Internet DRAFT - draft-wang-ccamp-gmpls-sson-rsvpte
draft-wang-ccamp-gmpls-sson-rsvpte
Network Working Group Qilei Wang
Internet-Draft Xihua Fu
Intended status: Standards Track ZTE Corporation
Expires: April 25, 2013 Oct 22, 2012
RSVP-TE Extensions for GMPLS control of Spectrum Switched Optical
Networks (SSONs)
draft-wang-ccamp-gmpls-sson-rsvpte-02.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 large chunk of contiguous spectrum which may be wider
than the spectrum occupied by a single optical channel signal.
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 this kind of new spectrum utilization and
implementation way. This document also addresses the interworking
between WSON optical channel and SSON (Spectrum Switched Optical
Network) optical channel.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 25, 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions used in this document . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Requirements and Modeling of SSON . . . . . . . . . . . . . . 5
3.1. Hierarchy between Optical Channel and Media Channel . . . 5
3.2. Switching Type . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Media 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 OCh signal and SSON OCh
signal . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Signaling Protocol Extensions to Support Control of Media
Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Switching Type . . . . . . . . . . . . . . . . . . . . . . 9
4.2. Label Format Extensions of Media Channel Layer . . . . . . 9
4.3. Traffic Parameters of Media Channel Layer . . . . . . . . 10
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. Interwork 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. A
new kind of entity called media channel which is similar to LSP is
introduced. According to the description in [G.872v16], the media
channel is a topological construct that represents both the path
through the media and the resource (frequency slot) that it occupies.
A media channel is bounded by ports on media elements. A media
channel may be dimensioned to carry more than one OCh-P signal. That
is to say, a chunk of contiguous spectrum which can be occupied by a
group of optical 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.
Following is the description taken from [G.872v16], "below the OCh,
the entities that provide for configuration of the media channels are
described separately from the entities that provide management of the
collections of the OCh-P signals that traverse the media". According
to the description, we can conclude that the containment relationship
exists between media channels and OCh signals, and the containment
relationship should be announced to the source and end nodes of the
media channels. Intermediate nodes are unnecessary to know the
containment relationship because the media channel can be switched as
a whole without filtering and switching everything down to individual
OCh level.
Two kinds of entities which are spectrum configuration entity and
signal management entity should be provide by nodes creating media
channels from the perspective of control plane.
Note: Optical channels switched in a media channel may have different
spectrum bandwidth.
From the perspective of management plane and control plane,
containment relationship indicates that hierarchy exists between the
media channel and optical channel. GMPLS protocol are needed to
extent to help manage this kind of spectrum utilization and
implementation way. This document first describes the coexistence of
media channel and optical channel, then the layer model base on the
hierarchy between optical channels (OCh) and media channel from
management plane or control plane perspective and defines signaling
protocol extension to support the control of media channel. As the
flexible grid framework document describes both the media channel and
optical channel, this document also give a detail description about
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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.
o Media channel: as defined in [G.872v16], media channel is used to
indicate a media association that represents both the topology
(i.e., the path through the media) and the resource (frequency
slot) that it occupies. A media channel is bounded by ports on
media elements and can span any combination of network elements
and fibers.
o Effective frequency slot: The effective frequency slot of a media
channel is that part of the frequency slots of the filters along
the media channel that is common to all of the filters' frequency
slots. It is described by its nominal central frequency and its
slot width.
o Nominal central frequency (of a frequency slot) - as used by Q6/
SG15 in G.694.1. This parameter is associated with a grid
position on the fixed grid and a slot in the flexible grid.
o Network media channel: The end-to-end channel allocated to
transport a single OCh payload signal is called a network media
channel and supports a single OCh payload network connection.
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.
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3. Requirements and Modeling of SSON
3.1. Hierarchy between Optical Channel and Media Channel
Spectrum may be allocated in larger and contiguous piece than
spectrum occupied by a single optical channel which is called
Frequency Slot. The frequency slot is described by its nominal
central frequency and its slot width [ITU-T G.694.1]. The media
Channel is a topological construct that represents both the path
through the media and the resource (frequency slot) that it occupies.
A media channel is bounded by ports on media elements and can span
any combination of network elements and fibers, while the frequency
slot is a local concept, while the media channel has an end-to-end
meaning. A media channel may be dimensioned to carry more than one
OCh P signal. Network media channel is a specific type of media
channel which can only be used to transport a single OCh signal and
support a single OCh connection.
From the perspective of control plane or management plane, hierarchy
exists between media channel and optical channel, as media channel
can be used to transport optical channel signals. During the process
of path setup, containment relationship between optical channel
signal and media channel should be conveyed through signaling and
announced to source node and end node in order to help group and
detach optical channel signals from one another. Dependency
relationship needs to be explicitly told.
Notes: no hierarchy exists in either media channels or optical
channels.
Media channels can be switched in a media Matrix. The media channel
matrix provides flexible connectivity for the media channels. Media
ports at the edge of a media channel matrix may be created and broken
to help route media channel path. Media channel connection will
limit the connectivity of optical channel signals over the network
element within the frequency slot. Media channel matrixes are not
mandatory to have the function of optical channel matrix as signals
in the media channel can be switched as a whole.
In the case where the switching granularity of the media 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 network media channel Matrix
Connection of the same spectrum slot width, and the network media
Matrix Connection can be released when the OCh connection is
released.
As more than one optical channel signal can be carried in a media
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channel, notion of 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 media layer. Optical channel layer
can be modeled as higher layer and media channel layer can be modeled
as lower layer. Media layer LSP created in high layer appear as a
data link in optical channel layer. One or more optical channel LSPs
can be nested into media channel LSP. That is to say, media channel
LSP appears as a H-LSP in the higher layer optical channel LSP.
As a kind of resource, spectrum allows for the utilization by both
optical channel layer and media layer. It's not necessary to setup
media LSP first before the setup of OCh LSP. Coexistence of OCh and
media channel in the same link is permitted.
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 switching type should be defined to
indicate the switching capability of media channel layer.
3.3. Media 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 media 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 media
channel with RSVP-TE signaling, a new media 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 (i.e., bitrates) 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 media channel, the most critical
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traffic characteristic of a media channel 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 media 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 this chunk
of spectrum can bear. So when we use signaling to set up a media
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
Media matrix connection may interconnect one or more media channels,
which in turn may carry one or more OCh signals. In the case the
media matrix just allow the switching of spectrum as a whole,
internal flexible grid or fixed grid attributes are unnecessary to be
known by the forwarding adjacency end points.
3.4. Optical Channel
[Notes: This section mainly addresses the current status of optical
channel interconnection, including interconnection between WSON
optical channel signal and SSON optical channel signal.]
3.4.1. Overview of Flexible Grid and Fixed Grid
Fixed grid signals have fixed slot width (e.g., 50GHz), while
flexible grid signals allow different slot widths (e.g., 50GHz,
87.5GHz).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 OCh signal and SSON OCh 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.
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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.
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 Media Layer
This section mainly addresses the signaling protocol extension in
order to support the control of spectrum-switched optical network
media layer and the facilitating of the setup of forwarding adjacency
in G.872 optical transport network.
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4.1. Switching Type
A new switching type is defined here for media channel layer.
Value Type
------- -------
XX(IANA) Media Channel Switched Capable (MCSC)
Figure 1: Switching Capability
4.2. Label Format Extensions of Media 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 media 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: 3. A new grid value to support flexible grid.
The meaning of C.S. and identifier is maintained from [RFC6205] and
[draft-farrkingel-ccamp-flexigrid-lambda-label].
Similar to the definition in
[draft-farrkingel-ccamp-flexigrid-lambda-label], n is used to
identify the nominal central frequency, and m (16bits) is used to
identify slot width of the media channel.
[Notes: here we use 16 bits to represent the "m" value, because 8
bits maybe not enough for the setup of media channel with large chunk
of spectrum. This document is different from current flexible grid
document in CCAMP because of different model way.]
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4.3. Traffic Parameters of Media Channel Layer
Similar to the original signaling which carry the information of
Bandwidth (i.e., bitrates) that a LSP may reserve at each node along
the path, signaling that is used to set up media channel SHOULD be
able to carry the information of spectrum width. The spectrum width
traffic parameters can be organized as follow, and this information
is 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.
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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 media
channel. A Label_set object SHALL be added to the path message,
which contains the candidate available spectrum for the LSP on the
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 media 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. Interwork between WSON signal and SSON signal
The path setup procedure of WSON OCh signal's interworking with SSON
OCh signal is described as follows:
Let's take the following network 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
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Figure 4: Interworking between WSON OCh and SSON OCh
In this scenario, R1 and R2 are traditional WSON signal capable
nodes, A and B are both WSON optical channel signal and SSON optical
channel signal capable nodes, the other nodes are SSON optical
channel 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 fist send a path computation request to the path computation
element in order to compute an end-to-end path from R1 to R2. After
path computation, PCRep message which contains ERO and label
information is send back to R1 from PCE.
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.
In this scenario of interconnection between WSON OCh and SSON OCh,
dynamic stitching LSP setup is frequent, static stitching LSP
configuration may not be needed here.
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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 v6]
International Telecommunications Union, "Draft revised
G.694.1 version 1.6".
[G.872 v16]
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-
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 .
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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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