Internet DRAFT - draft-lee-pce-wson-impairments
draft-lee-pce-wson-impairments
Network Working Group Y. Lee
Internet Draft Huawei
Intended status: Standard Track
Expires: June 16, 2018 G. Bernstein
Grotto Networking
Jonas Martensson
Acreo
T. Takeda
NTT
T. Tsuritani
KDDI
December 17, 2018
PCEP Extensions for WSON Impairments
draft-lee-pce-wson-impairments-08
Abstract
As an optical signal progresses along its path it may be altered by
the various physical processes in the optical fibers and devices it
encounters. When such alterations result in signal degradation,
these processes are usually referred to as "impairments". These
physical characteristics may be important constraints to consider in
path computation process in wavelength switched optical networks.
This document provides PCEP extensions to support Impairment Aware
Routing and Wavelength Assignment (IA-RWA) in wavelength switched
optical networks.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with
the provisions of BCP 78 and BCP 79.
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Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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Table of Contents
1. Introduction...................................................3
1.1. WSON RWA Processes (no impairments).......................5
1.2. WSON IA-RWA Processes.....................................6
2. WSON PCE Architectures and Requirements........................8
2.1. RWA PCC to PCE Interface..................................9
2.1.1. A new RWA path request...............................9
2.1.1.1. Signal Quality Measure TLV.....................10
2.1.2. A new RWA path reply................................12
2.1.2.1. Signal Quality Measure TLV.....................12
2.2. RWA-PCE to IV-PCE Interface..............................14
2.2.1. A new impairment-validated (IV) path request........15
2.2.2. A new impairment-validated (IV) path reply..........15
3. Manageability Considerations..................................15
3.1. Control of Function and Policy...........................15
3.2. Information and Data Models, e.g. MIB module.............16
3.3. Liveness Detection and Monitoring........................16
3.4. Verifying Correct Operation..............................16
3.5. Requirements on Other Protocols and Functional Components16
3.6. Impact on Network Operation..............................17
4. Security Considerations.......................................17
5. IANA Considerations...........................................17
6. References....................................................17
6.1. Normative References.....................................17
6.2. Informative References...................................18
Authors' Addresses...............................................18
7. Acknowledgments...............................................19
1. Introduction
[RFC4655] defines the PCE based architecture and explains how a Path
Computation Element (PCE) may compute Label Switched Paths (LSP) in
Multiprotocol Label Switching Traffic Engineering (MPLS-TE) and
Generalized MPLS (GMPLS) networks at the request of Path Computation
Clients (PCCs). A PCC is shown to be any network component that
makes such a request and may be for instance an Optical Switching
Element within a Wavelength Division Multiplexing (WDM) network.
The PCE, itself, can be located anywhere within the network, and may
be within an optical switching element, a Network Management System
(NMS) or Operational Support System (OSS), or may be an independent
network server.
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The PCE communication Protocol (PCEP) is the communication protocol
used between PCC and PCE, and may also be used between cooperating
PCEs. [RFC4657] sets out the common protocol requirements for PCEP.
Additional application-specific requirements for PCEP are deferred
to separate documents.
This document provides a set of application-specific PCEP
requirements for support of path computation in Wavelength Switched
Optical Networks (WSON) with impairments. WSON refers to WDM based
optical networks in which switching is performed selectively based
on the wavelength of an optical signal.
The path in WSON is referred to as an optical path. An optical path
may span multiple fiber links and the path should be assigned a
wavelength for each link. A transparent optical network is made up
of optical devices that can switch but not convert from one
wavelength to another. In a transparent optical network, an optical
path operates on the same wavelength across all fiber links that it
traverses. In such case, the optical path is said to satisfy the
wavelength-continuity constraint. Two optical paths that share a
common fiber link can not be assigned the same wavelength. To do
otherwise would result in both signals interfering with each other.
Note that advanced additional multiplexing techniques such as
polarization based multiplexing are not addressed in this document
since the physical layer aspects are not currently standardized.
Therefore, assigning the proper wavelength on an optical path is an
essential requirement in the optical path computation process.
When a switching node has the ability to perform wavelength
conversion the wavelength-continuity constraint can be relaxed, and
a may use different wavelengths on different links along its route
from origin to destination. It is, however, to be noted that
wavelength converters may be limited due to their relatively high
cost, while the number of WDM channels that can be supported in a
fiber is also limited. As a WSON can be composed of network nodes
that cannot perform wavelength conversion, nodes with limited
wavelength conversion, and nodes with full wavelength conversion
abilities, wavelength assignment is an additional routing constraint
to be considered in all optical path computation.
One of the most basic questions in communications is whether one can
successfully transmit information from a transmitter to a receiver
within a prescribed error tolerance, usually specified as a maximum
permissible bit error ratio (BER). This generally depends on the
nature of the signal transmitted between the sender and receiver and
the nature of the communications channel between the sender and
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receiver. The optical path utilized (along with the wavelength)
determines the communications channel.
The optical impairments incurred by the signal along the fiber and
at each optical network element along the path determine whether the
BER performance or any other measure of signal quality can be met
for this particular signal on this particular path. Given the
existing standards covering optical characteristics (impairments)
and the knowledge of how the impact of impairments may be estimated
along a path, [RFC6566] provides a framework for impairment aware
path computation and establishment utilizing GMPLS protocols and the
PCE architecture.
Some transparent optical subnetworks are designed such that over any
path the degradation to an optical signal due to impairments never
exceeds prescribed bounds. This may be due to the limited geographic
extent of the network, the network topology, and/or the quality of
the fiber and devices employed. In such networks the path selection
problem reduces to determining a continuous wavelength from source
to destination (the Routing and Wavelength Assignment problem).
These networks are discussed in [RFC6163]. In other optical
networks, impairments are important and the path selection process
must be impairment-aware.
In this document we first review the processes for routing and
wavelength assignment (RWA) used when wavelength continuity
constraints are present. We then review the processes for optical
impairment aware RWA (IA-RWA). Based on selected process models we
then specify requirements for PCEP to support IA-RWA. Note that
requirements for PCEP to support RWA are specified in a separate
document [RFC7449].
The remainder of this document uses terminology from [RFC4655].
1.1. WSON RWA Processes (no impairments)
In [RFC6163] three alternative process architectures were given for
performing routing and wavelength assignment. These are shown
schematically in Figure 1.
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+-------------------+
| +-------+ +--+ | +-------+ +--+ +-------+ +---+
| |Routing| |WA| | |Routing|--->|WA| |Routing|--->|DWA|
| +-------+ +--+ | +-------+ +--+ +-------+ +---+
| Combined | Separate Processes Separate Processes
| Processes | WA performed in a
+-------------------+ Distributed manner
(a) (b) (c)
Figure 1 RWA process alternatives.
Detail description of each alternative can be found in [RFC6163].
1.2. WSON IA-RWA Processes
In [RFC6566] impairments were addressed by adding an "impairment
validation" (IV) process. For approximate impairment validation
three process alternatives were given in [RFC6566] and are shown in
Figure 2. Since there are many possible alternative combinations,
these are just three examples. Please note that the requirements for
all possible architectures can be reduced to the cases in Figure 3
in section 2.
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+-----------------------------------+
| +--+ +-------+ +--+ |
| |IV| |Routing| |WA| |
| +--+ +-------+ +--+ |
| |
| Combined Processes |
+-----------------------------------+
(a)
+--------------+ +----------------------+
| +----------+ | | +-------+ +--+ |
| | IV | | | |Routing| |WA| |
| |candidates| |----->| +-------+ +--+ |
| +----------+ | | Combined Processes |
+--------------+ +----------------------+
(b)
+-----------+ +----------------------+
| +-------+ | | +--+ +--+ |
| |Routing| |------->| |WA| |IV| |
| +-------+ | | +--+ +--+ |
+-----------+ | Distributed Processes|
+----------------------+
(c)
Figure 2 Process flows for the three main approximate impairment
architectural alternatives.
These alternatives have the following properties and impact on PCEP
requirements in this document.
1. Combined IV and RWA Process - Here the processes of impairment
validation, routing and wavelength assignment are aggregated into
a single PCE. The requirements for PCC-PCE interaction with such
a combined IV-RWA process PCE is addressed in this document.
2. IV-Candidates + RWA Process - As explained in [RFC6566]
separating the impairment validation process from the RWA process
maybe necessary to deal with impairment sharing constraints. In
this architecture one PCE computes impairment candidates and
another PCE uses this information while performing RWA. The
requirements for PCE-to-PCE interaction of this architecture will
be addressed in this document.
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3. Routing + Distributed WA and IV - Here a standard path
computation (unaware of detailed wavelength availability or
optical impairments) takes place, then wavelength assignment and
impairment validation is performed along this path in a
distributed manner via signaling (RSVP-TE). This alternative
should be covered by existing or emerging GMPLS PCEP extensions
and does not present new WSON specific requirements.
2. WSON PCE Architectures and Requirements
In the previous section we reviewed various process architectures
for implementing RWA with and without regard for optical impairment.
In Figure 3 we reduce these alternatives to two PCE based
implementations. As specified in [RFC6566], the PCE in Figure 3(a)
should be given the necessary information for RWA and impairment
validation, including WSON topology, link wavelength utilization as
well as impairment information such as the adjustment range of
tunable parameters, etc. Similarly, RWA-PCE should be equipped with
all the information other than impairment-related ones which is a
necessity for IV-PCE.
In Figure 3(a) we show the three processes of routing, wavelength
assignment and impairment validation accessed via a single PCE. The
implementation details of the interactions of the processes are not
subject to standardization; this document concerns only the PCC to
PCE communications.
In Figure 3(b) the impairment validation process is implemented in a
separate PCE. Here the RWA-PCE acts as a coordinator and the PCC to
RWA-PCE interface will be the same as in Figure 3(a), however in
this case we have additional requirements for the RWA-PCE to IV-PCE
interface.
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+-----------------------------------+
+-----+ | +--+ +-------+ +--+ |
| | | |IV| |Routing| |WA| |
| PCC |<----->| +--+ +-------+ +--+ |
| | | |
+-----+ | PCE |
+-----------------------------------+
(a)
+----------------------+ +--------------+
+-----+ | +-------+ +--+ | | |
| | | |Routing| |WA| | | IV |
| PCC |<----->| +-------+ +--+ |<--->| candidates |
| | | | | |
+-----+ | RWA-PCE (coordinator)| | IV-PCE |
+----------------------+ +--------------+
(b)
Figure 3 PCE architectures for IA-RWA.
2.1. RWA PCC to PCE Interface
The PCC to PCE interface of Figure 3(a) and the PCC to RWA-PCE
(coordinator) interface of Figure 3(b) are the same and we will
cover both in this section. The following requirements for these
interfaces are arranged by use cases:
2.1.1. A new RWA path request
The PCReq Message MUST include one or more specific measures of
optical signal quality to which all feasible paths should conform:
o BER limit
o OSNR + Margin
o Power
o PMD
o Residual Dispersion (RD)
o Q factor
o TBD
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(Editor's Note: this is not a complete list of optical signal
quality measure and subject to further change.)
If the PCReq Message does not include the BER limit and no BER limit
information related to the specific path request is provisioned at
the PCE then the PCE will return an error specifying that a BER
limit must be provided.
"Margin" means "insurance" (e.g. 3~6dB) for suppliers and operators
which are set against unpredictable degradation and other
degradation not included in the provided estimates such as that due
to fiber nonlinearity.
In non-coherent WDM networks, PMD and CD should be carefully
considered. However, coherent WDM networks usually have a high
tolerance with these two optical signal quality measurements and
thus it may not need to be considered.
2.1.1.1. Signal Quality Measure TLV
This TLV represents all impairment constraints that need to be
considered by the PCE to calculate a path that passes the requested
measure of signal quality for a signal for a given source and
destination.
This TLV is repeated one after another until all signal quality
types are specified.
The TLV type is TBD.
The TLV data is defined as follow:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P| Signal Quality Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The P bit (1 bit): Indicates if the associated impairment is a path
level or not.
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The P bit is set to 1 indicates that the associated impairment is a
path level. This means that the impairment is associated with the
end-to-end path and the threshold must be satisfied on a path level.
The P bit is set to 0 indicates that the associated impairment is a
link level. This means the impairment is associated with the link
and the threshold must be satisfied on every link of the end-to-end
path.
The Signal Quality Type (15 bits): indicates the kind of optical
signal quality of interest.
0: reserved
1: BER limit
2: OSNR+ Margin
3: Power
4: PMD
5: CD
6: Q factor
7-up: Reserved for future use
Threshold (32 bits) indicates the threshold (upper or lower) to
which the specified signal quality measure must satisfy for the
path/link (depending on the P bit).
The reserved bits MUST be set to 0 on transmit and MUST be ignored
on receive.
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2.1.2. A new RWA path reply
The PCRep Message MUST include the route, wavelengths assigned to
the route, and an indicator that says if the path conforms to the
required quality or not. Moreover, it should also be able to specify
a list of impairment compensation information along the chosen
route, i.e., the value or value range of optical signal quality
parameter that needs to be adjusted, such as power level, in order
to achieve the resultant measure of signal quality as given in
Section 2.1.2.1. It is suggested to carry this information in the
PCEP ERO object. According to [RFC5440], PCEP ERO object is
identical to RSVP-TE ERO object. Therefore, it is suggested to
modify the RSVP-TE ERO object to accommodate this need. This will be
included in a separate draft in the future.
In the case where a valid path is not found, the PCRep Message MUST
include why the path is not found (e.g., no route, wavelength not
found, BER failure, etc.)
2.1.2.1. Signal Quality Measure TLV
This TLV represents the result of the requested measure of signal
quality for a signal for a given source and destination.
This TLV is repeated one after another until all signal quality
types are specified.
The TLV type is TBD.
The TLV data is defined as follow:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P| Signal Quality Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Signal Quality Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The P bit (1 bit): Indicates if the associated signal quality
measure has passed the threshold or not.
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The P bit is set to 1 indicates that the associated signal quality
measure has passed the threshold.
The P bit is set to 0 indicates that the associated signal quality
measure has failed the threshold.
The Signal Quality Type (15 bits): indicates the kind of optical
signal quality of interest.
0: reserved
1: BER limit
2: OSNR_ Margin
3: Power
4: PMD
5: CD
6: Q factor
7-up: Reserved for future use
Signal Quality Value (32 bits) indicates the actual estimated value
of the specified signal quality measure for the end-to-end path.
TBD: How to encode link based value needs to be determined in the
revision.
The reserved bits MUST be set to 0 on transmit and MUST be ignored
on reception.
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2.2. RWA-PCE to IV-PCE Interface
In [RFC6566] a sequence diagram for the interaction of the PCC, RWA-
PCE and IV-PCE of Figure 3(b) was given and is repeated here in
Figure 4. The interface between the PCC and the RWA-PCE (acting as
the coordinator) was covered in section 2.1.
+---+ +-------------+ +-----------------+
|PCC| |RWA-Coord-PCE| |IV-Candidates-PCE|
+-+-+ +------+------+ +---------+-------+
...___ (a) | |
| ````---...____ | |
| ```-->| |
| | |
| |--..___ (b) |
| | ```---...___ |
| | ```---->|
| | |
| | |
| | (c) ___...|
| | ___....---'''' |
| |<--'''' |
| | |
| | |
| (d) ___...| |
| ___....---''' | |
|<--''' | |
| | |
| | |
Figure 4 Sequence diagram for the interactions between PCC, RWA-
Coordinating-PCE and the IV-Candidates-PCE.
The interface between the RWA-Coord-PCE and the IV-Candidates-PCE is
specified by the following requirements:
1. The PCReq Message from the RWA-Coord-PCE to the IV-Candidate-PCE
MUST include an indicator that more than one (candidate) path
between source and destination is desired.
2. The PCReq message from the RWA-Coord-PCE to the IV-Candidates-PCE
MUST include a limit on the number of optical impairment
qualified paths to be returned by the IV-PCE.
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3. The PCReq message from the RWA-Coord-PCE to the IV-Candidates-PCE
MAY include wavelength constraints. Note that optical impairments
are wavelength sensitive and hence specifying a wavelength
constraint may help limit the search for valid paths. This
requirement has been already covered in [RFC7449] and is
presented here for an illustration purpose.
4. The PCRep Message from the IV-Candidates-PCE to RWA-Coord-PCE
MUST include a set of optical impairment qualified paths along
with any wavelength constraints on those paths.
5. The PCRep Message from the IV-Candidates-PCE to RWA-Coord-PCE
MUST indicate "no path found" in case where a valid path is not
found.
6. The PCReq Message from the RWA-Coord-PCE to the IV-Candidate-PCE
MAY include one or more specified paths and wavelengths that is
to be verified by the IV-PCE. This requirement is necessary when
the IV-PCE is allowed to verify specific paths.
Note that once the RWA-Coord-PCE receives the resulting paths from
the IV Candidates PCE, then the RWA-Coord-PCE computes RWA for the
IV qualified candidate paths and sends the result back to the PCC.
2.2.1. A new impairment-validated (IV) path request
Details on encoding are TBD.
2.2.2. A new impairment-validated (IV) path reply
Details on encoding are TBD.
3. Manageability Considerations
Manageability of WSON Routing and Wavelength Assignment (RWA) with
PCE must address the following considerations:
3.1. Control of Function and Policy
In addition to the parameters already listed in Section 8.1 of
[RFC5440], a PCEP implementation SHOULD allow configuring the
following PCEP session parameters on a PCC:
o The ability to send a WSON IA-RWA request.
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In addition to the parameters already listed in Section 8.1 of
[RFC5440], a PCEP implementation SHOULD allow configuring the
following PCEP session parameters on a PCE:
o The support for WSON IA-RWA.
o The maximum number of synchronized path requests associated with
WSON IA-RWA per request message.
o A set of WSON IA-RWA specific policies (authorized sender,
request rate limiter, etc).
These parameters may be configured as default parameters for any
PCEP session the PCEP speaker participates in, or may apply to a
specific session with a given PCEP peer or a specific group of
sessions with a specific group of PCEP peers.
3.2. Information and Data Models, e.g. MIB module
Extensions to the PCEP MIB module defined in [PCEP-MIB] should be
defined, so as to cover the WSON IA-RWA information introduced in
this document. A future revision of this document will list the
information that should be added to the MIB module.
3.3. Liveness Detection and Monitoring
Mechanisms defined in this document do not imply any new liveness
detection and monitoring requirements in addition to those already
listed in section 8.3 of [RFC5440].
3.4. Verifying Correct Operation
Mechanisms defined in this document do not imply any new
verification requirements in addition to those already listed in
section 8.4 of [RFC5440]
3.5. Requirements on Other Protocols and Functional Components
The PCE Discovery mechanisms ([RFC5089] and [RFC5088]) may be used
to advertise WSON IA-RWA path computation capabilities to PCCs.
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3.6. Impact on Network Operation
Mechanisms defined in this document do not imply any new network
operation requirements in addition to those already listed in
section 8.6 of [RFC5440].
4. Security Considerations
This document has no requirement for a change to the security models
within PCEP [PCEP]. However the additional information distributed
in order to address the RWA problem represents a disclosure of
network capabilities that an operator may wish to keep private.
Consideration should be given to securing this information.
5. IANA Considerations
A future revision of this document will present requests to IANA for
codepoint allocation.
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3471] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Functional Description", RFC 3471,
January 2003.
[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
January 2003.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) communication Protocol (PCEP)", RFC 5440,
March 2009.
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6.2. Informative References
[RFC6163] Lee, Y. and Bernstein, G., W. Imajuku, "Framework for
GMPLS and PCE Control of Wavelength Switched Optical
Networks", RFC 6163, April 2011.
[RFC6566] Lee, Y. and Bernstein, G. (Editors), and D. Li, "Framework
for GMPLS and PCE Control of Wavelength Switched Optical
Networks", RFC 6566, March, 2012.
[RFC7449] Y. Lee, G. Bernstein, J. Martensson, T. Takeda and T.
Otani, "PCEP Requirements for WSON Routing and Wavelength
Assignment", RFC 7449, February 2015.
[RFC5088] Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
Zhang, "OSPF Protocol Extensions for Path Computation
Element (PCE) Discovery", RFC 5088, January 2008.
[RFC5089] Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
Zhang, "IS-IS Protocol Extensions for Path Computation
Element (PCE) Discovery", RFC 5089, January 2008.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC4657] Ash, J. and J. Le Roux, "Path Computation Element (PCE)
Communication Protocol Generic Requirements", RFC 4657,
September 2006.
[RFC8174] B. Leiba, "Ambiguity of Uppercase vs Lowercase in RFC 2119
Key Words", RFC 8174, May 2017.
Authors' Addresses
Young Lee (Ed.)
Huawei Technologies
Email: leeyoung@huawei.com
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Greg Bernstein (Ed.)
Grotto Networking
Fremont, CA, USA
Phone: (510) 573-2237
Email: gregb@grotto-networking.com
Jonas Martensson
Acreo
Email:Jonas.Martensson@acreo.se
Tomonori Takeda
NTT Corporation
3-9-11, Midori-Cho
Musashino-Shi, Tokyo 180-8585, Japan
Email: takeda.tomonori@lab.ntt.co.jp
Takehiro Tsuritani
2-1-15 Ohara, Fujimino, Saitama, 356-8502, JAPAN
KDDI R&D Laboratories Inc.
Phone: +81-49-278-7806
Email: tsuri@kddilabs.jp
Xian Zhang
Huawei Technologies
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28972913
Email: zhang.xian@huawei.com
7. Acknowledgments
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