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draft-ietf-ccamp-rwa-wson-framework
Network Working Group G. Bernstein (ed.)
Internet Draft Grotto Networking
Intended status: Informational Y. Lee (ed.)
Expires: April 2009 Huawei
Wataru Imajuku
NTT
October 31, 2008
Framework for GMPLS and PCE Control of Wavelength Switched Optical
Networks (WSON)
draft-ietf-ccamp-wavelength-switched-framework-01.txt
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Abstract
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This memo 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 we provide control plane models for
key wavelength switched optical network subsystems and processes. The
subsystems include wavelength division multiplexed links, tunable
laser transmitters, reconfigurable optical add/drop multiplexers
(ROADM) and wavelength converters.
Lightpath provisioning, in general, requires the routing and
wavelength assignment (RWA) process. This process is reviewed and the
information requirements, both static and dynamic for this process
are presented, along with alternative implementation scenarios that
could be realized via GMPLS/PCE and/or extended GMPLS/PCE protocols.
This memo does NOT address optical impairments in any depth and
focuses on topological elements and path selection constraints that
are common across different WSON environments. It is expected that a
variety of different techniques will be applied to optical
impairments depending on the type of WSON, such as access, metro or
long haul.
Table of Contents
1. Introduction...................................................3
2. Terminology....................................................4
3. Wavelength Switched Optical Networks...........................5
3.1. WDM and CWDM Links........................................5
3.2. Optical Transmitters......................................7
3.2.1. Lasers...............................................7
3.2.2. Spectral Characteristics & Modulation Type...........8
3.2.3. Signal Rates and Error Correction....................9
3.3. ROADMs, OXCs, Splitters, Combiners and FOADMs............10
3.3.1. Reconfigurable Add/Drop Multiplexers and OXCs.......10
3.3.2. Splitters...........................................12
3.3.3. Combiners...........................................12
3.3.4. Fixed Optical Add/Drop Multiplexers.................12
3.4. Wavelength Converters....................................13
4. Routing and Wavelength Assignment and the Control Plane.......15
4.1. Architectural Approaches to RWA..........................16
4.1.1. Combined RWA (R&WA).................................16
4.1.2. Separated R and WA (R+WA)...........................17
4.1.3. Routing and Distributed WA (R+DWA)..................17
4.2. Conveying information needed by RWA......................18
4.3. Lightpath Temporal Characteristics.......................19
5. GMPLS & PCE Implications......................................20
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5.1. Implications for GMPLS signaling.........................20
5.1.1. Identifying Wavelengths and Signals.................20
5.1.2. Combined RWA/Separate Routing WA support............20
5.1.3. Distributed Wavelength Assignment: Unidirectional, No
Converters.................................................21
5.1.4. Distributed Wavelength Assignment: Unidirectional,
Limited Converters.........................................22
5.1.5. Distributed Wavelength Assignment: Bidirectional, No
Converters.................................................22
5.2. Implications for GMPLS Routing...........................23
5.2.1. Need for Wavelength-Specific Maximum Bandwidth
Information................................................23
5.2.2. Need for Wavelength-Specific Availability Information24
5.2.3. Relationship to Link Bundling and Layering..........24
5.2.4. WSON Routing Information Summary....................24
5.3. Optical Path Computation and Implications for PCE........26
5.3.1. Lightpath Constraints and Characteristics...........26
5.3.2. Computation Architecture Implications...............27
5.3.3. Discovery of RWA Capable PCEs.......................27
5.4. Scaling Implications.....................................27
5.4.1. Routing.............................................28
5.4.2. Signaling...........................................28
5.4.3. Path computation....................................28
5.5. Summary of Impacts by RWA Architecture...................28
6. Security Considerations.......................................29
7. IANA Considerations...........................................29
8. Acknowledgments...............................................30
9. References....................................................31
9.1. Normative References.....................................31
9.2. Informative References...................................32
10. Contributors.................................................35
Author's Addresses...............................................35
Intellectual Property Statement..................................36
Disclaimer of Validity...........................................37
1. Introduction
From its beginning Generalized Multi-Protocol Label Switching (GMPLS)
was intended to control wavelength switched optical networks (WSON)
with the GMPLS architecture document [RFC3945] explicitly mentioning
both wavelength and waveband switching and equating wavelengths
(lambdas) with GMPLS labels. In addition a discussion of optical
impairments and other constraints on optical routing can be found in
[RFC4054]. However, optical technologies have advanced in ways that
make them significantly different from other circuit switched
technologies such as Time Division Multiplexing (TDM). Service
providers have already deployed many of these new optical
technologies such as ROADMs and tunable lasers and desire the same
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automation and restoration capabilities that GMPLS has provided to
TDM and packet switched networks. Another important application of an
automated control plane such as GMPLS is the possibility to improve,
via recovery schemes, the availability of the network. One of the
key points of GMPLS based recovery schemes is the capability to
survive multiple failures while legacy protection mechanism such as
1+1 path protection can survive from a single failure. Moreover this
improved availability can be obtained using less network resources.
This document will focus on the unique 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 will NOT
address optical impairments in any depth, but instead focus on
properties that are common across a variety of WSONs.
This memo provides a framework for applying GMPLS and the Path
Computation Element (PCE) architecture to the control of WSONs. In
particular we provide control plane models for key wavelength
switched optical network subsystems and processes. The subsystems
include wavelength division multiplexed links, tunable laser
transmitters, reconfigurable optical add/drop multiplexers (ROADM)
and wavelength converters.
Lightpath provisioning, in general, requires the routing and
wavelength assignment (RWA) process. This process is reviewed and the
information requirements, both static and dynamic for this process
are presented, along with alternative implementation architectures
that could be realized via various combinations of extended GMPLS and
PCE protocols.
2. Terminology
CWDM: Coarse Wavelength Division Multiplexing.
DWDM: Dense Wavelength Division Multiplexing.
FOADM: Fixed Optical Add/Drop Multiplexer.
OXC: Optical cross connect. A symmetric optical switching element in
which a signal on any ingress port can reach any egress port.
ROADM: Reconfigurable Optical Add/Drop Multiplexer. An asymmetric
wavelength selective switching element featuring ingress and egress
line side ports as well as add/drop side ports.
RWA: Routing and Wavelength Assignment.
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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 (WSON): 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 come in a variety of shapes and sizes from continent spanning
long haul networks, to metropolitan networks, to residential access
networks. In all these cases we are concerned with 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 the following we examine
and model some major subsystems of a WSON with an emphasis on those
aspects that are of relevance to the control plane. In particular we
look at WDM links, Optical Transmitters, ROADMs, and Wavelength
Converters.
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 from access networks, metro, long haul, and submarine
links to name a few. ITU-T and IEC standards exist for various types
of fibers. For the purposes here we are concerned only with single
mode fibers (SMF). The following SMF fiber types are typically
encountered in optical networks:
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 |
------------------------------------------------------------
These fiber types are differentiated by their optical impairment
characteristics such as attenuation, chromatic dispersion,
polarization mode dispersion, four wave mixing, etc. Since these
effects can be dependent upon wavelength, channel spacing and input
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power level, the net effect for our modeling purposes here is to
restrict the range of wavelengths that can be used.
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 we can have a discontinuous
acceptable wavelength range for a particular link. Also some systems
will utilize more than one band. This is particularly true for coarse
WDM (CWDM) systems.
[Editor's note: the previous text is primarily tutorial in nature and
maybe deleted or moved to an appendix in a future draft]
Current technology breaks up 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] 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] describes a CWDM grid
define 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 allocated to
lambda switching. A fixed mapping between the GMPLS label space and
these ITU-T WDM grids as proposed in [Otani] would not only allow a
common vocabulary to be used in signaling lightpaths but also in
describing WDM links, ROADM ports, and wavelength converters for the
purposes path selection.
With a tremendous existing base of fiber 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
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requires much system engineering and a fairly limited range of
wavelengths. Hence for our basic, impairment unaware, modeling of a
WDM link we will need the following information:
o Wavelength range(s): Given a mapping between labels and the ITU-T
grids each range could be expressed in terms of a doublet
(lambda1, lambda2) or (freq1, freq1) where the lambdas or
frequencies can be represented by 32 bit integers.
o Channel spacing: currently there are about five channel spacings
used in DWDM systems 12.5GHz to 200GHz and one defined CWDM
spacing.
For a particular link this information is relatively static, i.e.,
changes to these properties generally require hardware upgrades. Such
information could be used locally during wavelength assignment via
signaling, similar to label restrictions in MPLS or used by a PCE in
solving the combined routing and wavelength assignment problem.
3.2. Optical Transmitters
3.2.1. Lasers
WDM optical systems make use of laser transmitters utilizing
different wavelengths (frequencies). Some laser transmitters were and
are manufactured for a specific wavelength of operation, that is, the
manufactured frequency cannot be changed. First introduced to reduce
inventory costs, tunable optical laser transmitters are becoming
widely deployed in some systems [Coldren04], [Buus06]. This allows
flexibility in the wavelength used for optical transmission and aids
in the control of path selection.
Fundamental modeling parameters from the control plane perspective
optical transmitters are:
o Tunable: Is this transmitter tunable or fixed.
o Tuning range: This is the frequency or wavelength range over which
the laser can be tuned. With the fixed mapping of labels to
lambda's of [Otani] this can be expressed as a doublet (lambda1,
lambda2) or (freq1, freq2) where lambda1 and lambda2 or freq1 and
freq2 are the labels representing the lower and upper bounds in
wavelength or frequency.
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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 applicable for fast protection applications.
o Spectral Characteristics and stability: The spectral shape of the
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 finest channel spacing on which
the transmitter can be used.
Note that ITU-T recommendations specify many other aspects of a
laser's such as spectral characteristics and stability. Many of these
parameters are key in designing WDM subsystems consisting of
transmitters, WDM links and receivers however they do not furnish
additional information that will influence label switched path (LSP)
provisioning in a properly designed system.
Also note that lasers transmitters as a component 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 laser
transmitter will still be failed on the alternate optical path.
3.2.2. Spectral Characteristics & Modulation Type
Contrary to some marketing claims optical systems are not truly
"transparent" to the content of the signals that they carry. Each
lightpath will have spectral characteristics based on its content,
and the spacing of wavelengths in a WDM link will ultimately put
constraints on that spectrum.
For analog signals such as used in closed access television (CATV) or
"radio over fiber" links spectral characteristics are given in terms
of various bandwidth measures. However digital signals consist of our
main focus here and in the ITU-T G series optical specifications. In
this case the spectral characteristics can be more accurately
inferred from the modulation format and the bit rate.
Although Non-Return to Zero (NRZ) is currently the dominant form of
optical modulation, new modulation formats are being researched
[Winzer06] and deployed. With a choice in modulation formats we no
longer have a one to one relationship between digital bandwidth in
bytes or bits per second and the amount of optical spectrum (optical
bandwidth) consumed. To simplify the specification of optical signals
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the ITU-T, in recommendation G.959.1, combined a rate bound and
modulation format designator [G.959.1]. For example, two of the
signal classes defined in [G.959.1] are:
Optical tributary signal class NRZ 1.25G:
"Applies to continuous digital signals with non-return to zero line
coding, from nominally 622 Mbit/s to nominally 1.25 Gbit/s. Optical
tributary signal class NRZ 1.25G includes a signal with STM-4 bit
rate according to ITU-T Rec. G.707/Y.1322." Note that Gigabit
Ethernet falls into this signaling class as well.
Optical tributary signal class RZ 40G:
"Applies to continuous digital signals with return to zero line
coding, from nominally 9.9 Gbit/s to nominally 43.02 Gbit/s.
Optical tributary signal class RZ 40G includes a signal with STM-
256 bit rate according to ITU-T Rec. G.707/Y.1322 and OTU3 bit rate
according to ITU-T Rec. G.709/Y.1331."
From a modeling perspective we have:
o Analog signals: bandwidth parameters, e.g., 3dB parameters and
similar.
o Digital signals: there are predefined modulation bit rate classes
that we can encode.
This information can be important in constraining route selection,
for example some signals may not be compatible with some links or
wavelength converters. In addition it lets the endpoints understand
if it can process the signal.
3.2.3. Signal Rates and Error Correction
Although, the spectral characteristics of a signal determine its
basic compatibility with a WDM system, more information is generally
needed for various processing activities such as regeneration and
reception. Many digital signals such as Ethernet, G.709, and SDH have
well defined encoding which includes forward error correction (FEC).
However many subsystem vendors offer additional FEC options for a
given signal type. The use of different FECs can lead to different
overall signal rates. If the FEC and rate used is not compatible
between the sender and receiver the signal can not be correctly
processed. Note that the rates of "standard" signals may be extended
to accommodate different payloads. For example there are
transmitters capable of directly mapping 10GE LAN-PHY traffic into
G.709 ODU2 frame with slightly higher clock rate [G.Sup43].
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3.3. ROADMs, OXCs, Splitters, Combiners and FOADMs
Definitions of various optical devices and their parameters can be
found in [G.671], we only look at a subset of these and their non-
impairement related properties.
3.3.1. Reconfigurable Add/Drop Multiplexers and OXCs
Reconfigurable add/drop optical multiplexers (ROADM) have matured and
are available in different forms and technologies [Basch06]. This is
a key technology that allows wavelength based optical switching. A
classic degree-2 ROADM is shown in Figure 1.
Line side ingress +---------------------+ Line side egress
--->| |--->
| |
| ROADM |
| |
| |
+---------------------+
| | | | o o o o
| | | | | | | |
O O O O | | | |
Tributary Side: Drop (egress) Add (ingress)
Figure 1 Degree-2 ROADM
The key feature across all ROADM types is their highly asymmetric
switching capability. In the ROADM of Figure 1, the "add" ingress
ports can only egress on the line side egress port and not on any of
the "drop" egress ports. The degree of a ROADM or switch is given by
the number of line side ports (ingress and egress) and does not
include the number of "add" or "drop" ports. Sometimes the "add"
"drop" ports are 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 we must know the switched
connectivity offered by such a network element to effectively utilize
it. A straight forward way to do this is via a "switched
connectivity" matrix A where Amn = 0 or 1, depending upon whether a
wavelength on ingress port m can be connected to egress port n
[Imajuku]. For the ROADM of Figure 1 the switched connectivity matrix
can be expressed as
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Ingress Egress 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 ingress ports 2-5 are add ports, egress ports 2-5 are drop
ports and ingress port #1 and egress port #1 are the line side (WDM)
ports.
For ROADMs this matrix will be very sparse, and for OXCs the
complement of the matrix will be very sparse, compact encodings and
usage including high degree ROADMs/OXCs are given in [WSON-Encode].
Additional constraints may also apply to the various ports in a
ROADM/OXC. In the literature of optical switches and ROADMs the
following restrictions/terms are used:
Colored port: An ingress or more typically an egress (drop) port
restricted to a single channel of fixed wavelength.
Colorless port: An ingress or more typically an egress (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 (like wave band
switching)
To model these restrictions we need 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].
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3.3.2. Splitters
An optical splitter consists of a single ingress port and two or more
egress ports. The ingress optical signaled is essentially copied
(with loss) to all egress ports.
Using the modeling notions of section 3.3.1. the ingress and egress
ports of a splitter would have the same wavelength restrictions. In
addition we can describe a splitter by a connectivity matrix Amn as
follows:
Ingress Egress 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.
3.3.3. Combiners
A optical combiner is somewhat the dual of a splitter in that it has
a single multi-wavelength egress port and multiple ingress ports.
The contents of all the ingress ports are copied and combined to the
single egress 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
egress port. The fixed connectivity matrix Amn for a combiner would
look like:
Ingress Egress Port
Port #1
---
#1: 1
#2 1
A = #3 1
... 1
#N 1
3.3.4. Fixed Optical Add/Drop Multiplexers
A fixed optical add/drop multiplexer can alter the course of an
ingress wavelength in a preset way. In particular a particular
wavelength (or waveband) from a line side ingress port would be
dropped to a particular "tributary" egress port. Depending on the
device's fixed configuration that same wavelength may or may not be
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"continued" to the line side egress port ("drop and continue"
operation). Further there may exist tributary ingress ports ("add"
ports) whose signals are combined with each other and "continued"
line side signals.
In general to represent the routing properties of an FOADM we need a
fixed connectivity matrix Amn as previously discussed and we need the
precise wavelength restrictions for all ingress and egress ports.
From the wavelength restrictions on the tributary egress ports (drop
ports) we can see what wavelengths have been dropped. From the
wavelength restrictions on the tributary ingress (add) ports we can
see which wavelengths have been added to the line side egress port.
Finally from the added wavelength information and the line side
egress wavelength restrictions we can infer which wavelengths have
been continued.
To summarize, the modeling methodology introduced in section 3.3.1.
consisting of a connectivity matrix and port wavelength restrictions
can be used to describe a large set of fixed optical devices such as
combiners, splitters and FOADMs. Hybrid devices consisting of both
switched and fixed parts are modeled in [WSON-Info].
3.4. Wavelength Converters
Wavelength converters take an ingress optical signal at one
wavelength and emit an equivalent content optical signal at another
wavelength on egress. There are currently two approaches to building
wavelength converters. One approach is based on optical to electrical
to optical (OEO) conversion with tunable lasers on egress. This
approach can be dependent upon the signal rate and format, i.e., this
is basically an electrical regenerator combined with a tunable laser.
The other 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 tunable
laser transmitters. In this case there are plenty of converters to
go around since we can think of each tunable output laser
transmitter on an OEO switch as a potential wavelength converter.
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2. Wavelength conversion associated with ROADMs/OXCs. In this case we
may have a limited amount of conversion 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 we may have a limited amount of conversion. Also in
this case the conversion may be used as part of light path routing.
Based on the above contexts a tentative modeling approach for
wavelength converters could be 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 ingress 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 we can associate them with ingress ports.
3. Wavelength converters have range restrictions that are either
independent or dependent upon the ingress wavelength. [TBD: for
those that depend on ingress wavelength can we have a standard
formula? Also note that this type of converter introduces
additional optical impairments.]
4. Wavelength converters that are O-E-O based will have a restriction
based on the modulation format and transmission speed.
Note that since O-E-O wavelength converters also serve as
regenerators we can include regenerators in our model of wavelength
converters. O-E-O Regenerators come in three general types known as
1R, 2R, and 3R regenerators. 1R regenerators re-amplify the signal to
combat attenuation, 2R regenerators reshape as well as amplify the
signal, 3R regenerators amplify, reshape and retime the signal. As we
go from 1R to 3R regenerators the signal is ''cleaned up'' better but
at the same time the regeneration process becomes more dependent on
the signal characteristics such as format and rate.
In WSONs where wavelength converters are sparse we may actually see a
light path appear to loop or ''backtrack'' upon itself in order to
reach a wavelength converter prior to continuing on to its
destination. The lambda used on the "detour" out to the wavelength
converter would be different from that coming back from the "detour"
to the wavelength converter.
A model for an O-E-O wavelength converter would consist of:
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o Input lambda or frequency range
o Output lambda or frequency range
o Equivalent regeneration level (1R, 2R, 3R)
o Signal restrictions if a 2R or 3R regeneration: formats and rates
[FFS: Model for an all optical wavelength converter]
4. Routing and Wavelength Assignment and the Control Plane
In wavelength switched optical networks consisting of tunable lasers
and wavelength selective switches with wavelength converters on every
interface, path selection is similar to the MPLS and TDM circuit
switched cases in that the labels, in this case wavelengths
(lambdas), have only local significance. That is, a wavelength-
convertible network with full wavelength-conversion capability at
each node is equivalent to a circuit-switched TDM network with full
time slot interchange capability; thus, 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 channel - OCh -) 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". To ease up on this constraint while keeping network
costs in check a limited number of wavelength converters maybe
introduce at key points in the network [Chu03].
In the general case of limited or no wavelength converters this
computation is known as the Routing and Wavelength Assignment (RWA)
problem [HZang00]. The "hardness" of this problem is well documented.
There, however, exist a number of reasonable approximate methods for
its solution [HZang00].
The inputs to the basic RWA problem are the requested light paths
source and destination, the networks 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
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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 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 signaling, routing and PCE.
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.
4.1.1. Combined RWA (R&WA)
In this case, a unique entity is in charge of performing routing and
wavelength assignment. This choice assumes that computational entity
has sufficient WSON network link/nodal information and topology to be
able to compute RWA. This solution relies on a sufficient knowledge
of network topology, of available network resources and of network
nodes capabilities. This knowledge has to be accessible to the entity
performing the routing and wavelength assignment.
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 dissemination.
Such a computational entity could reside in two different logical
places:
o In a separate Path Computation Element (PCE) which hence owns the
complete and updated knowledge of network state and provides path
computation services to node.
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.
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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 [Ozdaglar03]. 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 available
resources and on network nodes capabilities.
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 manner along the previously
computed route. This mechanism relies on updating of a list of
potential wavelengths used to ensure 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 it 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 egress nodes selects one label in the
Label Set received at the node, which is also up to the node local
policy.
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Depending on these policies a spectral assignment may not be found or
one consuming too many conversion resources relatively to what a
dedicated wavelength assignment policy would have achieved. Hence,
this 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
performances relatively to blocking. On the other hand this solution
is not stressing the information dissemination processes.
The first entity may be a PCE or the ingress node of the LSP. This
solution is applicable inside network where resource optimization is
not the most crucial constraint.
4.2. Conveying information needed by RWA
The previous sections have characterized WSONs and lightpath
requests. In particular high level models of the information by the
RWA process were presented. We can view this information as either
static, changing with hardware changes (including possibly failures),
or dynamic, 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 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. Static information currently
conveyed includes items like router options and such.
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. Not intended
for dynamic information.
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:
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o Tailor message content to WSON. For example the use of wavelength
ranges, or wavelength occupation bit maps.
Utilize incremental updates if feasible.
4.3. Lightpath Temporal Characteristics
The temporal characteristics of a light path connection is another
aspect that can affect the choice of solution to the RWA process. For
our purposes here we look at the timeliness of connection
establishment/teardown, and the duration of the connection.
Connection Establishment/Teardown Timeliness can be thought of in
approximately three time frames:
1. Time Critical: For example those lightpath establishments used for
restoration of service or other high priority real time service
requests.
2. Soft time bounds: This is a more typical new connection request.
While expected to be responsive, there should be more time to take
into account network optimization.
3. Scheduled or Advanced reservations. Here lightpath connections are
requested significantly ahead of their intended "in service" time.
There is the potential for significant network optimization if
multiple lightpaths can be computed concurrently to achieve network
optimization objectives.
Lightpath connection duration has typically been thought of as
approximately three time frames:
1. Dynamic: those lightpaths with relatively short duration (holding
times).
2. Pseudo-static: lightpaths with moderately long durations.
3. Static: lightpaths with long durations.
Different types of RWA algorithms have been developed for dealing
with dynamic versus pseudo-static conditions. These can address
service provider's needs for: (a) network optimization, (b)
restoration, and (c) highly dynamic lightpath provisioning.
Hence we can model timescale related lightpath requirements via the
following notions:
o Batch or Sequential light path connection requests
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o Timeliness of Connection establishment
o Duration of lightpath connection
5. GMPLS & 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.
5.1. 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.
5.1.1. Identifying Wavelengths and Signals
As previously stated a global fixed mapping between wavelengths and
labels simplifies the characterization of WDM links and WSON devices.
Furthermore such a mapping as described in [Otani] eases
communication between PCE and WSON PCCs.
An alternative to a global network map of labels to wavelengths would
be to use LMP to assign the map for each link then convey that
information to any path computation entities, e.g., label switch
routers or stand alone PCEs. The local label map approach will
require the label-set contents in the RSVP-TE Path message to be
translated every time the map changes between an incoming link and
the outgoing link.
In the future, it maybe worthwhile to define traffic parameters for
lambda LSPs that include a signal type field that includes modulation
format/rate information. This is similar to what was done in
reference [RFC4606] for SONET/SDH signal types.
5.1.2. 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
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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
node. In case the local label map approach is used the label sub-
object entry in the ERO has to be translated appropriately.
5.1.3. 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 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. For example, the following is
a non-exhaustive subset of wavelength assignment (WA) approaches
discussed in [HZang00]:
1. Random: Looks at all available wavelengths for the light path then
chooses from those available at random.
2. First Fit: Wavelengths are ordered, first available (on all links)
is chosen.
3. Most Used: Out of the wavelengths available on the path attempts
to select most use wavelength in network.
4. Least Loaded: For multi-fiber networks. Chooses the wavelength j
that maximizes minimum of the difference between the number of
fibers on link l and the number of fibers on link l with
wavelength j occupied.
As can be seen from the above short list, wavelength assignment
methods have differing information or processing requirements. The
information requirements of these methods are as follows:
1. Random: nothing more than the available wavelength set.
2. First Fit: nothing more than the available wavelength set.
3. Most Used: the available wavelength set and information on global
wavelength use in the network.
4. Least Loaded: the available wavelength set and information
concerning the wavelength dependent loading for each link (this
applies to multi-fiber links). This could be obtained via global
information or via supplemental information passed via the
signaling protocol.
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In case (3) above the global information needed by the wavelength
assignment could be derived from suitably enhanced GMPLS routing.
Note however this information need not be accurate enough for
combined RWA computation. Currently, GMPLS signaling does not provide
a way to indicate that a particular wavelength assignment algorithm
should be used.
5.1.4. Distributed Wavelength Assignment: Unidirectional, Limited
Converters
The previous outlined the case with no wavelength 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 egress 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
egress link. The record route option in RVSP-TE signaling can be used
to show where wavelength conversion has taken place.
5.1.5. 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. We can
try to use the above procedure to determine the available
bidirectional lambda set if we use the interpretation 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, 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
bidirectional lightpaths is not supported.
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5.2. Implications for GMPLS Routing
GMPLS routing [RFC4202] currently defines an interface capability
descriptor for "lambda switch capable" (LSC) which we can use 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, we would need to convey the following subsystem
properties to minimally characterize a WSON:
1. WDM Link properties (allowed wavelengths).
2. Laser 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).
In most cases we should be able to combine items (1) and (2) into the
information in item (3). Except for the number of wavelength
converters that are available in a shared pool, and the previous
information is fairly static. In the next two sections we discuss
dynamic available link bandwidth information.
5.2.1. Need for Wavelength-Specific Maximum Bandwidth Information
Difficulties are encountered when trying to use the bandwidth
accounting methods of [RFC4202] and [RFC3630] to describe the
availability of wavelengths on a WDM link. The current RFCs give
three link resource measures: Maximum Bandwidth, Maximum Reservable
Bandwidth, and Unreserved Bandwidth. Although these can be used to
describe a WDM span they do not provide the fundamental information
needed for RWA. We are not given the maximum bandwidth per wavelength
for the span. If we did then we could use the aforementioned measures
to tell us the maximum wavelength count and the number of available
wavelengths.
For example, suppose we have a 32 channel WDM span, and that the
system in general supports ITU-T NRZ signals up to NRZ 10Gbps.
Further suppose that the first 20 channels are carrying 1Gbps
Ethernet, then the maximum bandwidth would be 320Gbps and the maximum
reservable bandwidth would be 120Gbps (12 wavelengths).
Alternatively, consider the case where the first 8 channels are
carrying 2.5Gbps SDH STM-16 channels, then the maximum bandwidth
would still be 320Gbps and the maximum reservable bandwidth would be
240Gbps (24 wavelengths).
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Such information would be useful in the routing with distributed WA
approach of section 4.1.3.
5.2.2. Need for Wavelength-Specific Availability Information
Even if we know the number of available wavelengths on a link, we
actually need to know which specific wavelengths are available and
which are occupied if we are going to run a combined RWA process or
separate WA process 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 current
dense WDM (DWDM) systems range from 16 channels to 128 channels with
advanced laboratory systems with as many as 300 channels. Given these
channel limitations and if we take the approach of a global
wavelength to label mapping or furnishing the local mappings to the
PCEs then representing the use of wavelengths via a simple bit-map is
feasible.
5.2.3. Relationship to Link Bundling and Layering
When dealing with static DWDM systems, particularly from a SONET/SDH
or G.709 digital wrapper layer, each lambda looks like a separate
link. Typically a bunch of unnumbered links, as supported in GMPLS
routing extensions [RFC4202], would be used to describe a static DWDM
system. In addition these links can be bundled into a TE link
([RFC4202], [RFC4201]) for more efficient dissemination of resource
information. However, in the case discussed here we want to control a
dynamic WDM layer and must deal with wavelengths as labels and not
just as links or component links from the perspective of an upper
(client) layer. In addition, a typical point to point optical cable
contains many optical fibers and hence it may be desirable to bundle
these separate fibers into a TE link. Note that in the no wavelength
conversion or limited wavelength conversion situations that we will
need information on wavelength usage on the individual component
links.
5.2.4. WSON Routing Information Summary
The following table summarizes the WSON information that could be
conveyed via GMPLS routing and attempts to classify that information
as to its static or dynamic nature and whether that information would
tend to be associated with either a link or a node.
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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
Laser Transmitter range Static Link(2)
Wavelength conversion capabilities Static(3) Node
Maximum bandwidth per Wavelength Static Link
Wavelength Availability Dynamic(4) Link
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 we may want 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 + distribute WA via signaling
we only need the following information:
Information Static/Dynamic Node/Link
------------------------------------------------------------------
Connectivity matrix Static Node
Wavelength conversion capabilities Static(3) Node
Information models and compact encodings for this information is
provided in [WSON-Info].
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5.3. Optical Path Computation and Implications for PCE
As previously noted the RWA problem can be computationally intensive
[HZang00]. Such computationally intensive path computations and
optimizations were part of the impetus for the PCE (path computation
element) architecture.
As the PCEP defines the procedures necessary to support both
sequential [PCEP] and global concurrent path computations [PCE-GCO],
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.
5.3.1. 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.
o Lightpath(s) and backup lightpath(s) requested at one time.
o Single lightpath requested at a time.
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.
Lightpath characteristics can include:
o Duration information (how long this connection may last)
o Timeliness/Urgency information (how quickly is this connection
needed)
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5.3.2. Computation Architecture Implications
When a PCE performs a combined RWA computation per section 4.1.1. it
requires accurate an up to date wavelength utilization on all links
in the network.
When a PCE is used to perform wavelength assignment (WA) in the
separate routing WA architecture then the entity requesting WA needs
to furnish the pre-selected route to the PCE as well as any of the
lightpath constraints/characteristics previously mentioned. This
architecture also requires the PCE performing WA to have accurate and
up to date network wavelength utilization information.
When a PCE is used to perform routing in a routing with distribute WA
architecture, then the PCE does not necessarily need the most up to
date network wavelength utilization information, however timely
information can contributed to reducing failed signaling attempts
related to blocking.
5.3.3. 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 [PCE-OF] 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.
5.4. Scaling Implications
This section provides a summary of the scaling issue for WSON
routing, signaling and path computation introduced by the concepts
discussed in this document.
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5.4.1. Routing
In large WSONs label availability and cross connect capability
information being advertised may generate a significant amount of
routing information.
5.4.2. Signaling
When dealing with a large number of simultaneous end-to-end
wavelength service requests and service deletions the network may
have to process a significant number of forward and backward service
messages. Also, similar situation possibly happens in the case of
link or node failure, if the WSON support dynamic restoration
capability.
5.4.3. Path computation
If a PCE is handling path computation requests for end-to-end
wavelength services within the WSON, then the complexity of the
network and number of service path computation requests being sent to
the PCE may have an impact on the PCEs ability to process requests in
a timely manner.
5.5. Summary of Impacts by RWA Architecture
The following table summarizes for each RWA strategy the list of
mandatory ("M") and optional ("O") control plane features according
to GMPLS architectural blocks:
o Information required by the path computation entity,
o LSP request parameters used in either PCC to PCE situations or in
signaling,
o RSVP-TE LSP signaling parameters used in LSP establishment.
The table shows which enhancements are common to all architectures
(R&WA, R+WA, R+DWA), which apply only to R&WA and R+WA (R+&WA), and
which apply only to R+DWA.
+-------------------------------------+-----+-------+-------+-------+
| | |Common | R+&WA | R+DWA |
| Feature | ref +---+---+---+---+---+---+
| | | M | O | M | O | M | O |
+-------------------------------------+-----+---+---+---+---+---+---+
| Generalized Label for Wavelength |5.1.1| x | | | | | |
+-------------------------------------+-----+---+---+---+---+---+---+
| Flooding of information for the | | | | | | | |
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| routing phase | | | | | | | |
| Node features | 3.3 | | | | | | |
| Node type | | | x | | | | |
| spectral X-connect constraint | | | | x | | | |
| port X-connect constraint | | | | x | | | |
| Transponders availability | | | x | | | | |
| Transponders features | 3.2 | | x | | | | |
| Converter availability | | | | x | | | |
| Converter features | 3.4 | | | x | | | x |
| TE-parameters of WDM links | 3.1 | x | | | | | |
| Total Number of wavelength | | x | | | | | |
| Number of wavelengths available | | x | | | | | |
| Grid spacing | | x | | | | | |
| Wavelength availability on links | 5.2 | | | x | | | |
+-------------------------------------+-----+---+---+---+---+---+---+
| LSP request parameters | | | | | | | |
| Signal features | 5.1 | | x | | | x | |
| Modulation format | | | x | | | x | |
| Modulation parameters | | | x | | | x | |
| Specification of RWA method | 5.1 | | x | | | x | |
| LSP time features | 4.3 | | x | | | | |
+-------------------------------------+-----+---+---+---+---+---+---+
| Enriching signaling messages | | | | | | | |
| Signal features | 5.1 | | | | | x | |
+-------------------------------------+-----+---+---+---+---+---+---+
6. 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.
7. IANA Considerations
This document makes no request for IANA actions.
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8. 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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9. References
9.1. Normative References
[RFC3471] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Functional Description", RFC 3471,
January 2003.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630, September
2003.
[RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching
(GMPLS) Architecture", RFC 3945, October 2004.
[RFC4201] Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling in
MPLS Traffic Engineering (TE)", RFC 4201, October 2005.
[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.
[PCE-GCO] 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", work in progress, draft-ietf-pce-
global-concurrent-optimization-05.txt, November 2007.
[PCEP] J.P. Vasseur and J.L. Le Roux (Editors), "Path Computation
Element (PCE) Communication Protocol (PCEP)", work in
progress, draft-ietf-pce-pcep-16.txt, February 2008.
[PCE-OF] J.L. Le Roux, J.P. Vasseur, and Y. Lee, "Encoding of
Objective Functions in Path Computation Element (PCE)
communication and discovery protocols", work in progress,
draft-ietf-pce-of-05.txt, February 2008.
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[WSON-Encode] G. Bernstein, Y. Lee, D. Li, and W. Imajuku, "Routing
and Wavelength Assignment Information Encoding for
Wavelength Switched Optical Networks", draft-bernstein-
ccamp-wson-encode-00.txt, July 2008.
[WSON-Info] G. Bernstein, Y. Lee, D. Li, W. Imajuku," Routing and
Wavelength Assignment Information for Wavelength Switched
Optical Networks", draft-bernstein-ccamp-wson-info-03.txt,
July, 2008.
9.2. Informative References
[HZang00] H. Zang, J. Jue and B. Mukherjeee, "A review of routing and
wavelength assignment approaches for wavelength-routed
optical WDM networks", Optical Networks Magazine, January
2000.
[Coldren04] Larry A. Coldren, G. A. Fish, Y. Akulova, J. S.
Barton, L. Johansson and C. W. Coldren, "Tunable
Seiconductor Lasers: A Tutorial", Journal of Lightwave
Technology, vol. 22, no. 1, pp. 193-202, January 2004.
[Chu03] Xiaowen Chu, Bo Li and Chlamtac I, "Wavelength converter
placement under different RWA algorithms in wavelength-
routed all-optical networks", IEEE Transactions on
Communications, vol. 51, no. 4, pp. 607-617, April 2003.
[Buus06] Jens Buus EJM, "Tunable Lasers in Optical Networks",
Journal of Lightware Technology, vol. 24, no. 1, pp. 5-11,
January 2006.
[Basch06] E. Bert Bash, Roman Egorov, Steven Gringeri and Stuart
Elby, "Architectural Tradeoffs for Reconfigurable Dense
Wavelength-Division Multiplexing Systems", IEEE Journal of
Selected Topics in Quantum Electronics, vol. 12, no. 4, pp.
615-626, July/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-lambda-
labels-02.txt, November 2007.
[Winzer06] Peter J. Winzer and Rene-Jean Essiambre, "Advanced
Optical Modulation Formats", Proceedings of the IEEE, vol.
94, no. 5, pp. 952-985, May 2006.
[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-02.txt, July 2007.
[Ozdaglar03] Asuman E. Ozdaglar and Dimitri P. Bertsekas, ''Routing
and wavelength assignment in optical networks,'' IEEE/ACM
Transactions on Networking, vol. 11, 2003, pp. 259 -272.
[RFC4054] Strand, J. and A. Chiu, "Impairments and Other Constraints
on Optical Layer Routing", RFC 4054, May 2005.
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[RFC4606] Mannie, E. and D. Papadimitriou, "Generalized Multi-
Protocol Label Switching (GMPLS) Extensions for Synchronous
Optical Network (SONET) and Synchronous Digital Hierarchy
(SDH) Control", RFC 4606, August 2006.
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10. 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
Aria Networks
Email: daniel.king@aria-networks.com
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
Author's Addresses
Greg M. Bernstein (ed.)
Grotto Networking
Fremont California, USA
Phone: (510) 573-2237
Email: gregb@grotto-networking.com
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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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