Network Working Group O. Gonzalez de Dios, Ed.
Internet-Draft Telefonica I+D
Intended status: Standards Track R. Casellas, Ed.
Expires: January 7, 2013 CTTC
F. Zhang
Huawei
X. Fu
ZTE
D. Ceccarelli
Ericsson
I. Hussain
Infinera
July 6, 2012
Framework for GMPLS based control of Flexi-grid DWDM networks
draft-ogrcetal-ccamp-flexi-grid-fwk-00
Abstract
This document defines a framework and the associated control plane
requirements for the GMPLS based control of flexi-grid DWDM networks.
To allow efficient allocation of optical spectral bandwidth for high
bit-rate systems, the International Telecommunication Union
Telecommunication Standardization Sector (ITU-T) is extending the
standard [G.694.1] to include the concept of flexible grid: a new
DWDM grid has been developed within the ITU-T Study Group 15, by
defining a set of nominal central frequencies, smaller channel
spacings and the concept of "frequency slot". In such environment, a
data plane connection is switched based on the allocated, variable-
width optical spectrum frequency slot.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on January 7, 2013.
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Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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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.
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Table of Contents
1. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. DWDM flexi-grid enabled network element models . . . . . . . . 11
5.1. Switched Resources and Labels . . . . . . . . . . . . . . 11
5.2. Physical links . . . . . . . . . . . . . . . . . . . . . . 12
5.3. Transceivers . . . . . . . . . . . . . . . . . . . . . . . 12
5.4. ROADMs . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6. Layered Network Model . . . . . . . . . . . . . . . . . . . . 14
7. Topology view in Control Plane . . . . . . . . . . . . . . . . 15
8. Control Plane Requirements . . . . . . . . . . . . . . . . . . 15
8.1. Neighbor Discovery and Link Property Correlation . . . . . 16
8.2. Path Computation / Routing and Spectrum Assignment
(RSA) . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8.2.1. Architectural Approaches to RSA . . . . . . . . . . . 17
8.3. Routing / Topology dissemination . . . . . . . . . . . . . 17
8.3.1. Available Frequency Ranges/slots of DWDM Links . . . . 18
8.3.2. Available Slot Width Ranges of DWDM Links . . . . . . 18
8.3.3. Tunable Optical Transmitters and Receivers . . . . . . 18
8.3.4. Hierarchical Spectrum Management . . . . . . . . . . . 18
8.3.5. Information Model . . . . . . . . . . . . . . . . . . 19
8.4. Signaling requirements . . . . . . . . . . . . . . . . . . 20
8.4.1. Slot Width Requirement . . . . . . . . . . . . . . . . 20
8.4.2. Frequency Slot Representation . . . . . . . . . . . . 20
8.4.3. Relationship with MRN/MLN . . . . . . . . . . . . . . 20
9. Control Plane Procedures . . . . . . . . . . . . . . . . . . . 20
10. Backwards (fixed-grid) compatibility, and WSON interworking . 21
11. Misc & Summary of open Issues [To be removed at later
versions] . . . . . . . . . . . . . . . . . . . . . . . . . . 22
12. Security Considerations . . . . . . . . . . . . . . . . . . . 23
13. Contributing Authors . . . . . . . . . . . . . . . . . . . . . 23
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 25
15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
15.1. Normative References . . . . . . . . . . . . . . . . . . . 25
15.2. Informative References . . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
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1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Introduction
The term "Flexible grid" (flexi-grid for short) as defined by the
International Telecommunication Union Telecommunication
Standardization Sector (ITU-T) study group 15 in the latest version
of [G.694.1], refers to the updated set of nominal central
frequencies (a frequency grid), channel spacings and optical spectrum
management/allocation considerations that have been defined in order
to allow an efficient and flexible allocation and configuration of
optical spectral bandwidth for high bit-rate systems.
A key concept of flexi-grid is the "frequency slot"; a variable-sized
optical frequency range that can be allocated to a data connection.
As detailed later in the document, a frequency slot is characterized
by its nominal central frequency, selected from the set of reference
frequencies, 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 100 or 50 GHz, a flexible grid network can
select its data channels with with a more flexible choice of slot
widths, allocating as much optical spectrum as required, and allowing
higher bitrates (e.g., 100G or 400G or higher).
From a networking perspective, a flexible grid network is assumed to
be a layered network [G.872][G.805], extending the OTN architecture
and interfaces [G.709], in which the flexi-grid layer (also referred
to as the media layer) is the server layer and the OCh Layer (also
referred to as the signal layer) is the client layer. In the media
layer, switching is based on a frequency slot, and the size of a
media channel is given by the properties of the associated frequency
slot. In this layered network, the media channel itself can be
dimensioned to contain one or more Optical Channels.
As described in [RFC3945], GMPLS extends MPLS from supporting only
Packet Switching Capable (PSC) interfaces and switching to also
support four new classes of interfaces and switching that include
Lambda Switch Capable (LSC).
A Wavelength Switched Optical Network (WSON), addressed in [RFC6163],
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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. [editors' note: we need to think of the relationship of
WSON and OCh switching. Are they equivalent? WSON includes
regeneration, OCh does not? decoupling of lambda/OCh/OCC]
This document defines the framework for a GMPLS-based control of
flexi-grid enabled DWDM networks (in the scope defined by ITU-T
layered Optical Transport Networks [G.872], as well as a set of
associated control plane requirements. An important design
consideration relates to the decoupling of the management of the
optical spectrum resource and the client signals to be transported.
[Editor's note: a point was raised during the meeting that WSON has
not made separation between Och and Lambda (spectrum and signal are
bundled). This needs to be confirmed.] A direct consequence of this
"separation of concerns" is that, although not in scope of the
present document, single-carrier / multi-carrier and related
modulation formats, etc. could be supported. [Editor's note: the
concept of frequency slot channel supporting multiple OCHs is defined
in an ITU contribution. It is not a standard document yet.]
[Editors' note: this document will track changes and evolutions of
[G.694.1] [G.872] documents until their final publication. This
document is not expected to become RFC until then. Likewise, as
agreed during IETF83, the consideration of the concepts of Super-
channel (a collection of one or more frequency slots to be treated as
unified entity for management and control plane) and consequently
Contiguous Spectrum Super-channel (a super-channel with a single
frequency slot) and Split-Spectrum super-channel (a super-channel
with multiple frequency slots) is postponed until the ITU-T data
plane includes such physical layer entities, e.g., an ITU-T
contribution exists]
3. Acronyms
FS: Frequency Slot
FSCh: Frequency Slot Channel
NCF: Nominal Central Frequency
OCG: Optical Carrier Group
OCh: Optical Channel
OCC: Optical Channel Carrier
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OTUk: Optical channel Transport Unit level k
ODUk: Optical channel Data Unit Level k
ODUj: Optical channel Data Unit Level j
SWG: Slot Width Granularity
4. Terminology
The following is a list of terms (see [G.694.1] and [G.872])
reproduced here for completeness. [Editors' note: regarding
wavebands, we agreed NOT to use the term in flexigrid. The term has
been used inconsistently in fixed-grid networks and overlaps with the
definition of frequency slot. If need be, a question will be sent to
ITU-T asking for clarification regarding wavebands.]
[Editors' note: *important* these terms are not yet final and they
may change / be replaced or obsoleted at any time.]
o Optical Channel Slot (definition in the scope of a fixed grid DWDM
network, to be adapted to a flexi-grid). The optical spectrum
frequency range (portion of optical spectrum) allocated / occupied
by a single optical channel. Each optical channel signal has a
defined carrier central frequency and required frequency slot
width (the supported optical channel signal bandwidth plus source
stability). Optical Channel slots within an optical multiplex
section may be allocated (in-service) or may be unallocated (out-
of-service). An in-service Optical Channel Slot may be carrying
an Optical Channel Signal or not. Optical Channel Slots are
switched in an Optical Channel Matrix.
o Nominal Central Frequency Granularity: 6.25 GHz (note: sometimes
referred to as 0.00625 THz).
o Nominal Central Frequency: each of the allowed frequences as per
the definition of flexible DWDM grid in [G.694.1]. The set of
nominal central frequencies can be built using the following
expression f = 193.1 THz + n x 0.00625 THz, where 193.1 THz is
ITU-T ''anchor frequency'' for transmission over the C band, n is
a positive or negative integer including 0.
-5 -4 -3 -2 -1 0 1 2 3 4 5 <- values of n
...+--+--+--+--+--+--+--+--+--+--+-
^
193.1 THz <- anchor frequency
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Figure 1. Anchor frequency and set of nominal central frequencies
o Slot Width Granularity: 12.5 GHz, as defined in [G.694.1].
o Slot Width: The slot width determines the "amount" of optical
spectrum regardless of its actual "position" in the frequency
axis. A slot width is constrained to be m x SWG (that is, m x
12.5 GHz), where m is an integer greater than or equal to 1.
o Frequency Slot: The frequency range allocated to a slot within the
flexible grid. A frequency slot is defined by its nominal central
frequency and its slot width. Assuming a fixed and known central
nominal frequency granularity, and assuming a fixed and known slot
width granularity, a frequency slot is fully characterized by the
values of 'n' and 'm'. Note that an equivalent characterization
of a frequency slot is given by the start and end frequencies
(i.e., a frequency range) which can, in turn, be defined by their
respective values of 'n'. Note that a bidirectional optical
transmission section layer network connection may be supported by
one optical fiber for both directions (single fiber), or each
direction of the connection may be supported by different fibers
(pair of fibers). Since a frequency slot is a unidirectional
entity (the same nominal central frequency cannot be used in two
directions of transmission), the single fiber case is carried out
by a pair of unidirectional frequency slots on the same fiber, and
the pair of fibers case may have frequency slots that use the same
nominal central frequencies.
Frequency Slot 1 Frequency Slot 2
------------- -------------------
| | | |
-3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
..--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--...
------------- -------------------
^ ^
Central F = 193.1THz Central F = 193.14375 THz
Slot width = 25 GHz Slot width = 37.5 GHz
Figure 2. Example Frequency slots
The symbol '+' represents the allowed nominal central frequencies,
the '--' represents the nominal central frequency granularity, and
the '^' represents the slot nominal central frequency. The number
on the top of the '+' symbol represents the 'n' in the frequency
calculation formula. The nominal central frequency is 193.1 THz
when n equals zero. Note that over a single frequency slot, one
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or multiple Optical Channels may be transported.
o Fiber Frequency Slot: the total allocable spectrum on a fiber (n=0
and m= infinity?). [Editors' note/CM: is this useful? is the
spectrum bounded/symmetric w.r.t anchor frequency?]
o Frequency Slot Channel: a topological construct that represents a
piece of spectrum supported by a concatenation of media elements
(fiber, amplifiers, filters..). 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. [Editors' note:
* MB: a frequency slot is a local (i.e., to the link) concept,
while a frequency slot channel has an end to end meaning.
* IH: the FSCh is the CTP layer that is defining the frequency
slot connection matrix.
* CM: the CTP is the Frequency Slot and the Frequency Slot
Channel the trail, the OCh being on top of the Channel.
* ITU-T mailing list defines Common Frequency Slot which may
replace Frequency Slot Channel (?).
]
o Common Frequency Slot: the optical frequency range that is common
to all of the devices in a particular path through the optical
network. It is a logical construct derived from the frequency
slots allocated to each device in the path (intersection). As an
example, if there are two devices having slots with the same n but
different m, then the common frequency slot has the smaller of the
two m values. [Editors' note: this definition overlaps with
Effective Frequency Slot] [Editors' note: clarify what happens
when the resulting slot cannot be characterized with n and m, see
Figure. Are we assuming that the same "n" applies?].
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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--+--+--+--+--+--+--+--+--+--+--+--...
=============================================== Common
Common Frequency Slot (valid?, CF?)
----------
| |
-3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
..--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--...
Figure 4. Common Frequency Slot
o [Note: Following terminology is copied from ITU-T WP3 Q12 interim
meeting [WD12R2]].
o [Editors' note: if we accept that a frequency slot can support one
or more optical channel signals do we need the following two
definitions?).
o Single-Channel Frequency Slot: a frequency slot associated with a
single optical channel signal ((that carries a single OCh
payload).
o Multi-Channel Frequency Slot: a frequency slot associated with
multiple optical channel signals (i.e. multiple OChs). Note that
if there are multiple optical signals within frequency slot, then
each signal still has its own central frequency. That is, the
term "central frequency" applies to an Optical signal and the term
"nominal central frequency" applies to a frequency slot. In other
words, the Frequency Slot central frequency is independent of the
signals central frequencies.
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Frequency Slot
-----------------------------------+
| Optical Optical |
| Channel Channel |
| Signal Signal |
| +-----+ +-----------+ |
| | | | | |
| | o | | o | |
-4 -3 -2 -1 0 1 2 3 4 5 6 7 8
... +--+--+--+--+--X--+--+--+--+--+--+-+--...
^
+-- Frequency Slot
Central Frequency
o - signal central frequency
Figure 3. Frequency slot with 2 Optical channel signals
o Network Channel (NCh): An end-to-end path through an optical
network from a port on an OCh termination source to a port on an
OCh termination sink (i.e. one OEO to another OEO). It is
constructed from a concatenation of link channels and subnetwork
channels.
o Link Channel (LCh): A partial path through an optical network that
provides a fixed relationship between the ports on a "subnetwork"
or "access group" and the ports on another "subnetwork" or "access
group". [Note: the terms subnetwork and access group are defined
in G.805].
o Subnetwork Channel (SNCh): A path through an optical subnetwork
that provides a relationship across a subnetwork. It is formed by
the association of "ports" on the boundary of the subnetwork.
o Matrix Channel (MCh): A path through an optical matrix that
provides a relationship across a matrix. It is formed by the
association of "ports" on the boundary of the matrix.
o Effective Frequency Slot: An attribute of a channel which
identifies that part of the frequency slots allocated to the
devices along the channel that is common to all
The following terms are defined in the scope of a GMPLS control
plane. [Editors' note: the following ones were *not* agreed during
IETF83 but are put here to be discussed.]
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o SSON: Spectrum-Switched Optical Network. An optical network in
which a data plane connection is switched based on an optical
spectrum frequency slot of a variable slot width, rather than
based on a fixed grid and fixed slot width. Please note that a
Wavelength Switched Optical Network (WSON) can be seen as a
particular case of SSON in which all slot widths are equal and
depend on the used channel spacing.
o Flexi-LSP: a control plane construct that represents a data plane
connection in which the switching involves a frequency slot.
Different Flexi-LSPs may have different slot widths. The term
flexi-LSP is used when needed to differentiate from regular WSON
LSP in which switching is based on a nominal wavelength.
o RSA: Routing and Spectrum Assignment. As opposed to the typical
Routing and Wavelength Assignment (RWA) problem of traditional WDM
networks, the flexibility in SSON leads to spectral contiguous
constraint, which means that when assigning the spectral resources
to single connections, the resources assigned to them must be
contiguous over the entire connections in the spectrum domain.
5. 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,
Reconfigurable Optical Add/Drop Multiplexers (ROADMs), wavelength
converters, and 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).
5.1. Switched Resources and Labels
As per [G.872] [Editor's note/CM: we need to better distinguish
between G.872 and contributions, it would help to see what is agreed
and what is still open, the list below contains items as per MB/XF
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slides]:
o OCh Slots are switched in an Optical Channel Matrix.
o The (link) physical layer entity, as defined by ITU-T is the
Frequency Slot.
o A frequency slot channel may be switched in a Frequency Slot
Matrix [ITU-T contribution draft].
o The frequency slot matrix connection cannot modify the center
frequency or increase the bandwidth of the frequency slots present
at its ports [Editors' note: this text comes from G.872 updated.
This seems to constrain / limit to only a transparent segment? the
"m" must be the same end to end while "n" can be change by the
equivalent of a wavelength converter, but WC are not defined.
Currently, we only consider the case that the frequency slot
matrix connection cannot modify the center frequency or the
bandwidth of the frequency slots present at its ports. The use
cases of dynamically modifying the center frequency or the
bandwidth of the frequency slots are for further study after the
clear definition by ITU-T].
o [Editors' note: we are not discarding O/E/O. If defined in a ITU-T
network reference model with trail/terminations, considering
optical channels i.e. with well-defined interfaces, reference
points, and architectures. The implications of O/E/O will be also
addressed once we have another context that includes them. In OTN
from an OCh point of view end to end means from transponder to
transponder, so if there is a 3R from ingress to egress there are
2 OCh which can have different 'n' and 'm'].
5.2. Physical links
5.3. Transceivers
Optical transmitters/receivers may have different restrictions on the
following properties:
o Available central frequencies: The set of central frequencies
which can be used by an optical transmitter/receiver.
o Slot width: The slot width needed by a transmitter/receiver. The
slot width is dependent on bit rate and modulation format. For
one specific transmitter, the bit rate and modulation format may
be tunable, so slot width would be determined by the modulation
format used at a given bit rate.
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o The minimum and maximum slot width.
o The step granularity: the optical hardare may not be able to
select parameters with the lowest granulairy (e.g. 6.25 GHz for
nominal central frequencies or 12.5 GHz for slot width
granularity).
5.4. ROADMs
Tributary Side: E5 I5 E6 I6
O | O |
| | | |
| O | O
+-----------------------+
|+-----+ +-----+|
Line side-1 --->||Split| |WSS-2||---> Line side-2
Input (I1) |+-----+ +-----+| Output (E2)
Line side-1 <---||WSS-1| |Split||<--- Line side-2
Output (E1) |+-----+ +-----+| Input (I2)
| ROADM |
|+-----+ +-----+|
Line side-3 --->||Split| |WSS-4||---> Line side-4
Input (I3) |+-----+ +-----+| Output (E4)
Line side-3 <---||WSS-3| |Split||<--- Line side-4
Output (E3) |+-----+ +-----+| Input (I4)
+-----------------------+
| O | O
| | | |
O | O |
Tributary Side: E7 I7 E8 I8
Figure 5. Simplified ROADM model with Line Sides and Tributaries
[Editor's note: different ROADM configuration such as C/CD/CDC will
be added later.]
A Frequency slot matrix may have switching restrictions, for example
, when it is realized using flexi-grid enabled ROADMs. A key feature
of ROADMs is their highly asymmetric switching capability which is
described in [RFC6163] in detail. The ports on ROADM include line
side ports which are connected to DWDM links and tributary side
input/output ports which can be connected to transmitters/receivers.
The capability of ports on ROADM, which are characterized as follows:
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
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usually referred to as ''fragmentation''.
o Available slot width ranges: the set or union of slot width ranges
supported by ROADM. It includes the following information.
* Slot width threshold: the minimum and maximum Slot Width
supported by ROADM. For example, the slot width can be from
50GHz to 200GHz.
* Step granularity: the minimum step by which the optical filter
bandwidth of ROADM can be increased or decreased. This
parameter is typically equal to slot width granularity (i.e.
12.5GHz) or integer multiples of 12.5GHz.
6. Layered Network Model
[Editors' note: OTN hierarchy is not fully covered. It is important
to understand, where the FSC sits in the OTN hierarchy. This is also
important from control plane perspective as this layer becomes the
connection end points of optical layer service]. OCh / flexi-grid
layered model.
AP Trail (OCh) AP
O- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O
TCP Link Connection (OCh) TCP
o------------o-------------------------------------------o---------o
Subnetwork Subnetwork
Connection Connection
| Media Path |
AP O- - - - - - - - - - - - - - - - - - - - - -O AP
| |
| Link (Fiber) |
TCP o---------------o-----------o---------------o
Subnet. channel Link channel Subnet. chan
(freq slot) (freq slot) (freq slot)
Figure 6. Layered Network Model G.805
[Editors' note: we are replicating the figure here for reference,
until the ITU-T document is official.
The media path is a piece of spectrum that has been allocated to a
path between two ports of a media device. [Editors'note/CM/IH: it
seems the media path is equivalent to the FSC (freq.slot channel is
between the AP?. Why use a new term media path?]
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7. Topology view in Control Plane
[Note: the frequency slot matrix connection may interconnect one or
more frequency slot channels which in turn may carry one or more Och
signals.]
+--------------+ +--------------+
| Signal (OCh) | TE | Signal (OCh) | Virtual TE
| | link | | link
| Matrix |o- - - - - - - - - - - - - o| Matrix |o- - - - - -
| | | |
+--------------+ +--------------+
| +---------+ |
| |Freq Slot| |
|o------| Matrix |---------o|
| |
+---------+
Figure 7. MRN/MLN topology view with TE link / FA
8. Control Plane Requirements
[Editor's note: The considered topology view is a layered network, in
which the media layer corresponds to the server layer (flexigrid) and
the signal layer corresponds to the client layer (Och). This data
plane modeling considers the flexigrid and the OCh as separate
layers, especially considering both the single and multi-channel
frequency slots. However, this has implications on the interop/
interworking with WSON and OCh switching. We need to manage a MRN
for OCh and stitching for WSON? In other words, a key part of the
fwk is to define how can we have MRN/MLN hierarchical relationship
with Och/FS and yet stitching 1:1 between WSON and SSON? In this
line: how does OCh switching and WSON relate, actually?]
[Editor's note: formal requirements such as noted in the comments
will be added in a later version of the document].
Hierarchy spectrum management decouples media and signal, but from
the point of view of the control plane, such separation of concerns
implies the management of a MRN/MLN network. So Control Plane needs
to differentiate signal LSP and media LSP. It should also need to
support Hierarchy-LSP [RFC4206] The central frequency of each hop
should be same along end-to-end media or signal LSP because of
Spectrum Continuity Constraint. Otherwise some nodes need to convert
the central frequency along media or signal LSP.
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8.1. Neighbor Discovery and Link Property Correlation
[Editors' note: text from draft-li-ccamp-grid-property-lmp-01]
During the practical deployment procedure, fixed-grid optical nodes
will be gradually replaced by flexible nodes. This will lead to an
interworking problem between fixed-grid DWDM and flexible-grid DWDM
nodes. 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.
8.2. Path Computation / Routing and Spectrum Assignment (RSA)
Much like in WSON, in which if there is no (available) wavelength
converters in an optical network, an LSP is subject to the
''wavelength continuity constraint'' (see section 4 of [RFC6163]), if
the capability of shifting or converting an allocated frequency slot,
the LSP is subject to the Optical ''Spectrum Continuity Constraint''.
Because of the limited availability of wavelength/spectrum converters
(sparse translucent optical network) the wavelength/spectrum
continuity constraint should always be considered. When available,
information regarding spectrum conversion capabilities at the optical
nodes may be used by RSA mechanisms.
The RSA process determines a route and frequency slot for a LSP.
Hence, when a route is computed the spectrum assignment process (SA)
should determine the central frequency and slot width based on the
slot width and available central frequencies information of the
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transmitter and receiver, and the available frequency ranges
information and available slot width ranges of the links that the
route traverses.
8.2.1. Architectural Approaches to RSA
Similar to RWA for fixed grids, different ways of performing RSA in
conjunction with the control plane can be considered. The approaches
included in this document are provided for reference purposes only;
other possible options could also be deployed.
8.2.1.1. Combined RSA (R&SA)
In this case, a computation entity performs both routing and
frequency slot assignment. The computation entity should have the
detailed network information, e.g. connectivity topology constructed
by nodes/links information, available frequency ranges on each link,
node capabilities, etc.
The computation entity could reside either on a PCE or the ingress
node.
8.2.1.2. Separated RSA (R+SA)
In this case, routing computation and frequency slot assignment are
performed by different entities. The first entity computes the
routes and provides them to the second entity; the second entity
assigns the frequency slot.
The first entity should get the connectivity topology to compute the
proper routes; the second entity should get the available frequency
ranges of the links and nodes' capabilities information to assign the
spectrum.
8.2.1.3. Routing and Distributed SA (R+DSA)
In this case, one entity computes the route but the frequency slot
assignment is performed hop-by-hop in a distributed way along the
route. The available central frequencies which meet the spectrum
continuity constraint should be collected hop by hop along the route.
This procedure can be implemented by the GMPLS signaling protocol.
8.3. Routing / Topology dissemination
In the case of combined RSA architecture, the computation entity
needs to get the detailed network information, i.e. connectivity
topology, node capabilities and available frequency ranges of the
links. Route computation is performed based on the connectivity
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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.
8.3.1. Available Frequency Ranges/slots of DWDM Links
In the case of flexible grids, channel central frequencies span from
193.1 THz towards both ends of the C band spectrum with 6.25 GHz
granularity. Different LSPs could make use of different slot widths
on the same link. Hence, the available frequency ranges should be
advertised.
8.3.2. Available Slot Width Ranges of DWDM Links
The available slot width ranges needs to be advertised, in
combination with the Available frequency ranges, in order to verify
whether a LSP with a given slot width can be set up or not; this is
is constrained by the available slot width ranges of the flexi-grid
enabled ROADMs (the flexi-grid Frequency slot matrix). Depending on
the availability of the slot width ranges, it is possible to allocate
more spectrum than strictly needed by the LSP.
8.3.3. Tunable Optical Transmitters and Receivers
The slot width of a LSP is determined by the transmitter and receiver
that could be mapped to ADD/DROP interfaces in WSON. Moreover their
central frequency could be fixed or tunable, hence, both the slot
width of an ADD/DROP interface and the available central frequencies
should be advertised.
8.3.4. Hierarchical Spectrum Management
[Editors' note: the part on the hierarchy of the optical spectrum
could be confusing, we can discuss it]. The total available spectrum
on a fiber could be described as a resource that can be divided by a
media device into a set of Frequency Slots. In terms of managing
spectrum, it is necessary to be able to speak about different
granularities of managed spectrum. For example, a part of the
spectrum could be assigned to a third party to manage. This need to
partition creates the impression that spectrum is a hierarchy in view
of Management and Control Plane. The hierarchy is created within a
management system, and it is an access right hierarchy only. It is a
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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.
8.3.5. Information Model
Fixed DM grids can also be described via suitable choices of slots in
a flexible DWDM grid. However, devices or applications that make use
of the flexible grid may not be capable of supporting every possible
slot width or central frequency position. Following is the
definition of information model, not intended to limit any IGP
encoding implementation. For example, information required for
routing/path selection may be the set of available nominal central
frequencies from which a frequency slot of the required width can be
allocated. A convenient encoding for this information (may be as a
frequency slot or sets of contiguous slices) is further study in IGP
encoding document.
[Editor's note: to be discussed]
<Available Spectrum in Fiber for frequency slot> ::=
<Available Frequency Range-List>
<Available Central Frequency Granularity >
<Available Slot Width Granularity>
<Minimal Slot Width>
<Maximal Slot Width>
<Available Frequency Range-List> ::=
<Available Frequency Range >[< Available Frequency Range-List>]
<Available Frequency Range >::=
<Start Spectrum Position><End Spectrum Position> |
<Sets of contiguous slices>
<Available Central Frequency Granularity> ::= n x 6.25GHz,
where n is positive integer, such as 6.25GHz, 12.5GHz, 25GHz, 50GHz
or 100GHz
<Available Slot Width Granularity> ::= m x 12.5GHz,
where m is positive integer
<Minimal Slot Width> ::= j x 12.5GHz,
j is a positive integer
<Maximal Slot Width> ::= k x 12.5GHz,
k is a positive integer (k >= j)
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Figure 8. Routing Information model
8.4. Signaling requirements
Note on explicit label control
Compared with [RFC6163], except identifying the resource (i.e., fixed
wavelength for WSON and frequency resource for flexible grids), the
other signaling requirements (e.g., unidirectional or bidirectional,
with or without converters) are the same as WSON described in the
section 6.1 of [RFC6163]. In the case of routing and distributed SA,
GMPLS signaling can be used to allocate the frequency slot to a LSP.
For R+DSA, the GMPLS signaling procedure is similar to the one
described in section 4.1.3 of [RFC6163] except that the label set
should specify the available nominal central frequencies that meet
the slot width requirement of the LSP.
8.4.1. Slot Width Requirement
[Editors' note: the signaling requirements need to be discussed.
This is just preliminary text].
In order to allocate a proper frequency slot for a LSP, the signaling
should specify its slot width requirement. The intermediate nodes
can collect the acceptable central frequencies that meet the slot
width requirement hop by hop. The tail-end node also needs to know
the slot width of a LSP to assign the proper frequency resource.
Hence, the slot width requirement should be specified in the
signaling message when a LSP is being set up. [Note: other methods
may not need to collect availability]
8.4.2. Frequency Slot Representation
The frequency slot can be determined by the central frequency (n
value) and slot width (m value). Such parameters should be able to
be specified by the signaling protocol.
8.4.3. Relationship with MRN/MLN
8.4.3.1. OCh Layer
8.4.3.2. Media (frequency slot) layer
9. Control Plane Procedures
Resizing existing LSP(s) without deletion: refers to increase or
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decrease of slot width value 'm' without changing the value of 'n'
[Editor's note: Restoration / Resizing a single LSP without deletion
as well as timing constraints. As per ITU-T clarification on service
affecting or non-service affecting (i.e., hitless) restoration, at
present no hitless resizing protocol has been defined for OCh.
Hitless resizing is defined for an ODU entity only.]
10. Backwards (fixed-grid) compatibility, and WSON interworking
o SSON as evolution of WSON, same LSC, different Swcap?
o Potential problems with having the same swcap but the label format
changes w.r.t. wson
o A new SwCap may need to be defined, LSC swcap already defined ISCD
which can not be modified
o Role of LSP encoding type?
o Notion of hierarchy? There is no notion of hierarchy between WSON
and flexi-grid / SSON - only interop / interwork.
Arguments for LSC switching capability
[QW] A LSP for an optical signal which has a bandwidth of 50GHz
passes through both a fixed grid network and a flexible grid network.
We assume that no OEOs exist in the LSP, so both the fixed grid path
and flexible grid path occupy 50GHz. From the perspective of data
plane, there is no change of the signal and no multiplexing when the
fixed grid path interconnects with flexible grid path. From this
scenario we can conclude that both fixed grid network path and
flexible grid network path belong to the same layer. No notion of
hierarchy exists between them.
[QW] stitching LSP which is described in [RFC5150] can be applied in
one layer. LSP hierarchy allows more than one LSP to be mapped to an
H-LSP, but in case of S-LSP, at most one LSP may be associated with
an S-LSP. This is similar to the scenario of interconnection between
fixed grid LSP and flexible grid LSP. Similar to an H-LSP, an S-LSP
could be managed and advertised, although it is not required, as a TE
link, either in the same TE domain as it was provisioned or a
different one. Path setup procedure of stitching LSP can be applied
in the scenario of interconnection between fixed grid path and
flexible grid path.
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e2e LSP
+++++++++++++++++++++++++++++++++++> (LSP1-2)
LSP segment (flexi-LSP)
====================> (LSP-AB)
C --- E --- G
/|\ | / |\
/ | \ | / | \
R1 ---- A \ | \ | / | / B --- R2
\| \ |/ |/
D --- F --- H
fixed grid --A-- flexi-grid --B-- fixed grid
Figure 9. LSP Stitching [RFC5150] and relationship with fixed-flexi
11. Misc & Summary of open Issues [To be removed at later versions]
o Will reuse a lot of work / procedures / encodings defined in the
context of WSON
o At data rates of GBps / TBps, encoding bandwidths with bytes per
second unit and IEEE 32-bit floating may be problematic / non
scalable.
o Bandwidth fields not relevant since there is not a 1-to-1 mapping
between bps and Hz, since it depends on the modulation format,
fec, either there is an agreement on assuming best / worst case
modulations and spectral efficiency.
o Label I: "m" is inherent part of the label, part of the switching,
allows encode the "lightpath" in a ERO using Explicit Label
Control, Still maintains that feature a cross-connect is defined
by the tuple (port-in, label-in, port-out, label-out), allows a
kind-of "best effort LSP"
o Label II: "m" is not part of the label but of the TSPEC, neds to
be in the TSPEC to decouple client signal traffic specification
and management of the optical spectrum, having in both places is
redundant and open to incoherences, extra error checking.
o Label III: both, It reflects both the concept of resource request
allocation / reservation and the concept of being inherent part of
the switching.
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12. Security Considerations
TBD
13. Contributing Authors
Qilei Wang
ZTE
Ruanjian Avenue, Nanjing, China
wang.qilei@zte.com.cn
Malcolm Betts
ZTE
malcolm.betts@zte.com.cn
Sergio Belotti
Alcatel Lucent
Optics CTO
Via Trento 30 20059 Vimercate (Milano) Italy
+39 039 6863033
sergio.belotti@alcatel-lucent.com
Cyril Margaria
Nokia Siemens Networks
St Martin Strasse 76, Munich, 81541, Germany
+49 89 5159 16934
cyril.margaria@nsn.com
Xian Zhang
Huawei
zhang.xian@huawei.com
Yao Li
ZTE
Zijinghua Road, Nanjing, China
li.yao3@zte.com.cn
Fei Zhang
ZTE
Zijinghua Road, Nanjing, China
zhang.fei3@zte.com.cn
Lei Wang
ZTE
East Huayuan Road, Haidian district, Beijing, China
wang.lei131@zte.com.cn
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Guoying Zhang
China Academy of Telecom Research
No.52 Huayuan Bei Road, Beijing, China
zhangguoying@ritt.cn
Takehiro Tsuritani
KDDI R&D Laboratories Inc.
2-1-15 Ohara, Fujimino, Saitama, Japan
tsuri@kddilabs.jp
Lei Liu
KDDI R&D Laboratories Inc.
2-1-15 Ohara, Fujimino, Saitama, Japan
le-liu@kddilabs.jp
Eve Varma
Alcatel-Lucent
+1 732 239 7656
eve.varma@alcatel-lucent.com
Young Lee
Huawei
Jianrui Han
Huawei
Sharfuddin Syed
Infinera
Rajan Rao
Infinera
Marco Sosa
Infinera
Biao Lu
Infinera
Abinder Dhillon
Infinera
Felipe Jimenez Arribas
Telefonica I+D
Andrew G. Malis
Verizon
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Adrian Farrel
Old Dog Consulting
Daniel King
Old Dog Consulting
14. Acknowledgments
The authors would like to thank Pete Anslow for his insights and
clarifications.
15. References
15.1. Normative References
[G.709] International Telecomunications Union, "ITU-T
Recommendation G.709: Interfaces for the Optical Transport
Network (OTN).", March 2009.
[G.805] International Telecomunications Union, "ITU-T
Recommendation G.805: Generic functional architecture of
transport networks.", March 2000.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching
(GMPLS) Architecture", RFC 3945, October 2004.
[RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching
(GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.
[RFC5150] Ayyangar, A., Kompella, K., Vasseur, JP., and A. Farrel,
"Label Switched Path Stitching with Generalized
Multiprotocol Label Switching Traffic Engineering (GMPLS
TE)", RFC 5150, February 2008.
[RFC6163] Lee, Y., Bernstein, G., and W. Imajuku, "Framework for
GMPLS and Path Computation Element (PCE) Control of
Wavelength Switched Optical Networks (WSONs)", RFC 6163,
April 2011.
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15.2. Informative References
[G.694.1] International Telecomunications Union, "ITU-T
Recommendation G.694.1, Spectral grids for WDM
applications: DWDM frequency grid, draft v1.6 2011/12",
2011.
[G.872] International Telecomunications Union, "ITU-T
Recommendation G.872, Architecture of optical transport
networks, draft v0.12 2012/03 (for discussion)", 2012.
[WD12R2] International Telecomunications Union, WD12R2, Q12-SG15,
ZTE, Ciena WP3, "Proposed media layer terminology for
G.872", 05 2012.
Authors' Addresses
Oscar Gonzalez de Dios (editor)
Telefonica I+D
Don Ramon de la Cruz 82-84
Madrid, 28045
Spain
Phone: +34913128832
Email: ogondio@tid.es
Ramon Casellas (editor)
CTTC
Av. Carl Friedrich Gauss n.7
Castelldefels, Barcelona
Spain
Phone: +34 93 645 29 00
Email: ramon.casellas@cttc.es
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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