One document matched: draft-ogrcetal-ccamp-flexi-grid-fwk-00.xml
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<rfc category="std" docName="draft-ogrcetal-ccamp-flexi-grid-fwk-00" ipr="trust200902" >
<front>
<title abbrev="GMPLS Flexi-grid Framework">Framework for GMPLS based control of Flexi-grid DWDM networks</title>
<author fullname="Oscar Gonzalez de Dios" initials="O." role="editor" surname="Gonzalez de Dios">
<organization>Telefónica I+D</organization>
<address>
<postal>
<street>Don Ramon de la Cruz 82-84</street>
<city>Madrid</city>
<region></region>
<code>28045</code>
<country>Spain</country>
</postal>
<phone>+34913128832</phone>
<email>ogondio@tid.es</email>
</address>
</author>
<author fullname="Ramon Casellas" initials="R." role="editor" surname="Casellas">
<organization>CTTC</organization>
<address>
<postal>
<street>Av. Carl Friedrich Gauss n.7</street>
<city>Castelldefels</city>
<region></region>
<code>Barcelona</code>
<country>Spain</country>
</postal>
<phone>+34 93 645 29 00</phone>
<email>ramon.casellas@cttc.es</email>
</address>
</author>
<author fullname="Fatai Zhang" initials="F." surname="Zhang">
<organization>Huawei</organization>
<address>
<postal>
<street>Huawei Base, Bantian, Longgang District</street>
<city>Shenzhen</city>
<region></region>
<code>518129</code>
<country>China</country>
</postal>
<phone>+86-755-28972912</phone>
<email>zhangfatai@huawei.com</email>
</address>
</author>
<author fullname="Xihua Fu" initials="X" surname="Fu">
<organization>ZTE</organization>
<address>
<postal>
<street>Ruanjian Avenue</street>
<city>Nanjing</city>
<region></region>
<code></code>
<country>China</country>
</postal>
<email>fu.xihua@zte.com.cn</email>
</address>
</author>
<author fullname="Daniele Ceccarelli" initials="D." surname="Ceccarelli">
<organization>Ericsson</organization>
<address>
<postal>
<street>Via Calda 5</street>
<city>Genova</city>
<region></region>
<code></code>
<country>Italy</country>
</postal>
<phone>+39 010 600 2512</phone>
<email>daniele.ceccarelli@ericsson.com</email>
</address>
</author>
<author fullname="Iftekhar Hussain" initials="I." surname="Hussain">
<organization>Infinera</organization>
<address>
<postal>
<street>140 Caspian Ct.</street>
<city>Sunnyvale</city>
<region></region>
<code>94089</code>
<country>USA</country>
</postal>
<phone>408-572-5233</phone>
<email> ihussain@infinera.com</email>
</address>
</author>
<!-- date day="24" month="April" year="2012" or autocompleted -->
<date year="2012" />
<area>Routing</area>
<workgroup>Network Working Group</workgroup>
<keyword>DWDM</keyword>
<keyword>flexi-grid</keyword>
<keyword>GMPLS</keyword>
<abstract>
<t>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 <xref target="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.</t>
</abstract>
</front>
<middle>
<!-- ===================================================================
Requirements Language
=================================================================== -->
<section title ="Requirements Language">
<t> 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 <xref
target="RFC2119"/>.
</t>
</section>
<!-- ===================================================================
Introduction
=================================================================== -->
<section title="Introduction">
<t>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 <xref
target="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.</t>
<t>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 <xref target="G.694.1"/>,
is constrained to be a multiple of a given slot width granularity.</t>
<t>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). </t>
<t>From a networking perspective, a flexible grid network is assumed to be
a layered network <xref target="G.872"/><xref target="G.805"/>, extending
the OTN architecture and interfaces <xref target="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.</t>
<t>As described in <xref target="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).</t>
<t>A Wavelength Switched Optical Network (WSON), addressed in <xref
target="RFC6163"/>, is a term commonly used to refer to the
application/deployment of a Generalized Multi-Protocol Label Switching
(GMPLS)-based control plane for the control (provisioning/recovery, etc)
of a fixed grid WDM network. [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]</t>
<t>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 <xref target="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.]</t>
<t>[Editors' note: this document will track changes and evolutions of <xref
target="G.694.1"/> <xref target="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]</t>
</section>
<!-- ===================================================================
Acronyms
=================================================================== -->
<section title="Acronyms">
<t>FS: Frequency Slot</t>
<t>FSCh: Frequency Slot Channel</t>
<t>NCF: Nominal Central Frequency</t>
<t>OCG: Optical Carrier Group</t>
<t>OCh: Optical Channel</t>
<t>OCC: Optical Channel Carrier</t>
<t>OTUk: Optical channel Transport Unit level k</t>
<t>ODUk: Optical channel Data Unit Level k</t>
<t>ODUj: Optical channel Data Unit Level j</t>
<t>SWG: Slot Width Granularity</t>
</section>
<!-- ===================================================================
Terminology
=================================================================== -->
<section title="Terminology">
<t>The following is a list of terms (see <xref target="G.694.1"/> and <xref
target="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.]</t>
<t>[Editors' note: *important* these terms are not yet final and they
may change / be replaced or obsoleted at any time.]</t>
<t>
<list style="symbols">
<t>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.</t>
<t>Nominal Central Frequency Granularity: 6.25 GHz (note: sometimes
referred to as 0.00625 THz).</t>
<t>Nominal Central Frequency: each of the allowed frequences as per the
definition of flexible DWDM grid in <xref target="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.
<figure title="Figure 1. Anchor frequency and set of nominal central frequencies">
<artwork>
<![CDATA[
-5 -4 -3 -2 -1 0 1 2 3 4 5 <- values of n
...+--+--+--+--+--+--+--+--+--+--+-
^
193.1 THz <- anchor frequency
]]>
</artwork>
</figure>
</t>
<t>Slot Width Granularity: 12.5 GHz, as defined in <xref
target="G.694.1"/>.</t>
<t>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.</t>
<t>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.
<figure title="Figure 2. Example Frequency slots">
<artwork>
<![CDATA[
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
]]>
</artwork>
</figure>
The symbol '+' represents the allowed nominal central frequencies,
the '--' represents the nominal central frequency granularity, and
the '^' represents the slot nominal central frequency. The number on
the top of the '+' symbol represents the 'n' in the frequency
calculation formula. The nominal central frequency is 193.1 THz when
n equals zero. Note that over a single frequency slot, one or
multiple Optical Channels may be transported. </t>
<t>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?]</t>
<t>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:
<list>
<t>MB: a frequency slot is a local (i.e., to the link) concept,
while a frequency slot channel has an end to end meaning.</t>
<t>IH: the FSCh is the CTP layer that is defining the frequency
slot connection matrix.</t>
<t>CM: the CTP is the Frequency Slot and the Frequency Slot Channel
the trail, the OCh being on top of the Channel.</t>
<t>ITU-T mailing list defines Common Frequency Slot which may replace
Frequency Slot Channel (?).</t>
</list>
]
</t>
<t>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?].
<figure title="Figure 4. Common Frequency Slot">
<artwork>
<![CDATA[
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
..--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--...
]]>
</artwork>
</figure>
</t>
<t>[Note: Following terminology is copied from ITU-T WP3 Q12
interim meeting <xref target="WD12R2"/>].</t>
<t>[Editors' note: if we accept that a frequency slot can
support one or more optical channel signals do we need the following
two definitions?).</t>
<t>Single-Channel Frequency Slot: a frequency slot associated with a
single optical channel signal ((that carries a single OCh payload).</t>
<t>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.
<figure title="Figure 3. Frequency slot with 2 Optical channel signals">
<artwork>
<![CDATA[
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
]]>
</artwork>
</figure>
</t>
<t>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.</t>
<t>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].</t>
<t>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. </t>
<t>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.</t>
<t>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</t>
</list>
</t>
<t>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.]
<list style="symbols">
<t>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.
</t>
<t>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. </t>
<t>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. </t>
</list>
</t>
</section>
<!-- ===================================================================
Network element models
=================================================================== -->
<section title="DWDM flexi-grid enabled network element models">
<t>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.</t>
<t>As stated in <xref target="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).</t>
<section title="Switched Resources and Labels">
<t>As per <xref target="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 slides]:
<list style="symbols">
<t>OCh Slots are switched in an Optical Channel Matrix.</t>
<t>The (link) physical layer entity, as defined by ITU-T is the
Frequency Slot.</t>
<t>A frequency slot channel may be switched in a Frequency Slot
Matrix [ITU-T contribution draft].</t>
<t>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].</t>
<t>[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'].</t>
</list>
</t>
</section>
<section title="Physical links">
</section>
<section title="Transceivers">
<t> Optical transmitters/receivers may have different restrictions on the
following properties:
<list style="symbols">
<t>Available central frequencies: The set of central frequencies
which can be used by an optical transmitter/receiver.</t>
<t>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. </t>
<t>The minimum and maximum slot width.</t>
<t>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).</t>
</list>
</t>
</section>
<section title="ROADMs">
<t>
<figure title="Figure 5. Simplified ROADM model with Line Sides and Tributaries">
<artwork><![CDATA[
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
]]></artwork>
</figure>
</t>
<t>[Editor's note: different ROADM configuration such as C/CD/CDC will be
added later.]</t>
<t>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 <xref target="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:
<list style="symbols">
<t>Available frequency ranges: the set or union of frequency ranges
that are not allocated (i.e. available). The relative grouping and
distribution of available frequency ranges in a fiber is usually
referred to as ''fragmentation''. </t>
<t>Available slot width ranges: the set or union of slot width ranges
supported by ROADM. It includes the following information.
<list style="symbols">
<t>Slot width threshold: the minimum and maximum Slot Width supported
by ROADM. For example, the slot width can be from 50GHz to
200GHz.</t>
<t>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.</t>
</list>
</t>
</list>
</t>
</section>
</section>
<!-- ===================================================================
Layered model
=================================================================== -->
<section title="Layered Network Model">
<t>[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.
<figure title="Figure 6. Layered Network Model G.805">
<artwork><![CDATA[
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)
]]></artwork>
</figure>
</t>
<t>[Editors' note: we are replicating the figure here for reference, until
the ITU-T document is official.</t>
<t>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?]</t>
</section>
<!-- ===================================================================
Topology View in Control Plane
=================================================================== -->
<section title="Topology view in Control Plane">
<t>[Note: the frequency slot matrix connection may interconnect one or more
frequency slot channels which in turn may carry one or more Och signals.]
<figure title="Figure 7. MRN/MLN topology view with TE link / FA">
<artwork>
<![CDATA[
+--------------+ +--------------+
| Signal (OCh) | TE | Signal (OCh) | Virtual TE
| | link | | link
| Matrix |o- - - - - - - - - - - - - o| Matrix |o- - - - - -
| | | |
+--------------+ +--------------+
| +---------+ |
| |Freq Slot| |
|o------| Matrix |---------o|
| |
+---------+
]]>
</artwork>
</figure>
</t>
</section>
<!-- ===================================================================
Control plane requirements
=================================================================== -->
<section title="Control Plane Requirements">
<t>[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?]</t>
<t>[Editor's note: formal requirements such as noted in the comments will
be added in a later version of the document].</t>
<t>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 <xref target="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.</t>
<section title="Neighbor Discovery and Link Property Correlation">
<t>[Editors' note: text from draft-li-ccamp-grid-property-lmp-01]</t>
<t>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.</t>
<t>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.</t>
<t>In summary, in a DWDM Link between two nodes, at least the following properties
should be negotiated:
<list>
<t>Grid capability (channel spacing) - Between fixed-grid and
flexible-grid nodes.</t>
<t>Grid granularity - Between two flexible-grid nodes.</t>
<t>Slot width tuning range - Between two flexible-grid nodes.</t>
</list>
</t>
</section>
<section title="Path Computation / Routing and Spectrum Assignment (RSA)">
<t> 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 <xref target="RFC6163"/>), if
the capability of shifting or converting an allocated frequency slot, the
LSP is subject to the Optical ''Spectrum Continuity Constraint''.</t>
<t>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.</t>
<t>The RSA process determines a route and frequency slot for a LSP.
Hence, when a route is computed the spectrum assignment process (SA)
should determine the central frequency and slot width based on the slot
width and available central frequencies information of the transmitter
and receiver, and the available frequency ranges information and
available slot width ranges of the links that the route traverses.</t>
<section title="Architectural Approaches to RSA">
<t>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. </t>
<section title="Combined RSA (R&SA)">
<t>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. </t>
<t>The computation entity could reside either on a PCE or the
ingress node.</t>
</section>
<section title="Separated RSA (R+SA)">
<t>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.</t>
<t>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.</t>
</section>
<section title=" Routing and Distributed SA (R+DSA)">
<t>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.</t>
</section>
</section>
</section>
<section title="Routing / Topology dissemination">
<t>In the case of combined RSA architecture, the computation
entity needs to get the detailed network information, i.e. connectivity
topology, node capabilities and available frequency ranges of the
links. Route computation is performed based on the connectivity
topology and node capabilities; spectrum assignment is performed based
on the available frequency ranges of the links. The computation entity
may get the detailed network information by the GMPLS routing protocol.
Compared with <xref target="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 <xref target="RFC6163"/>.
This section analyses the necessary changes on link information brought
by flexible grids.</t>
<section title="Available Frequency Ranges/slots of DWDM Links">
<t>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.
</t>
</section>
<section title="Available Slot Width Ranges of DWDM Links">
<t>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.</t>
</section>
<section title="Tunable Optical Transmitters and Receivers">
<t>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.</t>
</section>
<section title="Hierarchical Spectrum Management">
<t>[Editors' note: the part on the hierarchy of the optical spectrum
could be confusing, we can discuss it]. The total available spectrum
on a fiber could be described as a resource that can be divided by a
media device into a set of Frequency Slots. In terms of managing
spectrum, it is necessary to be able to speak about different
granularities of managed spectrum. For example, a part of the spectrum
could be assigned to a third party to manage. This need to partition
creates the impression that spectrum is a hierarchy in view of
Management and Control Plane. The hierarchy is created within a
management system, and it is an access right hierarchy only. It is a
management hierarchy without any actual resource hierarchy within
fiber. The end of fiber is a link end and presents a fiber port which
represents all of spectrum available on the fiber. Each spectrum
allocation appears as Link Channel Port (i.e., frequency slot port)
within fiber.
</t>
</section>
<section title="Information Model">
<t>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.
</t>
<t>[Editor's note: to be discussed]
<figure title="Figure 8. Routing Information model">
<artwork><![CDATA[
<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 × 6.25GHz,
where n is positive integer, such as 6.25GHz, 12.5GHz, 25GHz, 50GHz
or 100GHz
<Available Slot Width Granularity> ::= m × 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)
]]>
</artwork>
</figure>
</t>
</section>
</section>
<section title="Signaling requirements">
<t>Note on explicit label control</t>
<t>Compared with <xref target="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 <xref target="RFC6163"/>. In the case
of routing and distributed SA, GMPLS signaling can be used to allocate
the frequency slot to a LSP. </t>
<t>For R+DSA, the GMPLS signaling procedure is similar to the one described in
section 4.1.3 of <xref target="RFC6163"/> except that the label set
should specify the available nominal central frequencies that meet
the slot width requirement of the LSP.</t>
<section title="Slot Width Requirement">
<t>[Editors' note: the signaling requirements need to be discussed.
This is just preliminary text]. </t>
<t>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]</t>
</section>
<section title="Frequency Slot Representation">
<t>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.</t>
</section>
<section title="Relationship with MRN/MLN">
<section title="OCh Layer">
</section>
<section title="Media (frequency slot) layer">
</section>
</section>
</section> <!-- end signaling requirements -->
</section> <!-- end control plane requirements -->
<!-- ===================================================================
Control plane procedures
=================================================================== -->
<section title="Control Plane Procedures">
<t>Resizing existing LSP(s) without deletion: refers to increase or
decrease of slot width value 'm' without changing the value of 'n' </t>
<t>[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.]</t>
</section>
<!-- ===================================================================
Backwards compatibility / WSON interworking
=================================================================== -->
<section title="Backwards (fixed-grid) compatibility, and WSON interworking">
<t>
<list style="symbols">
<t>SSON as evolution of WSON, same LSC, different Swcap?</t>
<t>Potential problems with having the same swcap but the label format
changes w.r.t. wson </t>
<t>A new SwCap may need to be defined, LSC swcap already defined ISCD
which can not be modified</t>
<t>Role of LSP encoding type?</t>
<t>Notion of hierarchy? There is no notion of hierarchy between WSON
and flexi-grid / SSON - only interop / interwork.</t>
</list>
</t>
<t>Arguments for LSC switching capability</t>
<t>[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.</t>
<t>[QW] stitching LSP which is described in <xref target="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.</t>
<figure title="Figure 9. LSP Stitching [RFC5150] and relationship with fixed-flexi">
<artwork><![CDATA[
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
]]></artwork>
</figure>
</section>
<!-- ===================================================================
Open Issues and Misc
=================================================================== -->
<section title="Misc & Summary of open Issues [To be removed at later versions]">
<t>
<list style="symbols">
<t>Will reuse a lot of work / procedures / encodings defined in the
context of WSON</t>
<t>At data rates of GBps / TBps, encoding bandwidths with bytes per
second unit and IEEE 32-bit floating may be problematic / non
scalable.</t>
<t>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.</t>
<t>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"</t>
<t>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.</t>
<t>Label III: both, It reflects both the concept of resource request
allocation / reservation and the concept of being inherent part of
the switching.</t>
</list>
</t>
</section>
<!-- ===================================================================
SECURITY CONSIDERATIONS
=================================================================== -->
<section title="Security Considerations">
<t>TBD</t>
</section>
<!-- ===================================================================
CONTRIBUTING AUTHORS
=================================================================== -->
<section title="Contributing Authors">
<t>
<list>
<t>
Qilei Wang<vspace blankLines='0'/>
ZTE<vspace blankLines='0'/>
Ruanjian Avenue, Nanjing, China<vspace blankLines='0'/>
wang.qilei@zte.com.cn<vspace blankLines='0'/>
</t>
<t>
Malcolm Betts<vspace blankLines='0'/>
ZTE<vspace blankLines='0'/>
malcolm.betts@zte.com.cn<vspace blankLines='0'/>
</t>
<t>
Sergio Belotti<vspace blankLines='0'/>
Alcatel Lucent<vspace blankLines='0'/>
Optics CTO<vspace blankLines='0'/>
Via Trento 30 20059 Vimercate (Milano) Italy<vspace blankLines='0'/>
+39 039 6863033<vspace blankLines='0'/>
sergio.belotti@alcatel-lucent.com<vspace blankLines='0'/>
</t>
<t>
Cyril Margaria<vspace blankLines='0'/>
Nokia Siemens Networks<vspace blankLines='0'/>
St Martin Strasse 76, Munich, 81541, Germany<vspace blankLines='0'/>
+49 89 5159 16934<vspace blankLines='0'/>
cyril.margaria@nsn.com<vspace blankLines='0'/>
</t>
<t>
Xian Zhang<vspace blankLines='0'/>
Huawei<vspace blankLines='0'/>
zhang.xian@huawei.com<vspace blankLines='0'/>
</t>
<t>
Yao Li<vspace blankLines='0'/>
ZTE<vspace blankLines='0'/>
Zijinghua Road, Nanjing, China<vspace blankLines='0'/>
li.yao3@zte.com.cn<vspace blankLines='0'/>
</t>
<t>
Fei Zhang<vspace blankLines='0'/>
ZTE<vspace blankLines='0'/>
Zijinghua Road, Nanjing, China<vspace blankLines='0'/>
zhang.fei3@zte.com.cn<vspace blankLines='0'/>
</t>
<t>
Lei Wang<vspace blankLines='0'/>
ZTE<vspace blankLines='0'/>
East Huayuan Road, Haidian district, Beijing, China<vspace blankLines='0'/>
wang.lei131@zte.com.cn <vspace blankLines='0'/>
</t>
<t>
Guoying Zhang<vspace blankLines='0'/>
China Academy of Telecom Research<vspace blankLines='0'/>
No.52 Huayuan Bei Road, Beijing, China<vspace blankLines='0'/>
zhangguoying@ritt.cn<vspace blankLines='0'/>
</t>
<t>
Takehiro Tsuritani<vspace blankLines='0'/>
KDDI R&D Laboratories Inc.<vspace blankLines='0'/>
2-1-15 Ohara, Fujimino, Saitama, Japan<vspace blankLines='0'/>
tsuri@kddilabs.jp<vspace blankLines='0'/>
</t>
<t>
Lei Liu<vspace blankLines='0'/>
KDDI R&D Laboratories Inc.<vspace blankLines='0'/>
2-1-15 Ohara, Fujimino, Saitama, Japan<vspace blankLines='0'/>
le-liu@kddilabs.jp<vspace blankLines='0'/>
</t>
<t>
Eve Varma<vspace blankLines='0'/>
Alcatel-Lucent<vspace blankLines='0'/>
+1 732 239 7656<vspace blankLines='0'/>
eve.varma@alcatel-lucent.com<vspace blankLines='0'/>
</t>
<t>
Young Lee<vspace blankLines='0'/>
Huawei<vspace blankLines='0'/>
</t>
<t>
Jianrui Han<vspace blankLines='0'/>
Huawei<vspace blankLines='0'/>
</t>
<t>
Sharfuddin Syed<vspace blankLines='0'/>
Infinera<vspace blankLines='0'/>
</t>
<t>
Rajan Rao<vspace blankLines='0'/>
Infinera<vspace blankLines='0'/>
</t>
<t>
Marco Sosa<vspace blankLines='0'/>
Infinera<vspace blankLines='0'/>
</t>
<t>
Biao Lu<vspace blankLines='0'/>
Infinera<vspace blankLines='0'/>
</t>
<t>
Abinder Dhillon<vspace blankLines='0'/>
Infinera<vspace blankLines='0'/>
</t>
<t>
Felipe Jimenez Arribas<vspace blankLines='0'/>
Telefónica I+D<vspace blankLines='0'/>
</t>
<t>
Andrew G. Malis<vspace blankLines='0'/>
Verizon<vspace blankLines='0'/>
</t>
<t>
Adrian Farrel<vspace blankLines='0'/>
Old Dog Consulting<vspace blankLines='0'/>
</t>
<t>
Daniel King<vspace blankLines='0'/>
Old Dog Consulting<vspace blankLines='0'/>
</t>
</list>
</t>
</section>
<!-- ===================================================================
ACKNOWLEDGEMENTS
=================================================================== -->
<section title="Acknowledgments">
<t>The authors would like to thank Pete Anslow for his insights and
clarifications.</t>
</section>
</middle>
<back>
<references title="Normative References">
&RFC2119;
&RFC3945;
&RFC4206;
&RFC5150;
&RFC6163;
<reference anchor="G.805">
<front>
<title>ITU-T Recommendation G.805: Generic functional architecture of transport networks.</title>
<author> <organization abbrev="ITU-T">International Telecomunications Union</organization></author>
<date year="2000" month="March"/>
</front>
</reference>
<reference anchor="G.709">
<front>
<title>ITU-T Recommendation G.709: Interfaces for the Optical Transport Network (OTN).</title>
<author> <organization abbrev="ITU-T">International Telecomunications Union</organization></author>
<date year="2009" month="March"/>
</front>
</reference>
</references>
<references title="Informative References">
<reference anchor="G.694.1">
<front>
<title>ITU-T Recommendation G.694.1, Spectral grids for WDM applications: DWDM frequency grid, draft v1.6 2011/12</title>
<author> <organization abbrev="ITU-T">International Telecomunications Union</organization></author>
<date year="2011"/>
</front>
</reference>
<reference anchor="G.872">
<front>
<title>ITU-T Recommendation G.872, Architecture of optical transport networks, draft v0.12 2012/03 (for discussion)</title>
<author><organization abbrev="ITU-T">International Telecomunications Union</organization></author>
<date year="2012"/>
</front>
</reference>
<reference anchor="WD12R2">
<front>
<title>Proposed media layer terminology for G.872</title>
<author><organization abbrev="ITU-T">International Telecomunications Union, WD12R2, Q12-SG15, ZTE, Ciena WP3</organization></author>
<date year="2012" month="05"/>
</front>
</reference>
</references>
</back>
</rfc>
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