draft-ietf-ccamp-wson-impairments-02.txt   draft-ietf-ccamp-wson-impairments-03.txt 
Network Working Group Y. Lee Network Working Group Y. Lee
Internet Draft Huawei Internet Draft Huawei
G. Bernstein G. Bernstein
Grotto Networking Grotto Networking
D. Li D. Li
Huawei Huawei
G. Martinelli G. Martinelli
Cisco Cisco
Intended status: Informational May 20, 2010 Intended status: Informational July 9, 2010
Expires: November 2010 Expires: November 2010
A Framework for the Control of Wavelength Switched Optical Networks A Framework for the Control of Wavelength Switched Optical Networks
(WSON) with Impairments (WSON) with Impairments
draft-ietf-ccamp-wson-impairments-02.txt draft-ietf-ccamp-wson-impairments-03.txt
Status of this Memo Status of this Memo
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publication of this document. Please review these documents publication of this document. Please review these documents
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characterization of optical fiber, devices, subsystems, and network characterization of optical fiber, devices, subsystems, and network
elements contained in various ITU-T recommendations can be combined elements contained in various ITU-T recommendations can be combined
with GMPLS control plane protocols and mechanisms to support with GMPLS control plane protocols and mechanisms to support
Impairment Aware Routing and Wavelength Assignment (IA-RWA) in Impairment Aware Routing and Wavelength Assignment (IA-RWA) in
optical networks. optical networks.
Table of Contents Table of Contents
1. Introduction...................................................3 1. Introduction...................................................3
1.1. Revision History..........................................4 1.1. Revision History..........................................4
2. Motivation.....................................................5 2. Motivation.....................................................4
3. Impairment Aware Optical Path Computation......................5 3. Impairment Aware Optical Path Computation......................5
3.1. Optical Network Requirements and Constraints..............6 3.1. Optical Network Requirements and Constraints..............6
3.1.1. Categories of Impairment Aware Computation...........6 3.1.1. Impairment Aware Computation Scenarios ..............7
3.1.2. Impairment Computation and Information Sharing 3.1.2. Impairment Computation and Information Sharing
Constraints.................................................7 Constraints.................................................8
3.1.3. Impairment Estimation Functional Blocks..............8 3.1.3. Impairment Estimation Functional Blocks..............9
3.2. IA-RWA Computing and Control Plane Architectures.........10 3.2. IA-RWA Computation and Control Plane Architectures.......11
3.2.1. Combined Routing, WA, and IV........................11 3.2.1. Combined Routing, WA, and IV........................12
3.2.2. Separate Routing, WA, or IV.........................11 3.2.2. Separate Routing, WA, or IV.........................12
3.2.3. Distributed WA and/or IV............................12 3.2.3. Distributed WA and/or IV............................13
3.3. Mapping Network Requirements to Architectures............12 3.3. Mapping Network Requirements to Architectures............14
4. Protocol Implications.........................................15 4. Protocol Implications.........................................17
4.1. Information Model for Impairments........................15 4.1. Information Model for Impairments........................17
4.1.1. Properties of an Impairment Information Model.......16 4.1.1. Properties of an Impairment Information Model.......18
4.2. Routing..................................................17 4.2. Routing..................................................19
4.3. Signaling................................................17 4.3. Signaling................................................19
4.4. PCE......................................................18 4.4. PCE......................................................20
4.4.1. Combined IV & RWA...................................18 4.4.1. Combined IV & RWA...................................20
4.4.2. IV-Candidates + RWA.................................18 4.4.2. IV-Candidates + RWA.................................20
4.4.3. Approximate IA-RWA + Separate Detailed IV...........20 4.4.3. Approximate IA-RWA + Separate Detailed IV...........22
5. Security Considerations.......................................22 5. Security Considerations.......................................24
6. IANA Considerations...........................................22 6. IANA Considerations...........................................24
7. Acknowledgments...............................................22 7. Acknowledgments...............................................24
APPENDIX A: Overview of Optical Layer ITU-T Recommendations......23 8. References....................................................32
A.1. Fiber and Cables.........................................23 8.1. Normative References.....................................32
A.2. Devices..................................................24 8.2. Informative References...................................34
A.2.1. Optical Amplifiers..................................24
A.2.2. Dispersion Compensation.............................25
A.2.3. Optical Transmitters................................26
A.2.4. Optical Receivers...................................26
A.3. Components and Subsystems................................27
A.4. Network Elements.........................................28
8. References....................................................30
8.1. Normative References.....................................30
8.2. Informative References...................................32
Author's Addresses...............................................32
Intellectual Property Statement..................................34
Disclaimer of Validity...........................................34
1. Introduction 1. Introduction
As an optical signal progresses along its path it may be altered by As an optical signal progresses along its path it may be altered by
the various physical processes in the optical fibers and devices it the various physical processes in the optical fibers and devices it
encounters. When such alterations result in signal degradation, we encounters. When such alterations result in signal degradation, we
usually refer to these processes as "impairments". An overview of usually refer to these processes as "impairments". An overview of
some critical optical impairments and their routing (path selection) some critical optical impairments and their routing (path selection)
implications can be found in [RFC4054]. Roughly speaking, optical implications can be found in [RFC4054]. Roughly speaking, optical
impairments accumulate along the path (without 3R regeneration) impairments accumulate along the path (without 3R regeneration)
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Added to discussion of interface parameters in section 3.1.3. Added to discussion of interface parameters in section 3.1.3.
Added to discussion of IV Candidates function in section 3.2. Added to discussion of IV Candidates function in section 3.2.
Changes from 01 to 02: Changes from 01 to 02:
Correct and refine use of "black link" concept based on liaison with Correct and refine use of "black link" concept based on liaison with
ITU-T and WG feedback. ITU-T and WG feedback.
Changes from 02 to 03:
Insert additional information on use and considerations for
regenerators in section 3.
2. Motivation 2. Motivation
There are deployment scenarios for WSON networks where not all There are deployment scenarios for WSON networks where not all
possible paths will yield suitable signal quality. There are possible paths will yield suitable signal quality. There are
multiple reasons behind this choice; here below is a non-exhaustive multiple reasons behind this choice; here below is a non-exhaustive
list of examples: list of examples:
o WSON is evolving using multi-degree optical cross connects in a o WSON is evolving using multi-degree optical cross connects in a
way that network topologies are changing from rings (and way that network topologies are changing from rings (and
interconnected rings) to a full mesh. Adding network equipment interconnected rings) to a full mesh. Adding network equipment
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considerations may apply to other network equipment upgrades, the considerations may apply to other network equipment upgrades, the
optical physical interfaces are a typical case because they are optical physical interfaces are a typical case because they are
typically provisioned at various stages of the network's life span typically provisioned at various stages of the network's life span
as needed by traffic demands. as needed by traffic demands.
o There are cases where a network is upgraded by adding new optical o There are cases where a network is upgraded by adding new optical
cross connects to increase network flexibility. In such cases cross connects to increase network flexibility. In such cases
existing paths will have their feasibility modified while new existing paths will have their feasibility modified while new
paths will need to have their feasibility assessed. paths will need to have their feasibility assessed.
o With the recent bit rate increases from 10G to 40G and 100G over a
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 Not having an impairment aware control plane for such networks will
require a more complex network design phase that has to also take require a more complex network design phase that has to also take
into account evolving network status in term of equipments and into account evolving network status in term of equipments and
traffic. Moreover, network operations such as path establishment, traffic. Moreover, network operations such as path establishment,
will require significant pre-design via non-control plane processes will require significant pre-design via non-control plane processes
resulting in significantly slower network provisioning. resulting in significantly slower network provisioning.
3. Impairment Aware Optical Path Computation 3. Impairment Aware Optical Path Computation
The basic criteria for path selection is whether one can successfully The basic criteria for path selection is whether one can successfully
transmit the signal from a transmitter to a receiver within a transmit the signal from a transmitter to a receiver within a
prescribed error tolerance, usually specified as a maximum prescribed error tolerance, usually specified as a maximum
permissible bit error ratio (BER). This generally depends on the permissible bit error ratio (BER). This generally depends on the
nature of the signal transmitted between the sender and receiver and nature of the signal transmitted between the sender and receiver and
the nature of the communications channel between the sender and the nature of the communications channel between the sender and
receiver. The optical path utilized (along with the wavelength) receiver. The optical path utilized (along with the wavelength)
determines the communications channel. determines the communications channel.
The optical impairments incurred by the signal along the fiber and at The optical impairments incurred by the signal along the fiber and at
each optical network element along the path determine whether the BER each optical network element along the path determine whether the BER
performance or any other measure of signal quality can be met for a performance or any other measure of signal quality can be met for a
signal on a particular end-to-end path. signal on a particular end-to-end path.
The impairment-aware path calculation needs also to take into account The impairment-aware path calculation needs also to take into account
when regeneration happens along the path. Regeneration points could when regeneration happens along the path. [WSON-Frame] introduces the
happen for two reasons: (i) because of wavelength conversion to cope concept of Optical translucent network that contains transparent
with the RWA to avoid wavelength blocking (See [WSON-Frame]) or (ii) elements and electro-optical elements such as OEO regenerations. In
because optical signal is too degraded. In both cases the optical such networks a generic lightpath can go through a certain number of
impairments estimation needs to be reset. 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 lightpath 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 Lightpath as a set of transparent segments
For example, Figure 1 represents a lightpath from node I to node E with
a regeneration point R in between. The lightpath is from an impairment
validation perspective if each segment (I, N1, N2, R) and (R, N3, E) is
feasible.
3.1. Optical Network Requirements and Constraints 3.1. Optical Network Requirements and Constraints
This section examines the various optical network requirements and This section examines the various optical network requirements and
constraints that an impairment aware optical control plane may have constraints that an impairment aware optical control plane may have
to operate under. These requirements and constraints motivate the IA- to operate under. These requirements and constraints motivate the IA-
RWA architectural alternatives to be presented in the following RWA architectural alternatives to be presented in the following
section. We can break the different optical networks contexts up section. We can break the different optical networks contexts up
along two main criteria: (a) the accuracy required in the estimation along two main criteria: (a) the accuracy required in the estimation
of impairment effects, and (b) the constraints on the impairment of impairment effects, and (b) the constraints on the impairment
estimation computation and/or sharing of impairment information. estimation computation and/or sharing of impairment information.
3.1.1. Categories of Impairment Aware Computation 3.1.1. Impairment Aware Computation Scenarios
A. No concern for impairments or Wavelength Continuity Constraints A. No concern for impairments or Wavelength Continuity Constraints
This situation is covered by existing GMPLS with local wavelength This situation is covered by existing GMPLS with local wavelength
(label) assignment. (label) assignment.
B. No concern for impairments but Wavelength Continuity Constraints B. No concern for impairments but Wavelength Continuity Constraints
This situation is applicable to networks designed such that every This situation is applicable to networks designed such that every
possible path is valid for the signal types permitted on the network. possible path is valid for the signal types permitted on the network.
In this case impairments are only taken into account during network In this case impairments are only taken into account during network
design and after that, for example during optical path computation, design and after that, for example during optical path computation,
they can be ignored. This is the case discussed in [WSON-Frame] where they can be ignored. This is the case discussed in [WSON-Frame] where
impairments may be ignored by the control plane. impairments may be ignored by the control plane and only optical
parameters related to signal compatibility are considered..
C. Approximated Impairment Estimation C. Approximated Impairment Estimation
This situation is applicable to networks in which impairment effects This situation is applicable to networks in which impairment effects
need to be considered but there is sufficient margin such that they need to be considered but there is sufficient margin such that they
can be estimated via approximation techniques such as link budgets can be estimated via approximation techniques such as link budgets
and dispersion[G.680],[G.sup39]. The viability of optical paths for a and dispersion[G.680],[G.sup39]. The viability of optical paths for a
particular class of signals can be estimated using well defined particular class of signals can be estimated using well defined
approximation techniques [G.680], [G.sup39]. Also, adding or removing approximation techniques [G.680], [G.sup39]. Note that currently only
an optical signal on the path will not render any of the existing linear impairments are considered. Also, 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- signals in the network as non-viable. For example, one form of non-
viability is the occurrence of transients in existing links of viability is the occurrence of transients in existing links of
sufficient magnitude to impact the BER of those existing signals. sufficient magnitude to impact the BER of those existing signals.
Much work at ITU-T has gone into developing impairment models at this Much work at ITU-T has gone into developing impairment models at this
and more detailed levels. Impairment characterization of network and more detailed levels. Impairment characterization of network
elements could then may be used to calculate which paths are elements could then may be used to calculate which paths are
conformant with a specified BER for a particular signal type. In such conformant with a specified BER for a particular signal type. In such
a case, we can combine the impairment aware (IA) path computation a case, we can combine the impairment aware (IA) path computation
with the RWA process to permit more optimal IA-RWA computations. with the RWA process to permit more optimal IA-RWA computations.
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Much work at ITU-T has gone into developing impairment models at this Much work at ITU-T has gone into developing impairment models at this
and more detailed levels. Impairment characterization of network and more detailed levels. Impairment characterization of network
elements could then may be used to calculate which paths are elements could then may be used to calculate which paths are
conformant with a specified BER for a particular signal type. In such conformant with a specified BER for a particular signal type. In such
a case, we can combine the impairment aware (IA) path computation a case, we can combine the impairment aware (IA) path computation
with the RWA process to permit more optimal IA-RWA computations. with the RWA process to permit more optimal IA-RWA computations.
Note, the IA path computation may also take place in a separate Note, the IA path computation may also take place in a separate
entity, i.e., a PCE. entity, i.e., a PCE.
D. Detailed Impairment Computation D. Detailed Impairment Computation
This situation is applicable to networks in which impairment effects This situation is applicable to networks in which impairment effects
must be more accurately computed. For these networks, a full must be more accurately computed. For these networks, a full
computation and evaluation of the impact to any existing paths needs computation and evaluation of the impact to any existing paths needs
to be performed prior to the addition of a new path. This scenario is to be performed prior to the addition of a new path. Currently no
impairment models are available from ITU-T and this scenario is
outside the scope of this document. outside the scope of this document.
3.1.2. Impairment Computation and Information Sharing Constraints 3.1.2. Impairment Computation and Information Sharing Constraints
In GMPLS, information used for path computation is standardized for In GMPLS, information used for path computation is standardized for
distribution amongst the elements participating in the control plane distribution amongst the elements participating in the control plane
and any appropriately equipped PCE can perform path computation. For and any appropriately equipped PCE can perform path computation. For
optical systems this may not be possible. This is typically due to optical systems this may not be possible. This is typically due to
only portions of an optical system being subject to standardization. only portions of an optical system being subject to standardization.
In ITU-T recommendations [G.698.1] and [G.698.2] which specify single In ITU-T recommendations [G.698.1] and [G.698.2] which specify single
channel interfaces to multi-channel DWDM systems only the single channel interfaces to multi-channel DWDM systems only the single
channel interfaces (transmit and receive) are specified while the channel interfaces (transmit and receive) are specified while the
multi-channel links are not standardized. These DWDM links are multi-channel links are not standardized. These DWDM links are
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C. The authority in control of the "black links" can provide a PCE C. The authority in control of the "black links" can provide a PCE
that performs full IA-RWA services. The difficulty is this that performs full IA-RWA services. The difficulty is this
requires the one authority to also become the sole source of all requires the one authority to also become the sole source of all
RWA optimization algorithms and such. RWA optimization algorithms and such.
In all the above cases it would be the responsibility of the In all the above cases it would be the responsibility of the
authority in control of the "black links" to import the shared authority in control of the "black links" to import the shared
impairment information from the other NEs via the control plane or impairment information from the other NEs via the control plane or
other means as necessary. other means as necessary.
3.1.3. Impairment Estimation Functional Blocks 3.1.3. Impairment Estimation Functional Blocks
The Impairment Estimation process can be modeled by the following The Impairment Estimation process can be modeled by the following
functional blocks. These blocks are independent of any Control Plane functional blocks. These blocks are independent of any Control Plane
architecture, that is, they can be implemented by the same or by architecture, that is, they can be implemented by the same or by
different control plane functional blocks. different control plane functional blocks.
+-----------------+ +-----------------+
+------------+ +-----------+ | +------------+ | +------------+ +-----------+ | +------------+ |
| | | | | | | | | | | | | | | |
| Optical | | Optical | | | Optical | | | Optical | | Optical | | | Optical | |
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nodes. In the case where the control plane has no IA this block will nodes. In the case where the control plane has no IA this block will
not be present. Otherwise, this function must be implemented in some 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 way via the control plane. Options for this will be given in the next
section on control plane architectural alternatives. section on control plane architectural alternatives.
The last block implements the decision function for path feasibility. The last block implements the decision function for path feasibility.
Depending on the IA level of approximation this function can be more 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 or less complex. For example in case of no IA only the signal class
compatibility will be verified. compatibility will be verified.
3.2. IA-RWA Computing and Control Plane Architectures 3.2. IA-RWA Computation and Control Plane Architectures
From a control plane point of view optical impairments are additional From a control plane point of view optical impairments are additional
constraints to the impairment-free RWA process described in [WSON- constraints to the impairment-free RWA process described in [WSON-
Frame]. In impairment aware routing and wavelength assignment (IA- Frame]. In impairment aware routing and wavelength assignment (IA-
RWA), there are conceptually three general classes of processes to be RWA), there are conceptually three general classes of processes to be
considered: Routing (R), Wavelength Assignment (WA), and Impairment considered: Routing (R), Wavelength Assignment (WA), and Impairment
Validation (estimation) (IV). Validation (estimation) (IV).
Impairment validation may come in many forms, and maybe invoked at Impairment validation may come in many forms, and maybe invoked at
different levels of detail in the IA-RWA process. From a process different levels of detail in the IA-RWA process. From a process
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o IV-Candidates o IV-Candidates
In this case an Impairment Validation (IV) process furnishes a set of In this case an Impairment Validation (IV) process furnishes a set of
paths between two nodes along with any wavelength restrictions such paths between two nodes along with any wavelength restrictions such
that the paths are valid with respect to optical impairments. These that the paths are valid with respect to optical impairments. These
paths and wavelengths may not be actually available in the network paths and wavelengths may not be actually available in the network
due to its current usage state. This set of paths would be returned due to its current usage state. This set of paths would be returned
in response to a request for a set of at most K valid paths between in response to a request for a set of at most K valid paths between
two specified nodes. Note that such a process never directly two specified nodes. Note that such a process never directly
discloses optical impairment information. discloses optical impairment information. 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 In this case the control plane simply makes use of candidate paths
but does not know any optical impairment information. Another option but does not know any optical impairment information. Another option
is when the path validity is assessed within the control plane. The is when the path validity is assessed within the control plane. The
following cases highlight this situation. following cases highlight this situation.
o IV-Approximate Verification
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 o IV-Detailed Verification
In this case an IV process is given a particular path and wavelength In this case an IV process is given a particular path and wavelength
through an optical network and is asked to verify whether the overall through an optical network and is asked to verify whether the overall
quality objectives for the signal over this path can be met. Note quality objectives for the signal over this path can be met. Note
that such a process never directly discloses optical impairment that such a process never directly discloses optical impairment
information. information.
o IV-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.
o IV-Distributed o IV-Distributed
In this distributed IV process, impairment approximate degradation In the distributed IV process, impairment approximate degradation
measures such as OSNR, dispersion, DGD, etc. are accumulated along measures such as OSNR, dispersion, DGD, etc. are accumulated along
the path via a signaling like protocol. When the accumulated measures the path via a signaling like protocol. When the accumulated measures
reach the destination node a decision on the impairment validity of reach the destination node a decision on the impairment validity of
the path can be made. Note that such a process would entail revealing the path can be made. Note that such a process would entail revealing
an individual network element's impairment information. an individual network element's impairment information.
The Control Plane however must not preclude the possibility to
operate any 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 The following subsections present three major classes of IA-RWA path
computation architectures and their respective advantages and computation architectures and their respective advantages and
disadvantages. disadvantages.
3.2.1. Combined Routing, WA, and IV 3.2.1. Combined Routing, WA, and IV
From the point of view of optimality, the "best" IA-RWA solutions can From the point of view of optimality, the "best" IA-RWA solutions can
be achieved if the path computation entity (PCE) can be achieved if the path computation entity (PCE) can
conceptually/algorithmically combine the processes of routing, conceptually/algorithmically combine the processes of routing,
wavelength assignment and impairment validation. wavelength assignment and impairment validation.
Such a combination can take place if the PCE is given: (a) the Such a combination can take place if the PCE is given: (a) the
impairment-free WSON network information as discussed in [WSON-Frame] impairment-free WSON network information as discussed in [WSON-Frame]
and (b) impairment information to validate potential paths. and (b) impairment information to validate potential paths.
3.2.2. Separate Routing, WA, or IV 3.2.2. Separate Routing, WA, or IV
Separating the processes of routing, WA and/or IV can reduce the need Separating the processes of routing, WA and/or IV can reduce the need
for sharing of different types of information used in path for sharing of different types of information used in path
computation. This was discussed for routing separate from WA in computation. This was discussed for routing separate from WA in
[WSON-Frame]. In addition, as will be discussed in the section on [WSON-Frame]. In addition, as will be discussed in the section on
network contexts some impairment information may not be shared and network contexts some impairment information may not be shared and
this may lead to the need to separate IV from RWA. In addition, as 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 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 done at a high level of precision it may be advantageous to offload
this computation to a specialized server. this computation to a specialized server.
The following conceptual architectures belong in this general The following conceptual architectures belong in this general
category: category:
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o (RWA)+IV - combined routing and wavelength assignment with a o (RWA)+IV - combined routing and wavelength assignment with a
separate impairment validation process. separate impairment validation process.
Note that the IV process may come before or after the RWA processes. Note that the IV process may come before or after the RWA processes.
If RWA comes first then IV is just rendering a yes/no decision on the If RWA comes first then IV is just rendering a yes/no decision on the
selected path and wavelength. If IV comes first it would need to selected path and wavelength. If IV comes first it would need to
furnish a list of possible (valid with respect to impairments) routes furnish a list of possible (valid with respect to impairments) routes
and wavelengths to the RWA processes. and wavelengths to the RWA processes.
3.2.3. Distributed WA and/or IV 3.2.3. Distributed WA and/or IV
In the non-impairment RWA situation [WSON-Frame] it was shown that a In the non-impairment RWA situation [WSON-Frame] it was shown that a
distributed wavelength assignment (WA) process carried out via distributed wavelength assignment (WA) process carried out via
signaling can eliminate the need to distribute wavelength signaling can eliminate the need to distribute wavelength
availability information via an IGP. A similar approach can allow for availability information via an IGP. A similar approach can allow for
the distributed computation of impairment effects and avoid the need the distributed computation of impairment effects and avoid the need
to distribute impairment characteristics of network elements and to distribute impairment characteristics of network elements and
links via route protocols or by other means. An example of such an links via route protocols or by other means. An example of such an
approach is given in [Martinelli] and utilizes enhancements to RSVP approach is given in [Martinelli] and utilizes enhancements to RSVP
signaling to carry accumulated impairment related information. signaling to carry accumulated impairment related information.
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in (dBs) at each intermediate point along the path. in (dBs) at each intermediate point along the path.
If distributed WA is being done at the same time as distributed IV If distributed WA is being done at the same time as distributed IV
then we may need to accumulate impairment related information for all then we may need to accumulate impairment related information for all
wavelengths that could be used. This is somewhat winnowed down as wavelengths that could be used. This is somewhat winnowed down as
potential wavelengths are discovered to be in use, but could be a potential wavelengths are discovered to be in use, but could be a
significant burden for lightly loaded high channel count networks. significant burden for lightly loaded high channel count networks.
3.3. Mapping Network Requirements to Architectures 3.3. Mapping Network Requirements to Architectures
In Figure 1 we show process flows for three main architectural In Figure 2 we show process flows for three main architectural
alternatives to IA-RWA when approximate impairment validation alternatives to IA-RWA when approximate impairment validation
suffices. In Figure 2 we show process flows for two main suffices. In Figure 3 we show process flows for two main
architectural alternatives when detailed impairment verification is architectural alternatives when detailed impairment verification is
required. required.
+-----------------------------------+ +-----------------------------------+
| +--+ +-------+ +--+ | | +--+ +-------+ +--+ |
| |IV| |Routing| |WA| | | |IV| |Routing| |WA| |
| +--+ +-------+ +--+ | | +--+ +-------+ +--+ |
| | | |
| Combined Processes | | Combined Processes |
+-----------------------------------+ +-----------------------------------+
skipping to change at page 13, line 29 skipping to change at page 15, line 29
+--------------+ +----------------------+ +--------------+ +----------------------+
(b) (b)
+-----------+ +----------------------+ +-----------+ +----------------------+
| +-------+ | | +--+ +--+ | | +-------+ | | +--+ +--+ |
| |Routing| |------->| |WA| |IV| | | |Routing| |------->| |WA| |IV| |
| +-------+ | | +--+ +--+ | | +-------+ | | +--+ +--+ |
+-----------+ | Distributed Processes| +-----------+ | Distributed Processes|
+----------------------+ +----------------------+
(c) (c)
Figure 1 Process flows for the three main approximate impairment Figure 2 Process flows for the three main approximate impairment
architectural alternatives. architectural alternatives.
The advantages, requirements and suitability of these options are as The advantages, requirements and suitability of these options are as
follows: follows:
o Combined IV & RWA process o Combined IV & RWA process
This alternative combines RWA and IV within a single computation This alternative combines RWA and IV within a single computation
entity enabling highest potential optimality and efficiency in IA- entity enabling highest potential optimality and efficiency in IA-
RWA. This alternative requires that the computational entity knows RWA. This alternative requires that the computational entity knows
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+-----------------------------------+ +------------+ +-----------------------------------+ +------------+
(a) (a)
+--------------+ +----------------------+ +------------+ +--------------+ +----------------------+ +------------+
| +----------+ | | +-------+ +--+ | | +--------+ | | +----------+ | | +-------+ +--+ | | +--------+ |
| | IV | | | |Routing| |WA| |---->| | IV | | | | IV | | | |Routing| |WA| |---->| | IV | |
| |candidates| |----->| +-------+ +--+ | | |Detailed| | | |candidates| |----->| +-------+ +--+ | | |Detailed| |
| +----------+ | | Combined Processes | | +--------+ | | +----------+ | | Combined Processes | | +--------+ |
+--------------+ +----------------------+ | | +--------------+ +----------------------+ | |
(b) +------------+ (b) +------------+
Figure 2 Process flows for the two main detailed impairment Figure 3 Process flows for the two main detailed impairment
validation architectural options. validation architectural options.
The advantages, requirements and suitability of these detailed The advantages, requirements and suitability of these detailed
validation options are as follows: validation options are as follows:
o Combined approximate IV & RWA + Detailed-IV o Combined approximate IV & RWA + Detailed-IV
This alternative combines RWA and approximate IV within a single This alternative combines RWA and approximate IV within a single
computation entity enabling highest potential optimality and computation entity enabling highest potential optimality and
efficiency in IA-RWA; then has a separate entity performing detailed efficiency in IA-RWA; then has a separate entity performing detailed
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Note that detailed impairment estimation is not standardized. Note that detailed impairment estimation is not standardized.
4. Protocol Implications 4. Protocol Implications
The previous IA-RWA architectural alternatives and process flows make The previous IA-RWA architectural alternatives and process flows make
differing demands on a GMPLS/PCE based control plane. In this section 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 we discuss the use of (a) an impairment information model, (b) PCE as
computational entity assuming the various process roles and computational entity assuming the various process roles and
consequences for PCEP, (c)any needed extensions to signaling, and (d) consequences for PCEP, (c)any needed extensions to signaling, and (d)
extensions to routing. The impacts to the control plane for IA-RWA extensions to routing. The impacts to the control plane for IA-RWA
are summarized in Figure 3. are summarized in Figure 4.
+-------------------+----+----+----------+--------+ +-------------------+----+----+----------+--------+
| IA-RWA Option |PCE |Sig |Info Model| Routing| | IA-RWA Option |PCE |Sig |Info Model| Routing|
+-------------------+----+----+----------+--------+ +-------------------+----+----+----------+--------+
| Combined |Yes | No | Yes | Yes | | Combined |Yes | No | Yes | Yes |
| IV & RWA | | | | | | IV & RWA | | | | |
+-------------------+----+----+----------+--------+- +-------------------+----+----+----------+--------+-
| IV-Candidates |Yes | No | Yes | Yes | | IV-Candidates |Yes | No | Yes | Yes |
| + RWA | | | | | | + RWA | | | | |
+-------------------+----+----+----------+--------+ +-------------------+----+----+----------+--------+
| Routing + |No | Yes| Yes | No | | Routing + |No | Yes| Yes | No |
|Distributed IV, RWA| | | | | |Distributed IV, RWA| | | | |
+-------------------+----+----+----------+--------+ +-------------------+----+----+----------+--------+
| Detailed IV |Yes | No | Yes | Yes | | Detailed IV |Yes | No | Yes | Yes |
+-------------------+----+----+----------+--------+ +-------------------+----+----+----------+--------+
Figure 3 IA-RWA architectural options and control plane impacts. Figure 4 IA-RWA architectural options and control plane impacts.
4.1. Information Model for Impairments 4.1. Information Model for Impairments
As previously discussed all IA-RWA scenarios to a greater or lesser As previously discussed all IA-RWA scenarios to a greater or lesser
extent rely on a common impairment information model. A number of extent rely on a common impairment information model. A number of
ITU-T recommendations cover detailed as well as approximate ITU-T recommendations cover detailed as well as approximate
impairment characteristics of fibers and a variety of devices and impairment characteristics of fibers and a variety of devices and
subsystems. A well integrated impairment model for optical network subsystems. A well integrated impairment model for optical network
elements is given in [G.680] and is used to form the basis for an elements is given in [G.680] and is used to form the basis for an
optical impairment model in a companion document [Imp-Info]. optical impairment model in a companion document [Imp-Info].
skipping to change at page 16, line 25 skipping to change at page 18, line 25
more than an impairment information model. In particular, it needs a more than an impairment information model. In particular, it needs a
common impairment "computation" model. In the distributed IV case one common impairment "computation" model. In the distributed IV case one
needs to standardize the accumulated impairment measures that will be needs to standardize the accumulated impairment measures that will be
conveyed and updated at each node. Section 9 of [G.680] provides conveyed and updated at each node. Section 9 of [G.680] provides
guidance in this area with specific formulas given for OSNR, residual guidance in this area with specific formulas given for OSNR, residual
dispersion, polarization mode dispersion/polarization dependent loss, dispersion, polarization mode dispersion/polarization dependent loss,
effects of channel uniformity, etc... However, specifics of what effects of channel uniformity, etc... However, specifics of what
intermediate results are kept and in what form would need to be intermediate results are kept and in what form would need to be
standardized. standardized.
4.1.1. Properties of an Impairment Information Model 4.1.1. Properties of an Impairment Information Model
In term of information model there are a set of property that needs In term of information model there are a set of property that needs
to be defined for each optical parameters that need to be in some way to be defined for each optical parameters that need to be in some way
considered within an impairment aware control plane. considered within an impairment aware control plane.
The properties will help to determine how the control plane can deal The properties will help to determine how the control plane can deal
with it depending also on the above control plane architectural with it depending also on the above control plane architectural
options. In some case properties value will help to indentify the options. In some case properties value will help to indentify the
level of approximation supported by the IV process. level of approximation supported by the IV process.
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IV scenarios. IV scenarios.
4.4. PCE 4.4. PCE
In section 3.3. we gave a number of computation architectural In section 3.3. we gave a number of computation architectural
alternatives that could be used to meet the various requirements and alternatives that could be used to meet the various requirements and
constraints of section 3.1. Here we look at how these alternatives 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 could be implemented via either a single PCE or a set of two or more
cooperating PCEs, and the impacts on the PCEP protocol. cooperating PCEs, and the impacts on the PCEP protocol.
4.4.1. Combined IV & RWA 4.4.1. Combined IV & RWA
In this situation, shown in Figure 1(a), a single PCE performs all In this situation, shown in Figure 2(a), a single PCE performs all
the computations needed for IA-RWA. the computations needed for IA-RWA.
o TE Database Requirements o TE Database Requirements
WSON Topology and switching capabilities, WSON WDM link wavelength WSON Topology and switching capabilities, WSON WDM link wavelength
utilization, and WSON impairment information utilization, and WSON impairment information
o PCC to PCE Request Information o PCC to PCE Request Information
Signal characteristics/type, required quality, source node, Signal characteristics/type, required quality, source node,
skipping to change at page 18, line 40 skipping to change at page 20, line 40
o PCE to PCC Reply Information o PCE to PCC Reply Information
If the computations completed successfully then the PCE returns If the computations completed successfully then the PCE returns
the path and its assigned wavelength. If the computations could the path and its assigned wavelength. If the computations could
not complete successfully it would be potentially useful to know 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 the reason why. At a very crude level we'd like to know if this
was due to lack of wavelength availability or impairment was due to lack of wavelength availability or impairment
considerations or a bit of both. The information to be conveyed is considerations or a bit of both. The information to be conveyed is
for further study. for further study.
4.4.2. IV-Candidates + RWA 4.4.2. IV-Candidates + RWA
In this situation, shown in Figure 1(b), we have two separate In this situation, shown in Figure 2(b), we have two separate
processes involved in the IA-RWA computation. This requires at least processes involved in the IA-RWA computation. This requires at least
two cooperating PCEs: one for the Candidates-IV process and another two cooperating PCEs: one for the Candidates-IV process and another
for the RWA process. In addition, the overall process needs to be 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 coordinated. This could be done with yet another PCE or we can add
this functionality to one of previously defined PCEs. We choose this this functionality to one of previously defined PCEs. We choose this
later option and require the RWA PCE to also act as the overall later option and require the RWA PCE to also act as the overall
process coordinator. The roles, responsibilities and information process coordinator. The roles, responsibilities and information
requirements for these two PCEs are given below. requirements for these two PCEs are given below.
RWA and Coordinator PCE (RWA-Coord-PCE): RWA and Coordinator PCE (RWA-Coord-PCE):
skipping to change at page 19, line 23 skipping to change at page 21, line 23
WSON Topology and switching capabilities and WSON WDM link WSON Topology and switching capabilities and WSON WDM link
wavelength utilization (no impairment information). wavelength utilization (no impairment information).
o PCC to RWA-PCE request: same as in the combined case. o PCC to RWA-PCE request: same as in the combined case.
o RWA-PCE to PCC reply: same as in the combined case. o RWA-PCE to PCC reply: same as in the combined case.
o RWA-PCE to IV-Candidates-PCE request o RWA-PCE to IV-Candidates-PCE request
The RWA-PCE asks for a set of at most K routes along with The RWA-PCE asks for a set of at most K routes along with acceptable
acceptable wavelengths between nodes specified in the original PCC wavelengths between nodes specified in the original PCC request.
request.
o IV-Candidates-PCE reply to RWA-PCE o IV-Candidates-PCE reply to RWA-PCE
The Candidates-PCE returns a set of at most K routes along with The Candidates-PCE returns a set of at most K routes along with
acceptable wavelengths between nodes specified in the RWA-PCE acceptable wavelengths between nodes specified in the RWA-PCE
request. request.
IV-Candidates-PCE: IV-Candidates-PCE:
The IV-Candidates-PCE is responsible for impairment aware path The IV-Candidates-PCE is responsible for impairment aware path
computation. It needs not take into account current link computation. It needs not take into account current link
wavelength utilization, but this is not prohibited. The wavelength utilization, but this is not prohibited. The
Candidates-PCE is only required to interact with the RWA-PCE as Candidates-PCE is only required to interact with the RWA-PCE as
indicated above and not the PCC. indicated above and not the PCC.
o TE Database Requirements o TE Database Requirements
WSON Topology and switching capabilities and WSON impairment WSON Topology and switching capabilities and WSON impairment
information (no information link wavelength utilization required). information (no information link wavelength utilization required).
In Figure 4 we show a sequence diagram for the interactions between In Figure 5 we show a sequence diagram for the interactions between
the PCC, RWA-PCE and IV-Candidates-PCE. the PCC, RWA-PCE and IV-Candidates-PCE.
+---+ +-------------+ +-----------------+ +---+ +-------------+ +-----------------+
|PCC| |RWA-Coord-PCE| |IV-Candidates-PCE| |PCC| |RWA-Coord-PCE| |IV-Candidates-PCE|
+-+-+ +------+------+ +---------+-------+ +-+-+ +------+------+ +---------+-------+
...___ (a) | | ...___ (a) | |
| ````---...____ | | | ````---...____ | |
| ```-->| | | ```-->| |
| | | | | |
| |--..___ (b) | | |--..___ (b) |
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| | ___....---'''' | | | ___....---'''' |
| |<--'''' | | |<--'''' |
| | | | | |
| | | | | |
| (d) ___...| | | (d) ___...| |
| ___....---''' | | | ___....---''' | |
|<--''' | | |<--''' | |
| | | | | |
| | | | | |
Figure 4 Sequence diagram for the interactions between PCC, RWA- Figure 5 Sequence diagram for the interactions between PCC, RWA-
Coordinating-PCE and the IV-Candidates-PCE. Coordinating-PCE and the IV-Candidates-PCE.
In step (a) the PCC requests a path meeting specified quality In step (a) the PCC requests a path meeting specified quality
constraints between two nodes (A and Z) for a given signal constraints between two nodes (A and Z) for a given signal
represented either by a specific type or a general class with represented either by a specific type or a general class with
associated parameters. In step (b) the RWA-Coordinating-PCE requests associated parameters. In step (b) the RWA-Coordinating-PCE requests
up to K candidate paths between nodes A and Z and associated up to K candidate paths between nodes A and Z and associated
acceptable wavelengths. In step (c) The IV-Candidates-PCE returns acceptable wavelengths. In step (c) The IV-Candidates-PCE returns
this list to the RWA-Coordinating PCE which then uses this set of 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 paths and wavelengths as input (e.g. a constraint) to its RWA
computation. In step (d) the RWA-Coordinating-PCE returns the overall computation. In step (d) the RWA-Coordinating-PCE returns the overall
IA-RWA computation results to the PCC. IA-RWA computation results to the PCC.
4.4.3. Approximate IA-RWA + Separate Detailed IV 4.4.3. Approximate IA-RWA + Separate Detailed IV
In Figure 2 we showed two cases where a separate detailed impairment In Figure 3 we showed two cases where a separate detailed impairment
validation process could be utilized. We can place the detailed validation process could be utilized. We can place the detailed
validation process into a separate PCE. Assuming that a different PCE validation process into a separate PCE. Assuming that a different PCE
assumes a coordinating role and interacts with the PCC we can keep assumes a coordinating role and interacts with the PCC we can keep
the interactions with this separate IV-Detailed-PCE very simple. the interactions with this separate IV-Detailed-PCE very simple.
IV-Detailed-PCE: IV-Detailed-PCE:
o TE Database Requirements o TE Database Requirements
The IV-Detailed-PCE will need optical impairment information, WSON The IV-Detailed-PCE will need optical impairment information, WSON
topology, and possibly WDM link wavelength usage information. This topology, and possibly WDM link wavelength usage information. This
document puts no restrictions on the type of information that may document puts no restrictions on the type of information that may
be used in these computations. be used in these computations.
o Coordinating-PCE to IV-Detailed-PCE request o Coordinating-PCE to IV-Detailed-PCE request
The coordinating-PCE will furnish signal characteristics, quality The coordinating-PCE will furnish signal characteristics, quality
requirements, path and wavelength to the IV-Detailed-PCE. requirements, path and wavelength to the IV-Detailed-PCE.
o IV-Detailed-PCE to Coordinating-PCE reply o IV-Detailed-PCE to Coordinating-PCE reply
The reply is essential an yes/no decision as to whether the The reply is essential an yes/no decision as to whether the
requirements could actually be met. In the case where the requirements could actually be met. In the case where the
impairment validation fails it would be helpful to convey impairment validation fails it would be helpful to convey
information related to cause or quantify the failure, e.g., so a information related to cause or quantify the failure, e.g., so a
judgment can be made whether to try a different signal or adjust judgment can be made whether to try a different signal or adjust
signal parameters. signal parameters.
In Figure 5 we show a sequence diagram for the interactions for the In Figure 6 we show a sequence diagram for the interactions for the
process shown in Figure 2(b). This involves interactions between the process shown in Figure 3(b). This involves interactions between the
PCC, RWA-PCE (acting as coordinator), IV-Candidates-PCE and the IV- PCC, RWA-PCE (acting as coordinator), IV-Candidates-PCE and the IV-
Detailed-PCE. Detailed-PCE.
In step (a) the PCC requests a path meeting specified quality In step (a) the PCC requests a path meeting specified quality
constraints between two nodes (A and Z) for a given signal constraints between two nodes (A and Z) for a given signal
represented either by a specific type or a general class with represented either by a specific type or a general class with
associated parameters. In step (b) the RWA-Coordinating-PCE requests associated parameters. In step (b) the RWA-Coordinating-PCE requests
up to K candidate paths between nodes A and Z and associated up to K candidate paths between nodes A and Z and associated
acceptable wavelengths. In step (c) The IV-Candidates-PCE returns acceptable wavelengths. In step (c) The IV-Candidates-PCE returns
this list to the RWA-Coordinating PCE which then uses this set of this list to the RWA-Coordinating PCE which then uses this set of
skipping to change at page 22, line 31 skipping to change at page 24, line 31
| | `````-----....._____ | | | `````-----....._____ |
| | `````----->| | | `````----->|
| | | | | |
| | (e) _____.....+ | | (e) _____.....+
| | _____.....-----''''' | | | _____.....-----''''' |
| |<----''''' | | |<----''''' |
| (f) __.| | | (f) __.| |
| __.--'' | | __.--'' |
|<-'' | |<-'' |
| | | |
Figure 5 Sequence diagram for the interactions between PCC, RWA- Figure 6 Sequence diagram for the interactions between PCC, RWA-
Coordinating-PCE, IV-Candidates-PCE and IV-Detailed-PCE. Coordinating-PCE, IV-Candidates-PCE and IV-Detailed-PCE.
5. Security Considerations 5. Security Considerations
This document discusses a number of control plane architectures that This document discusses a number of control plane architectures that
incorporate knowledge of impairments in optical networks. If such incorporate knowledge of impairments in optical networks. If such
architecture is put into use within a network it will by its nature architecture is put into use within a network it will by its nature
contain details of the physical characteristics of an optical contain details of the physical characteristics of an optical
network. Such information would need to be protected from intentional network. Such information would need to be protected from intentional
or unintentional disclosure. or unintentional disclosure.
skipping to change at page 28, line 20 skipping to change at page 30, line 20
o optical splice; o optical splice;
o optical switch; o optical switch;
o optical termination; o optical termination;
o tuneable filter; o tuneable filter;
o optical wavelength multiplexer (MUX)/demultiplexer (DMUX); o optical wavelength multiplexer (MUX)/demultiplexer (DMUX);
- coarse WDM device; - coarse WDM device;
- dense WDM device; - dense WDM device;
- wide WDM device. - wide WDM device.
Reference [G.671] then specifies applicable parameters for these Reference [G.671] then specifies applicable parameters for these
components. For example an OADM subsystem will have parameters such components. For example an OADM subsystem will have parameters such
as: insertion loss (input to output, input to drop, add to output), as: insertion loss (input to output, input to drop, add to output),
number of add, drop and through channels, polarization dependent number of add, drop and through channels, polarization dependent
loss, adjacent channel isolation, allowable input power, polarization loss, adjacent channel isolation, allowable input power, polarization
mode dispersion, etc... mode dispersion, etc...
A.4. Network Elements A.4. Network Elements
skipping to change at page 34, line 20 skipping to change at page 36, line 20
Email: ggalimbe@cisco.com Email: ggalimbe@cisco.com
Alberto Tanzi Alberto Tanzi
Cisco Cisco
Via Philips 12, Via Philips 12,
20052 Monza, Italy 20052 Monza, Italy
Phone: +39 039 2091469 Phone: +39 039 2091469
Email: altanzi@cisco.com Email: altanzi@cisco.com
David Bianchi
Cisco
Via Philips 12,
20052 Monza, Italy
Email: davbianc@cisco.com
Moustafa Kattan
Cisco
Email: mkattan@cisco.com
Dirk Schroetter
Cisco
Email: dschroet@cisco.com
Intellectual Property Statement Intellectual Property Statement
The IETF Trust takes no position regarding the validity or scope of The IETF Trust takes no position regarding the validity or scope of
any Intellectual Property Rights or other rights that might be any Intellectual Property Rights or other rights that might be
claimed to pertain to the implementation or use of the technology claimed to pertain to the implementation or use of the technology
described in any IETF Document or the extent to which any license described in any IETF Document or the extent to which any license
under such rights might or might not be available; nor does it under such rights might or might not be available; nor does it
represent that it has made any independent effort to identify any represent that it has made any independent effort to identify any
such rights. such rights.
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