One document matched: draft-ietf-ccamp-rwa-wson-framework-06.txt
Differences from draft-ietf-ccamp-rwa-wson-framework-05.txt
Network Working Group Y. Lee (ed.)
Internet Draft Huawei
Intended status: Informational G. Bernstein (ed.)
Expires: October 2010 Grotto Networking
Wataru Imajuku
NTT
April 5, 2010
Framework for GMPLS and PCE Control of Wavelength Switched Optical
Networks (WSON)
draft-ietf-ccamp-rwa-wson-framework-06.txt
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on October 5, 2010.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
Bernstein and Lee Expires October 5, 2010 [Page 1]
Internet-Draft Wavelength Switched Optical Networks April 2010
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect to this document. Code Components extracted from this
document must include Simplified BSD License text as described in
Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the Simplified BSD License.
Abstract
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. In addition, electro-optical
network elements and their compatibility constraints relative to
optical signal parameters are characterized.
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.
This memo 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.
Table of Contents
1. Introduction...................................................4
1.1. Revision History..........................................5
1.1.1. Changes from 00......................................5
1.1.2. Changes from 01......................................5
1.1.3. Changes from 02......................................5
1.1.4. Changes from 03......................................6
1.1.5. Changes from 04......................................6
1.1.6. Changes from 05......................................6
2. Terminology....................................................6
3. Wavelength Switched Optical Networks...........................7
3.1. WDM and CWDM Links........................................7
Bernstein and Lee Expires October 5, 2010 [Page 2]
Internet-Draft Wavelength Switched Optical Networks April 2010
3.2. Optical Transmitters......................................9
3.3. Optical Signals in WSONs.................................10
3.3.1. Optical Tributary Signals...........................11
3.3.2. WSON Signal Characteristics.........................12
3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs............12
3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs.......13
3.4.2. Splitters...........................................16
3.4.3. Combiners...........................................16
3.4.4. Fixed Optical Add/Drop Multiplexers.................17
3.5. Electro-Optical Systems..................................17
3.5.1. Regenerators........................................17
3.5.2. OEO Switches........................................20
3.6. Wavelength Converters....................................20
3.6.1. Wavelength Converter Pool Modeling..................22
3.7. Characterizing Electro-Optical Network Elements..........26
3.7.1. Input Constraints...................................27
3.7.2. Output Constraints..................................27
3.7.3. Processing Capabilities.............................28
4. Routing and Wavelength Assignment and the Control Plane.......29
4.1. Architectural Approaches to RWA..........................30
4.1.1. Combined RWA (R&WA).................................30
4.1.2. Separated R and WA (R+WA)...........................30
4.1.3. Routing and Distributed WA (R+DWA)..................31
4.2. Conveying information needed by RWA......................32
5. Modeling Examples and Control Plane Use Cases.................33
5.1. Network Modeling for GMPLS/PCE Control...................33
5.1.1. Describing the WSON nodes...........................33
5.1.2. Describing the links................................35
5.2. RWA Path Computation and Establishment...................36
5.3. Resource Optimization....................................37
5.4. Support for Rerouting....................................38
5.5. Electro-Optical Networking Scenarios.....................38
5.5.1. Fixed Regeneration Points...........................38
5.5.2. Shared Regeneration Pools...........................39
5.5.3. Reconfigurable Regenerators.........................39
5.5.4. Relation to Translucent Networks....................39
6. GMPLS & PCE Implications......................................40
6.1. Implications for GMPLS signaling.........................40
6.1.1. Identifying Wavelengths and Signals.................41
6.1.2. WSON Signals and Network Element Processing.........41
6.1.3. Combined RWA/Separate Routing WA support............41
6.1.4. Distributed Wavelength Assignment: Unidirectional, No
Converters.................................................42
6.1.5. Distributed Wavelength Assignment: Unidirectional,
Limited Converters.........................................42
6.1.6. Distributed Wavelength Assignment: Bidirectional, No
Converters.................................................42
6.2. Implications for GMPLS Routing...........................43
Bernstein and Lee Expires October 5, 2010 [Page 3]
Internet-Draft Wavelength Switched Optical Networks April 2010
6.2.1. Electro-Optical Element Signal Compatibility........43
6.2.2. Wavelength-Specific Availability Information........44
6.2.3. WSON Routing Information Summary....................45
6.3. Optical Path Computation and Implications for PCE........46
6.3.1. Lightpath Constraints and Characteristics...........46
6.3.2. Electro-Optical Element Signal Compatibility........47
6.3.3. Discovery of RWA Capable PCEs.......................47
7. Security Considerations.......................................48
8. IANA Considerations...........................................48
9. Acknowledgments...............................................48
10. References...................................................49
10.1. Normative References....................................49
10.2. Informative References..................................50
11. Contributors.................................................53
Author's Addresses...............................................54
Intellectual Property Statement..................................54
Disclaimer of Validity...........................................55
1. Introduction
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. In addition, electro-optical network
elements and their compatibility constraints relative to optical
signal parameters are characterized.
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.
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. For more on how
the GMPLS control plane can aid in dealing with optical impairments
see [WSON-Imp].
Bernstein and Lee Expires October 5, 2010 [Page 4]
Internet-Draft Wavelength Switched Optical Networks April 2010
1.1. Revision History
1.1.1. 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.
1.1.2. Changes from 01
Fixed error in wavelength converter pool example.
1.1.3. 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.
Bernstein and Lee Expires October 5, 2010 [Page 5]
Internet-Draft Wavelength Switched Optical Networks April 2010
In section 6 removed discussion of "Scaling Implications" as this
material was redundant with text that occurs earlier in the document.
1.1.4. Changes from 03
In Section 3.3.1 added 4-degree ROADM example and its connectivity
matrix.
1.1.5. 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].
1.1.6. 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.
2. Terminology
CWDM: Coarse Wavelength Division Multiplexing.
DWDM: Dense Wavelength Division Multiplexing.
FOADM: Fixed Optical Add/Drop Multiplexer.
Bernstein and Lee Expires October 5, 2010 [Page 6]
Internet-Draft Wavelength Switched Optical Networks April 2010
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.
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.
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 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. 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
Bernstein and Lee Expires October 5, 2010 [Page 7]
Internet-Draft Wavelength Switched Optical Networks April 2010
applications from access networks, metro, long haul, and submarine
links to name a few. ITU-T 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 |
------------------------------------------------------------
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.
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
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 allocated to
lambda switching. A label representation for these ITU-T grids is
given in [Otani] and allows a common vocabulary to be used in
signaling lightpaths. Further, these ITU-T grid based labels can also
Bernstein and Lee Expires October 5, 2010 [Page 8]
Internet-Draft Wavelength Switched Optical Networks April 2010
be used to describe WDM links, ROADM ports, and wavelength converters
for the purposes of 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
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
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 path selection.
Fundamental modeling parameters from the control plane perspective
optical transmitters are:
o Tunable: Is this transmitter tunable or fixed.
Bernstein and Lee Expires October 5, 2010 [Page 9]
Internet-Draft Wavelength Switched Optical Networks April 2010
o Tuning range: This is the frequency or wavelength range over which
the laser can be tuned. With the fixed mapping of labels to
lambdas 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.
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 aspects of a laser
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 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.
3.3. Optical Signals in WSONs
In wavelength switched optical networks (WSONs) our 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 we are generally concerned with
multichannel dense wavelength division multiplexing (DWDM) networks
with single channel interfaces. Interfaces of this type are defined
in ITU-T recommendations [G.698.1] and [G.698.1]. Key non-impairment
related parameters defined in [G.698.1] and [G.698.2] are:
(a) Minimum Channel Spacing (GHz)
Bernstein and Lee Expires October 5, 2010 [Page 10]
Internet-Draft Wavelength Switched Optical Networks April 2010
(b) Minimum and Maximum central frequency
(c) Bit-rate/Line coding (modulation) of optical tributary signals
In for the purposes of modeling the WSON in the control plane we can
consider (a) and (b) 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 a currently a number of different "flavors" of optical
tributary signals, 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
deployment 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)[Winzer06].
Note that according to [G.698.2] it is important to fully specify the
bit rate of the optical tributary signal:
"When an optical system uses one of these codes, therefore, it is
necessary to specify both the application code and also the exact bit
rate of the system. In other words, there is no requirement for
equipment compliant with one of these codes to operate over the
complete range of bit rates specified for its optical tributary
signal class."
Bernstein and Lee Expires October 5, 2010 [Page 11]
Internet-Draft Wavelength Switched Optical Networks April 2010
Hence we see 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
We refer an optical tributary signal defined in ITU-T G.698.1 and .2
to as the signal in this document. This is an "entity" that can be
put on an optical communications channel formed from links and
network elements in a WSON. This corresponds to the "lambda" LSP in
GMPLS. For signal compatibility purposes with electro-optical network
elements we will be interested in the following signal
characteristics:
List 1. WSON Signal Characteristics
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 a network with regenerators, OEO switches, or wavelength
converters.
Bit rate and GPID 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 "pre-standard" or proprietary modulation
formats and FEC codes are commonly used in WSONs. For some digital
bit streams the presence of 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 OTUk is all zeros or not.
3.4. 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-
impairment related properties.
Bernstein and Lee Expires October 5, 2010 [Page 12]
Internet-Draft Wavelength Switched Optical Networks April 2010
3.4.1. 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
Bernstein and Lee Expires October 5, 2010 [Page 13]
Internet-Draft Wavelength Switched Optical Networks April 2010
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
examples, including high degree ROADMs/OXCs, are given in [WSON-
Encode]. A classic degree-4 ROADM is shown in Figure 2.
+-----------------------+
Line side-1 --->| |---> Line side-2
ingress (I1) | | egress (E2)
Line side-1 <---| |<--- Line side-2
Egress (E1) | | Ingress (I2)
| ROADM |
Line side-3 --->| |---> Line side-4
ingress (I3) | | egress (E4)
Line side-3 <---| |<--- Line side-4
Egress (E3) | | Ingress (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 "bi-directional", i.e. if ingress port X can be connected to
egress port Y, typically ingress port Y can be connected to egress
port X, assuming the numbering is done in such a way that ingress X
Bernstein and Lee Expires October 5, 2010 [Page 14]
Internet-Draft Wavelength Switched Optical Networks April 2010
and egress X correspond to the same line side direction or the same
add/drop port. This makes the connectivity matrix symmetrical as
shown below.
Ingress Egress 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
that diagonal elements are zero since it is assumed that loopback is
not supported. If ports support loopback, diagonal elements would be
one.
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 (for example wave band
switching)
To model these restrictions we need two pieces of information for
each port: (a) number of wavelengths, (b) wavelength range and
Bernstein and Lee Expires October 5, 2010 [Page 15]
Internet-Draft Wavelength Switched Optical Networks April 2010
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 ingress port and two or more
egress ports. The ingress optical signaled is essentially copied
(with power loss) to all egress ports.
Using the modeling notions of section 3.4.1. 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
(potential) connectivity matrix but the fixed connectivity matrix of
the device.
3.4.3. 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
Bernstein and Lee Expires October 5, 2010 [Page 16]
Internet-Draft Wavelength Switched Optical Networks April 2010
3.4.4. 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 given wavelength
(or waveband) from a line side ingress port would be dropped to a
fixed "tributary" egress port. Depending on the device's construction
that same wavelength may or may not be "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 3.4.1.
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].
3.5. Electro-Optical Systems
This section describes how Electro-Optical Systems (e.g., OEO
switches, wavelength converters, and regenerators) interact with the
WSON signal characteristics defined in List 1 in Section 2.3. 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 so we
start by describing their properties.
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:
Bernstein and Lee Expires October 5, 2010 [Page 17]
Internet-Draft Wavelength Switched Optical Networks April 2010
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.
--------------------------------------------------------------------
From the previous table we can see 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. We see
that 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.
However, in the most common usage of regenerators the digital bit
stream may be slightly modified for performance monitoring and fault
management purposes. SONET, SDH and 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 (Optical Channel Transport Unit-k). These
Bernstein and Lee Expires October 5, 2010 [Page 18]
Internet-Draft Wavelength Switched Optical Networks April 2010
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.
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 we see support for frame alignment, signal
identification, and FEC. 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.
Bernstein and Lee Expires October 5, 2010 [Page 19]
Internet-Draft Wavelength Switched Optical Networks April 2010
Hence we see that depending upon the regenerator technology we may
have the following constraints imposed by a regenerator device:
Table 3. Regenerator Compatibility Constraints
+--------------------------------------------------------+
| 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 Limited Wavelength Range constraint is already modeled in
GMPLS for WSON and that Modulation Type Restriction constraint
includes FEC.
3.5.2. OEO Switches
A common place where optical-to-electrical-to-optical (OEO)
processing may take place is in WSON switches that utilize (or
contain) regenerators. A vendor may add regenerators to a switching
system for a number of reasons. One obvious 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 egress 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 we described for regenerators in
Table 3.
3.6. 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
Bernstein and Lee Expires October 5, 2010 [Page 20]
Internet-Draft Wavelength Switched Optical Networks April 2010
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.
Hence, this type wavelength converter has signal processing
restrictions that are essentially the same as those we described for
regenerators in Table 3 of section 3.5.1.
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.
2. Wavelength conversion associated with ROADMs/OXCs. In this case we
may have 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 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 considerations we model wavelength converters 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.
Bernstein and Lee Expires October 5, 2010 [Page 21]
Internet-Draft Wavelength Switched Optical Networks April 2010
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 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 we need 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 ingress wavelength on a particular ingress
port to a desired egress wavelength on a particular egress port.
3. Limitations on the types of signals that can be converted and the
conversions that can be performed.
To model point 2 above we can use a similar technique as 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 we will also want our model to include as a minimum the
usage state of individual wavelength converters in the pool.
We utilize a three stage model as shown schematically in Figure 3. In
this model we assume N ingress ports (fibers), P wavelength
converters, and M egress ports (fibers). Since not all ingress ports
can necessarily reach the converter pool, the model starts with a
wavelength pool ingress matrix WI(i,p) = {0,1} whether ingress port i
can reach potentially reach wavelength converter p.
Bernstein and Lee Expires October 5, 2010 [Page 22]
Internet-Draft Wavelength Switched Optical Networks April 2010
Since not all wavelength can necessarily reach all the converters or
the converters may have limited input wavelength range we have a set
of ingress port constraints for each wavelength converter. Currently
we assume that a wavelength converter can only take a single
wavelength on input. We can model each wavelength converter ingress
port constraint via a wavelength set mechanism.
Next we have 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, we have a set of wavelength converter egress wavelength
constraints. These constraints indicate what wavelengths a particular
wavelength converter can generate or are restricted to generating due
to internal switch structure.
Finally, we have a wavelength pool egress matrix WE(p,k) = {0,1}
depending on whether the output from wavelength converter p can reach
egress port k. Examples of this method being used to model wavelength
converter pools for several switch architectures from the literature
are given in reference [WSON-Encode].
Bernstein and Lee Expires October 5, 2010 [Page 23]
Internet-Draft Wavelength Switched Optical Networks April 2010
I1 +-------------+ +-------------+ E1
----->| | +--------+ | |----->
I2 | +------+ WC #1 +-------+ | E2
----->| | +--------+ | |----->
| Wavelength | | Wavelength |
| Converter | +--------+ | Converter |
| Pool +------+ WC #2 +-------+ Pool |
| | +--------+ | |
| Ingress | | Egress |
| Connection | . | Connection |
| Matrix | . | Matrix |
| | . | |
| | | |
IN | | +--------+ | | EM
----->| +------+ WC #P +-------+ |----->
| | +--------+ | |
+-------------+ ^ ^ +-------------+
| |
| |
| |
| |
Ingress wavelength Egress wavelength
constraints for constraints for
each converter each converter
Figure 3 Schematic diagram of wavelength converter pool model.
Example: Shared Per Node
In Figure 4 below we show a simple optical switch in a four
wavelength DWDM system sharing wavelength converters in a general
"per node" fashion.
Bernstein and Lee Expires October 5, 2010 [Page 24]
Internet-Draft Wavelength Switched Optical Networks April 2010
+-----------+ ___________ +------+
| |--------------------------->| |
| |--------------------------->| 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 ingress and egress pool matrices are simply:
+-----+ +-----+
| 1 1 | | 1 1 |
WI =| |, WE =| |
| 1 1 | | 1 1 |
+-----+ +-----+
Example: Shared Per Link
In Figure 5 we show a different wavelength pool architecture know as
"shared per fiber". In this case the ingress and egress pool matrices
are simply:
Bernstein and Lee Expires October 5, 2010 [Page 25]
Internet-Draft Wavelength Switched Optical Networks April 2010
+-----+ +-----+
| 1 1 | | 1 0 |
WI =| |, WE =| |
| 1 1 | | 0 1 |
+-----+ +-----+
+-----------+ +------+
| |--------------------------->| |
| |--------------------------->| 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 we characterize Electro-Optical WSON network elements
by the three key functional components: Input constraints, Output
constraints and Processing Capabilities.
Bernstein and Lee Expires October 5, 2010 [Page 26]
Internet-Draft Wavelength Switched Optical Networks April 2010
WSON Network Element
+-----------------------+
WSON Signal | | | | WSON Signal
| | | |
---------------> | | | | ----------------->
| | | |
+-----------------------+
<-----> <-------> <----->
Input Processing Output
Figure 6 WSON Network Element
3.7.1. Input Constraints
Section 3 discussed the basic properties regenerators, OEO switches
and wavelength converters from these we have the following possible
types of input constraints and properties:
1. Acceptable Modulation formats
2. Client Signal (GPID) restrictions
3. Bit Rate restrictions
4. FEC coding restrictions
5. Configurability: (a) none, (b) self-configuring, (c) required
We can represent these constraints 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 we've added
item 5, which describes the devices configurability.
Note that such input constraints also apply to the final destination,
sink or 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 we'd see the
following types of output constraints:
Bernstein and Lee Expires October 5, 2010 [Page 27]
Internet-Draft Wavelength Switched Optical Networks April 2010
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
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
Item(D) can be modeled with existing GMPLS mechanisms.
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 we 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 (ingress & egress 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.
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 as part of an LSP then the control plane
Bernstein and Lee Expires October 5, 2010 [Page 28]
Internet-Draft Wavelength Switched Optical Networks April 2010
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.
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 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". To
ease up on this constraint while keeping network costs in check a
limited number of wavelength converters may be introduced 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 network's 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.
Bernstein and Lee Expires October 5, 2010 [Page 29]
Internet-Draft Wavelength Switched Optical Networks April 2010
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 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 In a separate Path Computation Element (PCE) which owns the
complete and updated knowledge of network state and provides path
computation services to nodes.
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.
Bernstein and Lee Expires October 5, 2010 [Page 30]
Internet-Draft Wavelength Switched Optical Networks April 2010
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's available
resources and on network node 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 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 egress nodes selects one label in the
Label Set received at the node, which is also up to the node local
policy.
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
Bernstein and Lee Expires October 5, 2010 [Page 31]
Internet-Draft Wavelength Switched Optical Networks April 2010
performances relatively to blocking. Note that this approach requires
less information dissemination than the others.
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. We can view this information 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
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:
o Tailor message content to WSON. For example the use of wavelength
ranges, or wavelength occupation bit maps.
Utilize incremental updates if feasible.
Bernstein and Lee Expires October 5, 2010 [Page 32]
Internet-Draft Wavelength Switched Optical Networks April 2010
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.
+--+ +--+ +--+ +--------+
+-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+-+
+--+
5.1.1. Describing the WSON nodes
The eight WSON nodes in this example have the following properties:
o Nodes N1, N2, N3 have fixed OADMs (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.
Bernstein and Lee Expires October 5, 2010 [Page 33]
Internet-Draft Wavelength Switched Optical Networks April 2010
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.
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).
Bernstein and Lee Expires October 5, 2010 [Page 34]
Internet-Draft Wavelength Switched Optical Networks April 2010
+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:
Bernstein and Lee Expires October 5, 2010 [Page 35]
Internet-Draft Wavelength Switched Optical Networks April 2010
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 egress 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 egress 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:
Bernstein and Lee Expires October 5, 2010 [Page 36]
Internet-Draft Wavelength Switched Optical Networks April 2010
+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
Bernstein and Lee Expires October 5, 2010 [Page 37]
Internet-Draft Wavelength Switched Optical Networks April 2010
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 we look at various networking scenarios involving
regenerators, OEO switches and wavelength converters. We group these
scenarios 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
Bernstein and Lee Expires October 5, 2010 [Page 38]
Internet-Draft Wavelength Switched Optical Networks April 2010
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 we need to 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
In this scenario we have regenerators that require configuration
prior to use on an optical signal. We discussed previously that 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 we will need information concerning
regenerator properties for selection of compatible paths and for IA-
RWA computations. In addition during LSP setup we need 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
In the literature, networks that contain both transparent network
elements such as reconfigurable optical add drop multiplexers
(ROADMs) and electro-optical network elements such regenerators or
Bernstein and Lee Expires October 5, 2010 [Page 39]
Internet-Draft Wavelength Switched Optical Networks April 2010
OEO switches are frequently referred to as Translucent optical
networks [Trans07]. Earlier work suggesting GMPLS extensions for
translucent optical networks can be found in [Yang05] while a more
comprehensive evaluation of differing GMPLS control plane approaches
to translucent networks can be found in [Sambo09].
Three main types of translucent optical networks have been discussed:
4. Transparent "islands" surrounded by regenerators. This is
frequently seen when transitioning from a metro optical sub-
network to a long haul optical sub-network.
5. 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 [Sen08].
6. 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 either
the networking scenarios of sections 5.5.1. and 5.5.2. above. And
hence, can be accommodated by the GMPLS extensions suggested in this
document.
6. 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.
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.
Bernstein and Lee Expires October 5, 2010 [Page 40]
Internet-Draft Wavelength Switched Optical Networks April 2010
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.
Furthermore such a mapping as described in [Otani] eases
communication between PCE and WSON PCCs.
6.1.2. WSON Signals and Network Element Processing
We saw in section 3.3.2. 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 (section 5.5.1. ) 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 (section 5.5.2. ) we need to
be able to indicate to a node that it should perform regeneration on
a particular signal. Viewed another way, for an LSP we want 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 (section 5.5.3. ) is very
similar to the previous except that now there are potentially many
more items that we may want to configure 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 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
Bernstein and Lee Expires October 5, 2010 [Page 41]
Internet-Draft Wavelength Switched Optical Networks April 2010
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 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
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.
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. 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
Bernstein and Lee Expires October 5, 2010 [Page 42]
Internet-Draft Wavelength Switched Optical Networks April 2010
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 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).
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 we need
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.
Bernstein and Lee Expires October 5, 2010 [Page 43]
Internet-Draft Wavelength Switched Optical Networks April 2010
Note that since the bit rate of the signal does not change over the
LSP. We can make this an LSP parameter and hence this information
would be available for any NE that needs to use it for configuration.
Hence we do not need "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)GPID particular capabilities
TBD, (b) optical performance monitoring capabilities TBD.
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 we 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 [WSON-Encode].
Bernstein and Lee Expires October 5, 2010 [Page 44]
Internet-Draft Wavelength Switched Optical Networks April 2010
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
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
Laser Transmitter range Static Link(2)
Wavelength conversion capabilities Static(3) Node
Maximum bandwidth per Wavelength Static Link
Wavelength Availability Dynamic(4) Link
Signal Compatibility & 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 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:
Bernstein and Lee Expires October 5, 2010 [Page 45]
Internet-Draft Wavelength Switched Optical Networks April 2010
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], [Gen-Encode] and [WSON-Encode].
6.3. 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 [RFC5440] and global concurrent path computations
[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.
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.
Bernstein and Lee Expires October 5, 2010 [Page 46]
Internet-Draft Wavelength Switched Optical Networks April 2010
o Tuning range constraint on optical transmitter.
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 GPID 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.
Bernstein and Lee Expires October 5, 2010 [Page 47]
Internet-Draft Wavelength Switched Optical Networks April 2010
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.
Bernstein and Lee Expires October 5, 2010 [Page 48]
Internet-Draft Wavelength Switched Optical Networks April 2010
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.
[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.
[RFC5440] J.P. Vasseur and J.L. Le Roux (Editors), "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440, May
2009.
Bernstein and Lee Expires October 5, 2010 [Page 49]
Internet-Draft Wavelength Switched Optical Networks April 2010
[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
[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.
Bernstein and Lee Expires October 5, 2010 [Page 50]
Internet-Draft Wavelength Switched Optical Networks April 2010
[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-g-694-
lambda-labels, work in progress.
[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.
[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.
Bernstein and Lee Expires October 5, 2010 [Page 51]
Internet-Draft Wavelength Switched Optical Networks April 2010
[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.
[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.
[Sambo09] N. Sambo, N. Andriolli, A. Giorgetti, L. Valcarenghi, I.
Cerutti, P. Castoldi, and F. Cugini, "GMPLS-controlled
dynamic translucent optical networks," Network, IEEE, vol.
23, 2009, pp. 34-40.
[Sen08] A. Sen, S. Murthy, and S. Bandyopadhyay, "On Sparse Placement
of Regenerator Nodes in Translucent Optical Network,"
Global Telecommunications Conference, 2008. IEEE GLOBECOM
2008. IEEE, 2008, pp. 1-6.
[Trans07] Gangxiang Shen and Rodney S. Tucker, "Translucent optical
networks: the way forward [Topics in Optical
Communications]," Communications Magazine, IEEE, vol. 45,
2007, pp. 48-54.
[Yang05] Xi Yang and B. Ramamurthy, "Dynamic routing in translucent
WDM optical networks: the intradomain case," Lightwave
Technology, Journal of, vol. 23, 2005, pp. 955-971.
Bernstein and Lee Expires October 5, 2010 [Page 52]
Internet-Draft Wavelength Switched Optical Networks April 2010
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
Aria Networks
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
Cisco
Email: dschroet@cisco.com
Jonas Martensson
Acreo
Electrum 236
Bernstein and Lee Expires October 5, 2010 [Page 53]
Internet-Draft Wavelength Switched Optical Networks April 2010
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
Intellectual Property Statement
The IETF Trust takes no position regarding the validity or scope of
any Intellectual Property Rights or other rights that might be
claimed to pertain to the implementation or use of the technology
described in any IETF Document or the extent to which any license
under such rights might or might not be available; nor does it
represent that it has made any independent effort to identify any
such rights.
Copies of Intellectual Property disclosures made to the IETF
Secretariat and any assurances of licenses to be made available, or
Bernstein and Lee Expires October 5, 2010 [Page 54]
Internet-Draft Wavelength Switched Optical Networks April 2010
the result of an attempt made to obtain a general license or
permission for the use of such proprietary rights by implementers or
users of this specification can be obtained from the IETF on-line IPR
repository at http://www.ietf.org/ipr
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
any standard or specification contained in an IETF Document. Please
address the information to the IETF at ietf-ipr@ietf.org.
Disclaimer of Validity
All IETF Documents and the information contained therein are provided
on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE
IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL
WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY
WARRANTY THAT THE USE OF THE INFORMATION THEREIN WILL NOT INFRINGE
ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS
FOR A PARTICULAR PURPOSE.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Bernstein and Lee Expires October 5, 2010 [Page 55]
| PAFTECH AB 2003-2026 | 2026-04-23 05:59:47 |