aware control plane and set implementations. The use of an impairment aware control plane and
of information distributed will need to be evaluated on a case by set of information distributed will need to be evaluated on a case
case scenario. by case scenario.
4. Impairment Aware Optical Path Computation 4. Impairment Aware Optical Path Computation
The basic criteria for path selection is whether one can successfully The basic criteria for path selection is whether one can
transmit the signal from a transmitter to a receiver within a successfully transmit the signal from a transmitter to a receiver
prescribed error tolerance, usually specified as a maximum within a prescribed error tolerance, usually specified as a maximum
permissible bit error ratio (BER). This generally depends on the permissible bit error ratio (BER). This generally depends on the
nature of the signal transmitted between the sender and receiver and nature of the signal transmitted between the sender and receiver and
the nature of the communications channel between the sender and the nature of the communications channel between the sender and
receiver. The optical path utilized (along with the wavelength) receiver. The optical path utilized (along with the wavelength)
determines the communications channel. determines the communications channel.
The optical impairments incurred by the signal along the fiber and at The optical impairments incurred by the signal along the fiber and
each optical network element along the path determine whether the BER at each optical network element along the path determine whether the
performance or any other measure of signal quality can be met for a BER performance or any other measure of signal quality can be met
signal on a particular end-to-end path. for a signal on a particular end-to-end path.
Impairment-aware path calculation also needs to take into account Impairment-aware path calculation also needs to take into account
when regeneration is used along the path. [RFC6163] provides when regeneration is used along the path. [RFC6163] provides
background on the concept of optical translucent networks which background on the concept of optical translucent networks which
contains transparent elements and electro-optical elements such as contains transparent elements and electro-optical elements such as
OEO regenerations. In such networks a generic light path can go OEO regenerations. In such networks, a generic light path can go
through a number of regeneration points. through a number of regeneration points.
Regeneration points could happen for two reasons: Regeneration points could happen for two reasons:
(i) wavelength conversion to assist RWA to avoid wavelength blocking. (i) Due to wavelength conversion to assist RWA to avoid wavelength
This is the impairment free case covered by [RFC6163]. blocking. This is the impairment free case covered by [RFC6163].
(ii) the optical signal without regeneration would be too degraded (ii) The optical signal without regeneration would be too degraded
to meet end to end BER requirements. This is the case when RWA to meet end to end BER requirements. This is the case when RWA
takes into consideration impairment estimation covered by this takes into consideration impairment estimation covered by this
document. document.
In the latter case an optical path can be seen as a set of transparent In the latter case, an optical path can be seen as a set of
segments. The optical impairments calculation needs to be reset at each transparent segments. The optical impairments calculation needs to
regeneration point so each transparent segment will have its own be reset at each regeneration point so each transparent segment will
impairment evaluation. have its own impairment evaluation.
+---+ +----+ +----+ +-----+ +----+ +---+ +---+ +----+ +----+ +-----+ +----+ +---+
| I |----| N1 |---| N2 |-----| REG |-----| N3 |----| E | | I |----| N1 |---| N2 |-----| REG |-----| N3 |----| E |
+---+ +----+ +----+ +-----+ +----+ +---+ +---+ +----+ +----+ +-----+ +----+ +---+
|<----------------------------->|<-------------------->| |<----------------------------->|<-------------------->|
Segment 1 Segment 2 Segment 1 Segment 2
Figure 1 Optical path as a set of transparent segments Figure 1 Optical path as a set of transparent segments
For example, Figure 1 represents an optical path from node I to node E For example, Figure 1 represents an optical path from node I to node
with a regeneration point REG in between. It is feasible from an E with a regeneration point REG in between. It is feasible from an
impairment validation perspective if both segments (I, N1, N2, REG) and impairment validation perspective if both segments (I, N1, N2, REG)
(REG, N3, E) are feasible. and (REG, N3, E) are feasible.
4.1. Optical Network Requirements and Constraints 4.1. Optical Network Requirements and Constraints
This section examines the various optical network requirements and This section examines the various optical network requirements and
constraints that an impairment aware optical control plane may have constraints under which an impairment aware optical control plane
to operate under. These requirements and constraints motivate the IA- may have to operate under. These requirements and constraints
RWA architectural alternatives to be presented in the following motivate the IA-RWA architectural alternatives to be presented in
section. Different optical networks contexts can be broken into two the following section. Different optical networks contexts can be
main criteria: (a) the accuracy required in the estimation of broken into two main criteria: (a) the accuracy required in the
impairment effects, and (b) the constraints on the impairment estimation of impairment effects, and (b) the constraints on the
estimation computation and/or sharing of impairment information. impairment estimation computation and/or sharing of impairment
information.
4.1.1. Impairment Aware Computation Scenarios 4.1.1. Impairment Aware Computation Scenarios
A. No concern for impairments or Wavelength Continuity Constraints A. No concern for impairments or Wavelength Continuity Constraints
This situation is covered by existing GMPLS with local wavelength This situation is covered by existing GMPLS with local wavelength
(label) assignment. (label) assignment.
B. No concern for impairments but Wavelength Continuity Constraints B. No concern for impairments but Wavelength Continuity Constraints
This situation is applicable to networks designed such that every This situation is applicable to networks designed such that every
possible path is valid for the signal types permitted on the network. possible path is valid for the signal types permitted on the
In this case impairments are only taken into account during network network. In this case, impairments are only taken into account
design and after that, for example during optical path computation, during network design and after that, for example during optical
they can be ignored. This is the case discussed in [RFC6163] where path computation, they can be ignored. This is the case discussed in
impairments may be ignored by the control plane and only optical [RFC6163] where impairments may be ignored by the control plane and
parameters related to signal compatibility are considered. only optical parameters related to signal compatibility are
considered.
C. Approximated Impairment Estimation C. Approximated Impairment Estimation
This situation is applicable to networks in which impairment effects This situation is applicable to networks in which impairment effects
need to be considered but there is sufficient margin such that they need to be considered but there is sufficient margin such that they
can be estimated via approximation techniques such as link budgets can be estimated via approximation techniques such as link budgets
and dispersion [G.680],[G.sup39]. The viability of optical paths for and dispersion [G.680],[G.sup39]. The viability of optical paths for
a particular class of signals can be estimated using well defined a particular class of signals can be estimated using well defined
approximation techniques [G.680], [G.sup39]. This is the generally approximation techniques [G.680], [G.sup39]. This is the generally
known as linear case where only linear effects are taken into known as linear case where only linear effects are taken into
account. Note that adding or removing an optical signal on the path account. Note that adding or removing an optical signal on the path
should not render any of the existing signals in the network as non- should not render any of the existing signals in the network as non-
viable. For example, one form of non-viability is the occurrence of viable. For example, one form of non-viability is the occurrence of
transients in existing links of sufficient magnitude to impact the transients in existing links of sufficient magnitude to impact the
BER of existing signals. BER of 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
and more detailed levels. Impairment characterization of network this and more detailed levels. Impairment characterization of
elements may be used to calculate which paths are conformant with a network elements may be used to calculate which paths are conformant
specified BER for a particular signal type. In such a case, the with a specified BER for a particular signal type. In such a case,
impairment aware (IA) path computation can be combined with the RWA the impairment aware (IA) path computation can be combined with the
process to permit more optimal IA-RWA computations. Note that the IA RWA process to permit more optimal IA-RWA computations. Note that
path computation may also take place in a separate entity, i.e., a the IA path computation may also take place in a separate entity,
PCE. i.e., a PCE.
D. Accurate 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. Currently no to be performed prior to the addition of a new path. Currently no
impairment models are available from ITU-T and this scenario is impairment models are available from ITU-T and this scenario is
outside the scope of this document. outside the scope of this document.
4.1.2. Impairment Computation and Information Sharing Constraints 4.1.2. Impairment Computation and Information Sharing Constraints
In GMPLS, information used for path computation is standardized for In GMPLS, information used for path computation is standardized for
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
channel interfaces to multi-channel DWDM systems only the single single channel interfaces to multi-channel DWDM systems, only the
channel interfaces (transmit and receive) are specified while the single channel interfaces (transmit and receive) are specified while
multi-channel links are not standardized. These DWDM links are the 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. However, note that the overall impact of a black link at
single channel interface points is limited by [G.698.1] and the single channel interface points is limited by [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 in order to estimate the validity of optical paths. For
models of optical nonlinearities are not currently standardized. example, models of optical nonlinearities are not currently
Vendors may also choose not to publish impairment details for links standardized. Vendors may also choose not to publish impairment
or a set of network elements in order not to divulge their optical details for links or a set of network elements in order not to
system designs. divulge their optical 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" in the path could not be
by a general purpose impairment aware (IA) computation entity since performed by a general purpose impairment aware (IA) computation
it would not have access to or understand the "black link" impairment entity since it would not have access to or understand the "black
parameters. However, impairment estimation (optical path validation) link" impairment parameters. However, impairment estimation (optical
could be performed by a vendor specific impairment aware computation path validation) could be performed by a vendor specific impairment
entity. Such a vendor specific IA computation, could utilize aware computation entity. Such a vendor specific IA computation
standardized impairment information imported from other network could utilize standardized impairment information imported from
elements in these proprietary computations. other network elements in these proprietary computations.
In the following the term "black links" will be used to describe In the following, the term "black links" will be used to describe
these computation and information sharing constraints in optical these computation and information sharing constraints in optical
networks. From the control plane perspective the following options networks. From the control plane perspective the following options
are considered: are considered:
1. The authority in control of the "black links" can furnish a list 1. The authority in control of the "black links" can furnish a list
of all viable paths between all viable node pairs to a of all viable paths between all viable node pairs to a
computational entity. This information would be particularly computational entity. This information would be particularly
useful as an input to RWA optimization to be performed by another useful as an input to RWA optimization to be performed by another
computation entity. The difficulty here is for larger networks computation entity. The difficulty here is that such a list of
such a list of paths along with any wavelength constraints could paths along with any wavelength constraints could get
get unmanageably large. unmanageably large as the size of the network increases.
2. The authority in control of the "black links" could provide a PCE 2. The authority in control of the "black links" could provide a
like entity a list of viable paths/wavelengths between two PCE-like entity a list of viable paths/wavelengths between two
requested nodes. This is useful as an input to RWA optimizations requested nodes. This is useful as an input to RWA optimizations
and can reduce the scaling issue previously mentioned. Such a PCE and can reduce the scaling issue previously mentioned. Such a
like entity would not need to perform a full RWA computation, PCE-like entity would not need to perform a full RWA computation,
i.e., it would not need to take into account current wavelength i.e., it would not need to take into account current wavelength
availability on links. Such an approach may require PCEP availability on links. Such an approach may require PCEP
extensions for both the request and response information. extensions for both the request and response information.
3. The authority in control of the "black links" provides a PCE that 3. The authority in control of the "black links" provides a PCE that
performs full IA-RWA services. The difficulty is this requires the performs full IA-RWA services. The difficulty is this requires
one authority to also become the sole source of all RWA the one authority to also become the sole source of all RWA
optimization algorithms. optimization algorithms.
In all the above cases it would be the responsibility of the In all the above cases it would be the responsibility of the
authority in control of the "black links" to import the shared authority in control of the "black links" to import the shared
impairment information from the other NEs via the control plane or impairment information from the other NEs via the control plane or
other means as necessary. other means as necessary.
4.1.3. Impairment Estimation Process 4.1.3. Impairment Estimation Process
The Impairment Estimation Process can be modeled through the The Impairment Estimation Process can be modeled through the
following functional blocks. These blocks are independent of any following functional blocks. These blocks are independent of any
Control Plane architecture, that is, they can be implemented by the Control Plane architecture, that is, they can be implemented by the
same or by different control plane functions as detailed in following same or by different control plane functions as detailed in
sections. following sections.
+-----------------+ +-----------------+
+------------+ +-----------+ | +------------+ | +------------+ +-----------+ | +------------+ |
| | | | | | | | | | | | | | | |
| Optical | | Optical | | | Optical | | | Optical | | Optical | | | Optical | |
| Interface |------->| Impairment|--->| | Channel | | | Interface |------->| Impairment|--->| | Channel | |
| (Transmit/ | | Path | | | Estimation | | | (Transmit/ | | Path | | | Estimation | |
| Receive) | | | | | | | | Receive) | | | | | | |
+------------+ +-----------+ | +------------+ | +------------+ +-----------+ | +------------+ |
| || | | || |
| || | | || |
| Estimation | | Estimation |
| || | | || |
| \/ | | \/ |
| +------------+ | | +------------+ |
| | BER / | | | | BER / | |
| | Q Factor | | | | Q Factor | |
| +------------+ | | +------------+ |
+-----------------+ +-----------------+
Starting from functional block on the left the Optical Interface Starting from functional block on the left, the Optical Interface
represents where the optical signal is transmitted or received and represents where the optical signal is transmitted or received and
defines the properties at the path end points. Even the no-impairment defines the properties at the path end points. Even the impairment-
case like scenario B in section 4.1.1 needs to consider a minimum set free case, like scenario B in section 4.1.1, needs to consider a
of interface characteristics. In such case only a few parameters used minimum set of interface characteristics. In such case, only a few
to assess the signal compatibility will be taken into account (see parameters used to assess the signal compatibility will be taken
[RFC6163]). For the impairment-aware case these parameters may be into account (see [RFC6163]). For the impairment-aware case, these
sufficient or not depending on the accepted level of approximation parameters may be sufficient or not depending on the accepted level
(scenarios C and D). This functional block highlights the need to of approximation (scenarios C and D). This functional block
consider a set of interface parameters during an Impairment highlights the need to consider a set of interface parameters during
Validation Process. the Impairment Validation Process.
The block "Optical Impairment Path" represents the types of The block "Optical Impairment Path" represents the types of
impairments affecting a wavelength as it traverses the networks impairments affecting a wavelength as it traverses the networks
through links and nodes. In the case of a network where there are no through links and nodes. In the case of a network where there are no
impairments (Scenario A), this block will not be present. Otherwise, impairments (Scenario A), this block will not be present. Otherwise,
this function must be implemented in some way via the control plane. this function must be implemented in some way via the control plane.
Options for this will be given in the next section on architectural Architectural alternatives to accomplish this are provided in
alternatives. This block implementation (e.g. through routing, section 4.2. This block implementation (e.g., through routing,
signaling or PCE) may influence the way the control plane distributes signaling, or PCE) may influence the way the control plane
impairment information within the network. distributes impairment information within the network.
The last block implements the decision function for path feasibility. The last block implements the decision function for path
Depending on the IA level of approximation this function can be more feasibility. Depending on the IA level of approximation, this
or less complex. For example in case of no IA only the signal class function can be more or less complex. For example in case of no IA
compatibility will be verified. In addition to feasible/not-feasible only the signal class compatibility will be verified. In addition to
result, it may be worthwhile for decision functions to consider the feasible/not-feasible result, it may be worthwhile for decision
case in which paths can be likely-to-be-feasible within some degree functions to consider the case in which paths can be likely-to-be-
of confidence. The optical impairments are usually not fixed values feasible within some degree of confidence. The optical impairments
as they may vary within ranges of values according to the approach are usually not fixed values as they may vary within ranges of
taken in the physical modeling (worst-case, statistical or based on values according to the approach taken in the physical modeling
typical values). For example, the utilization of the worst-case value (worst-case, statistical, or based on typical values). For example,
for each parameter within impairment validation process may lead to the utilization of the worst-case value for each parameter within
marking some paths as not-feasible while they are very likely to be impairment validation process may lead to marking some paths as not-
feasible in reality. feasible while they are very likely to be, in reality, feasible.
4.2. IA-RWA Computation and Control Plane Architectures 4.2. IA-RWA Computation and Control Plane Architectures
From a control plane point of view optical impairments are additional From a control plane point of view, optical impairments are
constraints to the impairment-free RWA process described in additional constraints to the impairment-free RWA process described
[RFC6163]. In impairment aware routing and wavelength assignment (IA- in [RFC6163]. In impairment aware routing and wavelength assignment
RWA), there are conceptually three general classes of processes to be (IA-RWA), there are conceptually three general classes of processes
considered: Routing (R), Wavelength Assignment (WA), and Impairment to be considered: Routing (R), Wavelength Assignment (WA), and
Validation (estimation) (IV). Impairment Validation (IV), i.e., estimation.
Impairment validation may come in many forms, and may be invoked at Impairment validation may come in many forms, and may be invoked at
different levels of detail in the IA-RWA process. From a process different levels of detail in the IA-RWA process. All the variations
point of view the following three forms of impairment validation will of impairment validation discussed in this section is based on
be considered: Scenario C (Approximated Impairment Estimation) as discussed in
Section 4.1.1. From a process point of view, the following three
forms of impairment validation will be considered:
o IV-Candidates o IV-Candidates
In this case an Impairment Validation (IV) process furnishes a set of In this case, an Impairment Validation (IV) process furnishes a set
paths between two nodes along with any wavelength restrictions such of paths between two nodes along with any wavelength restrictions
that the paths are valid with respect to optical impairments. These such that the paths are valid with respect to optical impairments.
paths and wavelengths may not be actually available in the network These paths and wavelengths may not be actually available in the
due to its current usage state. This set of paths could be returned network due to its current usage state. This set of paths could be
in response to a request for a set of at most K valid paths between returned in response to a request for a set of at most K valid paths
two specified nodes. Note that such a process never directly between two specified nodes. Note that such a process never directly
discloses optical impairment information. Note that that this case discloses optical impairment information. Note that that this case
includes any paths between source and destination that may have been includes any paths between source and destination that may have been
"pre-validated". "pre-validated".
In this case the control plane simply makes use of candidate paths In this case, the control plane simply makes use of candidate paths
but does not know any optical impairment information. Another option but does not know any optical impairment information. Another option
is 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-Approximate Verification o IV-Approximate Verification
Here approximation methods are used to estimate the impairments Here approximation methods are used to estimate the impairments
experienced by a signal. Impairments are typically approximated by experienced by a signal. Impairments are typically approximated by
linear and/or statistical characteristics of individual or combined linear and/or statistical characteristics of individual or combined
components and fibers along the signal path. components and fibers along the signal path.
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
through an optical network and is asked to verify whether the overall wavelength through an optical network and is asked to verify whether
quality objectives for the signal over this path can be met. Note the overall quality objectives for the signal over this path can be
that such a process never directly discloses optical impairment met. Note that such a process never directly discloses optical
information. impairment information.
The next two cases refer to the way an impairment validation The next two cases refer to the way an impairment validation
computation can be performed. computation can be performed.
o IV-Centralized o IV-Centralized
In this case impairments to a path are computed at a single entity. In this case, impairments to a path are computed at a single entity.
The information concerning impairments, however, may still be The information concerning impairments, however, may still be
gathered from network elements. Depending how information is gathered gathered from network elements. Depending how information is
this may put additional requirements on routing protocols. This will gathered, this may put additional requirements on routing protocols.
be detailed in later sections. This will be detailed in later sections.
o IV-Distributed o IV-Distributed
In the distributed IV process, approximate degradation measures such In the distributed IV process, approximate degradation measures such
as OSNR, dispersion, DGD, etc. may be accumulated along the path via as OSNR, dispersion, DGD, etc., may be accumulated along the path
signaling. Each node on the path may already perform some part of the via signaling. Each node on the path may already perform some part
impairment computation (i.e. distributed). When the accumulated of the impairment computation (i.e. distributed). When the
measures reach the destination node a decision on the impairment accumulated measures reach the destination node, a decision on the
validity of the path can be made. Note that such a process would impairment validity of the path can be made. Note that such a
entail revealing an individual network element's impairment process would entail revealing an individual network element's
information but it does not generally require distributing optical impairment information but it does not generally require
parameters to the entire network. distributing optical parameters to the entire network.
The Control Plane must not preclude the possibility to operate one or The Control Plane must not preclude the possibility to concurrently
all the above cases concurrently in the same network. For example perform one or all the above cases in the same network. For example,
there could be cases where a certain number of paths are already pre- there could be cases where a certain number of paths are already
validated (IV-Candidates) so the control plane may setup one of those pre-validated (IV-Candidates) so the control plane may setup one of
paths without requesting any impairment validation procedure. On the those paths without requesting any impairment validation procedure.
same network however the control plane may compute a path outside the On the same network, however, the control plane may compute a path
set of IV-Candidates for which an impairment evaluation can be outside the set of IV-Candidates for which an impairment evaluation
necessary. can be necessary.
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 reviews some of their respective computation architectures and reviews some of their respective
advantages and disadvantages. advantages and disadvantages.
4.2.1. Combined Routing, WA, and IV 4.2.1. Combined Routing, WA, and IV
From the point of view of optimality, reasonably good IA-RWA From the point of view of optimality, reasonably good IA-RWA
solutions can be achieved if the path computation entity (PCE) can solutions can be achieved if the path computation entity (PCE) can
conceptually/algorithmically combine the processes of routing, conceptually/algorithmically combine the processes of routing,
wavelength assignment and impairment validation. wavelength assignment and impairment validation.
Such a combination can take place if the PCE is given: (a) the Such a combination can take place if the PCE is given: (a) the
impairment-free WSON network information as discussed in [RFC6163] impairment-free WSON network information as discussed in [RFC6163]
and (b) impairment information to validate potential paths. and (b) impairment information to validate potential paths.
4.2.2. Separate Routing, WA, or IV 4.2.2. Separate Routing, WA, or IV
Separating the processes of routing, WA and/or IV can reduce the need Separating the processes of routing, WA, and/or IV can reduce the
for sharing of different types of information used in path need for sharing of different types of information used in path
computation. This was discussed for routing separate from WA in computation. This was discussed for routing separate from WA in
[RFC6163]. In addition, as was discussed some impairment information [RFC6163]. In addition, as was discussed, some impairment
may not be shared and this may lead to the need to separate IV from information may not be shared and this may lead to the need to
RWA. In addition, if IV needs to be done at a high level of separate IV from RWA. In addition, if IV needs to be done at a high
precision it may be advantageous to offload this computation to a level of precision, it may be advantageous to offload this
specialized server. computation to a specialized server.
The following conceptual architectures belong in this general The following conceptual architectures belong in this general
category: category:
o R+WA+IV -- separate routing, wavelength assignment, and impairment o R+WA+IV -- separate routing, wavelength assignment, and
validation. impairment validation.
o R + (WA & IV) -- routing separate from a combined wavelength o R + (WA & IV) -- routing separate from a combined wavelength
assignment and impairment validation process. Note that impairment assignment and impairment validation process. Note that
validation is typically wavelength dependent hence combining WA impairment validation is typically wavelength dependent. Hence
with IV can lead to efficiencies. combining WA with IV can lead to efficiencies.
o (RWA)+IV - combined routing and wavelength assignment with a o (RWA)+IV - combined routing and wavelength assignment with a
separate impairment validation process. separate impairment validation process.
Note that the IV process may come before or after the RWA processes. Note that the IV process may come before or after the RWA processes.
If RWA comes first then IV is just rendering a yes/no decision on the If RWA comes first, then IV is just rendering a yes/no decision on
selected path and wavelength. If IV comes first it would need to the selected path and wavelength. If IV comes first it would need to
furnish a list of possible (valid with respect to impairments) routes furnish a list of possible (valid with respect to impairments)
and wavelengths to the RWA processes. routes and wavelengths to the RWA processes.
4.2.3. Distributed WA and/or IV 4.2.3. Distributed WA and/or IV
In the non-impairment RWA situation [RFC6163] it was shown that a In the non-impairment RWA situation [RFC6163], it was shown that a
distributed wavelength assignment (WA) process carried out via distributed wavelength assignment (WA) process carried out via
signaling can eliminate the need to distribute wavelength signaling can eliminate the need to distribute wavelength
availability information via an interior gateway protocol (IGP). A availability information via an interior gateway protocol (IGP). A
similar approach can allow for the distributed computation of similar approach can allow for the distributed computation of
impairment effects and avoid the need to distribute impairment impairment effects and avoid the need to distribute impairment
characteristics of network elements and links via routing protocols characteristics of network elements and links by routing protocols
or by other means. So the following conceptual options belong to this or by other means. So the following conceptual options belong to
category: this category:
o RWA + D(IV) - Combined routing and wavelength assignment and o RWA + D(IV) - Combined routing and wavelength assignment and
distributed impairment validation. distributed impairment validation.
o R + D(WA & IV) -- routing separate from a distributed wavelength o R + D(WA & IV) -- routing separate from a distributed wavelength
assignment and impairment validation process. assignment and impairment validation process.
Distributed impairment validation for a prescribed network path Distributed impairment validation for a prescribed network path
requires that the effects of impairments be calculated by approximate requires that the effects of impairments be calculated by
models with cumulative quality measures such as those given in approximate models with cumulative quality measures such as those
[G.680]. The protocol encoding of the impairment related information given in [G.680]. The protocol encoding of the impairment related
from [G.680] would need to be agreed upon. information from [G.680] would need to be agreed upon.
If distributed WA is being done at the same time as distributed IV If distributed WA is being done at the same time as distributed IV
then it is necessary to accumulate impairment related information for then it is necessary to accumulate impairment related information
all wavelengths that could be used. This is somewhat windowed down as for all wavelengths that could be used. The amount of information is
potential wavelengths are discovered to be in use, but could be a reduced somewhat as potential wavelengths are discovered to be in
significant burden for lightly loaded high channel count networks. use, but could be a significant burden for lightly loaded high
channel count networks.
4.3. Mapping Network Requirements to Architectures 4.3. Mapping Network Requirements to Architectures
Figure 2 shows process flows for three main architectural Figure 2 shows process flows for the three main architectural
alternatives to IA-RWA when approximate impairment validation is alternatives to IA-RWA when approximate impairment validation is
sufficient. Figure 3 shows process flows for two main architectural sufficient. Figure 3 shows process flows for the two main
alternatives when detailed impairment verification is required. architectural alternatives when detailed impairment verification is
required.
+-----------------------------------+ +-----------------------------------+
| +--+ +-------+ +--+ | | +--+ +-------+ +--+ |
| |IV| |Routing| |WA| | | |IV| |Routing| |WA| |
| +--+ +-------+ +--+ | | +--+ +-------+ +--+ |
| | | |
| Combined Processes | | Combined Processes |
+-----------------------------------+ +-----------------------------------+
(a) (a)
skipping to change at page 16, line 32 skipping to change at page 16, line 47
+-----------+ +----------------------+ +-----------+ +----------------------+
| +-------+ | | +--+ +--+ | | +-------+ | | +--+ +--+ |
| |Routing| |------->| |WA| |IV| | | |Routing| |------->| |WA| |IV| |
| +-------+ | | +--+ +--+ | | +-------+ | | +--+ +--+ |
+-----------+ | Distributed Processes| +-----------+ | Distributed Processes|
+----------------------+ +----------------------+
(c) (c)
Figure 2 Process flows for the three main approximate impairment Figure 2 Process flows for the three main approximate impairment
architectural alternatives. architectural alternatives.
The advantages, requirements and suitability of these options are as The advantages, requirements, and suitability of these options are
follows: as 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 authority 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
computational entities while still maintaining a high degree of two 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
elements, while the RWA process needs to know non-impairment RWA network elements, while the RWA process needs to know non-impairment
information from the network elements. This alternative can be used RWA information from the network elements. This alternative can be
with "black links", but the authority in control of the "black links" used with "black links", but the authority in control of the "black
would need to provide the functionality of the IV-candidates process. links" would need to provide the functionality of the IV-candidates
Note that this is still very useful since the algorithmic areas of IV process. Note that this is still very useful since the algorithmic
and RWA are very different and prone to specialization. areas of IV and RWA are very different and conducive to
specialization.
o Routing + Distributed WA and IV o Routing + Distributed WA and IV
In this alternative a signaling protocol may be extended and In this alternative, a signaling protocol may be extended and
leveraged in the wavelength assignment and impairment validation leveraged in the wavelength assignment and impairment validation
processes. Although this doesn't enable as high a potential degree of processes. Although this doesn't enable as high a potential degree
optimality of optimality as (a) or (b), it does not require of optimality as (a) or (b), it does not require distribution of
distribution of either link wavelength usage or link/node impairment either link wavelength usage or link/node impairment information.
information. Note that this is most likely not suitable for "black Note that this is most likely not suitable for "black links".
links".
+-----------------------------------+ +------------+ +-----------------------------------+ +------------+
| +-----------+ +-------+ +--+ | | +--------+ | | +-----------+ +-------+ +--+ | | +--------+ |
| | IV | |Routing| |WA| | | | IV | | | | IV | |Routing| |WA| | | | IV | |
| |approximate| +-------+ +--+ |---->| |Detailed| | | |approximate| +-------+ +--+ |---->| |Detailed| |
| +-----------+ | | +--------+ | | +-----------+ | | +--------+ |
| Combined Processes | | | | Combined Processes | | |
+-----------------------------------+ +------------+ +-----------------------------------+ +------------+
(a) (a)
+--------------+ +----------------------+ +------------+ +--------------+ +----------------------+ +------------+
| +----------+ | | +-------+ +--+ | | +--------+ | | +----------+ | | +-------+ +--+ | | +--------+ |
| | IV | | | |Routing| |WA| |---->| | IV | | | | IV | | | |Routing| |WA| |---->| | IV | |
| |candidates| |----->| +-------+ +--+ | | |Detailed| | | |candidates| |----->| +-------+ +--+ | | |Detailed| |
| +----------+ | | Combined Processes | | +--------+ | | +----------+ | | Combined Processes | | +--------+ |
+--------------+ +----------------------+ | | +--------------+ +----------------------+ | |
(b) +------------+ (b) +------------+
Figure 3 Process flows for the two main detailed impairment Figure 3 Process flows for the two main detailed impairment
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 the highest potential optimality and
efficiency in IA-RWA; then has a separate entity performing detailed efficiency in IA-RWA while keeping a separate entity performing
impairment validation. In the case of "black links" the authority detailed impairment validation. In the case of "black links" the
controlling the "black links" would need to provide all authority 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.
5. Protocol Implications 5. Protocol Implications
The previous IA-RWA architectural alternatives and process flows make The previous IA-RWA architectural alternatives and process flows
differing demands on a GMPLS/PCE based control plane. This section make differing demands on a GMPLS/PCE based control plane. This
discusses the use of (a) an impairment information model, (b) PCE as section discusses the use of (a) an impairment information model,
computational entity assuming the various process roles and (b) PCE as computational entity assuming the various process roles
consequences for PCEP, (c) possible extensions to signaling, and (d) and consequences for PCEP, (c) possible extensions to signaling, and
possible extensions to routing. This document is providing this (d) possible extensions to routing. This document is providing this
evaluation to aid protocol solutions work. The protocol evaluation to aid protocol solutions work. The protocol
specifications may deviate from this assessment. The assessment of specifications may deviate from this assessment. The assessment of
the impacts to the control plane for IA-RWA is summarized in Figure the impacts to the control plane for IA-RWA is summarized in Figure
4. 4.
+-------------------+----+----+----------+--------+ +-------------------+----+----+----------+--------+
| IA-RWA Option |PCE |Sig |Info Model| Routing| | IA-RWA Option |PCE |Sig |Info Model| Routing|
+-------------------+----+----+----------+--------+ +-------------------+----+----+----------+--------+
| Combined |Yes | No | Yes | Yes | | Combined |Yes | No | Yes | Yes |
| IV & RWA | | | | | | IV & RWA | | | | |
skipping to change at page 18, line 43 skipping to change at page 19, line 25
| + RWA | | | | | | + RWA | | | | |
+-------------------+----+----+----------+--------+ +-------------------+----+----+----------+--------+
| Routing + |No | Yes| Yes | No | | Routing + |No | Yes| Yes | No |
|Distributed IV, RWA| | | | | |Distributed IV, RWA| | | | |
+-------------------+----+----+----------+--------+ +-------------------+----+----+----------+--------+
Figure 4 IA-RWA architectural options and control plane impacts. Figure 4 IA-RWA architectural options and control plane impacts.
5.1. Information Model for Impairments 5.1. Information Model for Impairments
As previously discussed most IA-RWA scenarios to a greater or lesser As previously discussed, most IA-RWA scenarios rely, to a greater or
extent rely on a common impairment information model. A number of lesser extent, on a common impairment information model. A number of
ITU-T recommendations cover detailed as well as approximate ITU-T recommendations cover detailed, as well as, approximate
impairment characteristics of fibers and a variety of devices and impairment characteristics of fibers, and a variety of devices, and
subsystems. An impairment model which can be used as a guideline for subsystems. An impairment model which can be used as a guideline for
optical network elements and assessment of path viability is given in optical network elements and assessment of path viability is given
[G.680]. in [G.680].
It should be noted that the current version of [G.680] is limited to It should be noted that the current version of [G.680] is limited to
the networks composed of a single WDM line system vendor combined networks composed of a single WDM line system vendor combined with
with OADMs and/or PXCs from potentially multiple other vendors, this OADMs and/or PXCs from potentially multiple other vendors. This is
is known as situation 1 and is shown in Figure 1-1 of [G.680]. It is known as situation 1 and is shown in Figure 1-1 of [G.680]. It is
planed in the future that [G.680] will include networks incorporating planned in the future that [G.680] will include networks
line systems from multiple vendors as well as OADMs and/or PXCs from incorporating line systems from multiple vendors, as well as, OADMs
potentially multiple other vendors, this is known as situation 2 and and/or PXCs from potentially multiple other vendors. This is known
is shown in Figure 1-2 of [G.680]. as situation 2 and is shown in Figure 1-2 of [G.680].
For the case of distributed impairment validation (distributed IV), For the case of distributed impairment validation (distributed IV),
this would require more than an impairment information model. It this would require more than an impairment information model. It
would need a common impairment "computation" model. In the would need a common impairment "computation" model. In the
distributed IV case one needs to standardize the accumulated distributed IV case, one needs to standardize the accumulated
impairment measures that will be conveyed and updated at each node. impairment measures that will be conveyed and updated at each node.
Section 9 of [G.680] provides guidance in this area with specific Section 9 of [G.680] provides guidance in this area with specific
formulas given for OSNR, residual dispersion, polarization mode formulas given for OSNR, residual dispersion, polarization mode
dispersion/polarization dependent loss, and effects of channel dispersion/polarization dependent loss, and effects of channel
uniformity. However, specifics of what intermediate results are kept uniformity. However, specifics of what intermediate results are kept
and in what form for the protocol would need to be standardized for and in what form would need to be standardized for interoperability.
interoperability. As noted in [G.680], this information may possibly As noted in [G.680], this information may possibly not be
not be sufficient, and in such case the applicability would be sufficient, and in such case the applicability would be network
network dependent. dependent.
5.2. Routing 5.2. Routing
Different approaches to path/wavelength impairment validation gives Different approaches to path/wavelength impairment validation give
rise to different demands placed on GMPLS routing protocols. In the rise to different demands placed on GMPLS routing protocols. In the
case where approximate impairment information is used to validate case where approximate impairment information is used to validate
paths GMPLS routing may be used to distribute the impairment paths, GMPLS routing may be used to distribute the impairment
characteristics of the network elements and links based on the characteristics of the network elements and links based on the
impairment information model previously discussed. impairment information model previously discussed.
Depending on the computational alternative the routing protocol may Depending on the computational alternative, the routing protocol may
need to advertise information necessary to impairment validation need to advertise information necessary to the impairment validation
process. This can potentially cause scalability issues due to the process. This can potentially cause scalability issues due to the
high amount of data that need to be advertised. Such issue can be high volume of data that need to be advertised. Such issue can be
addressed separating data that need to be advertised rarely and data addressed separating data that need to be advertised rarely from
that need to be advertised more frequently or adopting other form of data that need to be advertised more frequently or adopting other
awareness solutions described in previous sections (e.g. centralized form of awareness solutions described in previous sections (e.g.,
and/or external IV entity). centralized and/or external IV entity).
In term of approximated scenario (see Section 4.1.1.) the model In term of approximated scenario (see Section 4.1.1.), the model
defined by [G.680] will apply and routing protocol will need to defined by [G.680] will apply and the routing protocol will need to
gather information required for such computation. gather information required for such computation.
In the case of distributed-IV no new demands would be placed on the In the case of distributed-IV, no new demands would be placed on the
routing protocol. routing protocol.
5.3. Signaling 5.3. Signaling
The largest impacts on signaling occur in the cases where distributed The largest impacts on signaling occur in the cases where
impairment validation is performed. In this case, it ie necessary to distributed impairment validation is performed. In this case, it ie
accumulate impairment information as previously discussed. In necessary to accumulate impairment information as previously
addition, since the characteristics of the signal itself, such as discussed. In addition, since the characteristics of the signal
modulation type, can play a major role in the tolerance of itself, such as modulation type, can play a major role in the
impairments, this type of information will need to be implicitly or tolerance of impairments, this type of information will need to be
explicitly signaled so that an impairment validation decision can be implicitly or explicitly signaled so that an impairment validation
made at the destination node. decision can be made at the destination node.
It remains for further study if it may be beneficial to include It remains for further study if it may be beneficial to include
additional information to a connection request such as desired egress additional information to a connection request such as desired
signal quality (defined in some appropriate sense) in non-distributed egress signal quality (defined in some appropriate sense) in non-
IV scenarios. distributed IV scenarios.
5.4. PCE 5.4. PCE
In section 4.3. a number of computation architectural alternatives In section 4.3. a number of computation architectural alternatives
were given that could be used to meet the various requirements and were given that could be used to meet the various requirements and
constraints of section 4.1. Here the focus is how these alternatives constraints of section 4.1. Here the focus is how these
could be implemented via either a single PCE or a set of two or more alternatives could be implemented via either a single PCE or a set
cooperating PCEs, and the impacts on the PCEP protocol. This document of two or more cooperating PCEs, and the impacts on the PCEP. This
is providing this evaluation to aid solutions work. The protocol document provides this evaluation to aid solutions work. The
specifications may deviate from this assessment. protocol specifications may deviate from this assessment.
5.4.1. Combined IV & RWA 5.4.1. Combined IV & RWA
In this situation, shown in Figure 2(a), a single PCE performs all In this situation, shown in Figure 2(a), a single PCE performs all
the computations needed for IA-RWA. the computations needed for IA-RWA.
o TE Database Requirements: WSON Topology and switching o TE Database Requirements: WSON Topology and switching
capabilities, WSON WDM link wavelength utilization, and WSON capabilities, WSON WDM link wavelength utilization, and WSON
impairment information impairment information
o PCC to PCE Request Information: Signal characteristics/type, o PCC to PCE Request Information: Signal characteristics/type,
required quality, source node, destination node required quality, source node, destination node
o PCE to PCC Reply Information: If the computations completed o PCE to PCC Reply Information: If the computations completed
successfully then the PCE returns the path and its assigned successfully then the PCE returns the path and its assigned
wavelength. If the computations could not complete successfully it wavelength. If the computations could not complete successfully,
would be potentially useful to know the reason why. At a minimum, it would be potentially useful to know the reason why. At a
it is of interest to know if this was due to lack of wavelength minimum, it is of interest to know if this was due to lack of
availability or impairment considerations or both. The information wavelength availability, impairment considerations, or both. The
to be conveyed is for further study. information to be conveyed is for further study.
5.4.2. IV-Candidates + RWA 5.4.2. IV-Candidates + RWA
In this situation, as shown in Figure 2(b), two separate processes In this situation, as shown in Figure 2(b), two separate processes
are involved in the IA-RWA computation. This requires two cooperating are involved in the IA-RWA computation. This requires two
path computation entities: one for the Candidates-IV process and cooperating path computation entities: one for the Candidates-IV
another for the RWA process. In addition, the overall process needs process and another for the RWA process. In addition, the overall
to be coordinated. This could be done with yet another PCE or this process needs to be coordinated. This could be done with yet another
functionality can be added to one of previously defined entities. PCE or this functionality could be added to one of previously
This later option requires the RWA entity to also act as the overall defined entities. This later option requires the RWA entity to also
process coordinator. The roles, responsibilities and information act as the overall process coordinator. The roles, responsibilities,
requirements for these two entities when instantiated as PCEs are and information requirements for these two entities when
given below. instantiated as PCEs are given below.
RWA and Coordinator PCE (RWA-Coord-PCE): RWA and Coordinator PCE (RWA-Coord-PCE):
Responsible for interacting with PCC and for utilizing Candidates-PCE Responsible for interacting with PCC and for utilizing Candidates-
as needed during RWA computations. In particular it needs to know to PCE as needed during RWA computations. In particular, it needs to
use the Candidates-PCE to obtain potential set of routes and know to use the Candidates-PCE to obtain potential set of routes and
wavelengths. wavelengths.
o TE Database Requirements: WSON Topology and switching capabilities o TE Database Requirements: WSON Topology and switching
and WSON WDM link wavelength utilization (no impairment capabilities and WSON WDM link wavelength utilization (no
information). impairment information).
o PCC to RWA-PCE request: same as in the combined case. o PCC to RWA-PCE request: same as in the combined case.
o RWA-PCE to PCC reply: same as in the combined case. o RWA-PCE to PCC reply: same as in the combined case.
o RWA-PCE to IV-Candidates-PCE request: The RWA-PCE asks for a set o RWA-PCE to IV-Candidates-PCE request: The RWA-PCE asks for a set
of at most K routes along with acceptable wavelengths between of at most K routes along with acceptable wavelengths between
nodes specified in the original PCC request. nodes specified in the original PCC request.
o IV-Candidates-PCE reply to RWA-PCE: The Candidates-PCE returns a o IV-Candidates-PCE reply to RWA-PCE: The Candidates-PCE returns a
set of at most K routes along with acceptable wavelengths between set of at most K routes along with acceptable wavelengths between
nodes specified in the RWA-PCE request. nodes specified in the RWA-PCE request.
IV-Candidates-PCE: IV-Candidates-PCE:
The IV-Candidates PCE is responsible for impairment aware path The IV-Candidates PCE is responsible for impairment aware path
computation. It needs not take into account current link wavelength computation. It need not take into account current link wavelength
utilization, but this is not prohibited. The Candidates-PCE is only utilization, but this is not prohibited. The Candidates-PCE is only
required to interact with the RWA-PCE as indicated above and not the required to interact with the RWA-PCE as indicated above and not the
initiating PCC. (Note: RWA-Coord PCE is also a PCC with respect to initiating PCC. Note: RWA-Coord PCE is also a PCC with respect to
the IV-Candidate) the IV-Candidate.
o TE Database Requirements: WSON Topology and switching capabilities o TE Database Requirements: WSON Topology and switching
and WSON impairment information (no information link wavelength capabilities and WSON impairment information (no information link
utilization required). wavelength utilization required).
Figure 5 shows a sequence diagram for the possible interactions Figure 5 shows a sequence diagram for the possible interactions
between the PCC, RWA-Coord PCE and IV-Candidates PCE. between the PCC, RWA-Coord PCE, and IV-Candidates PCE.
+---+ +-------------+ +-----------------+ +---+ +-------------+ +-----------------+
|PCC| |RWA-Coord PCE| |IV-Candidates PCE| |PCC| |RWA-Coord PCE| |IV-Candidates PCE|
+-+-+ +------+------+ +---------+-------+ +-+-+ +------+------+ +---------+-------+
...___ (a) | | ...___ (a) | |
| ````---...____ | | | ````---...____ | |
| ```-->| | | ```-->| |
| | | | | |
| |--..___ (b) | | |--..___ (b) |
| | ```---...___ | | | ```---...___ |
skipping to change at page 22, line 40 skipping to change at page 23, line 29
| |<--'''' | | |<--'''' |
| | | | | |
| | | | | |
| (d) ___...| | | (d) ___...| |
| ___....---''' | | | ___....---''' | |
|<--''' | | |<--''' | |
| | | | | |
| | | | | |
Figure 5 Sequence diagram for the interactions between PCC, RWA- Figure 5 Sequence diagram for the interactions between PCC, RWA-
Coordinating-PCE and the IV-Candidates-PCE. Coordinating-PCE, and the IV-Candidates-PCE.
In step (a) the PCC requests a path meeting specified quality In step (a), the PCC requests a path meeting specified quality
constraints between two nodes (A and Z) for a given signal constraints between two nodes (A and Z) for a given signal
represented either by a specific type or a general class with represented either by a specific type or a general class with
associated parameters. In step (b) the RWA-Coordinating-PCE requests associated parameters. In step (b), the RWA-Coordinating-PCE
up to K candidate paths between nodes A and Z and associated requests up to K candidate paths between nodes A and Z and
acceptable wavelengths. In step (c) The IV-Candidates PCE returns associated acceptable wavelengths. The term "K candidate paths" is
this list to the RWA-Coordinating PCE which then uses this set of associated with K-shortest path algorithm. It refers to an algorithm
paths and wavelengths as input (e.g. a constraint) to its RWA that finds multiple K short paths connecting the source and the
computation. In step (d) the RWA-Coordinating PCE returns the overall destination in a graph (allowing repeated vertices and edges in the
IA-RWA computation results to the PCC. paths) [Eppstein].
In step (c), The IV-Candidates PCE returns this list to the RWA-
Coordinating PCE which then uses this set of paths and wavelengths
as input (e.g., a constraint) to its RWA computation. In step (d)
the RWA-Coordinating PCE returns the overall IA-RWA computation
results to the PCC.
5.4.3. Approximate IA-RWA + Separate Detailed IV 5.4.3. Approximate IA-RWA + Separate Detailed IV
Previously Figure 3 showed two cases where a separate detailed Previously, Figure 3 showed two cases where a separate detailed
impairment validation process could be utilized. It is possible to impairment validation process could be utilized. It is possible to
place the detailed validation process into a separate PCE. Assuming place the detailed validation process into a separate PCE. Assuming
that a different PCE assumes a coordinating role and interacts with that a different PCE assumes a coordinating role and interacts with
the PCC it is possible to keep the interactions with this separate the PCC, it is possible to keep the interactions with this separate
IV-Detailed-PCE very simple. IV-Detailed-PCE very simple. Please note that there is some
inefficiency by separating the IV-Candidates-PCE from the IV-
Detailed-PCE from a message flow perspective in order to achieve a
high degree of potential optimality.
IV-Detailed-PCE: IV-Detailed-PCE:
o TE Database Requirements: The IV-Detailed-PCE will need optical o TE Database Requirements: The IV-Detailed-PCE will need optical
impairment information, WSON topology, and possibly WDM link impairment information, WSON topology, and possibly WDM link
wavelength usage information. This document puts no restrictions wavelength usage information. This document puts no restrictions
on the type of information that may be used in these computations. on the type of information that may be used in these
computations.
o Coordinating-PCE to IV-Detailed-PCE request: The coordinating-PCE o Coordinating-PCE to IV-Detailed-PCE request: The coordinating-PCE
will furnish signal characteristics, quality requirements, path will furnish signal characteristics, quality requirements, path,
and wavelength to the IV-Detailed-PCE. and wavelength to the IV-Detailed-PCE.
o IV-Detailed-PCE to Coordinating-PCE reply: The reply is o IV-Detailed-PCE to Coordinating-PCE reply: The reply is
essentially a yes/no decision as to whether the requirements could essentially a yes/no decision as to whether the requirements
actually be met. In the case where the impairment validation fails could actually be met. In the case where the impairment
it would be helpful to convey information related to cause or validation fails, it would be helpful to convey information
quantify the failure, e.g., so a judgment can be made whether to related to cause or quantify the failure, e.g., so that a
try a different signal or adjust signal parameters. judgment can be made whether to try a different signal or adjust
signal parameters.
Figure 6 shows a sequence diagram for the interactions for the Figure 6 shows a sequence diagram for the interactions corresponding
process shown in Figure 3(b). This involves interactions between the to the process shown in Figure 3(b). This involves interactions
PCC, RWA-PCE (acting as coordinator), IV-Candidates-PCE and the IV- between the PCC, RWA-PCE (acting as coordinator), IV-Candidates-PCE,
Detailed-PCE. and the IV-Detailed-PCE.
In step (a) the PCC requests a path meeting specified quality In step (a), the PCC requests a path meeting specified quality
constraints between two nodes (A and Z) for a given signal constraints between two nodes (A and Z) for a given signal
represented either by a specific type or a general class with represented either by a specific type or a general class with
associated parameters. In step (b) the RWA-Coordinating-PCE requests associated parameters. In step (b), the RWA-Coordinating-PCE
up to K candidate paths between nodes A and Z and associated requests up to K candidate paths between nodes A and Z and
acceptable wavelengths. In step (c) The IV-Candidates-PCE returns associated acceptable wavelengths. In step (c), The IV-Candidates-
this list to the RWA-Coordinating PCE which then uses this set of PCE returns this list to the RWA-Coordinating PCE which then uses
paths and wavelengths as input (e.g. a constraint) to its RWA this set of paths and wavelengths as input (e.g., a constraint) to
computation. In step (d) the RWA-Coordinating-PCE request a detailed its RWA computation. In step (d), the RWA-Coordinating-PCE request a
verification of the path and wavelength that it has computed. In step detailed verification of the path and wavelength that it has
(e) the IV-Detailed-PCE returns the results of the validation to the computed. In step (e), the IV-Detailed-PCE returns the results of
RWA-Coordinating-PCE. Finally in step (f)IA-RWA-Coordinating PCE the validation to the RWA-Coordinating-PCE. Finally in step (f), the
returns the final results (either a path and wavelength or cause for IA-RWA-Coordinating PCE returns the final results (either a path and
the failure to compute a path and wavelength) to the PCC. wavelength or cause for the failure to compute a path and
wavelength) to the PCC.
+----------+ +--------------+ +------------+ +----------+ +--------------+ +------------+
+---+ |RWA-Coord | |IV-Candidates | |IV-Detailed | +---+ |RWA-Coord | |IV-Candidates | |IV-Detailed |
|PCC| | PCE | | PCE | | PCE | |PCC| | PCE | | PCE | | PCE |
+-+-+ +----+-----+ +------+-------+ +-----+------+ +-+-+ +----+-----+ +------+-------+ +-----+------+
|.._ (a) | | | |.._ (a) | | |
| ``--.__ | | | | ``--.__ | | |
| `-->| | | | `-->| | |
| | (b) | | | | (b) | |
| |--....____ | | | |--....____ | |
skipping to change at page 24, line 35 skipping to change at page 25, line 37
| | | | | |
| | (e) _____.....+ | | (e) _____.....+
| | _____.....-----''''' | | | _____.....-----''''' |
| |<----''''' | | |<----''''' |
| (f) __.| | | (f) __.| |
| __.--'' | | __.--'' |
|<-'' | |<-'' |
| | | |
Figure 6 Sequence diagram for the interactions between PCC, RWA- Figure 6 Sequence diagram for the interactions between PCC, RWA-
Coordinating-PCE, IV-Candidates-PCE and IV-Detailed-PCE. Coordinating-PCE, IV-Candidates-PCE, and IV-Detailed-PCE.
6. Security Considerations 6. Security Considerations
This document discusses a number of control plane architectures that This document discusses a number of control plane architectures that
incorporate knowledge of impairments in optical networks. If such incorporate knowledge of impairments in optical networks. If such
architecture is put into use within a network it will by its nature architecture is put into use within a network, it will by its nature
contain details of the physical characteristics of an optical contain details of the physical characteristics of an optical
network. Such information would need to be protected from intentional network. Such information would need to be protected from
or unintentional disclosure similar to other network information used intentional or unintentional disclosure similar to other network
within intra-domain protocols. It is expected that protocol solutions information used within intra-domain protocols.
work will address any issues on the use of impairment information.
This document does not require changes to the security models within
GMPLS and associated protocols. That is, the OSPF-TE, RSVP-TE, and
PCEP security models could be operated unchanged. However,
satisfying the requirements for impairment information dissemination
using the existing protocols may significantly affect the loading of
those protocols.
This may make the operation of the network more vulnerable to active
attacks such as injections, impersonation, and MITMs. Therefore,
additional care maybe required to ensure that the protocols are
secure in the impairment-aware WSON environment.
Furthermore, the additional information distributed in order to
address impairment information represents a disclosure of network
capabilities that an operator may wish to keep private.
Consideration should be given to securing this information. For a
general discussion on MPLS- and GMPLS-related security issues, see
the MPLS/GMPLS security framework [RFC5920] and, in particular, text
detailing security issues when Control Plane is physically separated
from Data Plane.
7. IANA Considerations 7. IANA Considerations
This draft does not currently require any consideration from IANA. This draft does not currently require any consideration from IANA.
8. References 8. References
8.1. Normative References 8.1. Normative References
[G.680] ITU-T Recommendation G.680, Physical transfer functions of [G.680] ITU-T Recommendation G.680, Physical transfer functions of
optical network elements, July 2007. optical network elements, July 2007.
[RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label [RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", RFC 3945, October 2004. Switching (GMPLS) Architecture", RFC 3945, October 2004.
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path Computation [RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Element (PCE)-Based Architecture", RFC 4655, August 2006. Computation Element (PCE)-Based Architecture", RFC 4655,
August 2006.
8.2. Informative References 8.2. Informative References
[G.Sup39] ITU-T Series G Supplement 39, Optical system design and [G.Sup39] ITU-T Series G Supplement 39, Optical system design and
engineering considerations, February 2006. engineering considerations, February 2006.
[G.698.1] ITU-T Recommendation G.698.1, Multichannel DWDM [G.698.1] ITU-T Recommendation G.698.1, Multichannel DWDM
applications with Single-Channel optical interface, applications with Single-Channel optical interface,
December 2006. December 2006.
[G.698.2] ITU-T Recommendation G.698.2, Amplified multichannel DWDM [G.698.2] ITU-T Recommendation G.698.2, Amplified multichannel DWDM
applications with Single-Channel optical interface, July applications with Single-Channel optical interface, July
2007. 2007.
[RFC4054] Strand, J., Ed., and A. Chiu, Ed., "Impairments and Other [RFC4054] Strand, J., Ed., and A. Chiu, Ed., "Impairments and Other
Constraints on Optical Layer Routing", RFC 4054, May 2005. Constraints on Optical Layer Routing", RFC 4054, May 2005.
[RFC6163] Y. Lee, G. Bernstein, W. Imajuku, "Framework for GMPLS and [RFC6163] Y. Lee, G. Bernstein, W. Imajuku, "Framework for GMPLS and
PCE Control of Wavelength Switched Optical Networks", RFC PCE Control of Wavelength Switched Optical Networks", RFC
6163, April 2011. 6163, April 2011. [Eppstein]D. Eppstein, "Finding the k
shortest paths," 35th IEEE Symp. Foundations of Comp.
Sci., Santa Fe, pp. 154-165, 1994.
9. Acknowledgments 9. Acknowledgments
This document was prepared using 2-Word-v2.0.template.dot. This document was prepared using 2-Word-v2.0.template.dot.
Copyright (c) 2011 IETF Trust and the persons identified as authors Copyright (c) 2011 IETF Trust and the persons identified as authors
of the code. All rights reserved. of the code. All rights reserved.
Redistribution and use in source and binary forms, with or without Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions modification, are permitted provided that the following conditions
skipping to change at page 26, line 19 skipping to change at page 27, line 43
o Redistributions of source code must retain the above copyright o Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer. notice, this list of conditions and the following disclaimer.
o Redistributions in binary form must reproduce the above copyright o Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the the documentation and/or other materials provided with the
distribution. distribution.
o Neither the name of Internet Society, IETF or IETF Trust, nor the o Neither the name of Internet Society, IETF or IETF Trust, nor the
names of specific contributors, may be used to endorse or promote names of specific contributors, may be used to endorse or promote
products derived from this software without specific prior written products derived from this software without specific prior
permission. written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
Authors' Addresses Authors' Addresses
Young Lee (ed.) Young Lee (ed.)
Huawei Technologies Huawei Technologies
1700 Alma Drive, Suite 100 1700 Alma Drive, Suite 100
Plano, TX 75075 Plano, TX 75075
USA USA
Phone: (972) 509-5599 (x2240) Phone: (972) 509-5599 (x2240)
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