draft-ietf-ccamp-wson-impairments-04.txt   draft-ietf-ccamp-wson-impairments-05.txt 
Network Working Group Y. Lee Network Working Group Y. Lee
Internet Draft Huawei Huawei
G. Bernstein G. Bernstein
Grotto Networking Grotto Networking
D. Li D. Li
Huawei Huawei
G. Martinelli G. Martinelli
Cisco Cisco
Intended status: Informational October 21, 2010
Expires: April 2011 Internet Draft
Intended status: Informational March 9, 2011
Expires: September 2011
A Framework for the Control of Wavelength Switched Optical Networks A Framework for the Control of Wavelength Switched Optical Networks
(WSON) with Impairments (WSON) with Impairments
draft-ietf-ccamp-wson-impairments-04.txt draft-ietf-ccamp-wson-impairments-05.txt
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Abstract Abstract
The operation of optical networks requires information on the As an optical signal progresses along its path it may be altered by
physical characterization of optical network elements, subsystems, the various physical processes in the optical fibers and devices it
devices, and cabling. These physical characteristics may be important encounters. When such alterations result in signal degradation, we
to consider when using a GMPLS control plane to support path setup usually refer to these processes as "impairments". These physical
and maintenance. This document discusses how the definition and characteristics may be important constraints to consider when using a
characterization of optical fiber, devices, subsystems, and network GMPLS control plane to support path setup and maintenance in
elements contained in various ITU-T recommendations can be combined wavelength switched optical networks.
with GMPLS control plane protocols and mechanisms to support
Impairment Aware Routing and Wavelength Assignment (IA-RWA) in This document provides a framework for applying GMPLS protocols and
optical networks. the PCE architecture to support Impairment Aware Routing and
Wavelength Assignment (IA-RWA) in wavelength switched optical
networks.
Table of Contents Table of Contents
1. Introduction...................................................4 1. Introduction...................................................3
1.1. Revision History..........................................5 2. Terminology....................................................4
2. Motivation.....................................................5 3. Applicability..................................................5
3. Impairment Aware Optical Path Computation......................6 4. Impairment Aware Optical Path Computation......................6
3.1. Optical Network Requirements and Constraints..............7 4.1. Optical Network Requirements and Constraints..............7
3.1.1. Impairment Aware Computation Scenarios...............7 4.1.1. Impairment Aware Computation Scenarios...............7
3.1.2. Impairment Computation and Information Sharing 4.1.2. Impairment Computation and Information Sharing
Constraints.................................................8 Constraints.................................................8
3.1.3. Impairment Estimation Process.......................10 4.1.3. Impairment Estimation Process.......................10
3.2. IA-RWA Computation and Control Plane Architectures.......11 4.2. IA-RWA Computation and Control Plane Architectures.......11
3.2.1. Combined Routing, WA, and IV........................13 4.2.1. Combined Routing, WA, and IV........................13
3.2.2. Separate Routing, WA, or IV.........................13 4.2.2. Separate Routing, WA, or IV.........................13
3.2.3. Distributed WA and/or IV............................13 4.2.3. Distributed WA and/or IV............................14
3.3. Mapping Network Requirements to Architectures............14 4.3. Mapping Network Requirements to Architectures............15
5. Protocol Implications.........................................17
4. Protocol Implications.........................................17 5.1. Information Model for Impairments........................17
4.1. Information Model for Impairments........................17 5.2. Routing..................................................18
4.2. Routing..................................................18 5.3. Signaling................................................19
4.3. Signaling................................................18 5.4. PCE......................................................19
4.4. PCE......................................................19 5.4.1. Combined IV & RWA...................................19
4.4.1. Combined IV & RWA...................................19 5.4.2. IV-Candidates + RWA.................................20
4.4.2. IV-Candidates + RWA.................................19 6. Security Considerations.......................................22
4.4.3. Approximate IA-RWA + Separate Detailed IV...........21 7. IANA Considerations...........................................22
5. Security Considerations.......................................23 8. References....................................................22
6. IANA Considerations...........................................23 8.1. Normative References.....................................22
7. Acknowledgments...............................................23 8.2. Informative References...................................24
8. References....................................................31 9. Acknowledgments...............................................24
8.1. Normative References.....................................31
8.2. Informative References...................................33
1. Introduction
As an optical signal progresses along its path it may be altered
by the various physical processes in the optical fibers and
devices it encounters. When such alterations result in signal
degradation, we usually refer to these processes as "impairments".
An overview of some critical optical impairments and their routing
(path selection) implications can be found in [RFC4054]. Roughly
speaking, optical impairments accumulate along the path (without
3R regeneration) traversed by the signal. They are influenced by
the type of fiber used, the types and placement of various optical
devices and the presence of other optical signals that may share a
fiber segment along the signal's path. The degradation of the
optical signals due to impairments can result in unacceptable bit
error rates or even a complete failure to demodulate and/or detect
the received signal. Therefore, path selection in any WSON
requires consideration of optical impairments so that the signal
will be propagated from the network ingress point to the egress
point with an acceptable signal quality.
Some optical subnetworks are designed such that over any path the
degradation to an optical signal due to impairments never exceeds
prescribed bounds. This may be due to the limited geographic
extent of the network, the network topology, and/or the quality of
the fiber and devices employed. In such networks the path
selection problem reduces to determining a continuous wavelength
from source to destination (the Routing and Wavelength Assignment
problem). These networks are discussed in [WSON-Frame]. In other
optical networks, impairments are important and the path selection
process must be impairment-aware.
Although [RFC4054] describes a number of key optical impairments,
a more complete description of optical impairments and processes
can be found in the ITU-T Recommendations. Appendix A of this
document provides an overview of the extensive ITU-T documentation
in this area.
The benefits of operating networks using the Generalized
Multiprotocol Label Switching (GMPLS) control plane is described
in [RFC3945]. The advantages of using a path computation element
(PCE) to perform complex path computations are discussed in
[RFC4655].
Based on the existing ITU-T standards covering optical
characteristics (impairments) and the knowledge of how the impact
of impairments may be estimated along a path, this document
provides a framework for impairment aware path computation and
establishment utilizing GMPLS protocols and the PCE architecture.
As in the impairment free case covered in [WSON-Frame], a number
of different control plane architectural options are described.
1.1. Revision History
Changes from 00 to 01:
Added discussion of regenerators to section 3.
Added to discussion of interface parameters in section 3.1.3.
Added to discussion of IV Candidates function in section 3.2.
Changes from 01 to 02:
Correct and refine use of "black link" concept based on liaison
with ITU-T and WG feedback.
Changes from 02 to 03:
Insert additional information on use and considerations for
regenerators in section 3.
2. Motivation
There are deployment scenarios for WSON networks where not all
possible paths will yield suitable signal quality. There are
multiple reasons behind this choice; here below is a non-
exhaustive list of examples:
o WSON is evolving using multi-degree optical cross connects in a
way that network topologies are changing from rings (and
interconnected rings) to a full mesh. Adding network equipment
such as amplifiers or regenerators, to make all paths feasible,
leads to an over-provisioned network. Indeed, even with over
provisioning, the network could still have some infeasible
paths.
o Within a given network, the optical physical interface may
change over the network life, e.g., the optical interfaces might
be upgraded to higher bit-rates. Such changes could result in
paths being unsuitable for the optical signal. Although the same
considerations may apply to other network equipment upgrades,
the optical physical interfaces are a typical case because they
are typically provisioned at various stages of the network's
life span as needed by traffic demands.
o There are cases where a network is upgraded by adding new
optical cross connects to increase network flexibility. In such
cases existing paths will have their feasibility modified while
new paths will need to have their feasibility assessed.
o With the recent bit rate increases from 10G to 40G and 100G over
a single wavelength, WSON networks will likely be operated with
a mix of wavelengths at different bit rates. This operational
scenario will impose some impairment considerations due to
different physical behavior of different bit rates and
associated modulation formats.
Not having an impairment aware control plane for such networks
will require a more complex network design phase that, since the
beginning, takes into account evolving network status in term of
equipments and traffic. This could result in over-engineering the
DWDM network with additional regenerators nodes and optical
amplifiers. Optical impairment awareness allows for the concept of
photonic switching where possible and provides regeneration when
it is a must. In addition, network operations such as path
establishment, will require significant pre-design via non-control
plane processes resulting in significantly slower network
provisioning.
3. Impairment Aware Optical Path Computation
The basic criteria for path selection is whether one can
successfully transmit the signal from a transmitter to a receiver
within a prescribed error tolerance, usually specified as a
maximum permissible bit error ratio (BER). This generally depends
on the nature of the signal transmitted between the sender and
receiver and the nature of the communications channel between the
sender and receiver. The optical path utilized (along with the
wavelength) determines the communications channel.
The optical impairments incurred by the signal along the fiber and
at each optical network element along the path determine whether
the BER performance or any other measure of signal quality can be
met for a signal on a particular end-to-end path. This could
include parameters such as the Q factor to correlate both linear
and non-linear parameters into one value.
The impairment-aware path calculation needs also to take into
account when regeneration happens along the path. [WSON-Frame]
introduces the concept of Optical translucent network that
contains transparent elements and electro-optical elements such as
OEO regenerations. In such networks a generic light path can go
through a certain number of regeneration points.
Regeneration points could happen for two reasons:
(i) wavelength conversion to assist the RWA process to avoid
wavelength blocking. This is the impairment free case covered
by[WSON-Frame].
(ii) the optical signal is too degraded. This is the case when
the RWA take into consideration impairment estimation covered by
this document.
In the latter case a light path can be seen as a set of transparent
segments. The optical impairments calculation needs to be reset at
each regeneration point so each transparent segment will have its own
impairment evaluation.
+---+ +----+ +----+ +---+ +----+ +---+
| I |----| N1 |---| N2 |-----| R |-----| N3 |----| E |
+--+ +----+ +----+ +---+ +----+ +---+
|.--------------------------.|.------------------.|
Segment 1 Segment 2
Figure 1 Light path as a set of transparent segments
For example, Figure 1 represents a Light path from node I to node E
with a regeneration point R in between. It is feasible from an
impairment validation perspective if both segments (I, N1, N2, R) and
(R, N3, E) are feasible.
3.1. Optical Network Requirements and Constraints
This section examines the various optical network requirements and
constraints that an impairment aware optical control plane may
have to operate under. These requirements and constraints motivate
the IA-RWA architectural alternatives to be presented in the
following section. We can break the different optical networks
contexts up along two main criteria: (a) the accuracy required in
the estimation of impairment effects, and (b) the constraints on
the impairment estimation computation and/or sharing of impairment
information.
3.1.1. Impairment Aware Computation Scenarios
A. No concern for impairments or Wavelength Continuity Constraints
This situation is covered by existing GMPLS with local wavelength
(label) assignment.
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
network. In this case impairments are only taken into account
during network design and after that, for example during optical
path computation, they can be ignored. This is the case discussed
in [WSON-Frame] where impairments may be ignored by the control
plane and only optical parameters related to signal compatibility
are considered.
C. Approximated Impairment Estimation
This situation is applicable to networks in which impairment
effects need to be considered but there is sufficient margin such
that they can be estimated via approximation techniques such as
link budgets and dispersion[G.680],[G.sup39]. The viability of
optical paths for a particular class of signals can be estimated
using well defined approximation techniques [G.680], [G.sup39].
This is the generally known as linear case where only linear
effects are taken into account. Adding or removing an optical
signal on the path will not render any of the existing signals in
the network as non-viable. For example, one form of non-viability
is the occurrence of transients in existing links of sufficient
magnitude to impact the BER of those existing signals.
Much work at ITU-T has gone into developing impairment models at
this and more detailed levels. Impairment characterization of
network elements could then may be used to calculate which paths
are conformant with a specified BER for a particular signal type.
In such a case, we can combine the impairment aware (IA) path
computation with the RWA process to permit more optimal IA-RWA
computations. Note, the IA path computation may also take place in
a separate entity, i.e., a PCE.
D. Detailed Impairment Computation
This situation is applicable to networks in which impairment
effects must be more accurately computed. For these networks, a
full computation and evaluation of the impact to any existing
paths needs to be performed prior to the addition of a new path.
Currently no impairment models are available from ITU-T and this
scenario is outside the scope of this document.
3.1.2. Impairment Computation and Information Sharing Constraints
In GMPLS, information used for path computation is standardized
for distribution amongst the elements participating in the control
plane and any appropriately equipped PCE can perform path
computation. For optical systems this may not be possible. This is
typically due to only portions of an optical system being subject
to standardization. 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 (transmit and
receive) are specified while the multi-channel links are not
standardized. These DWDM links are referred to as "black links"
since their details are not generally available. Note however the
overall impact of a black link at the single channel interface
points is limited by [G.698.1] and [G.698.2].
Typically a vendor might use proprietary impairment models for
DWDM spans and to estimate the validity of optical paths. For
example, models of optical nonlinearities are not currently
standardized. Vendors may also choose not to publish impairment
details for links or a set of network elements in order not to
divulge their optical system designs.
In general, the impairment estimation/validation of an optical
path for optical networks with "black links" (path) could not be
performed by a general purpose impairment aware (IA) computation
entity since it would not have access to or understand the "black
link" impairment parameters. However, impairment estimation
(optical path validation) could be performed by a vendor specific
impairment aware computation entity. Such a vendor specific IA
computation, could utilize standardized impairment information
imported from other network elements in these proprietary
computations.
In the following we will use the term "black links" to describe
these computation and information sharing constraints in optical
networks. From the control plane perspective we have the following
options:
A. The authority in control of the "black links" can furnish a
list of all viable paths between all viable node pairs to a
computational entity. This information would be particularly
useful as an input to RWA optimization to be performed by
another computation entity. The difficulty here is for larger
networks such a list of paths along with any wavelength
constraints could get unmanageably large.
B. The authority in control of the "black links" could provide a
PCE like entity that would furnish a list of viable
paths/wavelengths between two requested nodes. This is useful
as an input to RWA optimizations and can reduce the scaling
issue previously mentioned. Such a PCE like entity would not
need to perform a full RWA computation, i.e., it would not need
to take into account current wavelength availability on links.
Such an approach may require PCEP extensions for both the
request and response information.
C. The authority in control of the "black links" can provide a PCE
that performs full IA-RWA services. The difficulty is this
requires the one authority to also become the sole source of
all RWA optimization algorithms and such.
In all the above cases it would be the responsibility of the
authority in control of the "black links" to import the shared
impairment information from the other NEs via the control plane or
other means as necessary.
3.1.3. Impairment Estimation Process
The Impairment Estimation Process can be modeled through the
following functional blocks. These blocks are independent from any
Control Plane architecture, that is, they can be implemented by
the same or by different control plane functions as detailed in
following sections.
+-----------------+
+------------+ +-----------+ | +------------+ |
| | | | | | | |
| Optical | | Optical | | | Optical | |
| Interface |------->| Impairment|--->| | Channel | |
| (Transmit/ | | Path | | | Estimation | |
| Receive) | | | | | | |
+------------+ +-----------+ | +------------+ |
| || |
| || |
| Estimation |
| || |
| \/ |
| +------------+ |
| | BER / | |
| | Q Factor | |
| +------------+ |
+-----------------+
Starting from functional block on the left the Optical Interface
represents where the optical signal is transmitted or received and
defines the properties at the end points path. Even the no-
impairment case like scenario B in section 3.1.1 needs to consider
a minimum set of interface characteristics. In such case only few
parameters to assess the signal compatibility will be taken into
account (see [WSON-Frame]). For the impairment-awareness case
signal compatibility these parameters may be sufficient or not
depending on the accepted level of approximation (scenarios C and
D). This functional block highlights the need to consider a set of
interface parameters during an Impairment Validation Process.
The block "Optical Impairment Path" represents all kinds of
impairments affecting a wavelength as it traverses the networks
through links and nodes. In the case where the control plane has
no IV this block will not be present. Otherwise, this function
must be implemented in some way via the control plane. Options for
this will be given in the next section architectural alternatives.
This block implementation (e.g. through routing, signaling or PCE)
may influence the way the control plane distributes impairment
information within the network.
The last block implements the decision function for path
feasibility. Depending on the IA level of approximation this
function can be more or less complex. For example in case of no IA
only the signal class compatibility will be verified. In addition
to feasible/not-feasible result, it may be worth for decision
functions to consider the case in which paths can be likely-to-be-
feasible within some degree of confidence. The optical impairments
are usually not fixed values as they may vary within ranges of
values according to the approach taken in the physical modeling
(worst-case, statistical or based on typical values). For example,
the utilization of the worst-case value for each parameter within
impairment validation process may lead to marking some paths as
not-feasible while they are very likely to be feasible in reality.
3.2. IA-RWA Computation and Control Plane Architectures
From a control plane point of view optical impairments are
additional constraints to the impairment-free RWA process
described in [WSON-Frame]. In impairment aware routing and
wavelength assignment (IA-RWA), there are conceptually three
general classes of processes to be considered: Routing (R),
Wavelength Assignment (WA), and Impairment Validation (estimation)
(IV).
Impairment validation may come in many forms, and maybe invoked at
different levels of detail in the IA-RWA process. From a process
point of view we will consider the following three forms of
impairment validation:
o IV-Candidates
In this case an Impairment Validation (IV) process furnishes a set
of paths between two nodes along with any wavelength restrictions
such that the paths are valid with respect to optical impairments.
These paths and wavelengths may not be actually available in the
network due to its current usage state. This set of paths would be
returned in response to a request for a set of at most K valid
paths between two specified nodes. Note that such a process never
directly discloses optical impairment information. Note that that
this case includes any paths between source and destination that
may have been "pre-validated".
In this case the control plane simply makes use of candidate paths
but does not know any optical impairment information. Another
option is when the path validity is assessed within the control
plane. The following cases highlight this situation.
o IV-Approximate Verification
Here approximation methods are used to estimate the impairments
experienced by a signal. Impairments are typically approximated by
linear and/or statistical characteristics of individual or
combined components and fibers along the signal path.
o IV-Detailed Verification
In this case an IV process is given a particular path and
wavelength through an optical network and is asked to verify
whether the overall quality objectives for the signal over this
path can be met. Note that such a process never directly discloses
optical impairment information.
The next two cases refer to the way an impairment validation
computation can be performed.
o IV-Centralized
In this case impairments to a path are computed at a single
entity. The information concerning impairments may still be
gathered from network elements however. Depending how information
are gathered this may put requirements on routing protocols. This
will be detailed in following sections.
o IV-Distributed
In the distributed IV process, impairment approximate degradation
measures such as OSNR, dispersion, DGD, etc. are accumulated along
the path via a signaling like protocol. Each node on the path may
already perform some part of the impairment computation (i.e.
distributed). When the accumulated measures reach the destination
node a decision on the impairment validity of the path can be
made. Note that such a process would entail revealing an
individual network element's impairment information but it does
not generally require spreading optical parameters at network
level.
The Control Plane must not preclude the possibility to operate one
or all the above cases concurrently in the same network. For
example there could be cases where a certain number of paths are
already pre-validates (IV-Candidates) so the control plane may
setup one of those path without requesting any impairment
validation procedure. On the same network however the control
plane may compute a path outside the set of IV-Candidates for
which an impairment evaluation can be necessary.
The following subsections present three major classes of IA-RWA
path computation architectures and their respective advantages and
disadvantages.
3.2.1. Combined Routing, WA, and IV
From the point of view of optimality, the "best" IA-RWA solutions
can be achieved if the path computation entity (PCE) can
conceptually/algorithmically combine the processes of routing,
wavelength assignment and impairment validation.
Such a combination can take place if the PCE is given: (a) the
impairment-free WSON network information as discussed in [WSON-
Frame] and (b) impairment information to validate potential paths.
3.2.2. Separate Routing, WA, or IV
Separating the processes of routing, WA and/or IV can reduce the
need for sharing of different types of information used in path
computation. This was discussed for routing separate from WA in
[WSON-Frame]. In addition, as will be discussed in the section on
network contexts some impairment information may not be shared and
this may lead to the need to separate IV from RWA. In addition,
as also discussed in the section on network contexts, if IV needs
to be done at a high level of precision it may be advantageous to
offload this computation to a specialized server.
The following conceptual architectures belong in this general
category:
o R+WA+IV -- separate routing, wavelength assignment, and
impairment validation.
o R + (WA & IV) -- routing separate from a combined wavelength
assignment and impairment validation process. Note that
impairment validation is typically wavelength dependent hence
combining WA with IV can lead to efficiencies.
o (RWA)+IV - combined routing and wavelength assignment with a 1. Introduction
separate impairment validation process.
Note that the IV process may come before or after the RWA Wavelength Switched Optical Networks (WSONs) are constructed from
processes. If RWA comes first then IV is just rendering a yes/no subsystems that may include Wavelength Division Multiplexed (WDM)
decision on the selected path and wavelength. If IV comes first it links, tunable transmitters and receivers, Reconfigurable Optical
would need to furnish a list of possible (valid with respect to Add/Drop Multiplexers (ROADM), wavelength converters, and electro-
impairments) routes and wavelengths to the RWA processes. optical network elements. A WSON is a wavelength division
multiplexed (WDM)-based optical network in which switching is
performed selectively based on the center wavelength of an optical
signal.
3.2.3. Distributed WA and/or IV As an optical signal progresses along its path it may be altered by
the various physical processes in the optical fibers and devices it
encounters. When such alterations result in signal degradation, these
processes are usually referred to as "impairments". Optical
impairments accumulate along the path (without 3R regeneration)
traversed by the signal. They are influenced by the type of fiber
used, the types and placement of various optical devices and the
presence of other optical signals that may share a fiber segment
along the signal's path. The degradation of the optical signals due
to impairments can result in unacceptable bit error rates or even a
complete failure to demodulate and/or detect the received signal.
In the non-impairment RWA situation [WSON-Frame] it was shown that In order to provision an optical connection (an optical path) through
a distributed wavelength assignment (WA) process carried out via a WSON certain path continuity, resource availability and impairments
signaling can eliminate the need to distribute wavelength constraints must be met to determine viable and optimal paths through
availability information via an IGP. A similar approach can allow the network. The determination of paths is known as Impairment Aware
for the distributed computation of impairment effects and avoid Routing and Wavelength Assignment (IA-RWA).
the need to distribute impairment characteristics of network
elements and links via route protocols or by other means. An
example of such an approach is given in [Martinelli] and utilizes
enhancements to RSVP signaling to carry accumulated impairment
related information. So the following conceptual options belong to
this category:
o RWA+D(IV) - Combined routing and wavelength assignment and Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] includes
distributed impairment validation. a set of control plane protocols that can be used to operate data
networks ranging from packet switch capable networks, through those
networks that use time division multiplexing, and WDM. [RFC4054]
gives an overview of some critical optical impairments and their
routing (path selection) implications for GMPLS. The Path Computation
Element (PCE) architecture [RFC4655] defines functional components
that can be used to compute and suggest appropriate paths in
connection-oriented traffic-engineered networks.
o R + D(WA & IV) -- routing separate from a distributed wavelength This document provides a framework for applying GMPLS protocols and
assignment and impairment validation process. the PCE architecture to the control and operation of IA-RWA for
WSONs. To aid in this process this document also provides an
overview of the subsystems and processes that comprise WSONs, and
describes IA-RWA so that the information requirements can be
identified to explain how the information can be modeled for use by
GMPLS and PCE systems. This work will facilitate the development of
protocol solution models and protocol extensions within the GMPLS and
PCE protocol families.
A distributed impairment validation for a prescribed network path 2. Terminology
requires that the effects of impairments can be calculated by
approximate models with cumulative quality measures such as those
in [G.680]. For such a system to be interoperable the various
impairment measures to be accumulated would need to be agreed
according to [G.680].
If distributed WA is being done at the same time as distributed IV Add/Drop Multiplexers (ADM): An optical device used in WDM networks
then we may need to accumulate impairment related information for composed of one or more line side ports and typically many tributary
all wavelengths that could be used. This is somewhat winnowed down ports.
as potential wavelengths are discovered to be in use, but could be
a significant burden for lightly loaded high channel count
networks.
3.3. Mapping Network Requirements to Architectures CWDM: Coarse Wavelength Division Multiplexing.
In Figure 2 we show process flows for three main architectural DWDM: Dense Wavelength Division Multiplexing.
alternatives to IA-RWA when approximate impairment validation
suffices. In Figure 3 we show process flows for two main
architectural alternatives when detailed impairment verification
is required.
+-----------------------------------+ FOADM: Fixed Optical Add/Drop Multiplexer.
| +--+ +-------+ +--+ |
| |IV| |Routing| |WA| |
| +--+ +-------+ +--+ |
| |
| Combined Processes |
+-----------------------------------+
(a)
+--------------+ +----------------------+ GMPLS: Generalized Multi-Protocol Label Switching.
| +----------+ | | +-------+ +--+ |
| | IV | | | |Routing| |WA| |
| |candidates| |----->| +-------+ +--+ |
| +----------+ | | Combined Processes |
+--------------+ +----------------------+
(b)
+-----------+ +----------------------+ IA-RWA: Impairment Aware Routing and Wavelength Assignment
| +-------+ | | +--+ +--+ |
| |Routing| |------->| |WA| |IV| |
| +-------+ | | +--+ +--+ |
+-----------+ | Distributed Processes|
+----------------------+
(c)
Figure 2 Process flows for the three main approximate impairment
architectural alternatives.
The advantages, requirements and suitability of these options are Line side: In WDM system line side ports and links typically can
as follows: carry the full multiplex of wavelength signals, as compared to
tributary (add or drop ports) that typically carry a few (typically
one) wavelength signals.
o Combined IV & RWA process OXC: Optical cross connect. An optical switching element in which a
signal on any input port can reach any output port.
This alternative combines RWA and IV within a single computation PCC: Path Computation Client. Any client application requesting a
entity enabling highest potential optimality and efficiency in IA- path computation to be performed by the Path Computation Element.
RWA. This alternative requires that the computational entity knows
impairment information as well as non-impairment RWA 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 PCE: Path Computation Element. An entity (component, application, or
network node) that is capable of computing a network path or route
based on a network graph and applying computational constraints.
This alternative allows separation of impairment information into PCEP: PCE Communication Protocol. The communication protocol between
two computational entities while still maintaining a high degree a Path Computation Client and Path Computation Element.
of potential optimality and efficiency in IA-RWA. The candidates
IV process needs to know impairment information from all optical
network elements, while the RWA process needs to know non-
impairment RWA information from the network elements. This
alternative can be used with "black links", but the authority in
control of the "black links" would need to provide the
functionality of the IV-candidates process. Note that this is
still very useful since the algorithmic areas of IV and RWA are
very different and prone to specialization.
o Routing + Distributed WA and IV ROADM: Reconfigurable Optical Add/Drop Multiplexer. A wavelength
selective switching element featuring input and output line side
ports as well as add/drop tributary ports.
In this alternative a signaling protocol is extended and leveraged RWA: Routing and Wavelength Assignment.
in the wavelength assignment and impairment validation processes.
Although this doesn't enable as high a potential degree of
optimality of optimality as (a) or (b), it does not require
distribution of either link wavelength usage or link/node
impairment information. Note that this is most likely not suitable
for "black links".
+-----------------------------------+ +------------+ Transparent Network: A wavelength switched optical network that does
| +-----------+ +-------+ +--+ | | +--------+ | not contain regenerators or wavelength converters.
| | IV | |Routing| |WA| | | | IV | |
| |approximate| +-------+ +--+ |---->| |Detailed| |
| +-----------+ | | +--------+ |
| Combined Processes | | |
+-----------------------------------+ +------------+
(a)
+--------------+ +----------------------+ +------------+ Translucent Network: A wavelength switched optical network that is
| +----------+ | | +-------+ +--+ | | +--------+ | predominantly transparent but may also contain limited numbers of
| | IV | | | |Routing| |WA| |---->| | IV | | regenerators and/or wavelength converters.
| |candidates| |----->| +-------+ +--+ | | |Detailed| |
| +----------+ | | Combined Processes | | +--------+ |
+--------------+ +----------------------+ | |
(b) +------------+
Figure 3 Process flows for the two main detailed impairment
validation architectural options.
The advantages, requirements and suitability of these detailed Tributary: A link or port on a WDM system that can carry
validation options are as follows: significantly less than the full multiplex of wavelength signals
found on the line side links/ports. Typical tributary ports are the
add and drop ports on an ADM and these support only a single
wavelength channel.
o Combined approximate IV & RWA + Detailed-IV Wavelength Conversion/Converters: The process of converting
information bearing optical signal centered at a given wavelength to
one with "equivalent" content centered at a different wavelength.
Wavelength conversion can be implemented via an optical-electronic-
optical (OEO) process or via a strictly optical process.
This alternative combines RWA and approximate IV within a single WDM: Wavelength Division Multiplexing.
computation entity enabling highest potential optimality and
efficiency in IA-RWA; then has a separate entity performing
detailed impairment validation. In the case of "black links" the
authority controlling the "black links" would need to provide all
functionality.
o Candidates-IV + RWA + Detailed-IV Wavelength Switched Optical Networks (WSONs): WDM based optical
networks in which switching is performed selectively based on the
center wavelength of an optical signal.
This alternative allows separation of approximate impairment 3. Applicability
information into a computational entity while still maintaining a
high degree of potential optimality and efficiency in IA-RWA; then
a separate computation entity performs detailed impairment
validation. Note that detailed impairment estimation is not
standardized.
4. Protocol Implications There are deployment scenarios for WSON networks where not all
possible paths will yield suitable signal quality. There are
multiple reasons behind this choice; here below is a non-exhaustive
list of examples:
The previous IA-RWA architectural alternatives and process flows o WSON is evolving using multi-degree optical cross connects in a
make differing demands on a GMPLS/PCE based control plane. In this way that network topologies are changing from rings (and
section we discuss the use of (a) an impairment information model, interconnected rings) to general mesh. Adding network equipment
(b) PCE as computational entity assuming the various process roles such as amplifiers or regenerators, to make all paths feasible,
and consequences for PCEP, (c)any needed extensions to signaling, leads to an over-provisioned network. Indeed, even with over
and (d) extensions to routing. The impacts to the control plane provisioning, the network could still have some infeasible paths.
for IA-RWA are summarized in Figure 4.
+-------------------+----+----+----------+--------+ o Within a given network, the optical physical interface may change
| IA-RWA Option |PCE |Sig |Info Model| Routing| over the network life, e.g., the optical interfaces might be
+-------------------+----+----+----------+--------+ upgraded to higher bit-rates. Such changes could result in paths
| Combined |Yes | No | Yes | Yes | being unsuitable for the optical signal. Moreover, the optical
| IV & RWA | | | | | physical interfaces are typically provisioned at various stages of
+-------------------+----+----+----------+--------+- the network's life span as needed by traffic demands.
| IV-Candidates |Yes | No | Yes | Yes |
| + RWA | | | | |
+-------------------+----+----+----------+--------+
| Routing + |No | Yes| Yes | No |
|Distributed IV, RWA| | | | |
+-------------------+----+----+----------+--------+
| Detailed IV |Yes | No | Yes | Yes |
+-------------------+----+----+----------+--------+
Figure 4 IA-RWA architectural options and control plane impacts.
4.1. Information Model for Impairments o There are cases where a network is upgraded by adding new optical
cross connects to increase network flexibility. In such cases
existing paths will have their feasibility modified while new
paths will need to have their feasibility assessed.
As previously discussed all IA-RWA scenarios to a greater or o With the recent bit rate increases from 10G to 40G and 100G over a
lesser extent rely on a common impairment information model. A single wavelength, WSON networks will likely be operated with a
number of ITU-T recommendations cover detailed as well as mix of wavelengths at different bit rates. This operational
approximate impairment characteristics of fibers and a variety of scenario will impose impairment constraints due to different
devices and subsystems. A well integrated impairment model for physical behavior of different bit rates and associated modulation
optical network elements is given in [G.680] and is used to form formats.
the basis for an optical impairment model in a companion document
[Imp-Info].
It should be noted that the current version of [G.680] is limited Not having an impairment aware control plane for such networks will
to the networks composed of a single WDM line system vendor require a more complex network design phase that takes into account
combined with OADMs and/or PXCs from potentially multiple other evolving network status in term of equipments and traffic at the
vendors, this is known as situation 1 and is shown in Figure 1-1 beginning stage. This could result in over-engineering the DWDM
of [G.680]. It is planed in the future that [G.680] will include network with additional regenerators and optical amplifiers. In
networks incorporating line systems from multiple vendors as well addition, network operations such as path establishment, will
as OADMs and/or PXCs from potentially multiple other vendors, this require significant pre-design via non-control plane processes
is known as situation 2 and is shown in Figure 1-2 of [G.680]. resulting in significantly slower network provisioning.
The case of distributed impairment validation actually requires a 4. Impairment Aware Optical Path Computation
bit more than an impairment information model. In particular, it
needs a common impairment "computation" model. In the distributed
IV case one needs to standardize the accumulated impairment
measures that will be conveyed and updated at each node. Section 9
of [G.680] provides guidance in this area with specific formulas
given for OSNR, residual dispersion, polarization mode
dispersion/polarization dependent loss, effects of channel
uniformity, etc... However, specifics of what intermediate results
are kept and in what form would need to be standardized.
4.2. Routing The basic criteria for path selection is whether one can successfully
transmit the signal from a transmitter to a receiver within a
prescribed error tolerance, usually specified as a maximum
permissible bit error ratio (BER). This generally depends on the
nature of the signal transmitted between the sender and receiver and
the nature of the communications channel between the sender and
receiver. The optical path utilized (along with the wavelength)
determines the communications channel.
Different approaches to path/wavelength impairment validation The optical impairments incurred by the signal along the fiber and at
gives rise to different demands placed on GMPLS routing protocols. each optical network element along the path determine whether the BER
In the case where approximate impairment information is used to performance or any other measure of signal quality can be met for a
validate paths GMPLS routing may be used to distribute the signal on a particular end-to-end path.
impairment characteristics of the network elements and links based
on the impairment information model previously discussed.
Depending on the computational alternative the routing protocol Impairment-aware path calculation also needs to take into account
may need to advertise information necessary to impairment when regeneration is used along the path. [WSON-Frame] provides
validation process. This can potentially cause scalability issues background on the concept of optical translucent networks which
due to the high amount of data that need to be advertised. Such contains transparent elements and electro-optical elements such as
issue can be addressed separating data that need to be advertised OEO regenerations. In such networks a generic light path can go
rarely and data that need to be advertised more frequently or through a number of regeneration points.
adopting other form of awareness solutions described in previous
sections (e.g. centralized and/or external IV entity).
In term of approximated scenario (see Section 3.1.1. ) the model Regeneration points could happen for two reasons:
defined by [G.680] will apply and routing protocol will need to
gather information required for such computation.
In the case of distributed-IV no new demands would be placed on (i) wavelength conversion to assist RWA to avoid wavelength blocking.
the routing protocol. This is the impairment free case covered by [WSON-Frame].
4.3. Signaling (ii) the optical signal without regeneration would be too degraded
to meet end to end BER requirements. This is the case when RWA
takes into consideration impairment estimation covered by this
document.
The largest impacts on signaling occur in the cases where In the latter case an optical path can be seen as a set of transparent
distributed impairment validation is performed. In this we need to segments. The optical impairments calculation needs to be reset at each
accumulate impairment information as previously discussed. In regeneration point so each transparent segment will have its own
addition, since the characteristics of the signal itself, such as impairment evaluation.
modulation type, can play a major role in the tolerance of
impairments, this type of information will need to be implicitly
or explicitly signaled so that an impairment validation decision
can be made at the destination node.
It remains for further study if it may be beneficial to include +---+ +----+ +----+ +-----+ +----+ +---+
additional information to a connection request such as desired | I |----| N1 |---| N2 |-----| REG |-----| N3 |----| E |
egress signal quality (defined in some appropriate sense) in non- +---+ +----+ +----+ +-----+ +----+ +---+
distributed IV scenarios.
4.4. PCE |<----------------------------->|<-------------------->|
Segment 1 Segment 2
In section 3.3. we gave a number of computation architectural Figure 1 Optical path as a set of transparent segments
alternatives that could be used to meet the various requirements
and constraints of section 3.1. Here we look at how these
alternatives could be implemented via either a single PCE or a set
of two or more cooperating PCEs, and the impacts on the PCEP
protocol.
4.4.1. Combined IV & RWA For example, Figure 1 represents an optical path from node I to node E
with a regeneration point REG in between. It is feasible from an
impairment validation perspective if both segments (I, N1, N2, REG) and
(REG, N3, E) are feasible.
In this situation, shown in Figure 2(a), a single PCE performs all 4.1. Optical Network Requirements and Constraints
the computations needed for IA-RWA.
o TE Database Requirements This section examines the various optical network requirements and
constraints that an impairment aware optical control plane may have
to operate under. These requirements and constraints motivate the IA-
RWA architectural alternatives to be presented in the following
section. Different optical networks contexts can be broken into two
main criteria: (a) the accuracy required in the estimation of
impairment effects, and (b) the constraints on the impairment
estimation computation and/or sharing of impairment information.
WSON Topology and switching capabilities, WSON WDM link 4.1.1. Impairment Aware Computation Scenarios
wavelength utilization, and WSON impairment information
o PCC to PCE Request Information A. No concern for impairments or Wavelength Continuity Constraints
Signal characteristics/type, required quality, source node, This situation is covered by existing GMPLS with local wavelength
destination node (label) assignment.
o PCE to PCC Reply Information B. No concern for impairments but Wavelength Continuity Constraints
If the computations completed successfully then the PCE returns This situation is applicable to networks designed such that every
the path and its assigned wavelength. If the computations could possible path is valid for the signal types permitted on the network.
not complete successfully it would be potentially useful to know In this case impairments are only taken into account during network
the reason why. At a very crude level we'd like to know if this design and after that, for example during optical path computation,
was due to lack of wavelength availability or impairment they can be ignored. This is the case discussed in [WSON-Frame] where
considerations or a bit of both. The information to be conveyed impairments may be ignored by the control plane and only optical
is for further study. parameters related to signal compatibility are considered.
4.4.2. IV-Candidates + RWA C. Approximated Impairment Estimation
In this situation, shown in Figure 2(b), we have two separate This situation is applicable to networks in which impairment effects
processes involved in the IA-RWA computation. This requires at need to be considered but there is sufficient margin such that they
least two cooperating PCEs: one for the Candidates-IV process and can be estimated via approximation techniques such as link budgets
another for the RWA process. In addition, the overall process and dispersion [G.680],[G.sup39]. The viability of optical paths for
needs to be coordinated. This could be done with yet another PCE a particular class of signals can be estimated using well defined
or we can add this functionality to one of previously defined approximation techniques [G.680], [G.sup39]. This is the generally
PCEs. We choose this later option and require the RWA PCE to also known as linear case where only linear effects are taken into
act as the overall process coordinator. The roles, account. Note that adding or removing an optical signal on the path
responsibilities and information requirements for these two PCEs should not render any of the existing signals in the network as non-
are given below. viable. For example, one form of non-viability is the occurrence of
transients in existing links of sufficient magnitude to impact the
BER of existing signals.
RWA and Coordinator PCE (RWA-Coord-PCE): Much work at ITU-T has gone into developing impairment models at this
and more detailed levels. Impairment characterization of network
elements may be used to calculate which paths are conformant with a
specified BER for a particular signal type. In such a case, we can
combine the impairment aware (IA) path computation with the RWA
process to permit more optimal IA-RWA computations. Note that the IA
path computation may also take place in a separate entity, i.e., a
PCE.
Responsible for interacting with PCC and for utilizing Candidates- D. Detailed Impairment Computation
PCE as needed during RWA computations. In particular it needs to
know to use the Candidates-PCE to obtain potential set of routes
and wavelengths.
o TE Database Requirements This situation is applicable to networks in which impairment effects
must be more accurately computed. For these networks, a full
computation and evaluation of the impact to any existing paths needs
to be performed prior to the addition of a new path. Currently no
impairment models are available from ITU-T and this scenario is
outside the scope of this document.
WSON Topology and switching capabilities and WSON WDM link 4.1.2. Impairment Computation and Information Sharing Constraints
wavelength utilization (no impairment information).
o PCC to RWA-PCE request: same as in the combined case. In GMPLS, information used for path computation is standardized for
distribution amongst the elements participating in the control plane
and any appropriately equipped PCE can perform path computation. For
optical systems this may not be possible. This is typically due to
only portions of an optical system being subject to standardization.
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 (transmit and receive) are specified while the
multi-channel links are not standardized. These DWDM links are
referred to as "black links" since their details are not generally
available. Note however the overall impact of a black link at the
single channel interface points is limited by [G.698.1] and
[G.698.2].
o RWA-PCE to PCC reply: same as in the combined case. Typically a vendor might use proprietary impairment models for DWDM
spans and to estimate the validity of optical paths. For example,
models of optical nonlinearities are not currently standardized.
Vendors may also choose not to publish impairment details for links
or a set of network elements in order not to divulge their optical
system designs.
o RWA-PCE to IV-Candidates-PCE request In general, the impairment estimation/validation of an optical path
for optical networks with "black links" (path) could not be performed
by a general purpose impairment aware (IA) computation entity since
it would not have access to or understand the "black link" impairment
parameters. However, impairment estimation (optical path validation)
could be performed by a vendor specific impairment aware computation
entity. Such a vendor specific IA computation, could utilize
standardized impairment information imported from other network
elements in these proprietary computations.
The RWA-PCE asks for a set of at most K routes along with In the following the term "black links" will be used to describe
acceptable wavelengths between nodes specified in the original these computation and information sharing constraints in optical
PCC request. networks. From the control plane perspective the following options
are considered:
o IV-Candidates-PCE reply to RWA-PCE 1. The authority in control of the "black links" can furnish a list
of all viable paths between all viable node pairs to a
computational entity. This information would be particularly
useful as an input to RWA optimization to be performed by another
computation entity. The difficulty here is for larger networks
such a list of paths along with any wavelength constraints could
get unmanageably large.
The Candidates-PCE returns a set of at most K routes along with 2. The authority in control of the "black links" could provide a PCE
acceptable wavelengths between nodes specified in the RWA-PCE like entity that would furnish a list of viable paths/wavelengths
request. between two requested nodes. This is useful as an input to RWA
optimizations and can reduce the scaling issue previously
mentioned. Such a PCE like entity would not need to perform a full
RWA computation, i.e., it would not need to take into account
current wavelength availability on links. Such an approach may
require PCEP extensions for both the request and response
information.
IV-Candidates-PCE: 3. The authority in control of the "black links" can provide a PCE
that performs full IA-RWA services. The difficulty is this
requires the one authority to also become the sole source of all
RWA optimization algorithms and such.
The IV-Candidates-PCE is responsible for impairment aware path In all the above cases it would be the responsibility of the
computation. It needs not take into account current link authority in control of the "black links" to import the shared
wavelength utilization, but this is not prohibited. The impairment information from the other NEs via the control plane or
Candidates-PCE is only required to interact with the RWA-PCE as other means as necessary.
indicated above and not the PCC.
o TE Database Requirements 4.1.3. Impairment Estimation Process
WSON Topology and switching capabilities and WSON impairment The Impairment Estimation Process can be modeled through the
information (no information link wavelength utilization following functional blocks. These blocks are independent of any
required). Control Plane architecture, that is, they can be implemented by the
same or by different control plane functions as detailed in following
sections.
In Figure 5 we show a sequence diagram for the interactions +-----------------+
between the PCC, RWA-PCE and IV-Candidates-PCE. +------------+ +-----------+ | +------------+ |
| | | | | | | |
| Optical | | Optical | | | Optical | |
| Interface |------->| Impairment|--->| | Channel | |
| (Transmit/ | | Path | | | Estimation | |
| Receive) | | | | | | |
+------------+ +-----------+ | +------------+ |
| || |
| || |
| Estimation |
| || |
| \/ |
| +------------+ |
| | BER / | |
| | Q Factor | |
| +------------+ |
+-----------------+
+---+ +-------------+ +----------------- Starting from functional block on the left the Optical Interface
+ represents where the optical signal is transmitted or received and
|PCC| |RWA-Coord-PCE| |IV-Candidates- defines the properties at the end points path. Even the no-impairment
PCE| case like scenario B in section 4.1.1 needs to consider a minimum set
+-+-+ +------+------+ +---------+------- of interface characteristics. In such case only a few parameters used
+ to assess the signal compatibility will be taken into account (see
...___ (a) | | [WSON-Frame]). For the impairment-aware case these parameters may be
| ````---...____ | | sufficient or not depending on the accepted level of approximation
| ```-->| | (scenarios C and D). This functional block highlights the need to
| | | consider a set of interface parameters during an Impairment
| |--..___ (b) | Validation Process.
| | ```---...___ |
| | ```---->|
| | |
| | |
| | (c) ___...|
| | ___....---'''' |
| |<--'''' |
| | |
| | |
| (d) ___...| |
| ___....---''' | |
|<--''' | |
| | |
| | |
Figure 5 Sequence diagram for the interactions between PCC, RWA- The block "Optical Impairment Path" represents all kinds of
Coordinating-PCE and the IV-Candidates-PCE. impairments affecting a wavelength as it traverses the networks
through links and nodes. In the case where the control plane has no
IV this block will not be present. Otherwise, this function must be
implemented in some way via the control plane. Options for this will
be given in the next section on architectural alternatives. This
block implementation (e.g. through routing, signaling or PCE) may
influence the way the control plane distributes impairment
information within the network.
In step (a) the PCC requests a path meeting specified quality The last block implements the decision function for path feasibility.
constraints between two nodes (A and Z) for a given signal Depending on the IA level of approximation this function can be more
represented either by a specific type or a general class with or less complex. For example in case of no IA only the signal class
associated parameters. In step (b) the RWA-Coordinating-PCE compatibility will be verified. In addition to feasible/not-feasible
requests up to K candidate paths between nodes A and Z and result, it may be worthwhile for decision functions to consider the
associated acceptable wavelengths. In step (c) The IV-Candidates- case in which paths can be likely-to-be-feasible within some degree
PCE returns this list to the RWA-Coordinating PCE which then uses of confidence. The optical impairments are usually not fixed values
this set of paths and wavelengths as input (e.g. a constraint) to as they may vary within ranges of values according to the approach
its RWA computation. In step (d) the RWA-Coordinating-PCE returns taken in the physical modeling (worst-case, statistical or based on
the overall IA-RWA computation results to the PCC. typical values). For example, the utilization of the worst-case value
for each parameter within impairment validation process may lead to
marking some paths as not-feasible while they are very likely to be
feasible in reality.
4.4.3. Approximate IA-RWA + Separate Detailed IV 4.2. IA-RWA Computation and Control Plane Architectures
In Figure 3 we showed two cases where a separate detailed From a control plane point of view optical impairments are additional
impairment validation process could be utilized. We can place the constraints to the impairment-free RWA process described in [WSON-
detailed validation process into a separate PCE. Assuming that a Frame]. In impairment aware routing and wavelength assignment (IA-
different PCE assumes a coordinating role and interacts with the RWA), there are conceptually three general classes of processes to be
PCC we can keep the interactions with this separate IV-Detailed- considered: Routing (R), Wavelength Assignment (WA), and Impairment
PCE very simple. Validation (estimation) (IV).
IV-Detailed-PCE: Impairment validation may come in many forms, and maybe invoked at
different levels of detail in the IA-RWA process. From a process
point of view we will consider the following three forms of
impairment validation:
o TE Database Requirements o IV-Candidates
The IV-Detailed-PCE will need optical impairment information, WSON In this case an Impairment Validation (IV) process furnishes a set of
topology, and possibly WDM link wavelength usage information. paths between two nodes along with any wavelength restrictions such
This document puts no restrictions on the type of information that the paths are valid with respect to optical impairments. These
that may be used in these computations. paths and wavelengths may not be actually available in the network
due to its current usage state. This set of paths could be returned
in response to a request for a set of at most K valid paths between
two specified nodes. Note that such a process never directly
discloses optical impairment information. Note that that this case
includes any paths between source and destination that may have been
"pre-validated".
o Coordinating-PCE to IV-Detailed-PCE request In this case the control plane simply makes use of candidate paths
but does not know any optical impairment information. Another option
is when the path validity is assessed within the control plane. The
following cases highlight this situation.
The coordinating-PCE will furnish signal characteristics, quality o IV-Approximate Verification
requirements, path and wavelength to the IV-Detailed-PCE.
o IV-Detailed-PCE to Coordinating-PCE reply Here approximation methods are used to estimate the impairments
experienced by a signal. Impairments are typically approximated by
linear and/or statistical characteristics of individual or combined
components and fibers along the signal path.
The reply is essential an yes/no decision as to whether the o IV-Detailed Verification
requirements could actually be met. In the case where the
impairment validation fails it would be helpful to convey
information related to cause or quantify the failure, e.g., so a
judgment can be made whether to try a different signal or adjust
signal parameters.
In Figure 6 we show a sequence diagram for the interactions for In this case an IV process is given a particular path and wavelength
the process shown in Figure 3(b). This involves interactions through an optical network and is asked to verify whether the overall
between the PCC, RWA-PCE (acting as coordinator), IV-Candidates- quality objectives for the signal over this path can be met. Note
PCE and the IV-Detailed-PCE. that such a process never directly discloses optical impairment
information.
In step (a) the PCC requests a path meeting specified quality The next two cases refer to the way an impairment validation
constraints between two nodes (A and Z) for a given signal computation can be performed.
represented either by a specific type or a general class with
associated parameters. In step (b) the RWA-Coordinating-PCE
requests up to K candidate paths between nodes A and Z and
associated acceptable wavelengths. In step (c) The IV-Candidates-
PCE returns this list to the RWA-Coordinating PCE which then uses
this set of paths and wavelengths as input (e.g. a constraint) to
its RWA computation. In step (d) the RWA-Coordinating-PCE request
a detailed verification of the path and wavelength that it has
computed. In step (e) the IV-Detailed-PCE returns the results of
the validation to the RWA-Coordinating-PCE. Finally in step (f)IA-
RWA-Coordinating PCE returns the final results (either a path and
wavelength or cause for the failure to compute a path and
wavelength) to the PCC.
+----------+ +--------------+ +------------ o IV-Centralized
+
+---+ |RWA-Coord | |IV-Candidates | |IV-Detailed
|
|PCC| | PCE | | PCE | | PCE
|
+-+-+ +----+-----+ +------+-------+ +-----+------
+
|.._ (a) | | |
| ``--.__ | | |
| `-->| | |
| | (b) | |
| |--....____ | |
| | ````---.>| |
| | | |
| | (c) __..-| |
| | __..---'' | |
| |<--'' | |
| | |
| |...._____ (d) |
| | `````-----....._____ |
| | `````----->|
| | |
| | (e) _____.....+
| | _____.....-----''''' |
| |<----''''' |
| (f) __.| |
| __.--'' |
|<-'' |
| |
Figure 6 Sequence diagram for the interactions between PCC, RWA-
Coordinating-PCE, IV-Candidates-PCE and IV-Detailed-PCE.
5. Security Considerations In this case impairments to a path are computed at a single entity.
The information concerning impairments, however, may still be
gathered from network elements. Depending how information is gathered
this may put additional requirements on routing protocols. This will
be detailed in later sections.
This document discusses a number of control plane architectures o IV-Distributed
that incorporate knowledge of impairments in optical networks. If
such architecture is put into use within a network it will by its
nature contain details of the physical characteristics of an
optical network. Such information would need to be protected from
intentional or unintentional disclosure.
6. IANA Considerations In the distributed IV process, approximate degradation measures such
as OSNR, dispersion, DGD, etc. are accumulated along the path via a
signaling like protocol. Each node on the path may already perform
some part of the impairment computation (i.e. distributed). When the
accumulated measures reach the destination node a decision on the
impairment validity of the path can be made. Note that such a process
would entail revealing an individual network element's impairment
information but it does not generally require distributing optical
parameters to the entire network.
This draft does not currently require any consideration from IANA. The Control Plane must not preclude the possibility to operate one or
all the above cases concurrently in the same network. For example
there could be cases where a certain number of paths are already pre-
validated (IV-Candidates) so the control plane may setup one of those
path without requesting any impairment validation procedure. On the
same network however the control plane may compute a path outside the
set of IV-Candidates for which an impairment evaluation can be
necessary.
7. Acknowledgments The following subsections present three major classes of IA-RWA path
computation architectures and reviews some of their respective
advantages and disadvantages.
This document was prepared using 2-Word-v2.0.template.dot. 4.2.1. Combined Routing, WA, and IV
APPENDIX A: Overview of Optical Layer ITU-T Recommendations From the point of view of optimality, reasonably good IA-RWA
solutions can be achieved if the path computation entity (PCE) can
conceptually/algorithmically combine the processes of routing,
wavelength assignment and impairment validation.
For optical fiber, devices, subsystems and network elements the Such a combination can take place if the PCE is given: (a) the
ITU-T has a variety of recommendations that include definitions, impairment-free WSON network information as discussed in [WSON-Frame]
characterization parameters and test methods. In the following we and (b) impairment information to validate potential paths.
take a bottom up survey to emphasize the breadth and depth of the
existing recommendations. We focus on digital communications over
single mode optical fiber.
A.1. Fiber and Cables 4.2.2. Separate Routing, WA, or IV
Fibers and cables form a key component of what from the control Separating the processes of routing, WA and/or IV can reduce the need
plane perspective could be termed an optical link. Due to the wide for sharing of different types of information used in path
range of uses of optical networks a fairly wide range of fiber computation. This was discussed for routing separate from WA in
types are used in practice. The ITU-T has three main [WSON-Frame]. In addition, as was discussed some impairment
recommendations covering the definition of attributes and test information may not be shared and this may lead to the need to
methods for single mode fiber: separate IV from RWA. In addition, if IV needs to be done at a high
level of precision it may be advantageous to offload this computation
to a specialized server.
o Definitions and test methods for linear, deterministic The following conceptual architectures belong in this general
attributes of single-mode fibre and cable [G.650.1] category:
o Definitions and test methods for statistical and non-linear o R+WA+IV -- separate routing, wavelength assignment, and impairment
related attributes of single-mode fibre and cable [G.650.2] validation.
o Test methods for installed single-mode fibre cable sections o R + (WA & IV) -- routing separate from a combined wavelength
[G.650.3] assignment and impairment validation process. Note that impairment
validation is typically wavelength dependent hence combining WA
with IV can lead to efficiencies.
General Definitions[G.650.1]: Mechanical Characteristics o (RWA)+IV - combined routing and wavelength assignment with a
(numerous), Mode field characteristics(mode field, mode field separate impairment validation process.
diameter, mode field centre, mode field concentricity error, mode
field non-circularity), Glass geometry characteristics, Chromatic
dispersion definitions (chromatic dispersion, group delay,
chromatic dispersion coefficient, chromatic dispersion slope,
zero-dispersion wavelength, zero-dispersion slope), cut-off
wavelength, attenuation. Definition of equations and fitting
coefficients for chromatic dispersion (Annex A). [G.650.2]
polarization mode dispersion (PMD) - phenomenon of PMD, principal
states of polarization (PSP), differential group delay (DGD), PMD
value, PMD coefficient, random mode coupling, negligible mode
coupling, mathematical definitions in terms of Stokes or Jones
vectors. Nonlinear attributes: Effective area, correction factor
k, non-linear coefficient (refractive index dependent on
intensity), Stimulated Billouin scattering.
Tests defined [G.650.1]: Mode field diameter, cladding diameter, Note that the IV process may come before or after the RWA processes.
core concentricity error, cut-off wavelength, attenuation, If RWA comes first then IV is just rendering a yes/no decision on the
chromatic dispersion. [G.650.2]: test methods for polarization selected path and wavelength. If IV comes first it would need to
mode dispersion. [G.650.3] Test methods for characteristics of furnish a list of possible (valid with respect to impairments) routes
fibre cable sections following installation: attenuation, splice and wavelengths to the RWA processes.
loss, splice location, fibre uniformity and length of cable
sections (these are OTDR based), PMD, Chromatic dispersion.
With these definitions a variety of single mode fiber types are 4.2.3. Distributed WA and/or IV
defined as shown in the table below:
ITU-T Standard | Common Name In the non-impairment RWA situation [WSON-Frame] it was shown that a
------------------------------------------------------------ distributed wavelength assignment (WA) process carried out via
signaling can eliminate the need to distribute wavelength
availability information via an interior gateway protocol (IGP). A
similar approach can allow for the distributed computation of
impairment effects and avoid the need to distribute impairment
characteristics of network elements and links via routing protocols
or by other means. An example of such an approach is given in
[Martinelli] and utilizes enhancements to RSVP signaling to carry
accumulated impairment related information. So the following
conceptual options belong to this category:
G.652 [G.652] | Standard SMF | o RWA + D(IV) - Combined routing and wavelength assignment and
G.653 [G.653] | Dispersion shifted SMF | distributed impairment validation.
G.654 [G.654] | Cut-off shifted SMF |
G.655 [G.655] | Non-zero dispersion shifted SMF |
G.656 [G.656] | Wideband non-zero dispersion shifted SMF |
------------------------------------------------------------
A.2. Devices o R + D(WA & IV) -- routing separate from a distributed wavelength
assignment and impairment validation process.
A.2.1. Optical Amplifiers Distributed impairment validation for a prescribed network path
requires that the effects of impairments be calculated by approximate
models with cumulative quality measures such as those given in
[G.680]. For such a system to be interoperable the exact encoding of
the techniques from [G.680] would need to be agreed upon.
Optical amplifiers greatly extend the transmission distance of If distributed WA is being done at the same time as distributed IV
optical signals in both single channel and multi channel (WDM) then we may need to accumulate impairment related information for all
subsystems. The ITU-T has the following recommendations: wavelengths that could be used. This is somewhat winnowed down as
potential wavelengths are discovered to be in use, but could be a
significant burden for lightly loaded high channel count networks.
o Definition and test methods for the relevant generic parameters 4.3. Mapping Network Requirements to Architectures
of optical amplifier devices and subsystems [G.661]
o Generic characteristics of optical amplifier devices and Figure 2 shows process flows for three main architectural
subsystems [G.662] alternatives to IA-RWA when approximate impairment validation
suffices. Figure 3 shows process flows for two main architectural
alternatives when detailed impairment verification is required.
o Application related aspects of optical amplifier devices and +-----------------------------------+
subsystems [G.663] | +--+ +-------+ +--+ |
| |IV| |Routing| |WA| |
| +--+ +-------+ +--+ |
| |
| Combined Processes |
+-----------------------------------+
(a)
o Generic characteristics of Raman amplifiers and Raman amplified +--------------+ +----------------------+
subsystems [G.665] | +----------+ | | +-------+ +--+ |
| | IV | | | |Routing| |WA| |
| |candidates| |----->| +-------+ +--+ |
| +----------+ | | Combined Processes |
+--------------+ +----------------------+
(b)
Reference [G.661] starts with general classifications of optical +-----------+ +----------------------+
amplifiers based on technology and usage, and include a near | +-------+ | | +--+ +--+ |
exhaustive list of over 60 definitions for optical amplifier | |Routing| |------->| |WA| |IV| |
device attributes and parameters. In references [G.662] and | +-------+ | | +--+ +--+ |
[G.665] we have characterization of specific devices, e.g., +-----------+ | Distributed Processes|
semiconductor optical amplifier, used in a particular setting, +----------------------+
e.g., line amplifier. For example reference[G.662] gives the (c)
following minimum list of relevant parameters for the Figure 2 Process flows for the three main approximate impairment
specification of an optical amplifier device used as line architectural alternatives.
amplifier in a multichannel application:
a) Channel allocation. The advantages, requirements and suitability of these options are as
follows:
b) Total input power range. o Combined IV & RWA process
c) Channel input power range. This alternative combines RWA and IV within a single computation
entity enabling highest potential optimality and efficiency in IA-
RWA. This alternative requires that the computational entity knows
impairment information as well as non-impairment RWA information.
This alternative can be used with "black links", but would then need
to be provided by the authority controlling the "black links".
d) Channel output power range. o IV-Candidates + RWA process
This alternative allows separation of impairment information into two
computational entities while still maintaining a high degree of
potential optimality and efficiency in IA-RWA. The candidates IV
process needs to know impairment information from all optical network
elements, while the RWA process needs to know non-impairment RWA
information from the network elements. This alternative can be used
with "black links", but the authority in control of the "black links"
would need to provide the functionality of the IV-candidates process.
Note that this is still very useful since the algorithmic areas of IV
and RWA are very different and prone to specialization.
e) Channel signal-spontaneous noise figure. o Routing + Distributed WA and IV
f) Input reflectance. In this alternative a signaling protocol is extended and leveraged in
the wavelength assignment and impairment validation processes.
Although this doesn't enable as high a potential degree of optimality
of optimality as (a) or (b), it does not require distribution of
either link wavelength usage or link/node impairment information.
Note that this is most likely not suitable for "black links".
g) Output reflectance. +-----------------------------------+ +------------+
| +-----------+ +-------+ +--+ | | +--------+ |
| | IV | |Routing| |WA| | | | IV | |
| |approximate| +-------+ +--+ |---->| |Detailed| |
| +-----------+ | | +--------+ |
| Combined Processes | | |
+-----------------------------------+ +------------+
(a)
h) Maximum reflectance tolerable at input. +--------------+ +----------------------+ +------------+
| +----------+ | | +-------+ +--+ | | +--------+ |
| | IV | | | |Routing| |WA| |---->| | IV | |
| |candidates| |----->| +-------+ +--+ | | |Detailed| |
| +----------+ | | Combined Processes | | +--------+ |
+--------------+ +----------------------+ | |
(b) +------------+
Figure 3 Process flows for the two main detailed impairment
validation architectural options.
i) Maximum reflectance tolerable at output. The advantages, requirements and suitability of these detailed
validation options are as follows:
j) Maximum total output power. o Combined approximate IV & RWA + Detailed-IV
k) Channel addition/removal (steady-state) gain response. This alternative combines RWA and approximate IV within a single
computation entity enabling highest potential optimality and
efficiency in IA-RWA; then has a separate entity performing detailed
impairment validation. In the case of "black links" the authority
controlling the "black links" would need to provide all
functionality.
l) Channel addition/removal (transient) gain response. o Candidates-IV + RWA + Detailed-IV
m) Channel gain. This alternative allows separation of approximate impairment
information into a computational entity while still maintaining a
high degree of potential optimality and efficiency in IA-RWA; then a
separate computation entity performs detailed impairment validation.
Note that detailed impairment estimation is not standardized.
n) Multichannel gain variation (inter-channel gain difference). 5. Protocol Implications
o) Multichannel gain-change difference (inter-channel gain-change The previous IA-RWA architectural alternatives and process flows make
difference). differing demands on a GMPLS/PCE based control plane. In this section
we discuss the use of (a) an impairment information model, (b) PCE as
computational entity assuming the various process roles and
consequences for PCEP, (c)any needed extensions to signaling, and (d)
extensions to routing. The impacts to the control plane for IA-RWA
are summarized in Figure 4.
p) Multichannel gain tilt (inter-channel gain-change ratio). +-------------------+----+----+----------+--------+
| IA-RWA Option |PCE |Sig |Info Model| Routing|
+-------------------+----+----+----------+--------+
| Combined |Yes | No | Yes | Yes |
| IV & RWA | | | | |
+-------------------+----+----+----------+--------+-
| IV-Candidates |Yes | No | Yes | Yes |
| + RWA | | | | |
+-------------------+----+----+----------+--------+
| Routing + |No | Yes| Yes | No |
|Distributed IV, RWA| | | | |
+-------------------+----+----+----------+--------+
q) Polarization Mode Dispersion (PMD). Figure 4 IA-RWA architectural options and control plane impacts.
A.2.2. Dispersion Compensation 5.1. Information Model for Impairments
In optical systems two forms of dispersion are commonly As previously discussed all IA-RWA scenarios to a greater or lesser
encountered [RFC4054] chromatic dispersion and polarization mode extent rely on a common impairment information model. A number of
dispersion (PMD). There are a number of techniques and devices ITU-T recommendations cover detailed as well as approximate
used for compensating for these effects. The following ITU-T impairment characteristics of fibers and a variety of devices and
recommendations characterize such devices: subsystems. A well integrated impairment model for optical network
elements is given in [G.680] and is used to form the basis for an
optical impairment model in a companion document [Imp-Info].
o Characteristics of PMD compensators and PMD compensating It should be noted that the current version of [G.680] is limited to
receivers [G.666] the networks composed of a single WDM line system vendor combined
with 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
planed in the future that [G.680] will include networks incorporating
line systems from multiple vendors as well as OADMs and/or PXCs from
potentially multiple other vendors, this is known as situation 2 and
is shown in Figure 1-2 of [G.680].
o Characteristics of Adaptive Chromatic Dispersion Compensators The case of distributed impairment validation actually requires a bit
[G.667] more than an impairment information model. In particular, it needs a
common impairment "computation" model. In the distributed IV case one
needs to standardize the accumulated impairment measures that will be
conveyed and updated at each node. Section 9 of [G.680] provides
guidance in this area with specific formulas given for OSNR, residual
dispersion, polarization mode dispersion/polarization dependent loss,
effects of channel uniformity, etc... However, specifics of what
intermediate results are kept and in what form would need to be
standardized.
The above furnish definitions as well as parameters and 5.2. Routing
characteristics. For example in [G.667] adaptive chromatic
dispersion compensators are classified as being receiver,
transmitter or line based, while in [G.666] PMD compensators are
only defined for line and receiver configurations. Parameters that
are common to both PMD and chromatic dispersion compensators
include: line fiber type, maximum and minimum input power, maximum
and minimum bit rate, and modulation type. In addition there are a
great many parameters that apply to each type of device and
configuration.
A.2.3. Optical Transmitters Different approaches to path/wavelength impairment validation gives
rise to different demands placed on GMPLS routing protocols. In the
case where approximate impairment information is used to validate
paths GMPLS routing may be used to distribute the impairment
characteristics of the network elements and links based on the
impairment information model previously discussed.
The definitions of the characteristics of optical transmitters can Depending on the computational alternative the routing protocol may
be found in references [G.957], [G.691], [G.692] and [G.959.1]. In need to advertise information necessary to impairment validation
addition references [G.957], [G.691], and [G.959.1] define process. This can potentially cause scalability issues due to the
specific parameter values or parameter ranges for these high amount of data that need to be advertised. Such issue can be
characteristics for interfaces for use in particular situations. addressed separating data that need to be advertised rarely and data
that need to be advertised more frequently or adopting other form of
awareness solutions described in previous sections (e.g. centralized
and/or external IV entity).
We generally have the following types of parameters In term of approximated scenario (see Section 4.1.1. ) the model
defined by [G.680] will apply and routing protocol will need to
gather information required for such computation.
Wavelength related: Central frequency, Channel spacing, Central In the case of distributed-IV no new demands would be placed on the
frequency deviation[G.692]. routing protocol.
Spectral characteristics of the transmitter: Nominal source type 5.3. Signaling
(LED, MLM lasers, SLM lasers) [G.957], Maximum spectral width,
Chirp parameter, Side mode suppression ratio, Maximum spectral
power density [G.691].
Power related: Mean launched power, Extinction ration, Eye pattern The largest impacts on signaling occur in the cases where distributed
mask [G.691], Maximum and minimum mean channel output power impairment validation is performed. In this we need to accumulate
[G.959.1]. impairment information as previously discussed. In addition, since
the characteristics of the signal itself, such as modulation type,
can play a major role in the tolerance of impairments, this type of
information will need to be implicitly or explicitly signaled so that
an impairment validation decision can be made at the destination
node.
A.2.4. Optical Receivers It remains for further study if it may be beneficial to include
additional information to a connection request such as desired egress
signal quality (defined in some appropriate sense) in non-distributed
IV scenarios.
References [G.959.1], [G.691], [G.692] and [G.957], define optical 5.4. PCE
receiver characteristics and [G.959.1], [G.691] and [G.957]give
specific values of these parameters for particular interface types
and network contexts.
The receiver parameters include: In section 4.3. we gave a number of computation architectural
alternatives that could be used to meet the various requirements and
constraints of section 4.1. Here we look at how these alternatives
could be implemented via either a single PCE or a set of two or more
cooperating PCEs, and the impacts on the PCEP protocol.
Receiver sensitivity: minimum value of average received power to 5.4.1. Combined IV & RWA
achieve a 1x10-10 BER [G.957] or 1x10-12 BER [G.691]. See [G.957]
and [G.691] for assumptions on signal condition.
Receiver overload: Receiver overload is the maximum acceptable In this situation, shown in Figure 2(a), a single PCE performs all
value of the received average power for a 1x10.10 BER [G.957] or a the computations needed for IA-RWA.
1x10-12 BER [G.691].
Receiver reflectance: "Reflections from the receiver back to the o TE Database Requirements
cable plant are specified by the maximum permissible reflectance
of the receiver measured at reference point R."
Optical path power penalty: "The receiver is required to tolerate WSON Topology and switching capabilities, WSON WDM link wavelength
an optical path penalty not exceeding X dB to account for total utilization, and WSON impairment information
degradations due to reflections, intersymbol interference, mode
partition noise, and laser chirp."
When dealing with multi-channel systems or systems with optical o PCC to PCE Request Information
amplifiers we may also need:
Optical signal-to-noise ratio: "The minimum value of optical SNR Signal characteristics/type, required quality, source node,
required to obtain a 1x10-12 BER."[G.692] destination node
Receiver wavelength range: "The receiver wavelength range is o PCE to PCC Reply Information
defined as the acceptable range of wavelengths at point Rn. This If the computations completed successfully then the PCE returns
range must be wide enough to cover the entire range of central the path and its assigned wavelength. If the computations could
frequencies over the OA passband." [G.692] not complete successfully it would be potentially useful to know
the reason why. At a very crude level we'd like to know if this
was due to lack of wavelength availability or impairment
considerations or a bit of both. The information to be conveyed is
for further study.
Minimum equivalent sensitivity: "This is the minimum sensitivity 5.4.2. IV-Candidates + RWA
that would be required of a receiver placed at MPI-RM in
multichannel applications to achieve the specified maximum BER of
the application code if all except one of the channels were to be
removed (with an ideal loss-less filter) at point MPI-RM."
[G.959.1]
A.3. Components and Subsystems In this situation, shown in Figure 2(b), we have two separate
processes involved in the IA-RWA computation. This requires at two
cooperating PCEs: one for the Candidates-IV process and another for
the RWA process. In addition, the overall process needs to be
coordinated. This could be done with yet another PCE or we can add
this functionality to one of previously defined PCEs. We choose this
later option and require the RWA PCE to also act as the overall
process coordinator. The roles, responsibilities and information
requirements for these two PCEs are given below.
Reference [G.671] "Transmission characteristics of optical RWA and Coordinator PCE (RWA-Coord-PCE):
components and subsystems" covers the following components:
o optical add drop multiplexer (OADM) subsystem; Responsible for interacting with PCC and for utilizing Candidates-PCE
as needed during RWA computations. In particular it needs to know to
use the Candidates-PCE to obtain potential set of routes and
wavelengths.
o asymmetric branching component; o TE Database Requirements
o optical attenuator; WSON Topology and switching capabilities and WSON WDM link
wavelength utilization (no impairment information).
o optical branching component (wavelength non-selective); o PCC to RWA-PCE request: same as in the combined case.
o optical connector; o RWA-PCE to PCC reply: same as in the combined case.
o dynamic channel equalizer (DCE); o RWA-PCE to IV-Candidates-PCE request
o optical filter; The RWA-PCE asks for a set of at most K routes along with acceptable
wavelengths between nodes specified in the original PCC request.
o optical isolator; o IV-Candidates-PCE reply to RWA-PCE
o passive dispersion compensator; The Candidates-PCE returns a set of at most K routes along with
acceptable wavelengths between nodes specified in the RWA-PCE
request.
o optical splice; IV-Candidates-PCE:
o optical switch; The IV-Candidates-PCE is responsible for impairment aware path
computation. It needs not take into account current link
wavelength utilization, but this is not prohibited. The
Candidates-PCE is only required to interact with the RWA-PCE as
indicated above and not the PCC.
o optical termination; o TE Database Requirements
o tuneable filter; WSON Topology and switching capabilities and WSON impairment
o optical wavelength multiplexer (MUX)/demultiplexer (DMUX); information (no information link wavelength utilization required).
- coarse WDM device; In Figure 5 we show a sequence diagram for the interactions between
the PCC, RWA-Coord PCE and IV-Candidates PCE.
- dense WDM device; +---+ +-------------+ +-----------------+
|PCC| |RWA-Coord PCE| |IV-Candidates PCE|
+-+-+ +------+------+ +---------+-------+
...___ (a) | |
| ````---...____ | |
| ```-->| |
| | |
| |--..___ (b) |
| | ```---...___ |
| | ```---->|
| | |
| | |
| | (c) ___...|
| | ___....---'''' |
| |<--'''' |
| | |
| | |
| (d) ___...| |
| ___....---''' | |
|<--''' | |
| | |
| | |
- wide WDM device. Figure 5 Sequence diagram for the interactions between PCC, RWA-
Coordinating-PCE and the IV-Candidates-PCE.
Reference [G.671] then specifies applicable parameters for these In step (a) the PCC requests a path meeting specified quality
components. For example an OADM subsystem will have parameters constraints between two nodes (A and Z) for a given signal
such as: insertion loss (input to output, input to drop, add to represented either by a specific type or a general class with
output), number of add, drop and through channels, polarization associated parameters. In step (b) the RWA-Coordinating-PCE requests
dependent loss, adjacent channel isolation, allowable input power, up to K candidate paths between nodes A and Z and associated
polarization mode dispersion, etc... acceptable wavelengths. In step (c) The IV-Candidates PCE returns
this list to the RWA-Coordinating PCE which then uses this set of
paths and wavelengths as input (e.g. a constraint) to its RWA
computation. In step (d) the RWA-Coordinating PCE returns the overall
IA-RWA computation results to the PCC.
A.4. Network Elements 6. Security Considerations
The previously cited ITU-T recommendations provide a plethora of This document discusses a number of control plane architectures that
definitions and characterizations of optical fiber, devices, incorporate knowledge of impairments in optical networks. If such
components and subsystems. Reference [G.Sup39] "Optical system architecture is put into use within a network it will by its nature
design and engineering considerations" provides useful guidance on contain details of the physical characteristics of an optical
the use of such parameters. network. Such information would need to be protected from intentional
or unintentional disclosure.
In many situations the previous models while good don't encompass 7. IANA Considerations
the higher level network structures that one typically deals with
in the control plane, i.e, "links" and "nodes". In addition such
models include the full range of network applications from
planning, installation, and possibly day to day network
operations, while with the control plane we are generally
concerned with a subset of the later. In particular for many
control plane applications we are interested in formulating the
total degradation to an optical signal as it travels through
multiple optical subsystems, devices and fiber segments.
In reference [G.680] "Physical transfer functions of optical This draft does not currently require any consideration from IANA.
networks elements", a degradation function is currently defined
for the following optical network elements: (a) DWDM Line segment,
(b) Optical Add/Drop Multiplexers (OADM), and (c) Photonic cross-
connect (PXC). The scope of [G.680] is currently for optical
networks consisting of one vendors DWDM line systems along with
another vendors OADMs or PXCs.
The DWDM line system of [G.680] consists of the optical fiber, 8. References
line amplifiers and any embedded dispersion compensators.
Similarly the OADM/PXC network element may consist of the basic
OADM component and optionally included optical amplifiers. The
parameters for these optical network elements (ONE) are given
under the following circumstances:
o General ONE without optical amplifiers 8.1. Normative References
o General ONE with optical amplifiers
o OADM without optical amplifiers [G.650.1] ITU-T Recommendation G.650.1, Definitions and test methods
for linear, deterministic attributes of single-mode fibre
and cable, June 2004.
o OADM with optical amplifiers [G.650.2] ITU-T Recommendation G.650.2, Definitions and test methods
for statistical and non-linear related attributes of
single-mode fibre and cable, July 2007.
o Reconfigurable OADM (ROADM) without optical amplifiers [G.650.3] ITU-T Recommendation G.650.3
o ROADM with optical amplifiers [G.652] ITU-T Recommendation G.652, Characteristics of a single-mode
optical fibre and cable, June 2005.
o PXC without optical amplifiers [G.653] ITU-T Recommendation G.653, Characteristics of a dispersion-
shifted single-mode optical fibre and cable, December 2006.
o PXC with optical amplifiers [G.654] ITU-T Recommendation G.654, Characteristics of a cut-off
shifted single-mode optical fibre and cable, December 2006.
8. References [G.655] ITU-T Recommendation G.655, Characteristics of a non-zero
dispersion-shifted single-mode optical fibre and cable,
March 2006.
8.1. Normative References [G.656] ITU-T Recommendation G.656, Characteristics of a fibre and
cable with non-zero dispersion for wideband optical
transport, December 2006.
[G.650.1] ITU-T Recommendation G.650.1, Definitions and test [G.661] ITU-T Recommendation G.661, Definition and test methods for
methods for linear, deterministic attributes of single- the relevant generic parameters of optical amplifier
mode fibre and cable, June 2004. devices and subsystems, March 2006.
[650.2] ITU-T Recommendation G.650.2, Definitions and test [G.662] ITU-T Recommendation G.662, Generic characteristics of
methods for statistical and non-linear related optical amplifier devices and subsystems, July 2005.
attributes of single-mode fibre and cable, July 2007.
[650.3] ITU-T Recommendation G.650.3 [G.671] ITU-T Recommendation G.671, Transmission characteristics of
optical components and subsystems, January 2005.
[G.652] ITU-T Recommendation G.652, Characteristics of a single- [G.680] ITU-T Recommendation G.680, Physical transfer functions of
mode optical fibre and cable, June 2005. optical network elements, July 2007.
[G.653] ITU-T Recommendation G.653, Characteristics of a [G.691] ITU-T Recommendation G.691, Optical interfaces for
dispersion-shifted single-mode optical fibre and cable, multichannel systems with optical amplifiers, November
December 2006. 1998.
[G.654] ITU-T Recommendation G.654, Characteristics of a cut-off [G.692] ITU-T Recommendation G.692, Optical interfaces for single
shifted single-mode optical fibre and cable, December channel STM-64 and other SDH systems with optical
2006. amplifiers, March 2006.
[G.655] ITU-T Recommendation G.655, Characteristics of a non-zero [G.872] ITU-T Recommendation G.872, Architecture of optical
dispersion-shifted single-mode optical fibre and cable, transport networks, November 2001.
March 2006.
[G.656] ITU-T Recommendation G.656, Characteristics of a fibre and [G.957] ITU-T Recommendation G.957, Optical interfaces for
cable with non-zero dispersion for wideband optical equipments and systems relating to the synchronous digital
transport, December 2006. hierarchy, March 2006.
[G.661] ITU-T Recommendation G.661, Definition and test methods [G.959.1] ITU-T Recommendation G.959.1, Optical Transport Network
for the relevant generic parameters of optical amplifier Physical Layer Interfaces, March 2006.
devices and subsystems, March 2006.
[G.662] ITU-T Recommendation G.662, Generic characteristics of [G.694.1] ITU-T Recommendation G.694.1, Spectral grids for WDM
optical amplifier devices and subsystems, July 2005. applications: DWDM frequency grid, June 2002.
[G.671] ITU-T Recommendation G.671, Transmission characteristics [G.694.2] ITU-T Recommendation G.694.2, Spectral grids for WDM
of optical components and subsystems, January 2005. applications: CWDM wavelength grid, December 2003.
[G.680] ITU-T Recommendation G.680, Physical transfer functions [G.698.1] ITU-T Recommendation G.698.1, Multichannel DWDM
of optical network elements, July 2007. applications with Single-Channel optical interface,
December 2006.
[G.691] ITU-T Recommendation G.691, Optical interfaces for [G.698.2] ITU-T Recommendation G.698.2, Amplified multichannel DWDM
multichannel systems with optical amplifiers, November applications with Single-Channel optical interface, July
1998. 2007.
[G.692] ITU-T Recommendation G.692, Optical interfaces for single [G.Sup39] ITU-T Series G Supplement 39, Optical system design and
channel STM-64 and other SDH systems with optical engineering considerations, February 2006.
amplifiers, March 2006.
[G.872] ITU-T Recommendation G.872, Architecture of optical [RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label
transport networks, November 2001. Switching (GMPLS) Architecture", RFC 3945, October 2004.
[G.957] ITU-T Recommendation G.957, Optical interfaces for [RFC4054] Strand, J., Ed., and A. Chiu, Ed., "Impairments and Other
equipments and systems relating to the synchronous Constraints on Optical Layer Routing", RFC 4054, May 2005.
digital hierarchy, March 2006.
[G.959.1] ITU-T Recommendation G.959.1, Optical Transport Network [RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path Computation
Physical Layer Interfaces, March 2006. Element (PCE)-Based Architecture", RFC 4655, August 2006.
[G.694.1] ITU-T Recommendation G.694.1, Spectral grids for WDM 8.2. Informative References
applications: DWDM frequency grid, June 2002.
[G.694.2] ITU-T Recommendation G.694.2, Spectral grids for WDM [WSON-Frame] Y. Lee, G. Bernstein, W. Imajuku, "Framework for GMPLS
applications: CWDM wavelength grid, December 2003. and PCE Control of Wavelength Switched Optical Networks",
work in progress: draft-ietf-ccamp-wavelength-switched-
framework.
[G.698.1] ITU-T Recommendation G.698.1, Multichannel DWDM [Imp-Info] G. Bernstein, Y. Lee, D. Li, "A Framework for the Control
applications with Single-Channel optical interface, and Measurement of Wavelength Switched Optical Networks
December 2006. (WSON) with Impairments", work in progress: draft-
bernstein-wson-impairment-info.
[G.698.2] ITU-T Recommendation G.698.2, Amplified multichannel [Martinelli] G. Martinelli (ed.) and A. Zanardi (ed.), "GMPLS
DWDM applications with Single-Channel optical interface, Signaling Extensions for Optical Impairment Aware Lightpath
July 2007. Setup", Work in Progress: draft-martinelli-ccamp-optical-
imp-signaling.
[G.Sup39] ITU-T Series G Supplement 39, Optical system design and 9. Acknowledgments
engineering considerations, February 2006.
[RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label This document was prepared using 2-Word-v2.0.template.dot.
Switching (GMPLS) Architecture", RFC 3945, October 2004.
[RFC4054] Strand, J., Ed., and A. Chiu, Ed., "Impairments and Copyright (c) 2011 IETF Trust and the persons identified as authors
Other Constraints on Optical Layer Routing", RFC 4054, of the code. All rights reserved.
May 2005.
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path Redistribution and use in source and binary forms, with or without
Computation Element (PCE)-Based Architecture", RFC 4655, modification, are permitted provided that the following conditions
August 2006. are met:
[WSON-Frame] G. Bernstein, Y. Lee, W. Imajuku, "Framework for o Redistributions of source code must retain the above copyright
GMPLS and PCE Control of Wavelength Switched Optical notice, this list of conditions and the following disclaimer.
Networks", work in progress: draft-ietf-ccamp-
wavelength-switched-framework-02.txt, March 2009.
8.2. Informative References o Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
[Imp-Info] G. Bernstein, Y. Lee, D. Li, "A Framework for the o Neither the name of Internet Society, IETF or IETF Trust, nor the
Control and Measurement of Wavelength Switched Optical names of specific contributors, may be used to endorse or promote
Networks (WSON) with Impairments", work in progress: products derived from this software without specific prior written
draft-bernstein-wson-impairment-info. permission.
[Martinelli] G. Martinelli (ed.) and A. Zanardi (ed.), "GMPLS THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
Signaling Extensions for Optical Impairment Aware "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
Lightpath Setup", Work in Progress: draft-martinelli- LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
ccamp-optical-imp-signaling-02.txt, February 2008. 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.
[WSON-Comp] G. Bernstein, Y. Lee, Ben Mack-Crane, "WSON Signal Authors' Addresses
Characteristics and Network Element Compatibility
Constraints for GMPLS", work in progress: draft-
bernstein-ccamp-wson-signal.
Author's Addresses Greg M. Bernstein (ed.)
Grotto Networking
Fremont California, USA
Greg M. Bernstein (ed.) Phone: (510) 573-2237
Grotto Networking Email: gregb@grotto-networking.com
Fremont California, USA
Phone: (510) 573-2237 Young Lee (ed.)
Email: gregb@grotto-networking.com Huawei Technologies
1700 Alma Drive, Suite 100
Plano, TX 75075
USA
Young Lee (ed.) Phone: (972) 509-5599 (x2240)
Huawei Technologies Email: ylee@huawei.com
1700 Alma Drive, Suite 100
Plano, TX 75075
USA
Phone: (972) 509-5599 (x2240) Dan Li
Email: ylee@huawei.com Huawei Technologies Co., Ltd.
F3-5-B R&D Center, Huawei Base,
Bantian, Longgang District
Shenzhen 518129 P.R.China
Dan Li Phone: +86-755-28973237
Huawei Technologies Co., Ltd. Email: danli@huawei.com
F3-5-B R&D Center, Huawei Base,
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28973237 Giovanni Martinelli
Email: danli@huawei.com Cisco
Giovanni Martinelli Via Philips 12
Cisco 20052 Monza, Italy
Via Philips 12
20052 Monza, Italy
Phone: +39 039 2092044 Phone: +39 039 2092044
Email: giomarti@cisco.com Email: giomarti@cisco.com
Contributor's Addresses Contributor's Addresses
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
Email: mchen@huawei.com
Rebecca Han
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: hanjianrui@huawei.com
Gabriele Galimberti
Cisco
Via Philips 12,
20052 Monza, Italy
Phone: +39 039 2091462
Email: ggalimbe@cisco.com
Alberto Tanzi
Cisco
Via Philips 12,
20052 Monza, Italy
Phone: +39 039 2091469
Email: altanzi@cisco.com
David Bianchi
Cisco
Via Philips 12,
20052 Monza, Italy
Email: davbianc@cisco.com
Moustafa Kattan Phone: +86-755-28973237
Cisco Email: mchen@huawei.com
Dubai 500321
United Arab Emirates
Email: mkattan@cisco.com Rebecca Han
Huawei Technologies Co., Ltd.
Dirk Schroetter F3-5-B R&D Center, Huawei Base,
Cisco Bantian, Longgang District
Shenzhen 518129 P.R.China
Email: dschroet@cisco.com Phone: +86-755-28973237
Email: hanjianrui@huawei.com
Daniele Ceccarelli Gabriele Galimberti
Ericsson Cisco
Via A. Negrone 1/A Via Philips 12,
Genova - Sestri Ponente 20052 Monza, Italy
Italy
Email: daniele.ceccarelli@ericsson.com Phone: +39 039 2091462
Email: ggalimbe@cisco.com
Elisa Bellagamba Alberto Tanzi
Ericsson Cisco
Farogatan 6, Via Philips 12,
Kista 164 40 20052 Monza, Italy
Sweeden
Email: elisa.bellagamba@ericcson.com Phone: +39 039 2091469
Email: altanzi@cisco.com
Diego Caviglia David Bianchi
Ericsson Cisco
Via A. negrone 1/A Via Philips 12,
Genova - Sestri Ponente 20052 Monza, Italy
Italy
Email: diego.caviglia@ericcson.com Email: davbianc@cisco.com
Intellectual Property Statement Moustafa Kattan
Cisco
Dubai 500321
United Arab Emirates
The IETF Trust takes no position regarding the validity or scope Email: mkattan@cisco.com
of any Intellectual Property Rights or other rights that might be
claimed to pertain to the implementation or use of the technology
described in any IETF Document or the extent to which any license
under such rights might or might not be available; nor does it
represent that it has made any independent effort to identify any
such rights.
Copies of Intellectual Property disclosures made to the IETF Dirk Schroetter
Secretariat and any assurances of licenses to be made available, Cisco
or the result of an attempt made to obtain a general license or
permission for the use of such proprietary rights by implementers
or users of this specification can be obtained from the IETF on-
line IPR repository at http://www.ietf.org/ipr
The IETF invites any interested party to bring to its attention Email: dschroet@cisco.com
any copyrights, patents or patent applications, or other
proprietary rights that may cover technology that may be required
to implement any standard or specification contained in an IETF
Document. Please address the information to the IETF at ietf-
ipr@ietf.org.
Disclaimer of Validity Daniele Ceccarelli
Ericsson
Via A. Negrone 1/A
Genova - Sestri Ponente
Italy
Email: daniele.ceccarelli@ericsson.com
All IETF Documents and the information contained therein are Elisa Bellagamba
provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION Ericsson
HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET Farogatan 6,
SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE Kista 164 40
DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT Sweeden
LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION THEREIN
WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgment Email: elisa.bellagamba@ericcson.com
We thank Chen Ming of DICONNET Project who provided valuable Diego Caviglia
information relevant to this document. Ericsson
Via A. negrone 1/A
Genova - Sestri Ponente
Italy
We'd also like to thank Deborah Brungard for editorial and Email: diego.caviglia@ericcson.com
technical assistance.
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