RSVP-TE Extensions for GMPLS control of Spectrum Switched Optical Networks (SSONs)
draft-wang-ccamp-gmpls-sson-rsvpte-01
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draft-wang-ccamp-gmpls-sson-rsvpte-01
Network Working Group Qilei Wang
Internet-Draft Xihua Fu
Intended status: Standards Track ZTE Corporation
Expires: January 17, 2013 Jul 16, 2012
RSVP-TE Extensions for GMPLS control of Spectrum Switched Optical
Networks (SSONs)
draft-wang-ccamp-gmpls-sson-rsvpte-01.txt
Abstract
A new architecture of optical transport networks which is addressed
in the newest version of G.872 is being developed in ITU-T SG15.
Compared with previous G.872 technology, this new technology allows
the switch of group of optical channels as a whole.
Since current control plane technology isn't able to control this
kind of application, this document describes the signaling extension
to support the control of frequency slot channel (i.e., group of
optical channels). This document also addresses the interworking
between WSON optical channel and SSON (Spectrum Switched Optical
Network) optical channel.
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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and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 17, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions used in this document . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Requirements and Modeling of SSON . . . . . . . . . . . . . . 5
3.1. Hierarchy between Optical Channel and Frequency Slot
Channel . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Switching Type . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Frequency Slot Channel . . . . . . . . . . . . . . . . . . 6
3.3.1. Label Format . . . . . . . . . . . . . . . . . . . . . 6
3.3.2. Traffic Parameters . . . . . . . . . . . . . . . . . . 6
3.3.3. Grid Attributes of Forwarding Adjacency . . . . . . . 7
3.4. Optical Channel . . . . . . . . . . . . . . . . . . . . . 7
3.4.1. Overview of Flexible Grid and Fixed Grid . . . . . . . 7
3.4.2. Interwork between WSON signal and SSON signal . . . . 7
4. Signaling Protocol Extensions to Support Control of SSON . . . 8
4.1. Switching Type . . . . . . . . . . . . . . . . . . . . . . 8
4.2. Label Format Extensions of Frequency Slot Channel Layer . 9
4.3. Traffic Parameters of Frequency Slot Channel Layer . . . . 9
5. Signaling Procedures . . . . . . . . . . . . . . . . . . . . . 10
5.1. RSVP-TE Signaling Procedures to Support the Setup of
Frequency Slot Channel . . . . . . . . . . . . . . . . . . 10
5.1.1. Centralized Spectrum Assignment . . . . . . . . . . . 10
5.1.2. Distributed Spectrum Assignment . . . . . . . . . . . 10
5.2. Interconnection between WSON signal and SSON signal . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. Normative References . . . . . . . . . . . . . . . . . . . 13
7.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
In the newest version of G.872, a new kind of spectrum utilization
and implementation way is introduced to current optical network.
That is, a chunk of contiguous spectrum which is occupied by a group
of "express" channels can be forwarded via wide-band filters as a
whole without filtering and switching everything down to the
individual OCh (Optical Channel) level in long-haul systems.
Compared with narrowband, wideband filters and switching has many
advantages, for example, building OCh Signals for management
convenience, maximizing the reach and traversing more nodes. Optical
channels included in the group may have different sizes (more than
one OCh signal fits into a slot). From the perspective of management
plane and control plane, hierarchy exists between the channels and
optical channel group (frequency slot channel).
Detailed description about this kind of spectrum utilization and
implementation way could be found in the following sections base on
the terminology defined in ITU-T.
GMPLS protocol extensions are needed to help manage this kind of
spectrum utilization and implementation way. This document first
describes the layer model base on the hierarchy between optical
channels (OCh) and optical channel group (frequency slot channel)
from management plane or control plane perspective and defines
signaling protocol extension to support the control of frequency slot
channel. As the flexible grid framework document describes both the
frequency slot channel and optical channel, this document also give a
detail description about the interworking between WSON optical
channel and SSON (Spectrum Switched Optical Network) optical channel.
1.1. Conventions used in this document
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. Terminology
o Frequency slot: As defined by Q6 in clause 3.1.2 of G.694.1, a
frequency slot is a frequency range which is allocated to a slot
and unavailable to other slots within a flexible grid. A
frequency slot is defined by its nominal central frequency and its
slot width. Detailed description can be found in the framework
document.
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o Wavelength Range: [RFC6163] gives a description of this
terminology.Wavelength range given a mapping between labels and
the ITU-T grids, each range could be expressed in terms of a
tuple, (lambda1, lambda2) or (freq1, freq2), where the lambdas or
frequencies can be represented by 32-bit integers.
o Nominal central frequency (of a frequency slot) - as used by Q6 in
G.694.1. [Note: This parameter is associated with a grid position
on the fixed grid and a slot in the flexible grid.]
o Central frequency - this parameter is associated with an optical
signal. It is the nominal mid-point of the optical frequency
range over which the digital information of the particular OCh
payload is modulated.
o Single signal frequency slot: A frequency slot assigned to a
single optical signal (that carries a single OCh payload)
o Frequency Slot Channel: as defined in the newest version of G.872,
the Optical Channel Signal is switched by analogue elements
(matrices) and may be switched in larger pieces of spectrum than
that occupied by a single optical channel (optical channel slot).
The channel that may carry multiple optical channel signals is
called a Frequency Slot Channel.
o Fiber Frequency Slot: the total allocable spectrum on a fiber.
o SSON: Spectrum-Switched Optical Network. This concept and
definition is introduced from the framework document. 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.
o OCh Frequency Slot: The spectrum allocated to transport a single
OCh signal.
o Waveguide: anything that constrains the E/M radiation and guides
the E/M energy to its destination is a waveguide; copper pairs,
coaxial pairs and optical fibers are all waveguides.
o Media layer: media layer is described as the bottom of the client
server recursion.
o Media path: a path through a waveguide can be called media path.
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3. Requirements and Modeling of SSON
3.1. Hierarchy between Optical Channel and Frequency Slot Channel
Spectrum may be allocated in larger and contiguous piece than a
single OCh slot which is called Frequency Slot. Frequency Slot
Channel can be described as an optical media path (i.e., waveguide)
with a nominal center frequency and slot width across a sequence of
network elements. The concatenation of all media elements between
two points is called a Frequency Slot Channel. A frequency slot
channel is such an optical channel group that more than one optical
channel slot can be carried in and transport. SSON allows both
frequency slot channel switching and optical channel switching.
[Note: The term "channel" here implies all the media between two
points.]
Frequency Slot channels can be switched in a Frequency Slot Matrix.
The Frequency Slot Matrix Connection is described as an optical
matrix connection from one fiber to another that has a given nominal
center frequency and slot width. The Frequency Slot Matrix
connection may interconnect one or more Frequency Slot Channels,
which in turn may carry one or more OCh signals. Establishing a
Frequency Slot Matrix Connection will limit the connectivity of an
OCh signal over that network element within the spectral band of that
matrix connection to be between the input and output fibers of that
Frequency Slot Matrix Connection. The slots allocated to a single
OCh signal is called OCh slot.
In the case where the switching granularity of the Frequency Slot
Matrix allows for independent switching of each OCh, it can be
decided as a matter of policy that a request to establish an OCh
connection will, internal to the NE, establish a Frequency Slot
Matrix Connection of the same spectral width, and the Frequency Slot
Matrix Connection can be released when the OCh connection is
released.
The Frequency Slot channel is a topological construct which is
modeled from management perspective and can be chosen for convenience
of managing and describing the network. A frequency slot channel
represents a piece of spectrum supported by a concatenation of media
elements (e.g. fiber, filters, amplifier). More than one optical
channel signal can be carried in a frequency slot channel. As the
frequency slots and Optical channel are of different sizes, hierarchy
exists between them, current optical transport network can be modeled
into two layers and managed independently from the perspective of
management, one is optical channel layer and the other is frequency
slot channel layer. Frequency slots channel and optical channel
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signals can be managed independently. A frequency slot channel can
be switched as a whole by the frequency slot matrix without the need
to look into every optical channel.
[Notes: We are not going to address the OEO and wavelength converter
that may exist in a frequency slot channel, as current version of
G.872 doesn't cover the optical frequency changer along the frequency
slot channel.]
3.2. Switching Type
Switching type can be used to indicate the type of switching that
should be performed on a particular link. According to the modeling
in the previous section, a new value should be defined to indicate
the switching capability of frequency slot channel layer.
3.3. Frequency Slot Channel
3.3.1. Label Format
Section 3.3 of [RFC3471] defines waveband switching: "A waveband
represents a set of contiguous wavelengths which can be switched
together to a new waveband". This is similar to the frequency slot
channel switching, because they both switch multiple wavelengths or
spectrum as a unit.
But the wavelength label defined in [RFC3471] only has significance
between neighbors, in order to control the setup and release of
frequency slot channel with RSVP-TE signaling, a new frequency slot
channel label which has definite information of nominal central
frequency and slot width of the spectrum is needed. This chunk of
spectrum can be used for subsequent setup of optical channel path.
3.3.2. Traffic Parameters
In current network, like MPLS network, OTN network, signaling can be
used to reserve bandwidth at each node along the path when set up
LSPs. The bandwidth information describes the end-to-end traffic
characteristic of a LSP, so the signaling SHOULD be able to carry
bandwidth information that a LSP need to occupy.
In the process of the setup of frequency slot channel, the most
critical traffic characteristic of a LSP is spectrum, i.e., the
spectrum width that a LSP can occupy. For example, if a third party
wants to manage and operate a chunk of spectrum by itself, carrier
could use the signaling to set up a frequency slot channel with a
specific spectrum width to satisfy the requirement. Carrier doesn't
care how this spectrum can be used by the party and how many data
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this chunk of spectrum can bear.
According to the previous description, when we use signaling to set
up a frequency slot channel, spectrum resource information (i.e.,
spectrum width) should be carried in the signaling to reserve the
spectrum resource along the path.
3.3.3. Grid Attributes of Forwarding Adjacency
Frequency slot matrix connection may interconnect one or more
frequency slot channels, which in turn may carry one or more OCh
signals. In the case the frequency slot matrix just allow the
switching of spectrum as a whole, internal grid attributes should not
be known by the forwarding adjacency end points.
3.4. Optical Channel
[Notes: This section mainly addresses the current status of optical
channel, including WSON optical channel signal and SSON optical
channel signal. We will decouple this part and submit another
document if people think optical channel and frequency slot channel
belong to different layer and they have different signaling format,
so they should be decouple from each other.]
3.4.1. Overview of Flexible Grid and Fixed Grid
GMPLS and PCE control of fixed grid network (i.e., WSON, Wavelength
Switched Optical Network) is close to mature in IETF CCAMP, while
flexible grid control plane technology is still being developed in
IETF. This section mainly focuses on the interconnection between
WSON optical channel signal and SSON optical channel signal.
3.4.2. Interwork between WSON signal and SSON signal
Some open issues are listed in the recent flexible grid framework
document and still need to be resolved if we want to push the
framework document forward. Part of these issues which may have
relation to the interwork between SSON and WSON are listed here:
1). If a new switching capability is needed to represent SSON
optical channel layer?
2). Potential problems with having the same switching capability but
the label format changes compared with WSON optical channel layer.
3). Role of LSP encoding type? I think the issue listed here
intends to say if a new LSP encoding type is needed for flexible grid
optical channel layer.
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4). Notion of hierarchy? There is no notion of hierarchy between
flexible grid OCh and fixed grid OCh.
Just from my perspective, I think SSON optical channel layer should
use the same switching capability as WSON optical channel layer.
Some words are given here to describe my opinion. A LSP which has a
bandwidth of 50GHz pass through both WSON network and SSON network.
We assume that no OEOs exist in the LSP, so both the WSON optical
channel path and SSON optical channel path occupy 50GHz. From the
perspective of data plane, there is no change of the signal and no
multiplexing when the WSON optical channel path interconnects with
SSON optical channel path. From this scenario we can conclude that
both WSON optical channel layer and SSON optical channel layer belong
to the same layer. No notion of hierarchy exists between them. Base
on these words, I think both WSON optical channel layer and SSON
optical channel layer should use the same switching capability.
The previous words mention the issues 1) and 4). Another two issues
are to be discussed in the following description in the process of
path setup.
Because there is no notion of hierarchy exists between WSON optical
channel layer and SSON optical channel layer, hierarchy LSP which is
addressed in [RFC4206] and [RFC6107] can't be applied. But 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 WSON OCh LSP
and SSON OCh 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 WSON optical channel path and SSON optical
channel path.
4. Signaling Protocol Extensions to Support Control of SSON
This section mainly addresses the signaling protocol extension in
support of the control of spectrum-switched optical netwrok and the
facilitating of the setup of forwarding adjacency in G.872 optical
transport network.
4.1. Switching Type
A new switching type is needed.
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Value Type
------- -------
XX(IANA) Spectrum Switched Capable (SSC)
Figure 1: Switching Capability
4.2. Label Format Extensions of Frequency Slot Channel Layer
According to the description in the section 3.2, label should be able
to describe the frequency slot characteristic in order to facilitate
the switch of this large piece of spectrum. Label format of flexible
grid can be introduced here to depict the label of frequency slot
channel.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Grid | C.S. | Identifier | n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| m | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: label
Grid Type: no meaning should be inferred from this field, as
frequency slot channel can be used to carry any kind of grid.
Reserved value 0 defined in [RFC6205] or value 4 which can be used to
indicate any kind of grid is capable of fill in this field.
The meaning of C.S. and identifier is maintained from [RFC6205].
Similar to the definition in
[draft-farrkingel-ccamp-flexigrid-lambda-label], n is used to
identify the central frequency, and m (16bits) is used to identify
slot width of the frequency slot channel.
[Notes: here we use 16 bits to represent the "m" value, because 8
bits are not enough for the setup of frequency slot channel with
large spectrum.]
4.3. Traffic Parameters of Frequency Slot Channel Layer
Similar to the original signaling which carry the information of
bandwidth that a LSP may reserve at each node along the path,
signaling that is used to set up frequency slot channel SHOULD be
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able to carry the information of spectrum width. The spectrum width
traffic parameters can be organized as follow, and this information
can be carried in the Sender_Tspec object within a path message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| m | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: traffic parameter
m (16 bits): the spectrum width is specified by m*12.5 GHz.
5. Signaling Procedures
5.1. RSVP-TE Signaling Procedures to Support the Setup of Frequency
Slot Channel
5.1.1. Centralized Spectrum Assignment
In this case, both of the route and the frequency slot information
(i.e., central frequency and spectrum width) are provided by the PCE
or ingress node. When signaling a LSP, the assigned label
information is carried in the ERO label sub-object which is addressed
in [RFC3473]. When the nodes along the LSP receive the path message
carrying the ERO and ERO label sub-object, the procedure of path
setup is the same as the procedure which is described in [RFC3473]
and [RFC4003]. RRO and RRO label sub-object are used to record the
label information of the egress.
5.1.2. Distributed Spectrum Assignment
In this case, only the route is provided by a PCE or ingress node
before the signaling procedure. The available spectrum SHALL be
collected hop by hop and the egress node SHOULD select a proper label
for the LSP. After the route is computed, the ingress node SHOULD
find out the available spectrum for the LSP on the next link of the
route.
Then a path message is sent to the next node along the path according
to the route information. The path message MUST contain a
Sender_Tspec object to specify the spectrum width of the frequency
slot channel. A Label_set object SHALL be added to the path message,
which contains the candidate available spectrum for the LSP on the
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next link.
When an intermediate node receives the path message, it can deserve
the spectrum width information from the Sender_Tspec object. Then it
SHOULD find the available spectrum for the LSP on the next link of
the route similar to the ingress node. The common part of the two
available spectrum sets. If the new set is null, the path message
SHALL be rejected by a patherr message. Otherwise, the Label_set
object in the path message SHALL be updated according to the new set
and the path message is forwarded to the next node according to the
route.
When an egress node receives a path message, it SHOULD select an
available spectrum from the Label_set object based on local policy
and determine the frequency slot channel base on the spectrum width
and the available spectrum. Then a Resv message is responded so that
the nodes along the LSP can establish the optical cross-connect based
on the Label object which is determined by the spectrum width in the
traffic parameters and the available spectrum in the Label_set
object.
5.2. Interconnection between WSON signal and SSON signal
The path setup procedure of WSON OCh interworking with SSON OCh can
be described as follows:
Let's take the example of [RFC5150] into consideration.
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 4: stitching LSP
In this scenario, R1 and R2 are traditional WSON signal capable
nodes, A and B are both WSON signal and SSON signal capable nodes,
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the other nodes are only SSON capable nodes. We assume that a
40Gbit/s LSP from R1 to R2 needs to be set up.
Node R1 prepares signaling path message for the end-to-end path setup
from R1 to the destination node R2. Before R1 sends path message, R1
should send a path computation request to the path computation
element in order to compute an end-to-end path from R1 to R2. Path
computation response message from PCE to R1 contains ERO and label
information. Here we may classify the scenarios into two cases:
R1/R2 and the other nodes are in the same AS, R1/R2 and the other
nodes are not in the same AS.
In this scenario of interconnection between WSON OCh and SSON OCh, I
think dynamic stitching LSP setup is frequent, static stitching LSP
configuration may not be needed here.
1). R1/R2 and the other nodes are in the same AS:
R1 encapsulates the path message which contains ERO to explicitly
indicate the path and label used and RRO to record the path traversed
and label used by node traversed. Then R1 sends the path message to
the next hop node A. Here we assume path computation element is
capable of fixed grid and flexible grid path computation, and the ERO
contain the path information (R1, A, B, R2). When the path message
arrives at node A, node A verifies the path message and finds
incomplete ERO information, then send another path computation
request message to the PCE in order to obtain the whole path
information. PCE sends path computation response message which
contain ERO (A, D, F, H, B) and label information. Here the label is
flexible label information which is addressed in [draft-farrkingel].
To facilitate the control of stitching LSP boundaries, we may use a
different encoding type for flexible grid to help control. Encoding
type can be used to help stitching LSP boundaries control. Stitching
LSP boundaries control looks like FA-LSP boundaries control, but has
many differences.
After matching the switching type and encoding type of the interface,
Node A blocks the signaling process and decides to set up a stitching
LSP according to the flexible grid LSP setup procedure using another
signaling process. Procedure for set up stitching LSP can be found
in RFC5150. The stitching LSP can be seen as a TE link in the fixed
grid network. After the setup of stitching LSP between A and B, A
then continues the blocking signaling procedure and sends the path
message to the next hop B directly and finishes the end-to-end LSP.
2). R1/R2 and the other nodes are in different AS:
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From signaling perspective, path setup in this scenario is similar to
that in the last scenario. If A is a domain boundary node, A can
decide to set up a stitching LSP according to local configuration or
match of the switching type and encoding type when the R1-R2 path
message arrives at boundary node A. Path-key technology which is
addressed in [RFC5520] can be used here to help setup of the path.
6. Security Considerations
TBD
7. References
7.1. Normative References
[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.
7.2. Informative References
[G.694.1 v1]
International Telecommunications Union, "Draft revised
G.694.1 version 1.3".
[G.872 v11]
International Telecommunications Union, "Draft revised
Recommendation ITU-T G.872".
[flexible-grid-ospf-ext]
Fatai Zhang, Xiaobing Zi, Ramon Casellas, O. Gonzalez de
Dios, and D. Ceccarelli, "GMPLS OSPF-TE Extensions in
support of Flexible-Grid in DWDM Networks",
draft-zhang-ccamp-flexible-grid-ospf-ext-00.txt .
[flexible-grid-requirements]
Fatai Zhang, Xiaobing Zi, O. Gonzalez de Dios, and Ramon
Casellas, "Requirements for GMPLS Control of Flexible
Grids",
draft-zhang-ccamp-flexible-grid-requirements-01.txt .
[flexigrid-lambda-label]
D. King, A. Farrel, Y. Li, F. Zhang, and R. Casellas,
"Generalized Labels for the Flexi-Grid in Lambda-Switch-
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Capable (LSC) Label Switching Routers",
draft-farrkingel-ccamp-flexigrid-lambda-label-01.txt .
[ospf-ext-constraint-flexi-grid]
L Wang, Y Li, "OSPF Extensions for Routing Constraint
Encoding in Flexible-Grid Networks",
draft-wangl-ccamp-ospf-ext-constraint-flexi-grid-00.txt .
Authors' Addresses
Qilei Wang
ZTE Corporation
Email: wang.qilei@zte.com.cn
Xihua Fu
ZTE Corporation
ZTE Plaza, No.10, Tangyan South Road, Gaoxin District
Xi'an
P.R.China
Email: fu.xihua@zte.com.cn
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