Internet DRAFT - draft-dotaro-ipo-multi-granularity
draft-dotaro-ipo-multi-granularity
IPO Working Group E.Dotaro
D. Papadimitriou
L. Ciavaglia
M. Vigoureux
R. Douville
L. Noirie
Internet Draft Alcatel
Document: draft-dotaro-ipo-multi-granularity-01.txt November 2001
Category: Informational
Optical Multi-Granularity û Architectural Framework
draft-dotaro-ipo-multi-granularity-01.txt
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1. Abstract
The multi-granularity concept in optical networks is the ability to
simultaneously switch different levels of granularity inside a given
optical network. Optical multi-granularity and particularly waveband
switching raises some issues for GMPLS. These have been partially
addressed in [GMPLS-ARCH] and [GMPLS-SIG] from the CCAMP Working
Group. However, enabling multi-granularity in optical networks
demands the definition of a more complete set of requirements
considering the management, control, routing and signaling issues
and their impacts in the GMPLS protocols suite.
In this framework document we propose to extend GMPLS previous set
of switching capabilities in the optical domain. This by identifying
uncovered characteristics of the optical transport, taking into
account interest for optical components working at the band level
and its impact on the control of the optical networks.
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Optical Multi-Granularity û Architectural Framework November 2001
2. Introduction
Starting from MPLS labeled packet switching and MPLS-TE concepts,
Generalized MPLS (GMPLS) introduces a new architecture and new
building blocks to support additional switching layers, i.e. TDM,
wavelength, waveband and fiber switching. In the framework of
optical networking, the switching types of interest are mainly
wavelength, waveband and fiber. Multi-granularity consists in
combining and operating these switching layers in optical networks.
Optical multi-granularity is quite a new concept, however
feasibility and benefits of the approach have already been
demonstrated [ONDM00-MGOXC], [OFC01-MGOXC].
Available optical multi-granularity technologies spanning components
and systems (de/multiplexer, switch ,MG-OXC,...) indicate the
growing interest to multi-granularity concepts and applications,
while also answering demands and requirements from carriers for the
support and control of multiple switching layers in optical
networks. All this aspects concur to position multi-granularity as a
relevant item in today optical networking framework.
Optical multi-granularity and particularly waveband switching raises
some issues for GMPLS. These have been partially addressed in
[GMPLS-ARCH] and [GMPLS-SIG] from the CCAMP Working Group. However,
enabling multi-granularity in optical networks demands the
definition of a more complete set of requirements considering the
management, control, routing and signaling issues and their impacts
in the GMPLS protocols suite.
In this memo, we propose to use this concept of multiple optical
granularities in the GMPLS context in association with grooming
strategies. Among possible optical switching granularities, waveband
is an attractive trade-off for foreseen traffic volumes in next few
years and will be particularly considered in the following. For this
purpose, a new type of interface û WaveBand Switch Capable(WBSC) -
is introduced completing the existing set of interfaces.
Consequently a new type of Label Switched Path, the WaveBand-LSP
(WB-LSP), is considered along with a new class of Forwarding
Adjacencies (FA) as described in Section 4.3.
3. Rationale
The sub-IP area and IPO Working Group are the most suitable
locations for the proposed document as they addresse issues and
considerations related and specific to optical networking.
On basis of charter items, this memo fits into the IPO Working Group
since it documents issues and requirements of an optical specific
concept and technology. The document proposes and describes a
framework for optical multi-granularity and its impact on the GMPLS
protocols suite, notably routing and signaling aspects.
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A complementary work is being initiated in the CCAMP Working Group
based on the present document used as architectural framework. It
addresses GMPLS building blocks enhancement and protocol suite
extension to cover optical multi-granularity and particularly
waveband switching.
4. Terminology
Conventions, acronyms and abbreviations used in this document.
Terminology is based on the definitions from [GMPLS-ARCH] and
[GMPLS-SIG] plus specific addition for Multi-Granularity vocabulary.
L-LSP = Lambda-LSP
WB-LSP = WaveBand-LSP
F-LSP = Fiber-LSP
WXC = Wavelength Cross-Connect
WBXC = WaveBand Cross-Connect
FXC = Fiber Cross-Connect
LSC = Lambda Switch Capabale
WBSC = WaveBand Switch Capable
FSC = Fiber Switch Capable
MG-OXC = Multi-Granularity Cross-Connect
5. Multi-Granularity Considerations
5.1 Context and definition
Considering that traffic increases faster than connectivity,
widening switching granularity scope becomes valuable. Optical
multi-granularity concept, including particularly waveband
switching, allows to match those new requirements of granularity
diversity.
The use and exploitation of multiple granularities in optical
networks relies on availability of proper hardware (components and
systems), on methods to nest LSPs and especially on protocols
integrating the specific features of optical multi-granularity.
The multi-granularity concept in optical networks refers to the
ability to simultaneously switch different levels of granularity
inside a given optical network. The granularities considered at the
optical layer are single wavelengths (L-LSP), band of wavelengths,
i.e. wavebands (WB-LSP), and fibers (F-LSP).
In order to take benefits from these switching granularities, it is
necessary to be able to provision and handle LSPs at such
granularities. The operation to assemble and combine LSPs into
coarser LSPs is called grooming, also known as LSPs nesting. The
process of grooming lower granularity LSPs into larger ones is
analog to the LSP stacking scheme used in MPLS. Typical case of
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Optical Multi-Granularity û Architectural Framework November 2001
grooming consists in aggregating L-LSPs into WB-LSPs and WB-LSPs
into F-LSPs. Section 6.1 addresses the various aspects of grooming
strategies.
Therefore, extensions to GMPLS previous set of switching
capabilities in the optical domain are proposed in this framework
document. This is achieved by identifying uncovered characteristics
of the optical transport, taking into account interest for optical
components working at the band level and its impact on the control
of the optical networks.
In the efforts of describing the requirements and set of
capabilities for optical multi-granularity, three approaches to
waveband switching have been identified:
- Inverse Multiplexing
- Wavelength Concatenation
- Waveband
The availability of optical and/or photonic switching equipment
capable to work at the band level û i.e. build out of band
components and hardware - motivates the redefinition of waveband
switching as defined in the GMPLS architecture. Current definition
of waveband switching (see [GMPLS-ARCH] and [GMPLS-SIG]) refers to
inverse multiplexing mechanism or wavelength concatenation
(ôcontiguousö lambdas) were one can request a 10 Gbps L-LSP (logical
waveband) while the underlying (physical) wavelength operates at 2.5
Gbps. While this definition is still valid and applicable, it does
not consider the approach where band has a physical signification,
i.e. where the interface is waveband switch capable (WBSC). The
following paragraph shows the location of optical multi-granularity
and highlight the new definition of waveband switching.
5.2 Hierarchy Overview
The integration of optical multi-granularity in the GMPLS
architecture requires modifications and extensions to current
definitions. For this purpose, a new type of switch capable
interface is first introduced: the Waveband Switch Capable Interface
(WBSC). The WBSC interface materializes the physical reality of
optical waveband as an atomic entity or granularity. As with the
introduction of the waveband switch capable interface, a new class
of LSP is defined: the WaveBand LSP (WB-LSP).
LSP Hierarchy Interfaces Network Element
P-LSP <---> PSC <----> Router
L2-LSP <---> L2SC <----> Bridge,Switch
TDM-LSP <---> TDM <----> DXC
L-LSP <---> LSC <----> WXC -\
|
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WB-LSP <---> WBSC <----> WBXC > Optical
| MG
F-LSP <---> FSC <----> FXC -/
WXC, WBXC and FXC can be part of the same entity referred to as MG-
OXC or MG-PXC.
The above figure illustrates the hierarchy of the switching layers
and highlights the optical multi-granularity part. The network
element column shows typical real-life boxes that support such
interfaces. Note that this representation does not aim at
restricting interfaces that network elements can support.
Section 7 further details the extensions required to support the new
definition of waveband switching in GMPLS.
5.3 Optical networking with Multi-Granularity
Enabling multi-granularity into optical networks implies the use of
specific optical components and systems, which are band-specific
(filtering and switching functions).
The use of multi-granularity results in reduction of the number of
connections through each optical node. This means from the hardware
point of view a reduction of the number of ports both for the
switches and for the optical multiplexers and demultiplexers. Hence
the optical switches have to be seen as a combination of Fiber
Cross-Connects (FXC), WaveBand Cross-Connects (WBXC) and Wavelengths
Cross-Connects (WXC) with a significant size reduction.
Other benefits of multi-granularity systems, especially with
waveband-based components have to be considered in terms of physical
impairments since constraints are relaxed by decreasing the optical
losses.
The proposed multi-granularity scheme adds a relation between the
Wavelength layer and the Waveband layer which is similar to the
relation between IP and the optical layer from the connectivity
point of view. Hence, all the analysis made in order to justify the
sub-IP layers may be reuse. For instance the provisioning of cut-
trough WaveBand-LSP below wavelength layer will allow to save a
large amount of resource for this last layer. It is analog to
lightpaths, acting as tunnels for the IP layer. Finally, most of
existing routing and signaling protocols building blocks are
applicable, including dissemination of topology information with
Forwarding Adjacencies (FA) based on WB-LSP.
6. Multi-granularity Concept Applicability
6.1 Grooming strategies
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The relative limited number of nodes and the relative small
connectivity in an optical network allows assuming that there is
potentially a strong correlation between flows of traffic inside
such network. Hence, a grooming strategy can be envisaged to nest
low order L-LSPs into higher order LSPs (eg. WB-LSPs or F-LSPs) in
order to take benefit of the different switching level (i.e.
switching granularities).
Considering a set of L-LSPs sharing the same ingress and egress
nodes, a higher order LSP could be provisioned between theses nodes
and the L-LSPs nested into it. This provisioning method is called
End-To-End grooming.
Furthermore, we can assume that the correlation of traffic flows
will be greater in the core of the network than at its periphery.
Considering a set of L-LSPs not sharing the same ingress or/nor the
same egress nodes, but sharing a common sub-path, a higher order LSP
could be provisioned over this sub-path and the L-LSPs nested into
it. This grooming strategy is called Intermediate grooming. Note
that End-To-End grooming is just a peculiar case of Intermediate
grooming, where the sub-path shared by the L-LSPs equals the entire
path (i.e. same source-destination pair).
6.2 Grooming applicability scope
The current L-LSPs nesting definition under the concept of waveband,
as defined in [GMPLS-ARCH] and [GMPLS-SIG], has a restricted
applicability scope. We propose to enhance the grooming
possibilities of L-LSPs so as to widen this field.
From these definitions, two L-LSPs nesting scenarios have been
envisaged.
(1) Waveband switching refers to inverse multiplexing such that only
end-to-end grooming can be achieved and consequently quite
restrictive and limited in its applicability scope.
(2) Waveband switching refers to a kind of optical wavelength
virtual concatenation (wavebands are logically defined û at the
control plane level only - as a group of wavelengths). This scenario
is quite flexible in terms of L-LSP virtual nesting but is
incompatible with the physical constraints of effectively switching
a set of wavelengths as a single physical unit.
In the context of this memo, these two previous scenarios either do
not take advantage of the natural intermediate grooming strategy or
do not take advantage of the emerging waveband switching and
multiplexing technologies.
The principle of grooming optical granularities, taking into account
the new WB-LSP, is analog in the optical domain to LSPs stacking in
MPLS-TE and to the LSP hierarchy that ensues.
The following example illustrates the new grooming strategy combined
with the WB-LSP.
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+----+ +----+
| | *** WB-LSP | |
| | --- L-LSP | |
| | | |
| |-\ /-| |
| | \ / | |
| A |-\ \ / /-| C |
+----+ \ \ +----+ +----+ +----+ +----+ / / +----+
\ \-| | | | | | | |-/ /
\ | |-----| |-----| |-----| | /
+----+ \-| | | | | | | |-/ +----+
| |-------| |*****| |*****| |*****| |-------| |
| |-------| | | | | | | |-------| |
| |-------| E | | F | | G | | H |-------| |
| | +----+ +----+ +----+ +----+ | |
| | | |
| B | | D |
+----+ +----+
Let us consider, in this example, that wavebands are composed of
four wavelengths. Let us also consider that A has one L-LSP
established with C and one with D, that B has one L-LSP established
with C and two with D.
In a wavelength only switching network, these connections would have
been established and routed as L-LSPs and wavelengths switched. But
in a wavelength and waveband switching network, where nodes E, F, G
and H are wavelength and waveband switch capable, a WB-LSP could be
established and routed between nodes E and H. The WB-LSP formed is
composed of any four L-LSPs amongst the five ones entering node E.
6.3 Provisioning Strategies
The introduction of multi-granularity has proven its potential,
however the provisioning of the corresponding LSPs brings a new set
of problems such as information flooding, LSPs establishment
(dynamicity, triggering process, service disruption ...) and other
issues like protection.
In order to make efficient use of waveband switching concept, the
new WBSC interfaces should be advertised. It is envisaged that IGP
such as OSPF or IS-IS could flood the relative information. The
introduction of the new WBSC interface is compliant, considering few
minor enhancements, with Traffic Engineering extensions to OSPF
[OSPF-TE] or IS-IS [ISIS-TE].
Following information dissemination, different scenarii are
envisaged for the provisioning of WB-LSPs.
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Optical Multi-Granularity û Architectural Framework November 2001
Several provisioning/grooming strategies can be foreseen depending
on the various triggering mechanisms with more or less Traffic
Engineering implication.
From the simple point-and-click case to sophisticated traffic driven
one, these approaches will use the information resulting from the
flooding of the FAs. The definition of new traffic engineering
parameters associated to this new class of FA is beyond the scope of
this document.
Nevertheless two TE based approaches dealing with two different
grooming strategies may illustrate TE implication in provisioning/
grooming process.
- On one hand WaveBand-LSPs can be pre-provisioned and then
considered as tunnels for L-LSPs to be routed/nested into it. This
method is an application of intermediate grooming paradigm (see
Section 6.1). Provisioning of such WB-LSPs should be based on large
time scale rules.
- On the other hand WaveBand-LSPs can be dynamically established in
response to a specific triggering mechanism.
WB-LSPs can be established from end-to-end in response to a WB-LSP
request, or can be established following several L-LSPs requests.
Note that re-routing already established L-LSPs into WB-LSPs induces
an interruption of service during switching time.
7. GMPLS Protocol suite extensions
Enabling optical multi-granularity demands the definition of a
complete set of requirements considering the management, control,
routing and signaling issues. The details of the enhancement are
addressed in the companion document [CCAMP-WB] in the CCAMP WG. It
covers particularly the routing and signaling aspects.
The major extension is the introduction of a WaveBand Switch Capable
Interface (WBSC) with its associated components (WB-LSP, Link
Multiplex Capability Value and Descriptor,). Routing aspects also
include the definition of new sub-TLV descriptor for OSPF and IS-IS
to advertise waveband capable links (FAs). From a signaling point of
view, the Generalized Label Request is augmented to support WB-LSP
establishment, while the generalized label is kept unchanged.
Specific extensions to signaling protocols (RSVP-TE, CR-LDP) are
currently under definition.
Other open issues such as LMP considerations, definition of waveband
specific TE parameters will be further specified.
8. Security Considerations
This memo does not introduce new security consideration from the one
already detailed in the GMPLS protocol suite.
9. References
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Optical Multi-Granularity û Architectural Framework November 2001
1. [GMPLS-ARCH] E.Mannie et al., æGeneralized MPLS ArchitectureÆ,
Internet Draft, Work in progress, draft-ietf-ccamp-gmpls-
architecture-01.txt, June 2001.
2. [GMPLS-SIG] P.Ashwood-Smith, L.Berger et al., æGeneralized MPLS -
Signaling Functional DescriptionÆ, Internet Draft, Work in
progress, draft-ietf-mpls-generalized-signalling-06.txt, October
2001.
3. [OSPF-TE] K. Kompella et al., 'OSPF Extensions in Support of
Generalized MPLS', Internet Draft, Work in progress, draft-ietf-
ccamp-ospf-gmpls-extensions-00.txt, September 2001
4. [CCAMP-WB] R.Douville et al., æExtensions to GMPLS for Waveband
SwitchingÆ, Internet Draft, Work in progress, draft-douville-
ccamp-waveband-extension-00.txt, November 2001.
5. [OFC01-MGOXC] L.Noirie et al., æImpact of intermediate traffic
grouping on the dimensioning of multi-granularity optical
networksÆ, Paper presented during OFC 2001.
6. [ISIS-TE] K. Kompella et al., 'IS-IS Extensions in Support of
Generalized MPLS', Internet Draft, Work in progress, draft-ietf-
isis-gmpls-extensions-04.txt, September 2001
7. [ONDM00-MGOXC] C. Blaizot et al., æMulti-Granularity Optical
NetworksÆ, Paper presented during ONDM 2000.
10. Acknowledgments
The authors would like to thank Bernard Sales, Emmanuel Desmet and
Amaury Jourdan for their constructive support, comments and inputs.
11. Author's Addresses
Emmanuel Dotaro
Alcatel
Route de Nozay
91460 Marcoussis, France
Phone: +33 1 6963-1307
Email: emmanual.dotaro@alcatel.fr
Dimitri Papadimitriou
Alcatel
Francis Wellesplein 1,
B-2018 Antwerpen, Belgium
Phone: +32 3 240-8491
Email: dimitri.papadimitriou@alcatel.be
Ludovic Noirie
Alcatel
Route de Nozay
E.Dotaro et al. 9
Optical Multi-Granularity û Architectural Framework November 2001
91460 Marcoussis, France
Phone: +33 1 6963-1136
Email: ludovic.noirie@alcatel.fr
Laurent Ciavaglia
Alcatel
Route de Nozay
91460 Marcoussis, France
Phone: +33 1 6963-4429
Email: laurent.ciavaglia@alcatel.fr
Martin Vigoureux
Alcatel
Route de Nozay
91460 Marcoussis, France
Phone: +33 1 6963-1852
Email: martin.vigoureux@alcatel.fr
Richard Douville
Alcatel
Route de Nozay
91460 Marcoussis, France
Phone: +33 1 6963-4431
Email: richard.douville@alcatel.fr
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Optical Multi-Granularity û Architectural Framework November 2001
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E.Dotaro et al. 11
