Network Working Group O. Gonzalez de Dios, Ed.
Internet-Draft Telefonica I+D
Intended status: Standards Track R. Casellas, Ed.
Expires: April 25, 2013 CTTC
F. Zhang
Huawei
X. Fu
ZTE
D. Ceccarelli
Ericsson
I. Hussain
Infinera
October 22, 2012
Framework for GMPLS based control of Flexi-grid DWDM networks
draft-ogrcetal-ccamp-flexi-grid-fwk-01
Abstract
This document defines a framework and the associated control plane
requirements for the GMPLS based control of flexi-grid DWDM networks.
To allow efficient allocation of optical spectral bandwidth for high
bit-rate systems, the International Telecommunication Union
Telecommunication Standardization Sector (ITU-T) is extending the
recommendations [G.694.1] and [G.872] to include the concept of
flexible grid: a new DWDM grid has been developed within the ITU-T
Study Group 15, by defining a set of nominal central frequencies,
smaller channel spacings and the concept of "frequency slot". In
such environment, a data plane connection is switched based on
allocated, variable-sized frequency ranges within the ptical
spectrum.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
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This Internet-Draft will expire on April 25, 2013.
Copyright Notice
Copyright (c) 2012 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
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described in the Simplified BSD License.
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Table of Contents
1. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Frequency Slots . . . . . . . . . . . . . . . . . . . . . 6
4.2. Media Layer, Elements and Channels . . . . . . . . . . . . 9
4.3. Media Layer Switching . . . . . . . . . . . . . . . . . . 10
4.4. Control Plane Terms . . . . . . . . . . . . . . . . . . . 11
5. GMPLS applicability . . . . . . . . . . . . . . . . . . . . . 12
6. DWDM flexi-grid enabled network element models . . . . . . . . 12
6.1. Network element constraints . . . . . . . . . . . . . . . 13
7. Layered Network Model . . . . . . . . . . . . . . . . . . . . 14
8. Topology view in Control Plane . . . . . . . . . . . . . . . . 14
9. Control Plane Requirements . . . . . . . . . . . . . . . . . . 16
9.1. Neighbor Discovery and Link Property Correlation . . . . . 16
9.2. Path Computation / Routing and Spectrum Assignment
(RSA) . . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.2.1. Architectural Approaches to RSA . . . . . . . . . . . 17
9.3. Routing / Topology dissemination . . . . . . . . . . . . . 18
9.3.1. Available Frequency Ranges/slots of DWDM Links . . . . 19
9.3.2. Available Slot Width Ranges of DWDM Links . . . . . . 19
9.3.3. Tunable Optical Transmitters and Receivers . . . . . . 19
9.3.4. Hierarchical Spectrum Management . . . . . . . . . . . 19
9.3.5. Information Model . . . . . . . . . . . . . . . . . . 19
9.4. Signaling requirements . . . . . . . . . . . . . . . . . . 20
9.4.1. Slot Width Requirement . . . . . . . . . . . . . . . . 21
9.4.2. Frequency Slot Representation . . . . . . . . . . . . 21
9.4.3. Relationship with MRN/MLN . . . . . . . . . . . . . . 21
10. Control Plane Procedures . . . . . . . . . . . . . . . . . . . 21
11. Backwards (fixed-grid) compatibility, and WSON interworking . 21
12. Misc & Summary of open Issues [To be removed at later
versions] . . . . . . . . . . . . . . . . . . . . . . . . . . 23
13. Security Considerations . . . . . . . . . . . . . . . . . . . 24
14. Contributing Authors . . . . . . . . . . . . . . . . . . . . . 24
15. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 26
16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
16.1. Normative References . . . . . . . . . . . . . . . . . . . 26
16.2. Informative References . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27
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1. Requirements Language
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. Introduction
The term "Flexible grid" (flexi-grid for short) as defined by the
International Telecommunication Union Telecommunication
Standardization Sector (ITU-T) study group 15 in the latest version
of [G.694.1], refers to the updated set of nominal central
frequencies (a frequency grid), channel spacings and optical spectrum
management/allocation considerations that have been defined in order
to allow an efficient and flexible allocation and configuration of
optical spectral bandwidth for high bit-rate systems.
A key concept of flexi-grid is the "frequency slot"; a variable-sized
optical frequency range that can be allocated to a data connection.
As detailed later in the document, a frequency slot is characterized
by its nominal central frequency and its slot width which, as per
[G.694.1], is constrained to be a multiple of a given slot width
granularity.
Compared to a traditional fixed grid network, which uses fixed size
optical spectrum frequency ranges or "frequency slots" with typical
channel separations of 50 GHz, a flexible grid network can select its
media channels with a more flexible choice of slot widths, allocating
as much optical spectrum as required, and allowing higher bit rates
(e.g., 400G, 1T or higher).
From a networking perspective, a flexible grid network is assumed to
be a layered network [G.872][G.800] in which the flexi-grid layer
(also referred to as the media layer) is the server layer and the OCh
Layer (also referred to as the signal layer) is the client layer. In
the media layer, switching is based on a frequency slot, and the size
of a media channel is given by the properties of the associated
frequency slot. In this layered network, the media channel itself
can be dimensioned to contain one or more Optical Channels.
As described in [RFC3945], GMPLS extends MPLS from supporting only
Packet Switching Capable (PSC) interfaces and switching to also
support four new classes of interfaces and switching that include
Lambda Switch Capable (LSC).
A Wavelength Switched Optical Network (WSON), addressed in [RFC6163],
is a term commonly used to refer to the application/deployment of a
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Generalized Multi-Protocol Label Switching (GMPLS)-based control
plane for the control (provisioning/recovery, etc) of a fixed grid
WDM network. [editors' note: we need to think of the relationship of
WSON and OCh switching. Are they equivalent? WSON includes
regeneration, OCh does not? decoupling of lambda/OCh/OCC]
This document defines the framework for a GMPLS-based control of
flexi-grid enabled DWDM networks (in the scope defined by ITU-T
layered Optical Transport Networks [G.872], as well as a set of
associated control plane requirements. An important design
consideration relates to the decoupling of the management of the
optical spectrum resource and the client signals to be transported.
[Editor's note: a point was raised during the meeting that WSON has
not made the separation between Och and Lambda (spectrum and signal
are bundled)].
[Editors' note: this document will track changes and evolutions of
[G.694.1] [G.872] documents until their final publication. This
document is not expected to become RFC until then.]
[Editor's note: -00 as agreed during IETF83, the consideration of the
concepts of Super-channel (a collection of one or more frequency
slots to be treated as unified entity for management and control
plane) and consequently Contiguous Spectrum Super-channel (a super-
channel with a single frequency slot) and Split-Spectrum super-
channel (a super-channel with multiple frequency slots) is postponed
until the ITU-T data plane includes such physical layer entities,
e.g., an ITU-T contribution exists. ITU-T is still discussing B100G
Architecture]
[Editors' note: -01 this version reflects the agreements made during
IETF84, notably concerning the focus in the media layer, terminology
updates post ITU-T September meeting in Geneva and the deprecation of
the ROADM term, in favor of the more concrete media layer switching
element (media channel matrix).]
[Editors' note: -01 in partial answer to Gert question on the layered
model, [G.872] footnote explains that this separation is necessary to
allow the description of media elements that may act on more than a
single OCh-P signal. See appendix IV within.]
3. Acronyms
FS: Frequency Slot
NCF: Nominal Central Frequency
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OCh: Optical Channel
OCh-P: Optical Channel Payload
OCh-O: Optical Channel Overhead
OCC: Optical Channel Carrier
SWG: Slot Width Granularity
4. Terminology
The following is a list of terms (see [G.694.1] and [G.872])
reproduced here for completeness. [Editors' note: regarding
wavebands, we agreed NOT to use the term in flexigrid. The term has
been used inconsistently in fixed-grid networks and overlaps with the
definition of frequency slot. If need be, a question will be sent to
ITU-T asking for clarification regarding wavebands.]
Where appropriate, this documents also uses terminolgy and
lexicography from [RFC4397].
[Editors' note: *important* these terms are not yet final and they
may change / be replaced or obsoleted at any time.]
4.1. Frequency Slots
o Nominal Central Frequency Granularity: 6.25 GHz (note: sometimes
referred to as 0.00625 THz).
o Nominal Central Frequency: each of the allowed frequencies as per
the definition of flexible DWDM grid in [G.694.1]. The set of
nominal central frequencies can be built using the following
expression f = 193.1 THz + n x 0.00625 THz, where 193.1 THz is
ITU-T ''anchor frequency'' for transmission over the C band, n is
a positive or negative integer including 0.
-5 -4 -3 -2 -1 0 1 2 3 4 5 <- values of n
...+--+--+--+--+--+--+--+--+--+--+-
^
193.1 THz <- anchor frequency
Figure 1: Anchor frequency and set of nominal central frequencies
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o Slot Width Granularity: 12.5 GHz, as defined in [G.694.1].
o Slot Width: The slot width determines the "amount" of optical
spectrum regardless of its actual "position" in the frequency
axis. A slot width is constrained to be m x SWG (that is, m x
12.5 GHz), where m is an integer greater than or equal to 1.
o Frequency Slot: The frequency range allocated to a slot within the
flexible grid and unavailable to other slots. A frequency slot is
defined by its nominal central frequency and its slot width.
Assuming a fixed and known central nominal frequency granularity,
and assuming a fixed and known slot width granularity, a frequency
slot is fully characterized by the values of 'n' and 'm'. Note
that an equivalent characterization of a frequency slot is given
by the start and end frequencies (i.e., a frequency range) which
can, in turn, be defined by their respective values of 'n'.
Frequency Slot 1 Frequency Slot 2
------------- -------------------
| | | |
-3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
..--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--...
------------- -------------------
^ ^
Central F = 193.1THz Central F = 193.14375 THz
Slot width = 25 GHz Slot width = 37.5 GHz
Figure 2: Example Frequency slots
The symbol '+' represents the allowed nominal central frequencies,
the '--' represents the nominal central frequency granularity, and
the '^' represents the slot nominal central frequency. The number
on the top of the '+' symbol represents the 'n' in the frequency
calculation formula. The nominal central frequency is 193.1 THz
when n equals zero. Note that over a single frequency slot, one
or multiple Optical Channels may be transported. Note that when
there are multiple optical signals within frequency slot, then
each signal still has its own central frequency. That is, the
term "central frequency" applies to an Optical signal and the term
"nominal central frequency" applies to a frequency slot. In other
words, the Frequency Slot central frequency is independent of the
signals central frequencies.
o Effective Frequency Slot: the effective frequency slot of a media
channel is the common part of the frequency slots of the filter
components along the media channel through a particular path
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through the optical network. It is a logical construct derived
from the (intersection of) frequency slots allocated to each
device in the path. The effective frequency slot is an attribute
of a media channel and, being a frequencly slot, it is described
by its nominal central frequency and slot width. As an example,
if there are two filters having slots with the same n but
different m, then the common frequency slot has the smaller of the
two m values. [Editor's note: within the GMPLS label swapping
paradigm, the switched resource corresponds to the local frequency
slot defined by the observable filters of the media layer
switching element. The GMPLS label MUST identify the switched
resource locally, and (as agreed during IETF84) is locally scoped
to a link, even if the same frequency slot is allocated at all the
hops of the path. Note that the requested slot width and the
finally allocated slot witdh by a given node may be different,
e.g., due to restrictions in the slot width granularity of the
nodes. Due to the symmetric definition of frequency slot,
allocations seem to be constrained to have the same nominal
central frequency. It is important to note that if n changes
along the path, it cannot be guaranteed that there is a valid
common frequency slot. We must determine if different n's are
allowed. We need to explain this rationale. e.g. what happens
when the resulting slot cannot be characterized with n and m, see
Figure 3 and Figure 4.].
Frequency Slot 1
-------------
| |
-3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
..--+--+--+--+--X--+--+--+--+--+--+--+--+--+--+--+--...
Frequency Slot 2
-------------------
| |
-3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
..--+--+--+--+--X--+--+--+--+--+--+--+--+--+--+--+--...
===============================================
Effective Frequency Slot
-------------
| |
-3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
..--+--+--+--+--X--+--+--+--+--+--+--+--+--+--+--+--...
Figure 3: Effective Frequency Slot
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Frequency Slot 1
-------------
| |
-3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
..--+--+--X--+--+--+--+--+--+--+--+--+--+--+--+--+--...
Frequency Slot 2
-------------------
| |
-3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
..--+--+--+--+--X--+--+--+--+--+--+--+--+--+--+--+--...
===============================================
Invalid Effective Frequency Slot - (n, m?)
----------
| |
-3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
..--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--...
Figure 4: Invalid Effective Frequency Slot
4.2. Media Layer, Elements and Channels
o Media Element: a media element only directs the optical signal or
affects the properties of an optical signal, it does not modify
the properties of the information that has been modulated to
produce the optical signal. Examples of media elements include
fibers, amplifiers, filters, switching matrices[Note: the data
plane component of a LSR in the media layer is a media element,
but not all media elements correspond to data plane nodes in the
GMPLS network model.
o Media Channel: a media association that represents both the
topology (i.e., path through the media) and the resource
(frequency slot) that it occupies. As a topological construct, it
represents a (effective) frequency slot supported by a
concatenation of media elements (fibers, amplifiers, filters,
switching matrices...). This term is used to identify the end-to-
end physical layer entity with its corresponding (one or more)
frequency slots local at each link filters.
o Network Media Channel: a media channel (media association) that
supports a single OCh-P network connection. It represents the
concatenation of all media elements between an OCh-P source and an
OCh-P sink. [TODO: |Malcolm| explain the use case rationale to
support a hierarchy of media channels, where a media channel acts
as "pipe" for one or more network media channels and they are both
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separate entities (IETF84). This may be tied to the concept of a
"waveband" or express channel, as stated in [G.872] footnote 4.]
o OCh-P Frequency Slot: The spectrum allocated to a single OCh
signal supported on a Network Media Channel.
4.3. Media Layer Switching
[Editors' note: we are not discarding O/E/O. If defined in a ITU-T
network reference model with trail/terminations, considering optical
channels i.e. with well-defined interfaces, reference points, and
architectures. The implications of O/E/O will be also addressed once
we have another context that includes them. In OTN from an OCh point
of view end to end means from transponder to transponder, so if there
is a 3R from ingress to egress there are 2 OCh which can have
different 'n' and 'm'].
o Media Channel Matrixes: the media channel matrix provides flexible
connectivity for the media channels. That is, it represents a
point of flexibility where relationships between the media ports
at the edge of a media channel matrix may be created and broken.
The relationship between these ports is called a matrix channel.
(Network) Media Channels are switched in a Media Channel Matrix.
In summary, the concept of frequency slot is a logical abstraction
that represents a frequency range while the media layer represents
the underlying media support. Media Channels are media associations,
characterized by their (effective) frequency slot, respectively; and
media channels are switched in media channel matrixes. In Figure 5 ,
a Media Channel has been configured and dimensioned to support two
OCh-P, each transported in its own OCh-P frequency slot.
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Media Channel Frequency Slot
+-------------------------------X------------------------------+
| |
| OCh-P Frequency Slot OCh-P Frequency Slot |
| +------------X-----------+ +----------X-----------+ |
| | OCh-P | | OCh-P | |
| | o | | o | |
| | | | | | | |
-4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12
... +---+---+---+---+---+---+---+---+---+---+---+--+---+---+---+---+---...
... <- Network Media Channel-> <- Network Media Channel->
... <------------------------ Media Channel ----------------------->
X - Frequency Slot Central Frequency
o - signal central frequency
Figure 5: Example of Media Channel / Network Media Channels and
associated frequency slots
4.4. Control Plane Terms
The following terms are defined in the scope of a GMPLS control
plane. [Editors' note: the following ones were *not* agreed during
IETF83 but are put here to be discussed.]
o SSON: Spectrum-Switched Optical Network. An optical network in
which a LSP is switched based on an frequency slot of a variable
slot width of a media channel, rather than based on a fixed grid
and fixed slot width. Please note that a Wavelength Switched
Optical Network (WSON) can be seen as a particular case of SSON in
which all slot widths are equal and depend on the used channel
spacing.
o Flexi-LSP: a control plane construct that represents a data plane
connection in which the switching involves a frequency slot with
variable slot width. Different Flexi-LSPs may have different slot
widths. The term Flexi-LSP is used when needed to differentiate
from regular WSON LSP in which switching is based on a nominal
wavelength.
o RSA: Routing and Spectrum Assignment. As opposed to the typical
Routing and Wavelength Assignment (RWA) problem of traditional WDM
networks, the flexibility in SSON leads to spectral contiguous
constraint, which means that when assigning the spectral resources
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to single connections, the resources assigned to them must be
contiguous over the entire connections in the spectrum domain.
5. GMPLS applicability
The GMPLS control of the media layer deals with the establishment of
media channels, which are switched in media channel matrixes. GMPLS
labels locally represent the media channel and its associated
frequency slot.
[Editors'note: As agreed during IETF84, current focus is on the media
layer. Preliminaty agreement on the "m" parameter should appear in
the label *and* the traffic parameters.]
6. DWDM flexi-grid enabled network element models
Similar to fixed grid networks, a flexible grid network is also
constructed from subsystems that include Wavelength Division
Multiplexing (WDM) links, tunable transmitters and receivers, i.e,
media elements including media layer switching elements (media
matrices), as well as electro-optical network elements, all of them
with flexible grid characteristics.
[Editors' Note: In the scope of this document, and despite is
informal use, the term Reconfigurable Optical Add / Drop Multiplexer,
(ROADM) is avoided, in favor on media matrix. This avoid ambiguity.
A ROADM can be implemented in terms on media matrices.
Informationally, this document may provide an appendix on possible
implementations of flexi-ROADMs in terms of media layer switching
elements or matrices. XF: Whether ROADM is used or not doesn't
matter with GMPLS Control Plane. I suggest to delete this statement.
We may check G.798. Likewise, modeling of filters is out of scope of
the current document IETF84, and is also considered implementation
specific.]
As stated in [G.694.1] the flexible DWDM grid defined in Clause 7 has
a nominal central frequency granularity of 6.25 GHz and a slot width
granularity of 12.5 GHz. However, devices or applications that make
use of the flexible grid may not be capable of supporting every
possible slot width or position. In other words, applications may be
defined where only a subset of the possible slot widths and positions
are required to be supported. For example, an application could be
defined where the nominal central frequency granularity is 12.5 GHz
(by only requiring values of n that are even) and that only requires
slot widths as a multiple of 25 GHz (by only requiring values of m
that are even).
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6.1. Network element constraints
[TODO: section needs to be rewritten, remove redundancy].
Optical transmitters/receivers may have different tunability
constraints, and media channel matrixes may have switching
restrictions. Additionally, a key feature of their implementation is
their highly asymmetric switching capability which is described in
[RFC6163] in detail. Media matrices include line side ports which
are connected to DWDM links and tributary side input/output ports
which can be connected to transmitters/receivers.
A set of common constraints can be defined :
o Available central frequencies: The set of central frequencies
which can be used by an optical transmitter/receiver.
o Slot width: The slot width needed by a transmitter/receiver. The
slot width is dependent on bit rate and modulation format. For
one specific transmitter, the bit rate and modulation format may
be tunable, so slot width would be determined by the modulation
format used at a given bit rate.
o The minimum and maximum slot width.
o Granularity: the optical hardware may not be able to select
parameters with the lowest granularityy (e.g. 6.25 GHz for nominal
central frequencies or 12.5 GHz for slot width granularity).
o Available frequency ranges: the set or union of frequency ranges
that are not allocated (i.e. available). The relative grouping
and distribution of available frequency ranges in a fiber is
usually referred to as ''fragmentation''.
o Available slot width ranges: the set or union of slot width ranges
supported by media matrices. It includes the following
information.
* Slot width threshold: the minimum and maximum Slot Width
supported by the media matrix. For example, the slot width can
be from 50GHz to 200GHz.
* Step granularity: the minimum step by which the optical filter
bandwidth of the media matrix can be increased or decreased.
This parameter is typically equal to slot width granularity
(i.e. 12.5GHz) or integer multiples of 12.5GHz.
[Editor's note: different configurations such as C/CD/CDC will be
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added later. This section should state specifics to media channel
matrices, ROADM models need to be moved to an appendix].
7. Layered Network Model
[Editors' note: OTN hierarchy is not fully covered. It is important
to understand, where the FSC sits in the OTN hierarchy. This is also
important from control plane perspective as this layer becomes the
connection end points of optical layer service]. OCh / flexi-grid
layered model.
OCh AP Trail (OCh) OCh AP
O- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O
| |
--- OCh-P OCh-P ---
\ / source sink \ /
+ +
| OCh-P OCh-P Network Connection OCh-P |
O TCP - - - - - - - - - - - - - - - - - - - - - - - - - - - - -TCP O
| |
|Channel Port Network Media Channel Channel Port |
O - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O
| |
+--------+ +-----------+ +----------+
| \ (1) | OCh-P LC | (1) | OCh-P LC | (1) / |
| \----|-----------------|-----------|-------------------|-------/ |
+--------+ Link Channel +-----------+ Link Channel +----------+
Media Channel Media Channel Media Channel
Matrix Matrix Matrix
(1) - Matrix Channel
Figure 6: Layered Network Model G.805
[Editors' note: we are replicating the figure here for reference,
until the ITU-T document is official.
8. Topology view in Control Plane
[Note: the frequency slot matrix connection may interconnect one or
more frequency slot channels which in turn may carry one or more Och
signals.]
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+--------------+ +--------------+
| OCh-P | TE | OCh-P | Virtual TE
| | link | | link
| Matrix |o- - - - - - - - - - - - - o| Matrix |o- - - - - -
+--------------+ +--------------+
| +---------+ |
| | Media | |
|o------| Channel |---------o|
| |
| Matrix |
+---------+
Figure 7: MRN/MLN topology view with TE link / FA
A SSON (network) refers to the GMPLS control of flexi-grid enabled
DWDM optical networks and it encompasses both the signal and media
layers. The WSON also encompasses the signal and media layers but,
since there is no formal separation between OCh and OCC (1:1) this
layer separation is often not considered. A WSON is a particular
case of SSON in the which all slot widths are equal and depend on the
channel spacing. In other words, since there is only a 1:1
relationship between OCh : OCC there is no need to have separate
controlled layers, as if both layers are collapsed into one.
+=======================================+
| WSON | SSON |
+=======================================+
| OCh | OCh | Signal Layer
+------------------+--------------------+
| | Frequency Slot |
| Optical Channel | | Media Layer
| Carrier | |
+------------------+--------------------+
| 1:1 | N:1 | Relationship
| single layer | MRN/MLN | SL : ML
| network | (* see note) |
+------------------+--------------------+
Figure 8: Table Comparison WSON/SSON
Note that there is only one media layer switch matrix (one
implementation is FlexGrid ROADM) in SSON, while "signal layer LSP is
mainly for the purpose of management and control of individual
optical signal". Signal layer LSPs (OChs) with the same attributions
(such as source and destination) could be grouped into one media-
layer LSP (media channel), which has advantages in spectral
efficiency (reduce guard band between adjacent OChs in one FSC) and
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LSP management. However, assuming some network elements indeed
perform signal layer switch in SSON, there must be enough guard band
between adjacent OChs in one media channel, in order to compensate
filter concatenation effect and other effects caused by signal layer
switching elements. In such condition, the separation of signal
layer from media layer cannot bring any benefit in spectral
efficiency and in other aspects, but make the network switch and
control more complex. If two OChs must switch to different ports, it
is better to carry them by diferent FSCs and the media layer switch
is enough in this scenario.
9. Control Plane Requirements
[Editor's note: The considered topology view is a layered network, in
which the media layer corresponds to the server layer (flexigrid) and
the signal layer corresponds to the client layer (Och). This data
plane modeling considers the flexigrid and the OCh as separate
layers, However, this has implications on the interop/interworking
with WSON and OCh switching. We need to manage a MRN for OCh and
stitching for WSON? In other words, a key part of the fwk is to
define how can we have MRN/MLN hierarchical relationship with Och/FS
and yet stitching 1:1 between WSON and SSON? In this line: how does
OCh switching and WSON relate, actually?]
[Editor's note: formal requirements such as noted in the comments
will be added in a later version of the document].
Hierarchy spectrum management decouples media and signal, but from
the point of view of the control plane, such separation of concerns
implies the management of a MRN/MLN network. So Control Plane needs
to differentiate signal LSP and media LSP. It should also need to
support Hierarchy-LSP [RFC4206] The central frequency of each hop
should be same along end-to-end media or signal LSP because of
Spectrum Continuity Constraint. Otherwise some nodes need to convert
the central frequency along media or signal LSP.
9.1. Neighbor Discovery and Link Property Correlation
[Editors' note: text from draft-li-ccamp-grid-property-lmp-01]
Potential interworking problems between fixed-grid DWDM and flexible-
grid DWDM nodes, may appear. Additionally, even two flexible-grid
optical nodes may have different grid properties, leading to link
property conflict.
Devices or applications that make use of the flexible-grid may not be
able to support every possible slot width. In other words,
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applications may be defined where different grid granularity can be
supported. Taking node F as an example, an application could be
defined where the nominal central frequency granularity is 12.5 GHz
requiring slot widths being multiple of 25 GHz. Therefore the link
between two optical nodes with different grid granularity must be
configured to align with the larger of both granularities. Besides,
different nodes may have different slot width tuning ranges.
In summary, in a DWDM Link between two nodes, at least the following
properties should be negotiated:
Grid capability (channel spacing) - Between fixed-grid and
flexible-grid nodes.
Grid granularity - Between two flexible-grid nodes.
Slot width tuning range - Between two flexible-grid nodes.
9.2. Path Computation / Routing and Spectrum Assignment (RSA)
Much like in WSON, in which if there is no (available) wavelength
converters in an optical network, an LSP is subject to the
''wavelength continuity constraint'' (see section 4 of [RFC6163]), if
the capability of shifting or converting an allocated frequency slot,
the LSP is subject to the Optical ''Spectrum Continuity Constraint''.
Because of the limited availability of wavelength/spectrum converters
(sparse translucent optical network) the wavelength/spectrum
continuity constraint should always be considered. When available,
information regarding spectrum conversion capabilities at the optical
nodes may be used by RSA mechanisms.
The RSA process determines a route and frequency slot for a LSP.
Hence, when a route is computed the spectrum assignment process (SA)
should determine the central frequency and slot width based on the
slot width and available central frequencies information of the
transmitter and receiver, and the available frequency ranges
information and available slot width ranges of the links that the
route traverses.
9.2.1. Architectural Approaches to RSA
Similar to RWA for fixed grids, different ways of performing RSA in
conjunction with the control plane can be considered. The approaches
included in this document are provided for reference purposes only;
other possible options could also be deployed.
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9.2.1.1. Combined RSA (R&SA)
In this case, a computation entity performs both routing and
frequency slot assignment. The computation entity should have the
detailed network information, e.g. connectivity topology constructed
by nodes/links information, available frequency ranges on each link,
node capabilities, etc.
The computation entity could reside either on a PCE or the ingress
node.
9.2.1.2. Separated RSA (R+SA)
In this case, routing computation and frequency slot assignment are
performed by different entities. The first entity computes the
routes and provides them to the second entity; the second entity
assigns the frequency slot.
The first entity should get the connectivity topology to compute the
proper routes; the second entity should get the available frequency
ranges of the links and nodes' capabilities information to assign the
spectrum.
9.2.1.3. Routing and Distributed SA (R+DSA)
In this case, one entity computes the route but the frequency slot
assignment is performed hop-by-hop in a distributed way along the
route. The available central frequencies which meet the spectrum
continuity constraint should be collected hop by hop along the route.
This procedure can be implemented by the GMPLS signaling protocol.
9.3. Routing / Topology dissemination
In the case of combined RSA architecture, the computation entity
needs to get the detailed network information, i.e. connectivity
topology, node capabilities and available frequency ranges of the
links. Route computation is performed based on the connectivity
topology and node capabilities; spectrum assignment is performed
based on the available frequency ranges of the links. The
computation entity may get the detailed network information by the
GMPLS routing protocol. Compared with [RFC6163], except wavelength-
specific availability information, the connectivity topology and node
capabilities are the same as WSON, which can be advertised by GMPLS
routing protocol (refer to section 6.2 of [RFC6163]. This section
analyses the necessary changes on link information brought by
flexible grids.
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9.3.1. Available Frequency Ranges/slots of DWDM Links
In the case of flexible grids, channel central frequencies span from
193.1 THz towards both ends of the C band spectrum with 6.25 GHz
granularity. Different LSPs could make use of different slot widths
on the same link. Hence, the available frequency ranges should be
advertised.
9.3.2. Available Slot Width Ranges of DWDM Links
The available slot width ranges needs to be advertised, in
combination with the Available frequency ranges, in order to verify
whether a LSP with a given slot width can be set up or not; this is
is constrained by the available slot width ranges of the media matrix
Depending on the availability of the slot width ranges, it is
possible to allocate more spectrum than strictly needed by the LSP.
9.3.3. Tunable Optical Transmitters and Receivers
The slot width of a LSP is determined by the transmitter and receiver
that could be mapped to ADD/DROP interfaces in WSON. Moreover their
central frequency could be fixed or tunable, hence, both the slot
width of an ADD/DROP interface and the available central frequencies
should be advertised.
9.3.4. Hierarchical Spectrum Management
[Editors' note: the part on the hierarchy of the optical spectrum
could be confusing, we can discuss it]. The total available spectrum
on a fiber could be described as a resource that can be divided by a
media device into a set of Frequency Slots. In terms of managing
spectrum, it is necessary to be able to speak about different
granularities of managed spectrum. For example, a part of the
spectrum could be assigned to a third party to manage. This need to
partition creates the impression that spectrum is a hierarchy in view
of Management and Control Plane. The hierarchy is created within a
management system, and it is an access right hierarchy only. It is a
management hierarchy without any actual resource hierarchy within
fiber. The end of fiber is a link end and presents a fiber port
which represents all of spectrum available on the fiber. Each
spectrum allocation appears as Link Channel Port (i.e., frequency
slot port) within fiber.
9.3.5. Information Model
Fixed DM grids can also be described via suitable choices of slots in
a flexible DWDM grid. However, devices or applications that make use
of the flexible grid may not be capable of supporting every possible
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slot width or central frequency position. Following is the
definition of information model, not intended to limit any IGP
encoding implementation. For example, information required for
routing/path selection may be the set of available nominal central
frequencies from which a frequency slot of the required width can be
allocated. A convenient encoding for this information (may be as a
frequency slot or sets of contiguous slices) is further study in IGP
encoding document.
[Editor's note: to be discussed]
<Available Spectrum in Fiber for frequency slot> ::=
<Available Frequency Range-List>
<Available Central Frequency Granularity >
<Available Slot Width Granularity>
<Minimal Slot Width>
<Maximal Slot Width>
<Available Frequency Range-List> ::=
<Available Frequency Range >[< Available Frequency Range-List>]
<Available Frequency Range >::=
<Start Spectrum Position><End Spectrum Position> |
<Sets of contiguous slices>
<Available Central Frequency Granularity> ::= n x 6.25GHz,
where n is positive integer, such as 6.25GHz, 12.5GHz, 25GHz, 50GHz
or 100GHz
<Available Slot Width Granularity> ::= m x 12.5GHz,
where m is positive integer
<Minimal Slot Width> ::= j x 12.5GHz,
j is a positive integer
<Maximal Slot Width> ::= k x 12.5GHz,
k is a positive integer (k >= j)
Figure 9: Routing Information model
9.4. Signaling requirements
Note on explicit label control
Compared with [RFC6163], except identifying the resource (i.e., fixed
wavelength for WSON and frequency resource for flexible grids), the
other signaling requirements (e.g., unidirectional or bidirectional,
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with or without converters) are the same as WSON described in the
section 6.1 of [RFC6163]. In the case of routing and distributed SA,
GMPLS signaling can be used to allocate the frequency slot to a LSP.
For R+DSA, the GMPLS signaling procedure is similar to the one
described in section 4.1.3 of [RFC6163] except that the label set
should specify the available nominal central frequencies that meet
the slot width requirement of the LSP.
9.4.1. Slot Width Requirement
[Editors' note: the signaling requirements need to be discussed.
This is just preliminary text].
In order to allocate a proper frequency slot for a LSP, the signaling
should specify its slot width requirement. The intermediate nodes
can collect the acceptable central frequencies that meet the slot
width requirement hop by hop. The tail-end node also needs to know
the slot width of a LSP to assign the proper frequency resource.
Hence, the slot width requirement should be specified in the
signaling message when a LSP is being set up. [Note: other methods
may not need to collect availability]
9.4.2. Frequency Slot Representation
The frequency slot can be determined by the central frequency (n
value) and slot width (m value). Such parameters should be able to
be specified by the signaling protocol.
9.4.3. Relationship with MRN/MLN
9.4.3.1. OCh Layer
9.4.3.2. Media (frequency slot) layer
10. Control Plane Procedures
FFS. Postpone procedures such as resizing existing LSP(s) without
deletion, which refers to increase or decrease of slot width value
'm' without changing the value of 'n', etc. until requirements have
been identified. At present no hitless resizing protocol has been
defined for OCh. Hitless resizing is defined for an ODU entity only.
11. Backwards (fixed-grid) compatibility, and WSON interworking
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o SSON as evolution of WSON, same LSC, different Swcap?
o Potential problems with having the same swcap but the label format
changes w.r.t. wson
o A new SwCap may need to be defined, LSC swcap already defined ISCD
which can not be modified
o Role of LSP encoding type?
o Notion of hierarchy? There is no notion of hierarchy between WSON
and flexi-grid / SSON - only interop / interwork.
Arguments for LSC switching capability
[QW] A LSP for an optical signal which has a bandwidth of 50GHz
passes through both a fixed grid network and a flexible grid network.
We assume that no OEOs exist in the LSP, so both the fixed grid path
and flexible grid path occupy 50GHz. From the perspective of data
plane, there is no change of the signal and no multiplexing when the
fixed grid path interconnects with flexible grid path. From this
scenario we can conclude that both fixed grid network path and
flexible grid network path belong to the same layer. No notion of
hierarchy exists between them.
[QW] stitching LSP which is described in [RFC5150] can be applied in
one layer. LSP hierarchy allows more than one LSP to be mapped to an
H-LSP, but in case of S-LSP, at most one LSP may be associated with
an S-LSP. This is similar to the scenario of interconnection between
fixed grid LSP and flexible grid LSP. Similar to an H-LSP, an S-LSP
could be managed and advertised, although it is not required, as a TE
link, either in the same TE domain as it was provisioned or a
different one. Path setup procedure of stitching LSP can be applied
in the scenario of interconnection between fixed grid path and
flexible grid path.
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e2e LSP
+++++++++++++++++++++++++++++++++++> (LSP1-2)
LSP segment (flexi-LSP)
====================> (LSP-AB)
C --- E --- G
/|\ | / |\
/ | \ | / | \
R1 ---- A \ | \ | / | / B --- R2
\| \ |/ |/
D --- F --- H
fixed grid --A-- flexi-grid --B-- fixed grid
Figure 10: LSP Stitching [RFC5150] and relationship with fixed-flexi
12. Misc & Summary of open Issues [To be removed at later versions]
o Will reuse a lot of work / procedures / encodings defined in the
context of WSON
o At data rates of GBps / TBps, encoding bandwidths with bytes per
second unit and IEEE 32-bit floating may be problematic / non
scalable.
o Bandwidth fields not relevant since there is not a 1-to-1 mapping
between bps and Hz, since it depends on the modulation format,
fec, either there is an agreement on assuming best / worst case
modulations and spectral efficiency.
o Label I: "m" is inherent part of the label, part of the switching,
allows encode the "lightpath" in a ERO using Explicit Label
Control, Still maintains that feature a cross-connect is defined
by the tuple (port-in, label-in, port-out, label-out), allows a
kind-of "best effort LSP"
o Label II: "m" is not part of the label but of the TSPEC, neds to
be in the TSPEC to decouple client signal traffic specification
and management of the optical spectrum, having in both places is
redundant and open to incoherences, extra error checking.
o Label III: both, It reflects both the concept of resource request
allocation / reservation and the concept of being inherent part of
the switching.
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13. Security Considerations
TBD
14. Contributing Authors
Qilei Wang
ZTE
Ruanjian Avenue, Nanjing, China
wang.qilei@zte.com.cn
Malcolm Betts
ZTE
malcolm.betts@zte.com.cn
Sergio Belotti
Alcatel Lucent
Optics CTO
Via Trento 30 20059 Vimercate (Milano) Italy
+39 039 6863033
sergio.belotti@alcatel-lucent.com
Cyril Margaria
Nokia Siemens Networks
St Martin Strasse 76, Munich, 81541, Germany
+49 89 5159 16934
cyril.margaria@nsn.com
Xian Zhang
Huawei
zhang.xian@huawei.com
Yao Li
Nanjing University
wsliguotou@hotmail.com
Fei Zhang
ZTE
Zijinghua Road, Nanjing, China
zhang.fei3@zte.com.cn
Lei Wang
ZTE
East Huayuan Road, Haidian district, Beijing, China
wang.lei131@zte.com.cn
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Guoying Zhang
China Academy of Telecom Research
No.52 Huayuan Bei Road, Beijing, China
zhangguoying@ritt.cn
Takehiro Tsuritani
KDDI R&D Laboratories Inc.
2-1-15 Ohara, Fujimino, Saitama, Japan
tsuri@kddilabs.jp
Lei Liu
KDDI R&D Laboratories Inc.
2-1-15 Ohara, Fujimino, Saitama, Japan
le-liu@kddilabs.jp
Eve Varma
Alcatel-Lucent
+1 732 239 7656
eve.varma@alcatel-lucent.com
Young Lee
Huawei
Jianrui Han
Huawei
Sharfuddin Syed
Infinera
Rajan Rao
Infinera
Marco Sosa
Infinera
Biao Lu
Infinera
Abinder Dhillon
Infinera
Felipe Jimenez Arribas
Telefonica I+D
Andrew G. Malis
Verizon
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Adrian Farrel
Old Dog Consulting
Daniel King
Old Dog Consulting
15. Acknowledgments
The authors would like to thank Pete Anslow for his insights and
clarifications.
16. References
16.1. Normative References
[G.709] International Telecomunications Union, "ITU-T
Recommendation G.709: Interfaces for the Optical Transport
Network (OTN).", March 2009.
[G.800] International Telecomunications Union, "ITU-T
Recommendation G.800: Unified functional architecture of
transport networks.", February 2012.
[G.805] International Telecomunications Union, "ITU-T
Recommendation G.805: Generic functional architecture of
transport networks.", March 2000.
[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.
[RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching
(GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.
[RFC5150] Ayyangar, A., Kompella, K., Vasseur, JP., and A. Farrel,
"Label Switched Path Stitching with Generalized
Multiprotocol Label Switching Traffic Engineering (GMPLS
TE)", RFC 5150, February 2008.
[RFC6163] Lee, Y., Bernstein, G., and W. Imajuku, "Framework for
GMPLS and Path Computation Element (PCE) Control of
Wavelength Switched Optical Networks (WSONs)", RFC 6163,
April 2011.
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16.2. Informative References
[G.694.1] International Telecomunications Union, "ITU-T
Recommendation G.694.1, Spectral grids for WDM
applications: DWDM frequency grid, draft v1.6 2011/12",
2011.
[G.872] International Telecomunications Union, "ITU-T
Recommendation G.872, Architecture of optical transport
networks, draft v0.16 2012/09 (for discussion)", 2012.
[RFC4397] Bryskin, I. and A. Farrel, "A Lexicography for the
Interpretation of Generalized Multiprotocol Label
Switching (GMPLS) Terminology within the Context of the
ITU-T's Automatically Switched Optical Network (ASON)
Architecture", RFC 4397, February 2006.
[WD12R2] International Telecomunications Union, WD12R2, Q12-SG15,
ZTE, Ciena WP3, "Proposed media layer terminology for
G.872", 05 2012.
Authors' Addresses
Oscar Gonzalez de Dios (editor)
Telefonica I+D
Don Ramon de la Cruz 82-84
Madrid, 28045
Spain
Phone: +34913128832
Email: ogondio@tid.es
Ramon Casellas (editor)
CTTC
Av. Carl Friedrich Gauss n.7
Castelldefels, Barcelona
Spain
Phone: +34 93 645 29 00
Email: ramon.casellas@cttc.es
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Fatai Zhang
Huawei
Huawei Base, Bantian, Longgang District
Shenzhen, 518129
China
Phone: +86-755-28972912
Email: zhangfatai@huawei.com
Xihua Fu
ZTE
Ruanjian Avenue
Nanjing,
China
Email: fu.xihua@zte.com.cn
Daniele Ceccarelli
Ericsson
Via Calda 5
Genova,
Italy
Phone: +39 010 600 2512
Email: daniele.ceccarelli@ericsson.com
Iftekhar Hussain
Infinera
140 Caspian Ct.
Sunnyvale, 94089
USA
Phone: 408-572-5233
Email: ihussain@infinera.com
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