One document matched: draft-martinelli-ccamp-opt-imp-fwk-00.txt
Internet Engineering Task Force G. Martinelli, Ed.
Internet-Draft D. Bianchi, Ed.
Intended status: Informational A. Tanzi, Ed.
Expires: April 29, 2009 O. Gerstel, Ed.
Cisco Systems
A. Zanardi, Ed.
CREATE-NET
October 26, 2008
A Framework for defining Optical Parameters to be used in WSON networks
through GMPLS
draft-martinelli-ccamp-opt-imp-fwk-00
Status of this Memo
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This Internet-Draft will expire on April 29, 2009.
Abstract
In the context of Wavelength Switched Optical Networks (WSON) the
problem of selecting a lightpath might be constrained by an
evaluation of the optical impairments associated to a wavelength.
This is a critical step in a transparent dense wavelength division
multiplexing (DWDM) optical islands where a lightpath feasibility has
to be assessed between two regenerations nodes.
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This memo provides a framework in which optical parameters can be
considered a control plane. The document relies on information
already present in ITU documents and summarize in term of lightpath
constraints.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Motivation for an Impairment-Aware Control Plane . . . . . . . 3
3. Overview of Optical Impairment Evaluation . . . . . . . . . . 5
3.1. Impairments Evaluation Flow . . . . . . . . . . . . . . . 5
3.2. Parameter Classification According to its Information
Complexity . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Additional Parameter Sharing Properties . . . . . . . . . 9
4. Control Plane Considerations . . . . . . . . . . . . . . . . . 10
5. Optical Interface Characteristics . . . . . . . . . . . . . . 10
6. Optical Path Characteristics . . . . . . . . . . . . . . . . . 11
6.1. Linear Impairments . . . . . . . . . . . . . . . . . . . . 11
6.1.1. Fiber Losses . . . . . . . . . . . . . . . . . . . . . 11
6.1.2. Insertion Losses (Optical components looses) . . . . . 12
6.1.3. Amplifier Spontaneous Emission (ASE) . . . . . . . . . 12
6.1.4. Crosstalk . . . . . . . . . . . . . . . . . . . . . . 13
6.1.5. Fiber Chromatic Dispersion . . . . . . . . . . . . . . 13
6.1.6. Polarization Mode Dispersion (PMD) . . . . . . . . . . 14
6.1.7. Polarization Dependent Loss (PDL) . . . . . . . . . . 14
6.2. Fiber Optical Non-Linearities . . . . . . . . . . . . . . 15
7. Optical Channel Estimation . . . . . . . . . . . . . . . . . . 15
7.1. Optical Power . . . . . . . . . . . . . . . . . . . . . . 16
7.2. Optical Signal to Noise Ratio . . . . . . . . . . . . . . 16
7.3. Residual Chromatic Dispersion . . . . . . . . . . . . . . 16
7.4. Residual Differtial Group Delay (DGD) . . . . . . . . . . 16
7.5. Q-Factor . . . . . . . . . . . . . . . . . . . . . . . . . 16
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17
9. Contributing Authors . . . . . . . . . . . . . . . . . . . . . 17
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
11. Security Considerations . . . . . . . . . . . . . . . . . . . 18
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
12.1. Normative References . . . . . . . . . . . . . . . . . . . 19
12.2. Informative References . . . . . . . . . . . . . . . . . . 19
Appendix A. ITU Parameters Missing Information . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
Intellectual Property and Copyright Statements . . . . . . . . . . 23
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1. Introduction
Generalized Multi-Protocol Label Switching (GMPLS), [RFC3945],
applied to wavelength switched optical networks (WSON) needs to
address specific issues related to optical technologies. The
framework document
[I-D.draft-ietf-ccamp-wavelength-switched-framework] address specific
issues related to transparent optical networks and to the routing and
wavelength assignment (RWA) problem. Optical impairments, however,
are out of the scope of that document.
One of the key aspects while dealing with transparent DWDM optical
networks are the physical impairments incurred by non-ideal optical
transmission media, and how they accumulate along an optical path.
Because of these impairments, even if there is physical connectivity
(fibers, wavelengths, and nodes) between the ingress and egress
nodes, there is no guarantee that the optical signal (light) reaches
the Egress node with acceptable signal quality in terms of Bit Error
Rate (BER) or other quality measures (e.g. Q-factor).
Scope of this framework document is to provide an overview of optical
impairments and parameters that have to be considered to assess the
feasibility of an optical path (lightpath) and provide any useful
information for an impairment-aware protocol implementation. For
this purpose a classification and properties of optical impairment
are provided along with some considerations related to control plane.
The detailed definitions of the physical effects with related
mathematical models are, in general, already defined within ITU-T and
this documents will refer to ITU-T documentation whenever is
possible. This document will only report additional information to
determine how this information must be integrated into the control
plane.
The document [RFC4054] is another reference targeting optical network
routing along with impairments and constrains. The goal there was to
provide a survey of all optical constrains along with possible
approaches. In this contribution the scope is much more limited, as
we only list optical impairments and their salient properties with
respect to control plane implementation.
2. Motivation for an Impairment-Aware Control Plane
GMPLS today is not aware of optical impairments in the DWDM network.
This implies that it cannot determine whether an end to end optical
path is feasible or not. While there has been much work on adding
wavelength constraints and other simple parameters to the control
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plane ([I-D.draft-ietf-ccamp-rwa-info] and
[I-D.bernstein-ccamp-wson-signaling]), this information alone does
not help determine the feasibility of the path. In fact, the more
impairments are taken into account, the more aggressive the network
can be in terms to reach, and the lower the cost of the solution,
since less regenerators are needed. Conversely, if a limited number
of optical impairments is taken into account, the network must allow
for larger margins to account for uncertainty in the missing
parameters, and will have to regenerate more frequently.
One question that arises is: why add such information into the
control plane and not deal with it through planning tools that today
are in charge of optical feasibility determination? The reasons for
this are multi-fold:
1. Issues with offline planning tools.
Planning tools are typically off line tools and do not have
accurate information as to the real impairments in the network.
This adds uncertainty and requires higher margins, resulting in
more regeneration and a higher cost solution. This problem is
exacerbated with higher bit rates (40G+) when more accurate
feasibility analysis may be needed due the higher transmission
challenges. Moreover, if no feasible optical path exists between
the endpoints, planning tools cannot identify the currently
available regenerators if they do not have real time data from
the network, and therefore require multiple tools (e.g., also an
EMS) to be reconciled manually to determine the final path.
2. Issues with online planning tools.
To address the above issues, the planning tool must be constantly
online, however this represents another point of failure in the
network and requires extra overhead, e.g., for backing it up.
This is not desirable for many operators. So can the planning
tool be integrated into the EMS, to reduce the overhead for a
standalone tool? In certain cases it can, but many operators may
prefer using a higher level generic management tool, which is not
provided by the DWDM layer vendor.
3. Issues with pre-determining all feasible paths a-priori.
While the above approaches assume on-demand computation of a
feasible path, a different way to tackle the problem is to pre-
define a small number of feasible paths between all required end-
points a-priori. In this case, all the control plane needs to do
is select one of the feasible paths and set up a connection.
This approach will work in small networks, but the number of
feasible paths that need to be maintained in a large network may
be prohibitive as it requires O(N^2) paths. Another issue with
this approach is that it reduces the flexibility of choosing a
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path as not all feasible paths can be defined a-priori (otherwise
the number of paths becomes exponential). This will create
artificial blocking, when an alternate non-blocking path may
exist. An even worse problem is that when the optical layer
evolves (e.g., a fiber added), all paths have to be re-computed
which makes this set of paths operationally very hard to
maintain.
In summary, while there are ways to provide a control plane for an
optical network that is not aware of impairments, such a solution has
various limitations that imply either high capital cost or high
operational cost neither of which are acceptable in many SP networks
that are under pressure to optimize both CAPEX and OPEX.
3. Overview of Optical Impairment Evaluation
3.1. Impairments Evaluation Flow
The aim of this section is to provide an overview of a typical
decision flow for the evaluation of the feasibility of an optical
path. The feasibility is evaluated given the transmitter and
receiver characteristics, the characteristics of intermediate nodes,
and the optical impairments along the path from the lightpath source
to its destination.
+--------+ +--------+ +--------+
| | | | | |
| Node #-----------| Node |-----------# Node |
| | Link | | Link | |
+--------+ +--------+ +--------+
TX RX
Interface Interface
Figure 1
Figure 1 represents DWDM transparent network can be represented by
nodes, links and interfaces.
o Node. It's an optical network element providing wavelength
switching and multiplexing functionality. The WSON framework
document [I-D.draft-ietf-ccamp-wavelength-switched-framework]
completely describes different node types with their
peculiarities. An optical node can perturb a lightpath quality by
adding impairments due to its internal components. A node may
also change the value of some parameters like the optical power.
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o Link. The fiber is the physical medium of a lightpath and it adds
impairments to the optical signals. In general it causes a
degradation in the signal quality.
o Interface. Optical Interfaces contains both a transmitter (TX-
Interface) and a receiver (RX-Interface). Depending on its
function different parameters must be considered.
The measurement of a BER or a Q-Factor completely describes the
quality of an optical signal. However in transparent optical
networks there is no direct measurement of such information. Very
often the only way is to provide measurement of other parameter's
(i.e. impairments) and provide an estimation of the signal quality.
Following Figure 1 the signal get generated at the TX-Interface with
certain characteristics. Let's consider, for purposes of
illustration, only a couple of simple parameters: the power of the
signal and the signal to noise ratio (OSNR). Along the lightpath,
the signal goes though fiber which reduces its power and introduces
impairments that can be viewed as additional noise added by the fiber
characteristics. Traversing an optical node the signal might be
amplified so it recover in term of power but this might cause
additional noise to the signal. Optical components (e.g. switches)
within the node are themselves source of additional noise for the
signal. When the signal reaches the RX-Interface at the destination
it must have sufficient power and sufficient OSNR to be used by the
interface. The acceptable level of the OSNR at the destination as
well as the minimum acceptable power might depend on the
characteristics of the receiver interface.
The next Figure 2 provides the functional overview of such evaluation
process.
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+-----------------+ +-----------------+ +------------+
| | | | | |
| Optical | | Optical | | Optical |
| Interface |------->| Path |------->| Channel |
| Characteristics | | Characteristics | | Estimation |
| | | | | |
+-----------------+ +-----------------+ +------------+
||
||
Estimation
||
\/
+------------+
| BER / |
| Q Factor |
+------------+
Figure 2
Starting from the left the Optical Interface Characteristics
represents where the optical signal is transmitted or received and
represent the properties at the end points of a lightpath. In
principle a path computation with no impairments (RWA only) might use
only a minimum set of these parameters to assess the interface
compatibility. If impairments are considered additional parameters
become interesting. Section 5 details the parameters related to the
interfaces.
Within the block Optical Path Characteristics we represents all kind
of impairments affecting a lightpath while it traverse the networks
through links and nodes. Section 6 reports a list of of such
effects.
When reaching the destination node, an impairment-aware constrained
path computation must take a decision if the lightpath is feasible or
not. We call this operation Optical Channel Estimation because the
real signal quality must be estimated given the impairments along the
path. Section 7 reports a set of parameters that can be used to
asses such signal quality.
3.2. Parameter Classification According to its Information Complexity
As discussed in the previous section, the process of determining the
feasibility of an optical path includes constraints, impairments and
other data that relates to the transmitter (such as modulation
format, optical power, supported wavelengths etc.), data that relates
to the optical nodes along the path (loss, gain etc.), information
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that relates to the fiber links between the nodes (fiber loss,
dispersion etc), information that relates to other paths that
interact with the new path, and finally the capabilities of the
receiver (power sensitivity, error correction etc.).
However, not all the data must be shared over the control plane as
is. We distinguish between the following cases:
o Some attributes can be kept local to the node. For example,
receiver attributes may be kept at the end node, if this node will
make the decision on path feasibility. We call these attributes
LOCAL in this document.
o Other attributes can be shared in a summarized form since the
impairment can be accumulated hop by hop. For example optical
power can be added or reduced starting from the power at the
transmitter as the signaling message traverses various gain or
loss elements along the path. These attributes are termed SCALAR
herein
o Some attributes need to be calculated based on all the values of
the specific attribute for all the hops along the path. Such
values cannot be summarized and need to accumulate in a vector
reflecting all the hops along the path. These attributes are
termed MULTI-HOP herein (these attributes are called non-linear in
the optical jargon)
o Some values are impacted not just by the new path under
consideration but also by other channels that interact with it
along its route. The most obvious example for such an attribute
is wavelength: the available wavelength is a function of other
channels at nodes and links along the path. These attributes are
termed MULTI-CHANNEL herein.
o Finally, some attributes can be computed accurately only if values
are known for every channel and every hop along the path. These
attributes are termed MULTI-HOP-CHANNEL herein.
The main contribution of this document is the classification of the
various attributes along these cases (LOCAL, SCALAR, MULTI-HOP,
MULTI-CHANNEL and MULTI-HOP-CHANNEL). We believe that this
information is crucial in order to determine the control plane
mechanism needed to carry each attribute. To illustrate this let's
assume a particular attribute must be carried in the path signaling
message. The attribute will accumulate as follows for the different
attribute classes.
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o LOCAL attributes will not be carried in the message
o SCALAR attributes will be carried via a single field, with agreed
upon rules on how to compute the next value based on the value
from the incoming message and the value for the next node and/or
link
o MULTI-HOP attributes must be carried in a vector that fills up in
serial fashion from hop to hop, in which the value for the n-th
hop is carried in v[n]
o MULTI-CHANNEL attributes must be carried in a vector that contains
one value per channel and in which all values are updated in
parallel at every hop (a good example for this is the wavelength
bitmap defined in [ref TBD], in which one bit represents the
summarized information on the availability of a specific
wavelength along the path), and
o MULTI-HOP-CHANNEL attributes requires a matrix m[h,w] with h rows
(one per hop) and w columns (one per wavelength), in which row
m[n,*] represents the values for all channels for the n-th hops
along the path
3.3. Additional Parameter Sharing Properties
For the usage in a control plane, other properties for each parameter
should also be considered. The association between each parameter
and a set of its inherent properties is defined within ITU documents.
For a control plane usage however the following value of each
property should help in deciding the most appropriate protocol to
convey the parameter within he control plane.
o Time Dependency.
If a parameter is static then we assume it does not change during
the life of the network. In case there is a time dependency a
minimum refresh rate shall be provided. This may help determine,
for example whether the parameter should be considered once during
connection setup, or whether the properties should be refreshed
(e.g. via an IGP or signaling).
o Wavelength Dependency.
A parameter can be wavelength dependent if, for each wavelenght it
might have different value. On the contrary a parameter might
have a single value for all the wavelengths.
o Value type (real, discrete, etc.).
This kind of information should help in encoding the information
within the protocol. Because some of the parameters represent
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physical quantities discrete values might be used within certain
approximations, in other cases real (e.g. IEEE 754 standard)
might be required.
o Does the variance of the parameter need to be specified with it
(so an error may be computed along with it)?
4. Control Plane Considerations
[Editorial Note: This section has to be filled up. Current text only
as initial placeholder].
The use of optical impairments as path constrains would imply the
control plane (GMPLS) to be aware of some additional information
coming from the optical layer. The control plane shall be able to
convey the proper information for an to allow the optical path
feasibility calculation.
o Routing.
Routing extensions to support GMPLS are defined in [RFC4202].
Needs additional information to defines routing metrics with a
certain level of optical-impairment awareness.
o Signaling.
Optical constrains can be verified along the signaling phase.
Different options might be foreseen:
* Full optical impairment verification. If the routing phase has
no awareness of any optical impairments, the signaling phase
can verify all of them.
* Partial optical impairment verification. It might be possible
that a certain set of optical impairment are verified during
the routing phase while the remaining set can be performed
during the signaling phase.
o PCE Architecture [RFC4655].
In case a PCE is used to support path computation, an additional
solution might foresee a PCE capable of supporting an impairment-
aware path computation. Need to evaluate the information to
convey to the PCE for such computation.
5. Optical Interface Characteristics
Placeholder for details optical parameters that specifically refer to
the physical interface. Their knowledge is necessary to evaluate the
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path feasibility in term of optical impairments.
They can be classified for what related to transmitter (e.g. bit
rate, modulation format, FEC etc.) and receiver (e.g. stability, CD
robustness) interface. The document [ITU.G698.2] provide a detailed
list of parameteres with their values.
6. Optical Path Characteristics
This section describes the optical impairments associated to the path
optical elements defined in Section 3. For each impairment, the
following information is provided:
o A minimum impairment description with a reference to the related
ITU-T document where available.
o the impairment classification and properties as defined within
Section 3.2 and Section 3.3.
o the impairment evaluation/handling techniques.
o the impairment impact on the channel quality estimation as defined
by parameters in Section 3.3.
6.1. Linear Impairments
6.1.1. Fiber Losses
It's the optical power loss caused by a fiber span [ITU-T ref ?].
It's measured as the ratio (dB) between the input and the output
optical power.
The loss introduced by each fiber span depends on:
o fiber attenuation coefficient (dB/Km)
o fiber length (Km). Note that this value is one of the link
characteristics defined in [RFC4209] (section 2.3.5).
The fiber losses directly affect the signal optical power at the
receiver interface: losses are accumulated along the path and
compensated by Optical Amplifiers.
The fiber loss can be computed from the fiber nominal values (length
and attenuation coefficient), measured by the node (using a probe
signal) or provisioned as a link parameter.
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The impairment is SCALAR, wavelength independent, time independed
(apart from fiber aging but only on long period of times).
6.1.2. Insertion Losses (Optical components looses)
It's the optical power loss caused by the optical elements crossed by
the channel in a node. It's measured as the ratio (dB) between the
optical power at the input and output port (see [ITU.G671] Section
3.2.9). The possible channel paths in a node are (see [ITU.G680]
Section 3.2.1):
o from the input port to the output port for through channels
o from the input port to the drop port for dropped channels
o form the add port to the output port for added channels
This classification applies to any type of node: PXC, ROADM, etc.
The loss value for each path is dependent on the internal node
architecture and vendor device characteristics and could be different
for each different port pair.
The insertion losses directly affect the signal optical power at the
receiver interface: losses are accumulated along the path and
compensated by Optical Amplifiers.
The impairment is SCALAR, wavelength independent and time
independent.
6.1.3. Amplifier Spontaneous Emission (ASE)
It's the noise introduced by the node optical amplifiers spontaneous
emission that propagates with the amplified signal and is further
amplified along the path (see [ITU.G663] Section II.6.1). The
impairment is considered an OSNR contribution (dB) and directly
affects the signal SNR at the receiver interface (see [ITU.G663]
Section II.6.2).
The ASE noise contribution can be evaluated from the amplifier
parameters and the input signal characteristics (signal optical
power).
The impairment is SCALAR and wavelength independent. Regarding time-
dependency ASE depends on amplifier gain and this may change
depending on network stability.
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6.1.4. Crosstalk
It's the effect of signal power leakage from other channels inside
the node optical elements (multiplexer, de-multiplexer, optical
switches, etc.) and is measured as the ratio of the disturbing power
and the signal power (dB) (see [ITU.G692] Section 6.7.1).
The crosstalk value is dependent on the device characteristics and
the ratio of the optical power of involved channels. The device
characteristics can be considered constant in time, while the
channels configuration depends on the network status.
The crosstalk impairment affects the signal SNR and optical power at
the receiver interface: the accumulated crosstalk can be converted to
an SNR and power penalty.
The impairment is MULTI-CHANNEL (depends on existings active
channels) and wavelength independent.
6.1.5. Fiber Chromatic Dispersion
It's the degradation of the optical signal due to the different
propagation delay of the various spectral components causing the
broadening of the pulse and is defined by the slope of the delay with
respect to the wavelength (ps/nm) (see [ITU.G650] Section 1.5). The
effect can be compensated by means of fiber spans with an inverse
dispersion (DCF - Dispersion Compensation Fiber) usually deployed in
modules with pre-configured characteristics (DCU - Dispersion
Compensation Unit).
The chromatic dispersion introduced by each fiber span is dependent
on:
o fiber chromatic dispersion coefficient (ps/(nm * Km)) This
coefficient depends on the channel wavelength (it's usually
defined as the value for a reference wavelength and a slope
coefficient).
o fiber length (Km).
The chromatic dispersion of each fiber span can be evaluated from the
fiber characteristics and the channel wavelength.
The chromatic dispersion accumulates along the path compensated by
the DCU modules obtaining a residual chromatic dispersion at the
receiver interface the affects the signal SNR.
The impairment is SCALAR, Wavelength-Dependent and time-independent
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(apart from ageing effects over long period of times).
6.1.6. Polarization Mode Dispersion (PMD)
It's the degradation of the optical signal due to the different
propagation delay of the two principal states of polarization (DGD -
Differential Group Delay) causing the pulse distortion in shape and
width (see [ITU.G663] Section II.4.1 and [ITU.G661] Section 5.1.36)
and is measured in ps.
The PMD introduced by a fiber span depends on:
o the square root of the fiber length (Km)
o the fiber PMD coefficient (ps/sqrt(Km))
The PMD introduced by other components (e.g. amplifiers, DCU modules,
etc.) is provided as a device parameter.
The PMD coefficient may depend on temperature and operating
conditions and can be very variable.
The PMD can be evaluated from the fiber or device parameters; due to
the high variability, an upper bound value is usually considered.
The PMD accumulates along the path and affects the signal SNR at the
receiver interface.
The impairment is SCALAR.
6.1.7. Polarization Dependent Loss (PDL)
It's the difference in the signal power among different polarization
states caused by the medium irregularities (see [ITU.G663] Section
II.4.1 and [ITU.G671] Section 3.2.23) and is defined as the ratio
(dB) of the maximum and minimum peak transmission power with respect
to all polarization states. On amplifiers the same effect is called
Polarization Dependent Gain (PDG) (see [ITU.G661] Section 5.1.11).
The PDL introduced by a device appears as a random variation of the
signal power and can be managed as a statistical value (function of
the number of optical elements traversed) (see [ITU.G680] Section
9.3.2).
The PDL accumulates along the path and affects the signal SNR and
power at the receiver interface.
The impairment is and SCALAR wavelength independent.
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6.2. Fiber Optical Non-Linearities
In this section provide information about optical impairments called
Non-Linear. In general they will need a control plane able to
exploit multi-channel and multi-hop attibutes. Due to this
complexity leave this placeholder for further updates.
o Self Phase Modulation (SPM) (see [ITU.G663] Section II.3.1).
It's the degradation of the optical signal due to the time varying
fiber refraction index (the higher intensity portion of the pulse
is subject to a higher refractive index than the lower intensity
portion) causing the pulse broadening in the frequency domain.
o Cross Phase Modulation (XPM) (see [ITU.G663] Section II.3.3).
It's the degradation of the optical signal due to the time varying
fiber refraction index induced by the adjacent channels intensity
fluctuations.
o Four Wave Mixing (FWM) (see [ITU.G663] Section II.3.5).
It's the degradation of the optical signal due to the interaction
with the spurious optical wavelengths generated by three optical
channels that co-propagate inside a fiber.
o Stimulated Brillouin Scattering (SBS) (see [ITU.G663] Section
II.3.6).
It's the degradation of the optical signal due to the signal
scattering caused by the fiber medium when the input power is
above the SBS threshold.
o Stimulated Raman Scattering (SRS) (see [ITU.G663] Section II.3.6).
It's the degradation of the optical signal due to the signal
scattering caused by the fiber medium when the input power is
above the SBS threshold.
7. Optical Channel Estimation
The lightpath quality defines the ability of the receiver to
correctly decode the signal within a defined error rate (BER). The
BER depends on the signal encoding (e.g. FEC, modulation format,
etc.), the signal optical characteristics (optical power, OSNR, etc.)
and the receiver characteristics.
The goal of this section is to define the set of parameters that need
to be evaluated in order to get a direct estimation of the lightpath
quality at the receiver node; all the above described impairments can
be considered as an effect on these parameters.
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These optical parameters shall be considered together with their
statistical values: average and variance. This information helps in
understanding the error accumulated along with parameter evaluation.
7.1. Optical Power
The signal optical power must be within the dynamic range of the
receiver and above the receiver minimum power (receiver sensitivity).
The receiver minimum power is a receiver characteristic and depends
also on the signal characteristics as the used forward error
correction (FEC), [others ? mod-format ?]
[[Q3: Need to add a formal definition with the ITU reference --GM]]
7.2. Optical Signal to Noise Ratio
The optical signal-to-noise ratio (OSNR) is the ratio of the signal
power in the wanted channel to the highest noise power density
(referred to 0.1 nm) within the channel frequency range (see
[ITU.G661] Section 5.1.19). The signal OSNR must be above a receiver
minimum threshold (receiver sensitivity); the threshold is a receiver
characteristic and depends also on the signal characteristics ([which
ones ?]).
7.3. Residual Chromatic Dispersion
The residual chromatic dispersion is the signal chromatic dispersion
at the receiver interface (the accumulated and compensated dispersion
along). The signal dispersion value must be within a receiver
threshold for the signal to be correctly decoded.
The chromatic dispersion effects on the signal quality can be managed
as an OSNR or/and an optical power penalty.
7.4. Residual Differtial Group Delay (DGD)
[Editoral Note: TO BE FILLED]
7.5. Q-Factor
The Q-factor is a synthetic measure of the signal quality defined as
a function of the mean values of the '0' and '1' signal levels and
their standard deviation (see [ITU.G976] Section A.1).
The Q-factor is dependent on the signal OSNR and is directly related
to the BER.
The evaluation of the Q-factory requires the estimation of the signal
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waveform at the receiver interface.
8. Acknowledgements
Authors would like to thanks Adrian Farrel for all suggestions and
reviews of this work.
9. Contributing Authors
This document was the collective work of several authors. The text
and content of this document was contributed by the editors and the
co-authors listed below (the contact information for the editors
appears in appropriate section and is not repeated below):
Gabriele Maria Galimberti
Cisco Systems
via Philips 12
Monza 20052
Italy
Email: ggalimbe@cisco.com
Domenico La Fauci Maurizio Gazzola
Cisco Systems Cisco Systems
via Philips 12 via Philips 12
Monza 20052 Monza 20052
Italy Italy
Email: dlafauci@cisco.com Email: mgazzola@cisco.com
Roberto Cassata Zafar Ali
Cisco Systems Cisco Systems
via Philips 12 3000 Innovation Drive
Monza 20052 Kanata , ONTARIO K2K 3E8
Italy Canada
Email: rcassata@cisco.com Email: zali@cisco.com
Elio Salvadori Yabin Ye
CREATE-NET CREATE-NET
via alla Cascata 56 C, Povo via alla Cascata 56 C, Povo
Trento 38100 Trento 38100
Italy Italy
Email: elio.salvadori@create-net.org Email: yabin.ye@create-net.org
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Chava Vijaya Saradhi
CREATE-NET
via alla Cascata 56 C, Povo
Trento 38100
Italy
Email: saradhi.chava@create-net.org
Ernesto Damiani
University of Milan, Department of Information Technology
Via Bramante 65, 26013 Crema (CR)
Italy
Email: damiani@dti.unimi.it
Valerio Bellandi
University of Milan, Department of Information Technology
Via Bramante 65, 26013 Crema (CR)
Italy
Email: bellandi@dti.unimi.it
Marco Anisetti
University of Milan, Department of Information Technology
Via Bramante 65, 26013 Crema (CR)
Italy
Email: anisetti@dti.unimi.it
10. IANA Considerations
This memo includes no request to IANA.
11. Security Considerations
All drafts are required to have a security considerations section.
See RFC 3552 [RFC3552] for a guide.
12. References
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12.1. Normative References
[I-D.ietf-ccamp-wavelength-switched-framework]
Bernstein, G., Lee, Y., and W. Imajuku, "Framework for
GMPLS and PCE Control of Wavelength Switched Optical
Networks (WSON)",
draft-ietf-ccamp-wavelength-switched-framework-00 (work in
progress), May 2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching
(GMPLS) Architecture", RFC 3945, October 2004.
[RFC4202] Kompella, K. and Y. Rekhter, "Routing Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4202, October 2005.
[RFC4209] Fredette, A. and J. Lang, "Link Management Protocol (LMP)
for Dense Wavelength Division Multiplexing (DWDM) Optical
Line Systems", RFC 4209, October 2005.
12.2. Informative References
[I-D.bernstein-ccamp-wson-signaling]
Bernstein, G., "Signaling Extensions for Wavelength
Switched Optical Networks",
draft-bernstein-ccamp-wson-signaling-02 (work in
progress), July 2008.
[I-D.ietf-ccamp-rwa-info]
Bernstein, G., Lee, Y., Li, D., and W. Imajuku, "Routing
and Wavelength Assignment Information Model for Wavelength
Switched Optical Networks", draft-ietf-ccamp-rwa-info-00
(work in progress), August 2008.
[I-D.narten-iana-considerations-rfc2434bis]
Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs",
draft-narten-iana-considerations-rfc2434bis-09 (work in
progress), March 2008.
[ITU.G650]
International Telecommunications Union, "Definition and
test methods for the relevant parameters of single-mode
fibres", ITU-T Recommendation G.650, March 1993.
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[ITU.G661]
International Telecommunications Union, "Definitions and
test methods for the relevant generic parameters of
optical amplifier devices and subsystems", ITU-
T Recommendation G.661, July 2007.
[ITU.G663]
International Telecommunications Union, "Application
related aspects of optical amplifier devices and sub-
systems", ITU-T Recommendation G.663, April 2000.
[ITU.G671]
International Telecommunications Union, "Transmission
characteristics of optical components and subsystems",
ITU-T Recommendation G.671, Jannuary 2005.
[ITU.G680]
International Telecommunications Union, "Physical transfer
functions of optical network elements", ITU-
T Recommendation G.680, July 2007.
[ITU.G692]
International Telecommunications Union, "Optical
interfaces for multichannel systems with optical
amplifiers", ITU-T Recommendation G.692, October 1998.
[ITU.G697]
International Telecommunications Union, "Optical
monitoring for DWDM systems", ITU-T Recommendation G.697,
June 2004.
[ITU.G698.2]
International Telecommunications Union, "Amplified
multichannel DWDM applications with single channel optical
interfaces", ITU-T Recommendation G.697, July 2007.
[ITU.G976]
International Telecommunications Union, "Test methods
applicable to optical fibre submarine cable systems", ITU-
T Recommendation G.976, July 2007.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
July 2003.
[RFC4054] Strand, J. and A. Chiu, "Impairments and Other Constraints
on Optical Layer Routing", RFC 4054, May 2005.
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[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006.
Appendix A. ITU Parameters Missing Information
In this appendix we need to collects all information about optical
parameters that need to be verified with / requested from ITU.
Authors' Addresses
Giovanni Martinelli (editor)
Cisco Systems
via Philips 12
Monza 20052
Italy
Email: giomarti@cisco.com
David Bianchi (editor)
Cisco Systems
via Philips 12
Monza 20052
Italy
Email: davbianc@cisco.com
Alberto Tanzi (editor)
Cisco Systems
via Philips 12
Monza 20052
Italy
Email: altanzi@cisco.com
Ori Gerstel (editor)
Cisco Systems
3500 Cisco Way
San Jose CA 95134
United States
Email: ogerstel@cisco.com
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Andrea Zanardi (editor)
CREATE-NET
via alla Cascata 56 C, Povo
Trento 38100
Italy
Email: andrea.zanardi@create-net.org
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