Network Working Group Y. Lee (ed.)
Internet Draft Huawei
Intended status: Informational G. Bernstein (ed.)
Expires: April 2011 Grotto Networking
Wataru Imajuku
NTT
October 8, 2010
Framework for GMPLS and PCE Control of Wavelength Switched Optical
Networks (WSON)
draft-ietf-ccamp-rwa-wson-framework-07.txt
Abstract
This document provides a framework for applying Generalized Multi-
Protocol Label Switching (GMPLS) and the Path Computation Element
(PCE) architecture to the control of wavelength switched optical
networks (WSON). In particular, it examines the Routing and
Wavelength Assignment (RWA) problem.
This document focuses on topological elements and path selection
constraints that are common across different WSON environments as
such it does not address optical impairments in any depth.
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Table of Contents
1. Introduction..................................................4
2. Terminology....................................................4
3. Wavelength Switched Optical Networks...........................6
3.1. WDM and CWDM Links........................................6
3.2. Optical Transmitters and Receivers........................8
3.3. Optical Signals in WSONs..................................9
3.3.1. Optical Tributary Signals...........................10
3.3.2. WSON Signal Characteristics.........................10
3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs............11
3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs.......11
3.4.2. Splitters...........................................14
3.4.3. Combiners...........................................15
3.4.4. Fixed Optical Add/Drop Multiplexers.................15
3.5. Electro-Optical Systems..................................16
3.5.1. Regenerators........................................16
3.5.2. OEO Switches........................................19
3.6. Wavelength Converters....................................19
3.6.1. Wavelength Converter Pool Modeling..................21
3.7. Characterizing Electro-Optical Network Elements..........25
3.7.1. Input Constraints...................................26
3.7.2. Output Constraints..................................26
3.7.3. Processing Capabilities.............................27
4. Routing and Wavelength Assignment and the Control Plane.......28
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4.1. Architectural Approaches to RWA..........................28
4.1.1. Combined RWA (R&WA).................................29
4.1.2. Separated R and WA (R+WA)...........................29
4.1.3. Routing and Distributed WA (R+DWA)..................30
4.2. Conveying information needed by RWA......................30
5. Modeling Examples and Control Plane Use Cases.................31
5.1. Network Modeling for GMPLS/PCE Control...................31
5.1.1. Describing the WSON nodes...........................32
5.1.2. Describing the links................................34
5.2. RWA Path Computation and Establishment...................35
5.3. Resource Optimization....................................36
5.4. Support for Rerouting....................................37
5.5. Electro-Optical Networking Scenarios.....................37
5.5.1. Fixed Regeneration Points...........................37
5.5.2. Shared Regeneration Pools...........................38
5.5.3. Reconfigurable Regenerators.........................38
5.5.4. Relation to Translucent Networks....................38
6. GMPLS and PCE Implications....................................39
6.1. Implications for GMPLS signaling.........................39
6.1.1. Identifying Wavelengths and Signals.................39
6.1.2. WSON Signals and Network Element Processing.........40
6.1.3. Combined RWA/Separate Routing WA support............40
6.1.4. Distributed Wavelength Assignment: Unidirectional, No
Converters.................................................41
6.1.5. Distributed Wavelength Assignment: Unidirectional,
Limited Converters.........................................41
6.1.6. Distributed Wavelength Assignment: Bidirectional, No
Converters.................................................41
6.2. Implications for GMPLS Routing...........................42
6.2.1. Electro-Optical Element Signal Compatibility........42
6.2.2. Wavelength-Specific Availability Information........43
6.2.3. WSON Routing Information Summary....................43
6.3. Optical Path Computation and Implications for PCE........45
6.3.1. Lightpath Constraints and Characteristics...........45
6.3.2. Electro-Optical Element Signal Compatibility........46
6.3.3. Discovery of RWA Capable PCEs.......................46
7. Security Considerations.......................................47
8. IANA Considerations...........................................47
9. Acknowledgments...............................................47
10. References...................................................48
10.1. Normative References....................................48
10.2. Informative References..................................49
11. Contributors.................................................51
Author's Addresses...............................................52
Intellectual Property Statement..................................52
Disclaimer of Validity...........................................53
12. Appendix A Revision History..................................53
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1. Introduction
Wavelength Switched Optical Networks (WSONs) are constructed from
subsystems that include Wavelength Division Multiplexed (WDM) links,
tunable transmitters and receivers, Reconfigurable Optical Add/Drop
Multiplexers (ROADM), wavelength converters, and electro-optical
network elements. A WSON is a WDM-based optical network in which
switching is performed selectively based on the center wavelength of
an optical signal.
In order to provision an optical connection (a lightpath) through a
WSON certain path continuity and resource availability constraints
must be met to determine viable and optimal paths through the
network. The generic problem of determining such paths is known as
the Routing and Wavelength Assignment (RWA) problem.
Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] includes
a set of control plane protocols that can be used to operate data
networks ranging from packet switch capable networks, through those
networks that use time division multiplexing, to WDM networks. The
Path Computation Element (PCE) architecture [RFC4655] defines
functional components that can be used to compute and suggest
appropriate paths in connection-oriented traffic-engineered networks.
This document provides a framework for applying GMPLS protocols and
the PCE architecture to the control and operation of WSONs. To aid
in this process this document also provides an overview of the
subsystems and processes that comprise WSONs, and describes the RWA
problem so that the information requirements, both static and
dynamic, can be identified to explain how the information can be
modeled for use by GMPLS and PCE systems. This work will facilitate
the development of protocol solution models and protocol extensions
within the GMPLS and PCE protocol families.
Note that this document focuses on the generic properties of links,
switches and path selection constraints that occur in WSONs.
Different WSONs such as access, metro, and long haul may apply
different techniques for dealing with optical impairments hence this
document does not address optical impairments in any depth. See
[WSON-Imp] for more information on optical impairments and GMPLS.
2. Terminology
Add/Drop Multiplexers (ADM): An optical device used in WDM networks
composed of one or more line side ports and typically many tributary
ports.
CWDM: Coarse Wavelength Division Multiplexing.
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DWDM: Dense Wavelength Division Multiplexing.
Degree: The degree of an optical device (e.g., ROADM) is given by a
count of its line side ports.
Drop and continue: A simple multi-cast feature of some ADM where a
selected wavelength can be switched out of both a tributary (drop)
port and a line side port.
FOADM: Fixed Optical Add/Drop Multiplexer.
GMPLS: Generalized Multi-Protocol Label Switching.
Line side: In WDM system line side ports and links typically can
carry the full multiplex of wavelength signals, as compared to
tributary (add or drop ports) that typically carry a few (typically
one) wavelength signals.
OXC: Optical cross connect. An optical switching element in which a
signal on any input port can reach any output port.
PCC: Path Computation Client. Any client application requesting a
path computation to be performed by the Path Computation Element.
PCE: Path Computation Element. An entity (component, application, or
network node) that is capable of computing a network path or route
based on a network graph and applying computational constraints.
PCEP: PCE Communication Protocol. The communication protocol between
a Path Computation Client and Path Computation Element.
ROADM: Reconfigurable Optical Add/Drop Multiplexer. An wavelength
selective switching element featuring input and output line side
ports as well as add/drop side ports.
RWA: Routing and Wavelength Assignment.
Transparent Network: A wavelength switched optical network that does
not contain regenerators or wavelength converters.
Translucent Network: A wavelength switched optical network that is
predominantly transparent but may also contain limited numbers of
regenerators and/or wavelength converters.
Tributary: A link or port on a WDM system that can carry
significantly less than the full multiplex of wavelength signals
found on the line side links/ports. Typical tributary ports are the
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add and drop ports on an ADM and these support only a single
wavelength channel.
Wavelength Conversion/Converters: The process of converting an
information bearing optical signal centered at a given wavelength to
one with "equivalent" content centered at a different wavelength.
Wavelength conversion can be implemented via an optical-electronic-
optical (OEO) process or via a strictly optical process.
WDM: Wavelength Division Multiplexing.
Wavelength Switched Optical Networks (WSONs): WDM based optical
networks in which switching is performed selectively based on the
center wavelength of an optical signal.
3. Wavelength Switched Optical Networks
WSONs range in size from continent spanning long haul networks, to
metropolitan networks, to residential access networks. In all these
cases, the main concern is those properties that constrain the choice
of wavelengths that can be used, i.e., restrict the wavelength label
set, impact the path selection process, and limit the topological
connectivity. In addition, if electro-optical network elements are
used in the WSON, additional compatibility constraints may be imposed
by the network elements on various optical signal parameters. The
subsequent sections review and model some of the major subsystems of
a WSON with an emphasis on those aspects that are of relevance to the
control plane. In particular, WDM links, optical transmitters,
ROADMs, and wavelength converters are examined.
3.1. WDM and CWDM Links
WDM and CWDM links run over optical fibers, and optical fibers come
in a wide range of types that tend to be optimized for various
applications examples include access networks, metro, long haul, and
submarine links. International Telecommunication Union -
Telecommunication Standardization Sector (ITU-T) standards exist for
various types of fibers. Although fiber can be categorized into
Single mode fibers (SMF) and Multi-mode fibers (MMF), the latter are
typically used for short-reach campus and premise applications. SMF
are used for longer-reach applications and therefore are the primary
concern of this document. The following SMF fiber types are typically
encountered in optical networks:
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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 |
------------------------------------------------------------
Typically WDM links operate in one or more of the approximately
defined optical bands [G.Sup39]:
Band Range (nm) Common Name Raw Bandwidth (THz)
O-band 1260-1360 Original 17.5
E-band 1360-1460 Extended 15.1
S-band 1460-1530 Short 9.4
C-band 1530-1565 Conventional 4.4
L-band 1565-1625 Long 7.1
U-band 1625-1675 Ultra-long 5.5
Not all of a band may be usable, for example in many fibers that
support E-band there is significant attenuation due to a water
absorption peak at 1383nm. Hence a discontinuous acceptable
wavelength range for a particular link may be needed and is modeled.
Also some systems will utilize more than one band. This is
particularly true for CWDM systems.
Current technology subdivides the bandwidth capacity of fibers into
distinct channels based on either wavelength or frequency. There are
two standards covering wavelengths and channel spacing. ITU-T
Recommendation G.694.1, Spectral grids for WDM applications: DWDM
frequency grid [G.694.1] describes a DWDM grid defined in terms of
frequency grids of 12.5GHz, 25GHz, 50GHz, 100GHz, and other multiples
of 100GHz around a 193.1THz center frequency. At the narrowest
channel spacing this provides less than 4800 channels across the O
through U bands. ITU-T Recommendation G.694.2, Spectral grids for WDM
applications: CWDM wavelength grid [G.694.2] describes a CWDM grid
defined in terms of wavelength increments of 20nm running from 1271nm
to 1611nm for 18 or so channels. The number of channels is
significantly smaller than the 32 bit GMPLS label space defined for
GMPLS, see [RFC3471]. A label representation for these ITU-T grids
is given in [Otani] and provides a common label format to be used in
signaling lightpaths. Further, these ITU-T grid based labels can also
be used to describe WDM links, ROADM ports, and wavelength converters
for the purposes of path selection.
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Many WDM links are designed to take advantage of particular fiber
characteristics or to try to avoid undesirable properties. For
example dispersion shifted SMF [G.653] was originally designed for
good long distance performance in single channel systems, however
putting WDM over this type of fiber requires significant system
engineering and a fairly limited range of wavelengths. Hence the
following information is needed as parameters to perform basic,
impairment unaware, modeling of a WDM link:
o Wavelength range(s): Given a mapping between labels and the ITU-T
grids each range could be expressed in terms of a tuple (lambda1,
lambda2) or (freq1, freq1) where the lambdas or frequencies can be
represented by 32 bit integers.
o Channel spacing: Currently there are five channel spacings used in
DWDM systems and a single channel spacing defined for CWDM
systems.
For a particular link this information is relatively static, as
changes to these properties generally require hardware upgrades. Such
information may be used locally during wavelength assignment via
signaling, similar to label restrictions in MPLS or used by a PCE in
solving the combined RWA problem.
3.2. Optical Transmitters and Receivers
WDM optical systems make use of optical transmitters and receivers
utilizing different wavelengths (frequencies). Some transmitters are
manufactured for a specific wavelength of operation, that is, the
manufactured frequency cannot be changed. First introduced to reduce
inventory costs, tunable optical transmitters and receivers are
deployed in some systems, and allow flexibility in the wavelength
used for optical transmission/reception. Such tunable optics aid in
path selection.
Fundamental modeling parameters from the control plane perspective
optical transmitters and receivers are:
o Tunable: Do the transmitter and receivers operate at variable or
fixed wavelength.
o Tuning range: This is the frequency or wavelength range over which
the optics can be tuned. With the fixed mapping of labels to
lambdas as proposed in [Otani] this can be expressed as a tuple
(lambda1, lambda2) or (freq1, freq2) where lambda1 and lambda2 or
freq1 and freq2 are the labels representing the lower and upper
bounds in wavelength.
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o Tuning time: Tuning times highly depend on the technology used.
Thermal drift based tuning may take seconds to stabilize, whilst
electronic tuning might provide sub-ms tuning times. Depending on
the application this might be critical. For example, thermal drift
might not be usable for fast protection applications.
o Spectral characteristics and stability: The spectral shape of a
laser's emissions and its frequency stability put limits on
various properties of the overall WDM system. One relatively easy
to characterize constraint is the closest channel spacing with
which the transmitter can be used.
Note that ITU-T recommendations specify many aspects of an optical
transmitter. Many of these parameters, such as spectral
characteristics and stability, are used in the design of WDM
subsystems consisting of transmitters, WDM links and receivers
however they do not furnish additional information that will
influence the Label Switched Path (LSP) provisioning in a properly
designed system.
Also note that optical components can degrade and fail over time.
This presents the possibility of the failure of a LSP (lightpath)
without either a node or link failure. Hence, additional mechanisms
may be necessary to detect and differentiate this failure from the
others, e.g., one doesn't not want to initiate mesh restoration if
the source transmitter has failed, since the optical transmitter will
still be failed on the alternate optical path.
3.3. Optical Signals in WSONs
In WSONs the fundamental unit of switching is intuitively that of a
"wavelength". The transmitters and receivers in these networks will
deal with one wavelength at a time, while the switching systems
themselves can deal with multiple wavelengths at a time. Hence
multichannel DWDM networks with single channel interfaces are the
prime focus of this document general concern as opposed to multi-
channel interfaces. Interfaces of this type are defined in ITU-T
recommendations [G.698.1] and [G.698.2]. Key non-impairment related
parameters defined in [G.698.1] and [G.698.2] are:
(a) Minimum channel spacing (GHz)
(b) Minimum and maximum central frequency
(c) Bit-rate/Line coding (modulation) of optical tributary signals
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For the purposes of modeling the WSON in the control plane, (a) and
(b) are considered as properties of the link and restrictions on the
GMPLS labels while (c) is a property of the "signal".
3.3.1. Optical Tributary Signals
The optical interface specifications [G.698.1], [G.698.2], and
[G.959.1] all use the concept of an optical tributary signal which is
defined as "a single channel signal that is placed within an optical
channel for transport across the optical network". Note the use of
the qualifier "tributary" to indicate that this is a single channel
entity and not a multichannel optical signal.
There are currently a number of different types of optical tributary
signals, which are known as "optical tributary signal classes". These
are currently characterized by a modulation format and bit rate range
[G.959.1]:
(a) Optical tributary signal class NRZ 1.25G
(b) Optical tributary signal class NRZ 2.5G
(c) Optical tributary signal class NRZ 10G
(d) Optical tributary signal class NRZ 40G
(e) Optical tributary signal class RZ 40G
Note that with advances in technology more optical tributary signal
classes may be added and that this is currently an active area for
development and standardization. In particular at the 40G rate there
are a number of non-standardized advanced modulation formats that
have seen significant deployment including Differential Phase Shift
Keying (DPSK) and Phase Shaped Binary Transmission (PSBT).
According to [G.698.2] it is important to fully specify the bit rate
of the optical tributary signal. Hence it is seen that modulation
format (optical tributary signal class) and bit rate are key
parameters in characterizing the optical tributary signal.
3.3.2. WSON Signal Characteristics
An optical tributary signal defined in ITU-T [G.698.1] and [G.698.2]
is referred to as the "signal" in this document. This corresponds to
the "lambda" LSP in GMPLS. For signal compatibility purposes with
electro-optical network elements, the following signal
characteristics are considered:
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1. Optical tributary signal class (modulation format).
2. FEC: whether forward error correction is used in the digital stream
and what type of error correcting code is used.
3. Center frequency (wavelength).
4. Bit rate.
5. G-PID: general protocol identifier for the information format.
The first three items on this list can change as a WSON signal
traverses the optical network with elements that include
regenerators, Optical-to-Electrical (OEO) switches, or wavelength
converters.
Bit rate and G-PID would not change since they describe the encoded
bit stream. A set of G-PID values is already defined for lambda
switching in [RFC3471] and [RFC4328].
Note that a number of non-standard or proprietary modulation formats
and FEC codes are commonly used in WSONs. For some digital bit
streams the presence of Forwarding Equivalence Class (FEC) can be
detected, e.g., in [G.707] this is indicated in the signal itself via
the FEC Status Indication (FSI) byte, while in [G.709] this can be
inferred from whether the FEC field of the Optical Channel Transport
Unit-k (OTUk) is all zeros or not.
3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs
Definitions of various optical devices such as ROADMs, Optical Cross-
connects (OXCs), splitters, combiners and Fixed Optical Add-Drop
Multiplexers (FOADMs) and their parameters can be found in [G.671].
Only a subset of these and their non-impairment related properties
are considered in the following sections.
3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs
ROADMs are available in different forms and technologies. This is a
key technology that allows wavelength based optical switching. A
classic degree-2 ROADM is shown in Figure 1.
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Line side input +---------------------+ Line side output
--->| |--->
| |
| ROADM |
| |
| |
+---------------------+
| | | | o o o o
| | | | | | | |
O O O O | | | |
Tributary Side: Drop (output) Add (input)
Figure 1. Degree-2 ROADM
The key feature across all ROADM types is their highly asymmetric
switching capability. In the ROADM of Figure 1, signals introduced
via the add ports can only be sent on the line side output port and
not on any of the drop ports. The term "degree" is used to refer to
the number of line side ports (input and output) of a ROADM, and does
not include the number of "add" or "drop" ports. The add and drop
ports are sometimes also called tributary ports. As the degree of the
ROADM increases beyond two it can have properties of both a switch
(OXC) and a multiplexer and hence it is necessary to know the
switched connectivity offered by such a network element to
effectively utilize it. A straightforward way to represent this is
via a "switched connectivity" matrix A where Amn = 0 or 1, depending
upon whether a wavelength on input port m can be connected to output
port n [Imajuku]. For the ROADM shown in Figure 1 the switched
connectivity matrix can be expressed as:
Input Output Port
Port #1 #2 #3 #4 #5
--------------
#1: 1 1 1 1 1
#2 1 0 0 0 0
A = #3 1 0 0 0 0
#4 1 0 0 0 0
#5 1 0 0 0 0
Where input ports 2-5 are add ports, output ports 2-5 are drop ports
and input port #1 and output port #1 are the line side (WDM) ports.
For ROADMs, this matrix will be very sparse, and for OXCs the matrix
will be very dense, compact encodings and examples, including high
degree ROADMs/OXCs, are given in [WSON-Encode]. A degree-4 ROADM is
shown in Figure 2.
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+-----------------------+
Line side-1 --->| |---> Line side-2
Input (I1) | | Output (E2)
Line side-1 <---| |<--- Line side-2
Output (E1) | | Input (I2)
| ROADM |
Line side-3 --->| |---> Line side-4
Input (I3) | | Output (E4)
Line side-3 <---| |<--- Line side-4
Output (E3) | | Input (I4)
| |
+-----------------------+
| O | O | O | O
| | | | | | | |
O | O | O | O |
Tributary Side: E5 I5 E6 I6 E7 I7 E8 I8
Figure 2. Degree-4 ROADM
Note that this example is 4-degree example with one (potentially
multi-channel) add/drop per line side port.
Note also that the connectivity constraints for typical ROADM designs
are "bidirectional", i.e. if input port X can be connected to output
port Y, typically input port Y can be connected to output port X,
assuming the numbering is done in such a way that input X and output
X correspond to the same line side direction or the same add/drop
port. This makes the connectivity matrix symmetrical as shown below.
Input Output Port
Port E1 E2 E3 E4 E5 E6 E7 E8
-----------------------
I1 0 1 1 1 0 1 0 0
I2 1 0 1 1 0 0 1 0
A = I3 1 1 0 1 1 0 0 0
I4 1 1 1 0 0 0 0 1
I5 0 0 1 0 0 0 0 0
I6 1 0 0 0 0 0 0 0
I7 0 1 0 0 0 0 0 0
I8 0 0 0 1 0 0 0 0
Where I5/E5 are add/drop ports to/from line side-3, I6/E6 are
add/drop ports to/from line side-1, I7/E7 are add/drop ports to/from
line side-2 and I8/E8 are add/drop ports to/from line side-4. Note
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that diagonal elements are zero since loopback is not supported in
the example. If ports support loopback, diagonal elements would be
set to one.
Additional constraints may also apply to the various ports in a
ROADM/OXC. The following restrictions and terms may be used:
Colored port: an input or more typically an output (drop) port
restricted to a single channel of fixed wavelength.
Colorless port: an input or more typically an output (drop) port
restricted to a single channel of arbitrary wavelength.
In general a port on a ROADM could have any of the following
wavelength restrictions:
o Multiple wavelengths, full range port.
o Single wavelength, full range port.
o Single wavelength, fixed lambda port.
o Multiple wavelengths, reduced range port (for example wave band
switching).
To model these restrictions it is necessary to have two pieces of
information for each port: (a) number of wavelengths, (b) wavelength
range and spacing. Note that this information is relatively static.
More complicated wavelength constraints are modeled in [WSON-Info].
3.4.2. Splitters
An optical splitter consists of a single input port and two or more
output ports. The input optical signaled is essentially copied (with
power loss) to all output ports.
Using the modeling notions of Section 3.4.1. (Reconfigurable Add/Drop
Multiplexers and OXCs) the input and output ports of a splitter would
have the same wavelength restrictions. In addition a splitter is
modeled by a connectivity matrix Amn as follows:
Input Output Port
Port #1 #2 #3 ... #N
-----------------
A = #1 1 1 1 ... 1
The difference from a simple ROADM is that this is not a switched
connectivity matrix but the fixed connectivity matrix of the device.
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3.4.3. Combiners
An optical combiner is a device that combines the optical wavelengths
carried by multiple input ports into a single multi-wavelength output
output port. The various ports may have different wavelength
restrictions. It is generally the responsibility of those using the
combiner to assure that wavelength collision does not occur on the
output port. The fixed connectivity matrix Amn for a combiner would
look like:
Input Output Port
Port #1
---
#1: 1
#2 1
A = #3 1
... 1
#N 1
3.4.4. Fixed Optical Add/Drop Multiplexers
A fixed optical add/drop multiplexer can alter the course of an input
wavelength in a preset way. In particular a given wavelength (or
waveband) from a line side input port would be dropped to a fixed
"tributary" output port. Depending on the device's construction that
same wavelength may or may not also be sent out the line side output
port. This is commonly referred to as "drop and continue" operation.
There also may exist tributary input ports ("add" ports) whose
signals are combined with each other and other line side signals.
In general, to represent the routing properties of an FOADM it is
necessary to have both a fixed connectivity matrix Amn as previously
discussed and the precise wavelength restrictions for all input and
output ports. From the wavelength restrictions on the tributary
output ports, what wavelengths have been selected can be derived.
From the wavelength restrictions on the tributary input ports, it can
be seen which wavelengths have been added to the line side output
port. Finally from the added wavelength information and the line side
output wavelength restrictions it can be inferred which wavelengths
have been continued.
To summarize, the modeling methodology introduced in Section 3.4.1.
(Reconfigurable Add/Drop Multiplexers and OXCs) consisting of a
connectivity matrix and port wavelength restrictions can be used to
describe a large set of fixed optical devices such as combiners,
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splitters and FOADMs. Hybrid devices consisting of both switched and
fixed parts are modeled in [WSON-Info].
3.5. Electro-Optical Systems
This section describes how Electro-Optical Systems (e.g., OEO
switches, wavelength converters, and regenerators) interact with the
WSON signal characteristics listed in Section 3.3.2. (WSON Signal
Characteristics) OEO switches, wavelength converters and regenerators
all share a similar property: they can be more or less "transparent"
to an "optical signal" depending on their functionality and/or
implementation. Regenerators have been fairly well characterized in
this regard and hence their properties can be described first.
3.5.1. Regenerators
The various approaches to regeneration are discussed in ITU-T G.872
Annex A [G.872]. They map a number of functions into the so-called
1R, 2R and 3R categories of regenerators as summarized in Table 1
below:
Table 1. Regenerator functionality mapped to general regenerator
classes from [G.872].
---------------------------------------------------------------------
1R | Equal amplification of all frequencies within the amplification
| bandwidth. There is no restriction upon information formats.
+-----------------------------------------------------------------
| Amplification with different gain for frequencies within the
| amplification bandwidth. This could be applied to both single-
| channel and multi-channel systems.
+-----------------------------------------------------------------
| Dispersion compensation (phase distortion). This analogue
| process can be applied in either single-channel or multi-
| channel systems.
---------------------------------------------------------------------
2R | Any or all 1R functions. Noise suppression.
+-----------------------------------------------------------------
| Digital reshaping (Schmitt Trigger function) with no clock
| recovery. This is applicable to individual channels and can be
| used for different bit rates but is not transparent to line
| coding (modulation).
--------------------------------------------------------------------
3R | Any or all 1R and 2R functions. Complete regeneration of the
| pulse shape including clock recovery and retiming within
| required jitter limits.
--------------------------------------------------------------------
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From this table it is seen that 1R regenerators are generally
independent of signal modulation format (also known as line coding),
but may work over a limited range of wavelength/frequencies. 2R
regenerators are generally applicable to a single digital stream and
are dependent upon modulation format (line coding) and to a lesser
extent are limited to a range of bit rates (but not a specific bit
rate). Finally, 3R regenerators apply to a single channel, are
dependent upon the modulation format and generally sensitive to the
bit rate of digital signal, i.e., either are designed to only handle
a specific bit rate or need to be programmed to accept and regenerate
a specific bit rate. In all these types of regenerators the digital
bit stream contained within the optical or electrical signal is not
modified.
It is common for regenerators to modify the digital bit stream for
performance monitoring and fault management purposes. Synchronous
Optical Networking (SONET), Synchronous Digital Hierarchy (SDH) and
Interfaces for the Optical Transport Network (G.709) all have digital
signal "envelopes" designed to be used between "regenerators" (in
this case 3R regenerators). In SONET this is known as the "section"
signal, in SDH this is known as the "regenerator section" signal, in
G.709 this is known as an OTUk. These signals reserve a portion of
their frame structure (known as overhead) for use by regenerators.
The nature of this overhead is summarized in Table 2 below.
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Table 2. SONET, SDH, and G.709 regenerator related overhead.
+-----------------------------------------------------------------+
|Function | SONET/SDH | G.709 OTUk |
| | Regenerator | |
| | Section | |
|------------------+----------------------+-----------------------|
|Signal | J0 (section | Trail Trace |
|Identifier | trace) | Identifier (TTI) |
|------------------+----------------------+-----------------------|
|Performance | BIP-8 (B1) | BIP-8 (within SM) |
|Monitoring | | |
|------------------+----------------------+-----------------------|
|Management | D1-D3 bytes | GCC0 (general |
|Communications | | communications |
| | | channel) |
|------------------+----------------------+-----------------------|
|Fault Management | A1, A2 framing | FAS (frame alignment |
| | bytes | signal), BDI(backward|
| | | defect indication)BEI|
| | | (backward error |
| | | indication) |
+------------------+----------------------+-----------------------|
|Forward Error | P1,Q1 bytes | OTUk FEC |
|Correction (FEC) | | |
+-----------------------------------------------------------------+
In the previous table it is seen that frame alignment, signal
identification, and FEC are supported. What this table also shows by
its omission is that no switching or multiplexing occurs at this
layer. This is a significant simplification for the control plane
since control plane standards require a multi-layer approach when
there are multiple switching layers, but not for "layering" to
provide the management functions of Table 2. That is, many existing
technologies covered by GMPLS contain extra management related layers
that are essentially ignored by the control plane (though not by the
management plane!). Hence, the approach here is to include
regenerators and other devices at the WSON layer unless they provide
higher layer switching and then a multi-layer or multi-region
approach [RFC5212] is called for. However, this can result in
regenerators having a dependence on the client signal type.
Hence depending upon the regenerator technology the following
constraints may be imposed by a regenerator device:
Table 3. Regenerator Compatibility Constraints.
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+--------------------------------------------------------+
| Constraints | 1R | 2R | 3R |
+--------------------------------------------------------+
| Limited Wavelength Range | x | x | x |
+--------------------------------------------------------+
| Modulation Type Restriction | | x | x |
+--------------------------------------------------------+
| Bit Rate Range Restriction | | x | x |
+--------------------------------------------------------+
| Exact Bit Rate Restriction | | | x |
+--------------------------------------------------------+
| Client Signal Dependence | | | x |
+--------------------------------------------------------+
Note that the limited wavelength range constraint can be modeled for
GMPLS signaling with the label set defined in [RFC3471] and that the
modulation type restriction constraint includes FEC.
3.5.2. OEO Switches
A common place where OEO processing may take place is within WSON
switches that utilize (or contain) regenerators. Regenerators may be
added to a switching system for a number of reasons. One common
reason is to restore signal quality either before or after optical
processing (switching). Another reason may be to convert the signal
to an electronic form for switching then reconverting to an optical
signal prior to output from the switch. In this later case the
regeneration is applied to adapt the signal to the switch fabric
regardless of whether or not it is needed from a signal quality
perspective.
In either case these optical switches have essentially the same
compatibility constraints as those which are described for
regenerators in Table 3.
3.6. Wavelength Converters
Wavelength converters take an input optical signal at one wavelength
and emit an equivalent content optical signal at another wavelength
on output. There are multiple approaches to building wavelength
converters. One approach is based on OEO conversion with fixed or
tunable optics on output. This approach can be dependent upon the
signal rate and format, i.e., this is basically an electrical
regenerator combined with a laser/receiver. Hence, this type of
wavelength converter has signal processing restrictions that are
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essentially the same as those described for regenerators in Table 3
of section 3.5.1.
Another approach performs the wavelength conversion, optically via
non-linear optical effects, similar in spirit to the familiar
frequency mixing used in radio frequency systems, but significantly
harder to implement. Such processes/effects may place limits on the
range of achievable conversion. These may depend on the wavelength of
the input signal and the properties of the converter as opposed to
only the properties of the converter in the OEO case. Different WSON
system designs may choose to utilize this component to varying
degrees or not at all.
Current or envisioned contexts for wavelength converters are:
1. Wavelength conversion associated with OEO switches and fixed or
tunable optics. In this case there are typically multiple
converters available since each on the use of an OEO switch can be
thought of as a potential wavelength converter.
2. Wavelength conversion associated with ROADMs/OXCs. In this case
there may be a limited pool of wavelength converters available.
Conversion could be either all optical or via an OEO method.
3. Wavelength conversion associated with fixed devices such as FOADMs.
In this case there may be a limited amount of conversion. Also in
this case the conversion may be used as part of light path routing.
Based on the above considerations, wavelength converters are modeled
as follows:
1. Wavelength converters can always be modeled as associated with
network elements. This includes fixed wavelength routing elements.
2. A network element may have full wavelength conversion capability,
i.e., any input port and wavelength, or a limited number of
wavelengths and ports. On a box with a limited number of
converters there also may exist restrictions on which ports can
reach the converters. Hence regardless of where the converters
actually are they can be associated with input ports.
3. Wavelength converters have range restrictions that are either
independent or dependent upon the input wavelength.
In WSONs where wavelength converters are sparse a light path may
appear to loop or "backtrack" upon itself in order to reach a
wavelength converter prior to continuing on to its destination. The
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lambda used on input to the wavelength converter would be different
the lambda coming back from the wavelength converter.
A model for an individual O-E-O wavelength converter would consist
of:
o Input lambda or frequency range.
o Output lambda or frequency range.
3.6.1. Wavelength Converter Pool Modeling
A WSON node may include multiple wavelength converters. These are
usually arranged into some type of pool to promote resource sharing.
There are a number of different approaches used in the design of
switches with converter pools. However, from the point of view of
path computation it is necessary to know the following:
1. The nodes that support wavelength conversion.
2. The accessibility and availability of a wavelength converter to
convert from a given input wavelength on a particular input port
to a desired output wavelength on a particular output port.
3. Limitations on the types of signals that can be converted and the
conversions that can be performed.
To model point 2 above, a similar technique can be used to model
ROADMs and optical switches, i.e., matrices to indicate possible
connectivity along with wavelength constraints for links/ports. Since
wavelength converters are considered a scarce resource it will be
desirable to include as a minimum the usage state of individual
wavelength converters in the pool.
A three stage model is used as shown schematically in Figure 3.
(Schematic diagram of wavelength converter pool model). In this model
it is assumed N input ports (fibers), P wavelength converters, and M
output ports (fibers). Since not all input ports can necessarily
reach the converter pool, the model starts with a wavelength pool
input matrix WI(i,p) = {0,1} where input port i can reach potentially
reach wavelength converter p.
Since not all wavelength can necessarily reach all the converters or
the converters may have limited input wavelength range there is a set
of input port constraints for each wavelength converter. Currently it
is assumed that a wavelength converter can only take a single
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wavelength on input. Each wavelength converter input port constraint
can be modeled via a wavelength set mechanism.
Next a state vector WC(j) = {0,1} dependent upon whether wavelength
converter j in the pool is in use. This is the only state kept in the
converter pool model. This state is not necessary for modeling
"fixed" transponder system, i.e., systems where there is no sharing.
In addition, this state information may be encoded in a much more
compact form depending on the overall connectivity structure [WSON-
Encode].
After that, a set of wavelength converter output wavelength
constraints is used. These constraints indicate what wavelengths a
particular wavelength converter can generate or are restricted to
generating due to internal switch structure.
Finally, a wavelength pool output matrix WE(p,k) = {0,1} indicating
whether the output from wavelength converter p can reach output port
k. Examples of this method being used to model wavelength converter
pools for several switch architectures are given in reference [WSON-
Encode].
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I1 +-------------+ +-------------+ E1
----->| | +--------+ | |----->
I2 | +------+ WC #1 +-------+ | E2
----->| | +--------+ | |----->
| Wavelength | | Wavelength |
| Converter | +--------+ | Converter |
| Pool +------+ WC #2 +-------+ Pool |
| | +--------+ | |
| Input | | Output |
| Connection | . | Connection |
| Matrix | . | Matrix |
| | . | |
| | | |
IN | | +--------+ | | EM
----->| +------+ WC #P +-------+ |----->
| | +--------+ | |
+-------------+ ^ ^ +-------------+
| |
| |
| |
| |
Input wavelength Output wavelength
constraints for constraints for
each converter each converter
Figure 3. Schematic diagram of wavelength converter pool model.
Figure 4 below shows a simple optical switch in a four wavelength
DWDM system sharing wavelength converters in a general shared "per
node" fashion.
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+-----------+ ___________ +------+
| |--------------------------->| |
| |--------------------------->| C |
/| | |--------------------------->| o | E1
I1 /D+--->| |--------------------------->| m |
+ e+--->| | | b |====>
====>| M| | Optical | +-----------+ +----+ | i |
+ u+--->| Switch | | WC Pool | |O S|-->| n |
\x+--->| | | +-----+ | |p w|-->| e |
\| | +----+->|WC #1|--+->|t i| | r |
| | | +-----+ | |i t| +------+
| | | | |c c| +------+
/| | | | +-----+ | |a h|-->| |
I2 /D+--->| +----+->|WC #2|--+->|l |-->| C | E2
+ e+--->| | | +-----+ | | | | o |
====>| M| | | +-----------+ +----+ | m |====>
+ u+--->| | | b |
\x+--->| |--------------------------->| i |
\| | |--------------------------->| n |
| |--------------------------->| e |
|___________|--------------------------->| r |
+-----------+ +------+
Figure 4. An optical switch featuring a shared per node wavelength
converter pool architecture.
In this case the input and output pool matrices are simply:
+-----+ +-----+
| 1 1 | | 1 1 |
WI =| |, WE =| |
| 1 1 | | 1 1 |
+-----+ +-----+
Figure 5 shows a different wavelength pool architecture known as
"shared per fiber". In this case the input and output pool matrices
are simply:
+-----+ +-----+
| 1 1 | | 1 0 |
WI =| |, WE =| |
| 1 1 | | 0 1 |
+-----+ +-----+
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+-----------+ +------+
| |--------------------------->| |
| |--------------------------->| C |
/| | |--------------------------->| o | E1
I1 /D+--->| |--------------------------->| m |
+ e+--->| | | b |====>
====>| M| | Optical | +-----------+ | i |
+ u+--->| Switch | | WC Pool | | n |
\x+--->| | | +-----+ | | e |
\| | +----+->|WC #1|--+---------->| r |
| | | +-----+ | +------+
| | | | +------+
/| | | | +-----+ | | |
I2 /D+--->| +----+->|WC #2|--+---------->| C | E2
+ e+--->| | | +-----+ | | o |
====>| M| | | +-----------+ | m |====>
+ u+--->| | | b |
\x+--->| |--------------------------->| i |
\| | |--------------------------->| n |
| |--------------------------->| e |
|___________|--------------------------->| r |
+-----------+ +------+
Figure 5. An optical switch featuring a shared per fiber wavelength
converter pool architecture.
3.7. Characterizing Electro-Optical Network Elements
In this section electro-optical WSON network elements are
characterized by the three key functional components: input
constraints, output constraints and processing capabilities.
WSON Network Element
+-----------------------+
WSON Signal | | | | WSON Signal
| | | |
---------------> | | | | ----------------->
| | | |
+-----------------------+
<-----> <-------> <----->
Input Processing Output
Figure 6. WSON Network Element
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3.7.1. Input Constraints
Section 3. (Wavelength Switched Optical Networks) discussed the basic
properties regenerators, OEO switches and wavelength converters. From
these the following possible types of input constraints and
properties are derived:
1. Acceptable Modulation formats.
2. Client Signal (G-PID) restrictions.
3. Bit Rate restrictions.
4. FEC coding restrictions.
5. Configurability: (a) none, (b) self-configuring, (c) required.
These constraints are represented via simple lists. Note that the
device may need to be "provisioned" via signaling or some other means
to accept signals with some attributes versus others. In other cases
the devices maybe relatively transparent to some attributes, e.g.,
such as a 2R regenerator to bit rate. Finally, some devices maybe
able to auto-detect some attributes and configure themselves, e.g., a
3R regenerator with bit rate detection mechanisms and flexible phase
locking circuitry. To account for these different cases item 5 has
been added, which describes the devices configurability.
Note that such input constraints also apply to the termination of the
WSON signal.
3.7.2. Output Constraints
None of the network elements considered here modifies either the bit
rate or the basic type of the client signal. However, they may modify
the modulation format or the FEC code. Typically the following types
of output constraints are seen:
1. Output modulation is the same as input modulation (default).
2. A limited set of output modulations is available.
3. Output FEC is the same as input FEC code (default).
4. A limited set of output FEC codes is available.
Note that in cases (2) and (4) above, where there is more than one
choice in the output modulation or FEC code then the network element
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will need to be configured on a per LSP basis as to which choice to
use.
3.7.3. Processing Capabilities
A general WSON network element (NE) can perform a number of signal
processing functions including:
(A) Regeneration (possibly different types).
(B) Fault and Performance Monitoring.
(C) Wavelength Conversion.
(D) Switching.
An NE may or may not have the ability to perform regeneration (of the
one of the types previously discussed). In addition some nodes may
have limited regeneration capability, i.e., a shared pool, which may
be applied to selected signals traversing the NE. Hence to describe
the regeneration capability of a link or node it is necessary to have
at a minimum:
1. Regeneration capability: (a)fixed, (b) selective, (c) none.
2. Regeneration type: 1R, 2R, 3R.
3. Regeneration pool properties for the case of selective
regeneration (input and output restrictions, availability).
Note that the properties of shared regenerator pools would be
essentially the same at that of wavelength converter pools modeled in
section 3.6.1. (Wavelength Pool Convertor Modeling).
Item (B), fault and performance monitoring, is typically outside the
scope of the control plane. However, when the operations are to be
performed on an LSP basis or on part of an LSP then the control plane
can be of assistance in their configuration. Per LSP, per node, fault
and performance monitoring examples include setting up a "section
trace" (a regenerator overhead identifier) between two nodes, or
intermediate optical performance monitoring at selected nodes along a
path.
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4. Routing and Wavelength Assignment and the Control Plane
A wavelength-convertible network with full wavelength-conversion
capability at each node is equivalent to packet MPLS-labeled network
or a circuit-switched Time-division multiplexing (TDM) network with
full time slot interchange capability. In this case, the routing
problem needs to be addressed only at the level of the Traffic
Engineered (TE) link choice, and wavelength assignment can be
resolved locally by the switches on a hop-by-hop basis.
However, in the limiting case of an optical network with no
wavelength converters, a light path (optical signal) needs a route
from source to destination and must pick a single wavelength that can
be used along that path without "colliding" with the wavelength used
by any other light path that may share an optical fiber. This is
sometimes referred to as a "wavelength continuity constraint".
In the general case of limited or no wavelength converters this
computation is known as the RWA problem.
The inputs to the basic RWA problem are the requested light path's
source and destination, the network topology, the locations and
capabilities of any wavelength converters, and the wavelengths
available on each optical link. The output from an algorithm solving
the RWA problem is an explicit route through ROADMs, a wavelength for
the optical transmitter, and a set of locations (generally associated
with ROADMs or switches) where wavelength conversion is to occur and
the new wavelength to be used on each component link after that point
in the route.
It is to be noted that the choice of specific RWA algorithm is out of
the scope for this document. However there are a number of different
approaches to dealing with the RWA algorithm that can affect the
division of effort between path computation/routing and signaling.
4.1. Architectural Approaches to RWA
Two general computational approaches are taken to solving the RWA
problem. Some algorithms utilize a two step procedure of path
selection followed by wavelength assignment, and others solve the
problem in a combined fashion.
In the following, three different ways of performing RWA in
conjunction with the control plane are considered. The choice of one
of these architectural approaches over another generally impacts the
demands placed on the various control plane protocols.
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4.1.1. Combined RWA (R&WA)
In this case, a unique entity is in charge of performing routing and
wavelength assignment. This approach relies on a sufficient knowledge
of network topology, of available network resources and of network
nodes capabilities. This solution is compatible with most known RWA
algorithms, and in particular those concerned with network
optimization. On the other hand, this solution requires up-to-date
and detailed network information.
Such a computational entity could reside in two different logical
places:
o The PCE, which maintains a complete and updated view of network
state, provides path computation services to nodes (PCCs).
o In the ingress node, in that case all nodes have the R&WA
functionality; the knowledge of the network state is obtained by a
periodic flooding of information provided by the other nodes.
4.1.2. Separated R and WA (R+WA)
In this case a first entity performs routing, while a second performs
wavelength assignment. The first entity furnishes one or more paths
to the second entity that will perform wavelength assignment and
possibly final path selection.
As the entities computing the path and the wavelength assignment are
separated, this constrains the class of RWA algorithms that may be
implemented. Although it may seem that algorithms optimizing a joint
usage of the physical and spectral paths are excluded from this
solution, many practical optimization algorithms only consider a
limited set of possible paths, e.g., as computed via a k-shortest
path algorithm. Hence although there is no guarantee that the
selected final route and wavelength offers the optimal solution, by
allowing multiple routes to pass to the wavelength selection process
reasonable optimization can be performed.
The entity performing the routing assignment needs the topology
information of the network, whereas the entity performing the
wavelength assignment needs information on the network's available
resources and specific network node capabilities.
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4.1.3. Routing and Distributed WA (R+DWA)
In this case a first entity performs routing, while wavelength
assignment is performed on a hop-by-hop, distributed, manner along
the previously computed route. This mechanism relies on updating of a
list of potential wavelengths used to ensure conformance with the
wavelength continuity constraint.
As currently specified, the GMPLS protocol suite signaling protocol
can accommodate such an approach. Per [RFC3471], the Label Set
selection works according to an AND scheme. Each hop restricts the
Label Set sent to the next hop from the one received from the
previous hop by performing an AND operation between the wavelength
referred by the labels the message includes with the one available on
the ongoing interface. The constraint to perform this AND operation
is up to the node local policy (even if one expects a consistent
policy configuration throughout a given transparency domain). When
wavelength conversion is performed at an intermediate node, a new
Label Set is generated. The output node selects one label in the
Label Set which it received; additionally the node can apply local
policy during label selection.
Depending on these policies a spectral assignment may not be found or
one consuming too many conversion resources relative to what a
dedicated wavelength assignment policy would have achieved. Hence,
this approach may generate higher blocking probabilities in a heavily
loaded network.
On the one hand, this solution may be empowered with some signaling
extensions to ease its functioning and possibly enhance its
performance relatively to blocking. Note that this approach requires
less information dissemination than the other techniques described.
The first entity may be a PCE or the ingress node of the LSP. This
solution is applicable inside networks where resource optimization is
not as critical.
4.2. Conveying information needed by RWA
The previous sections have characterized WSONs and lightpath
requests. In particular, high level models of the information used by
the RWA process were presented. This information can be viewed as
either static, changing with hardware changes (including possibly
failures), or dynamic, those that can change with subsequent
lightpath provisioning. The timeliness in which an entity involved in
the RWA process is notified of such changes is fairly situational.
For example, for network restoration purposes, learning of a hardware
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failure or of new hardware coming online to provide restoration
capability can be critical.
Currently there are various methods for communicating RWA relevant
information, these include, but are not limited to:
o Existing control plane protocols such as GMPLS routing and
signaling. Note that routing protocols can be used to convey both
static and dynamic information.
o Management protocols such as NetConf, SNMPv3, CLI, CORBA, or
others.
o Directory services and accompanying protocols. These are good for
the dissemination of relatively static information. Directory
services are not suited to manage information in dynamic and fluid
environments.
o Other techniques for dynamic information: messaging straight from
NEs to PCE to avoid flooding. This would be useful if the number
of PCEs is significantly less than number of WSON NEs. Or other
ways to limit flooding to "interested" NEs.
Mechanisms to improve scaling of dynamic information:
o Tailor message content to WSON. For example the use of wavelength
ranges, or wavelength occupation bit maps.
o Utilize incremental updates if feasible.
5. Modeling Examples and Control Plane Use Cases
This section provides examples of the fixed and switch optical node
and wavelength constraint models of Section 3. and WSON control
plane use cases related to path computation, establishment,
rerouting, and optimization.
5.1. Network Modeling for GMPLS/PCE Control
Consider a network containing three routers (R1 through R3), eight
WSON nodes (N1 through N8) and 18 links (L1 through L18) and one OEO
converter (O1) in a topology shown below.
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+--+ +--+ +--+ +--------+
+-L3-+N2+-L5-+ +--------L12--+N6+--L15--+ N8 +
| +--+ |N4+-L8---+ +--+ ++--+---++
| | +-L9--+| | | |
+--+ +-+-+ ++-+ || | L17 L18
| ++-L1--+ | | ++++ +----L16---+ | |
|R1| | N1| L7 |R2| | | |
| ++-L2--+ | | ++-+ | ++---++
+--+ +-+-+ | | | + R3 |
| +--+ ++-+ | | +-----+
+-L4-+N3+-L6-+N5+-L10-+ ++----+
+--+ | +--------L11--+ N7 +
+--+ ++---++
| |
L13 L14
| |
++-+ |
|O1+-+
+--+
Figure 7. Routers and WSON nodes in a GMPLS and PCE Environment.
5.1.1. Describing the WSON nodes
The eight WSON nodes described in Figure 7 have the following
properties:
o Nodes N1, N2, N3 have FOADMs installed and can therefore only
access a static and pre-defined set of wavelengths.
o All other nodes contain ROADMs and can therefore access all
wavelengths.
o Nodes N4, N5, N7 and N8 are multi-degree nodes, allowing any
wavelength to be optically switched between any of the links. Note
however, that this does not automatically apply to wavelengths
that are being added or dropped at the particular node.
o Node N4 is an exception to that: This node can switch any
wavelength from its add/drop ports to any of its outgoing links
(L5, L7 and L12 in this case).
o The links from the routers are always only able to carry one
wavelength with the exception of links L8 and L9 which are capable
to add/drop any wavelength.
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o Node N7 contains an OEO transponder (O1) connected to the node via
links L13 and L14. That transponder operates in 3R mode and does
not change the wavelength of the signal. Assume that it can
regenerate any of the client signals, however only for a specific
wavelength.
Given the above restrictions, the node information for the eight
nodes can be expressed as follows: (where ID == identifier, SCM ==
switched connectivity matrix, and FCM == fixed connectivity matrix).
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+ID+SCM +FCM +
| | |L1 |L2 |L3 |L4 | | |L1 |L2 |L3 |L4 | |
| |L1 |0 |0 |0 |0 | |L1 |0 |0 |1 |0 | |
|N1|L2 |0 |0 |0 |0 | |L2 |0 |0 |0 |1 | |
| |L3 |0 |0 |0 |0 | |L3 |1 |0 |0 |1 | |
| |L4 |0 |0 |0 |0 | |L4 |0 |1 |1 |0 | |
+--+---+---+---+---+---+---+---+---+---+---+---+---+
| | |L3 |L5 | | | | |L3 |L5 | | | |
|N2|L3 |0 |0 | | | |L3 |0 |1 | | | |
| |L5 |0 |0 | | | |L5 |1 |0 | | | |
+--+---+---+---+---+---+---+---+---+---+---+---+---+
| | |L4 |L6 | | | | |L4 |L6 | | | |
|N3|L4 |0 |0 | | | |L4 |0 |1 | | | |
| |L6 |0 |0 | | | |L6 |1 |0 | | | |
+--+---+---+---+---+---+---+---+---+---+---+---+---+
| | |L5 |L7 |L8 |L9 |L12| |L5 |L7 |L8 |L9 |L12|
| |L5 |0 |1 |1 |1 |1 |L5 |0 |0 |0 |0 |0 |
|N4|L7 |1 |0 |1 |1 |1 |L7 |0 |0 |0 |0 |0 |
| |L8 |1 |1 |0 |1 |1 |L8 |0 |0 |0 |0 |0 |
| |L9 |1 |1 |1 |0 |1 |L9 |0 |0 |0 |0 |0 |
| |L12|1 |1 |1 |1 |0 |L12|0 |0 |0 |0 |0 |
+--+---+---+---+---+---+---+---+---+---+---+---+---+
| | |L6 |L7 |L10|L11| | |L6 |L7 |L10|L11| |
| |L6 |0 |1 |0 |1 | |L6 |0 |0 |1 |0 | |
|N5|L7 |1 |0 |0 |1 | |L7 |0 |0 |0 |0 | |
| |L10|0 |0 |0 |0 | |L10|1 |0 |0 |0 | |
| |L11|1 |1 |0 |0 | |L11|0 |0 |0 |0 | |
+--+---+---+---+---+---+---+---+---+---+---+---+---+
| | |L12|L15| | | | |L12|L15| | | |
|N6|L12|0 |1 | | | |L12|0 |0 | | | |
| |L15|1 |0 | | | |L15|0 |0 | | | |
+--+---+---+---+---+---+---+---+---+---+---+---+---+
| | |L11|L13|L14|L16| | |L11|L13|L14|L16| |
| |L11|0 |1 |0 |1 | |L11|0 |0 |0 |0 | |
|N7|L13|1 |0 |0 |0 | |L13|0 |0 |1 |0 | |
| |L14|0 |0 |0 |1 | |L14|0 |1 |0 |0 | |
| |L16|1 |0 |1 |0 | |L16|0 |0 |1 |0 | |
+--+---+---+---+---+---+---+---+---+---+---+---+---+
| | |L15|L16|L17|L18| | |L15|L16|L17|L18| |
| |L15|0 |1 |0 |0 | |L15|0 |0 |0 |1 | |
|N8|L16|1 |0 |0 |0 | |L16|0 |0 |1 |0 | |
| |L17|0 |0 |0 |0 | |L17|0 |1 |0 |0 | |
| |L18|0 |0 |0 |0 | |L18|1 |0 |1 |0 | |
+--+---+---+---+---+---+---+---+---+---+---+---+---+
5.1.2. Describing the links
For the following discussion some simplifying assumptions are made:
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o It is assumed that the WSON node support a total of four
wavelengths designated WL1 through WL4.
o It is assumed that the impairment feasibility of a path or path
segment is independent from the wavelength chosen.
For the discussion of the RWA operation to build LSPs between two
routers, the wavelength constraints on the links between the routers
and the WSON nodes as well as the connectivity matrix of these links
needs to be specified:
+Link+WLs supported +Possible output links+
| L1 | WL1 | L3 |
+----+-----------------+---------------------+
| L2 | WL2 | L4 |
+----+-----------------+---------------------+
| L8 | WL1 WL2 WL3 WL4 | L5 L7 L12 |
+----+-----------------+---------------------+
| L9 | WL1 WL2 WL3 WL4 | L5 L7 L12 |
+----+-----------------+---------------------+
| L10| WL2 | L6 |
+----+-----------------+---------------------+
| L13| WL1 WL2 WL3 WL4 | L11 L14 |
+----+-----------------+---------------------+
| L14| WL1 WL2 WL3 WL4 | L13 L16 |
+----+-----------------+---------------------+
| L17| WL2 | L16 |
+----+-----------------+---------------------+
| L18| WL1 | L15 |
+----+-----------------+---------------------+
Note that the possible output links for the links connecting to the
routers is inferred from the switched connectivity matrix and the
fixed connectivity matrix of the Nodes N1 through N8 and is show here
for convenience, i.e., this information does not need to be repeated.
5.2. RWA Path Computation and Establishment
The calculation of optical impairment feasible routes is outside the
scope of this framework document. In general impairment feasible
routes serve as an input to the RWA algorithm.
For the example use case shown here, assume the following feasible
routes:
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+Endpoint 1+Endpoint 2+Feasible Route +
| R1 | R2 | L1 L3 L5 L8 |
| R1 | R2 | L1 L3 L5 L9 |
| R1 | R2 | L2 L4 L6 L7 L8 |
| R1 | R2 | L2 L4 L6 L7 L9 |
| R1 | R2 | L2 L4 L6 L10 |
| R1 | R3 | L1 L3 L5 L12 L15 L18 |
| R1 | N7 | L2 L4 L6 L11 |
| N7 | R3 | L16 L17 |
| N7 | R2 | L16 L15 L12 L9 |
| R2 | R3 | L8 L12 L15 L18 |
| R2 | R3 | L8 L7 L11 L16 L17 |
| R2 | R3 | L9 L12 L15 L18 |
| R2 | R3 | L9 L7 L11 L16 L17 |
Given a request to establish a LSP between R1 and R2 the RWA
algorithm finds the following possible solutions:
+WL + Path +
| WL1| L1 L3 L5 L8 |
| WL1| L1 L3 L5 L9 |
| WL2| L2 L4 L6 L7 L8|
| WL2| L2 L4 L6 L7 L9|
| WL2| L2 L4 L6 L10 |
Assume now that the RWA chooses WL1 and the Path L1 L3 L5 L8 for the
requested LSP.
Next, another LSP is signaled from R1 to R2. Given the established
LSP using WL1, the following table shows the available paths:
+WL + Path +
| WL2| L2 L4 L6 L7 L9|
| WL2| L2 L4 L6 L10 |
Assume now that the RWA chooses WL2 and the path L2 L4 L6 L7 L9 for
the establishment of the new LSP.
Faced with another LSP request -this time from R2 to R3 - can not be
fulfilled since the only four possible paths (starting at L8 and L9)
are already in use.
5.3. Resource Optimization
The preceding example gives rise to another use case: the
optimization of network resources. Optimization can be achieved on a
number of layers (e.g. through electrical or optical multiplexing of
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client signals) or by re-optimizing the solutions found by the RWA
algorithm.
Given the above example again, assume that the RWA algorithm should
find a path between R2 and R3. The only possible path to reach R3
from R2 needs to use L9. L9 however is blocked by one of the LSPs
from R1.
5.4. Support for Rerouting
It is also envisioned that the extensions to GMPLS and PCE support
rerouting of wavelengths in case of failures.
Assume for this discussion that the only two LSPs in use in the
system are:
LSP1: WL1 L1 L3 L5 L8
LSP2: WL2 L2 L4 L6 L7 L9
Assume furthermore that the link L5 fails. The RWA can now find the
following alternate path and and establish that path:
R1 -> N7 -> R2
Level 3 regeneration will take place at N7, so that the complete path
looks like this:
R1 -> L2 L4 L6 L11 L13 -> O1 -> L14 L16 L15 L12 L9 -> R2
5.5. Electro-Optical Networking Scenarios
In the following various networking scenarios are considered
involving regenerators, OEO switches and wavelength converters. These
scenarios can be grouped roughly by type and number of extensions to
the GMPLS control plane that would be required.
5.5.1. Fixed Regeneration Points
In the simplest networking scenario involving regenerators, the
regeneration is associated with a WDM link or entire node and is not
optional, i.e., all signals traversing the link or node will be
regenerated. This includes OEO switches since they provide
regeneration on every port.
There maybe input constraints and output constraints on the
regenerators. Hence the path selection process will need to know from
an IGP or other means the regenerator constraints so that it can
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choose a compatible path. For impairment aware routing and wavelength
assignment (IA-RWA) the path selection process will also need to know
which links/nodes provide regeneration. Even for "regular" RWA, this
regeneration information is useful since wavelength converters
typically perform regeneration and the wavelength continuity
constraint can be relaxed at such a point.
Signaling does not need to be enhanced to include this scenario since
there are no reconfigurable regenerator options on input, output or
with respect to processing.
5.5.2. Shared Regeneration Pools
In this scenario there are nodes with shared regenerator pools within
the network in addition to fixed regenerators of the previous
scenario. These regenerators are shared within a node and their
application to a signal is optional. There are no reconfigurable
options on either input or output. The only processing option is to
"regenerate" a particular signal or not.
Regenerator information in this case is used in path computation to
select a path that ensures signal compatibility and IA-RWA criteria.
To setup an LSP that utilizes a regenerator from a node with a shared
regenerator pool one should be able to indicate that regeneration is
to take place at that particular node along the signal path. Such a
capability currently does not exist in GMPLS signaling.
5.5.3. Reconfigurable Regenerators
This scenario is concerned with regenerators that require
configuration prior to use on an optical signal. As discussed
previously, this could be due to a regenerator that must be
configured to accept signals with different characteristics, for
regenerators with a selection of output attributes, or for
regenerators with additional optional processing capabilities.
As in the previous scenarios it is necessary to have information
concerning regenerator properties for selection of compatible paths
and for IA-RWA computations. In addition during LSP setup it is
necessary to be able configure regenerator options at a particular
node along the path. Such a capability currently does not exist in
GMPLS signaling.
5.5.4. Relation to Translucent Networks
Networks that contain both transparent network elements such as
reconfigurable optical add drop multiplexers (ROADMs) and electro-
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optical network elements such regenerators or OEO switches are
frequently referred to as translucent optical networks.
Three main types of translucent optical networks have been discussed:
1. Transparent "islands" surrounded by regenerators. This is
frequently seen when transitioning from a metro optical sub-
network to a long haul optical sub-network.
2. Mostly transparent networks with a limited number of OEO
("opaque") nodes strategically placed. This takes advantage of the
inherent regeneration capabilities of OEO switches. In the
planning of such networks one has to determine the optimal
placement of the OEO switches.
3. Mostly transparent networks with a limited number of optical
switching nodes with "shared regenerator pools" that can be
optionally applied to signals passing through these switches.
These switches are sometimes called translucent nodes.
All three of these types of translucent networks fit within the
networking scenarios of Section 5.5.1. and Section 5.5.2. above.
And hence, can be accommodated by the GMPLS extensions suggested in
this document.
6. GMPLS and PCE Implications
The presence and amount of wavelength conversion available at a
wavelength switching interface has an impact on the information that
needs to be transferred by the control plane (GMPLS) and the PCE
architecture. Current GMPLS and PCE standards can address the full
wavelength conversion case so the following will only address the
limited and no wavelength conversion cases.
6.1. Implications for GMPLS signaling
Basic support for WSON signaling already exists in GMPLS with the
lambda (value 9) LSP encoding type [RFC3471], or for G.709 compatible
optical channels, the LSP encoding type (value = 13) "G.709 Optical
Channel" from [RFC4328]. However a number of practical issues arise
in the identification of wavelengths and signals, and distributed
wavelength assignment processes which are discussed below.
6.1.1. Identifying Wavelengths and Signals
As previously stated a global fixed mapping between wavelengths and
labels simplifies the characterization of WDM links and WSON devices.
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Furthermore such a mapping as described in [Otani] eases
communication between PCE and WSON PCCs.
6.1.2. WSON Signals and Network Element Processing
It was seen in Section 3.3.2. that a WSON signal at any point along
its path can be characterized by the (a) modulation format, (b) FEC,
(c) wavelength, (d)bit rate, and (d)G-PID.
Currently G-PID, wavelength (via labels), and bit rate (via bandwidth
encoding) are supported in [RFC3471] and [RFC3473]. These RFCs can
accommodate the wavelength changing at any node along the LSP and can
thus provide explicit control of wavelength converters.
In the fixed regeneration point scenario described in Section 5.5.1.
(Fixed Regeneration Points) no enhancements are required to signaling
since there are no additional configuration options for the LSP at a
node.
In the case of shared regeneration pools described in Section 5.5.2.
(Shared Regeneration Pools) it is necessary to indicate to a node
that it should perform regeneration on a particular signal. Viewed
another way, for an LSP, it is desirable to specify that certain
nodes along the path perform regeneration. Such a capability
currently does not exist in GMPLS signaling.
The case of configurable regenerators described in Section 5.5.3.
(Reconfigurable Regenerators) is very similar to the previous except
that now there are potentially many more items that can be configured
on a per node basis for an LSP.
Note that the techniques of [RFC5420] which allow for additional LSP
attributes and their recording in an Record Route Object (RRO) object
could be extended to allow for additional LSP attributes in an ERO.
This could allow one to indicate where optional 3R regeneration
should take place along a path, any modification of LSP attributes
such as modulation format, or any enhance processing such as
performance monitoring.
6.1.3. Combined RWA/Separate Routing WA support
In either the combined RWA or separate routing WA cases, the node
initiating the signaling will have a route from the source to
destination along with the wavelengths (generalized labels) to be
used along portions of the path. Current GMPLS signaling supports an
Explicit Route Object (ERO) and within an ERO an ERO Label subobject
can be use to indicate the wavelength to be used at a particular
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node. In case the local label map approach is used the label sub-
object entry in the ERO has to be translated appropriately.
6.1.4. Distributed Wavelength Assignment: Unidirectional, No
Converters
GMPLS signaling for a uni-directional lightpath LSP allows for the
use of a label set object in the Resource Reservation Protocol -
Traffic Engineering (RSVP-TE) path message. The processing of the
label set object to take the intersection of available lambdas along
a path can be performed resulting in the set of available lambda
being known to the destination that can then use a wavelength
selection algorithm to choose a lambda.
6.1.5. Distributed Wavelength Assignment: Unidirectional, Limited
Converters
In the case of wavelength converters, nodes with wavelength
converters would need to make the decision as to whether to perform
conversion. One indicator for this would be that the set of available
wavelengths which is obtained via the intersection of the incoming
label set and the output links available wavelengths is either null
or deemed too small to permit successful completion.
At this point the node would need to remember that it will apply
wavelength conversion and will be responsible for assigning the
wavelength on the previous lambda-contiguous segment when the RSVP-TE
RESV message passes by. The node will pass on an enlarged label set
reflecting only the limitations of the wavelength converter and the
output link. The record route option in RVSP-TE signaling can be used
to show where wavelength conversion has taken place.
6.1.6. Distributed Wavelength Assignment: Bidirectional, No
Converters
There are potential issues in the case of a bi-directional lightpath
which requires the use of the same lambda in both directions. The
above procedure can be used to determine the available bidirectional
lambda set if it is interpreted that the available label set is
available in both directions. However, a problem, arises in that
bidirectional LSPs setup, according to [RFC3471] Section 4.1.
(Architectural Approaches to RWA), is indicated by the presence of an
upstream label in the path message.
However, until the intersection of the available label sets is
obtained, e.g., at the destination node and the wavelength assignment
algorithm has been run the upstream label information will not be
available. Hence currently distributed wavelength assignment with
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bidirectional lightpaths is not supported.
6.2. Implications for GMPLS Routing
GMPLS routing [RFC4202] currently defines an interface capability
descriptor for "lambda switch capable" (LSC) which can be used to
describe the interfaces on a ROADM or other type of wavelength
selective switch. In addition to the topology information typically
conveyed via an IGP, it would be necessary to convey the following
subsystem properties to minimally characterize a WSON:
1. WDM Link properties (allowed wavelengths).
2. Optical transmitters (wavelength range).
3. ROADM/FOADM Properties (connectivity matrix, port wavelength
restrictions).
4. Wavelength converter properties (per network element, may change if
a common limited shared pool is used).
This information is modeled in detail in [WSON-Info] and a compact
encoding is given in [WSON-Encode].
6.2.1. Electro-Optical Element Signal Compatibility
In network scenarios where signal compatibility is a concern it is
necessary to add parameters to our existing node and link models to
take into account electro-optical input constraints, output
constraints, and the signal processing capabilities of a NE in path
computations.
Input constraints:
1. Permitted optical tributary signal classes: A list of optical
tributary signal classes that can be processed by this network
element or carried over this link. (configuration type)
2. Acceptable FEC codes. (configuration type)
3. Acceptable Bit Rate Set: a list of specific bit rates or bit rate
ranges that the device can accommodate. Coarse bit rate info is
included with the optical tributary signal class restrictions.
4. Acceptable G-PID list: a list of G-PIDs corresponding to the
"client" digital streams that is compatible with this device.
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Note that since the bit rate of the signal does not change over the
LSP. This can be made as an LSP parameter and hence this information
would be available for any NE that needs to use it for configuration.
Hence it is not necessary to have "configuration type" for the NE
with respect to bit rate.
Output constraints:
1. Output modulation: (a)same as input, (b) list of available types
2. FEC options: (a) same as input, (b) list of available codes
Processing capabilities:
1. Regeneration: (a) 1R, (b) 2R, (c) 3R, (d)list of selectable
regeneration types
2. Fault and performance monitoring: (a) G-PID particular
capabilities, (b) optical performance monitoring capabilities.
Note that such parameters could be specified on an (a) Network
element wide basis, (b) a per port basis, (c) on a per regenerator
basis. Typically such information has been on a per port basis,
e.g., the GMPLS interface switching capability descriptor [RFC4202].
6.2.2. Wavelength-Specific Availability Information
For wavelength assignment it is necessary to know which specific
wavelengths are available and which are occupied if a combined RWA
process or separate WA process is run as discussed in sections 4.1.1.
4.1.2. This is currently not possible with GMPLS routing extensions.
In the routing extensions for GMPLS [RFC4202], requirements for
layer-specific TE attributes are discussed. The RWA problem for
optical networks without wavelength converters imposes an additional
requirement for the lambda (or optical channel) layer: that of
knowing which specific wavelengths are in use. Note that currentDWDM
systems range from 16 channels to 128 channels with advanced
laboratory systems with as many as 300 channels. Given these channel
limitations and if the approach of a global wavelength to label
mapping or furnishing the local mappings to the PCEs is taken then
representing the use of wavelengths via a simple bit-map is feasible
[WSON-Encode].
6.2.3. WSON Routing Information Summary
The following table summarizes the WSON information that could be
conveyed via GMPLS routing and attempts to classify that information
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as to its static or dynamic nature and whether that information would
tend to be associated with either a link or a node.
Information Static/Dynamic Node/Link
------------------------------------------------------------------
Connectivity matrix Static Node
Per port wavelength restrictions Static Node(1)
WDM link (fiber) lambda ranges Static Link
WDM link channel spacing Static Link
Optical transmitter range Static
Link(2)
Wavelength conversion capabilities Static(3) Node
Maximum bandwidth per wavelength Static Link
Wavelength availability Dynamic(4) Link
Signal compatibility and processing Static/Dynamic Node
Notes:
1. These are the per port wavelength restrictions of an optical
device such as a ROADM and are independent of any optical
constraints imposed by a fiber link.
2. This could also be viewed as a node capability.
3. This could be dynamic in the case of a limited pool of converters
where the number available can change with connection
establishment. Note it may be desirable to include regeneration
capabilities here since OEO converters are also regenerators.
4. Not necessarily needed in the case of distributed wavelength
assignment via signaling.
While the full complement of the information from the previous table
is needed in the Combined RWA and the separate Routing and WA
architectures, in the case of Routing + distributed WA via signaling
only the following information is needed:
Information Static/Dynamic Node/Link
------------------------------------------------------------------
Connectivity matrix Static Node
Wavelength conversion capabilities Static(3) Node
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Information models and compact encodings for this information is
provided in [WSON-Info], [Gen-Encode] and [WSON-Encode].
6.3. Optical Path Computation and Implications for PCE
As previously noted the RWA problem can be computationally intensive.
Such computationally intensive path computations and optimizations
were part of the impetus for the PCE architecture [RFC4655].
The Path Computation Element Protocol (PCEP) defines the procedures
necessary to support both sequential [RFC5440] and global concurrent
path computations (PCE-GCO) [RFC5557], PCE is well positioned to
support WSON-enabled RWA computation with some protocol enhancement.
Implications for PCE generally fall into two main categories: (a)
lightpath constraints and characteristics, (b) computation
architectures.
6.3.1. Lightpath Constraints and Characteristics
For the varying degrees of optimization that may be encountered in a
network the following models of bulk and sequential lightpath
requests are encountered:
o Batch optimization, multiple lightpaths requested at one time
(PCE-GCO).
o Lightpath(s) and backup lightpath(s) requested at one time (PCEP).
o Single lightpath requested at a time (PCEP).
PCEP and PCE-GCO can be readily enhanced to support all of the
potential models of RWA computation.
Lightpath constraints include:
o Bidirectional Assignment of wavelengths.
o Possible simultaneous assignment of wavelength to primary and
backup paths.
o Tuning range constraint on optical transmitter.
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6.3.2. Electro-Optical Element Signal Compatibility
When requesting a path computation to PCE, the PCC should be able to
indicate the following:
o The G-PID type of an LSP.
o The signal attributes at the transmitter (at the source): (i)
modulation type; (ii) FEC type.
o The signal attributes at the receiver (at the sink): (i)
modulation type; (ii) FEC type.
The PCE should be able to respond to the PCC with the following:
o The conformity of the requested optical characteristics associated
with the resulting LSP with the source, sink and NE along the LSP.
o Additional LSP attributes modified along the path (e.g.,
modulation format change, etc.).
6.3.3. Discovery of RWA Capable PCEs
The algorithms and network information needed for solving the RWA are
somewhat specialized and computationally intensive hence not all PCEs
within a domain would necessarily need or want this capability.
Hence, it would be useful via the mechanisms being established for
PCE discovery [RFC5088] to indicate that a PCE has the ability to
deal with the RWA problem. Reference [RFC5088] indicates that a sub-
TLV could be allocated for this purpose.
Recent progress on objective functions in PCE [RFC5541] would allow
the operators to flexibly request differing objective functions per
their need and applications. For instance, this would allow the
operator to choose an objective function that minimizes the total
network cost associated with setting up a set of paths concurrently.
This would also allow operators to choose an objective function that
results in a most evenly distributed link utilization.
This implies that PCEP would easily accommodate wavelength selection
algorithm in its objective function to be able to optimize the path
computation from the perspective of wavelength assignment if chosen
by the operators.
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7. Security Considerations
This document has no requirement for a change to the security models
within GMPLS and associated protocols. That is the OSPF-TE, RSVP-TE,
and PCEP security models could be operated unchanged.
However satisfying the requirements for RWA using the existing
protocols may significantly affect the loading of those protocols.
This makes the operation of the network more vulnerable to denial of
service attacks. Therefore additional care maybe required to ensure
that the protocols are secure in the WSON environment.
Furthermore the additional information distributed in order to
address the RWA problem represents a disclosure of network
capabilities that an operator may wish to keep private. Consideration
should be given to securing this information.
8. IANA Considerations
This document makes no request for IANA actions.
9. Acknowledgments
The authors would like to thank Adrian Farrel for many helpful
comments that greatly improved the contents of this draft.
This document was prepared using 2-Word-v2.0.template.dot.
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10. References
10.1. Normative References
[RFC3471] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Functional Description", RFC 3471,
January 2003.
[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
January 2003.
[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.
[RFC4328] Papadimitriou, D., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Extensions for G.709 Optical
Transport Networks Control", RFC 4328, January 2006.
[G.694.1] ITU-T Recommendation G.694.1, "Spectral grids for WDM
applications: DWDM frequency grid", June, 2002.
[RFC5088] J.L. Le Roux, J.P. Vasseur, Yuichi Ikejiri, and Raymond
Zhang, "OSPF protocol extensions for Path Computation
Element (PCE) Discovery", January 2008.
[RFC5212] Shiomoto, K., Papadimitriou, D., Le Roux, JL., Vigoureux,
M., and D. Brungard, "Requirements for GMPLS-Based Multi-
Region and Multi-Layer Networks (MRN/MLN)", RFC 5212, July
2008.
[RFC5557] Y. Lee, J.L. Le Roux, D. King, and E. Oki, "Path
Computation Element Communication Protocol (PCECP)
Requirements and Protocol Extensions In Support of Global
Concurrent Optimization", RFC 5557, July 2009.
[RFC5420] Farrel, A., Ed., Papadimitriou, D., Vasseur, JP., and A.
Ayyangarps, "Encoding of Attributes for MPLS LSP
Establishment Using Resource Reservation Protocol Traffic
Engineering (RSVP-TE)", RFC 5420, February 2009.
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[RFC5440] J.P. Vasseur and J.L. Le Roux (Editors), "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440, May
2009.
[RFC5541] J.L. Le Roux, J.P. Vasseur, and Y. Lee, "Encoding of
Objective Functions in Path Computation Element (PCE)
communication and discovery protocols", RFC 5541, July
2009.
[WSON-Compat] G. Bernstein, Y. Lee, B. Mack-Crane, "WSON Signal
Characteristics and Network Element Compatibility
Constraints for GMPLS", draft-bernstein-ccamp-wson-
compatibility, work in progress.
[WSON-Encode] G. Bernstein, Y. Lee, D. Li, and W. Imajuku, "Routing
and Wavelength Assignment Information Encoding for
Wavelength Switched Optical Networks", draft-ietf-ccamp-
wson-encode, work in progress.
[Gen-Encode] G. Bernstein, Y. Lee, D. Li, and W. Imajuku, "General
Network Element Constraint Encoding for GMPLS Controlled
Networks", draft-ietf-ccamp-general-constraint-encode, work
in progress.
[WSON-Imp] Y. Lee, G. Bernstein, D. Li, G. Martinelli, "A Framework
for the Control of Wavelength Switched Optical Networks
(WSON) with Impairments", draft-ietf-ccamp-wson-
impairments, work in progress.
[WSON-Info] Y. Lee, G. Bernstein, D. Li, W. Imajuku, "Routing and
Wavelength Assignment Information for Wavelength Switched
Optical Networks", draft-bernstein-ccamp-wson-info, work in
progress
10.2. Informative References
[RFC4655] Farrel, A., Vasseur, JP., and Ash, J., "A Path Computation
Element (PCE)-Based Architecture ", RFC 4655, August 2006.
[Otani] T. Otani, H. Guo, K. Miyazaki, D. Caviglia, "Generalized
Labels of Lambda-Switching Capable Label Switching Routers
(LSR)", work in progress: draft-otani-ccamp-gmpls-g-694-
lambda-labels, work in progress.
[G.652] ITU-T Recommendation G.652, Characteristics of a single-mode
optical fibre and cable, June 2005.
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[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.671] ITU-T Recommendation G.671, Transmission characteristics of
optical components and subsystems, January 2005.
[G.872] ITU-T Recommendation G.872, Architecture of optical
transport networks, November 2001.
[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.Sup39] ITU-T Series G Supplement 39, Optical system design and
engineering considerations, February 2006.
[G.Sup43] ITU-T Series G Supplement 43, Transport of IEEE 10G base-R
in optical transport networks (OTN), November 2006.
[Imajuku] W. Imajuku, Y. Sone, I. Nishioka, S. Seno, "Routing
Extensions to Support Network Elements with Switching
Constraint", work in progress: draft-imajuku-ccamp-rtg-
switching-constraint.
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11. Contributors
Snigdho Bardalai
Fujitsu
Email: Snigdho.Bardalai@us.fujitsu.com
Diego Caviglia
Ericsson
Via A. Negrone 1/A 16153
Genoa Italy
Phone: +39 010 600 3736
Email: diego.caviglia@(marconi.com, ericsson.com)
Daniel King
Old Dog Consulting
UK
Email: daniel@olddog.co.uk
Itaru Nishioka
NEC Corp.
1753 Simonumabe, Nakahara-ku
Kawasaki, Kanagawa 211-8666
Japan
Phone: +81 44 396 3287
Email: i-nishioka@cb.jp.nec.com
Lyndon Ong
Ciena
Email: Lyong@Ciena.com
Pierre Peloso
Alcatel-Lucent
Route de Villejust, 91620 Nozay
France
Email: pierre.peloso@alcatel-lucent.fr
Jonathan Sadler
Tellabs
Email: Jonathan.Sadler@tellabs.com
Dirk Schroetter
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Cisco
Email: dschroet@cisco.com
Jonas Martensson
Acreo
Electrum 236
16440 Kista, Sweden
Email:Jonas.Martensson@acreo.se
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
Wataru Imajuku
NTT Network Innovation Labs
1-1 Hikari-no-oka, Yokosuka, Kanagawa
Japan
Phone: +81-(46) 859-4315
Email: imajuku.wataru@lab.ntt.co.jp
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12. Appendix A Revision History
This appendix to be removed before publication as an RFC.
A.1 Changes from 00
o Added new first level section on modeling examples and control
plane use cases.
o Added new third level section on wavelength converter pool
modeling
o Editorial clean up of English and updated references.
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A.2 Changes from 01
Fixed error in wavelength converter pool example.
A.3 Changes from 02
Updated the abstract to emphasize the focus of this draft and
differentiate it from WSON impairment [WSON-Imp] and WSON
compatibility [WSON-Compat] drafts.
Added references to [WSON-Imp] and [WSON-Compat].
Updated the introduction to explain the relationship between this
document and the [WSON-Imp] and [WSON-Compat] documents.
In section 3.1 removed discussion of optical impairments in fibers.
Merged section 3.2.2 and section 3.2.3. Deferred much of the
discussion of signal types and standards to [WSON-Compat].
In section 3.4 on Wavelength converters removed paragraphs dealing
with signal compatibility discussion as this is addressed in [WSON-
Compat].
In section 6.1 removed discussion of signaling extensions to deal
with different WSON signal types. This is deferred to [WSON-Compat].
In section 6 removed discussion of "Need for Wavelength Specific
Maximum Bandwidth Information".
In section 6 removed discussion of "Relationship to link bundling and
layering".
In section 6 removed discussion of "Computation Architecture
Implications" as this material was redundant with text that occurs
earlier in the document.
In section 6 removed discussion of "Scaling Implications" as this
material was redundant with text that occurs earlier in the document.
A.4 Changes from 03
In Section 3.3.1 added 4-degree ROADM example and its connectivity
matrix.
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A.5 Changes from 04
Added and enhanced sections on signal type and network element
compatibility.
Merged section 3.2.1 into section 3.2.
Created new section 3.3 on Optical signals with material from [WSON-
Compat].
Created new section 3.5 on Electro-Optical systems with material from
[WSON-Compat].
Created new section 3.7 on Characterizing Electro-Optical Network
Elements with material from [WSON-Compat].
Created new section 5.5 on Electro-Optical Networking Scenarios with
material from [WSON-Compat].
Created new section 6.1.2 on WSON Signals and Network Element
Processing with material from [WSON-Compat].
Created new section 6.3.2. Electro-Optical Related PCEP Extensions
with material from [WSON-Compat].
A.6 Changes from 05
Removal of Section 1.2; Removal of section on lightpath temporal
characteristics; Removal of details on wavelength assignment
algorithms; Removal of redundant summary in section 6.
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