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IETF RFC 7698
Last modified on Thursday, November 19th, 2015
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Internet Engineering Task Force (IETF) O. Gonzalez de Dios, Ed.
Request for Comments: 7698 Telefonica I+D
Category: Informational R. Casellas, Ed.
ISSN: 2070-1721 CTTC
F. Zhang
Huawei
X. Fu
Stairnote
D. Ceccarelli
Ericsson
I. Hussain
Infinera
November 2015
Framework and Requirements for GMPLS-Based Control
of Flexi-Grid Dense Wavelength Division Multiplexing (DWDM) Networks
 Abstract
To allow efficient allocation of optical spectral bandwidth for
systems that have high bit-rates, the International Telecommunication
Union Telecommunication Standardization Sector (ITU-T) has extended
its Recommendations G.694.1 and G.872 to include a new Dense
Wavelength Division Multiplexing (DWDM) grid by defining a set of
nominal central frequencies, channel spacings, and the concept of the
"frequency slot". In such an environment, a data-plane connection is
switched based on allocated, variable-sized frequency ranges within
the optical spectrum, creating what is known as a flexible grid
(flexi-grid).
Given the specific characteristics of flexi-grid optical networks and
their associated technology, this document defines a framework and
the associated control-plane requirements for the application of the
existing GMPLS architecture and control-plane protocols to the
control of flexi-grid DWDM networks. The actual extensions to the
GMPLS protocols will be defined in companion documents.
Gonzalez de Dios, et al. Informational PAGE 1 
RFC 7698 GMPLS Flexi-Grid Framework November 2015
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/RFC 7698.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Gonzalez de Dios, et al. Informational PAGE 2
RFC 7698 GMPLS Flexi-Grid Framework November 2015
Table of Contents
1. Introduction ....................................................4
2. Terminology .....................................................5
2.1. Requirements Language ......................................5
2.2. Abbreviations ..............................................5
3. Overview of Flexi-Grid Networks .................................6
3.1. Flexi-Grid in the Context of OTN ...........................6
3.2. Flexi-Grid Terminology .....................................6
3.2.1. Frequency Slots .....................................7
3.2.2. Media-Layer Elements ................................9
3.2.3. Media Channels .....................................10
3.2.4. Optical Tributary Signals ..........................10
3.2.5. Composite Media Channels ...........................11
3.3. Hierarchy in the Media Layer ..............................11
3.4. Flexi-Grid Layered Network Model ..........................12
3.4.1. DWDM Flexi-Grid Enabled Network Element Models .....13
4. GMPLS Applicability ............................................14
4.1. General Considerations ....................................14
4.2. Consideration of TE Links .................................14
4.3. Consideration of LSPs in Flexi-Grid .......................17
4.4. Control-Plane Modeling of Network Elements ................22
4.5. Media Layer Resource Allocation Considerations ............22
4.6. Neighbor Discovery and Link Property Correlation ..........26
4.7. Path Computation, Routing and Spectrum Assignment (RSA) ...27
4.7.1. Architectural Approaches to RSA ....................28
4.8. Routing and Topology Dissemination ........................29
4.8.1. Available Frequency Ranges (Frequency
Slots) of DWDM Links ...............................29
4.8.2. Available Slot Width Ranges of DWDM Links ..........29
4.8.3. Spectrum Management ................................29
4.8.4. Information Model ..................................30
5. Control-Plane Requirements .....................................31
5.1. Support for Media Channels ................................31
5.1.1. Signaling ..........................................32
5.1.2. Routing ............................................32
5.2. Support for Media Channel Resizing ........................33
5.3. Support for Logical Associations of Multiple Media
Channels ..................................................33
5.4. Support for Composite Media Channels ......................33
5.5. Support for Neighbor Discovery and Link Property
Correlation ...............................................34
6. Security Considerations ........................................34
7. Manageability Considerations ...................................35
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RFC 7698 GMPLS Flexi-Grid Framework November 2015
8. References .....................................................36
8.1. Normative References ......................................36
8.2. Informative References ....................................37
Acknowledgments ...................................................39
Contributors ......................................................39
Authors' Addresses ................................................41
1. 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 and allocation considerations that have been defined in
order to allow an efficient and flexible allocation and configuration
of optical spectral bandwidth for systems that have high bit-rates.
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.
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, a media channel can
transport more than one Optical Tributary Signal (OTSi), as defined
later in this document.
A Wavelength Switched Optical Network (WSON), addressed in [RFC 6163],
is a term commonly used to refer to the application/deployment of a
GMPLS-based control plane for the control (e.g., provisioning and
recovery) of a fixed-grid Wavelength Division Multiplexing (WDM)
network in which media (spectrum) and signal are jointly considered.
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This document defines the framework for a GMPLS-based control of
flexi-grid enabled Dense Wavelength Division Multiplexing (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.
2. Terminology
Further terminology specific to flexi-grid networks can be found in
Section 3.2.
2.1. 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 [RFC 2119].
While [RFC 2119] describes interpretations of these key words in terms
of protocol specifications and implementations, they are used in this
document to describe design requirements for protocol extensions.
2.2. Abbreviations
FS: Frequency Slot
FSC: Fiber-Switch Capable
LSR: Label Switching Router
NCF: Nominal Central Frequency
OCC: Optical Channel Carrier
OCh: Optical Channel
OCh-P: Optical Channel Payload
OTN: Optical Transport Network
OTSi: Optical Tributary Signal
OTSiG: OTSi Group is a set of OTSi
PCE: Path Computation Element
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ROADM: Reconfigurable Optical Add/Drop Multiplexer
SSON: Spectrum-Switched Optical Network
SWG: Slot Width Granularity
3. Overview of Flexi-Grid Networks
3.1. Flexi-Grid in the Context of OTN
[G.872] describes, from a network level, the functional architecture
of an OTN. It is decomposed into independent-layer networks with
client/layer relationships among them. A simplified view of the OTN
layers is shown in Figure 1.
+----------------+
| 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.
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. This document
mainly covers 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.
3.2. Flexi-Grid Terminology
This section presents the definitions of the terms used in flexi-grid
networks. More details about these terms can be found in ITU-T
Recommendations [G.694.1], [G.872], [G.870], [G.8080], and
[G.959.1-2013].
Where appropriate, this document also uses terminology and
lexicography from [RFC 4397].
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RFC 7698 GMPLS Flexi-Grid Framework November 2015
3.2.1. Frequency Slots
This subsection is focused on the frequency slot and 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.
o Nominal Central Frequency: Each of the allowed frequencies as per
the definition of the 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 the ITU-T "anchor frequency" for transmission
over the C-band and '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 2: Anchor Frequency and Set of Nominal Central Frequencies
o Nominal Central Frequency Granularity: The spacing between allowed
nominal central frequencies. It is set to 6.25 GHz [G.694.1].
o Slot Width Granularity (SWG): 12.5 GHz, as defined in [G.694.1].
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o 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
...--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--...
------------- -------------------
^ ^
Slot NCF = 193.1 THz Slot NCF = 193.14375 THz
Slot width = 25 GHz Slot width = 37.5 GHz
n = 0, m = 2 n = 7, m = 3
Figure 3: Example Frequency Slots
* The symbol '+' represents the allowed nominal central
frequencies.
* The '--' represents the nominal central frequency granularity
in units of 6.25 GHz.
* 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.
o Effective Frequency Slot [G.870]: That part of the frequency slots
of the filters along the media channel that is common to all of
the filters' frequency slots. Note that both the terms "frequency
slot" and "effective frequency slot" are applied locally.
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o Figure 4 shows the effect of combining two filters along a
channel. The combination of Frequency Slot 1 and Frequency Slot 2
applied to the media channel is the effective frequency slot
shown.
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
3.2.2. Media-Layer Elements
o Media Element: A media element directs an 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.
o Media Channel Matrix: 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.
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3.2.3. Media Channels
This section defines concepts such as the (network) media channel;
the mapping to GMPLS constructs (i.e., LSP) is detailed in Section 4.
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 frequency slot (an 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
filter.
o Network Media Channel: Defined in [G.870] as a media channel that
transports a single OTSi (defined in the next subsection).
3.2.4. Optical Tributary Signals
o Optical Tributary Signal (OTSi): 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. To
provide a connection between the OTSi source and the OTSi sink,
the optical signal must be assigned to a network media channel
(see also [G.959.1-2013]).
o OTSi Group (OTSiG): The set of OTSi that are carried by a group of
network media channels. Each OTSi is carried by one network media
channel. From a management perspective, it SHOULD be possible to
manage both the OTSiG and a group of network media channels as
single entities.
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RFC 7698 GMPLS Flexi-Grid Framework November 2015
3.2.5. Composite Media Channels
o It is possible to construct an end-to-end media channel as a
composite of more than one network media channel. A composite
media channel carries a group of OTSi (i.e., OTSiG). Each OTSi is
carried by one network media channel. This OTSiG is carried over
a single fiber.
o In this case, the effective frequency slots may be contiguous
(i.e., there is no spectrum between them that can be used for
other media channels) or non-contiguous.
o It is not currently envisaged that such composite media channels
may be constructed from slots carried on different fibers whether
those fibers traverse the same hop-by-hop path through the network
or not.
o Furthermore, it is not considered likely that a media channel may
be constructed from a different variation of slot composition on
each hop. That is, the slot composition (i.e., the group of OTSi
carried by the composite media channel) must be the same from one
end of the media channel to the other, even if the specific slot
for each OTSi and the spacing among slots may vary hop by hop.
o How the signal is carried across such groups of network media
channels is out of scope for this document.
3.3. Hierarchy in the Media Layer
In summary, the concept of the 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 respective (effective) frequency
slots, and media channels are switched in media channel matrices.
From the control and management perspective, a media channel can be
logically split into network media channels.
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In Figure 5, a media channel has been configured and dimensioned to
support two network media channels, each of them carrying one OTSi.
Media Channel Frequency Slot
+-------------------------------X------------------------------+
| |
| Frequency Slot Frequency Slot |
| +-----------X-----------+ +----------X-----------+ |
| | OTSi | | OTSi | |
| | 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
3.4. Flexi-Grid Layered Network Model
In the OTN layered network, the network media channel transports a
single OTSi (see Figure 6).
| OTSi |
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
The symbol (1) indicates a matrix channel
Figure 6: Simplified Layered Network Model
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RFC 7698 GMPLS Flexi-Grid Framework November 2015
Note that a particular example of OTSi is the OCh-P. Figure 7 shows
this specific example as defined in G.805 [G.805].
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
The symbol (1) indicates a matrix channel
"LC" indicates a link connection
Figure 7: Layered Network Model According to G.805
3.4.1. DWDM Flexi-Grid Enabled Network Element Models
A flexible-grid network is constructed from subsystems that include
WDM links, tunable transmitters, and receivers (i.e., media elements
including media-layer switching elements that are media matrices), as
well as electro-optical network elements. This is just the same as
in a fixed-grid network, except that each element has flexible-grid
characteristics.
As stated in Clause 7 of [G.694.1], the flexible DWDM grid 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 might 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
is 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 where slot widths
are a multiple of 25 GHz (by only requiring values of m that are
even).
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RFC 7698 GMPLS Flexi-Grid Framework November 2015
4. GMPLS Applicability
The goal of this section is to provide an insight into the
application of GMPLS as a control mechanism in flexi-grid networks.
Specific control-plane requirements for the support of flexi-grid
networks are covered in Section 5. This framework is aimed at
controlling the media layer within the OTN hierarchy and controlling
the required adaptations of the signal layer. This document also
defines the term "Spectrum-Switched Optical Network" (SSON) to refer
to a flexi-grid enabled DWDM network that is controlled by a GMPLS or
PCE control plane.
This section provides a mapping of the ITU-T G.872 architectural
aspects to GMPLS and control-plane terms and also considers the
relationship between the architectural concept or construct of a
media channel and its control-plane representations (e.g., as a TE
link, as defined in [RFC 3945]).
4.1. General Considerations
The GMPLS control of the media layer deals with the establishment of
media channels that are switched in media channel matrices. GMPLS
labels are used to locally represent the media channel and its
associated frequency slot. Network media channels are considered a
particular case of media channels when the endpoints are transceivers
(that is, the source and destination of an OTSi).
4.2. Consideration of TE Links
From a theoretical point of view, a fiber can be modeled as having a
frequency slot that ranges from minus infinity to plus infinity.
This representation helps us understand the relationship between
frequency slots and ranges.
The frequency slot is a local concept that applies within a component
or element. When applied to a media channel, we are referring to its
effective frequency slot as defined in [G.872].
The association sequence of the three components (i.e., a filter, a
fiber, and a filter) is a media channel in its most basic form. From
the control-plane perspective, this may be modeled as a (physical)
TE link with a contiguous optical spectrum. This can be represented
by saying 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 a one-hop
media channel. In practical terms, associating a fiber with the
terminating filters determines the usable optical spectrum.
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RFC 7698 GMPLS Flexi-Grid Framework November 2015
---------------+ +-----------------
| |
+--------+ +--------+
| | | | +---------
---o| =============================== o--|
| | Fiber | | | --\ /--
---o| | | o--| \/
| | | | | /\
---o| =============================== o--| --/ \--
| Filter | | Filter | |
| | | | +---------
+--------+ +--------+
| |
|------- Basic Media Channel ---------|
---------------+ +-----------------
--------+ +--------
|--------------------------------------|
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 resulting media support of joining basic media
channels is still a media channel, i.e., a longer association
sequence of media elements and its effective frequency slot. In
other words, it is possible to "concatenate" several media channels
(e.g., patch on intermediate nodes) to create a single media channel.
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RFC 7698 GMPLS Flexi-Grid Framework November 2015
The architectural construct resulting from the association sequence
of basic media channels and media-layer matrix cross-connects can be
represented as (i.e., corresponds to) a Label Switched Path (LSP)
from a control-plane perspective.
----------+ +------------------------------+ +---------
| | | |
+------+ +------+ +------+ +------+
| | | | +----------+ | | | |
--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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Furthermore, if appropriate, the media channel can also be
represented as a TE link or Forwarding Adjacency (FA) [RFC 4206],
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 or FA
4.3. Consideration of LSPs in Flexi-Grid
The flexi-grid LSP is 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
(without considering the adaptation functions). 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 and
egress nodes. The ports towards the client can still be represented
as interfaces from the control-plane perspective.
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Figure 11 shows an LSP routed between three 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 because 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: Flexi-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
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In Figure 12, a network media channel is represented as terminated at
the network side of the transceivers. This is commonly named an
OTSi-trail connection.
|--------------------- Network Media Channel ----------------------|
+----------------------+ +----------------------+
| | |
+------+ +------+ +------+ +------+
| | +----+ | | | | +----+ | |OTSi
OTSi| o-| |-o | +-----+ | o-| |-o |sink
src | | | | | ===+-+ +-+==| | | | | O---|R
T|***o******o********************************************************
| | |\ /| | | | | | | | |\ /| | |
| 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 (OTSi Trail)
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In a third case, a network media channel is terminated on the filter
ports of the ingress and egress nodes. This is defined in G.872 as
an OTSi Network Connection. As can be seen from the figures, from a
GMPLS modeling perspective there is no difference between these
cases, but they are shown as distinct examples to highlight the
differences in the data plane.
|--------------------- 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
<-------------------------------------------------------------->
+-----+ +--------+ +-----+
o--| |--------------------| |-------------------| |--o
| LSR | TE link | LSR | TE link | LSR |
| |--------------------| |-------------------| |
+-----+ +--------+ +-----+
Figure 13: LSP Representing a Network Media Channel
(OTSi Network Connection)
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Applying the notion of hierarchy at the media layer, by using the LSP
as an FA (i.e., by using hierarchical LSPs), the media channel
created can support multiple (sub-)media channels.
+--------------+ +--------------+
| Media Channel| TE | Media Channel| Virtual TE
| | link | | link
| Matrix |o- - - - - - - - - - o| Matrix |o- - - - - -
+--------------+ +--------------+
| +---------+ |
| | Media | |
|o----| Channel |-----o|
| |
| Matrix |
+---------+
Figure 14: Topology View with TE Link or FA
Note that there is only one media-layer switch matrix (one
implementation is a flexi-grid ROADM) in SSON, while a signal-layer
LSP (network media channel) is established mainly for the purpose of
management and control of individual optical signals. Signal-layer
LSPs with the same attributes (such as source and destination) can be
grouped into one media-layer LSP (media channel); this has advantages
in spectral efficiency (reduced guard band between adjacent OChs in
one FSC channel) and LSP management. However, assuming that some
network elements perform signal-layer switching in an SSON, there
must be enough guard band between adjacent OTSi in any media channel
to compensate for the filter concatenation effects and other effects
caused by signal-layer switching elements. In such a situation, the
separation of the signal layer from the media layer does not bring
any benefit in spectral efficiency or in other aspects, and it makes
the network switching and control more complex. If two OTSi must be
switched to different ports, it is better to carry them via different
FSC channels, and the media-layer switch is enough in this scenario.
As discussed in Section 3.2.5, a media channel may be constructed
from a composite of network media channels. This may be achieved in
two ways using LSPs. These mechanisms may be compared to the
techniques used in GMPLS to support inverse multiplexing in Time
Division Multiplexing (TDM) networks and in OTN [RFC 4606] [RFC 6344]
[RFC 7139].
o In the first case, a single LSP may be established in the control
plane. The signaling messages include information for all of the
component network media channels that make up the composite media
channel.
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o In the second case, each component network media channel is
established using a separate control-plane LSP, and these LSPs are
associated within the control plane so that the endpoints may see
them as a single media channel.
4.4. Control-Plane Modeling of Network Elements
Optical transmitters and receivers may have different tunability
constraints, and media channel matrices may have switching
restrictions. Additionally, a key feature of their implementation is
their highly asymmetric switching capability, which is described in
detail in [RFC 6163]. Media matrices include line-side ports that are
connected to DWDM links and tributary-side input/output ports that
can be connected to transmitters/receivers.
A set of common constraints can be defined:
o Slot widths: 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 have not been allocated (i.e., are available). The relative
grouping and distribution of available frequency ranges in a fiber
are 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
could be from 50 GHz to 200 GHz.
* 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., 12.5 GHz) or integer multiples of 12.5 GHz.
4.5. 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
seen as the "usable" end-to-end frequency slot. The establishment of
an LSP is related to the establishment of the media channel and the
configuration of the effective frequency slot.
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A "service request" is characterized (at a minimum) by its required
effective slot width. This does not preclude the request from adding
additional constraints, such as also imposing the nominal central
frequency. A given effective frequency slot may be requested for the
media channel in the control-plane LSP setup messages, and a specific
frequency slot can be requested on any specific hop of the LSP setup.
Regardless of the actual encoding, the LSP setup message specifies a
minimum effective frequency slot width that needs to be fulfilled in
order to successfully establish the requested LSP.
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, it must be
possible to determine the end-to-end values of the n and m
parameters. We refer to this by saying that the "effective frequency
slot of the media channel or LSP must be valid".
In GMPLS, the requested effective frequency slot is represented to
the TSpec present in the RSVP-TE Path message, and the effective
frequency slot is mapped to the FlowSpec carried in the RSVP-TE Resv
message.
In GMPLS-controlled systems, the switched element corresponds to the
'label'. In flexi-grid, the switched element is a frequency slot,
and the label represents a frequency slot. Consequently, the label
in flexi-grid conveys the necessary information to obtain the
frequency slot characteristics (i.e., central frequency and slot
width: the n and m parameters). The frequency slot is locally
identified by the label.
The local frequency slot may change at each hop, given hardware
constraints and capabilities (e.g., a given node might not support
the finest granularity). This means that the values of n and m may
change at each hop. As long as a given downstream node allocates
enough optical spectrum, m can be different along the path. This
covers the issue where media matrices can have different slot width
granularities. Such variations in the local value of m will appear
in the allocated label that encodes the frequency slot as well as in
the FlowSpec that describes the flow.
Different operational modes can be considered. For Routing and
Spectrum Assignment (RSA) with explicit label control, and for
Routing and Distributed Spectrum Assignment (R+DSA), the GMPLS
signaling procedures are similar to those described in Section 4.1.3
of [RFC 6163] for Routing and Wavelength Assignment (RWA) and for
Routing and Distributed Wavelength Assignment (R+DWA). The main
difference is that the label set specifies the available nominal
central frequencies that meet the slot width requirements of the LSP.
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The intermediate nodes use the control plane to 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
an LSP to assign the proper frequency resource. Except for
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 for WSON as described in Section 6.1 of
[RFC 6163].
Regarding how a GMPLS control plane can assign n and m hop by hop
along the path of an LSP, different cases can apply:
a. n and m can both change. It is the effective frequency slot that
matters; it needs to remain valid along the path.
b. m can change, but n needs to remain the same along the path.
This ensures that the nominal central frequency stays the same,
but the width of the slot can vary along the path. Again, the
important thing is that the effective frequency slot remains
valid and satisfies the requested parameters along the whole path
of the LSP.
c. n and m need to be unchanging along the path. This ensures that
the frequency slot is well known from end to end and is a simple
way to ensure that the effective frequency slot remains valid for
the whole LSP.
d. n can change, but m needs to remain the same along the path.
This ensures that the effective frequency slot remains valid but
also allows the frequency slot to be moved within the spectrum
from hop to hop.
The selection of a path that ensures n and m continuity can be
delegated to a dedicated entity such as a Path Computation Element
(PCE). Any constraint (including frequency slot and width
granularities) can be taken into account during path computation.
Alternatively, A PCE can compute a path, leaving the actual frequency
slot assignment to be done, for example, with a distributed
(signaling) procedure:
o Each downstream node ensures that m is >= requested_m.
o A downstream node cannot foresee what an upstream node will
allocate. A way to ensure that the effective frequency slot is
valid along the length of the LSP is to ensure that the same value
of n is allocated at each hop. By forcing the same value of n, we
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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).
o This may be too restrictive, since a node (or even a centralized/
combined RSA entity) may be able to ensure that the resulting
end-to-end effective frequency slot is valid, even if n varies
locally. That means that the effective frequency slot that
characterizes the media channel from end to end is consistent and
is determined by its n and m values but that the effective
frequency slot and those values are logical (i.e., do not map
"direct" to the physically assigned spectrum) in the sense that
they are the result of the intersection of locally assigned
frequency slots applicable at local components (such as filters),
each of which may have different frequency slots assigned to them.
As shown in Figure 15, the effective slot is made valid by ensuring
that the minimum m is greater than the requested m. The effective
slot (intersection) is the lowest m (bottleneck).
C B A
|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))
m_a, m_b, m_c: Selected frequency slot widths
Figure 15: Distributed Allocation with Different m and Same n
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In Figure 16, the effective slot is made valid by ensuring that it is
valid at each hop in the upstream direction. The intersection needs
to be computed; otherwise, invalid slots could result.
C B A
|Path(m_req) ^ | |
|---------> # | |
| # ^ ^
-^-------------#----------------#-----------------#--------
Effective # # # #
FS n, m # # # #
# # # #
-v-------------v----------------#-----------------#--------
| | # v
| | # Resv |
| | v <------ |
| | |FlowSpec(n_a, m_a)
| | <--------| |
| | FlowSpec(FSb [intersect] FSa)
<--------|
FlowSpec([intersect] FSa,FSb,FSc)
n_a: Selected nominal central frequency by node A
m_a: Selected frequency slot widths by node A
FSa, FSb, FSc: Frequency slot at each hop A, B, C
Figure 16: Distributed Allocation with Different m and Different n
Note that when a media channel is bound to one OTSi (i.e., is a
network media channel), the effective FS must be the frequency slot
of the OTSi. The media channel set up by the LSP may contain the
effective FS of the network media channel effective FS. This is an
endpoint property; the egress and ingress have to constrain the
effective FS to be the OTSi effective FS.
4.6. Neighbor Discovery and Link Property Correlation
There are potential interworking problems between fixed-grid DWDM
nodes and flexi-grid DWDM nodes. Additionally, even two flexi-grid
nodes may have different grid properties, leading to link property
conflict and resulting in limited interworking.
Devices or applications that make use of flexi-grid might not be able
to support every possible slot width. In other words, different
applications may be defined where each supports a different grid
granularity. In this case, the link between two optical nodes with
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different grid granularities must be configured to align with the
larger of both granularities. Furthermore, different nodes may have
different slot width tuning ranges.
In summary, in a DWDM link between two nodes, at a minimum, the
following properties need to be negotiated:
o Grid capability (channel spacing) - Between fixed-grid and
flexi-grid nodes.
o Grid granularity - Between two flexi-grid nodes.
o Slot width tuning range - Between two flexi-grid nodes.
4.7. Path Computation, Routing and Spectrum Assignment (RSA)
In WSON, if there is no (available) wavelength converter in an
optical network, an LSP is subject to the "wavelength continuity
constraint" (see Section 4 of [RFC 6163]). Similarly, in flexi-grid,
if the capability to shift or convert an allocated frequency slot is
absent, the LSP is subject to the "spectrum continuity constraint".
Because of the limited availability of spectrum converters (in what
is called a "sparse translucent optical network"), the spectrum
continuity constraint always has to 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 an LSP.
Hence, when a route is computed, the spectrum assignment process
determines the central frequency and slot width based on the
following:
o the requested slot width
o the information regarding the transmitter and receiver
capabilities, including the availability of central frequencies
and their slot width granularity
o the information regarding available frequency slots (frequency
ranges) and available slot widths of the links traversed along
the route
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4.7.1. Architectural Approaches to RSA
Similar to RWA for fixed grids [RFC 6163], 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.
Note that all of these models allow the concept of a composite media
channel supported by a single control-plane LSP or by a set of
associated LSPs.
4.7.1.1. Combined RSA (R&SA)
In this case, a computation entity performs both routing and
frequency slot assignment. The computation entity needs access to
detailed network information, e.g., the connectivity topology of the
nodes and links, available frequency ranges on each link, and node
capabilities.
The computation entity could reside on a dedicated PCE server, in
the provisioning application that requests the service, or on the
ingress node.
4.7.1.2. 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 needs the connectivity topology to compute the
proper routes. The second entity needs information about the
available frequency ranges of the links and the capabilities of the
nodes in order to assign the spectrum.
4.7.1.3. Routing and Distributed SA (R+DSA)
In this case, an 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 that meet the spectrum
continuity constraint need to be collected hop by hop along the
route. This procedure can be implemented by the GMPLS signaling
protocol.
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4.8. Routing and Topology Dissemination
In the case of the combined RSA architecture, the computation entity
needs 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, while spectrum assignment is performed based on
the available frequency ranges of the links. The computation entity
may get the detailed network information via the GMPLS routing
protocol.
For WSON, the connectivity topology and node capabilities can be
advertised by the GMPLS routing protocol (refer to Section 6.2 of
[RFC 6163]). Except for wavelength-specific availability information,
the information for flexi-grid is the same as for WSON and can
equally be distributed by the GMPLS routing protocol.
This section analyzes the necessary changes to link information
required by flexible grids.
4.8.1. Available Frequency Ranges (Frequency 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 a granularity
of 6.25 GHz. Different LSPs could make use of different slot widths
on the same link. Hence, the available frequency ranges need to be
advertised.
4.8.2. Available Slot Width Ranges of DWDM Links
The available slot width ranges need to be advertised in combination
with the available frequency ranges, so that the computing entity can
verify whether an LSP with a given slot width can be set up or not.
This 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 what is strictly needed by
the LSP.
4.8.3. Spectrum Management
The total available spectrum on a fiber can be described as a
resource that can be partitioned. For example, a part of the
spectrum could be assigned to a third party to manage, or parts of
the spectrum could be assigned by the operator for different classes
of traffic. This partitioning creates the impression that the
spectrum is a hierarchy in view of the management plane and the
control plane: each partition could itself be partitioned. However,
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the hierarchy is created purely within a management system; it
defines a hierarchy of access or management rights, but there is no
corresponding resource hierarchy within the fiber.
The end of the fiber is a link end and presents a fiber port that
represents all of the spectrum available on the fiber. Each spectrum
allocation appears as a Link Channel Port (i.e., frequency slot port)
within the fiber. Thus, while there is a hierarchy of ownership (the
Link Channel Port and corresponding LSP are located on a fiber and
therefore are associated with a fiber port), there is no continued
nesting hierarchy of frequency slots within larger frequency slots.
In its way, this mirrors the fixed-grid behavior where a wavelength
is associated with a fiber port but cannot be subdivided even though
it is a partition of the total spectrum available on the fiber.
4.8.4. Information Model
This section defines an information model to describe the data that
represents the capabilities and resources available in a flexi-grid
network. It is not a data model and is not intended to limit any
protocol solution such as an encoding for an IGP. For example,
information required for routing and 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 is left for further study in an IGP encoding document.
Fixed DWDM 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. Thus, the
information model needs to enable:
o the exchange of information to enable RSA in a flexi-grid network
o the representation of a fixed-grid device participating in a
flexi-grid network
o full interworking of fixed-grid and flexible-grid devices within
the same network
o interworking of flexible-grid devices with different capabilities
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The information model is represented using the Routing Backus-Naur
Format (RBNF) as defined in [RFC 5511].
<Available Spectrum> ::=
<Available Frequency Range-List>
<Available NCFs>
<Available Slot Widths>
where
<Available Frequency Range-List> ::=
<Available Frequency Range> [<Available Frequency Range-List>]
<Available Frequency Range> ::=
( <Start NCF> <End NCF> ) |
<FS defined by (n, m) containing contiguous available NCFs>
and
<Available NCFs> ::=
<Available NCF Granularity> [<Offset>]
-- Subset of supported n values given by p x n + q
-- where p is a positive integer
-- and q (offset) belongs to 0,..,p-1.
and
<Available Slot Widths> ::=
<Available Slot Width Granularity>
<Min Slot Width>
-- given by j x 12.5 GHz, with j a positive integer
<Max Slot Width>
-- given by k x 12.5 GHz, with k a positive integer (k >= j)
Figure 17: Routing Information Model
5. Control-Plane Requirements
The control of flexi-grid networks places additional requirements on
the GMPLS protocols. This section summarizes those requirements for
signaling and routing.
5.1. Support for Media Channels
The control plane SHALL be able to support media channels,
characterized by a single frequency slot. The representation of the
media channel in the GMPLS control plane is the so-called "flexi-grid
LSP". Since network media channels are media channels, an LSP may
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also be the control-plane representation of a network media channel.
Consequently, the control plane will also be able to support network
media channels.
5.1.1. Signaling
The signaling procedure SHALL be able to configure the nominal
central frequency (n) of a flexi-grid LSP.
The signaling procedure SHALL allow a flexible range of values for
the frequency slot width (m) parameter. Specifically, the control
plane SHALL allow setting up a media channel with frequency slot
width (m) ranging from a minimum of m = 1 (12.5 GHz) to a maximum of
the entire C-band (the wavelength range 1530 nm to 1565 nm, which
corresponds to the amplification range of erbium-doped fiber
amplifiers) with a slot width granularity of 12.5 GHz.
The signaling procedure SHALL be able to configure the minimum width
(m) of a flexi-grid LSP. In addition, the signaling procedure SHALL
be able to configure local frequency slots.
The control-plane architecture SHOULD allow for the support of the
L-band (the wavelength range 1565 nm to 1625 nm) and the S-band (the
wavelength range 1460 nm to 1530 nm).
The signaling process SHALL be able to collect the local frequency
slot assigned at each link along the path.
The signaling procedures SHALL support all of the RSA architectural
models (R&SA, R+SA, and R+DSA) within a single set of protocol
objects, although some objects may only be applicable within one of
the models.
5.1.2. Routing
The routing protocol will support all functions described in
[RFC 4202] and extend them to a flexi-grid data plane.
The routing protocol SHALL distribute sufficient information to
compute paths to enable the signaling procedure to establish LSPs as
described in the previous sections. This includes, at a minimum, the
data described by the information model in Figure 17.
The routing protocol SHALL update its advertisements of available
resources and capabilities as the usage of resources in the network
varies with the establishment or teardown of LSPs. These updates
SHOULD be amenable to damping and thresholds as in other traffic
engineering routing advertisements.
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The routing protocol SHALL support all of the RSA architectural
models (R&SA, R+SA, and R+DSA) without any configuration or change of
behavior. Thus, the routing protocols SHALL be agnostic to the
computation and signaling model that is in use.
5.2. Support for Media Channel Resizing
The signaling procedures SHALL allow the resizing (growing or
shrinking) of the frequency slot width of a media channel or network
media channel. The resizing MAY imply resizing the local frequency
slots along the path of the flexi-grid LSP.
The routing protocol SHALL update its advertisements of available
resources and capabilities as the usage of resources in the network
varies with the resizing of LSPs. These updates SHOULD be amenable
to damping and thresholds as in other traffic engineering routing
advertisements.
5.3. Support for Logical Associations of Multiple Media Channels
A set of media channels can be used to transport signals that have a
logical association between them. The control-plane architecture
SHOULD allow multiple media channels to be logically associated. The
control plane SHOULD allow the co-routing of a set of media channels
that are logically associated.
5.4. Support for Composite Media Channels
As described in Sections 3.2.5 and 4.3, a media channel may be
composed of multiple network media channels.
The signaling procedures SHOULD include support for signaling a
single control-plane LSP that includes information about multiple
network media channels that will comprise the single compound media
channel.
The signaling procedures SHOULD include a mechanism to associate
separately signaled control-plane LSPs so that the endpoints may
correlate them into a single compound media channel.
The signaling procedures MAY include a mechanism to dynamically vary
the composition of a composite media channel by allowing network
media channels to be added to or removed from the whole.
The routing protocols MUST provide sufficient information for the
computation of paths and slots for composite media channels using any
of the three RSA architectural models (R&SA, R+SA, and R+DSA).
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5.5. Support for Neighbor Discovery and Link Property Correlation
The control plane MAY include support for neighbor discovery such
that a flexi-grid network can be constructed in a "plug-and-play"
manner. Note, however, that in common operational practice,
validation processes are used rather than automatic discovery.
The control plane SHOULD allow the nodes at opposite ends of a link
to correlate the properties that they will apply to the link. Such a
correlation SHOULD include at least the identities of the nodes and
the identities that they apply to the link. Other properties, such
as the link characteristics described for the routing information
model in Figure 17, SHOULD also be correlated.
Such neighbor discovery and link property correlation, if provided,
MUST be able to operate in both an out-of-band and an out-of-fiber
control channel.
6. Security Considerations
The control-plane and data-plane aspects of a flexi-grid system are
fundamentally the same as a fixed-grid system, and there is no
substantial reason to expect the security considerations to be any
different.
A good overview of the security considerations for a GMPLS-based
control plane can be found in [RFC 5920].
[RFC 6163] includes a section describing security considerations for
WSON, and it is reasonable to infer that these considerations apply
and may be exacerbated in a flexi-grid SSON system. In particular,
the detailed and granular information describing a flexi-grid network
and the capabilities of nodes in that network could put stress on the
routing protocol or the out-of-band control channel used by the
protocol. An attacker might be able to cause small variations in the
use of the network or the available resources (perhaps by modifying
the environment of a fiber) and so trigger the routing protocol to
make new flooding announcements. This situation is explicitly
mitigated in the requirements for the routing protocol extensions
where it is noted that the protocol must include damping and
configurable thresholds as already exist in the core GMPLS routing
protocols.
Gonzalez de Dios, et al. Informational PAGE 34
RFC 7698 GMPLS Flexi-Grid Framework November 2015
7. Manageability Considerations
GMPLS systems already contain a number of management tools:
o MIB modules exist to model the control-plane protocols and the
network elements [RFC 4802] [RFC 4803], and there is early work to
provide similar access through YANG. The features described in
these models are currently designed to represent fixed-label
technologies such as optical networks using the fixed grid;
extensions may be needed in order to represent bandwidth,
frequency slots, and effective frequency slots in flexi-grid
networks.
o There are protocol extensions within GMPLS signaling to allow
control-plane systems to report the presence of faults that affect
LSPs [RFC 4783], although it must be carefully noted that these
mechanisms do not constitute an alarm mechanism that could be used
to rapidly propagate information about faults in a way that would
allow the data plane to perform protection switching. These
mechanisms could easily be enhanced with the addition of
technology-specific reason codes if any are needed.
o The GMPLS protocols, themselves, already include fault detection
and recovery mechanisms (such as the PathErr and Notify messages
in RSVP-TE signaling as used by GMPLS [RFC 3473]). It is not
anticipated that these mechanisms will need enhancement to support
flexi-grid, although additional reason codes may be needed to
describe technology-specific error cases.
o [RFC 7260] describes a framework for the control and configuration
of data-plane Operations, Administration, and Maintenance (OAM).
It would not be appropriate for the IETF to define or describe
data-plane OAM for optical systems, but the framework described in
RFC 7260 could be used (with minor protocol extensions) to enable
data-plane OAM that has been defined by the originators of the
flexi-grid data-plane technology (the ITU-T).
o The Link Management Protocol (LMP) [RFC 4204] is designed to allow
the two ends of a network link to coordinate and confirm the
configuration and capabilities that they will apply to the link.
LMP is particularly applicable to optical links, where the
characteristics of the network devices may considerably affect how
the link is used and where misconfiguration or mis-fibering could
make physical interoperability impossible. LMP could easily be
extended to collect and report information between the endpoints
of links in a flexi-grid network.
Gonzalez de Dios, et al. Informational PAGE 35
RFC 7698 GMPLS Flexi-Grid Framework November 2015
8. References
8.1. Normative References
[G.694.1] International Telecommunication Union, "Spectral grids for
WDM applications: DWDM frequency grid", ITU-T
Recommendation G.694.1, February 2012,
<https://www.itu.int/rec/T-REC-G.694.1/en>.
[G.800] International Telecommunication Union, "Unified functional
architecture of transport networks", ITU-T
Recommendation G.800, February 2012,
<http://www.itu.int/rec/T-REC-G.800/>.
[G.805] International Telecommunication Union, "Generic functional
architecture of transport networks", ITU-T
Recommendation G.805, March 2000,
<https://www.itu.int/rec/T-REC-G.805-200003-I/en>.
[G.8080] International Telecommunication Union, "Architecture for
the automatically switched optical network", ITU-T
Recommendation G.8080/Y.1304, February 2012,
<https://www.itu.int/rec/T-REC-G.8080-201202-I/en>.
[G.870] International Telecommunication Union, "Terms and
definitions for optical transport networks", ITU-T
Recommendation G.870/Y.1352, October 2012,
<https://www.itu.int/rec/T-REC-G.870/en>.
[G.872] International Telecommunication Union, "Architecture of
optical transport networks", ITU-T Recommendation G.872,
October 2012,
<http://www.itu.int/rec/T-REC-G.872-201210-I>.
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC 2119, March 1997,
<http://www.rfc-editor.org/info/RFC 2119>.
[RFC 3945] Mannie, E., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", RFC 3945,
DOI 10.17487/RFC 3945, October 2004,
<http://www.rfc-editor.org/info/RFC 3945>.
[RFC 4202] Kompella, K., Ed., and Y. Rekhter, Ed., "Routing
Extensions in Support of Generalized Multi-Protocol Label
Switching (GMPLS)", RFC 4202, DOI 10.17487/RFC 4202,
October 2005, <http://www.rfc-editor.org/info/RFC 4202>.
Gonzalez de Dios, et al. Informational PAGE 36
RFC 7698 GMPLS Flexi-Grid Framework November 2015
[RFC 4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching
(GMPLS) Traffic Engineering (TE)", RFC 4206,
DOI 10.17487/RFC 4206, October 2005,
<http://www.rfc-editor.org/info/RFC 4206>.
[RFC 5511] Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
Used to Form Encoding Rules in Various Routing Protocol
Specifications", RFC 5511, DOI 10.17487/RFC 5511,
April 2009, <http://www.rfc-editor.org/info/RFC 5511>.
8.2. Informative References
[G.959.1-2013]
International Telecommunication Union, "Optical transport
network physical layer interfaces", Update to ITU-T
Recommendation G.959.1, 2013.
[RFC 3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
DOI 10.17487/RFC 3473, January 2003,
<http://www.rfc-editor.org/info/RFC 3473>.
[RFC 4204] Lang, J., Ed., "Link Management Protocol (LMP)", RFC 4204,
DOI 10.17487/RFC 4204, October 2005,
<http://www.rfc-editor.org/info/RFC 4204>.
[RFC 4397] 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, DOI 10.17487/RFC 4397,
February 2006, <http://www.rfc-editor.org/info/RFC 4397>.
[RFC 4606] Mannie, E. and D. Papadimitriou, "Generalized
Multi-Protocol Label Switching (GMPLS) Extensions for
Synchronous Optical Network (SONET) and Synchronous
Digital Hierarchy (SDH) Control", RFC 4606,
DOI 10.17487/RFC 4606, August 2006,
<http://www.rfc-editor.org/info/RFC 4606>.
[RFC 4783] Berger, L., Ed., "GMPLS - Communication of Alarm
Information", RFC 4783, DOI 10.17487/RFC 4783,
December 2006, <http://www.rfc-editor.org/info/RFC 4783>.
Gonzalez de Dios, et al. Informational PAGE 37
RFC 7698 GMPLS Flexi-Grid Framework November 2015
[RFC 4802] Nadeau, T., Ed., Farrel, A., and , "Generalized
Multiprotocol Label Switching (GMPLS) Traffic Engineering
Management Information Base", RFC 4802,
DOI 10.17487/RFC 4802, February 2007,
<http://www.rfc-editor.org/info/RFC 4802>.
[RFC 4803] Nadeau, T., Ed., and A. Farrel, Ed., "Generalized
Multiprotocol Label Switching (GMPLS) Label Switching
Router (LSR) Management Information Base", RFC 4803,
DOI 10.17487/RFC 4803, February 2007,
<http://www.rfc-editor.org/info/RFC 4803>.
[RFC 5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, DOI 10.17487/RFC 5920, July 2010,
<http://www.rfc-editor.org/info/RFC 5920>.
[RFC 6163] Lee, Y., Ed., Bernstein, G., Ed., and W. Imajuku,
"Framework for GMPLS and Path Computation Element (PCE)
Control of Wavelength Switched Optical Networks (WSONs)",
RFC 6163, DOI 10.17487/RFC 6163, April 2011,
<http://www.rfc-editor.org/info/RFC 6163>.
[RFC 6344] Bernstein, G., Ed., Caviglia, D., Rabbat, R., and H. van
Helvoort, "Operating Virtual Concatenation (VCAT) and the
Link Capacity Adjustment Scheme (LCAS) with Generalized
Multi-Protocol Label Switching (GMPLS)", RFC 6344,
DOI 10.17487/RFC 6344, August 2011,
<http://www.rfc-editor.org/info/RFC 6344>.
[RFC 7139] Zhang, F., Ed., Zhang, G., Belotti, S., Ceccarelli, D.,
and K. Pithewan, "GMPLS Signaling Extensions for Control
of Evolving G.709 Optical Transport Networks", RFC 7139,
DOI 10.17487/RFC 7139, March 2014,
<http://www.rfc-editor.org/info/RFC 7139>.
[RFC 7260] Takacs, A., Fedyk, D., and J. He, "GMPLS RSVP-TE
Extensions for Operations, Administration, and Maintenance
(OAM) Configuration", RFC 7260, DOI 10.17487/RFC 7260,
June 2014, <http://www.rfc-editor.org/info/RFC 7260>.
Gonzalez de Dios, et al. Informational PAGE 38
RFC 7698 GMPLS Flexi-Grid Framework November 2015
Acknowledgments
The authors would like to thank Pete Anslow for his insights and
clarifications, and Matt Hartley and Jonas Maertensson for their
reviews.
This work was supported in part by the FP-7 IDEALIST project under
grant agreement number 317999.
Contributors
Adrian Farrel
Old Dog Consulting
Email: adrian@olddog.co.uk
Daniel King
Old Dog Consulting
Email: daniel@olddog.co.uk
Xian Zhang
Huawei
Email: zhang.xian@huawei.com
Cyril Margaria
Juniper Networks
Email: cmargaria@juniper.net
Qilei Wang
ZTE
Ruanjian Avenue, Nanjing, China
Email: wang.qilei@zte.com.cn
Malcolm Betts
ZTE
Email: malcolm.betts@zte.com.cn
Sergio Belotti
Alcatel-Lucent
Optics CTO
Via Trento 30 20059 Vimercate (Milano) Italy
Phone: +39 039 686 3033
Email: sergio.belotti@alcatel-lucent.com
Yao Li
Nanjing University
Email: wsliguotou@hotmail.com
Gonzalez de Dios, et al. Informational PAGE 39
RFC 7698 GMPLS Flexi-Grid Framework November 2015
Fei Zhang
Huawei
Email: zhangfei7@huawei.com
Lei Wang
Email: wang.lei@bupt.edu.cn
Guoying Zhang
China Academy of Telecom Research
No.52 Huayuan Bei Road, Beijing, China
Email: zhangguoying@ritt.cn
Takehiro Tsuritani
KDDI R&D Laboratories Inc.
2-1-15 Ohara, Fujimino, Saitama, Japan
Email: tsuri@kddilabs.jp
Lei Liu
UC Davis, United States
Email: leiliu@ucdavis.edu
Eve Varma
Alcatel-Lucent
Phone: +1 732 239 7656
Email: 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
Gonzalez de Dios, et al. Informational PAGE 40
RFC 7698 GMPLS Flexi-Grid Framework November 2015
Felipe Jimenez Arribas
Telefonica I+D
Andrew G. Malis
Huawei
Email: agmalis@gmail.com
Huub van Helvoort
Hai Gaoming BV
The Netherlands
Email: huubatwork@gmail.com
Authors' Addresses
Oscar Gonzalez de Dios (editor)
Telefonica I+D
Ronda de la Comunicacion s/n
Madrid 28050
Spain
Phone: +34 91 312 96 47
Email: oscar.gonzalezdedios@telefonica.com
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
Gonzalez de Dios, et al. Informational PAGE 41
RFC 7698 GMPLS Flexi-Grid Framework November 2015
Xihua Fu
Stairnote
No.118, Taibai Road, Yanta District
Xi'An
China
Email: fu.xihua@stairnote.com
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, CA 94089
United States
Phone: 408 572 5233
Email: ihussain@infinera.com
Gonzalez de Dios, et al. Informational PAGE 42
RFC TOTAL SIZE: 89787 bytes
PUBLICATION DATE: Thursday, November 19th, 2015
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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