Network Working Group Y. Lee
Internet Draft Huawei
G. Bernstein
Grotto Networking
D. Li
Huawei
G. Martinelli
Cisco
Intended status: Informational October 21, 2010
Expires: April 2011
A Framework for the Control of Wavelength Switched Optical Networks
(WSON) with Impairments
draft-ietf-ccamp-wson-impairments-04.txt
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Abstract
The operation of optical networks requires information on the
physical characterization of optical network elements, subsystems,
devices, and cabling. These physical characteristics may be important
to consider when using a GMPLS control plane to support path setup
and maintenance. This document discusses how the definition and
characterization of optical fiber, devices, subsystems, and network
elements contained in various ITU-T recommendations can be combined
with GMPLS control plane protocols and mechanisms to support
Impairment Aware Routing and Wavelength Assignment (IA-RWA) in
optical networks.
Table of Contents
1. Introduction...................................................4
1.1. Revision History..........................................5
2. Motivation.....................................................5
3. Impairment Aware Optical Path Computation......................6
3.1. Optical Network Requirements and Constraints..............7
3.1.1. Impairment Aware Computation Scenarios...............7
3.1.2. Impairment Computation and Information Sharing
Constraints.................................................8
3.1.3. Impairment Estimation Process.......................10
3.2. IA-RWA Computation and Control Plane Architectures.......11
3.2.1. Combined Routing, WA, and IV........................13
3.2.2. Separate Routing, WA, or IV.........................13
3.2.3. Distributed WA and/or IV............................13
3.3. Mapping Network Requirements to Architectures............14
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4. Protocol Implications.........................................17
4.1. Information Model for Impairments........................17
4.2. Routing..................................................18
4.3. Signaling................................................18
4.4. PCE......................................................19
4.4.1. Combined IV & RWA...................................19
4.4.2. IV-Candidates + RWA.................................19
4.4.3. Approximate IA-RWA + Separate Detailed IV...........21
5. Security Considerations.......................................23
6. IANA Considerations...........................................23
7. Acknowledgments...............................................23
8. References....................................................31
8.1. Normative References.....................................31
8.2. Informative References...................................33
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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.
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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.
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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].
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(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
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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
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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
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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)
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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.
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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.
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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
separate impairment validation process.
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 selected path and wavelength. If IV comes first it
would need to furnish a list of possible (valid with respect to
impairments) routes and wavelengths to the RWA processes.
3.2.3. Distributed WA and/or IV
In the non-impairment RWA situation [WSON-Frame] it was shown that
a distributed wavelength assignment (WA) process carried out via
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signaling can eliminate the need to distribute wavelength
availability information via an 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 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
distributed impairment validation.
o R + D(WA & IV) -- routing separate from a distributed wavelength
assignment and impairment validation process.
A distributed impairment validation for a prescribed network path
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
then we may need to accumulate impairment related information for
all 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.
3.3. Mapping Network Requirements to Architectures
In Figure 2 we show process flows for three main architectural
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.
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+-----------------------------------+
| +--+ +-------+ +--+ |
| |IV| |Routing| |WA| |
| +--+ +-------+ +--+ |
| |
| Combined Processes |
+-----------------------------------+
(a)
+--------------+ +----------------------+
| +----------+ | | +-------+ +--+ |
| | IV | | | |Routing| |WA| |
| |candidates| |----->| +-------+ +--+ |
| +----------+ | | Combined Processes |
+--------------+ +----------------------+
(b)
+-----------+ +----------------------+
| +-------+ | | +--+ +--+ |
| |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
as follows:
o Combined IV & RWA process
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".
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
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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
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".
+-----------------------------------+ +------------+
| +-----------+ +-------+ +--+ | | +--------+ |
| | IV | |Routing| |WA| | | | IV | |
| |approximate| +-------+ +--+ |---->| |Detailed| |
| +-----------+ | | +--------+ |
| Combined Processes | | |
+-----------------------------------+ +------------+
(a)
+--------------+ +----------------------+ +------------+
| +----------+ | | +-------+ +--+ | | +--------+ |
| | IV | | | |Routing| |WA| |---->| | IV | |
| |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
validation options are as follows:
o Combined approximate IV & RWA + Detailed-IV
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.
o Candidates-IV + RWA + Detailed-IV
This alternative allows separation of approximate impairment
information into a computational entity while still maintaining a
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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
The previous IA-RWA architectural alternatives and process flows
make 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.
+-------------------+----+----+----------+--------+
| 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| | | | |
+-------------------+----+----+----------+--------+
| Detailed IV |Yes | No | Yes | Yes |
+-------------------+----+----+----------+--------+
Figure 4 IA-RWA architectural options and control plane impacts.
4.1. Information Model for Impairments
As previously discussed all IA-RWA scenarios to a greater or
lesser extent rely on a common impairment information model. A
number of ITU-T recommendations cover detailed as well as
approximate impairment characteristics of fibers and a variety of
devices and 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].
It should be noted that the current version of [G.680] is limited
to the networks composed of a single WDM line system vendor
combined with OADMs and/or PXCs from potentially multiple other
vendors, this is known as situation 1 and is shown in Figure 1-1
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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].
The case of distributed impairment validation actually requires a
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
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.
Depending on the computational alternative the routing protocol
may need to advertise information necessary to impairment
validation process. This can potentially cause scalability issues
due to the high amount of data that need to be advertised. Such
issue can be 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).
In term of approximated scenario (see Section 3.1.1. ) the model
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
the routing protocol.
4.3. Signaling
The largest impacts on signaling occur in the cases where
distributed impairment validation is performed. In this we need to
accumulate 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
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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
egress signal quality (defined in some appropriate sense) in non-
distributed IV scenarios.
4.4. PCE
In section 3.3. we gave a number of computation architectural
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
In this situation, shown in Figure 2(a), a single PCE performs all
the computations needed for IA-RWA.
o TE Database Requirements
WSON Topology and switching capabilities, WSON WDM link
wavelength utilization, and WSON impairment information
o PCC to PCE Request Information
Signal characteristics/type, required quality, source node,
destination node
o PCE to PCC Reply Information
If the computations completed successfully then the PCE returns
the path and its assigned wavelength. If the computations could
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.
4.4.2. IV-Candidates + RWA
In this situation, shown in Figure 2(b), we have two separate
processes involved in the IA-RWA computation. This requires at
least 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
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act as the overall process coordinator. The roles,
responsibilities and information requirements for these two PCEs
are given below.
RWA and Coordinator PCE (RWA-Coord-PCE):
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 TE Database Requirements
WSON Topology and switching capabilities and WSON WDM link
wavelength utilization (no impairment information).
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 IV-Candidates-PCE request
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 IV-Candidates-PCE reply to RWA-PCE
The Candidates-PCE returns a set of at most K routes along with
acceptable wavelengths between nodes specified in the RWA-PCE
request.
IV-Candidates-PCE:
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 TE Database Requirements
WSON Topology and switching capabilities and WSON impairment
information (no information link wavelength utilization
required).
In Figure 5 we show a sequence diagram for the interactions
between the PCC, RWA-PCE and IV-Candidates-PCE.
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+---+ +-------------+ +-----------------
+
|PCC| |RWA-Coord-PCE| |IV-Candidates-
PCE|
+-+-+ +------+------+ +---------+-------
+
...___ (a) | |
| ````---...____ | |
| ```-->| |
| | |
| |--..___ (b) |
| | ```---...___ |
| | ```---->|
| | |
| | |
| | (c) ___...|
| | ___....---'''' |
| |<--'''' |
| | |
| | |
| (d) ___...| |
| ___....---''' | |
|<--''' | |
| | |
| | |
Figure 5 Sequence diagram for the interactions between PCC, RWA-
Coordinating-PCE and the IV-Candidates-PCE.
In step (a) the PCC requests a path meeting specified quality
constraints between two nodes (A and Z) for a given signal
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 returns
the overall IA-RWA computation results to the PCC.
4.4.3. Approximate IA-RWA + Separate Detailed IV
In Figure 3 we showed two cases where a separate detailed
impairment validation process could be utilized. We can place the
detailed validation process into a separate PCE. Assuming that a
different PCE assumes a coordinating role and interacts with the
PCC we can keep the interactions with this separate IV-Detailed-
PCE very simple.
IV-Detailed-PCE:
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o TE Database Requirements
The IV-Detailed-PCE will need optical impairment information, WSON
topology, and possibly WDM link wavelength usage information.
This document puts no restrictions on the type of information
that may be used in these computations.
o Coordinating-PCE to IV-Detailed-PCE request
The coordinating-PCE will furnish signal characteristics, quality
requirements, path and wavelength to the IV-Detailed-PCE.
o IV-Detailed-PCE to Coordinating-PCE reply
The reply is essential an yes/no decision as to whether the
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
the process shown in Figure 3(b). This involves interactions
between the PCC, RWA-PCE (acting as coordinator), IV-Candidates-
PCE and the IV-Detailed-PCE.
In step (a) the PCC requests a path meeting specified quality
constraints between two nodes (A and Z) for a given signal
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.
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+----------+ +--------------+ +------------
+
+---+ |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
This document discusses a number of control plane architectures
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
This draft does not currently require any consideration from IANA.
7. Acknowledgments
This document was prepared using 2-Word-v2.0.template.dot.
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APPENDIX A: Overview of Optical Layer ITU-T Recommendations
For optical fiber, devices, subsystems and network elements the
ITU-T has a variety of recommendations that include definitions,
characterization parameters and test methods. In the following we
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
Fibers and cables form a key component of what from the control
plane perspective could be termed an optical link. Due to the wide
range of uses of optical networks a fairly wide range of fiber
types are used in practice. The ITU-T has three main
recommendations covering the definition of attributes and test
methods for single mode fiber:
o Definitions and test methods for linear, deterministic
attributes of single-mode fibre and cable [G.650.1]
o Definitions and test methods for statistical and non-linear
related attributes of single-mode fibre and cable [G.650.2]
o Test methods for installed single-mode fibre cable sections
[G.650.3]
General Definitions[G.650.1]: Mechanical Characteristics
(numerous), Mode field characteristics(mode field, mode field
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,
core concentricity error, cut-off wavelength, attenuation,
chromatic dispersion. [G.650.2]: test methods for polarization
mode dispersion. [G.650.3] Test methods for characteristics of
fibre cable sections following installation: attenuation, splice
loss, splice location, fibre uniformity and length of cable
sections (these are OTDR based), PMD, Chromatic dispersion.
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With these definitions a variety of single mode fiber types are
defined as shown in the table below:
ITU-T Standard | Common Name
------------------------------------------------------------
G.652 [G.652] | Standard SMF |
G.653 [G.653] | Dispersion shifted SMF |
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
A.2.1. Optical Amplifiers
Optical amplifiers greatly extend the transmission distance of
optical signals in both single channel and multi channel (WDM)
subsystems. The ITU-T has the following recommendations:
o Definition and test methods for the relevant generic parameters
of optical amplifier devices and subsystems [G.661]
o Generic characteristics of optical amplifier devices and
subsystems [G.662]
o Application related aspects of optical amplifier devices and
subsystems [G.663]
o Generic characteristics of Raman amplifiers and Raman amplified
subsystems [G.665]
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
device attributes and parameters. In references [G.662] and
[G.665] we have characterization of specific devices, e.g.,
semiconductor optical amplifier, used in a particular setting,
e.g., line amplifier. For example reference[G.662] gives the
following minimum list of relevant parameters for the
specification of an optical amplifier device used as line
amplifier in a multichannel application:
a) Channel allocation.
b) Total input power range.
c) Channel input power range.
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d) Channel output power range.
e) Channel signal-spontaneous noise figure.
f) Input reflectance.
g) Output reflectance.
h) Maximum reflectance tolerable at input.
i) Maximum reflectance tolerable at output.
j) Maximum total output power.
k) Channel addition/removal (steady-state) gain response.
l) Channel addition/removal (transient) gain response.
m) Channel gain.
n) Multichannel gain variation (inter-channel gain difference).
o) Multichannel gain-change difference (inter-channel gain-change
difference).
p) Multichannel gain tilt (inter-channel gain-change ratio).
q) Polarization Mode Dispersion (PMD).
A.2.2. Dispersion Compensation
In optical systems two forms of dispersion are commonly
encountered [RFC4054] chromatic dispersion and polarization mode
dispersion (PMD). There are a number of techniques and devices
used for compensating for these effects. The following ITU-T
recommendations characterize such devices:
o Characteristics of PMD compensators and PMD compensating
receivers [G.666]
o Characteristics of Adaptive Chromatic Dispersion Compensators
[G.667]
The above furnish definitions as well as parameters and
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
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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
The definitions of the characteristics of optical transmitters can
be found in references [G.957], [G.691], [G.692] and [G.959.1]. In
addition references [G.957], [G.691], and [G.959.1] define
specific parameter values or parameter ranges for these
characteristics for interfaces for use in particular situations.
We generally have the following types of parameters
Wavelength related: Central frequency, Channel spacing, Central
frequency deviation[G.692].
Spectral characteristics of the transmitter: Nominal source type
(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
mask [G.691], Maximum and minimum mean channel output power
[G.959.1].
A.2.4. Optical Receivers
References [G.959.1], [G.691], [G.692] and [G.957], define optical
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:
Receiver sensitivity: minimum value of average received power to
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
value of the received average power for a 1x10.10 BER [G.957] or a
1x10-12 BER [G.691].
Receiver reflectance: "Reflections from the receiver back to the
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
an optical path penalty not exceeding X dB to account for total
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degradations due to reflections, intersymbol interference, mode
partition noise, and laser chirp."
When dealing with multi-channel systems or systems with optical
amplifiers we may also need:
Optical signal-to-noise ratio: "The minimum value of optical SNR
required to obtain a 1x10-12 BER."[G.692]
Receiver wavelength range: "The receiver wavelength range is
defined as the acceptable range of wavelengths at point Rn. This
range must be wide enough to cover the entire range of central
frequencies over the OA passband." [G.692]
Minimum equivalent sensitivity: "This is the minimum sensitivity
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
Reference [G.671] "Transmission characteristics of optical
components and subsystems" covers the following components:
o optical add drop multiplexer (OADM) subsystem;
o asymmetric branching component;
o optical attenuator;
o optical branching component (wavelength non-selective);
o optical connector;
o dynamic channel equalizer (DCE);
o optical filter;
o optical isolator;
o passive dispersion compensator;
o optical splice;
o optical switch;
o optical termination;
o tuneable filter;
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o optical wavelength multiplexer (MUX)/demultiplexer (DMUX);
- coarse WDM device;
- dense WDM device;
- wide WDM device.
Reference [G.671] then specifies applicable parameters for these
components. For example an OADM subsystem will have parameters
such as: insertion loss (input to output, input to drop, add to
output), number of add, drop and through channels, polarization
dependent loss, adjacent channel isolation, allowable input power,
polarization mode dispersion, etc...
A.4. Network Elements
The previously cited ITU-T recommendations provide a plethora of
definitions and characterizations of optical fiber, devices,
components and subsystems. Reference [G.Sup39] "Optical system
design and engineering considerations" provides useful guidance on
the use of such parameters.
In many situations the previous models while good don't encompass
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
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,
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
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o General ONE with optical amplifiers
o OADM without optical amplifiers
o OADM with optical amplifiers
o Reconfigurable OADM (ROADM) without optical amplifiers
o ROADM with optical amplifiers
o PXC without optical amplifiers
o PXC with optical amplifiers
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8. References
8.1. Normative References
[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.
[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.
[650.3] ITU-T Recommendation G.650.3
[G.652] ITU-T Recommendation G.652, Characteristics of a single-
mode optical fibre and cable, June 2005.
[G.653] ITU-T Recommendation G.653, Characteristics of a
dispersion-shifted single-mode optical fibre and cable,
December 2006.
[G.654] ITU-T Recommendation G.654, Characteristics of a cut-off
shifted single-mode optical fibre and cable, December
2006.
[G.655] ITU-T Recommendation G.655, Characteristics of a non-zero
dispersion-shifted single-mode optical fibre and cable,
March 2006.
[G.656] ITU-T Recommendation G.656, Characteristics of a fibre and
cable with non-zero dispersion for wideband optical
transport, December 2006.
[G.661] ITU-T Recommendation G.661, Definition and test methods
for the relevant generic parameters of optical amplifier
devices and subsystems, March 2006.
[G.662] ITU-T Recommendation G.662, Generic characteristics of
optical amplifier devices and subsystems, July 2005.
[G.671] ITU-T Recommendation G.671, Transmission characteristics
of optical components and subsystems, January 2005.
[G.680] ITU-T Recommendation G.680, Physical transfer functions
of optical network elements, July 2007.
[G.691] ITU-T Recommendation G.691, Optical interfaces for
multichannel systems with optical amplifiers, November
1998.
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[G.692] ITU-T Recommendation G.692, Optical interfaces for single
channel STM-64 and other SDH systems with optical
amplifiers, March 2006.
[G.872] ITU-T Recommendation G.872, Architecture of optical
transport networks, November 2001.
[G.957] ITU-T Recommendation G.957, Optical interfaces for
equipments and systems relating to the synchronous
digital hierarchy, March 2006.
[G.959.1] ITU-T Recommendation G.959.1, Optical Transport Network
Physical Layer Interfaces, March 2006.
[G.694.1] ITU-T Recommendation G.694.1, Spectral grids for WDM
applications: DWDM frequency grid, June 2002.
[G.694.2] ITU-T Recommendation G.694.2, Spectral grids for WDM
applications: CWDM wavelength grid, December 2003.
[G.698.1] ITU-T Recommendation G.698.1, Multichannel DWDM
applications with Single-Channel optical interface,
December 2006.
[G.698.2] ITU-T Recommendation G.698.2, Amplified multichannel
DWDM applications with Single-Channel optical interface,
July 2007.
[G.Sup39] ITU-T Series G Supplement 39, Optical system design and
engineering considerations, February 2006.
[RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", RFC 3945, October 2004.
[RFC4054] Strand, J., Ed., and A. Chiu, Ed., "Impairments and
Other Constraints on Optical Layer Routing", RFC 4054,
May 2005.
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
August 2006.
[WSON-Frame] G. Bernstein, Y. Lee, W. Imajuku, "Framework for
GMPLS and PCE Control of Wavelength Switched Optical
Networks", work in progress: draft-ietf-ccamp-
wavelength-switched-framework-02.txt, March 2009.
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8.2. Informative References
[Imp-Info] G. Bernstein, Y. Lee, D. Li, "A Framework for the
Control and Measurement of Wavelength Switched Optical
Networks (WSON) with Impairments", work in progress:
draft-bernstein-wson-impairment-info.
[Martinelli] G. Martinelli (ed.) and A. Zanardi (ed.), "GMPLS
Signaling Extensions for Optical Impairment Aware
Lightpath Setup", Work in Progress: draft-martinelli-
ccamp-optical-imp-signaling-02.txt, February 2008.
[WSON-Comp] G. Bernstein, Y. Lee, Ben Mack-Crane, "WSON Signal
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
Phone: (510) 573-2237
Email: gregb@grotto-networking.com
Young Lee (ed.)
Huawei Technologies
1700 Alma Drive, Suite 100
Plano, TX 75075
USA
Phone: (972) 509-5599 (x2240)
Email: ylee@huawei.com
Dan Li
Huawei Technologies Co., Ltd.
F3-5-B R&D Center, Huawei Base,
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28973237
Email: danli@huawei.com
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Giovanni Martinelli
Cisco
Via Philips 12
20052 Monza, Italy
Phone: +39 039 2092044
Email: giomarti@cisco.com
Contributor's Addresses
Ming Chen
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: 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
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David Bianchi
Cisco
Via Philips 12,
20052 Monza, Italy
Email: davbianc@cisco.com
Moustafa Kattan
Cisco
Dubai 500321
United Arab Emirates
Email: mkattan@cisco.com
Dirk Schroetter
Cisco
Email: dschroet@cisco.com
Daniele Ceccarelli
Ericsson
Via A. Negrone 1/A
Genova - Sestri Ponente
Italy
Email: daniele.ceccarelli@ericsson.com
Elisa Bellagamba
Ericsson
Farogatan 6,
Kista 164 40
Sweeden
Email: elisa.bellagamba@ericcson.com
Diego Caviglia
Ericsson
Via A. negrone 1/A
Genova - Sestri Ponente
Italy
Email: diego.caviglia@ericcson.com
Intellectual Property Statement
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Internet-Draft Framework for Networks with Impairments October 2010
claimed to pertain to the implementation or use of the technology
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Acknowledgment
We thank Chen Ming of DICONNET Project who provided valuable
information relevant to this document.
We'd also like to thank Deborah Brungard for editorial and
technical assistance.
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