Internet DRAFT - draft-ogrcetal-ccamp-flexi-grid-fwk
draft-ogrcetal-ccamp-flexi-grid-fwk
Network Working Group O. Gonzalez de Dios, Ed.
Internet-Draft Telefonica I+D
Intended status: Standards Track R. Casellas, Ed.
Expires: December 07, 2013 CTTC
F. Zhang
Huawei
X. Fu
ZTE
D. Ceccarelli
Ericsson
I. Hussain
Infinera
June 05, 2013
Framework and Requirements for GMPLS based control of Flexi-grid DWDM
networks
draft-ogrcetal-ccamp-flexi-grid-fwk-03
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) has extended 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,
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 optical spectrum.
Status of This Memo
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Copyright Notice
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Table of Contents
1. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Flexi-grid Networks . . . . . . . . . . . . . . . . . . . . . 4
4.1. Flexi-grid in the context of OTN . . . . . . . . . . . . 4
4.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
4.2.1. Frequency Slots . . . . . . . . . . . . . . . . . . . 5
4.2.2. Media Channels . . . . . . . . . . . . . . . . . . . 7
4.2.3. Media Layer Elements . . . . . . . . . . . . . . . . 7
4.2.4. Optical Tributary Signals . . . . . . . . . . . . . . 8
4.3. Flexi-grid layered network model . . . . . . . . . . . . 8
4.3.1. Hierarchy in the Media Layer . . . . . . . . . . . . 9
4.3.2. DWDM flexi-grid enabled network element models . . . 10
5. GMPLS applicability . . . . . . . . . . . . . . . . . . . . . 10
5.1. General considerations . . . . . . . . . . . . . . . . . 11
5.2. Considerations on TE Links . . . . . . . . . . . . . . . 11
5.3. Considerations on Labeled Switched Path (LSP) in Flexi-
grid . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.4. Control Plane modeling of Network elements . . . . . . . 17
5.5. Media Layer Resource Allocation considerations . . . . . 17
5.6. Neighbor Discovery and Link Property Correlation . . . . 21
5.7. Path Computation / Routing and Spectrum Assignment (RSA) 21
5.7.1. Architectural Approaches to RSA . . . . . . . . . . . 22
5.8. Routing / Topology dissemination . . . . . . . . . . . . 23
5.8.1. Available Frequency Ranges/slots of DWDM Links . . . 23
5.8.2. Available Slot Width Ranges of DWDM Links . . . . . . 23
5.8.3. Spectrum Management . . . . . . . . . . . . . . . . . 23
5.8.4. Information Model . . . . . . . . . . . . . . . . . . 24
6. Control Plane Requirements . . . . . . . . . . . . . . . . . 25
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6.1. Functional requirements . . . . . . . . . . . . . . . . . 25
6.2. Routing/Topology Dissemination requirements . . . . . . . 25
6.3. Signaling requirements . . . . . . . . . . . . . . . . . 25
7. Security Considerations . . . . . . . . . . . . . . . . . . . 25
8. Contributing Authors . . . . . . . . . . . . . . . . . . . . 25
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
10.1. Normative References . . . . . . . . . . . . . . . . . . 28
10.2. Informative References . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
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 spacing 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, allowing high bit rate signals
(e.g., 400G, 1T or higher) that do not fit in the fixed grid.
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From a networking perspective, a flexible grid network is assumed to
be a layered network [G.872][G.800] in which the media layer is the
server layer and the optical 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
transports an Optical Tributary Signal.
A Wavelength Switched Optical Network (WSON), addressed in [RFC6163],
is a term commonly used to refer to the application/deployment of a
Generalized Multi-Protocol Label Switching (GMPLS)-based control
plane for the control (provisioning/recovery, etc) of a fixed grid
WDM network in which media (spectrum) and signal are jointly
considered
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.
3. Acronyms
EFS: Effective Frequency Slot
FS: Frequency Slot
NCF: Nominal Central Frequency
OCh: Optical Channel
OCh-P: Optical Channel Payload
OTS: Optical Tributary Signal
OCC: Optical Channel Carrier
SWG: Slot Width Granularity
4. Flexi-grid Networks
4.1. Flexi-grid in the context of OTN
[G.872] describes from a network level the functional architecture of
Optical Transport Networks (OTN). The OTN is decomposed into
independent layer networks with client/layer relationships among
them. A simplified view of the OTN layers is shown in Figure 1.
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+----------------+
| Digital Layer |
+----------------+
| Signal Layer |
+----------------+
| Media Layer |
+----------------+
Figure 1: Generic OTN overview
In the OTN layering context, the media layer is the server layer of
the optical signal layer. The optical signal is guided to its
destination by the media layer by means of a network media channel.
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 scope, this document uses the term flexi-grid enabled DWDM
network to refer to a network in which switching is based on
frequency slots defined using the flexible grid, and covers mainly
the Media Layer as well as the required adaptations from the Signal
layer. The present document is thus focused on the control and
management of the media layer.
4.2. Terminology
This section presents the definition of the terms used in flexi-grid
networks. These terms are included in the ITU-T recommendations
[G.694.1], [G.872]), [G.870], [G.8080] and [G.959.1-2013].
Where appropriate, this documents also uses terminology and
lexicography from [RFC4397].
4.2.1. Frequency Slots
This subsection is focused on the frequency slot related terms.
o Frequency Slot [G.694.1]: 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.
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.
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-5 -4 -3 -2 -1 0 1 2 3 4 5 <- values of n
...+--+--+--+--+--+--+--+--+--+--+-
^
193.1 THz <- anchor frequency
Figure 2: Anchor frequency and set of nominal central frequencies
Nominal Central Frequency Granularity: It is the spacing between
allowed nominal central frequencies and it is set to 6.25 GHz (note:
sometimes referred to as 0.00625 THz).
Slot Width Granularity: 12.5 GHz, as defined in [G.694.1].
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.
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 3: Example Frequency slots
o 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.
Effective Frequency Slot: the effective frequency slot of a media
channel is the common part of the frequency slots along the media
channel through a particular path 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 frequency slot,
it is described by its nominal central frequency and slot width,
according to the already described rules.
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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--+--+--+--+--+--+--+--+--+--+--+--...
===============================================
Effective Frequency Slot
-------------
| |
-3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
..--+--+--+--+--X--+--+--+--+--+--+--+--+--+--+--+--...
Figure 4: Effective Frequency Slot
4.2.2. Media Channels
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.
Network Media Channel: It is a media channel that transports an
Optical Tributary Signal [Editor's note: this definition goes beyond
current G.870 definition, which is still tightened to a particular
case of OTS, the OCh-P]
4.2.3. Media Layer Elements
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 [G.870]. Examples of media elements include fibers,
amplifiers, filters and switching matrices.
Media Channel Matrixes: the media channel matrix provides flexible
connectivity for the media channels. That is, it represents a point
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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.
4.2.4. Optical Tributary Signals
Optical Tributary Signal [G.959.1-2013]: The optical signal that is
placed within a network media channel for transport across the
optical network. This may consist of a single modulated optical
carrier or a group of modulated optical carriers or subcarriers. One
particular example of Optical Tributary Signal is an Optical Channel
Payload (OCh-P) [G.872].
4.3. Flexi-grid layered network model
In the OTN layered network, the network media channel transports a
single Optical Tributary Signal (see Figure 5)
| Optical Tributary Signal |
O - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O
| |
| Channel Port Network Media Channel Channel Port |
O - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O
| |
+--------+ +-----------+ +--------+
| \ (1) | | (1) | | (1) / |
| \----|-----------------|-----------|-------------------|-----/ |
+--------+ Link Channel +-----------+ Link Channel +--------+
Media Channel Media Channel Media Channel
Matrix Matrix Matrix
(1) - Matrix Channel
Figure 5: Simplified Layered Network Model
A particular example of Optical Tributary Signal is the OCh-P. Figure
Figure 6 shows the example of the layered network model
particularized for the OCH-P case, as defined in G.805.
OCh AP Trail (OCh) OCh AP
O- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O
| |
--- OCh-P OCh-P ---
\ / source sink \ /
+ +
| OCh-P OCh-P Network Connection OCh-P |
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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 according to G.805
By definition a network media channel only supports a single Optical
Tributary signal. How several Optical Tributary signals are bound
together is out of the scope of the present document and is a matter
of the signal layer.
4.3.1. Hierarchy in the Media Layer
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. From the
control and management perspective, a media channel can be logically
splited in other media channels.
In Figure 7 , a Media Channel has been configured and dimensioned to
support two network media channels, each of them carrying one optical
tributary signal.
Media Channel Frequency Slot
+-------------------------------X------------------------------+
| |
| Frequency Slot Frequency Slot |
| +------------X-----------+ +----------X-----------+ |
| | Opt Tributary Signal | | Opt Tributary Signal | |
| | o | | o | |
| | | | | | | |
-4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12
+---+---+---+---+---+---+---+---+---+---+---+--+---+---+---+---+---
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<- Network Media Channel-> <- Network Media Channel->
<------------------------ Media Channel ----------------------->
X - Frequency Slot Central Frequency
o - signal central frequency
Figure 7: Example of Media Channel / Network Media Channels and
associated frequency slots
4.3.2. 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.
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).
5. GMPLS applicability
The goal of this section is to provide an insight of the application
of GMPLS to control flexi-grid networks, while specific requirements
are covered in the next section. The present framework is aimed at
controlling the media layer within the Optical Transport Network
(OTN) hierarchy and the required adaptations of the signal layer.
This document also defines the term SSON (Spectrum-Switched Optical
Network) to refer to a Flexi-grid enabled DWDM network that is
controlled by a GMPLS/PCE control plane.
This section provides a mapping of the ITU-T G.872 architectural
aspects to GMPLS/Control plane terms, and considers the relationship
between the architectural concept/construct of media channel and its
control plane representations (e.g. as a TE link).
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5.1. General considerations
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. Network media channels are considered a particular
case of media channels when the end points are transceivers (that is,
source and destination of an Optical Tributary Signal)
5.2. Considerations on TE Links
From a theoretical / abstract point of view, a fiber can be modeled
has having a frequency slot that ranges from (-inf, +inf). This
representation helps understand the relationship between frequency
slots / ranges.
The frequency slot is a local concept that applies locally to a
component / element. When applied to a media channel, we are
referring to its effective frequency slot as defined in [G.872].
The association of a filter, a fiber and a filter is a media channel
in its most basic form, which from the control plane perspective may
modeled as a (physical) TE-link with a contiguous optical spectrum at
start of day. A means to represent this is that the portion of
spectrum available at time t0 depends on which filters are placed at
the ends of the fiber and how they have been configured. Once
filters are placed we have the one hop media channel. In practical
terms, associating a fiber with the terminating filters determines
the usable optical spectrum.
-----------------+ +-----------------+
| |
+--------+ +--------+
| | | | +---------
---o| =============================== o--|
| | Fiber | | | --\ /--
---o| | | o--| \/
| | | | | /\
---o| =============================== o--| --/ \--
| Filter | | Filter | |
| | | | +---------
+--------+ +--------+
| |
|------- Basic Media Channel ---------|
-----------------+ +-----------------+
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--------+ +--------
|--------------------------------------|
LSR | TE link | LSR
|--------------------------------------|
+--------+ +--------
Figure 8: (Basic) Media channel and TE link
Additionally, when a cross-connect for a specific frequency slot is
considered, the underlying media support is still a media channel,
augmented, so to speak, with a bigger association of media elements
and a resulting effective slot. When this media channel is the
result of the association of basic media channels and media layer
matrix cross-connects, this architectural construct can be
represented as / corresponds to a Label Switched Path (LSP) from a
control plane perspective. In other words, It is possible to
"concatenate" several media channels (e.g. Patch on intermediate
nodes) to create a single media channel.
-----------+ +------------------------------+ +----------
| | | |
+------+ +------+ +------+ +------+
| | | | +----------+ | | | |
--o| ========= o--| |--o ========= o--
| | Fiber | | | --\ /-- | | | Fiber | |
--o| | | o--| \/ |--o | | o--
| | | | | /\ | | | | |
--o| ========= o--***********|--o ========= o--
|Filter| |Filter| | | |Filter| |Filter|
| | | | | | | |
+------+ +------+ +------+ +------+
| | | |
<- Basic Media -> <- Matrix -> <- Basic Media->
|Channel| Channel |Channel|
-----------+ +------------------------------+ +----------
<-------------------- Media Channel ---------------->
-----+ +---------------+ +-------
|------------------| |------------------|
LSR | TE link | LSR | TE link | LSR
|------------------| |------------------|
-----+ +---------------+ +-------
Figure 9: Extended Media Channel
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Additionally, if appropriate, it can also be represented as a TE link
or Forwarding Adjacency (FA), augmenting the control plane network
model.
-----------+ +------------------------------+ +----------
| | | |
+------+ +------+ +------+ +------+
| | | | +----------+ | | | |
--o| ========= o--| |--o ========= o--
| | Fiber | | | --\ /-- | | | Fiber | |
--o| | | o--| \/ |--o | | o--
| | | | | /\ | | | | |
--o| ========= o--***********|--o ========= o--
|Filter| |Filter| | | |Filter| |Filter|
| | | | | | | |
+------+ +------+ +------+ +------+
| | | |
-----------+ +------------------------------+ +----------
<------------------------ Media Channel ----------->
+-----+ +------
|------------------------------------------------------|
LSR | TE link | LSR
|------------------------------------------------------|
+-----+ +------
Figure 10: Extended Media Channel / TE Link / FA
5.3. Considerations on Labeled Switched Path (LSP) in Flexi-grid
The flexi-grid LSP is seen as a control plane representation of a
media channel. Since network media channels are media channels, an
LSP may also be the control plane representation of a network media
channel, in a particular context. From a control plane perspective,
the main difference (regardless of the actual effective frequency
slot which may be dimensioned arbitrarily) is that the LSP that
represents a network media channel also includes the endpoints
(transceivers) , including the cross-connects at the ingress / egress
nodes. The ports towards the client can still be represented as
interfaces from the control plane perspective.
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Figure 11 describes an LSP routed along 3 nodes. The LSP is
terminated before the optical matrix of the ingress and egress nodes
and can represent a Media Channel. This case does NOT (and cannot)
represent a network media channel as it does not include (and cannot
include) the transceivers.
----------+ +--------------------------------+ +---------
| | | |
+------+ +------+ +------+ +------+
| | | | +----------+ | | | |
-o| ========= o---| |---o ========= o-
| | Fiber | | | --\ /-- | | | Fiber | |
-o|>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>o-
| | | | | /\ | | | | |
-o| ========= o---***********|---o ========= o-
|Filter| |Filter| | | |Filter| |Filter|
| | | | | | | |
+------+ +------+ +------+ +------+
| | | |
----------+ +--------------------------------+ +---------
>>>>>>>>>>>>>>>>>>>>>>>>>>>> LSP >>>>>>>>>>>>>>>>>>>>>>>>
-----+ +---------------+ +-----
|------------------| |----------------|
LSR | TE link | LSR | TE link | LSR
|------------------| |----------------|
-----+ +---------------+ +-----
Figure 11: Flex-grid LSP representing a media channel that starts at
the filter of the outgoing interface of the ingress LSR and ends at
the filter of the incoming interface of the egress LSR
In Figure 12 a Network Media Channel is represented as terminated at
the DWDM side of the transponder, this is commonly named as OCh-trail
connection.
|--------------------- Network Media Channel ----------------------|
+----------------------+ +----------------------+
| | |
+------+ +------+ +------+ +------+
| | +----+ | | | | +----+ | |OCh-P
OCh-P| o-| |-o | +-----+ | o-| |-o |sink
src | | | | | ===+-+ +-+==| | | | | O---|R
T|***o******o********************************************************
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| | |\ /| | | | | | | | |\ /| | |
| o-| \/ |-o ===| | | |==| o-| \/ |-o |
| | | /\ | | | +-+ +-+ | | | /\ | | |
| o-|/ \|-o | | \/ | | o-|/ \|-o |
|Filter| | | |Filter| | /\ | |Filter| | | |Filter|
+------+ | | +------+ +-----+ +------+ | | +------+
| | | | | | | |
+----------------------+ +----------------------+
LSP
<------------------------------------------------------------------->
LSP
<------------------------------------------------------------------>
+-----+ +--------+ +-----+
o--- | |-------------------| |----------------| |---o
| LSR | TE link | LSR | TE link | LSR |
| |-------------------| |----------------| |
+-----+ +--------+ +-----+
Figure 12: LSP representing a network media channel (OCh-Trail)
In a third case, a Network Media Channel terminated on the Filter
ports of the Ingress and Egress nodes. This is named in G.872 as
OCh-NC (we need to discuss the implications, if any, once modeled at
the control plane level of models B and C).
|--------------------- Network Media Channel --------------------|
+------------------------+ +------------------------+
+------+ +------+ +------+ +------+
| | +----+ | | | | +----+ | |
| o-| |-o | +------+ | o-| |-o |
| | | | | =====+-+ +-+=====| | | | | |
T-o******o********************************************************O-R
| | |\ /| | | | | | | | |\ /| | |
| o-| \/ |-o =====| | | |=====| o-| \/ |-o |
| | | /\ | | | +-+ +-+ | | | /\ | | |
| o-|/ \|-o | | \/ | | o-|/ \|-o |
|Filter| | | |Filter| | /\ | |Filter| | | |Filter|
+------+ | | +------+ +------+ +------+ | | +------+
| | | | | | | |
+----------------------+ +----------------------+
<----------------------------------------------------------------->
LSP
LSP
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<-------------------------------------------------------------->
+-----+ +--------+ +-----+
o--| |--------------------| |-------------------| |--o
| LSR | TE link | LSR | TE link | LSR |
| |--------------------| |-------------------| |
+-----+ +--------+ +-----+
Figure 13: LSP representing a network media channel (OCh-P NC)
[Note: not clear the difference, from a control plane perspective, of
figs Figure 12 and Figure 13.]
Applying the notion of hierarchy at the media layer, by using the LSP
as a FA, the media channel created can support multiple (sub) media
channels. [Editot note : a specific behavior related to Hierarchies
will be verified at a later point in time].
+--------------+ +--------------+
| OCh-P | TE | OCh-P | Virtual TE
| | link | | link
| Matrix |o- - - - - - - - - - o| Matrix |o- - - - - -
+--------------+ +--------------+
| +---------+ |
| | Media | |
|o----| Channel |-----o|
| |
| Matrix |
+---------+
Figure 14: MRN/MLN topology view with TE link / FA
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
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
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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.
5.4. Control Plane modeling of Network elements
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 The minimum and maximum slot width.
o Granularity: the optical hardware may not be able to select
parameters with the lowest granularity (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
added later. This section should state specifics to media channel
matrices, ROADM models need to be moved to an appendix].
5.5. Media Layer Resource Allocation considerations
A media channel has an associated effective frequency slot. From the
perspective of network control and management, this effective slot is
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seen as the "usable" frequency slot end to end. The establishment of
an LSP related the establishment of the media channel and effective
frequency slot.
In this context, when used unqualified, the frequency slot is a local
term, which applies at each hop. An effective frequency slot applies
at the media chall (LSP) level
A "service" request is characterized as a minimum, by its required
effective slot width. This does not preclude that the request may
add additional constraints such as imposing also the nominal central
frequency. A given frequency slot is requested for the media channel
say, with the Path message. Regardless of the actual encoding, the
Path message sender descriptor sender_tspec shall specify a minimum
frequency slot width that needs to be fulfilled.
In order to allocate a proper effective frequency slot for a LSP, the
signaling should specify its required slot width.
An effective frequency slot must equally be described in terms of a
central nominal frequency and its slot width (in terms of usable
spectrum of the effective frequency slot). That is, one must be able
to obtain an end-to-end equivalent n and m parameters. We refer to
this as the "effective frequency slot of the media channel/LSP must
be valid".
In GMPLS the requested effective frequency slot is represented to the
TSpec and the effective frequency slot is mapped to the FlowSpec.
The switched element corresponds in GMPLS to the 'label'. As in
flexi-grid the switched element is a frequency slot, the label
represents a frequency slot. Consequently, the label in flexi-grid
must convey the necessary information to obtain the frequency slot
characteristics (i.e, center and width, the n and m parameters). The
frequency slot is locally identified by the label
The local frequency slot may change at each hop, typically given
hardware constraints (e.g. a given node cannot support the finest
granularity). Locally n and m may change. As long as a given
downstream node allocates enough optical spectrum, m can be different
along the path. This covers the issue where concrete media matrices
can have different slot width granularities. Such "local" m will
appear in the allocated label that encodes the frequency slot as well
as the flow descriptor flowspec.
Different modes are considered: RSA with explicit label control, and
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
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should specify the available nominal central frequencies that meet
the slot width requirement of the LSP. 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.
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,
with or without converters) are the same as WSON described in the
section 6.1 of [RFC6163].
Regarding how a GMPLS control plane can assign n and m, different
cases can apply:
a) n and m can both change. It is the effective slot what
matters. Some entity needs to make sure the effective frequency
slot remains valid.
b) m can change; n needs to be the same along the path. This
ensures that the nominal central frequency stays the same.
c) n and m need to be the same.
d)n can change, m needs to be the same.
In consequence, an entity such as a PCE can make sure that the n and
m stay the same along the path. Any constraint (including frequency
slot and width granularities) is taken into account during path
computation. alternatively, A PCE (or a source node) can compute a
path and the actual frequency slot assignment is done, for example,
with a distributed (signaling) procedure:
Each downstream node ensures that m is >= requested_m.
Since a downstream node cannot foresee what an upstream node will
allocate in turn, a way we can ensure that the effective frequency
slot is valid is then by ensuring that the same "n" is allocated.
By forcing the same n, we avoid cases where the effective
frequency slot of the media channel is invalid (that is, the
resulting frequency slot cannot be described by its n and m
parameters).
Maybe this is a too hard restriction, since a node (or even a
centralized/combined RSA entity) can make sure that the resulting
end to end (effective) frequency slot is valid, even if n is
different locally. That means, the effective (end to end)
frequency slot that characterizes the media channel is one and
determined by its n and m, but are logical, in the sense that they
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are the result of the intersection of local (filters) freq slots
which may have different freq. slots
For Figure Figure 15 the effective slot is valid by ensuring that the
minimum m is greater than the requested m. The effective slot
(intersection) is the lowest m (bottleneck).
For Figure Figure 16 the effective slot is valid by ensuring that it
is valid at each hop in the upstream direction. The intersection
needs to be computed. Invalid slots could result otherwise.
|Path(m_req) | ^ |
|---------> | # |
| | # ^
-^--------------^----------------#----------------#--
Effective # # # #
FS n, m # . . . . . . .#. . . . . . . . # . . . . . . . .# <-fixed
# # # # n
-v--------------v----------------#----------------#---
| | # v
| | # Resv |
| | v <------ |
| | |flowspec(n, m_a)|
| | <--------| |
| | flowspec (n, |
<--------| min(m_a, m_b))
flowspec (n, |
min(m_a, m_b, m_c))
Figure 15: Distributed allocation with different m and same n
|Path(m_req) ^ |
|---------> # | |
| # ^ ^
-^-------------#----------------#-----------------#--------
Effective # # # #
FS n, m # # # #
# # # #
-v-------------v----------------#-----------------#--------
| | # v
| | # Resv |
| | v <------ |
| | |flowspec(n_a, m_a)
| | <--------| |
| | flowspec (FSb [intersect] FSa)
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<--------|
flowspec ([intersect] FSa,FSb,FSc)
Figure 16: Distributed allocation with different m and different n
Note, when a media channel is bound to one OCh-P (i.e is a Network
media channel), the EFS must be the one of the Och-P. The media
channel setup by the LSP may contains the EFS of the network media
channel EFS. This is an endpoint property, the egress and ingress
SHOULD constrain the EFS to Och-P EFS .
5.6. Neighbor Discovery and Link Property Correlation
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,
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.
5.7. 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''.
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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 (Routing and Spectrum Assignment)
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.
5.7.1. 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.
5.7.1.1. 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.
5.7.1.2. 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.
5.7.1.3. Routing and Distributed SA (R+DSA)
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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.
5.8. 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.
5.8.1. 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.
5.8.2. 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.
5.8.3. 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
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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.
5.8.4. 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
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.
<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,
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k is a positive integer (k >= j)
Figure 17: Routing Information model
6. Control Plane Requirements
This section provides a high level view of the requirements for GMPLS
/PCE flexi-grid control plane. A detailed list of requirements will
be provided in the next version of the document
6.1. Functional requirements
o It must be able to dynamically set up media channels
o It must be able to dynamically set up network media channels
o It must must be able to dynamically set up a set of co-routed
network media channels, and associate them logically
6.2. Routing/Topology Dissemination requirements
The computation entity needs to get the detailed network information:
connectivity topology, node capabilities and available frequency
ranges of the links
6.3. Signaling requirements
o The signaling must be able to configure the minimum width (m) of
an LSP.
o The signaling must be able to configure the nominal central
frequency (n) of an LSP.
o It must be possible to collect the local frequency slot asigned at
each link along the path
7. Security Considerations
TBD
8. Contributing Authors
Qilei Wang
ZTE
Ruanjian Avenue, Nanjing, China
wang.qilei@zte.com.cn
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Malcolm Betts
ZTE
malcolm.betts@zte.com.cn
Xian Zhang
Huawei
zhang.xian@huawei.com
Cyril Margaria
Nokia Siemens Networks
St Martin Strasse 76, Munich, 81541, Germany
+49 89 5159 16934
cyril.margaria@nsn.com
Sergio Belotti
Alcatel Lucent
Optics CTO
Via Trento 30 20059 Vimercate (Milano) Italy
+39 039 6863033
sergio.belotti@alcatel-lucent.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
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
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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
Adrian Farrel
Old Dog Consulting
Daniel King
Old Dog Consulting
Huub van Helvoort
9. Acknowledgments
The authors would like to thank Pete Anslow for his insights and
clarifications.
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10. References
10.1. Normative References
[G.694.1] International Telecomunications Union, "ITU-T
Recommendation G.694.1, Spectral grids for WDM
applications: DWDM frequency grid", November 2012.
[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.
[G.8080] International Telecomunications Union, "ITU-T
Recommendation G.8080/Y.1304, Architecture for the
automatically switched optical network", 2012.
[G.870] International Telecomunications Union, "ITU-T
Recommendation G.870/Y.1352, Terms and definitions for
optical transport networks", November 2012.
[G.872] International Telecomunications Union, "ITU-T
Recommendation G.872, Architecture of optical transport
networks, draft v0.16 2012/09 (for discussion)", 2012.
[G.959.1-2013]
International Telecomunications Union, "Update of ITU-T
Recommendation G.959.1, Optical transport network physical
layer interfaces (to appear in July 2013)", 2013.
[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.
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[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.
10.2. Informative References
[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.
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
Fatai Zhang
Huawei
Huawei Base, Bantian, Longgang District
Shenzhen 518129
China
Phone: +86-755-28972912
Email: zhangfatai@huawei.com
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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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