draft-ietf-ccamp-wson-impairments-10.txt   rfc6566.txt 
Network Working Group Y. Lee
Huawei
G. Bernstein
Grotto Networking
D. Li
Huawei
G. Martinelli
Cisco
Internet Draft Internet Engineering Task Force (IETF) Y. Lee, Ed.
Intended status: Informational January 5, 2012 Request for Comments: 6566 Huawei
Expires: July 2012 Category: Informational G. Bernstein, Ed.
ISSN: 2070-1721 Grotto Networking
D. Li
Huawei
G. Martinelli
Cisco
March 2012
A Framework for the Control of Wavelength Switched Optical Networks A Framework for the Control of
(WSON) with Impairments Wavelength Switched Optical Networks (WSONs) with Impairments
draft-ietf-ccamp-wson-impairments-10.txt
Abstract Abstract
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, encounters. When such alterations result in signal degradation,
these processes are usually referred to as "impairments". These these processes are usually referred to as "impairments". These
physical characteristics may be important constraints to consider physical characteristics may be important constraints to consider
when using a GMPLS control plane to support path setup and when using a GMPLS control plane to support path setup and
maintenance in wavelength switched optical networks. maintenance in wavelength switched optical networks.
This document provides a framework for applying GMPLS protocols and This document provides a framework for applying GMPLS protocols and
the PCE architecture to support Impairment Aware Routing and the Path Computation Element (PCE) architecture to support
Wavelength Assignment (IA-RWA) in wavelength switched optical Impairment-Aware Routing and Wavelength Assignment (IA-RWA) in
networks. Specifically, this document discusses key computing wavelength switched optical networks. Specifically, this document
constraints, scenarios and architectural processes: Routing, discusses key computing constraints, scenarios, and architectural
Wavelength Assignment, and Impairment Validation. This document does processes: routing, wavelength assignment, and impairment validation.
not define optical data plane aspects; impairment parameters, This document does not define optical data plane aspects; impairment
measurement of, or assessment and qualification of a route, but parameters; or measurement of, or assessment and qualification of, a
rather it describes the architectural and information components for route; rather, it describes the architectural and information
protocol solutions. components for protocol solutions.
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Table of Contents Table of Contents
1. Introduction...................................................3 1. Introduction ....................................................3
2. Terminology....................................................4 2. Terminology .....................................................4
3. Applicability..................................................6 3. Applicability ...................................................6
4. Impairment Aware Optical Path Computation......................7 4. Impairment-Aware Optical Path Computation .......................7
4.1. Optical Network Requirements and Constraints..............8 4.1. Optical Network Requirements and Constraints ...............8
4.1.1. Impairment Aware Computation Scenarios...............8 4.1.1. Impairment-Aware Computation Scenarios ..............9
4.1.2. Impairment Computation and Information Sharing 4.1.2. Impairment Computation and
Constraints.................................................9 Information-Sharing Constraints ....................10
4.1.3. Impairment Estimation Process.......................11 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 ........13
4.2.1. Combined Routing, WA, and IV........................14 4.2.1. Combined Routing, WA, and IV .......................15
4.2.2. Separate Routing, WA, or IV.........................14 4.2.2. Separate Routing, WA, or IV ........................15
4.2.3. Distributed WA and/or IV............................15 4.2.3. Distributed WA and/or IV ...........................16
4.3. Mapping Network Requirements to Architectures............16 4.3. Mapping Network Requirements to Architectures .............16
5. Protocol Implications.........................................18 5. Protocol Implications ..........................................19
5.1. Information Model for Impairments........................19 5.1. Information Model for Impairments .........................19
5.2. Routing..................................................20 5.2. Routing ...................................................20
5.3. Signaling................................................20 5.3. Signaling .................................................21
5.4. PCE......................................................21 5.4. PCE .......................................................21
5.4.1. Combined IV & RWA...................................21 5.4.1. Combined IV & RWA ..................................21
5.4.2. IV-Candidates + RWA.................................21 5.4.2. IV-Candidates + RWA ................................22
5.4.3. Approximate IA-RWA + Separate Detailed IV...........23 5.4.3. Approximate IA-RWA + Separate Detailed-IV ..........24
6. Manageability and Operations..................................25 6. Manageability and Operations ...................................25
7. Security Considerations.......................................26 7. Security Considerations ........................................26
8. IANA Considerations...........................................27 8. References .....................................................27
9. References....................................................27 8.1. Normative References ......................................27
9.1. Normative References.....................................27 8.2. Informative References ....................................27
9.2. Informative References...................................27 9. Contributors ...................................................29
10. Acknowledgments..............................................28
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 links,
links, tunable transmitters and receivers, Reconfigurable Optical tunable transmitters and receivers, Reconfigurable Optical Add/Drop
Add/Drop Multiplexers (ROADM), wavelength converters, and electro- Multiplexers (ROADMs), wavelength converters, and electro-optical
optical network elements. A WSON is a wavelength division network elements. A WSON is a Wavelength Division Multiplexing
multiplexed (WDM)-based optical network in which switching is (WDM)-based optical network in which switching is performed
performed selectively based on the center wavelength of an optical 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, encounters. When such alterations result in signal degradation,
these 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 [G.680]) traversed by the signal. They are influenced by the type of
used, the types and placement of various optical devices, and the fiber used, the types and placement of various optical devices, and
presence of other optical signals that may share a fiber segment the 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) In order to provision an optical connection (an optical path) through
through a WSON, a combination of path continuity, resource a WSON, a combination of path continuity, resource availability, and
availability, and impairments constraints must be met to determine impairment constraints must be met to determine viable and optimal
viable and optimal paths through the network. The determination of paths through the network. The determination of appropriate paths is
appropriate paths is known as Impairment Aware Routing and known as Impairment-Aware Routing and Wavelength Assignment (IA-RWA).
Wavelength Assignment (IA-RWA).
Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] provides
provides a set of control plane protocols that can be used to a set of control plane protocols that can be used to operate networks
operate networks ranging from packet switch capable networks, ranging from packet switch capable networks to those networks that
through those networks that use time division multiplexing and WDM. use time division multiplexing and WDM. The Path Computation Element
The Path Computation Element (PCE) architecture [RFC4655] defines (PCE) architecture [RFC4655] defines functional computation
functional computation components that can be used in cooperation components that can be used in cooperation with the GMPLS control
with the GMPLS control plane to compute and suggest appropriate plane to compute and suggest appropriate paths. [RFC4054] provides
paths. [RFC4054] provides an overview of optical impairments and an overview of optical impairments and their routing (path selection)
their routing (path selection) implications for GMPLS. This document implications for GMPLS. This document uses [G.680] and other ITU-T
uses as reference [G.680] and other ITU-T Recommendations for the Recommendations as references for the optical data plane aspects.
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 WSONs. To aid in this evaluation, this document provides an overview
overview of the subsystems and processes that comprise WSONs and of the subsystems and processes that comprise WSONs and describes
describes IA-RWA models based on the corresponding ITU-T IA-RWA models based on the corresponding ITU-T Recommendations, so
Recommendations, so that the information requirements for use by that the information requirements for use by GMPLS and PCE systems
GMPLS and PCE systems can be identified. This work will facilitate can be identified. This work will facilitate the development of
the development of protocol extensions in support of IA-RWA within protocol extensions in support of IA-RWA within the GMPLS and PCE
the GMPLS and PCE protocol families. protocol families.
2. Terminology 2. Terminology
ADM: Add/Drop Multiplexers - An optical device used in WDM networks ADM: Add/Drop Multiplexer. An optical device used in WDM networks
composed of one or more line side ports and typically many tributary and composed of one or more line side ports and, typically, many
ports. tributary ports.
Black links: Black links refer to tributary interfaces where only Black Links: Black links refer to tributary interfaces where only
link characteristics are defined. This approach enables transverse link characteristics are defined. This approach enables
compatibility at the single-channel point using a direct wavelength- transverse compatibility at the single-channel point using a
multiplexing configuration. direct wavelength-multiplexing configuration.
CWDM: Coarse Wavelength Division Multiplexing CWDM: Coarse Wavelength Division Multiplexing
DGD: Differential Group Delay DGD: Differential Group Delay
DWDM: Dense Wavelength Division Multiplexing DWDM: Dense Wavelength Division Multiplexing
FOADM: Fixed Optical Add/Drop Multiplexer FOADM: Fixed Optical Add/Drop Multiplexer
GMPLS: Generalized Multi-Protocol Label Switching 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 a 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), which typically carry a few
one) wavelength signals. (typically one) wavelength signals.
NEs: Network Elements NEs: Network Elements
OADMs: Optical Add Drop Multiplexers OADMs: Optical Add/Drop Multiplexers
OSNR: Optical Signal to Noise Ratio OSNR: Optical Signal-to-Noise Ratio
OXC: Optical cross connect - An optical switching element in which a 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 that
path computation to be performed by the Path Computation Element. a path computation be performed by the Path Computation Element.
PCE: Path Computation Element - An entity (component, application, PCE: Path Computation Element. An entity (component, application, or
or network node) that is capable of computing a network path or network node) that is capable of computing a network path or route
route based on a network graph and applying computational based on a network graph and application of computational
constraints. constraints.
PCEP: PCE Communication Protocol - The communication protocol PCEP: PCE Communication Protocol. The communication protocol between
between a Path Computation Client and Path Computation Element. a Path Computation Client and Path Computation Element.
PXC: Photonic Cross Connects PXC: Photonic Cross-Connect
Q-factor: The Q-factor provides a qualitative description of the Q-Factor: The Q-factor provides a qualitative description of the
receiver performance. It is a function of the signal to optical receiver performance. It is a function of the optical signal-to-
noise ratio. The Q-factor suggests the minimum SNR (Signal Noise noise ratio. The Q-factor suggests the minimum SNR (Signal-to-
Ratio) required to obtain a specific BER for a given signal. Noise Ratio) required to obtain a specific bit error rate (BER)
for a given signal.
ROADM: Reconfigurable Optical Add/Drop Multiplexer - A wavelength 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
add and drop ports on an ADM and these support only a single the 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 an
information bearing optical signal centered at a given wavelength to information-bearing optical signal centered at a given wavelength
one with "equivalent" content centered at a different wavelength. to information with "equivalent" content centered at a different
Wavelength conversion can be implemented via an optical-electronic- wavelength. Wavelength conversion can be implemented via an
optical (OEO) process or via a strictly optical process. optical-electronic-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 WSONs where not all possible paths
possible paths will yield suitable signal quality. There are will yield suitable signal quality. There are multiple reasons;
multiple reasons; below is a non-exhaustive list of examples: below is a non-exhaustive list of examples:
o WSON is evolving using multi-degree optical cross connects in a o WSONs are evolving and are using multi-degree optical cross-
way that network topologies are changing from rings (and connects in such a way that network topologies are changing from
interconnected rings) to general mesh. Adding network equipment rings (and interconnected rings) to general mesh. Adding network
such as amplifiers or regenerators, to ensure all paths are equipment such as amplifiers or regenerators to ensure that all
feasible, leads to an over-provisioned network. Indeed, even with paths are feasible leads to an over-provisioned network. Indeed,
over provisioning, the network could still have some infeasible even with over-provisioning, the network could still have some
paths. infeasible 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's life; e.g., the optical interfaces might be
upgraded to higher bit-rates. Such changes could result in paths upgraded to higher bitrates. 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 physical interfaces are typically provisioned at various stages of
of the network's life span as needed by traffic demands. 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 o With the recent bitrate increases from 10G to 40G and 100G over a
a single wavelength, WSON networks will likely be operated with a single wavelength, WSONs will likely be operated with a mix of
mix of wavelengths at different bit rates. This operational wavelengths at different bitrates. This operational scenario will
scenario will impose impairment constraints due to different impose impairment constraints due to different physical behavior
physical behavior of different bit rates and associated of different bitrates and associated modulation 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 terms of equipment and traffic
traffic at the beginning stage. In addition, network operations such at the beginning stage. In addition, network operations such as path
as path establishment, will require significant pre-design via non- establishment will require significant pre-design via non-control-
control plane processes resulting in significantly slower network 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 implementations. The use of an impairment-aware control plane, and
set of information distributed will need to be evaluated on a case the set of information distributed, will need to be evaluated on a
by case scenario. case-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 The basic criterion for path selection is whether one can
successfully transmit the signal from a transmitter to a receiver successfully transmit the signal from a transmitter to a receiver
within a 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 BER. This generally depends on the nature of the signal
nature of the signal transmitted between the sender and receiver and transmitted between the sender and receiver and the nature of the
the nature of the communications channel between the sender and communications channel between the sender and receiver. The optical
receiver. The optical path utilized (along with the wavelength) path utilized (along with the wavelength) determines the
determines the communications channel. communications channel.
The optical impairments incurred by the signal along the fiber and The optical impairments incurred by the signal along the fiber and at
at each optical network element along the path determine whether the each optical network element along the path determine whether the BER
BER performance or any other measure of signal quality can be met performance or any other measure of signal quality can be met for a
for a signal on a particular end-to-end path. 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 that
contains transparent elements and electro-optical elements such as contain transparent elements and electro-optical elements such as OEO
OEO regenerations. In such networks, a generic light path can go regenerations. In such networks, a generic light path can go through
through a number of regeneration points. a number of regeneration points.
Regeneration points could happen for two reasons: Regeneration points could happen for two reasons:
(i) Due to wavelength conversion to assist RWA to avoid wavelength (i) Wavelength conversion is performed in order to assist RWA in
blocking. This is the impairment free case covered by [RFC6163]. avoiding wavelength 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
to meet end to end BER requirements. This is the case when RWA 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 In the latter case, an optical path can be seen as a set of
transparent segments. The optical impairments calculation needs to transparent segments. The calculation of optical impairments needs
be reset at each regeneration point so each transparent segment will to be reset at each regeneration point so each transparent segment
have its own impairment evaluation. will 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 For example, Figure 1 represents an optical path from node I to
E with a regeneration point REG in between. It is feasible from an node E with a regeneration point, REG, in between. This is feasible
impairment validation perspective if both segments (I, N1, N2, REG) from an impairment validation perspective if both segments (I, N1,
and (REG, N3, E) are feasible. N2, REG) 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 under which an impairment aware optical control plane constraints under which an impairment-aware optical control plane may
may have to operate under. These requirements and constraints have to operate. These requirements and constraints motivate the
motivate the IA-RWA architectural alternatives to be presented in IA-RWA architectural alternatives presented in Section 4.2.
the following section. Different optical networks contexts can be Different optical network contexts can be broken into two main
broken into two main criteria: (a) the accuracy required in the criteria: (a) the accuracy required in the estimation of impairment
estimation of impairment effects, and (b) the constraints on the effects and (b) the constraints on the impairment estimation
impairment estimation computation and/or sharing of impairment computation and/or sharing of impairment information.
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
possible path is valid for the signal types permitted on the This situation is applicable to networks designed such that every
network. In this case, impairments are only taken into account possible path is valid for the signal types permitted on the
during network design and after that, for example during optical network. In this case, impairments are only taken into account
path computation, they can be ignored. This is the case discussed in during network design; after that -- for example, during optical
[RFC6163] where impairments may be ignored by the control plane and path computation -- they can be ignored. This is the case
only optical parameters related to signal compatibility are discussed in [RFC6163] where impairments may be ignored by the
considered. control plane and 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
need to be considered but there is sufficient margin such that they effects need to be considered but where there is a sufficient
can be estimated via approximation techniques such as link budgets margin such that impairment effects can be estimated via such
and dispersion [G.680],[G.sup39]. The viability of optical paths for approximation techniques as link budgets and dispersion [G.680]
a particular class of signals can be estimated using well defined [G.Sup39]. The viability of optical paths for a particular class
approximation techniques [G.680], [G.sup39]. This is the generally of signals can be estimated using well-defined approximation
known as linear case where only linear effects are taken into techniques [G.680] [G.Sup39]. This is generally known as the
account. Note that adding or removing an optical signal on the path linear case, where only linear effects are taken into account.
should not render any of the existing signals in the network as non- Note that adding or removing an optical signal on the path should
viable. For example, one form of non-viability is the occurrence of not render any of the existing signals in the network non-viable.
transients in existing links of sufficient magnitude to impact the For example, one form of non-viability is the occurrence in
BER of existing signals. existing links of transients of sufficient magnitude to impact the
BER of existing signals.
Much work at ITU-T has gone into developing impairment models at Much work at ITU-T has gone into developing impairment models at
this and more detailed levels. Impairment characterization of this level and at more detailed levels. Impairment
network elements may be used to calculate which paths are conformant characterization of network elements may be used to calculate
with a specified BER for a particular signal type. In such a case, which paths are conformant with a specified BER for a particular
the impairment aware (IA) path computation can be combined with the signal type. In such a case, the impairment-aware (IA) path
RWA process to permit more optimal IA-RWA computations. Note that computation can be combined with the RWA process to permit more
the IA path computation may also take place in a separate entity, optimal IA-RWA computations. Note that the IA path computation
i.e., a PCE. may also take place in a separate entity, i.e., a PCE.
D. Accurate Impairment Computation D. Accurate Impairment Computation
This situation is applicable to networks in which impairment effects This situation is applicable to networks in which impairment
must be more accurately computed. For these networks, a full effects must be more accurately computed. For these networks, a
computation and evaluation of the impact to any existing paths needs full computation and evaluation of the impact to any existing
to be performed prior to the addition of a new path. Currently no paths need to be performed prior to the addition of a new path.
impairment models are available from ITU-T and this scenario is Currently, no impairment models are available from ITU-T, and this
outside the scope of this document. scenario is 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 In ITU-T Recommendations [G.698.1] and [G.698.2], which specify
single channel interfaces to multi-channel DWDM systems, only the single-channel interfaces to multi-channel DWDM systems, only the
single channel interfaces (transmit and receive) are specified while single-channel interfaces (transmit and receive) are specified, while
the 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. However, note that the overall impact of a black link at available. However, note that the overall impact of a black link at
the 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 in order to estimate the validity of optical paths. For spans in order to estimate the validity of optical paths. For
example, models of optical nonlinearities are not currently example, models of optical nonlinearities are not currently
standardized. Vendors may also choose not to publish impairment standardized. Vendors may also choose not to publish impairment
details for links or a set of network elements in order not to details for links or a set of network elements, in order not to
divulge their optical 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" in the path could not be for optical networks with black links in the path could not be
performed by a general purpose impairment aware (IA) computation performed by a general-purpose IA computation entity, since it would
entity since it would not have access to or understand the "black not have access to or understand the black-link impairment
link" impairment parameters. However, impairment estimation (optical parameters. However, impairment estimation (optical path validation)
path validation) could be performed by a vendor specific impairment could be performed by a vendor-specific IA computation entity. Such
aware computation entity. Such a vendor specific IA computation a vendor-specific IA computation entity could utilize standardized
could utilize standardized impairment information imported from impairment information imported from other network elements in these
other network elements in these proprietary computations. 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
of all viable paths between all viable node pairs to a all viable paths between all viable node pairs to a computation
computational entity. This information would be particularly entity. This information would be particularly useful as an input
useful as an input to RWA optimization to be performed by another to RWA optimization to be performed by another computation entity.
computation entity. The difficulty here is that such a list of The difficulty here is that such a list of paths, along with any
paths along with any wavelength constraints could get wavelength constraints, could get unmanageably large as the size
unmanageably large as the size of the network increases. of the network increases.
2. The authority in control of the "black links" could provide a 2. The authority in control of the black links could provide a
PCE-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 and can reduce the scaling issue previously mentioned. Such a
PCE-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 performs full IA-RWA services. The difficulty here is that this
the one authority to also become the sole source of all RWA option requires the one authority to also become the sole source
optimization algorithms. of all RWA optimization algorithms.
In all the above cases it would be the responsibility of the In all of 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 same or by different control plane functions, as detailed in the
following 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 the 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 impairment- defines the properties at the path endpoints. Even the impairment-
free case, like scenario B in section 4.1.1, needs to consider a free case, such as scenario B in Section 4.1.1, needs to consider a
minimum set of interface characteristics. In such case, only a few minimum set of interface characteristics. In such a case, only a few
parameters used to assess the signal compatibility will be taken parameters used to assess the signal compatibility will be taken into
into account (see [RFC6163]). For the impairment-aware case, these account (see [RFC6163]). For the impairment-aware case, these
parameters may be sufficient or not depending on the accepted level parameters may be sufficient or not, depending on the accepted level
of approximation (scenarios C and D). This functional block of approximation (scenarios C and D). This functional block
highlights the need to consider a set of interface parameters during highlights the need to consider a set of interface parameters during
the Impairment Validation Process. the impairment validation process.
The block "Optical Impairment Path" represents the types of The "Optical Impairment Path" block 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.
Architectural alternatives to accomplish this are provided in Architectural alternatives to accomplish this are provided in
section 4.2. 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 signaling, or a PCE) may influence the way the control plane
distributes impairment information within the network. distributes impairment information within the network.
The last block implements the decision function for path The last block implements the decision function for path feasibility.
feasibility. Depending on the IA level of approximation, this Depending on the IA level of approximation, this function can be more
function can be more or less complex. For example in case of no IA or less complex. For example, in the case of no IA approximation,
only the signal class compatibility will be verified. In addition to only the signal class compatibility will be verified. In addition to
feasible/not-feasible result, it may be worthwhile for decision a feasible/not-feasible result, it may be worthwhile for decision
functions to consider the case in which paths can be likely-to-be- functions to consider the case in which paths would likely be
feasible within some degree of confidence. The optical impairments feasible within some degree of confidence. The optical impairments
are usually not fixed values as they may vary within ranges of are usually not fixed values, as they may vary within ranges of
values according to the approach taken in the physical modeling values according to the approach taken in the physical modeling
(worst-case, statistical, or based on typical values). For example, (worst-case, statistical, or based on typical values). For example,
the utilization of the worst-case value for each parameter within the utilization of the worst-case value for each parameter within the
impairment validation process may lead to marking some paths as not- impairment validation process may lead to marking some paths as not
feasible while they are very likely to be, in reality, feasible. 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 From a control plane point of view, optical impairments are
additional constraints to the impairment-free RWA process described additional constraints to the impairment-free RWA process described
in [RFC6163]. In impairment aware routing and wavelength assignment in [RFC6163]. In IA-RWA, there are conceptually three general
(IA-RWA), there are conceptually three general classes of processes classes of processes to be considered: Routing (R), Wavelength
to be considered: Routing (R), Wavelength Assignment (WA), and Assignment (WA), and Impairment Validation (IV), i.e., estimation.
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. All the variations different levels of detail in the IA-RWA process. All of the
of impairment validation discussed in this section is based on variations of impairment validation discussed in this section are
Scenario C (Approximated Impairment Estimation) as discussed in based on scenario C ("Approximated Impairment Estimation") as
Section 4.1.1. From a process point of view, the following three discussed in Section 4.1.1. From a process point of view, the
forms of impairment validation will be considered: 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 In this case, an IV process furnishes a set of paths between two
of paths between two nodes along with any wavelength restrictions nodes along with any wavelength restrictions, such that the paths
such that the paths are valid with respect to optical impairments. are valid with respect to optical impairments. These paths and
These paths and wavelengths may not be actually available in the wavelengths may not actually be available in the network, due to
network due to its current usage state. This set of paths could be its current usage state. This set of paths could be returned in
returned in response to a request for a set of at most K valid paths response to a request for a set of at most K valid paths between
between two specified nodes. Note that such a process never directly two specified nodes. Note that such a process never directly
discloses optical impairment information. Note that that this case discloses optical impairment information. Note also that this
includes any paths between source and destination that may have been case includes any paths between the source and destination that
"pre-validated". may have been "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
but does not know any optical impairment information. Another option paths but does not have any optical impairment information.
is when the path validity is assessed within the control plane. The Another option is when the path validity is assessed within the
following cases highlight this situation. control plane. The 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
linear and/or statistical characteristics of individual or combined by linear and/or statistical characteristics of individual or
components and fibers along the signal path. combined 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 In this case, an IV process is given a particular path and
wavelength through an optical network and is asked to verify whether wavelength through an optical network and is asked to verify
the overall quality objectives for the signal over this path can be whether the overall quality objectives for the signal over this
met. Note that such a process never directly discloses optical path can be met. Note that such a process never directly
impairment information. discloses optical 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 from a decision-making point of view.
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
The information concerning impairments, however, may still be entity. The information concerning impairments, however, may
gathered from network elements. Depending how information is still be gathered from network elements. Depending on how
gathered, this may put additional requirements on routing protocols. information is gathered, this may put additional requirements on
This will be detailed in later sections. routing protocols. This topic 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
as OSNR, dispersion, DGD, etc., may be accumulated along the path such as OSNR, dispersion, DGD, etc., may be accumulated along the
via signaling. Each node on the path may already perform some part path via signaling. Each node on the path may already perform
of the impairment computation (i.e. distributed). When the some part of the impairment computation (i.e., distributed). When
accumulated measures reach the destination node, a decision on the the accumulated measures reach the destination node, a decision on
impairment validity of the path can be made. Note that such a the impairment validity of the path can be made. Note that such a
process would entail revealing an individual network element's process would entail revealing an individual network element's
impairment information but it does not generally require impairment information, but it does not generally require
distributing optical parameters to the entire network. distributing optical parameters to the entire network.
The Control Plane must not preclude the possibility to concurrently The control plane must not preclude the possibility of concurrently
perform one or all the above cases in the same network. For example, performing one or all of the above cases in the same network. For
there could be cases where a certain number of paths are already example, there could be cases where a certain number of paths are
pre-validated (IV-Candidates) so the control plane may setup one of already pre-validated (IV-Candidates), so the control plane may set
those paths without requesting any impairment validation procedure. up one of those paths without requesting any impairment validation
On the same network, however, the control plane may compute a path procedure. On the same network, however, the control plane may
outside the set of IV-Candidates for which an impairment evaluation compute a path outside the set of IV-Candidates for which an
can be necessary. impairment evaluation 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 review 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 PCE can conceptually/algorithmically
conceptually/algorithmically combine the processes of routing, combine the processes of routing, wavelength assignment, and
wavelength assignment and impairment validation. 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 information as discussed in [RFC6163] and (b)
and (b) impairment information to validate potential paths. 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 Separating the processes of routing, WA, and/or IV can reduce the
need for sharing of different types of information used in path need for the 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 [RFC6163]. In addition, as was discussed in Section 4.1.2, some
information may not be shared and this may lead to the need to impairment information may not be shared, and this may lead to the
separate IV from RWA. In addition, if IV needs to be done at a high need to separate IV from RWA. In addition, if IV needs to be done at
level of precision, it may be advantageous to offload this a high level of precision, it may be advantageous to offload this
computation to a 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 o R + WA + IV
impairment validation. separate routing, wavelength assignment, and impairment
validation.
o R + (WA & IV) -- routing separate from a combined wavelength o R + (WA & IV)
assignment and impairment validation process. Note that routing separate from a combined wavelength assignment and
impairment validation is typically wavelength dependent. Hence impairment validation process. Note that impairment validation is
combining WA with IV can lead to efficiencies. typically wavelength dependent. Hence, combining WA with IV can
lead to improved efficiency.
o (RWA)+IV - combined routing and wavelength assignment with a o (RWA) + IV
separate impairment validation process. combined routing and wavelength assignment with a 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 If RWA comes first, then IV is just rendering a yes/no decision on
the selected path and wavelength. If IV comes first it would need to the selected path and wavelength. If IV comes first, it would need
furnish a list of possible (valid with respect to impairments) to furnish a list of possible (valid with respect to impairments)
routes 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 WA process carried out via signaling can eliminate the
signaling can eliminate the need to distribute wavelength need to distribute wavelength availability information via an
availability information via an interior gateway protocol (IGP). A interior gateway protocol (IGP). A similar approach can allow for
similar approach can allow for the distributed computation of the distributed computation of impairment effects and avoid the need
impairment effects and avoid the need to distribute impairment to distribute impairment characteristics of network elements and
characteristics of network elements and links by routing protocols links by routing protocols or by other means. Therefore, the
or by other means. So the following conceptual options belong to following conceptual options belong to this category:
this category:
o RWA + D(IV) - Combined routing and wavelength assignment and o RWA + D(IV)
distributed impairment validation. combined routing and wavelength assignment and distributed
impairment validation.
o R + D(WA & IV) -- routing separate from a distributed wavelength o R + D(WA & IV)
assignment and impairment validation process. routing separate from a distributed wavelength 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 requires that the effects of impairments be calculated by approximate
approximate models with cumulative quality measures such as those models with cumulative quality measures such as those given in
given in [G.680]. The protocol encoding of the impairment related [G.680]. The protocol encoding of the impairment-related information
information from [G.680] would need to be agreed upon. 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 then it is necessary to accumulate impairment-related information for
for all wavelengths that could be used. The amount of information is all wavelengths that could be used. The amount of information is
reduced somewhat as potential wavelengths are discovered to be in reduced somewhat as potential wavelengths are discovered to be in use
use, but could be a significant burden for lightly loaded high but could be a significant burden for lightly loaded networks with
channel count networks. high channel counts.
4.3. Mapping Network Requirements to Architectures 4.3. Mapping Network Requirements to Architectures
Figure 2 shows process flows for the 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 that apply when approximate impairment
sufficient. Figure 3 shows process flows for the two main validation is sufficient. Figure 3 shows process flows for the two
architectural alternatives when detailed impairment verification is main architectural alternatives that apply when detailed impairment
required. verification is required.
+-----------------------------------+ +-----------------------------------+
| +--+ +-------+ +--+ | | +--+ +-------+ +--+ |
| |IV| |Routing| |WA| | | |IV| |Routing| |WA| |
| +--+ +-------+ +--+ | | +--+ +-------+ +--+ |
| | | |
| Combined Processes | | Combined Processes |
+-----------------------------------+ +-----------------------------------+
(a) (a)
+--------------+ +----------------------+ +--------------+ +----------------------+
| +----------+ | | +-------+ +--+ | | +----------+ | | +-------+ +--+ |
| | IV | | | |Routing| |WA| | | | IV | | | |Routing| |WA| |
| |candidates| |----->| +-------+ +--+ | | |Candidates| |----->| +-------+ +--+ |
| +----------+ | | Combined Processes | | +----------+ | | Combined Processes |
+--------------+ +----------------------+ +--------------+ +----------------------+
(b) (b)
+-----------+ +----------------------+ +-----------+ +----------------------+
| +-------+ | | +--+ +--+ | | +-------+ | | +--+ +--+ |
| |Routing| |------->| |WA| |IV| | | |Routing| |------->| |WA| |IV| |
| +-------+ | | +--+ +--+ | | +-------+ | | +--+ +--+ |
+-----------+ | Distributed Processes| +-----------+ | Distributed Processes|
+----------------------+ +----------------------+
(c) (c)
Figure 2 Process flows for the three main approximate impairment
architectural alternatives.
The advantages, requirements, and suitability of these options are Figure 2. Process Flows for the Three Main Approximate Impairment
as follows: Architectural Alternatives
The advantages, requirements, and suitability of these options are as
follows:
o Combined IV & RWA process o Combined IV & RWA process
This alternative combines RWA and IV within a single computation
entity enabling highest potential optimality and efficiency in IA- This alternative combines RWA and IV within a single computation
RWA. This alternative requires that the computational entity knows entity, enabling highest potential optimality and efficiency in
impairment information as well as non-impairment RWA information. IA-RWA. This alternative requires that the computation entity
This alternative can be used with "black links", but would then need have impairment information as well as non-impairment RWA
to be provided by the authority controlling the "black links". information. This alternative can be used with black links but
would then need 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 This alternative allows separation of impairment information into
two computational entities while still maintaining a high degree of two computation 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 IV-Candidates
process needs to know impairment information from all optical process needs to have impairment information from all optical
network elements, while the RWA process needs to know non-impairment network elements, while the RWA process needs to have
RWA information from the network elements. This alternative can be non-impairment RWA information from the network elements. This
used with "black links", but the authority in control of the "black alternative can be used with black links, but the authority in
links" would need to provide the functionality of the IV-candidates control of the black links would need to provide the functionality
process. Note that this is still very useful since the algorithmic of the IV-Candidates process. Note that this is still very
areas of IV and RWA are very different and conducive to useful, since the algorithmic areas of IV and RWA are very
specialization. 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 processes. Although this doesn't enable as high a potential
of optimality as (a) or (b), it does not require distribution of degree of optimality as (a) or (b), it does not require
either link wavelength usage or link/node impairment information. distribution of either link wavelength usage or link/node
Note that this is most likely not suitable for "black links". impairment information. Note that this is most likely not
suitable for black 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
validation architectural options.
The advantages, requirements, and suitability of these detailed Figure 3. Process Flows for the Two Main Detailed Impairment
validation options are as follows: Validation Architectural Options
The advantages, requirements, and suitability of these detailed
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 the highest potential optimality and computation entity, enabling the highest potential optimality and
efficiency in IA-RWA while keeping a separate entity performing efficiency in IA-RWA while keeping a separate entity performing
detailed impairment validation. In the case of "black links" the detailed impairment validation. In the case of black links, the
authority 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 IV-Candidates + 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 computation 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;
separate computation entity performs detailed impairment validation. then, a separate computation entity performs detailed impairment
Note that detailed impairment estimation is not standardized. validation. Note that detailed impairment estimation is not
standardized.
5. Protocol Implications 5. Protocol Implications
The previous IA-RWA architectural alternatives and process flows The previous IA-RWA architectural alternatives and process flows make
make differing demands on a GMPLS/PCE based control plane. This differing demands on a GMPLS/PCE-based control plane. This section
section discusses the use of (a) an impairment information model, discusses the use of (a) an impairment information model, (b) the PCE
(b) PCE as computational entity assuming the various process roles as computation entity assuming the various process roles and
and consequences for PCEP, (c) possible extensions to signaling, and consequences for PCEP, (c) possible extensions to signaling, and
(d) 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
4. Figure 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 | | | | |
+-------------------+----+----+----------+--------+- +--------------------+-----+-----+------------+---------+
| IV-Candidates |Yes | No | Yes | Yes | | IV-Candidates | Yes | No | Yes | Yes |
| + 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 rely, to a greater or As previously discussed, most IA-RWA scenarios rely, to a greater or
lesser extent, 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 both detailed and approximate impairment
impairment characteristics of fibers, and a variety of devices, and characteristics of fibers, a variety of devices, and a variety of
subsystems. An impairment model which can be used as a guideline for subsystems. An impairment model that can be used as a guideline for
optical network elements and assessment of path viability is given optical network elements and assessment of path viability is given
in [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
networks composed of a single WDM line system vendor combined with networks composed of a single WDM line system vendor combined with
OADMs and/or PXCs from potentially multiple other vendors. This is OADMs and/or PXCs from potentially multiple other vendors. This 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
planned in the future that [G.680] will include networks planned in the future that [G.680] will include networks
incorporating line systems from multiple vendors, as well as, OADMs incorporating line systems from multiple vendors, as well as OADMs
and/or PXCs from potentially multiple other vendors. This is known and/or PXCs from potentially multiple other vendors. This is known
as situation 2 and 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 IV, this would require more than an
this would require more than an impairment information model. It impairment information model. It would need a common impairment
would need a common impairment "computation" model. In the "computation" model. In the distributed IV case, one needs to
distributed IV case, one needs to standardize the accumulated standardize the accumulated impairment measures that will be conveyed
impairment measures that will be conveyed and updated at each node. and updated at each node. Section 9 of [G.680] provides guidance in
Section 9 of [G.680] provides guidance in this area with specific this area, with specific formulas given for OSNR, residual
formulas given for OSNR, residual dispersion, polarization mode dispersion, polarization mode dispersion/polarization-dependent loss,
dispersion/polarization dependent loss, and effects of channel and effects of channel uniformity. However, specifics of what
uniformity. However, specifics of what intermediate results are kept intermediate results are kept and in what form would need to be
and in what form would need to be standardized for interoperability. standardized for interoperability. As noted in [G.680], this
As noted in [G.680], this information may possibly not be information may possibly not be sufficient, and in such a case, the
sufficient, and in such case the applicability would be network applicability would be network dependent.
dependent.
5.2. Routing 5.2. Routing
Different approaches to path/wavelength impairment validation give 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 the 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 volume of data that need to be advertised. Such issue can be high volume of data that need to be advertised. Such issues can be
addressed separating data that need to be advertised rarely from addressed by separating data that need to be advertised only rarely
data that need to be advertised more frequently or adopting other from data that need to be advertised more frequently, or by adopting
form of awareness solutions described in previous sections (e.g., other forms of awareness solutions as described in previous sections
centralized and/or external IV entity). (e.g., a centralized and/or external IV entity).
In term of approximated scenario (see Section 4.1.1.), the model In terms of scenario C in Section 4.1.1, the model defined by [G.680]
defined by [G.680] will apply and the routing protocol will need to will apply, and the routing protocol will need to gather information
gather information required for such computation. required for such computations.
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 The largest impacts on signaling occur in the cases where distributed
distributed impairment validation is performed. In this case, it is impairment validation is performed. In this case, it is necessary to
necessary to accumulate impairment information as previously accumulate impairment information, as previously discussed. In
discussed. In addition, since the characteristics of the signal addition, since the characteristics of the signal itself, such as
itself, such as modulation type, can play a major role in the modulation type, can play a major role in the tolerance of
tolerance of impairments, this type of information will need to be impairments, this type of information will need to be implicitly or
implicitly or explicitly signaled so that an impairment validation explicitly signaled so that an impairment validation decision can be
decision can be made at the destination node. made at the destination node.
It remains for further study if it may be beneficial to include It remains for further study whether it may be beneficial to include
additional information to a connection request such as desired additional information to a connection request, such as desired
egress signal quality (defined in some appropriate sense) in non- egress signal quality (defined in some appropriate sense) in
distributed IV scenarios. non-distributed IV scenarios.
5.4. PCE 5.4. PCE
In section 4.3. a number of computation architectural alternatives In Section 4.2, a number of computational 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 constraints of Section 4.1. Here, the focus is on how these
alternatives could be implemented via either a single PCE or a set alternatives could be implemented via either a single PCE or a set of
of two or more cooperating PCEs, and the impacts on the PCEP. This two or more cooperating PCEs, and the impacts on the PCEP. This
document provides this evaluation to aid solutions work. The document provides this evaluation to aid solutions work. The
protocol 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 of
the computations needed for IA-RWA. the computations needed for IA-RWA.
o TE Database Requirements: WSON Topology and switching o Traffic Engineering (TE) Database requirements: WSON topology and
capabilities, WSON WDM link wavelength utilization, and WSON switching capabilities, WSON WDM link wavelength utilization, and
impairment information WSON 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, and 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, wavelength. If the computations could not complete successfully,
it would be potentially useful to know the reason why. At a it would be potentially useful to know why. At a minimum, it is
minimum, it is of interest to know if this was due to lack of of interest to know if this was due to lack of wavelength
wavelength availability, impairment considerations, or both. The availability, impairment considerations, or both. The information
information to be conveyed is for further study. 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 are involved in the IA-RWA computation. This requires two
cooperating path computation entities: one for the Candidates-IV cooperating path computation entities: one for the IV-Candidates
process and another for the RWA process. In addition, the overall process and another for the RWA process. In addition, the overall
process needs to be coordinated. This could be done with yet another process needs to be coordinated. This could be done with yet another
PCE or this functionality could be added to one of previously PCE, or this functionality could be added to one of a number of
defined entities. This later option requires the RWA entity to also previously defined entities. This later option requires that the RWA
act as the overall process coordinator. The roles, responsibilities, entity also act as the overall process coordinator. The roles,
and information requirements for these two entities when responsibilities, and information requirements for these two
instantiated as PCEs are given below. entities, when 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- The RWA-Coord PCE is responsible for interacting with the PCC and
PCE as needed during RWA computations. In particular, it needs to for utilizing the IV-Candidates PCE as needed during RWA
know to use the Candidates-PCE to obtain potential set of routes and computations. In particular, it needs to know that it is to use
wavelengths. the IV-Candidates PCE to obtain a potential set of routes and
wavelengths.
o TE Database Requirements: WSON Topology and switching o TE Database requirements: WSON topology and switching
capabilities and WSON WDM link wavelength utilization (no capabilities, and WSON WDM link wavelength utilization (no
impairment 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
of at most K routes along with acceptable wavelengths between set of at most K routes, along with acceptable wavelengths
nodes specified in the original PCC request. between 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 IV-Candidates PCE
set of at most K routes along with acceptable wavelengths between returns a set of at most K routes, along with acceptable
nodes specified in the RWA-PCE request. wavelengths between 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 need not take into account current link wavelength computation. It need not take into account current link
utilization, but this is not prohibited. The Candidates-PCE is only wavelength utilization, but this is not prohibited. The
required to interact with the RWA-PCE as indicated above and not the IV-Candidates PCE is only required to interact with the RWA PCE as
initiating PCC. Note: RWA-Coord PCE is also a PCC with respect to indicated above, and not the initiating PCC. Note: The
the IV-Candidate. RWA-Coord PCE is also a PCC with respect to the IV-Candidate.
o TE Database Requirements: WSON Topology and switching o TE Database requirements: WSON topology and switching
capabilities and WSON impairment information (no information link capabilities, and WSON impairment information (no information
wavelength utilization required). link 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) |
| | ```---...___ | | | ```---...___ |
| | ```---->| | | ```---->|
| | | | | |
| | | | | |
| | (c) ___...| | | (c) ___...|
| | ___....---'''' | | | ___....---'''' |
| |<--'''' | | |<--'''' |
| | | | | |
| | | | | |
| (d) ___...| | | (d) ___...| |
| ___....---''' | | | ___....---''' | |
|<--''' | | |<--''' | |
| | | | | |
| | | | | |
Figure 5 Sequence diagram for the interactions between PCC, RWA- Figure 5. Sequence Diagram for the Interactions between the PCC,
Coordinating-PCE, and the IV-Candidates-PCE. RWA-Coord PCE, and IV-Candidates PCE
In step (a), the PCC requests a path meeting specified quality In step (a), the PCC requests a path that meets 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 associated parameters. In step (b), the RWA-Coord PCE requests up to
requests up to K candidate paths between nodes A and Z and K candidate paths between nodes A and Z, and associated acceptable
associated acceptable wavelengths. The term "K candidate paths" is wavelengths. The term "K candidate paths" is associated with the k
associated with K-shortest path algorithm. It refers to an algorithm shortest path algorithm. It refers to an algorithm that finds
that finds multiple K short paths connecting the source and the multiple k short paths connecting the source and the destination in a
destination in a graph allowing repeated vertices and edges in the graph allowing repeated vertices and edges in the paths. See details
paths. See details in [Eppstein]. in [Eppstein].
In step (c), The IV-Candidates PCE returns this list to the RWA- In step (c), the IV-Candidates PCE returns this list to the
Coordinating PCE which then uses this set of paths and wavelengths RWA-Coord PCE, which then uses this set of paths and wavelengths as
as input (e.g., a constraint) to its RWA computation. In step (d) input (e.g., a constraint) to its RWA computation. In step (d), the
the RWA-Coordinating PCE returns the overall IA-RWA computation RWA-Coord PCE returns the overall IA-RWA computation results to
results to the PCC. 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. Please note that there is some IV-Detailed PCE very simple. Note that, from a message flow
inefficiency by separating the IV-Candidates-PCE from the IV- perspective, there is some inefficiency as a result of separating the
Detailed-PCE from a message flow perspective in order to achieve a IV-Candidates PCE from the IV-Detailed PCE in order to achieve a high
high degree of potential optimality. 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 on the type of information that may be used in these computations.
computations.
o Coordinating-PCE to IV-Detailed-PCE request: The coordinating-PCE o RWA-Coord PCE to IV-Detailed PCE request: The RWA-Coord PCE will
will furnish signal characteristics, quality requirements, path, furnish signal characteristics, quality requirements, path, and
and wavelength to the IV-Detailed-PCE. wavelength to the IV-Detailed PCE.
o IV-Detailed-PCE to Coordinating-PCE reply: The reply is o IV-Detailed PCE to RWA-Coord PCE reply: The reply is essentially a
essentially a yes/no decision as to whether the requirements yes/no decision as to whether the requirements could actually be
could actually be met. In the case where the impairment met. In the case where the impairment validation fails, it would
validation fails, it would be helpful to convey information be helpful to convey information related to the cause or to
related to cause or quantify the failure, e.g., so that a quantify the failure, e.g., so that a judgment can be made
judgment can be made whether to try a different signal or adjust regarding whether to try a different signal or adjust signal
signal parameters. parameters.
Figure 6 shows a sequence diagram for the interactions corresponding Figure 6 shows a sequence diagram for the interactions corresponding
to the process shown in Figure 3(b). This involves interactions to the process shown in Figure 3(b). This involves interactions
between the PCC, RWA-PCE (acting as coordinator), IV-Candidates-PCE, between the PCC, RWA PCE (acting as coordinator), IV-Candidates PCE,
and the IV-Detailed-PCE. and IV-Detailed PCE.
In step (a), the PCC requests a path meeting specified quality In step (a), the PCC requests a path that meets 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 associated parameters. In step (b), the RWA-Coord PCE requests up to
requests up to K candidate paths between nodes A and Z and K candidate paths between nodes A and Z, and associated acceptable
associated acceptable wavelengths. In step (c), The IV-Candidates- wavelengths. In step (c), the IV-Candidates PCE returns this list to
PCE returns this list to the RWA-Coordinating PCE which then uses the RWA-Coord PCE, which then uses this set of paths and wavelengths
this set of paths and wavelengths as input (e.g., a constraint) to as input (e.g., a constraint) to its RWA computation. In step (d),
its RWA computation. In step (d), the RWA-Coordinating-PCE request a the RWA-Coord PCE requests a detailed verification of the path and
detailed verification of the path and wavelength that it has wavelength that it has computed. In step (e), the IV-Detailed PCE
computed. In step (e), the IV-Detailed-PCE returns the results of returns the results of the validation to the RWA-Coord PCE. Finally,
the validation to the RWA-Coordinating-PCE. Finally in step (f), the in step (f), the RWA-Coord PCE returns the final results (either a
IA-RWA-Coordinating PCE returns the final results (either a path and path and wavelength, or a cause for the failure to compute a path and
wavelength or cause for the failure to compute a path and
wavelength) to the PCC. 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 25, line 32 skipping to change at page 25, line 40
| | `````----->| | | `````----->|
| | | | | |
| | (e) _____.....+ | | (e) _____.....+
| | _____.....-----''''' | | | _____.....-----''''' |
| |<----''''' | | |<----''''' |
| (f) __.| | | (f) __.| |
| __.--'' | | __.--'' |
|<-'' | |<-'' |
| | | |
Figure 6 Sequence diagram for the interactions between PCC, RWA- Figure 6. Sequence Diagram for the Interactions between the PCC,
Coordinating-PCE, IV-Candidates-PCE, and IV-Detailed-PCE. RWA-Coord PCE, IV-Candidates PCE, and IV-Detailed PCE
6. Manageability and Operations 6. Manageability and Operations
The issues concerning manageability and operations are beyond the The issues concerning manageability and operations are beyond the
scope of this document. The details of manageability and operational scope of this document. The details of manageability and operational
issues will have to be deferred to future protocol implementation. issues will have to be deferred to future protocol implementations.
On a high-level, the GMPLS-routing based architecture discussed in On a high level, the GMPLS-routing-based architecture discussed in
Section 5.2. may have to deal with how to resolve potential scaling Section 5.2 may have to deal with how to resolve potential scaling
issues associated with disseminating a large amount of impairment issues associated with disseminating a large amount of impairment
characteristics of the network elements and links. characteristics of the network elements and links.
From a scaling point of view, the GMPLS-signaling based architecture From a scaling point of view, the GMPLS-signaling-based architecture
discussed in Section 5.3. would be more scalable than other discussed in Section 5.3 would be more scalable than other
alternatives as this architecture would avoid the dissemination of a alternatives, as this architecture would avoid the dissemination of a
large amount of data to the networks. This benefit may come, large amount of data to the networks. This benefit may come,
however, at the expense of potentially inefficient use of network however, at the expense of potentially inefficient use of network
resources. resources.
The PCE-based architectures discussed in Section 5.4. would have to The PCE-based architectures discussed in Section 5.4 would have to
consider operational complexity when implementing options that consider operational complexity when implementing options that
require the use of multiple PCE servers. The most serious case is require the use of multiple PCE servers. The most serious case is
the option discussed in Section 5.4.3., namely, "Approximate IA-RWA the option discussed in Section 5.4.3 ("Approximate IA-RWA + Separate
+ Separate Detailed IV". The combined IV & RWA option (which was Detailed-IV"). The combined IV & RWA option (which was discussed in
discussed on Section 5.4.1.), on the other hand, is simpler than Section 5.4.1), on the other hand, is simpler to operate than are
other alternatives to operate as one PCE server handles all other alternatives, as one PCE server handles all functionality;
functionality; however, this option may suffer from a heavy however, this option may suffer from a heavy computation and
computation and processing burden compared to other alternatives. processing burden compared to other alternatives.
Interoperability may be a hurdle to overcome when trying to agree on Interoperability may be a hurdle to overcome when trying to agree on
some impairment parameters especially those which are associated some impairment parameters, especially those that are associated with
with the black links. This work has been in progress in ITU-T and the black links. This work has been in progress in ITU-T and needs
needs some more time to mature. some more time to mature.
7. Security Considerations 7. 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 an
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 network. Such information would need to be protected from
intentional or unintentional disclosure similar to other network intentional or unintentional disclosure, similar to other network
information used within intra-domain protocols. information used within intra-domain protocols.
This document does not require changes to the security models within This document does not require changes to the security models within
GMPLS and associated protocols. That is, the OSPF-TE, RSVP-TE, and GMPLS and associated protocols. That is, the OSPF-TE, RSVP-TE, and
PCEP security models could be operated unchanged. However, PCEP security models could be operated unchanged. However,
satisfying the requirements for impairment information dissemination satisfying the requirements for impairment information dissemination
using the existing protocols may significantly affect the loading of using the existing protocols may significantly affect the loading of
those protocols. those protocols and may make the operation of the network more
vulnerable to active attacks such as injections, impersonation, and
This may make the operation of the network more vulnerable to active man-in-the-middle attacks. Therefore, additional care may be
attacks such as injections, impersonation, and MITMs. Therefore, required to ensure that the protocols are secure in the impairment-
additional care may be required to ensure that the protocols are aware WSON environment.
secure in the impairment-aware WSON environment.
Furthermore, the additional information distributed in order to Furthermore, the additional information distributed in order to
address impairment information represents a disclosure of network address impairment information represents a disclosure of network
capabilities that an operator may wish to keep private. capabilities that an operator may wish to keep private.
Consideration should be given to securing this information. For a Consideration should be given to securing this information. For a
general discussion on MPLS- and GMPLS-related security issues, see general discussion on MPLS- and GMPLS-related security issues, see
the MPLS/GMPLS security framework [RFC5920] and, in particular, text the MPLS/GMPLS security framework [RFC5920] and, in particular, text
detailing security issues when Control Plane is physically separated detailing security issues when the control plane is physically
from Data Plane. separated from the data plane.
8. IANA Considerations
This draft does not currently require any consideration from IANA.
9. References
9.1. Normative References
[G.680] ITU-T Recommendation G.680, Physical transfer functions of
optical network elements, July 2007.
[RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", RFC 3945, October 2004.
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
August 2006.
9.2. Informative References
[G.Sup39] ITU-T Series G Supplement 39, Optical system design and
engineering considerations, February 2006.
[G.698.1] ITU-T Recommendation G.698.1, Multichannel DWDM
applications with Single-Channel optical interface,
December 2006.
[G.698.2] ITU-T Recommendation G.698.2, Amplified multichannel DWDM
applications with Single-Channel optical interface, July
2007.
[RFC4054] Strand, J., Ed., and A. Chiu, Ed., "Impairments and Other
Constraints on Optical Layer Routing", RFC 4054, May 2005.
[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, July 2010.
[RFC6163] Lee, Y., Ed., G. Bernstein, Ed., and W. Imajuku,
"Framework for GMPLS and PCE Control of Wavelength
Switched Optical Networks", RFC 6163, April 2011.
[Eppstein] Eppstein, D., "Finding the k shortest paths", 35th IEEE
Symp. Foundations of Comp. Sci., Santa Fe, pp. 154-165,
1994.
10. Acknowledgments
This document was prepared using 2-Word-v2.0.template.dot.
Copyright (c) 2012 IETF Trust and the persons identified as authors
of the code. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
o Redistributions of source code must retain the above copyright 8. References
notice, this list of conditions and the following disclaimer.
o Redistributions in binary form must reproduce the above copyright 8.1. Normative References
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
o Neither the name of Internet Society, IETF or IETF Trust, nor the [G.680] ITU-T Recommendation G.680, "Physical transfer functions
names of specific contributors, may be used to endorse or promote of optical network elements", July 2007.
products derived from this software without specific prior
written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS [RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT Switching (GMPLS) Architecture", RFC 3945, October 2004.
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
Authors' Addresses [RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
August 2006.
Young Lee (ed.) 8.2. Informative References
Huawei Technologies
1700 Alma Drive, Suite 100
Plano, TX 75075
USA
Phone: (972) 509-5599 (x2240) [Eppstein] Eppstein, D., "Finding the k shortest paths", 35th IEEE
Email: ylee@huawei.com Symposium on Foundations of Computer Science, Santa Fe,
pp. 154-165, 1994.
Greg M. Bernstein (ed.) [G.698.1] ITU-T Recommendation G.698.1, "Multichannel DWDM
Grotto Networking applications with single-channel optical interfaces",
Fremont California, USA November 2009.
Phone: (510) 573-2237 [G.698.2] ITU-T Recommendation G.698.2, "Amplified multichannel
Email: gregb@grotto-networking.com dense wavelength division multiplexing applications with
single channel optical interfaces", November 2009.
Dan Li [G.Sup39] ITU-T Series G Supplement 39, "Optical system design and
Huawei Technologies Co., Ltd. engineering considerations", February 2006.
F3-5-B R&D Center, Huawei Base,
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28973237 [RFC4054] Strand, J., Ed., and A. Chiu, Ed., "Impairments and Other
Email: danli@huawei.com Constraints on Optical Layer Routing", RFC 4054,
May 2005.
Giovanni Martinelli [RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Cisco Networks", RFC 5920, July 2010.
Via Philips 12
20052 Monza, Italy
Phone: +39 039 2092044 [RFC6163] Lee, Y., Ed., Bernstein, G., Ed., and W. Imajuku,
Email: giomarti@cisco.com "Framework for GMPLS and Path Computation Element (PCE)
Control of Wavelength Switched Optical Networks (WSONs)",
RFC 6163, April 2011.
Contributor's Addresses 9. Contributors
Ming Chen Ming Chen
Huawei Technologies Co., Ltd. Huawei Technologies Co., Ltd.
F3-5-B R&D Center, Huawei Base, F3-5-B R&D Center, Huawei Base
Bantian, Longgang District Bantian, Longgang District
Shenzhen 518129 P.R.China Shenzhen 518129
P.R. China
Phone: +86-755-28973237 Phone: +86-755-28973237
Email: mchen@huawei.com EMail: mchen@huawei.com
Rebecca Han Rebecca Han
Huawei Technologies Co., Ltd. Huawei Technologies Co., Ltd.
F3-5-B R&D Center, Huawei Base, F3-5-B R&D Center, Huawei Base
Bantian, Longgang District Bantian, Longgang District
Shenzhen 518129 P.R.China Shenzhen 518129
P.R.China
Phone: +86-755-28973237 Phone: +86-755-28973237
Email: hanjianrui@huawei.com EMail: hanjianrui@huawei.com
Gabriele Galimberti Gabriele Galimberti
Cisco Cisco
Via Philips 12, Via Philips 12
20052 Monza, Italy 20052 Monza
Italy
Phone: +39 039 2091462 Phone: +39 039 2091462
Email: ggalimbe@cisco.com EMail: ggalimbe@cisco.com
Alberto Tanzi Alberto Tanzi
Cisco Cisco
Via Philips 12, Via Philips 12
20052 Monza, Italy 20052 Monza
Italy
Phone: +39 039 2091469 Phone: +39 039 2091469
Email: altanzi@cisco.com EMail: altanzi@cisco.com
David Bianchi David Bianchi
Cisco Cisco
Via Philips 12, Via Philips 12
20052 Monza, Italy 20052 Monza
Italy
Email: davbianc@cisco.com EMail: davbianc@cisco.com
Moustafa Kattan Moustafa Kattan
Cisco Cisco
Dubai 500321 Dubai 500321
United Arab Emirates United Arab Emirates
Email: mkattan@cisco.com EMail: mkattan@cisco.com
Dirk Schroetter Dirk Schroetter
Cisco Cisco
Email: dschroet@cisco.com EMail: dschroet@cisco.com
Daniele Ceccarelli Daniele Ceccarelli
Ericsson Ericsson
Via A. Negrone 1/A Via A. Negrone 1/A
Genova - Sestri Ponente Genova - Sestri Ponente
Italy Italy
Email: daniele.ceccarelli@ericsson.com EMail: daniele.ceccarelli@ericsson.com
Elisa Bellagamba Elisa Bellagamba
Ericsson Ericsson
Farogatan 6, Farogatan 6
Kista 164 40 Kista 164 40
Sweeden Sweden
Email: elisa.bellagamba@ericcson.com EMail: elisa.bellagamba@ericsson.com
Diego Caviglia Diego Caviglia
Ericsson Ericsson
Via A. negrone 1/A Via A. Negrone 1/A
Genova - Sestri Ponente Genova - Sestri Ponente
Italy Italy
Email: diego.caviglia@ericcson.com EMail: diego.caviglia@ericsson.com
Authors' Addresses
Young Lee (editor)
Huawei Technologies
5340 Legacy Drive, Building 3
Plano, TX 75024
USA
Phone: (469) 277-5838
EMail: leeyoung@huawei.com
Greg M. Bernstein (editor)
Grotto Networking
Fremont, CA
USA
Phone: (510) 573-2237
EMail: gregb@grotto-networking.com
Dan Li
Huawei Technologies Co., Ltd.
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129
P.R. China
Phone: +86-755-28973237
EMail: danli@huawei.com
Giovanni Martinelli
Cisco
Via Philips 12
20052 Monza
Italy
Phone: +39 039 2092044
EMail: giomarti@cisco.com
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