Framework for GMPLS Control of Flexible Grid Network
draft-wang-ccamp-gmpls-flexigrid-framework-00
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draft-wang-ccamp-gmpls-flexigrid-framework-00
Network Working Group Qilei Wang
Internet-Draft Xihua Fu
Intended status: Standards Track ZTE Corporation
Expires: September 1, 2012 Feb 29, 2012
Framework for GMPLS Control of Flexible Grid Network
draft-wang-ccamp-gmpls-flexigrid-framework-00.txt
Abstract
This document provides a framework for applying Generalized Multi-
Protocol Label Switching (GMPLS) and the Path Computation Element
(PCE) architecture to control the flexible grid network base on the
Wavelength Switched Optical Networks (WSONs). GMPLS control of WSON
which is addressed in RFC6163 is out of the scope of this document.
This document focuses on the topological elements changes and new
path selection constraints that flexible grid technology takes.
Impairments related technology is not covered in this document.
Status of this Memo
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Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions used in this document . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Flexible Grid Networks . . . . . . . . . . . . . . . . . . . . 4
3.1. WDM Links . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Optical Transmitters and Receivers . . . . . . . . . . . . 5
3.3. Optical Signals in Flexible Grid Network . . . . . . . . . 5
3.3.1. Optical Tributary Signals . . . . . . . . . . . . . . 6
3.3.2. WSON Signal Characteristics . . . . . . . . . . . . . 6
3.4. ROADMs, OXCs, Splitters, Combiners, and FOADMs . . . . . . 6
3.4.1. Reconfigurable Optical Add/Drop Multiplexers, OXCs
and FOADM . . . . . . . . . . . . . . . . . . . . . . 7
3.4.2. Splitters and Combiners . . . . . . . . . . . . . . . 7
3.5. Electro-Optical Systems . . . . . . . . . . . . . . . . . 7
4. Routing and wavelength Assignment in flexible grid network . . 8
5. GMPLS and PCE Control . . . . . . . . . . . . . . . . . . . . 8
5.1. Extension to GMPLS Signaling . . . . . . . . . . . . . . . 9
5.2. Extension to GMPLS Routing . . . . . . . . . . . . . . . . 9
5.3. Optical Path Computation and Implications for PCE . . . . 11
5.3.1. Optical Path Constraints and Electro-Optical
Element Signal Compatibility . . . . . . . . . . . . . 11
5.3.2. Discovery of RWA-Capable PCEs . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
Flexible grid is a new DWDM application which is defined in the
newest version of [G.694.1]. A flexible grid network can select its
data channels with arbitrary slot width, and mainly be used to setup
path with higher bitrates. This is different from traditional fixed
grid DWDM technology, which uses fixed slot width. Flexible grid
network is a WDM-based optical network in which switching is
performed selectively based on the center wavelength of an optical
signal as well as WSON, and flexible grid network can be constructed
from subsystems that include Wavelength Division Multiplexing (WDM)
links, tunable transmitters and receivers, Reconfigurable Optical
Add/Drop Multiplexers (ROADMs), wavelength converters, and electro-
optical network elements which are used in WSON, whereas these
subsystems have flexible grid characteristics.
Wavelength Switched Optical Network (WSON) is the application of
Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945]
operation to traditional fixed grid WDM network. As described in the
previous section, flexible grid network is a new WDM network which
introduces some new characteristics, so GMPLS also can be used to
operate flexible grid network. WSON specific descriptions are out of
the scope of this document.
This document provides a framework for applying the GMPLS
architecture and protocols [RFC3945] and the PCE architecture
[RFC4655] to the control and operation of flexible grid networks. In
order to help GMPLS and PCE use for flexible grid network, this
document first focuses on the subsystems and new characteristics
information that flexible grid network brings and then modeled the
characteristics information by GMPLS and PCE. This work will help
facilitate the development of protocol solution models and protocol
extensions within the GMPLS and PCE protocol families.
1.1. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Terminology
o Flexible Grid: a new WDM technology different from traditional
fixed grid DWDM technology defined with the aim of allowing
flexible optical spectrum management, in which the Slot Width of
the wavelength ranges allocated to different channels are flexible
(variable sized).
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o Wavelength Range: [RFC6163] gives a description of this
terminology.Wavelength range given a mapping between labels and
the ITU-T grids, each range could be expressed in terms of a
tuple, (lambda1, lambda2) or (freq1, freq2), where the lambdas or
frequencies can be represented by 32-bit integers.
o Frequency slot: The definition in [G.694.1] is shown here. The
frequency range allocated to a channel and unavailable to other
channels within a flexible grid. A frequency slot is defined by
its nominal central frequency and its slot width.
o Slot width: The full width of a frequency slot in a flexible grid.
3. Flexible Grid Networks
Wavelength Switched Optical Network (WSON) related documents cover
the constraints information that needs to be considered by Path
Computation Element (PCE). Emergence of flexible grid DWDM
technology raises some new features that would be considered in the
process of path computation. This section examines the flexible grid
subsystems' new features and mainly focuses on the new features or
constraints information that impact the flexible grid path selection
process (i.e. wavelength selection). The subsequent sections which
follow the sequence of the section addressed in [RFC6163] review and
model some new features that need to be emphasized by control plane.
3.1. WDM Links
According to the newest version of [G.694.1], the nominal central
frequencies for the flexible grid network are defined with a
granularity of 6.25 GHz and the frequency slot widths are defined as
a multiple of 12.5 GHz. As described in section 3.1 of [RFC 6163],
parameters that include wavelength range and channel spacing is
needed to perform basic, impairment-unaware modeling of a WDM link.
Wavelength range can be used to give a mapping between labels and the
ITU-T grids and each range could be expressed in terms of a tuple,
(lambda1, lambda2) or (freq1, freq2). Wavelength range is also
needed in flexible grid network, but some changes are required when
consider the flexible feature. Channel spacing is also needed, but
new channel spacing needs to be added to this field base on WSON when
used in flexible grid network. In addition to the wavelength range
and channel spacing, indication SHOULD also be added to indicate the
link support flexible grid DWDM technology.
Similar to WSON, this information is relatively statically for a
particular link. Such information may be used locally during
wavelength assignment via signaling.
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3.2. Optical Transmitters and Receivers
WDM optical systems make use of optical transmitters and receivers
utilizing different wavelengths (frequencies). Flexible grid brings
some new features to transmitters and receivers compare to
traditional fixed grid technology. Besides characteristics like
"Tunable", "Tuning range", "Tuning time" and "Spectral
characteristics and stability" which are addressed in [RFC6163], some
new features could also impact optical transmitters and receivers in
the process of control plane path computation. Before model the new
features from control plane perspective, focus SHOULD be paid to the
old modeling parameters (here we mainly focus on "Tuning range"),
because flexible grid may bring changes to these parameters. "Tuning
range" may be encode by some different format from traditional fixed
grid technology, as nominal central frequencies can't be figured out
before the path setup in flexible grid network.
New features that would impact optical transmitters and receivers in
the process of control plane path computation are listed below:
Slot width: main difference between flexible grid and traditional
fixed grid is flexible grid network can select its data channels with
arbitrary slot width compare to fixed slot width in traditional fixed
grid network. This parameter indicates slot width needed by a
transmitter or receiver and SHOULD be considered in the process of
path computation.
3.3. Optical Signals in Flexible Grid Network
The fundamental unit of switching in WSONs 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. Key non-
impairment-related parameters which are listed in [RFC6163] are shown
below:
o (a) Minimum channel spacing (GHz)
o (b) Minimum and maximum central frequency
o (c) Bitrates/Line coding (modulation) of optical tributary signals
For the purposes of modeling the WSON in the control plane, new
parameters that SHOULD be considered are shown here:
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o (d) Minimum and Maximum Slot Width
o (e) Slot Width
(d) is considered properties of the link and restrictions on the
GMPLS Labels and (e) is a property of the "signal".
3.3.1. Optical Tributary Signals
In [RFC6163], "optical tributary signal classes" are characterized by
a modulation format and bitrates range and both of them are key
parameters in characterizing the optical tributary signal. Note
that, with advances in technology, more optical tributary signal
classes would be added in flexible grid network. Currently no more
parameters are needed to depict flexible grid network in the process
of path computation.
New parameter "slot width" is needed here, and SHOULD be specified in
the signaling process of flexible grid path, because paths in
flexible grid network often with variable slot width.
3.3.2. WSON Signal Characteristics
Description about WSON signal characteristics in [RFC6163] also can
be applied to this document. Fundamental unit of switching in
flexible grid network is also "wavelength". WSON signal
characteristics like optical tributary signal class (modulation
format), forward error correction (FEC), central frequency
(wavelength), bitrates and general protocol identifier (G-PID) are
still used in flexible grid network in the process of path
computation and some more modulation formats and FECs may be added to
describe flexible grid network signal characteristics.
Except the parameter that have been included in [RFC6163], the
parameter (i.e., slot width) described in the previous section is
also needed here, WSON signal would convey this value in the process
of path computation in order to select a suitable path.
3.4. ROADMs, OXCs, Splitters, Combiners, and FOADMs
This section mainly focuses on optical devices such as ROADMs,
Optical Cross-Connects (OXCs), splitters, combiners, and Fixed
Optical Add/Drop Multiplexers (FOADMs) which can be used in flexible
grid network and examines their parameters of these devices that can
be used in the process of control plane path computation.
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3.4.1. Reconfigurable Optical Add/Drop Multiplexers, OXCs and FOADM
Switched connectivity matrix is needed here to show whether a
wavelength on input port can be connected to an output port.
Besides switched connectivity matrix and wavelength restrictions
included in [RFC6163], new wavelength restriction of a port on a
ROADM which are brought by flexible grid SHOULD be considered. A
port on a ROADM could have following wavelength restrictions in
flexible grid:
o (a) Maximum/Minimum slot width that a port support
Requirements and descriptions about the restrictions information
can be found in
[draft-wangl-ccamp-ospf-ext-constraint-flexi-grid].
o (b) Wavelength ranges partition information according to bitrates
and/or modulation format
This restrictions information will help reduce fragments in
flexible grid network. Requirements related description can be
found in
[draft-wang-ccamp-flexible-grid-wavelength-range-ospf-te].
These restrictions information can also be applied to fixed optical
Add/Drop Multiplexers.
3.4.2. Splitters and Combiners
Nothing is new except switched connectivity matrix and this has been
addressed in [RFC6163].
3.5. Electro-Optical Systems
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. Properties that are described in [RFC6163] can be
applied to flexible grid, and these properties can satisfy path
computation without taking ant new features into consideration.
Modeling of OEO switches, wavelength converters and regenerators can
also be applied to flexible grid.
Regenerator can be used to restore signal quality. Bitrates range
and modulation formats that the regenerator support need to be used
to help path computation, whereas slot width do not (May be someone
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will talk about slot width). If one regenerator is designed to
handle signal with specific bitrates and modulation formats, then it
would support the corresponding slot width because slot width can be
derived by modulation format and bitrates. Even if the slot width is
changed by the electro-optical systems due to the change of
modulation format, the slot width that has already changed may not be
explicitly specified because bitrates and modulation format are
explicitly specified.
4. Routing and wavelength Assignment in flexible grid network
This section briefly describes the constraints information of routing
and wavelength assignment in the flexible grid network. The input to
basic RWA in flexible grid network are the requested optical path's
source and destination, the network topology, the locations and
capabilities of any wavelength converters, the wavelengths available
on each optical link and port label constraints information such as
slot width range that a port support and wavelength range partition
information by bitrates and/or modulation formats. The output that
provided by RWA in flexible grid network are an explicit route
through ROADMs, a wavelength for optical transmitter, the slot width
that this wavelength occupies, 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.
In [RFC6163], three different ways of performing RWA in conjunction
with the control plane are shown here:
1) Combined RWA
2) Separated R and WA (R + WA)
3) Routing and Distributed WA (R + DWA)
These ways can also be applied to flexible grid control plane path
computation. Related description about these three architectures can
be found in [RFC6163].
5. GMPLS and PCE Control
Flexible grid brings some new features to WDM network, and
consequently WSON would add some extensions or change in order to
adapt to control of flexible grid. Extensions to GMPLS signaling,
routing and PCE are described in this section.
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5.1. Extension to GMPLS Signaling
Support for WSON signaling exists in [RFC3471], [RFC4328] and
[draft-ietf-ccamp-wson-signaling]. However, a number of practical
issues arise in the identification of wavelengths and signals in
wavelength assignment in flexible grid.
A mapping between label and wavelength is needed to simplify the
characterization of WDM links and WSON devices. The mapping like the
one described in [draft-farrkingel-ccamp-flexigrid-lambda-label]
provides label and wavelength mapping for communication between PCE
and WSON PCCs. Different LSP may occupy different slot width if
paths have different bitrates and modulation format in flexible grid
network. So in the flexible grid network, not only central frequency
is needed, but also slot width SHOULD be included to identify a
channel in the process of path computation in flexible grid network.
GMPLS Signaling should be able to convey the central frequency and
slot width information in the process of path request of a LSC LSP.
If the slot width is changed due to the change of modulation format,
signaling should also be able to express this. Except methods that
are specified in [draft-farrkingel-ccamp-flexigrid-lambda-label],
[draft-hussain-ccamp-super-channel-label] and
[draft-zhang-ccamp-flexible-grid-rsvp-te-ext] also provide methods to
carry central frequency and slot width information in the process of
signaling.
Note: extension to GMPLS signaling SHOULD be compatible with current
signaling protocol.
5.2. Extension to GMPLS Routing
The following subsystem's properties are needed by IGP to minimally
characterize WSON, also these properties are needed to characterize
flexible grid control plane. This section addresses the constraints
information needed to model flexible grid from the control plane
perspective base on the Wavelength Switched Optical Network (WSON).
1) 1. WDM link properties (allowed wavelengths)
2) 2. Optical transmitters (wavelength range)
3) 3. ROADM/FOADM properties (connectivity matrix, port wavelength
restrictions)
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4) 4. Wavelength converter properties (per network element, may
change if a common limited shared pool is used)
Here 1, 2 and 3 are re-considered in the flexible grid network.
Firstly, wavelengths available on WDM link and port of optical
transmitters are advertised through routing protocol, the wavelength
available information can be used by path computation element to
compute a suitable end-to-end LSP. As different flexible grid
channels always have different slot widths and channels' central
frequency position and slot width can't be decided in advance, so
mapping between label and wavelength may not be able to use the
representation similar to [RFC6205] to represent every channel. New
label formats and representation of wavelength available are needed
in routing protocol to transfer IGP information between nodes and
PCEs. Extensions to label set field SHOULD be able to represent the
wavelength available validly in flexible grid network. Allowed
wavelengths on WDM link and wavelength range on optical transmitters
would adapt to this
change.[draft-dhillon-ccamp-super-channel-ospfte-ext],
[draft-wangl-ccamp-ospf-ext-constraint-flexi-grid] and
[draft-zhang-ccamp-flexible-grid-ospf-ext] give some different
methods to represent the available wavelengths.
Secondly, some new ROADM/FOADM properties brought by flexible grid
need to be advertised by routing protocol in order to help path
computation. In the section 3, properties of ROADM/FOADM are
described. The first one, maximum/minimum slot width supported on
one port need to be advertised. This slot width constraint
information of a port (i.e., slot width constraint information of a
WSS) SHOULD be known by path computation element in order to compute
a suitable path. Ports on a link may support different grid
granularities and slot widths. LMP can be run between two neighbor
nodes to negotiate these attributes and related extension can be
found in [draft-li-ccamp-grid-property-lmp]. This is optional
because routing protocol can also be used to deal with it. The
second one, wavelength range allocation information of ROADM/FOADM
needs to be advertised through routing protocol. Grouping of
wavelength of the same bitrates and/or modulation formats would help
reduce fragments. Channels in the same wavelength range with the
same bitrates looks almost like fixed grid technology, and they won't
generate much fragment in the path setup and release because every
channel use the same slot width. Requirements of wavelength range
allocation and protocol extensions can be found in
[draft-wang-ccamp-flexible-grid-wavelength-range-ospf-te].
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5.3. Optical Path Computation and Implications for PCE
Extensions to PCEP can be found in [draft-lee-pce-wson-rwa-ext] base
on Wavelength Switched Optical Network. Emergence of flexible grid
brings some extension to current draft. PCEP SHOULD be able to
support flexible grid path computation.
5.3.1. Optical Path Constraints and Electro-Optical Element Signal
Compatibility
Flexible grid may not change the computation architectures of WSON,
but new constraints information is needed in the process of path
computation. When requesting a path computation to PCE, the PCC
should be able to indicate the G-PID type of an LSP, the signal
attributes at the transmitter and receiver. As no new attribute need
to be considered, no implication is indicated here.
And the PCE should be able to respond to the PCC with the following
except the conformity of the requested optical characteristics
associated with the resulting LSP with the source, sink, and NE along
the LSP and additional LSP attributes modified along the path:
~ Slot width of the path should be respond to the PCC as flexible
grid channels may have different slot widths.
5.3.2. Discovery of RWA-Capable PCEs
> Not all PCEs within a domain would necessarily need the capability
of flexible grid path computation. Therefore, it would be useful to
indicate that a PCE has the ability to deal with flexible grid via
the discovery mechanisms being established for PCE discovery in
[RFC5088]. Extensions to [RFC5088] are needed to achieve this goal.
6. Security Considerations
TBD
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching
(GMPLS) Architecture", RFC 3945, October 2004.
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7.2. Informative References
[G.694.1 v1]
International Telecommunications Union, "Draft revised
G.694.1 version 1.3".
[flexible-grid-ospf-ext]
Fatai Zhang, Xiaobing Zi, Ramon Casellas, O. Gonzalez de
Dios, and D. Ceccarelli, "GMPLS OSPF-TE Extensions in
support of Flexible-Grid in DWDM Networks",
draft-zhang-ccamp-flexible-grid-ospf-ext-00.txt .
[flexible-grid-requirements]
Fatai Zhang, Xiaobing Zi, O. Gonzalez de Dios, and Ramon
Casellas, "Requirements for GMPLS Control of Flexible
Grids",
draft-zhang-ccamp-flexible-grid-requirements-01.txt .
[flexible-grid-rsvp-te]
Fatai Zhang, O. Gonzalez de Dios, and D. Ceccarelli,
"RSVP-TE Signaling Extensions in support of Flexible
Grid",
draft-zhang-ccamp-flexible-grid-rsvp-te-ext-00.txt .
[flexigrid-lambda-label]
D. King, A. Farrel, Y. Li, F. Zhang, and R. Casellas,
"Generalized Labels for the Flexi-Grid in Lambda-Switch-
Capable (LSC) Label Switching Routers",
draft-farrkingel-ccamp-flexigrid-lambda-label-01.txt .
[ospf-ext-constraint-flexi-grid]
L Wang, Y Li, "OSPF Extensions for Routing Constraint
Encoding in Flexible-Grid Networks",
draft-wangl-ccamp-ospf-ext-constraint-flexi-grid-00.txt .
[super-channel-label]
Iftekhar Hussain, Abinder Dhillon, Zhong Pan, Marco Sosa
and Bert Basch, Steve Liu, Andrew G. Malis, "Generalized
Label for Super-Channel Assignment on Flexible Grid",
draft-hussain-ccamp-super-channel-label-02.txt .
[super-channel-ospfte]
Abinder Dhillon, Iftekhar Hussain, Rajan Rao, Marco Sosa,
"OSPFTE extension to support GMPLS for Flex Grid",
draft-dhillon-ccamp-super-channel-ospfte-ext-02.txt .
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Authors' Addresses
Qilei Wang
ZTE Corporation
Email: wang.qilei@zte.com.cn
Xihua Fu
ZTE Corporation
ZTE Plaza, No.10, Tangyan South Road, Gaoxin District
Xi'an
P.R.China
Email: fu.xihua@zte.com.cn
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